Photosynthetic Characteristics of Sunflower (Helianthus Annuus L.) Leaves and Bracts

Photosynthetic characteristics and tissue organisation in bract as compared to leaf were studied in two sunflower cultivars, morden and MSFH-8. Ribulose biphosphate carboxylase activity in bract was many fold lower, while PEP carboxylase and malate dehydrogenase activities higher than in leaf. Leaf has a characteristic organisation, whereas, bract lacked palisade cells and comprised of mesophyll cells on adaxial side and loosely packed mesophyll cells with higher intercellular spaces on abaxial side. There was no characteristic tissue organisation like in C₄ plants, while the chlorophyll a:b ratio was typical of C₃ plant. The high PEPcase and malate dehydrogenase activity in bract could be to refix the respiratory realeased CO₂, which is 2.6 to 3.3 fold higher as compared to leaf.