Transmission characteristics of Spiroplasma citri and its effect on leafhopper vectors from the Circulifer tenellus complex

Several leafhopper variants of the Circulifer tenellus complex were collected in “citrus stubborn” affected areas in Israel. Two of these variants transmitted the Spiroplasma citri to Matthiola incana after being injected with the disease agent. The variant from Atriplex halimus was designated Circulifer tenellus-A (CTA) and the variant from Portulaca oleracea was designated Circulifer tenellus-? (CTP). Transmission characteristics were determined for both leafhoppers. A high rate of transmission (43.3%) was obtained by single CTA leafhoppers that were injected with the Amiad S. citri isolate from the Upper Galilee, compared with 7% transmission obtained with the CTP leafhoppers. The Gilgal S. citri isolate from the Jordan Valley, was not transmitted by either. Injection was more effective than acquisition access feeding to render the leafhopper infective for both CTA and CTP. The minimum acquisition access period needed for the CTA variant to transmit the Amiad isolate was 1 h. Longer AAPs did not necessarily result in a higher rate of transmission. The minimum incubation period was 6 days and the maximum was 32 days. The LP₅₀ calculated from the logarithmic curve y = 45.74Ln(x)–53.68 was 9.64 days. The minimum inoculation access period (IAP) was lh. The same transmission parameters for the CTP variant could not be determined, as no transmission was obtained even when groups of five-six insects were placed on a single plant.     

Patterns of junctional communication in skin: Studies on cultured keratinocytes

Junctional communication has long been suggested to play a role in coordinating the development of multicellular tissues. A better understanding of the patterns of communication between cells in such tissues is important for the identification of areas where this process may have a role. We have investigated the patterns of communication in cultures of human epidermal keratinocytes by iontophoretic injection of Lucifer Yellow CH, using involucrin expression as a marker of cells undergoing terminal differentiation. Cells that lack involucrin (i.e., the basal, proliferating cells) transfer dye preferentially to other involucrin-negative cells, whereas involucrin-positive cells either are not coupled or transfer dye with similar frequency to involucrin-positive and involucrin-negative neighbors. This decrease in communication associated with terminal differentiation was observed in both the presence and the absence of assembled desmosomes. Our observations lead us to speculate that loss of junctional communication may influence the commitment of basal keratinocytes to terminal differentiation.     

A Comparative Study on the Effects of H2S and SO2 Fumigation on the Growth and Accumulation of Sulphate and Sulphydryl Compounds in Trifolium pratense L., Glycine max Merr. and Phaseolus vulgaris L.

Maas, F. M., De Kok, L. J., Peters, J. L. and Kuiper, P. J.C. 1987. A comparative study on the effects of H₂S and SO₂ fumigationon the growth and accumulation of sulphate and sulphydryl compoundsin Trifolium pratense L., Glycine max Merr. and Phaseolus vulgarisL.—J. exp. Bot. 38: 1459-1469. The effects of 0—25 mm³ dm³ H₂S and SO₂ on growth andsulphur content of shoots of Trifolium pratense, Glycine maxand Phaseolus vulgaris were studied. After 2 weeks of fumigationthe yield of T. pralense was reduced by 32% by H₂S, but notaffected by SO₂. Yield of G. max was not affected by H₂S, butreduced by 20% by SO₂, whereas that of P. vulgaris was increasedby 11% by H₂S and not affected by SO₂. Increases in sulphydrylcontent were already observed after 24 h of exposure to H₂Sand SO₂ in all plants. The increase was greatest in T. pratenseand smallest in P. vulgaris and, except for T. pratense, alwaysgreater in the H₂S-exposed than the SO₂-exposed plants. Oneday of exposure resulted in an increase in sulphate contentonly in the SO₂-fumigated plants, with the highest accumulationin T. pratense and the lowest in P. vulgaris. After 2 weeksan increase in sulphate content was also observed in the H₂S-exposedplants. This increase was also highest in T. pratense and lowestin P. vulgaris. Transpiration rate was not affected by a 24 h exposure to H₂Sor SO₂ and was highest in T. pratense, intermediate in G. maxand lowest in P. vulgaris. The order of theoretical rates of deposition of H₂S and SO₂correlated with the observed increases in sulphydryl contentduring the first 24 h of exposure in both H₂S and SO₂-fumigatedplants and with the increase in sulphate content in the SO₂-exposedplants. The increases in sulphydryl content were only 8% ofthe theoretical H₂S and SO₂-deposition fluxes, whereas sulphateaccumulation accounted for at least 57% of the theoretical SO₂-depositionflux. Key words: Air pollution, clover, French bean, Glutathione, Soybean, sulphur metabolism.     

Out of hours workload of a suburban general practice: deprivation or expectation.

The out of hours workload of a training practice in a suburban and semirural area on the south coast of England was studied for one year. An overall rate of contact of 273/1000 patients was found, which indicated a workload greater than that reported in most other studies. The duty doctor received over 35 telephone calls from patients during some Saturdays (1200 Saturday to 0800 Sunday) and Sundays (0800 to 0800 Monday), up to five being between 2300 and 0700. Of the patients who contacted a general practitioner, 44% were given advice by telephone and 4.9% were admitted to hospital. The admission rate was lower than that given in other studies. A considerable proportion of the workload arose from doctors covering the casualty department of a cottage hospital. Patients having a high expectation of 24 hour care by general practitioners in an area of comparative affluence (Jarman indices -13.8 to 1.7) may account for this aspect of the workload.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

Role of T cells in regulating expression of the B cell repertoire. Anti-ssDNA precursor frequency of DBA/2 B cells is increased in the presence of T cells from NZB mice

Splenic B cells from DBA/2 and NZB mice were compared with regard to precursor frequency of anti-ssDNA-producing cells. Using a modification of the splenic fragment assay, we show that NZB T cells are capable of increasing the frequency of expression of anti-ssDNA precursors in DBA/2 splenic B cells. When limiting numbers of splenic B cells of DBA/2 origin were adoptively transferred into an irradiated (1200 rad) recipient, the co-transfer of NZB T cells markedly increased the frequency of anti-ssDNA precursors in cultured splenic fragments. The anti-ssDNA produced under these conditions was exclusively IgM and exhibited a high degree of cross-reactivity with TNP and fluorescein. Thus, the increase in anti-ssDNA precursor frequency reflected an expansion of the B cell repertoire to include precursors of polyspecific antibody-producing cells that under normal circumstances are not expressed. The ability of NZB T cells to increase the anti-ssDNA precursor frequency was further defined by the CBA/N immunodeficiency gene xid, in that B cells from DBA/2.xid donors did not exhibit increased anti-ssDNA precursor frequency in the presence of NZB T cells. When NZB splenic B cells were co-transferred with DBA/2 T cells, the anti-DNA precursor frequency of the NZB B cells was not reduced. This study demonstrates that T cells can influence the emergency of B cell clones in an Ag-nonspecific manner. The well documented in vivo spontaneous polyclonal activation of NZB B cells may be secondary to T cell-mediated expansion of the B cell repertoire.