Question

In succulent plants the stomata open in night and close in day. Which among the following would be best hypothesis to explain the mechanism of stomatal action in night only? 

(a) CO₂ accumulates, reduces pH, stimulate enzymes resulting in accumulation of sugars. 

(b) increase in CO₂ concentration, conversion of organic acids into starch resulting in the increased conversion into sugars resulting in K⁺ transport. 

(c) low CO₂ concentration accumulates organic acids resulting in the increased concentration of cell sap. 

(d) CO₂ used up, increase pH results in accumulation of sugars.

Answer 1

The correct option is: (b) increase in CO₂ concentration, conversion of organic acids into starch resulting in the increased conversion into sugars resulting in K⁺ transport. 

Explanation:

In CAM plants stomata open at night. In these plants night acidification occurs. i.e., malic acid is synthesised during night due to incomplete oxidation of carbohydrates.

At night malic acid fonned in guard cells dissociates into H⁺ and malate ions. K ⁺ ion exchange from subsidiary cells with H⁺ ions. Thus due to accumulation of K ⁺ ions osmotic pressure of guard cells increases, endosmosis occurs and guard cells become turgid due to which stomata opens. The malic acid at day time breaks into CO₂ and pyruvic acid thus increasing the concentration of CO₂ in mesophyll cells. This is utilised in Calvin cycle form sugar which is finally converted into starch.