Application of Red and Blue LED Light on Cultivation and Postharvest of Tomatoes (Solanum lycopersicum L.)

Currently, light-emitting diode (LED) technology has produced a more energy-efficient and versatile technology as an artificial lighting system that can be applied in the agricultural sector. Artificial lighting technology has been proven to be effective in increasing the production of agricultural products, especially horticultural commodities. As one of the primary horticulture commodities, tomatoes are the most common crop produced in controlled environments with LED artificial lighting. The focus of this study is to describe the application of LED lights in tomato cultivation and postharvest. We provide an amalgamation of the recent research achievements on the impact of LED lighting on photosynthesis, vegetative growth, flowering, production, and postharvest of tomatoes. Red-blue (RB) lighting induces photosynthesis; increases the content of chlorophyll a, chlorophyll b, and carotenoids in tomato leaves; regulates vegetative growth in tomatoes; and increases the production of tomatoes. In postharvest tomatoes, blue LED lighting treatment can slowly change the color of the tomato skin to red, maintain hardness, and increase shelf life. Future research may be carried out on the effect of LED artificial lighting on tomatoes' phytochemical, antioxidant and other crucial nutritional content. Different LED wavelengths can be explored to enhance various bioactive compounds and health-promoting components.


Introduction
Recently, agricultural research, especially using lightemitting diodes (LEDs), has produced a more energyefcient and versatile technology as a lighting system [1][2][3][4][5].Light-emitting diode (LED) illumination is widely used in cultivating several types of plants, especially horticultural plants because its power consumption is lower and its light efciency is higher than conventional fuorescent lights [6].LEDs can also be used in various horticultural lighting applications, such as tissue culture, controlled environment research, and supplemental and photoperiod lighting for greenhouses [2].Te application of LEDs in agricultural cultivation increases yield, quality [1,7], photosynthesis efciency [8][9][10], and the content of secondary metabolite compounds [11][12][13] in agricultural commodities, especially horticultural commodities.However, the efect of LEDs on plant growth and quality is species-specifc, and the efect is infuenced by cultivation conditions [6].
Besides infuencing the cultivation system, Bantis et al. [7] reported that lighting treatment during storage afects the shelf life and quality of horticultural products, which has the potential to (1) increase soluble carbohydrates, which are substrates for respiration during storage; (2) increase or maintain levels of vitamin C, anthocyanins, total phenolics, sugars dissolved, and antioxidants; and (3) enhance or maintain visual appearance by the accumulation of pigments (lycopene, carotenoids, and anthocyanins).Light-emitting diodes' (LEDs) illumination has the potential to play an important role in postharvest horticultural products [14].Perera et al. [15] also reported that applying light-emitting diodes (LEDs) in postharvest horticultural commodities is a new, nonchemical, and residue-free technique to preserve safe and nutritious fresh horticultural crop commodities.LED illumination during storage can be an alternative solution to reduce losses during the postharvest process and maintain the quality of horticultural products.Tis is because the application of LED can extend shelf life and produce low heat emissions, which allows its use in cold storage rooms and refrigerators as well as in refrigerated container cars, where the light spectrum can be adjusted along with other positive features of LED lights.Terefore, the potential application of LED utilization in horticultural products continues to grow, especially in tomato commodities.
As one of the most widely consumed vegetables in the human diet, tomatoes are a source of minerals, vitamins, and antioxidant compounds that beneft human health [16,17].Terefore, innovative cultivation technology is needed to increase tomato production and its nutritional content.In addition, tomatoes are one of the horticultural commodities that have a high weight loss during storage, and the shelf life of tomatoes is still relatively short.Postharvest loss can be caused by several factors, including physiological, pathological, physical, and a combination of these three factors.Ethylene production, chlorophyll degradation, lycopene synthesis, and cell wall softening are the main factors of tomato ripening.Te color and texture of fresh tomatoes are the main quality attributes directly related to marketing and consumer acceptance.Apart from being a determinant of color, lycopene and carotenoids are also benefcial to health [18].Te potential use of LEDs in tomato cultivation and postharvest systems needs to be discussed and studied in more depth.Te focus of this review is to describe the application of LED to tomato plants in the feld (cultivation) and during the postharvest phase.

