A maize mutant with decreased capacity to accumulate chloroplast protein synthesis elongation factor (EF-Tu) displays reduced tolerance to heat stress

Abstract

A chloroplast protein synthesis elongation factor, EF-Tu, accumulates in some maize ( Zea mays L.) genotypes that show increased tolerance to heat stress [Planta 212 (2001) 359]. Previous studies, have suggested that maize EF-Tu may play a role in the development of heat tolerance [Plant Sci. 163 (2002) 1075]. In the present study, we identified a maize mutant that has decreased capacity to synthesize and accumulate EF-Tu under heat stress and tested the ability of the mutant to tolerate heat stress. Experiments were conducted in the laboratory using 17-day old plants. Stress tolerance was assessed by examining heat stability of photosynthetic membranes (thylakoids), thermal aggregation of chloroplast stromal proteins, and plant growth after exposure to stress. Compared to wild type (non-mutant), the mutant showed reduced tolerance to heat stress. Importantly, chloroplast stromal proteins from the EF-Tu-deficient mutant displayed greater aggregation during exposure to high temperature than chloroplast stromal proteins from the wild type. The results strongly support the hypothesis that maize EF-Tu plays a role in the development of heat tolerance by acting as a molecular chaperone and protecting chloroplast stromal proteins from thermal aggregation.