CHEMICAL NATURE OF A SEMIPERMEABLE LAYER IN SEED COATS OF LEEK, ONION(LILIACEAE), TOMATO AND PEPPER (SOLANACEAE)

The chemical nature of the semipermeable layer in seed coats of non-ge rminable leek, onion, tomato, and pepper was studied. Histochemical an alyses were performed with stains under white or UV light. Callose, po lysaccharides and cellulose were not found within the semipermeable la yer in all species, indicating that these compounds were not responsib le for the impermeability. Staining did reveal the presence of lipoida l materials in the semipermeable layer of all species. However, tradit ional stains were not able to differentiate between cutin and suberin. Methods to differentiate cutin from suberin were developed based on t he model that suberin is composed of a cutin portion and a lignin-like component. Procedures included either an enzymatic or chemical hydrol ysis with cutinase or NaOH, respectively, to remove cutin or the cutin portion of suberin, followed by three different stains. The semiperme able layer in seed coats of leek and onion was composed of cutin, whil e in tomato and pepper the layer was composed of suberin. The hydrolys is procedures combined with histochemical staining provide a convenien t method to differentiate cutin from suberin where biochemical techniq ues are not feasible.