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Flooding events are highly detrimental to most terrestrial plant species. However, there is an impressive diversity of plant species that thrive in flood‐prone regions and represent a treasure trove of unexplored flood‐resilience mechanisms. Here we surveyed a panel of four species from the Cardamineae tribe representing a broad tolerance range. This included the flood‐tolerant Cardamine pratensis, Rorippa sylvestris and Rorippa palustris and the flood‐sensitive species Cardamine hirsuta. All four species displayed a quiescent strategy, evidenced by the repression of shoot growth underwater. Comparative transcriptomics analyses between the four species and the sensitive model species Arabidopsis thaliana were facilitated via de novo transcriptome assembly and identification of 16 902 universal orthogroups at a high resolution. Our results suggest that tolerance likely evolved separately in the Cardamine and Rorippa species. While the Rorippa response was marked by a strong downregulation of cell‐cycle genes, Cardamine minimized overall transcriptional regulation. However, a weak starvation response was a universal trait of tolerant species, potentially achieved in multiple ways. It could result from a strong decline in cell‐cycle activity, but is also intertwined with autophagy, senescence, day‐time photosynthesis and night‐time fermentation capacity. Our data set provides a rich source to study adaptational mechanisms of flooding tolerance. Summary Statement: This collection of submergence‐induced transcriptome responses of Brassicaceae species with strong variation in tolerance provides a treasure trove for the study of adaptational mechanisms of flooding tolerance. [ABSTRACT FROM AUTHOR]

Plant quiescence and seed dormancy can be triggered by reduced oxygen availability. Under water, oxygen depletion caused by flooding can culminate in a quiescent state, which is a plant strategy for energy preservation and survival. In adult plants, a quiescent state can be activated by sugar starvation, leading to metabolic depression. In seeds, secondary dormancy can be activated by reduced oxygen availability, which creates an unfavourable state for germination. The physical dormancy of some seeds and buds includes barriers to external conditions, which indirectly results in hypoxia. The molecular processes that support seed dormancy and plant survival through quiescence under hypoxia include the N-degron pathway, which enables the modulation of ethylene-responsive factors of group VII and downstream targets. This oxygen- and nitric oxide-dependent mechanism interacts with phytohormone-related pathways to control growth. [ABSTRACT FROM AUTHOR]

This article explores the submergence tolerance of rice landrace FR13A and its potential beyond the SUB1A gene. FR13A has hidden genetic variation that surpasses the submergence tolerance level of SUB1A. The article suggests studying the recovery ability of FR13A to identify new genes for enhanced submergence tolerance and proposes a connected breeding approach to introduce FR13A's genetic variation into popular rice varieties. The authors emphasize the importance of FR13A as a valuable genetic resource for further research. They also discuss the differences in regrowth ability and recovery ability between FR13A and SUB1A genotypes. [Extracted from the article]

Submergence stress challenges direct seeding in rice cultivation. In this study, we identified a heat shock protein, NAL11, with a DnaJ domain, which can regulate the length of rice coleoptiles under flooded conditions. Through bioinformatics analyses, we identified cis-regulatory elements in its promoter, making it responsive to abiotic stresses, such as hypoxia or anoxia. Expression of NAL11 was higher in the basal regions of shoots and coleoptiles during flooding. NAL11 knockout triggered the rapid accumulation of abscisic acid (ABA) and reduction of Gibberellin (GA), stimulating rice coleoptile elongation and contributes to flooding stress management. In addition, NAL11 mutants were found to be more sensitive to ABA treatments. Such knockout lines exhibited enhanced cell elongation for coleoptile extension. Quantitative RT-PCR analysis revealed that NAL11 mediated the gluconeogenic pathway, essential for the energy needed in cell expansion. Furthermore, NAL11 mutants reduced the accumulation of reactive oxygen species (ROS) and malondialdehyde under submerged stress, attributed to an improved antioxidant enzyme system compared to the wild-type. In conclusion, our findings underscore the pivotal role of NAL11 knockout in enhancing the tolerance of rice to submergence stress by elucidating its mechanisms. This insight offers a new strategy for improving resilience against flooding in rice cultivation. [ABSTRACT FROM AUTHOR]

Chilli (Capsicum annuum) is an important spice crop in Bangladesh. This crop is very sensitive to waterlogging. Floating agriculture is an innovative system led by the local people of the southern region of Bangladesh, in which seedlings of vegetables are produced in low-lying areas using different aquatic macrophytes. An experiment was carried out to evaluate the viability of chilli cultivation in waterlogged areas, based on physiological and biochemical responses using floating agriculture. Eight different chilli varieties were subjected to floating agriculture in two different agronomic seasons. A soil-based chilli cultivation system was also trialled, to compare the utility of this method. To evaluate the performance of chilli in floating beds, plant water status, photosynthetic parameters, and leaf tissue concentrations of Na+, K+, NO3− and PO43−, chlorophyll, ascorbic acid and proline were assessed. This study shows that macrophytes utilised in floating beds provide favourable conditions for chilli cultivation under waterlogged conditions. Among the different varieties, Sakata 653 in summer and Jhilik in winter responded better than others. As the performance of chilli in the floating agriculture system was satisfactory in comparison with soil-based cultivation, floating agriculture can be an alternative agronomic method for chilli cultivation in waterlogged areas of Bangladesh. Floating agriculture is a promising way of crop cultivation under submergence. Production of chilli (Capsicum annuum), an important spice crop, is greatly affected by waterlogging. In submerged conditions, floating agriculture serves an alternative agronomic means of chilli cultivation. [ABSTRACT FROM AUTHOR]

Cultivated soybean is an important legume crop that is generally sensitive to flooding stress, including submergence and waterlogging treatments. Wild soybeans, the ancestor of cultivated soybeans, have been potential genetic resources for resistance to abiotic or biotic stresses. The present study aimed to evaluate 163 wild soybean accessions for foliar damages at the early vegetative stage and 105 accessions for germination rates, normal seedling rates, and electrical conductivity at the germination stage under submergence stress. In addition, a genome-wide association study (GWAS) was conducted to identify genomic regions associated with phenotypic measurements at these two growth stages by using MLM and FarmCPU models with publicly available genotypic data. The phenotypic evaluation revealed six and three accessions were tolerant to submergence at the early vegetative and germination stages, respectively. Notably, only one wild soybean accession showed a tolerance reaction to submergence at two stages. Through GWAS analysis, 16 and 20 SNPs across different chromosomes were determined for the submergence-related traits at the early vegetative and germination stages, respectively. Based on the linkage disequilibrium block on the detected genomic regions, ten and four putative genes were identified at the early vegetative and germination stages, respectively. Of these genes, certain genes may be related to submergence stress in wild soybeans. Further studies should be performed to validate the function of these putative genes in the responses of wild soybeans to submergence stress. [ABSTRACT FROM AUTHOR]

