Different functions of vicilin and legumin are reflected in the histopattern of globulin mobilization during germination of vetch (Vicia sativa L.)

The temporal and spatial patterns of storage-globulin mobilization were imm unohistochemically pursued in the embryonic axis and cotyledons of vetch se ed (Vicia sativa L.) during germination and early seedling growth. Embryoni c axes as well as cotyledons of mature seeds contain protein bodies with st ored globulins. Prevascular strands of axes and cotyledons, the radicle and epidermal layers of axis organs were nearly exclusively stained by vicilin antibodies whereas the cotyledonous storage mesophyll gave similar stainin g for vicilin and legumin. Globulin breakdown started locally where growth and differentiation commenced in the axis. There, vicilin mobilization prec eded legumin mobilization. Thus vicilin represents the initial source of am ino acids for early growth and differentiation processes in vetch. Legumin presumably only serves as a bulk amino acid source for subsequent seedling growth during postgerminative globulin degradation. During the first 2-3 d after the start of imbibition the axis was depleted of globulins whereas no decrease in immunostainability was detected in the cotyledons except in th eir vascular strands where immunostainability was almost completely lost at this time. Continuous vascular strands were established at the third day w hen globulin breakdown was finished in the axis but had just started in the cotyledon mesophyll. Protein mobilization proceeded in a small zone from t he epidermis towards the vascular strands in the center of the cotyledons. In this zone the storage cells, which initially appeared densely packed wit h starch grains and protein bodies, concomitantly transformed into cells wi th a large central vacuole and only a thin cytoplasmic layer attached to th e cell wall. These results agree well with the hypothesis that during the f irst 2 d after imbibition the axis is autonomous in amino acid provision. A fter the endogenous reserves of the axis are depleted and the conductive ti ssue has differentiated, globulins are mobilized in the cotyledons, suggest ing that then the amino acid supply is taken over by the cotyledons. For co mparison with other degradation patterns we used garden bean (Phaseolus vul garis L) and rape (Brassica napus L.) as reference plants.