Effects of Topping and Hormone on Nicotine in Upper Tobacco Leaves and Analysis of Source Sink Relationship
In order to clarify the physiological mechanism of topping and hormone regulating nicotine synthesis and accumulation in flue-cured tobacco,the variety K326 was used to study the effects of different topping measure and hormone interactions on traits of root and upper leaf,contents of nicotine and total nitrogen in upper leaves,key enzymes activity of nitrogen metabolism,gene expression of nicotine synthesis and transport in roots,and analyze the source and sink relationship of nicotine accumulation.The results showed that topping significantly increased nicotine content and accumulation in upper tobacco leaves,which were 1.41 and 1.85 times those without topping respectively.Spraying methyl jasmonate(MeJA)without topping significantly increased nicotine content by 14.60%,while spraying N-1-naphthylphthalamic acid(NPA)significantly decreased nicotine content by 10.01%.Application of salicylhydroxamic acid(SHAM)and naphthylacetic acid(NAA)after topping significantly reduced nicotine content,with 23.07%and 16.92%reduction ranges respectively.Jasmonic acid(JA)had limited effect on root development,and mainly promoted nicotine synthesis through directly regulating the expression of nicotine synthesis and transport genes.Auxin(IAA)mainly indirectly affected nicotine synthesis and accumulation by regulating roots development.Path analysis showed that the number of root tips had the largest direct effect on nicotine accumulation in root traits,and the root surface area had the largest overall effect on nicotine accumulation,which were the main'source'indicators affecting nicotine synthesis.The direct effect of leaf area on nicotine accumulation was the largest among leaf traits,and the total effect of leaf dry weight on nicotine accumulation was the largest,which were the main'sink'indicators affecting nicotine accumulation.By comprehensive analysis,IAA content increased after topping,and promoted the increase of root tips number,which increased the number of nicotine synthesis'sources'.The activities of nitrate reductase(NR)and glutamine synthetase(GS)were enhanced after topping meanwhile,promoting nitrogen metabolism and nitrogen acquisition.JA increased in roots after topping,which directly enhanced the expression of PMT,QPT,A622 and NUP1 genes for nicotine synthesis and transport,and increased the intensity of nicotine synthesis.In addition,topping improved nicotine accumulation efficiency by promoting the increase of'sink'capacity such as leaf area and leaf dry weight.
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