ACTION SPECTRA FOR PHOTOTROPIC BALANCE IN Phycomyces blakesleeanus: DEPENDENCE ON REFERENCE WAVELENGTH and INTENSITY RANGE

Abstract— Action spectra for phototropic balance of Phycomyces blakesleeanus sporangiophores were measured for various reference wavelengths and intensity ranges. Balance action spectra were made at fluence rates of 10^-4 W m^-2 with reference wavelengths of 450 nm, 394 nm, 507 nm, and broadband blue light. For broad-blue light and 450 nm light as references, typical flavin-like action spectra were found with a ma jor peak at 455 nm, a secondary peak at 477 nm, and a minor peak at 383 nm; these peaks are wider for broad blue than for 450 nm light. With the 394 nm reference, there is a major peak at 455 nm, a secondary peak at 477 nm and a minor peak at 394 nm. An action spectrum with 507 nm reference has a major peak at 455 nm and a minor peak at 383 nm, but no peak at 477 nm. A balance action spectrum was made with 450 nm reference light near threshold intensity (2 times 10^-8 W m^-2); there, the 386 nm peak is greatly reduced, while the 455 nm peak is enhanced. The intensity dependence of the 386 nm peak was studied in detail for reference light of 450 nm. We found that the relative quantum efficiency of the 386 nm light increases with the logarithm of the 450 nm fluence rate; in the high intensity range (0.3 W m^-2) the relative quantum efficiency of the 386 nm light is 1.3 and approaches zero at 10^-9 W m^-2. These findings indicate that P. blakesleeanus phototropism is mediated by multiple interacting pigments or by a photochromic photoreceptor.     

LIGHT INDUCED FLUORESCENCE SPECTRAL CHANGES IN NATIVE PHYTOCHROME FROM Secale cereale L. AT LIQUID NITROGEN TEMPERATURE

Abstract— Fluorescence spectra of native rye phytochrome were determined under different light conditions at liquid nitrogen temperature. Fluorescence spectrum of the red-light-absorbing form (Pr) had a major peak at about 685 nm (14 600 cm⁻¹) and a broad sub-peak at about 515 nm (19 400 cm⁻¹). The peak height at 685 nm was reduced by irradiation with monochromatic light of 640 nm, and a new peak became obvious at about 702 nm (14250 cm⁻¹). This spectral change was almost completely reversed by subsequent irradiation with 700-nm light. Fluorescence spectrum of the photoequilibrium mixture of Pr and far-red-light absorbing form under continuous red light showed a sharp peak at about 685 nm having a peak height ca. 12% of Pr, and a broad sub-peak at about 508 nm (19 700 cm⁻¹). Light of 730 nm did not reduce the peak height at about 685 nm but induced a new shoulder at about 699 nm (14300 cm⁻¹). Monochromatic light of 640 and 700 nm given following the light of 730 nm could not reverse the spectral change at 699 nm induced by the irradiation with 730-nm light. Fluorescence spectrum of Pr in partially degraded phytochrome was similar to that in native phytochrome but the peak position in the red region was shifted by about 5 nm (100 cm⁻¹) to the blue.     

PHOTOBIOLOGIE DU MÉSOCOTYLE D''AVOINE-III. DOUBLE EFFET DE LA LUMIÈRE BLEUE

Abstract— Using excise sections of oat first-internodes, a dual effect of blue light can be demonstrated on elongation when the sections are first irradiated in distilled H₂O, then incubated with gibberellic acid (GA). At low light energies (230 ergs/cm² per sec, for 2 min), a pretreatment with blue light enhances the GA effect above the elongation it can produce in the dark. At high energies (650 ergs/cm²/sec for 45 min), the same wavelengths cause an inhibition of the GA-induced elongation. An action spectrum for the two effects show a maximum near 435 mμ in both cases. Neither light effect is visible when indoyl-3-acetic acid is used instead of GA. Several physiological effects distinguish the two blue effects. The promotive effect is most marked in the young regions of the mesocotyl, whereas the maximum inhibitive effect is located in slightly older tissues. Time-course experiments showed that the promotive effect is partly due to an extension of the duration of elongation. The inhibitory effect is only temporary and vanishes about 30 hr after the beginning of the experiment. The promotive effect of blue light resembles the effect of far-red light, but the former can be observed with gibberellins A₂, A₄, A₅, A₆ and A₇ which are practically inactive after an irradiation with far-red light. The inhibitory effect of blue light is different from the red-light effect as shown by the time-course experiments.     

