Response of endogenous brassinosteroids to nitrogen rates and its regulatory effect on spikelet degeneration in rice

Abstract

<p indent=0mm>In order to investigate whether and how brassinosteroids (BRs) mediate the effect of nitrogen (N) rates on spikelet degeneration of rice, rice cultivars Yangdao 6 and Yongyong 2640 were grown in pots subjected to three N rates in the whole growth periods. The contents of N, BRs, hydrogen peroxide (H₂O₂) and total antioxidant capacity (T-AOC) in young rice panicles at meiosis stage and their relationship with spikelet degeneration rate were observed. The results showed that the decreased spikelet degeneration rate was closely associated with enhanced 24-epicastasterone (24-epiCS) and 28-homobrassinolide (28-homBL) contents in young panicles. When N content of rice panicle was 1.25%, the BRs (24-epiCS and 28-homBL) content in young panicle increased significantly, and the spikelet degeneration rate decreased. The variation trend of T-AOC level was very consistent with BRs, and T-AOC was significantly negatively correlated with spikelet degeneration rate, whereas the variation trend of H₂O₂ content was opposite to that of T-AOC and BRs contents in the young panicles. Application of exogenous BRs (24-epiCS or 28-homBL) to young panicles could significantly increase the T-AOC level and contents of endogenous 24-epiCS and 28-homBL, but significantly reduce the H₂O₂ content and spikelet degeneration rate, while application of BRs synthesis inhibitor had the opposite effect. In summary, BRs mediated the effects of N application rates on spikelet degeneration, and elevated BRs contents in young panicles could inhibit spikelet degeneration by elevating antioxidant capacity under a proper panicle N content (1.25%) at meiosis stage in rice.