Investigating unexplained genetic variation and its expression in the arbuscular mycorrhizal fungus Rhizophagus irregularis

SummaryArbuscular mycorrhizal fungi (AMF) are important symbionts of plants. Recently, studies of the AMF Rhizophagus irregularis recorded within-isolate genetic variation that does not completely match the proposed homokaryon or heterokaryon state (where heterokaryons comprise a population of two distinct nucleus genotypes). We re-analysed published data showing that bi-allelic sites (and their frequencies), detected in proposed homo- and heterokaryote R. irregularis isolates, were similar across independent studies using different techniques. This indicated that observed within-fungus genetic variation was not an artefact of sequencing and that such within-fungus genetic variation possibly exists. We looked to see if bi-allelic transcripts from three R. irregularis isolates matched those observed in the genome as this would give a strong indication of whether bi-allelic sites recorded in the genome were reliable variants. In putative homokaryon isolates, very few bi-allelic transcripts matched those in the genome. In a putative heterokaryon, a large number of bi-allelic transcripts matched those in the genome. Bi-allelic transcripts also occurred in the same frequency in the putative heterokaryon as predicted from allele frequency in the genome. Our results indicate that while within-fungus genome variation in putative homokaryon and heterokaryon AMF was highly similar in 2 independent studies, there was little support that this variation is transcribed in homokaryons. In contrast, within-fungus variation thought to be segregated among two nucleus genotypes in a heterokaryon isolate was indeed transcribed in a way that is proportional to that seen in the genome.

Improved Nuclear Staining of Asparagus Microspores for Cytological Analysis

Clear visualization of asparagus (Asparagus officinalis L.) microspore nuclei with common stains such as acetocarmine or DAPI is difficult, hindering cytological analyses. The addition of saturated aqueous ferric chloride solution to Carnoy's I fixative (30 μL·mL-1) resulted in clear visualization of nuclei. A distinct nucleus was observed in uninucleate cells and the vegetative and generative nuclei were clearly visible in binucleate microspores. This method can be used reliably for determination of asparagus microspore developmental stage. Chemical name used: 4′,6-diamidino-2-phenylindole-2HCL (DAPI).

On the Structure and Function of the Wandering Cells in the Wall of the Alimentary Canal of Nudibranchiate Mollusca

1. The lining epithelium and subjacent tissues of the gut of nudibranch molluscs contain characteristic wandering cells. 2. Although probably amoeboid when alive, the wandering cells after fixation are seen to possess a very definite rounded form. They have a distinct nucleus. The cytoplasm contains a variety of inclusions, and, characteristically, a well-marked eosinophile area. 3. The reaction of the cells to stains is described. 4. The wandering cells were found to take up iron saccharate, which had been injected into the haemocoele. 5. The wandering cells are regarded as a special type of blood cell. 6. Evidence indicates that the wandering cells of nudibranchs are excretory, taking up effete matter from the haemocoele and discharging it into the lumen of the gut.

7. On the Cell-Walls of Hepatic Cells

Since Henle and Purkinje first described the cells which form the great mass of the liver, microscopists have maintained that these are what are termed “naked protoplasts”—that is, they possess, like the white blood corpuscle, no differentiated cell-walls. I may mention the names of Dr Lionel Beale, Ewald Hering (“Stricker's Histology,” section on the Liver), and Dr Klein (“Atlas of Histology”), who all agree in denying its existence. Indeed, the absence of this structure is emphatically insisted upon in most works on microscopical anatomy.If a liver-cell be examined with a power of about 300 diameters, it is seen to be a granular mass, of a somewhat spherical shape, containing a very distinct nucleus and nucleolus. The granules are but the optical expression of a delicate reticulum or stroma, which may be seen as such on using a higher power.