Development Of Drought Tolerance Research Articles

Identification of Drought Tolerant Mutant Lines of Tef [Eragrostis Tef (Zucc.) Trotter

Introduction: Tef [Eragrostis tef (Zucc.) Trotter] is the major food crop in Ethiopia where it is annually cultivated on about 30% of the total area allocated to cereals. The productivity of tef is, however, significantly reduced by drought which can occur at either the early or the late developmental stage of the crop. Methodology: A total of 10,000 EMS (ethyl methane sulfonate) mutagenized M2 tef populations were screened first for early and second for terminal drought tolerance. The performance of candidate lines was investigated using diverse agronomical and physiological parameters. Results and discussion: Several promising lines were obtained for both early and terminal drought tolerance. Among these, genotypes with outstanding performance were found for two drought tolerant tef lines targeting early drought tolerance (dtt2 and dtt13) and three terminal drought tolerant lines targeting terminal drought tolerance (tdt9, tdt15 and tdt19). Conclusions: Candidate lines for both early and terminal drought tolerance will play vital roles in developing drought tolerance in tef improvement.

Response of Mediterranean Ornamental Plants to Drought Stress

Ornamental plants use unique adaptive mechanisms to overcome the negative effects of drought stress. A large number of species grown in the Mediterranean area offer the opportunity to select some for ornamental purposes with the ability to adapt to drought conditions. The plants tolerant to drought stress show different adaptation mechanisms to overcome drought stress, including morphological, physiological, and biochemical modifications. These responses include increasing root/shoot ratio, growth reduction, leaf anatomy change, and reduction of leaf size and total leaf area to limit water loss and guarantee photosynthesis. In this review, the effect of drought stress on photosynthesis and chlorophyll a fluorescence is discussed. Recent information on the mechanisms of signal transduction and the development of drought tolerance in ornamental plants is provided. Finally, drought-induced oxidative stress is analyzed and discussed. The purpose of this review is to deepen our knowledge of how drought may modify the morphological and physiological characteristics of plants and reduce their aesthetic value—that is, the key parameter of assessment of ornamental plants.

Genetic engineering in developing drought tolerance maize and its new prospects

Maize is one of the most important cereals in human civilization. However, the productivity of crops has been being adversely affected by increasing droughts as a consequence of the global climate change. Recently, the yield and production of a number of maize growing regions witnessed a significant decrease due to continuously droughts. To minimize the impacts of the water-shortage condition, many measures have been taken. Among them, genetic engineering helps enhance plant survival by transferring drought-tolerance related genes into maize. Hundreds of drought-responsive genes from maize or other species have been isolated and characterized. Those genes encode transcription factors and proteins involving in signal transduction pathways as well as cell protection mechanisms. However, in order to highly and precisely express interested genes in transgenic maize, it is necessary to modify genes by using proper codon usage frequency, adding signals of post-transcriptional, translational and post-translational regulations. Additionally, other components of transformation process such as vector systems, promoters, gene delivery procedures, etc. are required to be optimized. Results from drought-tolerant trait related studies which has been being heavily invested in are worth the effort. Recently, new genetic engineering approaches known as genome editing are being accomplished and applied to a wide range of species. The advanced techniques including ZFNs, TALENs, and CRISPR/Cas9 hold enormous potential for drought-tolerant crop development. It is believed that in the near future, genome-edited based cultivars are more elite than traditional ones.

Metabolic responses to drought stress in the tissues of drought-tolerant and drought-sensitive wheat genotype seedlings.

