The transcriptional response of higher plants to light stress is mediated via hydrogen peroxide-dependent and -independent pathways. In order to analyze these two pathways at the genomic level, microarray analysis for expressional profiling was carried out with the aid of the whole genome GeneChip covering ca 23,000 genes of Arabidopsis thaliana. The analysis revealed that both of the hydrogen peroxide-dependent and -independent HL-activation constitute 40 % of the HL-inducible genes. One quarter of the former group responded to drought stress as well. Many heat shock-related genes including HSP and HSF were regulated by the hydrogen peroxide-dependent HL pathway. A group of genes regulated by the hydrogen peroxide-dependent pathway has been revealed to show transient expression with a peak after 1 h during high light irradiation. In addition, some high light-inducible genes have been found to be down-regulated by hydrogen peroxide. Our results suggest that hydrogen peroxide functions not only as a direct mediator of high light signaling but also as a modulator of expression patterns of some of the high light-responsive genes.
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