Biological complexity:plants sense light and temperature (Introduction)

by David Turell , Friday, October 28, 2016, 00:33 (2949 days ago) @ David Turell

Recently discovered cells sense light in the daytime and temperature at night:

http://phys.org/news/2016-10-thermometer-triggers-springtime-budding-night-time.html

"Researchers have revealed that molecules called phytochromes - used by plants to detect light during the day - actually change their function in darkness to become cellular temperature gauges that measure the heat of the night.

"The new findings, published today in the journal Science, show that phytochromes control genetic switches in response to temperature as well as light to dictate plant development.

"At night, these molecules change states, and the pace at which they change is "directly proportional to temperature" say scientists, who compare phytochromes to mercury in a thermometer. The warmer it is, the faster the molecular change - stimulating plant growth.

***

"The latest research pinpoints for the first time the molecular mechanism in plants that reacts to temperature - often triggering the buds of spring we long to see at the end of winter.

***

"If a plant finds itself in shade, phytochromes are quickly inactivated - enabling it to grow faster to find sunlight again. This is how plants compete to escape each other's shade. "Light driven changes to phytochrome activity occur very fast, in less than a second," says Wigge.

" At night, however, it's a different story. Instead of a rapid deactivation following sundown, the molecules gradually change from their active to inactive state. This is called "dark reversion".

"'Just as mercury rises in a thermometer, the rate at which phytochromes revert to their inactive state during the night is a direct measure of temperature," says Wigge.

"'The lower the temperature, the slower phytochromes revert to inactivity, so the molecules spend more time in their active, growth-suppressing state. This is why plants are slower to grow in winter.

"Warm temperatures accelerate dark reversion, so that phytochromes rapidly reach an inactive state and detach themselves from DNA - allowing genes to be expressed and plant growth to resume."

Additional information about how the molecules convert:

https://www.sciencedaily.com/releases/2016/10/161027094826.htm

"Plants contain specialized light-sensitive proteins that change shape when they absorb light, much as do the photopigments in the human eye. All plants have three main red-light photoreceptors, called phytochrome A, B and C.

"Vierstra explains that phytochrome proteins work by switching between two forms, called Pr and Pfr.

"The Pr form is best at absorbing red light, which is plentiful in full sun. When it absorbs red light, phytochrome converts to the Pfr state, which is better at absorbing far-red light that dominates in shade. When the Pfr absorbs far-red light, it switches back to the Pr form.

"This clever little system is able to detect many different qualities of light, including the light intensity (encoded in the speed at which the molecule bounces from one form to another), and the color of the light (encoded by the ratio of the Pfr form to the Pr form). Intensity tells a seed when to emerge from the soil and color tells the seeding when to grow tall to avoid shade."

Comment: How were these specialized molecules found and developed? Plants had to start equipped with them to take advantage of light and heat. Saltation?