RIMAPS analysis of fungal ascospore ornamentation

S. M. ROMERO; R. M. COMERIO; E. FAVRET

Manchester Central

Congreso; 15th European Microscopy Congress; 2012

Fungal spores frequently present marked or sculptured surfaces; this feature is commonly referred as ornamentation. The presence of some kind of ornamentation (bars, lines, spines, warts, etc.) is often critical for species delimitation. Eurotium amstelodami is an ascomycete which has ascospores ornamented with bars. The RIMAPS technique consists basically of rotating the image using algorithms of commercial software and calculating the x-step of the twodimensional Fourier transform for each y-line of the new image obtained after rotation. As a consequence, averaged power spectra are obtained for each angular position. The corresponding maximum values are plotted as a function of rotation angle to obtain the RIMAPS spectrum. The peaks (maxima) of the RIMAPS spectrum indicate main angular directions of the topographic pattern, the arrangement of the elements that constitute the surface. In this opportunity, the objective was to explore RIMAPS application to ascospore morphological features analysis. The present work deals with an original E. amstelodami spore image, and with some conceptualized spore images as well. Mature cleistothecia of an Eurotium amstelodami strain isolated from wheat grains were crushed and coated with gold. The original image was obtained using a scanning electron microscope Zeiss Supra 40 with field emission gun. For getting the stylize image, the stylize filter from the Adobe Photoshop software program was employed. For spectra comparison purposes two hand-made drawings were done as well: a copy of ornamentation edges and an abstraction built up with rectangles. RIMAPS was applied to all the images. Figure 5 shows the RIMAPS spectra of Figures 1 and 2 in polar coordinates. Similar maxima were found in both spectra indicating similar main directions. The values were 30º-45º (several peaks), 60º, 75º-95º (several peaks), 105º-110º (two peaks), 120º, 140º-150º (several peaks), 160º for Figure 1 and 35°, 45°, 80°, 107°, 120°, 135°-145º (several peaks), 167° for Figure 2. Besides, it was observed that the stylize filter worked as a useful tool gently highlighting the borders of the ornamentation pattern against a clear background. Figure 6 shows the RIMAPS spectra of Figures 3 and 4 in polar coordinates; similar maxima were found again. The values were 5º, 35°, 50º, 70°, 85°, 105°, 122°, 134°, 152°, 167° for Figure 3 and 0°, 14°, 45°, 60º-80º (four peaks), 103°, 122°, 136°, 150°-160º (several peaks) for Figure 4. In summary, many maxima appeared in the RIMAPS spectrum of Figure 1 due to the complexity of the ascospore surface. This complexity was progressively reduced using the stylize image and the hand-made drawings. Nevertheless, comparing the RIMAPS spectra of the four images, some common maxima remained in all spectra: 30º, 45º, 65º-80º, 107º, 120º, 135º and 160º. It can be seen that 30º and 120º, 45º and 135º, 65º-80º and 160º are pairs of complementary angles indicating the presence of rectangles. This result was consistent with the abstraction procedure which led to the Figure 4. RIMAPS technique recognized bars on ascospore surface. Further analysis of more strains and spores of E. amstelodami could give some clues for species RIMAPS characterization. This work constitutes the first report of RIMAPS fungal analysis.