Brief irradiation with red or blue light induces orientational movement of chloroplasts in dark-adapted prothallial cells of the fernAdiantum

Orientational movement of chloroplasts was induced by a brief irradiation with red light (R) or blue light (B) in dark-adapted prothallial cells ofAdiantum, whose chloroplasts had gathered along the cell dividing wall (i.e., the anticlinal wall). When the whole dark-adapted prothallia were irradiated from a horizontal direction (i.e., from their lobes) with horizontally vibrating polarized R (H pol. R) for 10 or 3 min, the chloroplast left the anticlinal walls and spread over the prothallial surface (i.e., the periclinal walls) within 1–2 hr after the onset of irradiation, returning to the anticlinal wall (dark-position) within 10 hr. However, vertically vibrating polarized R (V pol. R) for 10 min did not induce the movement towards periclinal walls. The R effect was cancelled by non-polarized far-red light (FR) irradiation just after the R irradiation. Irradiation with H pol. B for 10 or 3 min but not with V pol. B could also induce a similar movement of chloroplasts, although the chloroplasts returned within 4 hr. The effect of H pol. B, however, was not cancelled by the subsequent FR irradiation. When a part of the dark-adapted cell at the prothallial surface was irradiated from above with a microbeam of R or B for 1 min, chloroplasts of the cell in the dark-position moved towards the irradiated locus in subsequent darkness. However, in the neighboring cells, orientational movement was not induced by either R or B microbeams. These results show that in dark-adapted prothallial cells, both brief irradiation with R and B can induce chloroplast photo-orientation and that the photoreceptors are phytochrome and blue light-absorbing pigment, respectively. It is also clear that effects of both R and B irradiation do not transfer to neighboring cells.     

Phytochrome- and blue-light-absorbing pigment-mediated directional movement of chloroplasts in dark-adapted prothallial cells of fernAdiantum as analyzed by microbeam irradiation

When prothalli ofAdiantum capillus-veneris L. were kept for 2 d in the dark, chloroplasts gathered along the anticlinal walls (Kagawa and Wada, 1994, J Plant Res 107: 389–398). In these dark-adapted prothallial cells, irradiation with a microbeam (10 gm in diameter) of red (R) or blue light (B) for 60 s moved the chloroplasts towards the irradiated locus during a subsequent dark period. Chloroplasts located less than 20 gm from the center of the R microbeam (18 J·m^–2) moved towards the irradiated locus. The higher the fluence of the light, the greater the distance from which chloroplasts could be attracted. The B microbeam was less effective than the R microbeam. Chloroplasts started to move anytime up to 20 min after the R stimulus, but with the B microbeam the effect of the stimulus was usually apparent within 10 min after irradiation. The velocity of chloroplast migration was independent of light-fluence in both R and B and was about - 0.3 m·min^–1 between 15 min and 30 min after irradiation. Whole-cell irradiation with far-red light immediately after R- and B-microbeam irradiations demonstrated that these responses were mediated by phytochrome and a blue-light-absorbing pigment, respectively. Sequential treatment with R and B microbeams, whose fluence rates were less than the threshold values when applied separately, resulted in an additive effect and induced chloroplast movement, strongly suggesting that signals from phytochrome and the blue-light-absorbing pigment could interact at some point before the induction of chloroplast movement.Abbreviations B blue light - FR far-red light - IR infrared light - R red light     

Rapid Growth Responses of Dark-Grown Wheat Seedlings to Red Light-Irradiation: I. Kinetic Studies on the Short-Term Growth Responses of Intact Coleoptiles at Different Seedling Age

Continuous recordings of the effect of red light on intact darkgrown wheat seedlings (Triticum aestivum L. cv. Hatri) weremade at different times after sowing. When the coleoptile tipregion was irradiated 50, 70 or 90 h after sowing with red lightfrom two opposite fibre bundles a decrease in extension ratewas detectable after a latent period of 10 to 15 min. Growthrate reached a fluence dependent minimum at about 60 min, afterwhich growth acceleration towards the dark control rate wasobserved. When continuous red irradiation was started 50 or70 h after sowing the dark control rate was reached 2.5 h afteronset of irradiation and growth rate was little above this levelduring the next 2 h. With older coleoptiles (90 h after sowing)the growth rate recovery was only up to 50% of the dark controlrate and a second phase in growth inhibition became detectableabout 2.5 h after onset of red exposure, characterized by acontinuous decrease in extension rate. Under R/FR pulse irradiationboth the red-light-induced transient growth inhibition and thesecond phase of growth inhibition exhibit far-red reversibilityup to the level of far-red induced growth rate changes. (Received September 19, 1986; Accepted December 8, 1986)     

