促进稻麦同化物转运和籽粒灌浆的途径与机制

Approach and mechanism in enhancing the remobilization of assimilates and grain-filling in rice and wheat

协调植株衰老、光合作用与光合同化物向籽粒转运的关系是谷类作物的一个科学难题.研究解决这一难题,对阐明促进谷类作物同化物向籽粒转运和籽粒灌浆的调控途径与机制,解决目前生产上部分稻麦品种或在高氮水平下茎、鞘中同化物向籽粒转运率低、籽粒灌浆慢和充实不良等问题具有十分重要的理论和实践意义.本文概述了促进稻麦同化物向籽粒转运和籽粒灌浆的栽培途径和生理机制,重点介绍了3个重要发现:(1)稻麦花后适度土壤干旱可以协调植株衰老、光合作用与同化物向籽粒转运的关系,促进籽粒灌浆,提高收获指数、产量和水分利用效率;(2)花后适度土壤干旱通过提高脱落酸(abscisicacid,ABA)与乙烯、赤霉素(GAs)比值,有效促进籽粒灌浆;在水稻(Oryza sativa)和小麦(Triticum aestivum)活跃灌浆期,籽粒充实需要较高的内源ABA水平、较高的ABA与乙烯比值及ABA与GAs比值;(3)通过适度土壤干旱或施用低浓度ABA适度增加体内ABA水平,可以增强茎和籽粒中糖代谢关键酶活性,增加同化物在源端的装载与在库端的卸载能力,进而促进同化物向籽粒转运和淀粉在籽粒中的合成与累积.今后建议从信号传导等方面深入研究调控谷类作物同化物转运和籽粒灌浆的分子机理.

Monocarpic plants such as rice and wheat need to initiate the whole plant senescence before their pre-stored assimilates can be remobilized for the grain filling. However, plant senescence and photosynthesis are a pair of trade-off processes. How to coordinate plant senescence, photosynthesis, and remobilization of assimilates is a long-term unsolved problem in cereals. Solving this problem would have great significance in not only understanding the mechanism of the remobili- zation of assimilates to grain and grain-filling but also effectively coping with the poor remobilization of assimilates from vegetative tissues to grain and slow grain-filling for some cultivars or under the condition of heavy use of nitrogen in the current rice and wheat production systems. This paper reviewed crop management and physiological mechanism in en- hancing the remobilization of assimilates to grain and grain-filling in rice and wheat. There are three important findings. （i） Moderate soil-drying （MSD） during post-anthesis can regulate the relationship of plant senescence, photosynthesis, and remobilization of assimilates, and accelerate grain-filing. With post-anthesis MSD, plant can rehydrate overnight but not severely inhibit leaf photosynthesis at day time. More importantly, it can timely and appropriately initiate the process of plant senescence, trigger assimilate remobilization from vegetative tissues to grain, accelerate grain-filling, especially for the late-flowering inferior caryopses, and lead to increases in grain yield, harvest index, and water use efficiency. The MSD therefore provides a new way to coordinate the relationship among plant senescence, photosynthesis, and remobi- lization of assimilates during grain-filling and to achieve the dual goal of increasing grain yield and saving water in cere- als. （ii） Abscisic acid （ABA） and its interaction with ethylene and gibberellins （GAs） regulate assimilate remobitization and grain-filling. During the active grain-filling period, the filling of grain requires a higher level of endogenous ABA and higher ratios of ABA to ethylene and to GAs. Post-anthesis MDS enhances the remobilization of assimilates to grain and grain-filling through increases in ABA levels and the ratios of ABA to ethylene and/or to GAs, which reveals the mechanism in which plant hormones regulate assimilate remobilization and grain-filling, and provides a physiological regulation to improve grain-filling in cereals. （iii） A modest increase in ABA level in plants can enhance activities of the key enzymes involved in carbon metabolism, and thereby increase assimilate loading and unloading capacity. An elevated ABA level through MSD or applying ABA with a low concentration can increase activities of the key enzymes in starch or fructan degradation and sucrose synthesis in vegetative tissues, leading to the enhancement in assimilate loading ca- pacity, and enhance activities of the key enzymes in sucrose-to-starch conversion in the sink organ, and consequently, increase assimilate unloading capacity and starch synthesis in grain, which reveals the mechanism in which ABA regu- lates assimilate remobilization and grain-filling. Further research is needed to understand the molecular mechanism, such as from the aspect of signal transduction, in which assimilate remobilization and grain filling are regulated in cereals, to investigate the regulatory mechanism underlying nitrogen remobilization from vegetative tissues to grain, and to eluci- date the mechanism in which the MSD reduces spikelet degeneration and improves grain quality of cereals.