A biochemical and proteomic approach to the analysis of tomato mutant fruit growth

To assess the effects of ABA deficiency on tomato fruit growth, the ABA mutant flacca was grown in an optimal soil water regime and various analyzes were performed, including morphological (fruit number, diameter and fruit biomass), physiological (duration of growth and fruit growth rate), biochemical (ABA accumulation, enzyme cell wall peroxidase activity) as well as proteomics. The fruit growth analysis showed that the slower fruit growth rate and development resulted in smaller flacca fruits in comparison to the wild-type fruits. The comparison of the temporal dynamics of cell wall peroxidase activity and ABA content in our experiment indicated an opposite relationship during fruit development. Proteomic analysis and the down-regulation of most proteins from carbon and amino acid metabolism, the translation and processing of proteins, energy metabolism and cell wall-related metabolism in the flacca fruits compared to the wild type, indicated reduced metabolic flux which reflected a slower fruit growth and development and reduced fruit size in the ABA mutant. These findings also indicated that ABA limited carbon sources, which could be responsible for the reduced fruit growth and size of ABA-deficient tomato fruits. The up-regulation of sulfur and oxygen-evolving enhancer proteins in the flacca fruits implicated the maintenance of photosynthesis in the late expansion phase, which slows down transition to the ripening stage. The majority of antioxidative and stress defence proteins were down-regulated in the flacca fruits, which could be related to the role of ABA in the activity of different antioxidative enzymes as well as in regulating cell wall expansion and the cessation of fruit growth.