Phytochrome-mediated polarotropism of Adiantum capillus-veneris L. protonemata as analyzed by microbeam irradiation with polarized light

Summary Perception of polarized light inducing phytochrome-mediated polarotropism in protonemata of the fern Adiantum capillus-veneris L. was analyzed using brief microbeam irradiation with polarized red (R) or far-red light (FR). The polarotropic response inducible by irradiation of the subapical 10–30-m part with polarized R vibrating parallel to the cell axis was nullified by subsequently giving R at the apical 0–2.5-m region. This inhibitory effect of R showed an action dichroism, that is, polarized R vibrating normal to the cell axis was effective but the parallel-vibrating R was not. On the other hand, FR irradiation of the extreme tip after irradiation of the whole cell with depolarized R effectively induced a tropic response. This FR effect also showed action dichroism, with parallel-vibrating polarized FR being more effective than FR vibrating normal to the cell axis. When the apical-dome region and the adjacent subapical 10–20-m region were sequentially irradiated with polarized R vibrating obliquely in different directions, polarotropism took place depending on the vibrating direction of the light given to the apical-dome region. Obliquely vibrating polarized FR given to the apical dome after irradiation of the whole cell with depolarized R also induced polarotropism. Thus, the difference in amount (or percent) of the far-redabsorbing form of phytochrome (Pfr) between the extreme tip and the subapical region appears to be crucial in regulating the direction of apical growth; the difference in Pfr level between the two sides of the protonemal apex may occur mainly at the apical dome. Furthermore, the transition moments of the red-absorbing form of phytochrome (Pr) and Pfr seem to be aligned parallel and normal, respectively, to the cell surface at the periphery of the apical hemisphere.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Effects of Temperature and Various Red or Far-red Irradiations on Phytochrome- and Gibberellin A3-mediated Germination Control in Partially Hydrated Lettuce Seeds

Dark reversion of phytochrome in partially hydrated lettuceseeds (Lactuca sativa cv. Grand Rapids) is temperature dependent.After initial red irradiation (R) the higher the storage temperature,the higher the dark reversion rate. Following dark moist storage(DMS) at 30 ?C for 15 d none of the seeds receiving initialR germinated, whereas seeds stored at 0 ?C germinated nearlyas well (about 80%) as unstored controls. The half-time fordark reversion at 20 ?C and 30 ?C is 9 d and 3 d respectively.Repeated R treatments given at 5 d intervals during DMS at 20?C and 30 ?C maintained a high germination capacity. With threeor more R treatments the effect of high temperature largelydisappeared. Dark reversion of phytochrome was not observed in partiallyhydrated lettuce seeds receiving continuous red irradiation(cont R) for two or more days. The promotive effect of contR could be reversed at any time with a brief far-red irradiation(FR), indicating that the phytochrome system remained fullyphototransformable. With continuous far-red light (cont FR)the ability of gibberellin A₃ (GA₃) to stimulate germinationdisappeared and response to GA₃ also diminished in cont R followedby FR but at a slower rate indicating the induction of secondarydormancy in these partially hydrated seeds. This induction ofdormancy was retarded by repetitive or cont R but was enhancedby cont FR. The results of this study suggest a role for theaccumulated stable intermediates of phytochrome transformationin partially hydrated seeds with repeated or continuous R treatmentsand different effects of GA₃ and R in the regulation of germination. Key words: Phytochrome, Lactuca sativa, Seed germination, Temperature, Dark reversion of phytochrome, Seed water content     

Intracellular Photoreceptive Site for Polarotropism in Protonema of the Fern Adiantum capillus-veneris L.

