Cardosin A, an abundant aspartic proteinase, accumulates in protein storage vacuoles in the stigmatic papillae of Cynara cardunculus L. |
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Authors: | Miguel Ramalho-Santos José Pissarra Paula Veríssimo Susana Pereira Roberto Salema Euclides Pires Carlos J Faro |
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Institution: | (1) Departamento de Bioquímica, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Apartado 3126, P-3000 Coimbra, Portugal, PT;(2) Instituto de Botanica and Centro de Citologia Experimental, Universidade do Porto, P-4100 Porto, Portugal, PT |
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Abstract: | The function of aspartic proteinases (EC 3.4.23) present in flowers of Cynara species is still unknown. Cardosin A, as a highly abundant aspartic proteinase from Cynara cardunculus L., a relative of the artichoke, 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 approach
to address the question of its physiological relevance. A polyclonal antibody specific for cardosin A was raised against a
synthetic peptide corresponding to an amino acid sequence of the enzyme. This antibody was used to study the organ-specific,
tissue-specific and subcellular localization of cardosin A by immunoblotting, tissue printing and immunogold electron microscopy.
The results showed that expression of cardosin A is highly restricted to the pistils, and that the enzyme accumulates mainly
in protein storage vacuoles of the stigmatic papillae. 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 interaction, as well as in flower senescence.
Received: 10 December 1996 / Accepted: 14 March 1997 |
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Keywords: | : Aspartic proteinase Cardosin Cynara Pistil Stigmatic papilla Storage vacuole |
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