Article

Planta

, Volume 162, Issue 3, pp 276-282

First online:

Equilibrium freezing of leaf water and extracellular ice formation in Afroalpine ‘giant rosette’ plants

  • Erwin BeckAffiliated withLehrstuhl Pflanzenphysiologie der Universität
  • , Ernst-Detlef SchulzeAffiliated withLehrstuhl Pflanzenökologie der Universität
  • , Margot SenserAffiliated withBotanisches Institut der Universität
  • , Renate ScheibeAffiliated withLehrstuhl Pflanzenphysiologie der Universität

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Abstract

The water potentials of frozen leaves of Afroalpine plants were measured psychrometrically in the field. Comparison of these potentials with the osmotic potentials of an expressed cellular sap and the water potentials of ice indicated almost ideal freezing behaviour and suggested equilibrium freezing. On the basis of the osmotic potentials of expressed cellular sap, the fractions of frozen cellular water which correspond to the measured water potentials of the frozen leaves could be determined (e.g. 74% at -3.0° C). The freezing points of leaves were found to be in the range between 0° C and -0.5° C, rendering evidence for freezing of almost pure water and thus confirming the conclusions drawn from the water-potential measurements. The leaves proved to be frost resistant down to temperatures between -5° C and -15° C, as depending on the species. They tolerated short supercooling periods which were necessary in order to start ice nucleation. Extracellular ice caps and ice crystals in the intercellular space were observed when cross sections of frozen leaves were investigated microscopically at subfreezing temperatures.

Key words

Equilibrium freezing Freezing tolerance Leaf (water potential) Rosette plant (Afroalpine) Water potential