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ISSN : 1598-5504(Print)
ISSN : 2383-8272(Online)
Journal of Agriculture & Life Science Vol.50 No.5 pp.1-9

Response of Growth and Development of Young Tomato Plants to End-of-day Monochromatic Light from Various LEDs

Bekhzod Khoshimkhujaev1, Joon Kook Kwon1, Jae Han Lee1, Hyo Gil Choi1, Kyoung Sub Park1, Nam Jun Kang2*
1Protected Horticulture Research Institute, National Institute of Horticultural & Herbal Science, Haman, 52054, Korea
2Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, 52828, Korea
Corresponding author: Nam Jun Kang
August 31, 2015 April 23, 2016 August 2, 2016


Plant growth and development strongly influenced by light quantity and its spectral composition. Young tomato plants were cultivated in growth cabinets under artificial light provided by red and blue light emitting diodes(LEDs) during 12 hours, then plants were exposed to monochromatic ultraviolet, blue, green and red lights as an end-of-day(EOD) treatment during 4 hours to study their effect on plant growth parameters. EOD lighting from various LEDs increased total fresh and dry weights as well as assimilation area compared to those in control. Blue light increased stem height, internode length and stem diameter. Monochromatic UV-A light reduced stem elongation, highly increased stomatal conductance. Compactness and health index of young tomato plants were increased in UV-A and red light treatments.


    Rural Development Administration


    Light is an important environmental factor, it is responsible for photosynthesis in green plants, also it can trigger developmental responses. The search for optimal spectral composition is essential to optimize plant growth and various morphological events(leaf expansion, stem elongation, flowering, etc.). Controlling particular developmental processes in plants thorough modulation of light environment has been widely studied by many research groups. Such researches include application of different photo selective filters, various covering materials(Rajapakse et al., 1999), mulching films(Decoteau et al., 1988) or colored shading nets(Shahak, 2008; Stamps, 2009) to alter light environment for attaining desired physiological and morphological changes in plants. On the other hand, the application of EOD lighting using artificial light sources was also shown as an efficient tool to regulate plant development by manipulating specialized pigment systems. It was reported that tomato plants treated with EOD red light were shorter and had less total leaf length than plants that were not treated with EOD light(control)(Decoteau & Friend, 1991). John et al.(1993) observed increased internode elongation in yam(Dioscorea alata L.) plantlets when they were treated with EOD far-red light. Authors also observed that the effect of EOD far red light was reversed by red light, suggesting the involvement of two forms of phytochromes in these photoreversible processes. Previously conducted EOD experiments were carried out by utilizing either fluorescent tubes or incandescent bulbs with different light filters. However these lamps have a broad spectrum range and even with the light filters it is difficult to achieve desired accuracy in spectral output.

    Recent development in LED technology made it possible to study plant responses to every part of the spectrum with an increasing accuracy(Bourget, 2008). LEDs have a numerous advantages over traditional high intensity discharge or fluorescent lamps. Currently available LEDs have a high light output, they are energy efficient, and have a relatively low heat output as well as longer operating life(Mitchell et al., 2012). Spectrum and intensity of LED based irradiation sources can be also easily customized and effectively controlled using voltage regulation or pulse width modulation(PWM) techniques(Folta et al., 2005).

    Effects of monochromatic light from LEDs on the growth and morphogenesis of plants have been widely investigated(Mata & Botto, 2009). Islam et al.(2012) studied the effect of red LEDs in comparison with high pressure sodium lamps(HPS) as supplemental lighting on the stem elongation of two varieties of Euphorbia pulcherrima Willd. ex Klotzsch(poinsettia). It was reported that both cultivars were 20-34% shorter for LED compared to HPS grown plants. However it was also reported that application of EOD red light from LEDs during 30 minutes after main photoperiod with the intensity of 5 μmol m-2 s-1 had no further effect on plant height. It was shown that EOD light treatment also has a positive effect on yield of some crops. For example, total yield and fruit quality of greenhouse grown strawberries were enhanced when plants were irradiated with either monochromatic blue or mixed R:B light from LEDs during 6 hours, just after sunset(Choi et al., 2013).

    Analysis of available literature showed that vast majority of previously reported EOD experiments were carried out mostly by involvement of blue, red and far red radiation or their various combinations. The objective of this experiment was to examine the effects of monochromatic light from near ultra violet, blue, green and red LEDs on the gas exchange, growth and morphogenesis of young tomato plants.

    Materials and Methods

    1.Plant materials and growth conditions

    Tomato(Lycopersicon esculentum L. cv. Superdoterang, Koregon Seeds Co., Ltd., Anseong, Korea) seeds were germinated in a dark incubator(HB-101L, Hanbaek scientific Co., Bucheon, Korea) under 25°C for 2 days. Then emerged seeds were sowed in plastic pots(volume - 10 cm3) filled with the commercial peat based substrate. Pots were kept in nursery until appearance of the first true leaves, then pots with uniform seedlings were selected and transferred to the growth cabinets with specular walls and with the dimensions of 60 x 40 x 105 cm(L x W x H). Cabinets were equipped with fans to continuously air exchange with outside. Plants were cultivated for 4 weeks in the growth cabinets at 25±2°C of air temperature, 60±5% relative humidity and 400 μmol mol-1 (ambient) of CO2 concentration. Tomato seedlings were irrigated with half-strength Hoagland’s nutrient solution on a daily basis(pH = 6.7, EC = 1.3)(Hoagland & Arnon, 1950).

