A new paper presented by University of Pennsylvania researchers reveals that
the plant hormone gibberellin, once believed to promote flower formation in
annual plants also plays a role in inhibiting flowers from forming. Plant
scientists have always believed that short-lived plants, annuals or
bi-annuals, use a different strategy from long-lived plants, perennials, in
regulating flower production.

The study, led by Nobutoshi Yamaguchi and Doris Wagner, looked for new genes
important to the flower-forming process. The team used Arabidopsis thaliana
to find direct targets of the protein LEAFY, known to promote flower
formation. One gene that turned up was called ELA1, which produces a
cytochrome enzyme, known to play a role in breaking down gibberellin. Their
experiments showed that flowers formed much later in plants which lacked
LEAFY. The researchers also found that such plants had high levels of
gibberellin, while plants engineered to produce high levels of LEAFY had
lower levels of the hormone and were also shorter with greater levels of
chlorophyll - characteristics of gibberellin deficiency.

Results suggest that the two transition steps leading plants to produce
flowers both involve gibberellin. While gibberellin promotes the first
transition, when plants stop producing stems and leaves and produce an
inflorescence, it inhibited the second stage, in which flowers were formed.

[www.upenn.edu]