Detection of a natural point mutation in Potato virus A that overcomes resistance to vascular movement in Nicandra physaloides., and studies on seed-transmissibility of the mutant virus

Isolate M of Potato virus A (PVA‐M; genus Potyvirus) is avirulent in Nicandra physaloides L. (family Solanaceae). The inoculated leaves are infected but no systemic infection is observed. Forty plants of ‘Black Pod’ (BP) and ‘Black Pod Alba’ (BPA), two variants of N. physaloides described in this study, were inoculated with PVA‐M. Two plants of BP and one plant of BPA were systemically infected. Mosaic, blistering and dark green islands developed on the systemically infected leaves, and flowers showed colour‐break symptoms. PVAprogeny were sequence‐characterised for the 6K2 protein and viral genome‐linked protein (VPg) encoding regions known to control the long distance movement of PVA in N. physaloides. All virus progeny (designated as PVA‐Mm) in the systemically infected leaves of the plants inoculated with PVA‐M contained only a single amino acid substitution (Vail 16Met) in the central part of VPg due to a nucleotide substitution G6033A, as compared to PVA‐M. Other PVA isolates that infected N. physaloides systemically also contained Metll6 in VPg. In a previous study using chimeric viruses, Metl16 in VPg was shown to be a major determinant for vascular movement of PVA in N. physaloides, and this study reveals that the mutation for Metl16 can occur in vivo during replication of the avirulent PVA‐M in infected plants. Immunolocalisation studies on BP and BPA plants showed that the pods (berries) and seed coat contained PVA‐Mm in the developing seeds, but no virus was detected in embryons. Up to 27% of the mature seeds contained PVA‐Mm but no transmission to seedlings was observed in a total of 450 seeds tested, and no test plants were infected following mechanical inoculation with extracts prepared from the seeds.     

Timing of breeding of Tengmalm's Owl Aegolius funereus in relation to vole dynamics in western Finland

Timing of breeding in Tengmalm's Owl was studied in western Finland for 13 years. During 1973-85, half of the females started laying before 4 April, near the seasonal low of main food abundance (voles), and earlier than in southern Finland or as early as in southeastern Norway. The reason for this latitudinal trend is the shallow snow cover of the study area. The annual variation in the median laying dates was one month and was negatively correlated with the spring abundance of Microtus voles. The mean clutch size was related to the start of laying with early clutches being larger than late ones. These findings accord with the 'food limitation hypothesis', which states that laying begins as soon as the female can accumulate enough energy stores for forming eggs. Early breeding is adaptive, since juveniles of early clutches probably survive better during their first winter. In adults, early nesting improves the chances of rearing two broods per year, allows them to moult after breeding and gives more time to accumulate fat reserves to survive the winter. Tengmalm's Owl is one of the earliest breeders among North European birds. This is possible because of its hole-nesting and resident habits, small body-size in relation to the main prey and the greatest sexual size dimorphism among European owls.     

Interpopulation differences in pupal size and fecundity are not associated with occurrence of outbreaks in Epirrita autumnata (Lepidoptera, Geometridae)

Abstract.

• 1 Among-population differences in pupal mass were studied in a geometrid, Epirrita autumnata. Some Epirrita autumnata populations regularly reach outbreak densities while others are never known to do so. Because adults do not feed, pupal mass of females correlates strongly with fecundity.
• 2 Larvae were collected from twelve field sites. Ten of our sample populations originated within the outbreak range of the species and represented different phases of outbreaks. Two populations originated outside the outbreak range.
• 3 Pupal mass of field-collected E. autumnata varied significantly among populations. The peak phase populations had the smallest pupae and the biggest were found in low density populations outside the outbreak range.
• 4 Offspring of moths from each population were reared under identical conditions in two larval densities. Significant differences were not found in pupal mass among populations. That is, the inherent size, correlated with fecundity of moths, was not different between populations originating within and outside the outbreak range, nor among collections from different densities or phases of the outbreaks.
• 5 Rearing density did not interact in a consistent way with population.
• 6 As far as size and fecundity are concerned, the results do not support Chitty's hypothesis that differences in genetic composition of the population at low and high density phases generate cyclic fluctuations of population density.
• 7 Because no hereditary or maternal differences were found in size and fecundity between E.autumnata originating within and outside the outbreak range, variation in reproductive capacity cannot explain why outbreaks occur only in some populations.

