Relationship between abscisic acid content, dry weight and freezing tolerance in barley cv. Lunet

The role of abscisic acid (ABA) in freezing tolerance induction of hydroponically cultivated barley (Hordeum vulgare L. cv. Lunet) plants was studied using a number of approaches. First, the plants were hardened by cold at 3 degrees C. Second, the endogenous ABA content was increased by means of three established methods: (i) rapid dehydration of detached, fully expanded second leaves; (ii) application of 20 % polyethylene glycol 8000 (PEG) into the growth solution of plants, or (iii) 7.5 x 10(-5) mol/L ABA supplement into the growth solution. The changes in freezing tolerance, dry weight, and ABA content were measured in second leaves. Cold hardening of plants resulted in increased freezing tolerance and was related to accumulation of dry weight in leaves; however, only some ABA content fluctuation was observed. The rapid dehydration of detached leaves resulted in an increase of ABA content but not in any significant increase in freezing tolerance. The increase of ABA content in the leaves of intact plants, either due to application of PEG or addition of exogenous ABA into the growth medium, led only to a moderate increase of leaf dry weight content and freezing tolerance. Low temperature treatment accompanied by the accumulation of dry weight is essential to acquire a full measure of freezing tolerance. The involvement of ABA in cold hardening of plants could not simply be explained by increased content only.