Growth responses of marigold and salvia bedding plants as affected by monochromic or mixture radiation provided by a Light-Emitting Diode (LED)

The effects of light generated by monochromic blue, red or mixed radiation from a fluorescent lamp (FL) with light emitting diodes (LEDs) (blue, red, or far-red) on growth and morphogenesis of marigold and salvia seedlings were investigated and the responses compared with those of plantlets grown under a broad spectrum conventional fluorescent lamp (a 16 h photoperiod per day). Dry weight of marigold seedlings was significantly increased in monochromic red light (R), fluorescent light plus red LED (FLR) or fluorescent light (FL) but reduced when monochromic blue light (B) was used, whereas in salvia dry weight was significantly greater under fluorescent light plus blue LED (FLB), fluorescent light plus red LED (FLR) and fluorescent light plus far-red LED (FLFr) as compared to other treatments. Stem length in marigold was greatest in monochromic blue light, being three times greater than in FLR or FL treatments. In salvia, FLFr increased stem length but this was significantly decreased by R as compared to other treatments. The number of visible flower buds in marigold was much higher in FLR as well as in the control (FL), and it was about five times greater than in B or R. However, the number of open flowers in salvia varied slightly in all the treatments. Different light qualities also influenced the duration of the blooming period in both the species. No flower buds were formed when monochromic B or R was used in salvia and FLFr inhibited flower bud formation in marigold. In comparison with monochromic blue or red light, the number of stomata was greater in mixed radiation of FL with LEDs in both the plants. Our study demonstrates the effectiveness of a LED system for plantlet growth and morphogenesis in space-based plant research chambers.     

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     

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.     

Combination of Red and Blue Lights Improved the Growth and Development of Eggplant (Solanum melongena L.) Seedlings by Regulating Photosynthesis

The photosynthesis, photomorphogenesis, and photoperiod processes in plants are regulated according to light intensity and quality. The aim of this study was to investigate the effects of different light qualities on eggplant seedlings and determine the best light quality for growth. The seedlings of eggplant cultivar ‘Jingqiejingang’ were grown under light-emitting diodes (LEDs): white (W, the control), red (R), blue (B), and different ratios of B/R lights (B/R = 1/1, B/R = 1/3, B/R = 1/6, B/R = 1/9). The growth parameters, leaf morphology, photosynthetic performance, chlorophyll fluorescence, and the carbon and nitrogen metabolism in the leaves of eggplant seedlings under different LED light treatments were studied. The results showed that the plant height, leaf development, and photosynthetic characteristics were inhibited by red light but elevated by blue light compared with the control. Conversely, the contents of chlorophyll a, chlorophyll b, and carotenoids were all increased by red light, while decreased by blue light significantly. In addition, the contents of carbohydrates and the activities of nitrogen assimilation enzymes were not or little changed by the monochromatic blue and red light. The combined light of red and blue were more beneficial for growth than the monochromatic light, especially B/R = 1/3 light. Under B/R = 1/3 light, the parameter values of plant growth, leaf development, photosynthetic pigments and characteristics, and carbon and nitrogen metabolism were all maximum. Taken together, combined application lights of red and blue are good practice for the cultivation of eggplant seedlings, and LED B/R = 1/3 light was optimum.

     

不同光质对桑树幼苗生长和光合特性的影响

光质可影响植物光合特性、形态以及生理过程。本试验研究了不同光质(白光W、红光R、红蓝混合光RB、蓝光B)对桑树植株生长、形态和光合作用的影响。结果表明:与白光对照相比,红光、蓝光和红蓝混合光处理下植株的生长、干物质积累受到抑制;红光处理下植株的株高、叶面积显著高于白光、红蓝混合光、蓝光处理;而白光、红蓝混合光、蓝光处理下植株的LMA、叶绿素a/b比值、可溶性蛋白含量、蔗糖、淀粉含量和叶片总N含量显著高于红光处理;红蓝混合光处理下植株的Pn、Gs、ΦPSⅡ与白光处理相近,红光、蓝光处理下植株的Pn、ΦPSⅡ低于白光、红蓝混合光处理,同时红光、红蓝混合光、蓝光处理下植株的抗氧化酶活性高于白光处理,而MDA含量低于白光处理;红光处理下植株的叶片厚度、栅栏组织和海绵组织厚度显著小于白光处理。因此,一定比例的红蓝混合光可以使桑树植株的生长、光合特性、生理特征和叶片解剖结构与白光下生长植株相近,并减少单质红光、单质蓝光对植株生长发育的不利影响。     

