Causes of poor grain plumpness of two-line hybrids and their relationships to contents of hormones in the rice grain

Chinese. 阐明两系杂交稻籽粒充实特征及籽粒充实不良的成因与激素机理。 采用结实特性差异明显的两系杂交稻为材料，测定籽粒中蔗糖和淀粉含量、玉米素+玉米素核苷（Z+ZR）、吲哚-3-乙酸（IAA）和脱落酸（ABA）含量、乙烯释放速率、蔗糖合成酶（SuSase）和淀粉合成酶（StSase）活性以及籽粒灌浆充实指标，并进行相关分析。表明两系杂交稻结实率低，主要归咎于弱势粒的秕粒率高、充实度差。籽粒充实度差的组合，灌浆前、中期弱势粒中蔗糖含量高于强势粒，表明基质浓度不是两系杂交稻弱势粒灌浆速率慢和籽粒充实度差的主要限制因子。灌浆前期强势粒中的Z+ZR、IAA和ABA含量明显高于弱势粒，Z+ZR、IAA和ABA的最高含量和平均含量与籽粒最大灌浆速率、平均灌浆速率、谷粒充实度和粒重均呈极显著的正相关。灌浆前、中期弱势粒中的乙烯释放速率明显高于强势粒，籽粒充实度差的组合高于籽粒充实度好的组合，乙烯的释放速率与灌浆速率、谷粒充实度和粒重均呈极显著的负相关。在灌浆初期喷施乙烯合成促进剂（乙烯利），弱势粒的乙烯释放速率增加，ABA含量减少，SuSase和StSase活性降低，谷粒充实度和粒重下降；喷施乙烯合成的抑制剂（硝酸钴），结果则相反。表明籽粒中激素含量及其平衡对籽粒灌浆和酶的活性起调控作用，部分两系杂交稻籽粒充实不良与其弱势粒中Z+ZR、IAA和ABA含量低、乙烯浓度高有密切关系。激素对两系杂交稻籽粒充实起重要作用，通过调控激素含量，可以提高籽粒充实。

English. This study was designed to elucidate the grain filling characteristics and the causes of poor grain plumpness of some two-line hybrid rice combinations and their hormonal mechanism. With two-line hybrid rice combinations which show difference in seed-setting and grain filling as materials, starch , sucrose, zeatin (Z) + zeatin riboside (ZR), indole-3-acetic acid (IAA), abscisic acid (ABA), ethephon(ethylene-releasing agent), SuSase and StSase in grains and the seed-setting and grain filling were investigated. The correlations among them were analyzed. The poor grain filling of two-line hybrids was mainly attributed to higher unfilled grain rate and lower filling degree of inferior grains. At the early and mid grain filling stages, the sucrose content in inferior grains was greater than that in superior grains for the combinations with poor grain filling, indicating that the substrate concentration was not the principal factor for their slow grain filling and poor grain plumpness of the inferior grains of two-line hybrids. Z+ZR, IAA and ABA in superior grains were obviously greater than those in inferior grains at early grain filling stage. The maximum and mean contents of Z+ZR, IAA and ABA were positively and very significantly correlated with the maximum and mean grain-filling rate, filling degree, and grain weight. The evolution rate of ethylene was greater in inferior grains than in superior grains, and greater for the combinations with poor grain plumpness than those with good grain plumpness at early or mid filling stages. The evolution rate of ethylene was negatively and significantly correlated with grain filling rate, grain filling degree, and grain weight. Spraying ethephon at early grain filling stage increased the evolution rate of ethylene, reduced ABA content and activities of SuSase and StSase, and decreased grain filling degree and grain weight. The results were reversed when cobatous nitrate (an inhibitor of ethylene synthesis) was applied. The results suggested that the hormones and their balance play a role in the regulation of grain filling and enzymatic activities, and the poor grain filling is attributed to the low contents of Z+ZR, IAA, and ABA, and high evolution rate of ethylene in the inferior grains of some two-line hybrid rice combinations.The results suggested that hormones play important roles in the grain filling of some two-line hybrid rice combinations, and their filling degree could be improved through regulating hormonal contents.