Effects of pigment-deficient mutants on the accumulation of photosynthetic proteins in maize

Abstract

We have monitored the accumulation of photosynthetic proteins in developing pigment-deficient mutants of Zea mays. The proteins examined are the CO₂-fixing enzymes, phoshoenolpyruvate carboxylase (E.C. 4.1.1.31) and ribulose-1,5-bisphosphate carboxylase (E.C.4.1.1.39), and three thylakoid membrane proteins, the light-harvesting chlorophyll a/b binding protein (LHCP) of photosystem II, the 65 kilodalton chlorophyll a binding protein of photosystem I and the alpha subunit polypeptide of coupling factor I. Using a sensitive protein-blot technique, we have compared the relative quantities of each protein in mutants and their normal siblings. Carboxylase accumulation was found to be independent of chlorophyll content, while the amounts of the thylakoid proteins increase at about the same time as chlorophyll in delayed-greening mutants. The relative quantity of LHCP is closely correlated with the relative quantity of chlorophyll at all stages of development in all mutants. Because pigment-deficient mutants are arrested at early stages in chloroplast development, these findings suggest that the processes of chloroplast development, chlorophyll synthesis and thylakoid protein accumulation are coordinated during leaf development but that carboxylase accumulation is controlled by different regulatory mechanisms. A white leaf mutant was found to contain low levels of LHCP mRNA, demonstrating that the accumulation of LHCP mRNA is not controlled exclusively by phytochrome.