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Published online by Cambridge University Press: 04 August 2010
SUMMARY
A method for determining the amount of needle apoplastic water and bulk osmotic pressure in the symplast of spruce needles (Picea abies [L.] Karst.) is presented. The method is based upon a combined use of the pressure volume analysis of whole shoots and microcryoscopy of sap pressed from needles after being frozen in liquid nitrogen.
INTRODUCTION
Pressure-volume (PV) analysis (Tyree & Hammel, 1972) enables the determination of several plant water relations parameters. The measured values are “bulk tissue averages”, which characterize the plant tissues better when they are uniform {i.e. only leaves). In plant species with small leaves, for example conifers, PV analysis can only be performed on shoots which consist of leaves, wood and bark. The resultant water relation parameters then represent a complex tissue; this can be disadvantageous in studying the physiology of leaves or other plant parts.
Through the combined use of PV analysis of spruce shoots and capillary microcryoscopy of sap pressed from needles, determinations of the most important water relations parameters, needle apoplastic water content and bulk osmotic pressure in the needle symplast, were possible.
MATERIALS AND METHODS
Pressure-volume analysis
In late summer 1987, water potential isotherms from different sized shoots of a 25-year-old, 16 meter tall Norway Spruce {Picea abies [L.] Karst.) were generated (Gross & Koch, 1991a). The sample shoots were kept in a temperature regulated pressure chamber during the entire experiment (Gross & Pham-Nguyen, 1987) and were dehydrated through stepwise increases in pressure. From the water potential isotherms, the bulk osmotic pressure at full turgor (π0), and the bulk osmotic pressure when turgor initially reaches zero (πp), the amount of symplastic (Wo) and apoplastic (Wa) water was determined.
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