Impact of LED on the Growth and Development of Tomato
Light, water, and oxygen are the critical factors signifcantly infuencing plant growth and development.Light is essential in establishing desired morphological and photosynthetic characteristics among these factors.Light is an important factor in the photosynthesis process for food preparation to continue life processes and also controls many developments and physiological responses throughout the plant life cycle [19,20].Te spectrum greatly infuences plant growth and development response to light intensity and quality control [21].Plants need sunlight as a source of sufcient natural light to synthesize photosynthesis [22].However, the availability of natural light from sunlight used by plants for photosynthesis is infuenced by several factors, including the infuence of clouds, rain, and other climatic factors.Several studies have discussed the positive infuence of artifcial lighting on plant growth and the development of LED lighting.Tis efect is infuenced by the spectral composition of the LED source, lighting duration, and plant species [23].
Light-emitting diodes (LEDs) have been proven to be lowcost light sources and emit minimal heat [24].LEDs produce adjustable light intensity and suitable wavelengths, making them suitable for various plant species.LEDs also provide the advantage of reducing oxidative stress due to excessive light energy.Te wide variety of LED colors allows precise wavelength control without additional flters [25].A lighting system using specifc wavelengths can enrich the nutritional content of plants; however, special attention should be paid to the stress that artifcial light may exert on photosynthetic mechanisms and its consequences on biomass accumulation [23].Secondary metabolites show diferent characteristics than primary metabolites, involving carbohydrates and amino acids biosynthesized by plants.Phenolics and favonoids, which are included in the phenolic compounds, are secondary metabolite compounds produced by plants and play a role in plant adaptation to changes in the biotic and abiotic environments [26,27].As blue and red pigments, phenolic compounds function as antioxidants and protect against ultraviolet light.Anthocyanins are related to the color of fowers and fruit and function as insect attractants and antimicrobials.Blue light increases anthocyanin synthesis by increasing the expression of anthocyanin synthase and chalcone synthase (CHS) genes, and the anthocyanin protects cells from high-light damage.Carotenoids are terpenoid compounds that function as accessory pigments of orange and yellow lights [28].Carotenoids can limit damage to membranes caused by excess light because they play a role in the absorption of free radicals, as well as being able to absorb light energy, which is in the spectral region where chlorophyll does not exploit enough, and then transfer it to chlorophyll, thereby increasing the efciency of plant photosynthesis [28].Te defence mechanism of carotenoids and chlorophyll in excess light is nonphotochemical quenching (NPQ), where carotenoids are directly involved in the dissipation of excess excitation light as heat occurs in the outer antenna of photosystems II.All mechanisms to remove this trapped energy before passing it on to the electron transport chain are called NPQ.Tere are two diferent mechanisms depending on pH or energy: the frst involves zeaxanthin (Zea) (quenching type 1) and the second involves the carotenoid lutein (Lut) (quenching type 2).Te primary carotenoid in tomatoes is lycopene, which causes the red color of tomatoes.In pharmacology, lycopene has been reported to have anticancer, anti-infammatory, antidiabetic, antiallergic, antiatherogenic, antithrombotic, antimicrobial, antioxidant, vasodilator, and cardioprotective activities [16].In addition, lutein and β-carotene are also 2 Scientifca important carotenoids taking part in the light-harvesting complex in leaves.

