The gene pat-2, which induces natural parthenocarpy, alters the gibberellin content in unpollinated tomato ovaries.

We investigated the role of gibberellins (GAs) in the effect of pat-2, a recessive mutation that induces facultative parthenocarpic fruit development in tomato (Lycopersicon esculentum Mill.) using near-isogenic lines with two different genetic backgrounds. Unpollinated wild-type Madrigal (MA/wt) and Cuarenteno (CU/wt) ovaries degenerated, but GA(3) application induced parthenocarpic fruit growth. On the contrary, parthenocarpic growth of MA/pat-2 and CU/pat-2 fruits, which occurs in the absence of pollination and hormone application, was not affected by GA(3). Pollinated MA/wt and parthenocarpic MA/pat-2 ovary development was negated by paclobutrazol, and this inhibitory effect was counteracted by GA(3). The main GAs of the early-13-hydroxylation pathway (GA(1), GA(3), GA(8), GA(19), GA(20), GA(29), GA(44), GA(53), and, tentatively, GA(81)) and two GAs of the non-13-hydroxylation pathway (GA(9) and GA(34)) were identified in MA/wt ovaries by gas chromatography-selected ion monitoring. GAs were quantified in unpollinated ovaries at flower bud, pre-anthesis, and anthesis. In unpollinated MA/pat-2 and CU/pat-2 ovaries, the GA(20) content was much higher (up to 160 times higher) and the GA(19) content was lower than in the corresponding non-parthenocarpic ovaries. The application of an inhibitor of 2-oxoglutarate-dependent dioxygenases suggested that GA(20) is not active per se. The pat-2 mutation may increase GA 20-oxidase activity in unpollinated ovaries, leading to a higher synthesis of GA(20), the precursor of an active GA.

Mitochondrial DNA evolution in experimental populations of Drosophila subobscura.

When two mitochondrial DNA (mtDNA) haplotypes of Drosophila subobscura compete in experimental populations with discrete generations, one or the other approaches fixation, depending on the nuclear background with which they are associated. The approach to fixation, however, is strongly dependent on the effective number of females in the population, Nf. Whether or not the ultimate fate of a given mtDNA haplotype is determined by random genetic drift depends on Nf as well as on the relative fitnesses. Our experimental results show that the mtDNA polymorphisms observed in natural populations are affected by interactions among nuclear polymorphisms, random genetic drift, and direct selection on the mtDNA haplotypes.