BLUE LIGHT, PHYTOCHROME AND THE FLOWERING OF LEMNA PERPUSILLA 6746

Lemna perpusilla 6746 was grown on HUTNER'S medium with sucroseunder light schedules combining red, blue and far-red light.As shown earlier, brief red exposures added to a continuousblue schedule inhibit flowering although either schedule alonepermits it; hence red and blue act together in establishinga long day (flower inhibiting) condition. However, the red exposurerequired to inhibit flowering is greater with high intensitythan with low intensity continuous blue, suggesting in additiona blue-red antagonism. Blue light reverses the effects of abrief red exposure closing a blue or far-red main photoperiod,but it also reverses the effects of a brief far-red exposureclosing a red photoperiod. Thus, blue can act either like redor like far-red, depending on the situation. All effects ofblue light on the flowering of L. perpusilla 6746 are consistentwith the notion that it establishes a Pfr level intermediatebetween those established by red and far-red light; the postulationof an additional photoreaction to explain the effects of blueseems unnecessary. ¹Research carried out at Brookhaven National Laboratory underthe auspices of the U. S. Atomic Energy Commission.     

Photoinduction of Spore Germination in a Fern, Mohria caffrorum

Irradiation of spores of the fern Mohria caffrorum Sw. witheither red light (67.4 µW cm^–2) or far-red light(63.2 µW cm^–2) for a period of 24 h induced maximumlevels of germination. Brief irradiations with blue light (127.6µW cm^–2) administered before or after photoinductioncompletely nullified the effects of red or far-red light; however,with prolonged exposure to blue light, germination levels roseto near maximum. The similar effects of red and far-red lightin promoting spore germination makes the involvement of phytochromein this process questionable. Based on energy requirements,the promotive and inhibitory phases of blue light appear toinvolve independent modes of action. Mohria caffrorum, ferns, spore germination, photoinduction, phytochrome     

Red and blue light-stimulated proton efflux by epidermal leaf cells of the Argenteum mutant of Pisum sativum

Light stimulates leaf expansion in dicotyledons by increasingapoplastic acidification, cell wall loosening and solute accumulationfor turgor maintenance. Red and blue light enhance growth viadifferent photo-systems, but the cellular location and modesof action of these systems is not known. Here, the effect of red and blue light was studied on transportprocesses in epidermal cells of expanding leaves of the Argenteummutant of Pisum satlvum. Both red and blue light caused extraceiiuiaracidification by isolated epidermal tissue, which was stimulatedby extracellular K⁺ and inhibited by DCCD at 0.1 mol m^–3.Acidification induced by red compared with blue light showeddifferent saturating kinetics in fluence rate-response curves.Under near saturating light conditions the effects of red andblue light were additive. The red light-induced acidificationwas inhibited by far-red light while the blue light-inducedacidification was not. Light caused a hyperpoianzation of themembrane potential in epidermal strips, and stimulated ⁸⁶Rb⁺uptake by epidermal protoplasts. These results show that phytochromeand an additional blue light-photoreceptor function in isolatedepidermal cells to promote proton efflux, hyperpolarization,and cation uptake. Key words: Pisum sativum, light-induced acidification, ion transport, epidermis, photoreceptor     

SPECTRAL SENSITIVITY OF SEED GERMINATION IN ARTEMISIA MONOSPERMA

The absolute requirement for light in the germination of achenesof Artemisia monosperma is as satisfied by radiant energy inthe blue, green, yellow, red and far-red regions of the visiblespectrum, as by unfiltered white light. The same stimulationwas obtained by a short irradiation as by an uninterrupted one.Phytochrome seems to be either absent, or masked by a differentpigment which absorbs light in the entire visible spectrum andthus initiates germination. ¹ This study was supported by grant FG-Is-115 from the UnitedStates Department of Agriculture.     

Abscission: Response to Red and Far-Red Light

Craker, L. E., Zhao, S. Y. and Decoteau, D. R. 1987. Abscission:response to red and far-red light.—J. exp. Bot. 38: 883–888. The dose-response and time relationship of red and far-red lightin the inhibition and promotion, respectively, of dark-inducedleaf abscission was quantified using cuttings of coleus (ColeusBlumei Benth.). A continuous photon flux of approximately 15nM m^–2 s^–1 of red light was sufficient to preventleaf abscission. Abscission was promoted by exposure to a photonflux of approximately 10 nM m^–2 s^–1 of far-red lightThe inhibition of abscission by red light could be reversedby treatment with far-red and the promotion of abscission byfar-red light could be reversed by treatment with red lightThe data were consistent with a phytochrome receptor systemlocated in the leaves that controlled the presence of an abscission-inhibitingsubstance in the abscission zones. Key words: Abscission, Coleus Blumei, far-red light red light     

