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Objective: Heat stress is a significant factor leading to decreased crop yield. Exceeding the plant's temperature tolerance threshold in ecosystems often results in significant cellular damage and potentially cellular death. Signaling elicitors may mitigate elevated temperatures' detrimental impact and enhance plant defense mechanisms. Materials and Methods: The present study investigates the influence of varying temperatures (25, 30, 35, 40, and 45°C) and pre-harvest salicylic acid (SA) application (0, 0.5, 1.5, 2.5, 5, and 10 mM) on the morpho-physiological and biochemical attributes of maize. A factorial-based experiment was set up following a completely randomized design and conducted in a growth room. Results: The findings demonstrated that a 2.5 mM SA treatment at 35°C produced the largest plant leaf area and total chlorophyll content. The temperature and SA application interplay on carotenoid content were maximum at 5 mM. SA treatment under hightemperature conditions effectively elevated proline content, chl a, chl b, chl total, and malondialdehyde compared to untreated plants. The peak stomatal conductance was also observed with a 2.5 mM SA treatment at 30°C. The maximal catalase and peroxidase activities were recorded at 35°C. Furthermore, 2.5 mM SA at 25°C resulted in the highest levels of soluble proteins and RWC. SA (2.5 mM) applied at 30°C was more efficient at decreasing H2O2 production. The highest proline content was observed with 2.5 mM SA at 45°C. Conclusion: SA(2.5 mM) treatment can have optimal effects on maize plant growth parameters under high-temperature conditions, potentially mitigating the damaging effects of heat stress. [ABSTRACT FROM AUTHOR]

Chloroplast is one of the most sensitive organelles to heat stress in plants. In chloroplasts, various proteases affect photosynthesis by degrading proteins under stress conditions. Tomato Lutescent2 (SlL2), a chloroplast zinc metalloprotease, was previously reported to alter chloroplast development and delay fruit ripening. However, its enzyme activity and roles in plant response to abiotic stress are still unclear. Here, we confirmed that the SlL2 protein which localized on thylakoid membrane was an ATP-independent hydrolase, and SlL2 gene responded to heat stress. Phenotype analysis showed that SlL2 plays a negative role in the heat-response mechanism. Under heat stress, the transgenic plants overexpressing SlL2 (OE) grew worse than the wild type (WT), as reflected by their decreased membrane stability, osmotic-regulating substance, and antioxidative enzyme activities, as well as increased reactive oxygen species (ROS) accumulation. By contrast, l2 mutant line showed the opposite phenotype and corresponding physiological indices under heat stress. In addition, overexpression of SlL2 decreased the photosynthetic activities, especially photosystem II. Moreover, SlL2 was found to interact with chloroplast-located chaperone protein SlCDJ1, decreasing its content under heat stress. These results indicate that SlL2 reduces the thermotolerance of tomato by reducing the content of SlCDJ1. [ABSTRACT FROM AUTHOR]

It is necessary to identify the appropriate traits that influence yield in a given environment as part of a breeding programme. The objective of this study was to identify the morphological traits that contribute to maize grain weight (GWt) under abiotic stress conditions. Three drought-tolerant maize varieties were grown under no-stress (NHWS), heat-stress (HS), and combined heat- and water-stress (CHWS) conditions. Data from 19 morphological traits were analysed. The correlation results revealed that eight traits consistently produced a significant positive relationship with GWt under the three growth conditions. The path coefficient analysis revealed that in the NHWS, HS, and CHWS conditions, five traits consistently had a positive direct effect on the GWt. Given the magnitude of the positive direct effects, increasing dry biomass yield, harvest index, and grain number in the NHWS; grain number, harvest index, and ear width in the HS; and harvest index, days till silk appearance, leaf chlorophyll content, and grain number in the CHWS will increase GWt. Under various abiotic stress conditions, maize phenotypic expression varied. Therefore, the identified traits that contributed positively to GWt under various stress conditions should be considered when developing a maize improvement programme in a stress-prone environment. [ABSTRACT FROM AUTHOR]

Because high temperatures impair rice production, it is desirable to elucidate the regulatory mechanisms involved in rice response to heat stress. The objectives of this study were to identify candidate genes and characterize their response patterns during rice adaptation to high temperatures at the seedling stage. Ten heat-associated quantitative-trait loci were identified in a genome-wide association study. Comparison of transcript abundances in heat-sensitive and heat-tolerant rice pools under heat stress revealed approximately 400 differentially expressed genes. The expression of genes from heatsensitive accessions changed more than those from heat-tolerant accessions under heat stress. Alternative splicing (AS) events responded to heat stress in rice. The types of AS variants significant different between the heat-sensitive and heat-tolerant accessions. Expression patterns differing between the heat-sensitive and heat-tolerant accessions were identified for genes known to be involved in heat stress. We identified eleven genes associated with rice heat stress response. These genes could be pyramided to breed heat-tolerant rice accessions. [ABSTRACT FROM AUTHOR]

Research on the morphophysiological behavior of forest seeds during germination with respect to climate change is scarce. To date, there have been no studies on the biochemical or morphological aspects of Ormosia spp. In this study, we subjected Ormosia coarctata seeds to various temperature conditions to investigate temperature-dependent impacts on morphology, reactive oxygen species (ROS) generation, antioxidant systems, and storage systems. Analyses were performed on seeds exposed to 25, 35, and 40 °C for 48, 96, and 144 h. The morphology was evaluated by radiation using a Faxitron MX-20 device. ROS production (superoxide anion and hydrogen peroxide), malonaldehyde (MDA), carbonylated proteins, antioxidant enzyme activity (superoxide dismutase [SOD], ascorbate peroxidase [APX], catalase [CAT], and peroxidase [POX]), β-carotene, lycopene, glucose, and reserve enzyme activity (α- and β-amylase, lipase, and protease) were analyzed by spectrophotometry. Heat stress (40 °C) decreased germination by 76.2% and 78.1% (compared to 25 and 35 °C, respectively), caused damage to the external morphology of the seed, increased the content of ROS, MDA, and carbonylated proteins, and reduced APX, CAT, and POX activity. Furthermore, heat stress decreased glucose content and α-amylase activity. These results suggest that an increase of 5 °C in temperature negatively affects germination, promotes oxidative stress, and induces deterioration in O. coarctata seeds. [ABSTRACT FROM AUTHOR]

Wheat production is seriously influenced by extreme hot weather, which has attracted increasing attention. It is important to compare wheat responses to heat at seedling and reproductive stages, to explore the potential relationship between the performances at different growing stages and the possibility of early selection to accelerate heat tolerance breeding. In this study, forty wheat genotypes were screened under heat stress at both seedling and adult stages. It was found that root lengths at seedling stage were severely reduced by heat stress with significant variations among wheat genotypes. Heat-tolerant genotypes at seedling stage showed less root length decrease than susceptible ones. Wheat genotypes tolerant at seedling stage showed higher yield at adult stage after heat treatment. The performances of wheat genotypes screened under heat stress at seedling and adult stages were ranked by seedling damage index and adult damage index. A significant positive relationship was found between heat tolerance at seedling stage and at adult stage (r = 0.6930), suggesting a similar tolerant/susceptible mechanism at different plant growth stages and the possibility of early selection at seedling stage for breeding heat tolerance. Extremely tolerant and susceptible genotypes with consistent performances at seedling and adult stages were genetically compared and associated SNP markers and linked candidate genes were identified. [ABSTRACT FROM AUTHOR]

The rapeseed mustard is one of the most important sources of edible oil in India and contributes 28.6% in total oilseed production. The mustard growing areas in India are experiencing the vast diversity in the agro climatic conditions. Here, we studied forty-nine advanced breeding lines of Brassica juncea L. for two consecutive years (2016-18) to examine the variations in the remobilization of assimilates from flowering to maturity stage and their contribution to seed filling under stressed environment. Further, we investigated the impact of high temperature on dry matter accumulation and partitioning from source to sink in Brassica germplasm. The synchronization between the seed filling stage and the onset of heat spell is critical event that determines the overall yield. Imbalances caused due to miss-matching of above events created hindrance in source-sink translocation, thus resulted in yield losses. Amount of remobilized dry matter, remobilization efficiency and remobilization percentage increased significantly, while the dry matter accumulation, total carbohydrates content and seed yield per plant declined in the late sown genotypes during both crop seasons. Reduced accumulation of photo assimilates under stress and higher sink demand resulted in more number of shriveled seeds leading to yield depression. The higher remobilization efficiency in late sown genotypes was strongly associated with dry matter at flowering that consequently tended to affect the final seed weight. This study will provide insights for better understanding of source-sink relationships in Indian mustard under heat stress and the differential remobilization efficiencies in the advanced breeding lines. [ABSTRACT FROM AUTHOR]

