. Explain Mechanism of stomatal movement

Best Answer

Machanism of Stomatal Movement:

1. Hypothesis of photosynthetic guard cells

i. During day time chloroplast of guard cells perform photosynthesis.

ii. This produces sugars in guard cells which increases the osmotic pressure of guard cells causes absorption of water from nearby epidermal cells.

iii. Due to his guard cells become turgid and stomata open.

2. Starch 

a. Lloyd’s theory 

i. Starch of guard cells converted to sugar during day.

ii. It increases osmotic content that leads to endosmosis and stomata opens.

iii. During night, sugar converted back to starch, thus by exosmosis stomata closes.

b. pH theory

i. Given by Sayre and supported by Scarth.

ii.Sayre- Starch converts into sugars during day when pH of guard cell is high and sugar changes into starch during night at low pH in guard cells.

iii. During night CO2 reacts with water and form H2CO3, pH in guard cell decreased.

iv. Steward’s modification –He said that glucose-1-phosphate should be converted to glucose as glucose-1-phosphate is not capable of changing osmotic pressure.




Talk to Our counsellor