Wu Yajun, Jeong Beong-Reong, Fry Stephen C, Boyer John S
College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958-1298, USA.
Planta. 2005 Feb;220(4):593-601. doi: 10.1007/s00425-004-1369-4. Epub 2004 Sep 16.
In dark-grown soybean (Glycine max [L.] Merr.) seedlings, exposing the roots to water-deficient vermiculite (psi(w)=-0.36 MPa) inhibited hypocotyl (stem) elongation. The inhibition was associated with decreased extensibility of the cell walls in the elongation zone. A detailed spatial analysis showed xyloglucan endotransglucosylase (XET; EC 2.4.1.207) activity on the basis of unit cell wall dry weight was decreased in the elongation region after seedlings were transplanted to low psi(w). The decrease in XET activity was at least partially due to an accumulation of cell wall mass. Since cell number was only slightly altered, wall mass had increased per cell and probably led to increased wall thickness and decreased cell wall extensibility. Alternatively, an increase in cell wall mass may represent a mechanism for regulating enzyme activity in cell walls, XET in this case, and therefore cell wall extensibility. Hypocotyl elongation was partially recovered after seedlings were grown in low-psi(w) vermiculate for about 80 h. The partial recovery of hypocotyl elongation was associated with a partial recovery of cell wall extensibility and an enhancement of XET activity in the hypocotyl elongation zone. Our results indicate XTH proteins may play an important role in regulating cell wall extensibility and thus cell elongation in soybean hypocotyls. Our results also showed an imperfect correlation of spatial elongation and XET activity along the hypocotyls. Other potential functions of XTH and their regulation in soybean hypocotyl growth are discussed.
在黑暗中生长的大豆（Glycine max [L.] Merr.）幼苗中，将根部暴露于水分亏缺的蛭石（水势ψ(w)= -0.36 MPa）会抑制下胚轴（茎）的伸长。这种抑制作用与伸长区细胞壁伸展性的降低有关。详细的空间分析表明，在幼苗被转移到低水势环境后，基于单位细胞壁干重计算的木葡聚糖内转糖基酶（XET；EC 2.4.1.207）活性在伸长区降低。XET活性的降低至少部分是由于细胞壁物质的积累所致。由于细胞数量仅略有改变，每个细胞的细胞壁物质增加，可能导致细胞壁厚度增加和细胞壁伸展性降低。或者，细胞壁物质的增加可能代表一种调节细胞壁中酶活性（在这种情况下为XET）的机制，进而调节细胞壁伸展性。在低水势蛭石中生长约80小时后，下胚轴伸长部分恢复。下胚轴伸长的部分恢复与细胞壁伸展性的部分恢复以及下胚轴伸长区XET活性的增强有关。我们的结果表明，XTH蛋白可能在调节大豆下胚轴细胞壁伸展性以及细胞伸长方面发挥重要作用。我们的结果还表明，沿着下胚轴的空间伸长与XET活性之间存在不完全的相关性。本文还讨论了XTH在大豆下胚轴生长中的其他潜在功能及其调控。
