Factors determining starch function and molecular structure; how characteristic is enzymes of starch synthesis in plant origin

为了寻找植物来源淀粉特性的决定因素，本研究从高直链淀粉的分子结构和功能、颗粒结合淀粉合成酶（GBSS）含量与直链淀粉含量的关系、分支酶（BE）功能与支链淀粉结构的关系等方面进行了研究。结果表明，GBSS和BE在淀粉的表征中起着重要的作用.我们发现，两个高直链淀粉大麦品种的淀粉具有与普通大麦品种相似的直链淀粉和支链淀粉的分子结构，实际上是高直链淀粉，与标记稻的情况不同，并且非常难糊化.采用SDS-PAGE法测定了大麦（4个品种）、水稻（12个品种）、小麦（6个品种）、玉米（2个品种）和马铃薯（5个品种）淀粉的GBSS含量，发现GBSS含量与品种间存在如下关系。(1)根据GBSS量与实际直链淀粉含量之间的关系，发现两种类型的植株。一类是大麦和玉米，直链淀粉含量随GBSS用量的增加而增加。另一类是水稻、小麦和马铃薯，其直链淀粉含量随GBSS用量的增加而保持不变。(2)水稻GBSS合成直链淀粉，也可能延长部分支链淀粉链，产生类似直链淀粉的超长链.从大麦胚乳（开花后23天）中纯化BE。支链淀粉有两种异构体BE I和BE II，它们在链转移中的作用不同，其中BE I是决定支链淀粉短链分布的主要异构体。

In order to find out the determining factor of starch characteristic in plant origin, we examined 1) molecular structure and function of high-amylose starches, 2) the relation between amount of granule bound starch synthase (GBSS) and amylose content and 3) the relation between function of branching enzyme (BE) and amylopectin structure. The results obtained suggested that GBSS and BE played an important role in characterization of starch.1. We found that starches from two high-amylose cultivars of barley had similar molecular structures of amylose and amylopectin to a normal cultivar of barley, and were actually high-amylose, differing from in the case of indicia rice, and gelatinized with very difficulty.2. We determined GBSS amount of starches from barley (4 cultivars), rice (12 cultivars), wheat (6 cultivars), maize (2 cultivars) and potato (5 cultivars) by SDS-PAGE, and found the following relations on GBSS amount. (1) Two types of plants were found in terms of the relation between GBSS amount and actual amylose content. One type of plant was barley and maize in which amylose content increased with increase of GBSS amount. The other type was rice, wheat and potato in which amylose content was constant even with increase of GBSS amount. (2) Rice GBSS, which synthesizes amylose, might also elongate a part of amylopectin chains and produce amylose-like very long chains.3. BE was purified from barley endosperm (23 days later flowering). There were two isoforms (BE I and BE II), which had different function in chain transfer, and the main isoform, BE I, was suggested to determine short-chain distribution of amylopectin.