Molecular cloning of ascorbate peroxidase in potato tubers and its response during storage at low temperature

To investigate the response of ascorbate peroxidase (APx; EC 1.11.1.11) to low-temperature stress in potato tubers, a cDNA clone encoding APx was isolated from a potato tuber eDNA library. The full-length clone contains a cDNA that is 1039 bp in length and has an open reading frame of 750 by coding for 250 amino acids. The deduced amino acid sequence of APx had high homology with the cytosolic APx (cAPx) from other plant sources and lacked a transit peptide, implying that it encoded a cAPx. APx mRNA was detected by northern blot analysis using cAPx as a DNA probe. mRNA levels during storage at 1 degreesC increased 2.5-fold in 3 weeks as compared with the initial values. Activity staining of APx peaked at 12 weeks after harvest in tubers stored at 1 degreesC, and increased approximately 3.4-fold during the first 12 weeks of storage. APx amounts as determined by western blot analysis using anti-APx antibody correlated well with activity staining of APx. This shows that APx was highly induced by low temperature stress during storage. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.