Absorbance Changes in dimY Photoresponse Trichodermalstrains (Table I) were obtained from the collection at the De-partment of Plant Genetics, Weizmann Institute of Science, Rehovot,

Plant Physiol. (1986) 81, 726-7300032-0889/86/8 1/0726/05/$0 1.00/0

Modified Light-Induced Absorbance Changes in dimYPhotoresponse Mutants of Trichodermal

Received for publication November 14, 1985 and in revised form March 3, 1986

BENJAMIN A. HORWITZ2, CHAFIA H. TRAD, AND EDWARD D. LIPSON*Department ofPhysics, Syracuse University, Syracuse, New York 13244-1130

ABSTRACT

A brief pulse of blue light induces the common soil fungus Trichodermaharziaaum to sporulate. Photoresponse mutants with higher light require-ments than the wild type are available, including one class, dimY, withmodified absorption spectra. We found blue-light-induced absorbancechanges in the blue region of the spectrum, in wild-type and dimY mutantstrains. The light-minus-dark difference spectra of the wild type and ofseveral other strains indicate photoreduction of flavins and cytochromes,as reported for other fungi and plants. The difference spectra in strainswith normal photoinduced sporulation have a prominent peak at 440 nm.After actinic irradiation, this 440 nanometer difference peak decaysrapidly in the dark. In two dimY photoresponse mutants, the differencespectra were modified; in one of these, IS44, the 440 nanometer peakwas undetectable in difference spectra. Detailed study of the dark-decaykinetics in LS44 and the corresponding control indicated that the 440nanometer difference peak escaped detection in 1S44 because it decaysfaster than in the control. The action spectrum of the 440 nm differencepeak is quite different from that of photoinduced sporulation. The light-induced absorbance changes are thus unlikely to be identical to theprimary photochemical reaction triggering sporulation. Nevertheless,these results constitute genetic evidence that physiologically relevantpigments participate in these light-induced absorbance changes in Tri-choderma.

Early in the biochemical study ofblue-light responses in plantsand fungi, light-induced absorbance changes were suggested asan assay for the elusive photoreceptors (9-1 1). Photobleachingor a shift in the spectrum of the photoreceptor would be a likelyfirst step in the response chain. Light-minus-dark differencespectra in Dictyostelium, Phycomyces, and Neurospora led tomuch initial optimism that the LIAC3 would be an assay similarto phytochrome photoreversibility in plants. Dictyostelium pseu-doplasmodia respond phototactically to both blue and greenlight. Absorbance changes are induced in vivo by both green andblue light. There is a slowly decaying absorbance change inducedby blue only, and a rapidly decaying green/blue-induced LIAC(1 1). A purified pigment with green/blue LIAC activity matchedthe action spectrum quite well (12). Thus, in Dictyostelium, allavailable data are consistent with the idea that the green/blueLIAC is the primary photoreaction, or at least that the samephotoreceptor mediates the green/blue LIAC and phototaxis

'Supported by National Science Foundation grant DMB-8316458 toE.D.L. B.A.H. was supported by a Weizmann Postdoctoral Fellowship.

2 Present address: Carnegie Institution of Washington, Department ofPlant Biology, 290 Panama St., Stanford, CA 94305-1297.

3Abbreviation: LIAC, light-induced absorbance change.

(12).The action spectrum for Neurospora LIAC suggested a flavin

chromophore (10). A membrane fraction with a LIAC has beenpartially purified from etiolated corn coleoptiles, where blue lightmediates phototropism (7). Acifluorfen, a diphenyl ether herbi-cide, enhanced the LIAC ofan oat coleoptile membrane fraction.Acifluorfen also increased phototropic sensitivity, without affect-ing growth or gravitropism (8).Such LIACs, though, have also been detected in situations

