Title Page

Contents

LIST OF ABBREVIATIONS 16

ABSTRACT 17

CHAPTER 1. Introduction 19

Plant Factory 19

Light-emitting Diodes 20

Plant Growth and Development to Visible Light 21

Lettuce 25

Literature Cited 26

CHAPTER 2. Leaf Shape Index, Growth, and Phytochemicals in Two Leaf Lettuce Cultivars Grown under Monochromatic Light-emitting Diodes 34

Abstract 34

Introduction 36

Materials and Methods 38

Plant materials and growth conditions 38

Light spectrum 39

Growth characteristics and leaf shape of lettuce 39

Total phenolic concentration 41

Antioxidant capacity 42

PAL gene expression 43

Statistical analysis 45

Results and Discussion 45

Plant growth and leaf shape 45

Total phenolic concentration and antioxidant capacity 52

PAL gene expression 56

Literature Cited 59

CHAPTER 3. Leaf Shape, Growth, and Antioxidant Phenolic Compounds of Two Lettuce Cultivars Grown under Various Combinations of Blue and Red Light-emitting Diodes 65

Abstract 65

Introduction 68

Materials and Methods 71

Plant growth conditions and light spectrum 71

Growth characteristics 73

Chlorophyll fluorescence 74

Total phenolic concentration 74

Antioxidant capacity 75

Total flavonoid concentration 76

Statistical analysis 77

Results 78

Growth characteristics and leaf shape 78

Antioxidant phenolic compounds 83

Discussion 87

Literature Cited 97

CHAPTER 4. Growth, Photosynthetic and Antioxidant Parameters of Two Lettuce Cultivars as Affected by Red, Green, and Blue Light-emitting Diodes 104

Abstract 104

Introduction 106

Materials and methods 109

Plant growth conditions 109

Light treatments 110

Growth characteristics 113

Chlorophyll content 113

Photosynthetic rate and leaf transmittance 114

Cell division analysis 114

Leaf cell density 115

Antioxidant parameters; total phenolic concentration and antioxidant capacity 116

Statistical analysis 116

Results 117

Light spectrum 117

Growth characteristics 118

Photosynthetic rate and leaf transmittance 124

Cell division and leaf anatomy 126

Total phenolic concentration and antioxidant capacity 130

Discussion 133

Growth characteristics 133

Chlorophyll content 136

Photosynthesis and transmittance 138

Cell division and leaf anatomy 139

Total phenolic concentration and antioxidant capacity 140

Conclusion 141

Literature Cited 143

CHAPTER 5. Application of Supplementary White and Pulsed Light-emitting Diodes to a Closed-type Plant Production System 150

Abstract 150

Introduction 152

Materials and Methods 155

Plant materials and growing conditions (Study I & II) 155

Light treatments 156

Plant measurements 158

Efficiency Measurements 163

Statistical analysis 164

Results 164

Supplementary white LEDs (Study I) 164

Pulsed LEDs (Study II) 173

Discussion 177

Supplementary white LEDs (Study I) 177

Pulsed LEDs (Study II) 182

Conclusion 186

Literature Cited 187

CHAPTER 6. Growth and Bioactive Compounds Synthesis of Cultivated Lettuce Subject to Light Quality Changes by Red and Blue Light-emitting Diodes 195

Abstract 195

Introduction 197

Materials and Methods 199

Plant materials and growing conditions 199

LED treatment 200

Plant measurements 202

Secondary metabolites 204

Statistical analysis 208

Results 208

Monochromatic LED (Study I) 208

Secondary metabolites 210

RB combined LED (Study II) 213

Discussion 221

Growth 221

Chlorophyll contents and photosynthesis of lettuce 222

Secondary metabolites 222

Conclusion 227

Literature Cited 228

적요 231

List of Tables

Table 2.1. List of oligonucleotide primers used for quantitative-real-time PCR. 44

Table 2.2. Growth characteristics of lettuce plants grown under various LEDs and FL + HPS at 23 days after... 46

Table 3.1. Growth characteristics of lettuce plants grown under various combinations of blue and red light-emitting... 79

Table 3.2. Chlorophyll fluorescence (Fv/Fm) of green leaf lettuce ('Grand Rapid... 81

Table 4.1. Spectral data for various combinations of red (R) and blue (B), and RB... 111

Table 4.2. Growth characteristics of lettuce plants grown under various combinations of red (R) and blue (B), and RB... 119

Table 4.3. Chlorophyll (Chl) contents of lettuce plants grown under various... 123

Table 4.4. Total phenolic concentration and antioxidant capacity of red leaf lettuce... 132

Table 5.1. Spectral data for various combinations of red and blue LEDs supplemented with green (RGB) or white (RWB)... 159

Table 5.2. Electric current, photosynthetic photon flux density (PPFD), and light period according to frequency and duty... 160

Table 5.3. Growth characteristics of lettuce plants grown under various combinations of red and blue LEDs... 166

Table 5.4. Total phenolic concentration, antioxidant capacity and total flavonoid concentration of lettuce plants grown... 171

Table 5.5. Light use efficiency (LUE), energy use efficiency (EUE), and power... 172

Table 5.6. Growth characteristics of lettuce plants grown under various types of pulsed LEDs at 4 weeks after the onset... 175

Table 5.7. Light use efficiency (LUE), energy use efficiency (EUE), and relative... 178

Table 6.1. The 12 LED treatments used, based on monochromatic (M) blue (B) and... 201

Table 6.2. Primers used in the quantitative-real-time PCR and their target gene. 207

Table 6.3. Concentration and content of the individual phenolic compounds in lettuce plants grown under the several... 214

Table 6.4. Concentration and content of the individual phenolic compounds in lettuce plants grown under the several... 220

