Dj. Bagnall et Rw. King, Phytochrome, photosynthesis and flowering of Arabidopsis thaliana: photophysiological studies using mutants and transgenic lines, AUST J PLAN, 28(5), 2001, pp. 401-408
A number of phytochrome mutants have been examined for involvement in high
irradiance (HIR) or red/far-red (R/FR) end-of-day (EOD) photoresponses duri
ng flowering of the long-day (LD) plant, Arabidopsis thaliana (L.) Heynh. A
large component of phytochrome A (phyA) response is shown to involve an in
direct effect via photosynthesis. When grown autotrophically in soil at a l
ow irradiance (80 mu mol m(-2) s(-1)), the phyA-211 mutant flowered extreme
ly late compared with wild type and its leaf area was halved, both effects
being reversed by increase in photosynthetic irradiance. Supplying sucrose
via agar led to very early flowering with little indication of an additiona
l direct phyA HIR. For light-stable phytochrome apoprotein mutants (phyB, p
hyD) or chromophore mutants (hy1, hy2), flowering was early and R/FR photor
eversible EOD response was erased. Conversely, flowering was delayed in a t
ransgenic line overexpressing the PHYB apoprotein. The FR EOD promotion of
flowering via phyB was retained in darkness, brief night interruptions mimi
cking LD response. This novel finding emphasizes the importance of phyB-lik
e phytochromes, with phyA acting indirectly. Whether phyB influences time m
easurement remains uncertain as we found no rhythmicity in this response to
night interruptions. Overall, the role(s) of phytochromes in the regulatio
n of flowering of Arabidopsis include EOD phyB-type response, a minor phyA
photoperiodic response, and a large indirect phyA effect involving photosyn
thesis.