The effect of low ascorbic acid content on tomato fruit ripening.

The oxidant/antioxidant balance affects the ripening time of tomato fruit. Ripening of tomato fruit is associated with several modifications such as loss of cell wall firmness and transformation of chloroplasts to chromoplasts. Besides a peak in HO, reactive oxygen species (ROS) are observed at the transition stage. However, the role of different components of oxidative stress metabolism in fruit ripening has been scarcely addressed. Two GDP-L-galactose phosphorylase (GGP) Solanum lycopersicum L. cv Micro-Tom mutants which have fruit with low ascorbic acid content (30% of wild type) were used in this work to unravel the participation of ascorbic acid and HO in fruit maturation. Both GGP mutants show delayed fruit maturation with no peak of HO; treatment with ascorbic acid increases its own concentration and accelerates ripening only in mutants to become like wild type plants. Unexpectedly, the treatment with ascorbic acid increases HO synthesis in both mutants resembling what is observed in wild type fruit. Exogenous supplementation with HO decreases its own synthesis delaying fruit maturation in plants with low ascorbic acid content. The site of ROS production is localized in the chloroplasts of fruit of all genotypes as determined by confocal microscopy analysis. The results presented here demonstrate that both ascorbic acid and HO actively participate in tomato fruit ripening.