Waterlogged Plants Research Articles

High‐throughput phenotyping of plant growth rate to screen for waterlogging tolerance in lentil

AbstractThe combination of poorly drained soils and high rainfall can cause transient waterlogging and reduce yield of lentil. We screened 111 lentil lines for response to waterlogging in 2019 and 2020 using a pot assay outdoors. At 484 °Cd after emergence (38 d) in 2019 and 452 °Cd after emergence (42 d) in 2020, plants were waterlogged for 184 °Cd (11 d, 2019) and 167 °Cd (14 d, 2020) and allowed to recover for 323 °Cd (20 d, 2019) and 307 °Cd (26 d, 2020). We combined 2‐D digital images of canopy cover and plant height to derive a 3‐D trait that correlates with biomass to derive plant growth rate. Actual biomass at the end of recovery in the waterlogged plants varied 2.6‐fold with genotype, and genotypic and phenotypic correlations showed associations with plant growth rate both during (rg = .92; rp = .74) and after waterlogging (rg = .75; rp = .72); there was no trade‐off between maintenance of growth during waterlogging and growth during recovery. The ratio of biomass between waterlogged and control plants at the end of recovery was associated with growth rate during recovery (rg = .88, rp = .65) and biomass at the end of waterlogging (rg = .61, rp = .67). Broad‐sense heritability was 0.27 for growth rate during waterlogging, 0.37 for growth rate during recovery, 0.51 for biomass at the end of waterlogging and 0.47 for biomass at the end of recovery. High biomass at the end of recovery correlated with cooler canopies but correlations varied with season and measurement date, and heritability of canopy temperature was low. We identified genotypes with consistently higher tolerance to waterlogging and provide an improved understanding of the physiological response of lentil to hypoxia highlighting the importance of growth rate not only during waterlogging but also during recovery.

Leaf nutrient content and transcriptomic analyses of endive (Cichorium endivia) stressed by downpour-induced waterlog reveal a gene network regulating kestose and inulin contents

Endive (Cichorium endivia L.), a vegetable consumed as fresh or packaged salads, is mostly cultivated outdoors and known to be sensitive to waterlogging in terms of yield and quality. Phenotypic, metabolic and transcriptomic analyses were used to study variations in curly- (‘Domari’, ‘Myrna’) and smooth-leafed (‘Flester’, ‘Confiance’) cultivars grown in short-term waterlog due to rainfall excess before harvest. After recording loss of head weights in all cultivars (6-35%), which was minimal in ‘Flester’, NMR untargeted profiling revealed variations as influenced by genotype, environment and interactions, and included drop of total carbohydrates (6–50%) and polyols (3–37%), gain of organic acids (2–30%) and phenylpropanoids (98–560%), and cultivar-specific fluctuations of amino acids (−37 to +15%). The analysis of differentially expressed genes showed GO term enrichment consistent with waterlog stress and included the carbohydrate metabolic process. The loss of sucrose, kestose and inulin recurred in all cultivars and the sucrose-inulin route was investigated by covering over 50 genes of sucrose branch and key inulin synthesis (fructosyltransferases) and catabolism (fructan exohydrolases) genes. The lowered expression of a sucrose gene subset together with that of SUCROSE:SUCROSE-1-FRUCTOSYLTRANSFERASE (1-SST) may have accounted for sucrose and kestose contents drop in the leaves of waterlogged plants. Two anti-correlated modules harbouring candidate hub-genes, including 1-SST, were identified by weighted gene correlation network analysis, and proposed to control positively and negatively kestose levels. In silico analysis further pointed at transcription factors of GATA, DOF, WRKY types as putative regulators of 1-SST.