Effects of Blue Light on the Vertical Colonization of Space by White Clover and their Consequences for Dry Matter Distribution

The morphology of white clover is very sensitive to the lightenvironment, especially to the ratio of red:far-red light andto photon irradiance. However, less is known about the effectsof blue light on clover morphogenesis. Cuttings of white cloverwere grown for 56 d in two controlled chambers receiving lightwith similar photosynthetic efficiency and phytochrome photoequilibriumstate but different levels of blue light: some plants were grownunder orange light (very low blue light, 0.02 µmol m^-2s^-1)or under white light containing blue light (83 µmol m^-2s^-1).Other plants were switched from white light to orange lightorvice versa,after 30 d. The absence of blue light modifiedthe growth habit of clover and raised the laminae in the upperlayer of the canopy by increasing petiole length, and petioleangle from the horizontal, and by raising stolons above theground surface. Moreover, the absence of blue light had no effecton total leaf area and total dry weight per plant, but increasedthe leaf area and biomass of petioles of the main axis. Largerpetioles and laminae were associated with the allocation ofmore dry weight to the petiole at the same petiole thicknessbut with thinner laminae. These results indicate that a decreasein blue light is involved in the perception of, and adaptationto, shading by the plant.Copyright 1997 Annals of Botany Company Biomass allocation; blue light; growth habit; leaf area; light quality; photomorphogenesis; Trifolium repensL.; white clover     

RED LIGHT, BLUE LIGHT, AND COPPER ION IN THE PHOTOPERIODIC CONTROL OF FLOWERING IN LEMNA PERPUSILLA 6746

L. perpusilla, 6746 grown in HUTNER's medium (containing a highlevel of EDTA) responds as a short-day plant under white orred light, but is almost completely daylength-indifferent underblue. In a medium containing ca. 2µmoles/liter of unchelatedcopper ion, it flowers rapidly under all photoperiods, white,blue or red. Although certain long-day blue schedules permitflowering even on HUTNER's medium, blue is not simply "inactive"photoperiodically, since inclusion of a single brief red exposurein certain blue schedules is sufficient to prevent floweringas though the whole schedules were red. The indicated blue-redinteraction should prove important for further analyses of photoperiodismin this plant. ¹Research carried out at Brookhaven National Laboratory underthe auspices of the U.S. Atomic Energy Commission.     

The Photocontrol of Spore Germination in the Fern Ceratopteris richardii

This paper describes how different wavelengths of light regulatespore germination in the fern Ceratopteris richardii. This speciesdoes not exhibit any dark germination. Maximum photosensitivityof the spores is reached 7 to 10 d after imbibition. An increasein the red light fluence above the threshold fluence of 10¹⁶quanta.m^–2 leads to a corresponding increase in germination.In sequential irradiation experiments, farred light can reversethis red light-mediated germination to the level observed withthe far-red light control. Blue light fluences above 10²⁰ quanta.m^–2can also block the germination response to red light. Moreover,this antagonistic effect of blue light is not reversed by subsequentirradiation with red light. It is therefore concluded that phytochromeand a distinct blue light photoreceptor control C. richardiispore germination. These interpretations are entirely consistentwith the published literature on other fern genera. (Received November 28, 1986; Accepted April 6, 1987)     

Control of the Entry into S Phase by Phytochrome and Blue Light Receptor in the First Cell Cycle of Fern Spores

Phytochrome- and a blue light receptor-dependent pathway antagonisticallyregulate the first mitosis in spores of the fern Adiantum capillus-venerisL. This study focused on determining which phase(s) of the cellcycle is positively regulated by phytochrome and negativelyregulated by a blue light receptor in germinating spores. Incorporationof the radioactivity of ³H-thymidine into the acid-insolublematerial prepared from the spores indicated that phytochromein the PFR form induced the entry into S phase of the firstcell cycle in the spores 20-28 h after irradiation with redlight. Blue light treatment before or after red light treatmenttotally prevented the P_FR-induced DNA synthesis. Brief irradiationwith red, far-red or blue light showed no effects on mitosisif the irradiation was given 28 h after the red light induction,during S and M phases. These results indicate that phytochromeand a blue light receptor regulate the entry into S phase duringthe first cell cycle of fern spores. ( Accepted July 10, 1997)     

