Wall yielding of stem segments in adaptive growth recovery after osmotic stress

采用压力跳变法连续测量了渗透胁迫后生长的适应性渗透恢复过程中维格纳下胚轴段细胞壁在体内产壁特性的调节。在没有IAA的情况下，渗透胁迫下细胞壁的延伸性没有明显变化，但有效膨胀率（P-Y）下降到接近零，导致生长没有恢复。在IAA的作用下，细胞壁的延伸性略有下降，但生长明显恢复。然而，一旦熄灭有效的膨胀，就会完全恢复。在渗透胁迫下生长恢复过程中，有效的胀气（驱动力）调节壁屈服。胞内压力测量表明，有效膨压的恢复不是由P的调节引起的，而是Y的调节引起的。Y总是被调节到比P低约60 kPa，这与iaa诱导的促生长过程中有效膨压的升高相当。从豇豆长形下胚轴中分离到调节ph依赖性甘油中空柱体（GHC）产率阈值张力的壁结合蛋白产率。因此，利用RTPCR技术克隆了yieldin的cDNA。yieldin cDNA包含一个981个碱基对的开放阅读框，编码327个氨基酸。在大肠杆菌中表达的重组产率蛋白对GHC的ph依赖性产率阈值张力有较强的调节作用。同源性研究表明，产率酶与酸性III类几丁质酶和刀豆蛋白b同源，但几丁质酶活性与产率酶活性无直接关系。屈服作用的机理还有待进一步研究。

Regulation of the in vivo wall yielding properties of the cell wall of Vigna hypocotyl segments during adaptive osmotic recovery of growth after osmotic stress was investigated by successive measurements using pressure-jump method. In the absence of IAA, cell wall extensibility showed no significant change under osmotic stress but effective turgor (P-Y) reduced to nearly zero, resulting in no growth recovery. In the presence of IAA, cell wall extensibility slightly decreased eve though growth recovered distinctly. Once extinguished effective turgor, however, fully recovered. It is effective turgor (driving force) that regulates wall yielding in growth recovery under osmotic stress. Intracellular pressure measurements revealed that the recovery of effective turgor is not caused by the regulation of P but Y. Y is always adjusted to about 60 kPa below the P that is comparable to the elevated effective turgor during IAA-induced growth promotion.Wall bound protein yieldin that regulates pH-dependent yield threshold tension of glycerinated hollow cylinder (GHC) of cowpea hypocotyl was isolated from elongating hypocotyls of cowpea. Thus, cDNA of yieldin was cloned with RTPCR. The cDNA for yieldin contained an open reading frame of 981 base pairs encoding 327 amino acids. Recombinant yieldin expressed with E. coli showed potent activity of regulating the pH-dependent yield threshold tension of GHC. A homology search revealed that yieldin was homologous to acidic class III chitinase and concanavalin B. The chitinase activity, however, showed no direct relation to the yieldin activity. Mechanism of yieldin action remains to be studied.