CYTOKININ AND GIBBERELLIC ACID ALLEVIATE THE EFFECT OF WATERLOGGING IN MUNGBEAN (VIGNA RADIATA L. WILCZEK)

Recently, waterlogging damage of mungbean is most common in many mungbean growing areas of the world. The exogenous application of phytohormones cytokinin (CK) and gibberellic acid (GA) could be an effective way of managing mungbean under waterlogging stress. Therefore, we applied different levels of CK and GA at the onset of waterlogging and ten days after waterlogging, and the results were observed in waterlogged plants as compared to control. The CK and GA application showed much improvement in depressed morpho-physiological and yield-related traits and seed yield. However, the responses varied depending on the types and doses of CK and GA. The plant height and the number of leaves were higher in GA-applied plants than CK-treated plants. The GA responded more in shoot growth, whereas CK in root development under waterlogged situations. The application of CK at 150 mg/L displayed the highest 33.9% yield advantage. It reveals that exogenous CK could be a good management practice in areas prone to waterlogging stress for attaining better yield in mungbean.

Potassium Alleviates Post-anthesis Photosynthetic Reductions in Winter Wheat Caused by Waterlogging at the Stem Elongation Stage.

Waterlogging occurs frequently at the stem elongation stage of wheat in southern China, decreasing post-anthesis photosynthetic rates and constraining grain filling. This phenomenon, and the mitigating effect of nutrient application, should be investigated as it could lead to improved agronomic guidelines. We exposed pot-cultured wheat plants at the stem elongation stage to waterlogging treatment in combination with two rates of potassium (K) application. Waterlogging treatment resulted in grain yield losses, which we attributed to a reduction in the 1,000-grain weight caused by an early decline in the net photosynthetic rate (Pn) post-anthesis. These decreases were offset by increasing K application. Stomatal conductance (Gs) and the intercellular CO2 concentration (Ci) decreased in the period 7–21 days after anthesis (DAA), and these reductions were exacerbated by waterlogging. However, in the period 21–28 DAA, Gs and Ci increased, while Pn decreased continuously, suggesting that non-stomatal factors constrained photosynthesis. On DAA 21, Pn was reduced by waterlogging, but photochemical efficiency (ΦPSII) remained unchanged, indicating a reduction in the dissipation of energy captured by photosystem II (PSII) through the CO2 assimilation pathway. This reduction in energy dissipation increased the risk of photodamage, as shown by early reductions in ΦPSII in waterlogged plants on DAA 28. However, increased K application promoted root growth and nutrient status under waterlogging, thereby improving photosynthesis post-anthesis. In conclusion, the decrease in Pn caused by waterlogging was attributable to stomatal closure during early senescence; during later senescence, a reduction in CO2 assimilation accounted for the reduced Pn and elevated the risk of photodamage. However, K application mitigated waterlogging-accelerated photosynthetic reductions and reduced yield losses.

Effect of water stress on glucosinolate content of Brassica carinata and performance of Brevicoryne brassicae and Myzus persicae

Drought-related changes in plant chemical composition affect plant resistance to insect herbivores. Ethiopian mustard (Gomenzer) Brassica carinata (A) Braun var. Yellow Dodolla was grown under three different water treatments; drought-stressed, well-watered and water-logged conditions to evaluate glucosinolate content and performance of two aphid species, the generalist Myzus persicae (Sulzer) and specialist Brevicoryne brassicae (L.). The analysis of High Performance Liquid Chromatography showed that water stress altered the levels of glucosinolates in (B) carinata plants. Plants cultivated under water-logged showed significantly higher glucosinolate content (2.236 µmol/g) when compared to well-watered (1.307 µmol/g) plants, whereas plants grown under drought-stressed (0.773 µmol/g) showed significantly reduced glucosinolate content after two week stress. B. carinata plants grown under water-logged condition had significantly higher sugar level (785.8 µg/g) followed by well-watered (667.6 µg/g) and drought-stressed (637.9 µg/g) plants after two week stress. Both aphid species reacted differently to water stress-induced change in the host plants. Significantly higher number of B. brassicae was recorded on plants grown under drought-stressed (395 aphids) plants than well-watered (278 aphids) and water-logged plants (179 aphids). Populations of M. persicae were significantly larger on plants grown under water-logged (558 aphids) and followed by well-watered (329 aphids) and drought-stressed plants (193 aphids). Feeding by both aphid B. brassicae and M. persicae increased significantly the level of glucosinolates in B. carinata plants. B. brassicae induced higher amount of glucosinolate content (3.85 µmol/g) when feeding on drought-stressed plants whereas M. persicae induced higher glucosinolate content (3.55 µmol/g) on water-logged plants. Water stressed B. carinata plants resulted to lower glucosinolate content and higher aphid population.

