Heat‐stress Memory is Responsible for Acquired Thermotolerance in Bangia fuscopurpurea

The environmental stresses that sessile organisms experience usually fluctuate dramatically and are often recurrent. Terrestrial plants can acquire memory of exposure to sublethal heat stress to acquire thermotolerance and survive subsequent lethal high‐temperature stress; however, little is known concerning whether seaweeds acquire thermotolerance via heat‐stress memory. We have demonstrated that the red seaweed Bangia fuscopurpurea can indeed acquire memory of sublethal high‐temperature stress, resulting in the acquisition of thermotolerance that protects against subsequent lethal high‐temperature stress. Moreover, the maintenance of heat‐stress memory was associated with a slight increase in the saturation level of membrane fatty acids. This suggests that the modification of membrane fluidity via changes in membrane fatty acid composition is involved in the establishment and maintenance of heat‐stress memory in B. fuscopurpurea. These findings provide insights into the physiological survival and growth strategies of sessile red seaweeds to cope with recurrent changes in environmental conditions.     

The RHG Gene Is Involved in Root and Hypocotyl Gravitropism in Arabidopsis thaliana

In higher plants, shoots show negative gravitropism and rootsshow positive gravitropism. To elucidate the molecular mechanismsof root and hypocotyl gravitropism, we segregated the secondmutation from the original phyB-1 mutant line which impairedboth root and hypocotyl gravitropism and characterized thisnovel mutation named rhg (for root and hyzypocotyl gravitropism).The rhg is a single recessive nuclear mutation and it is mappedon the lower part of the chromosome 1. Analyses on the gravitropicresponses of the rhg mutant indicate that root and hypocotylgravitropism are severely impaired but inflorescence stem gravitropismis not affected by the rhg mutation. In the rhg mutant seedlings,amyloplasts (statoliths for gravity-perception) were presentin the presumptive statocytes of roots and hypocotyls. Phototropismby roots and hypocotyls was not impaired in the rhg mutant.These results suggest that the RHG gene product probably actson the gravity-perception and/or the gravity-signal transductionin root and hypocotyl gravitropism. This is the first reportabout the genetic locus specifically involved in both root andhypocotyl gravitropism but not inflorescence stem gravitropism,supporting our hypothesis that the mechanisms of gravitropismare genetically different between hypocotyls and inflorescencestems. (Received March 11, 1997; Accepted April 17, 1997)     

Further Isolation of a Recombinant Virus (H1N2, Formerly Hsw1N2) from a Pig in Japan in 1980

In September 1980, an outbreak of febrile respiratory disease was observed in a herd of sows (1-2 years of age) in Ehime Prefecture, Japan. Most of the swine showed clinical signs of disease such as depression, anorexia, fever, nasal discharge, and cough. A hemagglutinating agent was isolated from a nasal swab from one of the diseased pigs. By cross-hemagglutination-inhibition and neuraminidase-inhibition tests with antisera to influenza viruses of swine origin, the isolate was identified as an influenza A virus of the H1N2 (former designation, Hsw1N2) subtype, and designated A/swine/Ehime/1/80 (H1N2). Significant antibody rises against the surface antigens of the isolate were found in convalescent swine sera. The distribution of antibody against H1N2 virus in swine sera in Ehime Prefecture was examined. Seven (8%) of 93 sera collected after the outbreak (in 1981) showed antibodies to only H1 and N2 antigens but none of the sera before the outbreak contained such antibodies, indicating that H1N2 virus had been restrictedly prevalent among swine but was not wide-spread until 1981.     

Alternate Changes of Surface Antigen(s) in Adenovirus Type 12-Transformed and Tumor Cells1

Alternate changes of specific surface antigen(s) (S antigen) were examined in transformed and tumor cells induced by human adenovirus type 12. All of the hamster and mouse cells transformed in vitro showed ring-form membrane fluorescence staining by anti-S antigen rabbit sera, whereas tumor cells, either induced by the virus in vivo or produced by inoculation with the S(+)-transformed cells, did not show any fluorescence. When the S(–) tumor cells were serially subcultured in vitro, all of them converted to S(+) cells, although more than ten subcultures were necessary. For the S(+) cells to form tumors in hamsters about ten times as many cells were necessary as the S(–) cells. This difference became greater when tumor formation was tested in preimmunized hamsters, while little, if any, when tested in X-irradiated hamsters. In addition, immunogenicity of the S(+) cells was suggested to be higher than that of the S(–) cells. These findings indicate that the S(+) cells are more immunosensitive and immunogenic than the S(–) cells, and that in vivo conversion from S(+) to S(–) may be due to selection of S(–)-mutant cells. In vitro conversion from S(–) to S(+) was also suggested to be due to the appearance of S(+)-mutant cells.     

Salmon calcitonin induces pituitary tumor in rats.

Calcitonin is widely used in the treatment of post-menopausal osteoporosis. The present study was designed to investigate the effects of salmon calcitonin (SCT) on the incidence of the pituitary tumors in Sprague-Dawley (SD) rats. Subcutaneous injections of SCT at a dose of 160 IU/kg/day for 6 months reduced body weight and induced one pituitary hyperplasia and three pituitary adenomas in 4 of 5 animals, while 5 controls did not show any changes. Prolactin-positive cells were located at the periphery of the affected pituitaries adjacent to the prolactin-negative adenomas. In addition, serum concentrations of prolactin and TSH were lower than in the controls, although serum calcium or LH levels were not significantly different from the controls. Among 7 animals treated with SCT for 6 months followed by no medication for another 6 months, 5 adenomas were detected, one of which had invasive growth toward the adjacent tissue, whereas only one adenoma was found in 9 controls. These results suggest that SCT administration at a high dose may induce the formation of pituitary adenoma, or may accelerate the development of spontaneous pituitary adenomas, some of which show frequent mitotic figures and invasive growth into the surrounding tissue, possibly resulting in malignant transformation. This indicates the need for caution in considering whether calcitonin injections into patients with osteoporosis as well as Paget's disease may induce such pituitary tumors.