Polarotropic response was induced by short-term irradiationwith polarized red light in single-celled protonemata of thefern Adiantum capillus-veneris L. that had been grown apicallyunder red light for 6 days then for 15 hr in the dark. Sequentialobservation of the apical growth with a time-lapse video systemshowed that the direction of apical growth changed within 30min after the brief irradiation. Microbeam irradiation withpolarized red light of the subapical, dark-grown flank of theapical, 5–15 µm region of the protonema inducedthe polarotropic response most effectively. When both sidesof the flank were irradiated simultaneously with different fluencesof polarized red light with the same vibrating plane of 45°with protonemal axis, polarotropism took place normally, ifthe fluence ratio, B/A (B: fluence given to the side towardwhich the protonema should bend in polarotropism, A: fluencegiven to the other side) was not less than one-half. But, ifthe ratio became less than that, the protonemata no longer showedpolarotropism, they grew toward the side of higher fluence dependingon the difference in fluences between both sides. (Received August 1, 1981; Accepted September 29, 1981)     

Blue- and red-light action in photoorientation of chloroplasts in Adiantum protonemata

An action spectrum for the low-fluencerate response of chloroplast movement in protonemata of the fern Adiantum capillus-veneris L. was determined using polarized light vibrating perpendicularly to the protonema axis. The spectrum had several peaks in the blue region around 450 nm and one in the red region at 680 nm, the blue peaks being higher than the red one. The red-light action was suppressed by nonpolarized far-red light given simultaneously or alternately, whereas the bluelight action was not. Chloroplast movement was also induced by a local irradiation with a narrow beam of monochromatic light. A beam of blue light at low energy fluence rates (7.3·10^-3-1.0 W m^-2) caused movement of the chloroplasts to the beam area (positive response), while one at high fluence rates (10 W m^-2 and higher) caused movement to outside of the beam area (negative response). A red beam caused a positive response at fluence rates up to 100 W m^-2, but a negative response at very high fluence rates (230 and 470 W m^-2). When a far-red beam was combined with total background irradiation with red light at fluence rates causing a low-fluence-rate response in whole cells, chloroplasts moved out of the beam area. When blue light was used as background irradiation, however, a narrow far-red beam had no effect on chloroplast distribution. These results indicate that the light-oriented movement of Adiantum chloroplasts is caused by red and blue light, mediated by phytochrome and another, unidentified photoreceptor(s), respectively. This movement depends on a local gradient of the far-red-absorbing form of phytochrome or of a photoexcited blue-light photoreceptor, and it includes positive and negative responses for both red and blue light.Abbreviations BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light - UV ultraviolet     

Intracellular Localization and Dichroic Orientation of Phytochrome in Plasma Membrane and/or Ectoplasm of a Centrifuged Protonema of Fern Adiantum capillus-veneris L.

Protonemata of the fern Adiantum capillus-veneris grown undercontinuous red light for 6 days were kept in darkness for 15h and subsequently centrifuged 3 times in different directions,so that oil droplets and other cytoplasm were removed from theapical region of the protonemata. Electron micrographs clearlydemonstrated that cell wall, plasma membrane, ectoplasm andmicrotubules remained in the apical and subapical regions afterthe centrifugal treatments. A brief local exposure of the flankof the subapical region of the centrifuged protonemata to amicrobeam of red light effectively induced a phototropic responsetoward the irradiated side, suggesting that phytochrome is locatedin the ectoplasm and/or plasma membrane. When the flank of thecentrifuged protonema was irradiated with linearly polarizedred or far-red light, red light with an electrical vector parallelto the cell surface was more effective than that perpendicularto the cell surface. The direction of the electrical vectorof far-red light for reversion of the preirradiated red lighteffect, however, was opposite. These results suggest that differentdichroic orientations of P_R and P_FR exist in the plasma membraneor ectoplasm. (Received May 26, 1983; Accepted September 1, 1983)     

Apical Growth of Protonemata in Adiantum capillus-veneris IV. Phytochrome-Mediated Induction in Non-Growing Cells

In non-growing two-celled protonemata of Adiantum capillus-veneris,apical growth was induced most effectively by red light irradiation;half of the samples were induced to grow by 660 nm light ofca. 1.5 J m^–2 and the maximum number by ca. 70 J m^–2.The reciprocity law was valid in this photoinduction. The growthresumption became detectable 6 hr after the light irradiationand reached a plateau within 24 hr irrespective of given fluences.When non-growing samples were irradiated with red light of 4.6W m^–2 for 4 sec or shorter, the effect was fully reversedby a subsequent irradiation with far-red light to the far-redlight control level. But, when the red light was given for 16sec or longer, photoreversibility became partial. An interveningdark period of 2 min between red and far-red light did not significantlyinfluence the photoreversibility so that the escape reactionin the dark may not be attributed to the above-mentioned lossof photoreversibility. By means of a local irradiation with a narrow red light beam(10 µm in width), the apical cell was found to be photosensitivefor the growth induction, but basal cell was not. Photoreceptivesite was not localized in any particular region of the apicalcell, but was rather dispersed in the entire apical cell. (Received January 26, 1981; Accepted March 10, 1981)     