An in-depth understanding of the effects of drought stress on plant metabolism is necessary to improve the drought tolerance of wheat and to utilize genetic resources for the development of drought stress-tolerant wheat varieties. In this study, the profiles of 58 key metabolites produced by wheat seedlings in response to drought stress were investigated to determine various physiological processes related to drought tolerance between drought-tolerant and drought-sensitive wheat genotypes. Results showed that the wheat metabolome was dominated by sugars, organic acids and amino acids; the wheat metabolome played important roles to enhance the drought tolerance of shoots. Under drought stress, JD17 exhibited higher growth indices and higher photosynthesis ability than JD8. A high level of compatible solutes and energy in shoots were essential for wheat to develop drought tolerance. Drought also caused system alterations in widespread metabolic networks involving transamination, tricarboxylic acid cycle, glycolysis, glutamate-mediated proline biosynthesis, shikimate-mediated secondary metabolisms and γ-aminobutyric acid metabolisms. Long-term drought stress resulted in the drought-tolerant wheat genotype JD17, which induced metabolic shifts in the tricarboxylic acid cycle and glycolysis with the depletion of the γ-aminobutyric acid shut process. In JD17, the prolonged drought stress induced a progressive accumulation of osmolytes, including proline, sucrose, fructose, mannose and malic acid. This research extended our understanding of the mechanisms involved in wheat seedling drought tolerance; this study also demonstrated that gas chromatography-mass spectrometry metabolomics could be an effective approach to understand the drought effects on plant biochemistry.

Genomics based approaches to develop drought tolerance in wheat

Genomics based approaches to develop drought tolerance in wheat

An integrated and comparative approach towards identification, characterization and functional annotation of candidate genes for drought tolerance in sorghum (Sorghum bicolor (L.) Moench)

BackgroundDrought is the most disastrous abiotic stress that severely affects agricultural productivity worldwide. Understanding the biological basis of drought-regulated traits, requires identification and an in-depth characterization of genetic determinants using model organisms and high-throughput technologies. However, studies on drought tolerance have generally been limited to traditional candidate gene approach that targets only a single gene in a pathway that is related to a trait. In this study, we used sorghum, one of the model crops that is well adapted to arid regions, to mine genes and define determinants for drought tolerance using drought expression libraries and RNA-seq data.ResultsWe provide an integrated and comparative in silico candidate gene identification, characterization and annotation approach, with an emphasis on genes playing a prominent role in conferring drought tolerance in sorghum. A total of 470 non-redundant functionally annotated drought responsive genes (DRGs) were identified using experimental data from drought responses by employing pairwise sequence similarity searches, pathway and interpro-domain analysis, expression profiling and orthology relation. Comparison of the genomic locations between these genes and sorghum quantitative trait loci (QTLs) showed that 40% of these genes were co-localized with QTLs known for drought tolerance. The genome reannotation conducted using the Program to Assemble Spliced Alignment (PASA), resulted in 9.6% of existing single gene models being updated. In addition, 210 putative novel genes were identified using AUGUSTUS and PASA based analysis on expression dataset. Among these, 50% were single exonic, 69.5% represented drought responsive and 5.7% were complete gene structure models. Analysis of biochemical metabolism revealed 14 metabolic pathways that are related to drought tolerance and also had a strong biological network, among categories of genes involved. Identification of these pathways, signifies the interplay of biochemical reactions that make up the metabolic network, constituting fundamental interface for sorghum defence mechanism against drought stress.ConclusionsThis study suggests untapped natural variability in sorghum that could be used for developing drought tolerance. The data presented here, may be regarded as an initial reference point in functional and comparative genomics in the Gramineae family.

Genetic analysis of seedlings characters associated with drought tolerance in cowpea under a controlled environment

AbstractCowpea is a major source of vegetable protein but its production is constrained by drought resulting in yield loss. Developing drought tolerance varieties can enhance yield and reduce the need for supplemental irrigation. Breeding for drought tolerance requires the knowledge of its genetic basis. Genetic basis for some seedling traits in cowpea was investigated. Seven generations (P1, P2, F1, RF1, F2, BC1 and BC2) each derived from two crosses involving two highly drought tolerant (Danilla and IT97K-499-35) and one highly susceptible parents (Tvu7778) were evaluated for drought tolerance in the screen house. Data on Seedling height (SH), Seedling terminal leaflet area (SLA), Seedling Vigour (SV) and Recovery Capacity (RC) were collected. The SV was assessed on a scale of 1 (highly-tolerant) – 9 (highly-susceptible), while RC (%) was evaluated at 5 d interval for 30 d. The hybrids F1 and RF1 showed the best performances in both crosses with SV ranged from 2.50 ± 0.00 in Danilla × IT97K-499-35 cross to 6.50 ± 1.00 in the Danilla × TVU7778 cross. In both crosses, F1 and RF1 had 100.0% RC. Both dominance (46.5–68.6%) and additive (31.4–53.5%) effects were found similar and important in all the traits under water stressed. The six-parameter model indicated few cases of gene interactions, mostly dominance × dominance. Narrow sense heritability ranged from 33.5% for SH to 50.1% for SLA in the cross Danilla × TVU7778 at terminal water stress. Inheritance of these traits in cowpea involved both additive and dominance gene action. However, dominance and/or dominance × dominance effects had a more pronounced effect in genetic control of all characters.

