Stylet penetration by the bayberry whitefly, as affected by leaf age in lemon, Citrus limon

Bayberry whitefly (Parabemisia myricae [Kuwana]) crawlers were placed on young and mature lemon leaves and were allowed 7–9 days to settle. Afterwards, the nymphs were fixed and sectioned in situ on the leaves and the area of leaf under each whitefly was examined at 1 000 x for stylet penetration. Both stylets and stylet tracks were readily visible in the sections. The path of penetration was mostly intercellular and the objective appeared to be the phloem. Passage of the stylets through the plant tissue did not cause detectable damage to most cells; however, damaged plant cells occasionally were noticed. Nymphs that had moulted during the 7–9 day settling period reached the phloem significantly more often than those that were still in their first instar. In each of the three replicates, penetration in the mature leaf occurred significantly less often than penetration in the young leaf (4% vs. 72%, p<0.01, ²). Penetration appears to be inhibited in the mature leaf either by the leaf cuticle or by factors detected by the nymphs after very shallow penetration into the leaf. The cuticle of mature leaves was much thicker than the cuticle of young leaves and may have been a barrier to stylet penetration.

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Résumé Des larves de premier stade (avant la fixation) de l'aleurode, Parabemisia myricae (Kuwana), ont été placées, pour qu'elles se fixent, pendánt 2 à 9 jours, sur des feuilles jeunes ou mûres de citronnier. Des morceaux de feuilles avec des larves fixées ont été trempés dans 2% d'agar; ce procédé a permis de maintenir les larves à leurs sites de fixation finale. Des pièces d'agar contenant les morceaux de feuilles avec les larves ont ensuite été trempées dans de la paraffine, et sectionnées en séries de 10 . Il était nécessaire de maintenir une basse température pendant l'opération afin d'obtenir de bonnes sections des feuilles mûres durcies. Les stylets et leurs traces étaient faciles à voir dans les sections teintées aux safranins, et fast green. Presque toutes les traces des stylets étaient intercellulaires et leur destination semblaient être de phloème. En général, la plupart des cellules ne semblaient pas endommagées, les larves qui avaient mué pendant la période de 7 à 9 jours de fixation avaient atteint significantivement plus le phloeme que les larves du premier stade. Dans trois essais, la pénétration des feuilles mûres était significativement moins fréquente que celle des feuilles jeunes (p<0.01, ²).La pénétration dans des feuilles mûres semble être empêchée par la cuticule ou par des facteurs perçus par les nymphes après une pénétration superficielle. La cuticule des feuilles mûres était beaucoup plus épaisse que la cuticule des jeunes feuilles et pourrait donc représenter une barrière à la pénétration des stylets.

     

Crystal structure of subtilisin complexed with its trapped substrateStreptomyces subtilisin inhibitor—Protein-protein interaction and evolution of serine proteinases and their proteinaceous inhibitors

The complex of a bacterial alkaline serine proteinase, subtilisin BPN’, with its proteinaceous inhibitorStreptomyces subtilisin inhibitor is unique in several respects, compared with other similar complexes containing serine proteinases of trypsin family. In addition to the usual antiparallelβ-sheet involving P₁-P₃ residues of the inhibitor, P₄-P₆ residues form antiparallelβ-sheet with a previously unnoticed chain segment (the ‘S4-6 site’) of subtilisin. The ‘S4-6 site’ does not exist in serine proteinases of trypsin family, whether of mammalian or microbial origin. Global induced-fit movement seems to occur on the ‘trapped substrate’Streptomyces subtilisin inhibitor: a channel-like structure in SSI remote from the contact region becomes about 2 Å wider upon complexing with subtilisin. Main role of the secondary contact region ofStreptomyces subtilisin inhibitor seems to support the reactive site loop (primary contact region). Steric homology for the two contact regions is so high between the inhibitors ofStreptomyces subtilisin inhibitor family and those of pancreatic secretory trypsin inhibitor-ovomucoid inhibitor family that it seems to favour a divergent evolution and to support the general notion as to the relationship of prokaryotic and eukaryotic genes put forwarded by Doolittle(Nature (London),272, 581, 1978).     

Mesenchymal control of branching pattern in the fetal mouse lung

The effect of mesenchyme on specialization of respiratory epithelium in the fetal mouse was tested in organ cultures. Heterologous combinations were made between respiratory and non-respiratory lung epithelia and the corresponding mesenchymes. Isolated terminal respiratory buds of fetal mouse lungs were recombined with mesenchyme from chick lung parabronchi, mouse trachea or from the avascular, non-respiratory air sacs of chick lungs. Isolated non-branching chick air sacs were combined with mouse terminal bud mesenchyme or mesenchyme from the respiratory branches of chick lungs. Air sac epithelia branched in a pattern characteristic of the chick lung when combined with chick respiratory mesenchyme and in a pattern characteristic of mouse lung when combined with mouse terminal bud mesenchyme. Mouse terminal bud epithelia did not branch with either mouse tracheal mesenchyme or chick air sac mesenchyme but branched in a chick pattern with chick parabronchial mesenchyme. Electron microscopic examination of the cultures showed that all chick air sac epithelial cultures failed to produce surfactant (lamellar bodies) even when they branched. Control cultures of mouse terminal buds contained large numbers of lamellar bodies; mesenchyme which suppressed branching reduced the number of lamellar bodies to only a few in a small proportion of the cells. Culture medium supplemented with growth factors and hormones increased the number of lamellar bodies in heterologous mouse combinations but did not bring the number to control levels. Supplemented medium had no effect on lamellar body production by chick air sac epithelium. The results indicate that branching pattern is determined by the mesenchyme surrounding the epithelial primordium. However, the capacity to synthesize surfactant is determined by the source of the epithelium; mesenchyme may control the degree of expression but not the absolute presence or absence of the differentiated condition.     

