Greater Stress Tolerance Research Articles

Transcriptomic Insights into Drought Survival Strategy of Sorghum bicolor (L.) Moench during Early Growth under Polyethylene Glycol-Simulated Conditions

Drought stress during sorghum emergence significantly affects seedling establishment, adversely affecting both emergence and population growth. This study investigates drought tolerance mechanisms during sorghum germination by analyzing physiological changes and transcriptomic data from two lines: W069 (drought tolerant) and W040 (drought sensitive). Under drought conditions, a phenotypic analysis revealed that W069 exhibited longer shoots and roots than W040. Additionally, physiological data indicated higher osmotic substance and lower malondialdehyde levels in W069. Using Kyoto Encyclopedia of Genes and Genome analyses, we identified three key pathways (starch and sucrose metabolism, phenylpropanoid biosynthesis, and phytohormone signaling) as pivotal in the drought response during seed germination in sorghum plants. Expression profiling revealed that most drought tolerance-related genes in the three key pathways were expressed at higher levels in the drought-tolerant cultivar W069, possibly explaining its greater stress tolerance. These findings enhance our understanding of drought-responsive gene networks in sorghum seed germination, offering potential target genes and strategies for enhancing drought tolerance in this crop.

Multigenerational inheritance drives symbiotic interactions of the bacterium Bacillus subtilis with its plant host

Bacillus subtilis is a beneficial bacterium that supports plant growth and protects plants from bacterial, fungal, and viral infections. Using a simplified system of B. subtilis and Arabidopsis thaliana interactions, we studied the fitness and transcriptome of bacteria detached from the root over generations of growth in LB medium. We found that bacteria previously associated with the root or exposed to its secretions had greater stress tolerance and were more competitive in root colonization than bacteria not previously exposed to the root. Furthermore, our transcriptome results provide evidence that plant secretions induce a microbial stress response and fundamentally alter signaling by the cyclic nucleotide c-di-AMP, a signature maintained by their descendants. The changes in cellular physiology due to exposure to plant exudates were multigenerational, as they allowed not only the bacterial cells that colonized a new plant but also their descendants to have an advance over naive competitors of the same species, while the overall plasticity of gene expression and rapid adaptation were maintained. These changes were hereditary but not permanent. Our work demonstrates a bacterial memory manifested by multigenerational reversible adaptation to plant hosts in the form of activation of the stressosome, which confers an advantage to symbiotic bacteria during competition.

Putrescine Mitigates High Temperature Effects by Modulating Morpho-Physiological and Biochemical Attributes in Brassica juncea Seedlings

A variety of environmental issues are affecting crops all across the world, but rising temperatures are posing the greatest threat. High temperature has been found to drastically inhibit seedling emergence and cause leaf necrosis at the seedling stage, which results in poor plant stand and significantly decreased yields. Polyamines (PAs) are positively charged, low-molecular-weight aliphatic nitrogenous bases present in all living organisms and are involved in various biological processes in plant growth and development, including senescence and response to different abiotic stresses. Putrescine (Put) functions as a master growth regulator that promotes optimal plant development and greater stress tolerance. Here, the current study aimed to elucidate how Put (1 mM) functions in reducing the negative impacts of high temperature on four varieties of Brassica juncea (RH-1707, RH-1708, RH-1566 and RH-1999-42). Exposure of plants to high temperature resulted in decrease in growth parameters, chlorophyll content and relative water content. Simultaneously, increases were found in antioxidant enzymes, electrolyte leakage, lipid peroxidation, hydrogen peroxide content and stomatal density. High temperature more significantly affected varieties RH-1707 and RH-1708, while RH-1566 and RH-1999-42 showed lesser effects. Exogenous application of Put mitigated the negative impacts of high temperature by enhancing growth, chlorophyll content, relative water content and antioxidant enzyme activities and, simultaneously, it reduces oxidative damage and stomatal density. This study specifies that varieties RH-1707 and RH-1708 are sensitive whereas RH-1566 and RH-1999-42 are tolerant of high temperature and provides an insight into the effectiveness of Put in mitigating the effects of high temperature to a significant extent in B. juncea seedlings.