Abstract Maize is highly sensitive to waterlogging stress, and seeds fail to germinate under hypoxic conditions induced by submergence, leading to severe yield losses. We conducted a comparative transcriptome analysis during the initial stages of seed germination, exploring aerobic and hypoxic conditions in two inbred lines, B73 and Okcheon Chal-1. Notably, significant differences emerged between aerobic and hypoxic conditions on the first day of germination, particularly in genes associated with fermentation and phytohormone regulation. However, consistent transcriptomic changes were observed in primary metabolic pathways such as glycolysis, the TCA cycle, and the pentose phosphate pathway. These differences strongly correlate with each other, illustrating the efficacy of the hypoxic response for survival in water. Furthermore, this suggests that germinating seeds serve as a promising model for studying plant hypoxia responses with controlled environmental conditions. Insights from this study contribute to understanding the fundamental mechanisms of hypoxia response and hold promise for developing strategies to cultivate waterlogging-tolerant maize cultivars.

Flooding, as a natural disaster, plays a pivotal role in constraining the growth and development of plants. Flooding stress, including submergence and waterlogging, not only induces oxygen, light, and nutrient deprivation, but also alters soil properties through prolonged inundation, further impeding plant growth and development. However, hypoxia (or anoxia) is the most serious and direct damage to plants caused by flooding. Moreover, flooding disrupts the structural integrity of plant cell walls and compromises endoplasmic reticulum functionality, while hindering nutrient absorption and shifting metabolic processes from normal aerobic respiration to anaerobic respiration. It can be asserted that flooding exerts comprehensive effects on plants encompassing phenotypic changes, transcriptional alterations, protein dynamics, and metabolic shifts. To adapt to flooding environments, plants employ corresponding adaptive mechanisms at the phenotypic level while modulating transcriptomic profiles, proteomic characteristics, and metabolite levels. Hence, this study provides a comprehensive analysis of transcriptomic, proteomic, and metabolomics investigations conducted on flooding stress on model plants and major crops, elucidating their response mechanisms from diverse omics perspectives. [ABSTRACT FROM AUTHOR]

Maize is highly sensitive to waterlogging stress, and seeds fail to germinate under hypoxic conditions induced by submergence, leading to severe yield losses. We conducted a comparative transcriptome analysis during the initial stages of seed germination, exploring aerobic and hypoxic conditions in two inbred lines, B73 and Okcheon Chal-1. Notably, significant differences emerged between aerobic and hypoxic conditions on the first day of germination, particularly in genes associated with fermentation and phytohormone regulation. However, consistent transcriptomic changes were observed in primary metabolic pathways such as glycolysis, the TCA cycle, and the pentose phosphate pathway. These differences strongly correlate with each other, illustrating the efficacy of the hypoxic response for survival in water. Furthermore, this suggests that germinating seeds serve as a promising model for studying plant hypoxia responses with controlled environmental conditions. Insights from this study contribute to understanding the fundamental mechanisms of hypoxia response and hold promise for developing strategies to cultivate waterlogging-tolerant maize cultivars. [ABSTRACT FROM AUTHOR]

Rock weirs, typically created by the placement of loose rocks, are eco-friendly hydraulic structures used for raising the upstream water level, which has benefits for irrigation, shipping, and grade control. Although rock weirs are frequently submerged in rivers, few studies have systematically investigated their impacts on the upstream water level under submerged conditions. A series of flume experiments regarding this topic were conducted. Different flow discharges, tail-water depths, and void ratios were adopted in the experiments. The results show that (1) the submerged rock weirs primarily function to raise the upstream water level, while having a limited impact on the tail-water level; (2) for a given tail-water depth and void ratio, the upstream water level rise increases with increased discharge, although this response becomes insignificant as tail-water depth increases; (3) as void ratio increases, the upstream water level rise is expected to decrease for a given tail-water depth and discharge; and (4) based on the data and observations, a predictor including the effects of Froude number, submergence, and void ratio is proposed for estimating the upstream water level rise of submerged rock weirs. These results contribute to further understanding the hydraulic properties of rock weirs and are important for river training practices using rock weirs. [ABSTRACT FROM AUTHOR]

The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one‐ or two‐dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two‐dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds‐averaged Navier‐Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining. Plain Language Summary: Groynes are used for river training. Their positive effects include riverbank stabilization, improvement of navigability and prevention of ice jams. However, during floods they become submerged and increase the flood water depths by blocking the flow and increasing turbulence. This may lead to severe outcomes. Floods are among the most fatal disasters that affect the globe. Even an increase of flood water depths by some centimeters may cause disastrous outcomes. Engineers generally resort to approximate solutions for adding the effects of groynes into hydraulic flood models for long river reaches. In this paper, we assess the capabilities of these approximate models as well as those of more simplified and more advanced models. Insights were sought to help flood modelers for better prediction of flood water levels. Our study shows that the most widely used groyne resistance model leaves room for further development, despite demonstrated capabilities. Key Points: Characterizing the effect of groynes on river flow in two‐dimensional hydrodynamic models by using weir formulas was evaluatedAlternative methods to implement groynes into two‐ and three‐dimensional river models were proposed, and their reliability was testedThe performances of two of the available modeling options in simulating the groyne modifications were assessed [ABSTRACT FROM AUTHOR]

ABSTRACTExcessive soil moisture (ESM) is a critical factor limiting the productivity of buckwheat (Fagopyrum esculentum Moench) because ESM inhibits its germination. This study investigated the effects of pericarp and seed respiration on reduced buckwheat germination caused by submergence. Seeds were submerged prior to germination testing under aerobic conditions. The effects of days of submergence treatment and pericarp removal on germination percentage were significant. The germination percentage in the 3-day submergence treatment was low in seeds with pericarp (P+) but was significantly improved in seeds without pericarp (P−). Pericarp removal also improved the germination percentage of non-submerged seeds. Pericarp thickness and pericarp/seed dry weight ratio (PWR) were not significantly correlated with the germination percentage in 3-day submerged P+. However, both were significantly negatively correlated with the germination percentage in 1-day submerged P+. Seed respiration rate in water, measured on seeds not submerged before measurement, was significantly higher in P− than in P+; that of P− increased with time, while that of P+ showed a decreasing trend with time beyond the first 24 h. Seed respiration rate during the first 24 h was significantly negatively correlated with germination percentage in 3-day submerged P+. A negative influence of pericarp thickness and PWR on the seed respiration rate of P+ during the first 24 h was suggested. Suppressed seed respiration by the pericarp is probably a cause of inhibited buckwheat germination under ESM conditions.

