Enhanced Salt Tolerance of Pea (Pisum sativum L.) Seedlings Illuminated by LED Red Light

Light quality is an important variable affecting plant growth, so we aimed to explore the impact of light quality on plants under salt stress. The salt tolerance of pea (Pisum sativum L.) seedlings illuminated by LED red light and 4:1 of red/blue light in a hydroponic system was evaluated at three salinity levels (0, 50, and 100 mmol/L of NaCl) for their morphological and physiological parameters and their root growth characteristics in response to salt stress. Results demonstrated that, as salt stress intensified, the plant height, aboveground fresh/dry mass, root growth indices, and chlorophyll content of pea seedlings exhibited a decreasing trend, while the malondialdehyde (MDA) content and the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in leaves increased. Also, more sodium (Na⁺) but less potassium (K⁺) ions were detected due to the change in electrolyte balance. Compared with pea seedlings under no salt stress, the growth rate, plant height, and K⁺ ion content significantly increased with the red light treatments, but both lights did not affect the aboveground fresh/dry mass, chlorophyll content, or root growth index. Under medium salt stress (50 mmol/L), red light helped generate more chlorophylls by 17.06%, accelerate leaf electrolyte exudation by 23.84%, accumulate more K⁺ ions by 46.32%, and increase the K⁺/Na⁺ ratio by 45.45%. When pea seedlings were stressed by 100 mmol/L salinity stress, red light was able to maintain the leaf chlorophyll level by 114.66%, POD enzyme activity by 157.78%, MDA amount by 14.16%, leaf and stem electrolyte leakage rate by 38.76% and 21.80%, respectively, K⁺ ion content by 45.47%, and K⁺/Na⁺ ratio by 69.70%. In conclusion, the use of red light has proven to enhance the salt tolerance of pea seedlings in a hydroponic system, which can and should be a promising approach to prime pea seedlings for more salt tolerance.