In mid January, 2023, researchers from the University of California San Diego made an important discovery surrounding photosynthesis, specifically the plants stomata, with climate change implications.

Tomato leaf stomate 1-color

Scientists have understood photosynthesis for many years. As we learned in AP Bio, photosynthesis is the process by which plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of glucose. The process of photosynthesis can be divided into two stages: the light dependent reactions, and the Calvin cycle.

The light-dependent reactions occur in the thylakoid membranes of chloroplasts and involve the conversion of light energy into chemical energy in the form of ATP and NADPH. During these reactions, water molecules are split  into hydrogen ions, electrons, and oxygen gas. The electrons move through a series of electron carriers and ultimately end up on NADP+ to form NADPH. At the same time, hydrogen ions are pumped from the stroma into the thylakoid lumen, creating a concentration gradient that drives the synthesis of ATP through a process called photophosphorylation.

The Calvin cycle, occurs in the stroma of chloroplasts and involve the conversion of carbon dioxide into glucose. During these reactions, carbon dioxide is fixed into organic molecules by the enzyme rubisco. The resulting molecules are then reduced by NADPH and ATP produced during the light-dependent reactions to form glucose. The Calvin cycle also requires a source of hydrogen ions, which are provided by the light-dependent reactions through the production of NADPH.

The researchers at the university of California San Diego, have furthered this understanding by explaining how the stomata is able to sense when to open and close in order to allow carbon dioxide and water to enter and exit the plant. When the stomata is open for carbon dioxide to enter, it exposes the plant to the outside world, and water from the plant is lost, which can end up drying out the plant.

This research is important because as carbon dioxide in the atmosphere increases, it could lead to the stomata of vital plants being left open too much, which would dehydrate the plant.

Fortunately, the research pointed to a specific protein, known as HT1, that was able to activate the enzyme that opens up the stomata in a low CO2 environment. The researchers also found a second protein that blocked the HT1 from keeping the stomata open in environments with higher CO2 concentrations. This second protein that was found is the reason plants will die when the atmosphere has too much CO2, as the stomata wouldn’t be open for long enough to get the necessary resources for photosynthesis.

This can relate to what we learn in AP Bio, in regards to enzymes and proteins. In AP bio, we learned that proteins are large molecules made of amino acids. Enzymes are a type of protein that catalyze chemical reactions. Enzymes also lower the activation energy needed for a reaction to occur. They interact with specific substrates to form enzyme-substrate complexes. The active site of an enzyme undergoes conformational changes, allowing for catalysis. Specific substrates can only bind to a particular enzyme. Enzyme activity can be affected by temperature, pH, and concentration. Enzymes work most effectively within a specific range of those things. Changes outside that range can affect structure and function. Enzymes and proteins play critical roles in many processes. Examples include DNA replication, protein synthesis, and metabolic pathways. Understanding enzyme-substrate interaction is crucial to understanding how the HT1 that activates the enzyme was able to speed up the reactions that caused the stomata to open up.

As Richard Cyr, the program director stated, “Determining how plants control their stomata under changing CO2 levels creates a different kind of opening — one to new avenues of research and possibilities for addressing societal challenges.” Hopefully this research can result in positive steps for the agricultural community as it takes on the challenge that is climate change.