Growth and reproduction of an estuarine population of the colonial hydroidCordylophora caspia (Pallas) in the northern Baltic Sea

Growth and reproduction of the colonial hydroidCordylophora caspia were monitored during the breeding season in natural conditions. In 1987, a life history study was carried out on the upright stems of the main stolon. Mean size of uprights varied cyclically. The first peak coincided with the peak number of sexual hydranths, after which the mean upright length decreased, possibly indicating somatic costs of sexual reproduction. Extrinsic factors like flooding may also have contributed to cyclical changes in upright size. In 1988 and 1989, colonies were reared on experimental plates in the estuary. In 1988, colonies grew until mid July, after which they regressed to a dormant condition and then started growing again in mid August. Predation and space competition are discussed as possible causes for this dormancy in the middle of the growing season. In 1989, colonies grew continually, with the exception of a decline in colony biomass and number of feeding hydranths at the end of July, just following the peak of sexual reproduction. Sexual reproduction started in the early stages of colonial development for all years. During early summer,C. caspia allocated resources simultaneously in colonial growth and sexual reproduction. However, sexual reproduction had a clear peak in mid summer, and thereafter sexual reproduction ceased while colonial growth continued.     

Oxidative stress responses in transgenic tobacco containing altered levels of glutathione reductase activity

A pea glutathione reductase cDNA was expressed in tobacco. Three classes of construct were used which gave a range of elevated levels of glutathione reductase (GR) activity in the cytosol (GR32), chloroplasts (GR36), or in both chloroplasts and mitochondria (GR46). In some transgenic progeny (T₂) from self-fertilized GR32 and GR36 primary transformants, having approximately twofold elevation of GR activity as compared with recessive siblings, there was an amelioration of the effect on leaf discs of up to 15 µM paraquat. However, lines with similarly elevated levels of GR activity showed no decreased sensitivity to the herbicide. None of the GR32 and GR36 lines was less sensitive to ozone. Conversely, T₂ progeny of GR46 lines, with greater than 4.5-fold elevations of GR activity, showed no reduced sensitivity to paraquat but two out of four of these lines were less sensitive to ozone fumigation. The differential response to stress co-segregated with the presence of the transgene but there was no relationship between the degree of stress response and the level of GR activity. There was an elevation in the total glutathione pool in all lines showing increased GR activity but there was no change in the ratio of oxidized to reduced glutathione. These results demonstrate that the mechanisms of protection against ozone and paraquat are different although both can be mediated by elevated GR activity.     

L1 (LINE-1) retrotransposable elements provide a "fossil" record of the phylogenetic history of murid rodents

The single most difficult problem in phylogenetic analysis is deciding whether a shared taxonomic character is due to common ancestry or one that appeared independently due to convergence, parallelism, or reversion to an ancestral state. Mammalian L1 retrotransposons undergo periodic amplifications in which multiple copies of the elements are interspersed in the genome. Because these elements apparently are transmitted only by inheritance and are retained in the genome, a shared L1 amplification event can only be an inherited ancestral character. We propose that L1 amplification events can be an excellent tool for analyzing mammalian evolution and demonstrate here how we addressed several refractory problems in rodent systematics using L1 DNA as a taxonomic character.