Mechanisms Of Aluminum Uptake And Tolerance In Camellia Oleifera Abel

Aluminum(Al)is the most abundant metal element in the earth's curst,usually in the form of insoluble silicate or alumina which is not toxic to plants.However,soluble Al(mainly Al3+)is toxic to most plants grown in the acidic soil.Soluble A1 inhibits the growth of plants,reduces the economic output of plants,and decreases the edible quality of agricultural and forestry products.Therefore,understanding the mechanism of plant resistance to aluminum toxocity has important scientific value and application.Aluminium is a special element for oil tea(Camellia oleifera Abel.)because it is not only harmful but also enriched in oil tea plant.In order to explore the mechanism of the absorption,accumulation and aluminum tolerance,I selected the elite'Huajin' cultivar of Camellia oleifera and analyzed various aspects of Al on oil tea,including enzyme kinetics,molecular biology,plant physiology parameters.The Aluminum tolerance mechanism of oil tea was discussed in terms of the regulation of absorption and accumulation of Al3+,expression of genes induced by Aluminum treatments,physiological responses in roots and leaves.The main results are summarized as follows:(1)Study on the absorption and accumulation characteristics of aluminum in Camellia oil.Kinetics study on the curves of aluminum absorption in water culture showed that aluminum uptake was dominated by active transport,the absorption capacity was increased with time,and the absorption rate was decreased with the passage of time under the treatment of aluminum concentration ?2 mmol·L-1.When aluminum concentration>2 mmol·L-1,alumiun uptake was mainly controlled by passive diffusion.Under aluminum strees,the content of aluminum in the aerial part was 1.15?2.03 times of that in the roots,which indicated that aluminum was main encriched in the aerial part of oil tea.Further study on the distribution of aluminum in oil tea leaves showed that most of Al(80%?70%)was concentrated in the cell wall,which effectively prevented Al3+ from entering the cytoplasm and reduced the damage of aluminum to the cell structure.Different concentrations of aluminum treatment showed that it promoted the absorption of Cu and P elements but inhibited the absorption of Ca and Mg in oil tea plant.The absorption of K,Fe,Mn and Zn elements depends on the Al3+ concentration in the medium.The aluminum concentration at ?2 mmol·L-1 promoted the absorption,but inhibited the uptake of K,Fe,Mn and Zn elements in the plant.(2)Study on the molecular physiology of Al tolerance in oil tea.Race technology identified two aluminum resistant genes from the roots of oil tea seedlings.One of the clones(CoALMT4)contained the full-length cDNA sequence with 1725 bp in length,which putatively encoded a polypeptide with 574 amino acids;the other clone(CoMATE5)was a cDNA fragment.Blast search showed that the amino acid sequence between CoMATE5 and those from other species were more than 91%in similarity;wherease the protein sequence between CoALMT4 and those from other plants was above 70%in similarity.Further bioinformatic analysis showed that CoALMT4 was a stable hydrophobic protein,contained four putative transmembrane domains,and belonged to the alpha superfamily proteinformed by the alpha helix(accounting for about 56.45%),extension chain and beta angle,,the main characteristics of aluminum resistance genes.Real-time quantitative qRT-PCR results showed that the expression of CoMATES and CoALMT4 in roots was significantly induced in a dosage-dependented manner by aluminum concentration in the medium.The induction of resistance gene expression of aluminum,promotion of root secretion of malic acid and citric acid to chelate in rhizosphere of active aluminum might improve the tolerance of aluminum by Camellia oleifera.(3)Study on the root physiology of Al tolerance in oil tea.Root morphology observation and root physiological indexes showed that oil tea seedlings did not have symptoms of Al toxicity under the aluminum concentration of 0.5 mmol·L-1?2.0 mmol·L-1.Plant height,ground diameter,dry weight,root volume were increased with the increase of aluminum concentration.Root activity,xylem transport rate and free proline content in Al-treated plants were increased by 122%,50%and 90%of those in the control plant.These results indicated that low concentration of aluminum promoted the oil tea root growth and enhanced the transport capacity of root.When the aluminum concentration reached to 4 mmol·L-1,the growth of oil tea seedlings was inhibited,the root plasma membrane penetration significantly enhanced(1.77 times of that in control).Transmission electron microscopy(SEM)showed that the cell wall began to form vesicles,cell wall broken,membrane destroyed,plasmolysis phenomenon,little nuclear disintegration,reduction of inclusion in the surrounding cells of the root tip.This is evidence that the roots of oil tea were damaged by high concentration of Al.(4)Study on the photosynthetic physiology of A1 tolerance in oil tea.Oil tea seedlings were treated with different concentrations of aluminum.Photosynthetic physiological analyses showed that the appropriate concentration of aluminum(?2 mmol·L-1,)supplyincreased the photosynthetic pigment content,enhanced the net photosynthetic rate(Pn),stomatal conductance(Gs),and intercellular C02 concentration(Ci)and transpiration rate(Tr);The trend of PEPC activity was in contrast to that of Rubisco activity PEPC activity could effectively compensate for Rubisco activity to reduce the side effects of the high AL toxic effects;Aluminum concentration increased chlorophyll fluorescence parameter Fv/FM,Phi PSII value and NPQ values increased.Therefore,camellia oil tree has strong adaptability to the appropriate concentration of aluminum treatment.However,oiltea leaf photosynthesis was significantly inhibited,the leaf cell structure was changed,grana layer expansion,starch grains decreased significantly addicted to hungry particles increased when oil tree plants were cultured under aluminum concentration up to 4 mmol·L-1.(5)Study on the anti-oxidative physiology of Al tolerance in oil tea.The results of osmotic adjustment substance and protective enzyme system in oil tea leaves show that in the treatment of Al concentrations,2 mmol·L-1,the soluble protein content was significantly increased to 1.7 times of that in CK,soluble sugar content was increased 28%compared with the CK.SOD,POD and CAT activities were increased by 29%,63%and 28%,respectively,which indicates that anti-oxidative enzyme has relieving effect on alumium toxicity in plants.But this kind of action has a certain limit.When Al concentration reached 4.0 mmol·L-1,the activities of three kinds of protective enzymes showed a decreasing trend,MDA content increased significantly,indicating that the concentration of aluminum processing induces ROS excessive accumulation beyond the scavenging capacity of free radicals,resulting in damage to the mesophyll cell membranes.In conclusion,under the concentration of alumiunm?2 mmol·L-1,the aluminum tolerance gene expression were induced,which coulud promote root to secrete more malic acid and citric acid in the rhizosphere around active aluminum chelate,and reduce the toxic effect of aluminum on oil tea cammellia.The root photosynthetic protection system was started,which enhances the root activity and the accumulation of free proline,effective removal of reactive oxygen species metabolism,maintaining normal growth and development of root system.At the same time,the Al was enriched in the cell wall of the leaf,which prevents the Al3+ from entering into the cell and reduced the damage of aluminum to the cell structure.The increase of osmotic adjustment substances and the formation of strong antioxidant enzyme system in Camellia oil helps to maintain cell turgor,protect cells from aluminum toxicity,ease the cell membrane lipid peroxidation,then eventually enhance the tolerance of camellia oil to aluminum and ensure the normal growth of oilta camellia.