ABA Confers Salinity Tolerance in Lily Cultivars by Modulating Casparian Strip Development, Growth and Physiological Status

Supplementation with phytohormones represents an innovative strategy to mitigate the damage caused by salinity. The present study aimed to assess the effects of abscisic acid (ABA) on salinity tolerance of two lily cultivars. Seedlings were pretreated with five different concentrations of ABA solution (0.00, 1.25, 2.50, 3.75, and 5.00 mg·L) and then exposed to stress induced by a 0.50% NaCl solution for 4 weeks. Growth and physiological indices were assessed at the beginning of the experiment and at the end of each week. Furthermore, structure of Casparian strip (CS) and thickness of outer tangential wall of endodermis cells in roots were investigated at the end of stress. Results indicated that ABA promoted the formation and maturation of the CS, maintained a relatively rapid growth rate, reduced accumulation of malondialdehyde (MDA) (7.91%), and enhanced activities of antioxidant enzymes (16.79%), as well as contents of soluble sugars and chlorophyll (19.25% and 23.27%), along with photosynthesis levels. Based on a comprehensive evaluation, the optimal concentrations of ABA for L. ‘Sorbonne’ and L. ‘Sweet Zanica’ were determined to be 1.25 and 2.50 mg·L, respectively. Therefore, ABA-induced enhancement in the salinity tolerance of lilies were verified from the perspectives of CS development, phenotype and physiology. Further, more prominent improvement in the overall performance of L. ‘Sorbonne’ was confirmed. In summary, this research provided a new insight on enhancing the salinity tolerance of lilies, serving as a valuable reference for cultivar selection in production.