Spore Aquatic Stage Expansion 68
It appears likely that spores in which germination has been initiated but cortex degradation has not taken place represent an intermediate stage in spore germination, since cortex hydrolysis is normally significantly slower than DPA excretion and initial water uptake (21). However, this intermediate stage is impossible to study during wild-type spore germination because of the rapidity of cortex hydrolysis and the asynchrony of germination in spore populations. Therefore, we have analyzed the properties of mutant spores in which germination has been initiated but cortex hydrolysis cannot take place in order to characterize this intermediate stage in spore germination that we propose to call stage I.
Spore Aquatic Stage Expansion 68
The results obtained in this work indicate that spores which have initiated germination but have not degraded their cortex are in an intermediate stage of spore germination, which we propose to call stage I. These spores have released their DPA and presumably much of their divalent cations, and these components appear to have been replaced with some increased core water content, although this is not as high as in germinated wild-type spores, presumably because of the restriction on core expansion due to the continued presence of the cortex. In some other respects, however, these spores held in stage I of germination are more like dormant spores. Thus SASP, in particular α/β-type SASP, are degraded extremely slowly, as is also the case for 3PGA, and the stage I germinated spores have neither ATP nor readily accessible reducing equivalents, as is also the case in dormant spores (30, 32).
During sporulation, cortex synthesis around the developing forespore precedes DPA accumulation, as do loss of forespore ATP and accumulation of 3PGA and SASP, with enzyme action on the latter two compounds being very low in forespores even prior to DPA accumulation (20, 30, 32). Forespores at this stage of development are also more UV radiation resistant than are dormant spores and have acquired some heat resistance, although they are by no means as heat resistant as dormant spores (7, 16, 29). While there are no direct measurements of the core water content of these forespores, several analyses indicate that their core water content is lower than in the forespore compartment when the latter is first established (16). Thus, even though forespores which have acquired a cortex have not yet acquired their mature spore coat, the general properties of forespores at this intermediate stage of sporulation are very similar to those of spores in stage I of germination. If stage I germinated spores are, indeed, functionally equivalent to forespores in an intermediate stage of development, it is tempting to speculate that the latter stage was once the endpoint of the sporulation process, and it was only through further evolution that full spore dormancy and resistance were acquired, with these being attained only upon evolution of the capacity for mother cell synthesis and forespore acquisition of DPA and the attendant further reduction in spore water content. Many bacteria form quiescent, somewhat resistant forms in response to starvation (12), but it is the acquisition of DPA and the extreme degree of core (protoplast) dehydration that sets spores of Bacillus species and those of related genera apart from the quiescent forms of other bacteria.
Interactions between germinant and GRs play as key role in triggering of germination. Upon binding to specific germinant-like amino acid, inorganic salts, and sugars, GRs are activated and trigger spore germination irreversibly and therefore known as commitment step. Subsequent to this step, monovalent cations along with pyridine-2,6-dicarboxylic acid (dipicolinic acid, DPA) and divalent cations, especially Ca2+, in chelated form, i.e., CaDPA are released from spore core. This is followed by entry of water inside core region to initiate the process of rehydration. Further, release of CaDPA in Bacillus spores has also been found to contribute to peptidoglycan hydrolysis in spore cortex due to activating any of the two types, i.e., CwlJ and SleB of cortex lytic enzymes (CLEs). Subsequently, hydrolysis of spore cortex permits the core region for expansion and rehydration, which in turn activates enzymes and hence initiate the metabolic activities in spore core (Moir et al. 2002; Yi and Setlow 2010). During the phase of outgrowth, synthesis of RNA, proteins, and DNA recommences and thus results in conversion of spore to vegetative cell (Gupta et al. 2013). Under optimal conditions, this process occurs very rapidly, most probably within minutes (Carr et al. 2010). Several factors such as medium composition, temperature, pH, germinant type and concentration, and heat treatment are known to influence the rate and thus time of spore germination (Caipo et al. 2002). Further enhancement of germination, i.e., activation has been found to be associated with additional treatments like type of time-temperature combination, certain chemicals, etc. (Foster and Johnstone 1990). However, the mechanisms underlying in activation have not been clearly understood.
Various symptoms for this disease have been observed. The manifestation of these diverse symptoms is due to when infection occurs during a stage in mushroom development and the quantity of spores that cause the initial infection. The stage of development at which infection occurs, how many spores start the infection and knowing the time from spore to symptoms, all appear to influence the type of symptom we might find. Therefore, recognizing all symptoms will help to determine when the initial infection occurred and that information can be used to control this disease. Several good papers describing the relationship of spores and disease development have been written (Sinden, 1971; Gandy, 1973; North and Wuest, 1993).
As wheat ripens, the uredinial stage turns into a new stage known as the telial stage. Telia (fruiting bodies similar in size to uredinia) are black and develop beneath the epidermis primarily on leaf sheaths and blades. They produce brown-black spores known as teliospores. Telia are not always formed especially if rust infections occur late in the growing season.
We used two complementary strategies to expose hierarchically designed hygroscopic materials to rapidly changing relative humidity. We will discuss them in detail in the following sections. Briefly, the first strategy we used was to control the evaporation rate using a shutter mechanism (Fig. 1g). We will show that coupling the expansion and contraction of the spore-coated films to the shutters results in a self-starting oscillatory movement with net power output. The photo in Fig. 1h shows a fully assembled device that exhibit oscillations when placed above water (see Supplementary Movie 1). The second strategy we used was to move spores in and out of the humid zone. This can be achieved by coupling hydration-induced movements to a rotational motion. For example, gradients in relative humidity near the evaporating surface can induce different degrees of curvature in spore-coated films assembled around a freely rotating disk (Fig. 1i). We will show that the horizontal shift in the centre of mass of the entire structure creates torque that sustains the rotational motion. The photo in Fig. 1j depicts one such device that exhibits continuous rotation when the paper lining the inner surfaces of the device, shown in white, is wetted (see Supplementary Movie 2).
Figure 5. Phase-contrast microscopy images at 14days post inoculation demonstrating the morphological differences between WT, Δspo0A::bm, and complemented mutant strains. Phase-bright endospores were detectable only in samples containing WT or complemented strains. The Δspo0A::bm mutant did not display any spores or sporulating cells, suggesting that endospore formation ceased at the early stage. Scale bar 5μm.
Symptoms. Vinca infected with black root rot are often stunted and/or wilted and the leaves often curl under much like symptoms caused by other root rot pathogens. The most diagnostic symptom on vinca is leaf yellowing (chlorosis) of infected plants. The chlorosis is often the first symptom seen and is then followed by plant wilting and death. Roots infected with black root rot develop dark spots or bands that are easily seen against the normally white roots or a white background. Early infection is most often seen at the tips of secondary feeder roots, but as the disease progresses the entire root system becomes black and water-soaked. The black discoloration of the roots is due to the production of darkly colored fungal spores within the root. The spores can be seen with the aid of a good (15x-20x) magnifying glass, hand lens or microscope. All stages of vinca growth can be infected and killed. The disease can be especially destructive when temperatures are high and when potting medium pH is higher than 6.0.