ABSTRACT
This chapter re-examines the relations of water in plants subjected to frost hardening as to what are the possible implications of water potential modifications for cold acclimation and frost-resistance development in plants. The transition of overwintering plants to the freezing-resistant state proceeds in recognizable phases, both in woody perennials and in herbs such as winter rape, winter cereals, and alfalfa. The hardening process is governed mainly by the sequential action of cold, transient night frosts, and prolonged freezing, resulting in cell dehydration. The subfreezing treatment brought about a dramatic decrease in water potential of the cold-grown leaves. Determination of water potential in leaf petioles with a pressure chamber technique showed that the pattern of the subfreezing-induced ψw changes in xylem vessels was different from that registered for the parenchymatic tissue. Accumulation of abscisic acid (ABA) in the stress-affected tissue depends on modifications of water potential; the existence of a water potential threshold for the initiation of ABA accumulation.
