Relationship between the Degree of Polymerization of Chitooligomers and Their Activity Affecting the Growth of Wheat Seedlings under Salt Stress.

Seven chitooligomers (COSs) with determined degrees of polymerization (DPs) (chitotetraose to chitooctaose, DP 8-10, DP 10-12) and a heterogeneous COS with various DPs were first applied to explore the relationship between the DP of COSs and their effect on the growth of wheat seedlings under salt stress. The results showed that COS could promote the growth of wheat seedlings under salt stress. Moreover, chitohexaose, chitoheptaose, and chitooctaose exhibited stronger activity compared with other COS samples, which suggested that their activity had a close relationship with the DP. After 10 days of treatment with chitohexaose, chitoheptaose, and chitooctaose, the photosynthetic parameters were obviously improved. The soluble sugar and proline contents were improved by 26.7-53.3 and 43.6-70.2%, respectively, whereas the concentration of malondialdehyde (MDA) was reduced by 36.8-49.6%. In addition, the antioxidant enzyme activities were clearly activated. At the molecular level, the results revealed that they could obviously induce the expression of Na+/H+ antiporter genes.