Effects Of Nanopriming With Iron Oxide (Ⅲ) On Seed Germination And Drought Resistance Of Switchgrass (Panicum Virgatum)

Switchgrass（Panicum virgatum cv.Alamo L.）belongs to the perennial C4 herb of Panicum in Poaceae.It has the advantages of wide adaptability,drought tolerance and barren resistance.However,the seeds stored for a long time have some problems,such as decreased seed vigor,low germination rate and poor plant stress resistance.Nano iron oxide（n-Fe₂O₃）is a kind of iron formed by superposition of iron atoms one by one according to the nano level.Appropriate content of iron in n-Fe₂O₃ is beneficial for seed germination,seedling growth and various stress resistance.Seed nano-priming technology can be used to improve seed germination rate,promote seedling growth and enhance the ability of resistance to stress,but mainly in food crops,economic crops and crops.However,the response of the seedlings to drought stress caused by iron nanoparticles in switchgrass is rarely reported.In this study,based on the previous studies,switchgrass seeds（Alamo）are used as the materials.We used0,10,20,50,100,200,300,400 and 500 mg/L nano-iron priming and seed soaking for the following experimental design.The effects of nano iron on seed germination characteristics,amylase activity and chlorophyll content of seedlings were studied.The physiological and biochemical changes of photosynthetic characteristics,osmotic adjustment substances and antioxidant system of switchgrass seedlings under drought stress were studied by hydroponics method.Switchgrass seeds germination energy（GE）,germination rate（GR）,germination index（GI）,average germination rate,relative germination frequency,amylase activity and element content were measured in this study.In addition,we determined the effects of nano-iron priming on chlorophyll,photosynthetic characteristics,chlorophyll fluorescence,proline and malondialdehyde content and antioxidant enzyme systems（SOD,CAT,POD）in switchgrass seedlings by hydroponics under drought stress The main results are as follows:（1）Nano-Fe₂O₃ promotes seed germination and seedling growth of switchgrass.Nano-Fe₂O₃ priming and seed soaking treatments have no significant difference in the effects of switchgrass seed germination characteristics and seedling growth.Seed soaking speeds up the germination rate of seeds,but initiation promoted the growth of seedlings more than soaking.Under the treatment of seed soaking,it can significantly increase the speed of seed germination,and has little effect on the growth of seedlings.The optimal concentration for promoting switchgrass seed germination and seedling growth is 50 mg/L.Under the priming treatment,it has little effect on the germination rate of seeds.When the concentration is 10 mg/L or 300mg/L,it can significantly improve seed vigor and promote the growth of seedlings.The best concentration to promote the increase of chlorophyll content is 200 mg/L and priming has a linear correlation between the concentration and chlorophyll content.The result of combining seed soaking and initiation treatment,switchgrass seed germination and growth-related indexes generally didn’t show a significant decline after seed soaking and priming treatment,indicating that the nano-iron oxide suspension doesn’t have a negative effect on the germination characteristics of switchgrass seeds.Therefore,nano-iron oxide can be used as a seed pretreatment agent to improve the vigor of switchgrass seeds.