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The resistance of xylem conduits to embolism is a major factor defining drought tolerance and can set the distributional limits of species across rainfall gradients. Recent work suggests that the proximity of vessels to neighbors increases the vulnerability of a conduit. We therefore investigated whether the relative vessel area of xylem correlates with intra- and intergeneric variation in xylem embolism resistance in species pairs or triplets from the genera Acer, Cinnamomum, Ilex, Quercus, and Persea, adapted to environments differing in aridity. We used the optical vulnerability method to assess embolism resistance in stems and conducted anatomical measurements on the xylem in which embolism resistance was quantified. Vessel lumen fraction correlated with xylem embolism resistance across and within genera. A low vessel lumen fraction likely increases the resistance to gas movement between conduits, by diffusion or advection, while a high vessel lumen fraction enhances gas transport thorough increased conduit-to-conduit connectivity and reduced distances between conduits and therefore the likelihood of embolism propagation. We suggest that the rate of gas movement due to local pressure differences and xylem network connectivity is a central driver of embolism propagation in angiosperm vessels. One sentence summary. The proportion of vessels in the xylem correlates with embolism resistance across species and within genera.

Ongoing changes in climate, and the consequent mortality of natural and cultivated forests across the globe, highlight the urgent need to understand the plant traits associated with greater tolerance to drought. Here, we aimed at assessing key foliar traits, with a focus on the hydraulic component, that could confer a differential ability to tolerate drought in three commercial hybrids of the most important Eucalyptus species utilized in tropical silviculture: E. urophyla, E. grandis and E. camaldulensis. All genotypes exhibited similar water potential when the 90% stomatal closure (Ψgs90) occurs with Ψgs90 always preceding the start of embolism events. The drought-tolerant hybrid showed a higher leaf resistance to embolism, but the leaf hydraulic efficiency was similar among all genotypes. Other traits presented by the drought-tolerant hybrid were a higher cell wall reinforcement, lower value of osmotic potential at full turgor and greater bulk modulus of elasticity. We also identified that the leaf capacitance after the turgor loss, the ratio between cell wall thickness (t) and lumen breadth (b) ratio (t/b)3, and the minimal conductance might be good proxies for screening drought-tolerant Eucalyptus genotypes. Our findings suggest that xylem resistance to embolism can be an important component of drought tolerance in Eucalyptus in addition to other traits aimed at delaying the development of high tensions in the xylem. Highlight Drought tolerance in tropical Eucalyptus hybrids encompasses a high leaf resistance to embolism and a suite of traits aimed at delaying the development of high tensions in the xylem.

Auxins are known to regulate xylem development in plants, but their effects on water transport efficiency are poorly known. Here we used tomato plants with the diageotropica mutation (dgt), which has impaired function of a cyclophilin 1 cis–trans isomerase involved in auxin signaling, and the corresponding wild type (WT) to explore the mutation’s effects on plant hydraulics and leaf gas exchange. The xylem of the dgt mutant showed a reduced hydraulically weighted vessel diameter (Dh) (24–43%) and conduit number (25–58%) in petioles and stems, resulting in lower theoretical hydraulic conductivities (Kt); on the other hand, no changes in root Dh and Kt were observed. The measured stem and leaf hydraulic conductances of the dgt mutant were lower (up to 81%), in agreement with the Kt values; however, despite dgt and WT plants showing similar root Dh and Kt, the measured root hydraulic conductance of the dgt mutant was 75% lower. The dgt mutation increased the vein and stomatal density, which could potentially increase photosynthesis. Nevertheless, even though it had the same photosynthetic capacity as WT plants, the dgt mutant showed a photosynthetic rate c. 25% lower, coupled with a stomatal conductance reduction of 52%. These results clearly demonstrate that increases in minor vein and stomatal density only result in higher leaf gas exchange when accompanied by higher hydraulic efficiency.

Drought is a major constraint to plant growth and productivity worldwide and will aggravate as water availability becomes scarcer. Although elevated air [CO2] might mitigate some of these effects in plants, the mechanisms underlying the involved responses are poorly understood in woody economically important crops such as Coffea. This study analyzed transcriptome changes in Coffea canephora cv. CL153 and C. arabica cv. Icatu exposed to moderate (MWD) or severe water deficits (SWD) and grown under ambient (aCO2) or elevated (eCO2) air [CO2]. We found that changes in expression levels and regulatory pathways were barely affected by MWD, while the SWD condition led to a down-regulation of most differentially expressed genes (DEGs). eCO2 attenuated the impacts of drought in the transcripts of both genotypes but mostly in Icatu, in agreement with physiological and metabolic studies. A predominance of protective and reactive oxygen species (ROS)-scavenging-related genes, directly or indirectly associated with ABA signaling pathways, was found in Coffea responses, including genes involved in water deprivation and desiccation, such as protein phosphatases in Icatu, and aspartic proteases and dehydrins in CL153, whose expression was validated by qRT-PCR. The existence of a complex post-transcriptional regulatory mechanism appears to occur in Coffea explaining some apparent discrepancies between transcriptomic, proteomic, and physiological data in these genotypes. info:eu-repo/semantics/publishedVersion

This work received funding support from the European Union's Horizon 2020 research and innovation program (grant agreement No 727934 , project BreedCAFS), ( CEF ), - Individual Call (CEEC Individual) - 2021.01107.CEECIND/CP1689/CT0001 (IM) . Fellowships from the Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil (CNPq) , (to F.M. DaMatta and F.L. Partelli), and Fundação de Amparo à Pesquisa do Estado de Minas Gerais, Brazil (FAPEMIG, projects CRA-RED-00053-16 and APQ 01512-18 , to F.M. DaMatta) are also greatly acknowledged. Publisher Copyright: © 2022 Elsevier GmbH As drought threatens crop productivity it is crucial to characterize the defense mechanisms against water deficit and unveil their interaction with the expected rise in the air [CO2]. For that, plants of Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu grown under 380 (aCO2) or 700 μL L−1 (eCO2) were exposed to moderate (MWD) and severe (SWD) water deficits. Responses were characterized through the activity and/or abundance of a selected set of proteins associated with antioxidative (e.g., Violaxanthin de-epoxidase, Superoxide dismutase, Ascorbate peroxidases, Monodehydroascorbate reductase), energy/sugar (e.g., Ferredoxin-NADP reductase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, sucrose synthase, mannose-6-phosphate isomerase, Enolase), and lipid (Lineolate 13S-lipoxygenase) processes, as well as with other antioxidative (ascorbate) and protective (HSP70) molecules. MWD caused small changes in both genotypes regardless of [CO2] level while under the single imposition to SWD, only Icatu showed a global reinforcement of most studied proteins supporting its tolerance to drought. eCO2 alone did not promote remarkable changes but strengthened a robust multi-response under SWD, even supporting the reversion of impacts already observed by CL153 at aCO2. In the context of climate changes where water constraints and [CO2] levels are expected to increase, these results highlight why eCO2 might have an important role in improving drought tolerance in Coffea species. publishersversion published

