We just learned about plant hormones, which means we are beginning to discuss specific chemicals
that carry out important functions in plants. So let’s look at some other plant chemicals called
pigments. First, we should know what a pigment is. Pigments are organic
compounds that give living things their color and may also serve some other sort of function.
In plants, pigments give the leaves, flowers, and fruits their colors, but they’re also responsible
for things like food production. Let’s go through the different types of plant pigments now.
The first and most important plant pigment you will hear about is chlorophyll. There are actually
three types of chlorophyll that may appear in organisms which are capable of photosynthesis,
those being chlorophyll a, b, and c. Chlorophylls are large molecules with a cylic portion
that binds to a metal ion. This is extremely similar to another cyclic biomolecule found in our
bloodstream called hemoglobin, which we learned about in the anatomy and physiology series, except
that where the heme in hemoglobin involves iron, chlorophyll contains a magnesium ion instead.
Chlorophyll pigments reflect green light, which makes plants look green, and they absorb red,
yellow, and blue light. The light energy absorbed by chlorophyll pigments excites electrons in the
porphyrin ring, which provides the energy required to initiate the process of photosynthesis.
Once again, we covered this process in detail in the biochemistry series
so we won’t talk about it here. But this is the single most important process to understand
regarding plant physiology, so be sure to visit this tutorial if it is unfamiliar to you.
Now to be clear, chlorophyll doesn’t facilitate photosynthesis all on its own.
Another set of pigments, called carotenoids, assist with the function of photosynthesis.
You might notice that carotenoid sounds a bit like a certain orange vegetable,
and you’d be correct to associate the two. Carotenoid pigments give plant parts red,
yellow, or orange coloration. But beyond this, carotenoids are known as accessory pigments
because they assist chlorophyll in the collection and absorption of light energy.
Beyond red and orange vegetables like peppers and carrots, carotenoid pigments are also responsible
for the beautiful colors you see in autumn leaves, once all of the chlorophyll has degraded.
The next group of plant pigments we will discuss is called flavonoids. These are
usually found in the vacuoles of plant cells. As we recall, the vacuole is a large water-filled
compartment within each plant cell, which contains organic and inorganic substances
that are important for the cell. The most common flavonoids are the anthocyanins,
which often produce bright red coloration in plants. Anthocyanin pigments are usually found in
the petals of flowers and in the flesh of fruits, but they can also color the stems of plants.
Trees with especially vibrant red autumn leaves are expressing anthocyanins as well.
The last important plant pigment is a little different from the others that we’ve covered.
Phytochrome is a plant pigment that isn’t visible unless we separate it from the rest of the plant.
This pigment is less about creating visible color in a plant and more about triggering
certain events in a plant’s growth and development. Phytochrome absorbs light just
like all of the other pigments, but in this case the light absorbed acts like the flip of a switch
to start a new process, such as seed germination, stem and leaf growth, or bud flowering.
So with that, we know how pigment molecules give plants their colors,
as well as what processes these pigments facilitate inside a plant.
But what are all of the different kinds of plants? With sufficient foundational knowledge covered,
it’s time to start looking at the wide variety of plants that exist on Earth.