Modified light spectral conditions prior to cryopreservation alter growth characteristics and cryopreservation success of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) shoot tips in vitro

Light is one of the most important factors affecting growth and morphogenesis of plants. Light intensity, photoperiod and spectral composition greatly affect morphogenetic responses of in vitro plants. Modification of light spectra during recovery after cryopreservation improves survival and regeneration, but the effect of modified light conditions prior to cryopreservation are not known. Therefore, the aim of the present study was to follow the photomorphogenetic response of potato plants (Solanum tuberosum L.) under different light qualities i.e. cool white fluorescent (CW) used as control, warm white (HQI), white LEDs (W), blue LEDs (B), red LEDs (R) and a combination of red with 10?% of blue LEDs (RB) prior to cryopreservation, affecting recovery of cultivars Agrie Dzeltenie, Bintje, Maret, Anti and Désirée in vitro. Light spectral quality had a significant effect on growth characteristics of potato plants in vitro. Red light (R) promoted elongation growth but biomass accumulation remained low under monochromatic light treatments. Some of the pre-cryopreservation light treatments significantly affected post-cryopreservation success. Under blue LEDs, high early recovery was observed for all cultivars tested, whereas under red (R) or (HQI), lowest survival percentages were obtained 2–4 weeks after thawing. Specifically, during early recovery, blue light increased survival from 26 to 66?%, 4 to 31?% and 16 to 48?% for cultivars Agrie Dzeltenie, Anti, and Désirée, compared to illumination by red LEDs. Therefore, light spectral quality prior to cryopreservation can significantly affect the cryopreservation success of potato shoot tips.     

Growth of Tsuru-rindo (Tripterospermum japonicum) culturedin vitro under various sources of light-emitting diode (LED) irradiation

We studied the effects of light generated by LEDs on the growth of Tsururindo (Tripterospermum japonicum) shoots. Apical shoots (2–3 cm long) were cultured on MS basal media supplemented with 3% sucrose, and were maintained for four weeks under five different light qualities: F (fluorescent lamp), red LED (R), 70% red + 30% blue LED (R7B3), 50% red + 50% blue (R5B5), or blue LED (B). Rooting was promoted by red light (100%) but was inhibited by blue light. Plant growth, as defined by root number, fresh weight, and chlorophyll content, was generally healthier for cultures irradiated with mixed LEDs, and was the best under R7B3. Ventilation resulted in more rapid apical shoot growth and rooting compared with control plants, when both were treated with the R7B3 system. We demonstrated here that plant growth can be controlled by using LEDs to adjust for the most effective irradiation conditions, compared with the performance observed when conventional fluorescent lamps are utilized.     

Effects of light quality on growth and development,photosynthetic characteristics and content of carbohydrates in tobacco (<Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L.) plants

In this study, effects of yellow (Y), purple (P), red (R), blue (B), green (G), and white (W) light on growth and development of tobacco plants were evaluated. We showed that monochromatic light reduced the growth, net photosynthetic rate (P _N), stomatal conductance, intercellular CO₂, and transpiration rate of tobacco. Such a reduction in P _N occurred probably due to the stomatal limitation contrary to plants grown under W. Photochemical quenching coefficient (qP), maximal fluorescence of dark-adapted state, effective quantum yield of PSII photochemistry (Φ_PSII), and maximal quantum yield of PSII photochemistry (F_v/F_m) of plants decreased under all monochromatic illuminations. The decline in ΦPSII occurred mostly due to the reduction in qP. The increase in minimal fluorescence of dark-adapted state and the decrease in F_v/F_m indicated the damage or inactivation of the reaction center of PSII under monochromatic light. Plants under Y and G showed the maximal nonphotochemical quenching with minimum P _N compared with the W plants. Morphogenesis of plants was also affected by light quality. Under B light, plants exhibited smaller angles between stem and petiole, and the whole plants showed a compact type, while the angles increased under Y, P, R, and G and the plants were of an unconsolidated style. The total soluble sugar content increased significantly under B. The reducing sugar content increased under B but decreased significantly under R and G compared with W. In conclusion, different monochromatic light quality inhibited plants growth by reducing the activity of photosynthetic apparatus in plants. R and B light were more effective to drive photosynthesis and promote the plant growth, while Y and G light showed an suppression effect on plants growth. LEDs could be used as optimal light resources for plant cultivation in a greenhouse.     

