title: Maize D4;1 and D5 cyclin proteins in germinating maize. Associated kinase activity and regulation by phytohormones.
abstract: We have previously reported the expression of four different maize D cyclins during seed germination and showed that cytokinins and auxins stimulate the expression of every cyclin in a differential way. In this paper we characterize the behavior at the protein level of two of these cyclins, CycD5 and CycD4;1. Antibodies were raised against CycD5;2 (which very likely also recognizes D5;1) and CycD4;1 and Western blot studies demonstrated that neither BA nor indol-3 acetic acid (IAA) stimulate cyclin accumulation during germination, compared with control levels. However, phytohormones, particularly IAA, modify the kinase activity associated to D cyclins preferentially at early hours of germination. The associated kinase moiety to D cyclins appears to be of a Cdk-A type because this protein immunoprecipitates with D cyclins and because kinase activity is strongly inhibited by both olomoucine and also by a peptide corresponding to the carboxy end of a maize kip related protein (KRP) protein. There is thus no correlation between mRNA and protein expression for these maize D cyclins during seed germination, although phytohormones may stimulate a signaling cascade that stimulates activation of protein kinase activity in cyclin-Cdk complexes.
authors.affiliation: Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Avenida Universidad y Copilco, México D.F. 04510, México.
authors.forename: Aurora
authors.initials: A
authors.lastname: Lara-Núñez
authors.forename: Natividad
authors.initials: N
authors.lastname: de Jesús
authors.forename: Jorge M
authors.initials: JM
authors.lastname: Vázquez-Ramos
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003001:Cloning, Molecular; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D018525:Germination / Q000502:physiology*; D010937:Plant Growth Regulators / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D012639:Seeds / Q000378:metabolism; D003313:Zea mays / Q000235:genetics / Q000254:growth & development / Q000502:physiology*
chemical_list: D016213:Cyclins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D018844:Cyclin-Dependent Kinases