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.     

The effect of light quality on the growth and development of in vitro cultured Doritaenopsis plants

The influence of light quality on growth and development of in vitro grown Doritaenopsis hort. (Orchidaceae) plants was investigated. Growth parameters like leaf and root fresh/dry mass and leaf area were highest with plants grown under red plus blue light emitting diodes (LEDs). Leaf length was greater with the plants grown under red LED. Carbohydrate (starch, sucrose, glucose and fructose) and leaf pigment (chlorophylls and carotenoids) biosynthesis of the plants was significantly increased in plants grown under red plus blue LEDs compared to red or blue LED and fluorescent light treatments. This study suggests that the production of quality Doritaenopsis plants is possible by culturing the plants in vitro under a mixture of blue plus red light sources.     

Oak Seedlings Grown in Different Light Qualities

Seedlings of oak (Quercus robur) were germinated in darkness for 3 weeks and then given continuous light or short pulses of light (5–8 min every day). The morphological development was followed during 25 days. In continuous white, blue, and red light the stem growth terminated after about 10 days by formation of a resting bud. At that time the seedlings were about 100 mm high. In con tinuous long wavelength farred light (wavelength longer than 700 nm) the stem growth including leaf formation was continuous without the formation of resting buds, and the stem length was about 270 mm after 25 days. The number of nodes developed became twice that of the seedlings grown in while light. The leaves became well developed in all light colours, but leaf areas were largest in plants cultivated in white light. Compared to dark grown seedlings the mean area per leaf was increased about five times in continuous long wavelength far red light. A supplement with short (5 min) pulses of red light each day increased the leaf area up to 20 times. The stem elongation showed a high energy reaction response, i.e. the stem length increased only in continuous long wavelength far-red light but was not influenced by short pulses of red light or far-red light. The leaf expansion, however, was increased by short pulses of red light with a partial reversion of the effect by a subsequent pulse of far-red light. The fraction of the plant covered with periderm was higher in plants given continuous light. In respect to periderm inhibition continuous long wavelength far red light was the most effective. The transfer of seedlings from darkness to continuous white light gave anthocyanin formation in the stem 10–20 mm below the apex. This formation took place in the cortex and was evident in plants grown in darkness or under short pulses of light. Plants grown in continuous red, blue or long wavelength Far red light showed only traces of anthocyanin.     

THE RELATIONSHIP BETWEEN THE PROMOTION OF ELONGATION OF FERN PROTONEMATA BY LIGHT AND GROWTH SUBSTANCES

Germinating spores of the fern Onoclea sensibilis L. were grown in darkness, so that they developed as filaments (protonemata). Brief daily exposure of the filaments to red, far-red or blue light increased the rate of filament elongation. Filament elongation was also promoted by indoleacetic acid. When filament elongation was promoted with both indoleacetic acid and exposure to light, the growth promotions caused by red and far-red light were additive to auxin-induced growth. Blue light promoted elongation only at sub-optimal concentrations of auxin. Elongation induced by guanine was additive to red- and far-red-induced elongation. Gibberellic acid had no effect on elongation under any condition. Blue-light-induced elongation resembled auxin-induced elongation in its requirement for exogenous sucrose and sensitivity to inhibition by parachlorophenoxyisobutyric acid. Red and far-red light were active regardless of the presence or absence of sucrose and promoted elongation at a concentration of parachlorophenoxyisobutyric acid which completely inhibited blue-light-induced elongation.     

Influence of Light of Different Spectral Compositions on Growth and Metabolism of Citrus Seedlings

Sour orange (Citrus aurantium L.) seedlings grown for six months under covers transmitting light of different spectral composition, were compared with others grown under a white cover (control) and outside in full daylight. The intensity of transmitted light was equalized under all covers and attained only 20% of full daylight. Seedlings grown in daylight were shorter, had more internodes, smaller leaves, less chlorophyll and more ascorbic acid than the others. Blue + far-red covers (no transmission between 560–700 nm) enhanced seedling length, the protein and chlorophyll content and peroxidase activity of leaves. When also the wave-range above 700 nm was cut out (blue) seedlings were the shortest, and leaves had very high protein and chlorophyll content, but much less ascorbic acid and lower peroxidase activity. Red + far-red covers (no transmission below 500 nm) enhanced seedling length more than blue + far-red; leaves contained as much protein as control, but had relatively high chlorophyll and peroxidase activity. Ascorbic acid was as low as in blue light.     

