The Effects of Light and Photo- and Protein-synthetic Inhibitors on the Sekiguchi Lesion Formation by Magnaporthe grisea in Rice cv. Sekiguchi-asahi*

The significance of light irradiation in Sekiguchi lesion (SL) formation by infection with Magnaporthe grisea on rice cv. Sekiguchi-asahi was investigated. When the leaf blades of cv. Sekiguchi-asahi inoculated with M. grisea spores were kept under different wavelengths of light. SLs were formed under visible light regardless of the compatibility between fungal race and cv. Sekiguchi-asahi. On the contrary, typical blast and/or nectrotic spot lesions were formed under near ultraviolet radiation from the black light fluorescent lamps and near infrared radiation from infrared fluorescent lamps. The effective wavelength for light-dependent SL formation was 400–700 nm. Furthermore, the longer the wavelength of radiation, the bigger were the SLs. Such light-dependent induction of the SL was suppressed by pretreatment of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU) and cycloheximide (CY). These results suggested that photosynthetic and protein synthetic activities were involved in SL formation.     

Growth and photosynthesis of Chinese cabbage plants grown under light-emitting diode-based light source

We compared growth and the content of sugar, protein, and photosynthetic pigments, as well as chlorophyll fluorescence parameters in 15- and 27-day-old Chinese cabbage (Brassica chinensis L.) plants grown under a high-pressure sodium (HPS) lamps or a light source built on the basis of red (650 nm) and blue (470 nm) light-emitting diodes (LEDs) with a red to blue photon ratio of 7: 1. One group of plants was grown at a photosynthetic photon flux (PPF) level of 391 ± 24 μ mol/(m² s) (normal level); the other, at a PPF level of 107 ± 9 μ mol/(m² s) (low light). Plants of the third group were firstly grown at the low light and then (on the 12th day) transferred to the normal level. When grown at the normal PPF level, the plants grown under LEDs didn’t differ from plants grown under HPS lamps in shoot fresh weight, but they showed a lower root fresh and dry weights and the lower content of total sugar and sugar reserves in the leaves. No differences in the pigment content and photosystem II quantum yield were found; however, a higher Chl a/b ratio in plants grown under LEDs indicates a different proportion of functional complexes in thylakoid membranes. The response to low light conditions was mostly the same in plants grown under HPS lamps and LEDs; however, LED plants showed a lower growth rate and a higher nonphotochemical fluorescence quenching. In the case of the altered PPF level during growth, the plant photosynthetic apparatus adapted to new conditions of illumination within three days. Plants grown under HPS lamps at a constant normal PPF level and those transferred to the normal PPF level on the 12th day, on the 27th day didn’t differ in shoot fresh weight, but in plants grown under LEDs, the differences were considerable. Our results show that LED-based light sources can be used for plant growing. At the same time, some specific properties of plant photosynthesis and growth under these conditions of illumination were found.     

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.     

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 sourcefor 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 requirementsfor plant photosynthesis and photomorphogenesis for successfulgrowth and seed yield. To determine the influence of galliumaluminium arsenide (GaAIAs) red LEDs on wheat photomorphogenesis,photosynthesis, and seed yield, wheat (Triticum aestivum L.,cv. ‘USU-Super Dwarf’) plants were grown under redLEDs 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 whitelight-grown plants, wheat grown under red LEDs alone demonstratedless main culm development during vegetative growth throughpreanthesis, while showing a longer flag leaf at 40 DAP andgreater main culm length at final harvest (70 DAP). As supplementalBF light was increased with red LEDs, shoot dry matter and netleaf photosynthesis rate increased. At final harvest, wheatgrown under red LEDs alone displayed fewer subtillers and alower seed yield compared to plants grown under white light.Wheat grown under red LEDs+10% BF light had comparable shootdry matter accumulation and seed yield relative to wheat grownunder white light. These results indicate that wheat can completeits life cycle under red LEDs alone, but larger plants and greateramounts of seed are produced in the presence of red LEDs supplementedwith a quantity of blue light. Key words: Triticum aestivum L., red light, blue light, subtillering, bioregenerative advanced life support     

