Abstract
Remnant populations of Myricaria laxiflora on river islands along the Yangtze River enter dormancy and endure varying degrees of flooding in summer, with their growth and development recovering in autumn. In this study, M. laxiflora plants were subjected to controlled flooding, and the changes in plant hormones and metabolic enzymes in different stages of recovery growth were measured to elucidate the biochemical mechanisms of summer flooding on plant recovery. Our findings indicated that flooding duration and depth significantly affected the levels of hormones during recovery growth. Compared to the control, cytokinin (CTK), gibberellin (GA) and abscisic acid (ABA) increased by 120.04%-178.53%, 26.07%-56.20% and 36.71%-79.81, respectively, while indole-3-acetic acid (IAA) decreased by 4.88%-26.38% with different flooding durations. Moreover, summer flooding altered metabolic enzymes in M. laxiflora during recovery growth. Under different flooding durations, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and RuBisCO-activating enzyme (RCA) increased by 117.94%-185.93% and 55.51%-98.19%, respectively. With different flooding depths, RCA increased by 107.12%-190.55%, while phosphoenolpyruvate carboxylase (PEPC) decreased by 9.37%-20.92%. Pearson's correlation analysis indicated relationships between the changes in hormones (IAA, ABA, CTK and GA) and enzymes (RCA, RuBisCO and PEPC) induced by summer flooding. These correlations indicated that the alternations of hormones induced by summer flooding may influence plant physiology through the modulation of metabolic enzymes. The increasing CTK, GA, ABA, RuBisCO and RCA, and decreasing IAA and PEPC would enhance photosynthetic physiology and mitigate respiratory physiology, thereby facilitating plant recovery growth. It is suggested that riverbanks for population restoration of M. laxiflora have to annually experience a period of flooding in the in situ conservation.