Photomodulation of Stem Extension in Light-Grown Plants: Evidence for Two Reactions

Internode elongation was measured in plants of Phaseolus vulgarisand Glycine max grown under 8 h photoperiods at 25 W m^–2in white fluorescent light, followed by light-extensions varyingin quality, irradiance and duration. Two distinct responsesto light were observed under these conditions. A reduction in P_FR/P increased elongation, but elongation wasalso modified by a second reaction in which internode lengthincreased with increase in the duration and irradiance of theday-extension. This light-promoted response occurred in bothred and blue light. In the P_FR-inhibition response, light acteddirectly on the expanding internode. The light-promoted response,in contrast, required irradiation of the leaf. The response to a short end-of-day exposure to far-red lightprogressively diminished as successive internodes expanded underthe treatment, whereas the light-promoted response increased.The two processes appeared to interact and, in the later-expandinginternodes, the effect of a reduction in P_FR was greater underlong day-extensions with mixed red and far-red light than inthe end-of-day treatments. ¹ Present address: British Telecom, Brunel House, 2 FitzalanRoad, Cardiff, U.K.     

PHOTOMORPHOGENESIS IN PTERIS VITTATA: I. PHYTOCHROME-MEDIATED SPORE GERMINATION AND BLUE LIGHT INTERACTION

1. Spores of the fern Pteris vittata did not germinate under totaldark conditions, while an exposure of the spores to continuouswhite light brought about germination. The germination was mosteffectively induced by red light and somewhat by green and far-red,but not at all by blue light. The sensitivity of spores to redlight increased and leveled off about 4 days after sowing at27–28. The promoting effect of red light could be broughtabout by a single exposure of low intensity. Far-red light givenimmediately after red light almost completely reversed the redlight effect, and the photoresponse to red and far-red lightwas repeatedly reversible. The photoreversibility was lost duringan intervening darkness between red and far-red irradiations,and 50% of the initial reversibility was lost after about 6hr of darkness at 27–28. These observations suggest thatthe phytochrome system controls the germination of the fernspore.
2. When the imbibed spores were briefly exposed to a low-energyblue light immediately before or after red irradiation, theirgermination was completely inhibited. The blue light-inducedinhibition was never reversed by brief red irradiation givenimmediately after the blue light. The escape reaction of redlight-induced germination as indicated by blue light given aftervarious periods of intervening darkness was also observed, andits rate was very similar to that determined by using far-redlight. Spores exposed to blue light required 3 days' incubationin darkness at 27–28 to recover their sensitivity tored light. The recovery in darkness of this red sensitivitywas temperature-dependent. It is thus suggested that an unknownbluelight absorbing pigment may be involved in the inhibitionof phytochrome-mediated spore germination.

(Received August 21, 1967; )     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: III. THE WAVELENGTHS OF LIGHT EFFECTIVE IN PHOTOPERIODIC CONTROL

Growth and dormancy in Lunularia are controlled by daylength,short-day promoting active growth, long-day or light-break treatmentinducing dormancy. Light-breaks of red light are highly effectivein inducing dormancy, while irradiation with other wavebandsis much less inhibitory to growth. Far-red light given afterred irradiation causes substantial reversal of the red-lighteffect, suggesting strongly that phytochrome is involved inthe photoperiodic response mechanism of Lunularia. However,even short(15 sec.) exposures to far-red light alone cause significantgrowth inhibition, and it is considered possible that far-redirradiation also leads to the formation of some of the P 730form of phytochrome.     

Photoreversibility of flower initiation in Lemna perpusilla as affected by the light quality of the main light period

Reversible floral responses of Lemna perpusilla to red and far-redlights appeared only at the beginning of the inductive darkperiod when the 8 hr photoperiod consisted of white or red light.When blue or far-red light was given during the 8 hr photoperiod,the far-red given at the beginning of the dark period scarcelyinhibited flowering; red/far-red reversibility newly appearedat the middle of the dark period. This indicates that the photoregulationsystem in the flowering of L. perpusilla can be converted fromthe Pharbitis type to the Xanthium type by changing the lightquality of the main photoperiod from white or red to blue orto far-red, which is known to be effective for the so-calledhigh-energy photoreaction of photomorphogenesis. (Received July 2, 1975; )     

Haustoria of Cuscuta japonica, a Holoparasitic Flowering Plant, Are Induced by the Cooperative Effects of Far-Red Light and Tactile Stimuli

