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Article

Red and Blue LED Light Supplementation in the Morning Pre-activates the Photosynthetic System of Tomato (Solanum lycopersicum L.) Leaves and Promotes Plant Growth

by
Shuya Wang
1,2,
Xin Meng
1,
Zhongqi Tang
1,
Yue Wu
1,
Xuemei Xiao
1,
Guobin Zhang
1,
Linli Hu
1,
Zeci Liu
1,
Jian Lyu
1,2,* and
Jihua Yu
1,2,*
1
College of Horticulture, Gansu Agricultural University, Lanzhou 730070, China
2
State Key Laboratory of Aridland Crop Science (Gansu Agricultural University), Lanzhou 730070, China
*
Authors to whom correspondence should be addressed.
Agronomy 2022, 12(4), 897; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy12040897
Submission received: 1 March 2022 / Revised: 27 March 2022 / Accepted: 4 April 2022 / Published: 8 April 2022
Browse Figures
Versions Notes

Abstract

:
Supplementary light exposure using light-emitting diodes (LEDs) promotes the growth of tomato plants in greenhouses. Owing to the biological clock in plants, determining the period during which they must be exposed to supplementary light is essential to enhance growth. In this study, we used red and blue LEDs (red:blue = 7:2) as the supplementary light source, to determine the effects of different light supplemental periods on the growth and photosynthetic characteristics of tomato seedlings. Light supplementation in the morning and evening promoted the growth of tomato plants to varying degrees, including the accumulation of photosynthetic products in the leaves. Light supplementation in the morning enhanced dry matter accumulation, root growth, and the contents of chlorophyll and carotenoids in the leaves. Although both morning and evening light supplementation increased the levels of gas exchange parameters and Rubisco activity in tomato leaves, these effects were more prominent after morning light supplementation. Furthermore, red and blue light supplementation in the morning pre-activated the key photosynthetic enzymes, promoted the synthesis and accumulation of photosynthetic pigments, increased the photosynthetic capacity of, and photosynthate production in, tomato leaves. These findings suggest that light supplementation in the morning is more effective in promoting the growth and development of tomato plants cultivated in greenhouses.

1. Introduction

Light affects the energy metabolism of plants and is, therefore, a key determinant of plant growth and development. Insufficient light exposure during plant growth hinders the effective absorption and assimilation of carbon dioxide (CO2), which decreases photosynthetic efficiency, thereby affecting crop yield [1,2]. Tomato (Solanum lycopersicum L.) is the primary vegetable crop cultivated in greenhouses [3]. Long and cold winters in the northern hemisphere, with minimal sunlight exposure [4], slow the growth of crops cultivated in greenhouses and alter crop quality [5,6,7].
In recent years, artificial light supplementation has been used to overcome short-term sunlight exposure in greenhouse cultivation during winter months [8,9,10]. Light-emitting diodes (LEDs) have been used as supplementary light sources in greenhouse cultivation because of their efficiency, environment-friendly performance, availability of varying light intensities, and long-term use [11,12]. Red and blue lights maximally induce photosynthesis, while their combination provides the highest photon efficiency compared to other LED combinations [13]. Studies have shown that an appropriate ratio of red and blue light can promote photosynthesis and growth in cucumber and lettuce plants [14,15]. High-intensity red light irradiation promotes stem elongation, whereas blue light of the same intensity has inhibitory effects on stem growth, indicating that stem elongation is not only attributed the effect of red light, but also to the lack of blue light [16]. Blue LEDs promote the opening of stomata and increase the ratio of chlorophyll a to b (chl a/b) [17]. An appropriate ratio of red and blue LEDs improves the photosynthetic rate, photosynthetic pigment content, photosynthetic utilization efficiency, and root vitality of tomato seedlings [18,19]. Alternate irradiation with red and blue LEDs, at an interval of 1 h, improves the yield, taste, and energy metabolism of lettuce plants [20]. Red and blue LED combinations also increase the fresh and dry weights of cucumber seedlings [21]. Moreover, supplementing blue light to red LED light promotes the photosynthetic content of tomato leaves and growth, yield, and quality of tomatoes [22,23]. We have previously shown that LED light supplementation for 3 h at night promoted the growth and development of both tomatoes and cucumbers [24,25].
The biological clock of plants regulates growth and development, as well as metabolism [26]; thus, determining the appropriate time for light supplementation in plants can maximize yield. However, studies on the response of tomato plants to different periods of light supplementation are limited. Therefore, in the present study, red and blue LED plant growth lamps were used as supplementary light sources, to determine the effects of different light supplementation durations on the growth, photosynthetic system, and Rubisco activity of tomato seedlings cultivated in greenhouses. The findings of this study will provide insights into the biochemical and physiological mechanisms of light supplementation in greenhouse tomato production.

