Mechanism Of Low-nitrogen Enhanced Rice Resistance To Chilo Suppressalis

Nitrogen is one of the most nutrient element in crop,which not only affects crop growth and development,but also has a tight link with plant anti-herbivore ability.Nitrogen plays a dominant role in all fertilizer,because nitrogen is the main factor limiting plant growth and crop yield.Currently,the application of nitrogen fertilizer in China is far more than the world average level.The over-utilization of nitrogen fertilizer reduces rice anti-herbivore ability,resulting in increased dose of pesticides and enhanced danger of food security.In this study,we used rice(Oryza sativa L.cv.Nipponbare)as plant material and Chilo suppressalis Walker(SSB)as a pest to investigate effects of low-nitrogen on rice resistance to C.suppressalis.Under hydroponic conditions,short-term low-nitrogen or medium-and longterm low-nitrogen treatments and subsequent attack by SSB were used to study relation between nitrogen and jasmonate and ethylene signaling pathways and also to reveal molecular and cellular mechanism of enhanced rice anti-herbivore defense induced by low-nitrogen.The detailed results as follows:1.Rice plants were treated with low-nitrogen for 1,3,5 days,respectively,and then attacked by SSB for 7 days.The bioassay showed that both weight gain of SSB and rate of rice dead-heart were decreased,indicating that low-nitrogen treatment for short time could enhance rice resistance to SSB.Physiological and biochemical analyses showed that short-term low-nitrogen treatment and SSB inoculation caused more accumulation of reactive oxygen species(ROS)and nitric oxide(NO)in rice,which might enhance JA and ET signaling in rice defense,and promote the activation of polyphenol oxidase(PPO)and peroxidase,resulting in enhanced anti-herbivore ability.2.Rice plants were treated with low-nitrogen for two weeks,then attacked by SSB,results of weight gain of SSB and the rate of rice deadheart showed that low-nitrogen treatment for two weeks enhanced the resistance of rice to SSB.Physiological and biochemical analysis showed that low-nitrogen enhanced the content of soluble protein,but had little effect on total sugar content in rice plants.Meanwhile,low-nitrogen reduces rice photosynthesis and chlorophyll content.However,the activity of nitrate reductase(NR)has no significant difference from that in control,indicating NR-realted signaling is not the main pathway of rice against SSB invasion.The expression of genes involved in JA signaling was enhanced attacking by SSB.Additionally,the activity of PPO in rice stem was also increased after SSB attack,which is further demonstrated that low nitrogen for medium and long-term treatment also enhances the resistance of rice to SSB.Collectively,low-nitrogen could enhance the rice resistance to SSB regardless of short-term or long-term treatment.This study is important for discovering the mechanism of enhanced resistance of rice induced by low nitrogen,and it will lay a good foundation for use of nitrogen for pest management in agriculture.