DEFINING STERIC, ELECTRONIC AND CONFORMATIONAL REQUIREMENTS OF CARRIER-MEDIATED UPTAKE OF ABSCISIC-ACID IN BARLEY SUSPENSION-CULTURE CELLS

The structural and conformational requirements of a carrier responsibl e for the saturable component of the uptake of the plant hormone (+)-a bscisic acid in barley suspension culture cells have been probed throu gh the use of a defined series of optically pure ABA analogues. Two an alogues showed a tenfold increase over (+)-ABA inhibiting the uptake o f radiolabelled (+)-ABA. Results from different studies (molecular mod elling, low temperature NMR spectroscopy and assays with sterically ri gid analogues) have shown the likely conformation of ABA in the bindin g site of the carrier is that with the sidechain in an equatorial-like orientation. Structure/activity studies show that the C-1 carboxylic acid is essential for binding, the C-4 carbonyl is moderately importan t while the C-1' hydroxyl group is not important for binding to the ca rrier. (C) 1997 Elsevier Science Ltd.