We isolated a cytosolic ascorbate peroxidase (APX-c) from strawberry fruit at the turning (1/2 red) stage and determined its N-terminal amino acid sequence. Using degenerate oligonucleotides corresponding to a part of the N-terminal sequence and two sequences corresponding to conserved regions in previously reported plant ascorbate peroxidases, two RT-PCR products of 730 bp and 630 bp were synthesized. Screening of a strawberry Fruit cDNA library with the PCR-amplified DNA fragments as probes resulted in a cDNA which encodes a cytosolic APX isoform. DNA sequencing revealed that the cDNA contains an open reading Frame of 250 amino acids (27.3 kDa). The lack of a transit peptide in the deduced amino acid sequence implies that it encodes a cytosolic isoform. RNA blot analysis showed that the mRNA is strongly expressed in fruit and weakly in leaf, root? and petiole, but not in seed. Also, during ripening, the expression of the mRNA increased to the maximum level at the turning stage. This is the first report to identify a specific cytosolic APX isoform from multi-isoforms and characterize it at the molecular level in a nonclimacteric fruit. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.