Protein Phosphorylation in Plastids from Ripening Tomato Fruits (Lycopersicon esculentum)

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Incubation of plastids isolated from ripening tomato fruits (Lycopersicon esculentum) with [γ-^<32>P]ATP resulted in the rapid phosphorylation of several polypeptides. The optimal substrate as P_i donor for the reaction was Mg^<2+>-ATP, and the recovery of [^<32>P]serine after acid hydrolysis indicated predominance of protein serine kinases. The endogenous phosphorylating patterns in chromoplasts isolated from ripe tomato fruits were distinguishable from those observed in green fruit plastids, which in turn were different from those found in leaf plastids. Dark-light transitions had no influence on the pattern of phosphorylation observed in these plastids. The overall results strongly indicate that plastid-specific protein phosphorylation systems are present at defined stages during fruit formation. We also found that dark/light transitions induce a clear stimulation on the phosphorylation in serine rather than in threonine residues in endogenous thylakoid polypeptides of chloroplasts from tomato leaves.
日本植物生理学会の論文