| Cellular compartmentation and phytochelatin are important mechanisms for plant tolerance or resistance.It is rare that studies on mangrove plant cell wall and vacuole compartmentation,heavy metals fixed in cell-soluble fraction and organelle.Phytochelatins and other thiol compounds in resistance mechanism against heavy metals toxicity in mangrove have not been reported.The aim of this study focused on the change of non protein thiol(NPT),glutathione (GSH),phytochelatins(PCs) in leaves and roots of Kandelia candel under heavy metals stress and subcellular localisation of heavy metals in plants,thus to predict and evaluate the ecophysiological effects of mangrove plant to heavy metals,to find out biomarkers response to heavy metals pollution,to provide scientific basis to mangrove wetland protection.In this paper,Kandelia candel(L.) Druce seedlings were cultivated in a sandy culture system with zinc treatment of 0,50,100,200,400,600,800 mgkg-1,copper treatment of 0,10,20,40,60,80,100 mgkg-1,cadmium treatment of 0,2.5,5,10,20,40,60 mgkg-1 respectively.Samples were acquired at different processing time of 3d(T1) amd 30d(T2), then NPT,GSH and PCs of leaves and roots of Kandelia candel which responded to heavy metals were measured.1.Contents of NPT in leaves and roots of K.candlel seedling under different Zn,Cu, Cd treatment were significantly increased in comparison with CK.The content of NPT was enhanced by the increasing strength of Zinc treatment,while the content of NPT was enhanced by the increasing treatment strength of Copper at first then fell down.And the change of NPT under cadmium treatment is the same as the latter.The effects of NPT content to three heavy metals were different.2.As a substrate of the phytochelatin synthesis,GSH showed some response to the Zn, Cu and Cd treatment.With the increasing treatment strength of heavy metals,the content of GSH showed either increasing or decreasing trends except for the groups deal with Cu at T1.The GSH content at T2 were lower than at T1 in all groups.The synthesis of GSH was enhanced by heavy metals treatment,which was provided as the substrate for PCs generation,thus played an important role in resistanse of K.Candel to heavy metals.3.Phytochelatins(PCs) showed a strong response to Zn,Cu,Cd treatments.The PCs content of Cd2.5 at T1 reached the maximum of the series,and content of Cd2.5,Cd5 at T2 treatment were higher than the others.PCs content increased only in high treatment strength of Zn,Cu treatment,which indicated that Cd induced phytochelatins generation easily and high concentration of Zn,Cu could also promote the synthesis of PCs.The synthesis of PCs plays a key role in the clearance of free ions in vivo,thus alleviates the poisoning of heavy metal ions.4.Different parts of K.candel,were able to accumulate Zinc.The accumulation content of zinc was enhanced by the increasing strength of zinc treatment,and varied in different parts of K.candel,which can be ranked as follows:root＞hypocotyls＞stem and leaf.When treatment level reached 800 mg kg-1,the accumulation of Zn content in leaf was 9.31 times that of the CK,while stem,hypocotyls and root were 9.18,7.79 and 9.22 times of CK respectively.Results of sub-cellular distribution of Zn were as follows:Ratio of Zn in the components of cell wall ingredient in leaf was 48.06%-61.43%,while soluble components was 10.39%-14.41%,organelle ingredient was 13.70%-17.70%,protein ingredient was 5.13%-8.67%and membrane ingredient was 9.52%-16.36%.Ratio of these five ingredient in roots were 46.90%-51.89%,11.69%-15.17%,8.92%-19.75%, 4.82%-11.85%and 7.32%-13.34%.So these five ingredients of zinc in leaf and root of K. candel.can be ranked as follows:cell wall ingredient＞soluble components＞cell organelle ingredient＞protein ingredient＞membrane ingredient.5.Different parts of K.candel,were able to accumulate copper.The accumulation content of copper was enhanced by the increasing strength of copper treatment,and varied in different parts of K.candel,which can be ranked as follows:root＞hypocotyls＞stem and leaf.When treatment level reached 100 mg kg-1,the accumulation of Cu content in leaf was 9.58 times that of the CK,while stem,hypocotyls and root were 5.62,6.12 and 9.51 times of CK respectively.Results of sub-cellular distribution of Cu were as follows:Ratio of Cu in the components of cell wall ingredient in leaf was 45.39%-63.03%,while soluble components was 3.52%-8.69%,organelle ingredient was 14.76%-22.14%,protein ingredient was 9.59%-22.42%and membrane ingredient was 13.52%-19.90%.Ratio of these five ingredient in roots were 44.90%-56.45%,12.85%-23.40%,7.28%-15.62%, and 13.21%-24.29%.So these five ingredients of copper in K.candel,leaves in low concentration treatment groups and CK an be ranked as follows:cell wall ingredient＞soluble components＞protein component＞cell ingredient＞membrane ingredient,while in high concentration treatment groups the ratio were cell wall ingredient＞soluble components＞protein component＞membrane ingredient＞cell organelle ingredient.The trend of these components ratio in root was the same as in leaves under low concentration of copper treatment,while membrane ingredient was higher than cell organelle ingredient.6.Different parts of K.candel,were able to accumulate cadmium.The accumulation content of cadmium was enhanced by the increasing strength of cadmium treatment,and varied in different parts of K.candel,which can be ranked as follows:root＞hypocotyls＞stem and leaf.When treatment level reached 60 mg kg(-1),the accumulation of Cd content in leaf was 29.24 times that of the CK,while stem,hypocotyls and root were 38.15,106.14 and 1310.32 times of CK respectively.Results of sub-cellular distribution of cadmium were as follows:Ratio of cadmium in the components of cell wall ingredient in leaf was 53.25% -66.90%,while soluble components was 9.48%-13.99%,organelle ingredient was 9.76% -24.08%,protein ingredient was 5.16%-8.53%and membrane ingredient was 3.59%-7.78%.So these five ingredients of cadmium in K.candel,leaves in low concentration treatment groups and CK an be ranked as follows:cell wall ingredient＞soluble components＞protein component＞cell organelle ingredient＞membrane ingredient.The trend of these components ratio in leaf under high concentration treatment was the same except membrane ingredient was higher than cell organelle ingredient.Trend of these ratios in roots was cell wall ingredient＞soluble components＞cell organelle ingredient＞protein ingredient＞membrane ingredient.7.The content of heavy metals in different organs showed as:root＞hypocotyls＞stems and leaves;sub-cellular distribution showed as:cell wall ingredient＞soluble fraction＞cell organelle ingredient＞protein component＞membrane component.This indicates that heavy metals were mainly accumulated in the root,small number of which distributed in hypocotyl,stem and leaves.As for heavy metals in cells,most of them conjuncted with cell wall,some of them fixed in the vacuole and other soluble components. It is capable for cells,membrane components and protein components to combine with a small amount of heavy metals. |
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