14-3-3 Lambda Protein Affects Anthocyanin Production in Arabidopsis thaliana during Drought Stress

Plants evolve to adapt to environmental stresses, including changes at the genetic and molecular levels. For bioengineers to utilize genetic manipulation to build tolerance into crops, a better understanding of the mechanism is needed. Published studies have demonstrated that 14-3-3 Lambda (14-3-3 Lambda) protein affect the phenylpropanoid (Pp) biosynthetic pathway and alters production of flavonoids and downstream compounds of importance for stress tolerance. The 14-3-3 family of proteins binds to many different client proteins and serves as signaling scaffolds. In this study 14-3-3 Lambda knockout mutants were used to investigate changes in metabolite accumulation in the downstream Pp pathway. Amongst them are anthocyanins which are important antioxidants involved in a variety of plant functions including stress response. Investigating how drought stress influenced anthocyanin production identified nodes in the Pp pathway affected by 14-3-3 Lambda. A metabolomics analysis employing high resolution mass spectrometry (HRMS) and metabolomics software was used to identify metabolites in 14-3-3 knockout which changed relative to wild-type A. thaliana (Columbia-0) during drought stress. The metabolites Cy-3-p-coumaurolysinapoylsophoroside-5-diglucoside, 3-caffeoylferuloylsophoroside- 5-succinoylglucoside, 3-caffeoylferuloylsophoroside-5-malonyldiglucoside, 3-feruloylsophoroside-5-succinoyl glucoside, petunidin-3,5-O-diglucoside and malvidin-3-O-p-coumarylmonoglucoside show significant differences in their profiles ranging from 18- to > 500-fold between the Col-0 and 14-3-3 Lambda knockout in wet and dry groups. The findings suggest that 14-3-3 Lambda interacts along the CHS, and CHI nodes, which in turn regulate the downstream production of specific anthocyanins. The interaction of 14-3-3 Lambda with CHS was confirmed using co-immunoprecipitation and co-localization studies. This study supports the hypothesis that manipulation of gene expression of 14-3-3 Lambda can lead to development of drought tolerance in plants.

Impact of drought on photosynthesis: Molecular perspective

The reduction in the precipitation level and the occurrence of frequent drought will be among the top future worries for humans to tackle on this planet. Globally 80% of the agricultural land area is rainfed. According to current research and predictions of frequent drought in the future, there will be a substantial reduction in the economic yield of crop plants, a major threat to food security. Drought tolerance is a major economic consideration to yield. Various biological processes are getting affected by low water stress. Photosynthesis which is an essential biological process for the survival of plants is getting majorly influenced. However, plants have some inbuilt mechanisms to respond to drought stress to some extent. In this mini review, we have highlighted the impact of drought on crop plants, its impact on photosynthesis and responses of plants to drought stress. Understanding mechanism of drought stress tolerance will lead towards development of drought tolerance in crop plants.

Drought Induced Changes in Growth, Osmolyte Accumulation and Antioxidant Metabolism of Three Maize Hybrids.

