Yu Yongchao, Xu Xuemei, Hu Yuxiang, Ding Yanfeng, Chen Lin
College of Agriculture, Nanjing Agricultural University, Nanjing, 210095, China.
Xuzhou Institute of Agricultural Sciences in Jiangsu Xuhuai District, Xuzhou, China.
Rice (N Y). 2024 Oct 24;17(1):66. doi: 10.1186/s12284-024-00745-5.
The yield potential of large-panicle rice is often limited by grain-filling barriers caused by the development of inferior spikelets (IS). Photoassimilates, which are the main source of rice grain filling, mainly enter the caryopsis through the dorsal vascular bundle. The distribution of assimilates between superior spikelets (SS) and IS is influenced by auxin-mediated apical dominance; however, the mechanism involved is still unclear. In this study, the effect of auxin signaling on the grain filling of SS and IS was investigated in two large-panicle japonica rice varieties, W1844 and CJ03. Compared to SS, IS displayed delayed initiation of filling and a significantly lower grain weight. Furthermore, the endosperm development in IS remained stagnant at the coenocytic stage. The development of the dorsal vascular bundle in the IS was also slow, and poor sucrose-unloading was observed during the initial grain filling stage. However, the endosperm development in IS immediately started after the improvement of dorsal vascular bundle development. GUS activity staining further revealed that indole-3-acetic (IAA) was localized in the dorsal vascular bundle and surrounding areas, suggesting that the low IAA content observed in the IS during the initial grain filling stage may have delayed the development of the dorsal vascular bundle. Therefore, these results demonstrate that IAA may control sugar transport and unloading by regulating dorsal vascular bundle development, consequently affecting endosperm development in IS.
大穗型水稻的产量潜力常受弱势颖花（IS）发育导致的籽粒灌浆障碍限制。光合产物是水稻籽粒灌浆的主要来源，主要通过背部维管束进入颖果。同化物在强势颖花（SS）和IS之间的分配受生长素介导的顶端优势影响；然而，其中涉及的机制仍不清楚。在本研究中，以两个大穗型粳稻品种W1844和CJ03为材料，研究了生长素信号对SS和IS籽粒灌浆的影响。与SS相比，IS的灌浆启动延迟，粒重显著降低。此外，IS的胚乳发育在多核期停滞不前。IS中背部维管束的发育也较慢，在籽粒灌浆初期观察到蔗糖卸载不良。然而，背部维管束发育改善后，IS的胚乳发育立即开始。GUS活性染色进一步显示，吲哚-3-乙酸（IAA）定位于背部维管束及其周围区域，表明在籽粒灌浆初期IS中观察到的低IAA含量可能延迟了背部维管束的发育。因此，这些结果表明，IAA可能通过调节背部维管束发育来控制糖分运输和卸载，从而影响IS的胚乳发育。
