HORMONAL-REGULATION OF S-ADENOSYLMETHIONINE SYNTHASE TRANSCRIPTS IN PEA OVARIES

Two cDNA clones coding for S-adenosyl-L-methionine synthase (SAMs, EC2 .5.1.6)have been isolated from a cDNA library of gibberellic acid-trea ted unpollinated pea ovaries. Both cDNAs were sequenced showing a high degree of identity but coding for different SAMs polypeptides. The pr esence of two SAMs genes in pea was further confirmed by Southern anal ysis. Expression of the SAMs genes in the pea plant was found at diffe rent levels in vegetative and reproductive tissues. We characterized t he expression levels of SAMs genes during the development or senescenc e of pea ovaries. Northern analysis showed that transcription of SAMs genes in parthenocarpic fruits was upregulated by auxins in the same m anner as in fruits from pollinated ovaries. In both pollinated and 2,4 -dichlorophenoxyacetic acid-treated ovaries, an induction of SAMs mRNA levels was detected at the onset of fruit development. Gibberellic ac id and benzyladenine, although able to induce parthenocarpic developme nt, did not affect SAMs mRNA levels. These data are consistent with an active participation of auxins in the upregulation of SAMs during fru it setting in pea and suggest that, at the molecular level, parthenoca rpic development of pea ovaries is different for gibberellin- and cyto kinin-treated ovaries than for auxin-induced parthenocarpic fruits. In senescing ovaries, SAMs mRNA levels also increased, probably associat ed with ethylene biosynthesis since treatment of the ovaries with amin oethoxyvinylglycine resulted in a delay of senescence and prevention o f SAMs mRNA accumulation. A possible mechanism for hormonal regulation of SAMs during ovary development is discussed.