Question

According to Steward's starch hydrolysis theory, which one of the following is the principal reason for the opening of stomata during day time?
(a)Influx of ${ { K }^{ + } }$ ions guard cells under the influence of ABA hormone
 (b)Conversion of sugar into starch in guard cells
(c)Efflux of ${ { K }^{ + } }$ ions from guard cells under the influence of ABA hormone
(d) Photosynthetic utilization of ${ CO_{ 2 } }$ in guard cells

Answer 1

Hint: Frederick Campion Steward was known for his contribution to plant tissue culture and genetic engineering. His theory was on the utilization of the gas that is also used during respiration. He was born in Pimlico and further brought up in Yorkshire. He studied at Heckmondwike Grammar School and then attended the University of Leeds. He gained his B.Sc in biology in the late 1920s and then researched the botany department.

Complete answer:
Photosynthetic utilization of ${ CO_{ 2 } }$ in guard cells is the reason for the opening of stomata during the daytime. The theory states that the interconversion of starch in sugar is responsible for the opening and closing of the stomata during day time. Photosynthesis takes place in the guard cells and its carbon dioxide concentration decreases which leads to an increase in pH. Starch is then converted to glucose 1 phosphate which is followed by the conversion of glucose 6 phosphatases. Glucose 6 phosphate breaks into glucose and phosphate. It is soluble in the cytoplasm of guard cells. The water potential of guard cells increases due to the glucose which leads to endosmosis. This makes the guard cell turgid which causes the opening of the stoma.

Additional Information: The guard cells are the specialized cells that are surrounded by the stomatal pore and can integrate endogenous signals and environmental signals to control the stomatal aperture and gaseous exchange. The transportation of carbon dioxide is done with the loss of water and the size is controlled by the stomatal aperture which helps in optimizing the efficiency of water inside the turgor cells. The abiotic stress forces the activation of signal transduction which interacts with or is activated by phytohormones. The abscisic acid (ABA) is the stress hormone that closes the stomata. During the opening of stomata, the hydrogen ion and ATPase pump mediate the efflux of a hydrogen ion from the guard cells. The efflux of hydrogen ion five polarizers the PM and leads to the uptake via activation of potassium ions. The signal that activates the influx of potassium ions with potassium channels with the acidification of the apoplast as a result of hydrogen ions extrusion from guard cells.
So, the correct answer is 'Photosynthetic utilization of ${ CO_{ 2 } }$ in guard cells'.

Note: Steward contributed towards transportation and knowledge about salt absorption. He discovered that ion accumulation was linked with the metabolism. This was further connected with protein metabolism. They studied using chromatographic separation of amino acids. He later deals with the study of the ion accumulation process of meristematic tissues in plants of various substances.