Abstract
Gibberellin A4 (GA4) can substitute for light in the germination of Grand Rapids lettuce seeds. Seeds imbibed in [3H]GA4 do not convert this to other GAs prior to, or immediately following, visible germination: thus GA4 alone can promote radicle expansion. Abscisic acid inhibited [3H]GA4-induced germination, but did not significantly affect [3H]GA4 uptake or metabolism during germination. 6N-benzyladenine overcame the inhibitory effect of abscisic acid and increased [3H]GA4 uptake, although radicle emergence was delayed somewhat.
During hypocotyl extension there was a large conversion of [3H]GA4 to [3H]GA1 in light or darkness, the major conversion site being the growing root. Hypocotyls of dark-grown seedlings contained more [3H]GA1 than those of light-grown seedlings. The apparent inability of exogenous GA1 to promote greater hypocotyl extension than GA4 is related to its poorer uptake. Abacisic acid markedly inhibited hypocotyl expansion, root growth, and the conversion of [3H]GA4 to [3H]GA1.
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Selected References
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