Plant growth with new fluorescent lamps

Summary Bean and marigold plants were grown to maturity under several kinds of fluorescent lamps to evaluate the effects of spectral differences on development and reproduction. Six kinds of lamps were tested including five lamps that were used in closely related experiments on tomato seedling growth (Thomas and Dunn, 1967). Evaluation was by fresh- and dry-weight yields of immature and mature pods, and of vegetative tops of plants for bean; and by flowering and fresh-and dry-weight yields for marigold.Bean plants grown under two experimental lamps, Com I and IR III produced significantly higher fresh- and dry-weight yields of both mature and total pods than under Warm-white lamps. This effect could be attributed largely to the considerable energy emitted by the experimental lamps in the red and far-red, as compared to a larger emission in the green and blue for the Warm-white lamps. The differences in the yields for immature pods and vegetative portions of the mature tops were not significant.In a comparison of the effects of three experimental lamps with those of three commercial lamps on growth response of bean plants, the yields were in general higher for the experimental lamps, except for immature pods. The yields of vegetative tops were significantly greater for the 78/22 lamp over the yields for all other lamps. The larger proportion of red and far-red light emitted by the experimental lamps is again the probable cause of the higher yields with these lamps.Two sets of experiments on growth and flowering of marigold under various experimental and commercial lamps were largely inconclusive although there was some indication of beneficial effects by the experimental lamps.In general, the results with bean agree with those for tomato (Thomas and Dunn, 1967), in that best growth was obtained with a lamp high in red light emission, a moderate amount in the far-red, and very little in the blue part of the spectrum.This research was submitted by the senior author in partial fulfillment of the requirements for the M.S. degree in Botany at the University of New Hampshire.Published with the approval of the director of the New Hampshire Agricultural Experiment Station as Scientific Contribution No. 398. This study was part of the Northeast Regional Project, NE-35, Analysis of Northeastern Climatic Variables and Their Relationships to Plant Response.     

Morphological and physiological responses of bean plants to supplemental UV radiation in a Mediterranean climate

During the last few decades many experiments have been performed to evaluate the responses of plants to enhanced solar UV-B radiation (280–320 nm) that may occur because of stratospheric ozone depletion; most of them were performed in controlled environment conditions where plants were exposed to low photosynthetically active radiation (PAR) levels and high UV-B irradiance. Since environmental radiative regimes can play a role in the response of plants to UV-B enhancement, it appears doubtful whether it is valid to extrapolate the results from these experiments to plants grown in natural conditions. The objective of this work was to evaluate the effects on physiology and morphology of a bean (Phaseolus vulgaris L.) cultivar Nano Bobis, exposed to supplemental UV radiation in the open-air. UV-B radiation was supplied by fluorescent lamps to simulate a 20% stratospheric ozone reduction. Three groups of plants were grown: control (no supplemental UV), UV-A treatment (supplementation in the UV-A band) and UV-B treatment (supplemental UV-B and UV-A radiation). Each group was replicated three times. After 33 days of treatment plants grown under UV-B treatment had lower biomass, leaf area and reduced leaf elongation compared to UV-A treatment. No significant differences were detected in photosynthetic parameters, photosynthetic pigments and UV-B absorbing compounds among the three groups of plants. However, plants exposed to UV-A treatment showed a sort of 'stimulation' of their growth when compared to the control. The results of this experiment showed that plants may be sensitive to UV-A radiation, thus it is difficult to evaluate the specific effects of UV-B (280–320 nm) radiation from fluorescent lamps and it is important to choose the appropriate control. Environmental conditions strongly affect plant response to UV radiation so further field studies are necessary to assess the interaction between UV-B exposure and meteorological variability.     

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.     

The effect of exposure to enhanced UV-B radiation on the penetration of monochromatic and polychromatic UV-B radiation in leaves of Brassica napus

Using quartz optical fibres, penetration of both monochromatic (310 nm) and polychromatic UV-B (280–320 nm) radiation in leaves of Brassica napus L. (cv. Ceres) was measured. Plants were grown under either visible light (750 μmol m⁻² s⁻¹ photosynthetically active radiation) or with the addition of 8. 9 KJ m⁻² day⁻¹ biologically effective UV-B (UV-B_BE) radiation. Results showed that of the 310 nm radiation that penetreated the leaf, 90% was within the intial one third of the leaf with high attenuation in the leaf epidermis, especially in UV-treated plants. Polychromatic UV-B radiation, relative to incident radiation, showed a relatively uniform spectral distribution within the leaf, except for collimated radiation. Over 30% of the UV-screening pigments in the leaf, including flavonoids, were found in the adaxial epidermal layer, making this layer less transparent to UV-B radiation than the abaxial epidermis, which contained less than 12% of the UV-screening pigments. UV-screening pigments increased by 20% in UV-treated leaves relative to control leaves. Densely arranged epicuticular wax on the adaxial leaf surface of UV-treated plants may have further decreased penetration of UV-B radiation by reflectance. An increased leaf thickness, and decreases in leaf area and leaf dry weight were also found for UV-treated plants.     