Acclimations to light quality on plant and leaf level affect the vulnerability of pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) to water deficit

We investigated the influence of light quality on the vulnerability of pepper plants to water deficit. For this purpose plants were cultivated either under compact fluorescence lamps (CFL) or light-emitting diodes (LED) providing similar photon fluence rates (95 µmol m^?2 s^?1) but distinct light quality. CFL emit a wide-band spectrum with dominant peaks in the green and red spectral region, whereas LEDs offer narrow band spectra with dominant peaks at blue (445 nm) and red (665 nm) regions. After one-week acclimation to light conditions plants were exposed to water deficit by withholding irrigation; this period was followed by a one-week regeneration period and a second water deficit cycle. In general, plants grown under CFL suffered more from water deficit than plants grown under LED modules, as indicated by the impairment of the photosynthetic efficiency of PSII, resulting in less biomass accumulation compared to respective control plants. As affected by water shortage, plants grown under CFL had a stronger decrease in the electron transport rate (ETR) and more pronounced increase in heat dissipation (NPQ). The higher amount of blue light suppressed plant growth and biomass formation, and consequently reduced the water demand of plants grown under LEDs. Moreover, pepper plants exposed to high blue light underwent adjustments at chloroplast level (e.g., higher Chl a/Chl b ratio), increasing the photosynthetic performance under the LED spectrum. Differently than expected, stomatal conductance was comparable for water-deficit and control plants in both light conditions during the stress and recovery phases, indicating only minor adjustments at the stomatal level. Our results highlight the potential of the target-use of light quality to induce structural and functional acclimations improving plant performance under stress situations.     

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.     

Proteomic and Antioxidant Analysis Elucidates the Underlying Mechanism of Tolerance to Hyperhydricity Stress in In Vitro Shoot Cultures of <Emphasis Type="Italic">Dianthus caryophyllus</Emphasis>

Hyperhydric disorders occur frequently in plant tissues cultured in vitro and cause several morphological and physiological abnormalities. However, a systematic defense response is triggered by hyperhydric conditions. The accumulation of reactive oxygen species (ROS), activities of antioxidant enzymes and their immunoblots, and the proteome-level changes in normal versus hyperhydric shoots of carnation (Dianthus caryophyllus) cultured in vitro were investigated. Total proteins were also extracted from the shoot and analyzed by two-dimensional electrophoresis. Among a total of 700 spots detected, only 40 had significant changes in abundance in the hyperhydric compared to the normal shoots, which were further identified by a mass spectrometer (MALDI-TOF MS). Most of them were involved in photosynthesis, RNA processing, and general metabolisms, while the rest were involved in secondary metabolic processes. These identified proteins in carnation shoots may provide novel evidences for stress tolerance against hyperhydricity.     

Impact of light-emitting diode irradiation on photosynthesis,phytochemical composition and mineral element content of lettuce cv. Grizzly

Light-emitting diodes (LEDs) are a promising technology with a potential to improve the irradiance efficiency, light quality, and the light spectrum for increasing plant yield and quality. In this experiment, we investigated the impacts of various LED light qualities, including 100% red, 100% blue, 70% red + 30% blue, and 100% white, on the growth and photosynthesis, phytochemical contents, and mineral element concentrations in lettuce (Lactuca sativa L. cv. ‘Grizzly’) in comparison to normal greenhouse conditions. Photon flux of 300 µmol m^?2 s^?1 was provided for 14 h by 120 LEDs set on a 60 cm × 60 cm sheet of aluminum platform in the growth chambers, where plants were grown for 60 d. Fresh mass per plant was significantly higher when grown under 100% blue and 70% red + 30% blue LEDs compared to the other environments including greenhouse conditions. Phytochemical concentrations and a nutritive value of lettuce were also significantly affected by the light treatments. Chlorophyll and carotenoid concentrations increased in the plants grown under 70% red + 30% blue LEDs compared to those grown in the greenhouse. Vitamin C content was 2.25-fold higher in the plants grown under 100% blue LEDs compared to those grown in the greenhouse. Higher photosynthesis and maximal quantum yield of PSII photochemistry were also observed in the plants treated with LED lights. The application of LED light led to the elevated concentrations of macro-and micronutrients in lettuce possibly because of the direct effect of LED light and lower stress conditions in the growth chambers compared to the greenhouse. Although the mechanism of the changes in lettuce grown under LED is not well understood, the results of this study demonstrated that LED light could be used to enhance the growth and nutritional value of lettuce in indoor plant production facilities.     

