Protective effect of chitosan on photosynthesis and antioxidative defense system in edible rape (Brassica rapa L.) in the presence of cadmium

•Exogenous chitosan (CTS) reduced detrimental effect of Cd on rape plant growth.•Foliar application of CTS under Cd tress decreased shoot Cd2+ concentration.•CTS enhanced photosynthesis and antioxidant enzymes activities.

Chitosan (CTS) induces plant tolerance against several abiotic stresses, including salinity and drought exposure. However, the role of CTS in cadmium (Cd)-induced stress amelioration is largely unknown. In the present study, a hydroponic pot experiment was conducted to study the roles of CTS with different molecular weight (Mw) (10 kDa，5 kDa and 1 kDa) in alleviating Cd toxicity in edible rape (Brassica rapa L .). The results showed that Cd stress significantly decreased plant growth, leaf chlorophyll contents and increased the malondialdehyde (MDA) level in rape leaves. Foliar application of CTS promoted the plant growth and leaf chlorophyll contents, and decreased the malondialdehyde (MDA) level in edible rape leaves under Cd stress. The alleviation effect of CTS on toxicity was depended on its Mw and CTS with Mw of 1 kDa showed the best activity. Spraying 1 kDa CTS onto the leaves of edible rape under Cd-toxicity could decrease shoot Cd2+ concentration and improve photosynthetic characteristics of edible rape. Moreover, 1 kDa CTS also significantly enhanced non-enzymatic antioxidants (ascorbic acid) and enzyme activities (superoxide dismutase, catalase and guaiacol peroxidase) under Cd stress. Based on these findings, it can be concluded that application of exogenous CTS could be an effective approach to alleviate the harmful effects of Cd stress and could be explored in an agricultural production system.