Climate change is happening at a breakneck speed around the world. Due to continuous alterations, the climate has created various abiotic stress situations in which heat stress is among the most crucial that negatively impact the growth, development, and metabolism of crops. When stress is too intense, the signaling process leading to cell apoptosis is also triggered. The plant reaction to high temperature (HT) depends on the degree, time duration for exposure, and plant type. Heat stress affects plant development by causing a variety of biochemical, morphological, physiological, and molecular modifications. The ability of plants to sense the HT signals, create and forward them, to begin necessary biochemical or physiological modifications to tolerate the stress is critical for their capability during HT stress. Furthermore, the responses of plants to heat stress (HS) are complicated, with unknown physiological features as well as molecular or gene pathways. A noteworthy feature of plants is that they show numeric transgenic, epigenetic approaches against heat stress. This review describes and discusses the numerous ways to improve plant thermotolerance and different molecular and physiological responses, modifications, and tolerance to HT at the cellular level. [ABSTRACT FROM AUTHOR]

Background: Clematis species are attractive ornamental plants with a variety of flower colors and patterns. Heat stress is one of the main factors restricting the growth, development, and ornamental value of Clematis. Clematis lanuginosa and Clematis crassifolia are large-flowered and evergreen Clematis species, respectively, that show different tolerance to heat stress. We compared and analyzed the transcriptome of C. lanuginose and C. crassifolia under heat stress to determine the regulatory mechanism(s) of resistance. Results: A total of 1720 and 6178 differentially expressed genes were identified from C. lanuginose and C. crassifolia, respectively. The photosynthesis and oxidation–reduction processes of C. crassifolia were more sensitive than C. lanuginose under heat stress. Glycine/serine/threonine metabolism, glyoxylic metabolism, and thiamine metabolism were important pathways in response to heat stress in C. lanuginose, and flavonoid biosynthesis, phenylalanine metabolism, and arginine/proline metabolism were the key pathways in C. crassifolia. Six sHSPs (c176964_g1, c200771_g1, c204924_g1, c199407_g2, c201522_g2, c192936_g1), POD1 (c200317_g1), POD3 (c210145_g2), DREB2 (c182557_g1), and HSFA2 (c206233_g2) may be key genes in the response to heat stress in C. lanuginose and C. crassifolia. Conclusions: We compared important metabolic pathways and differentially expressed genes in response to heat stress between C. lanuginose and C. crassifolia. The results increase our understanding of the response mechanism and candidate genes of Clematis under heat stress. These data may contribute to the development of new Clematis varieties with greater heat tolerance. [ABSTRACT FROM AUTHOR]

Urban heat islands (UHI) and rapid urbanisation create new health risks for residents of urban territories. The authors consider lawns as an eco-stabilising factor of the urban environment and an element of ensuring the environmental safety of the capital. The purpose of this study was to determine the qualitative state of lawns to the factors of the urban ecosystem and their thermoregulatory function. To determine the impact of anthropogenic factors on research objects, the study assessed the amount of emissions into the atmospheric air from stationary and mobile sources, satellite maps of the intensity of nitrogen dioxide emissions (NO2) and sulphur dioxide (SO2) in the city’s air basin, heat distribution, and normalised difference moisture index (NDMI). To assess the condition and quality of lawns, the methods of assessing the grasslands of A. A. Laptev (1983) and an unmanned aerial vehicle (UAV) were used. It was established that the results of the evaluation of lawn coenoses using the method of O.O. Laptev and UAV are correlated (r=0.87). Lawn areas that were rated as in “satisfactory condition” are characterised by a higher temperature on the heat map and lower NDMI values. Indicators of lawn cover that were rated as in “good condition” correlate with surface temperature and NDMI. The difference in surface temperatures over the area of the experimental sites reaches 5°C and depends on the objects surrounding the perimeter. It was established that lawn areas adjust the thermal mode of the urban system in the warm period of the year, and reduce the temperature of the asphalt surface by about 0.5°C, and together with flower and woody plants – by about 0.9°C. The study results improve the understanding of the physiological effects of heat stress on lawn areas, which allows developing practical strategies for managing urban green spaces with limited water resources and anthropogenic loads. [ABSTRACT FROM AUTHOR]

Khuzestan province has good potential for oilseed crops production, such as soybeans. At present, however, there are no suitable soybean cultivars in the country that can tolerate the hot conditions of this province well. Therefore, Gelareh Kalhor Agriculture Company, in coordination with the Ministry of Agriculture Jihad, has imported four soybean cultivars (BRS391, BRS232, BRS511, and BRS284) from Brazil. This study aimed to compare the yield of imported soybean cultivars tolerant to heat stress with common cultivars in the country (Rahmat, Caspian, and SK-93) in Dezful climate conditions. The experiment was performed in 2021 in a randomized complete block design with three replications. Results of the analysis of variance showed that soybean cultivars had significant effects on the number of branches per plant, pod production per plant, seeds per pod, 1000-seed weight, and seed yield. But, there was no statistically significant difference among the cultivars studied for seed oil and protein contents. The results showed that imported soybean cultivars were able to produce about 25% more pods per plant, 21% more seeds per pod, and 8% higher seed weight, and in total, 20% higher seed yield than common cultivars. Conversely, the potential for branching in common soybean cultivars in the country was about 33% higher than that of the imported cultivars from Brazil. Among the cultivars imported, BRS232 and BRS284 with seed yields of 2793 and 2697 kg ha-1, respectively, showed higher production potential than the other two cultivars. [ABSTRACT FROM AUTHOR]

In-planta mechanisms of biochar (BC)-mediated improved growth were evaluated by examining oxidative stress, metabolic, and hormonal changes of Arabidopsis wild-type plants under basal or acute heat stress (–HS/ + HS) conditions with or without BC (+ BC/–BC). The oxidative stress was evaluated by using Arabidopsis expressing redox-sensitive green fluorescent protein in the plastids (pla-roGFP2). Fresh biomass and inflorescence height were greater in + BC(‒HS) plants than in the –BC(‒HS) plants, despite similar leaf nutrient levels, photosystem II (PSII) maximal efficiencies and similar oxidative poise. Endogenous levels of jasmonic and abscisic acids were higher in the + BC(‒HS) treatment, suggesting their role in growth improvement. HS in ‒BC plants caused reductions in inflorescence height and PSII maximum quantum yield, as well as significant oxidative stress symptoms manifested by increased lipid peroxidation, greater chloroplast redox poise (oxidized form of roGFP), increased expression of DNAJ heat shock proteins and Zn-finger genes, and reduced expression of glutathione-S-transferase gene in addition to higher abscisic acid and salicylic acid levels. Oxidative stress symptoms were significantly reduced by BC. Results suggest that growth improvements by BC occurring under basal and HS conditions are induced by acclimation mechanisms to 'microstresses' associated with basal growth and to oxidative stress of HS, respectively. [ABSTRACT FROM AUTHOR]

Spot blotch and terminal heat are two of the most important stresses for wheat in South Asia. A study was initiated to explore the use of spelt (Triticum spelta) to improve tolerance to these stresses in spring wheat (T. aestivum). We assessed 185 recombinant inbred lines (RILs) from the cross T. spelta (H + 26) × T. aestivum (cv. HUW234), under the individual stresses and their combination. H + 26 showed better tolerance to the single stresses and also their combination; grain yield in RILs was reduced by 21.9%, 27.7% and 39.0% under spot blotch, terminal heat and their combined effect, respectively. However, phenological and plant architectural traits were not affected by spot blotch itself. Multivariate analysis demonstrated a strong negative correlation between spikelet sterility and grain yield under spot blotch, terminal heat and their combination. However, four recombinant lines demonstrated high performance under both stresses and also under their combined stress. The four lines were significantly superior in grain yield and showed significantly lower AUDPC than the better parent. This study demonstrates the potential of spelt wheat in enhancing tolerance to spot blotch and terminal heat stresses. It also provides comprehensive evidence about the expression of yield and phenological traits under these stresses. [ABSTRACT FROM AUTHOR]

