The Journal of General Physiology, Vol 84, 739-751, Copyright © 1984 by The Rockefeller University Press
Wavelength dependence of dark adaptation in Phycomyces phototropism
P Galland, AS Pandya and ED Lipson
The wavelength dependence of phototropic dark adaptation in Phycomyces was
studied between 347 and 545 nm. Dark adaptation kinetics were measured for
wavelengths of 383, 409, 477, and 507 nm in the intensity range from 6.2 X
10(-2) to 2 X 10(-7) W X m-2. At these wavelengths, dark adaptation follows
a biexponential decay as found previously with broadband blue light (Russo,
V. E. A., and P. Galland, 1980, Struct. Bonding., 41:71; Lipson, E. D., and
S. M. Block, 1983, J. Gen. Physiol., 81:845). We have found that the time
constants of the fast and slow components depend critically on the
wavelength. At 507 nm, dark adaptation kinetics were found to be
monophasic. The phototropic latency after a step down by a factor of 500
was measured for 19 different wavelengths. Maximal latencies were found at
383, 477, and 530 nm; minimal latencies were found at 409 and 507 nm. With
irradiation programs that employ different wavelengths before and after the
step down, the dark adaptation kinetics depend critically on the sequence
in which the two wavelengths are given. We have found too that not only do
the adaptation kinetics vary with wavelength, but so also do the
phototropic bending rate and the phototropic latencies in experiments
without intensity change. The results imply that more than one
photoreceptor is mediating phototropism in Phycomyces and that sensory
adaptation is regulated by these photoreceptors.
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