Developmental regulation of a cytosolic ascorbate peroxidase gene from tomato plants.

This report describes the characterisation of a gene (APX20) from tomato plants that encodes a cytosolic isoform of ascorbate peroxidase which is involved in the detoxification of intracellular H2O2. Expression analysis of promoter-GUS fusions in transgenic plants reveals that the gene is under strict developmental control, becoming transcriptionally active in cells which are apparently undergoing mechanical stimulation generated during the different phases of growth. We show that the APX20 gene contains a large 5' leader intron which is required to confer constitutive gene expression in leaves, but not in other organs of the plant. Based on these observations, we propose that the observed transcriptional regulation of this gene may constitute a basic mechanism for deployment of antioxidative defences in plants, which act to limit the deleterious effects of H2O2 generated during normal plant development.