Effect And Mechanism Of Silicon On Alleviating Tobacco Seedling Cadmium Stress

With the development of industry and the destruction of nature by human activities,cadmium pollution has been recognized as a major threat to arable land,water resources and the food chain.Low concentrations of cadmium can also produce high toxicity in the soil and pose a threat of toxicity after being absorbed by crops.Cadmium stress induced exhibited metabolic disorders,growth inhibition,low biomass production,and oxidative damage,eventually lead to significant decline in production quality.Silicon?Si?accounts for approximately 28%of the earth's crust and 0.03%of the biosphere.And silicon application has been proven to alleviate cadmium poisoning in a large number of silicon-accumulating crops such as rice,corn and Sorghum,however,less research has been done on materials such as tobacco with low silicon accumulation.In order to explore the effect and mechanism of adding silicon element to alleviate cadmium stress in tobacco seedling,K326 was selected as material and cultivated in hydroponics solution in this experiment.The experiment include four treatments for instance Control,Si,Cd,Cd+Si.The growth parameters,photosynthetic indicators,and various stress-resistant enzymes activity and root water-uptake related substances were measured.The specific research results are as follows:?1?Silicon application can alleviate the effects of cadmium stress on the biomass of tobacco seedling.For example,compared with single cadmium stress,the dry and fresh weight of the root system with silicon increased by 147%and 33.3%respectively;leaf fresh weight and dry weight in silicon was 60.59%,37.66%higher than cadmium stress;In terms of stem dry weight and fresh weight,compared with the treatment with the addition of silicon and single cadmium,the weight increased by 290%and 79.13%,respectively.Adding silicon to the nutrient solution can also alleviate the root growth inhibition by cadmium stress.Compared with single cadmium stress,the total length of single root,average diameter of single root and number of root tips increased by 54.62%,45.58%,and 40.75%after adding silicon treatment;In terms of root surface area and root volume,the addition of silicon to the nutrient solution increased 48.45%and 125.93%compared with pure cadmium stress,respectively.?2?Silicon application can reduce cadmium content in shoots and roots.The content of cadmium in shoots and roots of tobacco exposed to cadmium were significantly increased.However,addition of silicon to the nutrient solution could significantly reduce the cadmium content in tobacco roots and shoots dry and fresh mass.Compared with single cadmium stress,the cadmium content in roots dry and fresh samples decreased by 39.97%and 66%,respectively.The cadmium content in shoots dry and fresh mass decreased by 20%and 31.01%,respectively.In addition,it was valuable to note that the cadmium content under fresh condition was much lower than dry condition,which indicates that the application of silicon significantly increases the water content.This may be an important mechanism for silicon to enhance the cadmium toxicity resistance of tobacco seedlings.?3?Application of silicon can alleviate the effects of cadmium on photosynthetic parameters and photosynthetic pigments of tobacco seedling.Cadmium stress caused different degrees of damage to the photosynthetic index of tobacco.The addition of silicon in the nutrient solution reduced the damage of photosynthetic system by cadmium.Specifically,Pn,Tr,and Gs under cadmium poisoning in tobacco seedling supplemented with silicon were increased by62.84%,49.19%,and 38.76%compared with single cadmium stress,respectively,but Compared with the single cadmium stress,the Ci value in the tobacco seedling poisoned by cadmium addition decreased by 25.09%.The application of silicon in the nutrient solution can alleviate the loss of photosynthetic pigment content caused by cadmium stress.Specifically,compared to cadmium application,the content of Chla,Chlb,and Car in tobacco seedling with silicon added stress increased by 56.87%,28.22%,and 16.44%,respectively,and the overall increase in chloroplast pigment content was very significant,Reached 39.06%.?4?Effects of silicon application on the antioxidant system of tobacco seedling under cadmium toxicity.Compared with single cadmium stress,the SOD,APX,GR and POD activities of tobacco seedling treated with silicon were significantly enhanced after cadmium stress,which increased by 20.33%,20.27%,42.08%,and 35.54%,respectively,for CAT activity,there was no significant difference between cadmium+silicon and single cadmium stress.In terms of MDA content,silicon application could significantly reduce the MDA content of the leaves,which was only 45.06%of the cadmium stress alone.?5?Silicon increases the content of osmotic adjustment substances in the root system,promotes water absorption in the root system,and increases the moisture content of tobacco seedling.Under cadmium stress,the RWC of silicon-treated leaves was significantly higher by9.1%than that of non-silicon treatment,which led to a decrease in the Cd²⁺concentration in the tissues of silicon-treated leaves,thereby alleviating cadmium stress.Silicon promotes root water absorption is an important mechanism for alleviating plant resistance to abiotic stress.The accumulation of osmotic substances in the root system is the driving force to promote water absorption in the root system.Therefore,the osmotic potential regulating substances related to water absorption have been studied and determined,the results showed that proline,soluble sugar,and soluble protein in tobacco roots were increased by 150%,14.40%,and 5.81%after silicon treatment.Taken as a whole,adding silicon can reduce the accumulation of cadmium content in tobacco seedling,increase the moisture content in leaves,increase the content of osmotic adjustment substances in the root system,protect the photosynthetic system of tobacco leaves,and increase the anti-stress enzyme activity to alleviate the inhibitory effect of cadmium on the growth of tobacco seedling.The results of this study will provide new ideas for the analysis of silicon to alleviate cadmium toxicity in tobacco seedling.