title: Endogenous protein kinase-C activity and phosphorylated proteins in messenger ribonucleoprotein complexes of developing embryos of alfalfa.
abstract: Developing somatic and zygotic embryos of alfalfa (Medicago sativa L.) exhibited endogenous protein kinase activity and protein acceptors of phosphate groups using both cell-free translational extracts and oligo(dT)-cellulose-column-purified mRNPs. The cell-free-translation extracts from pre-cotyledonary-stage somatic embryos had approximately 50- and 100-fold more protein kinase activity than cotyledonary-stage somatic and zygotic embryos. Several polypeptides were phosphorylated; some of them were unique to the early stage and some to the late-stage developing embryos. A 65 kDa protein was phosphorylated heavily in pre-cotyledonary-stage somatic embryos. This phosphorylated protein was comprised of three main components, two of which were phosphorylated heavily. Heat-shock treated-embryos lost their exitant kinase activity and at the same time another form of protein kinase activity was activated which phosphorylated a novel 28 kDa protein. Endogenous protein kinase activity was also observed within the mRNPs of polysomal and non-polysomal fractions of developing embryos, and this phosphorylated only 65, 43 and 30 kDa proteins within these fractions. A 30 kDa protein from the pre-cotyledonary-stage somatic embryos showed a higher affinity for accepting phosphate groups than the proteins from cotyledonary-stage somatic or zygotic embryos. The activity of protein kinase was largely c-AMP-independent, but was dependent on Ca2+, phospholipid and phorbol ester. The enzyme belongs to the protein kinase-C family; the 65 kDa protein cross-reacts with antibodies made against protein kinase-C (alpha- and beta-isoforms) and it may be an autophosphorylated protein.
authors.affiliation: Department of Botany, University of Guelph, Guelph, Ontario, N1G 2W1, Canada. Spramani@jewl.morgan.edu
authors.forename: S K
authors.initials: SK
authors.lastname: Pramanik
authors.forename: A L
authors.initials: AL
authors.lastname: Williams
authors.forename: J Derek
authors.initials: JD
authors.lastname: Bewley
mesh_terms: D018548:Cotyledon / Q000201:enzymology / Q000276:immunology; D000242:Cyclic AMP / Q000378:metabolism; D018869:Heat-Shock Response / Q000502:physiology; D000455:Medicago sativa / Q000196:embryology* / Q000201:enzymology* / Q000276:immunology; D010766:Phosphorylation; D010940:Plant Proteins / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D011493:Protein Kinase C / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D046188:Protein Modification, Translational / Q000502:physiology; D012261:Ribonucleoproteins / Q000378:metabolism*; D012639:Seeds / Q000201:enzymology / Q000276:immunology
chemical_list: D010940:Plant Proteins; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D000242:Cyclic AMP; D011493:Protein Kinase C