     

Cloning and sequence analysis of cDNA for rat corticotropin-releasing factor precursor

DNA complementary to the rat hypothalamic mRNA coding for the corticotropin-releasing factor precursor (prepro-CRF) has been cloned by screening a cDNA library with a human genomic DNA probe. Nucleotide sequence analysis of the cloned cDNA has revealed that rat prepro-CRF consists of 187 amino acid residues including a putative signal peptide. The CRF and putative signal peptide regions are more highly conserved among rat, human and ovine prepro-CRF than is the cryptic portion.     

Cloning and sequence analysis of human genomic DNA encoding gamma subunit precursor of muscle acetylcholine receptor

The limited proteolysis of human low-molecular-mass kininogen by kallikrein from tissue sources has been studied. Porcine pancreatic kallikrein applied in catalytic amounts split the kininogen molecule (apparent mass 68 kDa) with the release of lysyl-bradykinin (1 kDa). This generated a nicked kininogen molecule with a heavy chain and light chain interconnected via disulfide bridging. Following reductive cleavage of the disulfide bonds, the heavy chain of apparent mass 62 kDa was isolated by preparative sodium dodecyl sulfate electrophoresis, and the light chain of 5 kDa by reversed-phase high-performance liquid chromatography. The light chain was found to be composed of 38 amino acids with a single half-cystine residue. Amino-terminal sequence analysis revealed that the light chain is derived from the carboxy terminus of the kininogen molecule [Lottspeich et al. (1984) Eur. J. Biochem. 142, 227-232]. Immunological characterization of the isolated L chain indicated that it harbours antigenic site(s) unique for low-Mr kininogen as well as sites common to high-Mr and low-Mr kininogen.     

Relationship between chloroplast structure and O2 evolution rate of leaf discs in plants from different biotopes in South Finland

Abstract The chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O₂ evolution rate, chlorophyll (Chl) content and Chi a/b ratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO₂-saturated O₂ evolution rate (measured at 20°C and 1500 μmol photons m^?2s^?1) was at a maximum, ranging from 19.2 to 6.9 μmol O₂ cm^?2 h^?1. Among the species, the Chi a/b ratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non-appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O₂ evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O₂ evolution rate, the lower was the ratio of the total length of appressed to non-appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chi a/b ratio of the leaves was not as clear, a significant negative correlation existed between the Chi a/b ratio and the ratio of appressed to non-appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl- protein complexes.     

Identification of Mutations in the Pigment Cell-Specific Gene Located at the Brown Locus in Mouse

The pigment cell-specific gene, located at the brown (b)-locus in mouse, encodes the protein that determines the type of melanin synthesized. This protein is known as tyrosinase-related protein, but here we tentatively term it b-locus protein to avoid confusions with the related sequence cross-hybridizing to the tyrosinase gene. In order to identify the mutation at the b-locus, we have cloned and characterized the b-locus protein gene of BALB/c mouse (b/b, c/c). The gene is about 18 kb long and organized into 8 exons and 7 introns. Sequence analysis of the b-locus protein gene reveals four base changes within the protein-coding regions: two missense mutations and two silent mutations. Two missense mutations result in the Cys to Tyr substitution at position 86 (codon 110) and the Arg to His substitution at position 302 (codon 326) of a b-locus protein molecule. Using allele-specific amplification, we confirmed that these missense mutations are actually present in the genomic DNA of two b-mutant strains examined, BALB/c and DBA/2 (b/b, C/C) mice, suggesting that these mutations are specific for the mutant mice at the b-locus. Moreover, we are able to show that the b-locus protein containing Tyr 86 is not reactive with the anti-b-locus protein monoclonal antibody, TMH-1, in transient expression assays.