Changes in activities of superoxide dismutase, peroxidase and catalase from leaves of Impatiens flanaganiae in response to light intensity

Abstract

Impatiens flanaganiae Hemsl, is a plant species which preferentially grows in shady conditions at an average light intensity of 30–55 microeinsteins m− 2 sec −1 in its natural environment and exhibits strong apical dominance. Previous studies have shown that lateral branching in these plants can be induced by exposing them to a higher light intensity (280 microeinsteins m− 2 sec−1) under controlled laboratory conditions for up to seven weeks. Prolonged exposure to these light conditions lead to abnormal morphological and biochemical changes probably as a result of photo-oxidative stress. Antioxidative enzymes such as, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), are known to be involved in protecting plants against oxidative stress, Changes in isoenzyme patterns of SOD, POD and CAT from leaves of Impatiens flanaganiae in response to different light intensities (30 and 300 microeinsteins m−2 sec−1) were investigated over a period of nine weeks. Electrophoretic analysis indicated that the SOD and POD from crude extracts of I. flanaganiae leaves were composed of 5 and 10 distinct bands respectively, whereas catalase (CAT) appeared as a single band with low mobility. Four of the SOD’s showed sensitivity to cyanide, suggesting they were copper-zinc containing. The fifth SOD band was found to be resistant to both cyanide and hydrogen peroxide and was identified as a manganese containing SOD. The SOD, POD and CAT isoenzymes were found to respond differentially to changes in light intensity. Activities of all SOD’s and CAT increased under high light intensity whilst the increase in activities of some isoperoxidases was less pronounced, These results suggest a light dependent induction of SOD and CAT in leaves of I. flanaganiae probably in an attempt to protect the plants from the harmfull effect of superoxide (O2-) and hydrogenperoxide (H2O2) radicals which are considered to be generated at higher levels under photo-oxidative stress. The induced isoperoxidases are considered to be indirectly involved in the regulation of plant growth.