Analyzing photosynthetic activity and growth of Solanum lycopersicum seedlings exposed to different light qualities

To investigate how light quality influences tomato (Solanum lycopersicum L) seedlings, we examined changes in plant growth, chloroplast ultrastructure, photosynthetic parameters and some photosynthesis-related genes expression levels. For this, tomato plants were grown under different light qualities with the same photosynthetic photon flux density: red (R), blue (B), yellow (Y), green (G) and white (W) lights. Our results revealed that, compared with plants grown under W light, the growth of plants grown under monochromatic lights was inhibited with the growth reduction being more significant in the plants grown under Y and G lights. However, the monochromatic lights had their own effects on the growth and photosynthetic function of tomato seedlings. The plant height was reduced under blue light, but expression of rbcS, rbcL, psbA, psbB genes was up-regulated, and the ΦPSII and electron transport rate (ETR) values were enhanced. More starch grains were accumulated in chloroplasts. The root elongation, net photosynthetic rate (Pn), NPQ and rbcS and psbA genes expression were promoted under red light. Yellow light- and green light-illuminated plants grew badly with their lower Rubisco content and Pn value observed, and less starch grains accumulated in chloroplast. However, less influence was noted of light quality on chloroplast structure. Compared with yellow light, the values of ΦPSII, ETR, qP and NPQ of plants exposed to green light were significantly increased, suggesting that green light was beneficial to both the development of photosynthetic apparatus to some extent.     

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.     

Effects of light quality on growth and development of protocorm-like bodies of <Emphasis Type="Italic">Dendrobium officinale</Emphasis> in vitro

The effect of light quality on protocorm-like bodies (PLBs) of Dendrobium officinale was investigated. PLBs of D. officinale were incubated under a number of different light conditions in vitro, namely: dark conditions; fluorescent white light (Fw); red light-emitting diodes (LEDs); blue LEDs; half red plus half blue [RB (1:1)] LEDs; 67% red plus 33% blue [RB (2:1)] LEDs; and 33% red plus 67% blue [RB (1:2)] LEDs. Growth parameters, number of shoots produced per PLB, chlorophyll concentration and carotenoid concentration were measured after 90 days culture. The percentage of PLBs producing shoots was 85% under blue LEDs. In contrast, the percentage of PLBs producing shoots was less than 60% under dark conditions, fluorescent white light and red LEDs. The number of shoots produced per PLB was more than 1.5 times greater under blue LEDs, RB (1:1) LEDs and RB (1:2) LEDs than those cultured under other light treatments [dark, Fw, red LEDs and RB (2:1)]. Chlorophyll and carotenoid concentrations were significantly higher under blue LEDs and different red plus blue LED ratios, compared to other light treatments (dark, Fw and red LEDs). Blue LEDs, Fw, and RB (1:2) LEDs produced higher dry matter accumulations of PLBs and shoots. This study suggests that blue LEDs or RB (1:2) LEDs could significantly promote the production of shoots by protocorm-like bodies of D. officinale and increase the dry matter of PLBs and the accumulation of shoot dry matter in vitro.     

Hyperhydricity in micropropagated carnation shoots: the role of oxidative stress

The physiology of hyperhydricity in relation to oxidative stress, mineral nutrients, antioxidant enzymes and ethylene has been studied in three micropropagated carnation cultivars under experimentally induced hyperhydricity. A marked increase in Fe content in comparison with normal tissues was observed in the hyperhydric tissues from the three cultivars. The levels of ethylene, solute leakage and malondialdehyde content were also significantly higher in the hyperhydric tissues. In relation to the time course of H₂O₂ production measured by fluorescence quenching, a similar trend could be observed for the three cultivars, with a clear increase in the generation of hydrogen peroxide in hyperhydric tissues. The activities of all the antioxidative enzymes studied, except lipoxygenase, were higher in the hyperhydric shoots. Phenylalanine ammonia-lyase (PAL) showed a significant decrease in activity in the hyperhydric tissues in comparison with the controls for the three cultivars. Soluble guaiacol peroxidase had a strong increase in activity in hyperhydric shoots of the three cultivars. These results provide, for the first time, direct evidence of H₂O₂ generation in hyperhydric tissues, characterize the response of the antioxidant system to an oxidative stress during hyperhydricity in carnation leaves and point to the accumulation of toxic forms of oxygen as the inducer of some of the abnormalities observed.     