Improving the heat tolerance of cotton is a major concern for breeding programs. To address this need, a fast and effect way of quantifying thermotolerant phenotypes is required. Triphenyl tetrazolium chloride (TTC) based enzyme viability testing following high-temperature stress can be used as a vegetative heat tolerance phenotype. This is because when live cells encounter a TTC solution, TTC undergoes a chemical reduction producing a visible, insoluble red product called triphenyl formazan, that can be quantified spectrophotometrically. However, existing TTC based cell viability assays cannot easily be deployed at the scale required in a crop improvement program. In this study, a heat stress assay (HSA) based on the use of TTC enzyme viability testing has been refined and improved for efficiency, reliability, and ease of use through four experiments. Sampling factors that may influence assay results, such as leaf age, plant water status, and short-term cold storage, were also investigated. Experiments conducted in this study have successfully downscaled the assay and identified an optimal sampling regime, enabling measurement of large segregating populations for application in breeding programs. The improved HSA methodology is important as it is proposed that long-term improvements in cotton thermotolerance can be achieved through the concurrent selection of superior phenotypes based on the HSA and yield performance in hot environments. Additionally, a new way of interpreting both heat tolerance and heat resistance was developed, differentiating genotypes that perform well at the time of a heat stress event and those that maintain a similar performance level to a non-stressed control. [ABSTRACT FROM AUTHOR]

Hydroponic systems are known to provide a platform for uniform growth conditions until the reproductive stage. However, many plant species, including sunflower, show poor growth and survivability under conventional hydroponic systems due to poor nutrient availability, hypoxia and algal contamination. Thus, we tested various hydroponic systems to select a hydroponic system suitable for screening of sunflower germplasm. Sunflower accessions showed better growth and leaf gas exchange in newly-designed over conventional hydroponic systems. Selected hydroponic systems were further engaged in sunflower accession screening under heat and osmotic stress in a two-pan system (210 cm × 60 cm). Heat stress treatment was applied by growing sunflower germplasm at 42 °C and osmotic stress by adding polyethylene glycol 8000 which decreased the osmotic potential to − 0.6 MPa. There was significant variability among the sunflower accessions for their ability to survive under stress. Accessions such as C-2721 (43%), C-291 (46%) and D-14 (43%) had lower cell membrane injury percentage under osmotic stress and high seedling survivability (60‒80%) under heat stress when compared with susceptible accessions. Moreover, resistant accessions exhibited greater cuticular waxes and root length but lower transpiration losses. The newly designed hydroponic platform proved reliable for the selection of resistant sunflower accessions. Selected parental lines were validated by assessing their hybrids under field trials across two seasons under water and temperature stress during the reproductive phase (autumn). Hybrid H3 obtained by crossing drought and heat resistant parents had the highest seed yield and water use efficiency. [ABSTRACT FROM AUTHOR]

Understanding the changes in peanut (Arachis hypogaea L.) anther lipidome under heat stress (HT) will aid in understanding the mechanisms of heat tolerance. We profiled the anther lipidome of seven genotypes exposed to ambient temperature (AT) or HT during flowering. Under AT and HT, the lipidome was dominated by phosphatidylcholine (PC), phosphatidylethanolamine (PE), and triacylglycerol (TAG) species (> 50% of total lipids). Of 89 lipid analytes specified by total acyl carbons:total carbon–carbon double bonds, 36:6, 36:5, and 34:3 PC and 34:3 PE (all contain 18:3 fatty acid and decreased under HT) were the most important lipids that differentiated HT from AT. Heat stress caused decreases in unsaturation indices of membrane lipids, primarily due to decreases in highly-unsaturated lipid species that contained 18:3 fatty acids. In parallel, the expression of Fatty Acid Desaturase 3-2 (FAD3-2; converts 18:2 fatty acids to 18:3) decreased under HT for the heat-tolerant genotype SPT 06-07 but not for the susceptible genotype Bailey. Our results suggested that decreasing lipid unsaturation levels by lowering 18:3 fatty-acid amount through reducing FAD3 expression is likely an acclimation mechanism to heat stress in peanut. Thus, genotypes that are more efficient in doing so will be relatively more tolerant to HT. [ABSTRACT FROM AUTHOR]

Cowpea is one of the vital grain legumes used for human and animal nutrition. Due to its rich protein content, cowpea supplies the protein requirement, especially in the African continent. Although cowpea is morphologically similar to common bean, it is a more tolerant species to heat and drought conditions. So, cowpea production has various advantages in semi-arid regions. The aim of this study was to determine some agronomic traits of used cowpea genotypes and evaluate their correlations with yield components. Plant height (PH), stem diameter (SD), leaf surface temperature (LST), total chlorophyll content (TCC), number of pods per plant (NP), number of seeds per plant (NS) and seed yield (SY) changed between 54.6-91.3 cm, 3.1-7.6 mm, 27.9-31.7 °C, 39-56.1%, 25.7-49.1, 307.5-684 and 646-2381 kg ha-, respectively. It is noteworthy that Karagöz produced the maximum SY compared to the other varieties. Besides, it was determined that SY has positive significant correlation with NS (r=0.98**), NP (r=0.96**), TCC (r=0.93**), SD (r=0.91**) and PH (r=0.86**). [ABSTRACT FROM AUTHOR]

Years with high fruit production, known as mast years, are the usual reproduction strategy of European beech. Harsh weather conditions such as frost during flowering can lead to pollination failure in spring. It has been assumed that mast is controlled by flowering, and that after successful pollination, high amounts of fruits and seeds would be produced. However, the extremely hot and dry European summer of 2018 showed that despite successful pollination, beechnuts did not develop or were only abundant in a few forest stands. An in-depth analysis of three forest sites of European beech from the Swiss Long-Term Forest Ecosystem Research Programme over the last 15–19 years revealed for the first time that extreme summer heat and drought can act as an "environmental veto", leading to early fruit abortion. Within the forest stands in years with fruit abortion, summer mean temperatures were 1.5 °C higher and precipitation sums were 45% lower than the long-term average. Extreme summer heat and drought, together with frost during flowering, are therefore disrupting events of the assumed biennial fruiting cycle in European beech. [ABSTRACT FROM AUTHOR]

A plantation of small-leaved lime (Tilia cordata Mill.) containing two types of planting stock - large-sized transplants (LST) and standard-sized transplants (SST) - was planted on a site with strong weed competition. The aim was to compare the growth, survival and health of those types of planting stock under a weeded and non-weeded regime in a dry and warm climate. Recorded variables were: overall mortality, stem height, root-collar diameter and chlorophyll content. Increments in height and root collar diameter were calculated. Precipitation, soil and air temperatures were continuously monitored by an automatic climate station. Soil analysis revealed equal conditions for the treatments. Simple analysis of costs was calculated. The results showed that LST exhibited greater height increment than SST in the first 5 years after afforestation under strong weed competition. Non-weeded (under the regime of no weeding) SST also showed increased mortality. Weeding regime positively influenced the height increment of SST but did not influence the height increment of LST. Chlorophyll content was significantly higher in the leaves of LST than in SST in the first growing period. Economic analysis showed that the number of trees was the most important variable, while weeding was less important. LST can be recommended for reforestation of weed-infested sites, even if they have relatively low annual precipitation. [ABSTRACT FROM AUTHOR]

The increasing occurrence of heatwaves has intensified temperature stress on terrestrial vegetation. Here, we investigate how two contrasting isoprene-emitting tropical species, Ficus benjamina and Pachira aquatica , cope with heat stress and assess the role of internal plant carbon sources for isoprene biosynthesis in relation to thermotolerance. To our knowledge, this is the first study to report isoprene emissions from P. aquatica. We exposed plants to two levels of heat stress and determined the temperature response curves for isoprene and photosynthesis. To assess the use of internal C sources in isoprene biosynthesis, plants were fed with 13C position-labelled pyruvate. F. benjamina was more heat tolerant with higher constitutive isoprene emissions and stronger acclimation to higher temperatures than P. aquatica , which showed higher induced isoprene emissions at elevated temperatures. Under heat stress, both isoprene emissions and the proportion of cytosolic pyruvate allocated into isoprene synthesis increased. This represents a mechanism that P. aquatica , and to a lesser extent F. benjamina , has adopted as an immediate response to sudden increase in heat stress. However, in the long run under prolonged heat, the species with constitutive emissions (F. benjamina) was better adapted, indicating that plants that invest more carbon into protective emissions of biogenic volatile organic compounds tend to suffer less from heat stress. [ABSTRACT FROM AUTHOR]

