CARDOSIN-A, AN ABUNDANT ASPARTIC PROTEINASE, ACCUMULATES IN PROTEIN STORAGE VACUOLES IN THE STIGMATIC PAPILLAE OF CYNARA-CARDUNCULUS L

The function of aspartic proteinases (EC 3.4.23) present in flowers of Cynara species is still unknown. Cardosin Al as a highly abundant asp artic proteinase from Cynara cardunculus L.. a relative of the articho ke, is synthesised as a zymogen and subsequently undergoes proteolytic processing, yielding the mature and active enzyme. Here we report the study of the expression and localization of cardosin A-as a first app roach to address the question of its physiological relevance. A polycl onal antibody specific for cardosin A was raised against a synthetic p eptide corresponding to an amino acid sequence of the enzyme. This ant ibody was used to study the organ-specific, tissue specific and subcel lular localization of cardosin A by immunoblotting, tissue printing an d immunogold electron microscopy. The results showed that expression o f cardosin A is highly restricted to the pistils, and that the enzyme accumulates mainly in protein storage vacuoles of the stigmatic papill ae. Cardosin A is also present, although much less abundantly, in the vacuoles of the cells of the epidermis of the style. In view of these results, the possible physiological roles of cardosin A are discussed, namely an involvement in defense mechanisms or pollen-pistil interact ion, as well as in flower senescence.