COMPARATIVE ANALYSES OF ACTION SPECTRA OF GLYCOLATE EXCRETION ("PHOTORESPIRATION") AND PHOTOSYNTHESIS IN THE BLUE-GREEN ALGA AN ACYSTIS NIDULANS

Abstract. The action spectra were determined by measuring photosynthetic H¹⁴CO^-₃-fixation and ¹⁴C-glycolate excretion to the medium during 15 min exposure to light at 15 different wavelengths in the visible region using interference filters and a 2500 W high pressure Xe lamp at a constant photon flux of about 1.51 × 10¹⁹ quanta m^-2.s^-1 at all wavelengths.
When plotted on relative scales the action spectrum of glycolate excretion lies below that of photosynthesis at all wavelengths shorter than 517 nm. As glycolate excretion had an exponential relationship to photosynthetic rates, different methods were used to analyze for a specific blue light effect which demonstrated that the relative amount of glycolate excretion was depressed by blue light compared with that by green and red. The greatest difference was observed around 460–480 nm. However, on statistical grounds it is not permitted to draw a difference spectrum which might indicate the absorption characteristics of pigment(s) involved.
A hypothesis is discussed assuming that some glycolate is consumed in an oxidation process for supply of electrons to Photosystem I when Photosystem II is poorly excited in the blue region of the spectrum, which was the case for Anacystis used in the present investigation.     

THE QUANTUM EFFICIENCY FOR THE INTERPHOTOCONVERSION OF THE BLUE and PINK FORMS OF PURPLE MEMBRANE

When the cations bound to purple membrane are removed it turns blue, and when this blue membrane is irradiated its color changes to pink. Irradiation of pink membrane leads to the reformation of blue membrane. We have determined that the quantum efficiency for the formation of pink membrane from deionized blue membrane is 1.6 ± 0.6 ± 10 ⁴ at 0^oC, pH 5.0. We also found that the quantum efficiency for the back photoconversion, i.e. the formation of blue membrane from pink membrane, is 8.8 ± 1.6 ± 10^-3 at 0^oC, 55 times greater than that of the forward photoconversion reaction. The extinction coefficients of the pink membrane and blue membrane were determined to be 44 500 ± 670 cm^-1 M^-1 at 491 nm and 54 760 ± 830 cm^-1 M ^-1 at 603 nm, respectively, assuming light-adapted purple membrane is 63 000 cm^-1 M ^-1 at 568 nm. The quantum efficiency for forming pink membrane from blue membrane is much lower than that for forming the photointermediate of the blue membrane's photocycle. Their relationship is similar to that of light-adaptation and photocycle of the dark-adapted purple membrane.     

THE ACTION SPECTRUM OF DAPHNIA MAGNA (CRUSTACEA) PHOTOTAXIS IN A SIMULATED NATURAL ENVIRONMENT

Abstract— The action spectrum of phototaxis in Daphnia magna (Crustacea) was measured in a chamber which simulated a natural angular distribution of underwater light. A 17% step-down in irradiance was used to stimulate the phototactic response at all wavelengths and irradiances tested. Peaks in the spectral response curves depended on the fluence rate to which the zooplankton were acclimated. The wavelength of maximum response (Z_max) shifted from yellow-green at the highest acclimation fluence rate (5.1 × 10⁻² Wm⁻²) to blue-violet at moderate rates. At low acclimation fluence rates, the blue-violet maximum was retained and another maximum developed in the red. At the lowest fluence rate (1.6 × 10⁻⁵ Wm⁻²), the blue-violet and red maxima were lost and another maximum developed in the near ultraviolet. The action spectrum indicates the presence of three, and possibly four, photopigments with Z_max, at ∼405, 440, 570 and 690nm. The 440 and 690nm maxima may belong to the same photopigment; however, this was not tested. Changes in zooplankton swimming speed, caused either by large changes in irradiance or by mechanical stimuli, were accompanied by changes in the strength of the phototactic response to the −17% stimulus at any irradiance level for white and monochromatic light, and indicated the presence of a mechanism connecting swimming speed and photosensitivity.     