Elevated UV-B radiation effects on experimental grassland communities

Experimental grassland communities (turves) were exposed to supplemental levels of UV-B radiation (280–315 nm) at an outdoor facility, under treatment arrays of cellulose diacetate-filtered fluorescent lamps which also produce UV-A radiation (315–400 nm). Control treatments consisted of arrays of polyester-filtered lamps, which allowed for exposure to UV-A radiation alone, and arrays of unenergized lamps allowing for exposure to ambient levels of solar radiation.     

Translocation in colored light

The translocation of ¹⁴C-photosynthate in detached blades of sugarcane was studied under illumination from red, green, blue, and cool-white fluorescent lamps; under far-red illumination from the sun, and from incandescent lamps; and in total darkness.

The percentage of basipetal translocation and the accumulation against the concentration gradient were stimulated by light from the red or blue lamps more than by green or cool-white fluorescent illumination.

Basipetal translocation took place equally well in red light lacking blue irradiation and in blue light. Since the action spectrum for light-induced change in viscosity is a typical blue-type spectrum, the effect of light upon translocation is not due merely to changes in the physicochemical properties of protoplasm.

Basipetal translocation took place in red light lacking blue irradiation better than in cool-white fluorescent light, which may suggest a red stimulation of translocation.

Illumination in the far-red region of the spectrum did not support basipetal translocation but acted like total darkness.

Because of the wide emission characteristics of the fluorescent lamps employed, it is impossible to decide whether a chlorophyll-like system or some other pigment is involved in the light stimulation of phototranslocation.

Whatever the activating wavelength and whatever the pigment system involved, these results show that the phototranslocation of sucrose in the phloem is influenced by the quality of illumination.

     

The influence of spectral quality on the internodal response of intact bean plants to brassins

The response of pinto bean ( Phaseolus vulgaris L.) plants to single application of brassins (10 μg) in the second-internode assay was determined under equal levels (90 μE m⁻² s⁻¹) of photosynthetically active radiation in a controlled environment provided by cool-white fluorescent (CWF) lamps, incandescent (INC) lamps, or a combination of the two sources. Treatment of the second internode with brassins produced a characteristic swelling of the treated internode irrespective of the spectral source used. However, the increase in radial growth of the upper portion of brassin-treated internodes from plants grown under INC lamps was more than 50% greater than those of plants grown under CWF lamps for 7 days. Spectral quality also had a marked effect on the rate and extent of internode elongation. Brassin-treated internodes of plants grown for 7 days under CWF lamps were more than twice as long as those of control plants, whereas those from INC or CWF + INC grown plants were significantly shorter than those of control plants. The effect of brassins was largely confined to the treated internode.     

Visible light during mycelial growth and conidiation of Metarhizium robertsii produces conidia with increased stress tolerance

Light conditions during mycelial growth are known to influence fungi in many ways. The effect of visible-light exposure during mycelial growth was investigated on conidial tolerance to UVB irradiation and wet heat of Metarhizium robertsii, an insect-pathogenic fungus. Two nutrient media and two light regimens were compared. Conidia were produced on (A) potato dextrose agar plus yeast extract medium (PDAY) (A1) under dark conditions or (A2) under continuous visible light (provided by two fluorescent lamps with intensity 5.4 W m(-2)). For comparison, the fungus was also produced on (B) minimal medium (MM) under continuous-dark incubation, which is known to produce conidia with increased tolerance to heat and UVB radiation. The UVB tolerances of conidia produced on PDAY under continuous visible light were twofold higher than conidia produced on PDAY medium under dark conditions, and this elevated UVB tolerance was similar to that of conidia produced on MM in the dark. The heat tolerance of conidia produced under continuous light was, however, similar to that of conidia produced on MM or PDAY in the dark. Conidial yield on PDAY medium was equivalent when the fungus was grown either under continuous-dark or under continuous-light conditions.     

Photoreactions Controlling Flowering of Chrysanthemum morifolium (Ramat. and Hemfl.) Illuminated with Fluorescent Lamps

Flowering of chrysanthemum plants under short photoperiods, as is well known, is prevented when the plants are illuminated near the middle of the long night. Such illumination inhibits flowering whether it is given continuously or intermittently, and whether it comes from incandescent or from fluorescent lamps. We discovered, however, that fluorescent light applied intermittently (cyclically) throughout the entire 16-hour long night was far less inhibitory than when applied during only part of this dark period. By contrast, incandescent filament illumination is strongly inhibitory under these conditions. The cycles of fluorescent light usually lasted 15 minutes, 1.5 minutes of light followed by 13.5 minutes of dark. When such cycles were applied for only 12 hours, leaving 4 hours of uninterrupted darkness in each long night, inhibition of flowering was complete again.     