Application of LED Lighting in Tomato Cultivation
2.1.1.Photosynthesis.Plant growth and development are infuenced by light, and the response depends on the species and cultivar [29].Photosynthesis is an essential plant reaction that converts energy (light) into chemical energy stored in organic compounds.Te high light intensity can cause a lower accumulation of photosynthetic pigments [30].Generally, photosynthesis is impaired in plants growing under monochromatic light [31][32][33].In addition, plants growing under monochromatic light experience impaired photomorphogenesis due to the unbalanced activation of photoreceptors that mediate light-dependent plant development [34].In tomato plants, photosynthesis in seedlings under red light was inhibited by stomatal closure and caused a reduction in CO 2 assimilation [35].Te tomato plantlets showed at least a threefold decrease in photosynthesis rate and a signifcant abnormal stem elongation when grown under 100% red light [36].Furthermore, tomato plants grown under far-red light reduced leaf's maximum photosynthesis, leaf mass, thickness, and nitrogen and increased the resistance to CO 2 difusion [37].Plants grown under monochromatic red light show lower maximum photochemical efciency, unresponsive stomata, and lower photosynthetic capacity than plants grown with supplemental blue light [21,38].Meanwhile, blue light in tomato cultivation increases photosynthesis, which helps provide a nitrogen source and stimulate nitrate metabolism [39,40].Blue light plays a role in regulating growth because it is involved in several critical plant responses such as phototropism, photomorphogenesis, stomata opening, chloroplast development, and leaf expansion [41][42][43].In supplemental lighting indoors and in greenhouses, blue light has less or no growth inhibitory efect, so a small amount of blue is always included in the light spectrum [38].
Te previous research results reported that a combination of red and blue light has proven efective in encouraging tomato photosynthesis.Red-blue light increased the photosynthetic capacity of photosynthate production in tomato leaves [44].Photosynthesis of tomato plantlets was efciently enhanced by increasing the light fraction B in combination with RB light [36].Red-blue LED increased shoots' fresh and dry weight and leaf area, displaying signifcantly higher photosynthesis rates [9].Te combination of red and blue light has the most efective photosynthetic waveband.RB light's infuence on the photosynthetic pigment concentration increased the total chlorophyll [35].Plants grown under RB light have the most excellent photosynthetic efciency because this wavelength range closely coincides with the Chl absorption peak [45,46].Tomato plants show higher photosynthesis rates, pigment content, and reduced stomata closure [38].In contrast, combined red-blue LED light supplementation has signifcantly increased tomato rubisco activity [47].Te combination of red and blue light speeds up photosynthesis compared to red or blue light alone [48].Red and blue lights maximally induce photosynthesis, while their combination provides the highest photon efciency compared to other LED combinations [49].Te proper ratio of red and blue LEDs increases the photosynthesis rate, photosynthetic pigment content, and photosynthetic efciency in tomato seedlings [50,51].Te red-blue light spectrum is absorbed by plant leaves to carry out photosynthesis and photosynthesis is maximally induced by blue and red light [52,53].Te combination of red and blue lights promotes stomata opening and increases CO 2 uptake and assimilation by leaves [53].In addition, the red-blue LED lights increase the content of chlorophyll a, chlorophyll b, and carotenoids in tomato leaves [54].

