title: Cardosin A, an abundant aspartic proteinase, accumulates in protein storage vacuoles in the stigmatic papillae of Cynara cardunculus L.
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.
authors.affiliation: Departamento de Bioquímica, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Ramalho-Santos
authors.forename: J
authors.initials: J
authors.lastname: Pissarra
authors.forename: P
authors.initials: P
authors.lastname: Veríssimo
authors.forename: S
authors.initials: S
authors.lastname: Pereira
authors.forename: R
authors.initials: R
authors.lastname: Salema
authors.forename: E
authors.initials: E
authors.lastname: Pires
authors.forename: C J
authors.initials: CJ
authors.lastname: Faro
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies; D016282:Aspartic Acid Endopeptidases / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D010940:Plant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D018547:Plant Stems; D010944:Plants / Q000201:enzymology* / Q000648:ultrastructure; D014617:Vacuoles / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D000906:Antibodies; D010446:Peptide Fragments; D010940:Plant Proteins; D016282:Aspartic Acid Endopeptidases; C097455:aspartic proteinases, Cynara cardunculus