Despite being evolved in shaded environments, most coffee (Coffea arabica L.) is cultivated worldwide under sparse shade or at full sunlight. Coffee is ranked as greatly responsive to climate change (CC), and shading has been considered an important management strategy for mitigating the harmful CC outcomes on the crop. However, there is no information on the effects of enhanced [CO2] (eCa) on coffee performance in response to light availability. Here, we examined how carbon assimilation and use are affected by eCa in combination with contrasting light levels. For that, greenhouse-grown plants were submitted to varying light levels (16 or 7.5 mol photons m−2 day−1) and [CO2] (ca. 380 or 740 μmol mol−1 air) over six months. We demonstrated that both high light and eCa improved growth and photosynthetic performance, independently. Despite marginal alterations in biomass partitioning, some allometric changes, such as higher root biomass-to-total leaf area and lower leaf area ratio under the combination of eCa and high light were found. Stimulation of photosynthetic rates by eCa occurred with no direct effect on stomatal and mesophyll conductances, and no signs of photosynthetic down-regulation were found irrespective of treatments. Particularly at high light, eCa led to decreases in both photorespiration rates and oxidative pressure. Overall, our novel findings suggest that eCa could tandemly act with shading to mitigate the harmful CC effects on coffee sustainability.

As drought threatens crop productivity it is crucial to characterize the defense mechanisms against water deficit and unveil their interaction with the expected rise in the air [CO

Growing water restrictions associated with climate changes constitute daunting challenges to crop performance. This study unveils the impacts of moderate (MWD) or severe (SWD) water deficit, and their interaction with air [CO2], on the photosynthetic apparatus of Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu. Seven year-old potted plants grown under 380 (aCO2) or 700μLL−1 (eCO2) [CO2] gradually reached predawn water potentials between −1.6 to −2.1MPa (MWD), and below −3.5MPa (SWD). Under drought, stomata closure was chiefly related to ABA rise. Increasing drought severity progressively affected gas exchange and fluorescence parameters in both genotypes, with non-stomatal limitations becoming gradually dominating, especially regarding the photochemical and biochemical components of CL153 SWD plants. In contrast, Icatu plants were highly tolerant to SWD, with minor, if any, negative impacts on the potential photosynthetic functioning and components (e.g., Amax, Fv/Fm, electron carriers, photosystems (PSs) and RuBisCO activities). Besides, drought-stressed Icatu plants displayed increased abundance of a large set of proteins associated with the photosynthetic apparatus (photosystems, light harvesting complexes, cyclic electron flow, RuBisCO activase) regardless of [CO2]. Single eCO2 did not promote stomatal and photosynthetic down-regulation in both genotypes. Instead, eCO2 increased photosynthetic performance, moderately reinforced photochemical (PSs activity, electron carriers) and biochemical (RuBisCO, Ru5PK) components, whereas photoprotective mechanisms and protein abundance remained mostly unaffected. In both genotypes, under MWD, eCO2 superimposition delayed stress severity and promoted photosynthetic functioning with lower energy dissipation and PSII impacts, whereas stomatal closure was decoupled from increases in ABA. In SWD plants most impacts on the photosynthetic performance were reduced by eCO2, especially in the moderately drought affected CL153 genotype, although maintaining RuBisCO as the most sensitive component, deserving special breeder’s attention to improve coffee sustainability under future climate scenarios.

Leaf scald, caused by Monographella albescens, is a key disease affecting rice production worldwide. Alternative methods for leaf scald management are demanded by the growers and silicon (Si) application emerges as a promising way to decrease severity not only of leaf scald but also of other relevant rice diseases. Some evidence suggests that Si may preserve the photosynthetic performance of plants upon pathogen infection but the mechanistic basis for this remain unresolved. In the present study, mesophyll conductance (gm) was calculated to suitably parameterize the responses of net carbon assimilation rate (A) to chloroplastidic CO2 concentration (Cc) and to resolve the relative contributions of stomatal, mesophyll, and biochemical drawbacks to photosynthesis in rice plants challenged with M. albescens and how all of these facts may be influenced by Si application. Rice plants (cultivar “Primavera”) were hydroponically grown with 0 or 2 mM Si (− Si and + Si plants) and inoculated with M. albescens. Leaf scald-induced decreases in A were associated with roughly proportional decreases in CO2 diffusion (lower stomatal conductance and gm) and impaired photochemistry (e.g. reduced maximum electron transport rate) and biochemistry (e.g. RuBisCO activity) regardless of Si supply. The magnitude of these decreases were, overall, greater in − Si plants than in their + Si counterparts, and therefore a mitigating effect of Si on the preservation of the photosynthetic activity on diseased plants is evident. On infected leaves, gm was not scaled with maximum carboxylation rate (Vcmax) − Cc and, as a consequence, Cc increased accordingly, but only in + Si plants. In conclusion, the supply of Si to rice plants played a central role in decreasing leaf scald symptoms and, as such, preserving to a certain extent their photosynthetic performance. This preservation was not linked to differential impairments on the stomatal function or biochemical steps of photosynthesis but rather with increased CO2 diffusion throughout the mesophyll. This ultimately led to a lower photorespiration-to-gross photosynthesis ratio and less mesophyll limitations of photosynthesis in + Si plants than in their − Si counterparts during the infection process of M. albescens on rice leaves.

Changes in leaf size have been demonstrated to considerably affect leaf hydraulic properties, which in turn impact plant photosynthesis and productivity. In this study, we selected five genotypes from four coffee species (Coffea spp.) with highly contrasting individual leaf areas (from 25 to 280 cm2) to test whether changes in foliar area result in anatomical alterations and ultimately changes in leaf hydraulic function. Increasing leaf area was associated with xylem anatomical traits, such as lower major vein density, higher number of conduits and conduit diameter, and lower cell wall thickness-to-conduit diameter ratio [(t/b)3] in the midrib xylem. Such modifications, however, were not associated with changes in leaf hydraulic conductance (Kleaf) and resulted in minor, if at all, changes in the water potential causing 50% decline in Kleaf (P50), which demonstrate that leaves of coffee species have very similar hydraulic properties despite considerable variations in foliar area. We propose that declines in major vein density in larger coffee leaves are potentially balanced by increases in xylem conduit number and dimensions in the midrib, resulting in similar Kleaf when compared with smaller leaves. Finally, we demonstrate that C. racemosa plants have both the lowest P50 and the higher (t/b)3, and it should be considered as a putative candidate for breeders aiming at increasing drought tolerance in coffee plants.

