The Tomato Fruit: Import, Growth, Respiration and Carbon Metabolism at Different Fruit Sizes and Temperatures

Abstract

Measurements of a complete carbon balance sheet over a 48 h period for growing tomato fruits at different fruit sizes and temperature have been carried out. The rates of carbon import, respiration, and growth have been calculated and related to each other and to the levels of certain carbon metabolites in the fruit. It was found that there is an excellent linear relationship between the import rate and the sucrose level in the fruit, consistent with the hypothesis that, for the tomato fruit, carbon flows down the sucrose concentration gradient at a rate proportional to the gradient. This agrees with the findings of Mason and Maskell in cotton. Moreover, the resistance to transport was relatively independent of fruit size and temperature. The usual analysis of respiration in terms of growth and maintenance components allowed the determination of conversion efficiencies and maintenance coefficients for different fruit sizes and temperatures. As observed by other authors with other plants, the growth conversion efficiencies were temperature-independent, whereas the maintenance coefficients were strongly temperature-dependent. The overall conversion efficiency was optimum at 25°C. The specific growth rate and the starch level in the tomato fruit were found to be related.