Identification of an S-locus glycoprotein allele introgressed from B. napus ssp. rapifera to B. napus ssp. oleifera.

We have previously described a developmentally regulated mRNA in maize that accumulates in mature embryos and is involved in a variety of stress responses in the plant. The sequence of the encoded 16 kDa protein (MA16) predicts that it is an RNA-binding protein, since it possesses a ribonucleoprotein consensus sequence-type RNA-binding domain (CS-RBD). To assess the predicted RNA binding property of the protein and as a starting point to characterize its function we have used ribohomopolymer-binding assays. Here we show that the MA16-encoded protein binds preferentially to uridine- and guanosine-rich RNAs. In light of these results a likely role for this protein in RNA metabolism during late embryogenesis and in the stress response is discussed.     

Chemical treatment of soil to prevent transmission of tobacco rattle virus to potatoes by Trichodorus spp

Alternaria longipes (Ell. &Ev.) Mason survived on autoclaved maize stems for 6 months without losing its pathogenicity, but rapidly lost viability on non-autoclaved stems and could not be re-isolated 4 months after inoculation. In laboratory tests it infected both living and dead maize leaves. Some Alternaria isolates from non-solanaceous hosts infected tobacco leaves kept at high humidities for 10 days after inoculation, but not when this incubation period was reduced to 48 h. In the field, perennation on plants other than tobacco is unlikely to be important as a source of inoculum. Pathogenicity of Alternaria isolates was maintained from one season to the next when stored as conidia in sterile soil, or as dried, infected tobacco leaves; some isolates maintained on agar slopes under oil were still pathogenic after 5 years. Alternaria conidia collected from the surface of tobacco seedlings, and isolates from apparently healthy seedling leaves were pathogenic to mature tobacco. In the field conidia were detected on tobacco leaves soon after these emerged, and epiphytic colonies were occasionally found well in advance of symptoms. Many latent infections were also detected up to 5 weeks in advance of symptoms. Visual development of latent infections closely coincided with the end of leaf expansion.     

Phosphoglycerate Kinase Polymorphism in Kangaroos provides Further Evidence for Paternal <Emphasis Type="Italic">X</Emphasis> Inactivation

REDUCED activity of the glycolytic enzyme phosphoglycerate kinase (EC 2723 : ATP : 3 phospho-D-glycerate 1 phosphotransferase, PGK) is associated with hereditary haemolytic anaemia^1–3. A family study suggests that the gene involved is sex linked. Beutler has described a starch gel technique for electrophoresing and detecting the human erythrocytic enzyme⁴. He examined Caucasian, Negro and Oriental blood donors and found no variants. We have surveyed several hundred erythrocyte samples from a number of species of kangaroos (Macropodidae) using his technique.     

Inhibition of a nutrient-dependent pinocytosis in dictyostelium discoideum by the amino acid analogue hadacidin

In the present study we examine the effects of the drug hadacidin (N-formyl-N- hydroxyglycine) on pinocytosis in the eukaryotic microorganism dictyostelium discoideum. At concentrations of up to approximately 8 mg/ml, hadacidin inhibited the rate of pinocytosis of fluorescein isothiocyanate (FITC) dextran in cells in growth medium in a concentration-dependent manner but had no effect on cells in starvation medium. Because hadacidin also inhibits cellular proliferation at this concentration, the relationship between growth rate and pinocytosis was studied further using another drug, cerulenin, to produce growth-arrest. These experiments showed no changes in the rate pinocytosis even after complete cessation of cellular proliferation. Other studies showed that the transfer of cells from growth to starvation medium reduced the rate of pinocytosis by approximately 50 percent. A reduction of similar magnitude occurred if cells were transferred from growth to starvation medium containing hadacidin. Also, no additional reduction in pinocytosis occurred when cells that had been treated with hadacidin were transferred to starvation medium containing hadacidin. These cells were able to take up [(14)C]hadacidin in the starvation medium. In contrast to the results with hadacidin-treated cells, cells in a cerulenin-induced state of growth-arrest when transferred to starvation medium exhibited the same 50 percent reduction in pinocytosis observed in cells not previously exposed to either drug. Cells treated with azide, in either growth or starvation medium, exhibited an immediate inhibition of all pinocytotic activity. After the transfer of log-phase cells to starvation medium supplemented with glucose, the reduction in rate was only approximately 10-15 percent. In contrast, a 50 percent reduction was observed after supplementation of starvation medium with sucrose, KCl, or concanavalin A. Maintaining the cells in growth medium containing hadacidin for as long as 16 h had no effect on the rate at which cells aggregated. These results are consistent with the conclusion that D. discoideum exhibits two types of pinocytotic activity: one that is nutrient dependent and the other independent of nutrients. This latter activity persists in starvation medium and is unaffected by hadacidin, whereas the nutrient-dependent activity is present in growth medium and is inhibited by hadacidin.     

