Effect Of Nano-Cu（OH）₂ On Seed Germination And Seeding Growth Of Lettuce

Nanopesticide is one of the research hotspots,due to the extensive application of nanotechnology in agriculture.Accordingly,copper-based nano-pesticides have been widely employed to prevent plants from diseases caused by various fungi and bacteria.Currently,many researches focused on the physicochemical,antimicrobial and antifungal properties of nanopesticides,whereas the adverse effects of copper-based nanopesticides on plant physiology is still lack of investigation.Therefore,the impact of nano copper hydroxide（nano-Cu（OH）₂）on lettuce（Lactuca sativa L.）seed germination and seedling growth were considered in this study.The Cu uptake and transport in lettuce were determined under different exposure concentrations of nano-Cu（OH）₂;the chlorophyll amounts in lettuce affected by nano-Cu（OH）₂ were analyzed;enzyme activities and malondialdehyde（MDA）contents in lettuce that modified by nano-Cu（OH）₂ were also measured.The results were exhibited as follows:1.The germination potential,germination rate,bud length,fresh weight,chlorophyll and enzyme activities of lettuce seeds affected by nano-Cu（OH）₂ and Cu²⁺were investigated.The results showed that root length and vigor index of seed lettuce were significantly inhibited（p<0.01）by 10 mg/L of Cu(nano-Cu（OH）₂ and Cu²⁺)as compared to blank group.The ground parts of lettuce were hardly affected by nano-Cu（OH）₂ or Cu²⁺during the 7 d exposure period（p>0.05）,and non-significantly affected chlorophyll content in lettuce（p>0.05）.However,compared with the blank group,10 mg/L nano-Cu（OH）₂ and Cu²⁺exposure for 7 d resulted the contents of malondialdehyde（MDA）in underground part（root）of lettuce were increased significantly（p<0.05）,indicating the hazardous effects on underground part of lettuce.Therefore,under nano-Cu（OH）₂ and Cu²⁺stress,the underground part of lettuce could prevent the oxidative damage by regulating the activities of superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）in vivo.2.The effects of nano-Cu（OH）₂ and Cu²⁺on plant height,root length and fresh weight of lettuce were investigated,and the effects of nano-Cu（OH）₂ on chlorophyll,enzyme activities and copper ion content in lettuce were further analyzed.The results showed that during the foliar application of nano-Cu（OH）₂,Cu was dominatively accumulated in the target organs（old leaves）of lettuce,which resulted in greenness loss and yellow-turning of old leaves.Meanwhile,the Cu can transfer from in old leaves to new leaves（p<0.05）and root（p>0.05）.During the 14～28 d nano-Cu（OH）₂ exposure,nano-Cu（OH）₂ stress caused irreversible damage to lettuce,reflected by the drying,yellow-shedding and reduction of chlorophyll content on the old leaves of lettuce.Although the old leaves shed from the lettuce and resulted to block the further accumulation of Cu in the lettuce,the Cu in old leaves could continually transfer to new leaves and roots of lettuce.During the whole 28 d nano-Cu（OH）₂exposure,lettuce could mediate the content of superoxide dismutase（SOD）and peroxidase（POD）to resist the hazardous damage caused by Cu stress.In summary,nano-Cu（OH）₂ exposure can stimulate the growth of lettuce at low concentration（1 mg/L）and inhibit the growth of lettuce at high concentration（10 mg/L）.The main toxic mechanisms of nano-Cu（OH）₂ on lettuce were derived from resealed Cu ions.Moreover,under external stress,the capacity of antioxidant damage of lettuce plants was higher than the growth and development of lettuce seeds in the early stage.Therefore,the effects of nano-Cu（OH）₂ on ecological environment and human health safety should be seriously considered during its risk assessments.