The role of transposon inverted repeats in balancing drought tolerance and yield-related traits in maize.

The genomic basis underlying the selection for environmental adaptation and yield-related traits in maize remains poorly understood. Here we carried out genome-wide profiling of the small RNA (sRNA) transcriptome (sRNAome) and transcriptome landscapes of a global maize diversity panel under dry and wet conditions and uncover dozens of environment-specific regulatory hotspots. Transgenic and molecular studies of Drought-Related Environment-specific Super eQTL Hotspot on chromosome 8 (DRESH8) and ZmMYBR38, a target of DRESH8-derived small interfering RNAs, revealed a transposable element-mediated inverted repeats (TE-IR)-derived sRNA- and gene-regulatory network that balances plant drought tolerance with yield-related traits. A genome-wide scan revealed that TE-IRs associate with drought response and yield-related traits that were positively selected and expanded during maize domestication. These results indicate that TE-IR-mediated posttranscriptional regulation is a key molecular mechanism underlying the tradeoff between crop environmental adaptation and yield-related traits, providing potential genomic targets for the breeding of crops with greater stress tolerance but uncompromised yield.

Distribution and accumulation of mercury in pot-grown African rice cultivars (Oryza glaberrima Steud. and Oryza sativa L.) determined via LA-ICP-MS.

There is limited information concerning the distribution of mercury in rice, particularly in African rice. The objective was to compare the distribution of total mercury (THg) and methylmercury (MeHg) in African rice (Oryza glaberrima Steud.) and Asian rice (O. sativa L.). It is hypothesized that increased mineral accumulation and greater stress tolerance in O. glaberrima will affect the uptake and distribution of THg and MeHg, compared to O. sativa. Rice varieties from the Republic of Mali, including O. glaberrima (n =1) and O. sativa (n = 2), were cultivated in a greenhouse, in mercury-spiked soil (50 mg/kg) (n =3 replicates/variety). THg and MeHg concentrations were analyzed in the grain (brown rice), and the THg distribution was analyzed using laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS). THg and MeHg concentrations did not differ between O. glaberrima and O. sativa grain. However, in both O. sativa varieties, THg was highly concentrated in the scutellum, which surrounds the embryo and is removed during polishing. Conversely, in O. glaberrima grain, THg was widely distributed throughout the endosperm, the edible portion of the grain. Differences in the THg distribution in O. glaberrima grain, compared to O. sativa, may elevate the risk of mercury exposure through ingestion of polished rice. The novelty of this study includes the investigation of a less-studied rice species (O. glaberrima), the use of a highly sensitive elemental imaging technique (LA-ICP-MS), and its finding of a different grain THg distribution in O. glaberrima than has been observed in O. sativa.

A trampoline effect occurring in the stages of planetary reseeding

Impactors have hit the Earth since its formation and have continued to be infrequent guests throughout the Earth's history. Although the early part of the Earth's history was marked by these violent events, life was present early, possibly existing already in the Hadean Eon. It is possible that life has been, and still is, transported between the worlds of the solar system, owing to impacts leading material away from the impact region. Beyond this lithopanspermia hypothesis, in the so-called ‘refugium hypothesis’, ejected material has been suggested to also return to its home planet and 'reseed' life after the world has recovered after a global impactor, thus restarting evolution. In addition to such impactors, more frequent impacts from smaller non-sterilizing impactors existed during the Heavy Bombardment epoch, feeding material potentially harbouring viable organisms into near Earth space. During the three stages of planetary self-reseeding, the encapsulated microbial population experiences abiotic stressors; specifically, they experience pressure and heat shock twice, in stage 1 and after a recovery phase in stage 2, and again in stage 3. Although many circumstances have played a role in the endurance of life in the early history of the Earth, a particular biological effect could potentially be conferred on a microbial population in this scenario. Thus, the surviving population not only would experience an increase in the frequency of robust genotypes but also would be expected to have greater stress tolerance than non-stressed organisms of the same species. Hence, because of the trampoline effect, the mean robustness of the microbial population towards these stressors is higher in stage 3 than stage 1. In principle, the time between the impactor and the reimpactor need not be long before this trampoline effect appears. Experiments simulating stage 1 must take this effect into consideration in estimating the survival probabilities of a population of organisms in worlds such as the past Earth. Thus, the stages of planetary self-reseeding can themselves be considered facilitators of a process that enhances the stress capacity of the collected microbial organisms and thus their survival capacity. This process may have played a role in the survival of life through violent periods of Earth's history and thus may affect inhabited worlds in general.

