Studies On Dynamic Changes Of Physiological And Biochemical Indexes And Its Relationship With Quality In Burley Tobacco

Dynamic changes of physiological and biochemical indexes in burley tobacco leaf in maturing period at a filed trial and air-curing stage under the artificial conditions were studied in detail. During the air-curing stage, the air-curing mechanism of burley tobacco under the condition of high humidity, middle humidity and low humidity was studied by the artificial adjustment to air-curing environment, respectively. At the same time, the relationship between the changes in physiological and biochemical indexes and its quality was also discussed. The main results obtained from the studies were as follows:1 During maturing period at the trial field, K content in burley tobacco leaf showed an obviously decreasing tendency with maturing progress. Cl content in up-, middle- and down-leaves had a slender decreasing tendency as mature and senescence of tobacco leaf. Ca and Mg content showed a distinct ascending tendency, and the change of S content is not obviously.The soluble protein content changed from ascending to decreasing in maturing stage. The content of nicotine accumulated quickly after topping and then showed a ascending tendency in maturing stage. The content of chlorophyll decreased gradually along with the tobacco leaf matures, and the content of chlorophyll in upper leaf was highest and is lowest in lower leaf. The content of carbohydrate ascended in prophase of maturing because of photosynthesis and then decreased gradually in anaphase. Both electric conductivity and MDA content in burley tobacco leaf had an obvious ascending tendency in maturing stage.2 The changes of chemical component were most-harmonious in the barn with middle humidity treatment. Mineral elements are a kind of chemical component which kept steady by and large in the air-curing stage. K may flow backward to the stem of tobacco in the course of air-curing, which resulted in a decreasing tendency in leaf K content. The relative content of mineral elements had an ascending tendency for the reduction of organiccomponent in leaves as the air-curing of tobacco leaf, in which increase of Ca contentwas the most obvious.Nitrogen-containing compound and carbohydrate belonged to a kind of matter which kept dynamic change in the course of air-curing and this mainly occured in the wilting and yellowing period. Protein, chlorophyll and starch decomposed by catalyzing of enzyme. These chemical components correlatived with tobacco leaf quality decomposed more completely and harmoniously in the condition of middle humidity. The activity of enzyme, such as amylase, in the condition of middle humidity remained the highest which improved the metabolism of tobacco leaf well. However, the chemical component could not transform well because tissue decomposed due to overmuch water content in tobacco leaf in the condition of high humidity or leaf cell died since the loss of water too fast in the condition of low humidity. The extent of senescence of upper leaf was less than that in middle and lower leaf during harvesting, which kept higher ability of metabolizing in air-curing stage, especially in wilting and yellowing period.3 Correlation analysis on three parts of indexes related to tobacco leaf quality in the barn of middle humidity treatment showed: the variation of total soluble sugar and reducing sugar, MDA and electric conductivity, starch and amylase all had a good relativity separately. The correlation of variation between total soluble sugar and reducing sugar in middle leaves reached a high significant difference, and it in upper and lower leaves reached marked difference. The correlation of variation between MDA and electric conductivity in upper and middle leaves reached a significant difference, and it in lower leaves reached marked difference. The correlation of variation between starch and amylase in upper leaves reached significant difference, and it in middle and lower leaves reached a marked difference.4 The results of analysis on burley tobacco leaves tissue structure were as follows: the tissue structure transformed gradually from littler volume and arranging tightly to larger volume, arranging loosely and large intercellular gap in maturing stage along with the leaves senescence. The tissue structure of down-leaves was destroyed at harvesting period. Thevariation of tissue structure was mild in the condition of middle humidity which kept accordant with the variation of chemical component in leaves by and large and this was beneficial to form best quality during the burley tobacco air-curing.5 Comparative to some quality indexes of burley tobacco leaf in the condition of different humidity at the end of air-curing, the results showed that after air-curing, the k content, Cl content, K/Cl ratio, total N content, nicotine content, N/nicotine ratio, total protein content and reducing sugar content in burley tobacco leaves in the condition of middle humidity reached the standard of high grade burley tobacco leaf basically. The quality of burley tobacco leaf in the barn of high and low humidity treatment was worse relatively.