Physiological Mechanism Of Silicon-induced Tobacco Seedlings Resisting Drought And Cadmium Stress

To explore exogenous silicon processing for tobacco seedling drought stress and mitigation effect of cadmium poisoning,the nutrient solution hydroponics,tobacco varieties"yuyan10" as test materials,the use of different concentrations of exogenous silicon(0,0.5,1.0,tendency/L)to drought stress(10%PEG,20%PEG)of 100 mmol/L exogenous silicon tobacco seedling biomass under cadmium stress,cadmium accumulation,antioxidant enzyme activity,chlorophyll content and photosynthetic characteristics such as growth,leaf photosynthesis and physiological indicators.The main results are as follows1.Drought stress seriously inhibited the growth of tobacco seedlings.With the increase of drought stress level,growth indexes such as plant height,maximum leaf area,root volume and dry matter mass of tobacco seedlings without exogenous silicon treatment showed a trend of gradual decrease.At all drought stress levels,different concentrations of silicon promoted the growth of tobacco seedlings under stress.Especially on the indexes of plant height,leaf area and root volume of tobacco seedlings treated with drought stress,the inhibitory effect of 1.0 mmol/L exogenous silicon treatment on alleviating drought stress on tobacco seedling growth was better than that of 0.5 mmol/L exogenous silicon treatment.2.Water content and film stability coefficient of tobacco seedling leaves were reduced under drought stress,and the effects of drought stress on film stability coefficient and film water content of tobacco seedling leaves were improved after exogenous silicon treatment.Although the leaf film stability coefficient of tobacco seedlings treated with different concentrations of exogenous silicon was different in the absence of drought stress,the difference was not significant.When treated with 10%PEG and 20%PEG under drought stress,the leaf moisture content and membrane stability coefficient of tobacco seedlings were improved to different degrees after treated with 0.5 mmol/L exogenous silicon and 1.0 mmol/L exogenous silicon,compared with that without exogenous silicon.In terms of the effect of applying different concentrations of exogenous silicon,the improvement of water content and membrane stability coefficient of tobacco seedling leaves under 1.0 mmol/L Si treatment was better than that under 0.5 mmol/L Si treatment.At the same time,drought stress led to the imbalance of osmotic regulatory substances in tobacco seedling leaves,and the content of proline and soluble sugar was effectively increased after exogenous silicon treatment,and the effect of 1.0 mmol/L Si treatment was the best.3.Drought stress led to peroxidative stress in tobacco seedlings,and the more severe the peroxidative stress was,the more severe the stress was.In terms of MDA content and antioxidant enzyme activity indexes,MDA content gradually increased,while SOD,POD and CAT showed a trend of first increasing and then decreasing.Antioxidant enzyme activity was highest under 10%PEG treatment,and lowest under CK treatment.The exogenous silicon treatment effectively alleviated the peroxidative damage caused by drought stress,in which MDA content was significantly reduced,while antioxidant enzyme activities such as SOD,POD and CAT were significantly increased.In addition,the alleviating effect of 1.0 mmol/L exogenous silicon treatment on the peroxidation stress of tobacco seedling leaves caused by drought stress was better than that of 0.5 mmol/L exogenous silicon treatment.4.The content of chlorophyll a,chlorophyll b,chlorophyll a+b and carotenoids in tobacco seedlings decreased under drought stress.With the increase of drought stress level,the net photosynthetic rate,transpiration rate and stomatal conductance of tobacco seedling leaves without silicon treatment showed a trend of gradual decrease,while the intercellular CO2 concentration increased gradually.The net photosynthetic rate,transpiration rate and stomatal conductance of tobacco seedling leaves were significantly increased by exogenous silicon treatment at different concentrations,and the intercellular CO2 concentration was significantly reduced.Moreover,the photosynthetic characteristics of tobacco seedling leaves under drought stress were significantly improved by 1.0 mmol/L exogenous silicon treatment compared with 0.5 mmol/L exogenous silicon treatment.5.Under the stress of cadmium,the biomass of roots,stems and leaves of tobacco seedlings was significantly reduced by 74.77%,73.63%and 61.70%,while the accumulation of cadmium in various parts was increased by 76.50 times,71.77 times and 142.01 times.Compared with Cd treatment alone,the biomass of roots,stems and leaves of tobacco seedlings under Cd+Si treatment were increased by 57.69%,29.41%and 37.21%,respectively,and there were significant differences in each index between the two treatments.6.Under the stress of cadmium,plants undergo peroxidative stress reaction.MDA content,SOD,POD and CAT enzyme activities are all improved to varying degrees,and the cytoplasmic membrane is damaged to some extent.Compared with Cd treatment alone,Cd+Si treatment reduced MDA content by 13.69%,SOD enzyme activity by 29.47%,POD enzyme activity by 8.61%,and CAT enzyme activity by 11.15%,respectively.All indexes of the two treatments were significantly different.7.Photosynthetic pigment content in tobacco seedling leaves was significantly reduced under the stress of cadmium,which was manifested as a decrease of 39.94%in chlorophyll a content,a decrease of 47.01%in chlorophyll b content,and a decrease of 20.69%in carotenoid content.Exogenous silicon can improve tobacco seedlings under cadmium stress varying degrees of leaf photosynthetic pigment content,compared with the single Cd treatment,Cd+Si processing different levels to improve the tobacco seedlings under Cd treatment,leaf photosynthetic pigment content of chlorophyll content significantly increased by 60.35%and chlorophyll b content increased by 6.09%,but no significant differences between treatment),carotenoid content significantly increased by 44.93%;Cadmium stress significantly reduced the photosynthetic capacity of tobacco seedling leaves,and the net photosynthetic rate,stomatal conductance and transpiration rate were significantly reduced by 81.77%,81.57%and 88.89%,respectively,while the intercellular C02 concentration was increased by 2.48%.Compared with Cd treatment alone,the net photosynthetic rate,stomatal conductance and transpiration rate of tobacco seedling leaves under Cd+Si treatment were significantly increased by 173.61%,but the difference was not significant,and the intercellular C02 concentration was significantly reduced by 33.61%.