EFFECTS OF 24-EPIBRASSINOLIDE ON FREEZING AND THERMOTOLERANCE OF BROMEGRASS (BROMUS-INERMIS) CELL-CULTURES

The effect of 24-epibrassinolide (EBS), a brassinosteroid, on the resp onse of smooth bromegrass (Bromus inermis Leyss) cell suspension cultu res under low and high temperature stress was evaluated. EBS minimally increased freezing tolerance of bromegrass cells by 3-5-degrees C, bu t markedly enhanced cell viability following exposure to high temperat ure stress. The net effect on hardening was, however, less than that o btained with abscisic acid (ABA). Treatment of cells with EBS increase d the accumulation of a subset of ABA-inducible heat-stable proteins, but unlike ABA, EBS did not induce the expression of dehydrin transcri pts which hybridized to a barley dehydrin clone. EBS slightly increase d the hsp90 transcript levels, while ABA reduced the level of expressi on. These results confirm that brassinosteroids confer some stress tol erance to plant cells and further suggest that the mechanisms by which these compounds exert anti-stress effects may only in part be similar to that of ABA.