Dehydration stress memory: Insights from physiological responses of sugar apple (Annona squamosa L.) to repeated dehydration stress

Introduction - Evidence from drought hardening as a horticultural practice has demonstrated that exposing plants to repeated dehydration stress alters their physiological responses. Here we investigated the influence of repeated dehydration stress on physiological responses related to dehydration stress memory display in sugar apple. Materials and methods - Sugar apple seedlings were subjected to two successive bouts of dehydration stress with a recovery period in between, while seedlings watered throughout were an untreated control. Results - In the dehydration-stressed seedlings, concentrations of abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-Ile), proline and malondialdehyde (MDA) were significantly higher than in the untreated control. On the other hand, the leaf water potential, stomata! conductance, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity were lower in the treated seedlings, although the changes in total chlorophyll were insignificant. Furthermore, the seedlings displayed stress memory as demonstrated by accumulations of IAA and JA-Ile, an increase in MDA concentration, and decreases in total chlorophyll concentration, DPPH free radical scavenging activity, and leaf water potential in the second dehydration stress (S2) compared to the first stress (Si), indicating memory-mediated physiological responses. Meanwhile, ABA, JA, stomatal conductance, and proline concentration exhibited non-memory-mediated responses. Conclusion - These results suggest that accumulations of IAA and JA-Ile during repeated dehydration stress play significant roles as memory-mediated physiological responses for survival in sugar apple.