© 1994 Heron Publishing—Victoria, Canada
Fluxes of Ca2+, K+ and Cl– across the surfaces of detached needles from Sitka spruce trees: pathways and compartmentation
A. E. S. Macklon (1) and J. A. Armstrong (2)
1. Plants Division, Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QJ, U.K. / 2. Department of Forestry, University of Aberdeen, St. Machar Drive, Aberdeen AB9 2UU, U.K. / Received February 10, 1993
Summary
Uptake and efflux of 36Cl–, 45Ca2+ and 42K+ were measured in water-infiltrated detached needles from Sitka spruce (Picea sitchensis (Bong.) Carr.) trees incubated in 1 mol m–3 KCl or CaCl2 or 2 mol m–3 NaCl solutions or in artificial rain water containing mmol m–3 amounts of these ions. Surface efflux was measured separately from leakage from the cut ends of the needles. Needles loaded
with 36Cl– and killed in liquid N2 before elution displayed a rapid and extensive loss of radioisotope, indicating that mesophyll cell membranes were the limiting
factor for 36Cl– exchange. Data for live needles revealed a novel phase of 36Cl– efflux, with an exchange halftime of about 20 min, which was faster than that for either the vacuole or the cytoplasm, but
much slower than that for the free space. The novel phase was interpreted as representing diffusion of Cl– through the predominantly negatively charged cuticle. Killing needles loaded with 45Ca2+ or 42K+ also increased efflux relative to that from live needles, but only to a limited degree, indicating that the main factor limiting
cation efflux was the cuticle. During the first hours of 45Ca2+ uptake, the isotherms displayed a shoulder, indicating that there was a significant Donnan free space phase in the cuticle
for Ca2+. A shoulder was absent from 42K+ uptake isotherms because of the preferential adsorption of divalent cations on the exchange sites.
Keywords:
compartmental analysis, cuticle, efflux, influx, needle surface, Picea sitchensis, rate limiting factors.