Properties of root water transport in canola (Brassica napus) subjected to waterlogging at the seedling, flowering and podding growth stages

The objective was to clarify the role of root water transport in waterlogged canola plants. We examined the hypothesis that waterlogging triggers root suberization and lignification, which reduces the effectiveness of apoplastic bypass and increases the dependence of roots on the aquaporin-mediated water transport, and that this effect varies depending on the growth stage. Brassica napus plants at the seedling, flowering and podding growth stages were waterlogged for up to 8 days. Growth, gas exchange, leaf water potentials, and root hydraulic conductance were measured in addition to relative contributions of the aquaporin-mediated and apoplastic root water transport, gene expression levels of plasma membrane intrinsic proteins (BnPIPs), and lignin and suberin deposition in roots. Waterlogging decreased dry weights, gas exchange, leaf water potentials and root hydraulic conductivity more in plants at the seedling stage than other growth stages. It also accelerated root suberization and lignification resulting in an increase of a relative contribution of aquaporin-mediated water transport. The transcript levels of BnPIPs increased with an increasing duration of waterlogging. Effects on root water transport played an important role in the sensitivity of canola seedlings to waterlogging. Increased relative contribution of aquaporin-mediated water transport in waterlogged plants was accompanied by enhanced root suberization and lignification. The evidence points to the importance of maintaining functional aquaporins in plant survival of waterlogging.

Leaf carbohydrates assimilation and metabolism affect seed yield of rapeseed with different waterlogging tolerance under the interactive effects of nitrogen and waterlogging

AbstractWaterlogging is a main factor causing rapeseed (Brassica napus L.) yield loss, and reasonable nitrogen (N) applications can compensate for this loss. To investigate the effects of N rates on seed yield of waterlogged rapeseed, the waterlogging‐tolerant rapeseed variety ZS 9 and sensitive variety GH01 were waterlogged for 0 and 10 days with five leaves at the seedling stage under four N rates (0, 90, 180 and 270 kg/ha). Waterlogging significantly decreased seed yield, while N application can alleviate the yield loss. The yield decrease rate of waterlogged GH01 was greater than that of ZS 9 under the same N rate. During the seedling and bolting stage, the leaf photosynthetic rate (Pn) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) activity increased, while activities of adenosine diphosphate glucose pyrophosphorylase (AGPase), sucrose synthase (SuSy) and sucrose phosphate synthase (SPS) decreased with more N under the same watering conditions. Compared to the plants without waterlogging, the leaf Pn and Rubisco activity, starch and sucrose contents of waterlogged rapeseed decreased at the two stages; activities of AGPase, SuSy and SPS of waterlogged rapeseed decreased at the seedling while increased at the bolting stage for both the two varieties. At the flowering stage, the Pn, the activities of Rubisco, AGPase, SuSy, SPS and contents of sucrose, starch increased with more N application for both ZS 9 and GH01. Compared to the plants without waterlogging, the Pn and Rubisco activity for waterlogged plants of the two varieties increased; the waterlogged plants of tolerant variety had higher activities of AGPase, SuSy and SPS, while those of sensitive variety was significantly lower. However, the decreased starch and sucrose content were found in both tolerant and sensitive varieties. The activities of AGPase, SuSy and SPS at flowering were highly positively correlated with yield under the interactive effects of N and waterlogging. These results suggested that the flowering stage is the most important stage that N had the positive regulation on waterlogged rapeseed growth. The carbohydrates translocation from leaves to seeds of the tolerant variety were enhanced after waterlogging, while that of the sensitive variety was still inhibited. This was the main reason for the difference in yield between the two waterlogged varieties.

Foliar Glycine Betaine or Hydrogen Peroxide Sprays Ameliorate Waterlogging Stress in Cape Gooseberry.

