## 4 Discussion  
### Changes in the Physiology and Antioxidant Capacity of Leaf Extracts  
As an important environmental factor, light quality plays irreplaceable roles in the growth and development of plants. Uncovering the mechanisms of plants in response to light quality is beneficial for developing crop improvement strategies. Red and blue light are generally considered to be the most efficient wavelengths to drive photosynthesis [10]. We found that the photosynthetic rate of basil increased significantly under blue light and decreased under red light compared to white light (Figure 2). At the same time, the stomatal conductance (Gs) under blue light was the largest, followed by white light and red light, indicating that the change in photosynthesis may be caused by stomatal opening, which is consistent with the findings of previous studies [38; 39; 40]. In addition, as one of the most important pigments in plants, chlorophyll is essential for capturing light for photosynthesis, which plays key roles in the interaction with light during the whole growth cycle of the plant. Many studies have revealed that light quality affects photosynthesis by changing the content and composition of chlorophyll. In some plants, including _Cattleya loddigesii_ and _Tritcium aestivum_, the chlorophyll content was highest under red light compared to other light [41].However, blue light was more effective than red light in promoting chlorophyll accumulation in lettuce, _Anoectolius roxburghii_, and _Toona sinensis_[41; 42]. Herein, we also found that blue light stimulated chlorophyll accumulation in basil more significantly than the other two types of light, which may further facilitate the light harvesting capacity to improve photosynthesis. Light spectra affect plants' morphogenesis. For example, blue light significantly inhibited apples' plant growth and leaf extension, while red light treatment promoted apples' plant growth and root development [43]. In tomatoes, compared to white light, early photomorphogenesis was strongly promoted by red light and inhibited by blue light [44]. Conversely, it was found that blue light could promote plant growth and leaf  
Figure 10: Integration analysis of metabolome and transcriptome by O2 PLS: **(A)** The top 10 genes with transcriptomes strongly influencing the metabolome. **(B)** The top 10 metabolites substantially affecting the transcriptome. extension better than red light in some species, such as _Petunia_, _Chrysanthemum_, and _Cucumber_[45; 46; 47], and similar phenotypes were found in our study, suggesting that red and blue light have unique effects on different plants. Plant hormones mediate various aspects of plants' growth and development, and some hormonal pathways are often influenced by light to regulate the developmental changes [48; 49; 50]. We found that 688, 783, and 465 genes involved in plant hormone signal transduction were differentially expressed in the W vs. R, W vs. B, and B vs. R groups, respectively (Figure 10). The altered expression patterns of plants' hormone signals may give rise to morphological changes in basil under different light quality conditions. In addition to physiological and morphological changes, light spectra can also affect the synthesis of metabolites in herbs, thus modifying their biological activities. Blue LED irradiation increased the DPPH scavenging capacity of baby leaf lettuce and improved its antioxidant properties [51], and callus cultures of _Rliodola imbricata_ grown under blue light also displayed the highest antioxidant activity compared to other light conditions [52]. Consistently, in this study, antioxidant capacities--especially DPPH and ABTS scavenging activities--were significantly promoted by blue light and inhibited by red light. As the most abundant pigments in nature, chlorophylls and carotenoids are very potent natural antioxidants, which may be used for a range of health benefits in humans [53; 54]. [PERSON] et al.