Phytochrome regulation of nitrate reductase in wheat

In excised wheat leaves, the activity of nitrate reductase was enhanced by a brief pulse of red light and this increase was reversed by far-red light irradiation. Even under continuous far-red light, nitrate reductase activity increased by 258% after 18 h. When leaves were kept in distilled water during exposure to red light and then transferred to potassium nitrate, there was no difference in endogenous nitrate concentration. The nitrate reductase activity was the same whether leaves were floated in potassium nitrate or in distilled water during irradiation. Partial to complete inhibition of enzyme activity was observed when leaves were incubated in actinomycin-D and cycloheximide respectively, following 4 h of red light irradiation.In vitro irradiation of extract had no significant effect on nitrate reductase activity     

Rhizome transition to storage organ is under phytochrome control in lotus <Emphasis Type="Italic">(Nelumbo nucifera)</Emphasis>

We examined photoperiodic response of lotus (Nelumbo nucifera) rhizome morphogenesis (its transition to a storage organ) by using seed-derived plants. Rhizome enlargement (increase in girth) was brought about under 8, 10 and 12 h photoperiods, whereas the rhizomes elongated under 13 and 14 h photoperiods. Rhizomes elongated under 14 h light regimes supplied as 8 h of natural light plus 6 h supplemental hours of white, yellow or red light, but similar treatments with supplemental blue, green or far red light, caused enlargement in girth of the rhizomes. A 2 h interruption of the night with white, yellow or red light, in plants entrained to 8 h photoperiod brought rhizome elongation, whereas 2 h-blue, green or far red light night breaks still resulted in rhizome increase in girth. The inhibitory effect of a red (R) light night break on rhizome increase in girth was reversed by a far-red (FR) light given immediately afterwards. Irradiation with R/FR/R inhibited the rhizome increase in girth. FR light irradiation following R/FR/R irradiation cancelled the effect of the last R light irradiation. It was demonstrated that the critical photoperiod for rhizome transition to storage organ is between 12 and 13 h photoperiod. It was also evident that the optimal light quality range for interruption of dark period (night break) is between yellow and red light and that a R/FR reversible reaction is observed. From these results, we propose that phytochrome plays an important role in photoperiodic response of rhizome increase in girth in lotus. This is the first report on phytochrome-dependent morphogenesis of storage organs in rhizomous plants.     

Evidence of phytochrome involvement in the entrainment of the circadian rhythm of carbon dioxide metabolism in Bryophyllum

The rhythm of carbon dioxide output in Bryophyllum leaves was entrained on exposure to 0.25 h of white light every 24 h. Entrainment also occurred on similar exposure to monochromatic radiation in spectral bands centred at 660 nm and, to a lesser extent, at 730 nm, but a band centred at 450 nm was without effect. A skeleton irradiation programme comprising two 0.25-h exposures to white light per 24 h also entrained the rhythm when the intervening dark periods were either 7.5 h and 16 h, or 10.5 h and 13 h. The rhythm disappeared when the two exposures were separated by 11.5-h and 12-h dark periods. Regular 0.25-h exposures to red light separated by 11.75-h periods of darkness also resulted in loss of the rhythm. Red/far-red reversibility was observed in irradiation schedules having either one or two exposures to red light daily. In the latter case, far-red reversal of the effects of one of the exposures to red light resulted in entrainment of the rhythm by the other, instead of abolition of the rhythm. The occurrence of distinct red/far-red reversibility suggests strongly that phytochrome is the pigment involved in entrainment of this rhythm by cycles of light and darkness.Abbreviation LD light-dark rhythm     

An amino-terminal deletion of rice phytochrome A results in a dominant negative suppression of tobacco phytochrome A activity in transgenic tobacco seedlings

