THE EFFECT OF PROLONGED ABSCISIC-ACID TREATMENT ON THE GROWTH, FREEZING TOLERANCE AND PROTEIN-PATTERNS OF BROMUS-INERMIS (LEYSS) CELL-SUSPENSIONS CULTURED AT EITHER 3-DEGREES OR 25-DEGREES-C

The growth, freezing tolerance and two-dimensional protein profiles of bromegrass (Bromus inermis Leyss) cell cultures were investigated fol lowing repeated exposure to 75 mu M abscisic acid (ABA) for 5 weeks. F ollowing prolonged (36 d) exposure to ABA, freezing tolerance was enha nced and fresh-mass gain was reduced compared to a 10-d ABA treatment. Also, fifteen additional ABA-responsive proteins were detected after 5 weeks of ABA treatment that were not detected in cells treated for 1 0 d. In addition, intensity changes occurred in several ABA-responsive proteins that were detected after 10-d incubation periods. Two polype ptides (26 and 29 kD) initially responsive to ABA decreased over 5 wee ks of treatment. Transfer of ABA-treated cells to culture media lackin g ABA for 14 d resulted in a 22 degrees C decrease in freezing toleran ce and increased growth, but there was no detectable change in the ABA -responsive polypeptides. Abscisic acid treatment at 3 degrees C incre ased freezing tolerance at an accelerated rate and to a greater level than 3 degrees C alone, but less so than ABA treatments at 25 degrees C. However, the same ABA-responsive polypeptides detected at 25 degree s C were present in cells treated with ABA at 3 degrees C. These obser vations suggest that synthesis and accumulation of ABA-responsive poly peptides are only one component involved in freezing tolerance and oth er factors must be involved.