| The pot experiments were conducted using tobacco cultivar K326 as the experiment material on the He Nan Agricultural University campus.By measuring content of pigment content, antioxidant enzymes (SOD, POD, CAT) activities, active oxygen content, membrane lipid peroxidation and the main chemical components and physiological characteristics in upper leaves and roots, we have initially studied the mechanism of tobacco aging and the effects in different control technology. Test results are as followed:1. Different treatments have effects on chloroplasts pigment chlorophyll content and the activity of Chlorophyllase .With the time of topping, the amount of the pigment in all treatments deal with gradual decline in overall period. The chlorophyll content has been lower, showing a faster decline in pre-top, slow in the late. Luteins content is on the rise in the period of the topping 10 to 20d, decline in other period, The changed trend of the content of carotene was the same as chlorophyll. The content of chlorophyll of all control measure treatment was significantly lower than that of high nitrogen, and the content of carotenes were higher than the high nitrogen, It illustrated all measures were to promote the tobacco pigment degradation, it would be more appropriate to the leaf pigments ratio and it facilitated a timely maturity, the results of different measures harmonizing the ratio of pigment showed as followed: fixed-mature> sodium bicarbonate> aluminum chloride> calcium chloride. That is generally believed to be the first step Chlorophyll is resolved to homogentisate and chlide via the catalysis of Chlorophyllase.The activity of all treatments Chlorophyllase is upward in the entire period, the size order of Chlorophyllase is as followed: sodium bicarbonate> calcium chloride > aluminum chloride. The activity of fixed-mature treatment Chlorophyllase is higher than that of other in pre-period , in topping 30d on decline, and then continue to rise, other are smaller in pre-period, increase higher in the latter period. It shows fixed-mature can earlier promote degradation of chlorophyll.2. Different treatment have effects on t activity of antioxidant enzymes of upper leaves and roots.The activity of antioxidant enzymes of different organs were decreasing with the time of topping. SOD activity in the leaves except topping 10 to 20d is on the rise, the activity of SOD in the roots showed in decline in the other times except topping the day to 10 d on the rise. Because of the measure of topping, photosynthate flows from the reproductive centre to supply to nutrition organs, which makes the upper leaf blades in particular to obtain more nutrients and to the expansion of leaves. Root activity has also increased, the capacity of nicotine synthesis enhances. POD activity in the leaves throughout the period had gradually decreased, root POD activity declines faster in the former ande latter period, medium relatively smaller. The change trend of leaves CAT activity is the same as that of POD.3. Different treatment have effects on the content of the reactive oxygen and lipid peroxidation in upper leaves and roots.The content of superoxide in leaves and roots of anion radical is the same basic change trend with the extension of topping times, topping increasing, topping 10 to 20d decreasing, then continuing to maintain increased state. Root superoxide content is at the peak in the topping 30d, leaves the highest content topping 40d. MDA content of the leaves and roots are gradually increasing with the times of topping, showing the cells produce membrane lipid peroxidation after topping and gradually more serious with the extension of growing. The MDA content is a distinction among all treatments, in topping 40d,leaves is as followed: fixed-mature> sodium bicarbonate> calcium chloride> aluminum chloride. From the change of root MDA content, we can see the fixed-mature, sodium bicarbonate and calcium chloride play a immediate role in the membrane lipid peroxidation of root cell and remain stable throughout the period, aluminum chloride and sodium bicarbonate mainly play a role in the later.4. Different treatment have effect on the nucleic acid DNA,RNA and DAN content in upper leaves. The nucleic acid, DNA, RNA content throughout the period showed a downward trend, the three matures have the same change trend. The content increased after topping 10 to 20 d, its causes may be the SOD activity increasing, 02 - ? content decreasing, DNase, RNase activity decreasing, the DNA, RNA synthesis ability enhancing. The percentage of the nucleic acid content in topping 40d and 0d is as followed: normal plant (83.34%)> high nitrogen plant (82.54%)> calcium chloride (82.03%)> aluminum chloride (79.77%)> bicarbonate sodium (74.40%)> fixed-mature(72.62%), we can see that the control measures can accelerate DNA, RNA decomposition to a certain extent, the effect of fixed-mature and Sodium bicarbonate was the best.5. Different treatment have effect on the main chemical composition and physical characteristics in upper leaves.The content of sugar and starch in upper leaves was rising trend with the times of topping, It shows that nitrogen metabolism decreasing, carbon metabolism increasing after topping, meanwhile topping leads to the photosynthetic products from the supply center to nutrition organs accumulation and the carbohydrates increasing. The total sugar content of different treatment leaves is as follows: fixed-mature> normal plant> calcium chloride > sodium bicarbonate> aluminum chloride> high nitrogen plant , starch content: normal plant> fixed-mature>sodium bicarbonate> calcium chloride> aluminum chloride> high nitrogen plant. The content of nicotine and nitrate is up after topping, topping stimulates the nicotine synthesis and accumulation, the nitrate content increasing shows the nitrogen from the soil is accumulated in the leaves because of the reduction of NR activity, meanwhile causing feedback effect and inhibiting absorption of nitrogen. The content of protein and total nitrogen is on decline with the times of topping, after topping, the balance of protein synthesis and decomposition is destructed, decomposition gradually dominate. From enhancing carbohydrates and nitrogen content, controlling the accumulation of nicotine, leaf quality can be improved by various measures in a degree, the content and ratio of components is appropriate, the indicators of fixed-mature treatment were more close to normal plant, and some of the beneficial ingredients more than normal strains.The activity of NR and InV gradually reduce with the extension of topping days. The difference of measure treatments is significant in topping 20d, 30d, 40d. It illustrates the measures can effectively reduce the NR activity and is conducive to the change of carbon metabolism to nitrogen metabolism, decomposition of nitrogenous compounds and the accumulation of carbon water compounds have conditions. The reduction of InV activity shows that C fix and conversion is weaker and the accumulation of carbon metabolism gradually increase. |
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