Cosgrove D J
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Annu Rev Cell Dev Biol. 1997;13:171-201. doi: 10.1146/annurev.cellbio.13.1.171.
Growing plant cells are shaped by an extensible wall that is a complex amalgam of cellulose microfibrils bonded noncovalently to a matrix of hemicelluloses, pectins, and structural proteins. Cellulose is synthesized by complexes in the plasma membrane and is extruded as a self-assembling microfibril, whereas the matrix polymers are secreted by the Golgi apparatus and become integrated into the wall network by poorly understood mechanisms. The growing wall is under high tensile stress from cell turgor and is able to enlarge by a combination of stress relaxation and polymer creep. A pH-dependent mechanism of wall loosening, known as acid growth, is characteristic of growing walls and is mediated by a group of unusual wall proteins called expansins. Expansins appear to disrupt the noncovalent bonding of matrix hemicelluloses to the microfibril, thereby allowing the wall to yield to the mechanical forces generated by cell turgor. Other wall enzymes, such as (1-->4) beta-glucanases and pectinases, may make the wall more responsive to expansin-mediated wall creep whereas pectin methylesterases and peroxidases may alter the wall so as to make it resistant to expansin-mediated creep.
正在生长的植物细胞由一层可伸展的细胞壁塑造，这种细胞壁是纤维素微纤丝的复杂混合物，纤维素微纤丝通过非共价键与半纤维素、果胶和结构蛋白的基质结合。纤维素由质膜中的复合物合成，并作为自组装微纤丝挤出，而基质聚合物由高尔基体分泌，并通过鲜为人知的机制整合到细胞壁网络中。生长中的细胞壁承受着来自细胞膨压的高拉伸应力，能够通过应力松弛和聚合物蠕变的组合而扩大。一种依赖pH的细胞壁松弛机制，称为酸生长，是生长中细胞壁的特征，由一组称为扩展蛋白的特殊细胞壁蛋白介导。扩展蛋白似乎会破坏基质半纤维素与微纤丝之间的非共价键，从而使细胞壁能够屈服于细胞膨压产生的机械力。其他细胞壁酶，如（1→4）β-葡聚糖酶和果胶酶，可能会使细胞壁对扩展蛋白介导的细胞壁蠕变更敏感，而果胶甲酯酶和过氧化物酶可能会改变细胞壁，使其对扩展蛋白介导的蠕变具有抗性。
