Question

Active $K^{+}$ change mechanism for opening and closing of stomata was given by

• A. Darwin
• B. Levitt
• C. Scarth
• D. Khorana

Answer 1

Answer: (B)

Levitt

Levitt in 1974 gave a revised form of the structure of stomatal movement which was called the proton - potassium pump hypothesis. This inference explains K${}^{+}$ ions are transported into the guard cells in the presence of light. It is said to be series of steps takes place during this process.

(i) With the availability of light, protons build by breaking of malic acid and moves from cytoplasm in to the chloroplasts of guard cells.

(ii) From the circling mesophyll cells, K${}^{+}$ ions enter the guard cells to equate the exit of protons from the cell.

(iii) K${}^{+}$ ions react with the malate ions and form potassium malate.

(iv) With the help of potassium malate osmotic potential of guard cell increases. This results in the entry of water into guard cells cause stomata to open when they swell up.

(v) At night potassium malate gets dissociated and K${}^{+}$ ions exit out of guard cells as a result guard cells losses to water and so the stoma closes.

So, the correct answer is option B.