The Physiology and Biochemistry of Desiccating White Oak and Cherrybark Oak Acorns
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The recalcitrant behavior of white oak (Quercus alba L.) and cherrybark oak (Q. pagoda Raf.) acorns was examined in terms of effects of moisture content on seed longevity, viability, and biochemistry. Acorns of both species were fully hydrated and then subjected to drying under ambient conditions of temperature and relative humidity. Acorns were sampled regularly for moisture determination (gravimetric analysis), germination, and Fourier transform infrared spectro-scopic analysis. Invertase activity was also determined in the desiccating white oak acorns. Transmission/reflectance spectra were collected on dry and rehydrated samples of cotyledon and embryonic axis tissue. Germination was highly dependent on initial acorn moisture content, and there were significant changes in lipid profiles of desiccating embryonic axis and cotyledon tissues during short-term drying. A strong absorbance near 1740/cm in cherrybark cotyledon tissue indicated a highconcentration of ester carbonyl groups (storage lipids). Additionally, in acorns of both species, evidence of reversible shifts between gel and liquid crystalline phases were found in membranes of axes and cotyledons. Gas chromatographic analyses of desiccating white oak acorns revealed significantly greater sucrose concentrations in embryonic axes than in cotyledons; also, sucrose concentrations dropped dramatically with onset of root extension. It is possible that elevated sucrose concen-trations afford protection against cell collapse and cell-wall membrane damage during moisture stress.