Synthesis and Breakdown of Plant Cell Wall Polysaccharides by a Two-Step Process

为了更好地了解植物细胞壁多糖的合成和降解过程，需要进一步阐明其调控植物生长的机理。从初步的结果，我们假设，植物细胞壁的基质多糖的合成和降解的两个步骤的过程中，通过中间产品具有中等大小。在本研究中，我们分析了两种主要的基质多糖木葡聚糖和（1 * 3），（1 * 4）-β-葡聚糖的代谢，并获得了支持这一假设的数据。从通过木葡聚糖和（1 * 3），（1 * 4）-β-葡聚糖与粗细胞壁酶反应的产物的HPLC和GLG分析，表明在一定条件下产生具有中等大小的多糖。对于木葡聚糖，中间多糖的大小约为50 kDa，对于（1 * 3），（1 * 4）-β-葡聚糖，中间多糖的大小大于100 kDa。负责木葡聚糖分解第一步的木葡聚糖水解酶 关于我们 从红豆上胚轴细胞壁中分离纯化了一系列的蛋白质，并对其进行了表征。它们在分子结构上属于内切木葡聚糖转移酶（EXT）家族。然而，一种纯化的酶仅催化水解，另一种仅在有限的条件下显示内切转移酶活性。还从红豆上胚轴的细胞壁中纯化了能够触发木葡聚糖分解的第二步的α-岩藻糖苷酶。从水稻胚芽鞘细胞壁中分离纯化了两种（1 * 3），（1 * 4）-β-葡聚糖酶。一种酶显示出内切葡聚糖酶活性，并且似乎参与葡聚糖分解的第一步。分解的第二步可以通过外切葡聚糖酶进行。重力和光照均抑制木葡聚糖水解酶和（1 * 3），（1 * 4）-β-葡聚糖酶的活性。这种酶活性的降低可能导致这些聚合物的分子大小增加，导致壁延伸性降低，从而抑制植物生长。少

Processes of the synthesis and breakdown of plant cell wall polysaccharides should be clarified in order to understand the mechanism of regulation of plant growth. From preliminary results, we hypothesized that matrix polysaccharides of plant cell wall are synthesized and degraded by a two-step process via intermediate products with a medial size. In the present study we analyzed the metabolism of two major matrix polysaccharides, xyloglucans and (1 * 3), (1 * 4) -beta-glucans, and obtained the data supporting this hypothesis.1. From the analysis with HPLC and GLG of products by a reaction of xyloglucans and (1 * 3), (1 * 4)-beta-glucans with crude cell wall enzymes, it was shown that the polysaceharides with an intermediate size were produced under certain conditions. The size of the intermediate polysaccharides was about 50 kDa for xyloglucans and was higher than 100 kDa for (1 * 3), (1 * 4)-beta-glucans.2. Xyloglucan hydrolases responsible for the first step of xyloglucan breakdown … More were purified from the cell wall of azuki bean epicotyls and characterized. They were found to belong to endo xyloglucan-transferase (EXT) family in molecular structure. However, one enzyme purified catalyzed only hydrolysis and the other showed the endo-transferase activity only under limited conditions. An alpha-fucosidase capable of triggering the second step of xyloglucan breakdown was also purified from the cell wall of azuki bean epicotyls.3. Two types of (1 * 3), (1 * 4)-beta-glucanases were purified from the cell wall of rice coleoptiles. One enzyme showed an endoglucanase activity and appears to be involved in the first step of the breakdown of the glucans. The second step of the breakdown may be performed by an exoglucanase.4. Both gravity and light suppressed activities of xyloglucan hydrolases and (1 * 3), (1 * 4)-beta-glucanases. Such a decrease in enzyme activities may bring about the increase in molecular size of these polvsaccharides, leading to the decrease in the wall extensibility, thereby suppressing plant growth. Less