Drought priming at seedling stage improves photosynthetic performance and yield of potato exposed to a short-term drought stress

Potato (Solanum tuberosum L.) is an important food and vegetable crop worldwide. In recent years, the arid environment resulting from climate change has caused a sharp decline in potato yield. To clarify the effect of drought priming at the seedling stage on the tolerance of potato plants to drought stress during tuber expansion, we conducted a pot experiment to investigate the physiological response of the plants generated from seed potatoes of the variety 'Favorita' to varied water supply conditions: normal water supply at the seedling stage (control), normal water supply at the seedling stage and drought stress at the mid-tuber-expansion stage (non-primed), and drought priming at the seedling stage plus drought stress at the mid-tuber-expansion stage (primed). Drought priming resulted in an increase in the number of small vascular bundles in potato plants compared to non-primed plants. It also altered the shape and density of stomata, enhancing water use efficiency and reducing whole-plant transpiration. The primed plants maintained the basal stem cambium for a longer time under drought stress, which gained an extended differentiation ability to generate a greater number of small vascular bundles compared to non-primed plants. Drought priming increased the amount and rate of dry matter translocation, and so reduced the adverse effects on tubers of potato under drought stress. Therefore, drought priming at the seedling stage improved the photosynthetic performance and yield, and probably enhanced the drought tolerance of potato.

DNA methylation levels of TaP5CS and TaBADH are associated with enhanced tolerance to PEG-induced drought stress triggered by drought priming in wheat

Drought priming is a promising strategy to enhance tolerance to recurred drought in wheat. However, the underlying mechanisms of priming-induced tolerance are far from clear. Here, three different priming intensities (P1D, P2D, P3D) and two varieties with different sensitivities to drought priming were used to investigate the effects and mechanisms of drought priming. Results showed light (P1D) or moderate (P2D) drought priming intensity induced positive effects for the drought sensitive variety (YM16), while high (P3D) priming intensity brought a negative impact on the plant drought resistant. For drought insensitive one (XM33), light priming intensity had no significant effect on tolerance to drought, while moderate or high intensity showed better priming effects. Moderate priming induced higher leaf water potential and also the osmolytes levels. Consistent with the proline and betaine, the related synthetic enzymatic activities, as well as the expression of TaP5CS and TaBADH were higher in P2D in YM16 and P3D in XM33. The contents of proline and betaine showed a positive correlation with activities of SOD, CAT, GR, AsA, and GSH contents, and a negative correlation with O₂^.-, H₂O₂, and MDA contents. Further analysis revealed CG demethylation of ATG-proximal regions in the promoter of TaP5CS and TaBADH were involved in promoting the synthesis of proline and betaine in primed plants. Collectively, these findings demonstrate drought priming effect was variety independent but depended on the priming severity, and demethylation of TaP5CS and TaBADH involved in the accumulation of osmolytes which contribute to the enhanced drought tolerance induced by priming.

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.)

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.

Stress memory responses and seed priming correlate with drought tolerance in plants: an overview

Environmental-friendly techniques based on plant stress memory, cross-stress tolerance, and seed priming help sustainable agriculture by mitigating negative effects of dehydration stress. The frequently uneven rainfall distribution caused by global warming will lead to more irregular and multiple abiotic stresses, such as heat stress, dehydration stress, cold stress or the combination of these stresses. Dehydration stress is one of the major environmental factors affecting the survival rate and productivity of plants. Hence, there is an urgent need to develop improved resilient varieties. Presently, technologies based on plant stress memory, cross-stress tolerance and priming of seeds represent fruitful and promising areas of future research and applied agricultural science. In this review, we will provide an overview of plant drought stress memory from physiological, biochemical, molecular and epigenetic perspectives. Drought priming-induced cross-stress tolerance to cold and heat stress will be discussed and the application of seed priming will be illustrated for different species.

Abscisic acid and hydrogen peroxide are involved in drought priming-induced drought tolerance in wheat (Triticum aestivum L.)

Drought is one of the major stress factors in wheat production on a global scale. Drought priming during the early growth stage can enhance drought tolerance in wheat (Triticum aestivum L.). Abscisic acid (ABA) and hydrogen peroxide (H₂ O₂ ) are important signal molecules in the adaptation of plants to drought stress. However, the roles of ABA and H₂ O₂ in drought priming-induced drought tolerance are not clear. In the present study, we evaluated the responses of wheat to an ABA inhibitor, H₂ O₂ scavenger and an inhibitor to investigate the (i) relationship between ABA and H₂ O₂ in osmotic adjustment after drought priming in the vegetative stage and (ii) responses to drought stress during grain filling. In the drought priming alone treatments, chemical application resulted in the scavenging of ABA and H₂ O₂ , weakening the alleviation effects of drought priming on drought stress, as demonstrated by the lower leaf water potential and grain yield. The ABA inhibitor completely inhibited accumulation of ABA and H₂ O₂ ; the ABA inhibitor inhibited respiratory burst oxidase homologue expression, whereas the H₂ O₂ inhibitor resulted in higher 9-cis-epoxycarotenoid dioxygenase expression and ABA concentration in primed plants, indicating that ABA scavenging inhibited H₂ O₂ biosynthesis while H₂ O₂ scavenging did not inhibit ABA biosynthesis. The results further demonstrated that NADPH oxidase-mediated H₂ O₂ production functions downstream of ABA, which induces osmolyte transcript expression and accumulation, and thus contributes to drought priming-induced stress tolerance. These results provide a theoretical basis for a better understanding of the mechanisms involved in drought priming-induced tolerance in wheat plants.