Effects of water stress on the molecular species composition of polar lipids from Vigna unguiculata L. leaves

Abstract

Two Vigna unguiculata L. varieties, one drought-sensitive (IT-83D), and one drought-resistant (Epace) were subjected to water stress by withholding watering. At moderate water deficits, leaf polar lipid contents decreased in the sensitive variety and increased in the resistant one. At severe stress, lipid content was sharply reduced in both varieties. The degree of unsaturation in monogalactosyl-diacylglycerol (MGDG) and diglactosyl-diacylglycerol (DGDG) slightly increased in the resistant variety when subjected to moderate water stress, and this was due to an increase in the dilinolenoyl molecular species (18:3/18:3). At severe water deficits, in both varieties, the sharp decrease in dilinolenoyl-MGDG and dilinolenoyl-DGDG was responsible for the breakdown of these two galactolipid classes. All the molecular species of phosphatidylglycerol (PG) containing trans-hexadecenoic acid (16:1t) were severely reduced by drought stress, this reduction being related to a parallel increase in the 16:0-containing molecular species. This phenomenon was more pronounced in the susceptible variety. Whereas in the sensitive variety, phosphatidylcholine (PC) amount per leaf dry weight decreased with drought, in the resistant variety, PC amount increased, at all water potentials. This increase was also accompanied by an augmentation of all the molecular species containing linolenic acid (18:3).