Exogenous glycine betaine (GB) or hydrogen peroxide (H2O2) application has not been explored to mitigate waterlogging stress in Andean fruit trees. The objective of this study was to evaluate foliar GB or H2O2 application on the physiological behavior of Cape gooseberry plants under waterlogging. Two separate experiments were carried out. In the first trial, the treatment groups were: (1) plants without waterlogging and with no foliar applications, (2) plants with waterlogging and without foliar applications, and (3) waterlogged plants with 25, 50, or 100 mM of H2O2 or GB, respectively. The treatments in the second trial were: (1) plants without waterlogging and with no foliar applications, (2) plants with waterlogging and without foliar applications, and (3) waterlogged plants with 100 mM of H2O2 or GB, respectively. In the first experiment, plants with waterlogging and with exogenous GB or H2O2 applications at a dose of 100 mM showed higher leaf water potential (−0.5 Mpa), dry weight (1.0 g), and stomatal conductance (95 mmol·m−2·s−1) values. In the second experiment, exogenously supplied GB or H2O2 also increased the relative growth rate, and leaf photosynthesis mitigating waterlogging stress. These results show that short-term GB or H2O2 supply can be a tool in managing waterlogging in Cape gooseberry.

Short-term nitrate supply decreases fermentation and oxidative stress caused by waterlogging in soybean plants

Waterlogging is one of the main causes of agricultural losses around the world, and nitrate nutrition has been demonstrated to mitigate the negative effects of waterlogging in plants. Here we evaluate the effect of short- and long-term nitrate fertilization in waterlogged nodulated soybean plants and comprehensively examine the mechanisms underpinning nitrate fertilization and soybean tolerance against hypoxia. Waterlogging increased fermentation and oxidative stress and decreased ATP levels in the roots of soybean. Waterlogged plants that received nitrate nutrition (short- or long-term) increased the levels of nitric oxide (NO) and partially restored ATP levels. Also, nitrate nutrition reduced the activity of fermentative and antioxidant enzymes as well as the fermentation substrates and reactive oxygen species (ROS) in waterlogged plants. Few metabolic differences resulted from short- and long-term fertilization, and these differences were not sufficient to impair waterlogging tolerance in soybean plants. By infiltrating roots from waterlogged plants with cPTIO (an NO scavenger), we show that enhanced nitrate nutrition-induced accumulation of NO in waterlogged plants proved to be a key factor for soybean tolerance against waterlogging. Increased ATP accumulation and decreased levels of ROS and toxic products derived from fermentation reactions are suggested as crucial mechanisms underpinning the tolerance of soybean plants under waterlogged conditions.

Mitigation of the Impact of Vascular Wilt and Soil Hypoxia on Cape Gooseberry Plants by Foliar Application of Synthetic Elicitors

Physalis peruviana L. crops are exposed to different stress conditions that limit their productivity. Within these conditions, abiotic stress caused by water and biotic stress by Fusarium oxysporum f. sp. physali (Foph) are frequent at commercial levels. The foliar application of synthetic elicitors can be a tool to mitigate the negative impacts of these stresses. The objective of this study was to evaluate the interaction between Foph inoculation and three foliar applications of brassinosteroids (BR), salicylic acid (SA), and a commercial elicitor based on botanical extracts (BE) of Echinacea purpurea, Potentilla erecta, and Aloe vera on the physiological [stomatal conductance (gS), leaf water potential (Ψwf), chlorophyll fluorescence, and growth] and biochemical [photosynthetic pigments, malondialdehyde (MDA) production, and proline content] responses of cape gooseberry plants subjected to a 6-day waterlogging period. The established treatments were as follows: 1) waterlogged plants without Foph; 2) waterlogged plants with Foph; 3) waterlogged, noninoculated (Foph−) plants treated foliarly with BR, SA, or BE; and 4) waterlogged, inoculated (Foph+) plants treated foliarly with BR, SA, or BE. The results showed that the foliar application of BR or SA reduced vascular wilt development in plants subjected to a hypoxia period. In addition, three applications of BR, SA, or BE favored gS, Ψwf, growth, and chlorophyll fluorescence parameters in cape gooseberry plants under the interaction between Foph and oxygen deficit in the soil. Also, higher photosynthetic pigment and proline contents were observed in plants treated with elicitors under stress combination, whereas a lower MDA production was evidenced in this group of plants. In conclusion, BR, SA, or BE can help mitigate the negative effects of the simultaneous occurrence of Foph and a waterlogging condition for 6 days in cape gooseberry plants.

