Development of sensory innervation in chick skin: comparison of nerve fibre and chondroitin sulphate distributions in vivo and in vitro

In bird skin, nerve fibres develop in the dermis but do not enter the epidermis. In co-cultures of 7-day-old chick embryo dorsal root ganglia and epidermis, the neurites also avoid the epidermis. Previous studies have shown that chondroitin sulphate proteoglycans may be involved. Chondroitin sulphate has therefore been visualized by immunocytochemistry, using themonoclonal antibody CS-56, both in vivo and in vitro using light and electron microscopy. Its distribution was compared to those of 2 other chondroitin sulphate epitopes and to that of the growing nerve fibres. In cultures of epidermis from 7-day-old embryonic chicks, immunoreactivity is found uniformly around the epidermal cells while at 7.5 days the distribution in dermis is heterogeneous, and particularly marked in feather buds. In vivo, chondroitin sulphate immunoreactivity is detected in the epidermis, on the basal lamina, on the surfaces of fibroblasts and along collagen fibrils. This localization is complementary to the distribution of cutaneous nerves. Chondroitin sulphate in the basal lamina could prevent innervation of the epidermis and the dermal heterogeneities could partly explain the nerve fibres surrounding the base of the feathers. Chondroitin sulphate could therefore be important for neural guidance in developing chick skin.     

Mass Spectrometric Studies of the Effect of pH on the Accumulation of Intermediates in Denitrification by Paracoccus denitrificans

We have used a quadrupole mass spectrometer with a gas-permeable membrane inlet for continuous measurements of the production of N₂O and N₂ from nitrate or nitrite by cell suspensions of Paracoccus denitrificans. The use of nitrate and nitrite labeled with ¹⁵N was shown to simplify the interpretation of the results when these gases were measured. This approach was used to study the effect of pH on the production of denitrification intermediates from nitrate and nitrite under anoxic conditions. The kinetic patterns observed were quite different at acidic and alkaline pH values. At pH 5.5, first nitrate was converted to nitrite, then nitrite was converted to N₂O, and finally N₂O was converted to N₂. At pH 8.5, nitrate was converted directly to N₂, and the intermediates accumulated to only low steady-state concentrations. The sequential usage of nitrate, nitrite, and nitrous oxide observed at pH 5.5 was simulated by using a kinetic model of a branched electron transport chain in which alternative terminal reductases compete for a common reductant.     

Biotype-specific expression of dsRNA in the sweetpotato whitefly

This study was conducted to evaluate the effect of two different biotypes of the sweetpotato whitefly,Bemisia tabaci (Gennadius), on the induction of squash silverleaf (SSL), and to determine if double-stranded RNA (dsRNA) occurs in geographically remote populations of the two biotypes. Recently collected B-biotype whiteflies from Florida, Arizona, Mississippi, and Texas (SPW-B) all contained a 7.0 kb dsRNA molecule. Kb dsRNA molecule. Laboratory colonies of A-biotype whiteflies that were originally collected in 1981 from cotton in Arizona and California did not contain the 7.0 Kb dsRNA. When the two biotypes were compared only the SPW-B induced rapid onset, grade 5, SSL. DsRNA similar to that found in adult SPW-B was concentrated in whitefly nymphs, but host plant leaf tissue did not contain any consistent dsRNA molecules. SPW-A only induced low-grade SSL and progeny of SPW-A that were fed on pumpkin plants displaying SSL did not acquire the ability to express dsRNA or induce SSL. Our data suggest that dsRNA is not directly involved in the induction of SSL and that SSL is a host-specific response, to a feeding injury induced by B-biotype whiteflies. The origin and source of the 7.0 Kb dsRNA molecule remains enigmatic but its expression is constant in the whitefly biotype that is responsible for the induction of SSL and several other plant disorders in the U.S.     