Overexpression of phytochrome A results in an increased inhibition of hypocotyl elongation under red and far-red light. We used this approach to assay for the function of N-terminal mutations of rice (Oryza sativa L.) phytochrome A. Transgenic tobacco seedlings that express the wild-type rice phytochrome A (RW), a rice phytochrome A lacking the first 80 amino acids (NTD) or a rice phytochrome A with a conversion of the first 10 serines into alanine residues (S/A) were compared with untransformed wild-type tobacco (Nicotiana tabacum L. cv. Xanthi) seedlings. Experiments under different fluence rates showed that RW and, even more strongly, S/A increased the response under both red and far-red light, whereas NTD decreased the response under far-red light but hardly altered the response under red light. These results indicate that NTD not only lacks residues essential for an increased response under red light but also distorts the wild-type response under far-red light. Wild-type rice phytochrome A and, even more so, S/A mediate an enhanced phytochrome A as well as phytochrome B function, whereas NTD interferes with the function of endogenous tobacco phytochrome A as well as that of rice phytochrome A when co-expressed in a single host. Experiments with seedlings of different ages and various times of irradiation under far-red light demonstrated that the effect of NTD is dependent on the stage of development. Our results suggest that the lack of the first 80 amino acids still allows a rice phytochrome A to interact with the phytochrome transduction pathway, albeit nonproductively in tobacco seedlings.Abbreviations HIR high-irradiance response - NTD N-terminal deletion mutant of rice phytochrome A - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - RW rice wild-type phytochrome A - S/A serine-to-alanine mu-tant of rice phytochrome A - wNTD weakly expressing NTD line - XAN wild-type tobacco cv. Xanthi We thank Masaki Furuya (Adv. Research Laboratory, Hitachi, Saitama, Japan) and Akira Nagatani (RIKEN Institute, Saitama, Japan) for providing the monoclonal antibodies mAP5 and mAR14. The work was supported by a grant from the Human Frontier Science Program. K.E. was a recipient of a Landesgraduiertenförderung fellowship.     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Action spectra for the inhibition of growth in radish hypocotyls

In etiolated seedlings of Raphanus sativus L. the inhibition of hypocotyl elongation by continuous light showed a major bimodal peak of action in the red and far-red, and two minor peaks in the blue regions of the spectrum. It is argued that, under conditions of prolonged irradiation, phytochrome is the pigment controlling the inhibition of hypocotyl elongation by red and far-red light, but that its mode of action in far-red is different from that in red. A distinct pigment is postulated for blue light.Abbreviations B blue - FR far red - G green - R red - HIR high irradiance reaction - P_r and P_fr red and far red absorbing forms of phytochrome - R red     

Photocontrol of stem elongation in light-grown plants of Fuchsia hybrida

Stems of the caulescent long-day plant, Fuchsia hybrida cv Lord Byron, showed 2 types of response to light. In one, internode length was increased by far-red irradiation given at the end of an 8 h photoperiod: the response was no greater with prolonged exposure and was less when the start of far-red was delayed. The effect of far-red was reversible by a subsequent exposure to red light. Internode length was inversely proportional to the P_fr/P ratio established before entry to darkness and there was no evidence for loss of P_fr during a 16 h dark period. The inhibitory effect of P_fr acted at a relatively late stage of internode growth. With the development of successive internodes a second response appeared in which stems lengthened following prolonged daily exposures to red or far-red light, or mixtures of the two, or to brief breaks with red or white light. In these later internodes, a short exposure to far-red near the middle of the night was not reversible by red because red alone promoted elongation at this time. Internode length increased with increase in the daily duration of light and, when light was given throughout an otherwise dark period of 16 h, with increase in illuminance to a saturation value of 200 lx from tungsten lamps. Elongation increased as a linear function of decrease in photostationary state of phytochrome down to P_fr/P0.3; however, internodes were shorter in far-red light than in 25% red/red+far-red. It was concluded that stem length is a net response to two modes of phytochrome action. An inductive effect of P_fr inhibits a late stage in internode expansion, and a phytochrome reaction which operates only in light (and may involve pigment cycling) promotes an early stage of internode development. Stem elongation is thus a function both of the daily duration of light and its red/red+far-red content. The outgrowth of axillary buds was controlled by the first type of phytochrome action only.Abbreviations and symbols FR far red light - R red light - P phytochrome - P_fr phytochrome in the far-red light absorbing form - SD 8 h short days - LDP long-day plant - SDP short-day plant     

