Hormones in Rice Spikelets in Responses to Water Stress During Meiosis

Abstract

Meiosis stage is the most stress-sensitive period of reproduction in rice ( Oryza sativa L.). However, the underlying biochemical mechanism is poorly understood. This study was carried out to investigate whether and how plant hormones are involved in the regulation of spikelet sterility when exposed to water stress during meiosis. Two rice cultivars, Han A-3 (HA-3, drought-resistant) and Wuyujing 7 (WY-7, drought-susceptible), were used and subjected to well-watered (WW) and water-stressed (WS) treatments during meiosis (15 to 2 d before heading). Leaf water potentials of both cultivars markedly decreased during the period as a result of WS treatment, but panicle water potentials remained constant. The percentage of sterile spikelets in WS plants was increased by 48.5% to 50.9% for WY-7, whereas only by 12.6% to 12.8% for HA-3. The concentrations of zeatin + zeatin riboside (Z+ZR), indole-3-acetic acid and gibberellins (GA 1+GA 4) in spikelets showed no significant differences either between the WW and WS treatments or between the 2 cultivars. Abscisic acid (ABA), ethylene, and 1-aminocylopropane-1-carboxylic acid were all enhanced in spikelets following water stress, with further enhancement for ethylene than for ABA in WY-7, whereas elevated ABA balanced ethylene production in HA-3. The spikelet sterility was significantly reduced when amino-ethoxyvinylglycine (an inhibitor of ethylene synthesis) or ABA was applied to the panicles of WS plants at the early meiosis stage. Application of ethephon (an ethylene-releasing agent) or fluridone (an inhibitor of ABA synthesis) had the opposite effect. These results indicate that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of water stress on spikelet fertility. A higher ratio of ABA to ethylene would be a physiological trait of rice adaptation to water stress.