Plant networks of oscillating genes coordinate internal processes with external cues, contributing to increased fitness. We hypothesized that the response to submergence stress may dynamically change during different times of the day. In this work, we determined the transcriptome (RNA sequencing) of the model monocotyledonous plant, Brachypodium distachyon, during a day of submergence stress, low light, and normal growth. Two ecotypes of differential tolerance, Bd21 (sensitive) and Bd21-3 (tolerant), were included. We submerged 15-day-old plants under a long-day diurnal cycle (16 h light/8 h dark) and collected samples after 8 h of submergence at ZT0 (dawn), ZT8 (midday), ZT16 (dusk), ZT20 (midnight), and ZT24 (dawn). Rhythmic processes were enriched both with up- and down-regulated genes, and clustering highlighted that the morning and daytime oscillator components (PRRs) show peak expression in the night, and a decrease in the amplitude of the clock genes (GI, LHY, RVE) was observed. Outputs included photosynthesis-related genes losing their known rhythmic expression. Up-regulated genes included oscillating suppressors of growth, hormone-related genes with new late zeniths (e.g., JAZ1, ZEP), and mitochondrial and carbohydrate signaling genes with shifted zeniths. The results highlighted genes up-regulated in the tolerant ecotype such as METALLOTHIONEIN3 and ATPase INHIBITOR FACTOR. Finally, we show by luciferase assays that Arabidopsis thaliana clock genes are also altered by submergence changing their amplitude and phase. This study can guide the research of chronocultural strategies and diurnal-associated tolerance mechanisms.

Excessive soil moisture (ESM) is a critical factor limiting the productivity of buckwheat (Fagopyrum esculentum Moench) because ESM inhibits its germination. This study investigated the effects of pericarp and seed respiration on reduced buckwheat germination caused by submergence. Seeds were submerged prior to germination testing under aerobic conditions. The effects of days of submergence treatment and pericarp removal on germination percentage were significant. The germination percentage in the 3-day submergence treatment was low in seeds with pericarp (P+) but was significantly improved in seeds without pericarp (P−). Pericarp removal also improved the germination percentage of non-submerged seeds. Pericarp thickness and pericarp/seed dry weight ratio (PWR) were not significantly correlated with the germination percentage in 3-day submerged P+. However, both were significantly negatively correlated with the germination percentage in 1-day submerged P+. Seed respiration rate in water, measured on seeds not submerged before measurement, was significantly higher in P− than in P+; that of P− increased with time, while that of P+ showed a decreasing trend with time beyond the first 24 h. Seed respiration rate during the first 24 h was significantly negatively correlated with germination percentage in 3-day submerged P+. A negative influence of pericarp thickness and PWR on the seed respiration rate of P+ during the first 24 h was suggested. Suppressed seed respiration by the pericarp is probably a cause of inhibited buckwheat germination under ESM conditions. [ABSTRACT FROM AUTHOR]

Although Taxodium hybrid 'Zhongshanshan' 406 (Taxodium mucronatum Tenore ×  Taxodium distichum ; Taxodium 406) is an extremely flooding-tolerant woody plant, the physiological and molecular mechanisms underlying acclimation of its roots to long-term flooding remain largely unknown. Thus, we exposed saplings of Taxodium 406 to either non-flooding (control) or flooding for 2 months. Flooding resulted in reduced root biomass, which is in line with lower concentrations of citrate, α-ketoglutaric acid, fumaric acid, malic acid and adenosine triphosphate (ATP) in Taxodium 406 roots. Flooding led to elevated activities of pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, which is consistent with higher lactate concentration in the roots of Taxodium 406. Flooding brought about stimulated activities of superoxide dismutase and catalase and elevated reduced glutathione (GSH) concentration and GSH/oxidized glutathione, which is in agreement with reduced concentrations of O2− and H2O2 in Taxodium 406 roots. The levels of starch, soluble protein, indole-3-acetic acid, gibberellin A4 and jasmonate were decreased, whereas the concentrations of glucose, total non-structural carbohydrates, most amino acids and 1-aminocyclopropane-1-carboxylate (ACC) were improved in the roots of flooding-treated Taxodium 406. Underlying these changes in growth and physiological characteristics, 12,420 mRNAs and 42 miRNAs were significantly differentially expressed, and 886 miRNA–mRNA pairs were identified in the roots of flooding-exposed Taxodium 406. For instance, 1- aminocyclopropane- 1 -carboxylate synthase 8 (ACS8) was a target of Th-miR162-3p and 1 -aminocyclopropane- 1 -carboxylate oxidase 4 (ACO4) was a target of Th-miR166i, and the downregulation of Th-miR162-3p and Th-miR166i results in the upregulation of ACS8 and ACO4 , probably bringing about higher ACC content in flooding-treated roots. Overall, these results indicate that differentially expressed mRNA and miRNAs are involved in regulating tricarboxylic acid cycle, ATP production, fermentation, and metabolism of carbohydrates, amino acids and phytohormones, as well as reactive oxygen species detoxification of Taxodium 406 roots. These processes play pivotal roles in acclimation to flooding stress. These results will improve our understanding of the molecular and physiological bases underlying woody plant flooding acclimation and provide valuable insights into breeding-flooding tolerant trees. [ABSTRACT FROM AUTHOR]

Submergence stress challenges direct seeding in rice cultivation. In this study, we identified a heat shock protein, NAL11, with a DnaJ domain, which can regulate the length of rice coleoptiles under flooded conditions. Through bioinformatics analyses, we identified cis-regulatory elements in its promoter, making it responsive to abiotic stresses, such as hypoxia or anoxia. Expression of NAL11 was higher in the basal regions of shoots and coleoptiles during flooding. NAL11 knockout triggered the rapid accumulation of abscisic acid (ABA) and reduction of Gibberellin (GA), stimulating rice coleoptile elongation and contributes to flooding stress management. In addition, NAL11 mutants were found to be more sensitive to ABA treatments. Such knockout lines exhibited enhanced cell elongation for coleoptile extension. Quantitative RT-PCR analysis revealed that NAL11 mediated the gluconeogenic pathway, essential for the energy needed in cell expansion. Furthermore, NAL11 mutants reduced the accumulation of reactive oxygen species (ROS) and malondialdehyde under submerged stress, attributed to an improved antioxidant enzyme system compared to the wild-type. In conclusion, our findings underscore the pivotal role of NAL11 knockout in enhancing the tolerance of rice to submergence stress by elucidating its mechanisms. This insight offers a new strategy for improving resilience against flooding in rice cultivation.

