Fine Structure of Developing Spores of Thelohania bracteata (Strickland, 1913) (Microsporida,Nosematidae) Emphasizing Polar-Filament Formation*

SYNOPSIS. In the microsporidian, Thelohania bracteata, the polar filament, as it starts to develop in the sporoblast, apparently receives material synthesized by the granular endoplasmic reticulum and Golgi vesicles. In immature spores many dilated sacs are observed in areas where there is less endoplasmic reticulum. These sacs, that persist into the almost mature spore, are probably Golgi-type vesicles and may be related to the formation of the spore coat. The polar filament of the mature spore possesses 8 coils and in cross section or cross-fractured face the electron-dense central portion of the polar filament contains a tubular structure, ringed by 12–14 cylindrical structures. In thin sections, an electron-lucid zone is observed between the core and membrane of the polar filament. The polar filament runs through the highly laminated polaroplast which occupies the anterior portion of the spore. In cross-fractured face the lamellae of the polaroplast are arranged like the petals of a flower. The basal portion of the polar filament is enlarged, appearing arrow-shaped in thin sections and pear-shaped in frozen-etched preparations. Frozen-etched membranes differ in the size and distribution of the surface particles.     

Antitranspirant Activity in Xylem Sap of Maize Plants

Xylem sap from unwatered maize plants was collected and testedfor antitranspirant activity. Two assays were used. These werea transpiration assay with detached wheat leaves and a stomatalbio-assay involving the direct microscopic observation of epidermisof Commelina communis. The reduction in transpiration of detached wheat leaves promotedby xylem sap could be duplicated almost exactly by the applicationof solutions of ABA of equivalent concentration to that foundin the xylem sap. Removal of virtually all the ABA from thexylem sap, using an immunoaffinity column, removed virtuallyall the antitranspirant activity in both assays. These results are discussed in the context of other resultswhich suggest the presence of as-yet unidentified inhibitorsin the xylem sap of unwatered plants. We suggest that with maize plants at least, stomatal responsesto soil drying can be entirely explained by enhanced concentrationof ABA in the xylem stream. Key words: Antitranspirant activity, ABA, ABA bio-assay, xylem sap     

Drought-induced Closure of Phaseolus vulgaris L. Stomata Precedes Leaf Water Deficit and any Increase in Xylem ABA Concentration

Young seedlings of two cultivars of Phaseolus vulgaris L. (cv.Cacahuate-72 and Michoacan-12A3) were subjected to a soil dryingtreatment. Stomata started to close before any leaf water deficitcould be detected. Soil drying promoted a small degree of ABAaccumulation in roots, but, at the time stomatal closure wasinitiated, at least in one cultivar, xylem ABA and bulk leafABA concentration were not enhanced. The mechanism of the stomatalresponse is discussed in terms of an as-yet unidentified regulatorof stomatal behaviour, redistribution of existing ABA in plants,and a high sensitivity of stomata to small changes in ABA concentration.     

Maize stomatal conductance in the field: its relationship with soil and plant water potentials, mechanical constraints and ABA concentration in the xylem sap

Abstract. Stomatal conductance, leaf water potential, soil water potential and concentration of abscisic acid (ABA) in the xylem sap were measured on maize plants growing in the field, in two treatments with contrasting soil structures. Soil compaction affected the stomatal conductance, but this effect was no longer observed if the soil water potential was increased by irrigation. Differences in leaf water potential did not account for the differences in conductance between treatments. Conversely, the relationship between stomatal conductance and concentration of ABA in the xylem sap was consistent during the experiment. The proposed interpretation is that stomatal conductance was controlled by the root water potential via an ABA message. Control of the stomatal conductance by the leaf water potential or by an effect of mechanical stress on the roots is unlikely.     

Can Flow Cytometry Reduce the Workload For Cervical Screening? the Results of A Series of 622 Specimens

A simple method permitting the flow cytometric examination of cervical specimens has been developed and an assessment made of the feasibility of relying on this method to screen women for cervical neoplasia. Examination of four flow cytometric parameters showed differences between morphologically normal and abnormal specimens and allowed identification of a proportion of the normal specimens. The system had a false negative rate of 8%. Our experience with cervical specimens has revealed a number of problems associated with their examination by flow cytometry and these are discussed.     

Porcine malignant hyperthermia carrier detection and chromosomal assignment using a linked probe

In pigs, the gene for glucosephosphate isomerase (GPI) is linked to the halothane (HAL) gene which is responsible for malignant hyperthermia (MH). A single copy DNA probe, designated GPI8R, has been isolated from a pig genomic library using a porcine GPI cDNA probe. This probe detects, as was the case for the cDNA probe, a five allele polymorphism in SacI and PvuII digested pig DNA. Family studies show that this polymorphism is linked to the HAL locus and hence can be used in carrier detection. In situ hybridization with GPI8R assigned the GPI locus to bands p12-q22 of chromosome 6. We conclude that the HAL linkage group resides on chromosome 6.     

Effects of Soil Flooding on Growth and Grain Yield of Populations of Tetraploid and Hexaploid Species of Wheat

Single populations of three hexaploid species of wheat, Triticumaestivum, Triticum spelta and Triticum macha, and two populationsof the tetraploid wheat, Triticum dicoccum (Pontus and Bordeaux),were grown in a greenhouse experiment at a range of soil floodingregimes: free draining, two levels of transient flooding andcontinuous flooding. Increasing severity of flooding treatment resulted in increasedsoil reduction and an increase in the concentration of reducediron and manganese in the experimental soil, and also resultedin a reduction in vegetative growth, number of inflorescences,grain number and grain weight. There were, however, large differencesbetween the wheat populations in the degree of reduction inyield caused by flooding. The population of T. macha was muchmore flooding-tolerant than the other hexaploid species andthe ‘Pontus’ population of the emmer wheat, T. dicoccum,was more tolerant than the ‘Bordeaux’ populationof this species and than T. spelta and T. aestivum. The results are discussed in relation to the origin of the populations. Soil flooding, Triticum aeslivum, Triticum macha, Triticum spelta, Triticum dicoccum     

Pathogenicity of benomyl-tolerant variants of Verticillium dahliae to strawberry, cv. Cambridge Vigour

Plants of cv. Cambridge Vigour were inoculated either with a benomyl-sensitive isolate of Verticillium dahliae or with one of two variants selected from it in vitro; these variants, Ri/8 and Ri/ii, were tolerant of benomyl at concentrations of 5 and 10 ppm respectively in the culture medium. The parent isolate and Ri/8 caused only mild wilt symptoms, but Ri/n was strongly pathogenic. A single treatment with benomyl (0–04 g/plant, in 100 ml water), applied as a soil drench o, 14, 29 or 57 days after inoculation, tended to reduce the mild symptoms caused by the parent isolate; the treatments had no apparent effect on Ri/8, but they slightly increased the severity of the wilt caused by Ri/n, especially after the earlier applications.