Characterization of a rice mutant having an increased susceptibility to light stress at high temperature

The effect of light irradiation at high temperature was investigated in a rice mutant, spl‐2, which is sensitive to solar radiation. Dead spots appeared on the mutant leaves when cultured at a high temperature (40°C) under strong white‐light illumination (15 W m⁻²). A similar damage was also observed in the wild‐type leaves under the same conditions when the plants were preincubated in the dark for one day. Preillumination with weak light (6 W m⁻²) lessened the irradiation‐induced damage in the wild‐type. These observations suggest that in rice plants the acclimatization to weak light has a protective effect against strong irradiation at high temperature, and the spl‐2 locus participates in the mechanisms of the acclimatization. The action spectrum for the irradiation‐induced damage at the high temperature (40°C) in the spl‐2 leaves indicated that the maximum damage occurred at around 480 nm and, in a lesser extent, at around 680 nm. Activity of the O⁻₂₋ and H₂O₂₋scavenging enzymes in the spl−2 leaves were almost the same or somewhat higher than those in the wild‐type after irradiation with strong white light (15 W m⁻²) at 40°C, whereas the content of ascorbic acid in the spl−2 decreased significantly compared with the wild type.