Plants that perform the Crassulacean acid metabolism (CAM), which obtain CO2 overnight and convert it mainly in malic acid, successfully grow in environments with water and nutrient shortages, that is partly associated with their higher water- and nitrogen-use efficiencies. Water and nutrient limitations can impair photosynthesis through the reduction of RuBisCO and increment of photorespiration, disturbing the plant carbon balance. In this context, we conducted a controlled experiment with the epiphytic C3-CAM bromeliad Guzmania monostachia to investigate how the combined water and nutritional deficits affect the activity of RuBisCO and its activation state (RAS), and to evaluate the efficiency of photosynthesis during the transition from C3 to CAM. Apart from an increase in CAM activity, bromeliads submitted to both water and nutritional deficits showed higher RAS values and unaltered RuBisCO activity compared to C3 bromeliads and, surprisingly, the maximum quantum efficiency of photosynthesis increased. Glucose, fructose and starch levels were maintained, while sucrose concentrations increased over time. These results, combined with the high RAS values, suggest an increased efficiency of RuBisCO functioning. Our results reinforce the ability of epiphytic bromeliads to deal with stressful habitats by a higher efficiency of RuBisCO during the transition to CAM, another feature that may allow their evolution in the epiphytic environment.

Acidic soils with elevated aluminum (Al) saturations are worldwide distributed and harm the crop production in most of the tropical and subtropical regions. Under these conditions, root elongation may be impaired and thus disturbs water and nutrient uptake. Consequently, physiological responses of plants challenged with excess Al may resemble those of drought stresses. Here, we hypothesized that drought tolerant plants are also Al tolerant due to changes in growth, metabolic and physiological adjustments in leaves. Two maize genotypes, BRS1010 and BRS1055, sensitive and tolerant to drought, respectively, were hydroponically grown under controlled conditions and challenged with two Al concentrations (0 and 100 µM AlCl3) for 5 days. After treatment with Al, BRS1055 plants displayed increased leaf and stem elongation whereas the relative root growth rate remained unchanged. This was accompanied by unaltered root structure, photosynthetic efficiency and leaf primary metabolism. In sharp contrast, the BRS1010 plants were sensitive to Al, exhibiting a reduction in leaf and stem elongation and biomass accumulation in shoot and root, as well as greater structural damages in root tips. Additionally, in response to Al, lipid peroxidation increased in BRS1010 leaves in parallel to inhibition of photosynthetic performance and dark respiration. Moreover, compared to control treatment, the genotype BRS1010 displayed a large accumulation of sugars, amino acid, proteins and organic acids in leaves under Al stress. Therefore, the leaf physiology and metabolism are pivotal players in modulating Al tolerance in maize. © 2020, Brazilian Society of Plant Physiology. Made available in DSpace on 2020-08-07T11:12:32Z (GMT). No. of bitstreams: 1 Metabolic-physiological.pdf: 1044692 bytes, checksum: feb3f1f0d8a7f83450f712ea4604fde9 (MD5) Previous issue date: 2020

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and whether pre-existing embolism in neighbouring conduits alters this threshold. Observations were made on a diverse sample of angiosperm and conifer species through a cycle of dehydration, rehydration and subsequent dehydration to death. Upon rehydration after the formation of embolism, no refilling was observed. When little pre-existing embolism was present, xylem conduits had a conserved, individual, embolism resistance threshold that varied across the population of conduits. The consequence of a variable conduit-specific embolism threshold is that a small degree of pre-existing embolism in the xylem results in an apparently more resistant xylem in a subsequent dehydration, particularly in angiosperms with vessels. While our results suggest that pit membranes separating xylem conduits are critical for maintaining a conserved individual embolism threshold for given conduit when little pre-exisiting embolism is present, as the percentage of embolized conduits increases, gas movement, local pressure differences, and connectivity between conduits increasingly contribute to embolism spread.

Leaves were forced to accumulate starch as much as possible but maintained relatively low soluble sugar levels with no evidence of photosynthetic feedback downregulation. Here, we examined whether the regulation of photosynthesis in coffee depends on sink activity or carbohydrate build-up in source leaves and how the coffee tree adjusts its photosynthetic performance and primary metabolism to varying source-to-sink ratios. We designed a field experiment by girdling coffee branches that were further manipulated by controlled defoliation and/or defruiting such that three highly varying source-to-sink ratios were created. Under markedly high source-to-sink ratios, photosynthesis rates were primarily limited by diffusional factors, and feedback downregulation contributed a maximum of 7% of the photosynthetic reduction. Such responses were accompanied by a relatively enormous capacity for starch accumulation coupled with the maintenance of low levels of soluble sugars. Chronic photoinhibition and photodamage could be avoided by increases in nonphotochemical energy dissipation, photorespiration and respiration rates, thus diminishing the excitation pressure on photosystems. Overall, the activities of key enzymes (and their transcript abundance) associated with carbon metabolism varied only marginally across treatments. Leaf metabolic adjustments were more evident under high sink demand conditions, and nitrogen metabolism was more affected than carbon metabolism. In conclusion, our results offer novel insights into the high coordination between the source supply and sink demand in coffee, with a minor role of photosynthetic downregulation even under dramatically low sink conditions.

– Salinity is a major threat to agriculture. However, depending on the concentration of soluble salts in soil, increased secondary metabolite levels can occur with no major damages to plant growth and development. The phytoecdysteroid (PE) 20-hydroxyecdysone (20E) is a secondary metabolite with biotechnological, medicinal, pharmaceutical and agrochemical applicability. Here, we characterize the responses (growth and physiology) of Pfaffia glomerata under different NaCl concentrations and examine the production of 20E as affected by salinity. Forty-day-old plants grown in greenhouse were exposed to 0, 120, 240, 360 or 480 mM of NaCl for 11 days. Moderate salinity (i.e., 120 mM of NaCl) led to increased 20E concentrations in leaves (47%) relative to the control with no significant effect on photosynthesis and biomass accumulation, thus allowing improved 20E contents on a per whole-plant basis. In contrast, plants under high salinity (i.e., 240–480 mM of NaCl) displayed similar 20E concentrations in leaves compared to the control, but with marked impairments to biomass accumulation and photosynthetic performance (coupled with decreased sucrose and starch levels) in parallel to nutritional imbalance. High salinity also strongly increased salicylic acid levels, antioxidant enzyme activities, and osmoregulatory status. Regardless of stress severity, 20E production was accompanied by the upregulation of Spook and Phantom genes. Our findings suggest that P. glomerata cultivation in moderate salinity soils can be considered as a suitable agricultural option to increase 20E levels, since metabolic and structural complexity that makes its artificial synthesis very difficult.