2. Materials and Methods

2.1. Plant Material and Growth Conditions

The tomato cultivar ‘Hongyun’ was obtained from the Shandong Jinan Xuechao Seed Industry Co. (Jinan, Shandong, China) and used in this study. Tomato seeds were soaked in water at 55 °C, stirred for 30 min, and then soaked at 25 °C for 10 h to allow imbibition. The seeds were evenly placed on wet cotton yarn in a Petri dish and incubated for 30 h in an artificial growth chamber maintained at 28 °C and 75% relative humidity in dark to accelerate germination. Then, the seeds were sown in the nursery substrate and placed in the artificial growth chamber for seedling growth. The conditions in the climate box were as follows: 12 h light period, with 300 μmol·m−2·s−1 of photosynthetically active radiation (PAR) at 26 °C and 75% relative humidity and 12 h dark period at 18 °C and 75% relative humidity. The tomato seedlings at the four-leaf one-heart stage were transferred to the modern greenhouse facility at the Gansu Agricultural University.

2.2. Experimental Design

An LED light source (red:blue = 7:2), with a rated power of 108 W, was used in this experiment (HY-115CM-36×3W-RB; Shenzhen Hooyi Energy Saving Technology Co., Shenzhen, Guangdong, China). Following three treatments were set up in the experiment: no light supplementation or control (CK), light supplementation for 3 h before sunrise (T1), and light supplementation for 3 h after sunset (T2). The time of sunrise and sunset were 8:30 and 18:00; therefore, supplementary light was provided from 5:30 to 8:30 in the morning for the T1 treatment, and from 18:00 to 21:00 in the evening for the T2 treatment. The CK, T1, and T2 seedlings were exposed to natural light from 8:30 in the morning to 18:00 in the evening. The LED light source was installed 20 cm above the tomato plant canopy of the T1 and T2 treatments, with a PAR of 51 μmol·m−2·s−1. A shading cloth was used to prevent the influence of light between treatments (Figure 1). At the beginning of the supplementary light treatments, 20 tomato plants with consistent growth were selected for each treatment and their growth indices were measured at the start of the experiment and after every 10 days (d). After 30 d of light supplementation, 10 randomly selected tomato plants from each treatment were used to measure related physiological indices.

2.3. Growth Index Determination

Plant height was measured from the base of the stem to the tip using a steel tape measure. A Vernier caliper was used to measure plant diameter at 2 cm above the base of the stem. At the beginning of light supplementation, the third functional leaf of the upper part of the tomato plants was fixed, and the leaf area was determined as described by Xue et al. [27]. The third leaf of the plant from the growth point was selected, and a protractor was used to measure the angle between the petiole and the main stem.

