This week’s column, titled “The Pink Stuff,” states: “Carotenoids ae often found in conjunctin with chlorophyll, the chemical that makes plants green. When chlorophyll production stops in autumn, the green fades but the caroenoids remain, turning tre leaves red and orange.”
Bypassing the fact that the red and purple colors in leaves are ot caused by carotenoids, but by various hydrocarbons with unpronounceable names, I submit to you that green cannot hide red, purple, or orange. Try it on your wall and see.
True it is that the green will hide the dull brownish colors found on many mundane, lifeless leaves, but not true that it hides the brigher colors. The brighter colors don’t come into existence until after the cessation of the production of chlorophyll. When chlorophyll is no longer synthesized, the sugars in the leaves undergo a chemical reaction with the chlorophyll compounds and, voila (as the French say), we have these bright colors.
So, on the contrary, I submit to you again (but only if you will be my mistress -oh, no - that’s another thread) that on the contrary, chlorophyll does not hide the bright colors but is instrumental in producing them.
When I was in high school, we did an experiment on this in biology class: We took some green leaves, pulped them up and mixed thoroughly with water, and dangled strips of some porous material (blotter paper?) in the solution. As it climbed by capillary action, the different pigments separated out. As expected, the largest band was the green chlorophyll, but yellow xanthophyll and the others whose names I don’t recall were also present.
You can cover any color with any other color, provided you have enough of it.
Xanthophyll is a yellow and green can cover it. I’ve read that the reds and purples don’t come into existence until after the chlorophyll dies. They weren’t there all along and are the results of chemical reactions with sugars.
Cecil mentioned caretenoid derivates accounting for the pink in some sea animals. The chemicals that cause the reds and purples in leaves have a cyanide derivative. I don’t remember the names, but most of them end with a “cyanide” type suffix.
You’re thinking of anthocyanins. This site offers more information plus links.
From one of the links in the link (Science Made Simple):
[Q] The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves. [/Q]
BTW, the very young leaves of many tropical plants are also red, due to transitory production of anthocyanins. In this case they are thought to be an antifungal defense. Also, young leaves of tropical plants often have little or no chlorophyll until they reach full size and toughen up. This is probably due to the fact that young tender leaves are particularly vulnerable to being eaten, and the plant doesn’t want to risk valuable chlorophyll until it’s necessary.
In the genus Amelanchier (June Berry) the leaves are a dull green colour throughout the growing season, towards autumn, you can see patches of dull red forming in the leaves, but this red is very much darker than the green of the leaves and if held up to the light, the remaining green parts transmit more light than the patches which have turned red; the red can’t have been there all along.
Incidentally, when the leaves lose all of their green colour, it’s a very attractive tree for autumn colour.