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The stigma of Ornithogalum sigmoideum is of dry and papillate type. The papillae are covered by a cuticle-pellicle layer, as revealed by staining. The activity of nonspecific esterase, acid phosphatase and peroxidase increases in the pellicle during the receptivity period. The style of O. sigmoideum is of the hollow type. Ultrastructural study of the cells lining the canal indicated that they are secretory cells and contain abundant endoplasmic reticulum, dictyosomes, mitochondria, plastids and ribosomes. After anthesis these organelles show degeneration at the end of the secretory phase. In canal cells, cytochemical tests showed the presence of acidic polyanions, insoluble and acidic polysaccharides, proteins and lipids. Before anthesis the canal cells are rich in polysaccharides, proteins and lipids. At maturity the cuticle is ruptured and secretory materials from the canal cells are released into the canal. In the unpollinated style of O. sigmoideum the exudates accumulated in the center of the canal; in pollinated pistils the same secretion materials were dispersed through the canal, which became wider.
Secretory granules produced by the Mehlis' gland and by the wall of the distal ootype in Schistosoma haematobium females, were examined at the ultrastructural level by means of several cytochemical methods. Strong staining, due to a relatively high percentage of carbohydrates in the granules, was observed in polymethacrylate sections treated with a phosphotungstic acidhydrochloric acid mixture at pH ≈ 0.5. Staining with ferric chloride-mixed-diamine mixtures (the LID and the HID reaction) showed no detectable level of oligosaccharide carboxyl and sulphate groups. A periodic acid-thiocarbohydrazide-silver proteinate reaction which was performed on epoxy sections, revealed a relatively high level of glycopyranosidic 1,2-diol groups in the granules. These results as well as the sensitivity of the secretory granules to the proteolytic action of papain indicated that the secretions produced by the Mehlis' gland and by the ootype wall were neutral glycoproteins.
In this work, clover was shown to respond to infection with Rhizobium leguminosarum bv. trifolii by producing reactive oxygen species. Superoxide radical and hydrogen peroxide were detected in infection threads and nodule primordia. The role of reactive oxygen species in clover-Rhizobium leguminosarum bv. trifolii symbiosis is discussed
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