Fate of Radioactive Gibberellin A1 in Maturing and Germinating Seeds of Peas and Japanese Morning Glory

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Radioactive gibberellin A(1) ((3)H-GA(1)) was injected into excised fruits of peas and Japanese morning glory. These were then grown in sterile culture to maturity and the label was followed in the seeds during further development and subsequent germination. During development of both pea and morning-glory seeds a large part of the radioactivity became associated with the aqueous fraction, while another part of the (3)H-GA(1) was converted into 2 new, acidic, biologically active compounds, designated X(1) and X(2). A relatively small part of the neutral compounds could be converted back to (3)H-GA(1), X(1), and X(2) by means of mild acid hydrolysis. During germination of pea and morning-glory seeds, part of the bound compounds was released in the form of (3)H-GA(1), X(1) and X(2) while, particularly during rapid seedling growth, a further conversion of (3)H-GA(1), mainly to X(1), took place. In pea seedlings, growth during the first 2 to 3 days after imbibition was not affected by Amo-1618, an inhibitor of gibberellin biosynthesis. This, in conjunction with the findings on the interconversions between free and bound (3)H-GA(1) suggests that, at least in peas, early seedling growth may at least partly be regulated by gibberellins released from a bound form which was formed during seed development.