Action spectra of the light-growth response of Phycomyces

Abstract

The light-growth response of Phycomyces blakesleeanus (Burgeff) is a transient change in elongation rate of the sporangiophore caused by a change in light intensity. Previous investigators have found that the light-growth response has many features in common with phototropism; the major difference is that only the light-growth response is adaptive. In order to better understand the light-growth response and its relationship to phototropism, we have developed a novel experimental protocol for determining light-growth-response action spectra and have examined the effect of the reference wavelength and intensity on the shape of the action spectrum. The null-point action spectrum obtained with broadband-blue reference light has a small peak near 400 nm, a flat region from 430 nm to 470 nm, and an approximately linear decline in the logarithm of relative effectiveness above 490 nm. The shape of the action spectrum is different when 450-nm reference light is used, as has been shown previously for the phototropic-balance action spectrum. However, the action spectrum of the light-growth response differs from that for phototropic balance, even when the same reference light (450 nm) is used. Moreover, for the light-growth response, the relative effectiveness of 383-nm light decreases as the intensity of the 450-nm reference light increases; this trend is the opposite of that previously found for phototropic balance. The dependence of the lightgrowth-response action spectrum on the reference wavelength, its difference from the phototropic-balance action spectrum, and the reference-intensity dependence of the relative effectiveness at 383 nm may be attributable to dichroic effects of the oriented photoreceptor(s), and to transduction processes that are unique to the light-growth response.

Blue Light Reception in Phycomyces: Red Light Sensitization in madC Mutants

“…7). This observation was in accordance was previously published action spectra for the light-growth response (Delbriick and Shropshire, 1960;Ensminger et al, 1991).…”

“…Acts 108 (1995) [344][345][346][347][348][349][350] 0 Georg Thieme Verlag Stuttgart . New York Action spectroscopy for a variety of these responses has indicated the ubiquitous W/blue light receptor (Corrochano et al, 1988;Delbruck and Shropshire, 1960;Ensminger et al, 1991). Though the photoreceptor of Phycomyces, or to that effect of any other blue light sensitive fungus or plant, has not yet been isolated, several lines of evidence indicate that this receptor system contains flavins and pteridines as chromophores (Galland 1992;Hohl et al, 1992a-c).…”

Growth Rate Fluctuations in Phycomyces Sporangiophores

“…The hypertropic mutant L85 (madH) (15), night-blind mutant Clll (madB), and stiff mutants C285 (madD), C110 (madE), C376 (madF), and C288 (madG) (1) were isolated from the wild type after mutagenesis of spores with N-methyl-N'-nitro-N-nitrosoguanidine. Growth conditions were as previously described (9). Stage IVb sporangiophores, about 2 cm tall, from the second crop were used for all experiments.…”

“…During all experiments, sporangiophores were irradiated bilaterally with 450 nm light at a constant fluence rate of 100 ,uW m-2, calibrated as previously described (9). The growth rate was measured at 10-s intervals with the Phycomyces tracking machine (9,10) at a constant temperature of 200C.…”

“…The growth rate was measured at 10-s intervals with the Phycomyces tracking machine (9,10) at a constant temperature of 200C. Sporangiophores were adapted in the tracking machine chamber for 89.33 min, and the growth rate over the following 170.67 min (1024 measurements) was used for data analysis.…”