where they are unlikely to be part of a physiologically relevantresponse. In Phycomyces, the major features of the LIAC areidentical in mad photoresponse mutants and normal controls,as well as in HeLa cells (9). In vitro photochemical reactions alsosuggest that the LIAC may be a rather general property of flavinsand cytochromes (13). Much ofthe recent biochemistry has beendone on subcellular fractions from cauliflower inflorescences(14), again without any obvious connection to photophysiology.Despite the widespread occurrence of such LIACs, they mightbe relevant to photophysiology, but coupled to photoresponsesonly in certain organisms or under certain conditions. This viewis supported by results of Klemm and Ninnemann (6) with arhythmic albino strain of Neurospora: the LIAC was correlatedwith blue-light induced conidiation (sporulation) of starved my-celia, but not with light-induced phase shifts of conidiationbands. Brain et al. (1) found a clear correlation between defi-ciency in extramitochondrial Cyt, in the LIAC and in photo-suppression of conidial banding in a poky mutant. In the workon the poky mutant, the complete light-minus-dark differencespectra were not measured, so that a spectral shift might haveescaped attention.Mutants of Trichoderma with defects in photoinduced, but

not stress-induced, conidiation have recently been isolated (5).The dimY complementation group has defective absorption andaction spectra and is thus likely to be defective in the photore-ceptor(s), cryptochrome(s), an unknown blue-absorbing pigmentor pigment class defined only by its action spectrum (4). In thepresent work, we have measured the LIAC ofmutant and controlstrains in search of modified spectra or kinetics. Such differenceswould provide genetic evidence that the LIAC is related to theresponse. Ifthe LIAC is physiologically relevant, it could be usedas an assay for the photoreceptors, and may give some insightinto how they function.

MATERIALS AND METHODSCoulture of Mycelia and Sample Preparation. Trichoderma

strains (Table I) were obtained from the collection at the De-partment of Plant Genetics, Weizmann Institute of Science,Rehovot, Israel. The isolation and characterization of the dimstrains, and formation of heterokaryons, have been described (4,5). Mycelia were grown for 2 to 3 d in total darkness on completeagar medium overlaid with cellophane. The growing region(outer 1 cm) of the colony was harvested with a spatula, and

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LIGHT-INDUCED ABSORBANCE CHANGES IN TRICHODERMA MUTANTS

Table I. Strains of Trichoderma Used in this Work

Strain Phenotype Genotype PreviousAbbreviation'wt Wild type; green sporesLS Requires lysine; white spores lysJ33 W5 lys-

Normal photoresponseRB Requires riboflavin; brown spores ribJ83 Br rib-

Brown sporesLS*RB Green spores heterokaryon [rib-+lys-]

Grows on minimal mediumNormal photoresponse

LS44 Requires lysine; white spores IysJ33 W5 dimY44 lys-44Defective photoresponseExcess yellow pigment

RBIO Requires riboflavin; brown spores rib183 Br dimYlO rib-iODefective photoresponseExcess yellow pigment

LS44*RB10 Grows on minimal medium heterokaryon [riblO+lys-44]Green sporesDefective photoresponseExcess yellow pigment

a Horwitz et al. (4, 5).

gently packed into a cylindrical aluminum cuvet with a quartzwindow at the bottom; the measuring beam was incident fromabove. Samples, 1.5 to 2 mm thick, were prepared under redsafelight, and allowed to stand in the cuvets for 15 min beforemeasurements began. 'Dark-minus-dark' control difference spec-tra showed no wavelength-specific changes.

Actinic Irradiations. The actinic light from a 700 W xenon arclamp (model 991C0010, Canrad-Hanovia, Newark, NJ), wasfiltered through a 3 cm path of 15% copper sulfate solution,followed by a Corning 5-61 broadband-blue glass filter (passband350-520 nm, less than 10% transmission outside this range), anda Schott KG-l heat filter. Balzers B-40 interference filters (9-12nm half-bandwidth) were used to obtain the wavelength depend-ence; for wavelengths above 530 nm, a Schott OG530 cutofffilter was added after the interference filters. The irradiance atthe surface of the sample was calculated from measurementstaken through calibrated neutral density filters, with a photo-diode (UV-100, United Detector Technology, Santa Monica,CA) and an electrometer (model 610C, Keithley Instruments,Cleveland, OH). The photodiode and filters were calibrated witha thermopile (Eppley Laboratory, Newport, RI).

