© 2003 Heron Publishing—Victoria, Canada
Effects of desiccation on the physiology and biochemistry of Quercus alba acorns
Kristina F. Connor (1, 2) and Sharon Sowa (3)
1. USDA Forest Service, Center for Bottomland Hardwoods Research, Box 9681, Mississippi State, MS 39762, USA / 2. Author to whom correspondence should be addressed (kconnor@fs.fed.us) / 3. Department of Chemistry, Indiana University of Pennsylvania, Indiana, PA 15705, USA / Received October 17, 2002; accepted April 11, 2003; published online October 1, 2003
Summary
Seeds that lose viability when dried to a water content of less than 12% are said to be recalcitrant. We subjected acorns
of Quercus alba L., a species with recalcitrant seeds, to desiccation to determine the effects of drying on lipids, proteins and carbohydrates
of the embryonic axis and cotyledon tissues. Samples of fresh seed and seed dried for selected intervals were analyzed for
water content and germination, and for lipids, proteins and carbohydrates by Fourier transform-infrared (FT-IR) spectroscopy.
Carbohydrates were further analyzed by gas chromatography (GC).
The FT-IR analysis revealed that membrane lipid structure initially exhibited reversible shifts between gel and liquid crystalline
phases in response to drying and rehydration; however, reversibility declined as viability was lost. Changes in carbohydrate
concentration were observed based on peak height comparisons; sucrose concentration in the embryonic axis increased dramatically
after 5 days of drying. The most sensitive indicator of desiccation damage was the irreversible change in protein secondary
structure in embryonic axes and cotyledon tissue. These changes were illustrated by shifts in amide absorbance near 1650 cm–1. Gas chromatography indicated an abundance of sucrose in both the embryonic axes and the cotyledon tissue. Although sucrose
concentrations in these tissues were initially similar, sucrose concentration in the embryonic axes became significantly greater
than in the cotyledons as the acorns dried. We hypothesize that, in drying acorns, increased concentration of sucrose does
not prevent loss of viability, but acts as a glycoprotectant against cell collapse and cell wall membrane damage as water
stress increases.
Keywords:
carbohydrates, FT-IR, GC, glycoprotectant, lipids, proteins, recalcitrance.
