The Mechanism Of Nitrogen In Regulation Of Rice Resistance Against Chilo Suppressalis Walker And Nilaparvata Lugens

Nitrogen is not only one of the basic element in plant development,but also the key component of protein,nucleic acid and chloroplast.In natural environment,nitrogen is an element of scarcity for plant growth.And recently,artificial fertilizer has been widly used in agriculture.According to the statistical data,more and more agricultural pests and diseases were arised in recent years,representing in high frequency,shorter cycle and more serious harm.Previous studies have been proved nitrogen can regulate the resistance of plants,thus affecting the outbreak of diseases and insect pests,but the mechanism remains unclear.Rice(Oryza sativa L.)is one of the most important crops in china.Brown planthopper(BPH,Nilaparvata lugens),a phloem-feeding insect,and striped stem borer(SSB,Chilo suppressalis Walker),a chewing insect,are two main specialist leading to rice yield reduction.According to the study of plant resistance,Jasmonic acid(JA)and salicylic acid(SA)signalings are two main pathway in response to phloem-feeding insect and chewing insect,respectively.In this study,the effects of nitrogen concentration on rice resistance was investigated by comparing the enzyme activity,genes expression and alteration in rice nutrient content treated with different levels of nitrogen concentration feeding by SSB and BPH to reveal the mechanism of nitrogen in regulation of plant resistance.The major results are as follows:1.The comparision of key genes expression in the biosynthesis of main phytohormone in wild type rice treated with different level of nitrogen content showed that the key gene expression of JA biosynthesis was positively correlated with nitrogen content level,which suggest that plant resistance was probaly regulated by nitrogen content level by JA signaling.Further physiological and biochemical analysis by comparision with the OsAOS-RNAi,OsCOI1-RNAi and wild-type rice treated with different nitrogen content level showed no siganificant difference.However,the gene expression of OsJAZ1,downstream of JA signal pathway was positively correlated with nitrogen content level.These suggest that nitrogen regulates the change of the rice resistance by adjusting the gene expression of OsJAZ1.2.The invasion of SSB activated the JA signaling,resulting in increased downstream resistant genes expression.However,treatment with different nitrogen level in wild-type rice was showed a distinct resistant gene expression profile in strength and time.Under low nitrogen content treatment,rice resistance reaction was rapid,short duration and low intensity;while with high nitrogen content,the resistance of rice was slow to respond,long duration and higher strength.Above all,we hypothesized that increased nitrogen supply influenced the plant resistance by regulation of OsJAZ1 gene expression.When plant grow in high nitrogen condition,the high level of OsJAZ1 transcript act as a ‘buffer pool',which delay the plant response to insect feeding,showed as a reduce of plant resistance.3.BPH attack can activate the expression of resistant gene by SA signal pathway not the JA signal pathway.Beside,BPH attack also activated the plant defense system,such as defense enzymes and trypsin inhibitor.These suggest that nitrogen regulate the rice resistance not only by OsJAZ1 but also by other factors.4.The content of rice amino acid and glucide was altered after SSB infect.The amino acid content was arised universally in different nitrogen content treatment,and the glucide content was showed a descent in plant treated with low nitrogen content,while a rise in plant treat with high nitrogen content.These indicated that plant can switch the mode between growth and defense depending on the nitrogen concentration in external environment,which make plant adapt to different environment.