Xiaoxue FAN，Bo SONG，Hai XU，Longzheng CHEN*，Zhigang XU，Xihan YUAN

1.Institute of Vegetable Crops，Jiangsu Academy of Agricultural Sciences，Nanjing 210014，China；

2.College of Agronomy，Nanjing Agricultural University，Nanjing 210095，China

Effects of Different Light Emitting Diodes on Growth and Quality of Lettuce

Xiaoxue FAN1，Bo SONG1，Hai XU1，Longzheng CHEN1*，Zhigang XU2，Xihan YUAN1

1.Institute of Vegetable Crops，Jiangsu Academy of Agricultural Sciences，Nanjing 210014，China；

2.College of Agronomy，Nanjing Agricultural University，Nanjing 210095，China

The study investigated the effects on growth and quality of lettuce under six light treatments：yellow LED（Y），green LED（G），red LED（R），blue LED（B）and the red plus blue light（R∶B=3∶1）by dysprosium lamp as control（CK）.The re-sults showed that：under combination of red light and blue light，the fresh weight and dry weight were the largest，and the second was blue light treatment.Com-pared with the control，blue light and red plus blue light significantly enhanced the contents of soluble sugar，soluble protein，free amino acid and vitamin C.The study also showed that，red plus blue light significantly improved activity of nitrate reduc-tase and glutamine synthetase in lettuce leaves，which reduced the contents of ni-trate and nitrite and improved the safety effectively.

Light emitting diode（LED）；Light quality；Lettuce；Growth；Quality；Safety

L ight quality is an important envi-ronment factor that influences many aspects of plant growth and development，such as biomass，plantheight，leafarea and plant shape［1-3］.It was found in the research-es of a variety of crops including cow-pea seedlings，rice and seedlings of Chinese toon that blue light was bene-ficial to the accumulation of soluble protein［4-7］.Improving the proportion of blue light also can promote the nitro-gen metabolism of tobacco，improving the contents of total nitrogen，protein and amino acid［8］.Red light can pro-mote the metabolism of carbohydrates in plants，improving the content of car bohydrates［9-10］.Meanwhile，red light also can inhibit the transport process of photosynthate，facilitating the accu-mulation of starch in plant leaves［11］.

In recent years，novel energy-saving high-efficiency lightemitting diode （LED）has become a hotspot of research.Compared with conventional light sources，LED has the advantages of cold light source，low energy con-sumption，fixed light wavelength，high conversion rate，etc.In practical pro-duction，light density and light quality（red/blue light ratio or red/far-red light ratio）of LED light sources can be reg-ulated.Configuring light spectrum ac-curately according to the requirements by crops using LED light sources can promote high-yield high-quality envi-ronment-friendly crop production with high efficiency［12-13］.In addition，apply-ing LED light sources can solve the problem of impure light quality，result-ing in improved reliability of experi-ment results.In this paper，the effects of yellow light（Y），green light（G），red light（R），blue light（B）and red plus blue light（R∶B=3∶1）generated by LEDs on the growth and quality of lettuce were studied，aiming at understanding the effect of light quality on growth and various quality of lettuce and providing theoretical basis for application of LED light sources in protected cultivation of lettuce.

Materials and Methods

Experiment design

The experiment was carried out at the LED plant light source research center of Nanjing Agricultural Universi-ty in October of 2011，and the experi-ment material was lettuce（Lactvca sativa L.）.Seeds were subjected to soaking for accelerating germination and sown into aperture disks filled with turf，vermiculite and perlite（volume ratio at 3∶1∶1）under following environ-ment conditions：natural light，temper-ature of（20±2）℃，photoperiod of 12 h/d1 and relative humidity of about 80%.When the second true leaf was completely spread，lettuce seedlings with accordant morphologies and growth vigor were transplanted onto polyurethane foam seedling blocks in water planting boxes under LED light sources with 5 different light spectral energy distribution and dysprosium lamps as the control.The five LED treatments were blue light（B），red light（R），green light（G），yellow light（Y）and red plus blue light（R∶B=3∶1）with a light intensity of 100 μmol/（m2·s）.Oxy-gen was supplied into nutrient solution with inflator pumps，the nutrient solu-tion was replaced every 7 d once.The nutrient solution was prepared accord-ing to garden-type nutrientsolution formula，and the microelement formula adopted Aron formula.Each treatment was provided with 15 individual plants with three repetitions under the pho-toperiod of 12 h/d.After 20 d，random sampling was carried out to determine various indicators.Three individual plants were selected from each treat-ment randomly，and each indicator was determined thrice.

Light spectral energy distribution

The LED light source system was developed autonomously by the LED plant light source research center of Nanjing Agricultural University，and dysprosium lamps was used as the control.The light spectral energy dis-tribution was shown in Table 1.