Kentucky bluegrass growth under saline, waterlogging, and saline‐waterlogging conditions during germination and seedling growth

AbstractSalinity and waterlogging, two major problems in turfgrass management, often co‐occur in nature; however, information on the response of turfgrass to the combined salinity‐waterlogging stress is limited. The objective of this study was to determine growth response of nine Kentucky bluegrass (Poa pratensis L.) cultivars to the control (i.e., non‐stress), salinity, waterlogging, and the combined salinity‐waterlogging stress during the germination and seedling stage (six weeks) in pots in a greenhouse. Data including shoot and root dry weight, root‐to‐shoot dry weight ratio, root length, and specific root length were analyzed. Salinity‐waterlogging reduced dry weight of both shoots (556.1 mg) and roots (269.4 mg) compared with the controls (1295.1 and 686.7 mg) (P < .0001). The control plants had a root‐to‐shoot dry weight ratio of 52.9%, higher than the salinity‐treated ones (44.1%) (P = .0017). Root length was higher in the control and waterlogged plants than salinity and salinity‐waterlogged plants. Saline‐waterlogged and control plants had the highest and lowest specific root length, respectively. Among the Kentucky bluegrass cultivars, Sudden Impact, Award, Limousine, and Kenblue had higher tissue biomass, followed by America, Legend, and Arrowhead, whereas Moonlight and Blue Note performed poorly. Blue Note had a higher specific root length than all other grasses, except Moonlight. It may be a better management practice to use cultivars such as Sudden Impact, Award, Limousine, and Kenblue, which appear from this research to be relatively tolerant to salinity/waterlogging stress, when establishing a new turf surface under the aforementioned stresses.

Post-waterlogging Rescue Nitrogen Improves Waterlogging Tolerance in Mungbean (Vigna radiata)

The study was conducted at the Stress Research Site of the Department of Agronomy of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh during the period from April to July 2017 to evaluate the effect of rescue nitrogen fertilizer for improving the performance of waterlogging tolerance in mungbean genotype VC-6173A. Both waterlogged and non-waterlogged mungbean plants were received varying doses of rescue nitrogen from urea fertilizer. The rescue nitrogen (N) treatments were: N0-no rescue N; N30 - 20 and 10 kg ha-1 rescue N applied at 0-day and 15-day after removal of waterlogging (ARW); N40 - 30 and 10 kg ha-1 rescue N applied at 0-day and 15-day ARW and N50 - 40 and 10 kg ha-1 rescue N applied at 0-day and 15-day ARW. The study was laid out in a randomized complete block design with four replications. Different levels of rescue N improved plant height, leaf chlorophyll index, phonological period, plant growth, pod formation and seed yield of mungbean. N-treated plants showed higher relative SPAD chlorophyll values and the increment was higher for higher N-dose. Waterlogging reduced 40% root dry matter and 34% both shoot and total dry matter relative to non-waterlogged plants. Rescue N significantly increased both the root and shoot dry matter. The waterlogged plants without rescue N showed 29% reduction in the number of pods per plant and the reduction showed 13% for rescue N40 in waterlogged plants. The seed yield reduction was 25% in waterlogged plants without rescue N but with rescue N, seed yield remarkably increased particularly in N40-treated plants. Therefore, the study suggests that rescue N fertilizer application may be a viable practice in improving waterlogging tolerance and increasing yield of mungbean.
 The Agriculturists 2019; 17(1-2) 01-13

Nutritional status of ‘Hass’ and ‘Fuerte’ avocado (Persea americana Mill.) plants subjected to high soil moisture

