Action and Transmission Spectra of Phycomyces

Abstract. A method has been developed whereby the second positive phototropism can be observed separately from the first positive and negative phototropic responses w-hioh also oocur in oat coleoptiles. Although the second positive phototropic response has often been referred to as the base response, photoreception for it is shown to occur mainly in the apical 3 mm of the coleoptile. The Bunsen-Roscoe reciprocity law, so typical of first positive phototropism, does not apply to the second positive responses, and the amount of curvature increa.ses linearly with the duration of the stimulus. However, although this linear proportionality between stimulus duration and response is the major factor determining response at all intensities tested, the inten,sity of the stimulus does influence the Tesponse somewhat. The action spectrum for the response shows no activity above 510 nm and 'has peaks at 375 and 450 nm. In all but one particular it closely resembles the aotion spectrum ifor the first positive phototropism, and it is conoluded that the same, or similar, pigments may well be the photoreceptors for both types of response. The identity of this blue light absorbing pigment is not known.De-spite the availability of action spectra for the first positive phototropism in oats (15,17). the photoreceptor for this response has not been definitely characterized (9,17). Furthermore, the earlx experiments on phototropism demonstrated that in addition to first positive phototropic curvatures, oat coleoptiles also exhibit negative and second positive types of response (1, 4). From a study of th-e doseresponse curves for phototropism in Avena and of theoretical models for these data, Zimmerman and Briggs (19,20) suggested that Avena coleoptiles possess 3 different photoreceptor systems for the 3 types of phototropic response-first positive, negative, and second positive. If this be the case, then the photoreceptive pigment for the second positive type of curvature would he di'fferent from that for the first positive phototropism and might be identified from an action spectrum for the secolnd positive response. For this reason, and in order to characterize the little-known second positive response more clearly, the present experiments on second positive p)hototropism in coleoptiles of Are(nMa wer-e undertaken.Although the second positive phototropic response, which occurs with large stimulus energies or long stimulus durations, has not beeli extensively studied, there are strong indications that the B3unsen-Roscoe reciprocity law, which holds for first positive phototropism, is not applicable to it (2, 5. 17 ((20) subtracted the responses predicted by their theor-etical models for first positive and negative l)hototropism from their phototropic dose-response curves, the remaining responses, assume(d to be of the second positive type, increased linearly xvith stimulus duration and were not affected by a 10-fol(d vtariation in intensity. Unfortunately the overlap of first positive responces bv second positive otnes when low i...

Section: Methodsmentioning

confidence: 99%

Second Positive Phototropism in the Avena Coleoptile

Everett¹,

Thimann²

1968

“…These responses include: the stimulation of carotene biosynthesis in Fusarium aquaeductuum (21), stimulation of oxygen uptake in Chlorella pyrenoidosa (20), potentiation of oxygen evolution in Acetabularia crenulata (29), plastid movement in Lemna trisulca (35), retardation of flower opening in Oenothera (22), phototropic responses of Avena coleoptiles (31), polarotropic response of chloronema of the fern Dryopteris filix-mas (27), and polarotropism of Liverwort germ tubes (28), and phototropic bending of sporangiophores of Phycomyces (10) and Pilobolus (19). Thimann (30) noted that the action spectra of some responses are similar showing peaks near 445 nm, 472 nm, a shoulder at 425 nm, minima at 400 nm and 460 nm with a steep fall to nearly zero from 510 to 550 nm.…”

Section: Resultsmentioning

confidence: 99%

Action Spectrum of the Photoinduced Sexual Stage in the Fungus Nectria haematococca Berk. and Br. var cucurbitae (Snyder and Hansen) Dingley

Curtis¹

1972

An action spectrum was determined for the photoinduced formation of perithecia in a homothallic strain of Nectria haematococca Berk. and Br. var. cucurbitae (Snyder and Hansen) Dingley. Dose-response curves for perithecial formation were obtained from 340 to 510 nanometers at 10-nanometer intervals. Radiation longer than 510 nanometers was not effective for inducing perithecial formation. The action spectrum indicated peaks of activity near 360, 440, and 480 nanometers with shoulders near 420 and 460 nanometers. Minima occurred near 350 nanometers, 390 to 410 nanometers, and 470 nanometers. The general shape of this action spectrum appears to be similar to those obtained for many different near ultraviolet-blue-sensitive organisms in which a flavoprotein molecule was postulated to be the photoreceptor.Previous research has shown that a photorequirement exists for proper development of asexual and sexual reproductive structures in several closely related strains of the fungus Nectria haematococca Berk. and Br. var. cucurbitae (Snyder and Hansen) Dingley (2,8,9,25,33 Baker (2) found that light intensity in particular had a marked effect on the production of the sexual (perithecia) stage. Of three intensities used, the optimal intensity for stimulating the production of perithecia in heterothallic strains was 190 to 195 ft-c.In a more comprehensive study of the light requirement, Curtis (8) found a broad optimal range of intensity for the production of perithecia from 50 to 250 ft-c. Darkness or higher intensities of irradiation greatly inhibited the formation of perithecial primordia and perithecia. In addition, a region of spectral sensitivity in the near UV-blue portion of the spectrum was found for two heterothallic strains and a homothallic strain.

“…absorbing pigment in these fungi is different from the above mentioned near UV-and blue-absorbing pigment(s (4,6). In some action spectrum, the near UV peak and 7.…”

Section: Discussionmentioning

confidence: 99%

Perithecial Formation in Gelasinospora reticulispora

Inoue

Furuya²

1975

MATERIALS AND METHODS Action spectra for photoinduction of perithecia after different lengths of dark period were determined with apically growing mycelium of a sordariaceous fungus Gelasinospora reticulispora. When hyphae were exposed to monochromatic light in near ultraviolet and visible regions, reciprocity between intensity and exposure time was observed within the range of incident energy used. The resulting action spectrum determined after a dark period of 48 hours showed a peak at 460 nm with shoulders at 420 and 480 nm and another peak at 370 nm, indicating minima at 410, 430, and 470 nm. After 72 hours darkness the spectrum was very similar to the above, except that the major peak shifted to 450 nm and the near ultraviolet region was somewhat less effective. In both cases, wavelengths longer than 520 unm showed no effect.In addition, when irradiated with colored lamps, near ultraviolet light was relatively less effective after the 72-hour dark period than after the 48-hour dark period. The reason for this phenomenon is discussed.Sporulation of many Ascomycetes can be stimulated by exposing cultures to light (12). Leach (9) has pointed out that although the light relations of very few species have been studied precisely there is some evidence that suggests the possibility of two distinct groups; one group which is stimulated to ascocarp formation by only near UV wavelengths and another which responds to both blue and near UV wavelengths.The pyrenomycete fungus Gelasinospora reticulispora produced perithecia (sexual reproductive organs) by a brief exposure to blue and near UV light given after an inductive dark period, and lengthening of the dark period resulted in a shift of the effective range from near UV to blue (7). The inductive light was effective only with hyphae reaching the photobiologically distinguishable stage III (7). The reason for this shift of effective wavelength was obscure, and the precise property of the photoreceptor molecule was unknown.The present study aims to determine action spectra for the photoinduction of perithecia in G. reticulispora after different periods of dark incubation and to make clear the reason for the shift of effective wavelength.