Improve Plant Survival Research Articles

Mitsuaria sp. and Burkholderia sp. from Arabidopsis rhizosphere enhance drought tolerance in Arabidopsis thaliana and maize (Zea mays L.)

Some rhizosphere microbes, such as plant growth-promoting rhizobacteria (PGPR), can alleviate plant drought stress and improve water use efficiency and productivity under drought conditions. The aims of this study are: 1) isolation and characterization of PGPRs from the rhizosphere of Arabidopsis plants that could improve drought tolerance of Arabidopsis and maize; 2) studying the potential mechanisms of improved plant drought tolerance by the isolated bacteria. In this study, bacteria isolates were isolated from the rhizosphere of Arabidopsis plants subjected to water limitation. Subsequently, the isolates were cultured and screened for their ability to improve drought tolerance of Arabidopsis. Potential mechanisms of improved plant drought tolerance by these bacteria including bacterial exopolysaccharide and 1-aminocyclopropane-1-carboxylic acid deaminase production, plant root system architecture modification, and plant physiological responses were also explored. Two bacterial isolates that conferred the greatest drought tolerance to Arabidopsis were further characterized. Both bacteria exhibit 1-aminocyclopropane-1-carboxylic acid deaminase activity, which can promote drought tolerance by decreasing plant ethylene levels. In vitro study showed that both Mitsuaria sp. ADR17 and Burkholderia sp. ADR10 altered the root structure system of Arabidopsis. Moreover, inoculation of Zea mays L. with either strain reduced evapotranspiration (i.e., soil water loss), and changed the plant proline and malondialdehyde levels, antioxidant enzymes activity, and phytohormone contents under drought stress. These results indicate that both strains interact with plants in ways that allow them to alter root system architecture, plant physiological responses and phytohormone levels under drought conditions to alleviate stress and improve plant survival. The results also indicated that each individual isolate has a separate pleiotropic effect.

Super absorbent polymer seed coatings promote seed germination and seedling growth of Caragana korshinskii in drought.

Coating seeds with water absorbent materials can improve their survival, especially for those planted in drought or barren areas. In this study, effects of five kinds of super absorbent polymers (SAPs) on seed germination and seedling growth of Caragana korshinskii under drought conditions were investigated. Our results showed that SAP coatings could significantly improve the percentage and energy of seed germination, as well as reduce the relative electrical conductivity (REC), proline, malondialdehyde (MDA), H2O2 content, and peroxidase (POD) activity during germination. These results implied that seeds could uptake moisture from SAP coatings to alleviate drought-induced oxidative stress and membrane damage, thus exhibiting a better vigor and germination performance. After coating C. korshinskii seeds with SAPs, more seedlings emerged and grew better. Under the combined influence of the water absorption capacity of SAP and other factors, the efficiencies of five SAP coatings are in the sequence D>E>B>A>C. The function of the SAP coating on promoting seedling survival was confirmed in Mu Us Sandy Land in Ordos, Inner Mongolia Autonomous Region, China. The average seedling number of SAP D-coated seeds increased twofold on that of naked seeds. Our results are expected to be helpful in understanding and utilizing SAP seed coatings in improving plant survival under drought conditions.

Hydrogel Banding Improves Plant Growth, Survival, and Water Use Efficiency in Two Calcareous Soils

Improving water use efficiency in the agricultural sector, particularly in arid regions, is becoming increasingly important in response to increasing global population and concomitant demand for food, water, and land. The authors performed experiments to determine whether the use of super‐absorbent polymers, also known as hydrogels, can increase plant survival, plant growth, and plant water use efficiency. The effect of hydrogel application proportions and application methods on plant survival and growth in clay and sandy clay loam (SCL) soils was investigated. Two pot experiments using Zea mays and Pinus pinea as model plants were performed. The hydrogel was applied at concentrations of 0, 1, 2, 3, and 4 g kg−1 soil in one of two methods: Banding or mixing. Hydrogel effects on water retention in the two soil types were recorded. The results suggest that hydrogel banding at 0.4% application in SCL improves corn's fresh and dry above‐ground biomass by 25%, and prolongs survival time of pine seedlings by 90%. Evapotranspiration was greater in soils banded with hydrogel at 0.4% and water use efficiency increased by 10–13% in both soils. Additionally, hydrogel increased water retention of SCL by up to 33% at 100 kPa, but had negligible effects when applied in clay soils. Accordingly, the efficacy of hydrogels in agriculture water conservation depends on using appropriate application methods and quantities.

