Endogenous control of flowering
Many plants show a facultative response to environmental conditions that induce flowering. Therefore, they flower even if not exposed to inductive conditions. For example, summer annuals will flower eventually under short days, even if not exposed to inductive long-day conditions. Similar, in genetic terms, no single gene mutation prevents transition to flowering of Arabidopsis.
This suggests that parallel pathways, which include endogenous control developmental mechanisms, ensure flowering occurs even in the absence of a promotive environmental condition. In Arabidopsis, these involve the autonomous flowering pathway, growth regulators, and probably other so far undefined pathways.
The autonomous pathway includes genes that promote the floral transition under both short and long days. The growth regulators gibberellins have a strong effect on flowering time in Arabidopsis and other rosette plants (Lang, 1965) . In Arabidopsis gibberellins have an inductive effect, especially when plants are grown in short-day conditions (Koornneef and van der Veen, 1980; Koornneef et al., 1985).
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