Abstract
Sporangiophores of Phycomyces blakesleeanus Burgeff that have been grown in darkness and are then suddenly exposed to unilateral light show a two-step bending response rather than a smooth, monotonic response found in light-adapted specimens (Galland and Lipson, 1987, Proc. Natl. Acad. Sci. USA 84, 104–108). The stepwise bending is controlled by two photosystems optimized for the low-and high-intensity ranges. These two photosystems have now been studied in phototropism mutants with defects in genes madA, madB, and madC. All three mutations raise the threshold of the low-intensity (low-fluence) photosystem by about 106-fold and that of the high-intensity (high-fluence) system by about 103-fold. Estimates for the light-adaptation time constants of the low-and high-intensity photosystems show that the mutants are affected in adaptation. In the mutants, the light-adaptation kinetics are only slightly affected in the low-intensity photosystem but, for the high-intensity photosystem, the kinetics are considerably slower than in the wild type.
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Abbreviations
- WT:
-
wild type
References
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Palit, A., Galland, P. & Lipson, E.D. High-and low-intensity photosystems in Phycomyces phototropism: Effects of mutations in genes madA, madB, and madC . Planta 177, 547–553 (1989). https://doi.org/10.1007/BF00392623
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DOI: https://doi.org/10.1007/BF00392623