Light requirement,phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois

For dark-grown seedlings of Pharbitis nil capacity to flower in response to a single inductive dark period was established by 24 h white, far-red (FR) or ruby-red (BCJ) light and by a skeleton photoperiod of 10 min red (R)-24 h dark-10 min R. FR alone was ineffective without a brief terminal (R) irradiation, confirming that the form of phytochrome immediately prior to darkness is a crucial factor for flowering in Pharbitis. The magnitude of the flowering response was significantly greater after 24 h FR or white light (WL) (at 18° C and 27° C) than after two brief skeleton R irradiations, but the increased flowering response was not attributable to photosynthetic CO₂ uptake because this could not be detected in seedlings exposed to 24 h WL at 18° C. Photophosphorylation could have contributed to the increased flowering response as photosystem I fluorescence was detectable in plants exposed to FR, BCJ, or WL, but there were large differences between flowering response and photosystem I capacity as indicated by fluorescence. We conclude that phytochrome plays a major role in photoresponses regulating flowering. There was no simple correlation between developmental changes, such as cotyledon expansion and chlorophyll formation during the 24-h irradiation period, and the capacity to flower in response to a following inductive dark period. Changes in plastid ultrastructure were considerable in light from fluorescent lamps and there was complete breakdown of the prolamellar body with or without lamellar stacking at 27 or 18° C, respectively, but plastid reorganization was minimal in FR-irradiated seedlings.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing from of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Intracellular localisation of phytochrome and ubiquitin in red-light-irradiated oat coleoptiles by electron microscopy

The intracellular localisation of phytochrome and ubiquitin in irradiated oat coleoptiles was analysed by electron microscopy. We applied indirect immunolabeling with polyclonal antibodies against phytochrome from etiolated oat seedlings or polyclonal antibodies against ubiquitin from rabbit reticulocytes, together with a goldcoupled second antibody, on serial ultrathin sections of resin-embedded material. Immediately after a 5-min pulse of red light-converting phytochrome from the red-absorbing (Pr) to the far-redabsorbing (Pfr) form-the label for phytochrome was found to be sequestered in electron-dense areas. For up to 2 h after irradiation, the size of these areas increased with increasing dark periods. The ubiquitin label was found in the same electrondense areas only after a dark period of 30 min. A 5 min pulse of far-red light, which reverts Pfr to Pr, given immediately after the red light did not cause the electron-dense structures to disappear; moreover, they contained the phytochrome label immediately after the far-red pulse. In contrast, after the reverting far-red light pulse, ubiquitin could only be visualised in the electron-dense areas after prolonged dark periods (i.e. 60 min). The relevance of these data to light-induced phytochrome pelletability and to the destruction of both Pr and Pfr is discussed.Abbreviations FR far-red light; Pfr - Pr far-red-absorbing and red-absorbing forms of phytochrome, respectively - R red light     

Returning Dark-Induced Cell Cycle to the Beginning of G1 Phase by Red Light Irradiation in Fern Adiantum Protonemata

In filamentous protonemata of Adiantum capillus-veneris L. preculturedunder continuous red light, the progression of cell cycle whichwas induced by transferring the protonemata to the dark wasinhibited and the phase returned to the beginning of G1 by redlight irradiation unless the cell cycle had progressed to a"point of no return" which coincides with the beginning of Sphase. The effect of red light was reversed by subsequent far-redlight. Typical red far-red reversibility indicates that thephotoreceptive pigment is phytochrome. (Received May 17, 1984; Accepted June 21, 1984)     

Swelling of Etiolated Oat Protoplasts Induced by Phytochrome, cAMP and Gibberellic Acid: A Kinetic Study

