The poor grain-filling initiation often causes the poor development of inferior spikelets (IS) which limits the yield potential of large panicle rice (Oryza sativa L.). However, it remains unclear why IS often has poor grain-filling initiation. In addressing this problem, this study conducted a field experiment involving two large panicle rice varieties, namely CJ03 and W1844, in way of removing the superior spikelets (SS) during flowering to force enough photosynthate transport to the IS. The results of this study showed that the grain-filling initiation of SS was much earlier than the IS in CJ03 and W1844, whereas the grain-filling initiation of IS in W1844 was evidently more promoted compared with the IS of CJ03 by removing spikelets. The poor sucrose-unloading ability, i.e., carbohydrates contents, the expression patterns of OsSUTs, and activity of CWI, were highly improved in IS of CJ03 and W1844 by removing spikelets. However, there was a significantly higher rise in the efficiency of sucrose to starch metabolism, i.e., the expression patterns of OsSUS4 and OsAGPL1 and activities of SuSase and AGPase, for IS of W1844 than that of CJ03. Removing spikelets also led to the changes in sugar signaling of T6P and SnRK1 level. These changes might be related to the regulation of sucrose to starch metabolism. The findings of this study suggested that poor sucrose-unloading ability delays the grain-filling initiation of IS. Nonetheless, the efficiency of sucrose to starch metabolism is also strongly linked with the grain-filling initiation of IS.

灌浆启动不良往往导致劣质小穗发育不良，从而限制了大穗水稻的产量潜力。水稻L.）。然而，目前尚不清楚为什么 IS 通常具有较差的籽粒灌浆起始。为了解决这个问题，本研究进行了一项田间试验，涉及两个大穗水稻品种，即 CJ03 和 W1844，以去除开花期间的上位小穗 (SS)，以迫使足够的光合产物转运到 IS。本研究结果表明，在CJ03和W1844中，SS的籽粒灌浆开始早于IS，而W1844中IS的籽粒灌浆开始与CJ03的IS相比，通过去除小穗明显促进。蔗糖卸载能力差，即碳水化合物含量，表达模式OsSUT通过去除小穗，CW 和 CWI 的活性在 CJ03 和 W1844 的 IS 中得到了极大的提高。然而，蔗糖对淀粉代谢的效率显着提高，即OsSUS4 和 OsAGPL1SuSase 和 AGPase 的活性，W1844 的 IS 比 CJ03 的高。去除小穗也导致 T6P 和 SnRK1 水平的糖信号发生变化。这些变化可能与蔗糖对淀粉代谢的调节有关。这项研究的结果表明，较差的蔗糖卸载能力延迟了 IS 的籽粒灌浆开始。尽管如此，蔗糖对淀粉代谢的效率也与 IS 的灌浆起始密切相关。