Adventitious shoot regeneration from Begonia × erythrophylla petiole sections is developmentally sensitive to light quality

The influence of light quality on organogenesis in vitro was investigated using Begonia  ×  erythrophylla petiole explants. Pre-treatment of in vitro donor plants by growth in the dark or under far-red or blue light reduced their competence for shoot formation when compared with those grown under red or white light. Culture of competent petiole explants under far-red, blue light or in the dark reduced the number of shoots produced per explant compared to those cultured under red or white light. Explants were found to be developmentally sensitive to both far-red and blue light, because meristem, but not primordia development was inhibited. In addition, blue light inhibition of shoot formation is not mediated directly through phytochrome, as few shoots formed on explants cultured under a mixture of red and blue light which resulted in a high P _fr/ P _tot (0.82) and would allow shoot formation in the absence of blue light. Unlike the inhibitory influence of far-red light, which is reversible, exposure to blue light permanently reduces an explant's competence for shoot formation. Our results suggest that phytochrome and an independent blue light photoreceptor, possibly a cryptochrome, can regulate shoot production from B. erythrophylla petiole explants.     

Photomorphogenesis, Photosynthesis, and Early Growth of Primary Leaves of Phaseolus vulgaris

The response of leaf tissue to white, blue, red, and far-redlight has been examined. Leaves on plants grown in darknessshow increased cell number, cell volume, and area when exposedto long periods (up to 48 h) of low-intensity red, blue, orfar-red radiation. This is believed to be a photomorphogenicresponse which does not involve photosynthesis. Leaves fromplants exposed to white light during germination do not usuallyrespond to red, blue, or far-red light. An exception to thiswas found for leaf discs which showed a larger increase in areathan the dark controls following exposure to far-red light for24 h. Leaf tissue from light-grown plants responds to high-intensitywhite light, probably through photosynthesis. Discs cut fromdark-grown plants and cultured in white light grow equally wellin air and CO₂-free conditions. Application of the photosyntheticinhibitor DCMU reduces growth and chlorophyll formation, however. It is concluded that light, perhaps acting through the phytochromemechanism, has initially a number of morphogenic effects includinginitiation of development of the photosynthetic apparatus. Theresponses to photomorphogenically active radiation do not persistand light effects through photosynthesis are rapidly initiatedand dominate the later stages of leaf growth.     

Influence of mixed LED radiation on the growth of annual plants

We investigated the effect of mixed radiation from light-emitting diodes (LEDs) on the growth and flowering of ageratum, marigold, and salvia bedding plants. Blue, red, and far-red lights were applied under controlled environmental conditions for 28 d. Both the combination of blue-plus-red radiation as well as fluorescent lighting treatment (control) caused increases in dry weights, but shoot lengths were shortest when plants were exposed to blue plus red light compared with either red or blue plus far-red treatments. The number of floral buds as well as the occurrence of flower opening for ageratum and salvia plants was also enhanced under the blue plus red mixture. Likewise, carbohydrate accumulation was stimulated by that combination compared with the other radiation treatments.     

The effect of shading on photosynthesis,growth, and regrowth following defoliation for Bromus tectorum

Summary The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects.     

Tillering Responses to the Light Environment and to Defoliation in Populations of Perennial Ryegrass (Lolium perenneL.) Selected for Contrasting Leaf Length

Tillering responses to the light environment and to defoliationwere studied in two populations of perennial ryegrass (LoliumperenneL.) selected for contrasting leaf lengths. The objectiveof this study was to determine whether differences in tilleringresponses between populations, as a result of management practices,affected their competitive ability. Young seedlings were exposed,under controlled conditions, to defoliation, neutral shading(decreased photosynthetic photon flux), low red:far-red ratioand/or decreased blue light. Selection for longer leaves reducedthe tillering rate. After defoliation, this difference betweenshort- and long-leaved populations was magnified. Defoliationdecreased both site filling and phyllochron of the long-leavedpopulation but had no effect on the short-leaved population.Lowering the photosynthetic photon flux reduced the phyllochronin both population. Decreasing the red:far-red ratio reducedtillering rate by reducing site filling, whereas decreasingblue light had no significant effects on tillering. Tilleringresponses to photosynthetic photon flux and to red:far-red ratiowere similar in the two populations selected for contrastingleaf length. The implication of these tillering responses indefining the competitive ability of the grass plants is discussedin relation to their management.Copyright 1999 Annals of BotanyCompany Blue light, defoliation, far-red, irradiance, leaf size,Lolium perenne(L.), perennial ryegrass, photomorphogenesis, phyllochron, shading, site filling, tiller production.     

