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 ph ysiology occurs in droughted plants in the field. The evidence that AB A may play a role in such regulation is considered, and topics of rele vance to the worker interested in determining the ABA relations of pla nts in the field; such as the methods used for ABA quantification, the relevance of quantifying ABA in various plant tissues, methods of xyl em sap collection and timing of sap collection are reviewed. A possibl e role of tissue sensitivity to ABA in controlling the diurnal changes in stomatal conductance and leaf growth rate seen in the field is als o considered.