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     

Phytochrome control of plastid mRNA in mustard (Sinapis alba L.)

The steady-state levels of plastid RNA sequences in dark-grown and light-grown mustard (Sinapis alba L.) seedlings have been compared. Total cellular RNAs were labeled in vitro with ³²P and hybridized to separated restriction fragments of plastid DNA. Cloned DNA fragments which encode the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39] and a 35,000 plastid polypeptide were used as probes to assess the levels of these two plastid mRNAs. The 1.22-kilobase-pair mRNA for the 35,000 polypeptide is almost undetectable in dark-grown seedlings, but is a major plastid mRNA in light-grown seedlings. The hybridization analysis of RNA from seedlings which were irradiated with red and far-red light indicates that the level of this mRNA, but not of LS mRNA, is controlled by phytochrome.Abbreviations LS large subunit - RuBP ribulose-1,5-bisphosphate - ptDNA plastid DNA     

Ribosome-binding sites on chloroplastrbcL andpsbA mRNAs and light-induced initiation of D1 translation

Chloroplast ribosome-binding sites were identified on the plastidrbcL andpsbA mRNAs using toeprint analysis. TherbcL translation initiation domain is highly conserved and contains a prokaryotic Shine-Dalgarno (SD) sequence (GGAGG) located 4 to 12 nucleotides upstream of the initiator AUG. Toeprint analysis ofrbcL mRNA associated with plastid polysomes revealed strong toeprint signals 15 nucleotides downstream from the AUG indicating ribosome binding at the translation initiation site.Escherichia coli 30S ribosomes generated similar toeprint signals when mixed withrbcL mRNA in the presence of initiator tRNA. These results indicate that plastid SD sequences are functional in chloroplast translation initiation. ThepsbA initiator region lacks a SD sequence within 12 nucleotides of the initiator AUG. However, toeprint analysis of soluble and membrane polysome-associatedpsbA mRNA revealed ribosomes bound to the initiator region.E. coli 30S ribosomes did not associate with thepsbA translation initiation region.E. coli and chloroplast ribosomes bind to an upstream region which contains a conserved SD-like sequence. Therefore, translation initiation onpsbA mRNA may involve the transient binding of chloroplast ribosomes to this upstream SD-like sequence followed by scanning to localize the initiator AUG. Illumination 8-day-old dark-grown barley seedlings caused an increase in polysome-associatedpsbA mRNA and the abundance of initiation complexes bound topsbA mRNA. These results demonstrate that light modulates D1 translation initiation in plastids of older dark-grown barley seedlings.     

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.     

Inhibitory Action of Blue and Far-Red Light in the Flowering of Lemna paucicostata

In a new strain of short-day duckweed (Lemna paucicostata T-101), blue and far-red light-induced inhibition of flowering was investigated. Flowering of this strain failed to be induced under a short-day photoperiod of blue and far-red light, although it responded as a typical short-day plant in red and white light. When the short-day photoperiod of blue or far-red light was terminated by a 15 min red light pulse, flowering recovered completely. This inducing effect of red light was reversed by subsequent exposure to far-red light. Furthermore, it could be demonstrated that 30 min of blue light completely reversed the flowering inductive effect of 5 min red light and vice versa. Evidence is presented suggesting that the inhibitory action of blue and far red light may be due to the lowering of phytochrome P_fr levels below those required to start the dark reactions which lead to flowering. These results are discussed in relation to the time measurement system of photoperiodism.     

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     

Blue Light Induction of Barley Leaf Unfolding. A Phytochrome Reaction?

Low-energy blue light (450, 475 nm) has been found to induced unfolding of etiolated barley leaves (Hordeum rulgare cv. Ingrid). This induction can be reversed by far-red light. Barley leaf unfolding is normally stimulated by red light, reversed by far-red light, and can be considered to be a typical phytochrome controlled response. It is possible to explain the effects by red and blue light as mediated by the same photoreceptor. The phototransformation of this pigment results in two forms, P₂ and P₄, to which physiological activity can be ascribed. The red and blue light affect different steps in a cyclical photoconversion. Calculated theoretical dose response curves are presented for such a model in agreement with the experimental data.     

