Root Lipid Composition and Metabolism in Genetic Male‐Sterile Soybeans1

Abstract

Genetic male‐sterile soybeans produced approximately 85% fewer pods than their fertile siblings. Reduced seed production presumably was responsible for prolonged retention of green leaves on male‐sterile plants and allowed more photosynthate to be diverted to the legume root system for utilization in metabolic processes or for conversion to metabolic storage reserves. Because lipids may function as either membrane components or metabolic storage products, the objective of this study was to determine if the secondary effects of male‐sterility were associated with patterns in root lipid composition and metabolism, and to describe any differences from those of the male‐fertile soybean roots. Sterile and fertile plants from a population of the male‐sterile (ms1) maintainer line [Glycine max (L.) Merr. cv. N69‐2774] were sampled in a replicated experimentat 10‐day intervals from flowering to maturity. The total root lipid content of male‐sterile and malefertile plants was found to be significantly different between 110 and 140 days after emergence (DAE). During that period the lipid in male‐sterile roots increased from 1.3 to 3 times that present in male‐fertile roots. At 140 DAE the level of triacylglycerol (TG) was 6.2 times greater in the male‐sterile roots, yet phospholipids were the major glycerolipid fraction in both genotypes throughout development. Within the phospholipid fraction at 140 DAE, the most striking differences between genotypes were the increase of phosphatidylglycerol (PG) and cardiolipin (DPG) in the male‐sterile roots, and the differences in the concentration of palmitoleic acid (16:1) and linolenic acid (18:3). Similar patterns in the concentration of 16:1 and 18:3 were observed in TG. At 140 DAE the concentration of 16:1 was greater in TG than in phospholipids, and also greater in male‐fertile root lipids than in the malesterile counterparts. Although no direct biochemical association was discovered between 16:1 and 18:3, the relation of 18:3 concentration between TG and phospholipids, and also between male‐fertile and malesterile root tissue was opposite to that described for 16:1. Radioactive acetate was incorporated primarily into phospholipids by both genotypes throughout development. The rate of incorporation into lipid was significantly lower in male‐fertile roots after 110 DAE. These results have shown that in the absence of a large seed sink, the lipid biochemistry of soybean root tissues was altered significantly as reflected in the increased levels of storage lipid and the biosynthesis of membrane lipid components.