Indicator determination and meth-ods

Three individual plants were se-lected from each treatment randomly for the determination of plant height，and fresh weights were weighed with an electronic scales；deactivation of enzymes was carried out in a dryer for 15 min，and the plants were dried to constantweights at80 ℃ to be weighed.Soluble sugar contents were determined according to anthrone colorimetric method［14］；free amino acid contents were determined according to ninhydrin method［14］；soluble protein contents were determined according to CBB G-250 staining method［14］；ni-trate nitrogen contents were deter-mined according to sulfuric acid-sali-cylic acid method［14］；nitrate reductase activity was determined according to in vitro method［14］；nitrite contents were determined according to the method by QIN［15］；and glutamine synthetase activity was determined according to the method by YIN［16］.

Data analysis

All data was processed with Excel 2003，statistics was performed with SPSS 17.0，and variance analysis adopted Duncan's multiple compari-son method.The lowercase letters a，b，c，d and e in the tables represented significant difference of various treat-ments at 0.05 level.

Table 1 Major technique parameters of different light spectral energy distribution under LED

Table 2 Effects of different light quality on morphologies and biomass of lettuce seedlings

Results and Analysis

Effects of different light quality on morphologies and biomass of let-tuce seedlings

As shown in Table 1，in compari-son with the control，the fresh weight and dry weight of individual lettuce plant were the largest under red plus blue light，which were improved by 55.6%and 62.5%，respectively；the next was the blue light treatment，which improved the fresh weight and dry weight of individual lettuce plant by 37.7%and 25%，respectively；and the red light treatment improved the fresh weight and dry weight of individual let-tuce plant by 14.8%and 12.5%，re-spectively.However，yellow LED and Green LED remarkably reduced the fresh weight and dry weight of individu-al lettuce plant.The above results indi-cated that red light，blue light and red plus blue light had positive effect on plants.

Compared with CK，yellow LED，green LED and red LED obviously in-creased the plant height of lettuce；blue LED significantly suppressed the plant height of lettuce；and red plus blue light was not significantly different with CK.

Effects of different light quality on quality of lettuce seedlings

In Table 3，light quality could ob-viously affect the quality of lettuce.the soluble sugar content under the treat-ment by red light was remarkably high-er than those under other treatments，and increased by 24.1%compared with the control，red plus blue light and blue light increased the soluble sugar content by 21.5%and 14.3%com-pared with the control，respectively，while under the treatment by yellow light and green light，the soluble sugar content decreased notably.blue light，red plus blue light and red light result-ed in the soluble protein contents in-creased remarkably，which were high-er than that of the control by 25.2%，5.9%and 4.7%，respectively，while the treatments of yellow light and green light lowered the soluble protein con-tent.Blue light and red plus blue light also led to remarkably improved amino acid contents in lettuce，which were higher than that of the control by 43.4%and 32.8%，while other treat-ments were not significantly different with the control.The vitamin C con-tents in lettuce under blue light and red plus blue light were higher，and in-creased by 29.4%and 17.6%com-pared with that of the control，while un-der the treatments of red light，yellow light and green light，the content de-creased remarkably.

As shown in Table 4，the nitrate content was higher under green light and yellow light，there was no differ-ence between red light and blue light，while red plus blue light resulted in an obviously decreased nitrate content，which was lower than the control by 43.2%.The nitrite content had a trend accorded with that of the nitrate con-tent，and red plus blue light also result-ed in a lowest nitrite content.By the research on the activities of key en-zymes in nitrate metabolism，the activ-ity of nitrate reductase was the highest under red plus blue light，which in-creased by 3 times compared with the control，and blue light and red light al-so improved the activity by 1.5 and 1.75 times，respectively.Meanwhile， the red plus blue light also obviously improved the activity of glutamine syn-thetase by 66.7%compared with the control.It was thus clear that visible red light，blue light and red plus blue light could improve the activities of metabolic enzymes to lower nitrate content in lettuce，and red plus blue light had an optimal light effect.

By comprehensively analysis，compared with the control and other treatments，red plus blue light could better improve the contents of soluble sugar，soluble protein，free amino acid and vitamin C，while remarkably lower nitrate content，thus indicating the best quality of lettuce under the treatment of red plus blue light.

Table 3 Effects of different light quality on quality of lettuce seedlings

Table 4 Effects of different LED light quality on safety of lettuce seedlings

Conclusions and Discus-sion

A lot of researches showed that red light and blue light had an impor-tant regulation effect on protein metabolism of higher plant，and the protein contents in leaves and seeds of a variety of plants under blue lighttreatmentwere higher than those of red light treatment［9，11］.This study found that the contents of solu-ble protein and free amino acid in leaves of lettuce under blue LED treatment were the highest，which was the same as the results of previous studies.Previous studies found that blue light could obviously promote dark respiration ofmitochondrias，and thus provided energy and carbon frameworkfornitrogenmetabolism and protein synthesis［9］；and mean-while，blue light could activate NR，therebyproviding more assimilable carbon so-urces for protein synthe-sis［18-19］.Therefore，blue LED is benefi-cial to synthesis and accumulation of soluble protein and amino acid of lettuce.

