THE EFFECT OF REDUCED ACTIVITY OF PHYTOENE SYNTHASE ON ISOPRENOID LEVELS IN TOMATO PERICARP DURING FRUIT-DEVELOPMENT AND RIPENING

Carotenoids, gibberellins (GAs), sterols, abscisic acid and beta-amyri ns were analysed in tomato (Lycopersicon esculentum Mill.) pericarp du ring fruit development and ripening. The contents of these isoprenoids in wild-type (cv. Ailsa Craig) fruit were compared with those in frui t of the carotenoid-deficient R-mutant and a transgenic plant containi ng antisense RNA to a phytoene synthase gene. In both carotenoid-defic ient genotypes, a 14-fold reduction in carotene and twofold decrease i n xanthophyll content, compared to the wild type, was found in ripe fr uit. Immature green fruit from wildtype and R-mutant plants contained similar amounts of the C-19-GAs, GA(1) and GA(20), and their C-20 prec ursor, GA(19). Immature fruit from the transgenic plants contained thr ee- to fivefold higher contents of these GAs. In wild-type fruit at th e mature green stage the contents of these GAs had decreased to < 10% of the levels in immature fruit. A similar decrease in GA(19) content occurred in the other genotypes. However, the contents of GA(1) and GA (20) in fruit from phytoene synthase antisense plants decreased only t o 30% between the immature and mature green stages and did not decreas e at all in R-mutant fruit. At the breaker and ripe stages, the conten ts of each GA were much reduced for all genotypes. The amount of absci sic acid was the same in immature fruit from all three genotypes, but, on ripening, the levels of this hormone in antisense and R-mutant fru it were ca. 50% of those in the wild type. Quantitative differences in the amounts of the triterpenoid beta-amyrins, total sterols, as well as individual sterols, such as campesterol, stigmasterol and sitostero l, were apparent between all three genotypes during development. Amoun ts of free sterols of wild type and antisense fruit were greatest duri ng development and decreased during ripening, whereas the opposite was found in the R-mutant. This genotype also possessed less free sterol and more bound sterol in comparison to the other varieties. These data provide experimental evidence to support the concept of an integrated metabolic relationship amongst the isoprenoids.