Polyamine pattern during flower development in the parthenocarpic fruit (pat) mutant of tomato

Polyamine (PA) pattern was investigated in floral organs of Lycopersicon esculentum Mill. plants at four developmental stages from floral bud until 2 days after anthesis. Differences in putrescine (put), spermidine (spd) and spermine (spm) content, both free and conjugated, were evaluated in a control line (WT) and in the parthenocarpic fruit (pat) mutant. PA content turned out to be quite similar in WT and pat mutant ovaries, but the two lines showed a different PA pattern throughout flower development. A net accumulation of PAs, in particular spd and spm, was observed in concomitance with pre‐anthesis floral stages in pat mutant ovaries, while in control plants the PA pattern did not change significantly during the developmental stages considered. These differences seem to be strictly related to the physiological events that initiate ovary development, which have been shown to be precocious in the mutant ovaries and occurring at pre‐anthesis stages. The number of pericarp cell layers indeed increase in parthenocarpic ovaries at the stage of flower opening, and mitotic activity was followed by cell extension, as demonstrated by the increase in pericarp cell diameter. A decrease in free PA levels and an increase in the conjugated pool were associated with the initiation of cell expansion. The pattern of ornithine decarboxylase (ODC; EC 4.1.1.17), arginine decarboxylase (ADC; EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.1) gene expression, as well as the respective enzyme activities, were also analysed during development. The lack of correlation between transcript levels and enzyme activity suggests that post‐transcriptional control mechanisms must be acting in the regulation of biosynthetic genes.