Many fungal pathogens penetrate plant leaves from a specialized cell called an appressorium. The rice blast pathogen Magnaporthe gnsea can also penetrate synthetic surfaces such as poly (vinyl chloride). Previous experiments have suggested that penetration requires an elevated appressorial turgor pressure. In the present report we have used nonbiodegradable Mylar membranes, exhibiting a range of surface hardness, to test the proposition that penetration is driven by turgor. Reducing appressorial turgor by osmotic stress inhibited penetration of these membranes. The size of the turgor deficit required to inhibit penetration was a function of the surface hardness. Penetration of the hardest membranes was inhibited by small decreases in appressorial turgor, while penetration of the softer membranes was sensitive only to large decreases in turgor. Similarly, penetration of the host surface was inhibited in a manner comparable to penetration of the hardest Mylar membranes. Indirect measurements of turgor, obtained through osmotically induced collapse of appressoria, indicated that the infection apparatus can generate turgor pressures in excess of 8.0 MPa (80 bars). We conclude that penetration of synthetic membranes, and host epidermal cells, is accomplished by application of the physical force derived from appressorial turgor.The mechanism of host surface penetration by plant pathogenic fungi has been debated for nearly a century (1-6). The potential role of extracellular enzymes, to facilitate perforation of the host cuticle or cell wall during fungal invasion, is poorly understood (with one exception) due to the complex and ill-defined chemical nature of plant surfaces (7). On the other hand, an essential role for mechanical force during host surface penetration has been proposed for the rice blast fungus Magnaporthe grisea (Hebert) Barr (8). This pathogen produces unicellular infection structures, called appressoria, which adhere tightly to the host surface and produce slender infection pegs that pierce the underlying cell wall. The cell walls of appressoria contain a dense layer of pentaketidederived melanin whose presence is correlated with a build-up of appressorial turgor pressure (8) and is essential for penetration (8,9). In this study, we have inhibited penetration by exposing appressoria to solutions of high osmotic pressure. This approach was used to reduce the hydrostatic pressure (or turgor) within the infection apparatus and to estimate the magnitude of the turgor involved in penetration. Our results offer unequivocal evidence for an extraordinary mechanical component of the mechanism by which appressoria penetrate hard surfaces, but do not exclude a role in host penetration for some other factor such as extracellular enzymes. MATERIALS AND METHODSOrganism and Growth Conditions. These studies were conducted with strain 042 (see ref. 8) of M. grisea (Hebert) Barr, telomorph of Pyricularia grisea Sacc. (10). The time course of infection-structure development in vitro has been well documented ...
Osmotic pressures (II) of aqueous solutions of polyethylene glycols (PEGs) of average relative molecular weight (Mr) between 200 and 10,000 were measured using vapor pressure deficit osmometry. The relationships between molarity and II were described with high precision by second order polynomials for each of the PEGs studied. In contrast to previous reports, equivalent weights of different polymers in solution did not generate the same II; low M, PEGs generated a higher II than the higher M, PEGs. The effect of PEGs upon II represents an interaction between concentration and M,.
Ballistospore discharge is a feature of 30000 species of mushrooms, basidiomycete yeasts and pathogenic rusts and smuts. The biomechanics of discharge may involve an abrupt change in the center of mass associated with the coalescence of Buller's drop and the spore. However this process occurs so rapidly that the launch of the ballistospore has never been visualized. Here we report ultra high-speed video recordings of the earliest events of spore dispersal using the yeast Itersonilia perplexans and the distantly related jelly fungus Auricularia auricula. Images taken at camera speeds of up to 100,000 frames/ s demonstrate that ballistospore discharge does involve the coalescence of Buller's drop and the spore. Recordings of I. perplexans demonstrate that although coalescence may result from the directed collapse of Buller's drop onto the spore, it also may involve the movement of the spore toward the drop. The release of surface tension at coalescence provides the energy and directional momentum to propel the drop and spore away from the fungus. Analyses show that ballistospores launch into the air at initial accelerations in excess of 10,000 g. There is no known analog of this micromechanical process in animals, plants or bacteria, but the recent development of a surface tension motor may mimic the fungal biology described here.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.