| In these experiments, 18 high quality varieties and lines of soybean (Glycine max) from East China and nabe were tested for their tolerance to aluminum toxicity. With solution culture, sand culture and pot culture, two varieties of soybean (Zhechun No.3 and Huachun No. 18) were employed as the main material for the research of effect of aluminum (Al) on seed germination, growth of seedlings, micro flora in soybean rhizosphere soil, physiological characteristics of roots, morphology structure and agronomic property, cell ultra-structure, photosynthetic characteristics and chlorophyll fluorescence parameters, physiological characteristics and endogenous protective systems, 4 main isozyme and protein expression. The main results obtained from experiments are summarized as follows:1. Dry weight of roots, area leave and plant height were all closely related with its competence of resistance to Al toxicity, which can be considered as important indexes for the screening of genotype with tolerance to Al toxicity. A method for comprehensive evaluation of the tolerance on the using of average tolerance coefficient was established. The aluminum-resistant comprehensive coefficient was also calculated by using the critical indexes of being have screened out. Based on these, soybean varieties, Zhechun No.3, A1806 and 1517-2-1, were selected for their higher tolerance to Al toxicity, and Huachun No. 18 and North 9939 were relative weakly resistive to Al toxicity.2. Al treatment obviously affected the germination percentage of soybean seeds, POD activity and content of MDA, Pro and soluble sugar of seedlings. The treatment of low Al promoted the seed germination percentage and growth of seedlings, but too much Al would be harm to seed germination and seedling growth of soybean.3. Al also had remarkable effect on the microorganism and their metabolism in soybean rhizosphere soil. By influencing the number and activities of microorganism in soybean rhizosphere soil, Al affected nutrition supply from soil to soybean, the growth of soybean root and its absorption of nutrition in the soil.4. The seedling growth was restrained under Al stress. Al toxicity happened when theconcentration of Al treatment reached to 20 mg-L"1, and the more the concentration increased, the more the toxicity was. Under Al stress, the growth of root was inhibited obviously, root hair reduced, stein became thin and plant weight decreased. The growth of leaves was restrained, the area of leaves reduced, lamina mass per unit area decreased, the biomass of root and leaves both reduced, but the treatment of low Al concentration was benefit for the growth of soybean seedlings to some extent.5. Under Al stress, the apices of root enlarged, the tip of root became shorter and thicker. The damage suffering from Al caused different degree crack on surface of root tip, and this kind of damage became more serious as the concentration of Al increased. Meanwhile, Al destroyed the cell structure and membrane system of root, and the cytoplasm segregated from the cell wall by different degree. The mitochondrion became swelled and misshaped, the endomembrane system damaged, and the quantities of atrament and medullary sheath in vacuole increased obviously. With the treatment of high Al concentration, the cell wall deformed and broke, cytoplasm degraded and disappeared, some chloroplasts collapsed and some mitochondrion disappeared. The cell became emptied as a vacuole, which was filled with fungous.6. Al stress caused damage on the cell ultra-structure of soybean leaves. The damage on chloroplast suffering from Al stress was most distinguished. The chloroplast misshaped, membrane system of chloroplast damaged greatly, the thylakoid inside chloroplast became twisted and disordered and the number of lipid droplet increased, the chloroplast lamellae decomposed, and the number of starch vacuoles reduced remarkably even disappeared. Too much Al would induce some chloroplast to collapse. The mitochondrion also became swelled and misshaped, the crista was indistinct and the number of mitochondrion decreased. Some of mitochondrion was phagocytized by chloroplast. Because of the damage of endomembrane system under Al stress, the number of medullary sheath in cell was increased.7. The cell membrane and defense system of AOS was damaged under Al stress. The study showed that Al toxicity caused membrane lipid per-oxidation and increment of permeability of plasma membrane. The activity of SOD, POD and CAT increased as the concentration of Al were enhanced, but they decreased when the concentration of Al wastoo high. Under Al stress, the soluble sugar accumulated in roots, but its synthesis was inhibited and the content reduced in leaves.8. There were obvious effects of Al on the zymograms of 4 isozymes in leaves with different Al treatments. The responses to Al toxicity of these 4 isozymes were quite different between two soybean varieties. Under Al stress, the activities of SOD enzyme of two soybean varieties were both decreased, but the activities of POD were both enhanced and were induced some new bands to reject Al toxicity. In Zhechun No.3, the activities of EST isozyme were enhanced but those of CYT isozyme were weakened with the increasing of Al concentration. The response of Huachun No. 18 was just contrary.9. Al affected the photosynthesis of soybean and reduced the photosynthetic efficiency. There were stomas factors and non-stomas factors. The study showed that the content of Chi and the value of Chla / Chlb reduced, the stomatal resistance (gs) increased, stomatal conductance (rs), photosynthetic rate (Pn), transpiration rate (E), solar-energy utilization efficiency (SUE) and water utilization efficiency (WUE) decreased. The photosynthesis and transpiration of soybean were inhibited by Al toxicity. There was also obvious effect of Al on the chlorophyll fluorescence kinetic parameters of soybean leaves. With Al treatments, the ratio of the variable to maximum fluorescence (Fv / Fm), the ratio of the variable to minimal fluorescence (Fv / Fo), maximum fluorescence (Fm) of soybean leaves decreased, while the minimal fluorescence (Fo), variable fluorescence (Fv), non-photochemical quenching coefficient (qNP) and the photochemical quenching coefficient (qP) raised. These all indicated that photo system II was damaged, primary light energy conversion of PSII (Fv/Fm), potential activities of PSII (Fv / Fo) decreased, photosynthetic electron transport, photosynthetic primary reaction inhibited, and heat disseminate possess photo-protective effect increased.10. Not all the Al treatments would be toxic to plant. Our study showed that the treatment of low Al concentration could promote germination percentage of soybean seeds, the growth of seedlings, decreased the content of malondialehyde (MDA) and maintain stability of membrane, enhanced the anti-oxidant enzymes(including POD, SOD and CAT) and promoted the physiological metabolism such as photosynthesis. There was a threshold value of Al toxicity to plant. When the Al concentration plant suffered extended this...
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