生长素-糖调控水稻弱势粒灌浆的生理机制研究

Poor grain-filling of inferior spikelets can lower the yield and quality. The process of grain filling can be divided into three stages, stagnant phase, pre-storage phase and storage phase. The stagnant phase is mainly existed in the inferior spikelets. The physiological reason of the stagnant in inferior spikelets and how to eliminate this stage remains unclear. It is said that the stagnant phase in inferior spikelets is due to the apical dominance by plant hormone auxin (indole-3-acetic, IAA), but the detailed mechanism remains unknow. There is direct relations between IAA and vascular bundle development. Well-developed vascular is the base to guarantee the source-sink sugar transport efficiency. Dorsal vascular bundle plays a key role in sugar unloading. In this study, we used two large panicle rice and two common panicle cultivers analyze the character of their vascular bundle development in inferior spikelet. Physiological and molecular biology techniques are used to investigate the effects of IAA content on the dorsal vascular bundle, source-sink sugar distribution and the endosperm development of inferior spikelets. From the above experimental evidence we will propose a model for how to regulate the rice inferior spikelets grain filling and provide a theoretical basis for improving source-sink efficacy, facilitating the breeding of higher yielding plants.

弱势粒灌浆充实差是生产上限制水稻产量和品质的重要因素，也是亟待解决的科学问题。弱势粒在灌浆起始阶段存在停滞期，而强势粒的则很短或几近没有，这可能与生长素介导的糖在强、弱势粒之间的分配有关，但机理尚未明确。生长素与维管束发育直接相关，良好的维管束发育情况是保证糖等灌浆同化物源库转运高效率的基础，且籽粒背部维管束结构对籽粒糖的卸载量和强度有重要影响。本项目对比分析灌浆具有明显差异的大穗型和普通穗型水稻弱势粒背部维管束发育特征；同时调节弱势粒生长素水平，结合生理和分子生物学手段，研究生长素对籽粒背部维管束发育的影响，以及对水稻同化物转运（以糖装载—运输—卸载途径为主线）和籽粒胚乳发育的调控作用。通过以上研究，揭示生长素与灌浆初期弱势粒背部维管束发育、源库糖转运和籽粒胚乳发育的内在联系，明确生长素-糖调控弱势粒灌浆启动的途径，为今后在育种和栽培措施上改善弱势粒灌浆提供理论依据。

大穗型水稻品种的种植已成为生产上获得高产的有效途径。但大穗型水稻弱势粒灌浆障碍限制了产量潜力的发挥。光合同化产物是水稻灌浆的物质来源，同化物的源库转运直接关系到籽粒灌浆水平。生长素作为关键的信号物质几乎参与调节植物所有的生理活动，其介导的“粒间顶端优势”影响水稻强弱势粒同化物的竞争，但具体的调控机制尚不清楚。本研究选用两个前期筛选到的大穗型粳稻W1844和CJ03作为材料，通过比较强弱势粒灌浆差异发现，弱势粒开花后存在较长的灌浆启动延迟，CJ03弱势粒灌浆启动更为延迟，前期灌浆水平较W1844低，疏花处理后两品系材料弱势粒灌浆水平都有改善，表明同化物供应障碍是弱势粒灌浆差的主要原因；进一步研究发现W1844和CJ03灌浆初期弱势粒糖卸载通量低，与背部维管束发育延迟、韧皮部筛管疏通程度相关，且CJ03弱势粒背部维管束成熟及胚乳细胞化过程较W1844更慢，导致蔗糖转运能力更差。研究表明维管束发育与生长素密切相关，通过喷施外源IAA处理，W1844弱势粒灌浆启动提前，灌浆速率得到显著提高，喷施TIBA处理后，两个材料的前期灌浆质量都受到了抑制，表明生长素含量不足可能抑制了弱势粒背部维管束的发育。以上研究揭示了生长素与灌浆初期弱势粒背部维管束发育、源库同化物转运和籽粒胚乳发育的内在联系，明确了生长素-糖调控弱势粒灌浆启动的途径，为今后在育种和栽培措施上改善弱势粒灌浆提供了理论依据。