Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 2004. Sectio Biologiae. (Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 25)
Marschall, M. and Proctor M. C. F.: Aspects of stress tolerance in bryophytes
116 Marschall, M. and Proctor M. C. F. Cell water relations in bryophytes essentially are the same as those of other plant cells and described by the 'Höfler diagram' (Figure la, b): the relation between cell osmotic potential and water content can be described as a rectangular hyberbola. The relation of cell water potential to cell water content follows this hyperbola up to the turgor-loss point. It then breaks away to follow a line to the full-turgor (where RWC=1.0 and ¥=0). When the axes of the graph relating water potential to water content is plotted on a reciprocal scale, the hyperbola becomes a straight line (Figure 2a). The graph of 1/\|/ against (1-RWC) is referred as a pressure-volume (pv) curve. The horizontal dotted line indicates the turgor-loss point. After psychrometric measurements from the pv-curves \|/ MI turgo r, e B can be read (bryophyte cell walls are rather extensible =>low e B). Surface water amount can vary widely without affecting cell water status which can result in difficulties in expressing precise actual water content (3 types of water: capillary, apoplastic, symplastic). The knowledge of WC at full turgor is principal to calculate RWC. This value is physiologically comparable with those for vascular plants. RWC values based on „saturated" water content can be wholly misleading. Full turgor water content can often be obtained by carefully blotting samples. (Actual WC/ WC at full turgor)* 100 is expressed on fresh weight base or dry weight base. External capiliary water 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Relative cell volume (RWC') 1 0.8 0.6-1 ~S>A. 04-j Porella platyphylla — t— I— t— s— 1—!— i—*— I— r 1 2 3 4 5 Water potential (-MPa) Figure la, b: (a) Höfler diagram for a bryophyte illustrating the relationship of cell water potential (\|/) and its components to cell water content and external capillary water, (b) The relation of relative water content to water potential for the leafy liverwort Porella platyphylla, from thermocouple measurements. Water content was originally plotted as% dry weight, and the full-turgor point estimated by inspection from the graph, as described by Proctor et al. (1998). The horizontal dotted line indicates the turgor-loss point. A rectangular hyperbola has been fitted to the data point below this, and the a polynomial regression to the points between full turgor and turgor loss. Original figures from Proctor 2000.