Effect of light on abscisic acid content in photosensitive Scots pine (Pinus sylvestris L.) seed

Dormancy-breaking treatment of the photosensitive Scots pine (Pinus sylvestris L.) seed by white light incubation or a 15-min exposure to red light decreased the abscisic acid content prior to radicle protrusion. Incubation in the dark or exposure to red light followed by a 5-min far-red light irradiation did not cause as great a decrease in abscisic acid content nor was the dormancy relieved. The ability of the far-red light to keep the ABA level high and to prevent germination gradually disappeared as the length of the dark period between the red and far-red treatments was increased to 24 h. ABA was quantified on a gas chromatograph with an electron capture detector.     

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

The low chlorophyll content of cotyledons of Pharbitis nil grown for 24 h in far-red light (FR) or at 18° C in white light from fluorescent lamps (WL) allows spectrophotometric measurement of phytochrome in these tissues. The (A) measurements utilize measuring beams at 730/802 nm and an actinic irradiation in excess of 90 s. The constancy of the relationship between phytochrome content and sample thickness confirms that, under these conditions of measurement, a true maximum phytochrome signal was obtained. These techniques have been used to follow changes in the form and amount of phytochrome during an inductive dark period for flowering. Following exposure to 24h WL at 18° C with a terminal 10 min red (R), P_fr was lost rapidly in darkness and approached zero in less than 1 h; during this period there was no change in the total phytochrome signal. Following exposure to 24 h FR with a terminal 10 min R, P_fr approached zero in 3 h, and the total phytochrome signal decreased by about half. The relevance of these changes to photoperiodic time measurement is discussed.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Light germination ofAnthoceros miyabeanus spores

The effects of light on the spore germination of a hornwort species,Anthoceros miyabeanus Steph., were investigated. Spores of this species were photoblastic, but their sensitivities to light quality were different. Under either continuous white, red or diffused daylight, more than 80% of the spores germinated, but under blue light none or a few of them germinated. Under continuous far-red light or in total darkness, the spores did not germinate at all.Anthoceros spores required red light irradiation for a very long duration, i.e., over 12–24 hr of red light for saturated germination. However, the spore germination showed clear photo-reversibility by repeated irradiation of red and far-red light. The germination pattern clearly varied with the light quality. There were two fundamental patterns; (1) cell mass type in white or blue light: spores divide before germination, and the sporelings divide frequently and form 1–2 rhizoids soon after germination, and (2) germ tube type in red light: spores germinate without cell division, and the single-cell sporelings elongate without cell division and rhizoid formation.     

The effect of SAN 9789 and light on the germination of seeds from Taraxacum vulgare

Photoblastic seeds (achenes) of Taraxacum vulgare coll. were treated with a water solution of SAN 9789, 4-chloro-5 (methylamino) -2- (α,α,α-trifluoro- m -tolyl) -3(2H) pyridazinone. SAN-treatment increased the germination in darkness from 0 to 12%. An irradiation for 5 min with red light, giving a germination of 12% for seeds in water only, gave together with SAN treatment a germination of 60%. In both water and SAN, the effect of red irradiation could be reversed by a short irradiation (15 min) of far-red light. If far-red light was repeatedly given (5 min per h) it had hardly any effect on germination in water (4% germination), but for seeds in SAN solution, intermittent far-red light had a stimulating effect (63% germination). If far-red light was given continuously for 96 h, the germination in water was 1% and in SAN solution 17%. The results in the present paper indicate that SAN may broaden the concentration interval of P_fr for which germination is high.     

