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. $C{O}_2$ accumulates, reduces $pH$, stimulate enzymes resulting in accumulation of sugars
• B. Increase in $C{O}_2$ concentration, conversion of organic acids into starch resulting in the increased conversion into sugars resulting in $K^{+}$ transport
• C. Low $C{O}_2$ concentration accumulates organic acids resulting in the increased concentration of cell sap
• D. $C{O}_2$ used up, increase $pH$ results in accumulation of sugars

Answer 1

The correct option is A $C{O}_2$ accumulates, reduces $pH$, stimulate enzymes resulting in accumulation of sugars

In succulent plants, during the night, there is incomplete oxidation of carbohydrates and accumulation of organic acids without the release of C02 due to which, carbon dioxide accumulates in the guard cells. Amplified acidification of guard cells is seen due to the accumulation of CO${}_2$ and the formation of bicarbonate ions. Accumulation of organic acid is mainly in the form of malic acid in the dark period when an organic acid is stored in the central cell sap vacuole. Malic acid is the main osmoticum for the increase of guard cell turgor pressure and the contributions of K+ and sugar as osmotic materials are feeble. So, the correct option is 'CO2 accumulates, reduces pH, stimulate enzymes resulting in accumulation of sugars'.