Identification of the Submergence Tolerance QTL Come Quick Drowning1 (CQD1) in Arabidopsis thaliana.

Global climate change is predicted to increase water precipitation fluctuations and lead to localized prolonged floods in agricultural fields and natural plant communities. Thus, understanding the genetic basis of submergence tolerance is crucial in order to improve plant survival under these conditions. In this study, we performed a quantitative trait locus (QTL) analysis in Arabidopsis to identify novel candidate genes for increased submergence tolerance by using Kas-1 and Col (gl1) parental accessions and their derived recombinant inbred lines (RILs). We measured survival after submergence in dark for a 13-day period and used median lethal time, LT50 values for the QTL analysis. A major QTL, the Come Quick, Drowning (CQD1) locus, was detected in 2 independent experiments on the lower arm of chromosome 5 involved in higher submergence tolerance in the parental accession Kas-1. For fine-mapping, we then constructed near isogenic lines (NILs) by backcrossing the CQD1 QTL region. We also analyzed QTL regions related to size, leaf number, flowering, or survival in darkness and none of the QTL related to these traits overlapped with CQD1. The submergence tolerance QTL, CQD1, region detected in this study includes genes that have potential to be novel candidates effecting submergence tolerance such as trehalose-6-phosphate phosphatase and respiratory burst oxidase protein D. Gene expression and functional analysis for these genes under submergence would reveal the significance of these novel candidates and provide new perspectives for understanding genetic basis of submergence tolerance.

Jasmonate Regulates Plant Responses to Postsubmergence Reoxygenation through Transcriptional Activation of Antioxidant Synthesis.

Submergence induces hypoxia in plants; exposure to oxygen following submergence, termed reoxygenation, produces a burst of reactive oxygen species. The mechanisms of hypoxia sensing and signaling in plants have been well studied, but how plants respond to reoxygenation remains unclear. Here, we show that reoxygenation in Arabidopsis (Arabidopsis thaliana) involves rapid accumulation of jasmonates (JAs) and increased transcript levels of JA biosynthesis genes. Application of exogenous methyl jasmonate improved tolerance to reoxygenation in wild-type Arabidopsis; also, mutants deficient in JA biosynthesis and signaling were very sensitive to reoxygenation. Moreover, overexpression of the transcription factor gene MYC2 enhanced tolerance to posthypoxic stress, and myc2 knockout mutants showed increased sensitivity to reoxygenation, indicating that MYC2 functions as a key regulator in the JA-mediated reoxygenation response. MYC2 transcriptionally activates members of the VITAMIN C DEFECTIVE (VTC) and GLUTATHIONE SYNTHETASE (GSH) gene families, which encode rate-limiting enzymes in the ascorbate and glutathione synthesis pathways. Overexpression of VTC1 and GSH1 in the myc2-2 mutant suppressed the posthypoxic hypersensitive phenotype. The JA-inducible accumulation of antioxidants may alleviate oxidative damage caused by reoxygenation, improving plant survival after submergence. Taken together, our findings demonstrate that JA signaling interacts with the antioxidant pathway to regulate reoxygenation responses in Arabidopsis.

