The effect of benzyladenine on the levels of photosynthetic pigments, soluble protein and peroxidase activity during senescence of squash {Cucurbita pepo L.) and sunflower {Hetianthus annuus L.) cotyledons

SUMMARY In this study, the influence of benzyladenine (BA, a cytokinin) on the levels of photosynthetic pigments, soluble protein and peroxidase activity during senescence of squash {Cucurbita pepo L. ) and sunflower {Helianthus annuus L. ) cotyledons was investigated. For this purpose, changes in the levels of photosynthetic pigments, activity of peroxidase and amount of soluble protein were determined by spectrophotometric methods during senescence of the cotyledons. Also, the effect of BA on peroxidase isoenzymes were determined by polyacrylamide gel electrophoresis. While the senescence stage of the cotyledons progressed, peroxidase activity was found to be increased, whereas there was a decline in the levels of photosynthetic pigments and soluble protein. In the cotyledons of both plants, the amounts of earotenoids were found to be higher than those of chlorophylls. In addition, the amount of chlorophyll a decreased more than that of chlorophyll b. In the BA- treated cotyledons, the activity of peroxidase and the number of isoperoxidases decreased compared with the control, however, the levels of photosynthetic pigments and soluble protein were higher in comparison with control. From these results, it was concluded that reduced peroxidase activity in the BA-treated cotyledons was a contributing mechanism to the overall antisenescence action of cytokinins. Key Words: Cucurbita pepo, Helianthus annuus, senescence, benzyladenine, peroxidase VI