In this study, the effect of increased soil moisture on the nutritional status of two key commercial avocado (Persea americana Μill.) cultivars, ‘Fuerte’ and ‘Hass’, was examined. The results revealed that prolonged exposure of plants to high soil water content conditions (waterlogging) reduced the total nutrient content (absolute quantity) of almost all of the nutrients in scion’s tissues (leaves and stems) of both cultivars. The decrease of nutrient content in the ‘Fuerte’ leaves was more prominent/severe compared to the ‘Hass’ leaves, which could be the outcome of the reported higher sensitivity of the cultivar to soil waterlogged conditions in previous studies. Interestingly, the inability of ‘Fuerte’ avocado plants to withstand high soil moisture conditions was not reflected in the relative concentrations of most nutrients, both in leaves and stems. Indeed, significantly higher concentrations of P, K, B, Fe, and Zn were found in the leaves of ‘Fuerte’ waterlogged plants than in well-watered ones. This fact reveals that under marginal/stressful conditions, like waterlogging, nutrient concentration in tissues does not reflect potential negative effects on total nutrient uptake of avocado plants, obviously due to concentrated nutrient phenomena primarily created by the stress-dependent growth inhibition. Therefore, total nutrient content is proposed as a more representative indicator for assessing plant response to waterlogged conditions.

Flooding Responses on Grapevine: A Physiological, Transcriptional, and Metabolic Perspective.

Studies on model plants have shown that temporary soil flooding exposes roots to a significant hypoxic stress resulting in metabolic re-programming, accumulation of toxic metabolites and hormonal imbalance. To date, physiological and transcriptional responses to flooding in grapevine are poorly characterized. To fill this gap, we aimed to gain insights into the transcriptional and metabolic changes induced by flooding on grapevine roots (K5BB rootstocks), on which cv Sauvignon blanc (Vitis vinifera L.) plants were grafted. A preliminary experiment under hydroponic conditions enabled the identification of transiently and steadily regulated hypoxia-responsive marker genes and drafting a model for response to oxygen deprivation in grapevine roots. Afterward, over two consecutive vegetative seasons, flooding was imposed to potted vines during the late dormancy period, to mimick the most frequent waterlogging events occurring in the field. Untargeted transcriptomic and metabolic profiling approaches were applied to investigate early responses of grapevine roots during exposure to hypoxia and subsequent recovery after stress removal. The initial hypoxic response was marked by a significant increase of the hypoxia-inducible metabolites ethanol, GABA, succinic acid and alanine which remained high also 1 week after recovery from flooding with the exception of ethanol that leveled off. Transcriptomic data supported the metabolic changes by indicating a substantial rearrangement of primary metabolic pathways through enhancement of the glycolytic and fermentative enzymes and of a subset of enzymes involved in the TCA cycle. GO and KEGG pathway analyses of differentially expressed genes showed a general down-regulation of brassinosteroid, auxin and gibberellin biosynthesis in waterlogged plants, suggesting a general inhibition of root growth and lateral expansion. During recovery, transcriptional activation of gibberellin biosynthetic genes and down-regulation of the metabolic ones may support a role for gibberellins in signaling grapevine rootstocks waterlogging metabolic and hormonal changes to the above ground plant. The significant internode elongation measured upon budbreak during recovery in plants that had experienced flooding supported this hypothesis. Overall integration of these data enabled us to draft a first comprehensive view of the molecular and metabolic pathways involved in grapevine’s root responses highlighting a deep metabolic and transcriptomic reprogramming during and after exposure to waterlogging.

Morphological Changes and Expressions of AOX1A, CYP81D8, and Putative PFP Genes in a Large Set of Commercial Maize Hybrids Under Extreme Waterlogging.