The effects of phytochrome/light and other regulatory agentson the swelling of protoplasts from the primary leaves of etiolatedoat seedlings have been investigated. The protoplasts did notswell in darkness. Red (R) light immediately followed by far-red(FR) or FR light treatment alone for 4 h induced swelling slowly.In comparison, the protoplasts treated with R or FR-R swellmore rapidly and with a shorter lag period. The effect of redlight on the protoplast swelling was photoreversible by FR,suggesting the involvement of endogenous phytochrome. Exogenous gibberellic acid (GA₃) or dibutyryl cAMP (DBcAMP)stimulated the effect of R irradiation on the protoplast swelling.As with R irradiation, these agents were sufficient to causethe swelling of protoplasts in the dark with a shorter lag periodthan those maintained in darkness or a 5 min FR. The combinationof a 5 min R irradiation and GA₃ showed a synergistic effecton the enlargement of protoplast size. On the other hand, theincrease in protoplast size was proportional to the concentrationof DBcAMP with or without a 5 min R irradiation. (Received February 29, 1988; Accepted May 13, 1988)     

Spectral properties of soluble and pelletable phytochrome from epicotyls of etiolated pea seedlings

The red-light(R)-absorbing form of phytochrome (Pr) was detected spectrophotometrically in a 20,000 g particulate fraction prepared from a 1,000 g supernatant fraction from epicotyl tissue of pea (Pisum sativum L.) seedlings grown in the dark and only briefly exposed to dim green light. The difference spectrum of phytochrome in this fraction was essentially the same as that of soluble phytochrome from the same tissue. When the non-irradiated 20,000 g particulate fraction was incubated in the dark at 25° C, an absorbance change (decrease) of Pr after actinic red irradiation was found only in the far-red (FR) region. When the 20,000 g particulate fraction was irradiated with R and then incubated in the dark, the FR-absorbing form of phytochrome (Pfr) disappeared spectrally at a rate about half that in the soluble fraction, and the difference spectrum of the Pr which became detectable after dark incubation of the 20,000 g particulate fraction was markedly distorted. In contrast, Pfr in a 20,000 g particulate fraction prepared from tissues irradiated with R did not change optically during dark incubation at 25° C for 60 min, while Pfr in the soluble fraction from the same tissue disappeared in the dark. No dissociation of either Pr or Pfr from the 20,000 g particulate fraction was indicated during a 60-min dark incubation at 25° C, but Pfr in a 20,000 g particulate fraction prepared in vitro from R-irradiated 1,000 g supernatant fraction in the presence of CaCl₂ disappeared spectrally and the difference spectrum of Pr in the 20,000 g particulate fraction became quite distorted during the dark incubation.Abbreviations Pr red-light-absorbing form of phytochrome - Pfr far-red-light-absorbing form of phytochrome - FR far-red light - FR1 first actinic far-red light - FR2 second actinic far-red light - R red light - R1 first actinic red light - 1kS 1,000 g supernatant fraction - 20kS 20,000 g supernatant fraction - 20kP 20,000 g particulate fraction     

Photoorientation of chloroplasts in protonemal cells of the fernAdiantum as analyzed by use of a video-tracking system

Photoorientation of chloroplasts mediated by phytochrome and blue light-absorbing pigment in protonemal cells of the fernAdiantum was studied by use of inhibitors of the cytoskeleton and was analyzed with a video-tracking system. The photoorientation responses were inhibited by cytochalasin B and by N-ethylmaleimide (NEM) but not by colchicine, suggesting that the photomovement depends on the actomyosin system. In the dark, chloroplasts moved randomly, being independent of one another. After induction of photoorientation by polarized red light, most chloroplasts that had been located at the margin of cells moved almost perpendicularly to the cell axis toward the site of photoorientation. This type of movement was hardly ever observed in the dark. Under polarized blue light, such specific movements were less evident but were still observed in the case of a few chloroplasts. After photoorientation was complete, chloroplasts still moved in random directions but their mobility was lower than that in the dark, indicating the presence of some anchoring mechanism. When EGTA was applied, photoorientation was inhibited but this inhibition was overcome by the addition of CaCl₂. Video-tracking of chloroplasts in the dark revealed that the mobility of chloroplasts was higher in medium with EGTA than in medium with EGTA plus CaCl₂ and that many of the chloroplasts moved jerkily in the medium with EGTA. This change in the nature of movements was also seen under polarized light, resulting in the disturbance of photoorientation. These results indicate that the inhibition of photoorientation at low concentrations of Ca²⁺ ions may be due to change in the nature of chloroplast movement.     