Cherry leaf roll virus in the female gametophyte and seed of birch and its relevance to vertical virus transmission

ELISA detected cherry leaf roll virus (CLRV) in infected birch leaf sap diluted 1/320 in buffer, in extracts of one infected leaf with nine healthy leaves and in leaf sap frozen for 2 wk. Similarly, ELISA detected CLRV in mixtures of one infected bud with four virus-free buds. Intensive bioassays and ELISA showed that in some trees CLRV was restricted to only a few branches whereas in others it occurred throughout the tree. The prevalence of CLRV in unmanaged birch populations in Britain was less (3%) than in Midlands street trees (17%). In CLRV-free birch trees that received pollen from infected ones, ELISA indicated that antigen was introduced into, and multiplied within, the embryos but not the seed coat or the pericarp/wings. In one instance, antigen was detected in a branch of an experimentally pollinated tree but not in those parts of the crown that had been exposed to open pollination. The proportion of seed germinating after crosses in which both parents were CLRV-free was greater than when either or both parents were infected but the largest difference occurred with infection in the female parent. Few embryos seemed to escape invasion with CLRV when the maternal tissue was naturally infected. Overall, seed transmission ranged between 0 and 38% (mean 17%) when only females in a cross were infected, and between 11 and 75% (mean 30%) when only the males were infected. Assuming no selective advantage that would help infected plants to achieve reproductive age, we found that CLRV would be lost from a birch population within two generations if transmitted only through seed. Embryos in seeds from CLRV-infected birch that received CLRV-free pollen differed from their healthy counterparts in being shrunken and suspended in a loosely fibrillar matrix that contained numerous virus-like particles in tubular inclusions. In two trees, CLRV-free pollen tended to fertilise a greater percentage of ovules than did CLRV-infected pollen. Seedlings derived from infected seed and cuttings from naturally-infected trees grew less rapidly than their healthy counterparts. In still air, most birch pollen liberated from a height of 3·5 m fell within 3 m of the drop zone and none was detected 10 m from the source. Field observations on the patterns of virus spread as measured by seedling infection were consistent; about 3% of seedlings from a tree 6·9 m away from the nearest source of inoculum were infected but no infected seedlings were detected in more distant trees, even though each was experimentally infectible with CLRV and pollen from the infected tree germinated on their stigmas.     

Cycling of Amino-Nitrogen and other Nutrients between Shoots and Roots in Cereals--A Possible Mechanism Integrating Shoot and Root in the Regulation of Nutrient Uptake

A split root system was used to investigate the cycling of nitrogenbetween shoots and roots in young wheat and rye plants. ¹⁵N-nitratewas supplied to one part of the root system for various periods,at the end of which these roots were excised. Xylem sap wasthen collected from the other roots which had not been supplieddirectly with ¹⁵N-nitrate. ¹⁵N detected in the xylem sap indicatedcycling of nitrogen between shoots and roots. Calculations showedthat over 60% of the amino-N flux in the xylem was cycling.Thus nitrate assimilation in the root could account for onlya minor part of amino-N in the xylem sap. The specific activity of ¹⁵N in the total N of xylem sap washigher than in the total N of roots and shoots through whichit had cycled. This is because exchange between amino-N in thetransport pools and bulk tissue N is limited. It is proposedthat there is, in effect, a single regulatory pool of amino-N,common to shoots and roots, and that this pool may be a keyelement in the control of N uptake at the level of the wholeplant. The likely energy costs of cycling and implications for thepartitioning of N between shoots and roots are discussed. Infurther investigations the cycling of ⁴²K-potassium and ³²S-sulphurwas demonstrated. Key words: Potassium, sulphur, transport, xylem     

AUTOMATED 35S-LABELLED PROTEIN ELECTROPHORESIS FOR IDENTIFICATION OF STRAINS OF RHIZOBIUM LEGUMINOSARUM bv. TRIFOLII

A technique for strain-level identification within a Rhizobium biovar is described, based on automated sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of ³⁵S-labelled proteins, offering substantial improvements on existing SDS-PAGE methods particularly in the areas of standardization of electrophoresis conditions and rapidity of positive identification. Gels were analysed with a β-scanner, the beta particle emission data being directly relayed to an IBM PC/AT computer for subsequent manipulation. Analysis of the total protein profiles obtained by this method revealed regions of variability between strains of R. leguminosarum bv. trifolii. Automated comparison of these regions enabled identification of strains. The method was successfully used for identifying root nodule isolates obtained from competition studies between known pairs of R. leguminosarum bv. trifolii strains inoculated onto Trifolium repens.     

Absorption and Re-distribution of Nitrogen during Growth and Development of Field Bean, Vicia faba

The absorption of nitrate by field bean plants at different times of development was investigated to determine the distribution and subsequent utilization of N up to the maturity of the beans. Nodulated plants were grown in sand culture and pulse-labelled with ¹⁵NO₃ for 4 short periods during development. Whole plants were sampled at intervals until maturity and analysed for total nitrogen and ¹⁵N. There was a rapid increase in the bean dry weight and total N after fruit set and, at maturity, the beans contained about three times as much N as had ever been in the rest of the plant. Nitrate absorption continued steadily throughout plant development but nodule N fixation made a progressively greater contribution to the total N in the plant. Over a quarter of the total ¹⁵N absorbed was found in the roots immediately after each treatment and little of this was subsequently translocated upwards in spite of the large increase in shoot N taking place. Above ground the most powerful “sink” for recently absorbed and redistributed N was initially the youngest vegetative tissue. However after fruit set competition developed between the growing tip and the developing beans until at the later stages the beans became the more powerful. Quantitatively redistribution made only a small contribution to bean N.