2.4. Dry Matter Accumulation, Specific Leaf Weight, and Root Parameters

Dry matter accumulation was measured as follows. Six plants were selected from each treatment and their roots were washed and dried. Thereafter, an electronic scale was used to measure the fresh weight of roots, stems, and leaves. After estimating the fresh weight, the dry weight was measured by oven-drying plant parts at 105 °C for 30 min, followed by drying at 80 °C until a constant dry mass was obtained. Six leaves of uniform size from the same node were selected for each treatment, spread, and tiled under a scanner (STD 4800; Regent Instruments, Québec, QC, Canada). The leaves were scanned, their images were saved, and Win RHIZO 5.0 (Regent Instruments) was used for analyzing leaf area. The leaves were de-enzymed in an oven at 105 °C for 30 min, and then dried at 80 °C until the dry mass was obtained. Leaf weight was determined as follows:
Specific leaf weight = dry mass/leaf area.
Three plants with comparable growth in each treatment were excised from the root–shoot junction, and the roots were carefully washed and dried. A ruler was used to measure the length of the taproot. Then, roots were immersed in 300 mL of water in a 500 mL measuring cylinder, and root activity was measured using the triphenyl tetrazole chloride method [28].

2.5. Pigment Content and Gas Exchange Parameters

Six tomato plants were selected from each treatment to measure the gas exchange parameters of the third functional leaf of similar size and orientation as the growth point. Stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), and net photosynthesis (Pn) were measured. The parameters of portable photosynthetic apparatus (CIRAS-2; PP System Inc., Amesbury, MA, USA) were set according to the method of Wang et al. [25]: temperature, 25 °C; light intensity, 1000 μmol·m²·s−1; CO2 concentration, 380 μmol·mol−1; relative humidity, 75%. The content of photosynthetic pigments in tomato leaves, including chlorophyll a, chlorophyll b, and carotenoids, was determined using Arnon’s method [29]. Methods have been previously described by Tang et al. [30].

2.6. Determination of Ribulose 1, 5-Bisphosphate Carboxylase (Rubisco) Enzyme Activity

Six functional leaves of uniform size and at the same node position from each treatment were collected 2 min before the end of light supplementation in the morning and evening and at 1100 h in the morning under natural light. The samples were cut into pieces, weighed in 1g increments, frozen, and stored in liquid nitrogen. Leaves were ground with 9 mL phosphate buffered saline solution (pH 7.4) precooled at 4 °C. The homogenate was centrifuged at 5000 rpm for 25 min at 4 °C, and the supernatant was collected to determine rubisco activity using an enzyme-linked immunosorbent assay (ELISA) kit (Shanghai Guduo Biotechnology Co., Ltd., Shanghai, China) following manufacturer’s instructions. Finally, absorbance was measured at 450 nm using a microplate reader (SpectraMax CMax Plus; Molecular Devices, San Jose, CA, USA), and the enzyme activity in each treatment was calculated based on the corresponding standard curve. The final enzyme activity was expressed in U·L−1.

2.7. Determination of Photosynthetic Products

Six tomato plants were selected from each treatment, and the third functional leaf of comparable size and orientation at a similar growth point was selected for the determination of photosynthates. Glucose, fructose, and sucrose contents were determined using an ELISA kit (Shanghai Guduo Biotechnology Co., Ltd.) following manufacturer’s instructions. Finally, absorbance was measured at 450 nm using a microplate reader (SpectraMax CMax Plus; Molecular Devices, San Jose, CA, USA), and the contents of glucose, fructose, and sucrose in each treatment were calculated according to the corresponding standard curve. The total soluble sugar and starch contents in the tomato leaves were determined using the anthrone–sulfuric acid (H2SO4) method [28].

2.8. Statistical Analyses

Experimental results are presented as mean ± standard error (SE) of three replicates. SPSS ver.13 (SPSS, Inc., Chicago, IL, USA) was used to perform one-way analysis of variance. Duncan’s honestly significant difference test was used to determine the difference between groups, and p-value < 0.05 was deemed statistically significant.

3. Results

3.1. Growth and Morphology

Figure 2 shows the height, stem diameter, leaf area, and angle of stem and leaf of tomato plants in response to different durations of LED light supplementation. After 40 d of light supplementation, a significant increase in the height of the tomato plants was observed (Figure 2A), compared to the CK plants. Moreover, 3-h-long light supplementation in the evening significantly increased the stem diameter of tomato plants (Figure 2B). The leaf area also significantly increased under LED lighting, which was exacerbated after 3-h light supplementation in the evening (Figure 2C). Compared to the CK treatment, the leaf and stem angles of tomato plants exposed to red and blue LED lighting were significantly reduced, suggesting that light supplementation affected the growth of leaves facing the light source (Figure 2D).

