Publication Date


Advisor(s) - Committee Chair

Frank Toman, Valgene Dunham, Claire Rinehart

Degree Program

Department of Biology

Degree Type

Master of Science


The short-term effects of manganese toxicity on ribulose 1,5 bisphosphate carboxylase (Rubisco) activity and concentration in tobacco chloroplasts were examined. The activity of the enzyme from both manganese-treated and control plants was determined 6, 12, 18, 24 , and 48 h after introduction of manganese (80 mg/Li. Enzyme activity was determined by monitoring rates of radioactive CO2 fixation into acid stable products. A slight stimulation of the enzyme's activity was noted in experimental plants after 18 h of exposure to manganese as compared with control plants. A decrease in the enzyme's activity in experimental plants was noted after 48 h of exposure. Visible symptoms such as chlorosis and decreased leaf size were also observed after 48 h of manganese exposure in experimental plants. Using Rocket Immunoelectrophoresis, no appreciable difference between Rubisco concentration levels of the experimental plants and the control plants was noted after 6, 12, 18, 24, and 48 h of manganese exposure indicating that the effect on Rubisco activity is a post-translational phenomenon and that Rubisco is not being degraded at an accelerated rate. Even after 7 d of exposure to high manganese concentrations, when visible symptoms such as chlorosis and necrotic lesions were very evident, the level of Rubisco in the manganese-treated plants varied little from the levels in the control plants. Manganese accumulated in the experimental plants to concentrations as high as 3282 mg,/g dry wt as determined by atomic absorption spectrophotometry. A shuttling mechanism for manganese between young and old leaves was indicated by an observed decrease in the concentration of manganese in the young leaf tissue between 12 and 18 h after treatment .


Biology | Life Sciences | Plant Biology | Plant Sciences