Developmental changes of superoxide dismutase, peroxidase and catalase isoenzyme profiles in leaves of Impatiens flanaganiae Hemsl. associated with variations in light intensity

Abstract

Changes in isoenzyme profiles of antioxidative enzymes, superoxide dismutase, peroxidase and catalase, in leaves of Impatiens flanaganiae Hemsl. subjected to different light conditions were investigated. Unbranched plantlets of I. flanaganiae propagated from tubers were exposed to three light regimes: 55 μmol m− 2 sec− 1, 280 μmol m− 2 sec− 1 and 30 μmol m− 2 sec− 1 (variants I, II and III respectively) for a period of seven weeks. Isoenzymes of superoxide dismutase, peroxidase and catalase and their differential responses to light variations were studied in plant extracts prepared from leaves of all three variants at weekly intervals. The activity of most SOD isoenzymes from plants subjected to low light intensity (variants I and II) remained relatively constant except for one Cu/Zn-SOD that increased gradually during the course of development. Little or no change in catalase activity was observed during the initial stage development of plants from these variants. A profound enhancement of catalase level was detected only from the fifth week onward, especially in variant III. The induction of some SODs and CAT in plants from these variants could be related to possible oxidative stress associated with plant aging. In contrast to CAT, the activity of some of the peroxidase isoenzymes in variant III decreased from the second week onward and was lower than in the plants from the other two variants during the initial stages of development. Plants from variants I and III also showed a steady increase in activity of most isoperoxidases (low and high mobility) with time, which suggests their indirect involvement in the regulation of plant growth and development. A rapid increase in the activity of superoxide dismutase and catalase during the experimental period was observed in plants exposed to relatively high light intensity (variant II). The activities of both Mn, and some of the Cu/Zn- containing SODs increased sharply from the second week onward under high light intensity as compared to the other two variants subjected to low light intensity. The Mn-SOD activity remained high throughout the experimental period, while the light-induced Cu/Zn- SODs showed a reduction in activity after the third week. This light-induced response could be an attempt to protect plants from the harmful radicals generated due to photo-oxidative stress under high light. The low activity of some isoperoxidase observed under these conditions is considered to be compensated by high catalase activity as the active oxygen species, hydrogen peroxide, is removed by catalase and/or peroxidase. These metal containing enzymes seem to respond differentially to variations in light and could be suitable as a marker for the evaluation of light-induced oxidative stress in Impatiens flanaganiae plants.