Size effects of chitooligomers on the growth and photosynthetic characteristics of wheat seedlings

• We prepared nine single or narrow degrees of polymerization chitooligomers (COSs).
• We investigated the size effects of COSs on growth of wheat seedlings.
• COSs with DP > 3 had a significant promotion effect on the growth and photosynthesis.
• Chitoheptaose exhibited the optimal activity compared with other COS samples.

In this study, nine chitooligomers (COSs) including seven single COSs (chitobiose to chitooctaose) and two COS fractions with narrow degrees of polymerization (DPs) (DP8–10, DP10–12) were prepared and applied to wheat seedlings to investigate the size effects of COSs on the growth and photosynthesis parameters of wheat seedlings. The results showed that the activities of COS were closely related to their DPs, and DP > 3 was necessary to insure a significant promotion effect on the growth and photosynthesis. Moreover, chitoheptaose exhibited the optimal activity compared with other COS samples. After 7 days of chitoheptaose treatment, the growth parameters of wheat seedlings could be significantly improved and the contents of soluble sugar, soluble protein and chlorophyll were increased by 59.4%, 22.0% and 20.3%, respectively. In addition, chitoheptaose could significantly enhance the net photosynthetic rate of wheat seedlings with the values of Fv/Fo, qP and Rfd increased by 11.0%, 18.6% and 14.7%, respectively, while NPQ was decreased obviously, which might resulted in the promotion of light utilization efficiency and the growth of wheat seedlings.