Developmental regulation of a cytosolic ascorbate peroxidase gene from tomato plants

This report describes the characterisation of a gene (APX20) from tomato pl ants that encodes a cytosolic isoform of ascorbate peroxidase which is invo lved in the detoxification of intracellular H2O2 Expression analysis of pro moter-GUS fusions in transgenic plants reveals that the gene is under stric t developmental control, becoming transcriptionally active in cells which a re apparently undergoing mechanical stimulation generated during the differ ent phases of growth. We show that the APX20 gene contains a large 5' leade r intron which is required to confer constitutive gene expression in leaves , but not in other organs of the plant. Based on these observations, we pro pose that the observed trancriptional regulation of this gene may constitut e a basic mechanism for deployment of antioxidative defences in plants, whi ch act to limit the deleterious effects of H2O2 generated during normal pla nt development.