Thomas Tom Brutnell is a Missouri-based executive who serves as vice president of Gateway Biotechnology, Inc., and consults in the agricultural biotech sphere. Conversant in plant tissue culture and transformation, Thomas Brutnell has a longstanding interest in C4 photosynthesis.

Photosynthesis remains a complex process. It involves plants using photosynthetic enzymes to turn CO2, light, and H2O into sugars that enable growth. Most terrestrial plant species rely on C3 photosynthesis, where the initial carbon compounds produced are three carbon molecules. CO2 enters the plant via microscopic pores on the leaves, known as stomata. Once inside the leaf, the CO2 diffuses into the cell and moves into the chloroplast where it is converted via the Calvin-Benson cycle, into simple sugars.

When stomata open to allow CO2 in, they allow water vapor to escape and impacts plants that must tolerate high-temperature environments and endure drought. C4 photosynthesis resolves this issue by first converting CO2 into a four-carbon compound that is later used to concentrate CO2 around Rubisco in bundle sheath cells. The process effectively pumps CO2 directly to Rubisco, reducing photorespiration and promoting water retention. Importnatly, C4 plants, such as sugarcane, maize, and sorghum, can retain water and continue the carbon fixation process even when the stomata are closed.