Plant Vegetative Growth.
Red and blue light is essential in many plant growth and development factors.As a signifcant horticultural crop, tomato is often used as a model crop to study plant responses to red and blue light [55][56][57].Shoot elongation is one of the most essential morphological characteristics to determine the response of plants to red and blue lights.Blue light inhibits elongation growth by activating cryptochromes, positively correlated with blue light-dependent phosphorylation [58,59].In tomato plants, monochromatic blue light is induced in seedlings with the highest rubisco amount, more compact size, and reduced biomass [33].In addition, an increase in the blue light percentage resulted in a decreased plant height [60].Increased blue light negatively impacts plant elongation and leaf area, inhibiting cell division and expansion [61][62][63].However, the treatment of red LED increased the plant height and stem diameter of tomatoes [64].In addition, the red pure light induced hypocotyl elongation, cotyledon expansion, plant height, and leaf area [33].Plants grown under red light show increased hypocotyl elongation, internode spacing, and leaf surface [33].Te leaf area of plants grown under red light is comparable to that of plants grown under red-blue light, but the dry weight is lower due to the reduced leaf mass per area (LMA) on the leaves of plants grown under red light compared to blue and red-blue [33].Likewise, with the efect of far-red light on tomatoes, Hao et al. [65] reported that far-red light increased stem length and carotenoid content.Far-red light also increased stem length, leaf area, and total plant biomass [66,67].Adding FR light increases tomato plants' total dry mass at the vegetative growth stage [68].In addition, Gou et al. [69] also reported that adding far-red light with LEDs induced stem elongation and plant height, which resulted in a more light interception and increased plant growth.Similarly, Zhang et al. [66] reported higher total plant dry mass under FR light.Far-red light increases the height of tomato plants and shows the expression of shade avoidance syndrome (SAS) [70].
Although high doses of blue light inhibit plant growth and biomass production because the energy is not fully used in photosynthesis, a low percentage of blue light is needed to complement red light for optimal plant growth [71][72][73].Te right combination of red and blue LEDs can promote photosynthesis and regulate vegetative growth in most Scientifca species.In tomatoes, 95% red +5% blue light increased the number of nodes (stem segments) [74].Te RB LED improved the total plant biomass of tomatoes [75] and increased the plant height and stem diameter of tomatoes [64].In addition, the higher temperature combined with RB light is an indisputable optimal regime for tomato growth [76] and routine content in leaves, increased content of young leaf favonoids, and decreased content of favonoids in mature leaves [77].

Flowering.
As an energy-saving additional lighting option, LED increases plant fowering and photosynthetic efciency in greenhouse [78,79].Light is an essential factor that infuences plant growth, including fowering.Xie et al. [80] reported that blue light promoted early tomato fowering.Strawberries under blue light accelerate fowering than red light [81,82].In addition, increasing blue light induces faster fowering [83][84][85].Blue and red light induce photomorphogenic responses in plants through cryptochromes and phytochromes [86,87], where light interacts through photoreceptors with fowering genes to regulate fowering [88].Te cry1 and cry2, as cryptochrome receptors, induce fowering by responding to wavelengths of 390-480 nm [89].Phytochromes, absorbing red and far-red light (700-800 nm), express fowering genes to control fowering [90].Phytochromes exist in red (inactive) and farred (active) absorbing forms, and the quality of the incident radiation (especially red: far-red) forms phytochrome photoequilibrium (PPE).Far-red LED has been used in plant applications to regulate fowering in at least some long-day plants.Red + far-red LED promotes fowering in long-day plants [91].Adding far-red lighting from LEDs makes it possible to quick the fowering of some plants.Meijer et al. [70] reported that far-red light signifcantly accelerated fowering and increased the number of fowers per truss.