Cultivated soybean is an important legume crop that is generally sensitive to flooding stress, including submergence and waterlogging treatments. Wild soybeans, the ancestor of cultivated soybeans, have been potential genetic resources for resistance to abiotic or biotic stresses. The present study aimed to evaluate 163 wild soybean accessions for foliar damages at the early vegetative stage and 105 accessions for germination rates, normal seedling rates, and electrical conductivity at the germination stage under submergence stress. In addition, a genome-wide association study (GWAS) was conducted to identify genomic regions associated with phenotypic measurements at these two growth stages by using MLM and FarmCPU models with publicly available genotypic data. The phenotypic evaluation revealed six and three accessions were tolerant to submergence at the early vegetative and germination stages, respectively. Notably, only one wild soybean accession showed a tolerance reaction to submergence at two stages. Through GWAS analysis, 16 and 20 SNPs across different chromosomes were determined for the submergence-related traits at the early vegetative and germination stages, respectively. Based on the linkage disequilibrium block on the detected genomic regions, ten and four putative genes were identified at the early vegetative and germination stages, respectively. Of these genes, certain genes may be related to submergence stress in wild soybeans. Further studies should be performed to validate the function of these putative genes in the responses of wild soybeans to submergence stress.

With recent progress in active research on flooding and hypoxia/anoxia tolerance in native and agricultural crop plants, vast knowledge has been gained on both individual tolerance mechanisms and the general mechanisms of flooding tolerance in plants. Research on carbohydrate consumption, ethanolic and lactic acid fermentation, and their regulation under stress conditions has been accompanied by investigations on aerenchyma development and the emergence of the radial oxygen loss barrier in some plant species under flooded conditions. The discovery of the oxygen-sensing mechanism in plants and unravelling the intricacies of this mechanism have boosted this very international research effort. Recent studies have highlighted the importance of oxygen availability as a signalling component during plant development. The latest developments in determining actual oxygen concentrations using minute probes and molecular sensors in tissues and even within cells have provided new insights into the intracellular effects of flooding. The information amassed during recent years has been used in the breeding of new flood-tolerant crop cultivars. With the wealth of metabolic, anatomical, and genetic information, novel holistic approaches can be used to enhance crop species and their productivity under increasing stress conditions due to climate change and the subsequent changes in the environment. [ABSTRACT FROM AUTHOR]

Flooding is a predominant abiotic stress for cultivated plants, including barley. This cereal crop shows a large adaptability to different environmental conditions, suggesting the presence of key traits to tolerate adverse conditions. During germination, genetic variations account for dissimilarities in flooding tolerance. However, differences in the seed microbiota may also contribute to tolerance/sensitivity during seedling establishment. This work investigated differences in microbiome among the grains of barley accessions. Two barley phenotypes were compared, each either tolerant or sensitive to a short submergence period followed by a recovery. The study used a metataxonomic analysis based on 16S ribosomal RNA gene sequencing and subsequent functional prediction. Our results support the hypothesis that bacterial microbiota inhabiting the barley seeds are different between sensitive and tolerant barley accessions, which harbour specific bacterial phyla and families. Finally, bacteria detected in tolerant barley accessions show a peculiar functional enrichment that suggests a possible connection with successful germination and seedling establishment. [ABSTRACT FROM AUTHOR]

Background and Aims HCO3– can be a major carbon resource for photosynthesis in underwater environments. Here we investigate the underlying mechanism of uptake and membrane transport of HCO3– in submerged leaves of Hygrophila difformis , a heterophyllous amphibious plant. To characterize these mechanisms, we evaluated the sensitivity of underwater photosynthesis to an external carbonic anhydrase (CA) inhibitor and an anion exchanger protein inhibitor, and we attempted to identify components of the mechanism of HCO3– utilization. Methods We evaluated the effects of the external CA inhibitor and anion exchanger protein inhibitor on the NaHCO3 response of photosynthetic O2 evolution in submerged leaves of H. difformis. Furthermore, we performed a comparative transcriptomic analysis between terrestrial and submerged leaves. Key Results Photosynthesis in the submerged leaves was decreased by both the external CA inhibitor and anion exchanger protein inhibitor, but no additive effect was observed. Among upregulated genes in submerged leaves, two α-CAs, Hd α -CA1 and Hd α -CA2 , and one β-carbonic anhydrase, Hd β -CA1 , were detected. Based on their putative amino acid sequences, the α-CAs are predicted to be localized in the apoplastic region. Recombinant Hdα-CA1 and Hdβ-CA1 showed dominant CO2 hydration activity over HCO3– dehydration activity. Conclusions We propose that the use of HCO3– for photosynthesis in submerged leaves of H. difformis is driven by the cooperation between an external CA, Hdα-CA1, and an unidentified HCO3– transporter. [ABSTRACT FROM AUTHOR]

Plant submergence is a major abiotic stress that impairs plant performance. Under water, reduced gas diffusion exposes submerged plant cells to an environment that is enriched in gaseous ethylene and is limited in oxygen (O2) availability (hypoxia). The capacity for plant roots to avoid and/or sustain critical hypoxia damage is essential for plants to survive waterlogging. Plants use spatiotemporal ethylene and O2 dynamics as instrumental flooding signals to modulate potential adaptive root growth and hypoxia stress acclimation responses. However, how non-adapted plant species modulate root growth behaviour during actual waterlogged conditions to overcome flooding stress has hardly been investigated. Here we discuss how changes in the root growth rate, lateral root formation, density, and growth angle of non-flood adapted plant species (mainly Arabidopsis) could contribute to avoiding and enduring critical hypoxic conditions. In addition, we discuss current molecular understanding of how ethylene and hypoxia signalling control these adaptive root growth responses. We propose that future research would benefit from less artificial experimental designs to better understand how plant roots respond to and survive waterlogging. This acquired knowledge would be instrumental to guide targeted breeding of flood-tolerant crops with more resilient root systems. [ABSTRACT FROM AUTHOR]