Consequences of drought stress in crop production systems are perhaps more deleterious than other abiotic stresses under changing climatic scenarios. Regulations of physio-biochemical responses of plants under drought stress can be used as markers for drought stress tolerance in selection and breeding. The present study was conducted to appraise the performance of three different maize hybrids (Dong Dan 80, Wan Dan 13, and Run Nong 35) under well-watered, low, moderate and SD conditions maintained at 100, 80, 60, and 40% of field capacity, respectively. Compared with well-watered conditions, drought stress caused oxidative stress by excessive production of reactive oxygen species (ROS) which led to reduced growth and yield formation in all maize hybrids; nevertheless, negative effects of drought stress were more prominent in Run Nong 35. Drought-induced osmolyte accumulation and strong enzymatic and non-enzymatic defense systems prevented the severe damage in Dong Dan 80. Overall performance of all maize hybrids under drought stress was recorded as: Dong Dan 80 > Wan Dan 13 > Run Nong 35 with 6.39, 7.35, and 16.55% yield reductions. Consequently, these biochemical traits and differential physiological responses might be helpful to develop drought tolerance genotypes that can withstand water-deficit conditions with minimum yield losses.

MORPHO-PHYSIOLOGICAL AND BIOCHEMICAL TRAIT BASED SELECTION OF WHEAT GENOTYPES FOR DROUGHT TOLERANCE

Drought stress is now become the most important abiotic stress for wheat in Bangladesh. Rabi season often compromised wheat production by imposing drought stress. Therefore, it has been a priority to develop drought tolerant wheat variety for Bangladesh. However, the lack of genetic variability for drought tolerance in wheat has been a major bottleneck for developing drought tolerance wheat variety. The present investigation was carried out in an aim to evaluate several exotic and locally cultivated wheat genotypes for drought tolerance based on morpho-physiological and biochemical traits. Experiment was carried out at the net house of Field Laboratory of Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh with seven replications in a RCBD design. Ten locally cultivated and exotic wheat genotypes were grown under control (100% field capacity) and drought (30% field capacity) conditions. Genotypes used in the study were identified with different types of drought tolerance mechanisms, viz., Berkut for earliness, Shatabdi for grain weight, BARI Gom 26 for spike and grain number, along with Vorobey, Berkut for enhanced biosynthesis of proline, Sokoll for undamaged leaf Chlorophyll content and relative water content, Sakha8, Gaurav, Sonalika and Shatabdi for membrane thermostability; Sakha8 and Sourav for improved stress tolerance index. The genotypes screened out with different traits related to drought tolerance can be utilized as gene source for future breeding programs.

A dehydrin gene isolated from feral olive enhances drought tolerance in Arabidopsis transgenic plants.

Dehydrins belong to a protein family whose expression may be induced or enhanced by developmental process and environmental stresses that lead to cell dehydration. A dehydrin gene named OesDHN was isolated and characterized from oleaster (Olea europaea L. subsp. europaea, var. sylvestris), the wild form of olive. To elucidate the contribution of OesDHN in the development of drought tolerance, its expression levels were investigated in oleaster plants during development and under drought stress condition. The involvement of OesDHN in plant stress response was also evaluated in Arabidopsis transgenic lines, engineered to overexpress this gene, and exposed to a controlled mild osmotic stress. OesDHN expression was found to be modulated during development and induced under mild drought stress in oleaster plants. In addition, the Arabidopsis transgenic plants showed a better tolerance to osmotic stress than wild-type plants. The results demonstrated that OesDHN expression is induced by drought stress and is able to confer osmotic stress tolerance. We suggest a role for OesDHN, as a putative functional marker of plant stress tolerance.

Planning for food security in a changing climate.

The Intergovernmental Panel on Climate Change and other international agencies have concluded that global crop production is at risk due to climate change, population growth, and changing food preferences. Society expects that the agricultural sciences will innovate solutions to these problems and provide food security for the foreseeable future. My thesis is that an integrated research plan merging agronomic and genetic approaches has the greatest probability of success. I present a template for a research plan based on the lessons we have learned from the Green Revolution and from the development of genetically engineered crops that may guide us to meet this expectation. The plan starts with a vision of how the crop management system could change, and I give a few examples of innovations that are very much in their infancy but have significant potential. The opportunities need to be conceptualized on a regional basis for each crop to provide a target for change. The plan gives an overview of how the tools of plant biotechnology can be used to create the genetic diversity needed to implement the envisioned changes in the crop management system, using the development of drought tolerance in maize (Zea mays L.) as an example that has led recently to the commercial release of new hybrids in the USA. The plan requires an interdisciplinary approach that integrates and coordinates research on plant biotechnology, genetics, physiology, breeding, agronomy, and cropping systems to be successful.

