小麦可孕小花发育成粒特征及其细胞分裂素调控的生理机制

Spike grain number is suspected of being determined by the sudden death of most of the initiated floret primordia within a few days, which occurs at around booting.During early spring,wheat plants accumulata large number of floret primordia until flag leaf emergence.Only a small proportion reach anthesis and possibly set a grain which was survival florets.Since grain number is extremely important to determining crop yield, numerous studies have focused on floret death, why it occurs, and how to reduce its magnitude.Floret death occurs during rapid stem and spike elongation, at a time when nutrient requirements are high. It is therefore frequently argued that competition for assimilates eventually leads to a shortage of nutrients, resulting in primordia abortion. The carbon assimilate availability in the spike is likely not the critical variable in determining grain number.The amount of nitrogen apparently required in spikes at anthesis raises the hypothesis that the amount of nitrogen may have an important role in floret development. The evidence that plant nutrition during spike growth affects the future of the plant, including its grain number, leads therefore to the two following questions:(i) Do plants experience a systematic trophic crisis explaining and/or modulating the survival floret mortality peak?To what extent does trophic crisis determine the future grain number per spike? (ii)What are physiological mechanism and regulation approach of survival florets development grain setting? Most of the research aimed to identify physiological mechanisms of grain number determination has been focused on the early period when the floret primordia actually develop.The project trace the international research focus and connect closely with practical problems of wheat production in China,which focus on that the study of florets with develop all floral organs setting grain basis and the role of nitrogen availability and partitioning to the spikes during pre-anthesisare unknown under high potential field condition. The field and pot trials were conducted using ten genotypes of varying grain number and N efferency and combinations of nitrogen supply rate and stage.The appearance and development of florets was recorded.The ovary development and enlargement were quantified in eight specified positions within the spikes. We also investigated the growth of stem, spike and florets using a relative growth rate analysis,and in order to get an estimate of the intrinsic capacity of growth per unit of organ weight. Special attention was paid to find the relationshipsamo among expression levels cytokinin genes(CKX2.1, CKX2.2, CKX2.3, CKX2.4和CKX2.5),coordinate regulation of exogenous cytokinin (6-Benzylaminopurine) and endogenous cytokinin,nitrogen partitioning and survival floret development which might explain the physiological mechanism and regulation approach of grain setting, and support developing of increasing grain number technique in winter wheat.

穗粒数是冬小麦产量的主要构成因素，我国华北冬麦区小麦幼穗发育时间较长，但开花前的20天左右是决定穗粒数的关键时期，此期是小麦营养与生殖器官快速并进生长以及完善(可孕)小花向成粒发育的阶段，植株内源激素合成不足和资源竞争剧烈可能是影响其可孕小花发育成粒的重要原因。本项目瞄准我国小麦生产中穗粒数不足、调控效果不显著的实际问题，针对完善小花后发育形态与数量特征未知、细胞分裂素关键基因表达与可孕小花发育关系不明晰等科学问题，拟在分析近30年幼穗发育资料的基础上，在大田和盆栽试验条件下，采用镜检形态观察、氮碳积累分配测定与基因表达分析相结合的方法，探索不同生境条件下可孕小花发育成粒的形态与数量特征，研究分析小麦体内细胞分裂素代谢关键基因表达和外源细胞分裂素类物质协同调控与可孕小花发育成粒的关系，以探明冬小麦可孕小花发育成粒生理机制，完善冬小麦幼穗发育理论，为增加冬小麦穗粒数技术研发提供理论支撑。

穗粒数是小麦产量的主要构成因素，开花前的20天左右是决定穗粒数的关键时期。此期是小麦营养与生殖器官快速并进生长以及可孕小花向成粒发育的阶段，由此推断，植株体内内源激素合成不足和资源竞争剧烈是影响其可孕小花发育成粒的重要原因。本项目瞄准我国小麦生产中穗粒数不足、调控效果不显著的实际问题，在大田和盆栽试验条件下，采用镜检形态观察、氮碳积累分配测定与基因表达分析相结合的方法，针对完善小花后发育形态与数量特征进行了系统观察，对两种类型小麦品种小麦完善小花发育成粒过程中内源激素含量变化、穗器官物质积累分配比例、以及在外源细胞分裂素细胞分裂素调控作用下可孕小花内细胞分裂素含量和关键基因表达进行了分析。研究结果表明，小麦可孕小花发育成粒与穗器官干物质分配比例、细胞分裂素含量呈极显著的正相关关系，在拔节后期叶面喷施外源细胞分裂素-6BA，可明显促进可孕小花发育，显著提高开花期可孕小花数量和穗粒数，细胞分裂素合成基因IPT和氧化酶基因CKX表达分析结果表明，随可孕小花发育进程的推进，合成酶基因表达呈单峰曲线，而细胞分裂素降解酶基因表达呈双峰曲线，使可孕小花发育成粒过程中有较高的细胞分裂素含量是获得高穗粒数的生理基础。该研究结果为探明小麦体内细胞分裂素代谢关键基因表达和外源细胞分裂素类物质协同调控与可孕小花发育成粒的关系，确立冬小麦可孕小花发育成粒生理机制，完善冬小麦幼穗发育理论，为小麦穗粒数有效调控、增加籽粒产量具有极其重要的意义。