No abstract

Programmed cell death (PCD) is an essential part of the defence response in plants and animals against pathogens. Here, we report that PCD is also involved in defence against pathogens of fungi. Vegetative incompatibility is a self/non-self recognition system in fungi that results in PCD when cells of incompatible strains fuse. We quantified the frequency of cell death associated with six vegetative incompatibility (vic) genes in the filamentous ascomycete fungus Cryphonectria parasitica. Cell death frequencies were compared with the effects of vic genes on transmission of viruses between the same strains. We found a significant negative correlation between cell death and virus transmission. We also show that asymmetry in cell death correlates with asymmetry in virus transmission; greater transmission occurs into vic genotypes that exhibit delayed or infrequent PCD after fusion with an incompatible strain. Furthermore, we found that virus infection can have a significant, strain-specific, positive or negative effect on PCD. Specific interactions between vic gene function and viruses, along with correlations between cell death and transmission, strongly implicate PCD as a host-mediated pathogen defence strategy in fungi.

New applications of laser microbeam irradiation to cell and developmental biology include a new instrument with a tunable wavelength (217- to 800-nanometer) laser microbeam and a wide range of energies and exposure durations (down to 25 × 10 -12 second). Laser microbeams can be used for microirradiation of selected nucleolar genetic regions and for laser microdissection of mitotic and cytoplasmic organelles. They are also used to disrupt the developing neurosensory appendages of the cricket and the imaginal discs of Drosophila .

1971. The cytology and kinetics of cabbage root hair penetration by Plasmodiophora brassicae. Can. J. Bot. 49: 2023-2034. After a primary zoospore of Plasnlodiophora brassicae attaches to a cabbage root hair wall, the flagella coil, and the axonemes are soon retracted. During the next 2 h a dense-staining bullet-like Stachel is formed within a tubular cavity in the cyst, the Rohr. Possibly because of pressure created within an expanding cyst vacuole, the Rohr is quickly evaginated to form a bulbous adhesorium. The Stachel punctures the host wall and then, in a period of about 1 s, the parasite is injected into the root hair. The total time required for adhesorium formation and host penetration is about 1 min. Secondary zoospores were found to be capable of carrying out a similar penetration process. After penetration a callose-rich papilla is soon formed between the host wall and plasma membrane at the penetration site. Young amoebae in root hairs have no lipid bodies and are surrounded by seven-layered envelopes. Unidentified spherical inclusion bodies were seen sporadically in primary zoospores and cysts, and in uninucleate amoebae.

The anaphase-telophase spindle usually elongates, and it has been assumed that the spindle pushes the incipient daughter nuclei apart. To test this assumption, we used a laser microbeam to sever the central spindle of the fungus, Fusarium solani, and measured the rate of separation of incipient daughter nuclei . When the microbeam was aimed beside the spindle, separation occurred at a rate (8 .6 ,um/min) that did not differ significantly from the rate (7 .6 Am/min) in unirradiated cells. But when the spindle was irradiated, it broke, and the separation was much faster (22.4p,m/min) . Irradiation of cytoplasm lateral to one spindle pole resulted in a 1 .5 pin/min reduction in the rate (6 .1 ,um/min) of separation . From these and other data, we infer that extranuclear forces, presumably involving astral microtubules, pull on the incipient daughter nuclei and that the central spindle limits the separation rate . Astral microtubles are associated with the plasma membrane or, sometimes, with the rough endoplasmic reticulum . Most of the spindle microtubules that are present at metaphase are depolymerized during anaphase and early telophase.