PHOTOVOLTATC EFFICIENCIES OF MICROCRYSTALLINE AND ANHYDROUS CHLOROPHYLL a

Abstract— A thin layer of chlorophyll a (around 2000 Å). a p -type organic semiconductor. was sandwiched between two different metals. aluminum and silver. We used the photovoltaic effect in order to study the efficiency of light conversion by the crystalline and anhydrous forms of Chl a . When the photovoltaic cell is illuminated through the semi-transparent aluminum electrode. an action spectrum similar to the visible absorption spectrum of Chl a is obtained. The anhydrous form. always shows a maximum, in the red, at 672 nm and the crystalline one at 746 nm to 738 nm depending on the amount of water vapor present in the measuring area. The light conversion efficiency has been measured at the maximum absorption in the red for both forms of Chl a . For the anhydrous form, we found values as high as 0.036%, which is very significant even compared to 0.21%, the highest value found for the crystalline form. In both cases. the incident light power was approximately 10 μW on the cell. The light conversion efficiency of both forms of Chl a cells was found to depend on a combine effect of the nature of the gas (O₁. N₂. air. Ar. N₂O. SF ₆ , H₂) and the amount of water vapor present in the measuring area. The best conversion efficiency was obtained with O ₂ , or air saturated with water. This combined effect was very large for the crystalline form whereas the anhydrous form was only slightly affected.     

PHOTOBLEACHING OF A CYANINE DYE IN SOLUTION AND IN MEMBRANES

Abstract— N,N'-bis(2-ethyl-1,3-dioxolane)-kryptocyanine (EDKC), a lipophilic dye with a delocalized positive charge, photosensitizes cells to visible irradiation. In phosphate-buffered saline (PBS), EDKC absorbs maximally at 700 nm (ε= 1.2 × 10⁵ M⁻¹ cm⁻¹) and in methanol, the absorption maximum is at 706 nm (ε= 2.3 × 10⁵ M⁻¹ cm⁻¹). EDKC partitions from PBS into small unilamellar liposomes prepared from saturated phospholipids and into membranes prepared from red blood cells (RBC) and binds to human serum albumin (HSA). The EDKC fluorescence maximum red shifts from 713 nm in PBS to 720–725 nm in liposomes and RBC membranes and the fluorescence intensity is enhanced by factors of 14–35 compared to PBS (φ= 0.0046). EDKC is thermally unstable in PBS (T_1/2= 2 h at 1.3 × 10⁻⁵ M EDKC), but stable in methanol. In liposomes and RBC membranes, EDKC is 10 times more stable than in PBS, indicating that it is only partially exposed to the aqueous phase. Quenching of EDKC fluorescence in liposomes and RBC membranes by trinitrobenzene sulfonate also indicates that EDKC is not buried within the membranes. Photodecomposition of EDKC was oxygen-dependent and occurred with a low quantum yield (6.4 × 10⁻⁴ in PBS). Singlet oxygen was not detected upon irradiation of EDKC in membranes or with HSA since the self-sensitized oxidation of EDKC occurred at the same rate in D₂O as in H₂O and was not quenched by sodium azide or histidine.     

THE EFFECTS OF FAR ULTRAVIOLET RADIATION ON RESPIRATION AND CATION ACCUMULATION BY ISOLATED MITOCHONDRIA OF PHASEOLUS VULGARIS

Abstract. The respiration rates and respiratory control ratios of isolated bean mitochondria have been measured following exposure to 0, 150, 300 and 900 J/m² of far UV radiation (190–300 nm) from a mercury vapour light source with 90% total radiant intensity at 254 nm. Loss of respiratory control occurred at 150 J/m² and inhibition of respiration was significant at the highest exposure dosage. The uptake of both ⁴⁵Ca and ⁸⁵Sr have been measured following a 10min incubation of isolated mitochondria with 2 m M cation. Significant decreases in cation accumulation were observed following exposure to 900 J/m². The effect seemed to be associated with loss of active transport of the ions as a result of respiratory uncoupling or reduced electron transport. There was no significant effect of storage on respiration or ion transport nor was there any indirect effect of irradiated suspending medium on mitochondria.     

KINETICS OF PHOTOSYNTHETIC APPARATUS ADAPTATION IN Scenedesmus obliquus TO CHANGE IN IRRADIANCE AND LIGHT QUALITY

Abstract— Cells of the unicellular green alga Scenedesmus obliquus grown under high (20 W m^-2) or low (5 W m^-2) irradiancies of white light show all characteristics of sun or shade plants, respectively. When transferred to alternate light conditions, the cells adapt within 6 h. When cells grown under high irradiance of white light are transferred to red (683 nm) or blue (424 nm) light, they show characteristics similar to cells adapted to low or high irradiancies of white light, respectively. This adaptation to different wavelengths takes about 12 h. The underlying changes in the photosynthetic apparatus are discussed.     