Fruit Production.
Te fruit production of tomatoes in the LED and high-pressure sodium (HPS) treatments was insignifcant, but it was higher than without lighting/natural light [74].Even though there is no diference in results between HPS and LED treatments, the additional costs for LED applications are much cheaper than HPS lighting treatments [74].However, treatment using LED lights can generally show better tomato performance than without lighting or HPS lighting treatment (Table 1).Red or blue lighting can increase the fruit numbers [83,84].A more signifcant fruit number or weight per plant will afect other plant parts (leaves and stems).Fruit is a strong sink, so more of the assimilate produced by the leaves (source) is distributed to the fruit.Tis is indicated by the higher fruit ratio per biomass, meaning the fruit's weight is higher than the other biomass (leaves and stems) [75].Lighting at this wavelength stimulates the formation of chlorophyll and carotenoids; tomato plants do this to increase light absorption, thereby increasing the photosynthesis process [65].Increasing the rate of photosynthesis means that it can increase the production of assimilate, which will be transferred to the sink, one of which is fruit, so that a more signifcant number of fruits can be produced, and their size is larger (Table 1).In tomatoes, far-red lighting increases fruit number, fruit weight, and yield [65][66][67].In addition, previous research shows that red-blue lighting also increases fruit number, weight, and fruit ratio [74,75,94].In addition, the glucose content and fructose content in the red and blue LED lighting treatments were higher than in other lighting treatments [64].Tis is because red and blue lights are included in the optimum light spectra used in the photosynthesis process following light absorption in chlorophyll [64].Soluble carbohydrates such as sucrose, glucose, and fructose are essential substrates that aid plant metabolism in various developmental and physiological events by regulating carbon transfer to metabolically active.
Artifcial lighting also afects the color of tomatoes.Te red color of tomatoes was infuenced by the accumulation of lycopene [95].Lycopene is a natural antioxidant in ripe tomatoes and is very important for human health [96].Artifcial lighting signifcantly impacts lycopene biosynthesis, incredibly blue light [80].On the other hand, red lighting was involved in tomato carotenoid production through its receptor PHYs [97].Applying blue or red lighting accelerates the color change of tomato fruit by stimulating lycopene synthesis through the regulation of downstream light signaling components, such as HY5 and PIF, which have the potential to control the expression of lycopene biosynthetic genes, such as phytoene synthase 1 (PSY1) encoding for tomato.PSY enzyme produced the frst carotenoid, phytoene [8,80].Te presence of red and blue lights activates PHY and CRY receptors, which play a role in absorbing light.
An overall overview of the efects of red and blue light spectra on photosynthesis, vegetative plant growth, fowering, and fruit yield in tomatoes is presented in Table 2.

LED Lighting Application in Postharvest Tomatoes.
Tomatoes, one of the leading horticultural products, have a short shelf life and high losses.Te leading causes of high loss at the postharvest level are weight loss, senescence, fruit softening, spoilage, and certain physiological disorders.Applying LED lighting during storage can be an alternative solution to reduce postharvest losses and maintain product quality because of its advantages in extending the shelf life of fruit and resulting in low heat emissions.Previous research showed that LED lighting treatment on tomatoes during storage increases shelf life, fruit hardness, and lycopene content (Table 3).
For selling tomatoes at short distances (nearby markets), tomatoes are needed whose skin color can quickly change to red without decreasing other qualities.Tis is because consumers tend to be more interested in red tomatoes.Te lycopene content infuences the red color of tomatoes.Red LED lighting treatment increased the lycopene content in tomato fruit [18].Tomato fruit kept under red lighting at the ripe green stage increases lycopene accumulation, and this can be reversed after being exposed to far-red lighting, but fruit frmness and color are not signifcant [18,106,107,112].In addition, continuous red LED treatment on postharvest tomatoes also 4 Scientifca  16 Blue (430 nm) and red (660 nm) 12 hours (06.00-18.00),photosynthetic photon fux density (PPFD) was set at 50 μmol/m 2 s and the illumination period was extended from 06: 00 to 18: 00 h every day, with ambient temperature and ambient humidity (i) R and B: induced the synthesis of lycopene and β-carotene, and lutein induced earlier fruit maturing [80] (ii) R: accelerated the red discoloration of the fruit skin 17 HPS and red to far-red (FR: R) LED (450 and 660 nm) 18 h per day (04: 00-22: 00), 420 μmol/m 2 s FR: R LED increased the size of fruits [50] 18 8 Scientifca Scientifca increased total phenolic content, total favonoid, and antioxidant activity.However, frmness and chlorophyll content decreased, indicating that red lighting accelerates tomato fruit maturity [104].In addition, red light treatment can also increase the soluble carbohydrates and anthocyanins and reduce the chlorophyll content in fruit [102,113].Anthocyanins are water-soluble pigments that are naturally found in various types of plants.Anthocyanins also play a role in regulating color changes in fruit.Carbohydrates in tomatoes are essential compounds.Appropriate LED lighting color spectrum with light absorption spectrum for plants can increase the production of assimilate stored in the sink (especially fruit).Furthermore, red LED lighting treatment also encourages the formation of lycopene and β-carotene in fruit, which causes the color of the fruit to change to red [102].Light quality is an important environmental factor afecting pigment metabolism [114], and based on the results mentioned above, red light accelerates the breakdown of chlorophyll and carotenoid biosynthesis.Furthermore, LED lighting with a higher red: far-red ratio in the postharvest phase induced lycopene synthesis in tomato fruit than other dark or light treatments, and LED lighting with a red: far-red ratio afected the titratable acidity and frmness of tomato fruit, depending on the cultivar [103].Red: far-red lighting treatment reduces fruit frmness and increases the total acidity content [102,103].Red lighting encourages lycopene formation, which tends to be negatively correlated with fruit frmness.
Along with fruit ripening and coloring, the infuence of light qualities on fruit favor, such as sugar, acid, and aroma, is also interesting.Red-blue or far-red LED lighting increases the sugar content of tomato fruit [35,93].Treatment of tomatoes with red and blue light suppressed disease development and increased the production of carotenoids, TSS, and color without signifcant efects on frmness during postharvest storage.Tis suggests that postharvest lighting with red or blue LED lights regulates the synthesis and accumulation of carotenoids in tomatoes [108].
However, marketing tomatoes over long distances requires treatment that can extend the shelf life of tomatoes without reducing quality.Blue LED lighting treatment can slowly change the skin color of tomatoes to red and delay the decrease of tomato frmness [109].Monochromatic blue light can extend tomatoes' shelf life by delaying fruit softening and ripening [109].In contrast, additional blue light at 50 μmol induced blue light receptor gene, CRY3 expression and promoted fruit lycopene synthesis and β-carotene accumulation in tomato fruit [80].Te transcription factor ELONGATED HYPOCOTYL 5 (HY5) mediates CRYinduced gene expression in response to blue light [115,116].Terefore, increased lycopene content can be regulated by increasing HY5 levels under supplemental blue light [80].In addition, the contents of phytoene, β-carotene, α-carotene, and c-carotene, as well as accelerated fruit coloration, are improved by the addition of blue light by increasing potassium uptake in the roots and transport in the fruit during ripening [117].