Waterlogging is a severe abiotic stressor causing significant growth impairment and yield losses in many crops. Maize is highly sensitive to the excess of water, and against the background of climate change there is an urgent need for deeper insights into the mechanisms of crop adaptation to waterlogging. In the present study, changes in maize morphology at the 4–5 leaf stage and the expression of three candidate genes for flooding tolerance in plants subjected to six continuous days of waterlogging were recorded in 19 commercial hybrids and in the inbred line B73, with the aim of investigating the current variability in cultivated hybrids and identifying useful morphological and molecular markers for screening tolerant genotypes. Here it was demonstrated that root parameters (length, area, biomass) were more impaired by waterlogging than shoot parameters (shoot height and biomass). Culm height generally increased in stressed plants (by up to +24% vs. controls), while shoot biomass was significantly reduced in only two hybrids. Root biomass was reduced in all the hybrids, by an average of 30%, and significantly in 7 hybrids, while root length and area were even more severely reduced, by 30–55% vs. controls, depending on the hybrid. The earlier appearance of aerial roots seemed to be associated with greater root injuries. In leaves, the transcript of the PFP enzyme (phosphofructokinase), which is involved in glycolytic reactions, was markedly up-regulated (up to double the values) in half the waterlogged hybrids, but down-regulated in the others. The transcript of CYP81D8 (ROS-related proteins) in waterlogged plants exhibited relevant increases or strong decreases in level, depending on the hybrid. The transcript of the AOX1A gene, coding for a mitochondrial respiratory electron transport chain-related protein, was markedly down-regulated in all the treated hybrids. Expression analysis of these genes under extreme waterlogging only partially correlate with the shoot and root growth impairments observed, and AOX1A seems to be the most informative of them.

Melatonin Improved Waterlogging Tolerance in Alfalfa (Medicago sativa) by Reprogramming Polyamine and Ethylene Metabolism.

Melatonin (MT), polyamines (PAs), and ethylene have been suggested to play key roles in plant growth and development in response to environmental abiotic stresses. However, the effect of melatonin on polyamine and ethylene metabolism under waterlogging stress has rarely been elucidated. The main purpose of this study was to investigate the effect of melatonin pretreatment on waterlogging stress in alfalfa. The experiment was arranged into four treatment groups control with water pretreatment (CK-MT), control with melatonin pretreatment (CK+MT), waterlogging pretreated with water (WL-MT) and waterlogging pretreated with melatonin (WL+MT), with three replications. Six-week-old alfalfa seedlings were pretreated with 100 μM melatonin and exposed to waterlogging stress for 10 days. Plant growth rate, different physiological characteristics, and gene expression level were measured. Results showed that waterlogging induced melatonin accumulation, and melatonin pretreatment increased endogenous MT levels for the control and water-logged plants. Waterlogging stress caused a significant reduction in plant growth, chlorophyll content, photochemical efficiency (Fv/Fm) and net photosynthetic rate (Pn), while also causing increased leaf electrolyte leakage (EL) and malondialdehyde (MDA) content. Pretreatment with melatonin alleviated the waterlogging-induced damage and reduction in plant growth, chlorophyll content, Fv/Fm and Pn. Waterlogging stress significantly increased leaf polyamines (Put, Spd, Spm) and ethylene levels, and the increased PAs and ethylene levels are coupled with higher metabolic enzymes and gene expressions. While pretreatment with melatonin further increased Put, Spd and Spm levels, it also decreased ethylene levels under waterlogging, and those increased PAs levels or decreased ethylene levels are regulated by the metabolic enzymes and gene expressions. The results in this study provide more comprehensive insight into the physiological and molecular mechanisms of melatonin-improved waterlogging tolerance in alfalfa. Furthermore, they suggested that melatonin improved waterlogging tolerance in alfalfa at least partially by reprogramming ethylene and PA biosynthesis, attributable to the increased PAs and decreased ethylene levels, which leads to more enhanced membrane stability and photosynthesis as well as less leaf senescence caused by ethylene.

Waterlogging-induced adventitious root formation in cucumber is regulated by ethylene and auxin through reactive oxygen species signalling.

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP), the auxin transport inhibitor 1-naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin-induced AR formation was inhibited by 1-MCP, although ethylene-induced AR formation was not inhibited by NPA. Both ethylene- and auxin-induced AR formation were counteracted by DPI. These results indicate that auxin-induced AR formation is dependent on ethylene, whereas ethylene-induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene- and auxin-induced AR formation in cucumber plants.