Assessment of plant growth promoting bacterial populations in the rhizosphere of metallophytes from the Kettara mine, Marrakech

Soil heavy metal contamination resulting from mining activities constitutes a major environmental problem worldwide. The spread of heavy metals is often facilitated by scarce vegetation cover, so there is an urgent need to improve plant survival and establishment in these metalliferous areas. This study is aimed at the isolation and analysis of the phylogenetic relationship of culturable bacteria from the rhizosphere of metallophyte plants growing in the Kettara mine, in Marrakech, in order to select plant growth-promoting rhizobacteria (PGPR), which could be used in assisted-phytoremediation. Bacterial isolates were grouped by random amplified polymorphic DNA analysis and identified by 16S rRNA gene sequencing. Strains were further characterized for the production of plant growth-promoting (PGP) substances, such as NH3, siderophores, indol-3-acetic acid (IAA), hydrogen cyanide, and extracellular enzymes, for ACC-deaminase activity, their capacity to solubilize phosphate, and for their tolerance to heavy metals and acidic pH. Rhizosphere soils were highly contaminated with Cu and Zn and presented low fertility. Phylogenetic analysis showed that the rhizobacteria were affiliated to three major groups: γ-Proteobacteria (48%), β-Proteobacteria (17%), and Bacilli (17%). The most represented genera were Pseudomonas (38%), Bacillus (10%), Streptomyces (10%), and Tetrathiobacter (10%). Overall, rhizobacterial strains showed an ability to produce multiple, important PGP traits, which may be helpful when applied as plant growth promoter agents in contaminated soils. PGPR were also able to withstand high levels of metals (up to 2615.2mg Zn l-1, 953.29mg Cu l-1, and 1124.6mg Cd l-1) and the order of metal toxicity was Cd > Cu > Zn. The rhizobacterial strains isolated in the present study have the potential to be used as efficient bioinoculants in phytoremediation strategies for the recovery of Kettara mine soils.

Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse‐grained soil in an alpine eco‐engineering field experiment?

AbstractSteep vegetation‐free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco‐engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small‐scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotal = 1248) and soil core (ntotal = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long‐term field experimental monitoring before transferring laboratory results to the field.

CO2 leakage-induced vegetation decline is primarily driven by decreased soil O2

To assess the potential risks of carbon capture and storage (CCS), studies have focused on vegetation decline caused by leaking CO2. Excess soil CO2 caused by leakage can affect soil O2 concentrations and soil pH, but how these two factors affect plant development remains poorly understood. This hinders the selection of appropriate species to mitigate potential negative consequences of CCS. Through pot experiments, we simulated CO2 leakage to examine its effects on soil pH and soil O2 concentrations. We subsequently assessed how maize growth responded to these changes in soil pH and O2. Decreased soil O2 concentrations significantly reduced maize biomass, and explained 69% of the biomass variation under CO2 leakage conditions. In contrast, although leaked CO2 changed soil pH significantly (from 7.32 to 6.75), it remained within the optimum soil pH range for maize growth. This suggests that soil O2 concentration, not soil pH, influences plant growth in these conditions. Therefore, in case of potential CO2 leakage risks, hypoxia-tolerant species should be chosen to improve plant survival, growth, and yield.

Transplanting Soil Microbiomes Leads to Lasting Effects on Willow Growth, but not on the Rhizosphere Microbiome.

Plants interact closely with microbes, which are partly responsible for plant growth, health, and adaptation to stressful environments. Engineering the plant-associated microbiome could improve plant survival and performance in stressful environments such as contaminated soils. Here, willow cuttings were planted into highly petroleum-contaminated soils that had been gamma-irradiated and subjected to one of four treatments: inoculation with rhizosphere soil from a willow that grew well (LA) or sub-optimally (SM) in highly contaminated soils or with bulk soil in which the planted willow had died (DE) or no inoculation (CO). Samples were taken from the starting inoculum, at the beginning of the experiment (T0) and after 100 days of growth (TF). Short hypervariable regions of archaeal/bacterial 16S rRNA genes and the fungal ITS region were amplified from soil DNA extracts and sequenced on the Illumina MiSeq. Willow growth was monitored throughout the experiment, and plant biomass was measured at TF. CO willows were significantly smaller throughout the experiment, while DE willows were the largest at TF. Microbiomes of different treatments were divergent at T0, but for most samples, had converged on highly similar communities by TF. Willow biomass was more strongly linked to overall microbial community structure at T0 than to microbial community structure at TF, and the relative abundance of many genera at T0 was significantly correlated to final willow root and shoot biomass. Although microbial communities had mostly converged at TF, lasting differences in willow growth were observed, probably linked to differences in T0 microbial communities.