MIGRATION OF EXCITATION ENERGY FROM THIONINE TO METHYLENE BLUE IN MICELLES

Abstract— The main absorption bands of thionine (Th⁺) and methylene blue (MB⁺) in aqueous solution lie at 598 nm and 664 nm, respectively. This position permits excitation energy transfer from Th⁺ to MB⁺, but not vice versa. We describe here studies of such transfer between these molecules adsorbed on micelles of sodium lauryl sulfate (SLS), imitating, at least to some extent, the state of pigments in chloroplasts.
The SLS concentration was varied from 3.0 to 11 × 10^-3 M. In the presence of dye, aggregation to micelles, each containing 70–100 detergent molecules, begins at about 3.0 × 10^-3 M SLS. Practically all dye ions are adsorbed on these micelles as soon as their formation begins.
Energy transfer from adsorbed Th⁺ ions to adsorbed MB⁺ ions can be demonstrated by observing the quenching of the fluorescence of thionine and the sensitization of that of methylene blue.
At [Th⁺] = [MB⁺] = 1 × 10^-5 M , the most efficient energy transfer (82 per cent efficiency, as derived from measurements of the quenching of Th⁺ fluorescence, or 90 per cent, as derived from sensitization of MB⁺ fluorescence) is observed at the lowest SLS-concentration (3.0 × 10^-3 M ), when the only micelles present are those formed by aggregation of dye-carrying low molecular complexes of SLS with dye cations. Each micelle carries, under these conditions, 10–14 molecules of the two dyes, and the distance between two closest dye ions is about 16 A. Transfer becomes less efficient as the SLS-concentration increases, causing pigment molecules to distribute themselves among a greater number of micelles.     

PARTIAL CHARACTERIZATION and LIGHT-INDUCED REGULATION OF GTP-BINDING PROTEINS IN Lemna paucicostata

Binding of GTP-binding proteins with [³⁵S]GTP7S in the extract containing membrane components of Lemna paucicostata 441 was inhibited by red or far red light by 20 to 25%, but blue light showed no or little effect. The plant used for the preparation of the extract was subjected to single darkness for 8 h, as both red and far red light inhibit flowering. The extract treated with 1% Lubrol was fractionated by gel filtration. Four species of GTP-binding proteins, GL1, GL2, GL3 and GL4 were detected with Km values 3, 7, 80 and 4 n M , respectively. GL1, GL2 and GL3 were ADP-ribosylated by pertussis toxin. The extract activated by [³⁵S]GTP-γS in darkness, under red light or under far red light was treated with 1% Lubrol and subsequent gel filtration of the extracts made it possible to detect GTP-binding protein with a small molecular weight only in an extract labeled in darkness. The reduction in the molecular weight of GTP-binding protein from the larger molecule associated with the binding of [³⁵S]GTPγS was confirmed by rechromatography of the larger molecule activated by [³⁵S]GTPγS in darkness. The binding of GL2 and/or GL3 with [³⁵S]GTPγS was suggested to be inhibited by red or far red light.     

ACTION SPECTRUM FOR THE PHOTOINHIBITION OF BIOLUMINESCENCE IN THE MARINE DINOFLAGELLATE DISSODINIUM LUNULA

Abstract— The fractional photoinhibition of the mechanically stimulable bioluminescence in the vacuolar dinoflagellate Dissodinium lunula is proportional to the logarithm of the exposure. The action spectrum for this photoinhibition has been determined by measuring threshold exposures in absolute units of photons cm⁻². The threshold exposure at the wavelength of maximum sensitivity, 450 nm, was 2 ± 10⁻² photons cm⁻². The action spectrum is consistent with absorption by a blue light receptor pigment shielded by a nonphotoactive pigment which absorbs in the region of the bioluminescence emission spectrum. It is suggested that there may be some selective advantage for this absorbing pigment in the vacuolar dinoflagellates in order to prevent the organisms from being photoinhibited by their own bioluminescence.     

