The capacity of chlorophyll-a biosynthesis in the mustard seedling cotyledons as modulated by phytochrome and circadian rhythmicity

Within the temporal pattern of primary differentiation the capacity of chlorophyll — a biosynthesis in the cotyledons ofSinapis alba L. seedlings is controlled by phytochrome (in continuous light) or by releasing the circadian rhythm either with lightdark cycles or by a lightdark transition. The sensor pigment for this process is phytochrome. It is very probable that in continuous light as well as under conditions under which the circadian rhythm plays the major part, the capacity of chlorophyll a biosynthesis is limited by the capacity of the biosynthetic step which produces 5-aminolaevulinate.Abbreviations Chl chlorophyll(ide) a - ALA 5-aminolaevulinate - LA laevulinate - PChl protochlorophyll(ide) - ALAD aminolaevulinate dehydratase (EC4.2.1.24) - [P_fr]/[P_10c], photoequilibrium of the phytochrome system at the wavelength - whereby [P_10c] [P_r]+[P_fr]. P_fr is the physiologically active, far-red absorbing form of the phytochrome system