Cloning and Characterization of P5CS1 and P5CS2 Genes from <i>Saccharum officinarum</i> L. under Drought Stress

Increasing world sugar demand might be fulfilled with land extensification which include the use of dry area. Development of drought tolerance and high productivity sugarcane variety could be achieved by plant genetic engineering. Under drought condition, proline will be accumulated and functioned as an osmoregulator in plant cells. ∆1-pyrroline-5-carboxylate synthase (P5CS) is one of the important enzymes in proline biosynthesis. This enzyme is encoded by P5CS gene family. We cloned two homologous P5CS genes from sugarcane, SoP5CS1 (Accession Number : KF178299) and SoP5CS2 (Accession Number : KF178300), which encode 729 and 716 amino acid polypeptides. The identity between these two genes was 74% based on nucleotide sequences. The SoP5CS1 gene had 98% identity with SbP5CS1 (Accession Number : GQ377719.1) and SoP5CS2 had 99% identity with SaP5CS (Accession Number : EF113257.1). In this experiment, sugarcane plantlets were exposed to medium containing PEG 6000 (40%) for 12, 24, 48, and 72 hours. Proline concentration was measured after treatment and genes expression were analyzed by real time-qPCR. The results showed that the proline concentration was increased 12 folds (9.8 umol.g-1) after 48-hours stress treatment. The highest expression of SoP5CS1 occured at 24-hours treatment with approximately 16 times from plant without PEG (control plant) and decreased gradually at 48 and 72 hours treatment. The highest expression of SoP5CS2 occured at 24-hours drought stress with approximately 3.6 folds compared to control. In drought treatment, the expression level SoP5CS1 was higher than SoP5CS2 and has increased significantly at 12-hours treatment. It is suggested that the SoP5CS1 gene contributes more significantly to the production of proline during drought stress than SoP5CS2. Hence, SoP5CS1 could potentialy be used as a marker to screen sugarcane variety for drought tolerance and for the development of transgenic plant tolerant to drought.Keywords: cloning, drought, expression, P5CS, sugarcane

English

Drought is a solemn environmental factor that causes great loss of yield in maize crop. Maize is highly sensitive to drought. There is need to develop drought tolerance maize genotypes to fulfill demand of feed for livestock and food for human. For this propose prescribed study was conducted to estimate genetic components for various physiological traits under normal and water tress conditions in the research area of the Department of Plant Breeding and Genetics, University of Agriculture Faisalabad, Pakistan. It was concluded that P1 (WFTMS) parent performed better under drought conditions for stomata frequency, stomata conductance, stomata size, cell membrane thermo stability, leaf water potential and excised leaf water loss while BC2 for stomata conductance, F1 for stomata size, F2 leaf water potential and BC1 for leaf temperature. Positive [h] dominance effects were recorded for cell membrane thermo stability, stomata frequency and leaf water potential while [d] additive effects for leaf water potential under normal conditions. It was reported that [i] additive × additive interaction were found for cell membrane thermo stability, stomata frequency and excised leaf water loss while negative for leaf water potential under normal conditions while under drought for cell membrane thermo stability, stomata frequency, stomata conductance and excised leaf water loss. It was suggested that the traits showed [d] additive and [i] additive × additive interaction may be used to fix the increase in the expression of traits in next generations and selection for the development of synthetic varieties for drought resistance may be helpful. The [h] dominance effects showed that the traits may be used for the development of hybrid. On the basis of genetic effects it was concluded that stomata frequency, stomata size, cell membrane thermo stability, leaf water potential and excised leaf water loss may be helpful for

