The release of harmful wastes via different industrial activities is the main cause of heavy metal toxicity. The present study was conducted to assess the effects of heavy metal stress on the plant growth traits, antioxidant enzyme activities, chlorophyll content and proline content of Sesbania sesban with/without the inoculation of heavy-metal-tolerant Bacillus gibsonii and B. xiamenensis. Both PGP strains showed prominent ACC-deaminase, indole acetic acid, exopolysaccharides production and tolerance at different heavy metal concentrations (50–1000 mg/L). Further, in a pot experiment, S. sesban seeds were grown in contaminated and noncontaminated soils. After harvesting, plants were used for the further analysis of growth parameters. The experiment comprised of six different treatments. The effects of heavy metal stress and bacterial inoculation on the plant root length; shoot length; fresh and dry weight; photosynthetic pigments; proline content; antioxidant activity; and absorption of metals were observed at the end of the experiment. The results revealed that industrially contaminated soils distinctly reduced the growth of plants. However, both PGPR strains enhanced the root length up to 105% and 80%. The shoot length was increased by 133% and 75%, and the fresh weight was increased by 121% and 129%. The proline content and antioxidant enzymes posed dual effects on the plants growing in industrially contaminated soil, allowing them to cope with the metal stress, which enhanced the plant growth. The proline content was increased up to 190% and 179% by the inoculation of bacterial strains. Antioxidant enzymes, such as SOD, increased to about 216% and 245%, while POD increased up to 48% and 49%, respectively. The results clearly show that the utilized PGPR strains might be strong candidates to assist S. sesban growth under heavy metal stress conditions. We highly suggest these PGPR strains for further implementation in field experiments.

中文翻译：

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工业污染土壤中 PGPR 介导的田菁植物生长特性和金属提取能力

通过不同的工业活动释放有害废物是重金属中毒的主要原因。本研究旨在评估重金属胁迫对接种/不接种耐重金属吉布森芽孢杆菌和厦门芽孢杆菌的田菁的植物生长性状、抗氧化酶活性、叶绿素含量和脯氨酸含量的影响。两种 PGP 菌株都显示出显着的 ACC-脱氨酶、吲哚乙酸、胞外多糖产生和不同重金属浓度（50-1000 mg/L）的耐受性。此外，在盆栽实验中，S. sesban种子生长在受污染和未受污染的土壤中。收获后，将植物用于生长参数的进一步分析。该实验包括六种不同的处理。重金属胁迫和细菌接种对植物根长的影响；芽长；鲜重和干重；光合色素；脯氨酸含量；抗氧化活性；在实验结束时观察到金属的吸收。结果表明，工业污染的土壤明显减少了植物的生长。然而，两种 PGPR 菌株都将根长提高了 105% 和 80%。芽长分别增加了133%和75%，鲜重分别增加了121%和129%。脯氨酸含量和抗氧化酶对工业污染土壤中生长的植物产生双重影响，使它们能够应对金属压力，从而促进植物生长。通过接种菌株，脯氨酸含量分别增加了190%和179%。抗氧化酶，如 SOD，增加到约 216% 和 245%，而 POD 分别增加到 48% 和 49%。结果清楚地表明，利用的 PGPR 菌株可能是强有力的候选者，以协助S. sesban在重金属胁迫条件下的生长。我们强烈建议这些 PGPR 菌株在现场实验中进一步实施。