Mycorrhizal Inoculation and High Arsenic Concentrations in the Soil Increase the Survival of Soybean Plants Subjected to Strong Water Stress

Soybean (Glycine max L.) cropping is increasing in marginal environments, including water-limited lands, some of which are loaded with arsenic (As). Plants inoculated with mycorrhiza increased their tolerance to water stress. We studied the effect of a sudden and severe water stress on soybean inoculated with the mycorrhizal fungus Glomus intraradices in soils with increasing concentrations of As. Soybean plants were grown in greenhouse with adequate water supply for 60 days. Irrigation was stopped completely and soil abruptly reached the permanent wilting point. Most inoculated plants survived under such limiting water stress, but noninoculated plants were clearly affected. Arsenic showed a negative effect on plant growth but improved plant survival under this severe water stress. It seems that the negative effects of As on plant water equilibrium explain why plants affected by As survived extreme water stress events.

New insight into leaf drought tolerance

Drought-induced forest dieback appears to have increased in frequency over the last decade (Van Mantgem et al. 2009; Allen et al. 2010; Peng et al. 2011). These diebacks have occurred across a wide diversity of forest types, suggesting that no forest biome is invulnerable to climate change (Choat et al. 2012). However, drought-influenced mortality rates differ substantially between species growing at the same site (Breshears et al. 2005) and populations within the species’ distribution range (Benito-Garz on, Ruiz-Benito & Zavala 2013). These dieback episodes may therefore lead to major vegetation shifts, substantial decreases in carbon uptake by the ecosystem (Ciais et al. 2005), and interactions, with invading alien species, for example. We need to understand the mechanisms by which drought stress affects tree performance and causes tree dieback if we are to identify the forests most vulnerable to climate change and to predict important vegetation processes, such as changes in community composition caused by differential plant mortality among species. Many studies have tried to identify the traits associated with improved plant survival during periods of drought. Three main strategies have been identified: water stress tolerance, avoidance and escape (see Fig. 1). Escape is when plants are temporarily absent during the drought period, due to mechanisms such as the shedding of leaves, as in ephemerophytes that complete their life cycle very rapidly and enter a dormant state during the long dry period in deserts. Avoidance includes a variety of mechanisms delaying or preventing the negative impact of stress. For drought stress, this involves minimization of water loss in plants experiencing drought, for instance, through strong stomatal closure to prevent decreases in water potential and subsequent runaway embolism. Tolerance involves xylem vascular system and/or leaf cells resisting dehydration (in plants able to sustain very negative water potentials) through the construction of xylem conduits resistant to cavitation and the maintenance of cell turgor. New technologies developed over the last 15 years have made it possible to assess xylem resistance to cavitation in many species (Delzon et al. 2010; Cochard et al. 2013) and populations within species (Lamy et al. 2014). However, the broad characterization of turgor loss point has proved more of a challenge. In this issue of Functional Ecology, Mar echaux et al. 2015; report an investigation of the leaf water potential at turgor loss point (ptlp) for a broad range of tropical tree species (71 in total). They report significant differences in ptlp values between species and show that ptlp might be associated with ecological drought tolerance (species with high ptlp are more frequently distributed in the tropical forest studied). Species growing in drier biomes have also been shown to have more negative values of ptlp (Bartlett, Scoffoni & Sack 2012b). Mar echaux et al. 2015 also provide evidence for the absence of a link with leaf economic spectrum, particularly as concerns specific leaf area (SLA). Together with the lack of relationship between SLA and forest water availability, these results strongly suggest that the broad and untimely use of SLA to predict species drought tolerance and distribution is likely to yield misleading results. The inclusion of ptlp in process-based vegetation models could therefore improve the accuracy of predictions of climate change impacts on forest ecosystems. Future studies are nevertheless required to confirm the correlation between leaf water potential at turgor loss point and species habitat suitability over a broader range of soil water availability. In this study, Mar echaux et al. 2015; used a recently developed method based on the use of an osmometer to predict ptlp (Bartlett et al. 2012a). This method is based on the accurate prediction of ptlp by leaf osmotic water potential at full hydration, as experimentally determined for 30 species by Bartlett et al. (2012a). This is consistent with interspecific differences in ptlp being driven principally by osmotic rather than elastic adjustments (Lenz, Wright & Westoby 2006; Bartlett, Scoffoni & Sack 2012b). This technique is much faster than the commonly used pressure– volume curve approach, opening up new possibilities for studying leaf drought tolerance within (phenotypic plasticity and genetic differentiation) and between (at the community and biome levels) species. It is particularly useful for studies in tropical forests, in which most of the plant species present have long vessels, making it more difficult to measure xylem resistance to cavitation, and making it all the more necessary to identify traits useful for the assessment of drought tolerance. Many studies have shown that leaf water potential at turgor loss point (ptlp) plays a key role in maintaining gas exchanges and growth rate under moderate water stress (Brodribb et al. 2003; Mitchell et al. 2008), but the direct relationship between ptlp and drought-induced tree mortality has never been investigated. As in the xylem hydraulics community, which has used the xylem *Correspondence author. E-mail: sylvain.delzon@u-bordeaux.fr

