Plant water content can provide useful, if limited, information about the plant’s response to environmental stress.
Plant water content measurements offer easy ways to find out whether there is a change in plant water status. They are simple and useful indicators of the effects of treatments like drought, salinity, heat and cold on plant water status. They can measure the hydration status of particular tissues in relation to control treatments. They also reveal whether there has been a change in hydration status, but they do not provide information on whether the changes are beneficial or detrimental, or related to a change in turgor of cells.
The simple measurement of water content, which is the ratio of water to dry weight of a tissue, can indicate a change. However this can be due to less water or more dry weight in a given volume of tissue.
The almost equally simple measurement of relative water content (RWC) allows users to distinguish between loss of water, or gain in dry weight for a volume of tissue, as it compares the water content of freshly harvested tissue with that after a period of rehydration, on a dry weight basis. This has errors when plants have osmotically adjusted, as described in Boyer et al. (2008). However useful qualitative information can still be obtained. If the RWC has not fallen, the plant is not stressed and is fully turgid. However if the RWC has fallen, the plant is not necessarily stressed; it may have become dehydrated and lost turgor, or it may have osmotically adjusted to maintain turgor.
Protocols for these methods, and modifications of the RWC are described in the box to the left.
Boyer et al. 2008. Osmotic adjustment may lead to anomalously low estimates of relative water content in wheat and barley. Functional Plant Biology 35, 1172-1182. doi: 10.1071/FP08157