Water Stress

Abstract

The quantification of external water stress is expressed in terms of the water status of the environment, i.e. external water potential, relative humidity or as vapour pressure. Tissue dehydration may also be measured by changes in tissue water potential or changes in tissue water content (percentage of tissue weight). However, individual tissues differ widely in water contents at full turgidity. Thus, a fully turgid leaf may contain 85% water, whereas a fully imbibed seed storage cotyledon may contain only 60%; dehydration to 55% water would mean a relatively much greater water loss by the leaf than by the cotyledon. Consequently, the relative water content (RWC) is sometimes used in comparisons of water stress resistance in order to indicate the degree of water deficit:

$$\begin{array}{l}RWC = \frac{{tissuewatercontent}}{{tissuewatercontentatfullturgidity \times 100}} \\= \frac{{(freshweight) - (dryweight)}}{{(fullyturgidfreshweight) - (dryweight) \times 100}} \\\end{array}$$