Effects of light, temperature, gibberellin (GA3) and their interaction on coleoptile and leaf elongation of tall, semi-dwarf and dwarf wheat

Near-isogenic wheat lines differing in height-reducing (Rht) alleles, in each of two cultivars, were used to investigate the effects of light intensity and of their interaction with temperature and GA₃ application, on the elongation of the coleoptile and the first seedling leaf. Darkness caused a conspicuous increase in the lengths of the coleoptile and of the sheath and lamina of the first leaf, in GA₃ treated and untreated seedlings of all genotypes grown at 11 and 25°C. The genotype effects and the effects of light intensity and GA₃ application on leaf length were ascribed entirely to their effects on the rate of leaf elongation since the duration of leaf elongation was not affected by these factors. Temperature elevation from 11 to 25°C caused a 55% shortening of the duration of leaf elongation and a concomitant increase in elongation rate, which diminished with increased genotypic dwarfness. Accordingly, temperature elevation resulted in a significant reduction in leaf-length of the light-grown dwarf genotypes and the dark-grown dwarf and semi-dwarf genotypes. It is suggested that this temperature × light × genotype interaction effect is due to environmental dependent upper limits of elongation rate set by the Rht alleles.Abbreviations PAR Photosynthetic Active Radiation     

Hormonal Characterization of Transgenic Tobacco Plants Expressing the rolC Gene of Agrobacterium rhizogenes TL-DNA

Transgenic tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants expressing the Agrobacterium rhizogenes rolC gene under the control of the cauliflower mosaic virus 35S RNA promoter were constructed. These plants displayed several morphological alterations reminiscent of changes in indole-3-acetic acid (IAA), cytokinin, and gibberellin (GA) content. However, investigations showed that neither the IAA pool size nor its rate of turnover were altered significantly in the rolC plants. The biggest difference between rolC and wild-type plants was in the concentrations of the cytokinin, isopentenyladenosine (iPA) and the gibberellin GA19. Radio-immunoassay and liquid chromatography-mass spectrometry measurements revealed a drastic reduction in rolC plants of iPA as well as in several other cytokinins tested, suggesting a possible reduction in the synthesis rate of cytokinins. Furthermore, gas chromatography-mass spectrometry quantifications of GA19 showed a 5- to 6-fold increase in rolC plants compared with wild-type plants, indicating a reduced activity of the GA19 oxidase, a proposed regulatory step in the gibberellin biosynthesis. Thus, we conclude that RolC activity in transgenic plants leads to major alterations in the metabolism of cytokinins and gibberellins.     

The role of fire in terrestrial vertebrate richness patterns

Productivity is strongly associated with terrestrial species richness patterns, although the mechanisms underpinning such patterns have long been debated. Despite considerable consumption of primary productivity by fire, its influence on global diversity has received relatively little study. Here we examine the sensitivity of terrestrial vertebrate biodiversity (amphibians, birds and mammals) to fire, while accounting for other drivers. We analyse global data on terrestrial vertebrate richness, net primary productivity, fire occurrence (fraction of productivity consumed) and additional influences unrelated to productivity (i.e., historical phylogenetic and area effects) on species richness. For birds, fire is associated with higher diversity, rivalling the effects of productivity on richness, and for mammals, fire's positive association with diversity is even stronger than productivity; for amphibians, in contrast, there are few clear associations. Our findings suggest an underappreciated role for fire in the generation of animal species richness and the conservation of global biodiversity.     

THE EVOLUTIONARY HISTORY OF PARTHENOGENETIC CNEMIDOPHORUS LEMNISCATUS (SAURIA: TEIIDAE). II. MATERNAL ORIGIN AND AGE INFERRED FROM MITOCHONDRIAL DNA ANALYSES

Restriction endonuclease analyses were performed on mitochondrial DNAs (mtDNAs) representing unisexual parthenogenetic (cytotypes A, B, and C) and bisexual (cytotypes D and E) populations of Amazonian lizards presently regarded as Cnemidophorus lemniscatus. The results of mtDNA cleavage map comparisons among these C. lemniscatus indicated that (1) there was no cleavage site variation among the unisexuals, (2) mtDNAs from the bisexual cytotypes D and E differed in sequence from one another by about 13%, and (3) mtDNAs from cytotypes A–C differed from those of cytotype D by about 5% and from those of cytotype E by about 13%. Higher resolution restriction fragment size comparisons confirmed the high degree of similarity among the unisexual mtDNAs, but identified 12 cleavage site variants among the 13 cytotype D mtDNAs examined. Both cladistic and phenetic (UPGMA) analyses of the data indicate that the unisexual and cytotype D mtDNAs form a single clade, suggesting that a female of cytotype D was the maternal progenitor of the unisexuals. The similarity among the unisexual mtDNAs and the variability among those of cytotype D suggest that the three unisexual cytotypes arose recently from a common maternal lineage. The mtDNA variability observed among cytotype D individuals has a strong geographic component, suggesting that the unisexuals arose from one or a few geographically proximal populations. The mtDNA comparisons also support the conclusion, based on allozyme comparisons (Sites et al., 1990, this issue), that cytotypes D and E, although presently allocated to C. lemniscatus, are separate species.     