Anatomical features of pepper plants (Capsicum annuum L.) grown under red light-emitting diodes supplemented with blue or far-red light

Pepper plants (Capsicum annuum L. cv., Hungarian Wax) were grown under metal halide (MH) lamps or light-emitting diode (LED) arrays with different spectra to determine the effects of light quality on plant anatomy of leaves and stems. One LED (660) array supplied 90% red light at 660 nm (25nm band-width at half-peak height) and 1% far-red light between 700-800nm. A second LED (660/735) array supplied 83% red light at 660nm and 17% far-red light at 735nm (25nm band-width at half-peak height). A third LED (660/blue) array supplied 98% red light at 660nm, 1% blue light between 350-550nm, and 1% far-red light between 700-800nm. Control plants were grown under broad spectrum metal halide lamps. Plants were gron at a mean photon flux (300-800nm) of 330 micromol m-2 s-1 under a 12 h day-night photoperiod. Significant anatomical changes in stem and leaf morphologies were observed in plants grown under the LED arrays compared to plants grown under the broad-spectrum MH lamp. Cross-sectional areas of pepper stems, thickness of secondary xylem, numbers of intraxylary phloem bundles in the periphery of stem pith tissues, leaf thickness, numbers of choloplasts per palisade mesophyll cell, and thickness of palisade and spongy mesophyll tissues were greatest in peppers grown under MH lamps, intermediate in plants grown under the 660/blue LED array, and lowest in peppers grown under the 660 or 660/735 LED arrays. Most anatomical features of pepper stems and leaves were similar among plants grown under 660 or 660/735 LED arrays. The effects of spectral quality on anatomical changes in stem and leaf tissues of peppers generally correlate to the amount of blue light present in the primary light source.     

Light-quality and irradiance effects on pigments, light-harvesting proteins and Rubisco activity in a chlorophyll- and light- harvesting-deficient soybean mutant

Soybean ( Glycine max [L.] Merrill) plants, normal green (Clark L1) and mutant yellow (Clark y₉y₉), were grown in (1) full-spectrum solar irradiation; (2) either red plus far-red or blue plus far-red; (3) either red or blue light with no far-red light. Young leaves harvested from first (1TF) trifoliolate or fifth (5TF) trifoliolate stages of development showed that the mutant plants express pigment and protein deficiencies as a direct function of irradiance. Response of the mutant to light quality indicates that blue light slightly enhances expression of the mutation at higher irradiances. Direct response of light-harvesting proteins of photosystem 2 (LHCP2) and light-harvesting protein of photosystem 1 (LHCP1) to light quality increases the ratio of LHCP1/LHCP2 in blue light compared to that in red or red/far-red light. Rubisco proteins and Rubisco activity (leaf area basis) are directly related to irradiance level but are enhanced in blue light over equal irradiance red. This enhancement is not shown in the presence of far-red light.     

Light-quality effects on Arabidopsis development. Red, blue and far-red regulation of flowering and morphology

Arabidopsis thaliana (L.) Heynh. race Columbia plants were grown in red. blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m⁻² s⁻¹) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P_fr/P_tot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P_fr/P_tot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.     

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida‘Radrazz’ and Rosa chinensis‘Old Blush’, cultivated under two light qualities. Plants were grown from one‐node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO₂ assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO₂ concentrations. In ‘Radrazz’, the reduction in CO₂ assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses.     

Action Spectra for Light-induced Elongation in Fern Protonemata

The action spectrum for promotion of elongation of protonemata of Onoclea sensibilis has peaks at 400–420, 580–600 and 640–660 nm. The largest growth increments at saturating light doses are produced by yellow and far-red light. Elongation induced by yellow and far-red irradiation persists in old as well as young filaments, while red-light promotion is found only in young filaments. The growth promotion caused by yellow light is partially reversed by red light down to the level of growth produced by red irradiation alone. Elongation of rhizoids is under reversible red, far-red control, while yellow light is inactive. A model is proposed and discussed in which the light-sensitive elongation of filaments is accounted for by the presence of three distinct photoreceptors: phytochrome; a pigment absorbing yellow light. P₅₈₀; and a pigment absorbing blue light, P₄₂₀.     

Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting

Red light-emitting diodes (LEDs) are a potential light source for growing plants in spaceflight systems because of their safety, small mass and volume, wavelength specificity, and longevity. Despite these attractive features, red LEDs must satisfy requirements for plant photosynthesis and photomorphogenesis for successful growth and seed yield. To determine the influence of gallium aluminium arsenide (GaAlAs) red LEDs on wheat photomorphogenesis, photosynthesis, and seed yield, wheat (Triticum aestivum L., cv. 'USU-Super Dwarf') plants were grown under red LEDs and compared to plants grown under daylight fluorescent (white) lamps and red LEDs supplemented with either 1% or 10% blue light from blue fluorescent (BF) lamps. Compared to white light-grown plants, wheat grown under red LEDs alone demonstrated less main culm development during vegetative growth through preanthesis, while showing a longer flag leaf at 40 DAP and greater main culm length at final harvest (70 DAP). As supplemental BF light was increased with red LEDs, shoot dry matter and net leaf photosynthesis rate increased. At final harvest, wheat grown under red LEDs alone displayed fewer subtillers and a lower seed yield compared to plants grown under white light. Wheat grown under red LEDs+10% BF light had comparable shoot dry matter accumulation and seed yield relative to wheat grown under white light. These results indicate that wheat can complete its life cycle under red LEDs alone, but larger plants and greater amounts of seed are produced in the presence of red LEDs supplemented with a quantity of blue light.     

