Invertase protein, but not activity, is present throughout development of Lycopersicon esculentum and L. pimpinellifolium fruit

The presence and distribution of invertase is reported in two red fruited and hexose accumulating species of tomato, Lycopersicon esculentum and L. pimpinellifolium, which differ markedly in fruit invertase activity. Using antibodies raised against a highly conserved invertase peptide, all invertase isoforms in green and red tomato fruit were detected and visualized by chemi luminescence and western blotting techniques. Interacellular localization of invertase was examined by electron and light microscopy. Invertase activities were much lower in green fruit than in red fruit from all cultivars. However, invertase protein was evenly distributed between all tissues of green and red fruit in tissue blots that had been extensively treated with preimmune serum that eliminated all non-specific binding. Immune-gold labelling showed that invertase protein was present in the cell wall and vacuole, but not in the cytosol, of epidermal tissue from both species. Invertase protein is present throughout fruit development in tomato. However, the increase in activity during ripening is due to changes in the activation state of the protein rather than the amount of protein present.