| Potassium is the most important osmotic adjustment substance in plant, because of its high content, widespread distribution, quick movement and high reuse, it plays a major role in the relationship of plant-water. It is reported that we can improve the potassium nutrition condition, increase water use efficiency and enhance the drought resistance of plant by proper use of potassium .And now, it is considered that potassium can improve drought resistance of plant through osmotic adjustment, but on how potassium affect the water distribution under drought condition and why potassium distribute again in plant, there is still little research.. This study, we choose tonacum NC89 as material, which is a potassium like plant, via pot culture experiment, we have measured the distribution of potassium in the different part of tobacum and redistribution of potassium in the different organelle of the mesophyll cell and some physical indexes, such as membrane permeability, leaf water conservation, Pro content, transpiration rate, photosynthesis rate, chlorophyll content and so on.In this experiment, we have low, mid and high potassium three different treatment. The proportion of nitrate, phosphate, potassium are N:P2O5:K2O(g.kg-1dry soil), N:P2O5:K2O=0.2:0.2:0.4, N:P2O5:K2O=0.2:0.2:0.8 respectively. And we have two different water treatment: normal water supply(W1), water content is 75±5% of major field water holding content; drought treatment(W2), water is 40±5% of major field water holding content. The treatment begin ,only when the tobacum have eight leaves, we keep the water content on a basic constant level by weighing method ;at the same time, we stop tobacum water supply, so that water decrease naturally, then measure the water content and relative physical indexes at regular intervals.Results of experiment indicated:(1).Under drought stress ,when the proportion of nitrate ,phosphate and potassium is N:P2O5:K2O=0.2:0.2:0.4(g.kg-1dry soil), tobacum plant have stronger drought resistance and higher production. Whereas under the normal water supply ,the production is highest when the proportion of nitrate, phosphate and potassium is N:P2O5:K2O=0.2:0.2:0.8(g.kg-1dry soil). Constant and lower water content can increase the potassium content of tobacum leaves, (2).Under two different conditions, the potassium content of tobacum leaves is highest .We have concluded that the potassium content of vein is as high as 3-5 times of the mesophyll tissure, root and shoot ,and play a role of "potassium sink" and "water sink", thus, to some extent, the osmotic adjustment ability of cells is depended on the vein.Vacuole has the highest proportion of potassium in cell. Under the constant water stress, the distribution of potassium is higher in chloroplast than in mitochondrion, but when water decrease gradually, the thing is different. Under drought stress, the distribution of potassium decrease weakly in vacuole, but this can cause a tremendous change in chloroplast and mitochondrion ,because of its immense amount. Thus, the distribution of potassium increase significantly in chloroplas, but in mitochondrion weakly.(3). At the beginning of drought stress, the significant change of potassium content is the result of fight between the part on the ground and part underground, whereas the major reason of increased potassium content of leaves is probably the root have strengthened absorption to potassium under long constant water stress. Although root have strengthened, the absorption to potassium, the potassium content of root decrease significantly, because the transportion ability of potassium increase.(4).Under drought stress, the decreased photosynthesis rate of treatment without potassium is caused by nonstomatol factor, but in other treatment, stomatol factor is the chief reason. And it can enhance the adjustment ability of stoma with highest potassium, but the enormous change of stomatol aperture (or acute reaction) is ill to production. The production of tobacum leaves is closely related with transpiration... |
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