PTDC/ASP-AGR/31257/2017 Coffee, one of the most heavily globally traded agricultural commodities, has been categorized as a highly sensitive plant species to progressive climatic change. Here, we summarize recent insights on the coffee plant’s physiological performance at elevated atmospheric carbon dioxide concentration [CO 2 ]. We specifically (i) provide new data of crop yields obtained under free-air CO 2 enrichment conditions, (ii) discuss predictions on the future of the coffee crop as based on rising temperature and (iii) emphasize the role of [CO 2 ] as a key player for mitigating harmful effects of supra-optimal temperatures on coffee physiology and bean quality. We conclude that the effects of global warming on the climatic suitability of coffee may be lower than previously assumed. We highlight perspectives and priorities for further research to improve our understanding on how the coffee plant will respond to present and progressive climate change. publishersversion published

A previous stress exposure may result in a faster or stronger response when plants are challenged again by a stress event. This capacity of plants to “remember” a past stress and to respond in a different way to multiple stress exposures is called memory response. Despite the mechanisms promoting the plant memory response to abiotic stresses are not completely elucidated, a growing body of evidence has pointed to chromatin remodeling as an important memory mechanism. Additionally, transcriptomic studies have helped to clarify the transcriptional memory types and relevant functional classes of genes and pathways that potentially exhibit a memory behavior. This review focuses on the main concepts related to plant memory responses to abiotic stresses, especially drought which is by far the major environmental stress impairing crop production. We also review the main advances on the mechanisms underlying the plant stress memory responses such as the role of ABA and chromatin remodeling mechanisms. The most recent advances promoted by transcriptomic approaches are also highlighted.

Xylem resistance to embolism is a key metric determining plant survival during drought. Yet, we have a limited understanding of the degree of plasticity in vulnerability to embolism. Here, we tested whether light availability influences embolism resistance in leaves and stems. The optical vulnerability method was used to assess stem and leaf resistance to embolism in Phellodendron amurense and Ilex verticillata acclimated to sun and shade microenvironments within the same canopy. In both species, we found considerable segmentation in xylem resistance to embolism between leaves and stems, but only minor acclimation in response to light availability. With the addition of a third species, Betula pubescens, which shows no vulnerability segmentation, we sought to investigate xylem anatomical traits that might correlate with strong vulnerability segmentation. We found a correlation between the area fraction of vessels in the xylem and embolism resistance across species and tissue types. Our results suggest that minimal acclimation of embolism resistance occurs in response to light environment in the same individual and that the degree of vulnerability segmentation between leaves and stems might be determined by the vessel lumen fraction of the xylem.

Understanding the effect of extreme temperatures and elevated air (CO2) is crucial for mitigating the impacts of the coffee industry. In this work, leaf transcriptomic changes were evaluated in the diploid C. canephora and its polyploid C. arabica, grown at 25 °C and at two supra-optimal temperatures (37 °C, 42 °C), under ambient (aCO2) or elevated air CO2 (eCO2). Both species expressed fewer genes as temperature rose, although a high number of differentially expressed genes (DEGs) were observed, especially at 42 °C. An enrichment analysis revealed that the two species reacted differently to the high temperatures but with an overall up-regulation of the photosynthetic machinery until 37 °C. Although eCO2 helped to release stress, 42 °C had a severe impact on both species. A total of 667 photosynthetic and biochemical related-DEGs were altered with high temperatures and eCO2, which may be used as key probe genes in future studies. This was mostly felt in C. arabica, where genes related to ribulose-bisphosphate carboxylase (RuBisCO) activity, chlorophyll a-b binding, and the reaction centres of photosystems I and II were down-regulated, especially under 42°C, regardless of CO2. Transcriptomic changes showed that both species were strongly affected by the highest temperature, although they can endure higher temperatures (37 °C) than previously assumed.

Water scarcity is the most significant factor limiting coffee production, although some cultivars can still have important drought tolerance. This study analyzed leaf transcriptomes of two coffee cultivars with contrasting physiological responses, Coffea canephora cv. CL153 and Coffea. arabica cv. Icatu, subjected to moderate (MWD) or severe water deficits (SWD). We found that MWD had a low impact compared with SWD, where 10% of all genes in Icatu and 17% in CL153 reacted to drought, being mainly down-regulated upon stress. Drought triggered a genotype-specific response involving the up-regulation of reticuline oxidase genes in CL153 and heat shock proteins in Icatu. Responsiveness to drought also included desiccation protectant genes, but primarily, aspartic proteases, especially in CL153. A total of 83 Transcription Factors were found engaged in response to drought, mainly up-regulated, especially under SWD. Together with the enrollment of 49 phosphatases and 272 protein kinases, results suggest the involvement of ABA-signaling processes in drought acclimation. The integration of these findings with complementing physiological and biochemical studies reveals that both genotypes are more resilient to moderate drought than previously thought and suggests the existence of post-transcriptional mechanisms modulating the response to drought info:eu-repo/semantics/publishedVersion

PTDC/ASP-AGR/31257/2017 UIDB/00239/2020 UIDP/04035/2020 UID/AGR/04129/2020 UIDB/04551/2020 CRA-RED-00053-16 As atmospheric [CO2] continues to rise to unprecedented levels, understanding its impact on plants is imperative to improve crop performance and sustainability under future climate conditions. In this context, transcriptional changes promoted by elevated CO2 (eCO2) were studied in genotypes from the two major traded coffee species: the allopolyploid Coffea arabica (Icatu) and its diploid parent, C. canephora (CL153). While Icatu expressed more genes than CL153, a higher number of differentially expressed genes were found in CL153 as a response to eCO2. Although many genes were found to be commonly expressed by the two genotypes under eCO2, unique genes and pathways differed between them, with CL153 showing more enriched GO terms and metabolic pathways than Icatu. Divergent functional categories and significantly enriched pathways were found in these genotypes, which altogether supports contrasting responses to eCO2. A considerable number of genes linked to coffee physiological and biochemical responses were found to be affected by eCO2 with the significant upregulation of photosynthetic, antioxidant, and lipidic genes. This supports the absence of photosynthesis down-regulation and, therefore, the maintenance of increased photosynthetic potential promoted by eCO2 in these coffee genotypes. publishersversion published

