BackgroundA variety of spore discharge processes have evolved among the fungi. Those with the longest ranges are powered by hydrostatic pressure and include “squirt guns” that are most common in the Ascomycota and Zygomycota. In these fungi, fluid-filled stalks that support single spores or spore-filled sporangia, or cells called asci that contain multiple spores, are pressurized by osmosis. Because spores are discharged at such high speeds, most of the information on launch processes from previous studies has been inferred from mathematical models and is subject to a number of errors.Methodology/Principal FindingsIn this study, we have used ultra-high-speed video cameras running at maximum frame rates of 250,000 fps to analyze the entire launch process in four species of fungi that grow on the dung of herbivores. For the first time we have direct measurements of launch speeds and empirical estimates of acceleration in these fungi. Launch speeds ranged from 2 to 25 m s−1 and corresponding accelerations of 20,000 to 180,000 g propelled spores over distances of up to 2.5 meters. In addition, quantitative spectroscopic methods were used to identify the organic and inorganic osmolytes responsible for generating the turgor pressures that drive spore discharge.Conclusions/SignificanceThe new video data allowed us to test different models for the effect of viscous drag and identify errors in the previous approaches to modeling spore motion. The spectroscopic data show that high speed spore discharge mechanisms in fungi are powered by the same levels of turgor pressure that are characteristic of fungal hyphae and do not require any special mechanisms of osmolyte accumulation.
BackgroundSpore discharge in the majority of the 30,000 described species of Basidiomycota is powered by the rapid motion of a fluid droplet, called Buller's drop, over the spore surface. In basidiomycete yeasts, and phytopathogenic rusts and smuts, spores are discharged directly into the airflow around the fungal colony. Maximum discharge distances of 1–2 mm have been reported for these fungi. In mushroom-forming species, however, spores are propelled over much shorter ranges. In gilled mushrooms, for example, discharge distances of <0.1 mm ensure that spores do not collide with opposing gill surfaces. The way in which the range of the mechanism is controlled has not been studied previously.Methodology/Principal FindingsIn this study, we report high-speed video analysis of spore discharge in selected basidiomycetes ranging from yeasts to wood-decay fungi with poroid fruiting bodies. Analysis of these video data and mathematical modeling show that discharge distance is determined by both spore size and the size of the Buller's drop. Furthermore, because the size of Buller's drop is controlled by spore shape, these experiments suggest that seemingly minor changes in spore morphology exert major effects upon discharge distance.Conclusions/SignificanceThis biomechanical analysis of spore discharge mechanisms in mushroom-forming fungi and their relatives is the first of its kind and provides a novel view of the incredible variety of spore morphology that has been catalogued by traditional taxonomists for more than 200 years. Rather than representing non-selected variations in micromorphology, the new experiments show that changes in spore architecture have adaptive significance because they control the distance that the spores are shot through air. For this reason, evolutionary modifications to fruiting body architecture, including changes in gill separation and tube diameter in mushrooms, must be tightly linked to alterations in spore morphology.
Active discharge of basidiospores in most species of Basidiomycota is powered by the rapid movement of a droplet of fluid, called Buller’s drop, over the spore surface. This paper is concerned with the operation of the launch mechanism in species with the largest and smallest ballistospores. Aleurodiscus gigasporus (Russulales) produces the largest basidiospores on record. The maximum dimensions of the spores, 34 × 28 µm, correspond to a volume of 14 pL and to an estimated mass of 17 ng. The smallest recorded basidiospores are produced by Hyphodontia latitans (Hymenochaetales). Minimum spore dimensions in this species, 3.5 × 0.5 µm, correspond to a volume of 0.5 fL and mass of 0.6 pg. Neither species has been studied using high-speed video microscopy, but this technique was used to examine ballistospore discharge in species with spores of similar sizes (slightly smaller than A. gigasporus and slightly larger than those of H. latitans). Extrapolation of velocity measurements from these fungi provided estimates of discharge distances ranging from a maximum of almost 2 mm in A. gigasporus to a minimum of 4 µm in H. latitans. These are, respectively, the longest and shortest predicted discharge distances for ballistospores. Limitations to the distances traveled by basidiospores are discussed in relation to the mechanics of the discharge process and the types of fruit-bodies from which the spores are released.
Insight into the influence of UV-C radiation on the evolutionary relationship between prokaryotic and eukaryotic algae was studied in seven species of algae exposed to different UV-C irradiances. The order of their acclimation (from most tolerant to sensitive) is Synechococcus sp. PCC7942 (Cyanophyta), Synechocystis sp. PCC6803 (Cyanophyta), Chlorella protothecoides (Chlorophyta), Chlamydomonas reinhardtii (Chlorophyta), Phaeodactylum tricornutum (Bacillariophyta), Alexandrium tamarense (Pyrrhophyta) and Dicrateria zhanjiangensis (Chrysophyta). These results are in accordance with the algal evolution process that is generally accepted and proved by fossil record. It shows that UV-C radiation is an important environmental factor that cannot be ignored in the evolutionary process from prokaryotic algae to eukaryotic algae. The threshold of UV-C radiation at which prokaryotic algae can survive but eukaryotic algae cannot was found to be approximately 0.09 W m(-2). This was the first time to determine with precision the irradiance level at which UV-C contributed as a selection pressure of evolution. Furthermore, the effects of UV-C radiation on photosynthetic performance, growth rate and pigment content were investigated in two species of prokaryotic algae: Synechococcus sp. PCC7942 and Synechocystis sp. PCC6803, and two species of eukaryotic algae: C. reinhardtii and C. protothecoides. After 6 days of exposure, the contents of chlorophyll a and carotenoids decreased in all species, moreover reduction in C. reinhardtii and C. protothecoides was more obvious than in Synechococcus sp. PCC7942 and Synechocystis sp. PCC6803. The ability to photosynthesize followed the same trend as the pigments.
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