Hello, botany enthusiasts!
If you live in the Northern Hemisphere like me, you're probably witnessing the amazing
fall foliage that comes with this time of year.
The trees are dropping their leaves in preparation for winter, turning amazing shades of red,
orange and yellow in the process.
But why exactly does this happen, and what's going on inside of the plants to make it happen?
Well, I'm here to tell you!
This process of plants dropping their leaves in autumn is called seasonal leaf senescence.
It's thought that this senescence is triggered by the shortening of the days and the drop
in temperature that happens in fall.
A series of chemical reactions triggers the mechanisms of senescence, and the first thing
that happens in the destruction of chloroplasts in the leaves' plant cells.
The mitochondria may be the powerhouse of the cell, but in plant cells it's the chloroplasts
that rule.
Chloroplasts contain chlorophyll, the molecules necessary for photosynthesis.
It's through photosynthesis that plant cells use sunlight to create chemical energy.
Chlorophyll is what gives plants their token green color, and as the chloroplasts are destroyed,
the plant's leaves lose their color.
That doesn't explain, however, why leaves turn shades of yellow, orange and red.
Well, chlorophyll isn't the only pigment that helps with photosynthesis.
Chloroplasts also contain carotenoids, accessory pigments that have an orange color.
Β-carotene is a carotenoid, and it's what makes carrots orange.
Carotenoids actually help with photoprotection in plant cells.
Basically, if too much energy builds up in chlorophyll, it can trigger chemical reactions
that damage the cell.
Carotenoids quench this excess energy and protect the cell.
When it comes to vibrant fall foliage, it's maples that take center stage for color.
Red maples are known for their red leaves, a color that can't be explained by carotenoids
alone.
Maple leaves also contain lots of anthocyanins, Anthocyanins are found in a lot of plants
and can produce colors like pink, purple and blue.
In trees like maples, however, they create a startling red.
Seasonal leaf senescence, of course, is more than a color change.
The leaves shut down, leading to leaf abscission.
This is when the leaves to actually fall off the plant.
The petiole, the short stem that connects the leaf to the tree, is walled off by the
plant, causing the leaf to fall.
In summary, as the days shorten and the temperature drops, deciduous trees like maples begin the
process of senescence.
They shut down the plant cells in the leaves, starting with the chloroplasts, which causes
them to change color.
Eventually, as senescence continues, the leaves are cut off from the plant and fall to the
ground.
Hopefully now you know a little more about fall foliage!
If you have any questions, please let me know in the comments.
Thank you for watching; for daily posts about plant science you can check out www.brilliantbotany.com
or follow me over on twitter.
I'll see you all next time.