Nitrogen promotes changes in SLA through metabolism and anatomical traits in Capsicum plants. Specific leaf area (SLA) is a key trait influencing light interception and light use efficiency that often impacts plant growth and production. SLA is a key trait explaining growth variations of plant species under different environments. Both light and nitrogen (N) supply are important determinants of SLA. To better understand the effect of irradiance level and N on SLA in Capsicum chinense, we evaluated primary metabolites and morphological traits of two commercial cultivars (Biquinho and Habanero) in response to changes in both parameters. Both genotypes showed increased SLA with shading, and a decrease in SLA in response to increased N supply, however, with Habanero showing a stable SLA in the range of N deficiency to sufficient N doses. Correlation analyses indicated that decreased SLA in response to higher N supply was mediated by altered amino acids, protein, and starch levels, influencing leaf density. Moreover, in the range of moderate N deficiency to N sufficiency, both genotypes exhibited differences in SLA response, with Biquinho and Habanero displaying alterations on palisade and spongy parenchyma, respectively. Altogether, the results suggest that SLA responses to N supply are modulated by the balance between certain metabolites content and genotype-dependent changes in the parenchyma cells influencing leaf thickness and density.

The infection of wheat leaves by Pyricularia oryzae induced remarkable reprogramming of the primary metabolism (amino acids, sugars, and organic acids) in favor of a successful fungal infection and certain changes were conserved among cultivars regardless of their level of resistance to blast. Wheat blast, caused by Pyricularia oryzae, has become one of the major threats for food security worldwide. Here, we investigated the behavior of three wheat cultivars (BR-18, Embrapa-16, and BRS-Guamirim), differing in their level of resistance to blast, by analyzing changes in cellular damage, antioxidative metabolism, and defense compounds as well as their photosynthetic performance and metabolite profile. Blast severity was lower by 45 and 33% in Embrapa-16 and BR-18 cultivars (moderately resistant), respectively, at 120 h after inoculation in comparison to BRS-Guamirim cultivar (susceptible). Cellular damage caused by P. oryzae infection was great in BRS-Guamirim compared to BR-18. The photosynthetic performance of infected plants was altered due to diffusional and biochemical limitations for CO2 fixation. At the beginning of the infection process, dramatic changes in both carbohydrate metabolism and on the levels of amino acids, intermediate compounds of the tricarboxylic acid cycle, and polyamines were noticed regardless of cultivar suggesting an extensive metabolic reprogramming of the plants following fungal infection. Nevertheless, Embrapa-16 plants displayed a more robust and efficient antioxidant metabolism, higher phenylalanine ammonia-lyase and polyphenoloxidase activities and higher concentrations of phenolics and lignin, which, altogether, helped them to counteract more efficiently the infection by P. oryzae. Our results demonstrated that P. oryzae infection significantly modified the metabolism of wheat plants and different types of metabolic defence may act both additively and synergistically to provide additional plant protection to blast.

Dynamic variation of the stomatal pore in response to changes in leaf–air vapour pressure difference (VPD) constitutes a critical regulation of daytime gas exchange. The stomatal response to VPD has been associated with both foliage abscisic acid (ABA) and leaf water potential (Ψ l); however, causation remains a matter of debate. Here, we seek to separate hydraulic and hormonal control of stomatal aperture by manipulating the osmotic potential of sunflower leaves. In addition, we test whether stomatal responses to VPD in an ABA-deficient mutant (w-1) of sunflower are similar to the wild type. Stomatal apertures during VPD transitions were closely linked with foliage ABA levels in sunflower plants with contrasting osmotic potentials. In addition, we observed that the inability to synthesize ABA at high VPD in w-1 plants was associated with no dynamic or steady-state stomatal response to VPD. These results for sunflower are consistent with a hormonal, ABA-mediated stomatal responses to VPD rather than a hydraulic-driven stomatal response to VPD., In sunflower a plant hormone called abscisic acid closes the microscopic pores on the leaves to prevent excessive water loss when humidity decreases.

The overall coordination between gas exchanges and plant hydraulics may be affected by soil water availability and source-to-sink relationships. Here we evaluated how branch growth and mortality, leaf gas exchange and metabolism are affected in coffee (Coffea arabica L.) trees by drought and fruiting. Field-grown plants were irrigated or not, and maintained with full or no fruit load. Under mild water deficit, irrigation per se did not significantly impact growth but markedly reduced branch mortality in fruiting trees, despite similar leaf assimilate pools and water status. Fruiting increased net photosynthetic rate in parallel with an enhanced stomatal conductance, particularly in irrigated plants. Mesophyll conductance and maximum RuBisCO carboxylation rate remained unchanged across treatments. The increased stomatal conductance in fruiting trees over nonfruiting ones was unrelated to internal CO2 concentration, foliar abscisic acid (ABA) levels or differential ABA sensitivity. However, stomatal conductance was associated with higher stomatal density, lower stomatal sensitivity to vapor pressure deficit, and higher leaf hydraulic conductance and capacitance. Increased leaf transpiration rate in fruiting trees was supported by coordinated alterations in plant hydraulics, which explained the maintenance of plant water status. Finally, by preventing branch mortality, irrigation can mitigate biennial production fluctuations and improve the sustainability of coffee plantations. Universidad Federal de Viçosa, Brasl. Universidad Nacional, Costa Rica. Escuela de Ciencias Biológicas

Frogeye spot, caused by Cercospora sojina, is one of the major diseases causing yield losses in soybean. Considering the potential of silicon (Si) to attenuate the physiological impairments imposed by pathogens infection, this study investigated its effect on leaf gas exchange and chlorophyll (Chl) a fluorescence parameters as well as on the concentrations of photosynthetic pigments and carbohydrate pools on soybean plants from cultivars Bossier and Conquista (susceptible and resistant to frogeye spot, respectively) grown in hydroponic culture containing 0 or 2 mM Si (−Si and +Si plants, respectively) that were noninoculated or inoculated with C. sojina. Plants from cultivar Bossier were more susceptible to frogeye spot compared to cultivar Conquista regardless of Si supply. Frogeye spot severity increased by Si supply regardless of the cultivar. There were no changes in the physiological parameters for noninoculated +Si plants. Even though the susceptibility of plants from cultivar Bossier to frogeye spot increased by Si supply, they showed lower values for the leaf gas exchange parameters, photochemical efficiency and concentration of photosynthetic pigments. The impairments imposed by C. sojina infection on the physiology of plants from cultivar Conquista were governed chiefly by reductions in stomatal conductance regardless of Si supply. The increase in hexose concentration for inoculated plants of the two cultivars was associated with their resistance to frogeye spot. Considering that the increased susceptibility of +Si plants from cultivar Conquista did not result in physiological impairments, it is plausible to rule out that the lower photosynthetic efficiency of plants from cultivar Bossier occurred due to a sharp reduction in the photosynthetically active leaf tissue.