Recording, Storage and Processing of Data. Absorbancechanges and spectra were measured as described by Lipson andPresti (9), with some modifications. Absorption spectra and light-minus-dark difference spectra were obtained with a single meas-uring beam (bandwidth 0.9 nm). The wavelength was scannedin 10 s from 626 to 371 nm. The scans began as quickly aspossible (within 1 s) after the end of actinic irradiation, so that440 nm was reached about 9 s after the actinic beam was blocked.In some experiments (Fig. 3), the scan began at 500 nm; in thisway the earliest possible recording (3 s after actinic light) at 440nm was obtained.The output from the photomultiplier (type 9656B, Thorn-

EMI, Plainview, NY) was converted to a voltage by an electrom-eter amplifier (AD5 1 5LH, Analog Devices, Norwood, MA) andprocessed by a logarithmic amplifier (Analog Devices 755N); theoutput was digitized and stored in a Fabri-Tek model 1062instrument computer (Nicolet Instruments, Madison, WI), andtransferred to a VIC-20 microcomputer (Commodore BusinessMachines, Wayne, PA) which stored the spectra on cassette. Thedata were transferred from the Commodore computer to anApple Ile computer for data analysis and graphics. A secondVIC-20 controlled the wavelength scanning. 'Absolute' absorp-

tion spectra (Fig. la) were calculated by subtraction of thespectrum of eight layers of tissue paper from the uncorrectedspectrum of the sample. An approximation to the second deriv-ative of an absorption spectrum was obtained by second differ-ences: the wavelength was shifted by a small interval, and theoriginal spectrum subtracted from the shifted one (2). Thus the'second derivative' spectrum (actually second difference spec-trum) is still in absorbance units. The successive wavelengthshifts were 10 and 12 nm.For the experiments shown in Figure 2, replicate spectra on

equivalent samples were normalized and then averaged as fol-lows: (a) a prominent feature of the spectrum was chosen,generally a major peak and an adjacent valley, (b) the peak andvalley amplitudes were computed for each spectrum in theappropriate wavelength regions (i.e. the computer program de-termined the maximum value in the vicinity where the peak wasexpected and the minimum value where the valley was expected),(c) the spectrum was scaled and shifted so that the valley occurredat an amplitude of zero and the peak at a value of unity, (d) allsuch normalized spectra (measured on different samples underidentical conditions) were then averaged, and (e) the scale factorsthat were applied in step (c) were averaged to determine the scalebars shown on the figures in absorbance units. The scale factorsand offsets varied considerably from one sample to another,because of changes in thickness and/or packing of the samples.After normalization, though, the shape ofthe spectrum was veryconsistent from sample to sample.

In the dual-wavelength measuring mode, the bandwidth ofthemeasuring light from each monochromator was 5 nm. Theoutput ofthe lock-in amplifier (time constant 0.3 s) was recordedon a strip chart recorder. The two measuring beams, which werealternated by a mechanical chopper (145.7 Hz), passed verticallythrough the sample. The beams were obtained from the samelight source (200 W tungsten halogen lamp; General Electrictype Q6.6A/T4/CL-200W) split to enter the two monochroma-tors, and recombined just before they reached the sample. Abeam splitter and a mirror allowed the actinic beam and bothmeasuring beams to irradiate the entire sample. In order toprotect the photomultiplier, a light-tight shutter was closed dur-ing actinic irradiations. The anode current from the photomul-tiplier was converted to a voltage by a shunt resistance. Thissignal was then fed to the input of a lock-in amplifier (model120, EG&G Princeton Applied Research, Princeton, NJ).

