Abstract
Mechanical resistance to the gravitational force is a principal graviresponse in plants, comparable to gravitropism. We examined the role of membrane sterols in gravity resistance by extensive analyses of changes in membrane lipid composition and by analyzing growth behavior of loss of function mutants of HMGR under hypergravity conditions. Sterol levels of azuki bean epicotyls per fresh weight were kept high, as compared with 1 g controls, under hypergravity conditions. On the other hand, the level of phospholipids, glycolipids, or fatty acids, or fatty acid composition in any lipid class was not clearly modified by hypergravity. Hypergravity suppressed elongation growth and stimulated lateral expansion of stem organs. In hypocotyls of Arabidopsis hmg mutants, such changes in growth parameters occurred even under 1 g conditions. These results support the hypothesis that membrane sterols are involved in maintenance of normal growth capacity of stem organs against gravity.
