Changes in subcellular localization of enzymes involved in ascorbate-glutathione cycle during the maturation of sweet pepper (Capsicum annuum L.) fruit

Ascorbate-glutathione cycle is implicated in the scavenging of reactive oxygen species, and has an important role in defensive processes against oxidative damage. In a previous study, it was found that the ascorbate content and the enzyme activities of ascorbate-glutathione cycle in sweet pepper (Capsicum annuum L.) fruit increased during maturation, and that these processes were correlated (Imahori et al., 1998). Thus, changes in subcellular localization of enzymes involved in ascorbate-glutathione cycle during the maturation of the sweet pepper fruit were investigated in this study. The process of fruit maturity was divided into four stages: the green stage, the fruit has no yellow pigment. At the green/yellow stage, the fruit has 10-20% yellow surface, whereas, in the yellow/green stage, the fruit has 50-60% yellow surface. In the yellow stage, the fruit is completely yellow. Subcellular fractions were prepared by differential centrifugation. From the determination of marker enzyme activities in each fraction, all four enzymes (ascorbate peroxidase (APX), monodehydroascorbate reducatase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR)) were found in chloroplast, mitochondrial, microsomal, and cytosolic fractions. APX and MDHAR activities during the maturation of the sweet pepper fruit increased in chloroplast and cytosolic fractions but not in mitochondrial and microsomal fractions. GR activity during maturation increased in cytosolic fraction but not in chloroplast, mitochondrial and microsomal fractions. However, DHAR activity during maturation remained.