alpha-tocopherol synthesis by Capsicum fruit chromoplasts

Chromoplast envelope membranes isolated from mature fruits of the yellow variety of pepper (Capsicum annuum) contain lower carotenoid levels than corresponding ones from red fruits. Their pigment composition is like that of chloroplast envelopes. The present report is concerned with the pathway of alpha-tocopherol synthesis in this yellow variety of pepper. We report the radioactive incorporation of [methyl-C-14] -S-adenosylmethionine into metabolites of the tocopherol pathway, i.e. 2,3-dimethyl-5-phytylquinol (70-75 %), gamma- (0-10%) and alpha-tocopherol (20-25%), even without exogenous substrates. The presence of gamma-tocopherol stimulates alpha-tocopherol synthesis by a factor of five. Another aspect of this work is concerned with the fractionation of osmotically treated chromoplasts, which resulted in a low (d = 1.06 g/cm(3)) and a high (d = 1.1g/cm(3)) density fraction. We show data on the distribution of marker enzymes, the capacities for tocopherol synthesis and the lipid composition of these fractions.