Physiological Mechanism Of New Nanomaterials Regulating Maize Germination And Seedling Growth

Artificial nanoparticles have special physical and chemical properties,such as small-size effect,surface and interface effect,macro quantum tunneling effect and so on.They have a wide range of applications potential.Among them,multi walled carbon nanotubes（MWCNTs）and nano silica（nano-SiO₂）are widely used in the field of life science because of their special physical and chemical properties.In this study,the effects of different concentrations of MWCNTs(0 mg·L^-1,200 mg·L^-1,400 mg·L^-1,800mg·L^-1 and 1200 mg·L^-1)and nano-SiO₂(0 mg·L^-1,150 mg·L^-1,800 mg·L^-1,1500 mg·L^-1 and 2500 mg·L^-1)on maize seed germination and seedling growth were studied,and the biological effects of artificial nano materials on plant growth were revealed,and the mechanisms were explored.The main results are as follows:（1）MWCNTs and nano-SiO₂ can promote the germination of maize seeds,and the germination potential,germination rate,germination index,storage material transport rate,radicle and germ biomass of maize seeds are promoted.The promotion effect first increased and then decreased with the increase of treatment concentration.Among them,the treatment of MWCNTs with 800 mg·L^-1 and nano-SiO₂ with1500 mg·L^-1 had the best effect on the improvement of seed germination index,and the promoting effect of nano-SiO₂ was slightly higher than that of MWCNTs.MWCNTs and nano-SiO₂ can improve the activities of amylase in maize grain,COX and AOX in seed embryo and key enzymes of glycolysis,so as to accelerate the hydrolysis of carbohydrates such as starch,provide energy and material basis for seed germination,improve seed vitality and promote seed germination.Lower concentrations of MWCNTs and nano-SiO₂ can promote maize seed germination,radicle and germ growth,while higher concentrations of MWCNTs and nano-SiO₂ can inhibit it.（2）MWCNTs and nano-SiO₂ can promote the growth of maize seedlings,and promote the plant height,root length,dry and fresh weight of seedlings,root shoot ratio and so on.The dry and fresh weight of maize seedlings increased significantly,the ability to accumulate dry matter increased,the relative water content of leaves increased,the electrical conductivity of leaves decreased,the stability of cell membrane improved,and the water metabolism ability of maize seedlings increased.The promoting effect increased first and then decreased with the increase of treatment concentration.The treatment of MWCNTs with 800 mg·L^-1 and nano SiO₂ with 1500 mg·L^-1 had the best effect on seedling growth.（3）MWCNTs and nano-SiO₂ can promote the development of root morphology,increase root length,root surface area,average diameter,root volume and total root tip number,and improve root activity,so as to improve the absorption capacity of roots to water and nutrition.Among them,the treatment of MWCNTs with 800 mg·L^-1 and nano-SiO₂ with 1500 mg·L^-1 had the best effect on seedling growth,while the high concentration hindered the absorption of water and nutrition by seedling roots and affected root development.（4）After MWCNTs and nano-SiO₂ treatment,compared with the control,the contents of O₂·^-and H₂O₂ decreased,and the damage of reactive oxygen free radicals to cells decreased.MWCNTs and nano-SiO₂ can promote the clearance of reactive oxygen species and maintain the complete structure of cells,so as to slow down plant aging.The promoting effect of MWCNTs increased first and then decreased with the increase of treatment concentration.The promoting effect of MWCNTs treated with 800 mg·L^-1 and nano SiO₂ treated with 1500 mg·L^-1 had the best effect.（5）After treatment with MWCNTs and nano-SiO₂,the activities of key photosynthesis enzymes PEPC、Rubisco、NADP-ME、NADP-MDH and PPDK of maize seedlings increased,which promoted the opening of stomata,improved the fixation efficiency of CO₂,improved the photosynthetic process of maize plants and promoted plant growth.Among them,the promoting effect of maize was more significant under the treatment of lower concentration MWCNTs and nano-SiO₂,and the high concentration showed toxic effect.The promoting effect was the best when the concentration of MWCNTs was 800 mg·L^-1 and the concentration of nano-SiO₂ was 1500 mg·L^-1.（6）MWCNTs and nano-SiO₂ can increase the activities of enzymes GS,GOGAT,GAD and GDH related to nitrogen metabolism in maize leaves and roots,and increase the content of pyruvate,so as to promote the synthesis of carbohydrates and the utilization of nitrogen and promote plant growth.At high concentration,it interfered with plant nitrogen metabolism and hinders plant growth.The optimum concentrations of MWCNTs and nano-SiO₂ were 800 mg·L^-1 and 1500 mg·L^-1,respectively.（7）MWCNTs and nano-SiO₂ can regulate the endogenous hormone status of leaves and roots of maize seedlings.The contents of Me JA,IAA,GA and ZR increased,the content of ABA decreased,and the endogenous hormones in the leaves of maize seedlings tended to be in dynamic balance compared with control.MWCNTs and nano-SiO₂ promoted the growth of seedlings by regulating endogenous hormones and improved the ability of seedlings to resist stress.The promoting effect of MWCNTs(0-800mg·L^-1)and nano-SiO₂(0-1500 mg·L^-1)at low concentration was significantly higher than that of control,but it showed a certain inhibitory effect at high concentration.