I’m in Arizona for Thanksgiving. So let’s talk cacti!
The dry, desert environment means the plants here have to be careful about water.
They have developed quite the set of tricks in order to do so. For example, they are able to store water in their stems, and lack leaves that would otherwise lose water.
Today I found out another cool way they conserve water - cactus plants still photosynthesize like any other plant, but partially at night!
The photosynthesis process converts sunlight and CO2 into energy and oxygen. In order to collect the CO2, plants have stomata (basically mouths on their leaves) that open up and allow CO2 in, but it also allows water to evaporate out.
In order to prevent this water from evaporating during hot daylight hours, cacti are able to hold off and only open their stomata at night. They collect CO2 and then store it for use later.
This process of storing CO2 for later is known as the CAM mechanism (Crassulacean acid metabolism). Collected CO2 is stored as malate, a four carbon acid, inside the vacuoles, basically cell sized storage containers.
Then, during the day, the the acid is transported to the chloroplasts (the photosynthesis part of the plant) and converted back into CO2.
With the energy from the sun, the cactus is ready to photosynthesize, and the pathway continues as it usually would.
All of these steps are carried out by different proteins and enzymes, the chemists of the biological world.
Some of the enzymes, which are important catalysts for chemical reactions, are temperature dependent! So, when it becomes too hot, the cactus is able to stop the process of collecting CO2!