EFFECT OF ABSCISIC-ACID ON THE COLD-HARDINESS OF WHEAT SEEDLINGS

ABA treatment increased the frost resistance of the wheat varieties Ch eyenne, Martonvasari 14 and Chinese Spring to different extents when t hey were grown without cold hardening. A % survival equivalent to that of the cold-hardened plants was achieved without hardening if the pla nts were treated with 20 mg/L ABA 3 or 6 days prior to freezing at -6 degrees C. The ABA content in the crown in terms of fresh weight was t wice as high as in the leaves even before cold hardening, and this ten dency was observed throughout. In both plant organs a fairly substanti al accumulation of ABA occurred during the first 2 days of hardening, after which the concentration dropped, and remained at much the same v alue from the 5th ts the 20th day. For both the leaves and the crown, the poorly frost resistant Chinese Spring exhibited the smallest incre ase in ABA content. Endogenous changes in ABA were only correlated to the hardening level during the initial stages of hardening and the qua ntity of endogenous ABA depended on the genetic background of the vari ety. These facts would appear to indicate that ABA plays a role in the initial stages of frost resistance development,after which its effect weakens.