Inhibition of Phytophthora parasitica and P. capsici by Silver Nanoparticles Synthesized Using Aqueous Extract of Artemisia absinthium.

Application of nanoparticles for controlling plant pathogens is a rapidly emerging area in plant disease management, and nanoparticles synthesis methods that are economical and ecofriendly are extensively investigated. In this project, we investigated the potential of silver nanoparticles (AgNPs) synthesized with aqueous extract of Artemisia absinthium against several Phytophthora spp., which cause many economically important crop diseases. In in vitro dose-response tests conducted in microtiter plates, 10 µg ml⁻¹ of AgNPs inhibited mycelial growth of P. parasitica, P. infestans, P. palmivora, P. cinnamomi, P. tropicalis, P. capsici, and P. katsurae. Detailed in vitro dose-response analyses conducted with P. parasitica and P. capsici revealed that AgNPs synthesized with A. absinthium extract were highly potent (IC50: 2.1 to 8.3 µg ml⁻¹) and efficacious (100%) in inhibiting mycelial growth, zoospore germination, germ tube elongation, and zoospore production. Interestingly, AgNP treatment accelerated encystment of zoospores. Consistent with in vitro results, in planta experiments conducted in a greenhouse revealed that AgNP treatments prevented Phytophthora infection and improved plant survival. Moreover, AgNP in in planta experiments did not produce any adverse effects on plant growth. These investigations provide a simple and economical method for controlling Phytophthora with AgNP without affecting normal plant physiology.

Rootin, a compound that inhibits root development through modulating PIN-mediated auxin distribution

Plant roots anchor the plant to the soil and absorb water and nutrients for growth. Understanding the molecular mechanisms regulating root development is essential for improving plant survival and agricultural productivity. Extensive molecular genetic studies have provided important information on crucial components for the root development control over the last few decades. However, it is becoming difficult to identify new regulatory components in root development due to the functional redundancy and lethality of genes involved in root development. In this study, we performed a chemical genetic screen to identify novel synthetic compounds that regulate root development in Arabidopsis seedlings. The screen yielded a root growth inhibitor designated as ‘rootin’, which inhibited Arabidopsis root development by modulating cell division and elongation, but did not significantly affect shoot development. Transcript analysis of phytohormone marker genes revealed that rootin preferentially altered the expression of auxin-regulated genes. Furthermore, rootin reduced the accumulation of PIN1, PIN3, and PIN7 proteins, and affected the auxin distribution in roots, which consequently may lead to the observed defects in root development. Our results suggest that rootin could be utilized to unravel the mechanisms underlying root development and to investigate dynamic changes in PIN-mediated auxin distribution.

