Membrane-associated protein kinase activities in the developing mesocarp of grape berry.

Fruit development is a process involving various signals and gene expression. Protein phosphorylation catalyzed by protein kinases is known to play a key role in eukaryotic cell signalling and so may be involved in the regulation of fruit development. Using the method of exogenous substrate phosphorylation, we characterised the calcium-dependent and calmodulin-independent protein kinase (CDPK) activity and the myelin basic protein (MBP)-phosphoralating activity that could be due to a mitogen-activated protein kinase (MAPK)-like activity in the developing mesocarp of grape berry. The CDPK activity was shown to be predominantly localised in the plasma membrane, while the MAPK-like activity was predominantly associated with endomembranes. The assays of bivalent cation requirement showed that Mn2+ could to a certain extent replace Mg2+ in the incubation system for the protein kinase activities. Both CDPK and MAPK-like activities were resistant to heat treatment. The activities of the two enzymes were fruit developmental stage-specific with the highest activities of both enzymes in the lag growth phase before the ripening stage, suggesting strongly the important roles of the detected CDPK and MAPK-like activities in the fruit development.

Membrane-associated protein kinase activities in developing apple fruit.

Fruit development is a process involving various signals and gene expression. Protein phosphorylation catalysed by protein kinases is known to play a key role in eukaryotic cell signalling and so may be involved in the regulation of fruit development. Using the method of exogenous substrate phosphorylation, the activity of calcium-dependent and calmodulin-independent protein kinase (CDPK) that was stimulated by phosphatidylserine, and the myelin basic protein (MBP)-phosphorylating activity that could be due to a calcium-independent mitogen-activated protein kinase-like (MAPK-like) activity in the developing apple fruits were identified. The CDPK activity was shown to be predominantly localized in the plasma membrane, whereas in the presence of phosphatidylserine, the high activity of CDPK was detected in both plasma membrane and endomembranes. The MAPK-like activity was predominantly associated with endomembranes. The assays of bivalent cation requirement showed that Mn2+ could replace Mg2+ in the incubation system for the protein kinase activities and stimulate CDPK activity more than Mg2+. Heat treatment abolished CDPK but stimulated MAPK-like activity. The activities of the phosphatidylserine-stimulated CDPK and of the MAPK-like were fruit developmental stage-specific with higher activities of both enzymes in the early and middle developmental stages in comparison with the late developmental stage. These data suggest that the detected protein kinases may play an important role in the fruit development.