Chemical regulation of gas exchange and growth of plants in drying soil in the field

There is now substantial evidence that chemical regulation of shoot physiology occurs in droughted plants in the field. The evidence that ABA may play a role in such regulation is considered, and topics of relevance to the worker interested in determining the ABA relations of plants in the field; such as the methods used for ABA quantification, the relevance of quantifying ABA in various plant tissues, methods of xylem sap collection and timing of sap collection are reviewed. A possible role of tissue sensitivity to ABA in controlling the diurnal changes in stomatal conductance and leaf growth rate seen in the field is also considered.