727

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Plant Physiol. Vol. 81, 1986

RESULTS AND DISCUSSION

Light-Induced Absorbance Changes in Mutants and Controls.Trichoderma mycelia gave substantial light-induced absorbancechanges. Light-minus-dark difference spectra recorded fromdark-grown mycelia of two strains are illustrated in Figure lb.The absolute spectra (Fig. la) were similar to those reportedpreviously for these strains (5); the broadened shoulder near 400nm in the dimY strain is due to an overproduced yellow sub-stance, as yet unidentified. Control strains (LS, RB, LS*RB, andthe wild type) had two sharp LIAC peaks at 415 and 440 nm.These difference peaks cannot be explained by a single b-typeCyt, and might indicate electron transfer between cytochromes.In fact, 440 nm seems too long a wavelength for a reduced b Cyt(typically 429 nm), and too short for reduced Cyt oxidase (444nm); perhaps pigments other than Cyt are involved. The broadminimum between 440 and 500 nm is probably due to photo-reduction of flavins. The pattern of the LIAC in the Cyt Soretregion (major peak) in LS44 differs greatly from the control (Fig.lb).The LIAC was altered also in the dimY strain RB10, and in

its heterokaryon with LS44. Second derivatives (strictly speaking,second differences, see "Materials and Methods") of the LIACspectra from replicate samples were averaged and compared fordifferent strains (Fig. 2). Three control strains (LS, RB, and theirheterokaryon) have second derivative peaks in the Cyt Soretregion at 415 and 440 nm, corresponding to the positive peaksin the light-minus-dark difference spectra (e.g. the spectrum ofLS in Fig. lb). The wild type (not shown) was similar to thecontrol strains. The relative heights of the 415 and 440 nmsecond-derivative peaks differed slightly among these strains.

In the dimY strain RB10, the long-wavelength peak in thelight-minus-dark spectrum was shifted to 435 nm. This shift wasalso apparent in the dimY heterokaryon RB0*LS44. In LS44,the sharp 440 nm peak is absent. A small amount of the 440 nmcomponent might account for the shoulder near 430 to 440 nmin the derivative spectrum of LS44. Control heterokaryonsLS*RBIO and RB*LS44 had LIAC spectra (not shown) similarto the controls in Figure 2. The LIAC was defective in bothindependently isolated dimY strains and in their heterokaryon.The altered LIAC is thus another defect associated with the dimY

400 500 600 400 500 600

WAVELENGTH, nmFIG. 1. In vivo absorption spectra and light-induced absorbance

changes in control and in dimY mutant mycelia. LS is a strain withnormal photoresponse; LS44 is a dimY mutant (Table I). a, Spectra ofsamples before irradiation. The scale bars indicate absorbance, relativeto a scattering reference ("Materials and Methods"). b, Light-minus-darkdifference spectra, obtained by subtraction of spectra recorded beforeand immediately after a 60 s exposure to broadband blue light (fluencerate 560 W m2). Scale bars indicate absorbance difference, AA.

JulILSw~~~~~~~

a RB1O*LS4I- U

w

U. .At.1| diY

0.

w

o RB*~~~LS4

w

IL ~ ~ ~ ~ RI

RBOLS44

(dimY)

400 440 480 520 560 600WAVELENGTH, nm

FIG. 2. Second derivatives oflight-minus-dark difference spectra. Theupper three curves are for control strains (normal, photoinduced conidia-tion, but with other genetic markers; Table I); the lower three are fordimY photoresponse mutants. Before the spectra were averaged, eachwas normalized with respect to the largest difference peak ("Materialsand Methods"). Derivative spectra of LS, RB, and RB*LS were dividedby the difference between 440 and 460 nm, RBIO and RBIO*LS44 bythe difference between 435 and 445 nm, and LS44 by the differencebetween 425 and 450 nm. The scale bar represents a AA (secondderivative of the difference spectrum) of about 0.015 absorbance units;the actual peak-to-valley amplitudes for the above wavelength pairs,eSEfor the indicated number of samples, were, in units of 10-( O.D.: LS,41.3M 1.0 (17); RB, 35.9iv3.7 (8); RB*LS, 49.0 ± 5.6 (11); LS44, 31.9by2.7 (18); RBe10,40.1b 4.8 (8); RB40*LS44, 46.6a 2.7(11). Thedotted lines indicate the standard errors of the normalized spectra.

phenotype and the dimY complementation group, which mayrepresent a single gene (4). The nature ofthese mutations cannotbe ascertained without recombination mapping; such mapping,is not yet practicable because Trichoderma, an imperfect fungus,lacks sex and has no parasexual cycle. In any case, the genemight be regulatory, and so could affect photoreception and the

HORWITZ ET AL.728



LIGHT-INDUCED ABSORBANCE CHANGES IN TRICHODERMA MUTANTS

LIAC even if these phenomena were unrelated. Nevertheless, thecorrelation is very suggestive, and worth pursuing biochemically.

