Yorio et al. (2001) reported that lettuce plants grown under RL supplemented with BL allowed the plants accumulate higher biomass than grown under RL alone [21]. The larger LA could increase the light interception, which contributed to the significant increase in biomass. Kim et al. (2004) demonstrated that BL:RL:GL (4:1:1) increased lettuce LA, which is a good parameter of higher photosynthetic surface area per unit investment in leaf tissue [22]. Although both RL and BL could promote stem elongation [23], Kong et al. (2012) revealed that BL was more effective than RL in suppressing shoot/leaf elongation in a range of plant species [24]. When grown arugula (Brassica eruca) and mustard (Brassica juncea) plants under continuous BL (24-h light/0-h dark; PPFD from 20 to 650 µmol m− 2 s− 1), the lightings could promote hypocotyl and petiole elongation compared to continuous RL [25]. Wang et al. (2016) also found that when the lettuce photosynthetic performance and growth by stimulating morphological and physiological responses were promoted when plants exposed to BL (200 µmol m-2 s-1 irradiance) [26]. Hernández and Kubota (2016) reported that plant height, hypocotyl length, and epicotyl length of cucumber (Cucumis sativus) seedlings were reduced when they were exposed to an increased BL, except for the controls (0% and 100% BL treatments) [27]. When the spectral light changes, the morphogenetic and photosynthetic responses are vary among different plant species. A feasibility of tailoring light spectra enables recent plant cultivation technologies and controls the plant growth, development, and nutritional quality. In our study, the growth and morphological features of control-treated coriander plants exhibited a tall appearance, large leaves, and shoot FW, indicating good plant growth under control conditions. Therefore, growth and development in the coriander plant are dependent on the spectral quality of light, and the addition of RL or BL under high (200 µmol m-2 s-1) and no (0 µmol m-2 s-1) light intensity may have further decreased plant growth and development due to high light conditions. Perhaps the control conditions achieved a balanced spectral environment for plants without any supplemention of RL or BL at high or low light intensity. Light treatments affected biomass accumulation in the shoot of the coriander plant, and shoot FW accumulation was about 2.5 ~ 3.4 times higher for coriander plants under control, high RL, and high BL at high PPFD treatments, than for plants under no RL and no BL treatments at low PPFD. Coriander shoot biomass was reduced under low-PPFD treatments (Figs. 1C, F), suggesting that lowering PPFD might inhibit photosynthesis and carbohydrate production, thus reducing shoot biomass accumulation. Perhaps, plant height, LA, and shoot FW accumulation responses under different combinations of RL and BL lighting may vary among species of crops. Reductions in total coriander FW and LA suggest that light quality and intensity can alter growth, decrease mean weight, and lower market value. Plants raised under the control conditions appeared similar to high market value plants grown in greenhouses, whereas either extra RL or BL-treated plants under high or low light intensity can cause reductions in shoot fresh weight and/or plant size, lowering market value.
Light is an important environmental signal, inducing biosynthesis of photosynthetic pigments and phytochemicals. In this study, the peak emissions of RL, BL, and GL LED closely coincide with the absorption peaks of Chl a and b, and reported wavelengths are at their respective maximum photosynthetic efficiency. Chl has high light absorption at 400 ~ 500 and 630 ~ 680 nm, and Car has high light absorption at 400 ~ 500. Both Chl and Car have low light absorption at 530 ~ 610 nm. Hoffmann et al. (2016) demonstrated that BL induces the synthesis of Chl and Car [28], although Chen et al. (2014) reported that Car levels were not responsive to light quality [20]. Tanaka et al. (1998) found that RL promoted Cymbidium leaf growth, but reduced Chl content. In the cucumber, a BL:RL ratio of 1:1 allows optimum leaf development, maximum photosynthesis, and Chl content [29, 30]. However, a 1:1 BL:RL ratio did not result in optimal basil growth when compared to any combination of the BL, RL, and GL wavelengths [31]. In our study, Chl and phytochemical contents were reduced as RL or BL lighting was enhanced. It is possible that 200 µmol m− 2 s− 1 of RL or BL suppressed Chl, Car, and Ant synthesis in the coriander leaves. Perhaps, 200 µmol m− 2 s− 1 PPFD reached a certain minimal PPFD at 50 µmol m− 2 s− 1, a level which is essential for the sufficient synthesis and activity of photosynthetic pigments and electron carriers. It would be interesting to test plant growth, Chl, and phytochemical contents under illumination by various monochromatic light spectra and combinations under a wide range of light intensities. This study provides deeper insight into the interception of light by photosynthetic and photo-protective phytochemicals as a function of light quality and intensity. This work enhances our understanding of plant biology, enabling the knowledge-driven selection of spectral lights for non-destructive Chl and phytochemical production in coriander plants.