Measuring ROS and redox markers in plant cells.

Reactive oxygen species (ROS) are produced throughout plant cells as a by-product of electron transfer processes. While highly oxidative and potentially damaging to a range of biomolecules, there exists a suite of ROS-scavenging antioxidant strategies that maintain a redox equilibrium. This balance can be disrupted in the event of cellular stress leading to increased ROS levels, which can act as a useful stress signal but, in excess, can result in cell damage and death. As crop plants become exposed to greater degrees of multiple stresses due to climate change, efforts are ongoing to engineer plants with greater stress tolerance. It is therefore important to understand the pathways underpinning ROS-mediated signalling and damage, both through measuring ROS themselves and other indicators of redox imbalance. The highly reactive and transient nature of ROS makes this challenging to achieve, particularly in a way that is specific to individual ROS species. In this review, we describe the range of chemical and biological tools and techniques currently available for ROS and redox marker measurement in plant cells and tissues. We discuss the limitations inherent in current methodology and opportunities for advancement.

Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass.

Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution.

Overexpression of AmDUF1517 enhanced tolerance to salinity, drought, and cold stress in transgenic cotton

As abiotic stresses become more severe as a result of global climate changes, the growth and development of plants are restricted. In the development of agricultural crops with greater stress tolerance, AmDUF1517 had been isolated from the highly stress-tolerant shrub Ammopiptanthus mongolicus, and can significantly enhance stress tolerance when inserted in Arabidopsis thaliana. In this study, we inserted this gene into cotton to analyze its potential for conferring stress tolerance. Two independent transgenic cotton lines were used. Southern blot analyses indicated that AmDUF1517 was integrated into the cotton genome. Physiological analysis demonstrated that AmDUF1517-transgenic cotton had stronger resistance than the control when treated with salt, drought, and cold stresses. Further analysis showed that trans-AmDUF1517 cotton displayed significantly higher antioxidant enzyme (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST)) activity and less reactive oxygen species (ROS) accumulation, which suggests that overexpression of AmDUF1517 can improve cotton resistance to stress by maintaining ROS homeostasis, as well as by alleviating cell membrane injury. These results imply that AmDUF1517 is a candidate gene in improving cotton resistance to abiotic stress.

A systems approach to a spatio-temporal understanding of the drought stress response in maize

Crops are often subjected to periods of drought stress during their life cycle. However, how stress response mechanisms contribute to the crosstalk between stress signaling pathways and developmental signaling pathways is still unknown. We built a gene co-expression network from a spatio-temporal transcriptomic map of the drought stress response in maize (Zea mays), profiled from three tissues and four developmental stages and characterized hub genes associated with duplication events, selection, and regulatory networks. Co-expression analysis grouped drought-response genes into ten modules, covering 844 highly connected genes (hub genes). Of these, 15.4% hub genes had diverged by whole-genome duplication events and 2.5% might then have been selected during natural domestication and artificial improvement processes, successively. We identified key transcription factor hubs in a transcriptional regulatory network, which may function as a crosstalk mechanism between drought stress and developmental signalling pathways in maize. Understanding the evolutionary biases that have evolved to enhance drought adaptation lays the foundation for further dissection of crosstalk between stress signalling pathways and developmental signalling pathways in maize, towards molecular design of new cultivars with desirable yield and greater stress tolerance.

Sex-related differences in stress tolerance in dioecious plants: a critical appraisal in a physiological context.

