Dynamics of Ultrastructural Characters of Drosophyllum lusitanicum Link (Droseraceae) Digestive Glands During Maturation and After Stimulation

A quantitative investigation was conducted on the endomembrane system of the secretory cells of Drosophyllum lusitanicum Link digestive glands exporting acid hydrolases. The surface density of rough endoplasmic reticulum (RER) membranes as well as the number of Golgi stacks, clathrin-coated vesicles (CCVs) and their smooth derivatives increased progressively with the gland maturation. On average secretory cells of the fully mature unstimulated gland, each contained RER with a surface area of 17500 µm2 and 16000 small vesicles (including CCVs of 81 nm average diameter and smooth vesicles as the derivatives of CCVs which average 46 nm). One hour after stimulation imitating prey capture, the surface density of RER, the number of Golgi stacks and 'protein' vesicles all increased greatly. The data obtained indicate that smooth vesicular derivatives of CCVs are involved in the secretion of digestive enzymes. Hydrolase secretion started in the immature glands and continued in the mature stage irrespective of whether or not an insect was actually captured. Stimulation resulting in the release of digestive fluid on the surface of the leaf by the digestive glands appeared to be accompanied by a significant increase in the rate of hydrolase synthesis and secretion. In addition to protein vesicles, two other types of larger secretory Golgi vesicles were produced: granular-fibrillar ones (~ 105 nm in diameter that were confined to cells at the meristem stage), and loosely-fibrillar vesicles (~ 250 nm in diameter that occurred only at the stage of wall ingrowth deposition). Models are proposed that depict digestive gland cell functioning both before and after stimulation