The Composition of Stigmatic Exudate from Lilium longiflorum: Labeling Studies with Myo-inositol, d-Glucose, and l-Proline.

Stigmatic exudate, a secretion product recovered from the upper surface of Lilium longiflorum pistils, has been examined. Over 99% of the exudate is accounted for as water, carbohydrate, and protein. Exclusive of water, 95% is a high molecular weight, protein-containing polysaccharide composed of galactose, arabinose, rhamnose, glucuronic acid, and galacturonic acid.Detached pistils supplied with myo-inositol-U-(14)C, myo-inositol-2-(3)H, d-glucose-1-(14)C, or l-proline-U-(14)C produce labeled stigmatic exudate. When myo-inositol is supplied, the exudate is rich in labeled arabinose and uronic acids, but some label also recycles through the hexose phosphate pool of secreting cells, causing label to appear in galactose and rhamnose residues. When glucose is provided, galactose is the major constituent labeled but all of the other carbohydrate constituents are also labeled. Proline produces a pattern very similar to that obtained with glucose.Stigmatic exudate also contains a small amount of low molecular weight carbohydrate. If myo-inositol is used to label exudate, free labeled myo-inositol cannot be detected in the low molecular weight fraction until it has been subjected to acid hydrolysis. Similarly, if d-glucose is the source of label, free labeled glucose is found in the low molecular weight fraction only after acid hydrolysis.