Effect Of Lead & Zinc On Roots Morphology And Anatomy Absortion Of Ricinus Communis L.

Ricinus Communist sorted in Euphorbiaceae and Euphorbia,is an annual or perennial herbaceous plant.Because of its rapid growth,strong deep root system and highly tolerance and accumulation to a variety of heavy metals,castor bean was considered as a potential industrial oil plant for remediating heavy metal contaminated soil,which have a production and application foreground.In the current paper,Ricinus communis seeds of variety XiuBi No.2 were potted in matrix of sand and perlite(volume ratio 5:4)containing signal or compound Pb2+and Zn2+respectively,Then radicle elongation,germination characteristics,shape and structure of root system,absorption and accumulation of heavy metals and,the main nutrient elements were investigated The correlation between the root growth,root system morphology and structure,concentrations of Pb2+,Zn2+,along with main nutrient elements accumulated in plants,plant growth of individual plant were analyzed,so as to ascertain the feedback and adaptive changes of root system to different concentration of lead and zinc stress,to provide reference and guidance of making reasonable cultivation strategy for improving the capacity of remediating Pb/Zn contaminated soils,The main results were as followings:1)Effects of single Pb2+,Zn2+and their compound were great different on radicel elongation,seed germination.At the same stress concentration,Zn2+ had stronger inhibitory on radicel elongation and seed germination than that of Pb2+.Plants potted in 200 mg/kg and 400 mg/k Pb2+matrix respectively,their radicle elongation and seed germination rate were higher than that of control plant;While potted in matrix with Zn2+ 200 mg/kg,the radicle elongation,germination rate and variability were inhibited seriously;When the total concentration of stress was 400 mg/kg,the inhibitory effect on radicle elongation and germination ranked as:Zn2+>(Pb2++Zn2+compound)>Pb2+.That radicle elongation and germination had little relation with Pb2+concentration,but significantly negative correlation with Zn2+concentration,(R21=-0.806**,R22=-0.487**respectively).2)There were great different impact on the total root length,root surface area,root volume and root tips among plants potted in matrix with different concentrations of Pb2+,Zn2+single and compound.And the inhibitory ranked as Pb2+<Zn2+<Pb2+?Zn2+ compound.Plants potted in matrix with Pb2+ 200 mg/kg,the proportion of root surface area and root tips rose by 7.8%and 33.3%respectively;when the concentration was up to 400 mg/kg,the root volume was inhibited slightly.However potted in matrix with Zn2+ 200 mg/kg,all root morphological index had been inhibited and the inhibitory would strengthen with the increasing of Zn2+concentration.And the same inhibitory effect as plant potted in Pb2+ and Zn2+ compound matrix.(3)The stressed of Pb2+?Zn2+ on plants resulted in changes of root anatomical structures.The volume of root cap and root cap cell would became progressively smaller,the arrangement of root cap cell was in irregular;the root tip meristematic cells became smaller,deeply stained and presented in irregular arrangement;the degree of suberification of cell walls of epidermis cell and exodermis cell increased;the parenchymal cell in cortex became smaller,the cytoplasm of it were colored deeply,and there were crystal in the cell.Its color and the size became deeper and bigger with the concentration of Pb2+ and Zn2+ rose,and they would occupy the whole cell in the high stress concentrate;the same suberification phenomenon happened in the cell walls of endodermis and pericycle..(4)The accumulation of Pb2+?Zn2+ in plant potted in matrix with different concentration of Pb2+?Zn2+ was different,which closely related with the root morphological index,The accumulation of Pb2+,Zn2+ showed a significantly positive correlation with the concentration of Pb2+,Zn2+ in the substrate;The total root length,root surface area,root tips showed a little negative correlation with the concentration of Pb2+ of underground part,and a little positive correlation with the upper part concentration of Pb2+.The root morphological index showed a significantly negative correlation with the upper and underground part concentration of Zn2+.Meanwhile the upper and underground parts concentration of Zn2+ showed a significant and extremely significant correlation with concentration of Pb2+,which means that the accumulation and distribution of Pb2+ and Zn2+ has certain competitive relationship in the plant.(5)The absorption and accumulation of nutrient elements N,P,K in plants were affected by the single and compound Pb2+,Zn2+ stress,which affected plant growth and development.When the single stress concentration was below 400mg/kg,the total N in upper and underground plant part was much higher than that of control group,however the single stress concentration was 600mg/kg or under the Pb2+,Zn2+compound stress,the total N content was lower than that of control;Under single stress the total P content was higher than that in control group,which was lower in compound stress;The total K content was higher than the control group,both under single and compound stress,and K content underground part was higher than that in upper part.With the concentration of Pb2+,Zn2+ increased,the growth of ground diameter had little difference among the treatments,but the plant height and inter-node length had decreased seriously.The total thickness of leaves became thinner,along with the cells of palisade tissue be smaller,the arrangement of cell became loose,the thickness of palisade tissue became thinner,the thickness of sponge layer became thicker,the cross section of conducting tissue became small(for the number of parenchymal cell and duct decreased).