Kinetics. We explored the kinetics of the 440 nm differencepeak in LS44 and its corresponding control, LS, to help ascertainwhy this peak was lacking in the difference spectrum of LS44.The spectra in Figures lb and 2 were obtained with dark-grownsamples, and represent the absorbance change induced by thefirst exposure to actinic light. The 440 nm difference peakdecayed within 2 min, while a shorter wavelength componentinduced by the first irradiation was much more stable. Repeatedirradiations given after decay of the 440 nm peak resulted inreversible changes in this component only (Fig. 3). When theusual procedure was followed, the wavelength of the measuringbeam reached 440 nm 8 s after the end of the irradiation. Ashorter scan (starting at 500 nm) was used to obtain the uppercurve in Figure 3b. In this spectrum, a 440 nm peak was apparentin the mutant LS44 approximately 3 s after the end of theirradiation. The result shown in Figure 3b was predicted frommeasurements with the dual-wavelength mode (see below). The440 nm peak is absent from difference spectra of LS44 (Figs. lband 3b) because its decay is almost three times faster in LS44than in the control, LS.We studied the kinetics quantitatively using the dual-wave-

length measurement mode, comparing 440 and 460 nm (Fig. 4).The dark decay of the 440 nm peak in all strains tested was fasterthan the decay recorded at different wavelengths for Phycomyces(half-time 70 s) (9) and Neurospora (half-time 30 s) (10). Thedecay of the 440 nm peak was faster in LS44 than in LS.Furthermore, during the actinic irradiation, the LIAC between440 and 460 nm accumulated faster in LS44 than in LS, thoughthis was difficult to resolve with our apparatus (the manualshutter did not allow exposures shorter than ls). It is clear,though, that LS44 does not require longer exposures than LS.The irradiance dependence of the 440 nm LIAC (AA440 460) wassimilar for mutant and control (Fig. 5). Irradiance-responsebehavior similar to that of LS and LS44 was found for the wildtype and for the control heterokaryon LS*RB (results not shown).

In a series of preliminary experiments done with the wild typeand LS*RB, we found that the 440 nm LIAC saturated quickly,but that the height of the plateau depended on the irradiance.

a MLS(control) b LS44 (dimY)

10.008 10.008a Ba

zmo 4089

400 440 480 400 440 480

WAVELENGTH. nm

FIG. 3. Spectra ofthe reversible LIAC at 440 nm. Absorbance changesare illustrated for samples of LS (a) and LS44 (b) that had alreadyreceived several previous irradiations. A spectrum was recorded after the440 nm LIAC peak had decayed (at least 2 min; Fig. 4). Anotherirradiation was given, a second spectrum recorded, and the differencewas plotted. For each curve, the times between the end of the actinicirradiation (20 s broadband blue at 560 W m-2) and the moment whenthe absorbance was recorded at 440 nm are indicated. The upper twocurves correspond to the half-times for dark decay in each strain (Fig. 4).For the lower curves, the second scan did not reach 440 nm until 40 safter the end of the actinic irradiation.

729

o 60%~~~~~~~~~~

z

CE0< g < j LS44 (dimY)

04812 16 o 0 4TIME,

FIG. 4. Kinetics ofthe 440 nm LIAC. The measuring beam alternatedbetween 440 and 460 nm. The light-on kinetics were inferred from thelevels reached at the end of actinic irradiations of various durations.Different symbols indicate different samples; each point is the average offive replicate recordings. For the dark decay, each point is the average oftwo recordings on the same sample; different symbols are differentsamples. Note change in time scales during and after actinic exposure.The vertical dashed line indicates the half-time for the decay in LS, 8 s.Both time courses are plotted relative to the maximum; the horizontaldashed lines indicate 50%. The half-time of the dark decay in LS44 is 3s.