Conclusions
Climate change, global warming, and related environmental constraints can reduce agricultural land availability and production and change the postharvest handling of agricultural products.One of the commodities most afected by this is horticultural commodities.As one of the primary horticulture commodities, tomatoes are the most common crop produced in controlled environments with LED artifcial lighting.Cultivation and postharvest of tomatoes can be optimized with LED artifcial lighting.LEDs have several advantages over traditional light sources, such as emitting a narrow range of light, high purity and efectiveness, compact size, longer shelf life, and lower power consumption.In our review, we provide a comprehensive treatise on recent achievements in the use of LEDs for tomato cultivation and postharvest.Te application of LED artifcial light infuences the cultivation and postharvest of tomatoes.Most light combinations (blue, red, red-blue, and far-red) have been studied extensively on the quality of tomato plants and fruit during cultivation and postharvest stages.Tomato leaves absorb the red-blue light spectrum to carry out photosynthesis, which is maximally induced by blue and red lights.In addition, red-blue LED lights increase the content of chlorophyll a, chlorophyll b, and carotenoids in tomato leaves and regulate vegetative growth in tomatoes.Tomato fowers are induced optimally with red + far-red LED lighting treatment.Red-blue lighting increases tomato production, such as fruit number, weight, and ratio.In postharvest tomatoes, blue LED lighting treatment can slowly change the color of the tomato skin to red, maintain frmness, and increase shelf life.Future research may be conducted on the efect of LED artifcial lighting on the content of phytochemicals, antioxidants, and other essential nutrients in tomatoes.Diferent LED wavelengths can be explored to enhance various bioactive compounds and health-promoting components.

Table 1 :
Te mean value of fruit parameters of tomato on the light treatments.

Table 2 :
Te impact of diferent LED light qualities on plant growth and development of tomato.

Table 3 :
Te postharvest efects of diferent LED lights on tomatoes.