Phytochrome-mediated branch formation in protonemata of the mossCeratodon purpureus |
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Authors: | Takatoshi Kagawa Tilman Lamparter Elmar Hartman Masamitsu Wada |
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Institution: | (1) Laboratory for Photoperception and Signal Transduction, FRP, RIKEN Institute, Wako, 351-01 Saitama, Japan;(2) Institute for Plant Physiology and Microbiology, Berlin Free University, D-14195 Berlin, Germany;(3) Department of Biology, Faculty of Science, Tokyo Metropolitan University, Hachioji, 192-03 Tokyo, Japan |
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Abstract: | We have analyzed light induction of side-branch formation and chloroplast re-arrangement in protonemata of the mossCeratodon purpureus. After 12 hr of dark adaptation, the rate of branch formation was as low as 5%. A red light treatment induced formation of
side branches up to 75% of the dark-adapted protonema. The frequency of light induced branch formation differed between cells
of different ages, the highest frequency being found in the 5th cell, the most distal cell studied from the apex. We examined
the effect of polarized light given parallel to the direction of filament growth. The position of branching within the cell
depended on the vibration plane of polarized red light. Branch formation was highest when the electric vector of polarized
light vibrates parallel to the cell surface and is fluence rate dependent. The positional effect of polarized red light could
be nullified to some extent by simultaneous irradiation with polarized far-red light. An aphototropic mutant,ptr116, shows characteristics of deficiency in biosynthesis of the phytochrome chromophore and exhibits no red-light induced branch
formation. Biliverdin, a precursor of the phytochrome chromophore, rescued the red-light induced branching when added to the
medium, supporting the conclusion that phytochrome acts as photoreceptor for red light induced branch formation. The light
effect on chloroplast re-arrangement was also analyzed in this study. We found that polarized blue light induced chloroplast
re-arrangement in wild-type cells, whereas polarized red light was inactive. This result suggests that chloroplast re-arrangement
is only controlled by a blue light photoreceptor, not by phytochrome inCeratodon. |
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Keywords: | Blue light photoreceptor Branching Ceratodon purpureus Chloroplast movement Phytochrome (action dichroism) |
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