Molecular cloning and characterization of a gene encoding pea cytosolic ascorbate peroxidase

A gene encoding cytosolic ascorbate peroxidase (ApxI) from pea (Pisum sativum L.) was isolated and its nucleotide sequence determined. By homologous alignment between the ApxI cDNA (Mittler, R., and Zilinskas, B. (1991) FEBS Lett. 289, 257-259) and the genomic clone, positions of introns and exons were determined. The isolated ApxI gene was found to contain 9 introns, the first of which was located within the 5'-untranslated region of the mRNA. Southern blot analysis of pea genomic DNA suggests that in pea cytosolic ascorbate peroxidase is encoded by a single copy gene. Steady state ApxI transcript levels were found to increase in response to several stresses imposed by drought, heat, and application of ethephon, abscisic acid, and the superoxide-generating agent paraquat. Increases in ascorbate peroxidase activity in response to stresses were less marked than changes observed in transcript levels; cytosolic ascorbate peroxidase protein levels measured by immunoblot analysis remained unchanged.