Biochemical evidence for a calcium-dependent protein kinase from Pharbitis nil and its involvement in photoperiodic flower induction.
A soluble Ca(2+)-dependent protein kinase (CDPK) was isolated from seedlings of the short-day plant Pharbitis nil and purified to homogeneity. Activity of Pharbitis nil CDPK (PnCDPK) was strictly dependent on the presence of Ca(2+) (K(0,5)=4,9 microM). The enzyme was autophosphorylated on serine and threonine residues and phosphorylated a wide diversity of substrates only on serine residues. Histone III-S and syntide-2 were the best phosphate acceptors (K(m) for histone III-S=0,178 mg ml(-1)). Polyclonal antibodies directed to a regulatory region of the soybean CDPK recognized 54 and 62 kDa polypeptides from Pharbitis nil. However, only 54 kDa protein was able to catalyse autophosphorylation and phosphorylation of substrates in a Ca(2+)-dependent manner. CDPK autophosphorylation was high in 5-day-old Pharbitis nil seedlings grown under non-inductive continuous white light and was reduced to one-half of its original when plants were grown in the long inductive night. Also, the pattern of proteins phosphorylation has changed. After 16-h-long inductive night phosphorylation of endogenous target (specific band of 82 kDa) increased in the presence of calcium ions. It may suggest that Ca(2+)-dependent protein kinase is involved in this process and it is dependent on light/dark conditions.
Jaworski
Krzysztof
K
Department of Plant Physiology and Morphogenesis, Nicholaus Copernicus University, Gagarina 9 St, PL 87-100 Torun, Poland. jaworski@biol.uni.torum.pl
Szmidt-Jaworska
Adriana
A
Tretyn
Andrzej
A
Kopcewicz
Jan
J
D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002940:Circadian Rhythm; D027722:Convolvulaceae / Q000201:enzymology* / Q000254:growth & development; D004591:Electrophoresis, Polyacrylamide Gel; D035264:Flowers / Q000201:enzymology* / Q000254:growth & development*; D006657:Histones / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008970:Molecular Weight; D010766:Phosphorylation; D017440:Photoperiod; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D036226:Seedlings / Q000201:enzymology / Q000254:growth & development; D013379:Substrate Specificity; D017871:Calcium-Calmodulin-Dependent Protein Kinases
D002118:Calcium; D002147:Calmodulin; D006657:Histones; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases