Drought priming induced thermotolerance in wheat (Triticum aestivum L.) during reproductive stage; a multifaceted tolerance approach against terminal heat stress.

In wheat (Triticum aestivum L.), terminal heat stress obstructs reproductive functioning eventually leading to yield loss. Drought priming during the vegetative stage can trigger a quicker and effective defense response against impending high temperature stress and improve crop production. In the present study, two contrasting wheat cultivars (PBW670 and C306) were subjected to moderate drought stress of 50-55% field capacity for eight days during the jointing stage to generate drought priming (DP) response. Fifteen days after anthesis heat stress (36 °C) was imposed for three days and physiological response of primed, and non-primed plants was assessed by analyzing membrane damage, water status and antioxidative enzymes. Heat shock transcription factors (14 TaHSFs), calmodulin (TaCaM5), antioxidative genes (TaSOD, TaPOX), polyamine biosynthesis genes and glutathione biosynthesis genes were analyzed. GC-MS based untargeted metabolite profiling was carried out to underpin the associated metabolic changes. Yield related parameters were recorded at maturity to finally assess the priming response. Heat stress response was visible from day one of exposure in terms of membrane damage and elevated antioxidative enzymes activity. DP reduced the impact of heat stress by lowering the membrane damage (ELI, MDA & LOX) and enhancing antioxidative enzyme activity except APX in both the cultivars. Drought priming upregulated the expression of HSFs, calmodulin, antioxidative genes, polyamines, and the glutathione biosynthesis genes. Drought priming altered key amino acids, carbohydrate, and fatty acid metabolism in PBW670 but also promoted thermotolerance in C306. Overall, DP provided a multifaceted approach against heat stress and positive association with yield.

Drought priming triggers diverse metabolic adjustments and induces chilling tolerance in chickpea (Cicer arietinum L.).

Chickpea (Cicer arietinum L.) suffers from chilling stress at the reproductive stage (<15 °C) which leads to significant yield loss. This study presents a comprehensive plant response to drought priming and its effect on chilling tolerance during the reproductive stage in two chickpea cultivars PBG1 and PBG5. Lipidome profiling (Fatty acid methyl esters analysis), metabolome profiling (GC-MS based untargeted analysis), fatty acid desaturases and antioxidative gene expression (qRT-PCR) were analyzed to monitor physiological and biochemical events after priming during flowering, podding and seed filling stages. Drought priming alleviated membrane damage and chlorophyll degradation by increasing membrane unsaturated fatty acids (18:3) along with up-regulation of various fatty acid desaturases (CaFADs) genes and antioxidative machinery during flowering and improved seed yield in PBG5. PCA, HCA, and KEGG pathway analysis of 87 identified metabolites showed that metabolites were regulated differently in both cultivars under non-primed and primed conditions. The plant response was more apparent at flowering and podding stages which coincided with chilling temperature (<15 °C). Drought priming stimulated many important genes, especially FADs, antioxidative proteins and accumulation of key metabolites (proline and TCA intermediates) required for defense especially in PBG5. This explains that plant's response to drought priming not only depends on developmental stage, and temperature regime (<15 °C) but also on the genotypic-specificity.

Drought priming induces chilling tolerance and improves reproductive functioning in chickpea (Cicer arietinum L.).

KEY MESSAGE: Priming alleviates membrane damage, chlorophyll degradation along with cryoprotectants accumulation during chilling stress that leads to improved reproductive functioning and increased seed yield. Chilling temperatures below 15 °C have severe implications on the reproductive growth and development of chickpea. The abnormal reproductive development and subsequent reproductive failure lead to substantial yield loss. We exposed five chickpea cultivars (PBG1, GPF2, PDG3, PDG4, and PBG5) to drought stress (Priming) during the vegetative stage and analyzed for chilling tolerance during the reproductive stage. These varieties were raised in the fields in two sets: one set of plants were subjected to drought stress at the vegetative stage for 30 days (priming) and the second set of plants were irrigated regularly (non-primed). The leaf samples were harvested at the flowering, podding, and seed filling stage and analyzed for membrane damage, water status, chlorophyll content, cellular respiration, and certain cryoprotective solutes. The reproductive development was analyzed by accessing pollen viability, in vivo and in vitro germination, pollen load, and in vivo pollen tube growth. Principal component analysis (PCA) revealed that priming improved membrane damage, chlorophyll b degradation, and accumulation of cryoprotectants in GPF2, PDG3, and PBG5 at the flowering stage (< 15 °C). Pearson's correlation analysis showed a negative correlation with the accumulation of proline and carbohydrates with flower, pod, and seed abortion. Only, PBG5 responded best to priming while PBG1 was worst. In PBG5, priming resulted in reduced membrane damage and lipid peroxidation, improved water content, reduced chlorophyll degradation, and enhanced cryoprotective solutes accumulation, which led to increased reproductive functioning and finally improved seed yield and harvest index. Lastly, the priming response is variable and cultivar-specific but overall improve plant tolerance.

Pseudomonas citronellolis alleviates arsenic toxicity and maintains cellular homeostasis in chickpea (Cicer arietinum L.).