A mating-type factors of Coprinus cinereus have variable numbers of specificity genes encoding two classes of homeodomain proteins

We have identified the seven genes that constitute the A43 mating-type factor of Coprinus cinereus and compare the organisation of A43 with the previously characterised A42 factor. In both, the genes that trigger clamp cell development, the so-called specificity genes, are separated into and loci by 7 kb of noncoding sequence and are flanked by homologous genes -fg and -fg. The specificity genes are known to encode two classes of dissimilar homeodomain (HD1 and HD2) proteins and have different allelic forms which show little or no cross-hybridisation. By partial sequencing we identified a divergently transcribed HD1 (a1-2) and HD2 (a2-2) gene in the A43 locus. a2-2 failed to elicit clamp cell development in three different hosts, suggesting that it is non-functional. a1-2 elicited clamp cells in an A42 host that has only an HD2 gene (a2-1) in its locus, thus demonstrating that the compatible A mating interaction is between an HD1 and an HD2 protein. The A43 locus contains three specificity genes, the divergently transcribed HD1 and HD2 genes b1-2 and b2-2 and a third HD1 gene (d1-1) that was shown by hybridisation and transformation analyses to be functionally equivalent to d1-1 in A42. An untranscribed footprint of a third A42 HD1 gene, c1-1, was detected between the A43 b2-2 and d1-1 genes by Southern hybridisation.     

Mössbauer spectra of the heme peptide (HP) 1–50 and the heme peptide:non-heme peptide (NHP) non-covalent complex 1–50:51–104 derived from cytochrome c: evidence for cytochrome c iron site solvation in aqueous solution

Mössbauer spectroscopic studies on a heme peptide (HP) derived from cytochrome c and on the HP recombined non-covalently with the remaining cleaved section are reported. The results suggest that the environment of the heme site in the known crystal structure of cytochrome c may differ in detail from the environment of the heme in the working protein.     

Molecular heterogeneity of Cowpea (Vigna unguiculata Fabaceae) seed storage proteins

81 wild forms and 110 cultivated cowpea,Vigna unguiculata, accessions from 21 countries of Africa were screened for variability in seed storage proteins. Total seed proteins, albumin and globulin fractions were investigated by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing (IEF) of nonreduced and/or reduced samples in one- and two-dimensional procedures. The globulin fraction is heterogeneous in molecular weight and contains both legumin-like components and three to six nondisulfide-linked subunits. Three globulin subunits, with molecular weights 110, 76, and 41 kD were found to be composed of disulfide-linked polypeptides. In the nondisulfide-linked fraction, both cultivated and wild forms exhibited patterns of four types (A–D). This fraction contains polypeptide subunits of molecular weights 62, 56, and 52 kD for A type, 62, 56, 54, and 52 kD for B type, 62, 56, 52, and 50 kD for C type, and at least 62, 56, 54, 52, 50, and 49 kD for D type. These subunits present similar multiple charge forms but C and D types possess more basic specific 50 and 49 kD nondisulfide linked components. Major albumin fraction contains subunits of 94, 86, 32, and 24kD. No infraspecific variation was observed in albumin or legumin-like fractions. The discussion is focussed on the relations between genetic variability assessed by storage protein coding genes and phenotypic variability.     

The structure of feeding behavior in the colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Feeding behavior, in an ad libitum situation on potato plants in the laboratory, was continuously observed for approximately 7 h/day on 2 successive days for 18 adult femaleLeptinotarsa decemlineata. Additional behaviors were also recorded including resting, walking, biting, local movements, grooming, defecating, and regurgitating. These data were used to calculate a time budget for the various behaviors. The feeding data were analyzed to describe the structure of feeding for young adult females on their normal host plant. The criterion for a meal (minimum intermeal interval) was determined to be 286 s. This criterion was used to distinguish between intra- and intermeal interruptions in feeding for all subsequent analyses. Meals taken from leaves that were young, medium aged, or old did not differ, but on average beetles took 60% of their meals from young leaves. Meal size and meal duration were equally good predictors of when a meal would end. Feeding from stems was a prominent feature for most beetles. The stem meals had much longer durations than leaf meals, but stem feeding did not affect subsequent leaf feeding. The structure of feeding by these beetles is compared with that found in other insects, especiallyLocusta migratoria.