Heat stress, a regular risk to wheat in the subtropics, is a growing threat in other wheat producing regions as the global temperature rises. This paper reports on three experiments evaluating 49 entries of the 13th High Temperature Wheat Yield Trial (13HTWYT) from the International Centre for Maize and Wheat Improvement (distributed in 2014), with Fang 60 as the local check, at two locations at Chiang Mai, Thailand, a designated representative of the wheat mega-environment 5, in which temperature for the coolest month averages >17.5 °C and the crop is subjected to high temperature for the entire growing season. The wheat was grown in the lowland (elevation 330 m) at Chiang Mai University in (i) sand culture to simulate the condition of non-limiting nutrient and water supply and (ii) in the field and (iii) as an on-farm trial in the highlands (elevation 800 m) at Mae Wang district of Chiang Mai province. Heat tolerance in the wheat germplasm, recently developed for adaptation to high temperature, was indicated by longer pre-heading duration, and the positive correlation between days to heading and grain yield all three experiments. The longer time before heading enabled development of larger spikes that produced more seeds from more and larger spikelets and more competent florets. However, with the number of spikes that was either lower than or similar to Fang 60, none of the recently developed 13HTWYT entries out-yielded the local check from the 1970s. [ABSTRACT FROM AUTHOR]

In vineyards, hourly soil heat flux (SHF) may account for as much as 30% of net radiation. Therefore, inaccurate estimates of SHF may lead to non-negligible errors when quantifying the surface energy balance. The typical canopy height to width ratio of two along with widely spaced rows (row spacing exceeding canopy height), and leaf biomass concentrated in the upper half of the vine canopy result in variable shading conditions producing sharp, sometimes abrupt, differences in SHF between adjacent points within the interrow space. Drip irrigation, which is also a typical practice in many vineyards in semi-arid regions, adds an additional source of variability in the interrow soil moisture which strongly affects SHF. Lastly, the common practice in Californian wine-grape vineyards to plant cover crop in the interrow, forming two distinct areas below the canopy—bare soil and crop cover, further increases SHF variability in the interrow. This small-scale variability challenges the measurement of SHF in such agrosystems. The objective of the research was to assess the micro-scale (within the interrow between two vine rows) spatial variability in SHF, and to determine which of the three variables—non-uniform (in both space and time) shading patterns, non-uniform surface cover (bare soil vs. cover crop) and non-uniform soil water content (due to the drip irrigation)—is the most significant driver for the local heterogeneity. The variability of incoming solar radiation reaching the ground was found to be the primary source for the spatial and temporal variation of SHF once the vine canopy was fully developed. The water content distribution and the grass cover in the interrow both had minor impacts on the spatial and temporal variation in SHF. It was further found that a transect of five equally distributed sensors across the interrow accurately represented the area-average SHF given by the 11-sensor array, particularly during the growing season. [ABSTRACT FROM AUTHOR]

Significant efforts have been made recently in the application of high-resolution remote sensing imagery (i.e., sub-meter) captured by unmanned aerial vehicles (UAVs) for precision agricultural applications for high-value crops such as wine grapes. However, at such high resolution, shadows will appear in the optical imagery effectively reducing the reflectance and emission signal received by imaging sensors. To date, research that evaluates procedures to identify the occurrence of shadows in imagery produced by UAVs is limited. In this study, the performance of four different shadow detection methods used in satellite imagery was evaluated for high-resolution UAV imagery collected over a California vineyard during the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) field campaigns. The performance of the shadow detection methods was compared and impacts of shadowed areas on the normalized difference vegetation index (NDVI) and estimated evapotranspiration (ET) using the Two-Source Energy Balance (TSEB) model are presented. The results indicated that two of the shadow detection methods, the supervised classification and index-based methods, had better performance than two other methods. Furthermore, assessment of shadowed pixels in the vine canopy led to significant differences in the calculated NDVI and ET in areas affected by shadows in the high-resolution imagery. Shadows are shown to have the greatest impact on modeled soil heat flux, while net radiation and sensible heat flux are less affected. Shadows also have an impact on the modeled Bowen ratio (ratio of sensible to latent heat) which can be used as an indicator of vine stress level. [ABSTRACT FROM AUTHOR]

Surface renewal (SR) is a biometeorological technique that uses high frequency air temperature measurements above a crop surface to estimate sensible heat flux (H). The H derived from SR is then combined with net radiation (Rn) and ground heat flux (G) measurements to estimate latent heat flux (LE) as the residual of an energy balance equation. Recent advances in SR theory enabled its use beyond research settings, and led to the development of an inexpensive, stand-alone SR system for use in commercial agricultural settings. However, these commercial applications require replacing expensive net radiometers with clear sky models designed to estimate Rn for the energy balance approach, while also assuming G is zero on a daily basis. The accuracy of substituting Rn measurements with modelled values is unknown, and the assumption of an inconsequential G requires additional testing. Here, we compare the accuracy of the SR derived estimates of H and LE when Rn is either measured directly or modelled, and we compare results to two eddy covariance (EC) LE observations, namely LE measured via EC with an infrared gas analyzer (ECIRGA) and LE solved as a residual in the surface energy balance (ECresid). These measurements were collected at the Grape Remote sensing Atmospheric Profile & Evapotranspiration eXperiment (GRAPEX) conducted over a vineyard within the Lodi, CA wine growing region. LE from SR using tower Rn data measured directly onsite was significantly correlated with LE from ECresid and from ECIRGA with a least squares regression slope ~ 1. LE derived with the modelled incoming solar radiation (SWi) and DisALEXI Rn approaches were also significantly correlated with LE from ECresid, but both modelling approaches overestimated LE at higher fluxes. Patterns were similar, but with more scatter for correlations between LE from ECIRGA and LE from SR using either modelled or remotely sensed Rn. Incorporating direct measurements of G had minimal impact on the agreement of several SR approaches and LE from both EC approaches, however, when differences did occur direct measures of G reduced scatter and bias especially for the empirical SR approach. Our results suggest that LE derived from the new SR method requires fairly accurate Rn modelling approaches to obtain reliable and unbiased estimates of daily LE in comparison to measured LE using EC techniques. [ABSTRACT FROM AUTHOR]

The unique vertical canopy structure and clumped plant distribution/row structure of vineyards and orchards creates an environment that is likely to cause the wind profile inside the canopy air space to deviate from how it is typically modelled for most crops. This in turn affects the efficiency of turbulent flux exchange and energy transport as well as their partitioning between the plant canopy and soil/substrate layers. The objective of this study was to evaluate a new wind profile formulation in the canopy air space that explicitly considers the unique vertical variation in plant biomass of vineyards. The validity of the new wind profile formulation was compared to a simpler wind attenuation profile that assumes attenuation through a homogeneous canopy. We evaluated both attenuation models using measurements of wind speed in a vineyard interrow, as well as turbulent flux estimates retrieved from a two-source energy balance model, which uses land surface temperature as the key boundary condition for flux estimation. This is relevant in developing a robust remote sensing-based energy balance modelling system for accurately monitoring vineyard water use or evapotranspiration that can be applied using satellite and airborne imagery for field-to-regional scale applications. These tools are needed in intensive agricultural production regions with arid climates such as the Central Valley of California, which experiences water shortages during extended drought periods requiring an effective water management policy based on robust water use estimates for allocating water resources. Results showed that the new wind profile model improved sensible heat flux estimates (RMSE reduction from 42 to 35 W m - 2 ) when the vine canopy is in early growth stage resulting in a strongly clumped canopy. [ABSTRACT FROM AUTHOR]

Highlights • CaHSP22.0 was expressed in different tissues of pepper plants. • Silence of CaHSP22.0 conferred peppers more sensitivity to high temperature and salt stress. • Overexpression of CaHSP22.0 did not enhance pepper resistance to high temperature and salt stress. Abstract Small heat shock proteins (sHSPs) are ubiquitous and diverse molecular chaperones. However, the contribution of sHSPs in pepper response to stress is controversial. In the study, we characterized a small heat shock protein gene CaHSP22.0 from pepper sHSP20s family, and found that the deduced amino acid sequence of CaHSP22.0 gene contained the conserved necessary domains and residue for sHSPs functions. Under normal condition, CaHSP22.0 was detected in all pepper organs, but its transcript level was up-regulated under high temperature and salt stress. CaHSP22.0-silenced pepper exhibits more sensitive to heat and salt stress, which was primarily reflected by aggravated chlorophyll degradation, increased leaf conductivity, level of superoxide anion free radical and malondialdehyde content. Interestingly, CaHSP22.0 overexpression also resulted in Arabidopsis sensitivity to high temperature and salt stress by inhibiting normal growth of leaves and roots, increasing superoxide anion free radical, decreasing activities of antioxidant enzymes and chlorophyll content, increasing malondialdehyde content, and disturbing low expression of genes involved in environment stress. Our results suggested that modified expression of CaHSP22.0 conferred peppers more sensitivity to high temperature and salt stress. The possible mechanism for CaHSP22.0 silencing is speculated to the damage to cell membrane; as for gene over-expression, the mechanism was complexed and might be the disruption of ROS caused by the improper levels of CaHSP22.0 with its substrates. [ABSTRACT FROM AUTHOR]