    2.Light treatments

    Tomato plants were cultivated in five growth cabinets equipped with LED modules(Delight Electronics Corp., Seoul, Korea). Plants continuously illuminated with mixed red blue(RB, 5:1) light with the intensity of 120±5 μmol m-2 s-1 during 12 hours photoperiod. After that plants were subjected to so called end-of-day(EOD) light with either ultraviolet - UV(376 nm, RB+UV), blue - B(465 nm, RB+B), green - G(522 nm, RB+G) or red - R(656 nm, RB+R) LEDs with the intensity of 50±2 μmol m-2 s-1 during 4 hours, thereby making total photoperiod of 16 hours. Plants received only RB light was considered as a control. Short description of light treatments is given in Table 1. Light spectra(Fig. 1) of various LEDs was analyzed by means of portable spectroradiometer(LI-1800 Licor, Lincoln, NE, USA), light intensity in each growth cells was measured using quantum sensors(LI-190 Licor, Lincoln, NE, USA). During the cultivation light intensity was adjusted by changing the distance between plants and LED modules. The pots with tomato seedling were interchanged every day to avoid variation in plant growth due to possible light nonuniformity within the growth cells.

    3.Leaf gas exchange parameters

    Instantaneous leaf net assimilation rate and stomatal conductance of young tomato plants subjected to various light treatments were analyzed by means of portable gas exchange analysis system(LI-6400, Licor, Lincoln, NE, USA) 20 days after starting light treatments. Fully expanded four terminal leaves from each treatment were chosen for these measurements. Measurements were taken during the main lighting period with red blue LED leaf chamber as well as at EOD lighting period with standard clear top chamber. Environmental conditions in leaf chamber were as follows: flow rate - 300 μmol sec-1, CO2 - 400 μmol mol-1(ambient), light intensity - 120 μmol m-2 s-1 in red blue LED leaf chamber and 50 ± 5 μmol m-2 s-1 in clear top chamber, temperature-26°C.

    4.Plant Growth Analysis

    Tomato plants were subjected to destructive sampling in order to study the effect of different LED treatments on growth characteristics of young tomato plants at 24 days after light treatments. Randomly selected four plants from each treatment were cut from stem base, root were thoroughly washed with tap water in order to clean from substrate. Plant height, leaf area, stem diameter and fresh weights of roots, leaves and stems were measured. To determine dry weights each plant part were dried separately in an oven at 70°C at least 3 days and then weighed with electronic balance. Plant compactness was expressed as dry mass / plant height as was suggested by Van Iersel & Nemali (2004) and plant health index was expressed as(stem diameter / height) x total dry weight as was suggested by Fan et al.(2013).

    5.Statistical analysis

    Experiment was arranged in a completely randomized design and replicated two times for reproducibility. Data presented for the growth parameters are the means of four replicates. All data were subjected to analysis of variance(ANOVA) followed by Fisher’s least significant difference test(at p≤0.05) using RStudio statistical software(Rstudio, Inc., Boston, MA, USA) with the “agricolae” package(Mendiburu, 2014).

    Results and Discussion

    Effect of different LEDs with various wavelengths on the growth and morphogenesis of plants has been extensively studied in mono-, di- and polychromatic systems both in controlled environment chambers and in greenhouses(for review refer to Olle and Viršile, 2013). In this experiment, all tomato plants were cultivated in growth cabinets under same RB LEDs during 12 hours photoperiod, and then plants during 4 hours were subjected to the so called EOD light treatments by utilizing various monochromatic LEDs.

    Growth and morphology of young tomato plants were strongly affected by application of EOD monochromatic light with various wavelengths(Table 2). Assimilation area of young tomato plants was positively influenced by EOD lighting, with the highest values observed for RB+R, RB+UV and RB+B treatments(Table 2). RB+B treatment resulted in taller plants, whereas plants in RB+UV treatment produced shorter plants. Monochromatic blue light also resulted in elongated and thicker internodes compared to other EOD treatments and control(Table 3). Similar results on the effect of monochromatic blue light on the stem elongation of chrysanthemum were reported by Jeong et al.(2014). Authors found that monochromatic EOD blue light can highly increase stem height which was determined by internode extension and which is consistent with our results. Stem elongation was also observed in marigold(Heo et al., 2002) and tomato plants(Kim et al., 2015) which were grown under sole blue light. Contrasting results were reported by Xiaoying et al.(2012). Authors found that tomato plants grown under monochromatic blue light with the intensity of 320 μmol m-2 s-1 produced much shorter stems compared to those grown under monochromatic red, orange or green LEDs with the same light intensity. Such discrepancies in results can be explained by the difference in light intensities used in these experiments. In our previous experiment, we found that monochromatic UV-A(with the peak at 367 nm) supplemented with two irradiation levels to the red LEDs had a beneficial effect on the growth of tomato plants(Khoshimkhujaev et al., 2014). Tomato seedlings grown under supplemented monochromatic UV-A light had higher assimilation area and shorter stems compared to those grown under sole red light which are in agreement with our current experimental results.