Effects of different spectral lights on <Emphasis Type="Italic">Oncidium</Emphasis> PLBs induction,proliferation, and plant regeneration

The effects of different spectral light distribution on in vitro induction and proliferation of Oncidium protocorm-like bodies (PLBs) and subsequent growth of plantlets were investigated. Shoot tips (5 mm in length) of proliferating shoots of Oncidium “Gower Ramsey” were vertically incubated on 1/2 Murashige and Skoog (MS) medium supplemented with 1.0 mg l⁻¹ 6-benzyladenine (BA), and grown under either monochromatic red light-emitting diodes (LEDs) (RR), blue LEDs (BB), yellow LEDs (YY) or green LEDs (GG). Cultures grown under fluorescent lamps (FL) were used as control. Selected FL-induced PLBs were cut into 3- to 4-mm sections and incubated on MS medium supplemented with 1.0 mg l⁻¹ BA and 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), and grown under RR, BB, YY, GG, or FL. Moreover, FL-differented shoots (15 mm in length with two leaves) were incubated on 1/2 MS medium with 0.5 mg l⁻¹ NAA, and grown under either FL, RR, 10% blue + 90% red LEDs (1BR), 20% blue + 80% red LEDs (2BR), 30% blue + 70% red LEDs (3BR), BB, 80% red + 10% blue + 10% far-red LEDs (RBFr), or 80% red + 10% blue + 10% green LEDs (RBG). Overall, the red light spectrum enhanced induction, proliferation, and the carbohydrate contents of PLBs, as well as subsequent plantlet lengths, while the blue spectrum promoted differentiation, protein accumulation, and enzyme activities in PLBs, as well as pigment content accumulation in PLBs and developing plantlets. The combination of red and blue LEDs resulted in higher energy efficiency as well as dry weight and enzyme activities in these plantlets.     

LED light mediates phenolic accumulation and enhances antioxidant activity in Melissa officinalis L. under drought stress condition

The popularity of lemon balm in conventional medicine is suggested by the existence of two groups of compounds, namely essential oil and phenylpropanoids pathway derivatives. One of the promising approaches to improve tolerance to drought stress induced oxidative damage in seedlings grown in greenhouses and plant growth chambers is replacing the traditional and high-cost light technologies by recently developed light emitting diodes (LED). In this experiment, we analyzed the role of various LED lights including red (R), blue (B), red (70%) + blue (30%) (RB), and white (W) as well as normal greenhouse light (as control) to stimulate defense mechanisms against drought stress in two genotypes of Melissa officinalis L. The present study demonstrates that pre-treatment with LEDs with high-intensity output for 4 weeks alleviated harmful effects of drought stress in the two genotypes. Under drought stress, RB LED pre-treated plantlets of the two genotypes exhibited the highest relative growth index of shoot and root and total phenolic and anthocyanin content compared to those irradiated with other LEDs and greenhouse lights. The highest amount of malondialdehyde level was detected in R LED exposed plants. In response to drought, LED-exposed plants especially RB light-irradiated plants of the two genotypes maintained significantly higher antioxidant and phenylalanine ammonia-lyase (PAL) enzyme activities and higher expression level of the PAL1 and 4CL-1 genes compared to those irradiated with greenhouse light. We concluded that RB LED light provides a better growth condition and resistance to drought stress for the two genotypes of lemon balm by the highest antioxidant activity and the least amount of damage to the cell membranes. Our data suggest that LED light pre-treatments as moderate stress activate antioxidant systems, enhance the scavenging of ROS and induce drought stress tolerance in the two genotypes of lemon balm plants.

     

Photosynthetic characteristics of rice leaves grown under red light with or without supplemental blue light

In rice plants grown under red light supplemented with blue light (red/blue-light PPFD ratio was 4/1), photosynthetic rates per unit leaf area measured under white light at 1,600 and 250 micromol m-2) s-1 were higher than those in the plants grown under red light alone. The higher photosynthetic rates were associated with higher total N content of leaves, which was accompanied by larger amounts of key components of photosynthesis-limiting processes, including Rubisco, Cyt f, Chl and LHCII. These results suggested that the increase in total N content of leaves induced by supplemental blue light enhanced both light-saturated and light-limited photosynthesis.     

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO₂ exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA₃) at the concentration of 25 g/1 (GA-plants), and then grown under 17 W/m² blue light (B-plants) or 11 W/m² red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA₃ suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.