DEVELOPING TOMATO SEEDS WHEN REMOVED FROM THE FRUIT PRODUCE MULTIPLE FORMS OF GERMINATIVE AND POSTGERMINATIVE ENDO-BETA-MANNANASE - RESPONSES TO DESICCATION, ABSCISIC-ACID AND OSMOTICUM

Several isoforms of endo-1,4 beta-D-mannanase (EC3.2.1.78) are produce d in the endosperm and embryo of tomato (Lycopersicon esculentium Mill .) seed prior to the completion of germination. Other isoforms appear in the embryo and in the lateral endosperm following germination. This occurs in seeds removed from the fruit prior to completion of develop ment at 45 d after pollination and placed directly on water, or follow ing drying. Hence desiccation is not required to induce either germina tion- or post-germination-related mannanase activity. Incubating seeds in abscisic acid or osmoticum results in a reduction of both germinat ion and total mannanase activity, but the isoforms that are produced i n the embryo and micropylar region of the endosperm are identical to t hose produced in water-imbibed seeds prior to germination. Incubation of seeds in a high concentration of abscisic acid prevents all enzyme production. Only after the completion of germination does mannanase in crease in the lateral regions of the endosperm. In contrast, mannanase is produced in the micropylar region regardless of whether the seed g erminates or not. The isoforms produced in the two regions of the endo sperm are different, those in the lateral endosperm being more similar to those produced in the cotyledons and axes of the embryo. Embryos a nd endosperms dissected prior to completion of germination and incubat ed separately produce far fewer isoforms than when these parts are tog ether in the intact seed.