Abstract

The toxic effects of heavy metals, including arsenic (As), cadmium (Cd) and lead (Pb), on length and biomass of shoots and roots, their respiratory rate, the gene expression levels of cytochrome oxidase (COD),isocitrate dehydrogenase (IDH) and malate dehydrogenase (MDH) isoenzymes were studied in the germination stage of wheat (var. ZhengZhou-9023). The results showed that both length and total dry biomass of wheat shoot and root increased at lower As concentrations (1 mg·L^-1 ) but decreased gradually at higher As concentrations (5 to 25 mg·L^-1). Similarly, the increase in the concentration of Pb, increased shoot length and biomass initially but later decreased gradually. Decline of root and shoot’s biomass was observed with increasing concentrations of Cd yet. The respiratory rate of root displayed an increasing trend at As concentrations lower than 1 mg·L^-1, but a decreasing trend was observed at higher concentrations in the root respiratory rate, while the respiratory rate of shoot increased gradually. Respiratory rates of shoot and root increased at lower concentrations of Cd or Pb but decreased at higher concentrations overall. The levels of COD, IDH and MDH isoenzymes in shoot and root were induced mainly with increasing concentrations of As. Interestingly, their levels were induced at lower concentrations of Cd and Pb, but could not be measured at higher concentrations of them. However, expression of a new IDH or a new MDH isoenzyme homologue in the root was induced at higher concentrations of Cd or Pb. Therefore, the presence of heavy metals could change the expression of some important enzymes in respiratory process such as COD, IDH or MDH isoenzymes, thereby affecting respiration in wheat, eventually leading to physiological changes in Wheat.

Key words: Wheat, arsenic, cadmium, lead, respiration, isoenzymes.