2 BARLEY CATALASE GENES RESPOND DIFFERENTIALLY TO LIGHT

Cloned catalase probes from barley (Hordeum vulgare L.) and maize (Zea mays L.) were used to examine catalase gene expression in greened and etiolated leaves of several barley lines. Etiolated leaves had greate r levels of an mRNA detected by barley Cat1, compared with greened lea ves, in all lines. In contrast, a Cat2-like mRNA (homologous to Cat2 o f maize) was induced by light and accumulated to high levels in greene d leaves, compared to the negligible levels detected in etiolated leav es. This suggests that barley contains light-inducible and light-repre ssible catalase genes. In the catalase-deficient barley mutant RPr 79/ 4, no hybridization signal was detected when RNA from greened or etiol ated leaves was probed with maize Cat2, indicating that this mutant is deficient for the light-induced Cat mRNA. In etiolated seedlings of b oth RPr 79/4 and its motherline, the level of the Cat1 mRNA increased coordinately with a steady increase in catalase activity. Even though the mutant RPr 79/4 was able to grow to maturity in normal air, it sus tained chlorosis and significant head sterility probably due to the la ck of a light-inducible catalase. Although the mutant RPr 79/4 is not completely lacking catalase (EC 1.11.1.6), the loss of the CAT-1 isozy me is evidently harmful. This observation underscores the protective r ole of catalases in plants.