Johkan et al. (2010) reported that addition of BL in combination with RL induces the accumulation of antioxidative compounds in lettuce plants [32]. Moreover, Son and Oh (2013) found that the ratio of 47% BL + 53% RL LED under 171 ± 7 µmol m− 2 s− 1 was important for the morphology, growth, and antioxidative phenolic compounds in lettuce [33]. Wu et al. (2007) discovered that RL LED enhanced the accumulation of antioxidants in pea (Pisum sativum L.) seedlings [34]. Similar results were reported by Bliznikas et al. (2012) and they revealed that supplemental RL increased antioxidant levels in parsley and dill plants [35]. De Souza et al. (2016) suggested that menthol mint (Mentha arvensis L.) plants grown under 137 µmol m− 2 s− 1 PPFD had the lowest biomass, but produced an essential oil with high level of neomenthol, menthol, and methyl acetate, whereas plants under 543 µmol m− 2s− 1 PPFD had a high biomass and essential oil content, but lower levels of menthol [36]. Ghasemzadeh et al. (2010) stated that total phenolic content of ginger leaves was the highest when plants were grown under 790 µmol m− 2 s− 1 [37]. Though light treatments were very different, there were some tendencies that enabled an assessment of the underlying mechanisms of the effects observed. For example, Fla, Pha, DPPH scavenging effect, and reducing power increased with increases in PPFD under high RL or BL; thus Fla and Pha contents may be responsible for the antioxidant activity in coriander plants. The intensity of RL or BL increased from 0, 50, to 200 µmol m− 2 s− 1 PPFD, and therefore any trend might be a response to RL or BL. Coriander plants had remarkably smaller plant height, LA, and Chl, Car, and Ant contents when treated with high RL or BL intensity. However, coriander plants grown under control conditions were taller, had larger leaves, and contained higher shoot FW, Chl, Car, and Ant contents. Different LED spectra are capable of triggering various morphological, phytochemical reactions, and antioxidant properties. Decreases in plant height and LA in coriander plants under higher RL or BL levels were the result of lowered Chl (Fig. 2), Car, and Ant contents (Fig. 3), but greater Fla and Pha levels (Figs. 4B-D), DPPH scavenging, reducing power, and chelating effect (Figs. 5A, B, D, E, and F) when these plants were subjected to high PPFD. These results suggest that stronger BL intensity might better penetrate the plant canopy than weaker BL intensity, rendering higher levels of Fla, Pha, DPPH scavenging effect, reducing power, and chelating effect. Coriander leaves appear to be sensitive to higher RL or BL intensity, which caused serious photoinhibition and photodamage, avoidance of excessive energy absorption in response to higher photosynthesis photochemical efficiencies, ultimately leading to lower plant height and LA in comparison to controls. However, the response of higher Fla, Pha, DPPH scavenging, reducing power, and chelating effect values was related to lower Chl and Ant contents of coriander plants under higher RL or BL intensity treatment. Protective mechanisms in coriander plants should prevent its leaves from excessive reduction in PSII acceptors. The assessment of Chl, Car, and Ant parameters under varying light quality and intensity is an important tool for understanding how to improve the photosynthetic productivity of plants. The application of light quality and intensity could beneficially influence growth, Chl, Car, and Ant contents in mature coriander plants, and properly selected RL plus BL LED could be used to produce antioxidant-rich spice culture.
