Question

Opening and dosing of stomata is due to

• A. $C{a}^{++}$
• B. $N{a}^{+}$
• C. $K^{+}$
• D. $C{l}^{-}$

Answer 1

Answer: (A)

Stomata are the minute specialized pores generally present on leaf epidermis. Each stoma is bounded by two guard cells that are generally kidney shaped. Stomata are the main avenues for transpiration.
Levitt proposed $K^{+}$ ion transport theory for stomatal opening and closing. When $K^{+}$ ions enter into guard cells, stomata open and when $K^{+}$ ions move out then stomata close. The phenomenon can be represented schematically as -
$(A)$ During day time :

$(B)$ During night or dark : $C{O}_2$ conc, increases in sub-stomatal cavities $\to$ ABA participation $\to$ $K^{+}$ ions exchange stopped $\to$ $K^{+}$ ions transported back into subsidiary cells $\to$ Decreased pH $\to$ Starch synthesized in guard cells $\to$ Decreased O.P. of guard cells $\to$ Exosmosis from guard cell $\to$ Stomata close.