Physiological Mechanism And Stress-specific Protein For Cr, Cd And Pb Toxicity Tolerance In Typha Angustifolia

Heavy metal pollution in soils poses a major environmental hazard to terrestrial plants and ultimately metal toxicity to animals and humans via food chain. It is crucially important to develop cost-effective remediation strategies for these metals. One of such emerging technology is phytoremediation through the use of green plants to extract, sequester and detoxify the pollutants. We found a kind of gramineous plant species, Typha angustifolia, with high resistance to heavy metal stress. The present research was conducted to evaluate its ability to tolerant Cr, Cd and Pb stress and the relevant physiological responses, and to identify stress-specific protein for Cr, Cd and Pb toxicity tolerance in T. angustifolia. The results were as follows:Pot experiments were conducted to study the potential of T. angustifolia plants for Cr, Cd and Pb toxicity tolerance and subsequent response in antioxidant defence system after 30 d exposure of 1 mM Cr, Cd or Pb. Typha angustifolia showed high tolerance to heavy metal toxicity with no visual toxic symptom when exposed to metal stress, and Cd/Pb addition also increased plant height and biomass especially in Pb treatment. Along with increased Cr, Cd and Pb uptake in metal treatments, there was enhanced uptake of plant nutrients including Ca and Fe; and Zn in Pb-treatment. A significant increase in MDA content, SOD and POD activities were recorded in plants subjected to Cr, Cd or Pb stress. Furthermore, Pb-stress also improved CAT, APX and GPX activities; whereas Cr-stress depressed APX and GPX. The results indicate that enzymatic antioxidants and Ca/Fe uptake were important for heavy metal detoxification in T. angustifolia, stimulated antioxidative enzymes and Ca, Fe and Zn uptake could partially explain its hyper-Pb-tolerance.Typha angustifolia of 90 (D90) and 130 d (D130) old plants were subjected to 1 mM Cr, Cd and Pb and samples were collected 30 d after treatment.2-DE coupled with MS (mass spectrometry) was used to analyze and identify Cr, Cd and Pb-responsive proteins. More than 1600 protein spots were reproducibly detected on each gel. wherein 44,46,66 and 33,26,62 spots in D90 and D130 samples were differentially expressed by Cr, Cd, Pb over the control, respectively. Of these differentially expressed proteins,3,1,8 overlapped in D90 and D130; while 5,8,5 with regulation factors above 3 in one of D90 or D130 samples. Total of 22 and 4 up-and down-regulated proteins were identified using MS and data bank analysis. Cr induced expression of ATP synthase, RuBisCO small subunit and coproporphyrinogenâ…¢oxidase; Cd induced RuBisCO large subunit; Pb up-regulated carbohydrate metabolic pathway enzymes of fructokinase, and improved RuBisCO activase and large subunit, Mg-protoporphyrinâ…¨chelatase. Contrarily, elF4F was inhibited by Cr/Pb, chloroplast FtsZ-like protein and GF14omega impeded by Cd and Pb respectively.Furthermore, we investigated ultrastructure of T. angustifolia in response to Cr, Cd and Pb stress. Cr, Cd and Pb toxicity stress distort the ultrastructure and the treated seedlings showed that the vacuoles were expanded and endoplasmic membrane appears to be rough. The levels of chloroplast in the plant cell were visible and prominent, yet the heavy metal stress caused an imbalance.