Water Potential
Water potential is the potential energy of water molecules. Regardless of
the reason (e.g., gravity, pressure, or concentration of solute particles) for
the water potential, water moves from a region where water potential is greater
to a region where water potential is lower. The greater the difference between
the water potentials of the two areas, the greater the pressure on the water
to move.
Water always flows via diffusion from areas of high water concentration to
lower water concentration. The lower water concentration in plants results from
the removal of water for use in photosynthesis at the leaf, storage in special
water storing cells, or loss of water through the stomata as a result of transpiration.
In addition, the addition of solute molecules (like sucrose) drastically reduces
the water concentration in such regions. Water molecules thus move from high
potential (high concentration) to lower potential (low concentration).
Long & Slichter