Ph ysiology and Bioch em istry of Recalcitrant Guarea guidonia (L.) Sleum er Seeds

Investigations of recalcitrant, or desiccation-sensitive, seeds have as yet failed to identify the causes of this phenomenon. Experiments with Guarea guidonia (L.) Sleumer (American muskwood) were initiated to determine the effects of desiccation on the physiology and biochemistry of the seeds of this tropical tree species. Seeds were air-dried at room temperature for 7 days. At intervals, germination was tested, moisture content determined, and lipids extracted. The bulk lipids, nonpolar lipids, monoglycerides, and phospholipids were analyzed by gas chromatography (GC), thermal characteristics of whole tissue samples were examined using differential scanning calorimetry (DSC), and moisture content was determined using the Karl Fisher analysis. DSC thermograms showed that as moisture content and germinability of seeds declined, so did enthalpy values and onset temperatures of cotyledon tissge and embryonic axes. GC analyses determined that unsaturated fatty acids accounted for approximately 70% of the bulk lipids; however, ratios of unsaturated/saturated fatty acids and amounts of individual fatty acids fluctuated between test periods. Palmitic acid was the most common saturated fatty acid, and linoleic acid was the most prevalent unsaturated fatty acid. Generally, Karl Fisher analyses of seed moisture content offered the best possibility of monitoring seed deterioration during drying.