Response of chlorina barley mutants to heat stress under low and high light

Barley plants ( Hordeum vulgare L.) of wild type and two chlorina mutants, chlorina 126 and chlorina f(2), were subjected to 42degreesC for 5 h at light intensities of 100 and 1000 mumol photons m(-2) s(-1). The exposure of plants to heat stress at a light intensity of 100 mumol m(-2) s(-1) induced enormous proline accumulation, indicating that the effect of heat stress was stronger when it was combined with low light intensity. The functional activity of PSII, O-2 evolution and flash-induced thermoluminescence B-band amplitude were strongly reduced when plants were exposed to heat at low light intensity. The results clearly showed that high light intensity had a protective effect on photosynthetic activity when barley plants were treated with high temperature. Comparison of the thermosensitivity of wild type plants and chlorina mutants revealed that O-2 evolution in chlorina 126 and, especially, in chlorina f(2) was more sensitive to heat than in wild type.