3.2. Dry Matter Accumulation

Figure 3 shows the effect of different LED light supplementation durations on dry matter accumulation in tomato plants. Compared with those in the CK treatment, the fresh weight of tomato leaves and roots significantly increased after 3 h of light supplementation in the morning, whereas that of roots and stems significantly increased after 3 h light supplementation in the evening (Figure 3A). The dry weight of leaves, stems, and roots significantly increased after 3 h light supplementation in the morning, and that of stems significantly increased after 3 h light supplementation in the evening (Figure 3B), as compared to the CK treatment. These results suggest that light supplementation for 3 h in the morning was more conducive to the accumulation of tomato dry matter than that in the evening.

3.3. Root Parameters and Specific Leaf Weight

Different LED light supplementation durations exhibited significant effects on the tomato root parameters and specific leaf weight. The main roots of tomato plants subjected to LED light supplementation for 3 h were significantly longer than those of the CK treatment (Figure 4A). Light supplementation for 3 h in the morning significantly increased root volume and activity in the tomato plants (Figure 4B,C). A similar trend in root volume and activity was observed following treatment with 3 h of supplementary light in the evening; however, no significant difference between the treated and CK plants was observed. The specific leaf weight of plants exposed to 3 h light supplementation treatment in the morning was significantly higher than that of the CK treatment, while the 3 h supplementary light treatment in the evening did not exhibit any significant difference from the CK treatment (Figure 4D). Therefore, supplementing LED light for 3 h in the morning was more beneficial for the growth of the root system and increase in specific leaf weight in tomato plants, which could improve the absorption and utilization of nutrients.

3.4. Photosynthetic Pigments

Plants absorb light mainly through photosynthetic pigments. As shown in Table 1, after 3 h light supplementation in the morning, the contents of chlorophyll a, total chlorophyll, carotenoid, and chl a/b in the tomato leaves were significantly higher than those in the CK plants. Therefore, compared to other treatments, supplementing light for 3 h in the morning was more beneficial for promoting the accumulation of chlorophyll a, total chlorophyll, and carotenoids and chl a/b in the tomato leaves.

3.5. Gas Exchange Parameters

The gas exchange parameters of leaves are indicators of photosynthesis. After 3 h light supplementation in the morning and evening, the Gs (Figure 5A), Tr (Figure 5B), and Pn (Figure 5D) of the tomato leaves were significantly higher than those of the CK plants. The Ci (Figure 5C) of the tomato leaves significantly decreased after 3 h light supplementation in the morning and evening, compared to that of the CK plants. Therefore, supplementation of light for 3 h in the morning and evening was beneficial for improving the gas exchange and photosynthetic capacity of the tomato leaves.

3.6. Rubisco Activity

Rubisco is a key enzyme involved in the fixation of CO2 in the Calvin cycle of plant leaves. As shown in Figure 6, at 8:30, the activity of rubisco in tomato leaves subjected to 3 h light supplementation in the morning was significantly higher (approximately 3.4-fold) than those of the CK plants. Following exposure to natural light at 11:00, the activity of rubisco in tomato leaves treated with supplementary light for 3 h in the morning and evening was significantly higher than those of the CK plants, and the activity of rubisco was significantly higher in the leaves exposed to supplementary light in the morning than those exposed to supplementary light in the evening. At the end of the 3 h supplementary light treatment in the evening (21:00), the activity of rubisco was significantly higher compared to that in the CK plants. Therefore, light supplementation for 3 h in the morning and evening improved the activity of rubisco in tomato leaves, while light supplementation for 3 h in the morning exhibited a greater effect on the activity of the enzyme.

