EFFECTS OF DESICCATION ON TEMPERATE RECALCITRANT SEEDS - DIFFERENTIALSCANNING CALORIMETRY, GAS-CHROMATOGRAPHY, ELECTRON-MICROSCOPY, AND MOISTURE STUDIES ON QUERCUS-NIGRA AND QUERCUS-ALBA

Investigations into the nature of desiccation-sensitive, or recalcitan t, seed behavior have as yet failed to identify exact causes of this p henomenon. Experiments with Quercus nigra L. and Quercus alba L. were conducted to examine physiological and biochemical changes brought abo ut by seed desiccation and to determine if there were predictable chan ges in seed moisture content, in enthalpy (heat content) of seed moist ure, in the lipid fraction, or in seed ultrastructure as viability dec lined. Quercus nigra intact acorn moisture contents at 50% and 5% viab ility were 15% and less than 14%, respectively; those of intact Q. alb a at 50% and 0% viability were much higher, 32% and 22%, respectively. Generally, it was found that as the seeds of both species dried, the moisture content of the axes remained high (26-27%), even after 9 days of drying. In e. nigra acorns, there was little difference in average percent moisture lost per day among axes, proximal cotyledon tissue, and distal cotyledon tissue. Quercus alba acorns, however, lost moistu re more rapidly from the axes than from the cotyledons. This was proba bly caused by the longitudinal splitting of the pericarp during the dr ying process. Lipids composed 28.4% of the dry weight of Q. nigra and 5.7% of Q. alba dry weight. Neither individual fatty acids nor total f atty acid content exhibited definite patterns of change over the cours e of the experiment. The most prevalent saturated fatty acid in both s pecies was palmitic acid, and the most common unsaturated fatty acid w as generally oleic acid. Electron microscopy studies of e. nigra showe d cell wall trauma after 3 days of drying (moisture content 23%); by d ay 7, when moisture content had dropped to 15.6%, there was a definite dissolution of cytoplasmic density and a reduction of spherosome conc entration. Quercus alba exhibited similar responses to drying, but cel l wall integrity was maintained. Differential scanning calorimetry stu dies revealed strong relationships between onset and enthalpy values o f all acorn tissues and percent germination as did regressions involvi ng moisture content and seed germination.