The starch-debranching enzymes isoamylase and pullulanase are both involved in amylopectin biosynthesis in rice endosperm
The starch-debranching enzymes isoamylase and pullulanase are both involved in amylopectin biosynthesis in rice endosperm
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DOI：
10.1104/pp.121.2.399
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发表时间：
1999-10-01
期刊：
影响因子：
7.4
通讯作者：
Nakamura, Y
中科院分区：
文献类型：
--
作者：
Kubo, A;Fujita, N;Nakamura, Y
水稻等位基因 Sugary-1 突变体 (Oryza sativa) 的胚乳中，异淀粉酶和普鲁兰酶这两种淀粉脱支酶的活性大大降低，其中异淀粉酶的降低比普鲁兰酶更明显。然而，如用普鲁兰酶观察到的，异淀粉酶活性的降低与糖表型的大小（胚乳植物糖原区域的比例）无关。在中度突变系EM-5中，植物糖原区域的支链淀粉酶活性明显低于淀粉区域，并且整个胚乳组织中的异淀粉酶活性极低或完全丧失。这些结果表明，两种脱支酶都参与水稻胚乳中支链淀粉的生物合成。我们推测异淀粉酶在支链淀粉合成中起主导作用，但支链淀粉酶也是必需的或可以补偿异淀粉酶在支链淀粉多簇结构构建中的作用。异淀粉酶很可能在一些 Sugary-1 突变体（如 EM-273 和 EM-5）中被修饰，因为它在这些突变体中分别以显着和微量存在，但显然没有活性。结果表明Sugary-1基因编码水稻基因组的异淀粉酶基因。
The activities of the two types of starch debranching enzymes, isoamylase and pullulanase, were greatly reduced in endosperms of allelic sugary-1 mutants of rice (Oryza sativa), with the decrease more pronounced for isoamylase than for pullulanase. However, the decrease in isoamylase activity was not related to the magnitude of the sugary phenotype (the proportion of the phytoglycogen region of the endosperm), as observed with pullulanase. In the moderately mutated line EM-5, the pullulanase activity was markedly lower in the phytoglycogen region than in the starch region, and isoamylase activity was extremely low or completely lost in the whole endosperm tissue. These results suggest that both debranching enzymes are involved in amylopectin biosynthesis in rice endosperm. We presume that isoamylase plays a predominant role in amylopectin synthesis, but pullulanase is also essential or can compensate for the role of isoamylase in the construction of the amylopectin multiple-cluster structure. It is highly possible that isoamylase was modified in some sugary-1 mutants such as EM-273 and EM-5, since it was present in significant and trace amounts, respectively, in these mutants but was apparently inactive. The results show that the Sugary-1 gene encodes the isoamylase gene of the rice genome.