The antagonistic effects of red and blue light radiation on leaf and stem development of pepper (Capsicum annuum L.) seedlings

Light spectrum plays an essential role in influencing the growth and development of vegetable seedlings in industrial seedling raising. Currently, blue light, red light, and their combination are utilized in industrial seedling raising. However, the theoretical basis behind the screening of red and blue light combinations remains unclear. Therefore, we utilized pepper seedlings to investigate the effects mechanism of B (blue light, 450 nm) and R (red light, 660 nm) light-emitting diodes (pc-LED) on stem and leaf development，the full spectrum light was used as a control (W). The growth of pepper seedlings was evaluated by measuring indicators such as leaf, stem growth, and cellular ultrastructure, and try to reveal the regulatory pathways of auxin in leaves at the level of gene expression and transcriptome analysis. The results indicated that compared to W, the blue light led to shorter internodes and reduced plant height, while the red light resulted in larger leaves and elongated internodes of pepper seedlings. Ultrastructural analysis revealed that the antagonism was associated with the longitudinal elongation and transverse expansion of the stem and the expansion efficiency of leaf epidermal cells. Further analysis indicated that cell proliferation and leaf growth were regulated by the phytohormone pathway through light signaling. The blue light upregulated the expression of CaRAX in the phytohormone pathway, while red light increased the expression of CaGRF and CaARF, thereby influencing leaf size. These findings offer new insights into spectral screening for industrial seedling cultivation.