Sucrolytic activities in cherry tomato fruits in relation to temperature and solar radiation

A study has been made concerning the influence of two environmental factors (temperature and solar radiation) on sugar content and sucrolytic activity in cherry tomato fruits during the crop cycle. For this, Solanum lycopersicum cv. Naomi plants were grown in an experimental greenhouse. Three fruit samples were taken over the entire production period: the first sampling at the beginning of harvest [85 days after transplanting (dat)], the second at mid-harvest (160 dat), and the third at the end of harvest (229 dat). The values for temperature and solar radiation peaked in the third sampling, coinciding with an increase in lipid peroxidation, without lowering yield with respect to previous samplings. Regarding the sugar content in the cherry tomatoes, our results showed that the increase in temperature and solar radiation diminished the sucrose content at 229 dat and raised the hexoses (glucose and fructose) as well as starch content, produced primarily by the enzyme sucrose synthase. On the contrary, the rest of the enzymes responsible for sucrose degradation, acid and neutral invertases, showed no notable changes in their activity at the end of the crop cycle. In short, our results suggest that the increase in sucrolytic activity, induced mainly by sucrose synthase under these conditions, contributes to the mechanisms of antioxidant defense by supplying precursors (glucose and fructose) of antioxidant compounds in order to restrict the massive accumulation of ROS and thereby avoid the appearance of cell necrosis and reduce yield losses. (C) 2007 Elsevier B.V. All rights reserved.