According to the proton transport theory of stomatal mechanism, protons are formed in guard cells when ____.

Step-by-step solution

According to the active potassium ion transport theory (proton transport theory) proposed by Levitt, stomatal opening during the daytime is driven by the accumulation of potassium ions in the guard cells. During the daytime, starch in the guard cells is converted into malic acid. Malic acid then dissociates into malate anions and protons ( H^+ ). These protons are actively pumped out of the guard cells into the surrounding subsidiary cells, and in exchange, potassium ions ( K^+ ) are transported into the guard cell