Sex-related differences in reproductive effort can lead to differences in vegetative growth and stress tolerance. However, do all dioecious plants show sex-related differences in stress tolerance? To what extent can the environmental context and modularity mask sex-related differences in stress tolerance? Finally, to what extent can physiological measurements help us understand secondary sexual dimorphism? This opinion paper aims to answer these three basic questions with special emphasis on developments in research in this area over the last decade. Compelling evidence indicates that dimorphic species do not always show differences in stress tolerance between sexes; and when sex-related differences do occur, they seem to be highly species-specific, with greater stress tolerance in females than males in some species, and the opposite in others. The causes of such sex-related species-specific differences are still poorly understood, and more physiological studies and diversity of plant species that allow comparative analyses are needed. Furthermore, studies performed thus far demonstrate that the expression of dioecy can lead to sex-related differences in physiological traits-from leaf gas exchange to gene expression-but the biological significance of modularity and sectoriality governing such differences has been poorly investigated. Future studies that consider the importance of modularity and sectoriality are essential for unravelling the mechanisms underlying stress adaptation in male and female plants growing in their natural habitat.

Mindfulness, Relaxed Breathing Can Amplify Good Patient Care

Back to table of contents Previous article ViewpointsFull AccessMindfulness, Relaxed Breathing Can Amplify Good Patient CareGary Weinstein,M.D.Gary Weinstein,Search for more papers by this authorM.D.Published Online:14 Jul 2015https://doi.org/10.1176/appi.pn.2015.7b25AbstractWe are trained quite well to use medication or psychotherapy or a combination of the two to help patients with the range of psychiatric disorders. While most patients experience a significant benefit, others either do not have a clinical response or may be treatment resistant, even after other somatic therapies are used. Thus, it is useful to have additional tools to help those patients.An array of therapeutic modalities is available that have been well researched and proven highly effective, including holistic and complementary approaches. Our profession is accustomed to skepticism from others about even a body-mind connection so our open-mindedness can help try a related evidence-based treatment.Two years ago, Dr. Dilip Jeste wrote in Psychiatric News about the positive neurobiological effects of meditation and the physical changes in the brain that occur when meditation is practiced. Other modalities such as breathing techniques and heart rhythm coherence training are also quite effective and easy to learn, but this article will focus on relaxation-response training and mindfulness meditation. Both techniques activate the parasympathetic nervous system, leading to many positive benefits. These include the ability to have a greater stress tolerance, improved concentration, more restful sleep, and a reduction in anxiety-related disorders.To master these techniques and maximize their effectiveness, patients must practice them regularly, optimally 10 to 20 minutes twice a day. For relaxation response in particular, patients should choose a quiet place that is free from distractions and sit in a comfortable, upright position; eyes should remain closed.The relaxation-response technique has demonstrated value over many years since its creation by Dr. Herbert Benson, a professor of medicine at Harvard. Even though a variety of methods can be used, patients should start by deeply relaxing their muscles beginning at their feet and breathing through their nose. While breathing out, they can say a word such as “one” or “peace” to themselves. This shifts the mind from logical, externally oriented thoughts to an internal focus. Patients should maintain this passive attitude, ignore distracting thoughts, and dismiss any concerns they may have about “success” in meditation.With mindfulness meditation, attaining a nonjudgmental, detached, self-observing stance is the goal with a moment-to-moment awareness of whatever is being experienced. Attention should be centered on inhalation and exhalation. The body is scanned starting with the toes, and tension is released with progression up the body to the head. Sounds, physical sensations, and breathing can also serve as vehicles for mindfulness. After practicing mindfulness, patients should be able to respond to stress with more calmness and clarity, reducing anxiety and fear.Since our time with patients is limited, I write down as “prescriptions” the names and URLs of free websites that I think may be useful to patients for whom I am recommending these techniques. Among them:Relaxation response technique: (http://www.relaxationresponse.org). The site is user friendly, and instructions may be printed out. Mindfulness meditation: (http://www.marc.UCLA.edu/body.cfm). The site provides short but effective guided meditations from the UCLA Mindful Awareness Research Center.These techniques may be useful not only to our patients but also to us. Psychiatry has changed greatly since I began 36 years ago, but a regular practice of meditation has helped me adapt. Sigmund Freud thought the ideal state of mind for a psychotherapist included suspending critical judgment and focusing impartially and equally on all there is to observe. These techniques may also be helpful in reducing stress from a psychiatric practice with overbooked schedules, coding and electronic health records miscues, insurance company demands, and prescriptions needing prior authorizations or substitutions. Learning and practicing these techniques can expand on our heritage and capability. ■Gary Weinstein, M.D., is a past speaker of the APA Assembly and a private practitioner in Louisville, Ky. ISSUES NewArchived