3.7. Photosynthates

Photosynthetic products play an important role in plant growth and development. Table 2 lists the effects of different LED light supplementation durations on the photosynthate content in tomato leaves. When sampled at 8:30, after 3 h supplementation with LED light in the morning, glucose, fructose, sucrose, and total soluble sugar contents in the leaves were significantly higher, while starch content was significantly lower compared to that in the CK plants. When sampling was conducted under natural light at 11:00, glucose content in the leaves of plants subjected to 3 h LED light supplementation in the morning and evening was significantly higher than the CK plants, and glucose content was significantly higher under morning LED light supplementation than LED light supplementation in the evening. Fructose content in the tomato leaves of each supplemental light treatment was significantly higher than that in the CK plants, while fructose content in the leaves was significantly higher under supplementary light treatment in the evening than under supplementary light treatment in the morning. Furthermore, sucrose content was significantly higher in leaves exposed to supplementary light in the evening than in those exposed to the CK treatment and supplementary light treatment in the morning. The starch content in the leaves of plants exposed to each supplementary light treatment was significantly lower than in the CK plants, while the starch content was significantly lower in the tomato leaves treated with light supplementation in the evening than those treated in the morning. The total soluble sugar content in the tomato leaves of plants exposed to each supplementary light treatment was significantly higher than that of the CK plants. At the end of the supplementary light treatment in the evening (21:00), glucose, fructose, sucrose, and total soluble sugar contents in the tomato leaves were significantly higher, while starch content was significantly lower compared to the CK treatment.