    Both total fresh and dry weights of young tomato plants exposed to EOD lighting were highly increased compared to non-exposed plants(control), however there was no difference among EOD treatments(Table 3). Additional four hours of irradiation from various monochromatic LEDs altered dry mass allocation among plant organs. Monochromatic blue light(RB+B) highly increased dry mass partitioning to the stem and decreased to the leaf, whereas plants in RB+UV and RB+R treatments showed opposite response. Dry mass partitioning to the roots was not significantly different among all experimental units. In this experiment tomato plants were grown under relatively low photon flux(120 μmol m-2 s-1), lower than actual plant requirements, and additional 4 hours of EOD lighting which was provided from different LEDs has improved biomass accumulation of young tomato plants by providing relatively better lighting conditions(longer photoperiod and higher daily light integral) compared with control.

    Gas exchange parameters of young tomatoes did not significantly differ during the main lighting period with RB LEDs(data were not given). However, it was found that during EOD lighting tomato plants differently responded to light from various LEDs. Photosynthetic rate of plants subjected to different EOD light treatments with the intensity of 50 μmol m-2 s-1 ranged within 0.8 and 1.4 μmol m-2 s-1. The highest value of photosynthetic rate showed plants received red and green light(RB + R and RB + G treatments, respectively), slightly lower rates were observed in plants exposed to monochromatic B and UV-A light, whereas, control plants showed no CO2 uptake, only release(Fig. 2). These results are generally coincident with the photosynthetic quantum efficiency curve experimentally determined by McCree(1971). The stomatal conductance values were the highest in plants subjected to monochromatic UV-A followed by plants in RB + B, RB + G, and RB + R treatments. Control plants showed the lowest stomatal conductance. Stomatal conductance is an important gas exchange parameter and it can be affected by various environmental factors(Kim et al., 2004). Phyo & Chung(2013) documented that transpiration rates of two rice cultivars treated with monochromatic UV-A(365 nm) combined with red light(660 nm) were increased with increasing of UV-A level. Since transpiration is regulated by stomatal aperture, these results are somewhat consistent with ours. Higher stomatal conductance values may be beneficial for the leaf gas exchange with the atmosphere, and consequently for photosynthesis too. However, it can also decrease water use efficiency through increased transpiration rates. In our opinion, additional research is needed to study the stomatal response to the monochromatic light with various wavelengths.

    In most cases, plant height is considered as a synonym of plant compactness. Islam et al.(2004) suggested defining compactness index as an increase in dry mass per unit plant height instead of just a reduction in stem height. Supplemental red light promoted compact growth of glasshouse grown sunflower(Helianthus annuus), whereas plant grown under supplemental blue light showed lower weight, leaf area and compactness(Schwend et al., 2015). In current experiment plant compactness and health index values of young tomato plants were highest in both of RB + R and RB + UV treatments and the lowest values were observed for plants in RED + B treatment and control(Fig. 3). Plants compactness under monochromatic green light was also relatively higher and was comparable with plants in RB + UV and RB + R.

    In conclusion, based on the experimental data, we can conclude that EOD light from LEDs with the appropriate intensities can improve plant growth and initiate morphological changes in tomato plants. EOD monochromatic UV light produced short plants, whereas blue light resulted in taller plants. Both red and UV light increased compactness and health index of tomato plants. Further researches are necessary to study more extreme regions of UV radiation on the plant growth, morphogenesis and gas exchange parameters.


    The authors would like to acknowledge financial assistance from the Rural Development Administration, Republic of Korea(PJ010918).



    Spectral output of main red-blue lighting(A) and monochromatic LED’s applied as an EOD lighting in this experiment(B).


    Net CO2 assimilation rate(A) and stomatal conductance(B) of young tomato plants exposed to various EOD monochromatic LEDs. Measurements were carried out using clear top chamber. Bars indicate standard errors of the mean(n=4). Different letter above the bars indicate significant differences at p≤0.05.


    Compactness and health index of young tomato seedlings exposed to various monochromatic LEDs. Bars indicate standard errors of the mean(n=4). Different letter above the bars indicate significant differences at p≤0.05.


    Description of LED light treatments used in this experiment

    zPlant received only red blue(RB) light were considered as a control.

    Leaf area, stem height, internode length, and stem diameter of young tomato plants exposed to various monochromatic LEDs

    zDifferent letters in columns indicate significant differences between means at p≤0.05(n=4).

    Total plant fresh weight, dry weight and its partitioning(%) to different parts of young tomato plants due to various EOD monochromatic light treatments

    zDifferent letters in columns indicate significant differences between means at p≤0.05(n=4).


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