The Ecophysiological And Protein Effect Of Heavy Metal Hg On Aegiceras Corniculatum Seedlings

Mangroves are woody plant communities which located in tropics and subtropics zone,possessing very important ecological and economic value.Mangrove plants have high ability to enrich mercury and have strong resistance and tolerance to heavy metals.At present,there are many physiological and ecological studies about mangrove plants under heavy metal stress,but few studies about mangrove plants in protein molecules level.Our study takes the typical salt secreting plant Aegiceras corniculatum seedlings as the experimental material.Observe Aegiceras corniculatum seedlings' physiological and ecological changes under the mercury stress with ion concentration in gradient(0,0.2,1,10,50 mg·L-1 Hg2+),try to study the mangrove plant protein's adaptive changes under the mercury stress at the same time.Combined with the mercury distribution of different leaves structures,in order to explore the mechanism of enrichment and tolerance of Aegiceras corniculatum on mercury.The main results were as follows:(1)The contents of heavy metal mercury in various structures(surface,cuticle and tissue)of Aegiceras corniculatum leaves was different.Leaves tissue was the main storage site of mercury in the Aegiceras corniculatum leaves,which was more than the other structures of leaves(leaves surface and cuticle).The mercury contents in Aegiceras corniculatum leaves tissue ranged from 31.245 to 413.761 ?g·kg-1,took 94.29?96.82 percent of leaves total mercury content;The mercury contents in leaves cuticle ranged from 0.775 to 8.909 ?g·kg-1,took 2.04?3.46 percent of leaves total mercury content;The mercury contents in leaves surface ranged from 0.250 to 4.742 ?g·kg-1,took 0.78?3.32 percent of leaves total mercury content.It might be:first,there were many components in the leaves tissue which can combine with the mercury so that it can be stored in the cells to reduce the toxic effects of mercury.Second,there was little active substances in the leaf cuticle,which show the weak combining capacity with mercury and the others.The mercury absorbed from the roots of Aegiceras corniculatum seedlings migrated to the site of leaves through the transport tissue under the action of capillary action and transpiration.Furthermore,the leaves can absorb the gaseous mercury in the atmosphere and store it in the leaves or transporte to other parts.However,there is little gaseous mercury in the atmosphere.So we can speculate that the mercury in the leaves is mainly absorbed by the Aegiceras corniculatum roots from the mercury stress liquid and then transported to the leaves.(2)The trend of proline contents in the leaves was the single peak curve under Hg stress.With the increase of Hg stress contents,proline contents in leaves of increased and then decreased.The range of proline contents ranged from 22.538 to 32.204 ?g·g-1.Aegiceras corniculatum seedlings could resist the damage of mercury by increasing the contents of proline in the leaves which shows that it has certain resistance for Hg,The increase of proline content was one of the mechanisms of mangrove plants to resist to the heavy metal stress.But with the increased concentration of mercury content or toxic time accumulated,the proline content showed a downward trend,indicating that proline's osomtic adjustment was limited.(3)The contents of NPT in leaves and roots of Aegiceras corniculatum seedlings increased with the increase of Hg2+ stress.The change of NPT contents in Aegiceras corniculatum leaves ranged from 1.044 to 4.193 mg·g-1,and ranged from 1.355 to 5.798 mg·g-1 in roots.It indicated that under the influence of mercury Aegiceras corniculatum made the adaptive response,the increasing of NPT in leaf and root aims to resist or reduce the toxic effects of mercury.At the same time,the contents of NPT in roots was higher than that in leaves,which was because the roots were the main sites for heavy metal uptake,and the roots contacted with the mercury solution directly.Mercury can form insoluble complexes with excess non-protein lily groups,which are not easily transported upward,lead tothe most of the mercury in the plant body was bound to the roots.(4)With the increase of mercury stress content,the soluble protein contents in leaves and roots increased first and then decreased,both higher than the blank control.The range of soluble protein contents in Aegiceras corniculatum leaves was 1.853 to 2.346 mg·g-1,was 0.560 to 0.646 mg·g-1 in roots.The results showed that the synthesis and metabolism of protein in plant cells were enhanced,and Hg induced more protein synthesis to improve its resistance by involved in osmotic regulation.Hg can induce the increase of soluble protein content,which may be a detoxification mechanism of plant to resist to Hg poisoning.(5)The results of SDS-polyacrylamide gel electrophoresis showed that the leaves and roots may produce new proteins under mercury stress.This is an adaptive mechanism of mangrove plants against the heavy metal stress.