Tissue-specific DNase I-sensitive sites of the maize P gene and their changes upon epimutation

A map has been developed of nuclease-hypersensitive sites of P-rr , the standard allele of the P -locus of Zea mays L. Using a traditional DNase I assay, eight such sites have been found that are specific for the expressing tissue and span a region of more than 25 kb of the P -locus, making it one of the largest plant genes yet described. The maps of the standard allele have also been compared with the recently described moderately stable P-pr allele, which arose from epimutation. Six of the eight sites exhibit the same tissue-specificity in P-pr plants, while two stay repressed as in non-expressing tissues of plants with the standard allele. Interestingly, the two repressed sites coincide with two hypermethylated restriction sites that have previously been correlated with the expression potential of the P-pr allele. On the other hand, four of the DNase I sites, coinciding with CpG islands that were not hypermethylated by the epimutation, also showed no differences in their sensitivity to DNase I between the standard allele and the P-pr allele. This suggests that the epimutation affects both site-specific methylation changes and a specific local chromatin structure of the P gene involved in its regulation.     

The preservation of infective spores of Octosporea muscaedomesticae in Phormia regina,of Nosema algerae in Anopheles stephensi,and of Nosema whitei in Tribolium castaneum by lyophilization

Infective spores of three species of microsporidia were subjected to the lyophilization process by employing varying media as cryoprotectants. The infectivity of the lyophilized spores was then tested against a standard fresh spore preparation in the appropriate host insect. Spores of Octosporea muscaedomesticae served as an experimental model and were rendered noninfective in host Phormia regina (Calliphoridae: Diptera) after lyophilization with the following cryoprotective agents: skim milk (12%), ascorbic acid (5%) combined with thiourea (5%), glycerol (10%), mesoinositol (5%), and equine serum. Spores of O. muscaedomesticae lyophilized or vacuum-dried in 50% sucrose as well as in the hosts' tissues remained highly infective for as long as 2 years at a dose of 10⁶ spores/fly and a trial length of 12 days. At a dose of 5 × 10⁴ spores/fly there was a slight decrease in infectivity of the spores which had been lyophilized in the host's abdomen after a 2-year storage period compared with that of fresh, nonlyophilized spores. Naked spores of Nosema algerae suspended in 50% sucrose and lyophilized produced infection in 50% of the host population of Anopheles stephensi (Culicidae: Diptera) compared with 70% infection produced by fresh non-lyophilized spores. Spores of Nosema whitei lyophilized within its host larva Tribolium castaneum (Tenebrionidae: Coleoptera) remained 100% infective at a dose of 5 × 10⁵ spores/gram diet. It is concluded that an aqueous solution of 50% sucrose and/or the host's tissues are excellent protectants for the cryogenic or vacuum-drying process of the above-named spores, and their protective function may apply also to other microsporidian species.     

The Pituitary Gland of the Roach Leuciscus rutilus

Three different endocrine cell types were identified by electron microscopy in the rostral pars distalis (RPD) of the roach, Leuciscus rutilus. The cells which are characterized by the morphology and sizes of their secretory granules are assumed to secrete prolactin, ACTH and TSH. Prolactin cells occur in two forms which could be separated on account of the sizes of their granules. Intra-peritoneal injections of reserpine had a strong and persistent effect 24 hours after the treatment. The prolactin cells with small granules reacted with a marked release of secretion. The border of the RPD is composed of a so-called double basement membrane in contact with the perivascular spaces and forms extensive ramifications into the rostral neurohypophysis (RNH). Nerve fibers of different categories terminate at the border and its network in the RNH. Substances released from these terminals may influence the endocrine cells of the RPD. The ACTH cells and the prolactin cells are innervated by axons with granules less than 100 nm. The nomenclature of type ‘A’ fibers and ‘B’ fibers is discussed because it was difficult to make a reliable discrimination of the fibers and their nature by the sizes of their granules. However, four types of nerve fibers were distinguished in connection with the RPD although the presence of more types was indicated. In all four types the size variations of the granules are great and overlapping. The average sizes of the granules in these fibers are 157, 114, 119 and 81 nm. The origin of the nerve fibers innervating the RPD is discussed. All morphological data indicate a complex hypothalamic control of the RPD of the roach.     

THE DARK ADAPTATION OF THE EYE OF THE HONEY BEE

Bees which are held in a fixed position so that only head movements can be made, respond to a moving stripe system in their visual field by a characteristic motion of the antennae. This reflex can be used to measure the bee''s state of photic adaptation. A curve describing the course of dark adaptation is obtained, which shows that the sensitivity of the light adapted bee''s eye increases rapidly during the first few minutes in darkness, then more slowly until it reaches a maximum level after 25 to 30 minutes. The total increase in sensitivity is about 1000 fold. The adaptive range of the human eye is about 10 times greater than for the bee''s eye. The range covered by the bee''s eye corresponds closely to the adapting range which is covered by the rods of the human eye.     

Changes in the phytoplankton of Lake Trummen induced by restoration

Lake Trummen, previously an oligotrophic lake, was heavily polluted during 1930–1957. The lake was restored by suction dredging of the top sediment layer. After restoration nutrien concentrations and phytoplankton biomass were drastically reduced. Eutrophic species disappeared and more oligotrophic species returned to the lake. The investigation covers 12 years-monthly-bimonthly countings of algae together with electronmicroscopical studies of taxonomically difficult taxa. The investigation was made at the species level (300 species identified and 80 quantitatively recorded).