Relationship between photoperiod, plasma concentration of ionic calcium and the histology of the prolactin-secreting cells of the rostral pars distalis of the pituitary gland, the corpuscles of stannius and the ultimobranchial gland in the goldfish, Carassius auratus L. /

The relationship between photoperiod, plasma concentration of ionic calcium and the histology of the prolactin-secreting cells of the rostral pars distalis of the pituitary gland, the Corpuscles of Stannius and the Ultimobranchial gland were investigated. Neither the plasma concentration of ionic calcium nor histologically apparent prolactin cell activity could be correlated with photoperiod. Some evidence of a photoperiodic effect on both the Corpuscles of Stannius and the Ultimobranchial gland was obtained. The expected reciprocal relationship between the activity of these glands was not obvious at the histological level . Quantitative and qualitative analysis at the light microscope level revealed, however, that the hormone prolactin-secreting eta cells of the rostral pars distalis and the hypocalcin-secreting cells of the Corpuscles of Stannius may be arranged in a lamellar pattern comprized of synchronous bands of cells in like-phase of a secretory cycle consisting of four stages - synthesis, storage, release and reorganization. Such synchronized cell cycles in these glands have not heretofore been described in literature. It is suggested that the maintenance of at least 255? of the cells in any one phase of the cycle ensures a supply of the required hormone at all times.

Light and electron microscope studies of host-parasite relations in a mycoparasite

Light microscope studies of the mycoparasite Piptocephalis virginiana revealed that the cylindrical spores of the parasite became spherical upon germination and produced 1-4 germ tubes. Generally t"l.vO germ tubes were produced by each spore. When this parasite was inoculated on its potential hosts, Choanephora cucurbitarum and Phascolomyces articulosus, the germ tube nearest to the host hypha continued to grow and made contact with the host hypha. The tip of the parasite's germ tube became swollen to form a distinct appressorium. Up to this stage the behavior of the parasite was similar regardless of the nature of the host. In the compatible host-parasite combination, the parasite penetrated the host, established a nutritional relationship and continued to grow to cover the host completely with its buff colored spores in 3-4 days. In the incompatible host-parasite combination, the parasite penetrated the host but its further advance was arrested. As a result of failure to establish a nutritional relationship with the resistant host, the parasite made further attempts to penetrate the host at different sites producing multiple infections. In the absence of nutrition the parasite weakened and the host outgrew the parasite completely. In the presence of a non-host species, Linderina pennispora the parasite continued to grow across the non-host 1).yp_hae vlithout establishing an initial contact. Germination studies showed that the parasite germinated equally well in the presence of host and non-host species. Further electron microscope studies revealed that the host-parasite interaction between P. virginiana and its host, C. cucurbi tarum, was compatible when the host hyphae were young slender, with a thin cell wall of one layer. The parasite appeared to penetrate mechanically by pushing the host-cell wall inward. The host plasma membrane invaginated along the involuted cell wall. The older hyphae of C. cucurbitarum possessed two distinct layers of cell wall and-showed an incompatible interaction when challenged vlith the parasite. At the point of contact, the outer layer of the host-cell wall dissolved, probably by enzymatic digestion, and the inner layer became thickened and developed a papilla as a result of its response to the parasite. The haustoria of the parasite in the old hyphae were always surrounded by a thick, well developed sheath, whereas the haustoria of the same age in the young host mycelium were devoid of a sheath during early stages of infection. Instead, they were in direct contact with the host protoplast. The incompatible interaction between a resistant host, P. articulosus and the parasite showed similar results as with the old hyphae of C. cucurbitarum. The cell wall of P. articulosus appeared thick-with two or more layers even in the 18-22 h-old hyphae. No contact or interaction was established between the parasite and the non-host L. pennispora. The role of cell wall in the resistance mechanism is discussed.