Highlights • Sweet and hot pepper are more sensitive to heat stress in the reproductive stage. • The dominant fatty acid of the pepper leaves was found to be linolenic acid in all conditions. • Both pepper species follow the same antioxidant and phenol defense system changes again heat in vegetative and reproductive stage. Abstract High ambient temperature has adverse effects on plant vegetative and reproductive development and reduces crop yield. This experiment was designed to better understand the effects of unforeseen heat stresses on reproductive and vegetative growth of two species of pepper, and to find out whether or not Ca and hydrogen peroxide (H 2 O 2) have any significant effects on the levels of heat tolerance as well as on the reproductive and vegetative traits of the peppers. Two species of hot and sweet peppers, exposed to exogenous H 2 O 2 and CaCl 2, were subject to the high temperature (40° ±2C). Both species showed higher stress indices, including MDA, H 2 O 2 , electrolyte leakage, antioxidant capacity, phenol content, and chlorophyll fluorescence under heat stresses. Moreover, the given parameters were greater in the reproductive stage compared with the vegetative stage. Also, sweet peppers absorbed greater amounts of Ca in comparison with the hot peppers under stress conditions. The dominant fatty acid of the pepper leaves was found to be linolenic acid in all conditions. Under heat stresses, the saturate/unsaturated ratio of the fatty acid changed. This ratio increased in the hot pepper and conversely, decreased in the sweet pepper. On the other hand, a decrease in the levels of glucose and fructose was observed under heat stresses, while hydrogen peroxide significantly increased the two sugars. Nonetheless, the changes observed were greater in the sweet pepper in comparison with the hot pepper. All in all, it seems that, under the treatment, on the one hand, the fatty acids and existing sugars due to applying hydrogen peroxide, and on the other hand, the biochemical defense system of the peppers increased due to the presence of Ca, increasing its heat tolerance. [ABSTRACT FROM AUTHOR]

Abstract High temperature is a common stress, which influences the growth and reproduction of plants. Maize is one of the most important crops all over the world. However, heat stress reduces significantly the yield and quality of maize. Therefore, it is important to illuminate molecular mechanism of maize response to heat stress. To estimate genes related to heat stress, we analyzed the transcriptome of maize in response to heat stress. In this study, six cDNA libraries were constructed form total RNA isolated from leaves of maize. A total of 35,209,446 and 35,205,472 clean reads were generated from CK (Control condition) and HTP (Heat stress condition) treatments, respectively. The results showed that 1857 DEGs were identified in maize after heat stress (1029 up-regulated and 828 down-regulated). KEGG pathway enrichment analysis for DEGs indicated that protein processing in endoplasmic reticulum pathways play a central role in maize response to heat stress. In addition, in the present study, 167 putative TFs were identified, which belong to various TF families (e.g., MYB, AP2-EREBP, b-ZIP, bHLH, NAC and WRKY), and may be associated with heat stress response of maize. This research may contribute to understand the molecular mechanism of maize inbred line B73 response to heat stress, which is beneficial for developing maize cultivars to improve yield and quality. Highlights • The present study highlights 1857 differentially expression genes (DEGs) of maize seedling leave in response to heat stress. • Functional enrichment analyses revealed associated genes and transcription factors as important players in the response of maize to heat stress. • This research contributes to understand molecular mechanism of maize response to heat stress and develop cultivars to improve yield and quality. [ABSTRACT FROM AUTHOR]

We assessed the effects of heater wattage on sap flux estimates from heat dissipation sensors and generated calibrated equations for 1-year-old Eucalyptus grandis Hill ex Maiden trees. We used a total of eight trees ranging from 3 to 6 cm in diameter. Our calibration experiment was performed with a modified tree-cut approach, which allowed us to estimate gravimetric water use manually weighing 20 l buckets every 15 min while sap flux was monitored on each tree. Our results indicate that changes the current supplied to the heaters from 0.15 to 0.25 W does not significantly influence sap flux estimates, as long as the maximum temperature (T max) is properly determined for each period when wattage is different, and natural temperature gradients are corrected. Using the original parameters developed for this method, sap flux density and sap flow had an average underestimation of 53%, which according to our analysis had a reduced but relevant correlation with tree diameter (R 2 = 0.3, linear regression). These results may allow researchers to supply different currents to heat dissipation sensors to increase sensitivity or to reduce power consumption. They also provide evidence in favor of the correction and use of raw data collected when unwanted changes in wattage occur. The relationship observed between estimation error and tree diameter, while not strongly significant, suggests that diameter plays an important role in the estimation errors that has not been previously considered, and requires further research. [ABSTRACT FROM AUTHOR]

Heat stress and extreme temperatures negatively affect plant development by disrupting regular cellular and biochemical functions, ultimately leading to reduced crop production. Alfalfa (Medicago sativa) is an important forage crop grown worldwide as forage for livestock feed. Limiting the effects of abiotic stress by developing alfalfa cultivars that are stress tolerant would help mitigate losses to crop production. Members of the microRNA156 (miR156) family regulate the Squamosa Promoter‐Binding Protein‐Like (SPL) genes that in turn impact plant growth and development by regulating downstream genes in response to various abiotic stresses. In this study, alfalfa with miR156 overexpression and SPL13 RNAi knockdown show increased tolerance to heat stress (40°C). Transgenic plants show high water potential and increased non‐enzymatic antioxidant content under heat stress. Moreover, anthocyanin content and chlorophyll abundance were increased under stress. Expression of some important transcription factors and downstream genes involved in abiotic stress response were altered in miR156‐overexpressing genotypes under heat. Taken together, our results demonstrate that the miR156/SPL13 network contributes to improving heat stress tolerance in alfalfa. [ABSTRACT FROM AUTHOR]

Highlights • Post anthesis heat stress had more profound effects than elevated CO 2 on protein quality. • Contents of grain proteins decreased due to elevated CO 2 but increased by heat stress. • Elevated CO 2 decreased glutenin macropolyers (GMP) content and large GMP fraction. • Combination of elevated CO 2 and heat stress decreased the contents of storage proteins. • Co-occurring elevated CO 2 and heat stress did not affect GMP and amino acid content. Abstract Spring wheat plants were grown under two CO 2 concentrations (380 and 550 μmol mol−1) and two temperature treatments (ambient and post-anthesis heat stress) to investigate the effects of elevated CO 2 and heat stress on grain protein quality. Contents of protein components, glutenin macropolymers (GMP) and amino acids in grains decreased due to elevated CO 2 , while increased by high temperature. The combination of elevated CO 2 and heat stress increased the contents of total protein and albumin, but decreased the contents of gliadin and glutenin, while the content and particle size distribution of GMP as well as the contents of amino acids were not significantly affected. Furthermore, we found that the content and particle size distribution of GMP were not only determined by the contents of proteins and high-molecular-weight glutenin subunits, but also related to the contents of amino acids containing disulfide bonds, which favor the formation of large insoluble polymers. [ABSTRACT FROM AUTHOR]

Abstract The surge in sorghum-based foods as a gluten-free alternative for cereals like wheat, has directed sorghum research towards understanding and improving grain quality parameters. Since sorghum is usually grown in arid and semi-arid environments, is often prone to terminal water deficit and heat stress, inducing significant yield and quality losses. In environment 1, 24 genotypes assembled from diverse geographic locations, representing major sorghum growing regions of the world were grown in irrigated and dryland conditions. In environment 2, heat stress was imposed on the same 24 genotypes by placing custom-built field-based heat tents on already established plants, starting from booting until maturity. Water-deficit stress increased kernel hardness and total protein in grain, decreased protein digestibility, and micronutrient composition. Heat stress recorded lower total protein, protein digestibility, micronutrient composition and higher kernel hardness than control. Irrespective of the stress, larger kernels recorded higher total protein, protein digestibility and micronutrient composition, but lower total starch and kernel hardness. Almost all the measured grain micronutrients (Zn, Fe, Mn and Cu) were reduced under both stresses compared to control. Genotypes such as SC372 and RTx7000 which maintained desired grain quality parameters under stress conditions can help in incorporating quality traits into sorghum improvement programs. Highlights • Wide genetic variation for grain physical & micronutrient composition recorded. • Water deficit & heat stress decreased protein digestibility and micronutrients. • Water deficit & heat stress increased kernel hardness. • Larger kernels had better protein content, digestibility & micronutrient composition. • Donors that maintain grain nutrition under water-deficit & heat stress identified. [ABSTRACT FROM AUTHOR]

