Molecular Mechanism Of Nitrogen,Sucrose And Nitric Oxide Regulating Flowering In Plants

Application of nitrogen(N)fertilizer would delay flowering has long been known in agriculture.The level of carbon source(cell sugar content)regulates flowering by affecting the expression of the circadian clock oscillator gene(PRR7).Nitric oxide(NO)was the product of nitrogen assimilation(nitrate reductase catalysis),it was also involved in various growth and developmental processes and stress responses of plants.This research used Arabidopsis as the experimental material to study the mechanism of N,S,NO on root elongation and flowering of Arabidopsis.The main results were as follows:1.The effects of N?S?NO on root elongation and floweringPlants flowered earlier under the treatment of Low Nitrogen(LN),in contrast,they flowered later under the treatment of High Nitrogen(HN).Blue light(Blue)and high Fe SO4·7H2O(H Fe & S)promoted the expression of CRY1 and FNR1 respectively,thus reversed the late flowering caused by HN.NO could strengthen the vegetative growth of plants,delay the flowering time,increase the number of rosette leaves,and delay root growth.But sucrose could reverse the growth inhibition caused by high levels of NO.(1)The fnr1 mutant flowered later than Col-0,and it was not sensitive to the change of N level;(2)There was no obvious difference between the flowering time of cry1 mutant and Col-0;(3)prr7 mutant flowered later than Col-0 under the treatments of N and NO,it was less sensitive to sucrose than Col-0;(4)cue1-6 mutant(high NO level)flowered later than Col-0,it was sensitive to the changes of NO levels;(5)noa mutant(low NO level)flowered earlier than Col-0,it was more sensitive to NO change than Col-0;(6)co mutant flowered earlier than Col-0;(7)gi mutant was flowered later than Col-0 and all mutants,and the rosette leaves of gi were significantly more than Col-0 and all mutants.2.The influence of N?S on the endogenous NO level and energy metabolism(1)The phenotype like root disorder,cell fragmentation,and disordered root structure caused by NO could be reversed by high sugar treatment;HN,LN,NO,and sucrose treatment could promote the endogenous NO level of Arabidopsis.Sucrose could reverse the root disorder phenotype,but there was no relationship with endogenous NO content.(2)N and NO decreased the ratios of ATP/AMP and NADPH/DADP~+ obviously.Thus,there was a connection between sucrose reversed the growth repression caused by NO and plants cell energy charge.3.The effects of N?S?NO on the expression of flowering related genesThe phase of the photoperiod key genes CCA1 and LHY were opposite to the phase of TOC1,CCA1 and LHY expression peaks in the dawn time and down to the lowest in the evening while the expression of TOC1 was reached the lowest and highest in the dawn and evening respectively.The output genes GI and CO have the opposite phases,the expression of GI was highest in the evening,lowest in the morning.N declined the amplitudes of photoperiod gene,but NO increased the amplitudes of input and oscillator genes CRY1?CCA1?TOC1and LHY,and decreased the amplitudes of output genes GI and CO.Sucrose had a contrary effect to NO,hence,it reversed the late flowering phenotype caused by NO was related to its antagonistic regulation of photoperiod genes expressions.4.Screening the flowering genes regulated by NO through SSHThe photoperiod was in the downstream of flowering.In order to find the flowering genes regulated by NO in the upstream of the photoperiod,we used two kinds of SSH methods for gene screening.Two methods both got 23 genes,there were 5 common genes: ACX1?EPS15?GDH2?RNP1?XTH4.The molecular mechanism of these genes regulating photoperiod need to be further studied.N and NO were led to late flower,but they have different molecular mechanisms.N negatively regulated the expression of photoperiod genes,while NO had an opposite effect on the input,oscillator and output elements of the photoperiod(the input and oscillator genes amplitudes became larger and the output genes amplitudes became smaller).Furthermore,Blue could reverse the late flowering caused by HN,but sucrose could not.Sucrose could reverse the root elongation inhibition and flowering delay,but Blue could not.This study confirmed that N,C,and NO interact in the regulation of plant growth and development,but its specific molecular mechanism remains to be further studied.