Hormonal Trees

Vivid reds, oranges, yellows and vibrant hues between. The leave’s bright green suits are shed to reveal true colors come autumn. The reception is a glorious wonder. Pops of color race by as we travel through town. Neighborhoods are littered with golden dazzling ovals skipping down the sidewalks hand-in-hand with the wind. Ryder asks, “Why do leaves fall when it gets cold?”

 

A perfect question for our next Science Friday, I start mulling over my theories and cannot wait for him to climb into bed so I can thoroughly research the answer to his question. “Senescence” is the first word to come into color: the loss of a cell’s power of division and growth, in short, deterioration. I am lost before I begin. What does this have to do with leaves falling? Is talking about cells too, ah-hem, beyond kindergarten? No! (Sure, teachers everywhere start giggling at my ambition. But thank you Jenny Sue for always inspiring science and being our go-to Science Lady! Science rocks!).

“Abscission” is the next word popping from the page. “Ab” means away and scission (like scissors) means “to cut”. Putting cells with this can only mean cells are breaking away or cut from the tree. Now we are getting somewhere. But why do they break away?

Trees, specifically deciduous (“falling” in Latin), are trees that lose most of their leaves at one time. Leaves provide food for the tree, so why would they do this?

I seem to have more questions than answers!

Finally, a resource from the University of Georgia gets the light bulbs to turn on. A tree provides water to leaves so they are alive and well to absorb the sun. This is done through a hormone called auxin.

As auxin flows leaf grows.

Like wide and beautiful dinner plates waiting to be filled with delicious food for the tree, the leaves turn the sun and water into starch that feed the tree. This trade off is evident in the bright green leaves throughout the warmer seasons. Green being evidence of water/starch exchange.

But come shorter days (less light/food to absorb) and colder temperatures, water will freeze. The tree knows the risk it is facing in keeping the “leaf dinner plates”. Better to buy new dishes come spring, the tree will tell the leaves to break away (abscises).

Enter hormone, “ethylene”, like a nasty wave of menopause, the hot flashes come. One can only imagine the burning bush taking this process all too seriously. The weeping willow going a step too far. The signal of “ethylene” raging through the trees limbs is anything short of a mother’s grouchiest days. The ethylene gas tells the water to stop and the leaves start to rage in its absence. All color of emotions is revealed under the usual calm green! The colors had always been there. Bright reds, oranges, yellows and vibrant hues between as the bright green suits are shed. The water source is gone! Leaf cells swell in frustration and like a giant marshmallow turn to carbs that cannot make it back into the tree, it is now a one-way street. The ethylene gas is in full force causing the tissues of the leaves to age rapidly. As my Nannie always said, “Getting old is not for the feint of heart!”

Fruit bearing trees ripen with speed as the relationship of the tree and its food source come to their final break-up. Cell walls become weak where the leaf’s stem meets the tree’s branch. This line is called the “abscission layer” or “fracture line”, a thin line of smaller cells that start to separate from each other’s once happy and warm summer party.

Brown, crunchy, dry, every cell once vibrant with water from the tree are all but cell walls, shells of a greater and brighter existence.

Ryder and Rory suck the water from the bowls through bright straws. Pretending to be leaves in the summer enjoying the hydration from the tree.

They in turn give back to the tree in the form of small pom-pom balls. Shooting them back through the straw to the imaginary tree. They giggle with delight. Ryder catches on to the seasons causing the change in what’s delivered.

The water is gone from the bowl and Rory begins to fuss. He tells her, “Rory, its fall! Time to breakaway!” She and Cody stuff their faces with marshmallows reenacting the ethylene surging through their leaf bodies. It almost feels like we have switched from Science Fridays to a high school game of “Chubby Bunny”, seeing who can shove as many “char-mallows” into their mouth at once (Cody won by a landslide).

Ryder taps me on the shoulder and says, “I am the tree. Guess which season it is!” Distracted by the Chubby Bunnies I don’t quite follow his train of thought. He helps me along, “Mom, the green one is water and the orange one is…” he giggles, “gas! Ya know, eth…ethylene!” A bright green pom-pom hits me on the forehead and I yell “Summer!” He laughs and fires another. I look under the table to find a bright and sparkly orange one, “FALL!!!” I scream with excitement. He beams. I beam. We did it.

Happy fall everyone!

 

P.S. ironically as I finish this post Taylor Swift’s Are We Out of the Woods Yet is playing in the background. I digress.