Two
cDNA clones coding for
S-adenosyl-L-methionine synthase (
SAMs, EC 2.5.1.6) have been isolated from a cDNA library of
gibberellic acid-treated unpollinated pea ovaries. Both cDNAs were sequenced showing a high degree of identity but coding for different
SAMs polypeptides. The presence of two
SAMs genes in pea was further confirmed by Southern analysis. Expression of the
SAMs genes in the pea plant was found at different levels in vegetative and reproductive tissues. We characterized the expression levels of
SAMs genes during the development or senescence of pea ovaries. Northern analysis showed that transcription of
SAMs genes in parthenocarpic fruits was upregulated by
auxins in the same manner as in fruits from pollinated ovaries. In both pollinated and
2,4-dichlorophenoxyacetic acid-treated ovaries, and benzyladenine, although able to induce parthenocarpic development, did not affect
SAMs mRNA levels. These data are consistent with an active participation of
auxins in the upregulation of
SAMs during fruit setting in pea and suggest that, at the molecular level, parthenocarpic development of pea ovaries is different for
gibberellin- and
cytokinin-treated ovaries than for
auxin-induced parthenocarpic biosynthesis since treatment of the ovaries with
aminoethoxyvinylglycine resulted in a delay of senescence and prevention of
SAMs mRNA accumulation. A possible mechanism for hormonal regulation of
SAMs during ovary development is discussed.