Expression of S-adenosyl methionine decarboxylase gene for polyamine accumulation in Egyptian cotton Giza 88 and Giza 90

Developing drought tolerance in Egyptian cotton varieties is a strategic goal considering the need to expand cotton cultivated area and water scarcity in the Nile valley. In the present study, increasing levels of polyamine accumulation via expressing S-adenosyl methionine decarboxylase (SAMDC) gene was the main goal. SAMDC cDNA isolated from Saccharomyces cerevisiae isolate was isolated and genetically engineered into Egyptian cotton varieties Giza 88 as an extra long staple and Giza 90 as a long staple by means of particle bombardment through meristem transformation.T0 transgenic plants were screened using basta herbicide (200 mg/l). RT- PCR analysis was used to confirm gene expression while gene integration was confirmed by Southern blot analysis. Control plants from Giza 88 and Giza 90 were subjected to drought regime using different concentrations of PEG 6000 (2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17%, and 20%) for 9 hrs to record drought stress symptoms and determine the potential concentration level for inducing polyamine accumulation. 17% of PEG 6000 was considered the sublethal concentration showing drought stress symptoms and therefore was used as potential stress concentration for estimating the level for spermine accumulation in both control and transgenic Giza varieties. T1 transgenic plants grown under induced drought stress regime were tested positive for gene integration and expression and subjected to HPLC analysis to determine levels of spermine as polyamine accumulated compound in response to drought stress regime. Elevated spermine accumulation in Egyptian cotton varieties Giza 88 and Giza 90, were compared as non transgenic plants grown under same induced drought conditions with T1 transgenic plants using reverse-phase HPLC analysis. Elevated spermine accumulation expressing SAMDC gene reflect main cause for increasing drought tolerance in both transgenic varieties.

Biological Flora of the British Isles: Primula elatior (L.) Hill

Summary This account presents information on all aspects of the biology of Primula elatior that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation. Primula elatior is a native perennial herb, within a compact area in the British Isles, in ancient woods and copses on the chalky boulder clay in East Anglia, where it is abundant locally although scarce nationally. British material is ssp. elatior, which extends across much of Europe, becoming rarer towards the south. Primula elatior is a shade tolerant species, but only flowers in profusion in the increased light levels following tree felling in traditionally coppiced woods. It is confined to an area of the British Isles where the soils are seasonally waterlogged and ill‐aerated, and is very tolerant of the toxic levels of ferrous iron which accumulate in the surface horizons in the spring months. It has a poorly developed drought tolerance. An early flowering plant, P. elatior is an insect‐pollinated obligate outbreeder, with two self‐incompatible morphs (pin and thrum). The low colonizing ability of this ancient woodland species can be attributed to both seed dispersal and seedling recruitment limitation. There has been a steady reduction in the density of P. elatior in woodland sites during the past centuries. However, there has been little change in the 10‐km distribution in the British Isles. Studies of populations involve three groups of factors: genetic variation, environmental changes and population structure. Potentially these factors have a greater effect on small and isolated populations than on large and integrated ones. There is no evidence that the species suffers from a loss of genetic diversity in the smaller populations. Primula elatior seems to have a relatively high level of genetic diversity that is maintained despite a fragmented distribution. Within its restricted distribution area P. elatior replaces P. vulgaris completely. At the margins of their distributions the two species occur together in a number of woodland sites, providing the opportunity for hybridization. As they are highly interfertile, hybridization is restricted mainly by differences in their habitat preferences. The hybrid P. vulgaris × P. elatior = P. × digenea is fertile and gives rise to hybrid swarms which are found in all British sites where both parents occur together. Changes in climate, woodland management practices and intensities of deer grazing, especially by Fallow deer (Dama dama), are likely to have a major effect on populations of P. elatior. Since the species colonizes new or secondary woodlands very slowly, management should focus on the conservation of ancient semi‐natural woodlands.