List of Figures

Fig. 2.1. Relative spectral distribution of the LEDs (A) and FL + HPS (fluorescent lamp + high pressure sodium lamp)... 40

Fig. 2.2. SPAD value of lettuce plants grown under various LEDs and FL + HPS... 50

Fig. 2.3. Leaf shape index at 0, 9 and 23 days after transplanting and lettuce plants... 51

Fig. 2.4. Total phenolic concentrations of lettuce plants grown under various LEDs... 53

Fig. 2.5. Antioxidant capacity of lettuce plants grown under various LEDs and FL... 55

Fig. 2.6. Expression of PAL (phenylalanine ammonia-lyase) gene of red leaf... 57

Fig. 3.1. Relative spectral distribution of various combinations of blue and red light-emitting diodes (LEDs) used in this... 72

Fig. 3.2. SPAD value (chlorophyll content) of 2 lettuce cultivars grown under... 82

Fig. 3.3. Leaf shape index at 2 and 4 weeks after the onset of LED treatment (left)... 84

Fig. 3.4. Total phenolic concentrations of lettuce plants grown under various... 85

Fig. 3.5. Antioxidant capacity of lettuce plants grown under various combinations... 86

Fig. 3.6. Total flavonoid concentration of lettuce plants grown under various... 88

Fig. 3.7. Correlation of total phenolic concentration and shoot fresh weight for... 95

Fig. 4.1. Relative spectral distribution of various combinations of red (R) and blue... 112

Fig. 4.2. Lettuce plants grown under various combinations of red (R) and blue (B),... 121

Fig. 4.3. Single leaf photosynthesis of both 'Sunmang' (A) and 'Grand Rapid TBR' (B) grown under various... 125

Fig. 4.4. Spectral distribution of light transmitted by red leaf lettuce ('Sunmang')... 127

Fig. 4.5. Spectral distribution of light transmitted by green leaf lettuce ('Grand... 128

Fig. 4.6. Cell division of red leaf lettuce 'Sunmang' grown under various... 129

Fig. 4.7. Epidermal cell density (A, C) and stomatal density (B, D) in leaves of 'Sunmang' (A, B) and 'Grand Rapid... 131

Fig. 5.1. Relative spectral distribution of various combinations of red and blue LEDs supplemented with green (RGB) or... 157

Fig. 5.2. Waveform of photosynthetic photon flux density (PPFD) of various types... 161

Fig. 5.3. Leaf shape index at 0, 2, and 4 weeks after the onset of the LED treatment (A), and lettuce plants grown under... 168

Fig. 5.4. SPAD (chlorophyll index) of lettuce plants grown under various... 169

Fig. 5.5. SPAD value (A) and photosynthetic rate (B) of lettuce plants grown under various types of pulsed LEDs at 4... 176

Fig. 6.1. Growth characteristics of lettuce plants grown under various LED... 209

Fig. 6.2. SPAD (a) and net photosynthesis (b) of lettuce plants grown under the monochromatic LEDs (blue, B; red, R)... 211

Fig. 6.3. Total phenolic concentration (a) and content (c) and antioxidant capacity... 212

Fig. 6.4. Growth characteristics of lettuce plants grown under several combined... 215

Fig. 6.5. SPAD (a) and net photosynthesis (b) of lettuce plants grown under several combined LED treatments at... 217

Fig. 6.6. Total phenolic concentration (a) and content (c) and antioxidant capacity... 218

Fig. 6.7. Expression of PAL (phenylalanine ammonia-lyase) and CHS (chalcone synthase) genes in lettuce plants grown... 225

Fig. 6.8. Lettuce plants (a), projected leaf area (b), predictive planting density (c), and predictive total phenolic... 226

Final goal of this study was to explore the effect of visible light qualities using light-emitting diodes (LEDs) on growth, photomorphogenesis, and secondary metabolites in lettuce (Lactuca sativa L.). Monochromatic red LEDs mainly induced the improvement of growth characteristics such as fresh and dry weights of shoots and leaf area. In contrast, monochromatic blue LEDs stimulated chlorophylls biosynthesis and the accumulation of antioxidant phenolic compounds via the activation of phenylalanine ammonia-lyase (PAL) gene. In combinations of red and blue LEDs, which are typically known to be effective for plant growth, the ratios of red and blue LEDs influenced both growth and accumulation of antioxidant phenolic compounds in lettuce plants. Increased ratio of red to blue LEDs had a positive effect on the growth and decreased ratio induced the accumulation of secondary metabolites. Green light in visible wavelengths had been considered to be an ineffective light for crop production due to low response in photosynthesis. However, the supplementation of green LEDs with appropriate ratios of red to blue LEDs stimulated leaf expansion and cell division and thereby enhanced lettuce growth. In addition, this positive effect of green light on growth was replaced by white LEDs including green wavelength. The substitution of green LEDs with white LEDs based on the combination of red and blue LEDs was effective for improving light and energy use efficiency. Moreover, the irradiation of pulsed LEDs by controlling frequency and duty ratio was effective to save electric power maintaining similar plant growth compared to continuous light. Finally, changing light quality within monochromatic red and blue LEDs or the combined red and blue LEDs at a specific growth stage may be used as a potential strategy to improve phytochemical production as well as yield.

In conclusion, this study suggests that each wavelength such as red, green and blue wavelength or the combination of the LEDs is a crucial factor for growth, photomorphogenesis and secondary metabolism in lettuce plants. Moreover, in terms of saving cost of energy or light use efficiency, the supplementary white LEDs and the application of pulsed LEDs may be additional consideration for designing commercial lighting source. Furthermore, changing light quality may be applied to commercial plant factory systems for improving phytochemicals. This dissertation provides both basic and practical information for designing artificial lighting sources using LEDs in closed-type plant production systems.