When seedlings of Cuscuta japonica were grown with Vigna radiata(the host plant) in a flower pot for 6 d under white light andthen irradiated with far-red or blue light (ca. 6 µmolphotons m^–2 s^–1), the seedlings parasitized V. radiata.However, no parasitism of the seedlings was observed under redor white light or in darkness. The parasitic behavior of seedlingsof C. japonica was observed even if an acrylic rod was usedas a substitute for the host plant. Upon incubation under far-redlight, the seedling twined tightly around the rod and developedhaustoria towards it. Haustoria also developed when apical andsubapical regions of seedlings were held between two glass platesthat were about 0.7 mm apart and were irradiated with far-redlight. However, no haustoria were induced by either the holdor irradiation alone. These results indicate that parasitismof Cuscuta japonica is controlled by the cooperative effectsof two physical signals, far-red light and appropriate tactilepressure. Our findings suggest that parasitism by the genusCuscuta involves a novel strategy. (Received April 10, 1996; Accepted August 21, 1996)     

Effects of disalicylidenepropandiamine and near far-red light on 14CO2-fixation in Chlorella cells

1) With Chlorella ellipsoidea cells, in the presence of 5x10^–6M DSPD, or in its absence, the amounts of ¹⁴CO₂ incorporatedin P-esters, serine-plus-glycine and alanine were larger underred light than under blue light, whereas blue light specificallyincreased ¹⁴CO₂-incorporation in aspartate, glutamate, malateand fumarate (blue light effect). The amount of total ¹⁴C fixedunder blue or red light was greatly decreased by the additionof DSPD. When the concentration of DSPD was raised to 5x10^–4M, practically no radioactivity was found, under blue or redlight, in aspartate, glutamate and fumarate. Radioactivity inalanine was greatly increased. Effects of higher concentrationof DSPD are explained as due to the inhibition of PEP carboxylaseactivity in Chlorella cells. 2) The percentage incorporation of ¹⁴C into aspartate and theother compounds mentioned above, under near infra-red illuminationwas significantly smaller than that under blue light and wasalmost equal to that under red light. These results along withthe effect of 5x10^–6 M DSPD, exclude the possibility thatcyclic photophosphorylation is involved in the "blue light effect"mechanism. (Received December 12, 1969; )     

Removal by chemicals of photoperiodic light requirements of Lemna gibba G3

Both the initial and the terminal 1 hr portions of the subjectiveday fraction, namely the L1- arid L2-phases, of a 24 hr daymust be illuminated in order for the day to be perceived asa long day in the min-LD determination by the long-day plant,Lemna gibba G3 (9). The light requirement of the L1-phase wassatisfied by a 10 min red light pulse given at the beginningof the phase. The red light effect was erased by a subsequent10 min far-red light, indicating phytochrome-mediated processesoccurring in the L1-phase. The light requirement of the L2-phasewas satisfied by blue or far-red light given during the terminal10 min period of the phase; there was no indication of phytochromeinvolvement. The light action on the L1-phase was replaced by10^–5 M of cyclic AMP or 10^–7 M of DL-isoproterenol.The isoproterenol action was antagonized by 10^–7 M ofDL-propranolol. Cyclic AMP (10^–5 M) combined with salicylicacid (10^–6 M), which can remove the light requirementof the L2-phase (10), rendered a completely dark day physiologicallyequivalent to a long day. Acetylcholine (10^–5 M) exertednyctomimetic action on the L1-phase of the second light day.The action of acetylcholine was antagonized by cyclic AMP (10^–5M). The L2-phase required no light in the presence of 10^–7M of DL-propranolol, and this propranolol action was not affectedby isoproterenol. These findings suggest changes in membranepermeability caused by the light given during the L1- and L2-phases. (Received July 7, 1976; )     

The Role of the Red/Far-Red Ratio in the Response of Tropical Tree Seedlings to Shade

The West African species Khaya senegalensis and Terminalia ivorensiswere grown in a controlled environment, varying the photon fluxdensity in the range 18–610 µmol m^–2 s^–1and the red/far-red ratio over an appropriate range to simulatethe shade of a tree canopy versus unattenuated daylight. Theshade tolerant seedlings of Khaya were relatively insensitiveto the red/far-red ratio. The light demanding Terminalia wasconsiderably affected: when the ratio was low the specific leafarea was increased and the leaves produced were very much largerin area. Thus, the Leaf Area Ratio was enhanced and the plantsdisplayed an increase in Relative Growth Rate. Khaya, Terminalia, tropical trees, shade, red/far-red ratio     

