Oxalis in the morning : Oxalis in the morning Wilting in the afternoon as the motor cells lose water and potassium
Slide 2 : When water or temperature becomes limiting
Such as in the cold of winter or during prolonged drought . Why do you think some trees
get rid of their leaves ?
Water movement in a leaf : Water movement in a leaf
Slide 4 : Stomata help in regulating the movement of gases in and out of the leaf. The two guard cells are surrounded by accessory cells.
Slide 5 : DAY TIME
CO2 is released during respiration
Photosynthesis occurs in mesophyll cells
Decrease in H+ concentration in guard cell
pH increases
Conversion of starch into sugar
Osmotic pressure increases in guard cells
Guard cell become turgid
Endosmosis occurs
Stomata open
Slide 6 : IN DARKNESS
In guard cells CO2 accumulates
Lack of photosynthesis
Increase in H+ ion concentration in guard cell
Low pH
Sugar is converted to starch
Osmotic pressure decreases in guard cells
Guard cell becomes flaccid
Exosmosis occurs
Stomata close
5. Theory of Levitt or Potassium ion pump theory : 5. Theory of Levitt or Potassium ion pump theory This modern theory was put forward by Levitt (1974).
It was also called the theory of proton transport.
According to this mechanism guard cells make large amounts of organic acids during stomatal opening.
The most abundant of these is malic acid, which ionizes and releases H+ into the cytoplasm of the guard cells
The H + is pumped out of the guard cell as K+ is pumped in and stored in the vacuole.
The accumulation of K+ in guard cells may reach 0.5 M, which decreases the solute potential of the guard cell, despite a twofold dilution resulting from expansion of the guard cell .
Theory of Levitt : Theory of Levitt Similarly, stomata close when guard cells pump K+ into the apoplast.
This causes water to leave the guard cells and the pores to close.
There is an accumulation of K+ ions in the guard cells during the day
The protons (H+) are 'pumped out' from the guard cells into 'the adjacent epidermal cells and in exchange K+ ions are 'pumped' into them from the adjacent epidermal cells.
This exchange of H+ and K+ ions is followed by the entry of CI -anions into the guard cells.
Theory of Levitt : Theory of Levitt The accumulation of K+ ions in guard cells is also accompanied by increased pH and organic acid (malic acid) build up.
The accumulation of K+ ions together with CI - and malic acid ions is sufficient enough to increase the osmotic-pressure of guard cells during day light.
Consequently water enters into the guard cells thereby increasing the turgor pressure and opening of the stomatal pore.
Reverse situation prevails during dark when stomata are closed.
There is no accumulation of K+ in guard cells in dark