Differential responses of the enzymes involved in proline biosynthesis and degradation in drought tolerant and sensitive cotton genotypes during drought stress and recovery

The relative water content (RWC), free proline levels and the activities of enzymes involved in proline metabolism were studied in drought tolerant (Ca/H 680) and drought sensitive (Ca/H 148) genotypes of cotton (Gossypium hirsutum L.) during induction of water stress and posterior recovery. Water stress caused a significant increase in proline levels and P5CS activity in leaves of both tolerant and sensitive genotypes, whereas the activity of P5CR increased minimally and the activity of OAT remains unchanged. The activity of PDH decreased under drought stress in both the genotypes. The leaf of tolerant genotype maintained higher RWC, photosynthetic activity and proline levels, as well as higher P5CS and P5CR activities under water stress than that of drought sensitive genotype. The drought induced proline levels and activities of P5CS and P5CR declined and tend to be equal to their respective controls, during recovery, whereas the PDH activity tends to increase. These results indicate that induction of proline levels by up regulation of P5CS and down regulation of PDH may be involved in the development of drought tolerance in cotton.

The Induction of Abscisic-Acid-Mediated Drought Tolerance is Independent of Ethylene Signaling in Arabidopsis Plants Responding to a Harpin Protein

Harpin proteins from plant pathogenic bacteria can activate distinct signaling pathways and cause multiple effects in plants. When Arabidopsis thaliana (Arabidopsis) plants are treated with the HrpNEa harpin produced by Erwinia amylovora, a bacterial pathogen that causes fire blight in rosaceous plants, abscisic acid (ABA) is stimulated to mediate drought tolerance, and ethylene signaling is activated to regulate plant growth enhancement and insect resistance. It is unclear if ABA and ethylene signaling interacts in response to harpin proteins. Here we report that ethylene signaling is dispensable to the induction of ABA-mediated drought tolerance in Arabidopsis. In wild-type (WT) plants growing under drought stress conditions, ABA, but not ethylene, was required for HrpNEa to promote cellular adaptive responses and decrease drought severity of plants. During the induction of drought tolerance in HrpNEa-treated WT plants, expression of the ABA signaling gene ABI2 was induced coincidently with decreases in transcripts of ETR1, which encodes an ethylene receptor, and several other genes that are also involved in ABA and ethylene signal transduction pathways. In response to HrpNEa, the Arabidopsis etr1-1 mutant developed drought tolerance similarly as did WT, but the abi2-1 mutant did not, suggesting that sensing of ABA is essential, but sensing of ethylene is not. Consistently, the induction of drought tolerance was abolished by inhibiting WT to synthesize ABA, instead of ethylene. Our results suggest that HrpNEa treatment enables plants to prioritize the ABA signal transduction pathway over ethylene signaling in accordance with the real-time requirement to survive under drought stress conditions.

Genotypic variability for carbon isotope discrimination in the mutant and improved lines of barley

Drought tolerance is an important breeding objective in dry and semi-dry conditions. Carbon isotope discrimination (Δ) is a tool that may be used to improve water-use efficiency (WUE) as an indirect selection criterion. The study investigated the variability for Δ in improved F7 lines and their parents (three cultivars and two mutant lines), which were sampled randomly from an F6 nursery performing well under semi-dry conditions. In total, 40 entries were grown in sand culture, arranged in three-replicated randomized complete block designs in two sets of experiments in Antalya, Turkey. There were statistically significant differences (p<0.01) among genotypes in both sets of experiments for Δ, and Δ values range from 20.14 to 21.86. Low coefficient of variation (C.V.) values, i.e. 2 and 1.65 %, for both data sets revealed efficient control of experimental error for Δ and indicated little effect of environment. Consequently, broad-sense heritability estimates for Δ were 0.63 and 0.74. As Δ showed a considerably high heritability and consistency over the two sets of experiments and low C.V. values, it was concluded that this trait could be used in breeding programmes aimed at developing drought tolerance lines. The early heading mutant, M-K-88, and the cultivar selected from land race, Tokak 157-37, showed lowest Δ values, indicating that they had the best water-use efficiency. Low Δ values of these two genotypes were inheritable.