Jintong XIN,Houcheng LIU,Shiwei SONG,Riyuan CHEN,Guangwen SUN

Lab of Vegetable Physiology in South China,College of Horticulture,South China Agricultural University,Guangzhou 510642,China

Many studies on the effect of light on plants have shown that both light intensity and lightquality are importantforthe growth and development of plants.The growth of spinach,radish and leaf lettuce were improved under red lightemitting diodes (LEDs)with blue light supplementation[1-2].The growth of leaf lettuce was enhanced by addition of greenLEDsunderred and blue LEDs[3].Under red LEDs,nitrate concentration decreased,but the concentrations of vitamin C,soluble sugar increased in leaf lettuce[4].The concentrations of vitamin C increased while nitrate concentration decreased in leaf lettuce and komatsuna under blue and red-blue fluorescent lamp[5].Under red LEDs,carbohydrate accumulation was enhanced by blue LEDs in leaf lettuce seedling[6].The Chinese kale(Brassica alboglabra Bailey)is one of the famous special vegetable in South China,it has great cultivation area and yield in local area.Flower stalk of Chinese kale is the edible organ,which is crisp and full of nutrient.The growth and quality of Chinese kale was affected by different color net(unpublished data).In this study,the effect of different LEDs (red,blue and green)on plant growth and quality of flower stalk in Chinese kale were studied.

Materials and Methods

Growth of plant material

The experiment was conducted in a plastic greenhouse in Guangzhou,China in 2011.Chinese Kale(cv.Lvbao)was sown on June 6 and plug seedlings were transplanted in plastic boxes (61 cm×42 cm×8 cm)(12 plants/box)with 15 L nutrient solution(including N 200 mg/L,P 30 mg/L,K 240 mg/L,Ca 130 mg/L,Mg 48 mg/L,Fe 2 mg/L,B 0.5 mg/L,Mn 0.5 mg/L,Zn 0.05 mg/L,Cu 0.02 mg/L,Mo 0.02 mg/L)on July 4.The nutrient solution was refreshed every 9 d.Three different LED treatments were applied:red ∶blue=8∶1(8R1B),red∶blue=6∶3(6R3B)and red∶green∶blue=6∶2∶1(6R2G1B)(red:630-660 nm,green:520-540 nm and blue:450-460 nm),12 h light,50 μmol/(m2·s).The LED treatments were started on July 4.Each treatment had four repeats,with randomized block arrangement.During the experiment,the day/night temperature was 28-32℃/18-22℃.

Growth measurement

After 30 d of LED treatments,Chinese kale plants were harvested at market maturity stage.Five representative plants in each repeat were taken randomly to measure plant height and stem diameter(at 5-6 node of flower stalk)with a ruler and a vernier caliper respectively.The plant was divided into rootand shootand theirfresh weight and dry weight(after drying at 70℃to constant weight)were measured.

Quality measurement

The concentration of soluble protein was measured with Coomassie brilliant blue method[7].The concentration of vitamin C was measured according to the procedure developed by Sparrman and Danielson[8].Nitrate concentration was determined by UV-spectrophotometric method[9].The concentrations of soluble phenols and flavonoids were analyzed according to Pirie and Mullins[10].The concentration of soluble sugar was measured with anthrone colorimetric method and the concentration of free amino acid with ninhydrine method according to Li[11].Nitrate reductase activity was determined by measuring the formation of NO2-according to Riens and Heldt[12].

Statistical analyses

The data was analyzed by SPSS 10.0 and EXCEL.The least squares difference (LSD)test was used for testing statistical significance between treatments.

Results and Analysis

Effect of different LEDs on growth of Chinese kale

The growth of Chinese kale was affected by different LEDs (Table 1).There was no significant difference in plant height,diameter of flower stalk and leaf number.The fresh weight of shoot,root and plant and the dry weight of root in 6R3B was significantly lower than those in the other two treatments.The dry weight of shoot and plant in 8R1B was significantly higher than in 6R3B.

Effect of different LEDs on quality of Chinese kale

The quality of flower stalk in ChinesekalewasaffectedbyLEDs(Table 2).The concentration of vitamin C,soluble protein and soluble sugar in 6R3B was significantly higher than in 8R1B and 6R2G1B.However,there was no significant difference in the concentration of free amino acid,soluble phenol,flavonoids and reducing sugar among the three treatments.

The nitrate concentration in 6R3B was remarkably lower than those in the other two treatments with 46%of that in 8R1B and 53%of that in 6R2G1B,respectively.While the activities of nitrate reductase in 6R3B was remarkably higher than those in the other two treatments,with 70%higher than in 8R1B and 137%higher than in 6R2G1B,respectively.

Discussion

Red LEDs combined with blue LEDs was favorable to plant growth.The total dry weight accumulation of spinach,radish and leaf lettuce grown under red LEDs alone was significantly lower than under red LEDs+10%blue light[1].The biomasses of shoot,root and plant of Chines kale in more red light treatment(8R1B)were the highest,while those in more blue light treatment (6R3B)was the lowest(Table 1).Green light may be necessary to some plant,as the addition of 24%green light to red and blue LEDs enhanced plant growth of leaf lettuce[3],plant height of Chinese kale was also increased by the addition of green light in the present study.

The nutrition quality of vegetable was affected by different light quality.Under red LEDs,concentrations of vitamin C,soluble sugar especially sucrose increased in leaf lettuce[4],concentrations of soluble sugar significantly increased in seedling of cucumber,pepper,tomato and radish[13].The concentrations of vitamin C increased in leaf lettuce and komatsuna under blue and red-blue fluorescent lamp by comparing with that under white fluorescent lamp[5].Under red LEDs,carbohydrate accumulation in leaf lettuce seedling was enhanced by blue LEDs[14].The concentrations of vitamin C,soluble protein and soluble sugar in more blue light treatment(6R3B)were the highest,and those in with green light treatment(6R2G1B)were the lowest.

Blue light affected nitrate accumulation and nitrate reductase activity.Nitrate concentration was decreased by 30%in leaf lettuce under red LEDs(638 nm)[4],nitrate concentration was decreased in leaf lettuce and komatsuna under blue and red-blue fluorescent lamp by comparing with that white fluorescent lamp[5].Nitrate concentration in Chinese kale of 6R3B treatment was about 50%lower than in the other two treatments(Table 2).In green algae blue light improved nitrate reductase activity and biosynthesis of nitrite reductase[15],nitrate reductase activity of Chinese kale in 6R3B treatment was 70%to 137%higher than in the other two treatments.

The fresh weight of Chinese kale plant in 6R3B treatments was about 30%lower than that in 8R1B treatment,however the concentration of vitamin C,soluble protein and soluble sugar in 6R3B treatment was about 27%higher than those in 8R1B treatment,and nitrate concentration in 6R3B treatments was about 55%lower than that in 8R1B treatment,so more blue light improved nutritional value of Chinese kale.Thus more blue light treatment(6R3B)was more suit-able for the growth of Chinese kale.

Table 1 Effect of different LEDs on growth of Chinese kale

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