01.0

< 0.8

ul0Z 0.6m0co a4to

w2a

J-w

1U' 102IRRADIANCE, W m-2

103

FIG. 5. Dependence of the reversible 440 nm LIAC on irradiance.Irradiances of broadband blue light were adjusted with calibrated neutraldensity filters. Exposure time was always 1O s. Each point is the mean offive recordings on each sample; different symbols indicate differentsamples. The inset shows the first three points plotted on a linear scale;the error bars represent SE. Differences between samples can be explainedby different thickness and scattering properties (namely, the samplerepresented by the filled triangles may have been somewhat thicker ormore tightly packed).

Specifically, the half-time for the increase in A at 440 nm (relativeto 460 nm) was about 5 s at the lowest irradiance used; a 40 sexposure at 10 or 20W m-2 gave a change in A indistinguishablefrom that obtained with a 10 s exposure, but still much lowerthan the saturation level obtained at 560 W m-2 (results notshown).

Reciprocity between irradiance and exposure time was there-fore not obeyed (although it might, perhaps, hold at very lowirradiances and short times, for which the signal approached thenoise level). Furthermore, saturation with respect to irradiance

'I I I* 1 I I 1 I I*ON OFF ti

LS (control)

/r 1'.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I

* LS

° LS44-

AD

. . .- . . . . . . .. . . . I . I I I I

tII a a I A .~~~~~~~| . .I.^ .4 !



Plant Physiol. Vol. 81, 1986

was not reached (Fig. 5). Because this behavior precluded com-plete action spectroscopy with fluence-response curves, we ob-tained instead a wavelength-dependence curve. Irradiances weregiven in the linear range of the irradiance-response curve forbroadband blue light (inset, Fig. 5). Both blue and green lightwere active (Fig. 6). No response was detectable at 575 or 606nm, but the irradiance available from our actinic light sourcewas several-fold lower than at 545 nm. These two points havebeen omitted from Figure 6, as the response may have been lostin the noise. The wavelength dependence in Figure 6 may bedistorted relative to the true action spectrum because of themethod used. Even more likely is a significant distortion causedby screening; the O.D. near 420 nm is much higher than in thegreen region (Fig. la).The action spectrum could be refined further by estimates of

screening based on measurements of spectral reflectance andtransmittance. It is unlikely though that, even after correctionfor screening, the LIAC action spectrum will resemble the actionspectrum for sporulation (3). The Phycomyces LIAC (9) alsoshowed more activity (by several orders of magnitude) in thegreen than was expected from the action spectra for phototropismand the light-growth response of sporangiophores. Completeaction spectra for mycelial photoresponses of Phycomyces arenot yet available. Green light was very effective in inducing theLIAC in Dictyostelium pseudoplasmodia. In contrast to Trichod-erma, the action spectrum of the green/blue LIAC in Dictyoste-lium matched the phototaxis action spectrum quite well, withthe possible exception of a screening correction (12).The Trichoderma LIAC, as studied here, does not correspond

quantitatively to the primary phototransduction step in photoin-duced sporulation, for several reasons. First, much more light isrequired: sporulation both of controls and of dimY mutants is

C,)

w 1.0z

w

0.80w

U-

U. 0.6w

w

> 0.4

I-w 0.2:

400 440 480WAVELENGTH. nm

520

FIG. 6. Wavelength dependence of the 440 nm LIAC. The photonirradiance was 80 to 190 mol m-2 s-1, and the responses were alwayswithin the linear range (20% or less of the maximum response inducedby broadband blue, inset, Fig. 5). Exposure time was always 10 s. Thebars represent SE for 10 measurements for each strain; five recordingswere made on each of two samples at each wavelength.