VuDREB2A, a novel DREB2-type transcription factor in the drought-tolerant legume cowpea, mediates DRE-dependent expression of stress-responsive genes and confers enhanced drought resistance in transgenic Arabidopsis.

VuDREB2A exists in cowpea as a canonical DREB2-type transcription factor, having the ability to bind dehydration-responsive elements in vitro and confer enhanced drought resistance in transgenic Arabidopsis. Cowpea (Vigna unguiculata L. Walp) is an important cultivated legume that can survive better in arid conditions than other crops. But the molecular mechanisms involved in the drought tolerance of this species remain elusive with very few reported candidate genes. The Dehydration-Responsive Element-Binding Protein2 (DREB2) group of transcription factors plays key roles in plant responses to drought. However, no DREB2 ortholog has been reported from cowpea so far. In this study, we isolated and characterized a gene from cowpea, namely VuDREB2A, encoding a protein of 377 amino acids exhibiting features of reported DREB2-type proteins. In cowpea, VuDREB2A transcript accumulation was highly induced by desiccation, heat and salt, but slightly by exogenous abscisic acid (ABA) treatment. We also isolated the VuDREB2A promoter and predicted stress-responsive cis-elements in it using Arabidopsis microarray data. The E. coli-expressed VuDREB2A protein showed binding to synthetic oligonucleotides with Dehydration-Responsive Elements (DREs) from Arabidopsis, in electrophoretic mobility shift assays. Heterologous expression of VuDREB2A in Arabidopsis significantly improved plant survival under drought. In addition, overexpression of a truncated version of VuDREB2A, after removal of a putative negative regulatory domain (between amino acids 132-182) led to a dwarf phenotype in the transgenic plants. Microarray and quantitative PCR analyses of VuDREB2A overexpressing Arabidopsis revealed up-regulation of stress-responsive genes having DRE overrepresented in their promoters. In summary, our results indicate that VuDREB2A conserves the basic functionality and mode of regulation of DREB2A in Arabidopsis and could be a potent candidate gene for the genetic improvement of drought resistance in cowpea.

Genetic Variation for Epidermal Conductance in Peanut

ABSTRACTPeanut (Arachis hypogaea L.) is an important legume that is often grown in drought‐prone areas. Low epidermal conductance (EC) may delay the dehydration of leaves and improve plant survival of severe water‐deficit stress. No reports of genetic variation for EC in peanut have been found in the literature. Therefore, the main objective of this study was to document genetic variation for EC among 21 peanut (Arachis spp.) genotypes in two greenhouse experiments and a field experiment. The effects of water‐deficit stress on EC and the association between EC and stomata density (SD) were also investigated. Tests for an influence of water‐deficit stress on EC were inconclusive. Comparison of EC and SD among genotypes failed to show any significant correlations in the various test environments. However, genetic variation for EC in peanut was found in both greenhouse experiments, with genotypes TMV 2, PI 298639, and VA 98R having very low EC. In the field, genotype SPT 06‐07 was found to have low EC. These results indicate that selection of genotypes with low EC is a viable approach in identifying peanut genotypes with improved capacity to survive severe soil water deficits.