Photosensory mechanisms in the lettuce seedling hypocotyl

Summary A number of differences in the responses of Great Lakes lettuce seedlings to blue and far-red light indicate that more than one photo-sensitive pigment is involved in the photo-inhibition of hypocotyl elongation under highenergy conditions. In far-red light the inhibitory effect is restricted to young seedlings and is of limited duration; after 24 hours in far-red a rapid growth rate similar to that of plants maintained in darkness is resumed, despite continued irradiation. The onset of inhibition is relatively slow. Blue light, in contrast, exerts a strongly inhibitory effect on elongation at any age, and a slow rate of growth persists throughout the entire irradiation period. The onset of inhibition is very rapid. Furthermore, even when the inhibition in far-red had already been exhausted after prolonged exposure, transfer to blue light resulted in a prompt reduction in growth rate. Also the effect of far-red is almost completely lost after a pre-irradiation with red light which does not affect the response to blue. It is concluded that the responses to blue and far-red light in Great Lakes lettuce are not mediated by a single pigment system and that a distinct blue-sensitive pigment is present in addition to phytochrome. Red light has a number of different effects depending on conditions: (1) a pretreatment with red light almost completely prevents the inhibitory effect of a subsequent far-red irradiation, (2) a brief terminal treatment with red increases the inhibitory effect of either far-red or blue light; this is reversed by far-red, and (3) prolonged exposure to red light given alone increases the growth rate relative to darkness, because the more rapid elongation rate characteristic of young seedlings continues for longer with red light than in plants grown in darkness throughout.     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome     

Light quantity and quality interactions in the control of elongation growth in light-grown Chenopodium rubrum L. seedlings

The spectral control of hypocotyl elongation in light-grown Chenopodium rubrum L. seedlings has been studied. The results showed that although the seedlings responded to changes in the quantity of combined red and far-red radiation, they were also very sensitive to changes in the quantity of blue radiation reaching the plant. Altering the proportion of red: far-red radiation in broad waveband white light caused marked differences in hypocotyl extension. Comparison of the responses of green and chlorophyll-free seedlings indicated no qualitative difference in the response to any of the light sources used, although photosynthetically incompetent plants were more sensitive to all wavelengths. Blue light was found to act primarily of a photoreceptor which is different from phytochrome. It is concluded that hypocotyl extension rate in vegetation shade is photoregulated by the quantity of blue light and the proportion of red: far-red radiation. In neutral shade, such as that caused by stones or overlying soil, hypocotyl extension appears to be regulated primarily by the quantity of light in the blue waveband and secondarily by the quantity of light in the red and far-red wavebands.Abbreviations B blue - FR far-red - k ₁, k ₂ rate constants for photoconverison of Pr to Pfr and Pfr to Pr, respective - k ₁/k ₁ +k ₂= phytochrome photoequilibrium - k ₁ +k ₂= phytochrome cycling rate - Pr=R absorbing form of phytochrome - Pfr=FR absorbing form of phytochrome - P_tot Pr+Pfr - PAR photosynthetically active radiation = 400–700 nm - R red - WL white light     

Time Dependence of Phytochrome-mediated Carotenoid and Chlorophyll Synthesis in Sorghum bicolor L

In 5-day-old etiolated Sorghum seedlings, red light irradiationfor 1 s enhanced carotenoid and chlorophyll accumulation, and5 min of red light treatment saturated the photoresponse. Thedegree of red/far-red photoreversibility of carotenoid accumulationwas dependent on the age of the plant. No significant escapefrom far-red reversibility was observed up to 30 min after theonset of a saturating red light pulse in 5-day-old etiolatedseedlings. Thereafter, the escape was relatively fast and completedwithin 180 min. Sorghum bicolor L, carotenogenesis, phytochrome, time dependence, chlorophyll synthesis     

Effects of red and far-red light on cell division in the shoot apex ofSilene coeli-rosa L.

Summary 28-day-old plant ofSilene coeli-rosa were exposed at 1,700 hours to 5 or 10 minutes red light, 5 or 10 minutes far-red light, red followed by far-red, far-red followed by red or maintained in darkness. Measurements of the proportions of cells with the 2 C and 4 C amounts of DNA in the shoot apex of the plants, sampled at 2,000 hours, showed that far-red light promoted an increase in the G2 proportion whereas red light resulted in an increase in the G1 proportion of the cell cycle, relative to the dark controls. Moreover these changes were red, far-red reversible. All light treatments resulted in increases in the mitotic index in the apex compared with the dark controls, suggesting increases in the growth rate. The data implicate phytochrome in a low energy response and suggest that, in the shoot apex, G1 is shortened markedly following exposure to farred light, whilst G2 is shortened the most following exposure to red light. The results are discussed in relation to flower-initiation.     

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