Ethylene and polyamines interact in rice spikelet degeneration in response to water stress during meiosis

This study aimed to investigate whether an interaction existed between ethylene and polyamines (PAs), which mediated the effects of water stress (WS) during meiosis on rice (Oryza sativa L.) spikelet degeneration. Two indica hybrid rice cultivars, HY113 (a drought-resistant rice cultivar) and ZZY8 (a drought-susceptible rice cultivar), were used in the present study, which were exposed to two soil moisture treatments: well water (WW) and WS. The spikelet degeneration rate (SDR) in WS plants increased by 12.1% for HY113 and 29.5% for ZZY8 compared with WW plants. The concentration of free spermidine (Spd) and free spermine (Spm) and the activities of S-adenosyl-l-methionine decarboxylase and Spd synthase were all significantly reduced in young panicles by the WS, with more reduction for ZZY8 than for HY113. The ethylene evolution rate, the concentrations of putrescine (Put), 1-aminocylopropane-1-car-boxylic acid (ACC), and H2O2, and the activities of ACC synthase and ACC oxidase in young panicles significantly increased for both cultivars under WS treatment, with more increase for ZZY8 than for HY113. Furthermore, when Spd or aminoethoxyvinylglycine (an inhibitor of ethylene synthesis) was applied to the young panicles of WS plants in the pollen mother cell meiosis prophase, the SDR significantly reduced. An opposite effect was observed when ACC or methylglyoxal-bis(guanylhydrazone) (an inhibitor of Spd and Spm synthesis) was applied to young panicles of WS plants. The results of the present study suggested the existence of an antagonistic interaction between ethylene and PA biosynthesis, which likely mediated the effect of WS during meiosis on rice spikelet degeneration.