Effect of Cd and Exogenous NO on the Physiological Response, Rhizosphere Soil Enzyme Activity, and Bacterial Community of WT and Transgenic SmZIP8 Tobacco

The effects of Cd stress and exogenous nitric oxide (NO) on Cd accumulation, Cd translocation, physiological biochemical response, rhizosphere soil enzyme activities, and soil bacterial communities were investigated. Wild-type (WT) and SmZIP8 -expressed tobaccos were selected as objects. Conventional physiological and biochemical methods were used for determining the physiological biochemical indicators and soil enzyme activities. 16S rRNA high-throughput sequencing was performed for soil bacterial community determination. Cd stress inhibited the growth and physiological parameters of WT and SmZIP8 -expressed tobaccos. Exogenous NO reduced Cd absorption and accumulation, but promoted plant growth/biomass by advancing trance element utilization, increasing antioxidant enzyme activities, and enhancing photosynthesis. The phytoremediation efficiency was not decreased after NO application based on Cd amount per plant. Rhizosphere soil urease (URE), sucrase (SUC), catalase (CAT), Cd stress, and exogenous NO were the principal factors influencing the microbial communities, although plant genotype also influenced bacterial communities. The bacterial diversity indexes (including richness (Chao), evenness (ACE), and diversity (Simpson and Shannon)) were inhibited by Cd stress, and the inhibition was alleviated after NO application. The two most abundant bacterial phyla were Proteobacteria and Chloroflexi . The relative abundance of Proteobacteria , Gemmatimonadetes , and Bacteroidetes increased to varying degree, but Chloroflexi , Actinobacteria , and Acidobacteria showed a decreased abundance after Cd stress compared to the control, implying that Cd-tolerant bacteria participated in Cd activation in rhizosphere to promote Cd absorption and accumulation. The study enriched our knowledge of exogenous substances’ utilization to alleviate Cd toxicity and rhizosphere bacterial communities’ response to Cd stress.