光质对植物光合作用的调控及其机理

光合作用是植物生长发育的基础.光质对植物光合作用的调控主要包括可见光对植物气孔器运动、叶片生长、叶绿体结构、光合色素、D1蛋白及其编码基因和光合碳同化等的调节,以及紫外光对植物光系统Ⅱ的影响.蓝光和红光能促进气孔的开张,而绿光能够逆转这种作用.蓝光有利于叶绿体的发育,红、蓝、绿复合光有利于叶面积的扩展,而红光更有利于光合产物的积累;不同光质对不同植物、不同组织器官叶绿素积累的影响不同.蓝光和远红光可以促进psbA基因转录物质的积累.大多数高等植物和绿藻在橙、红光下光合速率最高,蓝紫光其次,绿光最低.紫外光可以导致光系统Ⅱ的电子传递活性下降.此外,针对光质与光合作用研究领域中存在的问题,对今后的研究方向进行了讨论.     

The impact of red and blue light-emitting diode illumination on radish physiological indices

The objective was to evaluate the effect of different combinations of red (638 nm) and blue (455 nm) light produced by solid-state light-emitting diodes (LEDs) on physiological indices (net assimilation rate, hypocotyl-to-leaf ratio, leaf area, leaf dry weight, hypocotyl length and diameter, plant length, developed leaves), variation of photosynthetic pigments and non-structural carbohydrates in radish (Raphanus sativus L., var. ‘Faraon’). Lighting experiments were performed under controlled conditions (total PPFD - 200 μmol m⁻² s⁻¹; 16 h photoperiod; 14/18°C night/day temperature). The LED conditions: 638 nm; 638 + 5% 455 nm; 638 + 10% 455 nm; 638 + 10% 455 + 731 nm; 638 + 10% 455 + 731 + 669 nm. Our results showed that radishes grown under red (638 nm) alone were elongated, and the formation of hypocotyl was weak. The net assimilation rate, hypocotyl-to-leaf ratio, and leaf dry weight also were low due to the low accumulation of photosynthetic pigments and non-structural carbohydrates in leaves. The supplemented blue (455 nm) light was necessary for the non-structural carbohydrates distribution between radish storage organs and leaves which resulted in hypocotyl thickening. Red alone (638 nm) or in combination with far-red (731 nm), or red669 for radish generative development was required.     

The effect of light quality on leaf production and development of in vitro-cultured plants of Alternanthera brasiliana Kuntze

We investigated the influence of light quality on the leaf development of Alternanthera brasiliana Kuntze (Amaranthaceae) grown in vitro. Growth parameters including specific leaf mass, thickness, and leaf density were lowest in plants grown under red light. Blue light induced the largest number of leaves/plant, and the largest thickness and area of the leafblade. Green and red lights induced the smallest leaf areas. The thickness of the abaxial-face epidermis and spongy parenchyma of the plants was significantly reduced in plants grown under red light. The thickness of the palisade parenchyma and upper epidermis were significantly increased in plants grown under blue light, compared to the other fluorescent-light treatments. The specific spectral band also influenced the differentiation of mesophyll cells. In the dark and under red light, the mesophyll was homogenous; and in the dark and under green light, the leaves were more compact. Under blue light, the cells displayed the characteristic palisade morphology. The results showed that the increase of a specific parenchyma type was related to a specific spectral band. All spectral-quality treatments reduced the numbers of stomata and trichomes. The results for green light were in some respects similar to those for red light, and in other respects similar to those for blue light, probably because phytochromes and cryptochromes are green-light receptors. This study indicated that Alternanthera plants have strong morphological plasticity induced by light. The results suggest that high-quality Alternanthera can be achieved by culturing the plants in vitro under a combination of blue and red light.     

The Effect of Colored Light on Pigment Synthesis in Cultured Fern Leaf Primordia

The effect of white, blue, yellow, red and far-red light on the quantitative synthesis of the primary and auxilliary photosynthetic pigments in cultured leaf primordia of Osmunda cinnamomea L. is reported. The P₆₆₀ form of the now classical photoreceptor pigment system, phytochrome, has been demonstrated to be active in chlorophyll synthesis in cultured cinnamon fern leaf primordia as shown by red/far-red reversibility of chlorophyll synthesis. Also, it is apparent from the data presented that a blue absorbing pigment (P₄₂₀) is responsible for the extensive accumulation of chlorophylls and carotenoids in these cultured leaves.