Green Light Drives CO2 Fixation Deep within Leaves

Maximal ^l4CO₂-fixation in spinach occurs in the middle of thepalisade mesophyll [Nishio et al. (1993) Plant Cell 5: 953],however, ninety percent of the blue and red light is attenuatedin the upper twenty percent of a spinach leaf [Cui et al. (1991)Plant Cell Environ. 14: 493]. In this report, we showed thatgreen light drives ¹⁴CO₂-fixation deep within spinach leavescompared to red and blue light. Blue light caused fixation mainlyin the palisade mesophyll of the leaf, whereas red light drovefixation slightly deeper into the leaf than did blue light.¹⁴CO₂-fixation measured under green light resulted in less fixationin the upper epidermal layer (guard cells) and upper most palisademesophyll compared to red and blue light, but led to more fixationdeeper in the leaf than that caused by either red or blue light.Saturating white, red, or green light resulted in similar maximal¹⁴CO₂-fixation rates, whereas under the highest irradiance ofblue light given, carbon fixation was not saturated, but itasymptotically approached the maximal ¹⁴CO₂-fixation rates attainedunder the other types of light. The importance of green lightin photosynthesis is discussed. ¹Supported in part by grants from Competitive Research GrantsOffice, U.S. Department of Agriculture (Nos. 91-37100-6672 and93-37100-8855).     

The Effects of Red, Far-red, and Blue Light on the Geotropic Response of Coleoptiles of Zea mays

The effects of red, far-red, and blue light on the geotropicresponse of excised coleoptiles of Zea mays have been investigated.Seedlings were grown in darkness for 5 or 6 days, exposed tovarious light treatments, and then returned to darkness fordetermination of the geotropic response. The rate of response of the coleoptiles is decreased after theyhave been exposed to red light (620–700 mµ, 560ergs cm^–2sec^–1 for the 24 hrs, but not for the 4hrs, preceding stimulation by gravity. Furthermore, their rateof response is greatly reduced if they are exposed to red lightfor 10 min and then returned to darkness for 20 hrs before geotropicstimulation. At 25° C an interval of 6 to 8 hrs elapses between a 10-minexposure to red light and the first detectable decrease in thegeotropic response of the coleoptile. This interval can be lengthenedby exposing the seedlings to low temperatures (0° to 2°C) after the light treatment but cannot be greatly shortenedby increasing the duration of exposure to red light. Using a standard procedure of exposing 5-day-old etiolated seedlingsto light for various times, replacing them in darkness for 20hrs and then determining the response of the coleoptiles to4 hrs geotropic stimulation, it has been found that: (a) Exposureto red light for 15 sec significantly decreases the geotropiccurvature of the coleoptiles and that further reduction occurson increasing the length of the light treatment to 2 and 5 min.(b) Far-red light has no effect on the geotropic response ofthe coleoptiles but it can completely reverse the effect ofred light. After repeated alternate exposure to red and far-redlight the geotropic response of the coleoptile is determinedby the nature of the last exposure, (c) Complete reversal ofthe effect of red light by far-red radiation only occurs whenexposure to far-red follows immediately after exposure to red.The reversing effect of far-red radiation is reduced if a periodof darkness intervenes between the red and far-red light treatments,and is lost after a dark interval of approximately 2 hrs. The effect of red light on the rate of geotropic response ofthe coleoptiles is independent of their age and length at thetime of excision. Blue light acts in a similar way to red light, but the seedlingsare less sensitive to blue than to red light. Coleoptiles grown throughout in a mixture of continuous, weak,red, and far-red light have a lower rate of geotropic responsethan etiolated coleoptiles.     

Effects of Far-red Light on the Labelling of Acyl Lipids during the Greening of Barley (Hordeum vulgare)

Etiolated Hordeum vulgare (barley) Plants were greened underwhite light or far-red (> 700 nm) light. Exposure to far-redlight inhibited chlorophyll synthesis (especially chlorophyllb) and the development of photosystem II which were seen whengreening took place under white light. Primary leaves were detachedand the labelling of their acyl lipids from [¹⁴C]acetate wasstudied under white light or far-red light illumination. Greeningwith far-red light caused a reduction in the radiolabellingof polyunsaturated fatty acids and diacylgalactosylglycerol.Total fatty acid labelling rates were unaffected. Phosphatidylethanolamine,which was normally poorly labelled, accounted for up to 15 percent of the total radioactivity in acyl moieties of lipids inleaves greened with far-red light. The results are discussedin connection with the role that acyl lipids may play in normalthylakoid structure and function. Hordeum vulgare, barley, acyl lipids, white light, far-red light, chloroplasts, thylakoids