Ecotoxicological Effects of Cadmium on Physiochemical,Ultrastructural,and Transcriptomic Profiling in Rheum officinale

Heavy metal accumulation causes huge environmental problems,particularly in agricultural ecosystems which have deteriorative effects on the yield and quality of crops. Cadmium (Cd) effects have been investigated extensively in food crop; however, Cd induced stress on Rheum officinale Baill. is still unclear. In the present experiment, the effects of Cd were studied in Rheum officinale. Results showed that the application of Cd stress had shown a significant adverse effect on plant growth Biomass and photosynthetic pigment were decreased remarkably. Treatments of Cd cause the accumulation of ROS,lipid peroxidation and Cd content. Moreover, the activities of antioxidant enzymes such as superoxide dismutase(SOD), ascorbate peroxidase(Apx), catalase (CAT), and peroxidase(POD), were decreased. But glutathione reductase(GR) was increased.Additionally, nonenzymatic antioxidants like reduced and oxidized glutathione showed a differential activity pattern in roots and leaves of Rheum officinale . Moreover, cadmium has obvious toxicity to the root tip cells and mesophyll cells of Rheum officinale.Transcriptome analysis revealed 2681(1546 up and 1135 down) genes were differentially expressed in Rheum officinale. GO and KEGG analyses indicate that DEGs were assigned and enriched in different pathways. Plenty of critical Cd-induced DEGs such as Hormones, SODs, PODs, ABCs, ZIPs, HMA and WRKYs and so on were identified. The DEGs involved 11 metal-responsive gene clusters,including plant hormones, antioxidant activities, translocator,osmotic adjustment, metal transport,mineral nutrition,metal cell compartmentalization, chelation of heavy metals, membrane integrity, growth dilution and so on.The results of this study will help to provide a basis for further research on reducing the accumulation of Cd in Rheum officinale and improving the quality of Rheum officinale.