Effect of oligosaccharides from Enteromorpha clathrata on tolerance of wheat (Triticum aestivum L.) seedings to saline-alkali stress

Polysaccharides from algae have received considerable attention owing to their ability to enhance crop tolerance to abiotic stress effectively. In this study, four oligosaccharides (EC1-EC4) of different molecular weights (11.66, 3.55, 2.21, and 1.61 kDa), respectively) enzymatically cleaved from Enteromorpha clathrata were applied to wheat seedlings (Triticum aestivum) under saline-alkali stress. Their effects on enhancing plant tolerance to saline-alkali stress were investigated at 24 h and 120 h and compared in terms of alleviating oxidative stress, osmotic stress, ion toxicity, and stimulation of abscisic acid homeostasis. The application of EC3 (2.21 kDa) for 120 h reduced the malondialdehyde content by 11.0 % in leaves and 27.2 % in roots compared with those in the negative control (Na) group. The EC4 (1.61 kDa) group showed reductions of 15.4 % and 23.6 %, respectively. Treatment with EC3 increased the peroxidase enzyme activity enhancement of roots to 1051.6 U·gFw⁻¹·min⁻¹ compared to 887.7 gFw⁻¹·min⁻¹ in the Na group. Its application was the most effective in enhancing proline accumulation and synthesis. Several aquaporins were further up-regulated to better defend against osmotic stress, following EC2 treatment (3.55 kDa) treatment. In addition, the expression of several ionotropic proteins was significantly enhanced in cells treated with EC3 maintain ion homeostasis and reduce ion toxicity. Furthermore, EC3 stimulated abscisic acid (ABA) synthesis and ABA-dependent signaling to enhance saline-alkali resistance in wheat seedlings. In conclusion, the oligosaccharide with 2.21 kDa from E. clathrata represents an effective way to improve the resistance of wheat seedlings to saline-alkali stress.