The plant cell wall provides each cell with structural support and mechanical strength, and thus, it plays an important role in supporting the plant body against the gravitational force. We investigated the effects of microgravity on the composition of cell wall polysaccharides and on the expression levels of genes involved in cell wall metabolism using rice shoots cultivated under artificial 1 g and microgravity conditions on the International Space Station. The bulk amount of the cell wall obtained from microgravity-grown shoots was comparable with that from 1 g-grown shoots. However, the analysis of sugar constituents of matrix polysaccharides showed that microgravity specifically reduced the amount of glucose (Glc)-containing polysaccharides such as 1,3:1,4-β-glucans, in shoot cell walls. The expression level of a gene for endo-1,3:1,4-β-glucanase, which hydrolyzes 1,3:1,4-β-glucans, largely increased under microgravity conditions. However, the expression levels of genes involved in the biosynthesis of 1,3:1,4-β-glucans were almost the same under both gravity conditions. On the contrary, microgravity scarcely affected the level and the metabolism of arabinoxylans. These results suggest that a microgravity environment promotes the breakdown of 1,3:1,4-β-glucans, which, in turn, causes the reduced level of these polysaccharides in growing rice shoots. Changes in 1,3:1,4-β-glucan level may be involved in the modification of mechanical properties of cell walls under microgravity conditions in space.

中文翻译：

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微重力通过增加参与其分解的基因的表达水平来影响水稻芽细胞壁中基质多糖1,3：1,4-β-葡聚糖的水平。

植物细胞壁为每个细胞提供结构支撑和机械强度，因此，在支撑植物体抵抗重力方面起着重要作用。我们研究了微重力对细胞壁多糖组成和细胞壁代谢相关基因表达水平的影响，其中使用了在国际空间站人工1 g和微重力条件下培养的稻芽。从微重力生长的芽中获得的细胞壁的堆积量与1 g的堆积量相当-长出的芽。然而，对基质多糖的糖成分的分析表明，微重力特异性地减少了芽细胞壁中含葡萄糖（Glc）的多糖如1,3：1,4-β-葡聚糖的数量。内切1,3：1,4-β-葡聚糖酶的基因的表达水平在微重力条件下大大提高，该酶水解1,3：1,4-β-葡聚糖。然而，在两种重力条件下，参与1,3：1,4-β-葡聚糖生物合成的基因的表达水平几乎相同。相反，微重力几乎不影响阿拉伯木聚糖的水平和代谢。这些结果表明，微重力环境促进了1,3：1,4-β-葡聚糖的分解，这反过来导致了正在生长的水稻芽中这些多糖的含量降低。1,3：1的变化，