Autumn leaf colours were there all along, they're just visible now the green has gone. Really?

[Mangetout]

I’ve often heard it authoritatively stated that autumn leaf colours were always there in the leaf and that they’re merely rendered visible by the subtraction of the normal green colour from the leaf.

This makes sense for leaves that turn a paler colour (such as yellow) before they fall, but for leaves that turn deep red or dark purple, how can it possibly be true? The final leaf colour is often so much darker than that of mature living leaves, surely leaves that turn red when the green is removed should have been brownish or coppery when alive, if the red was there alongside the green.

And it’s not as if the red could be underneath the green, because for most leaves, they can be seen as pale and green by both reflected and transmitted light.

Understood that these colours are typically carotenoids - is it just the case that they are there, but not brightly coloured until some sort of modification happens to them as the leaf dies?

So what’s the deal?

[Captain_Amazing]

The yellow and orange were there under the green, the red and purple come from the glucose in the leaf reacting.

[Mangetout]

Aha! That makes much more sense. Why don’t they ever say that?

[Chronos]

They certainly are there: I did an experiment in a biology class once where we started with a green leaf and separated out all of the pigments, and we definitely saw some red and yellow. Of course, that still leaves the possibility that there’s more of those pigments in the fall.

[Mangetout]

You know, I’ve got the terrible feeling I’ve asked exactly this question here before.

[Ostrya]

tree care person here…

Anthocyanins

From the wiki article -

The reds, the purples, and their blended combinations that decorate autumn foliage come from another group of pigments in the cells called anthocyanins. Unlike the carotenoids, these pigments are not present in the leaf throughout the growing season, but are actively produced towards the end of summer. They develop in late summer in the sap of the cells of the leaf, and this development is the result of complex interactions of many influences — both inside and outside the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced.

Some of the most brilliant fall colors are produced by bright sunny days combined with cold/cooler night temperatures - causing extra sugars to accumulate - left behind during the cooler phase photosynthetic night cycle.

[capybara]

This is very interesting. I love teh Derp!

[Yllaria]

Don’t you listen to them. The trees are screaming - screaming, I say!

[Duckster]

http://www.fs.fed.us/news/fallcolors/faq.shtml

[El_Zagna]

Well, here’s how it was explained to me, although based on the previous posts, there’s more to it.

Imagine a bucket filled with red marbles and green paint. All you are going to see is green, but let the green paint drain out, and presto - red! The red was always there, it was just covered up by the green.

[barbitu8]

@Mangetout

You know, I’ve got the terrible feeling I’ve asked exactly this question here before.

You did, but a few years back.

El Zagna:

Well, here’s how it was explained to me, although based on the previous posts, there’s more to it.

Imagine a bucket filled with red marbles and green paint. All you are going to see is green, but let the green paint drain out, and presto - red! The red was always there, it was just covered up by the green.

From Duckster’s link:

Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.

[Mangetout]

@barbitu8

You did, but a few years back.

Thought so. Can’t find the thread though…

[Mangetout]

@El_Zagna

Well, here’s how it was explained to me, although based on the previous posts, there’s more to it.

Imagine a bucket filled with red marbles and green paint. All you are going to see is green, but let the green paint drain out, and presto - red! The red was always there, it was just covered up by the green.

Thanks. Yeah - that’s pretty much how I’d heard it explained, but the analogy never made sense because most deciduous leaves are not opaque - they’re translucent and you can see light shining through them, making it plain that there is not a lot of red or purple in there - that’s why the widely-repeated blanket statement about the colours always being there just didn’t ring true to me.