Activity of antioxidant enzymes in leaves and bracts of sunflower (Helianthus Annuus L.)

A study was conducted to examine the activity of super oxide dismutase (SOD) and its isozymes, ascorbate peroxidase (APOX) and peroxides (POX) in bracts and in the upper most 1^st and 3^rd leaves of sunflower at flower opening stage (50 days after sowing) and seed filling stage (70 DAS). The upper most leaf has smaller amounts of chlorophyll and carotenoids and lower activity of SOD, its isozymes, ascorbate peroxidase and peroxidase than the third leaf at flower-opening stage but increased significantly at seed filling stage. Relative water content (RWC) did not differ significantly in any of the leaves at the two stages. Soluble protein content did not differ at the 1^st stage but was higher in 1^st leaf at seed filling stage. Bracts in upper and lower rows contained significantly lower contents of chl a, chl b, total chl and carotenoids as compared to leaves at both the stages. The antioxidant enzyme activities were also very low in bract. Among SOD isozymes (Mn-SOD, Fe-SOD and Cu/Zn-SOD), only Cu/Zn-SOD contributed largely to the total SOD activity in bracts, while Mn-SOD and Fe-SOD activities were very rudimentary. Ascorbate peroxidase (APOX) activity decreased in bracts at the seed-filling stage, while peroxidase activity increased. The role of antioxidant enzymes in maintenance of protein and pigment contents in bracts and leaves has been discussed.