Wakabayashi Yu, Morita Ryutaro, Aoki Naohiro
Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
J Plant Physiol. 2021 Nov;266:153536. doi: 10.1016/j.jplph.2021.153536. Epub 2021 Sep 27.
Many high-yielding rice cultivars with large sink size (total number of spikelet per unit area × mean grain weight) have been developed, but some japonica cultivars developed in Japan often fail to attain the expected high yield due to low sink strength of spikelets. Although there is natural variation in sink strength of spikelets among high-yielding cultivars, metabolic factors involved in the natural variation and relationships of sink strength in spikelets with final percentage of filled spikelets are not fully understood. In the present study, we examined cultivar differences in sink strength for superior and inferior spikelets (i.e. earlier fertilizing spikelets with faster growth and later fertilizing ones with slower growth, respectively) in a panicle, using each spikelet at 10 d after the onset of development (10 DAD) when starch accumulation in endosperm was actively proceeding. Nine high-yielding cultivars were used: five japonica-dominant and four indica-dominant cultivars. Cultivar differences were observed in starch contents at 10 DAD in each spikelet type, and indica cultivars had higher starch contents than japonica cultivars in both superior and inferior spikelets. In addition, starch contents at 10 DAD were closely related to percentage of filled grains at maturity in both spikelet types. The activities of sucrose synthase (SUS) and uridine diphosphoglucose pyrophosphorylase (UGP), and the protein levels of phosphorylase 1 (Pho1), were higher in indica than japonica cultivars, and were positively correlated with starch contents at 10 DAD for both superior and inferior spikelets; although metabolic states, revealed from relations between intermediate metabolites and starch contents, differed among spikelet types. Consequently, it was considered that SUS and UGP at the step from sucrose cleavage to adenosine diphosphoglucose synthesis, and Pho1 at the starch biosynthesis step, were key metabolic factors involved in cultivar differences of sink strength (ability to synthesize starch).
人们已经培育出了许多具有大库容（单位面积颖花总数×平均粒重）的高产水稻品种，但日本培育的一些粳稻品种常常由于颖花库强较低而无法达到预期的高产。尽管高产品种间颖花库强存在自然变异，但参与这种自然变异的代谢因子以及颖花库强与最终颖花结实率之间的关系尚未完全明确。在本研究中，我们以发育开始后10天（10 DAD）的颖花为材料，此时胚乳中的淀粉积累正在活跃进行，研究了穗中优、劣势颖花（即分别为受精早、生长快的颖花和受精晚、生长慢的颖花）的库强品种间差异。使用了9个高产品种：5个粳稻为主的品种和4个籼稻为主的品种。在每种颖花类型中，10 DAD时的淀粉含量存在品种间差异，籼稻品种的优、劣势颖花中的淀粉含量均高于粳稻品种。此外，两种颖花类型中10 DAD时的淀粉含量与成熟时的结实粒百分数密切相关。籼稻品种中蔗糖合酶（SUS）和尿苷二磷酸葡萄糖焦磷酸化酶（UGP）的活性以及磷酸化酶1（Pho1）的蛋白水平高于粳稻品种，且与优、劣势颖花中10 DAD时的淀粉含量呈正相关；尽管中间代谢物与淀粉含量之间关系所揭示的代谢状态在颖花类型间存在差异。因此，认为从蔗糖裂解到腺苷二磷酸葡萄糖合成步骤中的SUS和UGP以及淀粉生物合成步骤中的Pho1是参与库强（淀粉合成能力）品种间差异的关键代谢因子。
