Abstract:
Fresh leaves from flue-cured tobacco variety Hongda and K326 were used as materials in this study.Based on classical five-level leaf maturity taxonomy and chlorophyll SPAD values,and with indoor experiments using paraffin method and physiological and biochemical assays,five maturity grades (M1 to M5) from upper,middle and lower parts on the tobacco stem position,structure and pigments and other biochemical properties of fresh tobacco leaves were studied.The results showed that:① leaves of K326 had more loose structure than Hongda;leaves of Hongda had more pigments than that of k326,K326 had more total nitrogen and proteins,higher nitrate reductase and amylase activity than those of Hongda,while the content of malonate aldehydeis was hardly affected by species or leaf positions;② By the rise of leaf positions,the organizational structure of the tobacco leaves tended to get more dense,while the pigment content tended to decline.Leaf thickness,spongy tissue,palisade tissue thickness,the ratio of carotenoids,nitrate reductase activity,total nitrogencontent and malondialdehyde index tended to increase.There were no significant difference between the two varieties;③ Structures between different maturity levels varied significantly at the same leaf position.Leaf thickness,leaf epidermal thickness,thickness of palisade and spongy tissue showed a significant parabolic change pattern by different levels fromM1 to M5.There was a "turning point" feature between M2 and M4.Leaf pigment content,nitrate reductase activity,soluble protein and total nitrogen content decreased from M1 to M5.While the ratio of carotenoids,malondialdehyde content increased from M1 to M5.Therefore,in this study,the change pattern of fresh leaves in leaf structure and physiological and biochemical properties between different maturity levels was discovered,which provides a theoretical basis for the scientific development of harvest maturity digitized standards.