Transport in Plants

Opening and closing of stomata

  • Change in osmotic pressure and turgidity in guard cells govern the stomatal opening and closing.
  • The stomatal pore is open when the guard cells are turgid and is closed when they are flaccid.
  • Three different theories are proposed for opening and closing of stomata, which differ in the factor causes turgidity.
  • According to Schwendener (Hypothesis of guard cell, photosynthesis), starch is the agent that increases the osmotic pressure and turgidity to open the apparatus of stomatal pore during the day time, as photosynthesis occurs in the day time.
  • Classical starch hydrolysis theory as proposed by Lloyd and Sayne, later modified by Steward, states that glucose increases the turgidity, that is being formed / produced due to the hydrolytic reaction upon starch
  • Potasium (or) malate ion pump theory was given by Fujino and later modified by Levitt is the most accepted modern theory.
  • According to the theory malate (or) potassium, that has been released into the guard cells due to the production of phospho end pyruvate and Oxaloacetic acid is governing the stomatal opening process in the day time.
  • During night time, Exosmosis happens from guard cells, that decrease the turgidity and osmotic pressure to close the stomatal pore
  • During the seedling transplant, antitranspirants are employed to decrease the rate of transpiration without affecting CO2 fixation in photosynthesis.
  • Examples of anti – transpiration agents are colourless plastics, Dodecenyl saccinic acid, phenyl mercuric acetate, Abscisic acid (ABA) CO2

View this video for the topic Opening and closing of stomata from 29:53 to 34:14

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