Fucosyltransferase and the biosynthesis of storage and structural xyloglucan in developing nasturtium fruits
Fucosyltransferase and the biosynthesis of storage and structural xyloglucan in developing nasturtium fruits
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DOI：
10.1104/pp.118.3.885
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发表时间：
1998-11-01
期刊：
影响因子：
7.4
通讯作者：
Maclachlan, G
中科院分区：
文献类型：
--
作者：
Desveaux, D;Faik, A;Maclachlan, G
金莲花(Tropaeolum Majus L.)在子叶细胞的周质间隙中积累大量非岩藻糖化的木葡聚糖(XG)。这种“储存”的XG在体外可以被一种根瘤转移酶岩藻糖基化，但这在体内不会发生，甚至作为分泌的短暂信号也不会发生。在这些果实中，唯一明显岩藻糖化的XG是与生长中的初生壁中的纤维素结合的结构部分(总共约1%)。体外形成的两个岩藻糖化亚基与体内结构XG中发现的相同。膜组分的XC-岩藻糖基转移酶活性在最年轻的果实中单位鲜重产量最高，尤其是在解剖的子叶中，但在贮藏XG形成时下降。在幼子叶细胞的分泌机制中，在半乳糖化和岩藻糖化新生XG的部位之间似乎形成了一个区块。在广泛的半乳糖化后，XG的交通被转移到周质，而不是岩藻糖化。埋藏在堆积物XG下面的原生壁最终会膨胀并失去凝聚力，可能是因为它们继续延伸，而没有加入维持墙壁完整性所需的岩藻糖化XG等成分。
Young, developing fruits of nasturtium (Tropaeolum majus L.) accumulate large deposits of nonfucosylated xyloglucan (XG) in periplasmic spaces of cotyledon cells. This "storage" XG can be fucosylated by a nasturtium transferase in vitro, but this does not happen in vivo, even as a transitory signal for secretion. The only XG that is clearly fucosylated in these fruits is the structural fraction (approximately 1% total) that is bound to cellulose in growing primary walls. The two fucosylated subunits that are formed in vitro are identical to those found in structural XG in vivo. The yield of XC-fucosyltransferase activity from membrane fractions is highest per unit fresh weight in the youngest fruits, especially in dissected cotyledons, but declines when storage XG is forming. A block appears to develop in the secretory machinery of young cotyledon cells between sites that galactosylate and those that fucosylate nascent XG. After extensive galactosylation, XG traffic is diverted to the periplasm without fucosylation. The primary walls buried beneath accretions of storage XG eventually swell and lose cohesion, probably because they continue to extend without incorporating components such as fucosylated XG that are needed to maintain wall integrity.