ABSTRACT
The induction of freezing and chilling tolerance in temperate plant species requires a sensory mechanism for detecting environmental cues. The leaves of woody plants produce both translocatable hardiness inhibitors and translocatable hardiness promoters depending upon the environmental cues. There is considerable evidence that environmentally controlled, endogenous growth regulators such as abscisic acid (ABA) and gibberellic acid (GA) are involved in the adaptive response. Exogenous application of ABA to induce cold acclimation or chilling resistance has resulted in either no response, partial enhancement, or a dramatic increase. Ethanol is often used to aid solvation of ABA, which is sparingly water soluble. ABA and other growth regulators are routinely dissolved in an alkaline solution, e.g., NaOH, prior to addition to the medium. There are several mechanisms by which plant growth regulators control cold hardiness. Gene transcription and protein synthesis are required for the manifold changes involved in hardening.
