鹽逆境對大豆葉綠體膜合成脂質的影響

Effects of Salt-Stress on the Biosynthesis of Lipids in Chloroplast Membranes of Soybean Plant

大豆生長於正常情況（Ψw Haogland solution = -0.8 MPa）四天，然後移植於鹽逆境（Ψw = -1.6 MPa）情況下四天，或先適應於Ψw = -1.2 MPa四天，再培養於鹽逆境情況下四天。收取葉片，分離葉綠體，使用freezing and thawing方法把葉綠體破壞，再利用linear density sucrose gradient centrifugation方法把葉綠體分離為外膜及內膜。所得葉綠體膜的純度，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處理葉綠體15, 30, 45, 60分鐘，然後再把葉綠體分為外膜及內膜，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，葉綠體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，與馴化及葉綠體內膜的脂質分解與合成有密切相關。此顯示葉綠體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。

Soybean plants were grown under salt-stressed condition (Ψw = -1 .6 MPa) without or with previous acclimation at Ψw = -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 Ψw = -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.