saturated by a 10 s exposure to 10 W m-2 of broadband bluelight, while 50-fold higher irradiances for 10 s could not saturatethe LIAC (Fig. 5). Second, LS and LS44 had the same lightrequirement (with respect to irradiance, Fig. 5) for the LIAC,while, for sporulation, LS44 needed over 15-fold more light thanLS did (4). The time-course ofthe LIAC actually saturated fasterin LS44 than in LS (Fig. 4). A simple first-order photochemicalmodel with dark decay predicts a faster rise-time for a mutantwith faster dark decay, so this is not surprising. Finally, thewavelength dependence in Figure 6 is very different from thatfor sporulation (3). All but the last discrepancy can be explainedby photochemical kinetics: it is likely that a few percent or lessphotoconversion could saturate sporulation. The wavelengthdependence, though, suggests that different pigments mediatethe LIAC and sporulation.

Nevertheless, the modification of the LIAC in the dimY mu-tants is genetic evidence that the LIAC is related to photorecep-tion. Perhaps, under physiological conditions, the heme proteinsand flavins that appear to contribute to the LIAC are part of anelectron transport chain initiated or modulated by light. Someof the interconvertible forms might well accumulate in thick,partly anaerobic samples exposed to very bright light.

LITERATURE CITED

1. BRAIN RD, DO WOODWARD, WR BRIGGS 1977 Correlative studies of lightsensitivity and cytochrome content in Neurospora crassa. Carnegie Inst WashYear Book 76: 295-299

2. BUTLER WL 1972 Absorption spectroscopy of biological material. MethodsEnzymol 24: 3-25

3. GRESSEL J, KM HARTMANN 1968 Morphogenesis in Trichoderma: Actionspectrum of photoinduced sporulation. Planta 79: 271-274

4. HORWITZ BA, J GRESSEL, S MALKIN, BL EPEL 1985 Modified cryptochromein vivo absorption in dim photosporulation mutants of Trichoderma. ProcNatI Acad Sci USA 82: 2736-2740

5. HORWITZ BA, J GRESSEL, S MALKIN 1985 Photoperception mutants of Tri-choderma: mutants that sporulate in response to stress but not light. CurrGenet 9: 605-614

6. KLEMM E, H NINNEMANN 1978 Correlation between absorbance changes anda physiological response induced by blue light in Neurospora. PhotochemPhotobiol 28: 227-230

7. LEONG TY, WR BRIGGS 1981 Partial purification and characterization of ablue light-sensitive cytochrome-flavin complex from corn membranes. PlantPhysiol 67: 1042-1046

8. LEONG TY, WR BRIGGS 1982 Evidence from studies with acifluorfen forparticipation of a flavin-cytochrome complex in blue light photoreceptionfor phototropism of oat coleoptiles. Plant Physiol 70: 875-881

9. LIPSON ED, D PREsTI 1977 Light induced absorbance changes in Phycomycesphotomutants. Photochem Photobiol 25: 203-208

10. MuNoz V, WL BUTLER 1975 Photoreceptor pigment for blue light in Neuro-spora crassa. Plant Physiol 55: 421-426

11. POFF KL, WL BUTLER 1974 Absorbance changes induced by blue light inPhycomyces blakesleeanus and Dictyostelium discoideum. Nature 248: 799-801

12. POFF KL, WL BUTLER 1974 Spectral characteristics of the photoreceptorpigment of phototaxis in Dictyostelium discoideum. Photochem Photobiol20: 241-244

13. SCHMIDT W, WL BUTLER 1976 Flavin-mediated photoreactions in artificialsystems: A possible model for the blue-light photoreceptor pigment in livingsystems. Photochem Photobiol 24: 71-75

14. WIDELL S, C LARSSON 1984 Blue light effects and the role of membranes. InH Senger, ed, Blue Light Effects in Biological Systems. Springer-Verlag,Berlin, pp 177-184

I I I I I I I I . I , I . I

1

- LS(control)° LS44 (dimY)

I . I* . I . I . I . a . . I

730 HORWITsZ ET AL.

IF


Documents

Absorbance Changes in dimY Photoresponse Trichodermalstrains (Table I) were obtained from the collection at the De-partment of Plant Genetics, Weizmann Institute of Science, Rehovot,