Submergence negatively affects the plant growth and yield of rice genotypes, which in turn results in huge financial loss. Thus, identification of submergence tolerance rice genotypes is needed for sustainable rice cultivation in flood-prone areas. Keeping this in view, a two-year (2019 and 2020) field study was undertaken at Rice Research Farm of Bihar Agricultural College, Bihar Agricultural University, Sabour, Bhagalpur to investigate and compare the yield responses of rice genotypes under submergence and normal growing conditions. Twenty-five days old seedlings of 25 rice genotypes were transplanted in a randomized complete block design in two replicates, which were allowed to grow under normal practice for the next 25 days. Thereafter, the 50-day old plants were completely submerged with turbid water of 1.5 m height for the next 18 days. After de-submergence, all the recommended agronomic practices were adopted during the rest of the crop period. Under submergence, higher grain yield was recorded under all the genotypes during 2020 as compared to 2019 mainly due to higher temperature and lesser rainfall during 2020. Under submergence conditions, Jalmagna, Nona Bokra and Swarna Sub 1 were the best performers having produced average yields of 3,167, 2,786 and 2,741 kg/ha, respectively. Whereas under normal growing practice, Swarna Sub 1, Jalmagna and Sudha were the first three best performing genotypes producing average yields of 5,063, 4,565 and 4,456 kg/ha, respectively. Therefore, Jalmagna should be preferred for cultivation in the flood-prone regions of the state, however in non-flooded areas; Swarna Sub 1 may be cultivated. [ABSTRACT FROM AUTHOR]

Wetland plants, including rice (Oryza spp.), have developed multiple functional adaptive traits to survive soil flooding, partial submergence or even complete submergence. In waterlogged soils and under water, diffusion of O2 and CO2 is extremely slow with severe impacts on photosynthesis and respiration. As a response to shallow floods or rising floodwater, several rice varieties, including deepwater rice, elongate their stems to keep their leaves above the water surface so that photosynthesis can occur unhindered during partial submergence. In stark contrast, some other varieties hardly elongate even if they become completely submerged. Instead, their metabolism is reduced to an absolute minimum so that carbohydrates are conserved enabling fast regrowth once the floodwater recedes. This review focuses on the fascinating functional adaptive traits conferring tolerance to soil flooding, partial or complete submergence. We provide a general analysis of these traits focusing on molecular, anatomical and morphological, physiological and ecological levels. Some of these key traits have already been introgressed into modern highyielding genotypes improving flood tolerance of several cultivars used by millions of farmers in Asia. However, with the ongoing changes in climate, we propose that even more emphasis should be placed on improving flood tolerance of rice by breeding for rice that can tolerate longer periods of complete submergence or stagnant flooding. Such tolerance could be achieved via additional tissues; i.e. aquatic adventitious roots relevant during partial submergence, and leaves with higher underwater photosynthesis caused by a longer gas film retention time. [ABSTRACT FROM AUTHOR]

This article presents a robust methodology for long-term offshore structural health monitoring (SHM) using the Global Navigation Satellite Systems (GNSS). The methodology relies on recently developed regional reference frames and single-receiver phase-ambiguity-fixed Precise Point Positioning techniques. The stable Gulf of Mexico Reference Frame 2020 (GOM20) provides a robust and consistent reference system for long-term offshore SHM in the Gulf of Mexico (GOM). Continuous GNSS observations (DEV1, 2010–2020) on a fixed platform in the Eugene Island 330 oil field are used to illustrate the methodology. The platform was installed in 1982 in 82-m water about 130 km away from the Mississippi Delta coastline. The major monitoring items include horizontal movements, seafloor subsidence, structure submergence, and seasonal oscillations. The stand-alone GNSS monitoring achieves 3- to 4-mm root-mean-square accuracy in the horizontal direction and 7 mm in the vertical direction for daily positions in the GOM region. According to this study, the GNSS antenna (DEV1) has moved 6 cm toward the northeast with respect to GOM20 since 2010; the ongoing structure submergence rate in the Eugene Island 330 oil field area is approximately 15 mm/year, a combination of seafloor subsidence (12 mm/year) and sea-level rise (2.6 mm/year) with respect to GOM20. The submergence in the future 40 years (2021–2060) would be greater than 0.6 m, likely between 0.8 and 1.0 m, but is unlikely to exceed 1.3 m. The peak-to-trough amplitudes of the seasonal movements at the top of the platform are below 5 mm in all three directions, comparable with the seasonal movements recorded by onshore GNSS in the Louisiana coastal region. The methodology introduced in this article can be applied to SHM in other offshore regions where stable regional reference frames are available. [ABSTRACT FROM AUTHOR]

Main conclusion: Adaptive traits in rice responding to flooding, a compound stress, are associated with morpho-anatomical and physiological changes which are regulated at the genetic level. Therefore, understanding submergence stress tolerance in rice will help development of adapted cultivars that can help mitigate agricultural losses. Rice is an important dietary component of daily human consumption and is cultivated as a staple crop worldwide. Flooding is a compound stress which imposes significant financial losses to farmers. Flood-affected rainfed rice ecosystems led to the development of various adaptive traits in different cultivars for their optimal growth and survival. Some cultivars can tolerate hypoxia by temporarily arresting elongation and conserving their energy sources, which they utilize to regrow after the stress conditions subside. However, few other cultivars rapidly elongate to escape hypoxia using carbohydrate resources. These contrasting characters are regulated at the genetic level through different quantitative trait loci that contain ERF transcription factors (TFs), Submergence and Snorkels. TFs can simultaneously activate the transcription of various genes involved in stress and development responses. These TFs are of prime importance because the introgressed and near-isogenic lines showed promising results with increased submergence tolerance without affecting yield or quality. However, the entire landscape of submergence tolerance is not entirely depicted, and further exploration in the field is necessary to understand the mechanism in rice completely. Therefore, this review will highlight the significant adaptive traits observed in flooded rice varieties and how they are regulated mechanistically. [ABSTRACT FROM AUTHOR]

Please insert a Abstract as per journal style: This discussion paper is regarding the values of coefficient of discharge (Cd) and submergence (S) of a vertical type of sluice gate mounted on a broad casted weir. Discusser has used open channel specific energy principles justifying the values of Cd found by the author theoretically. Discusser has furnished the experimental values of Cd for a vertical type and tainter type gates. Discusser has also added the experimental values of Cd under free and submerged flow conditions in a model study for Salal dam spillway. An innovative proportional type flow meter developed by the discusser has been furnished for flow measurement within a given flow range. [ABSTRACT FROM AUTHOR]

Rock weirs, typically created by the placement of loose rocks, are eco-friendly hydraulic structures used for raising the upstream water level, which has benefits for irrigation, shipping, and grade control. Although rock weirs are frequently submerged in rivers, few studies have systematically investigated their impacts on the upstream water level under submerged conditions. A series of flume experiments regarding this topic were conducted. Different flow discharges, tail-water depths, and void ratios were adopted in the experiments. The results show that (1) the submerged rock weirs primarily function to raise the upstream water level, while having a limited impact on the tail-water level; (2) for a given tail-water depth and void ratio, the upstream water level rise increases with increased discharge, although this response becomes insignificant as tail-water depth increases; (3) as void ratio increases, the upstream water level rise is expected to decrease for a given tail-water depth and discharge; and (4) based on the data and observations, a predictor including the effects of Froude number, submergence, and void ratio is proposed for estimating the upstream water level rise of submerged rock weirs. These results contribute to further understanding the hydraulic properties of rock weirs and are important for river training practices using rock weirs.

