Size effects of chitooligomers with certain degrees of polymerization on the chilling tolerance of wheat seedlings

In this study, six fully deacetylated single chitooligomers (COSs, chitobiose to chitoheptaose) and one fully deacetylated COS mixture were applied to wheat seedlings to investigate their effects on the plants' defence response under chilling stress. The results showed that exogenous COS with different degrees of polymerization (DPs) could promote the growth of plants, decrease the concentration of malondialdehyde (MDA), increase the content of chlorophyll and modulate the activities of antioxidant enzymes. The analysis of genes expression suggested that COS could alleviate the damage of chilling stress by effectively regulating the expression of antioxidant enzyme genes. Furthermore, chitohexaose and chitoheptaose had the most effective activities of alleviating chilling stress to wheat seedlings, which suggested the DP played important roles in the activities of COS. The close relationship between the activities of COSs and their DPs reveals that the activities of COSs are dependent upon a specific structure to interact with elicitor receptors on plant cell membrane.