Antioxidant responses play a crucial role in combating free radical damage induced by drought stress. In guar plants, the antioxidant mechanism is crucial for stress tolerance; however, the specific antioxidant response in individual guar genotypes remains unclear. This study investigates the physiological, biochemical, and transcriptional responses of four guar genotypes to drought stress by maintaining soil moisture content (SMC) at varying levels: control (100% FC), medium (60% FC), and severe (20% FC). Among the genotypes examined, HG-563 and HG-365 exhibit higher leaf relative water content (RWC) and total chlorophyll/carotenoid content, indicating lesser inhibition under drought stress compared to HG-75 and RGC-936. Notably, HG-563 and HG-365 demonstrate a significant increase in activities of key antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate (AsA), and glutathione (GSH) during medium and severe drought stress conditions. This observation is further supported by in-gel activity assays revealing a notable upregulation of Cu/ZnSOD and POD isozymes, which is consistent with higher expression levels of Cu/ZnSOD and POD genes at the transcriptional level. Consequently, these results highlight the comparatively higher drought tolerance of HG-563 and HG-365 genotypes. The findings shed light on the activation of antioxidant responses in drought-tolerant guar genotypes under stress conditions, emphasizing the crucial role of antioxidant enzymes in the drought tolerance mechanism of guar plants.

Plants leverage past stress experiences, whether occurring individually or in sequential combinations, to bolster their responses to future stressful situations, a phenomenon known as stress memory. Hydration cycles imitate a natural process within the environment when seeds are integrated into the soil seed bank, and experience numerous hydration and dehydration cycles due to inconsistent water supply. This study investigates the potential for stress exposure during the seed stage to enhance stress tolerance in subsequent seedlings, shedding light on the potential transfer of stress-related memories between various life stages following multiple stress-inducing experiences. We specifically employed hydration (soaking) and dehydration (simulating drought stress) cycles (0, 1, and 2 HD cycles) as stimuli to activate stress memory in seeds. Following germination, a randomized experiment was conducted, subjecting the seedlings to various water treatments, including control conditions, 50% and 75% reductions in soil humidity, and rewatering, with a focus on assessing recovery. Remarkably, all germinative parameters exhibited similar responses irrespective of the number of HD cycles. However, notable variations in plant growth and biomass accumulation were observed in seedlings subjected to HD cycles. These plants displayed reduced sensitivity to drought-induced damage, maintaining growth rates even under stressful conditions. Importantly, the relative water content remained unaltered in plants subjected to stress resulting from HD cycles. Consistently, the results highlight that intermittent hydration supports plant survival under stress by mitigating drought-induced damage. Stress memory acquired through stress exposure during the seed stage stress enhances drought resistance by delaying dehydration and reducing water loss, ultimately preserving growth.