LIGHT-MODULATED AND CALCIUM-MODULATED PHOSPHORYLATION OF PROTEINS FROM WHEAT SEEDLINGS

In vivo white light irradiation (for 1 hr or more) of four-day-old eti olated wheat seedlings followed by in vitro phosphorylation decreased the phosphorylation of 52 and 48 kDa polypeptides in the proteins of t he soluble fraction; short pulses of white light or red/far-red were n ot effective. Studies using norflurazon, a bleaching herbicide, sugges t that dephosphorylation of this polypeptide may be linked with light- dependent development of plastids. Studies employing a Ca2+ chelator, EGTA, and several calmodulin (CaM) inhibitors indicate that phosphoryl ation of 52, 48, 34 and 31 kDa polypeptides, both in the dialysed and undialysed soluble fractions, is Ca2+-CaM dependent. The depletion of Ca2+ also retarded the mobility of a 52 kDa polypeptide by 4-6 kDa, pa rticularly in the undialysed fraction, which was restored to control l evel by increasing the Ca2+ level, a property unique to Ca2+-binding p roteins. Strikingly, the phosphorylation status of a doublet (17 and 1 5 kDa phosphopolypeptides), visible primarily in the dialysed fraction , was not affected by light and/or Ca2+-CaM antagonists. The results s uggest the existence of Ca2+/CaM-dependent protein kinase(s) in young wheat seedlings, whose activity, directly or indirectly, is down-regul ated by white light. Copyright (C) 1997 Elsevier Science Ltd.