Abstract
Seedlings of Phavbitis nil and Chenopodium rubrum flower in response to a single inductive dark
period preceded and followed by continuous fluorescent light. However, when a far-red irradiation
for 1 h or longer was substituted for fluorescent light, the flowering response to an ensuing dark
period could be completely inhibited or enhanced up to threefold depending on when the far-red
exposure commenced.
Evidence of red/far-red photoreversibility established phytochrome as the photoreceptor controlling
these responses. There was no indication of the involvement of photosynthetic pigments.
For P. nil prolonged exposure (1.5-6 h) to far-red radiation during the photoperiod could shorten
(2-3 h) or lengthen (2 h) the duration of darkness required for flowering. The degree of change
depended on whether the far-red radiation was imposed just prior to darkness (shortening) or about
9 h prior to darkness (lengthening). In a similar manner the spectral composition of the photoperiod
influenced the timing during darkness for earliest sensitivity to brief (5 min) red light interruptions.
The shorter the critical dark period, the earlier in darkness the seedlings became sensitive to red
light interruptions of darkness.
It is clear that the form of phytochrome during the photoperiod influences the timing of phytochrome-
linked processes in darkness. Two explanations discussed are a coupling via rhythmic
changes in substrate on which phytochrome acts, and an effect on phytochrome reactions which
alters the timing of Pf, disappearance during a subsequent dark period.
Subject
Plant Science,Agronomy and Crop Science
Cited by
7 articles.
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