4. Discussion

Light is an important environmental factor affecting plant growth. LED supplementary lighting has garnered attention for its ability to stimulate the growth of greenhouse crops. Studies have shown that red and blue LED supplementary lighting at night effectively promotes the growth of tomato plants and thereby increases yield [31]. The right proportion of red and blue LED light supplementation can enhance cucumber plant height and stem diameter [32]. Compared with white LED light, red LED light promotes the growth of pea seedling leaves [33], and compared with high-pressure sodium light supplementation, LED light supplementation promotes growth and chlorophyll accumulation in tomato plants [34]. Supplementation with a combination of red–blue (9:1) LEDs promoted the accumulation of dry matter in cucumber plants [35].
In this study, we used red and blue LEDs as light sources in the morning and evening, at a ratio of 7:2, for growing tomato seedlings and evaluated the effects of different light supplementation periods on the growth and photosynthetic characteristics of tomato seedlings. Our results showed that 40 d of supplementation with a combination of red–blue LEDs (3 h in the morning and evening) significantly increased the plant height (Figure 2A) and the leaf area of the third functional leaf (Figure 2C) of tomato plants.
Light supplementation in the evening for 3 h significantly increased stem thickness (Figure 2B). Although a similar trend in stem thickness was observed upon morning light supplementation for 3 h, no significant difference was observed compared to the CK treatment. Both morning and evening light supplementation for 3 h significantly decreased the angle between the stems and leaves (Figure 2D). The red and blue LED light sources were placed on top of the plants because tomato leaves grew towards the light source, consequently decreasing the angle between the leaves and stem and indicating that exposure to the combination of red–blue LEDs for 3 h in the morning and evening had the same effect on the growth of tomato leaves. Yan et al. [36] showed that combining red light to white light significantly increased the fresh and dry weights of purple lettuce leaves. Similarly, Liu et al. [37] showed that supplementation with red–blue light (red: blue = 1:1) promoted the accumulation of dry matter in tomato plants. Red and blue LED (red: blue = 8:2) supplementation has also been shown to promote fruit growth in tomato by improving photosynthetic efficiency and regulating root activity [19]. Ren et al. [38] showed that red and blue (at a ratio of 2:1) LED supplementation significantly increased the stem thickness, root biomass, and total biomass of Codonopsis lanceolata. Lin et al. [39] showed that combined red–blue LED light treatment improved root activity and dry matter accumulation in lettuce plants. Compared to the CK plants, the fresh and dry weights of tomato leaves and roots increased significantly after supplementation with combined red–blue LED light for 3 h in the morning (Figure 3A,B). After 3 h of light supplementation in the evening, the fresh weight of tomato stems and roots and the dry weight of stems significantly increased (Figure 3A,B). Combined red–blue LED light supplementation for 3 h in the morning and evening significantly increased the length of the main root (Figure 4A), whereas supplementation for 3 h in the morning significantly increased root volume (Figure 4B), root activity (Figure 4C), and specific leaf weight (Figure 4D). The tomato seedlings treated with combined red–blue LED light for 3 h in the morning had a smaller leaf area compared to those treated with 3 h of light in the evening, while plants exposed to 3 h of light in the morning had greater leaf dry weight, suggesting that the 3 h light supplementation in the morning can increase the thickness of tomato leaves. Combined red–blue LED light supplementation for 3 h in the morning may increase nutrient absorption in tomato seedlings by promoting the growth and vigor of roots, thereby improving their growth and dry matter accumulation.
The growth and development of plants is primarily dependent on photosynthesis. Plant leaves use photosynthetic pigments to absorb light in the red and blue regions of the spectrum and perform photosynthesis [40,41]; that is, photosynthesis is maximally induced by blue and red light [42]. Previous studies have shown that a combination of red and blue light promotes the opening of stomata and increases the absorption and assimilation of CO2 by the leaves [41]. Additionally, red light promotes the expression of photosynthesis-related genes [43]. Compared with high-pressure sodium lamps, combined red–blue LED light significantly improved the photosynthetic capacity of tomato leaves [44]. Using combined red–blue LED light supplementation, Song et al. reported that tomato seedlings exhibited a higher photosynthetic rate and pigment content and reduced stomatal closure [45]. In contrast, combined red–blue LED light supplementation has been shown to significantly improve the activity of rubisco in tomato and lettuce leaves [2,46]. The combination of red and blue light accelerates photosynthesis compared to that by either red or blue light alone [47]. We showed that combined red–blue LED light supplementation for 3 h in the morning significantly increased chlorophyll a, chlorophyll b, and carotenoid contents in tomato leaves, which was consistent with the results of Wei et al. [48]. Compared with those of the CK treatment, the Gs (Figure 5A), Tr (Figure 5B), and Pn (Figure 5D) significantly increased after using combined red–blue light supplementation for 3 h in the morning and evening, whereas the Ci (Figure 5C) significantly decreased in the leaves. This indicates that combined red–blue LED light supplementation for 3 h in the morning and evening improved photosynthesis in tomato leaves. Compared to the CK plants, rubisco activity was significantly increased after LED light supplementation for 3 h in the morning and evening; at the end of the morning 3 h light supplementation, the enzymatic activity of rubisco was three-fold higher than that in the CK plants during the same period, approximately reaching the level of the rubisco activity at 11:00 a.m. (Figure 6). A previous study reported that combined red–blue LED light supplementation with white LED light improved the stomatal characteristics of C. pilosula seedlings and increased soluble sugar content in their leaves [38]. Supplementation of a certain intensity of blue light to red LED light has been shown to increase the number of photosynthetic products [49]. Fang et al. [50] showed that red LED light promoted the accumulation of soluble sugars and starch in soybean seedlings during the day. In this study, combined red–blue LED light supplementation for 3 h in the morning and evening increased glucose, fructose, sucrose, and total soluble sugar contents and reduced starch content in the leaves (Table 2). Light supplementation for 3 h in the morning had a more significant effect on photosynthate production in the leaves compared to other treatments, suggesting that combined red–blue LED light supplementation in the morning may increase the absorption and utilization of light energy by promoting the generation of photosynthetic pigments and increasing the activities of key enzymes involved in the Calvin cycle. This improves the photosynthetic capacity of the leaves, which eventually enhances the production and accumulation of photosynthates in the leaves, thereby promoting the growth and development of tomato plants during harsh winters.

