粳稻不同穗部籽粒的淀粉与垩白品质差异及分子机制

Difference and molecular mechanism of soluble sugar metabolism and quality of different rice panicle in japonica rice

为探讨粳稻不同穗部籽粒的淀粉与垩白品质差异及分子机制。将稻穗籽粒按一次枝梗在主穗上的节点划分为稻穗上部、中部和下部籽粒,比较了嘉58等6个品种不同穗部籽粒成熟后的淀粉含量及垩白度等品质差异,同时测定了不同穗部籽粒灌浆期游离糖与淀粉含量,淀粉合成途径相关酶活,相关基因表达量的动态变化。结果显示:除秀水134外,其余5个品种直链淀粉含量均表现为上部籽粒>中部>下部;2个垩白度较高品种嘉58和中嘉8号则表现为上部籽粒垩白>下部>中部。扫描电镜观察发现不同垩白度籽粒中淀粉粒的大小和形状差异显著,高垩白籽粒垩白部位淀粉粒普遍表现为半椭球形或其他曲面球形的形状,淀粉粒排布比较疏散,而低垩白籽粒对应部位的淀粉粒外形多为规则多面体,淀粉粒排布相对紧密。不同品种及部位籽粒在灌浆期内蔗糖、葡萄糖和果糖含量差异较大,但蔗糖含量动态变化均为先下降后微微上升,葡萄糖和果糖则基本表现为先上升后下降。淀粉合成相关催化酶中蔗糖转化酶(Invertase)和ADPG焦磷酸化酶(AGPase)的活性在不同部位间的差异最为显著,其中, AGPase在整个灌浆期内均表现为上部>中部>下部,而Invertase前期表现为上部<中部<下部,后期完全相反。编码Invertase的OsCIN2、OsCIN5基因在不同穗部籽粒中的表达量均表现为中部籽粒>下部>上部,而编码AGPase的OsAGPL1、OsAGPL2、Os AGPs1a基因均表现为上部籽粒>中部≈下部。不同穗部籽粒的直链淀粉含量与垩白度存在不同程度的差异,同时也受品种本身的影响。游离糖含量、淀粉合成相关酶活和编码相关酶的基因表达对淀粉合成均有影响。OsCIN2、OsCIN5、OsAGPL1、OsAGPL2、OsAGPs1a等基因在决定不同穗部籽粒的淀粉含量与垩白品质差异上起着重要作用。

This study investigated the mechanism of starch and rice quality differences on different parts of spikelet in japonica rice. According to the internodes of the primary stem on main panicle, rice grains on the panicles were divided into top, middle,and the bottom spikelets. The dynamic changes of soluble carbohydrate and starch, starch biosynthesis related enzyme activity,gene expression on different parts of panicles at different filling stage and the starch content, chalkiness degree after harvest of six varieties were measured. The results showed that the amylose content of the five varieties was in an order as top > middle > bottom except Xiushui 134. The chalkiness degree of Jia 58 and Zhongjia 8 was higher than the other varieties, and the chalkiness degree of rice grains on the middle part of panicles was lower than that on the bottom part, and the rice grains on the top part had the highest chalkiness degree. Rice grains of high chalkiness degree had significant difference in starch granules size and shape.We found that the shape of starch granules was semi-ellipsoid or other spherical curved in rice grains with high chalkiness degree and mostly regular polyhedra in rice grains with low chalkiness degree. The contents of sucrose, glucose, and fructose in grains of different varieties and parts were different during grain filling period, but the dynamic changes of sucrose content were first decreased and then slightly increased, while glucose and fructose were basically increased first and then decreased. The contents of invertase and AGPase were significantly different among rice grains on top, middle, and bottom parts of panicles. However, the relative expression levels of AGPase were in an order as top > middle > bottom during the whole filling stage. The relative expression levels of invertase were in an order as top < middle < bottom during the early filling stage, and the rule was completely the opposite at late filling stage. The expression levels of Os CIN2 and OsCIN5 encoding sucrose invertase genes were in an order as middle > bottom > top, and the expression levels of OsAGPL1, OsAGPL2, and Os AGPS1a encoding AGPase genes were in an order as top > middle ≈ bottom. It concluded that the amylose content and chalkiness degree of grains in different panicles had significant difference and also affected by varieties. The content of soluble carbohydrate, starch biosynthesis related enzyme activity, and the gene expression of encoding related enzymes had an effect on starch biosynthesis. The genes of Os CIN2, OsCIN5,OsAGPL1, OsAGPL2, and OsAGPS1a played an important role in the difference of starch content and chalkiness degree in different panicles.