Study On The Effects Of Uranium On The Photosynthesis And Stress-resistant Physiological Characteristics In Three Different Plants

With the rapid development of nuclear industry,tailing were produced in the process of uranium mining and metallurgy, which brought the serious pollution to ecological environment. The heavy metal pollution control is regarded as an urgent work. The soil cultivation experiment was used to investigate the effects of uranium on the photosynthetic characteristics of spinach?Spinacia oleracea L.??mustard?Brassica juncea L.?and green cabbage?Brassica chinensis L.?leaves. Mustard?Green cabbage and Spinach seedlings of the six-leaf stage were treated with different concentration uranium [UO₂?CH3CO₂?2 ·2H2O](0, 20, 50, 100, 150 mg·kg^-1), and photosynthetic pigment content, photosynthetic gas exchange parameters, chlorophyll fluorescence parameters of leaves, growth indexes, CAT?POD and SOD activities of leaves,MDA and free proline content,were investigated after 7, 14, 21 and 28 day of uranium treatment.The results showed that:1. Mustard ? green cabbage and spinach have different capability of uranium accumulation, and the descending order of accumulation capability was mustard,spinach,green cabbage. These three plants uranium content showed positive relationship with treatment time and soil uranium content. The distribution of uranium content in mustard ? green cabbage and spinach was: roots>leaves>stems. Under different processing time, the turn from high to low of the bioconcentration factor of These three plants was roots, leaves, and stems, and the turn from big to small of the transfer factor was leaves, stems.2. Root length, plant height and biomass showed a obvious rise under low concentrations of uranium treatments, and a decline under high concentrations uranium treatments. When the uranium concentration was 150mg·kg^-1, seedling stem, root, leaf and biomass were significantly inhibited, and green cabbage was more sensitive to copper than the mustard and spinach.3. Photosynthetic pigment content of leaves significantly changed with the increasing uranium concentration and it was characterized by low concentration promotion but high concentration inhibition. Sensitivity of photosynthetic pigments to uranium between different species plants was significantly different. Photosynthetic pigments content of mustard and Spinach achieved the maximum under 50 mg·kg^-1treatment, photosynthetic pigments content of green cabbage achieved the maximum under 20 mg·kg^-1 treatment and then significantly decreased with the increasing uranium concentration. Compared with the control, net photosynthesis?Pn?, stomatal conductance?Gs?, transpiration rate?Tr? of these three plants significantly were improved by low uranium concentration(20, 50 mg·kg^-1), after that with the increase of uranium concentration all of the parameters significantly decreased, and along with elevated levels of uranium as well as the duration of treatment,all the parameters then decreased significantly compared with the control while intercellular CO₂ concentration?Ci? was getting rise, it showed that the decline of Pn was caused by nonstomatal factors. High uranium concentrations obviously influence on the chlorophyll fluorescence parameters of plant leaves. Photosystem ?? PS ?? maximum fluorescence?Fm?,PSII maximum photochemical efficiency?Fv/Fm?, PSII potential activity?Fv/Fo?, declined obviously,while minimum fluorescence?Fo? and were obviously rise.4. Considering resistance to oxidative stress effects, CAT, POD and SOD activities of these three plants showed a obvious rise under low concentrations of uranium, and a decline under high concentrations of uranium. The results showed that the three enzymes had the effect of scavenging active oxygen radical. But the capability of clearing up the harmful peroxide for CAT, POD and SOD were limited,then CAT, POD and SOD were inhibited under higher uranium concentration,and antioxidant system were impaired in some way. Heavy metal uranium produced different degrees of stress on three species, uranium promoted the content of Proline and MDA significantly. The content of MDA and proline increased with the metal concentration increase, At the same time, when the uranium reached maximum concentrations, the proline content of green cabbage decreased. It indicates that the uranium concentration may have exceeded the tolerance ability of green cabbage.