Question

Opening and closing of stomata is due to which of the following ions?
(a) ${Ca}^{2+}$
(b) ${Na}^{+}$
(c) ${K}^{+}$
(d) ${Cl}^{-}$

Answer 1

 Hint: Stomata are the pores present in the mesophylls of the leaves that allow for the gaseous exchange. The opening and closing of these stomata are controlled by the guard cells which are in turn controlled by the concentration of certain ions belonging to group 4 in the periodic table. They are the ions that also help in nerve conduction and muscle contractions.

Complete Step by Step Answer:
Stomatal openings allow for the transpiration and exchange of gases in plants. They are present in the mesophyll of the leaves. The opening and closing of these pores are controlled by kidney- shaped guard cells. Ion uptake is required by the guard cells to cause stomatal opening. Potassium pumps and channels have been identified and are demonstrated to function in the uptake of ions and cause the opening of stomatal apertures. These cells are thus controlled by the concentration of potassium ions (${K}^{+}$) . When the ions are released out from the guard cells, stomatal closure occurs.
Guard cells perceive environmental stimuli such as light, humidity, temperature, drought, etc to trigger the cellular responses. These signal transduction pathways play a role in determining how quickly a plant will lose water, or how much water has to be lost. Accordingly, the guard cells regulate the concentration of potassium ions by opening and closing the potassium channels.
So, the correct answer is, ‘(a) ${K}^{+}$’.

Note:
- Other ion channels have also been identified in the guard cells that mediate the release of potassium ions from the channels.
- Certain anion channels were identified as important controllers for stomatal closure.
- They release anions, such as chloride and malate in low concentrations from the guard cells, which is required for stomatal closing.
- The release of negatively charged anions results in an electrical shift of the membrane to depolarize. This electrical depolarization of the guard cells leads to the activation of the outward potassium channels and thus the release of potassium through these channels