Heterologous hybridization of Azospirillum DNA to Rhizobium nod and fix genes

Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains.     

Effect of domestic sewage on sand beach meiofauna at Goa,India

Meiofauna of a sewage-polluted sandy beach, where sand alone constituted > 90%, was surveyed. Nematodes dominated the fauna numerically at all stations, followed by harpacticoid copepods. Most of the animals were confined to the top 5 cm of the sediment. A seasonal pattern was observed in the distribution of the fauna. There were significant spatial and temporal variations in mean meiofauna density, attributed to organic discharge via sewage and prevailing environmental conditions in the study area.     

A comparison of the effects of different substrata on chondrocyte morphology and the synthesis of collagen types IX and X

Summary Embryonic chick sternal chondrocytes were cultured either within three dimensional gels of type I collagen, type II collagen or agar, or as monolayers on plastic dishes coated with air-dried films of these matrix macromolecules. It was observed that cell shape and cell growth varied markedly between the different culture conditions. Flattened monolayers of cells on plastic or films of type I or type II collagen, proliferated more rapidly and reached a higher final cell density per culture than the more rounded cells found in the cultures on agar films or within three-dimensional gels. Biosynthetic studies demonstrated that in addition to the synthesis of type II collagen, all the cultures were producing collagen types IX and X. Chondrocytes cultured on plastic or films of the different matrix macromolecules all showed a similar expression of types IX and X collagen, independent of whether they displayed a flattened or round cell morphology. In contrast, marked variations in the proportions of the minor collagens, particularly type X collagen, were observed when the cells were cultured within three-dimensional gels. The data suggest that direct interaction of the cell surface with matrix constituents displaying a particular spatial array could be an important aspect in the control of type IX and X collagen expression by chondrocytes. The financial support of the Arthritis & Rheumatism Council and the Medical Research Council is gratefully acknowledged.     

Influence of dietary supplementation with thiamine on lead intoxication in rats

The influence of dietary supplementation with thiamine on lead (Pb) contents in blood and tissues, blood δ-aminolevulinic acid dehydratase (δ-ALAD) activity, and urinary excretion of δ-aminolevulinic acid (δ-ALA) was evaluated in male Sprague-Dawley rats. Groups of randomly selected animals were given a thiamine-deficient diet, a diet containing normal thiamine (20 mg/kg), or a thiamine-supplemented diet (50 mg/kg), along with control drinking water or water containing 100 ppm Pb, for 4 mo. Animals fed the thiamine-supplemented diet (50 mg/kg) and Pb showed decreased urinary excretion of δ-ALA and a decreased inhibition of δ-ALAD activity in blood compared to those given Pb with normal thiamine diet. The liver, kidney, and blood of rats receiving supplemental thiamine also contained significantly less Pb than the other two treatment groups given Pb-containing water. The protective effect of thiamine against Pb toxicity may be attributed to its interference with retention of the metal in body tissue, possibly resulting from the formation of excretable thiamine-lead complexes.     

Behavioural response of spider mites (Tetranychus urticae) to induced resistance of cotton plants

ABSTRACT.

• 1 Spider mites (Tetranychus urticae Koch) given a choice between a cotton plant previously damaged by mites and an undamaged control preferentially moved to the control plant.
• 2 This host-choice behaviour was seen in adult female mites but not in immatures.
• 3 Adult females were not found to be significantly more fecund on control plants than on previously damaged plants, but the duration of this choice experiment precluded full assessment of effects on fecundity.
• 4 Mites responded very quickly, choosing previously undamaged plants without contacting or feeding on the test plants. This suggests that an olfactory response to a chemical substance(s) is involved.

     

Socialization processes in a female lowland gorilla

A low-interactive, captive, female lowland gorilla, Molly, was studied following the introduction into her enclosure of three gorillas, two males and a female, raised from birth in captive gorilla groups. Observations were made 6 mo after the new gorillas were introduced. Throughout the period of observation, Molly interacted in an affiliative manner with one of the males, playing or sitting quietly with him in a tree (where Molly spent most of her time) and occasionally on the ground. Agonistic displays between Molly and the new female decreased after they were released in the enclosure without the males for a series of days. Molly, however, continued to react to the other male, the most dominant, in an agonistic manner, and usually retreated from his reach, climbed the tree, and/or grimaced and piloerected whenever he approached. Although Molly's continued avoidance of the dominant male impeded her complete socialization, we propose that the interventions employed in this study—introduction of new younger gorillas into and an enclosure, and a series of dyadic separations between the noninteractive gorilla and each of the new group members—are possible strategies that can be used to facilitate socialization of captive, noninteractive gorillas.     

Liposome-mediated labeling of adrenocorticotropin fragments parallels their biological activity

To test our hypothesis that specific interactions of ACTH peptides with model lipid membranes reflect the biological importance of similar interactions on target cells, we investigated the liposome-mediated labeling of ACTH fragments with the extremely hydrophobic photolabel, 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine. Correlations were found between the labeling rates and the agonistic and antagonistic potencies of the peptides for in vitro steroidogenesis and inhibition of a synaptosomal protein kinase. A model for the cross-reactivity between ACTH and opioid peptides is discussed.