A) Rise in pH of guard cells causes hydrolysis of starch
B) Cytokinin and cyclic AMP are required
C) Abscisic acid promotes closure
D) All of the above
Correct Answer: D
Solution :
The guard cells contain starch. At low \[C{{O}_{2}}\]concentration pH of guard cell rise, it stimulates phosphorylase which converts starch into glucose 1-phosphate, (according to classical starch hydrolysis theory). Abscisic acid promotes closure of stomata. The malic acid in guard cell dissociates into Hf and malate. H+ pass out of the guard celles in exchange of K?. Some K+ are also absorbed actively from adjacent epidermal cells with the help of cAMP, ATP and cytokinins. (K+ pump hypothesis).
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