Effect Of Different Nitrogen Levels And Nitrogen Deficiency And Nitrogen Deficiency Models At Mature Stage On Pigment Metabolism And Aroma Constituent Contents In Flue-cured Tobacco

In light of the problems of delaying supply of nitrogen, which leads to lowdegree of maturity of tobacco and insufficient degradation of aroma precursors during tobaccomature, in the tobacco-growing area of central Henan Province, pot experiments wereconducted to investigate the influence of nitrogen supply levels in early stage and equalnitrogen deficiency after topping and the different nitrogen deficiency models at maturingstage on yield and quality, key metabolism enzyme genes expression level and neutral aromaconstituent contents in flue-cured tobacco, and the reasonable nitrogen deficiency model wasdetermined, which would provide the theoretical basis and reference for high quality tobaccoproduction by increasing the permeability of the soil and by accurately supplying fertilizer andwater to promote the reasonable transformation of nitrogen metabolism, aroma precursorsdegradation and to improve tobacco leaf maturity. The main research results are as follows:1. Effect of different nitrogen levels before topping and equal nitrogen deficiency aftertopping on plastid pigment and key enzyme genes expression levels in flue-cured tobaccoThe economic characters of tobacco leaves were higher in high and medium to highnitrogen level treatments N1, N2. Physical properties were best in medium to high nitrogentreatments N2. Appearance quality was the lowest for low nitrogen level N4, while the otherswere good. With the increase of the nitrogen level, reducing sugar and total sugar contentsdecreased, while the contents of total nitrogen, nicotine and protein were increased, thepotassium/chloride increased first then decreased. The petroleum ether extract contentsincreased with the increase of nitrogen level. These suggested that abundant nitrogen nutritioncoupled with nitrogen deficiency at maturing stage were beneficial to the improvement ofproduction and quality of tobacco leaves.30d and60d after transplanting, the contents of plastid pigment in tobacco leavesincreased with the increase of nitrogen level. The net photosynthetic rates were consistentwith the changes of plastid pigment contents. The contents of osmiophilic granule andthylakoid lamella of chloroplast were improved, while the aging and degradation rates delayed with the increase of nitrogen level during the maturity period. The expression of Nicotianatabacum senescence-specific cysteine protease (CP1) was gradually decreased.The expression of pheophorbide a monooxygenase (PAO) in high nitrogen leveltreatment N1was significantly higher than that of other treatments at the end of the maturestage. This suggested that chlorophyll catabolism remained at a high level, the chlorophylldegradation metabolism postponed in high nitrogen level and nitrogen deficiency at maturingstage. ZDS, CCDs and NCED in plastid pigment metabolism pathways, Inv in sugar metabolicpathways, GS in nitrogen metabolic pathways and HMGR in terpenoids metabolism MVApathways were all sensitive to nitrogen level. Expression peaks of those sensitive key enzymegenes were postponed with the rising of the nitrogen level in60d to80d after transplanting.In conclusion, the timing of expression peak of gene PAO、ZDS、CCDs、NCED、Inv、GSand HMGR can be used as the index for the evaluation of nitrogen nutrition conditions of thetobacco plants. Abundant nitrogen nutrition and nitrogen deficiency at maturing stage couldcontrol the expression peak of metabolic key enzyme genes, thereby regulate the coordinatetransformation in tobacco metabolisms, providing physiological basis and material basis forhigh quality tobacco.The contents of aroma products degraded from carotenoid、phenylalanine，aromaproducts of browning reaction, neophytadiene and the total contents of neutral aromaconstituents in N1were highest in the middle leaves. While they increased first thendecreased with the increase of nitrogen level in the upper leaves, with N2nitrogen levelreaching its maximum value. The variation of solanene content was great in upper leaves, itscontent significantly decreased with the increasing nitrogen level which lied in the area from37.65μg/g to74.08μg/g. Smoking quality was highest in N1(5.250g/pot) in the middle leaves,while it was highest in N2in upper leaves. In conclusion, treatment N2(4.375g/pot) withabundant nitrogen supply before topping and then lowering nitrogen supply after topping wasthe best. These suggested that abundant nitrogen nutrition and nitrogen deficiency at maturingstage were conducive to improve the coordination and contents of aroma and flavour.In conclusion, abundant nitrogen nutrition coupled with nitrogen deficiency at maturingstage was conducive to improving production and quality, and to increasing the aromacontents. Abundant nitrogen nutrition in early stage provided the material basis for vigorouscarbon and nitrogen metabolism, formation of photosynthetic product and accumulation ofaroma precursor. Nitrogen deficiency after topping would promote tobacco mature timely byweakening nitrogen metabolism in time; which provide the conditions for aroma precursors todegradate, especially the aroma precursors. Appropriate cell senescence speed, cell environmental, physiological metabolism were conductive to the coordination of terpenoidsecondary metabolism2. Effects of different nitrogen deficiency models at maturing stage on quality, plastidpigment and neutral aroma constituent contents in flue-cured tobacco leavesWith the decrease of the nitrogen deficiency level, leaf length, leaf width, maximum leafarea increased first then decreased, single leaf quality weight and stem ratio increased in turnin middle leaves and upper leaves. Single leaf quality weight were highest in N3treatment,followed by N4treatment, then N2treatment and N1treatment in middle leaves; whileN4>N3>N2>N1in upper leaves. Appearance quality achieved a higher performance in N2and N3treatment. With the decrease of the nitrogen deficiency level, reducing sugar and totalsugar contents decreased in turn, while the contents of total nitrogen, nicotine and starchincreased. The harmony of chemical components was achieved to a high level in N2and N3treatment.Both plastid pigment residues and carotenoid residues in cured leaves were increasedwith the decrease of nitrogen deficiency level. Range of variation of plastid pigment residueswas greater in upper leaves than in middle leaves. With the decrease of the nitrogendeficiency level, products of degraded carotenoid contents and the neutral aroma constituentcontents increased first then decreased. The maximum value of which were at T2treatment(nitrogen deficiency50%from the fifth day after topping, then nitrogen deficiency100%from fifteen days after topping) for middle leaves and at T3treatment (direct nitrogendeficiency100%from fifteenth day after topping) for upper leaves, respectively. There wasno significant relationship between chlorophyll residues and neophytadiene contents. In total,the T2treatment and T3treatment were in high value. In other words, the best nitrogendeficiency model was nitrogen deficiency in the range between50%and100%since five daysafter topping, then cutting off the nitrogen supply--100%nitrogen deficiency since fifteendays after topping. It was suggested that the continuous nitrogen supply after topping accountfor between7.14%and13.33%of total nitrogen supply of the whole growth period.