Kinetic Study on the Development of the Capacity to Accumulate Chlorophyll A without a Lag Phase during Continuous Far-Red Irradiation in Pharbitis nil Seedlings

To analyze how the capacity to accumulate chlorophyll a (Chia) without a lag phase develops by continuous far-red light(FR) irradiation, the time course of the capacity was investigatedunder various FR-dark conditions in Pharbitis seedlings. Thecapacity, which is negligible in darkness, rapidly developedon transfer to continuous FR irrespective of the age of theseedlings, the maximum level being attained about 18-24 h afterthe onset of.FR irradiation. The-capacity gradually decreasedthereafter whether in darkness or under extended FR irradiation.When the seedlings pretreated by 6-12 h of FR followed by 66-60h darkness (which have no capacity) were exposed to the secondFR irradiation for up to 72 h, the level of the capacity acquiredduring the second FR irradiation was the lower the higher thelevel acquired by the first FR irradiation. A possible mechanismwhich determines the time course of the development of the capacityis discussed. (Received July 2, 1990; Accepted March 25, 1991)     

Visualization of a rapid,red/far-red light-dependent reaction by centrifuge microscopy

Summary Using a centrifuge microscope with stroboscopic illumination, we examined the effects of light irradiation on the passive movement of chloroplasts in dark-adapted mesophyll cells ofVallisneria gigantea. While irradiation with red light accelerates the passive gliding of chloroplasts produced by centrifugal force, irradiation with far-red light negates this effect. Irradiation with blue light does not accelerate the passive gliding, while red light is completely effective even in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthesis. An apparently active movement of chloroplasts can be induced by irradiation with red or blue light only in the presence of the far-red light-absorbing form of phytochrome. The significance of the reaction in the light with respect to the regulation of cytoplasmic streaming is discussed.Abbreviations APW artificial pond water - CMS centrifuge microscope of the stroboscopic type - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Pfr phytochrome, far-red light-absorbing form - Pr phytochrome, red light-absorbing form     

The response of Cuscuta planiflora seedlings to red and far-red, blue light and end-of-day irradiations

Irradiation of excised stem segments from de-etiolated seedlings of Cuscuta planiflora for 24 h with mixtures of red and far-red light with red to far-red ratios between 0.02 to 1.0 enhanced coiling and formation of prehaustoria. Maximum number of prehaustoria were recorded when red:far-red was near 0.1. Coiling and prehaustoria were observed whenever estimated in vivo Pfr/Ptotal at photoequilibrium was between 0.06 and 0.67. Irradiation of excised stem segments from white light grown seedlings with 12 h blue light also promoted coiling and prehaustoria formation after another 38 h in darkness. Coiling and prehaustoria were not observed in segments pulsed with 10 min red light at the end of 12 h in blue light. Coiling and prehaustoria were observed after photoreversible end-of-day far-red/red/far-red pulses but not after red/far-red/red pulses. A far-red pulse may not reverse inhibition by end-of-day red pulse when far-red is given more than 12 h after the red pulse.     

Integral association of phytochrome with a membranous fraction from etiolatedAvena shoots: red/far-red photoreversibility and in vitro characterization

The results reported in this paper provide strong evidence to support the belief that the small percentage of phytochrome recovered in low-speed centrifugation pellets, when prepared in the absence of divalent cations after various in vivo irradiations, is not simply a manifestation of non-specific co-precipitation of soluble phytochrome.The far-red reversibility of the observed near-doubling of phytochrome pelletability after in vivo red irradiation indicates that phytochrome pelletability in the absence of divalent cations is a phytochrome-controlled response. The characteristics of the pelleted phytochrome indicate a strong, hydrophobic interaction with membranes. A tentative proposal to explain the observed characteristics of the association of phytochrome with membranous material in the absence of divalent cations after different in vivo irradiations has been put forward.Abbreviations Pfr phytochrome in the far-red light absorbing form - Pr phytochrome in the fat-red light absorbing form - Ptot total phytochrome - R red light irradiation - FR far-red light irradiation     

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