水稻颖花退化机理与调控途径

Mechanism and Regulation in Spikelet Degeneration of Rice

水稻颖花退化现象在水稻生长发育中普遍存在,是限制产量进一步提高的重要因素。颖花退化既受内在的遗传和生理的调控,也受外在环境的影响。以往有研究曾用不同遗传作图群体定位了分布在第1至第11号染色体上的多个水稻颖花退化数量性状基因座(QTL),但这些QTL对颖花退化的贡献率均不大;利用突变体材料确定了多个颖花退化候选基因,并克隆了其中的3个基因,但其分子机制仍不清楚。关于颖花退化的生理生化机制有很多假设,包括资源限制、自组织过程、化学调节等,但均缺乏有力证据。近年的研究表明,水稻穗分化期特别是减数分裂期内源油菜素甾醇(BRs)和多胺(PAs)水平较低、乙烯水平较高与颖花退化有密切的关系,提高BRs、PAs或PAs与乙烯的比值,可以减少颖花退化。水稻颖花退化的另一个重要原因是三磷酸腺苷(ATP)含量和能荷水平过低及活性氧(ROS)过度积累,使得膜脂过氧化伤害和小穗程序性细胞死亡,导致颖花退化。通过栽培措施适度提高减数分裂期植株含氮量或BRs含量可提高幼穗能荷水平,减少ROS积累,进而显著减少水稻颖花退化。今后需要从内在因素(遗传、生理生化)、植株整体水平、栽培调控和环境条件等方面深入研究水稻颖花退化的机理及其调控途径,破解水稻颖花退化的科学难题。

The phenomenon of spikelet degeneration is very common in developmental processes of rice,which is a major factor limiting grain yield.Spikelet degeneration is regulated both by genetics,physiology and environment factors.In the previous work,rice spikelet degeneration quantitative trait loci(QTL)distributed on chromosomes 1 to 11 have been mapped using different genetic mapping populations,however,the contribution rate of these QTLs to spikelet degeneration is small;many candidate genes for spikelet degradation have been identified using mutant materials,and 3 of them were successfully cloned,but their molecular mechanism remains unclear.There are many explanations about the physiological and biochemical mechanism on the spikelet degeneration,including resource limitation,self-organization,and chemical regulation.However,convincing evidences are still lacking to support the hypotheses.Recent studies have shown that low content of brassinosteroids(BRs)and polyamines(PAs)and a high ethylene level in young rice panicles during panicle development especially during meiosis are closely associated with spikelet degeneration,and spikelet degeneration could be decreased through increases in BRs and PAs levels and the ratio of PAs to ethylene.Another important reason for rice spikelet degeneration is low levels of adenosine triphosphate(ATP)content and energy charge and excessive accumulation of reactive oxygen species(ROS),which lead to injury of membrane lipid peroxidation and programmed cell death in spikelets,resulting in spikelet degeneration.An appropriate increase in contents of nitrogen or BRs in plants during meiosis through cultivation practices can enhance energy and decrease ROS levels,and consequently reduce spikelet degeneration.Further investigations are needed to deeply understand the mechanism underlying spikelet degeneration and regulation approaches from the internal factors of spikelets(genetic factors,physiological and biochemical factors),from the whole plant level,cultivation practices and environmental conditions,so that the difficult scientific problem of spikelet degeneration may be solved.