Abstract Background Flooding is among the most severe abiotic stresses in plant growth and development. The mechanism of submergence tolerance of cotton in response to submergence stress is unknown. Results The transcriptome results showed that a total of 6,893 differentially expressed genes (DEGs) were discovered under submergence stress. Gene Ontology (GO) enrichment analysis showed that DEGs were involved in various stress or stimulus responses. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs related to plant hormone signal transduction, starch and sucrose metabolism, glycolysis and the biosynthesis of secondary metabolites were regulated by submergence stress. Eight DEGs related to ethylene signaling and 3 ethylene synthesis genes were identified in the hormone signal transduction. For respiratory metabolism, alcohol dehydrogenase (ADH, GH_A02G0728) and pyruvate decarboxylase (PDC, GH_D09G1778) were significantly upregulated but 6-phosphofructokinase (PFK, GH_D05G0280), phosphoglycerate kinase (PGK, GH_A01G0945 and GH_D01G0967) and sucrose synthase genes (SUS, GH_A06G0873 and GH_D06G0851) were significantly downregulated in the submergence treatment. Terpene biosynthetic pathway-related genes in the secondary metabolites were regulated in submergence stress. Conclusions Regulation of terpene biosynthesis by respiratory metabolism may play a role in enhancing the tolerance of cotton to submergence under flooding. Our findings showed that the mevalonate pathway, which occurs in the cytoplasm of the terpenoid backbone biosynthesis pathway (ko00900), may be the main response to submergence stress.

Oxygen deficiency is an environmental challenge which affects plant growth, the development and distribution in land and aquatic ecosystems, as well as crop yield losses worldwide. The capacity to exist in the conditions of deficiency or the complete lack of oxygen depends on a number of anatomic, developmental and molecular adaptations. The lack of molecular oxygen leads to an inhibition of aerobic respiration, which causes energy starvation and the acceleration of glycolysis passing into fermentations. We focus on systemic metabolic alterations revealed with the different approaches of metabolomics. Oxygen deprivation stimulates the accumulation of glucose, pyruvate and lactate, indicating the acceleration of the sugar metabolism, glycolysis and lactic fermentation, respectively. Among the Krebs-cycle metabolites, only the succinate level increases. Amino acids related to glycolysis, including the phosphoglycerate family (Ser and Gly), shikimate family (Phe, Tyr and Trp) and pyruvate family (Ala, Leu and Val), are greatly elevated. Members of the Asp family (Asn, Lys, Met, Thr and Ile), as well as the Glu family (Glu, Pro, Arg and GABA), accumulate as well. These metabolites are important members of the metabolic signature of oxygen deficiency in plants, linking glycolysis with an altered Krebs cycle and allowing alternative pathways of NAD(P)H reoxidation to avoid the excessive accumulation of toxic fermentation products (lactate, acetaldehyde, ethanol). Reoxygenation induces the downregulation of the levels of major anaerobically induced metabolites, including lactate, succinate and amino acids, especially members of the pyruvate family (Ala, Leu and Val), Tyr and Glu family (GABA and Glu) and Asp family (Asn, Met, Thr and Ile). The metabolic profiles during native and environmental hypoxia are rather similar, consisting in the accumulation of fermentation products, succinate, fumarate and amino acids, particularly Ala, Gly and GABA. The most intriguing fact is that metabolic alterations during oxidative stress are very much similar, with plant response to oxygen deprivation but not to reoxygenation. [ABSTRACT FROM AUTHOR]

Rice is the only crop which is well adapted to aquatic environment but, it is unable to survive if completely submerged for several weeks. Breeding rice varieties with submergence tolerance is one of the best approaches to alleviate the adverse effect of submergence which requires the introgression of Sub1 gene into elite rice varieties. Hence, the study was undertaken to introgress submergence tolerant gene into the rice variety Jaya through Marker-Assisted Backcross Breeding. Also the physiological and biochemical responses like survival percentage, underwater shoot elongation, total carbohydrate content and superoxide dismutase activity were also studied in Sub1 introgressed lines. We could develop twenty Sub1 introgressed lines with Sub1 region of 3.1–5.1mb and with 80.0- 95.3% recurrent parent genome recovery. Sub1 introgressed Jaya lines and the tolerant checks FR13A and Swarna Sub1 had lower shoot elongation under water, higher superoxide dismutase activity (about 5 times) upto 4 h after de-submergence which resulted in higher survival percentage. The reduced shoot elongation of tolerant varieties reduced the utilization of stored carbohydrate. Through our research we introgressed Sub1 gene into rice variety Jaya through Marker-Assisted Backcross Breeding and could study the physiological responses under submergence by which we confirmed the presence of Sub1 gene in these lines. These lines could be field evaluated and could be released as a new variety thus helping the farmers of flood prone areas of Kerala. [ABSTRACT FROM AUTHOR]

Lower plants such as bryophytes often encounter submergence stress, even in low precipitation conditions. Our study aimed to understand the mechanism of submergence tolerance to withstand this frequent stress in moss (Semibarbula orientalis) during the day and at night. These findings emphasise that light plays a crucial role in photoreactivation of PSII in S. orientalis, which indicates that light not only fuels photosynthesis but also aids in repairing the photosynthetic machinery in plants. Submergence negatively affects photosynthesis parameters such as specific and phenomenological fluxes, density of functional PSII reaction centres (RC/CS), photochemical and non-photochemical quenching (Kp and Kn), quantum yields (φP0, φE0, φD0), primary and secondary photochemistry, performance indices (PIcs and PIabs), etc. Excessive antenna size caused photoinhibition at the PSII acceptor side, reducing the plastoquinone pool through the formation of PSII triplets and reactive oxygen species (ROS). This ROS-induced protein and PSII damage triggered the initiation of the repair cycle in presence of sunlight, eventually leading to the resumption of PSII activity. However, ROS production was regulated by antioxidants like superoxide dismutase (SOD) and catalase (CAT) activity. The rapid recovery of RS/CS observed specifically under sunlight conditions emphasises the vital role of light in enabling the assembly of essential units, such as the D1 protein of PSII, during stress in S. orientalis. Overall, light is instrumental in restoring the photosynthetic potential in S. orientalis growing under submergence stress. Additionally, it was observed that plants subjected to submergence stress during daylight hours rapidly recover their photosynthetic performance. However, submergence stress during the night requires a comparatively longer period for the restoration of photosynthesis in the moss S. orientalis. [ABSTRACT FROM AUTHOR]

