Toxicological effects of Cr<sup>6+</sup> on <i>Potamogeton crispus</i> L. under different pH values

Abstract

对Cr⁶⁺胁迫条件下不同pH处理对菹草无菌苗元素、光合色素、活性氧、丙二醛、抗氧化酶、脯氨酸(Pro)及多胺(PAs)含量的影响进行研究,以探讨不同pH处理影响水生植物Cr⁶⁺毒害效应的机制.结果表明:(1)偏酸性pH处理加剧菹草对铬的蓄积,而pH为7.0时Cr⁶⁺胁迫所造成的矿质元素失衡有所减弱;(2)Cr⁶⁺胁迫下pH为6.0~8.0的处理延缓了菹草的失绿症状,促进了光合色素的合成;(3)Cr⁶⁺胁迫下菹草超氧化物歧化酶、过氧化氢酶的活性在pH为6.0和7.0的处理组诱导程度最小;(4)Cr⁶⁺胁迫下pH为6.0和7.0处理的菹草Pro含量显著提高;(5)pH为4.0和5.0的处理使腐胺(Put)含量显著提高,而pH为6.0和7.0的处理则促进亚精胺(Spd)含量及游离态(Spd+Spm)/Put比值上升,精胺(Spm)含量总体趋势为随pH值升高而逐步上升,仅在pH为4.0和5.0的处理组中低于Cr⁶⁺胁迫对照组.因此,pH条件可影响菹草对铬及营养元素的积累,抗氧化酶、Pro、PAs代谢等生理生化过程,导致铬毒性效应差异.在pH为6.0~7.0的范围内,菹草能调节抗氧化酶系统,较有效地清除体内活性氧,提高机体中Pro、PAs含量及游离态(Spd+Spm)/Put比值,减轻膜系统脂质过氧化,维持机体内矿质元素平衡,致使毒性效应达到最小程度.;Sterile seedlings of Potamogeton crispus were cultured by tissue culture technique which was used as experimental material. In this study, we investigated contents of element, photosynthetic pigments, reactive oxygen species(ROS), malondialdehyde (MDA) and proline(Pro), polyamines(PAs) as well as activities of antioxidant enzymes in Cr⁶⁺-treated P. crispus under different pH values so as to approach the physiological and biochemical mechanisms of pH value in affecting Cr⁶⁺ toxicity of aquatic plants. The results indicated that, (1) Acidic conditions enhanced the accumulation of Cr while pH 7.0 treatment helped P. crispus maintain the balance of nutrient elements; (2) pH 6.0, 7.0 and 8.0 treatments could retard the chlorosis and promote the biosynthesis of photosynthetic pigments; (3) Contents of ROS and MDA increased when the pH was 4.0, 5.0 and 9.0. Activities of superoxide dismutase and catalase were improved when the pH value was 4.0 and 5.0; However, activity of peroxides decreased with the increase of pH value; (4) In response to Cr⁶⁺ stress, plants showed sharp increase in proine content when the pH was 6.0 and 7.0; (5) An improved level of putrescine(Put) was noted in pH 4.0 and 5.0 treatments while spermidine(Spd) and free (Spd + Spm)/Put ratio increased in pH 6.0 and 7.0 treatments; For spermine(Spm) content, it generally increased with pH value and it was lower of the pH 4.0 and 5.0 treatments than that of the control group. Our results demonstrated that resistance of P. crispus to Cr⁶⁺ stress could be enhanced by reducing the excessive accumulation of Cr, promoting photosynthetic pigments, removing ROS efficiently, maintaining the balance of nutrient elements and keeping high levels of Pro, PAs as well as free (Spd + Spm)/Put ratio when pH value was within the range of 6.0-7.0.