Water deprivation is an important limiting factor in the productivity of crops like coffee. In addition to transcription factors (TFs) and small non-coding RNAs, transcriptional memory seems to act in gene expression modulation during plant drought response. Here, a RNA-Seq approach was used to investigate the drought responses of Coffea canephora clones 109 and 120, which are respectively sensitive and tolerant to drought. Illumina sequencing allowed us to identify differentially expressed genes (DEG) in the tolerant (826) and sensitive (135) clones and their enriched categories. Our results indicate that the sensitive clone may trigger an oxidative stress response, possibly leading to programmed cell death, when exposed to multiple drought episodes. The acclimation of tolerant plants, on the other hand, seems to involve antioxidant secondary metabolism and the ABA response. Most importantly, 49 memory genes were identified in the tolerant clone. They were mainly linked to the ABA pathway, protein folding and biotic stress. Small RNA profiling also identified regulatory microRNAs in coffee leaves, including hundreds of putative novel ones. Our findings strongly suggest that transcriptional memory modulates the expression of drought-responsive genes and contributes to drought tolerance in C. canephora.

Malate is a central metabolite involved in a multiplicity of plant metabolic pathways, being associated with mitochondrial metabolism and playing significant roles in stomatal movements. Vacuolar malate transport has been characterized at the molecular level and is performed by at least one carrier protein and two channels in Arabidopsis (Arabidopsis thaliana) vacuoles. The absence of the Arabidopsis tonoplast Dicarboxylate Transporter (tDT) in the tdt knockout mutant was associated previously with an impaired accumulation of malate and fumarate in leaves. Here, we investigated the consequences of this lower accumulation on stomatal behavior and photosynthetic capacity as well as its putative metabolic impacts. Neither the stomatal conductance nor the kinetic responses to dark, light, or high CO2 were highly affected in tdt plants. In addition, we did not observe any impact on stomatal aperture following incubation with abscisic acid, malate, or citrate. Furthermore, an effect on photosynthetic capacity was not observed in the mutant lines. However, leaf mitochondrial metabolism was affected in the tdt plants. Levels of the intermediates of the tricarboxylic acid cycle were altered, and increases in both light and dark respiration were observed. We conclude that manipulation of the tonoplastic organic acid transporter impacted mitochondrial metabolism, while the overall stomatal and photosynthetic capacity were unaffected.

Two experiments were carried out to assess the changes associated with photoassimilate production and partitioning in the source–sink relationship of flag leaves and spikes of wheat plants infected with Pyricularia oryzae, the causal agent of blast. Flag leaves and spikes were inoculated at 10 and 20 days after anthesis (daa) with a conidial suspension of P. oryzae. Analysis of chlorophyll a fluorescence using maximal photosystem II quantum efficiency (Fv⁄Fm), fraction of energy absorbed that is used in photochemistry (YII), quantum yield of non-regulated energy dissipation (Y(NO)) and quantum yield of regulated energy dissipation (Y(NPQ)), showed an impairment of the photosynthetic performance in both infected flag leaves and spikes, coupled with reduced concentrations of chlorophyll a + b and carotenoids. Compared to non-inoculated controls, there was lower capacity for CO2 fixation by RuBisCO in the infected flag leaves. Similarly, in the infected flag leaves and grains (obtained from infected spikes), there were lower concentrations of soluble sugars, while the hexoses-to-sucrose ratio increased in infected flag leaves. Compared to non-inoculated controls, infected flag leaves showed lower sucrose phosphate synthase (SPS) activity and lower expression of the sucrose synthesis (SuSy) gene, while higher expression and activity of acid invertases also occurred. At the advanced stages of fungal infection, the concentration of starch in grains decreased but remained high for the infected flag leaves. There were reductions in ADP-glucose pyrophosphorylase activity and the expression of ADP-glucose pyrophosphorylase genes and a down-regulation of β- and α-amylase expression at the advanced stages of fungal infection on flag leaves and spikes. In conclusion, the effect of blast on both grain quality and yield can be associated with alterations in both production and partitioning of carbohydrates during the grain filling process.

Plants that perform the Crassulacean acid metabolism (CAM), which obtain CO

Iron (Fe) toxicity is often observed in lowland rice (Oryza sativa L.) plants, disrupting cell homeostasis and impairing growth and crop yields. Silicon (Si) can mitigate the effects of Fe excess on rice by decreasing tissue Fe concentrations, but no information exists whether Si could prevent the harmful effects of Fe toxicity on the photosynthesis and carbon metabolism. Two rice cultivars with contrasting abilities to tolerate Fe excess were hydroponically grown under two Fe levels (25 μM or 5 mM) and amended or not with Si (0 or 2 mM). Fe toxicity caused decreases in net photosynthetic rate (A), particularly in the sensitive cultivar. These decreases were correlated with reductions in stomatal (gs) and mesophyll (gm) conductances, as well as with increasing photorespiration. Photochemical (e.g. electron transport rate) and biochemical (e.g., maximum RuBisCO carboxylation capacity and RuBisCO activity) parameters of photosynthesis, and activities of a range of carbon metabolism enzymes, were minimally, if at all, affected by the treatments. Si attenuated the decreases in A by presumably reducing the Fe content. In fact, A as well as gs and gm, correlated significantly with leaf Fe contents. In summary, our data suggest a remarkable metabolic homeostasis under Fe toxicity, and that Si attenuated the impairments of Fe excess on the photosynthetic apparatus by affecting the leaf diffusive conductance with minimal impacts on carbon metabolism.

El déficit hídrico tiene un impacto negativo en el crecimiento y desarrollo de las plantas a través de alteraciones morfo-fisiológicas. Esta investigación se centró en la dinámica de los rasgos ecofisiológicos y arquitectura de dosel en dos cultivares de café, RUBI-MG1192 (Rubi) y IAPAR59 (I59), sensible y tolerante a la sequía, respectivamente. Los ensayos fueron durante dos años con tres tratamientos de riego, seis muestreos y 7-10 plantas por tratamiento. I59 retuvo sus hojas durante la sequía y demostró ser más isohidríco y plástico para rasgos de funcionamiento hídrico, con un ajuste precoz a la sequía. En contraste, Rubi tuvo desprendimiento de hojas y fue más anisohídrico y plástico para rasgos tardíos a la sequía. Se concluye que la aptitud de las plantas de café sometidas a eventos climáticos depende del ajuste entre las características morfo-fisiológicas y órgano-morfológicas. Estos rasgos deberán ser considerados en los programas de mejoramiento de café.