Plant seedlings adjust the growth of the hypocotyl in response to surrounding environmental changes. Genetic studies have revealed key players and pathways in hypocotyl growth, such as phytohormones and light signaling. However, because of genetic redundancy in the genome, it is expected that not-yet-revealed mechanisms can be elucidated through approaches different from genetic ones. Here, we identified a small compound, HYGIC (HG), that simultaneously induces hypocotyl elongation and thickening, accompanied by increased nuclear size and enlargement of cortex cells. HG-induced hypocotyl growth required the ethylene signaling pathway activated by endogenous ethylene, involving CONSTITUTIVE PHOTOMORPHOGENIC 1, ETHYLENE INSENSITIVE 2 (EIN2) and redundant transcription factors for ethylene responses, ETHYLENE INSENSITIVE 3 (EIN3) and EIN3 LIKE 1. By using EBS:GUS , a transcriptional reporter of ethylene responses based on an EIN3-binding- cis -element, we found that HG treatment ectopically activates ethylene responses at the epidermis and cortex of the hypocotyl. RNA-seq and subsequent gene ontology analysis revealed that a significant number of HG-induced genes are related to responses to hypoxia. Indeed, submergence, a representative environment where the hypoxia response is induced in nature, promoted ethylene-signaling-dependent hypocotyl elongation and thickening accompanied by ethylene responses at the epidermis and cortex, which resembled the HG treatment. Collectively, the identification and analysis of HG revealed that ectopic responsiveness to ethylene promotes hypocotyl growth, and this mechanism is activated under submergence. [ABSTRACT FROM AUTHOR]

Role of microRNAs (miRNAs) in submergence tolerance, especially for escape strategy is not well established till date. Present study takes an attempt to predict miRNAs (osa-MIR1319b and osa-MIR1439 were selected in this case) which target two ethylene response factors (ERFs), namely SNORKEL1 and SNORKEL2 involved in escaping mode of adaptation in tall type rice under submergence. As SK1 and SK2 are located on 12th rice chromosome. Thus, it was aimed to find out more targets on the same chromosome as miRNAs can have multiple targets either in the same gene or different genes at a time. All the predicted binding sequences were aligned with their respective miRNAs to find out the most probable binding region showing more than 70% base conservation. Secondary structure of these miRNAs was predicted for the minimum free energy (MFE) to determine structure–function relationship of the miRNAs. Lastly, these bioinformatically predicted putative miRNAs were validated for their binding with the target sequences through qRT-PCR-based expression analysis of both the miRNAs and respective target sequences in a selected indigenous semi-deep rice line (var. Kumrogarh) carrying both the components of SK loci linked with elongated growth under submergence. The experiment conducted in this study constructed a basic framework for miRNA-regulated snorkeling type elongation in rice during prolonged deep submergence. [ABSTRACT FROM AUTHOR]

Rice, often termed the golden cereal, sustains billions globally but faces submergence as a significant constraint in semi deep and deep-water ecosystems in India. The primary aim of this study was to evaluate the genetic potential of yield and yield-contributing traits in the cross ASD 16 x BIL of CO 51 Sub1 (12 x 9-7-6-12-3-45) across the F2 and F3 generations. The research revealed a wide range of variation for all traits in both generations. Specifically, positively skewed and platykurtic curves were observed for the number of productive tillers per plant and the number of chaffy grains per panicle, indicating the influence of a large number of genes with dominance-based gene interaction on these traits. The study also found highly significant correlation and regression coefficients for all recorded traits. Interestingly, while broad sense heritability showed high values for certain traits, narrow sense heritability percentages were only moderate for the same traits. Thus, focusing on selecting individuals based on narrow sense heritability would be more effective in improving those traits, as it targets the genetic variation that can be passed on to future generations

Ammonium (NH4+) serves as a vital nitrogen source for plants, but it can turn toxic when it accumulates in excessive amounts. Toxicity is aggravated under hypoxic/anaerobic conditions, e.g., during flooding or submergence, due to a lower assimilation capacity. AMT1; 1 mediates NH4+ uptake into roots. Under conditions of oxygen-deficiency, i.e., submergence, the CBL-interacting protein kinase OsCIPK15 has been shown to trigger SnRK1A signaling, promoting starch mobilization, thereby the increasing availability of ATP, reduction equivalents and acceptors for NH4+ assimilation in rice. Our previous study in Arabidopsis demonstrates that AtCIPK15 phosphorylates AMT1; 1 whose activity is under allosteric feedback control by phosphorylation of T460 in the cytosolic C-terminus. Here we show that submergence cause higher NH4+ accumulation in wild-type, plant but not of nitrate, nor in a quadruple amt knock-out mutant. In addition, submergence triggers rapid accumulation of AtAMT1;1 and AtCIPK15 transcripts as well as AMT1 phosphorylation. Significantly, cipk15 knock-out mutants do not exhibit an increase in AMT1 phosphorylation; however, they do display heightened sensitivity to submergence. These findings suggest that CIPK15 suppresses AMT activity, resulting in decreased NH4+ accumulation during submergence, a period when NH4+ assimilation capacity may be impaired.

In this review, we focus on ethylene transcription factors (ERFs), which are a crucial family of transcription factors that regulate plant development and stress responses. ERFVII transcription factors have been identified and studied in several crop species, including rice, wheat, maize, barley, and soybean. These transcription factors are known to be involved in regulating the plant's response to low oxygen stress--hypoxia and could thus improve crop yields under suboptimal growing conditions. In rice (Oryza sativa) several ERFVII genes have been identified and characterized, including SUBMERGENCE 1A (SUB1A), which enables rice to tolerate submergence. The SUB1A gene was used in the development of SUB1 rice varieties, which are now widely grown in flood-prone areas and have been shown to improve yields and farmer livelihoods. The oxygen sensor in plants was discovered using the model plant Arabidopsis. The mechanism is based on the destabilization of ERFVII protein via the N-degron pathway under aerobic conditions. During hypoxia, the stabilized ERFVIIs translocate to the nucleus where they activate the transcription of hypoxia-responsive genes (HRGs). In summary, the identification and characterization of ERFVII transcription factors and their mechanism of action could lead to the development of new crop varieties with improved tolerance to low oxygen stress, which could have important implications for global food security. [ABSTRACT FROM AUTHOR]

