EXPRESSION OF ACID INVERTASE GENE CONTROLS SUGAR COMPOSITION IN TOMATO (LYCOPERSICON) FRUIT

A wild tomato species, Lycopersicon chmielewskii, accumulates high lev els of soluble sugar in mature fruit and, unlike the domesticated toma to species, Lycopersicon esculentum, accumulates sucrose rather than g lucose and fructose. Genetic and biochemical analyses of progeny resul ting from a cross of L. chmielewskii with L. esculentum have previousl y indicated that the trait of sucrose accumulation is controlled by a single recessive gene and is associated with low levels of acid invert ase protein in the developing fruit. Analysis of progeny from the BC2F 3 generation from the L. esculentum x L. chmielewskii cross revealed t hat sucrose-accumulating fruit accumulate sugar in two phases correspo nding to fruit expansion and fruit maturation and that the majority of the sucrose was stored in the latter phase after the fruit had reache d maximum size. The only significant enzymic difference between the su crose-accumulating and hexose-accumulating fruit was the lack of acid invertase activity in sucrose-accumulating fruit. Sucrose phosphate sy nthase activity did not increase in the sucrose-accumulating fruit dur ing late development when the rate of sucrose accumulation increased. The lack of acid invertase activity in sucrose-accumulating fruit was correlated with inheritance of the L. chmielewskii acid invertase gene and the absence of acid invertase mRNA in developing fruit. This sugg ests that the L. chmielewskii invertase gene is transcriptionally sile nt in fruit and that this is the basis for sucrose accumulation in pro geny derived from the interspecific cross of L. esculentum and L. chmi elewskii.