Abstract

C4 plants have a highly effective carbon concentrating mechanism that pumps CO2 from mesophyll to bundle sheath cells, the compartment where the carboxylating enzyme Rubisco is located. The high CO2 concentration effectively suppresses the oxygenase activity of Rubisco. As a result under certain environmental conditions (high temperature, high light) C4 plants have higher efficiency compared to C3 plants. A useful way to study C4 physiology is addressing the energy losses that occur under limiting conditions when the C4 pathway is less competitive (low light, low temperature) when some CO2 escapes from bundle sheath.

Leakiness can be estimated measuring gas exchange, photosystem II yield and carbon isotope discrimination during photosynthesis. By means of a C4 photosynthesis model, parameters such as bundle sheath conductance and the concentration of CO2 in the bundle sheath can be calculated. My initial study has been comparing leakiness and photosynthesis efficiency of maize plants grown under high and low light conditions. The aim is to define why leakiness increases at low light, and whether low light plants can adjust their photosynthetic operating efficiency. Understanding C4 process is relevant both for improving crop productivity in dense crop stands (self-shading) and for understanding the photochemical demands, should the C4 pathway be introduced into a C3 crop such as rice.