5. Conclusions

The findings of this study show that red and blue LED light supplementation in the morning and evening exhibits different effects on the growth and photosynthetic system of tomato plants. Light supplementation in the morning and evening increased the height and leaf area of tomato plants, while light supplementation in the evening increased the stem diameter. Morning light supplementation promoted dry matter accumulation and root growth, and significantly increased chlorophyll and carotenoid contents in the leaves. Light supplementation in the morning and evening increased the levels of gas exchange parameters in, and enhanced the photosynthetic capacity of, tomato leaves. Both morning and evening light supplementation increased the activity of the enzyme Rubisco in tomato leaves; this effect was more prominent after morning light supplementation. Light supplementation in the morning and evening significantly promoted the accumulation of photosynthetic products in tomato leaves. Thus, illumination using red and blue LED light in the morning, via the early activation of key photosynthesis-associated enzymes, promoted the synthesis and accumulation of photosynthetic pigments in the leaves, ultimately increasing their photosynthetic activity and synthesis of photosynthate and promoting root growth and dry matter accumulation in tomato plants. Furthermore, light supplementation in the morning was shown to be much more effective in promoting the growth and development of tomato plants than light supplementation in the evening (Figure 7).

Author Contributions

Conceptualization, J.L. and J.Y.; Data curation, S.W. and L.H.; Formal analysis, X.M.; Funding acquisition, J.L. and J.Y.; Investigation, Z.T. and Z.L.; Methodology, S.W.; Project administration, J.Y.; Resources, Y.W. and X.X.; Software, S.W.; Supervision, J.L.; Visualization, S.W.; Writing—original draft, S.W. and X.M.; Writing—review and editing, G.Z. and J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Education science and technology innovation project of Gansu Province (GSSYLXM-02), the Special project of central government guiding local science and technology development (ZCYD-2021-07), Gansu people’s livelihood science and technology project (20CX9NA099), the Fuxi Young Talents Fund of Gansu Agricultural University (GAUfx-04Y03), Gansu top-notch leading talent plan (GSBJLJ-2021-14), and the Gansu provincial education department excellent postgraduates ‘innovation star’ project (2021CXZX-374).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 12 00897 g001 550
Figure 1. Schematic illustration of supplementary light treatments.
Figure 1. Schematic illustration of supplementary light treatments.
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Figure 2. Plant height (A), stem diameter (B), leaf area (C), and angle of stem and leaf (D) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
Figure 2. Plant height (A), stem diameter (B), leaf area (C), and angle of stem and leaf (D) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Figure 3. Fresh weight (A) and dry weight (B) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
Figure 3. Fresh weight (A) and dry weight (B) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Figure 4. Length of main root (A), root volume (B), root activity (C), and specific leaf weight (D) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
Figure 4. Length of main root (A), root volume (B), root activity (C), and specific leaf weight (D) of tomato plants exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Figure 5. Stomatal conductance (A), transpiration rate (B), intercellular CO2 concentration (C), and net photosynthetic rate (D) of tomato leaves exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Bars indicate standard errors. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
Figure 5. Stomatal conductance (A), transpiration rate (B), intercellular CO2 concentration (C), and net photosynthetic rate (D) of tomato leaves exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Bars indicate standard errors. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Figure 6. Rubisco activity in tomato leaves exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