（2）Nano-Fe₂O₃could improve the photosynthetic characteristics of switchgrass seedlings under drought stress.Drought stress led to a decrease in chlorophyll content.Under 10%and 20%PEG-6000 treatment,the chlorophyll of switchgrass seedlings increased by 46.7%,76.4%and 58.7%,75.5%in the pretreatment of nano-iron oxide priming.PEG-6000reduced the net photosynthetic rate（P_n）,stomatal conductance（G_s）,intercellular CO₂concentration（C_i）,and transpiration rate（T_r）.The F_m,F_v/F₀,F_v/F_m,F_v′/F_m′,q P andΦ_PSⅡof switchgrass seedlings decreased,while F₀ and NPQ increased,indicated that drought stress can inhibit PSⅡof original light energy conversion efficiency and PSⅡpotential activity of switchgrass seedlings,and enhance the non-radiative energy dissipation of PSⅡ.Under the drought stress,compared with CK,10%PEG-6000 stress,the 300 mg/L triggered F0 of Liuzhi added 64.2%,while NPQ decreased by 400 mg/L and 500 mg/L concentration,and the rest of treatment not large,while 20%PEG-6000 stress,200 mg/L initiated concentration of F₀increased by 54.5%（P<0.05）,200 mg/L initiated concentration NPQ increased by 21.6%.Moreover,both 200 mg/L and 300 mg/L nano-iron oxide priming has better defense ability against drought stress for the photosynthetic system of switchgrass seedlings.（3）Nano-Fe₂O₃ priming can alleviate the effects of drought stress on the growth and physiological characteristics of switchgrass seedlings.To a certain extent,drought stress promoted the growth of switchgrass root and inhibited the growth of aboveground part,under non-stress teatment,the plant height increased by 23.6%caused by 300 mg/L,and root length increased by 26.6%at 200 mg/L（P<0.05）.Under 10%PEG-6000 stress,plant height increased by 100 mg/L nano-Fe₂O₃ priming.Under 20%PEG-6000 stress,the root and shoot length triggered by 50 mg/L increased by 9.48%and 13.4%compared to drought treatment alone,respectively.Therefore,under normal growth conditions,300 mg/L nano-Fe₂O₃ priming plays an important role in improving seedlings growth,while 100 and 50 mg/L nano-Fe₂O₃priming showed an positive effects on drought tolerance in switchgrass seedlings.With the increased of PEG-6000 concentration,the leaf area,leaf circumference,leaf length,and leaf width of seedlings decreased.However,when the concentration of n-Fe₂O₃ was 200mg/L,the correlation index decreased to the lowest,which could better alleviate the negative effects of drought on its growth.（4）Nano-Fe₂O₃ initiation can alleviate the damage of antioxidant enzyme system in switchgrass seedlings under drought stress.With the increase of malondialdehyde and proline content,200 mg/L n-Fe₂O₃ was the best initiator concentration,followed by 100 mg/L and 300mg/L.The activities of CAT,POD and SOD protective enzymes increased first and then ecreased with the drought concentration increased.No drought treatment,the CAT reduction with the PEG-6000 concentration is increased,and the CAT activity treated with 50～300 mg/L concentration of nano-Fe₂O₃ is increased,and the optimum concentration is 200 mg/L under 10%PEG-6000 treatment,20%PEG-6000 treatment under the optimum concentration of 100 mg/L;SOD activity of switchgrass seedlings caused a significant level of 200mg/L under 20%drought stress,and decreased when it was higher than200 mg/L;POD has an overall increase in drought stress,and the increase in POD content increases in 10%PEG stress,and 20%PEG has a decrease in PEG at 100～300 mg/L concentration,the change is not large,and in general mild under dry,water caused and 50mg/L can effectively improve antioxidant activity,and after the degree of drought increases,200 mg/L nano-Fe₂O₃ causes better and promotes an increase in antioxidant enzyme.Compared with CK,10%PEG-6000 stress caused the largest increase in POD content and decreased under 20%PEG-6000 stress;Under mild drought,water priming and 50 mg/L nano-Fe₂O₃ can effectively enhance antioxidant enzyme activity,As the drought degree increases,200 mg/L nano-Fe₂O₃ trigger can better promote the increase of antioxidant enzyme activity,however,100～300 mg/L nano-Fe₂O₃ treatment resulted in little change in antioxidant enzyme activity.Taken together,300 mg/L nano-Fe₂O₃ could effectively improve the seed vigor and promote the seedling growth of panicum virgatum under normal growth conditions,200 mg/L nano-Fe₂O₃ priming could induce the activitives of antioxidant enzymes,reduce the oxidative damage of the seedlings and maintain higher photosynthetic efficiency,thus alleviating the damage caused by drought stress.