Ripening Behavior of the Green Ripe Tomato Mutant

Abstract

The fruit ripening behavior of the green ripe mutant ( Gr ) of tomato ( Lycopersicon esculentum Mill.) was examined. Green ripe fruit are climacteric and evolve increasing amounts of ethylene after harvest; however, the time course for these events is dramatically altered in comparison with ‘Rutgers’. Maximal rates of C 2 H 4 evolution from Gr fruit were achieved 20 days after the initial increase, and 7 to 10 days prior to maximal respiratory rates. Fruit age at harvest did not affect either the rate or the magnitude of these processes. Wavelength scans of pigment extracts from 60 day postharvest Gr fruit indicated low levels of carotenoids. Mutant fruit also remain firm a long time after harvest. Polygalacturonase activity in Gr fruit increases with fruit age, but reaches only 3% to 5% of the total activity in ‘Rutgers’. PG activity was only slightly reduced when extracts were heated to 65°C for 5 min, suggesting that a heat stable isoenzyme of PG is predominant in mature mutant fruit in contrast to ‘Rutgers’ in which 90% to 95% of PG activity in ripe fruit is heat labile under these conditions. When heterozygous, the Gr mutation is dominant in its effects on total PG activity and on the time course from the initiation of C 2 H 4 and respiratory increases to their maximal rates of evolution. The magnitude of other changes in heterozygous mutant fruit was intermediate between normal and homozygous Gr .