Effects of temperature and gibberellic acid on 4-desmethylsterol composition of Avena sativa stem segments

Of the three morphological subunits of Avena sativa stem segments (node, leaf-sheath and internode) examined, internodes constituted the richest source of phospholipids and sterols, yielding almost double the concentration of lipid found in the leaf-sheath. The phospholipid compositions of nodes and internodes were similar, comprising mostly phosphatidylcholine (PC) and phosphatidylethanolamine (PE), with linoleic, linolenic and palmitic acids as the predominant component fatty acids. Leaf-sheath tissue contained mainly PE, with equally high amounts of palmitic, linoleic and linolenic acids. β-Sitosterol and cholesterol were the major 4-desmethylsterols of the internode, while β-sitosterol was predominant in the node and leaf-sheath tissues. The growth temperature of segments prior to isolation produced its major effect on the concentration of stigmasterol, which decreased markedly with temperature. The sitosterol/stigmasterol ratio increased significantly as temperature decreased. Stem segments isolated from plants treated with gibberellic acid (GA₃) for 3 weeks, showed a significant reduction in the amounts of 4-desmethyl sterols on a dry wt basis when compared with control segments. However, when stem segments were incubated with GA₃ for 20 hr, no change in 4-desmethylsterol composition or concentration was observed, even though significant growth in response to GA₃ occurred.