Keywords: Barley; genome-wide association analysis; germination; hypoxia; laccase; lignification; secondary dormancy; submergence EN Barley genome-wide association analysis germination hypoxia laccase lignification secondary dormancy submergence 3883 3886 4 08/08/23 20230803 NES 230803 The important crop species barley, I Hordeum vulgare i , is prone to flooding stress and has difficulties germinating under hypoxic conditions. The wheat and barley lines have been collected globally with a focus on germplasm more adapted to European conditions, and the barley collections contains two- and six-row cultivars, landraces, and accessions of spring and winter growth habits. Barley, genome-wide association analysis, germination, hypoxia, laccase, lignification, secondary dormancy, submergence. [Extracted from the article]

Global climate change has dramatically increased flooding events, which have a strong impact on crop production. Barley (Hordeum vulgare) is one of the most important cereals and its cultivation includes a broad range of different environments. We tested the capacity to germinate of a large barley panel after a short period of submergence followed by a period of recovery. We demonstrate that sensitive barley varieties activate underwater secondary dormancy because of a lower permeability to oxygen dissolved in water. In sensitive barley accessions, secondary dormancy is removed by nitric oxide donors. The results of a genome-wide association study uncovered a Laccase gene located in a region of significant marker-trait association that is differently regulated during grain development and plays a key role in this process. Our findings will help breeders to improve the genetics of barley, thereby increasing the capacity of seeds to germinate after a short period of flooding. [ABSTRACT FROM AUTHOR]

Vegetation condition has declined along many regulated river systems globally due to alteration of flow regimes via flow regulation. Understanding how plants respond to inundation is critical for managing regulated river flows to improve riparian vegetation condition. We experimentally tested the effects of inundation duration on the survival and growth of six tufted grass species commonly found in riparian zones in south-eastern Australia. We conducted three nursery-based experiments in late winter/early spring, corresponding with natural temperate flow peaks and managed flows, with inundation treatments on: (1) established plants, up to 35 days inundation; (2) seedlings, up to 25 days inundation; and (3) established plants, up to 53 days inundation including additional shaded treatments. Plant survival, height and biomass growth, and onset of flowering were recorded for established plants, and, for seedlings, survival only. Plant height and biomass growth declined with longer inundation duration across all species, although surprisingly few established plants died. Unexpectedly, grass seedlings were generally tolerant of inundation also, although there was some evidence of increased mortality for the longest treatment (25 days inundation). Shading did not result in increased mortality or reduced height growth of inundated plants. Inundation effects on the onset of flowering were modest and varied between species ranging from earlier to delayed onset. Our results suggest that tufted grasses are tolerant of cool-season inundation. Given that mortality of these species has been observed in the field and experimentally under shorter inundation periods in warmer conditions (late spring and summer), we suggest that seasonal timing of inundation is critical in determining plant responses to inundation. [ABSTRACT FROM AUTHOR]

Adequate tissue O2 supply is crucial for plant function. We aimed to identify the environmental conditions and plant characteristics that affect plant tissue O2 status. We extracted data and performed meta-analysis on >1500 published tissue O2 measurements from 112 species. Tissue O2 status ranged from anoxic conditions in roots to >53 kPa in submerged, photosynthesising shoots. Using information-theoretic model selection, we identified 'submergence', 'light', 'tissue type' as well as 'light × submergence' interaction as significant drivers of tissue O2 status. Median O2 status were especially low (<50% of atmospheric equilibrium) in belowground rhizomes, potato (Solanum tuberosum) tubers and root nodules. Mean shoot and root O2 were ~25% higher in light than in dark when shoots had atmospheric contact. However, light showed a significant interaction with submergence on plant O2, with a submergence-induced 44% increase in light, compared with a 42% decline in dark, relative to plants with atmospheric contact. During submergence, ambient water column O2 and shoot tissue O2 correlated stronger in darkness than in light conditions. Although use of miniaturised Clark-type O2 electrodes has enhanced understanding of plant O2 dynamics, application of non-invasive methods in plants is still lacking behind its widespread use in mammalian tissues. We collected all (>1500) published measurements of plant O2 levels ever recorded, some measured more than 100 years ago. We found that plant O2 levels depended on in which plant part (e.g. roots or leaves) O2 was measured, and that plant O2 levels become low when plants are flooded, or in darkness. Our findings show that in terms of O2 supply, plants are especially vulnerable to flooded conditions. [ABSTRACT FROM AUTHOR]

Background: Flooding is among the most severe abiotic stresses in plant growth and development. The mechanism of submergence tolerance of cotton in response to submergence stress is unknown. Results: The transcriptome results showed that a total of 6,893 differentially expressed genes (DEGs) were discovered under submergence stress. Gene Ontology (GO) enrichment analysis showed that DEGs were involved in various stress or stimulus responses. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs related to plant hormone signal transduction, starch and sucrose metabolism, glycolysis and the biosynthesis of secondary metabolites were regulated by submergence stress. Eight DEGs related to ethylene signaling and 3 ethylene synthesis genes were identified in the hormone signal transduction. For respiratory metabolism, alcohol dehydrogenase (ADH, GH_A02G0728) and pyruvate decarboxylase (PDC, GH_D09G1778) were significantly upregulated but 6-phosphofructokinase (PFK, GH_D05G0280), phosphoglycerate kinase (PGK, GH_A01G0945 and GH_D01G0967) and sucrose synthase genes (SUS, GH_A06G0873 and GH_D06G0851) were significantly downregulated in the submergence treatment. Terpene biosynthetic pathway-related genes in the secondary metabolites were regulated in submergence stress. Conclusions: Regulation of terpene biosynthesis by respiratory metabolism may play a role in enhancing the tolerance of cotton to submergence under flooding. Our findings showed that the mevalonate pathway, which occurs in the cytoplasm of the terpenoid backbone biosynthesis pathway (ko00900), may be the main response to submergence stress. [ABSTRACT FROM AUTHOR]

A compound sharp-crested weir is often used to measure a wide range of flows with appropriate accuracy in open channels. In this study, experiments were performed to investigate the hydraulic flow through a compound weir of circular-rectangular with changes in hydraulic and geometric parameters in free and submerged flow conditions. The characteristics of the weirs include rectangular spans width of 39 cm, a circular radius of 5, 7.5, and 12.5 cm, and heights of 10 and 15 cm. The results showed that by increasing the radius and height of the Weir, upstream water depth increases around 28.4%. At a constant h/p, the discharge coefficient increases with the increasing radius of the circular arc. Also, in the submerged conditions, the discharge coefficient is less (around 40%) than in the free flow condition, which is due to the resistance of the depth of the created stream against the passage of the flow.