Nitrogen Dose-Dependent Metabolic Shift from Nitrate Reduction to Starch Accumulation in Flue-Cured Tobacco Varieties

摘要

A sand culture experiment was conducted with three tobacco varieties and three levels of nitrogen (4.54, 9.08 and 18.16 g/plant) using McMutrey's nutrient solution. Nitrate reduction measured as leaf in vivo nitrate reductase activity increased with increased level of applied nitrogen in all the three varieties. Leaf photosynthetic pigments, total nitrogen and nitrate nitrogen were higher at 45 days after planting and decreased to lower levels when leaves were at the stage of harvest, irrespective ofnitrogen dose and variety. Specific leaf weight was lower during plant growth period but reached its maximum when the leaves were at harvest. Depending on nitrogen dose leaf pigments and total nitrogen increased in K-326 as compared to Gouthami and Hema. Specific leaf weight decreased with increased level of applied nitrogen in all the three varieties during plant growth period but it was higher at the time of harvest. Specific leaf weight was higher in K-326 followed by Gouthami and Hema. Leaf starchcontent was higher when nitrogen dose was lower and it decreased with increased level of N. Higher nitrogen levels led to delay in shift from nitrogen utilization to starch accumulation resulting in lower starch, sugars and higher nitrogen and nicotine.Metabolic shift from nitrogen utilization to starch accumulation is of prime significance in flue-cured tobacco from the stand point of its quality as sugar-nicotine ratio determines the utility of the leaf as a smoking product.