Arbuscular mycorrhizal fungi as a tool to ameliorate the phytoremediation potential of poplar: biochemical and molecular aspects

Abstract: Poplar is a suitable species for phytoremediation, able to tolerate high concentrations of heavy metals (HMs). Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the roots of most land plants; they improve nutrient uptake and enhance phytoextraction of HMs while alleviating stress in the host plant. This review summarizes previous results from field and greenhouse studies conducted by us and dealing with this topic. In a field trial on a highly Zn- and Cu-contaminated site, differences in plant survival and growth were observed among 168 clones originating from natural populations of Populus alba L. and Populus nigra L. from northern Italy. After two and a half years from planting, the density, activity and metabolic versatility of the culturable fraction of the soil bacteria in the HM-polluted field was higher in the soil close to where larger poplar plants were growing, in spite of comparable HM concentrations recorded in these soils. One well-performing clone of P. alba (AL35), which accumulated a higher concentration of both metals and had high foliar polyamine (PA) levels, was used for further investigation. In a greenhouse study, AL35 cuttings pre-inoculated with AMF (Glomus mosseae or Glomus intraradices) and then transferred to pots containing soil, collected from the HM-polluted site, displayed growth comparable to that of controls grown on unpolluted soil, in spite of higher Cu and Zn accumulation. Such plants also showed an overall up-regulation of metallothionein (MT) and PA biosynthetic genes, together with increased PA levels. A genome-wide transcriptomic (cDNA-AFLP) analysis allowed the identification of a number of genes, mostly belonging to stress-related functional categories of defense and secondary metabolism, that were differentially regulated in mycorrhizal vs. non mycorrhizal plants. A proteomic analysis revealed that, depending on sampling time, changes in protein profiles were differentially affected by AMF and/or HMs. It is concluded that soil-borne microorganisms affect plant performance on HM-polluted soil. In particular, mycorrhizal plants exhibited increased capacity for phytostabilization of HMs, together with improved growth. Their greater stress tolerance may derive from the protective role of PAs, and from the strong modulation in the expression profiles of stress-related genes and proteins.

Chlorophyll fluorescence as a diagnostic tool for abiotic stress tolerance in wild and cultivated strawberry species

Chlorophyll (Chl) fluorescence analysis was used to assess stress tolerance in wild and cultivated strawberry species. We found that the parameters, photochemical quenching (1-qP), non-photochemical quenching (qN), and maximum quantum yield (Fv/Fm), can serve as stress indicators because they are sensitive to early responses to stress. The most sensitive region used for measuring Chl fluorescence in strawberry leaves was the upper surfaces of leaflets located in the middle of new leaves. An analysis of the Chl fluorescence characteristics of strawberry species showed that octoploid species had greater stress tolerance than diploid species. The ‘Whiteberry’ maintained high levels of 1-qP and qN through the dissipation of excess excitation energy as heat during early stress treatment. These results suggest that ‘Whiteberry’ has a photoinhibition system that allows it to respond to stress in a more sensitive manner than other cultivars. Therefore, among the Chl fluorescence parameters examined, 1-qP and qN, can serve as good indicators for comparing stress tolerance, and they can be used to simultaneously screen many plants for stress tolerance in strawberry breeding programs.