Morphological assessments evidence that higher number of pneumatophores improves tolerance to long-term waterlogging in oil palm (Elaeis guineensis) seedlings

Oil palm (Elaeis guineensis Jacq.) apparently tolerates long-term waterlogging and numerous pneumatophores are evident morphological adaptation. The number of pneumatophores per plant is, however, quite variable. Thus we hypothesized that a higher number of pneumatophores may attenuate the stress effects on root system growth and induce higher tolerance to long-term waterlogging in oil palm seedlings. To test this hypothesis we compared morphological and physiological traits in well-watered (control) and waterlogged plants with 2–10, 30–40, 60–70, and 90–120 pneumatophores after ca. 77 days of waterlogging. Plant height was similar between control and waterlogged plants with 90–120 pneumatophores, but it was 21% lower in plants with 2–10 pneumatophores than in control. The stem diameter and bulb diameter and biomass were 16, 20 and 42% higher in waterlogged plants than in control, independent of number of pneumatophores. Similar number of leaves and leaflets were observed regardless of watering regime and pneumatophore number, but total leaflet area and leaflet biomass were higher in plants with 90–120 pneumatophores than in other plants. Root system biomass was remarkably decreased in waterlogged plants; however, such decreases were more expressive in plants with 2–10 pneumatophores. Leaf water potential, leaf gas exchange and chlorophyll fluorescence were unaffected by waterlogging. Thus, we conclude that waterlogging causes few changes in seedlings’ above-ground morphology but remarkably affects root system development, mainly in those plants with lower number of pneumatophores. Regardless of pneumatophores, the stressed oil palm seedlings were able to adjust their leaf water status and gas exchange to cope properly with the imposed waterlogging.

MORPHOANATOMY OF Garcinia madruno (KUNTH) HAMMEL (CLUSIACEAE) UNDER WATERLOGGED CONDITIONS

ABSTRACT Garcinia madruno (Kunth) Hammel is a neotropical tree that naturally occurs in terra firme forests and is important as a source of income and medicine for Amazonian populations. This study describes and compares the morphoanatomical responses of plants under conditions of stress and normoxia. Young plants of Garcinia madruno were subjected to two water regimes: daily controlled irrigation and waterlogged for 84 days. Hypertrophic lenticels, adventitious roots and anatomical characteristics of the roots and leaves were evaluated on days 0, 21, 42, 63 and 84. There were no changes in leaf structure, but cracks and hypertrophic lenticels appeared on the stems, there was an increase in blackness of the roots and the plants formed adventitious roots to adapt to the flooded environment. The anatomical changes in the roots of the flooded plants were thickening of the exodermis in the main root and of the pericycle in the lateral roots, and a large increase in the amount of aerenchyma. Histochemical tests detected starch in the midrib, mesophyll, stem and root of flooded plants, and in the petiole of control plants. In the waterlogged plants, phenolic compounds were found in the petiole and alkaloids were found in the midrib, petiole and root.

Global gene expression in cotton (Gossypium hirsutum L.) leaves to waterlogging stress.

Cotton is sensitive to waterlogging stress, which usually results in stunted growth and yield loss. To date, the molecular mechanisms underlying the responses to waterlogging in cotton remain elusive. Cotton was grown in a rain-shelter and subjected to 0 (control)-, 10-, 15- and 20-d waterlogging at flowering stage. The fourth-leaves on the main-stem from the top were sampled and immediately frozen in liquid nitrogen for physiological measurement. Global gene transcription in the leaves of 15-d waterlogged plants was analyzed by RNA-Seq. Seven hundred and ninety four genes were up-regulated and 1018 genes were down-regulated in waterlogged cotton leaves compared with non-waterlogged control. The differentially expressed genes were mainly related to photosynthesis, nitrogen metabolism, starch and sucrose metabolism, glycolysis and plant hormone signal transduction. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis indicated that most genes related to flavonoid biosynthesis, oxidative phosphorylation, amino acid metabolism and biosynthesis as well as circadian rhythm pathways were differently expressed. Waterlogging increased the expression of anaerobic fermentation related genes, such as alcohol dehydrogenase (ADH), but decreased the leaf chlorophyll concentration and photosynthesis by down-regulating the expression of photosynthesis related genes. Many genes related to plant hormones and transcription factors were differently expressed under waterlogging stress. Most of the ethylene related genes and ethylene-responsive factor-type transcription factors were up-regulated under water-logging stress, suggesting that ethylene may play key roles in the survival of cotton under waterlogging stress.