Improved Management Options for Submergence-Tolerant (Sub1) Rice Genotype in Flood-Prone Rainfed Lowlands of West Bengal

Flash flood or submergence is a common phenomenon in rice growing rainfed lowland areas that seriously affects crop establishment leading to severe yield losses. A few submergence-tolerant rice varieties have been developed by introgressing SUB1 gene into mega rice varieties of South Asia. Two of these, Swarna-Sub1 and Sambha Mahsuri-Sub1, are already released in India for the commercial cultivation. Performance of these varieties can be further enhanced through adoption of appropriate management practices both in nursery and in main field. Two on-station field experiments were conducted using Swarna-Sub1 during the wet season (kharif) of 2011 at Rice Research Station, Chinsurah, Hooghly, West Bengal (India). Results of these experiments revealed that the use of lower seeding density (25 g m-2), application of balanced doses of N-P2O5-K2O @ 80-40-40 kg ha-1 in nursery and transplanting of aged seedlings (44 days) significantly improved plant survival, yield attributing traits and grain yield. An additional N-dose of 20 kg ha-1 at 7 days after receding of flood water resulted in better post-submergence recovery and maximum grain yield. In the on-farm trials conducted at three different locations in West Bengal, nursery raising of seedlings with the application of N-P2O5-K2O @ 80-40-40 kg ha-1, transplanting them at an optimum age (35 days) and application of 20 kg·N ha-1 after 7 days of de-submergence produced maximum grain yield of Swarna-Sub1.

An evaluation of lucerne for persistence under grazing in New Zealand

Abstract The on-farm use of lucerne (Medicago sativa) for grazing and conserved feed has increased in New Zealand over recent years, with new cultivars coming onto the market, including more winter-active ones. The extent to which the winter active types contribute to annual feed production, and the relationship to critical traits like persistence, has not been systematically tested. Two concurrent trials over a 4-year period were used to evaluate a range of lucerne cultivars and elite experimental populations ranging in dormancy from 2 (highly dormant) to 10 (non-dormant) under contrasting grazing regimes near Lincoln, New Zealand. More winter-active cultivars in the higher fall dormancy (FD) classes had similar growth to lower FD classes in all seasons except autumn, where they exhibited 18% greater yield than the lowest FD entry. However, these higher FD populations do not persist as well under heavy grazing, with a reduction in ground cover of up to 90% after four years, compared with only a 25% loss in lower FD classes. There was a negative correlation between FD and persistence measured as plant survival over 4 years (R2=0.73). However, one high FD entry showed increased survival under grazing, suggesting there is scope for selection of types with improved cool season growth and grazing tolerance. The concurrent lucerne trial subjected to a low-frequency grazing/ cutting regime showed faster recovery from defoliation than the adjacent hard grazed regime, suggesting stored underground reserves were more available for regrowth. We concluded that lucerne cultivars with FD ratings in the 3 to 5 range are most suitable for yield and persistence under grazing in these conditions. There is also scope for breeding to improve plant survival and dry matter yield within FD class. Keywords: Lucerne (Medicago sativa), grazing tolerance, persistence, fall dormancy

Effects of Hydrogen Sulfide on Growth, Antioxidative Capacity, and Ultrastructural Changes in Oilseed Rape Seedlings Under Aluminum Toxicity

The present study evaluates the beneficial effects of the hydrogen sulfide (H2S) donor, sodium hydrosulfide (0 and 0.3 mM), on the growth of oilseed rape (Brassica napus L. cv. ZS 758) seedlings under aluminum (Al) stress (0, 0.1, and 0.3 mM). Results showed that Al stress decreased the seedling growth by reducing the shoot and root length, biomass, and antioxidant enzymes, which could be illustrated by increased levels of malondialdehyde (MDA), production of hydrogen peroxide (H2O2), and accumulation of Al in the shoots. Pretreatment with H2S reduced MDA and H2O2 levels in the leaves and roots of B. napus seedlings. Moreover, activities of antioxidant enzymes (APX, CAT, APX, SOD, POD, and GR) were elevated significantly with the application of H2S under Al stress. The microscopic examination confirmed that higher levels of Al completely impaired leaf mesophyll and root tip cells. Chloroplasts were spongy shaped with dissolved thylakoid membranes and more starch grains. Root tip cells showed visible symptoms under Al toxicity such as deposition of Al in vacuoles and disruption of whole cell organelles. Under pretreatment with exogenous H2S, cell structures were improved and presented a clean mesophyll cell and chloroplast possessing well-developed thylakoid membranes as well as fewer starch grains. A number of modifications could be observed in root tip cells, that is, mature mitochondria, long endoplasmic reticulum as well as golgi bodies, under the combined application of H2S and Al. On the basis of our results, we can conclude that H2S has a promotive effect which could improve plant survival under Al stress.

