The purpose of this study is to determine the effect of light quality on growth, carbon and nitrogen metabolism, and antioxidant defense system of rice seedlings. Six light conditions were employed, including white (W), red (R), blue (B), combined LED of R and B at 3:1 (R3B1), combined LED of R and B at 1:1 (R1B1), as well as combined LED of R and B at 1:3 (R1B3). Combined application of red light and blue light could promote the growth of rice seedling leaves and roots under low light stress to varying degrees, increase the photosynthetic area by increasing the leaf area, improve the root characteristics by increasing the root volume, and increase the dry matter accumulation of rice seedlings. In addition, the combination of red light and blue light could increase carbon and nitrogen metabolites in rice seedling leaves, regulate the expression of genes related to carbon and nitrogen metabolism and enzyme activity, and enhance the antioxidant enzyme activity of rice seedlings. These results indicate that red light and blue light directly have synergistic effects which can regulate the carbon and nitrogen metabolism of rice seedlings, promote the morphogenesis of rice seedlings under low light stress, and promote growth, which has never been reported in previous studies. This study is a new discovery in the application of light quality in crop production and provides new avenues to enhance crop stress resistance. However, further study is needed to explore the physio-biochemical and molecular mechanisms of light quality in crop production.

The purpose of this study is to determine the effects of red and blue lights on the photomorphogenesis and photosynthetic traits of rice seedlings. The rice seedlings were cultured with red light (R), blue light (B), combined red and blue lights (R3B1/R1B1/R1B3), and white light (CK) as the control. The combined application of red and blue lights could promote the growth of rice seedlings to varying degrees; enhance photosynthesis by increasing the seedling leaf area, chlorophyll content, and chlorophyll fluorescence; improve root characteristics by increasing root number, root volume, and root activity; and thus increase the dry matter accumulation of rice seedlings. In addition, the combination of red and blue lights could regulate the expression of genes related to photosynthesis in rice leaves, affect the activity of the Rubisco enzyme, and then affect the photosynthesis of rice seedlings. These results indicate that red and blue lights have direct synergistic effects, which can regulate the growth of rice seedlings and promote the morphogenesis of rice seedlings. The combined application of red and blue lights can be used to supplement the light in rice-factory seedling raising.

Pak choi needs to be exposed to low temperature (vernalized) before flowering will initiate. Early bolting caused by low temperature often occurs in spring and leads to significant economic losses. Therefore, it is of great practical significance to study the flowering process of pak choi. Brassinolide (BR) plays a certain role in the flowering process of pak choi. In order to better understand the role of BR in the flowering process of pak choi, the BR content in the shoot apices of pak choi at different growth stages was determined by enzyme-linked immunosorbent assay (ELISA). The results showed that the BR content increased after low-temperature treatment. With the progress of vegetative growth, the BR content decreased and reached the lowest at 10 days after transplanting (V10), then the content increased and reached a small peak at the critical period of floral bud differentiation (S0). After initiation of floral bud differentiation, the content decreased at floral bud differentiation stage 1 (S1), and then gradually increased and reached a peak at floral bud differentiation stage 3 (S3). In order to clarify the molecular mechanism of BR content changes, we analyzed the expressions of key enzymes coding genes in the BR metabolic pathway, and found that six major synthase-encoding genes (Bra008760, Bra030023, Bra036097, Bra027405, Bra011678, and Bra025409) were upregulated at the critical period of floral bud differentiation, leading to the increase in BR content, which were consistent with changes in the BR content. By analyzing the functions of differentially expressed genes (DEGs) between the vegetative growth stage (V10) and the critical period of floral bud differentiation (S0), 21 DEGs were found to be related to BR metabolism. These findings can provide a reference for elucidating the molecular mechanism of BR regulating the flowering process of pak choi.

Given that the problem of insufficient light intensity is prevalent in the cultivation of rice seedlings under facility conditions, and light quality plays a crucial role in regulating crop growth, it is necessary to explore the most suitable proportion of red light for improving the quality and photosynthetic capacity of the seedlings. In this study, two different types of rice varieties (conventional rice, Xiangzaoxian 24, XZX24 and hybrid rice, Huazheyou 261, HZY261) were selected as experimental materials. A systematic investigation was conducted to examine the effects of different red light ratios on the morphological development of rice seedlings, the structure development of leaves and roots, as well as the photosynthetic characteristics. Six light quality treatments were applied, including white light (W, control), monochromatic red light (R), and combined white plus red light with different ratios (WR20, WR40, WR60, WR80). The results demonstrated that appropriate compound white-red light significantly coordinated shoot and root development; under the WR40 treatment (60% white light + 40% red light), the total seedling dry weight of the two varieties increased by 25.75% and 28.56% relative to the white light control, respectively. Gradually elevated red light proportion continuously boosted leaf pigment accumulation, with WR80 achieving the maximum total chlorophyll content, while WR60 optimized the non-photochemical quenching (NPQ) photoprotective capacity of leaves. Moderate red supplementation (WR20–WR60) maintained high Rubisco activity and upregulated the transcription of OsRBCS2 and OsRBCS3 , whereas the expression of OsRBCS4 showed no significant difference across all light treatments. Single monochromatic red light failed to balance root branching and carbon assimilation efficiency despite promoting vertical leaf and stem elongation. This work provides quantitative spectral reference parameters for intelligent supplementary lighting in factory rice seedling raising, and clarifies the multi-dimensional physiological and molecular response differences of rice seedlings to graded red-white composite spectra. Further field verification trials are required to validate the applicability of the WR40 scheme under fluctuating natural environmental conditions.