Controlling light quality and intensity is effective in optimizing the yield and quality of coriander plants. Currently, there is little information available on the effect of light treatments on the accumulation of flavor compounds in coriander. Variations of the essential oil constituents in C. sativum have been observed, depending on genetic and environmental factors as well as tissue part, ontogeny, and analytical methods [38]. Several studies have shown that the major identified volatile compounds in essential oil of coriander leaves were 2-dodecenal, decanal, E-2-decenal, linalool, tetradecenal, 2-decen-1-ol, dodecan-1-ol, undecenal, dodecane, E-2-tridecenal, trans-tetradec-2-enal, E-2-hexadecenal, cyclodecane, menthone, pentadecenal, and pinene [39, 40]. Shahwar et al. (2012) identified 27 and 21 compounds from coriander leaves and seeds, respectively. Among them, there were only 10 compounds from coriander leaves identified in our study as shown in Table S2, and the rest of compounds of coriander leaves under the light treatments were unique in our study [41]. Shahwar et al. (2012) reported that decenal is one of the major volatile compounds identified in coriander leaves, and is an essential oil that produces the oily, sweet, or grassy odor of the plant [41]. Liu et al. (2012) also indicated that decenal had antioxidant activity and inhibitory of bactericidal effects on the microorganisms [42]. Sankhuan et al. (2022) statted that Artemisia annua plants grown under blue spectra at 445 nm had higher leaf fresh weight, increased amounts of artemisinin, and enhanced production of several terpenoids against the malarial parasite Plasmodium falciparum NF54, whereas red spectrum at 660 nm led to decreased production of bioactive compounds and decreasing anti-malarial activity [43]. In our study, decanal in leaves was found to have the highest compound area (554,848,800, RT 48.46 min), whereas area of decanal ranked 14th in their coriander leaves. However, high RL led to significantly diminished productions of decenal compared with other light treatments. The antioxidant activity and the inhibitory of bactericidal function of octanal have been reported by Liu et al. (2012) [42]. In our study, plants grown under low BL exhibited significantly decreases in the amounts of decenal, suggesting that coriander plants growth under high RL or low BL condition would decrease the bactericidal compounds. Interestingly, (E)-2-decenal was the second highest compound area (241,858,419, RT 52.34 min) identified in our study, but it was the highest compound area detected in their coriander leaves. Apparently, both decenal and (E)-2-decenal can be useful for the production of essential oil from coriander leaves. Naidu and Priyadarshi (2019) also revealed that the most common compounds identified by GC-MS in two popular varieties of Coriandrum sativum were decanal, 2-decenal, undecanal, dodecanal, E-2-dodecenal, E-2-tridecenal, tetradecanal, E-9-tetradecenal, 7-hexadecenal, and n-hexadecanoic acid. The cyclooxygenase-2 (COX-2) is an enzyme responsible for formation of prostanoids, and pharmaceutical inhibition of COX-2 can provide relief from the symptoms of inflammation and pain [44]. Dodecane has been isolated from the essential oils of various plants including ginger (Zingiber officinale) with strong inhibitory effects on COX-2 enzyme activity [45]. Our results show that there has been a significant decrease in the amounts of dodecane, the levels of antioxidants, Chl, Car, Ant, and Fla, and the plant heights as well when the plants grown under high RL conditions, implying that antibacterial effectiveness and economic efficiency of the metabolites production may not be maximized by the management of light treatment under high RL conditions.
In our study, among 15 identified compounds (Table 1), the highest compound of DCP, DO, and DOCP was detected in low RL, control, and low BL treatments, respectively, suggesting that coriander plants responding to light treatment with a low intensity of RL or BL exhibited an enhanced accumulation of both DCP and DOCP in cells. Since both DCP and DOCP metabolism in coriander leaves are more sensitive to light intensity than DO metabolism, the biosynthesis of DCP and DOCP in coriander leaves can be optimally activated by applying such light stimuli. Thus, an understanding of the effects of the light treatments upon the content of DCP, DO, and DCP compounds in coriander plants is an important aspect of the strategic implementation of their production and culinary and clinical applications. Differing responses in Chl, Car, Ant, antioxidants, and metabolite accumulations for optimizing plant growth and development in a controlled-climate setting are dependent upon various light quality and intensity culture systems, which may be used to satisfy commercial requirements for rapid, large-scale, and precise management of coriander plant production. Various growth-regulating strategies can be carefully chosen to produce the desired features of coriander for use as cooking materials, raw materials, or medicinal materials.