MITOCHONDRIAL-DNA ANALYSES AND THE ORIGIN AND RELATIVE AGE OF PARTHENOGENETIC LIZARDS (GENUS CNEMIDOPHORUS). III. C. VELOX AND C. EXSANGUIS

Mitochondrial DNAs (mtDNAs) of two unisexual, parthenogenetically reproducing species of whiptail lizards (Cnemidophorus velox and C. exsanguis) and their bisexual relatives were compared by restriction-enzyme analysis to assess levels of mtDNA variation and to establish the maternal ancestry of the unisexuals. No cleavage-site differences were found to be diagnostic between C. velox and C. exsanguis mtDNAs, suggesting an ancestry rooted in the same maternal lineage. The mtDNA of the unisexuals is relatively homogeneous, indicating that these lineages are of recent origin. Phylogenetic analysis revealed that the maternal ancestor of both C. velox and C. exsanguis was most probably C. burti stictogrammus, C. costatus barrancorum, or an unidentified taxon closely related to them. In addition, the mtDNA analyses demonstrate conclusively that the triploid species C. velox could not have been formed by the fertilization of an unreduced (diploid) C. inornatus egg, further strengthening the hypothesis that parthenogenesis in Cnemidophorus results from hybridization.     

THE ORIGIN AND EVOLUTION OF PARTHENOGENESIS IN HETERONOTIA BINOEI (GEKKONIDAE): EXTENSIVE GENOTYPIC DIVERSITY AMONG PARTHENOGENS

Variation at 18 allozyme loci was assayed among representatives of the geographically widespread, triploid parthenogenetic form of Heteronotia binoei. A minimum of 52 different genotypes were observed among 143 individuals. Virtually all localities sampled had multiple genotypes among the unisexuals. This represents unusually high genotypic diversity for a unisexual vertebrate. Heterozygosity in the triploids was higher than in diploid bisexual populations of H. binoei. Comparison with the alleles present in the diploid bisexuals confirms that the parthenogens are hybrids and indicates that most of the genotypic diversity stems from repetitive hybrid origins. However, the presence of some alleles unique to the parthenogens suggests that mutation adds to their genetic diversity. The genetic structure of this geographically widespread parthenogen suggests the hypothesis that the persistence and spread of the unisexual lineages is facilitated by genotypic diversity.     

Genetic population structure of the Greater Bilby Macrotis lagotis, a marsupial in decline

The Greater Bilby has shown a rapid decline in range during this century and now occupies only a small isolated area in south-western Queensland (QLD) and a larger, but mostly low-density area in the north-western deserts of the Northern Territory (NT) and Western Australia (WA). We have examined variation in the control region of mitochondrial DNA (mtDNA) and at nine microsatellite loci in order to investigate the extent of current and historical subdivision across the species range, and to provide a preliminary assessment of genetic structuring and mating system on a finer scale within the QLD population. Both mtDNA and microsatellite loci had substantial variation within and among populations, with mtDNA divergence being greater between QLD and NT than between NT and WA. The QLD population had two unique and divergent mtDNA lineages, but there was no evidence for strong phylogeographical structure across the range. The available evidence suggests that the bilby should be considered as a single Evolutionarily Significant Unit consisting of multiple Management Units. Augmentation of the remnant QLD population from the NT does not appear necessary at this stage, at least not on genetic grounds. Finer-scale analysis of microsatellite variation for two QLD colonies revealed a deficiency of heterozygotes and significantly greater relatedness within than between colonies. However, structuring was observed only for males; relatedness values for females did not depart from those expected under panmixia. Parentage exclusion analysis for one colony allowed the construction of a partial pedigree which indicated strong polygyny, with one male fathering all but one of the eight offspring assigned. The extent to which fine-scale genetic structuring and differences between sexes is due to sex-biased dispersal vs. effects of mating system remain to be determined.     

Age-dependent alterations of linoleic, arachidonic and eicosapentaenoic acids in renal cortex and medulla of spontaneously hypertensive rats

The lipid content as well as the fatty acid pattern of triglycerides, free fatty acids (FFA), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were estimated in renal cortex and medulla of spontaneously hypertensive rats (SHR) and normotensive Wistar rats (WR) at 4,8,26 and 52 weeks of age. In general, the level of triglycerides in renal medulla appeared higher when compared with the cortex. On the other hand, PC and PE, increasing with age, were usually higher in the cortex. A decreased percentage of linoleic acid (LA) in triglycerides, of arachidonic acid (AA) in PC and of eicosapentaenoic acid (EPA) in triglycerides, FFA, PC and PE could be found in the kidneys of SHR at 8 weeks of age, i.e. during the development of hypertension. This was accompanied with a rise of AA in FFA of SHR at 8 weeks of age, which occurred with delay in WR (at 26 weeks of age). From the data presented it can be concluded that systematic alterations in the availability of individual polyunsaturated fatty acids (PUFA) in various renal lipids might be related to the onset of hypertension in SHR which should be elucidated in more detail.     

Monthly incidence of Theileria cervi and seroconversion to Babesia odocoilei in white-tailed deer (Odocoileus virginianus) in Texas.

Monthly monitoring of fawns collected from an area in Texas endemic for Theileria cervi and Babesia odocoilei showed that transmission of T. cervi occurred during July and August, a time period consistent with the occurrence of Amblyomma americanum. Seroconversion to B. odocoilei occurred during October to December and possibly continued through January and February. The time of seroconversion was more suggestive of transmission of B. odocoilei by Ixodes scapularis than by Amblyomma americanum.