Hydrogen sulfide ameliorates lead-induced morphological, photosynthetic, oxidative damages and biochemical changes in cotton

Poisonous lead (Pb), among heavy metals, is a potential pollutant that readily accumulates in soils and thus adversely affects physiological processes in plants. We have evaluated how exogenous H2S affects cotton plant physiological attributes and Pb uptake under Pb stress thereby understanding the role of H2S in physiological processes in plants. Two concentrations (0 and 200μM) of H2S donor sodium hydrosulfide (NaHS) were experimented on cotton plants under Pb stress (0, 50, and 100μM). Results have shown that Pb stress decreased plant growth, chlorophyll contents, SPAD value, photosynthesis, antioxidant activity. On the other hand, Pb stress increased the level of malondialdehyde (MDA), electrolyte leakage (EL), and production of H2O2 and uptake of Pb contents in all three parts of plant, viz. root, stem, and leaf. Application of H2S slightly increased plant growth, chlorophyll contents, SPAD value, photosynthesis, and antioxidant activity as compared to control. Hydrogen sulfide supply alleviated the toxic effects of lead on plant growth, chlorophyll contents, SPAD value, photosynthesis, and antioxidant activity in cotton plants. Hydrogen sulfide also reduced MDA, EL, and production of H2O2 and endogenous Pb levels in the three mentioned plant parts. On the basis of our results, we conclude that H2S has promotive effects which could improve plant survival under Pb stress.

Zinc ameliorates copper-induced oxidative stress in developing rice (Oryza sativa L.) seedlings

Rice (Oryza sativa L.) seedlings were treated with different concentrations of copper (Cu) either in presence or absence of zinc (Zn), and different events were investigated to evaluate the ameliorative effect of Zn on Cu stress. In presence of high Cu concentration, growth of both root and shoots were considerably reduced. Decline in elongation and fresh mass was observed in root and shoot. Zn alone did not show any considerable difference as compared to control, but when supplemented along with high concentration Cu, it prompted the growth of both root and shoot. After 7 days, root growth was 9.36 and 9.59 cm, respectively, at 200 and 500 μM of Cu alone as compared to 10.59 and 12.26 cm at similar Cu concentrations, respectively, in presence of Zn. Cu accumulation was considerably high after 7 days of treatment. In absence of Zn, significant accumulation of Cu was observed. Zn supplementation ameliorated the toxic impact of Cu and minimized its accumulation. Cu treatment for 1 and 7 days resulted in a dose-dependent increase in hydrogen peroxide (H2O2). When Cu was added in presence of Zn, the H2O2 production in root and shoot was reduced significantly. The increase in H2O2 production under Cu stress was accompanied by augmentation of lipid peroxidation. In absence of Zn, Cu alone enhanced the malondialdehyde (MDA) production in both root and shoot after 1 and 7 days of treatment. The MDA content drastically reduced in root and shoot as when Zn was added during Cu treatment. The activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPX) were elevated under Cu stress both in root and shoot. Addition of Zn further stimulated the activities of these enzymes. Both ascorbate (AsA) and glutathione (GSH) contents were high under Cu stress either in presence or absence of Zn. The results suggests that Zn supplementation improves plant survival capacity under high Cu stress by modulating oxidative stress through stimulation of antioxidant mechanisms and restricts the accumulation of toxic concentrations of Cu.