Chitooligosaccharide Seed Priming Enhances Photosynthetic Efficiency in Pea (Pisum sativum) Under Salinity

Low-molecular-weight chitosan derivatives emerged as promising plant growth biostimulants due to their favorable properties, such as biocompatibility, antibacterial and antifungal activity, enhancement of stress resistance, and yield improvement. In the present study, we evaluated the effect of pea seed priming with two types of chitooligosaccarides (aminochitooligosaccaride and chitooligosaccaride hydrochloride) applied at concentrations of 100 and 500 mg/L under non-stress conditions and 50 mM chronic NaCl stress. We characterized the seed surface topology by atomic force microscopy, the germination process by evaluation of seed germinability and synchrony, root emergence, seed imbibition capacity and ion leakage. Early plant growth and physiological performance were further evaluated in 14-day-old seedlings by measuring leaf water potential, Na⁺ accumulation in roots and leaves, photosystem II activity, leaf pigment content, and membrane stability. The results revealed changes in seed coat topology, i.e., higher surface roughness in 100 and 500 mg/L chitooligosaccaride hydrochloride and 500 mg/L aminochitooligosaccaride primed variants. Concentration-dependent effects of the two chitooligosaccarides under both non-stress and salt stress conditions were evident in 14-day-old seedlings. Under chronic salt stress, seed priming with 100 mg/L chitooligosaccharide hydrochloride and 500 mg/L aminochitooligosaccharide produced the most pronounced improvements in the primary photochemical reactions of photosynthesis, particularly the performance index on an absorption basis and the total performance index. Moreover, the investigated chitooligosaccharide, particularly chitooligosaccaride hydrochloride, preserved membrane integrity and maintained flavonol and anthocyanin levels, indicating a strong protective effect against salt stress. Overall, the data indicate beneficial effects on pea physiological status following seed priming with chitooligosaccarides under chronic salt stress conditions. This highlights the approach as a promising strategy for enhancing plant resilience in challenging environments, and it is worth further investigation and verification at the whole-plant level.