BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Cytokinin hormone controls the opening of stomata. They also regulate plant growth and cytokinesis in different parts of the plant. It also has a major role in plant pathogenesis by inducing disease resistance to certain pathogens.

Detailed explanation-2: -It has been shown that an increased cytokinin concentration in xylem sap promotes stomatal opening and decreases sensitivity to ABA. Drought stress inhibits the synthesis of cytokinins in roots and its transport to shoots, which in turn results in stomatal closure (Pospísilova, 2003; Pustovoitova et al., 2003).

Detailed explanation-3: -Cytokinin activity increases stomatal density and transpiration rate in tomato.

Detailed explanation-4: -Generally, ABA and JA are positive regulators of stomatal closure, while auxin and cytokinins are positive regulators of stomatal opening.

Detailed explanation-5: -The above observations suggest that cytokinins and auxins inhibit ABA-induced stomatal closure through the modulation of ethylene biosynthesis, and that ethylene inhibits the ABA-induced reduction of osmotic pressure in the guard cells.