Study On The Distribution Of Aloe-emodin In Leaf Blade And Its Spectral Properties Under The Influence Of ZnO NPs

Zinc oxide nanoparticles(ZnO NPs)have unique physical and chemical properties and important application values in many fields,which has also been resulted that it was released into different environment,and increased the interaction with creatures,which is the most important aspect of the toxic effects of ZnO NPs.Aloe is a lily family of evergreen and fleshy herbs,which has important ornamental and medicinal value,Aloe-emodin(Aloe emodin,AE)is an important pigment molecule in aloe,and is also an important active ingredient of aloe as a medicinal plant.Although a number of studies have found that ZnO NPs have negative effects on plant systems,but for aloe vera,only the effects of ZnO NPs on the protoplast activity and calcium ions metabolism are investigated.As for the effect of ZnO NPs on the active substances in aloe cells is still unclear.Therefore,this thesis mainly studied the effect of ZnO NPs on aloe-emodin,which is an important bioactive substance in aloe leaf.It turned out that ZnO NPs could discolor the aloe-emodin solution,and the spectral properties of aloe-emodin has also been changed.First,the longitudinal distribution of aloe-emodin in aloe leaves was observed under fluorescence microscopy.The longitudinal and lateral sections of aloe leaf were prepared by hand slicing method.Under the fluorescence microscope,the structure of the leaves was observed under white,blue and ultraviolet light irradiation,and the lateral and longitudinal microscopic image of the leaves were obtained.The results showed that in the longitudinal section of aloe leaf irradiated by blue light(460-490 nm),the assimilating tissue appeared red,whereas the vascular bundle emitted bright yellow fluorescence;in the cross section,there were a large number of bright yellow fluorescent points in the vascular bundle sheath cells,they were also found in parenchyma cells at the junction of assimilated tissues and the water-storage tissues,as well as in the cells of the assimilated tissues,but very few were found in the vascular bundle sheath cells,which indicated that the parenchyma cells of assimilate tissue were the place where aloe anthraquinone compounds were synthesized.These bright yellow fluorescent material is aloe-emodin and other anthraquinone substances.Secondly,the effect of ZnO NPs on the color of aloe-emodin solution was studied.The spherical ZnO NPs with a diameter of about 5 nm were prepared by sol-gel method.6 mg/L and 10 mg/L of ZnO NPs suspensions were mixed with freshly extracted aloe-emodin solution,and placed under dark and ultraviolet conditions,respectively.The changes of the color of the mixture were recorded at regular intervals.It was found that the aloe-emodin aqueous solution containing ZnO NPs was discolored in the dark condition or under thetreatment of ultraviolet light.The difference is that the aloe-emodin solution color becomes orange-red under the ultraviolet light,and orange in dark conditions.The reason may be that under the ultraviolet light treatment,because of the photocatalysis effect of the ZnO NPs,the hydroxyl and superoxide radicals generated on the surface of the ZnO NPs could react with the aloe-emodin and causing the changes of the position and number of the phenolic hydroxyl and other auxiliary groups on the benzene ring of aloe-emodin,and the color changes from canary yellow to orange-red.Finally,the effect of ZnO nanoparticles on the spectrum of aloe-emodin solution was studied.10 ?g/ml ZnO NPs suspension was mixed with aloe-emodin aqueous solution of the same concentration,which was taken as the experimental group.The pure aloe-emodin aqueous solution was used as the control group.The fluorescence and absorption spectra were measured at intervals of a certain time and was used to analyze the effect of ZnO NPs on aloe-emodin.The results of the fluorescence spectra show that when excited by 460 nm,the mixture of zinc oxide NPs and aloe-emodin has four emission peaks,namely,500 nm,540 nm,580 nm and 630 nm.The I540/I580 ratio increased with the increase of processing time,no matter whether or not the zinc oxide NPs were added or not.However,the addition of zinc oxide NPs can accelerate the I540/I580 ratio increase.The change of this ratio may due to that aloe-emodin is an kind of anthraquinone compounds containing phenolic hydroxyl group,which is prone to discoloration with the reactive oxygen groups that are generated in the surface of ZnO NPs.These reactions eliminate the reactive oxygen species on the surface of ZnO NPs and help to reduce the biological toxicity of ZnO NPs.The detailed mechanism of the color change of aloe-emodin under the action of ZnO NPs will be further analyzed and studied.The results of this thesis is important for further investigations of the mechanism of biological toxicity of ZnO NPs.