八仙花对铅锌的抗性及富集特征

Lead and Zinc Tolerance Mechanisms and Accumulation Characteristics of Hydrangea macrophylla

以选自温室中生长健壮的1年生八仙花(Hydrangea macrophylla)扦插苗、采集自实验基地附近农田表层土壤(0~15 cm)为基材,以硝酸铅溶液(Pb(NO)质量分数为500、1 000、2 000 mg/kg)、七水硫酸锌溶液(ZnSO·7HO质量分数为300、600、1 200 mg/kg)为铅锌胁迫处理剂,试验在西北农林科技大学科研温室进行。将采集的土壤在干燥通风处风干、粉碎、用4 mm筛过筛后,按照试验设计方案,将铅锌胁迫处理剂(单一、协同)均匀喷洒入处理好的基材土壤,然后置于阴凉处30 d,使土壤中的重金属稳定(污染土壤)。将污染土壤加入提前清洗好的花盆中,每盆含有6.0 kg土壤、种植1株1年生八仙花,每个处理3个重复;生长试验持续50 d(2020年11月7日—2020年12月27日)后,收获八仙花植株,测定生长指标、生理指标、光合指标、重金属质量分数及亚细胞分布。应用方差分析法、最小显著差异法,分析八仙花对铅、锌的单一胁迫和协同胁迫的防御机制和富集特征。结果表明:八仙花在重金属胁迫处理时,根系生长受到抑制,与对照相比,根长在质量分数为2 000 mg/kg的硝酸铅胁迫处理时降低了25.1%。此外,八仙花在铅、锌胁迫时生理指标也发生了明显变化。与对照相比,质量分数为2 000 mg/kg的硝酸铅胁迫处理、质量分数为1 200 mg/kg的七水硫酸锌胁迫处理、“质量分数为2 000 mg/kg的硝酸铅+质量分数为1 200 mg/kg的七水硫酸锌”协同胁迫处理,八仙花的丙二醛质量摩尔浓度分别增加85.26、73.65、48.41μmol·g,脯氨酸质量分数分别增加661.06、663.23、402.68μg·g,超氧化物歧化酶(SOD)活性分别增加0.26、0.38、0.32 U·g·h,过氧化物酶(POD)活性分别增加50.27、92.51、85.47 U·g·h,过氧化氢酶(CAT)活性分别增加3.91、0.19、1.20 U·g·h;质量分数为2 000 mg/kg的硝酸铅胁迫处理时类胡萝卜素质量分数减少0.006μg·g,质量分数为1 200 mg/kg的七水硫酸锌胁迫处理、“质量分数为2 000 mg/kg的硝酸铅+质量分数为1 200 mg/kg的七水硫酸锌”协同胁迫处理,类胡萝卜素质量分数分别增加0.008、0.01μg·g;说明高质量分数的重金属胁迫处理时,八仙花体内渗透调节物质和抗氧化酶活性增加,类胡萝卜素质量分数增加,保护光合系统,从而增强八仙花对重金属胁迫的抗性。与对照相比,质量分数为2 000 mg/kg的硝酸铅胁迫处理、质量分数为1 200 mg/kg的七水硫酸锌胁迫处理,八仙花根部积累的铅和锌的质量分数,分别高于地上部54.56、103.09 mg/kg。八仙花重金属亚细胞分布,铅积累在八仙花根部的细胞壁部分(39.45%),而大部分的锌可以穿过细胞壁,进入细胞器和细胞可溶性部分。此外,铅和锌对八仙花的毒害机制不同:铅对八仙花的根系毒害作用大,造成根系的缩短更明显;锌对八仙花光合和抗氧化酶系统毒害作用大,相关的生理指标变化更明显。在铅锌协同胁迫时,与对照相比八仙花对两种金属的吸收量增加,但形态与生理指标的变化程度较单一金属小,说明铅锌协同胁迫对植株的毒害作用减弱。八仙花对铅锌具有一定的抗性,虽然没有达到超富集植物的标准,但具有一定的植物稳定的潜力。

To study the resistance and enrichment characteristics of Hydrangea macrophylla to lead and zinc pollution, a pot experiment was carried out on H. macrophylla with lead(500, 1 000 and 2 000 mg/kg) and zinc(300, 600 and 1 200 mg/kg) single and synergistic treatment for 50 d. The morphology, physiology, photosynthesis, accumulation concentration of heavy metals and subcellular distribution of H. macrophylla under lead and zinc stress were studied. The root growth of H. macrophylla was inhibited under heavy metal treatments, and the root length was reduced by 25.1% under the stress treatment with the content of 2 000 mg/kg of lead nitrate compared to the control. In addition, H. macrophylla also showed significant changes in physiological indicators under lead and zinc stress. Compared with the control, the content of 2 000 mg/kg lead nitrate stress treatment, 1 200 mg/kg of zinc sulfate heptahydrate stress treatment, 2 000 mg/kg of lead nitrate+1 200 mg/kg of zinc sulfate heptahydrate synergistic stress treatment, the malondialdehyde mass molar concentration of H. macrophylla increased by 85.26, 73.65 and 48.41 μmol·g, the proline content increased by 661.06, 663.23 and 402.68 μg·g, and the superoxide dismutase(SOD) activity increased by 0.26, 0.38 and 0.32 U·g·h, the peroxidase(POD) activity increased by 50.27, 92.51 and 85.47 U·g·h, the catalase(CAT) activity increased by 3.91, 0.19 and 1.20 U·g·h, respectively, and carotenoid content decreased by 0.006 μg·g, increased by 0.008, and 0.01 μg·g, respectively, indicating that the content of osmotic adjustment substances and antioxidant enzyme activity in H. macrophylla was increased under high concentration of heavy metal treatment, and the carotenoid content was increased to protect the photosynthetic system, thereby enhancing the H. macrophylla resistance to heavy metals. Compared with the control, the lead concentration of lead and zinc accumulated in H. macrophylla roots was higher than that in aboveground parts by 54.56 and 103.09 mg/kg for lead nitrate stress treatment with mass fraction of 2 000 mg/kg and zinc sulfate stress treatment with mass fraction of 1 200 mg/kg heptahydrate, respectively. At the subcellular level, lead accumulated in the cell wall fraction(39.45%) in the roots of H. macrophylla, while most of the zinc could cross the cell wall and enter the organelles and the soluble fraction of the cells. In addition, the toxic effects of lead and zinc on H. macrophylla were different: lead had a large toxic effect on the root system of H. macrophylla, causing more pronounced root shortening, while zinc had a large toxic effect on the photosynthetic system and antioxidant enzyme system, with more pronounced changes in related physiological indicators. When lead and zinc synergistic stress was applied, the absorption of both metals by H. macrophylla increased compared with the control, but the degree of change in morphological and physiological indicators was less than that of the single metal, indicating that the toxic effect of lead and zinc synergistic stress on H. macrophylla was weakened. Therefore, H. macrophylla had a certain resistance to lead and zinc, although it does not reach the standard of hyperaccumulator, it had certain potential of phytostabilization.