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L1: Hyaline; 0. L2: A layer that thickens initially by formation of pale yellow to tan sublayers or laminae with ovoid concave depressions on the surface. These depressions are 0. Sublayers sometimes appear to split and consist of two groups of near-equal thickness, one including depressions and the other underlying the depressions, composite thickness 4. L3: A layer designated as a discrete component of the spore wall only because it sometimes separates slightly from the spore wall and has defined boundaries.
When separated, it can be interpreted as a separate flexible inner wall which we have done until recently. However, it is considered to be part of the spore wall because it usually is integral adherent and sometimes shows evidence of just being another sublayer lamina of the spore wall. It is analagous to L3 found in other species with ornamented spore walls, such as A.
In some other species e. GW1: Two tightly adherent hyaline layers are formed L1 and L2 , both of near equal thickness, together measuring 1. This wall often is positioned close to the spore wall except in vigorously crushed spores and occasionally may not even be easy to detect.
In other spores, iw1 may produce one to many folds, thus giving the appearance of a bewildering array of flexible inner walls and making diagnosis difficult. GW2: Two tightly adherent hyaline layers formed L1 and L2.
L1 is 0. L2 is 1. A circular to ovoid scar indicating region of contact between spore and saccule neck during spore synthesis; the depression within the scar is smooth, 7. The connection between saccule neck and spore is somewhat complex in that it initially consists of only the L1 layer of the spore continuous with the wall of the saccule neck , followed by synthesis of sublayers of the L2 laminate layer which form between saccule neck and spore.
After degradation and sloughing of L1, these sublayers form a ridge 2. Mode of formation of this region is analagous to that which occurs during synthesis of spore wall layers in Glomus species. This orb is difficult to see except in older spores where contents have cleared with fusion of lipid globules in the spore lumen, mostly because it is wide enough to span most of the diameter of the spore and so edges of the orb are seen only with a limited range of spore orientations.
Spain reports orbs of A. The photo above was provided courtesy of Joyce Spain from her publication. Arbuscules often stain lightly in trypan blue, but sometimes stain more darkly; intensity of staining appears to vary with many factors that have yet to be resolved possibly age of the mycorrhizae and of the host root. Infection units are patchy because they often do not overlap and appear merged.
Vesicles often form most abundantly near entry points and range from spherical to oblong to irregularly shaped. Note the last photo in the sequence below, in which the tip of a corn root is filled with many coiled hyphae. The fungus and host respond dynamically to structural and physiological changes in root regions, and this accounts for the wide range of morphological structure and pattern in the same root system.
Inner wall structure often is very difficult to define clearly for several reasons: 1 ornamentations on L2 of the spore wall cause considerable light-scattering which reduces the ability to resolve hyaline flexible walls within the spore and 2 L3 of the spore wall and iw1 can produce numerous folds that make it almost impossible to define inner wall structure clearly. The trick is to focus first on the second germinal wall gw2 as a positional reference; its easy to start with because the wall consistently separates readily from the rest of the spore and has a beaded surface if examined at least within 30 days of mounting.
Then proceed back to the spore wall. If there are many folds, ignore that spore and move to another one. When it was not detected, the spores were classified as being a separate usually undefined species. It should be remembered that the granules on L1 of gw2 are not permanently fixed in place unless spores have been stored for more than 60 days in formalin or some other preservative and can disperse upon crushing of the spore and disappear.
They also appear to dissolve or lose refractivity in PVLG -based mountants after days varying with condition of spores and fungal species. Spores mounted in PVLG. Arbuscules in cortical cells of corn root. Mature Spores. In PVLG. In Melzer's Reagent. Germination Orb. Ornamented Surface Layer.
Mongolian Journal of Biological Sciences
Acaulospora scrobiculata Trappe. Spore wall composed of three layers swl Layer 1 evanescent, hyaline, 1. Layer 2 laminate, yellowish white 3A2 to pale yellow 3A3 , 3.
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