Question

Which is the latest explanation for the closure of stomata?

• A. Starch glucose theory
• B. Active $K^{+}$ ion theory
• C. ABA theory
• D. None of the above

Answer 1

Answer: (B)

Active $K^{+}$ ion theory

• K+ ion theory was proposed by Levitt in 1974. K ions are balanced by malate ions present in guard cells and also by taking in some Cl ions.
• This ion exchange occurs through the expenditure of ATP energy.
• Plant hormone ABA acts on guard cells, which interfere with the exchange of K+ H+ ions in guard cells, results in a reverse of the reaction of the opening of stomata, hence stomata closed.
  
• Hence, Active K+ ion theory is the latest explanation for the closure of stomata.
• So, the correct answer is 'Active K+ ion theory'.