Question

You learned in your plant physiology class that stomatal aperture is regulated by an integration of signals from endogenous and environmental stimuli. Compare and contrast signal transduction pathways of the two types of environmental signals regulating stomatal aperture. What is the role of hormones in these processes?

Expected length: 1-1 ½ pages

Answer 1

Stomatal aperture is regulated by the endogenous conditions of the plant and the environmental condition in which it is present. Each stomatal aperture is surrounded by guard cells and subsidiary cells that are involved in regulating the stomatal aperture size.

Turgor pressure in guard cells plays an important role. When guard cells are flaccid, the stomatal aperture is closed and when they are swollen then the aperture is large. A high turgor pressure opens up stomata.

Guard cells are hydraulic valves that sense environmental factors which include temperature, humidity, CO2 concentration and light intensity.

When plant sense light after a period of darkness, they respond by opening pores of stomata. Upon sensing early morning blue light, proton pumps are activated in the guard cells. Because of changers in metabolism, the osmotic potential is decreased. Water enters into the cells and turgor pressure increases.

Water availability is another way of regulating stomatal opening. When water is less then stomata close to reducing water evaporation. This is due to decrease in turgor pressure of the guard cells. Upon dehydration, ABA also plays an important role in regulating stomatal opening. Brassinosteroids and jasmonic acid are other hormones involved in the pathway.