Temperature and respiration affect the growth and stress resistance of Lactobacillus plantarum C17

The aim of the study is to gain further insight on the respiratory behaviour of Lactobacillus plantarum and its consequences on stress tolerance. We investigated the effect of temperature and respiration on the growth and stress (heat, oxidative, freezing, freeze-drying) response of Lact.plantarum C17 during batch cultivations. Temperature as well as respiration clearly affected the physiological state of cells, and generally, cultures grown under respiratory conditions exhibited improved tolerance of some stresses (heat, oxidative, freezing) compared to those obtained in anaerobiosis. Our results revealed that the activities in cell-free extracts of the main enzymes related to aerobic metabolism, POX (pyruvate oxidase) and NPR (NADH peroxidase), were significantly affected by temperature. POX was completely inhibited at 37°C, while the activity of NPR slightly increased at 25°C, indicating that in Lact.plantarum, the temperature of growth may be involved in the activation and modulation of aerobic/respiratory metabolism. We confirmed that respiration confers robustness to Lact.plantarum cells, allowing a greater stress tolerance and advantages in the production of starter and probiotic cultures. This is the first study on respiratory metabolism on a strain other than the model strains WCFS1; novel information on the role of temperature in the modulation of aerobic/respiratory metabolism in Lact.plantarum is presented.

The Role of Plant Mediator as a Gene Regulator to Tackle Climate Change: A Review

The current rate of climate change predicts that plants will become subject to increasing extremes of environmental stress. Rapid population increase in developing countries also demand higher yield from crop production, often from sub-optimal agricultural areas. Genetic engineering can help to meet these needs through the development of crops with greater stress tolerance. Mediator is transcriptional co-activators which convey DNA bound transcriptional regulators and enhancers to the general RNA polymerase II transcription machinery and mediator genes are recently identified in plants. So far it has been showed that their great involvement in regulation of plant stress tolerance by controlling transcription of stress genes. Therefore, Mediator genes will be a good source in future molecular biology researches on manipulation of crop plants with multiple stress tolerance. DOI: http://dx.doi.org/10.4038/jepsl.v1i1.5141 Journal of Environmental Professionals Sri Lanka Vol.1(1) 2012 43-56

Agronomic Responses of Corn Hybrids to Row Width and Plant Density

Increased corn (Zea mays L.) seed costs and hybrids with greater stress tolerance than in the past make it important to know if the optimum plant density for corn grain yield differs with hybrid relative maturity (RM) or row width. In 2009 and 2010 at two locations in southern Minnesota, agronomic responses of corn to plant densities ranging from 40,700 to 108,700 plants ha−1 were evaluated for 95‐, 101‐, and 105‐d RM hybrids in 51‐ and 76‐cm row widths. Stalk diameter, intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) at silking, root and stalk lodging, grain yield, and yield components did not differ with row width, and the response of these variables to plant density was not affected by hybrid or row width. Yield of the 105‐d RM hybrid was 13% higher than that of the 95‐d RM hybrid due to greater kernel number despite lower kernel weight, but was similar to the 101‐d RM hybrid. There was a quadratic‐plateau response of grain yield to plant density, with the plateau occurring at 84,500 plants ha−1. Net return was not affected by row width, hybrid, or 23 of 25 scenarios for seed cost and grain price. The economically optimum plant density was 62,200 plants ha−1 for US$350 per 80,000 seeds and US$120 Mg−1, and 87,000 plants ha−1 for US$150 per 80,000 seeds and US$280 Mg−1. These results demonstrate that grain yield can be maximized with mid‐ and late‐RM hybrids and plant densities ≥84,500 plants ha−1 in either 51‐ or 76‐cm rows.

TRANSCRIPTOMIC AND PROTEOMIC RESPONSE OF FRUIT TREES TO ABIOTIC STRESS

Together, temperature and water availability are the primary determinants of the global distribution of major vegetation biomes and as such have a major impact on the cultivation of temperate fruit trees. The regulation of both low temperature and water deficit stress has been widely studied in herbaceous plants using transcriptomics, proteomics, and transformation technologies. These studies have revealed stress signaling pathways, specific stress-tolerance genes, and transcriptional regulators. Using direct data or empirical approaches, biotechnology has been utilized to produce transgenic plants that have greater stress tolerance. For example, plants overexpressing the transcription factor CBF (under the control of a low-temperature-inducible promoter) have increased freezing tolerance. However, only recently, have these same approaches been used to study stress tolerance in woody plants and more specifically fruit trees. Evidence suggests that although there is a high level of conservation in mechanisms of stress tolerance between annual herbaceous plants and perennial woody plants, the perennial habit has also resulted in additional mechanisms that are specific to perennial plants. We have utilized several different global approaches to study stress tolerance in apple and peach. These include subtractive hybridization (SSH), bioinformatics analysis of ESTs derived from stress-induced cDNA libraries, and 2D Difference in-Gel Electrophoresis (DiGE) for proteomic analyses. These approaches are beginning to reveal the complexity of stress response in fruit trees and helping us develop a comprehensive understanding of stress tolerance in fruit trees. An overview of the results of these studies is presented and discussed.

