Kimpara Tomoya, Aohara Tsutomu, Soga Kouichi, Wakabayashi Kazuyuki, Hoson Takayuki, Tsumuraya Yoichi, Kotake Toshihisa
Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
Ann Bot. 2008 Aug;102(2):221-6. doi: 10.1093/aob/mcn077. Epub 2008 May 16.
The metabolism of beta-1,3 : 1,4-glucan regulates the mechanical properties of cell walls, and thereby changes the elongation growth of Poaceae plants. A previous study has shown that elongation growth of rice coleoptiles under water is enhanced by increased activity of beta-1,3 : 1,4-glucan hydrolases; however, the involvement of beta-1,3 : 1,4-glucan synthase activity in elongation growth under water has not yet been clarified.
The beta-1,3 : 1,4-glucan synthase activity in a microsomal fraction prepared from rice seedlings grown under water was compared with that from control seedlings grown in air. The change under water in the relative expression level of CslF6, a major isoform of the beta-1,3 : 1,4-glucan synthase genes, was examined by quantitative reverse-transcriptase PCR.
The level of beta-1,3 : 1,4-glucan synthase activity in submerged seedlings decreased to less than 40 % of that of the control seedlings and was accompanied by a significant reduction in the amount of beta-1,3 : 1,4-glucan in the cell walls. Under water, the expression of CslF6 was reduced to less than 20 % of the unsubmerged control. Bubble aeration partially restored both beta-1,3 : 1,4-glucan synthase activity and the expression of CslF6 under water, correlating with suppression of the submergence-induced elongation growth of coleoptiles.
Submergence down-regulates the expression of the CslF6 gene, leading to a decreased level of beta-1,3 : 1,4-glucan synthase activity. Together with the increased activity of beta-1,3 : 1,4-glucan hydrolases, the decreased activity of beta-1,3 : 1,4-glucan synthase contributes to the decrease in the amount of beta-1,3 : 1,4-glucan in the cell walls under water. The suppression of beta-1,3 : 1,4-glucan synthesis under water may be mainly due to oxygen depletion.
β-1,3:1,4-葡聚糖的代谢调节细胞壁的机械性能，从而改变禾本科植物的伸长生长。先前的一项研究表明，β-1,3:1,4-葡聚糖水解酶活性增加可增强水稻胚芽鞘在水下的伸长生长；然而，β-1,3:1,4-葡聚糖合酶活性在水下伸长生长中的作用尚未阐明。
将水下生长的水稻幼苗制备的微粒体部分中的β-1,3:1,4-葡聚糖合酶活性与空气中生长的对照幼苗的进行比较。通过定量逆转录PCR检测β-1,3:1,4-葡聚糖合酶基因的主要同工型CslF6在水下的相对表达水平变化。
淹水幼苗中β-1,3:1,4-葡聚糖合酶活性水平降至对照幼苗的40%以下，并伴随着细胞壁中β-1,3:1,4-葡聚糖含量的显著降低。在水下，CslF6的表达降至未淹水对照的20%以下。气泡曝气部分恢复了水下β-1,3:1,4-葡聚糖合酶活性和CslF6的表达，这与胚芽鞘淹水诱导的伸长生长的抑制相关。
淹水下调CslF6基因的表达，导致β-1,3:1,4-葡聚糖合酶活性水平降低。与β-1,3:1,4-葡聚糖水解酶活性增加一起，β-1,3:1,4-葡聚糖合酶活性降低导致水下细胞壁中β-1,3:1,4-葡聚糖含量减少。水下β-1,3:1,4-葡聚糖合成的抑制可能主要是由于氧气耗尽。
