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 f₂, were subjected to 42°C for 5 h at light intensities of 100 and 1000 μmol photons m^-2 s^-1. The exposure of plants to heat stress at a light intensity of 100 μmol 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, O₂evolution 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 O₂ evolution in chlorina 126 and, especially, in chlorina f₂ was more sensitive to heat than in wild type.