The Effect of an Incandescent Supplement on the Growth of Tomato Plants in Low Light

Young tomato plants were grown at low light flux densities (21W m^-2 for 8 h days) in growth cabinets under three types offluorescent lamps or under a fluorescent/incandescent mixedsource. Whilst net assimilation rates under the fluorescentlamps were in agreement with those calculated from the lampcharacteristics and the photosynthetic action spectrum, therate under the mixed source was about 20 per cent higher thanexpected. Relative growth rates and relative leaf area growthrates were also higher and leaf area ratios lower under thefluorescent/incandescent lamp combination than under the purefluorescent sources. Small differences in stem elongation, leaftemperature and dry weight distribution which were associatedwith the addition of incandescent radiation were not consideredto be responsible for these increases. When the light flux densityfrom the mixed source was reduced by 20 per cent, the plantgrowth parameters were then similar to those in fluorescentlight alone.     

Effect of light on the formation of atypical fruiting structures inGanoderma lucidum

Ganoderma lucidum develops atypical fruiting structures (AFSs) with non-basidiocarpous basidiospores during the incubation under light on nutrient agar media. To examine the light quality effective in inducing AFSs, 17 isolates ofG. lucidum were incubated on agar media under light from different colored fluorescent lamps. Of the 17 isolates, 13 isolates produced AFSs and basidiospores under fluorescent lamps. Nine isolates formed AFSs in a broad light region from P-B (pure blue) to P-R (pure red) lamps. The remaining 4 isolates produced AFSs under different colored fluorescent lamps. No isolates formed AFSs in the dark or under BLB (black light blue) illumination. The mycelial growth was inhibited by light illumination, especially BLB light. Although the AFSs were induced at a very low light intensity such as 0.5µmol m^–2s^–1, the optimum light intensity for the AFS formation varied depending on the kind of fluorescent lamp and the isolate. The AFS formation inG. lucidum isolates was also tested under monochromatic light produced by the combination of interference filters and colored glass filters.G. lucidum isolates were separable into various types in the responses of AFS formation to monochromatic light, indicating thatG. lucidum is heterogeneous in its photo-response with regard to AFS formation.     

The effects of light intensity and spectral quality on growth and shoot initiation in tobacco callus

The effects of eight different narrow band-emitting fluorescent lamps (371-750 nm) and four commercial broad band-emitting fluorescent sources upon growth and shoot initiation in tobacco callus (Nicotiana tabacum var. Wisconsin 38) have been characterized. Wavelength and intensity are equally important parameters in determining morphogenic changes. Near ultraviolet light (371 nm) was found to stimulate (0.024 mw/cm²) or inhibit (above 0.15 mw/cm²) callus growth and shoot initiation, depending on the light intensity. Stimulation of growth and shoot production occurs also in blue light region, but at higher intensity than in the near ultraviolet. Red and far red light (up to 1.7 mw/cm²) do not appear to affect callus growth or stimulate shoot initiation. The enhancement of callus growth and the stimulation of shoot initiation are controlled by the same near ultraviolet-absorbing photoreceptor system present in a small enough concentration that it cannot be recognized in the absorption spectrum of the intact tissue. Carotenoids, porphyrins, and phytochrome associated with the high irradiance response do not appear to qualify as the photoreceptor. Flavonoids are possible candidates. Radiation emitted by fluorescent lamps outside the near visible region was determined, and we concluded that energy levels were not sufficient to affect the reported results. The spectral output of several commercial lamps in the visible and near visible regions is such that there could be different effects on growth and development of tissue cultures.     

Long-day effects on growth and flower initiation of tomato plants in low light

Young tomato plants (cv. Minibelle) were grown in plant growth cabinets in 575 kJ m^-2 (400–700 nm) daily radiation. Plants grown in an 8 h day were then compared with those in which 10% of the radiation was taken from the main 8 h light period and supplied over the next 8 h period. After 41 days from sowing the 16 h day plants had almost twice the dry weight of those in short days and a 55 % greater leaf area. Net assimilation rate, relative growth rate and relative leaf area growth rates were all greater in long days, although the differences in growth diminished with time. The long-day treatment also increased the proportion of dry weight in the leaves, a function which is usually relatively stable in different environments. The beneficial effect of the long days may arise from a reduction in night respiration, or an increase in rate of photosynthesis through the observed increase in chlorophyll content. The 8 h light period resulted in flower initiation one or two nodes lower than the 16 h period so that the cultivar is a quantitative short-day plant.     

