New aspect of the “mycetome” of a thrips,Bactrothrips brevitubus Takahashi (Insecta: Thysanoptera)

Morphology and cytochemical properties of “mycetomes” are described in the developing oocytes and eggs of an idolothripine thrips, Bactrothrips brevitubus (Thysanoptera). The “mycetome” is an aggregation of numerous granules of various sizes. We found no membrane encapsulating the aggregation of granules. Two types of granules are distinguishable: the smaller ones filled with electron-dense material and the larger ones with inclusion of myelin-like structures. Each of the granules has a limiting membrane. The limiting membrane is a simple unit membrane but shows no characteristics of cell walls. No nucleoid or nucleoplasm is detected in the granules. The “mycetome” takes up dyes whose specific incorporation into lysosomes has been demonstrated. In addition, a high activity of acid phosphatase is demonstrated in the “mycetome.” These characteristics apparently indicated that the “mycetome” of Bactrothrips brevitubus is an aggregation of lysosomes but not a clump of microorganisms. Thus we propose that the structure being regarded as the mycetome should be renamed the “lysosomal aggregation.” © 1994 Wiley-Liss, Inc.     

Molecular changes in UV-induced and γ-ray-induced mutations in human lymphoblastoid cells

We have characterized the structural changes in the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene of 14 UV-induced, 15 γ-ray-induced and 17 spontaneous mutants of human lymphoblastoid cells selected for 6-thioguanine (6TG) resistance. Southern blot analysis using the full-length HPRT cDNA as a probe revealed that 29% (5/17) of the spontaneous mutants contained detectable alterations in their restriction fragment patterns. Among the 15 mutants induced by γ rays, 7 (47%) had such alterations indicative of large deletions in the HPRT gene. In contrast, all 14 UV-induced mutants exhibited hybridization patterns indistinguishable from those of the wild-type cells. These results suggest that UV is likely to induce point mutations at the HPRT locus on the human chromosome and that the molecular mechanism of UV-induced mutation is quite different from that of ionizing radiation-induced mutation or spontaneous mutation in human cells.     

Salt Adaptation of K+ Channels in the Plasma Membrane of Tobacco Cells in Suspension Culture

The patch-clamp technique was used to study and compare thecharacteristics of cation channels in the plasma membrane ofcultured lines of tobacco (Nicotiana tabacum L. cv. Bright Yellow-2)cells that were unadapted (NaCl-unadapted cells) and adaptedto 50 and 100 mM NaCl (Na50-adapted and Na100-adapted cells).In these three types of tobacco cell, the outward whole-cellcurrent activated by depolarization was dominated mainly bythe activity of the outward rectifying K⁺ channels with a single-channelconductance of 20 pS. The steady-state amplitude of the outwardwhole-cell currents at all the positive potentials examineddecreased in the following order: NaCl-unadapted cells>Na50-adaptedcells>Na100-adapted cells. There were no significant differencesbetween the NaCl-unadapted and the Na50-adapted cells in termsof the ratio of permeabilities of these channels to K⁺ and Na⁺ions. Furthermore, no significant differences in terms of thesingle-channel conductance of these channels were observed amongthe NaCl-unadapted, the Na50-adapted and the Na100-adapted cells.These observations suggest that adaptation to salinity of tobaccocells in suspension results in reduced permeability of the K⁺channels to both K⁺ and Na⁺ ions, without any change in theK⁺/Na⁺ selectivity and single-channel conductance of these channels. ¹Present address: Research Laboratory of Applied Biochemistry,Tanabe Seiyaku Co., Ltd.16-89 Kashima 3-chome, Yodogawaku, Osaka,532 Japan