PERTURBATION OF CHLOROPLAST DEVELOPMENT IN MAIZE BY LOW GROWTH TEMPERATURE

The chloroplast development in maize (Zea mays L.) is retarded at low growth temperatures. The composition of thylakoid membranes isolated f rom fully-expanded leaves of plants grown at 17/14 or 14/12-degrees-C (day/night) differed markedly from that of 25/22-degrees-C-grown plant s due to a deficiency of chloroplast-encoded gene products. Appreciabl e net synthesis of thylakoid proteins in vivo was observed in a 3-h la belling period with [S-35]-methionine at 14/12-degrees-C, but the rati o of accumulated chloroplast- to nuclear-encoded products was lesser t han at 25/22-degrees-C. The protein synthesis by chloroplasts in vitro demonstrated that the accumulation of thylakoid membrane proteins was markedly temperature-dependent. Both the protein assembly into thylak oids and its subsequent breakdown took place more rapidly at higher te mperatures. Extensive differences in nuclear protein composition were observed between maize leaves grown at 14/12 and 25/22-degrees-C, sugg esting a possible role for nuclear factors in suppressing the expressi on of genes for chloroplast proteins at temperatures which inhibit thy lakoid assembly.