Enhancement in leaf photosynthesis and upregulation of Rubisco in the C4 sorghum plant at elevated growth carbon dioxide and temperature occur at early stages of leaf ontogeny

Rising atmospheric carbon dioxide (CO2) concentration and temperaturewill influence photosynthesis, growth andyield of agronomic crops.To investigate effects of elevatedCO2andhigh temperature on leaf gas exchanges, activities of Rubisco and phosphoenolpyruvate carboxylase (PEPC) and growth of grain sorghum (Sorghum bicolorL.Moench), plants were grown in controlled environments at day-time maximum/night-time minimum temperatures of 30/20 C or 36/26 C at ambient (350mmolmol) or elevated (700mmolmol) CO2. Gas-exchange rates, activities of Rubisco and PEPC and growth parameters (leaf, stem and total dryweights) were determined at different stages of leaf development. Between 6 and 25 days after leaf tip emergence, leaf carbon exchange rate (CER) of elevatedCO2 plantswas greater at 30/20 Cand36/26 C than that of ambientCO2plants at the same temperatures. Thepositive response ofCER to elevatedCO2wasgreater in young leaves than in old leaves. In young leaves, elevated CO2 enhanced Rubisco activity at 30/20 C and 36/26 C, whereas PEPC activity was not affected by elevated CO2 at 30/20 C but was marginally enhanced at 36/26 C. At 30/20 C, growth parameters were not affected by elevated CO2 until 50 days after sowing (DAS); at 36/26 C, they were progressively enhanced by elevated CO2 to as high as 49 to 62% by 50 DAS. Leaf CER and Rubisco activity were enhanced by elevated CO2 at early stages of leaf ontogeny for the C4 grain sorghum. Such enhancement should have a significant role in drymatter production under elevated CO2. Additional keywords: climate change, dry matter production, heat stress, leaf development, leaf growth, Sorghum bicolor.