Effects of mercury concentration on the growth of tobacco seedlings and its physiological mechanism
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Graphical Abstract
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Abstract
【Objective】This study aimed to investigate the effects and physiological mechanisms of different mercury concentration treatments on the growth of tobacco seedlings,providing a theoretical basis for reducing mercury content in tobacco leaves.【Method】Using Zhongyan 100 as the experimental material,a hydroponic experiment was conducted with five mercury concentrations (calculated as Hg2+) at 0,0.5,5,20,and 60 mg/L,0 mg/L treatment was control(CK).The growth,physiological indicators,and root morphology of tobacco seedlings were measured under different treatments,and correlation analysis was conducted on the obtained indicators.【Result】With the increase of mercury con‐centration,the plant leaves showed a yellowing trend,height,stem girth,maximum length of leaf,maximum width of leaf,total root length,root surface area,root volume,root tip number,average root diameter,and main root diameter of tobacco seedlings all exhibited an initial increase followed by a decrease.The maximum width of leaf peaked at 5 mg/L mercury concentration,while all other indicators reached their maximum at the mercury concentration of 0.5 mg/L.The accumulation of dry matter in all parts decreased,while the moisture content increased.The chlorophyll content of to‐bacco seedling leaves decreased with increasing mercury concentration.At a concentration of 60 mg/L,the total chloro‐phyll content was significantly reduced by 58.66%compared to CK (P<0.05,the same below).With the increase of mer‐cury concentration,the activities of superoxide dismutase (SOD),peroxidase (POD),and catalase (CAT) in tobacco seedling leaves gradually decreased.At a concentration of 60 mg/L,they were significantly reduced by 70.31%,58.85%and 68.21%compared to CK,respectively.The contents of malondialdehyde (MDA) and proline increased significantly.The soluble sugar and soluble protein contents first increased and then decreased,all reaching their peak at a concentra‐tion of 20 mg/L.Correlation analysis revealed significant or extremely significant(P<0.01) negative correlations between mercury concentration and the growth indicators of aboveground and root systems,biomass indicators,chlorophyll con‐tent,and antioxidant enzyme activity of tobacco seedlings.MDA content in leaves showed a significant positive correla‐tion with mercury concentration.【Conclusion】Low mercury concentrations inhibits the growth and root morphology of to‐bacco seedlings,while high mercury concentrations promotes the growth and root morphology of tobacco seedlings.A mercury concentration of 0.5 mg/L has a certain promoting effect on the growth of tobacco seedlings.When the mercury concentration is≥5 mg/L,the growth of tobacco seedlings is inhibited,chlorophyll content decreases,and the antioxi‐dant system is severely damaged,which is not conducive to the growth of tobacco seedlings.
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