Chitosan oligosaccharides (collectively, oligochitosan, or COS) are considered to be potent plant immunity elicitors. In this article, the induction of resistance to Sclerotinia sclerotiorum in Brassica napus L. var. Huyou 15 by COS is studied. Even though COS (50 μg mL−1) did not affect radial growth of this pathogen in vitro, it reduced the disease symptoms in vivo relative to control plants. The disease control rates were 25.8%, 41.4%, 57.1%, 68.7%, and 48.8% with COS pretreatment 0, 24, 48, 72, and 96 h before S. sclerotiorum inoculation, respectively. Specific binding of COS to B. napus epidermis cells was validated by competition experiments. Simultaneously, it was observed that COS induced bursts of cytosolic Ca2+, nitric oxide (NO), and hydrogen peroxide (H2O2). NO and H2O2 inhibitors were used to prove the interaction between NO and H2O2. Furthermore, treatments of B. napus with NO and H2O2 inhibitors reduced the induction effect of the jasmonic acid–ethylene (JA/ET) signaling marker BnPDF1.2 by COS, indicating that NO and H2O2 participate in COS-induced JA/ET signaling. In conclusion, this article provides a comprehensive study of the effect and mechanism of COS-induced resistance to S. sclerotiorum in B. napus.

NO (nitric oxide) and H2O2 (hydrogen peroxide) are important signaling molecule in plants. Brassica napus L. was used to understand oligochitosan inducing production of NO (nitric oxide) and H2O2 (hydrogen peroxide) and their physiological function. The result showed that the production of NO and H2O2 in epidermal cells of B. napus L. was induced with oligochitosan by fluorescence microscope. And it was proved that there was an interaction between NO and H2O2 with L-NAME (NG-nitro-l-arg-methyl eater), which is an inhibitor of NOS (NO synthase) in mammalian cells that also inhibits plant NO synthesis, and CAT (catalase), which is an important H2O2 scavenger, respectively. It was found that NO and H2O2 induced by oligochitosan took part in inducing reduction in stomatal aperture and LEA protein gene expression of leaves of B. napus L. All these results showed that oligochitosan have potential activities of improving resistance to water stress.