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-amyrins were analysed in tomato (Lycopersicon esculentum Mill.) pericarp during fruit development and ripening. The contents of these isoprenoids in wild-type (cv. Ailsa Craig) fruit were compared with those in fruit of the carotenoid-deficient R-mutant and a transgenic plant containing antisense RNA to a phytoene synthase gene. In both carotenoid-deficient genotypes, a 14-fold reduction in carotene and twofold decrease in xanthophyll content, compared to the wild type, was found in ripe fruit. Immature green fruit from wild-type and R-mutant plants contained similar amounts of the C19-GAs, GA1 and GA20, and their C20 precursor, GA19. Immature fruit from the transgenic plants contained three- to fivefold higher contents of these GAs. In wild-type fruit at the mature green stage the contents of these GAs had decreased to < 10% of the levels in immature fruit. A similar decrease in GA19 content occurred in the other genotypes. However, the contents of GA1 and GA20 in fruit from phytoene synthase antisense plants decreased only to 30% between the immature and mature green stages and did not decrease at all in R-mutant fruit. At the breaker and ripe stages, the contents of each GA were much reduced for all genotypes. The amount of abscisic acid was the same in immature fruit from all three genotypes, but, on ripening, the levels of this hormone in antisense and R-mutant fruit 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 sitosterol, were apparent between all three genotypes during development. Amounts of free sterols of wild type and antisense fruit were greatest during 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.