Saccharides were the starting matter for organic metabolism，and were the main energysource for maintaining vital movement［20］.Previ-ous studies found that red light im-proved soluble sugar contents in a va-riety of vegetables including tomato，Chinese toon seedlings and Chinese cabbage［7，21-22］；and there were also studies reporting that red plus blue light improved soluble sugar content in rice seedlings［23］.In this study，it was al-so found that the soluble sugar content was the highest in the lettuce under the red light treatment，and the second was the soluble sugar content in the lettuce under the treatment of red plus blue light，which was in accordance with the results by previous studies.

Vitamins are essential for human health.There were researches indicat-ing that blue light could promote the synthesis of vitamin C.Under blue light treatment， pea seedlings， radish sprouts and garlic seedlings have higher vitamin C contents［24-26］.Proper ratio of blue light to red light can effec-tively improve vitamin C content in plants［27］.In the researches on oilseed rape，it was found that vitamin C con-tent in leaves of tissue culture seedlings was the highest at the ratio of 3∶1 of blue light to red light［28］.In this study，we found that the treatments of blue light and red plus blue light resulted in higher vitamin C contents，which was in accordance with previ-ous studies.

Illumination plays an important role in nitrate metabolism in plants，and is one of the main factors deter-mining nitrate content.Nitrate reduc-tase （NR）and glutamine synthetase（GS）are two kinds of key enzymes in the assimilation process of NO3-［18］.Dif-ferentlight quality can obviously change the activities of NR and GS. There were researches indicating that blue light was likely to stimulate NR di-rectly，and meanwhile，red light andphytochrome also could regulate and control NR activity［29-30］.In addition，GS activity can be promoted by NR activity to some extent［31］.The results of this study showed that red plus blue LEDs at a ratio of 3：1 had a positive effect on the regulation and control of NR and GS of lettuce，while the effects by monochromatic red light and blue light were less obvious than red plus blue light，which might be related to the in-teraction of phytochrome with cry-tochrome.Nitrate accumulation in vegetables was caused by frustrated nitrogen metabolism，and its content was in positive correlation with NR and GS activities，which was verified by the results of this study in that the combi-nation of red and blue light improved the activities of nitrate metabolic en-zymes and effectively reduced the ni-trate content in lettuce.

Because the spectral energy dis-tribution of red light and blue light accords with the peak areas of ab-sorption spectrum of chlorophyll，red plus blue light can influence grow and development of plants positively，and proper spectral proportion，which may vary from species to species，can give full play to growth potential of plants［27，32］.

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Responsible editor：Yingzhi GUANG

Responsible proofreader：Xiaoyan WU

不同LED光源对生菜生长和品质的影响

樊小雪1，宋波1，徐海1，陈龙正1*，徐志刚2，袁希汉1（1.江苏省农业科学院蔬菜研究所，江苏南京 210014；2.南京农业大学农学院，江苏南京210095）

［目的］探明光质对生菜生长和各项品质的影响，为LED光源在生菜设施栽培上的应用提供理论依据。［方法］以生菜为材料，利用LED精量调制光源，设置黄光（Y）、绿光（G）、红光（R）、蓝光（B）和红蓝组合光（R∶B=3∶1）5个LED光处理，以镝灯白光为对照，探讨不同LED光源对生菜生长和品质的影响。［结果］红蓝组合光下生菜植株鲜样质量和干样质量最大，其次是蓝光处理。与对照相比，蓝光和红蓝组合光显著提高了生菜可溶性糖、可溶性蛋白、游离氨基酸和维生素C含量。试验还发现，红蓝组合光显著提高了生菜叶片中硝酸还原酶和谷氨酰胺合成酶活性，从而降低了硝酸盐和亚硝酸盐含量，有效提高了其安全品质。［结论］适宜的光谱比例能够充分发挥植物的生长潜力。

LED光源；光质；生菜；生长；营养品质；安全性

农业部公益性行业（农业）科研专项经费项目（201403032）；江苏省自主创新基金项目［CX（13）2004］。

樊小雪（1983-），女，山东淄博人，博士，助理研究员，研究方向为蔬菜育种与生理生态，E-mail：fxx600@163.com。*通讯作者，男，博士，副教授，研究方向为蔬菜育种与分子育种。

2015-07-08

Supported by the Special Fund for Agro-scientific Research in the Public Interest by the Ministry of Agriculture （201403032）and the Jiangsu Province Agricultural Science and Technology Independent Fund Project［CX（13）2004］.

*Corresponding author.E-mail：fxx600@163.com

Received：July 8，2015 Accepted：September 20，2015

修回日期 2015-09-20