PROTOCHLOROPHYLL(IDE)630 PHOTOSENSITIZES ACTIVE Ca2+ ACCUMULATION IN MICROSOMAL AND MITOCHONDRIAL FRACTIONS ISOLATED FROM PLANTS

— White light irradiation of a microsomal fraction from etiolated plants affects their ATP-dependent Ca2+ accumulation by inhibiting active uptake and enhancing passive efflux. The succinate-dependent mitochondrial Ca2+ accumulation as well is decreased by light. The wavelength dependence of these light effects as well as their low quantum yield suggest non-phototransformable protochloro-phyll(ide) [PChl(ide)] to be the photoreceptor. PChlide has been isolated from corn leaves pretreated with 5-amino levulinic acid. Addition of Pchlide causes photosensitization of an otherwise light insensitive microsomal Ca2+ accumulation. The observed light effect may be due to contamination of the mitochondrial as well as the microsomal fractions with PChl(ide)‡ containing particles. Irradiation of the intact tissue leads to the almost complete disappearance of the light effect on the in vitro Ca2+ accumulation.