Abstract

Soybean plants were grown under salt-stressed condition ( w = -1.6 Mpa) without or with previous acclimation at w = -1.2 Mpa. The chloroplasts that isolated from those salt-stressed plants were incubated with [14C] acetate. The chloroplast membranes were then subfractionated using linear density sucrose gradient centrifugations into outer envelope membrane (o. e. m.) and inner envelope membranes (i. e. m.). The acyl-CoA synthetase and UDP-galactose diacylglycerol galactosyltransferase activities in both envelope membranes were assayed. Oleic and palmitic acid were the major fatty acids in lipid of these two envelope membranes. Salt-stress reduced chloroplasts to synthesize oleic and palmitic acid, but acclimation caused chloroplasts to recover partially the levels of fatty acids biosynthetic activity. Oleic and palmaitic acid contents in lipid of o.e.m. increased from 6 to 19 %, and 4.6 to 17 % of the control levels if plants had acclimated previously to w = -1.2 Mpa. The concentrations of these two kinds of fatty acid in lipid of i.e.m., likely in o.e.m., were recovered from 1.8 to 45 %, and 4.6 to 17 % of the control ones. Over-all, lipid biosynthesis in i.e.m. of chloroplast were more sensitive to salt-stress treatment compared to o.e.m.. This suggested that activities of lipid biosynthesis in i. e. m. of chloroplast might have a regulatory mechanism for plants to adapt the salt-stressed environment.

中文摘要

大豆生長於正常情況 (wHaogland solution = -0.8 Mpa) 四天，然後移植於鹽逆境 (w = -1.6 Mpa) 情況下四天，或先適應於 w = -1.2 Mpa 四天，再培養於鹽逆境情況下四天。收取葉片,分離葉綠体，使用 freezing and thawing 方法把葉綠体破壞，再利用linear density sucrose gradient centrifugation 方法把葉綠体分離為外膜及內膜。所得葉綠体膜的純度,除以比重方法檢定外，分別以 acyl-CoA synthetase 及 UDP-galactose diacylglycerol galactosyl- transferase 的活性測定之。本實驗獲得外膜及內膜的純度分別為 80% 和 85%. 以 [14C] acetate 處理葉綠体 15, 30, 45, 60 分鐘，然後再把葉綠体分為外膜及內膜，測定膜中 [14C] 脂質及脂質中脂肪酸的含量變化。因膜脂質中 [14C] 油酸 / 棕櫚酸含量較高，且於鹽逆境情況下含量變化也較大，所以測定膜中 [14C] 油酸及 棕櫚酸含量變化，作為膜中脂質分解及合成的指標。鹽逆境使膜中油酸及棕櫚酸含量巨減，唯經鹽馴化的植物其外膜中油酸 / 棕櫚酸的濃度，由逆境時的 6% / 4.6% 增加為 19% / 17%。內膜中則由 1.8% / 4.6% 增加為 45% / 17%. 整體而言，葉綠体內膜的脂質分解及合成比外膜者易受鹽逆境所影響。而植物於逆境下，葉的凋萎與其凋萎後的恢復程度，與馴化及葉綠体內膜的脂質分解與合成有密切相關。此顯示葉綠体內膜脂質的含量變化與植物對鹽逆境的適應性，有調控的機制或功能.。 關鍵字：鹽逆境，葉綠体，外膜，內膜，馴化，油酸，棕櫚酸。

Keyword: Acclimation, Chloroplast, Inner envelope membrane, Oleic acid, Outer envelope membrane, Palmitic acid, Salt-stress.