PHYTOCHROME CONVERSION BY ULTRAVIOLET LIGHT

Abstract— Light absorbed primarily by the protein of phytochrome is active in transforming both the red and far-red absorbing forms. P _r and P _fr. The ratio of quantum yields for the conversions of P _r and P _fr by u.v. radiation (φ_r/φ_fr)_u.v.= 1.5 and does not differ significantly from the ratio obtained with red and far-red light absorbed directly by the chromophores (φ_r/φ_fr)v_vis. Thus, the efficiency of energy transfer from protein to chromophore is essentially the same for both forms of the chromoprotein. The ratio of the relative quantum yields for u.v. and visible light (φ^r)^u.v./(φ^r)^vis was 0.32 indicating that 30–35 per cent of the light energy absorbed by the protein was transferred to the chromophore.     

In situ COMPARISON OF 665 nm and 633 nm WAVELENGTH LIGHT PENETRATION IN THE HUMAN PROSTATE GLAND

Abstract— The depth of treatment in photodynamic therapy (PDT) of tumors varies with the wavelength of light activating the photosensitizer. New generation photosensitizers that are excited at longer wavelengths have the potential for increasing treatment depths. Tin ethyl etiopurpurin (SnET2), a promising second-generation photosensitizer is maximally activated at 665 nm, which may be significantly more penetrating than 633 nm light currently used with porphyrins in PDT. The penetration of 665 nm and 633 nm wavelength red light in the prostate gland was compared in 11 patients undergoing prostatic biopsies for suspected prostatic cancer. Interstitial optical fibers determined the light attenuation within the prostate gland. Of the 11 patients, 7 had dual wavelength and 4 had single wavelength studies. The mean attenuation coefficients, μ_eff, for 665 nm and 633 nm wavelength light were 0.32 ± 0.05 mm^-1 and 0.39 ± 0.05 mm^-1, respectively, showing a statistically significant difference (P = 0.0003). This represented a 22% increase in the mean penetration depth and at 10 mm from the delivery fiber there was 1.8 times as much 665 nm light fluence than 633 nm. The mean μ_eff at 665 nm for benign and malignant prostate tissue were similar ( P = 0.42), however, there was significant interpatient variation (μ_eff ranging from 0.24 to 0.42 mm^-1) reflecting biological differences of therapeutic importance. The enhanced light fluence and penetration depth with 665 nm light should allow significantly larger volumes of prostatic tissue to be treated with SnET2-mediated PDT.     

PHOTOCHEMICAL REACTION OF 13-CIS-BACTERIORHODOPSIN STUDIED BY LOW TEMPERATURE SPECTROPHOTOMETRY

Abstract— The photoreaction cycle of 13- cis -bacteriorhodopsin (13- cis -bR) was investigated by low temperature spectrophotometry using two different preparations; 13- cis -bR constituted from bacterioopsin and 13- cis -retinal, and dark-adapted bacteriorhodopsin (bR^D), which is an equi-molar mixture of 13- cis -bR and trans -bR.
By irradiation with 500 nm light at — 190°C, 13- cis -bR was converted to its batho-product, batho-13- cis -bR (batho-bR¹³), which is different from batho-product from trans -bR, batho-bR^t. On warming batho-bR¹³ to -5°C in the dark, it completely changed to trans -bR. We estimated the composition of 13- cis -bR and trans -bR in the warmed sample spectrophotometrically and then the absorption spectrum of batho-bR¹³ was calculated. The absorption maximum lies at 608 nm, 1250 cm⁻¹ longer than that of 13- cis -bR; the molar extinction coefficient (ε) is about 74000 M ⁻¹ cm⁻¹, larger than that of 13- cis -bR (52000 M ⁻¹ cm⁻¹).
On the warming the sample containing batho-bR¹³ formed by irradiating 13- cis -bR or bR^D at — 190°C, we could not detect other intermediates such as the lumi- or meta-intermediates seen in trans-bR system.     

