Physiological Responses And Gene Identification Of Sweet Sorghum Under Cadmium Stress

Nowadays a large amount of land is contaminated by heavy metals due to industrial development and human activities. Cadmium(Cd) is one of the most toxic and non-essential heavy metals. Cd can be easily absorbed by plants and accumulated in agricultural products. Many methods and processes of preventing, removing and correcting the negative effects of pollutants released into the environments exist, but their application for this purpose has either been poorly implemented or not at all. Thus, all major research studies ponder on the use of biological factors to deal and repair environment. Phytoremediation is defined as the use of plants to remove pollutants from the environment or to render them harmless. This process is cost effective without creating disturbance to the landscape.Sorghum(Sorghum bicolor L.) is a pro-poor multipurpose crop providing food, feed, fiber and fuel across a range of agro-ecosystems. Sweet sorghum consists of natural variant cultivars of sorghum with abundant sucrose storage in culm and great biomass, and is thereby considered as an ideal feedstock for biofuel production. To preliminarily evaluate its potential for phytoremediation, a number of morphological and physiological characteristics of sorghum were investigated under heavy metal stresses(Cd, Pb, Zn, Cu) in previous studies. Sorghum could not only tolerate high concentrations of heavy metals, but also capture and translocate metal ions to aerial parts. Therefore, despite potential usability of crop plants including sorghum in soil cleanup, the possible risk of introducing heavy metals accumulated in edible parts into food chains must be avoided. Due to non-food usage, sweet sorghum will attract more attention for phytoremediation in heavy-metal contaminated areas. Sweet sorghum will be a competitive candidate species for soil remediation due to its great biomass and strong resistance to adverse environmental conditions. Nevertheless, physiological behaviors and genetic control of sweet sorghum cultivars in response to heavy metal exposures are still poorly understood.The objectives of the present study were:(1) Study effects of Cd on growth and physiology response of sweet sorghum.(2) Identify potential Cd tolerant sweet sorghum genotypes.(3) Determine Cd induced modification of sugar accumulation and translocation along sweet sorghum stem.(4) Gene identification of sweet sorghum under Cd metal stress.In order to meet of these objectives, two sweet sorghum cultivars(KE and ET) and five Cd concentration treatments were conducted. Harvest time was determined at the seedling and hard dough stage. From this study, morphological and physiological response of two sweet sorghum cultivars was observed. In addition, comparison of the different in response of Cd treated plants and control plants, which indicated the effect of Cd on morphological and physiological characteristics of sweet sorghum. On another hand, this study identified potential Cd tolerant sweet sorghum genotypes and Cd accumulation in different plant organs. Analyzed effects of Cd on uptake and transfer of some essential elements into sweet sorghum. Moreover, this study analyzed effect of Cd on sugar transport and distribution of sugar content along the stem. This is an innovation of this research, provides novel insights into understanding and application of sweet sorghum for combining biofuel production with phytoremediation of heavy metal in soil. To understand the molecular mechanism of sweet sorghum(KE) response to Cd toxicity, the transcriptome were analyzed by using RNA-seq. 668 and 286 genes displayed significant expression difference in response to Cd treatment in the internode and leaf of KE line. Detected about 35 of heavy metal transporter and detoxification genes, which displayed significant expression in sweet sorghum under Cd stress. The findings may be a valuable resource for future in-depth studies of gene network to apply for Cd phytoremediation from contaminated soils.