Arsenic is a hazardous metalloid that causes detrimental effects on plant growth and metabolism. Plants accumulate arsenic in edible parts that consequently enter the food chain leading to many health problems. Metal tolerant plant growth-promoting bacteria (PGPB) ameliorate heavy metal toxicity. In this study, the effect of arsenic (As5+) and the role of PGPB Pseudomonas citronellolis (PC) in mitigating As5+ toxicity and associated metabolic alterations in chickpea were assessed. Five chickpea varieties (PBG1, GPF2, PDG3, PDG4 and PBG5) were evaluated for arsenic accumulation, translocation, and its interference with metabolic and defense processes. As5+ (40 mg kg-1) interfered with plant metabolism and enhanced the antioxidative and carbohydrate metabolizing enzyme's activity but PC treatment maintained the activity at par with control. PC also facilitated the accumulation of As5+ in the root system and restricted its translocation to the shoot. Further, to map the metabolic changes, Gas chromatography Mass Spectroscopy (GC-MS) based metabolite profiling and gene expression analysis (qRT-PCR) were performed in the best and worst-performing chickpea varieties (PBG1 and PBG5). 48 metabolites of various metabolic pathways (amino acid, carbohydrate, and fatty acid) were altered in As5+ and PC treatment. Gene expressions showed correlation with biochemical analysis of the antioxidative enzymes and carbohydrate metabolizing enzymes while PC treatment improved chlorophyll biosynthesis enzyme CaDALA expression in As5+ treated plants. Therefore, PC mitigates As5+ toxicity by restricting it in the roots thereby maintaining the cellular homeostasis under As5+ stress in chickpeas.

Unravelling cross priming induced heat stress, combinatorial heat and drought stress response in contrasting chickpea varieties.

Drought and high temperature stress affect chickpea growth and productivity. Often these stresses occur simultaneously in the field and lead to a wide range of molecular and metabolic adaptations. Two chickpea varieties; GPF2 (heat sensitive) and PDG4 variety (heat tolerant) were exposed to 35 °C for 24 h individually and along with drought stress. Five heat responsive signalling genes and 11 structural genes were analyzed using qPCR along with untargeted metabolites analysis using GC MS. Expression of antioxidant genes (CaSOD and CaGPX, CaAPX and CaCAT), transcription factors (CaHSFB2, CaHSFB2A, CaHSFB2B, CaHSP17.5 and CaHSP22.7) and signalling genes (CaCAM, CaGAD, and CaMAPK) were upregulated in GPF2 as compared to PDG4 variety. Principal component analysis (PCA), partial least-square discriminant analysis (PLS-DA), and heat map analysis were applied to the metabolomics data to identify the differential response of metabolites in two chickpea varieties. GC-MS analysis identified 107 and 83 metabolites in PDG4 and GPF2 varieties respectively. PDG4 variety accumulated more sugars, amino acids, sugar alcohols, TCA cycle intermediates which provided heat resistance. Additionally, the differential metabolic pathways involved in heat tolerance were alanine, aspartate, and glutamate metabolism, pantothenate CoA biosynthesis, fructose and mannose metabolism and pentose phosphate pathway in PDG4 variety. There was less accumulation of metabolites in the primed plants of both varieties as compared to the non-primed plants indicating less damage due to heat stress. The present study gives an overview of the molecular changes occurring in response to heat stress in sensitive and tolerant chickpea.

Nutrient enhancement of chickpea grown with plant growth promoting bacteria in local soil of Bathinda, Northwestern India.

Plant growth promoting bacteria (PGPB) enhance crop productivity as part of green technology to reduce the use of chemical fertilizers. They also have the capability to enhance macro- and micronutrient content of plants. In the present study, PGPB isolates belonging to Pseudomonas citronellis (PC), Pseudomonas sp. RA6, Serratia sp. S2, Serratia marcescens CDP13, and Frateuria aurantia (Symbion-K) were tested on two chickpea varieties, PBG1 and PBG5 grown for 30 days in local soil from Bathinda region in Northwestern India. PC and CDP13 were found to be better chickpea growth stimulators compared to the commercial Symbion-K based on shoot length and biomass. Most PGPB enhanced macro- and micronutrients in shoots to varying degrees compared to the control. PBG5 gave better response compared to PBG1 with reference to plant growth attributes and enhancement of the macronutrients, calcium, nitrogen and phosphorus and micronutrients, boron, copper, iron, and zinc. PBG5 is a high yielding variety with better resistance compared to PBG1. Overall, PGPB isolated from the local soil and PGPB from other parts of India were shown to be useful for enhancement of nutrient content and plant growth.

Pseudomonas citronellolis; a multi-metal resistant and potential plant growth promoter against arsenic (V) stress in chickpea.

Soil micro-biota plays a vital role in maintaining plant growth and fitness under normal and adverse conditions. Pseudomonas is one of the most important free-living and copious genera in south-west Punjab and involved in plant growth promotion under heavy metal stress. In this study, we have studied microbial diversity of the agricultural and marginal land based on 16S rRNA gene and screened eight strains of Pseudomonas for its tolerances towards various heavy metals and for plant growth promoting properties (PGP). The best strain is tested in chickpea plants against Arsenic (As5+) stress. All the strains responded differently to heavy metals viz. Arsenic, (As5+ (0.3-0.5M) and As3+ (250 µg mL-1) Cadmium (Cd2+) (250-350 µg mL-1), Chromium (Cr2+) (200-350 µg mL-1) and Mercury (Hg2+) (1-2 µg mL-1). Out of eight strains, only two strains (KM594398 and KM594397) showed plant growth promoting characters, concurrently they were highly tolerant to Arsenic (As5+). Pseudomonas citronellolis (PC) (KM594397) showed the best results in terms of As5+ tolerance and plant growth promoting activity, hence further tested for actual plant growth response in chickpea (Cicer arietinum L.) under As5+ (10-160 mg kg-1) stress. Pseudomonas citronellolis enhanced plant growth and dry biomass under As5+ stress. High As5+ tolerance and plant growth promoting activity of Pseudomonas citronellolis in chickpea especially designate this strain suitable for marginal lands and heavy metals contaminated sites.