Inoculation of Paraburkholderia sp. GD17 improves seedling growth and tolerance to Cadmium in Chinese cabbage

This study provided evidence at the first time showing that root inoculation with the plant growth-promoting rhizobacteria Paraburkholderia sp. GD17 improved the growth and tolerance to Cd stress in Chinese cabbage seedlings. Under normal conditions, the shoot fresh and dry weight of GD17-inoculated 30-day-old plants increased by about 29 % and 33 %, and their root fresh and dry weight by 104 % and 67 %, respectively, compared with their non-inoculated partners. The GD17-mediated growth promotion could be attributed to its facilitating influence on plant acquisition of nutrient elements and photosynthetic efficiency, and decreasing abscisic acid production. Under Cd stress, an effective alleviation in Cd-induced growth inhibition was observed in GD17 plants relative to non-inoculated control, suggesting that the root inoculation with GD17 played a systemic protective role. The Cd concentration in plant aerial tissues was comparable between GD17 plants and non-inoculated ones, but it was substantially decreased in GD17 plant roots. In response to Cd, GD17-inoculated plants generally showed a stronger ability to absorb and transport nutrient elements to shoots. The GD17-conferred plant tolerance to Cd was also associated with an increased antioxidative capacity companied by declined oxidative damage, optimal levels of phytohormones, increased flavonoid synthesis as indicated by significantly upregulated expression of related genes and activity of phenylalanine ammonia-lyase. Additionally, root inoculation with GD17 effectively mitigated the Cd-induced decline in photosynthetic efficiency. Collectively, this study firstly showed that GD17-conferred growth-promotion and Cd-tolerance in Chinese cabbage was correlated with multiple regulatory roles in plant metabolism, which, in most cases, was involved in the regulation at the transcription levels of relevant genes.