Plant Physiol, January 2003, Vol. 131, pp. 359-366

Polyamine Metabolism Is Altered in Unpollinated Parthenocarpic pat-2 Tomato Ovaries¹

Departamento de Biología Vegetal (M.F.), Instituto de Biología Molecular y Celular de Plantas (M.F., K.P., D.A., J.C., J.L.G.-M.), and Centro de Conservación y Mejora de la Agrodiversidad (F.N.), Universidad Politécnica de Valencia, 46022-Valencia, Spain

Facultative parthenocarpy induced by the recessive mutation pat-2 in tomato (Lycopersicon esculentum Mill.) depends on gibberellins (GAs) and is associated with changes in GA content in unpollinated ovaries. Polyamines (PAs) have also been proposed to play a role in early tomato fruit development. We therefore investigated whether PAs are able to induce parthenocarpy and whether the pat-2 mutation alters the content and metabolism of PAs in unpollinated ovaries. Application of putrescine, spermidine, and spermine to wild-type unpollinated tomato ovaries (cv Madrigal [MA/wt]) induced partial parthenocarpy. Parthenocarpic growth of MA/pat-2 (a parthenocarpic near-isogenic line to MA/wt) ovaries was negated by paclobutrazol (GA biosynthesis inhibitor), and this inhibition was counteracted by spermidine. Application of -difluoromethyl-ornithine (-Orn) and/or -difluoromethyl-arginine (-Arg), irreversible inhibitors of the putrescine biosynthesis enzymes Orn decarboxylase (ODC) and Arg decarboxylase, respectively, prevented growth of unpollinated MA/pat-2 ovaries. -Difluoromethyl-Arg inhibition was counteracted by putrescine and GA₃, whereas that of -difluoromethyl-Orn was counteracted by GA₃ but not by putrescine or spermidine. In unpollinated MA/pat-2 ovaries, the content of free spermine was significantly higher than in MA/wt ovaries. ODC activity was higher in pat-2 ovaries than in MA/wt. Transcript levels of genes encoding ODC and spermidine synthase were also higher in MA/pat-2. All together, these results strongly suggest that the parthenocarpic ability of pat-2 mutants depends on elevated PAs levels in unpollinated mutant ovaries, which correlate with an activation of the ODC pathway, probably as a consequence of elevated GA content in unpollinated pat-2 tomato ovaries.