Effect of Nitrogen Nutrition on Starch Accumulation and Activity of SPS and Diastase in Tobacco Leaves

The accumulation dynamics of starch in two tobacco cultivars (K 326 and HD)were studied under field conditions. The effect of levels and forms of nitrogen applied on starch content, activity of SPS and diastase in tobacco leaves were also analyzed. The amounts of starch accumulation in tobacco leaves increased rapidly during the ripening process, and reached maximum in tobacco maturation, about 40% for HD and 25%for K 326 in cutters, respectively. Starch content and SPS activity in tobacco leaves was negatively related to the levels of nitrogen applied, diastase activity in HD decreased with increasing nitrogen applied during the ripening period, and the correlation between starch content in K 326 and nitrogen levels applied was negative just after topping and was positive in maturation. Either less or extra levels of nitrogen applied led to a high content of starch in cured tobacco. Forms of nitrogen influenced metabolism of starch in K 326 more significantly than that in HD. Content of starch, activity of SPS and diastase in K 326 kept a low level with 1:1 of N-NH₄⁺:N-NO₃^-.