Effects of nuclear gene mutations on the structure and function of plastids in pea

Abstract

Two chlorophyll-deficient mutants of Pisum sativum L. were investigated to elucidate the effect of mutations of nuclear genes on the synthesis and function of the light-harvesting chlorophyll a/b protein (LHCP). Both mutants, a chlorotic as well as a chlorophyll b-less mutant, exhibited chloroplasts differentiated into grana and stroma regions, but, for the most part, grana formation was reduced and the number of lamellae per granum was decreased. The major LHCP-apoprotein was reduced in the thylakoid membranes of the chlorotic mutant and was missing (or very greatly reduced) in the membranes of the chlorophyll b-less mutant. The polyadenylated RNA of both mutants was isolated from young green leaves and translated in a wheat germ cell-free system. Using immunoprecipitation, it was demonstrated that both mutants contained the mRNA for the LHCP-apoprotein and that this message is taken up into polysomes, as shown by read-through translation. From these experimental data it is concluded that transcription and translation of the major protein of the light-harvesting complex are not affected by these genetic defects. A close correlation between the amount of chlorophyll b and the amount of LHCP incorporated into the membrane was observed.