One of the earliest responses to insufficient moisture supply is a reduction in turgor pressure; cell expansion and growth are immediately inhibited, and unsuberized shoots soon wilt.

The concept of water deficit, as developed by Stocker in the 1920s, is a useful index of the balance in the plant between uptake and loss of water. Slight water deficits are normal and do not impair the functioning of the plant, while greater deficits disrupt normal plant processes.