The Mechanism On Nano Silica Against Phytophthora Infestans

Late blight is one of the most serious diseases of potatoes,resulting to more than ten billion dollars lost every year.Nano silica is a kind of widely used nanomaterial but few application reports on Phytophthora infestans.In this work,three kinds of nano silica particles（normal spherical,mesoporous,and virus-like）were synthesized,and characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray powder diffraction method（XRD）,BET method,and Zeta potential measurement.The results showed they have significant differences in surface morphology,size,specific surface area and surface charge,but all were amorphous crystals with electronegativity.The inhibition rates of ordinary,mesoporous and virus-like nano silica against potato P.infestans were 37.41%,81.11%and 6.17%,respectively,indicating that the morphology,size and specific surface area of the nanomaterial would affect its antimicrobial ability.Mesoporous silica(EC₅₀=15.28μg/m L)with the strongest P.infestans bioactivity was selected for further antimicrobial mechanism study.Silica has been observed to deform the mycelium and sporangium,and promote the reproductive growth（when 12.5μg/m L silica added,the sporulation time was about 120 h earlier）.The ultrastructure of P.infestans observed by SEM,TEM and laser confocal microscope（CLSM）,have shown the mycelium to be damaged and the deformity was obvious.Agarose gel electrophoresis revealed that after exposure to mesoporous silica,the genetic material of mycelium was leaked and DNA was damaged.With the increasing of mesoporous silica concentration,the activity of SOD and the content of MDA was first increased and then later decreased,indicating the oxidative stress reaction of P.infestans.Further measurement of dissolved oxygen content demonstrated the suppression of the metabolic intensity of intracellular respiration and ROS probe DCFH-DA confirmed the generation of ROS in vivo,while EPR combined with spin capture technology determined the type of free radicals generated.Based on these results,the P.infestans is sensitive to mesoporous silica.Moreover,under mesoporous silica stress the P.infestans produce hydroxyl radicals（·OH）,super oxide free radical(·O^2-)and singlet oxygen（¹O₂）.Those radicals lead to oxidative stress response,which cause the DNA damage and intracellular MDA content to increased.MDA then result in the membrane structure breakage,inclusions leaking,respiration intensity reducing,physiological activity suppressed and even may lead to cell death.