Leaf Volatile Compounds And Associated Gene Expression During Short-term Nitrogen Deficient Treatments In Cucumis Seedlings

Excessive application of nitrogen fertilizer could cause series of enviroment problems,reduce crop qualities and resistance of abioitc and biotic abilities.Reduction of nitrogen application,improvement of the nitrogen efficienct are the importamt points during crop growth.Cucumber 9930 and other 56 inbred lines were used for nitrogen defficient treatments in a hydroponic system,the second fully expanded apical leaves were used for detection of short-chain volatiles,gene expression level.1,Short-chain volatiles were significantly improved in 9 930 leaves during nitrogen deficient treatments.A total of 24 volatile components were identified including 15 aldehydes,two ketones,two alkenes,and five other volatile compounds in 9,930 leaves.Principal component analysis using volatile compounds from cucumber leaves provided good separation between N-sufficient and N-deficient treatments.The main volatiles in cucumber leaves were found to be C6 and C9 aldehydes,especially(E)-2-hexanal and(E,Z)-2,6-nonadienal.(E)-2-hexanal belonged to the C6 aldehyde and was the most abundant compound,whereas(E,Z)-2,6-nonadienal was the chief component of C9 aldehydes.During N-deficient treatment,short-chain volatile content was significantly improved at 5 d,other volatiles displayed significant reduction or no significantly changes in all sampling points.2,Nitrogen could affect the biosynthesis of short-chain volatiles in cucumber.In natural population,(E)-2-hexenal was the main component among short-chain volatiles,and(E,Z)-2,6-nonadienal was the most abandunt component of C9 volatiles.In natural population,28-folds varation of total volatiles was observed.In nitrogen deficient treatments,volatiles of 17 inbred lines were significantly improved and 10 inbred lines were reduced.Principal component analysis using volatile compounds from cucumber leaves provided good separation between N-sufficient and N-deficient treatments.3,Some genes of LOX-HPL pathway were involved in reponse to nitrogen deflcieny and caused the significant improvement of short-chain volatiles.The expression analysis of 12 cucumber LOX genes and two HPL genes revealed that CsLOX19,CsLOX20,and CsLOX22 had common up-regulated expression patterns in response to N-deficient stress in most inbred lines;meanwhile,most sample points of CsHPLl also had significant up-regulated expression patterns.4,Exogenous and endogenous(E)-2-hexenal could induce expression of abiotic and biotic stress.Among 44 abiotic and biotic cucumber genes,only 6(CsHSFA2,CsHSP101-1,CsERF1-1?CsHSP1-1,CsERF1-2 and CsHSP70B-2)were down-regulated during exogenous(E)-2-hexenal treatments and other 37 genes were significantly up-regulated at least one time in all sample points.From 1 to 3 d during N-deficient treatments,most genes were down-regulated,but at 5 d,13 genes were significantly up-regulated than other 4 points because of the improvement of endogenous(E)-2-hexenal.