Differential Sensitivity of Macrocarpa and Microcarpa Types of Chickpea (Cicer arietinum L.) to Water Stress: Association of Contrasting Stress Response with Oxidative Injury

Chickpea (Cicer arietinum L.) is particularly sensitive to water stress at its reproductive phase and, under conditions of water stress, will abort flowers and pods, thus reducing yield potential. There are two types of chickpea: (i) Macrocarpa (“Kabuli”), which has large, rams head-shaped, light brown seeds; and (ii) Microcarpa (“Desi”), which has small, angular and dark-brown seeds. Relatively speaking, “Kabuli” has been reported to be more sensitive to water stress than “Desi”. The underlying mechanisms associated with contrasting sensitivity to water stress at the metabolic level are not well understood. We hypothesized that one of the reasons for contrasting water stress sensitivity in the two types of chickpea may be a variation in oxidative injury. In the present study, plants of both types were water stressed at the reproductive stage for 14 d. As a result of the stress, the “Kabuli” type exhibited an 80% reduction in seed yield over control compared with a 64% reduction observed for the “Desi” type. The decrease in leaf water potential (Ψw) was faster in the “Kabuli” compared with the “Desi” type. At the end of the water stress period, Ψw was reduced to −2.9 and −3.1 MPa in the “Desi” and “Kabuli” types, respectively, without any significant difference between them. On the last day of stress, “Kabuli” experienced 20% more membrane injury than “Desi”. The chlorophyll content and photosynthetic rate were significantly greater in “Desi” compared with “Kabuli”. The malondialdehyde and H2O2 content were markedly higher at the end of the water stress in “Kabuli” compared with “Desi”, indicating greater oxidative stress in the former. Levels of anti-oxidants, such as ascorbic acid and glutathione, were significantly higher in “Desi” than “Kabuli”. Superoxide dismutase and catalase activity did not differ significantly between the two types of chickpea, whereas on the 10th day, the activities of ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase were higher in “Desi”. These findings indicate that the greater stress tolerance in the “Desi” type may be ascribed to its superior ability to maintain better water status, which results in less oxidative damage. In addition, laboratory studies conducted by subjecting both types of chickpea to similar levels of polyethylene glycol-induced water stress and to 10 μ.mol/L abscisic acid indicated a greater capacity of the “Desi” type to deal with oxidative stress than the “Kabuli” type.

Growth and stress tolerance of tomato seedlings (Lycopersicon esculentum Mill.) in response to seed treatment with paclobutrazol

SUMMARY‘Marglobe’ tomato seeds were soaked (24 h at 22°C) or matric primed (-1.0 MPa for 7 d at 22° C) in 50 mgl-1 of paclobutrazol (PB), a triazole growth retardant. Plants from these treatments and from non-treated seeds or seedlings whose shoots were sprayed with 10 mg PB l-1 at 14 days after planting (DAP) were assessed for growth and physiological responses before and after factorially combined stresses of drought (a 14 d period of drying cycles until severe wilting) or heat (4 h at 50° C) were initiated at 24 DAP in the greenhouse. At 23 DAP, shoot heights and shoot and root dry weights of plants from PB-soaked seeds or PB-sprayed plants were similar, but lower than those from non-treated or PB-primed seeds. This pre-stress PB-mediated growth suppression was associated with greater stress tolerance as revealed by greater increases in shoot and root dry weights during the 10 d post-stress recovery period. Further support for the increased stress tolerance of plants from PB-soaked seeds or PB-sprayed plants than occurred with plants from non-treated seeds or PB-primed seeds was their higher leaf xylem pressure potential, lower leaf electrolyte leakage, and lower loss of leaf total chlorophyll during the 10 d post-stress recovery period.