Figure 6. Rubisco activity in tomato leaves exposed to different LED light supplementation durations. Data are expressed as average values (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). Standard errors are indicated by bars. CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Figure 7. Schematic illustration of the response of tomato plants to red and blue LED light supplementation in the morning and evening. Illumination using red and blue LED light in the morning, via the early activation of key photosynthesis-associated enzymes, promoted the synthesis and accumulation of photosynthetic pigments, ultimately increasing the photosynthetic activity and synthesis of photosynthates and promoting root growth and dry matter accumulation in tomato plants. Red arrows represent increase, and the thicker the arrow, the greater the increase.
Figure 7. Schematic illustration of the response of tomato plants to red and blue LED light supplementation in the morning and evening. Illumination using red and blue LED light in the morning, via the early activation of key photosynthesis-associated enzymes, promoted the synthesis and accumulation of photosynthetic pigments, ultimately increasing the photosynthetic activity and synthesis of photosynthates and promoting root growth and dry matter accumulation in tomato plants. Red arrows represent increase, and the thicker the arrow, the greater the increase.
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Table
Table 1. Photosynthetic pigment content in tomato leaves of plants exposed to different LED light supplementation durations.
Table 1. Photosynthetic pigment content in tomato leaves of plants exposed to different LED light supplementation durations.
TreatmentPhotosynthetic Pigment Content (mg·g–1·FW–1)Chlorophyll a/b
Chlorophyll aChlorophyll bTotal
Chlorophyll		Carotenoid
CK1.54 ± 0.118b0.40 ± 0.019a1.94 ± 0.110b0.72 ± 0.051b3.68 ± 0.243b
T11.81 ± 0.296a0.43 ± 0.042a2.23 ± 0.362a0.82 ± 0.055a4.24 ± 0.351a
T21.61 ± 0.113ab0.44 ± 0.036a2.06 ± 0.156ab0.78 ± 0.027ab3.66 ± 0.205b
Data are expressed as average values ± standard error (n = 3). Different lowercase letters indicate significant differences between treatments determined using Duncan’s multiple range test (p < 0.05). CK: no light supplementation or control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening; FW: fresh weight.
Table
Table 2. Photosynthates in tomato leaves exposed to different LED light supplementation durations.
Table 2. Photosynthates in tomato leaves exposed to different LED light supplementation durations.
Sampling TimeTreatmentPhotosynthate Content (mg·g–1)
GlucoseFructoseSucroseStarchTotal Soluble Sugar
8:00 amCK14.23 ± 1.62b6.63 ± 0.79b11.35 ± 1.67b7.1 ± 3.4a46.15 ± 8.21b
T117.13 ± 0.98a11.95 ± 1.43a22.71 ± 1.35a4.4 ± 1.2b98.23 ± 4.93a
11:00 amCK3.05 ± 0.57c3.94 ± 1.07c6.64 ± 0.61b18.1 ± 2.1a56.12 ± 3.11b
T17.42 ± 0.23a6.43 ± 0.39b7.03 ± 0.94b8.1 ± 1.6b109.21 ± 11.25a
T26.79 ± 0.19b8.18 ± 0.61a12.71 ± 1.38a2.4 ± 1.2c95.86 ± 10.43a
21:00 pmCK3.38 ± 1.02b3.86 ± 0.42b6.61 ± 1.09b11.6 ± 2.1a40.94 ± 2.44b
T29.89 ± 0.96a5.67 ± 0.73a9.02 ± 0.46a5.1 ± 1.0b92.89 ± 7.76a
The data are expressed as average values ± standard errors (n = 3). Used the Duncan’s multiple range test, different lowercase letters indicated significant differences between treatments (p < 0.05). CK: no light supplementation control; T1: light supplementation for 3 h in the morning; T2: light supplementation for 3 h in the evening.
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Wang, S.; Meng, X.; Tang, Z.; Wu, Y.; Xiao, X.; Zhang, G.; Hu, L.; Liu, Z.; Lyu, J.; Yu, J. Red and Blue LED Light Supplementation in the Morning Pre-activates the Photosynthetic System of Tomato (Solanum lycopersicum L.) Leaves and Promotes Plant Growth. Agronomy 2022, 12, 897. https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy12040897

AMA Style

Wang S, Meng X, Tang Z, Wu Y, Xiao X, Zhang G, Hu L, Liu Z, Lyu J, Yu J. Red and Blue LED Light Supplementation in the Morning Pre-activates the Photosynthetic System of Tomato (Solanum lycopersicum L.) Leaves and Promotes Plant Growth. Agronomy. 2022; 12(4):897. https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy12040897

Chicago/Turabian Style

Wang, Shuya, Xin Meng, Zhongqi Tang, Yue Wu, Xuemei Xiao, Guobin Zhang, Linli Hu, Zeci Liu, Jian Lyu, and Jihua Yu. 2022. "Red and Blue LED Light Supplementation in the Morning Pre-activates the Photosynthetic System of Tomato (Solanum lycopersicum L.) Leaves and Promotes Plant Growth" Agronomy 12, no. 4: 897. https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy12040897

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