Heat stress at the pollen mother cell (PMC) meiotic stage leads to pollen sterility in rice, in which the reactive oxygen species (ROS) and sugar homeostasis are always adversely affected. This damage is reversed by abscisic acid (ABA), but the mechanisms underlying the interactions among the ABA, sugar metabolism, ROS and heat shock proteins in rice spikelets under heat stress are unclear. Two rice genotypes, Zhefu802 (a recurrent parent) and fgl (its near‐isogenic line) were subjected to heat stress of 40°C after pre‐foliage sprayed with ABA and its biosynthetic inhibitor fluridone at the meiotic stage of PMC. The results revealed that exogenous application of ABA reduced pollen sterility caused by heat stress. This was achieved through various means, including: increased levels of soluble sugars, starch and non‐structural carbohydrates, markedly higher relative expression levels of heat shock proteins (HSP24.1 and HSP71.1) and genes related to sugar metabolism and transport, such as sucrose transporters (SUT) genes, sucrose synthase (SUS) genes and invertase (INV) genes as well as increased antioxidant activities and increased content of adenosine triphosphate and endogenous ABA in spikelets. In short, exogenous application of ABA prior to heat stress enhanced sucrose transport and accelerated sucrose metabolism to maintain the carbon balance and energy homeostasis, thus ABA contributed to heat tolerance in rice. [ABSTRACT FROM AUTHOR]

Plants code for a multitude of heat stress transcription factors (Hsfs). Three of them act as central regulators of heat stress (HS) response in tomato (Solanum lycopersicum). HsfA1a regulates the initial response, and HsfA2 controls acquired thermotolerance. HsfB1 is a transcriptional repressor but can also act as co‐activator of HsfA1a. Currently, the mode of action and the relevance of the dual function of HsfB1 remain elusive. We examined this in HsfB1 overexpression or suppression transgenic tomato lines. Proteome analysis revealed that HsfB1 overexpression stimulates the co‐activator function of HsfB1 and consequently the accumulation of HS‐related proteins under non‐stress conditions. Plants with enhanced levels of HsfB1 show aberrant growth and development but enhanced thermotolerance. HsfB1 suppression has no significant effect prior to stress. Upon HS, HsfB1 suppression strongly enhances the induction of heat shock proteins due to the higher activity of other HS‐induced Hsfs, resulting in increased thermotolerance compared with wild‐type. Thereby, HsfB1 acts as co‐activator of HsfA1a for several Hsps, but as a transcriptional repressor on other Hsfs, including HsfA1b and HsfA2. The dual function explains the activation of chaperones to enhance protection and regulate the balance between growth and stress response upon deviations from the homeostatic levels of HsfB1. Solanum lycopersicum HsfB1 acts as a coactivator of HsfA1a to induce Hsps in response to temperature elevations, but also as a repressor of other Hsfs to adjust the demand for chaperones during stress. Thereby, HsfB1 has a central role in balancing the activity of stress and developmental networks. [ABSTRACT FROM AUTHOR]

Plants encounter biotic and abiotic stresses many times during their life cycle and this limits their productivity. Moderate heat stress (HS) primes a plant to survive higher temperatures that are lethal in the naïve state. Once temperature stress subsides, the memory of the priming event is actively retained for several days preparing the plant to better cope with recurring HS. Recently, chromatin regulation at different levels has been implicated in HS memory. Here, we report that the chromatin protein BRUSHY1 (BRU1)/TONSOKU/MGOUN3 plays a role in the HS memory in Arabidopsis thaliana. BRU1 is also involved in transcriptional gene silencing and DNA damage repair. This corresponds with the functions of its mammalian orthologue TONSOKU‐LIKE/NFΚBIL2. During HS memory, BRU1 is required to maintain sustained induction of HS memory‐associated genes, whereas it is dispensable for the acquisition of thermotolerance. In summary, we report that BRU1 is required for HS memory in A. thaliana, and propose a model where BRU1 mediates the epigenetic inheritance of chromatin states across DNA replication and cell division. Plants can be primed by a heat stress exposure to deal more efficiently with a future heat stress incident that occurs after a lag phase at normal growth temperatures. Studying the molecular basis of priming and memory in response to heat stress, we show here that the chromatin protein BRUSHY1 is required for heat stress memory and that it acts through sustaining the activation of heat stress‐memory related gene expression during the lag phase. Our findings suggest a model where heat stress memory is mediated through the epigenetic inheritance of chromatin states across cell divisions. [ABSTRACT FROM AUTHOR]

Stress priming by exposing plants to a mild or moderate drought could enhance plant tolerance to subsequent heat stress. Lipids play vital roles in stress adaptation, but how lipidomic profiles change, affecting the cross‐stress tolerance, is largely unknown. The objectives of this study were to perform lipidomics, to analyse the content, composition, and saturation levels of lipids in leaves of tall fescue (Festuca arundinacea) following drought priming and subsequent heat stress, and to identify major lipids and molecular species associated with priming‐enhanced heat tolerance. Plants were initially exposed to drought for 8 days by withholding irrigation and subsequently subjected to 25 days of heat stress (38/33°C day/night) in growth chambers. Drought‐primed plants maintained significantly higher leaf relative water content, chlorophyll content, photochemical efficiency, and lower electrolyte leakage than nonprimed plants under heat stress. Drought priming enhanced the accumulation of phospholipids and glycolipids involved in membrane stabilization and stress signalling (phosphatidic acid, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, and digalactosyl diacylglycerol) during subsequent exposure to heat stress. The reprogramming of lipid metabolism for membrane stabilization and signalling in response to drought priming and subsequent exposure to heat stress could contribute to drought priming‐enhanced heat tolerance in cool‐season grass species. Heat stress is a detrimental abiotic stress limiting growth of cool‐season plant species, whereas drought priming has been proved to improve plants tolerance to subsequent heat stress; however, the underlying mechanisms are not well understood. This study first used a lipidomics approach to identify lipids and specific molecular species responsive to drought priming and subsequent heat stress. Our results showed that the accumulation of molecular species of both phospholipids and glycolipids for membrane stabilization and phospholipid second‐messenger molecules for stress signalling could be involved in drought priming‐enhanced heat tolerance. Cross‐stress tolerance may involve reprogramming or adjustment of membrane lipid profiles. [ABSTRACT FROM AUTHOR]

