In plant-water relationships, the symbol `Yw` is used to represent water potential. Water potential refers to the potential energy of water molecules in a system, specifically in relation to their concentration and pressure. It is a measure of the tendency of water to move from one area to another, such as from the soil into a plant`s roots or from the roots to other parts of the plant.

Option 1: Osmotic pressure is the pressure needed to prevent the movement of water across a semipermeable membrane due to osmosis. While osmotic pressure is related to plant-water relationships, it is not represented by the symbol `Yw` in this context.

Option 3: Solute potential, also known as osmotic potential, is a component of water potential. It measures the effect of solute concentration on the movement of water. However, it is not represented by the symbol `Yw`.

Option 4: Osmosis is the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. While osmosis is related to plant-water relationships, it is not represented by the symbol `Yw` in this context.

Therefore, the correct answer is