Ulva clathrata Enzymatic Hydrolysate Protects Wheat from Salt–Alkaline Stress by Regulating ABA Biosynthesis

Extracts of Ulva clathrata improve the salt–alkaline tolerance of plants. However, the underlying relevant mechanisms remain to be elucidated. In this study, transcriptome technology was used to explore the mechanisms underlying the protective effects of enzymatic hydrolysate of Ulva clathrate (EU) on 5-day-old wheat seedling roots under salt–alkaline stress. A total of 3,141 differentially expressed genes (DEGs) were identified. The KEGG pathway and GO enrichment analyses showed that EU enhanced abscisic acid (ABA) signal transduction in the roots. Further analysis revealed the involvement of several DEGs in amino acid metabolism and transduction of calcium signals. Following treatment with sodium tungstate, an ABA inhibitor, the activity of nitric oxide synthase (NOS) in TE group (salt solution, sodium tungstate and 0.1 mg/mL EU solution treatments) increased by 55.10% compared with that in the T group (salt solution and sodium tungstate treatments) after 24 h stress. EU strengthened the pathway of nitric oxide (NO) synthesis using arginine by regulating ABA synthesis. The expression of TaCBL and TaCDPK9-1 in the TE group were 2.53 times and 6.83 times higher than those in the T group after 10 days of stress, respectively. Based on these findings, it was concluded that EU treatment enhanced the synthesis of NO and calcium signal transduction by regulating ABA content.