Soil waterlogging negatively impacts plants due to reduced oxygen availability in the rhizosphere. Here we selected two Coffea canephora clones with contrasting tolerance to drought and oxidative stress to test whether they would also exhibit contrasting tolerance to waterlogging and post-waterlogging reoxygenation. Plants were exposed to six days of waterlogging followed by 40 days of reoxygenation. During waterlogging, both clones exhibited lower leaf gas exchange rate, electron transport rate and photochemical quenching as well as increased non-photochemical quenching; overall, these changes were stronger in the drought tolerant (DT) clones over the drought sentitive (DS) ones. Photosynthetic limitations were essentially linked to diffusional constraints regardless of clone. In both clones, declines in stomatal conductance were not associated with foliar ABA or ethylene levels, however stomatal conductance correlated with the plant hydraulic conductance. After reoxygenation, DT plants mostly recovered leaf function and plant mortality was less than 10%. Conversely, DS plants displayed very low water potentials after reoxygenation, which was accompanied by photosynthetic and membrane damage and 40% plant mortality. Our findings confirmed that the DT clone is less impaired by soil waterlogging and reoxygenation than the DS one. The differences between clones were more evident during the reoxygenation than during waterlogging, likely due to the drought experienced by the DS but not DT plants. Collectively, this information leads us to a common path to find new coffee genotypes with increased tolerance to both drought and waterlogging aiming at increased coffee sustainability under an ongoing climate changing scenario.

The aim of this study was to investigate the effect of magnesium (Mg) on the photosynthetic gas exchange parameters ([net CO2 assimilation rate (A), stomatal conductance (gs), and internal CO2 concentration (Ci)], chlorophyll (Chl) fluorescence a parameters {minimal fluorescence (F0), maximum fluorescence (Fm), maximum quantum yield of photosystem II (Fv/Fm), photochemical quenching coefficient (qp), yield of photochemistry [Y(II)], yield of regulated energy dissipation [Y(NPQ)] and yield of non-regulated dissipation losses [Y(NO)]} as well as on the concentrations of chloroplastidic pigments in rice plants grown in a nutrient solution containing 0.5 or 1.5 mM of Mg (-Mg or + Mg plants, respectively) and non-inoculated or inoculated with Monographella albescens. A higher Mg supply decreased the leaf scald symptoms in addition to partially preserving the photosynthetic performance of rice leaves challenged with M. albescens. Photosynthetic impairments were associated with photochemical and biochemical dysfunctions at the chloroplast level. The images of Chl a fluorescence evidenced increases in both the Y(II) and qp coupled with decreases in Y(NPQ) associated with a higher Mg supply regardless of inoculation, suggesting increased electron transport rates and lower energy dissipation as heat. Notably, as the leaf scald developed, the use of light energy through photochemical reactions was continuously lost, especially for the inoculated -Mg plants. Interestingly, the lower values for F0, Fm, and Fv/Fm for -Mg plants were associated with greater photochemical dysfunctions and a progressive loss of photosynthetic pigments during the infection process of M. albescens. The underlying mechanism through which Mg can affect rice resistance against M. albescens remains to be fully elucidated.

Silicon (Si) has been recognized as a beneficial element to improve rice (Oryza sativa L.) grain yield. Despite some evidence suggesting that this positive effect is observed when Si is supplied along the reproductive growth stage (from panicle initiation to heading), it remains unclear whether its supplementation during distinct growth phases can differentially impact physiological aspects of rice and its yield and the underlying mechanisms. Here, we investigated the effects of additions/removals of Si at different growth stages and their impacts on rice yield components, photosynthetic performance, and expression of genes (Lsi1, Lsi2 and Lsi6) involved in Si distribution within rice shoots. Positive effects of Si on rice production and photosynthesis were manifested when it was specifically supplied during the reproductive growth stage, as demonstrated by: (1) a high crop yield associated with higher grain number and higher 1000-grain weight, whereas the leaf area and whole-plant biomass remained unchanged; (2) an increased sink strength which, in turn, exerted a feed-forward effect on photosynthesis that was coupled with increases in both stomatal conductance and biochemical capacity to fix CO2; (3) higher Si amounts in the developing panicles (and grain husks) in good agreement with a remarkable up-regulation of Lsi6 (and to a lesser extent Lsi1). We suggest that proper levels of Si in these reproductive structures seem to play an as yet unidentified role culminating with higher grain number and size.

Frogeye leaf spot (FLS), caused by the fungus Cercospora sojina, is one of the most important soybean diseases and can cause great yield losses. Several studies have demonstrated that silicon (Si) enhances the plant antioxidant system, especially when they are subjected to stresses. Thus, this study was designed to evaluate the effect of Si on soybean resistance to FLS, on the antioxidant system, on the concentration of reactive oxygen species and on cellular damage during the infection process of C. sojina. Plants from cultivars Bossier and Conquista, susceptible and resistant to FLS, respectively, were supplied with either 0 (−Si) or 2 mm (+Si) and non-inoculated or inoculated with C. sojina. FLS severity was greater for Bossier than for Conquista, regardless of the Si supply, and it was increased by Si for both cultivars. The activities of the most antioxidant enzymes were lower in the +Si plants than in the −Si plants when they were not inoculated. Inoculated plants usually showed an increased enzyme activities and higher concentrations of ascorbate and reduced glutathione than did the non-inoculated plants, regardless of Si supply. At advanced stages of fungal infection, the +Si-inoculated plants from Bossier had higher activity of most antioxidant enzymes and higher concentrations of superoxide and malondialdehyde compared to the non-inoculated plants as a result of an increased oxidative stress. The results from this study provide the first evidence that Si reduces the basal activity of antioxidant enzymes in soybean leaves leading to an increase in host susceptibility to FLS.

Mango wilt, caused by Ceratocystis fimbriata, is one of the most serious diseases affecting mango production worldwide. Considering the great variation in the basal level of wilt resistance among mango cultivars, this study aimed to assess changes in photosynthesis and the role played by the carbon metabolism on two mango cultivars with contrasting responses to C. fimbriata infection. Assessment of disease and plant physiology variables was performed over 21 days. The response of the mango cultivars against fungal infection was associated with an increase on the mobilization of starch from the leaf tissue around the infection sites on stems. Plants of cv. Uba were less susceptible to mango wilt and, presumably, better capable of mobilizing reserves for the production of defense compounds, which prevented colonization of the stem inner tissues and the consequent disruption of xylem hydraulic conductivity and leaf photosynthesis. On the other hand, the inability in mobilizing and targeting carbon for the production of defense-related compounds should have accounted for the higher susceptibility of cv. Palmer to C. fimbriata infection.