Highlights • PRI, CIred-edge, and NDRE can detect heat stress, which is related to Fv/Fm, LCC, and Pn, respectively. • F v / F m is the most sensitive physiological parameter to indicate the start and end of slight heat stress. • PRI is the most sensitive VI, while it only works well at the heavy level or the late stage. • F v / F m is more sensitive than PRI to the heat stress especially at the slight level or early stage. Abstract With the changing of the climate, the detection of heat stress as early as possible has become increasingly important for wheat (Triticum aestivum L.) production. Previous studies have demonstrated that photosynthetic parameters can serve as indicators of the stress conditions, and vegetation indices (VIs) provide the ability to non-destructively monitor photosynthetic parameters. However, it remains unclear whether VIs can be used to detect heat stress in a similar manner as the photosynthetic parameters. In addition, the optimal VIs for indicating heat stress and detecting the stress status are also currently unknown. In the present study, a heat stress experiment was designed with four temperature levels [T1, 17 °C/27 °C (T min /T max), T2 (25 °C/35 °C), T3 (29 °C/39 °C), and T4 (33 °C/43 °C)] and three treatment durations [three days (D1), six days (D2) and nine days (D3)]. Three photosynthetic parameters [leaf chlorophyll content (LCC), net photosynthesis rate (P n), and maximum efficiency of photosystem II (F v / F m)] and 17 published VIs were selected to compare their sensitivity and assess their feasibility for detecting heat stress. The results showed that F v / F m was the most sensitive photosynthetic parameter to heat stress and had the ability to indicate the start and end of heat stress at the slight level or the early stage. The chlorophyll index-red edge (CI red-edge), normalized difference red edge index (NDRE) and photochemical reflectance index (PRI) were sensitive to heat stress owing to their close relationships with photosynthetic parameters. Among these three VIs, PRI displayed the highest sensitivity. Nevertheless, the sensitivity of PRI was less than that of F v / F m , and it failed to detect the beginning and end of heat stress lasting for three days. The ability of PRI to detect heat stress became similar to that of F v / F m when the duration of heat stress was increased to seven days. In conclusion, F v / F m is the optimum indicator for detecting early-stage heat stress, in which only the photosynthetic functions change. In contrast, PRI, a non-destructive indicator, works well to indicate relatively late-stage heat stress, in which the chemical and physical characteristics of leaves (e.g., chlorophyll content) are affected. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Effects of high pressure on pumpkin cubes was compared with thermal treatment. • The effect of three different pressures was evaluated on two pumpkin species. • After high pressure treatment parenchyma cells exhibited collapses and separations. • Treatment at 400 MPa and at 85 °C resulted the most effective on pectin methylesterase. • High pressure treatment decreased antioxidant activity that increased during storage. Abstract The effects of high pressure treatments (200, 400, 600 MPa for 5 min) and a thermal treatment (85 °C for 5 min) were evaluated on cubes of two pumpkin species (Cucurbita maxima L. var. Delica and Cucurbita moschata Duchesne var. Butternut) up to 2 months of refrigerated storage. Increasing the pressure, small parenchyma cells from the pumpkin tissue exhibited collapses and separations, especially for Butternut. This species showed a lower hardness than Delica at time 0. For both species, 400 MPa and thermal treatment were the most effective in the inactivation of pectinmethylesterase, which reactivated after 2 months, especially for Butternut. Colorimetric parameters decreased after all treatments. Antioxidant activity resulted affected by pressure, showing a significant increase during storage especially for the samples treated at 200 MPa after 2 months, comparable to the thermal treated ones. Among the tested treatments, 400 MPa may be considered as the best option for the quality retention during storage. [ABSTRACT FROM AUTHOR]

Highlights • The effect of heat stress can be alleviated by nitric oxide (150 μM) treatment in wheat. • Nitric oxide triggers the expression of SAGs and enhances the scavenging potential of wheat under heat stress. • Nitric oxide improves the quality of wheat grain by enhancing the accumulation of gliadin protein and starch. • Nitric oxide maintains the quality of starch in wheat grain by reducing the amylolytic activity under heat stress. • Nitric oxide enhances the accumulation of soluble protein, free amino acids and osmolyte in developing grains under HS. Abstract Heat stress (HS) drastically reduces the yield and quality of wheat grains. High temperature during critical stages (pollination and grain-filling) causes improper fertilization and formation of defragmented granules and shriveled seeds. Hormones and signaling molecules modulates the tolerance potential of the plants under stress. Nitric oxide (NO) is an important signaling molecule involved in triggering diverse physiological and biochemical processes under adverse conditions. Here, we studied the effect of sodium nitroprusside (SNP) (150 μM set based on pilot experiment) on heat stress-tolerance and grain quality related traits of two contrasting wheat cultivars Raj3765 as thermotolerant and HD2932 as thermosusceptible under differential HS (T 1 - 30 °C, 1 h; T 2 - 38 °C, 1 h), as compared to control (22 ± 2 °C) at different stages of growth. The expression of many important stress-associated genes (previously identified through Transcriptome sequencing) was observed upregulated in response to NO and HS; small HSP17 showed maximum fold increase in Raj3765. Similarly, the networks of antioxidant enzymes (SOD, CAT, and GPX) were observed triggered in response to NO, HS and NO + HS treatment in Raj3765 than HD2932. The accumulation of proline and free amino acid in cytoplasm were also reported higher under NO and HS treatment respectively in Raj3765, as compared to HD2932. Grain quality related traits like carbohydrate (starch) and proteins (gliadin) were observed higher in response to NO under HS in Raj3765. Heat stress was observed to increase the activities of α/β amylases in developing grains involved in degrading the starch quality. NO was observed to decrease the amylolytic activity in both the cultivars; very low amylolytic activity was observed in thermotolerant, as compared to thermosusceptible cultivars. Exogenous application of NO (150 μM) at different stages can be used as inexpensive technology for mitigating the problem of terminal HS in wheat – a farmer friendly approach for maintaining the quality of grains under present threat of global climate change. [ABSTRACT FROM AUTHOR]

ContentsSummary1215I.Introduction1215II.Molecular organization of the plant circadian clock1216III.Temperature compensation1219IV.Temperature regulation of circadian behaviors1220V.Thermal adaptation of the clock: evolutionary considerations1223VI.Light and temperature information for the clock function – synergic or individual?1224VII.Concluding remarks and future prospects1225Acknowledgements1225References1225 Summary: Plant growth and development is widely affected by diverse temperature conditions. Although studies have been focused mainly on the effects of stressful temperature extremes in recent decades, nonstressful ambient temperatures also influence an array of plant growth and morphogenic aspects, a process termed thermomorphogenesis. Notably, accumulating evidence indicates that both stressful and nonstressful temperatures modulate the functional process of the circadian clock, a molecular timer of biological rhythms in higher eukaryotes and photosynthetic prokaryotes. The circadian clock can sustain robust and precise timing over a range of physiological temperatures. Genes and molecular mechanisms governing the temperature compensation process have been explored in different plant species. In addition, a ZEITLUPE/HSP90‐mediated protein quality control mechanism helps plants maintain the thermal stability of the clock under heat stress. The thermal adaptation capability and plasticity of the clock are of particular interest in view of the growing concern about global climate changes. Considering these circumstances in the field, we believe that it is timely to provide a provoking discussion on the current knowledge of temperature regulation of the clock function. The review also will discuss stimulating ideas on this topic along with ecosystem management and future agricultural innovation. [ABSTRACT FROM AUTHOR]

This study aimed to phenotype young tomato (Solanum lycopersicum L.) plants for heat tolerance by measuring F v/ F m after short-term heat treatments in climate chambers and selected sensitive (low F v/ F m) and tolerant (high F v/ F m) cultivars to investigate their in-field performance. Twenty-eight genotypes were phenotyped at 40 : 28°C for 2 days in climate chambers. A second screening (four high F v/ F m and four low F v/ F m genotypes) was conducted for 4 days at 38 : 28°C, followed by 5 days' recovery (26 : 20°C). The tolerant genotypes maintained high net photosynthesis (P N) and increased stomatal conductance (g s) at 38°C, allowing better leaf cooling. Sensitive genotypes had lower F v/ F m and P N at 38°C, and g s increased less than in the tolerant group, reducing leaf cooling. Under controlled conditions, all eight genotypes had the same plant size and pollen viability, but after heat stress, plant size and pollen viability reduced dramatically in the sensitive group. Two tolerant and two sensitive genotypes were grown in the field during a heat wave (38 : 26°C). Tolerant genotypes accumulated more biomass, had a lower heat injury index and higher fruit yield. To our knowledge, this is the first time screening for heat tolerance by F v/ F m in climate chambers was verified by a field trial under natural heat stress. The differences after heat stress in controlled environments were comparable to those in yield between tolerant and sensitive groups under heat stress in the field. The results suggest that F v/ F m is effective for early detection of heat tolerance, and screening seedlings for heat sensitivity can speed crop improvement. Heat stress is limiting tomato production globally. Tolerant genotypes screened for heat stress using chl a fluorescence had better growth under controlled conditions and maintained high fruit production in the field. These results may help downscale laboratory-based high-throughput phenotyping techniques used to develop heat-tolerant tomato varieties. [ABSTRACT FROM AUTHOR]