Differential response of a sensitive and tolerant sugarbeet line to Cercospora beticola infection and UV-B radiation

Increased ultraviolet-B (UV-B, 280–320 nm) radiation, due to depletion of stratospheric ozone, is an increasing threat to living organisms. Furthermore, increased ground level temperatures as a consequence of global warming may favour development of pathogens, such as Cercospora beticola , that thrive at high temperatures. This study evaluates the effect of combined UV stress and Cercospora leaf-spot disease on young sugarbeet plants ( Beta vulgaris L . ). An inoculum consisting of twelve European isolates of C. beticola Sacc. was used in the experiments. One Cercospora -sensitive and one Cercospora -tolerant sugarbeet line were analysed from growth regimes where plants were grown either under visible radiation alone or with supplemental UV-B. Photosynthetic pigments and partial reactions of photosynthesis, including potential yield and quantum yield under illumination, non-photochemical quenching (q_NPQ) and photochemical quenching (q_P), were measured to assess plant response. The combination of Cercospora and supplemental UV-B radiation in the sensitive line resulted in a decreased photosynthetic efficiency, shown by q_NPQ and quantum yield under illumination as compared with that for either stress applied alone. The F_v/F_m was unchanged for plants subjected to UV-B radiation without infection, although the q_NPQ decreased. The Cercospora -tolerant line showed no significant differences under the different treatments. Thus, the line tolerant to Cercospora infection also proved to be tolerant to UV-B radiation alone and in combination with the infection.     

Transformation of plastids in soil‐shaded lowermost hypocotyl segments of bean (Phaseolus vulgaris) during a 60‐day cultivation period

The maintenance but substantial transformation of plastids was found in lowermost hypocotyl segments of soil‐grown bean plants (Phaseolus vulgaris cv. Magnum) during a 60‐day cultivation period. Although the plants were grown under natural light–dark cycles, this hypocotyl segment was under full coverage of the soil in 5–7 cm depth, thus it was never exposed to light. The 4‐day‐old plants were fully etiolated: amyloplasts, occasionally prolamellar bodies, protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in the hypocotyls of these young seedlings. The 633 and 654 nm bands in the 77 K fluorescence emission spectra indicated the presence of Pchlide and Pchl pigments. During aging, both the Pchlide and Pchl contents increased, however, the Pchl to Pchlide ratio gradually increased. In parallel, the contribution of the 654 nm form decreased and in the spectra of the 60‐day‐old samples, the main band shifted to 631 nm, and a new form appeared with an emission maximum at 641 nm. The photoactivity had been lost; bleaching took place at continuous illumination. The inner membranes of the plastids disappeared, the amount of starch storing amyloplasts decreased. These data may indicate the general importance of plastids for plant cell metabolism, which can be the reason for their maintenance. Also the general heterogeneity of plastid forms can be concluded: in tissues not exposed to light, Pchl accumulating plastids develop and are maintained even for a long period.     

Spectral quality and UV-B stress stimulate glycyrrhizin concentration of Glycyrrhiza uralensis in hydroponic and pot system

Glycyrrhizin, the major bioactive component of Glycyrrhiza uralensis, is widely used as a natural sweetener. Recently glycyrrhizin has been shown to have anti-tumor activity, highly active in inhibiting replication of HIV-1 and SARS-associated virus and exhibits a number of pharmacological effects. The principle objective of the current study was to evaluate the effects of different spectral quality including red, blue, white and UV-B radiation on the production of glycyrrhizin, in a controlled environment. Plants were grown under artificial lights with elevated CO(2) concentration and both the pot and hydroponic plants were assigned to red and blue light treatments and those grown under white fluorescent lamps were used as control. In a separate experiment, pot plants were exposed to ultraviolet (UV)-B radiation (wavelength: 280-315 nm). The net photosynthetic rates (NPR) of the leaves reduced significantly immediately after exposure to the high intensity UV-B radiation (3 days at 1.13 W m(-2)). In case of the low intensity UV-B radiation (15 days at 0.43 W m(-2)), NPR was also reduced, but the rate of reduction was significantly slower than that of the high intensity treatment. The concentrations of glycyrrhizin quantified in the root tissues were highest in the plants grown under red light in both hydroponic and pot systems and the concentration increased linearly from 1- to 3-month-old pot plants. Both the low and high intensity of UV-B exposure increased the concentration of glycyrrhizin in the root tissues of 3-month-old pot plants, the values being nearly X1.5 those of the control. The results also indicate that the glycyrrhizin concentrations of 3-6 months old pot plants were similar or even higher than the previously reported values for 3-4 years old field-grown plants and confirm that high concentration of glycyrrhizin production is possible within a very short production period under controlled environments.