Journal archives for November 2020

November 02, 2020

Dormancy: A Plant’s Way to Hibernate

Happy Monday, CVNP-goers! Hopefully you aren’t feeling too groggy today after Daylight Saving Time this weekend. In the spirit of the changing seasons, let’s talk about dormancy.

Dormancy is a plant’s response to suboptimal growing conditions. This includes periods of intense heat, drought, lower temperatures, and nutrient shortages. Dormancy in plants is similar to hibernation in animals. Just as a bear gathers food and hides in a cave to sleep all winter, plants will conserve their last bits of water and nutrients by decreasing their activity and receding to their core and roots.

In Northeast Ohio, our plants enter dormancy in the fall when trees and shrubs lose their leaves and perennial grasses and forbs shrivel and brown (Side note: annual plants complete their life cycle in one growing season, and thus, do not enter dormancy in the fall. Examples include jewelweed, black-eyed Susan, and Miami mist). In this feature, I’ll explain how our plants know when to become dormant and for how long they should stay dormant. I’ll be using information from Richard Amasino’s research on vernalization, joint research on epigenetics done by Catherine Dupont, D. Randall Armant, and Carol A. Brenner, and from Britannica.com. All sources are cited at the end of this journal post.

How Do Plants Know When It’s Time to Enter Dormancy?

When plants conduct photosynthesis, there are two interdependent reactions going on. The first set of reactions is called the light-harvesting reactions. This is the part in photosynthesis where the plant converts sunlight energy into chemical energy. The enzymes (or substances that catalyze biochemical reactions) that drive light-harvesting reactions require sunlight to do their job. The second set of reactions are called the dark reactions. In this step, plants use the chemical energy created by the light-harvesting reactions to convert the carbon in CO2 into sugar molecules (like glucose). They are called the dark reactions because the enzymes that drive them do not require sunlight. Instead, the dark reactions’ enzymes require optimal temperature conditions. As daylight becomes shorter and temperatures dip in the fall, the enzymes driving these processes begin to slow down. Thus, the plant’s food production slows, growth pauses, and the plant becomes dormant.

How Do Plants Know How Long to Stay Dormant?

Plants have something called a “winter memory”. The mechanisms for a plant’s “winter memory” vary in different plant species and they are still being studied. So far, scientists have determined that environmental cues like light and temperature create modifications to a plant’s chromosomes that let the plant know how long they’ve been dormant for the winter. Some scientists call these epigenetic changes, but the jury is still out on this one. Epigenetic changes happen when environmental variations apply “on and off” switches to one’s DNA, resulting in changes to one’s physical characteristics. Epigenetic switches are heritable, but the switches that create a plant’s “winter memory” are not.

Plant enzyme activity in response to environmental changes tell a plant when it’s time to enter dormancy and “on and off” switches in a plant’s DNA tell it how long to stay that way. Feel free to comment with any questions, ideas, or corrections that you notice! This journal post will conclude our weekly wildflower features for this season. Thank you all so much for contributing your observations to this project. It’s been wonderful seeing everyone’s photos and helping one another identify what we’ve seen. Best wishes to everyone! Catch you on the flip side!

Citations:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC520954/
Richard Amasino 2004. Vernalization, Competence, and the Epigenetic Memory of Winter. The Plant Cell 16(10): 2553–2559.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2791696/
Dupont et al. 2009. Epigenetics: Definition, Mechanisms, and Clinical Perspectives. Seminars in Reproductive Medicine 27(5): 351-357.
https://www.britannica.com/plant/plant/Pathways-and-cycles
Dickison et al. 2009. Online Encyclopedia entry: Plant. Encyclopedia Britannica Online.

Posted on November 02, 2020 19:40 by mklein1216 mklein1216 | 2 comments | Leave a comment