Li+,Eu3+共掺杂La2MoO6红色荧光粉的Pechini法合成及近紫外/蓝光激发下的发光特征

采用Pechini法合成了白光LED用红色荧光粉La_1.9-xMoO₆:0.10Eu³⁺,xLi⁺(x=0,0.10,0.20,0.25),并对样品分别进行了X射线衍射(XRD)、扫描电子显微镜(SEM)、电子能谱(EDX)以及荧光光谱(PL)等技术手段分析。 PL光谱显示该荧光粉可被近紫外光(395 nm)和蓝光(466 nm)有效激发,产生616和623 nm强的红光发射,归属于Eu³⁺的⁵D₀→⁷F₂电偶极跃迁。该荧光粉与近紫外LED芯片(370~410 nm)和蓝光LED芯片(450~470 nm)均匹配良好,具有潜在的商业应用价值。 共掺Li⁺离子作为敏化剂能显著提高荧光粉的发光强度,且最优掺杂量为x=0.20。     

CHEMILUMINESCENCE IN THE PROCESS OF OXIDATIVE RING-OPENING OF PURPUROGALLINQUINONES

Abstract— The oxidation of purpurogalline (PPG) by alkaline solution of H₂O₂ pH 9–11 at 298°K is accompanied by chemiluminescence (CL) in the spectral range 400–600 nm with the maximum at 500 nm and quantum yield about 10^-6. The optimal concentrations of reactants with respect to maximal intensity are: 2 × 10^-4 M PPG, 10^-2 M NaOH, 1 M H₂O₂. Activation energy calculated from the maximum intensity of CL is 8.1×0.4 kcal/mole. Light emission occurs only when OH-groups of the phenolic ring of PPG undergo oxidation and the blue anion of o -PPG-quinone is formed. The rate that determines step in the reaction associated with luminescence is the nucleophilic attack of OOH^- ion on the blue anion of o -PPG-quinone. In this exergonic step (-ΔH = 63 to 230kcal/mole) the o - and/or p -quinone ring is opened and carbonyl derivatives of α-tropolone are produced. They display fluorescence in the region 400–600 nm. The fluorescence spectrum of the reaction mixture after oxidation of PPG is very close to that of CL. It is likely that carbonyl derivatives of α-tropolone are emitters of CL.     

Effects of Calmodulin Inhibitors and Blue Light on Rhythmic Movement of Robinia pseudoacacia Leaflets

Abstract— The effect of several calmodulin (CAM) antagonists, blue light and an intracellular calcium inhibitor, on the circadian rhythm of Robinia pseudoacacia leaflet movement has been studied. The CAM antagonists, chlorpromazine (CPZ), trifluoperazine (TFP), calmidazolium and N -(6-aminohexyI)-5-chloro-1-naphthalenesulfonamide (W₇) shifted the phase of the circadian rhythmic movement while W₅, an inactive analogue of W₇, had no effect. Two hour pulses of calmidazolium (10–50 μ M ) gave rise to a phase-response curve with maximum advances (up to 9 h) at circadian time (CT) 6 and maximum delays (up to 7 h) at CT 22. No effect was found on transition from subjective day to subjective night and vice versa. The TFP (10–50 μ M ), applied as 2 h pulses during the circadian cycle, shifted the phase of the circadian leaflet movement and also produced maximum advances in the middle of subjective day. Two hour blue light pulses shifted the phase of leaflet rhythmic movement. The phase-response curve obtained showed maximum advances (up to 5 h) in the middle of subjective day and maximum delays on transition from subjective day to subjective night. Two hour pulses of 50 μ M 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hypochloride (TMB-8), an intracellular calcium inhibitor, caused the same type of phase-response curve, with maximum advances and delays occurring at the same time as those produced by blue light. These results indicate that CAM might be involved in controlling the circadian oscillator that drives Robinia leaflet movement. The relationship between CAM and calcium with red and blue light is discussed.     

ANALYSIS OF MULTIPLE PHOTORECEPTOR PIGMENTS FOR PHOTOTROPISM IN A MUTANT OF Arabidopsis thaliana

Abstract
The shape of the fluence-response relationship for the phototropic response of the JK224 strain of Arabidopsis thaliana depends on the fluence rate and wavelength of the actinic light. At low fluence rate (0.1 μmol m^-2s^-1), the response to 450-nm light is characterized by a single maximum at about 9 μmol m^-2. At higher fluence rate (0.4 μmol m^-2s^-1), the response shows two maxima, at 4.5 and 9 μmol m^-2. The response to 510-nm light shows a single maximum at 4.5 μmol m^-2. Unilateral preirradiation with high fluence rate (25 μmol m^-2s^-1) 510-nm light eliminates the maximum at 4.5 μmol m^-2 in the fluence response curve to a subsequent unilateral 450-nm irradiation, while the second maximum at 9 μmol m^-2 is unaffected. Based on these results, it is concluded that a single photoreceptor pigment has been altered in the JK224 strain of Arabidopsis thaliana.