| Antioxidative responses of Aralia elata var. inermis leaves and heavy metal accumulation within varied growth stages under treatment of different Cd, Cr and Pb doses and accumulation capacity, distribution model, transportation potential of Cd, Cr and Pb in different A elata organs and time-dependent variance of heavy metal content in leaves were studied. The main results were follows:Accumulation potential of Cd in A. elata was higher than that of Cr, much higher than that of Pb. The distribution of heavy metals Cd, Cr were in the order of root> leaf> stem, and Pb was in the order of root>stem>leaf. With elevated treatment doses, the bioconcetration-factor (BCF) of Cr and Pb in root increased fast, while the BCF of leaf and stem declined. The transport potential of three heavy metals were in the order of Cd-Cr>Pb, with elevating treatment doses, the transport factor of Cr, Pb decreased, leaf transport factor of Cd firstly increased later declined, while Cd transport factor in stem was stable. The content of Cd in leaf grew as time went on, Cr, Pb content climaxed at middle-growth stage, and then decreased, Pb content changed more significantly. Among three metals, Cd had most serious damage on A. elata, thus the prevention of Cd pollution is most urgent in agricultural development.Accumulation amount of heavy metal in A. elata differed with growth period, Cr and Pb content maximum show at pre-flowering stage, earlier than that of Cd, then contents of the two decreased, the decrease was even obvious in Pb treatment at second year. Cd accumulation amount increased constantly, and had good proportional relation with time. The tendency of leaf Cd and Pb content variation with season was not changed by treatment dosages, but that of Cr did.Cd content in new leaf first decreased and then increased with leaf length increase, the minimum of Cd content showed in 15cm leaf, the BCF in leaves were above 0.4. The concentration potential at 5mg-kg-1Cd treatment overweighted the control, as doses increased the potential dropped. Chromium content increased a little, then fell, at last climbed to the highest, with fewer responses to dose changes. The lowest Cr content also was in 15cm leaf, BCF show a decrease as treatment doses increased. The accumulating potential of Pb was lower than that of Cd, Cr. Pb content in leaves varied like that of Cd, but the highest content was not in longest leaf, but was in 5cm leaf. As the BCF of highest treatment increased, Pb BCF differences between treatments decreased, while the difference was large in leaves shorter than 10cm. At late leaf-spreading stage, A. elata leaves accumulated small amount of Cd, in general, the effect of Cd on A elata growth was somewhat stimulatory. Cr had a substantial influence on CAT activity. As the increase of Cd, POD activity and content of chlorophyll first increased and then decreased; the content of MDA declined at low doses and increased at high doses. Cr treatments increased POD activity greatly, decreased CAT activity sharply, which had significant differences from those of controls; at this stage the content of MDA and chlorophyll showed somewhat elevations, but no significant difference from those of control. At this stage, Pb content was lowest, Pb made chrolophyll content increase in some degree, CAT activity increased at 1000Pb treatment, while POD activity didnot change obviously, with consideration of no main MDA elevation compared to control, it could be suggested that Pb did not harm A. elata yet.A. elata absorbed Cd mainly before middle-growth stage, with elevated Cd doses, POD activity declined dramatically, reached the minimum of whole growth stage, CAT activity was enhanced at low doses and inhibited at high ones, chlorophyll content dropped constantly, with lowest content of 70% of control, however, MDA content was elevated to 130% of that of control at this stage. Cr content in leaves reached the climax at middle-growth stage, under Cr treatments the activity of CAT waved largely, first increased then declined as the elevation of Cr doses, POD activity drop fast, with some having significant differences from controls. But the content of MDA abated largely than control, chlorophyll had some but not significant increase. At this stage, Pb content in leaves was highest, POD and CAT activity reduced largely as Pb doses elevated. However, content of MDA and chlorophyll did not change significantly compared with controls. Therefore, Pb did not harm the plant much at the stage.At early leaf-falling stage content of Cd in A. elata leaves peaked, as Cd treatment enhancing, POD activity reduced constantly; in general, CAT activity being lower than that of middle-growth stage, increased at low Cd doses, but decreased at high ones; chlorophyll content dropped continually; MDA content at this stage, declined compared with that of early middle-growth stage at low Cd treatments, while elevated greatly at high doses. At this stage, Cr made POD activity abated in general, but elevated it for about 25% in 200mg-kg-1Cr treatment, reduced CAT activity not significantly; MDA was lowered in general not greatly, but some Cr treatments elevated chlorophyll content substantially. Cr enforced the growth of A. elata at this stage. At early leaf-falling, Pb content decreased than middle-growth stage; as treatments enhanced, Pb made CAT activity and MDA content first decrease and then elevated, POD activity were made waved, lower than control only at highest treatment, chlorophyll even increased, showing Pb did not harm A. elata much. |
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