My son quickly informed me that people would look at this and say "That's a boring title"
Thanks kiddo, love you too. Well, I liked the title, after all the poster describes what occurs within the cells of leaves as they change from summer to fall to dead.
When leaves are green, they have lots of chlorophyll, which means lots of photosynthesis is occurring. Chlorophyll gives the leaves their nice green coloration. The leaves are doing photosynthesis and thus making lots and of sugars which can be sent out to the rest of the tree. The tree then sends water up to the leaves, keeping them hydrated.
As fall sets in, nights get longer and temperature decrease. This is a signal to the tree that it is time to start preparing for the approaching winter. The tree starts to close off the stem to the leaf, slowing down water flow and decreasing the amount of sugar that escapes the leaf. At this stage, chlorophyll starts to break down and anthocyanins are created. These anthocyanins are a protective substance, helping to protect the leaf from the upcoming stressors and stored in the vacuole. They are a nice bright red, color. Plants, such as maple, that have bright red leaves are rich in anthocyanins.
Colder temperatures cause water flow to cease and chlorophyll content to be negligible. Carotenoids, which are yellow/orange pigments, accumulate in the plastids (the same organelle in the cell where chlorophyll is found). Anthocyanins also continue to acculumate and the leaf gets deeper and deeper red. If you have a plant, such as an oak, that only turn yellow that's from the accumulation of carotenoids and not anthocyanins. Now we have bright, beautiful fall leaf.
Now it's time for the leaf to be shed, the stem is completely sealed. No more anthocyanins accumulate and the carotenoids break down, leaving a brown shade. The dead leaf now falls away and the tree hunkers down til spring when it can produce more sun catching, food making, green leaves.
So as you watch the leaves change colors, remember, you are watching the leaf die. This is one of my favorite comics about the fall:
|Fall Colors by The Awkward Yeti|