Studies On Maturity Characteristics Of Tobacco Leaves In Shandong Tobacco-growing Area

This paper took the main cultivated tobacco variety NC55in Shandong tobacco-growing area asexperimental material. On one hand, studies were conducted on the feature of tobacco plant stratifiedyellowing, mature tobacco leaves yellowing homogeneity of representative leaf position of various parts,and mature tobacco leaves yellowing law. On the other hand, systematic research was conducted on thevariations in tissue structure, SPAD readings, pigments, enzyme activities and main chemicalcomponents of tobacco leaves in the maturing process. Besides, the most appropriate harvest maturitydegree and resistance to ripe period were determined through flue-curing and boilable experiments.Meanwhile, comprehensive studies about the correspondence between appearance changes of freshleaves and internal physiological and biochemical indexes was conducted for the first time, according towhich some indexes evaluating the maturity degree of tobacco leaves were initially proposed, such asthe palisade cell number per unit length, cell clearances rate, SPAD readings, pigment content, starchcontent, amylase activity and PPO activity. Compared with former studies, the research was moresystematic and pertinent. Therefore, it could support local authorities to formulate the suitable tobaccoproduction technical specifications according to local zoology and productive circumstance. The mainlyresults are as follows：（1） The overall stratified yellowing of tobacco plant was significant.（2） Along with the improvement of tobacco leaves maturity, on the whole, the thickness of leaves,palisade tissue, spongy tissue, the thickness ratio of the two tissues and cell number per unit length werereduced gradually, whereas the cell clearances rate was increased. When the bottom leaves were mostsuitable for harvest maturity, the palisade cell number per unit length was51.1cell/mm and the cellclearances rate was30.17%. As to middle leaves and upper leaves, the two indexes were50.7cell/mm,27.40%and51.3cell/mm,25.48%, respectively.（3） Along with the improvement of maturity, SPAD readings and chlorophyll content in tobaccoleaves of the same part decreased gradually, while the ratio of carotenoid and chlorophyll contentgradually increased. With the increasing of parts, chlorophyll and carotenoid content in tobacco leavesof the same maturity gradually increased. When bottom leaves were most suitable for harvest maturity,the SPAD readings was25.4, chlorophyll content was1.0873mg/g, carotenoid content was0.1387mg/g,and the ratio of carotenoid and chlorophyll content was12.78%. As to middle leaves, the four indexeswere26.3,1.1384mg/g,0.1572mg/g and13.78%, respectively. And for upper leaves, they were23.8,0.7224mg/g,0.1266mg/g and17.52%, respectively.（4） Along with the improvement of tobacco leaves maturity, on the whole, amylase activity, PPOactivity, starch content and protein content ascended firstly and then decreased; the content of total sugar,reducing sugar and nicotine of bottom and middle leaves increased firstly and then reduced, whereas thecontent of total sugar and reducing sugar of upper leaves increased slightly and then reduced. Totalnitrogen content of bottom and middle leaves both decreased gradually, while the change rule of totalnitrogen and nicotine content of upper leaves was not obvious. When bottom leaves were most suitablefor harvest maturity, amylase activity was5.353mg.g^-1FW.min^-1, PPO activity was0.315△ OD.g^-1FW.min^-1, and total sugar content was16.47%. As to middle leaves, the three indexes were8.369mg.g^-1FW.min^-1,0.781△OD.g^-1FW.min^-1and27.06%, respectively. For upper leaves, they were7.420mg.g^-1FW.min^-1,0.565△OD.g^-1FW.min^-1and32.83%, respectively.（5） To comprehensively analyze cured tobacco leaves, the appearance quality, the economic benefit,the chemical composition and the smoking quality should all be considered. This study showed thatwhen tobacco leaves were most suitable for harvest maturity, the color changing area for bottom leaveswas sixty to seventy percent, for middle leaves, seventy to eighty percent, and for upper leaves, eightyto ninety percent.（6） The yellowing maturity for tobacco leaves of various parts was well consistency, and the rule oftobacco leaf yellowing was from leaf apex to base gradually.（7） In the process of resistant to senescence, quality differences between mature and delayedharvest of cured tobacco leaves gradually increased. The resistance to ripe period for middle leaves wasfour days.