Under zero transpiration conditions dark RH 100 a short pla

Under zero transpiration conditions (dark, RH = 100%), a short plant is in water potential equilibrium with a soil having a _m of -0.08 MPa but no solutes (_s=0). In the leaf mesophyll cells, _s is -1.0 MPa, but assume that there are no apoplastic solutes initially.

a) What turgor would you expect to find in the leaf mesophyll cells?

b) What do you think would happen to the turgor in the leaf mesophyll cells, if the root stele and cortical cells suddenly released a substantial quantity of solute directly into the root xylem (assume that all the root cells and structures, such as the casparian strip, maintain their integrity)?

c) What should happen to the turgor in the leaf cells, if the root cortical cells suddenly released a substantial quantity of solute into their own apoplast (otherwise, same assumptions as in d.)?

Solution

a) The plant is in equilibrium with soil and no transpiration is taking place. So,no absorption of water. Matric potential has negligible role here. In the mesophyll, solute potential -1 MPa. Since it is a short plant, so water potential at equilibrium is -1 + -.08 = -1.08 MPa. So, the turgor pressure is very low.

b) If solutes are directly released into the xylem, they will be transported to the leaf and increase the osmotic pressure of leaf mesophyll cells. As a result of which endosmosis will occur in the leaf mesophyll cells and turgor pressure will increase.

c) If solutes are released suddenly in the apoplast of the root cortical cells, then those salt particles will increase the matric potential. Water may be drawn from cytoplasm of the cortical cells, Water potential of cortical cells will decrease and it will create a negative pressure in the xylem. Water will be drawn from the leaf mesophyll cells. Their turgor pressure will fall.