The physiology of frost resistance
Recent results on the physico-chemical properties of a plant cell, related to frost hardiness, e.g., cell permeability, viscosity of cytoplasma, and the osmotic potential of the cell, are briefly summarized. In detail a survey is presented on the metabolic processes casually involved in frost hardiness and which, at very low temperatures or in nonhardened cells, ultimately lead to an irreversible injury of the cell. Thus, the sulfhydril-disulfide hypothesis of LEVITT ( 1956) is mentioned, and the investigations of HEBER and SANTARIUS (1964) on the inactivation of phosphorylating systems by temperatures below the freezing point of water as well as the protective action of soluble carbohydrates, amino acids and electrolytes on chloroplasts and mitochondria are discussed critically. From these results it is concluded that the frost resistance of a plant may be regarded as a dynamic phenomenon and that metabolic mechanisms play a mayor role. The consequences in respect to frost protection of crop plants, especially the possibility to increase frost resistance by exogenous application of metabolites, have been outlined. ZUSAMMENFASSUNG Ausgehend von physico-chemischen Anderungen des Cytoplasmas wfihrend einer Temperaturerniedrigung werden die jiingsten stoffwechselphysiologischen Erkenntnisse des Frosttodes einer Zelle dargelegt. Besondere Erwfihnung finden die Schutzfunktion des Zuckers sowie die Sulfhydryl-Disulfid-Hypothese von LEVITT (1956) und der Nachweis der Entkopplung der ATP-Synthese in der zyklischen und oxydativen Phosphorylierung dutch tiefe Temperaturen (HEBER und SANTARIUS, 1964). Die Bedeutung dieser Befunde ftir die Frostresistenz der Zelle und far den neuzeitlichen Frostschutz werden hervorgehoben. EINLEITUNG Die Theorie der Frostresistenz der Zelle erfuhr mit den Vorstellungen yon MAXIMOV (1912) und ILJl~ (1933) einen vorl~iufigen Abschluss. Obgleich spS.terhin