Thermal Stability of Protein Import into Chloroplasts in Response to Temperature Stress

Abstract

Temperature has a profound effect on chloroplast biogenesis and associated greening processes. Therefore, the import efficiency of in vitro translated precursor of nuclear coded small subunit of ribulose 1,5 bisphosphate carboxylase/ oxygenase (pRSS) into chloroplasts isolated from pea plants exposed to chill-stress (7°C), and heat-stress (40°C) for 24-48 h was studied. The binding of precursor proteins to the envelope membranes was not affected in chill-stressed plants. The protein import into chloroplasts in chill-stressed plants was reduced. In heat-stress, binding of pRSS was impaired most likely due to reduced presence of the receptor. When isolated intact chloroplasts were given 10 min of heat stress at 35°C their protein import efficiency was severely inhibited implying that protein import apparatus in pea has a low thermal stability. Down-regulation of plastid development in temperature stress could be partly attributed to reduced protein import into chloroplast.