Study On The Resistant Ability Of Families And Clones From Hybrid Tulip Tree Seedlings To Pb And Cd Stress

To disclose deeply and systematically the toxicity and tolerance mechanisms of hybrid tulip tree to heavy metals stress, this paper was carried out to study effects of Pb and Cd single and combined pollution on the growth, membrane lipid peroxidation, antioxidant enzymes system, photosynthetic characteristics, endogenous hormones, mineral elements metabolice. The paper offered scientific basis for its selective breeding, planting, and phytoremediation to polluted environment. The main results were shown as follows:1. Under Pb and Cd stress the leaves of all clones and families lost green, the leaves border became dried and yellow. The roots were rotten. Compared with CK, the height growth, diameter growth and the roots activities dropped obviously. With the increasing of Pb and Cd concentrations, they dropped more obviously.2. With the increasing of Pb and Cd concentration and the prolongation of the time, membrane penetrability and MDA content increased, the increase of the stress-resistance clones and families was less. With the prolongation of the time of Pb and Cd stress, POD and SOD activities were induced to first increase and later decline mostly. But with the increasing of Pb and Cd concentration, the changes of POD and SOD activities were difference between the clones and the families.3. Under Pb and Cd stress, free proline content of the clones was induced to first increase and later decline. The content of the stress-resistance clones was higher than relative levels. During the earlier period of stress, the soluble protein of all clones increased. But with the prolongation of the time of Pb and Cd stress, the changes of content were difference among the clones and also among the degrees of treatment. The content of the stress-resistance clones were induced to increase-deline-increase, the peak values were appeared at the end of the treatment. The content of the stress-sensitive clones fluctuated obviously while at the end of the treatment the content decreased much more.4. Indexes measured were treated by using principal component analysis and subordinative function to make comprehensive evaluation to 4 clones and 5 families. The sequence of resisting to Pb and Cd stress was ranked as follows: the clones: NE60>NE13>NE04>NE43; the families:NEF14>NEF13>NEF15>NEF12> NEF115. With the prolongation of the time of Pb and Cd stress, the chlorophyll content of the clones and families were induced to first increase and later decrease, except that NEF14 and NEF12 were downtrend at all times. With the increasing of Pb and Cd concentration the chlorophyll content decreased fastly in the latter stress period. The downtrends of NE60 and NEF14 which were stress-resistence were small. But chlorophyll a/b was increased a little in the latter stress period, and the differences among the degree of treatment were inapparent. 6. With the increasing of Pb and Cd concentration and the prolongation of the time, the net photosynthetic rate, stomatal conductance, transpiration rate of all hybrid tulip trees decreased and the downtrends of NE60 and NEF14 which were stress- resistence were small. But the changes of intercellular CO2 concentration were difference.7. With the prolongation of the time of Pb and Cd stress, the change of ABA content was different under the different stress concentration. ZR content increased. IAA content showed a trend of fall-rise-fall, but under the Pb2 stress, it showed a trend of rise-fall-rise-fall. The differences among the degree of treatment were inapparent. The change extent of endogenous hormones in NE60 was smaller than the stress-sensitive clones.8. The results of this investigation indicated that there were significant effects of Pb and Cd single and combined stress on the content of Ca and Mg in different organs of hybrid tulip tree. Over 90 percent of the accumulation of hybrid tulip tree uptake to Pb and Cd was in root, and the following distribution was in stem and leaf.