The presence of a phytochrome-mediated phenomenon
is evidenced in the photoreaction that can
be induced by exposure to red light and reversed by
following far-red light exposure during the dark period
(for review see Thomas and Vince-Prue, 1997).
Parker et al. (1946) and Downs (1956) found that nightbreak
with red light inhibits flowering of soybean. In the
present study, it was found that effects of night-break
after flowering also depend on whether R or FR is given
as the final exposure in a series of R and FR light interruptions
of the dark period. This phenomenon is similar
to that reported for other Pfr-mediated responses (for
review see Thomas and Vince-Prue, 1997). Final exposure
to red light delayed or inhibited the reproductive
development of Zigongdongdou, and the effects
of red light could be reversed by exposure to far-red
light. It is confirmed that the response of soybean to
postflowering daylength is a typical phenomenon of
photoperiodism. Based on previous (Han and Wang,
1995) and current results, it can be concluded that photoperiod
responses of soybean exist from emergence
to maturation, and phytochromes are the receptors of
photoperiod signals throughout the whole life cycle of
soybean. That is, soybean has the similar signal receiving
mechanism before and after flowering.