The present study aimed to verify the effects of induced polyploidization on Pfaffia glomerata regarding its 20-hydroxyecdysone (20E) production both in vitro and under greenhouse conditions, its in vitro photoautotrophic potential, and its ex vitro biomass accumulation and photosynthetic performance. Synthetic polyploidization efficiently produced individuals with increased in vitro photoautotrophic potential and ex vitro biomass accumulation, although photosynthetic rates per leaf area did not vary between diploids and tetraploids. Among the five tetraploids tested (P28, P60, P68, P74, and P75), P28 showed significantly increased biomass both in vitro and ex vitro when compared with diploid plants, whereas the other tetraploids did not differ significantly from the diploids in terms of biomass accumulation. Although photosynthetic rates per unit leaf area remained constant among all the plants tested, P28 showed a significantly greater total leaf area, which may have resulted in an increase in net photosynthesis on a whole-plant basis. Under greenhouse conditions, the 20E content in the tetraploid P28 was 31% higher than that in diploid plants, and the final 20E mass per plant produced by P28 ex vitro was approximately twice that produced by diploid plants. Accumulation of 20E in vitro did not follow the same pattern observed among the plants ex vitro; instead, greater accumulation was observed in diploid plants. The induction of polyploidy in P. glomerata appears to be a promising strategy for producing plants with higher biomass accumulation and 20E production ex vitro, in addition to its higher in vitro photoautotrophic potential.

Stomatal responsiveness to vapour pressure deficit (VPD) results in continuous regulation of daytime gas-exchange directly influencing leaf water status and carbon gain. Current models can reasonably predict steady-state stomatal conductance (gs ) to changes in VPD but the gs dynamics between steady-states are poorly known. Here, we used a diverse sample of conifers and ferns to show that leaf hydraulic architecture, in particular leaf capacitance, has a major role in determining the gs response time to perturbations in VPD. By using simultaneous measurements of liquid and vapour fluxes into and out of leaves, the in situ fluctuations in leaf water balance were calculated and appeared to be closely tracked by changes in gs thus supporting a passive model of stomatal control. Indeed, good agreement was found between observed and predicted gs when using a hydropassive model based on hydraulic traits. We contend that a simple passive hydraulic control of stomata in response to changes in leaf water status provides for efficient stomatal responses to VPD in ferns and conifers, leading to closure rates as fast or faster than those seen in most angiosperms.

Rising air CO2 concentration ([CO2]) is believed to mitigate the negative impacts of global climate changes such as increased air temperatures and drought events on plant growth and survival. Nonetheless, how elevated [CO2] affects the way coffee (Coffea arabica L.) plants sense and respond to drought remains a critical unknown. In this study, potted coffee plants were cultivated under two air [CO2] (ca. 400 ppm or 700 ppm) in open top chambers under greenhouse conditions. After a 5-month exposure to [CO2] treatments, plants were submitted to a progressive, controlled soil water deficit down to 20 % soil field capacity. Under well-watered (100 % field capacity) conditions, 700-plants displayed lower whole-plant transpiration rates (T) than their 400-counterparts. Changes in T were unrelated to stomatal conductances at the leaf scale (as well as stomatal morphology) or foliar ABA levels, but they were rather associated with faster stomata closure rates upon rapid increases in vapor pressure deficit in the 700-plants. During drought, 700-plants were able to maintain higher water potentials and plant hydraulic conductances for longer in parallel to higher T than their 400-counterparts. Under elevated [CO2], the faster stomatal closure rates (irrigated conditions) or the maintenance of plant hydraulic conductances (drought conditions) were associated with higher (3 to 40-fold) transcript abundance of most aquaporin genes. Altogether, our results suggest that elevated [CO2] has marked implications on how coffee plants respond to soil water deficit, ultimately permitting 700-plants to have improved fitness under drought when compared to 400-plants.

Excess iron (Fe) is commonly observed in wetland rice (Oryza sativa L.) plants, impairing crop growth and productivity. Some information suggests that silicon (Si) can reduce Fe content in leaves and roots of rice (vegetative phase), but nothing is known if Si could mitigate the effects of Fe toxicity on rice production and photosynthesis. Here, we assessed the role of Si in alleviating the well-known effects of Fe toxicity on nutritional imbalances, biomass accumulation, photosynthesis and grain yield using two rice cultivars having differential abilities to tolerate excess Fe. Plants were hydroponically grown under two Fe levels (25 μM or 5 mM) and the nutrient solutions were amended with Si (0 or 2 mM). Under excess Fe were detected (i) nutritional deficiencies, especially of calcium and magnesium in leaves; (ii) negligible changes in grain nutritional composition, independently of Si application; (iii) decreases in net photosynthetic rates, stomatal conductance and electron transport rate, in parallel to decreased grain yield components (total grain biomass, 1000-grain mass, percentage of filled grains, number of grains per plant and harvest index), especially in the Fe-sensitive cultivar. These impairments were partially reversed by the application of Si. Results also suggest that Si alleviated the negative impacts of Fe on spikelet sterility. In summary, we conclude that the use of Si can be recommended as an effective management strategy to reduce the negative impacts of Fe toxicity on rice photosynthetic performance and crop yield.

The xylem cavitation threshold water potential establishes a hydraulic limit on the ability of woody species to survive in water-limiting environments, but herbs may be more plastic in terms of their ability to adapt to drying conditions. Here, we examined the capacity of sunflower (Helianthus annuus L.) leaves to adapt to reduced water availability by modifying the sensitivity of xylem and stomata to soil water deficit. We found that sunflower plants grown under water-limited conditions significantly adjusted leaf osmotic potential, which was linked to a prolongation of stomatal opening as soil dried and a reduced sensitivity of photosynthesis to water-stress-induced damage. At the same time, the vulnerability of midrib xylem to water-stress-induced cavitation was observed to be highly responsive to growth conditions, with water-limited plants producing conduits with thicker cell walls which were more resistant to xylem cavitation. Coordinated plasticity in osmotic potential and xylem vulnerability enabled water-limited sunflowers to safely extract water from the soil, while protecting leaf xylem against embolism. High plasticity in sunflower xylem contrasts with data from woody plants and may suggest an alternative strategy in herbs.