Relationship Between Physiological and Biochemical Effects of Cadmium Toxicity in Nicotiana rustica

Cadmium (Cd) is a non-essential heavy metal that does not have any metabolic use. In this study the impacts of Cd added in nutrient solution on growth, physiology and carbon metabolism of tobacco (Nicotiana rustica) were investigated. Tobacco plants were grown in media containing CdCl2 at 0, 10, 20, 50 or 100 M for 30 days. Regarding leaves, Dry Weight (DW) and leaf surface area were negatively affected by Cd. Soluble sugar content was decreased parallel with a reduce of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP) activity. The reduction in RuBP activity was accompanied by a decrease in Rubisco subunit amounts. These changes came with a dramatic loss in photosynthetic pigments. In another way, Cd stress enhanced the activities of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) and NADP-isocitrate dehydrogenase (NADP-ICDH, EC 1.1.1.42) in tobacco leaves. This study suggested that readjustment of the C metabolism via modulation of Krebs cycle enzymes activities and C flow towards the amino acid biosynthesis were a strategy of tobacco plants to tolerate Cd stress.