For most of the year, deciduous trees are green because of chlorophyll in the chloroplasts.  This pigment helps harness energy from the sun to fuel photosynthesis, or food production.  In the fall, days become shorter and sunlight more sparse, so plants begin to prepare for the winter – a period during which they rely on stored nutrients.   Nutrients are stored and superfluous leaves are shed , but before that, the chlorophyll begins to disappear, revealing other pigments such as yellow and orange that weren’t visible before.  Sometimes during this process, new pigments (such as reds) are produced as well.

This is controlled by up to 35 genes that can turn on and off in response to the reduction of sunlight hours.  It is a great example of the interaction between an organism’s DNA and its environment, a phenomenon many people are unaware of.  The traits and characteristics of all living things are the result of a combination of its genetic makeup and its physical and chemical surroundings.  To learn more about this type of interaction, go to chapter 35, “DNA responds to signals from outside the cell.”

A sea slug species, Elysia chlorotica, found in the marshes of New England and Canada has a unique trait. It produces chlorophyll and can use photosynthesis to make it’s own food – just like a plant! There are other organisms, not classified as plants, that have this trait as well such as the Euglena, a single-celled protist. This sea slug happens to be the first multicellular animal with such a trait. Scientists believe that they steal genes for this trait from the algae that they eat. They also steal chloroplasts, the organelle where photosynthesis takes place.

The stolen genes can be passed from one generation to the next, so that next generation sea slugs can also produce their own chlorophyll. Interestingly enough, the babies still need to eat lots of algae to get the chloroplasts they need to carry out photosynthesis. So maybe there is hope for green people after all?