© 1997 Heron Publishing—Victoria, Canada
Physiological implications of seasonal variation in membrane-associated calcium in red spruce mesophyll cells
D. H. DeHayes (1), P. G. Schaberg (2), G. J. Hawley (1), C. H. Borer (1), J. R. Cumming (3) and G. R. Strimbeck (1)
1. School of Natural Resources, The University of Vermont, Burlington, VT 05405, USA / 2. USDA Forest Service, Northeastern Forest Experiment Station, P.O. Box 968, Burlington, VT 05402, USA / 3. Department of Biology, West Virginia University, Morgantown, WV 26506, USA / Received December 20, 1996
Summary
We examined the pattern of seasonal variation in total foliar calcium (Ca) pools and plasma membrane-associated Ca (mCa) in
mesophyll cells of current-year and 1-year-old needles of red spruce (Picea rubens Sarg.) and the relationship between mCa and total foliar Ca on an individual plant and seasonal basis. Foliar samples were
collected from seedlings and analyzed on 16 dated at 2- to 3-week intervals between June 1994 and March 1995. Concentrations
of mCa in current-year needles were more seasonally dynamic and responsive to temporal environmental changes than either mCa
concentrations of 1-year-old needles, which were largely stable, or total foliar Ca concentrations in both tissues. In current-year
needles, mCa was barely evident in early summer, increased steadily through summer, and then increased dramatically in early
fall and surpassed the concentration in 1-year-old needles. Coincident with the first severe frost, mCa concentrations in
current-year needles declined significantly and subsequently maintained concentrations comparable to those of 1-year-old needles.
Following an extended January thaw, which included 5 days of minimum temperatures > 5 °C, mCa concentrations of current-year
needles temporarily, but significantly, declined. However, there was no change in mCa concentrations of 1-year-old needles
or total Ca concentrations of either tissue. Total Ca concentrations were stable through midsummer in both tissues, doubled
in late summer, and then were stable in both tissues throughout fall and winter. Total Ca concentrations were consistently
higher in 1-year-old than in current-year needles. Correlations between concentrations of mCa and total foliar Ca were consistently
low and mostly nonsignificant. Thus, the dominant, but insoluble, extracellular Ca pool reflected in commonly measured total
foliar Ca concentrations is not a meaningful surrogate for the physiologically important and labile pool associated with the
plasma membrane–cell wall compartment of red spruce mesophyll cells. It is likely that shifts in the critical mCa compartment
would not be detected by analysis of total foliar Ca pools. Seasonal changes in mCa concentration seemed to parallel seasonal
changes in membrane structure, and possibly the important role of extracellular Ca in transducing messages associated with
environmental signals.
Keywords:
cold acclimation, compartmentation, extracellular calcium, frost, Picea rubens, plasma membrane, total foliar calcium, winter thaw.
