Drought stimulation by hypocotyl exposure altered physiological responses to subsequent drought stress in peanut seedlings

Drought stress occurring at the seedling stage of peanut (Arachis hypogaea L.) plants is a limiting factor resulting in considerable reductions in production. Plants can improve their resistance to subsequent stresses after experiencing an initial stress. The aim of this study was to explore the possible role of drought priming by hypocotyl exposure in alleviating subsequent severe drought stress in peanut. Hypocotyl exposure in peanut seedlings as a drought stimulus induced xerophytophysiological regulation, shown by induced osmotic adjustment, activated antioxidant enzymes, anthocyanin accumulation, up-regulation of Gdi-15 and fewer amyloplasts. The seedlings primed by hypocotyl exposure showed improved leaf water retention and reduced proline content when exposed to subsequent drought stress. The alleviated oxidative damage and lower antioxidant enzyme activities indicated rapid acclimation following past hypocotyl exposure and further defenses against subsequent drought stress by retaining ‘memories’ to enable more rapid or stronger physiological responses. The improved leaf photosynthesis and low photosynthetic hysteresis as drought ended indicated a positive effect of drought priming in peanut seedlings. The peanut seedlings ‘remembered’ the xerophytophysiological responses caused by the prior drought stimulation from hypocotyl exposure and displayed quicker and more potent physiological responses to following drought stress. The results showed that hypocotyl exposure could help peanut seedlings survive the severe environments that occurred in the later growth stages.