Abstract Environmental stresses are the major factors that limit the geographical distribution of plants. As a consequence, plants have developed different strategies to adapt to these environmental changes among which can be outlined the maintenance of membranes' integrity and fluidity. Lipids are key molecules for this environmental adaptation and a comprehensive understand of the molecular mechanisms underlying is still required. Here, lipidome changes in Japanese rice (Oryza sativa var. Japonica) upon heat and hydric stresses are assessed using an untargeted approach based on liquid chromatography coupled with mass spectrometry (LC-MS). The obtained data were analyzed using different multivariate data analysis tools. A total number of 298 lipids responded to these abiotic stresses, and 128 of them were tentatively identified. Diacylglycerols (DG), triacylglycerols (TG), phosphatidylcholines (PC) and phosphatidylethanolamines (PE) were the most altered lipid families heat and hydric stress. Interpretation of the obtained results showed relevant changes related to the unsaturation degree in the identified lipids. In the case of heat stress, a decrease in the unsaturation degree of lipids can be linked to an increase in the cell membranes' rigidity. In contrast, the hydric stress produced an increase in the lipids unsaturation degree causing an increase in the cell membranes' fluidity, in an attempt to adapt to these non-optimal conditions. Highlights • Climatic stresses on rice were evaluated by an untargeted lipidomics approach. • A ROI MCR based strategy was used to analyze LC-MS data. • 298 rice lipids were good indicators of heat and hydric stresses on rice. • Heat stress appeared to cause more severe effects than hydric stress. [ABSTRACT FROM AUTHOR]

Tree crowns are spatially heterogeneous, sometimes resulting in significant variation in microclimate across the canopy, particularly with respect to temperature. Yet it is not known whether such localised temperature variation equates to intracanopy variation in leaf-level physiological thermal tolerance. Here, we studied whether microclimate variation across the canopy of a dominant desert tree equated to localised variation in leaf thermal thresholds (T50) among four canopy positions: upper south, upper north, lower south, lower north. Principal component analysis was used to generate a composite climatic stress variable (CSTRESS) from canopy temperature, vapour pressure deficit, and relative humidity. We also determined the average number of days that maximum temperatures exceeded the air temperature equating to this species' critical threshold of 49 °C (AT49). To estimate how closely leaf temperatures track ambient temperature, we predicted the thermal time constant (τ) for leaves at each canopy position. We found that CSTRESS and AT49 were significantly greater in lower and north-facing positions in the canopy. Differences in wind speed with height resulted in significantly longer predicted τ for leaves positioned at lower, north-facing positions. Variation in these drivers was correlated with significantly higher T50 for leaves in these more environmentally stressful canopy positions. Our findings suggest that this species may optimise resources to protect against thermal damage at a whole-plant level. They also indicate that, particularly in desert environments with steep intracanopy microclimatic gradients, whole-plant carbon models could substantially under- or overestimate productivity under heat stress, depending on where in the canopy T50 is measured. [ABSTRACT FROM AUTHOR]

Summer vegetables production is enormously influenced by elevated temperature above thresh hold level which finally brings about a threat to food security in Indo-Pak region. Genetic variability is a significant tool to address this issue. The current study was intended to screen out heat tolerant cucumber genotypes and assessment of certain heat tolerant and sensitive genotypes for some water related, physiological and biochemical attributes. After one-month emergence of seedlings of twentyfive cucumber genotypes were subjected to elevated temperature (40°C/32°C day/night) for one week. Selection of cucumber genotypes for heat tolerance and sensitive was done based on several morphological, physiological and biochemical attributes. Substantial variation among genotypes was observed according to their capability to tolerate heat stress. Genotypes L3466 and Desi-cucumber (having electrolyte leakage of 50.5 and 46.5%, respectively) were found the most heat tolerant, while Suyo Long and Poinsett were found sensitive to heat stress (having electrolyte leakage of 52.3 and 54.5%, respectively). The significant difference was observed in water-related attributes, antioxidant activities, osmoprotectants and lipid peroxidation in leaves of tolerant (L3466 and Desi-cucumber) and sensitive (Suyo Long and Poinsett) genotypes under heat stress (40°C/32°C) when further analyzed. It was concluded that a few genotypes were more tolerant to elevated temperature (40°C) than others under study. [ABSTRACT FROM AUTHOR]

Field pea (Pisum sativum), a major grain legume crop, is autogamous and adapted to temperate climates. The objectives of this study were to investigate effects of high temperature stress on stamen chemical composition, anther dehiscence, pollen viability, pollen interactions with pistil and ovules, and ovule growth and viability. Two cultivars ("CDC Golden" and "CDC Sage") were exposed to 24/18°C (day/night) continually or to 35/18°C for 4 or 7 days. Heat stress altered stamen chemical composition, with lipid composition of "CDC Sage" being more stable compared with "CDC Golden." Heat stress reduced pollen viability and the proportion of ovules that received a pollen tube. After 4 days at 35°C, pollen viability in flower buds decreased in "CDC Golden," but not in "CDC Sage." After 7 days, partial to full failure of anthers to dehisce resulted in subnormal pollen loads on stigmas. Although growth (ovule size) of fertilized ovules was stimulated by 35°C, heat stress tended to decrease ovule viability. Pollen appears susceptible to stress, but not many grains are needed for successful fertilization. Ovule fertilization and embryos are less susceptible to heat, but further research is warranted to link the exact degree of resilience to stress intensity. Heat stress induced anther indehiscence and reduced pollen viability and the proportion of ovules that received a pollen tube in field pea. Heat stress also altered stamen chemical composition, with the lipid composition of "CDC Sage" being more stable than "CDC Golden," which may explain the greater robustness of pollen viability in "CDC Sage" to heat. Ovule viability is less susceptible to heat stress. [ABSTRACT FROM AUTHOR]

Terminal droughts, along with high temperatures, are becoming more frequent to strongly influence the seed development in cool‐season pulses like lentil. In the present study, the lentil plants growing outdoors under natural environment were subjected to following treatments at the time of seed filling till maturity: (a) 28/23 °C day/night temperature as controls; (b) drought stressed, plants maintained at 50% field capacity, under the same growth conditions as in a; (c) heat stressed, 33/28 °C day/night temperature, under the same growth conditions as in a; and (d) drought + heat stressed, plants at 50% field capacity, 33/28 °C day/night temperature, under the same growth conditions as in (a). Both heat and drought resulted in marked reduction in the rate and duration of seed filling to decrease the final seed size; drought resulted in more damage than heat stress; combined stresses accentuated the damage to seed starch, storage proteins and their fractions, minerals, and several amino acids. Comparison of a drought‐tolerant and a drought‐sensitive genotype indicated the former type showed significantly less damage to various components of seeds, under drought as well as heat stress suggesting a cross tolerance, which was linked to its (drought tolerant) better capacity to retain more water in leaves and hence more photo‐assimilation ability, compared with drought‐sensitive genotype. Lentil is a cool‐season food legume, which is strongly influenced by terminal droughts associated with heat stress at the time of seed filling. The present study showed that these two stresses, especially in combination would diminish the seed yields severely and would also result in poor‐quality seeds, deficient in starch, proteins, and minerals. Drought tolerant lentil genotypes might prove to be promising under combined stress treatments. [ABSTRACT FROM AUTHOR]

Key message: Tomato pollen grains have the capacity for ethylene production, possessing specific components of the ethylene-biosynthesis and -signaling pathways, being affected/responsive to high-temperature conditions.Abstract: Exposure of plants to heat stress (HS) conditions reduces crop yield and quality, mainly due to sensitivity of pollen grains. Recently, it was demonstrated that ethylene, a gaseous plant hormone, plays a significant role in tomato pollen heat-tolerance. It is not clear, however, whether, or to what extent, pollen grains are dependent on the capacity of the surrounding anther tissues for ethylene synthesis and signaling, or can synthesize this hormone and possess an active signaling pathway. The aim of this work was (1) to investigate if isolated, maturing and mature, tomato pollen grains have the capacity for ethylene production, (2) to find out whether pollen grains possess an active ethylene-biosynthesis and -signaling pathway and characterize the respective tomato pollen components at the transcript level, (3) to look into the effect of short-term HS conditions. Results from accumulation studies showed that pollen, anthers, and flowers produced ethylene and HS affected differentially ethylene production by (rehydrated) mature pollen, compared to anthers and flowers, causing elevated ethylene levels. Furthermore, several ethylene synthesis genes were expressed, with SlACS3 and SlACS11 standing out as highly HS-induced genes of the pollen ethylene biosynthesis pathway. Specific components of the ethylene-signaling pathway as well as several ethylene-responsive factors were expressed in pollen, with SlETR3 (ethylene receptor; named also NR, for never ripe) and SlCTR2 (constitutive triple response2) being HS responsive. This work shows that tomato pollen grains have the capacity for ethylene production, possessing active ethylene-biosynthesis and -signaling pathways, highlighting specific pollen components that serve as a valuable resource for future research on the role of ethylene in pollen thermotolerance. [ABSTRACT FROM AUTHOR]