黄瓜子叶细胞壁扩大生长机理的研究

本文以离体黄瓜子叶为材料,研究了胞质过氧化物酶(POD)、离子 POD 和共价 POD 以愈创木酚为底物的催化动力学和以 Fe~(2+)为抑制剂的抑制动力学特性,发现 Fe~(2+)对这三种 POD都具有非竞争性抑制作用。外源 Fe~(2+)促进了子叶的扩大生长,同时也降低了 RCW 中羟脯比(Hyp/Pro)和异酪比(Idt/Tyr),且 Fe~(2+)浓度越大,促进生长的百分率就越高,这两种比值也就越小;而外源 POD(尤其是共价 POD)则抑制扩大生长,同时共价 POD 也明显增加了这两种比值,表明共价 POD 在壁中具催化 Idt 形成和肽酰脯氨酸羟化酶的作用,并认为其中的 Idt构成了伸展素多肽的内部交联,而 Hyp-O-Ara 则实现了伸展素与壁多糖的外部联系,这种“外系内联”使壁形成一个网络,从而降低了壁的伸展性乃至限制细胞的生长。

A STUDY ON MECHANISM OF EXPANSION OF CELL WALL OF CUCUMBER COTYLEDON

This paper reports that Fe~(2+) has non-competitive inhibition on the PODs of the cytoplasm, SECW(salt Extractable cell wall)and RCW(residual cell wall)from the excised and aerated cotyledons of the cucumber which have been incubated with the 1/15 mol/l phosphate Na~+-K~+ buffer containing 10 ppm 6BA,pH 6.0,for 36 hours in dark. The exogenous Fe~(2+) promoted the expansion of the excised and aerated cotyledons of the cucumber,and simultaneously decreased the Hyp/Pro and the Idt/Tyr of RCW,what is more, the higher the Fe~(2+) concentration,the higher the percentage of promotion,and the less both the Hyp/Pro and the Idt/Tyr.Conversely,the exogenous POD of RCW as tested with Fe~(2+) enormously inhibited this expansion and increased the Idt/Tyr of RCW,but the PODs of the cytoplasm and SECW haven't such obvious effect as the POD of RCW.It suggests that the POD of RCW not only can convert the Pro of extension to Hyp,and cross-link with the polysac- charides of cell wall via the Hyp-o-Ara,but also catalyze coupling of two tyrosine units to form ldt(isodityrosine)which is an inter-polypeptide cross-link.So the extensibility of cell walls is decreased and the growth of plant cell is limitted.