| Currently, mangrove wetlands facing more serious heavy metal pollution, heavy metal pollution in mangrove wetlands restoration become a hot topic in recent years, however, the mechanism of heavy metal tolerance of mangrove and its influencing factors are still not fully revealed. Mangrove plants suffer periodic seawater inundation, seawater significant impact on its major elements Ca. Ca is the large number of elements necessary for plant growth and development, has been proved that the role of Ca can increase tolerance of plants to heavy metals, and for Ca and its mechanism in heavy metal tolerance of mangrove plant research has not yet been reported. This paper made from an academic ideology may be an important factor in Ca high tolerance to heavy metal pollution in the affected mangrove plants.The aims of this study were to investigate the effects of Ca on mangrove species of Cd stress. In this paper, the research mangrove plant Kandelia obovata, using Hoagland nutrient solution culture experiment under a completely randomized design located9deal, Cd concentrations were arranged in0,0.5,5.0mg L-1; and Ca concentrations were0,400,800mg L-1, The results showed as following:1. In Cd supply treatments, the net photosynthetic rate K. obovata seedling leaves, stomatal conductance, intercellular CO2concentration and transpiration rate with increasing Cd concentration decreased. Under the same Cd treatment level, plus Ca-treated group compared to the group treated with and without Ca, net photosynthetic rate K. obovata seedling leaves, stomatal conductance, intercellular CO2concentration and transpiration rate increased to varying degrees. K. obovata seedlings photosynthetic parameters imposed certain concentration Ca (400mg L-1) treatment group maximum. When the Ca concentration of800mg L-1, the photosynthetic indicators K. obovata reduced. Showed Cd on photosynthesis Leaves K. obovata toxic, applied to ease the amount of exogenous Ca Cd stress on leaf photosynthesis K. obovata.2. K. obovata seedlings under the stress conditions of Cd stress, chlorophyll content decreased, root activity was significantly reduced, the body may lead to an increase in reactive oxygen species, malondialdehyde (MDA) content increased, the soluble sugar content increased tannin content increased. Appropriate concentration of Ca (400mg L-1) can relieve Cd K. obovata seedlings of physical harm, chlorophyll content, and enhance the root activity, reduced MDA levels, reduce stress Cd K.obovata membrane lipid peroxidation, improve resistance to Cd K. obovata seedlings by ability, but high concentrations of Ca K. obovata seedlings will produce physiological stress. Results indicate that applying the right amount of exogenous Ca can effectively relieve the stress of heavy metals on plants.3. K. obovata seedlings of various organs (roots, stems, leaves) Cd content with Cd concentration increased with increasing concentrations of Cd accumulation in various organs:roots> stems> leaves. The same concentration of Cd, Cd content is much larger than the root stems and leaves, indicating heavy metals Cd difficult to transport to the shoots, roots become K. obovata seedlings Cd accumulation of major organs. Under the same Cd treatment level, plus different levels of Ca treatment reduced the amount of Cd accumulation in various organs K. obovata seedlings, and with the Ca concentration increased absorption of various organs seedlings Cd accumulation decreased. Under the same treatment level Ca, Cd treatment reduced the various organs K. obovata seedlings Ca content, and with the various organs of Cd concentration increased Ca content K. obovata seedlings decreased gradually accumulate in various organs K. obovata Ca concentration:leaf> stem> root.4. Mangrove plant blades generally have thick waxy cuticle thin shape, and can reduce the loss due to moisture transpiration. Under Cd stress, palisade tissue of K. obovata seedlings to increase the proportion of palisade tissue more closely aligned, reducing the cell gap of the leaf tissue, and enhance the safety of the water to ease. Cd concentration in a certain range, K. obovata seedlings with increasing blade thickness Cd concentration increases, however, a high concentration of Cd (5mg L-1) reduces the thickness of the blade. With Cd concentration increased, the changes did not show spongy tissue thickness variation, showing a certain degree of volatility. Thickness and relative thickness of the blade up and down the stratum corneum (the cuticle and leaf thickness ratio), with increasing Cd concentration increases. Ca applied to some extent alleviate the heavy metal stress K. obovata leaf anatomy formed "dry biochemistry", however differences in the anatomy of the change was not significant level.5. TEM observations showed that: Cd K. obovata seedlings of different leaf cell chloroplasts, mitochondria and nuclei, such as the degree of toxicity major organelles, and the ability to impose exogenous Ca Cd organelle damage mitigation is also different. Organelles for Cd tolerance from strong to weak order: mitochondria, chloroplasts, the nucleus. Ca Cd-induced cell damage structure damage have some protection and relief, especially for nuclear and chloroplast under Cd stress has a strong repair.6. The cell ultrastructure analysis indicate that K. obovata seedlings control group cells, cell structural integrity, sharp edges and smooth cell wall and membrane, nucleus clear bilayer structure; complete and clear mitochondrial membrane structure, sudden steep clearly visible; multi chloroplast number, elongated oval, dense matrix, the containing a small amount of high electron density of small spherical lipid globules. Clear and chloroplast membrane structure, grana thylakoids neatly arranged closely with the matrix to form a continuous thylakoid membrane system. At low concentrations Cd (0.5mg L-1) treatment, edge blur nucleolus, nucleolus began to disintegrate; mitochondria is no obvious damage; significantly reduced the number of chloroplasts, mesophyll cells thylakoid sheet expansion, expansion, expansion chloroplast are spherical, the expansion occurs between the inner and outer layers of the outer membrane, thylakoid swelling, grana thylakoids derangement. High concentration Cd (5.0mg L-1) treatment, irregular cell structure, cell wall, cell membrane edge blur, nucleolus nuclear membrane, chromatin condensation occurs; complete mitochondrial shape rules, but began to swell, sudden steep decrease and there are steep sudden dissolution, some mitochondria into the vacuole; chloroplast expansion intensified thylakoid lamellae sparse, intracapsular vacuoles significant thylakoid lamellae dissolution phenomenon is clearly visible, part of the chloroplast membrane structure blurred, even disappeared, swelling of the thylakoid lamellae irregular, scattered in the cytoplasm, some thylakoid lamellae dissolved. Applying appropriate concentration of Ca, can protect the integrity of the cell structure, or partial disappearance of nucleoli still can see the double nuclear membrane; mitochondria remained spherical, tubular projection steep; clear chloroplast membrane structure grana complete grana thylakoid loose, the arrangement is still in regular. |
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