Q. What is the formula of the DPD for withered (shrunken) plant cells and how is that situation possible?
Withered plant cells are those that have shrunk due to loss of water by evaporation without sufficient replacement. In this situation the cell membrane detaches and retracts from the cell wall. The cell wall moreover expands in length to stimulate the entrance of water making TP < 0. Since DPD = SF - TP and TP is negative (< 0) its formula becomes DPD = SF + |TP|.