Effects of mercury concentration on the growth of tobacco seedlings and its physiological mechanism

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 Hg ²⁺) 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 concentration, 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 tobacco seedling leaves decreased with increasing mercury concentration. At a concentration of 60 mg/L, the total chlorophyll content was significantly reduced by 58.66% compared to CK ( P<0.05, the same below). With the increase of mercury 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 concentration 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 content, and antioxidant enzyme activity of tobacco seedlings. MDA content in leaves showed a significant positive correlation with mercury concentration.

[Conclusion] Low mercury concentrations inhibits the growth and root morphology of tobacco 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 antioxidant system is severely damaged, which is not conducive to the growth of tobacco seedlings.

Abstract

摘要：【目的】 研究不同汞浓度处理对烟草幼苗生长的影响及其生理机制, 为降低烟叶汞含量提供理论依据。 【方法】以中烟100为试验材料, 采用水培试验, 设5种汞浓度 (以Hg ²⁺计)处理, 分别为0、0.5、5、20、和60 mg/L, 其中0 mg/L 处理为对照 (CK) 。测定不同处理下烟草幼苗的各项生长生理指标及根系形态, 并对各项指标进行相关分析。 【结果】 随着汞浓度升高, 烟草幼苗的叶片色泽呈发黄趋势, 株高、茎围、最大叶长、最大叶宽、总根长、根表面积、根体积、根尖 数、平均根直径和主根直径均呈先增加后减少的变化趋势, 最大叶宽在5 mg/L浓度下最大, 其余指标均在0.5 mg/L浓 度下最大, 各部位干物质积累量下降, 含水率升高。烟草幼苗叶片的叶绿素含量随汞浓度升高而降低, 60 mg/L浓度 下总叶绿素含量较CK显著降低58.66% ( P<0.05, 下同) 。随着汞浓度升高, 烟草幼苗叶片的超氧化物歧化酶 (SOD) 、 过氧化物酶 (POD) 和过氧化氢酶 (CAT) 活性逐渐下降, 60 mg/L浓度下分别较CK显著降低70.31%、58.85%和 68.21%, 丙二醛 (MDA) 和脯氨酸含量显著升高, 可溶性糖和可溶性蛋白含量先升高后降低, 均在20 mg/L浓度下最 高。相关分析结果表明, 烟草幼苗地上部和根系生长指标、生物量指标、叶绿素含量和抗氧化酶活性均与汞浓度呈显 著或极显著 ( P<0.01) 负相关, 叶片MDA含量与汞浓度呈显著正相关。 【结论】不同汞浓度处理对烟草幼苗生长和根系 形态表现为低促高抑, 0.5 mg/L汞浓度对烟草幼苗生长有一定促进作用, 当汞浓度≥5 mg/L时烟草幼苗生长受到抑 制, 叶绿素含量降低, 抗氧化系统受到严重破坏, 不利于烟草幼苗生长。