INTRACELLULAR ACRIDINE ORANGE FLUORESCENCE IN PLANT VIRUS INFECTIONS

In situ localization of light-induced chalcone synthase mRNA, chalcone synthase, and flavonoid end products in epidermal cells of parsley leaves

Methods involving in situ RNA hybridization, immunohistochemistry, and microspectrophotometry of individual cells were used to localize the mRNA encoding chalcone synthase (the key enzyme of flavonoid biosynthesis), the enzyme protein, and the biosynthetic end products in cross sections of parsley leaves (Petroselinum crispum). The light-dependent, sequential occurrence of all three components was restricted to epidermal cells. The results are in agreement with the putative function of flavonoids (transcriptionally inducible, UV-protective pigments) and suggest that all biosynthetic steps occur in those cells in which the products accumulate.

Nonradioactive in situ hybridization for detection of hydrophobin mRNA in the phytopathogenic fungus Claviceps purpurea during infection of rye

Hydrophobins are unique fungal extracellular proteins that produce amphipathic films at interfaces, mediate contact to hydrophobic surfaces and are known to be important in phytopathogenicity. In the pathogenic ascomycete Claviceps purpurea, causing ergot disease in grasses and cereals and ergotism in livestock, a gene encoding an extraordinary type of hydrophobin has been detected, which appeared to be induced during alkaloid synthesis in axenic culture of an ergot-alkaloid producing strain of Claviceps (V. Garre and P. Tudzynski, pers. communication; Arntz and Tudzynski, 1997, Curr. Genet. 31, 357-360). To elucidate presence and function of this hydrophobin during infection of rye, the nonradioactive in situ hybridization technique was successfully adapted to the fungal organism and optimized in the pathogenic interaction system. Semithin cryosections proved to be suitable for microscopical gene expression analysis using immune-mediated alkaline-phosphatase staining for detection of digoxigenin-labeled cRNA probes. Specific hybridization of the prepared antisense riboprobe to hydrophobin mRNA was confirmed in nonradioactive Northern blots. While permeabilization by proteinase K had only a minor effect, the inclusion of detergent into the hybridization solutions enhanced specific RNA-RNA hybridization under maximum stringency. Hydrophobin mRNA was found in fungal cells, growing in axenic culture. In the disease cycle, hydrophobin transcripts were localized in abundance during vegetative fructification in conidiophores that actively produced conidia. No signals were observed in sclerotial hyphae during formation of the alkaloid-containing ergots, although they fluoresced intensely during total RNA detection using acridine orange. Notably, in situ hybridization experiments resulted in specific signals during early infection and colonization phases in the external mycelia and in hyphae penetrating the host epidermal layer. The presumed role of the hydrophobin gene product in ergot pathogenicity is discussed with respect to the described spatio-temporal distribution of the hydrophobin transcripts.

Fluorochromes for detection of callose in meiocytes of olive (Olea europaea L.)

The callosic wall which covers microsporocyte mother cells during meiotic division has been studied using different fluorochromes as alternatives to the widely used aniline blue. We have confirmed that both acridine orange and 4', 6' diamidino-2-phenylindole (DAPI) produce a fluorescent response to callose which is comparable in specificity and intensity to that of aniline blue; therefore, they can be used to study callose wall formation. Staining properties of these fluorochromes, as well of those of curcumin and sirofluor, reported earlier as fluorescent stains for callose, are discussed. We also discuss the efficacy of the combined use of sirofluor and DAPI to study particular aspects of the deposition of callose.

Role of bromine in the formation of the refractile inclusions of the vesicle cells of the Bonnemaisoniaceae (Rhodophyta)

Refractile inclusions characteristic of the vesicle cells of members of the Bonnemaisoniaceae fail to form if bromide is omitted from the culture medium. Electron microprobe analysis shows the localization of bromine in these cells. When grown in the presence of bromide, but not when grown in its absence, these organisms oxidize iodide to iodine; in Trailliella, this oxidation occurs at the vesicle cells.

Ultrastructural features of Beta leaves infected with beet yellows virus

A cytochemical and electron microscope study has been made of leaves of sugar beet infected with beet yellows virus. Inclusions of particles, which agree in size with beet yellows virus particles isolated by other investigators, have been localized in the ground cytoplasm, in the chloroplasts, and in the nuclei. These particles are circa 100 A in diameter and have an electron-transparent core of 30 to 40 A. Use of acridine orange, azure B, and pyronine Y has revealed that the cytoplasmic inclusion bodies, which consist wholly of the elongate particles, have a strong RNA reaction removable by RNase pretreatment. Particles observed in the chloroplasts may or may not be associated with lipid spheres. If they are, the particles are confined to the periphery of the spheres. In this position the particles are arranged tangentially and are further arranged parallel into groups which lie at various angles to one another. Within the groups the particles are regularly spaced in a three dimensional lattice. Particles located free in the stromal regions are often arranged regularly in curved rows which lie parallel to one another so that a three dimensional lattice is formed. The dispersed and compact forms of virus inclusions are described and related to the condition of the associated cytoplasm. The ground cytoplasm of cells associated with the sieve elements contains numerous ribosomes. A decrease in the number of ribosomes is concomitant with the increase in size of virus aggregations in a cell. Vesiculation of some component of the cytoplasm occurs during the period of virus replication. The vesicles are approximately 100 mmicro in diameter and could be derived from the dictyosomes. At later stages of infection these vesicles collapse and convoluted membranous material appears.