DPD is the amount by which the diffusion pressure of a solution is less than it's pure solvent.

Let's take an example.

Cell A hai and Cell B hai. Diffusion A to B ho Raha hai.

What can we infer from this?

A ka water potential zyada hai B se.

Isko agar DPD ke terms me define karna pade, toh we will say A ka DPD B se Kam hai. 

Remember, Low DPD to High DPD diffusudi hota hai. Reverse of Aater potential concentration concept.

DPD = Osmotic Pressure - Wall Pressure (Turgor Pressure)

Let's take a question.

Cell A has Osmotic Pressure of 10atm and Turgor Pressure of 6atm. Cell B has Osmotic Pressure of 10atm and Turgor Pressure of 4atm. Find out that in which direction water movement will occur.

DPD of A = OP-TP = 10-6 = 4

DPD of B = OP-TP = 10-4 = 6

Hence water movement will occur from A to B.

If you want to cross check, Turgor Pressure se kar sakte ho. A ka TP 6 hai, yani more water. B ka 4 hai, yani less water. Water potential concept se A to B hi hoga . ( High to Low)

Low DPD to high DPD diffusion hota hai.**

Reverse of water potential concept. **

Waste