Microfilaments Anchor Chloroplasts along the Outer Periclinal Wall in Vallisneria Epidermal Cells through Cooperation of PFR and Photosynthesis

In the cytoplasmic layer that faces the outer periclinal wallin epidermal cells of leaves of the aquatic angiosperm Vallisneriagigantea Graebner, we examined a possible interrelationshipamong the configuration of microfilaments, chloroplast motility,and anchoring of chloroplasts. In dark-adapted cells, microfilamentsare arranged in a network array. During a 10-min incubationin darkness 10 to 20 min after irradiation with red light (650nm, 0.41 W m^–2) for 5 min, the number of cells containinga network array decreased substantially while the number ofcells containing microfilaments in a honeycomb array increased.Irradiation with red light rapidly produces an increase in chloroplastmotility, but chloroplast motility declined almost to initiallevels during the 10-min incubation in darkness after the irradiation.Simultaneously, the chloroplasts in these cells became extremelyresistant to centrifugal forces. These effects of red lightwere negated either by far-red light or by the presence of DCMU,and were sensitive to cytochalasin B. It appears, therefore,that microfilaments not only drive the movement of chloroplastsbut also play a crucial role in accumulation of the chloroplastsalong the outer periclinal wall through dynamic changes in theconfiguration under cooperative regulation by P_FR and photosynthesis. (Received July 24, 1998; Accepted September 22, 1998)     

Dichroic Orientation of Phytochrome Intermediates in the Pathway from PR to PFR as Analyzed by Double Laser Flash Irradiations in Polarotropism of Adiantum Protonemata

The polarotropic response in protonemata of the fern Adiantumis regulated by phytochrome (Kadota et al. 1984); P_R and P_FRhave been shown to be dichroically oriented parallel and normalto the cell surface, respectively (Kadota et al. 1982). Thischange in the dichroic orientation of phytochrome during photoconversionwas analyzed by a newly-built, polarization plane-rotatabledouble laser flash irradiator. A polarotropic response was effectivelyinduced with a flash of polarized red (640 nm) light (6xl0^–7s) having the vibration plane of the electrical vector parallelto the protonemal cell axis. When a flash of polarized far-red(710 nm) light (6xl0^–7s) was given 30 sec after the redflash, the red flash-induced response was reversed by a far-redflash vibrating normal to the cell axis but not by one vibratingparallel. However, when given 2 µs or 2 ms after the redflash, the polarotropic response was not reversed by a polarizedfar-red flash vibrating normal to the cell axis but was reversedby a parallel-vibrating flash. These results suggest that theorientation of phototransformation intermediates existing 2µs or 2 ms after a red flash is still parallel to thecell surface, and that the change in the orientation of phytochromemolecules occurs between 2 ms and 30 s after the red flash. (Received February 3, 1986; Accepted April 23, 1986)     

Studies on the Photoreceptors for the Promotion and Inhibition of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy

Three-day-old etiolated seedlings of Pharbitis nil were exposedto red light for 10 min and sprayed with N⁶-benzyladenine beforetransfer to a 48-h inductive dark period, after which they weregrown under continuous white light. A second red irradiationpromoted flowering when given at the 5 and 24th hour of theinductive dark period but inhibited flowering at the 10 and15th hour. Far-red light inhibited flowering when given at anytime during the first 24 h of the dark period. Red/far-red reversibilitywas clearly observed at the 0, 5, 10 and 24th hour, but notat the 15th hour when both red and far-red lights completelyinhibited flowering. The action spectrum for the inhibition of flowering at the 15thhour of the inductive dark period had a sharply defined peakat 660 nm and closely resembled the absorption spectrum of theP_R form of phytochrome. The photoreceptors involved in thesephotoreactions are discussed. (Received June 10, 1983; Accepted July 6, 1983)     

Effects of blue and red light on unrolling of rice leaves

Unrolling of the second leaf of 8-day-old rice (Oryza sativa L.) seedlings was promoted by weak blue light (B), but not by red light (R). The effect of B was counteracted by irradiation with R just before or after the B. The counteracting effect of R was reversed by subsequent irradiation with far-red light but not by B, even if B was applied for 10 h. The B was effective when the region 0.5–2 cm from the tip of the leaf was irradiated. These results indicate that in rice photoreceptors for blue light located in the region 0.5–2 cm from the tip of the leaf play a key role in leaf unrolling and that a B-absorbing pigment and phytochrome participate in leaf unrolling in a closely related manner.Abbreviations B blue light - R red light - FR far-red light - W white light - D dark This work was presented at the Annual Meeting of the Japanese Society of Plant Physiologists on April 4, 1978, in Hiroshima