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COLOR:
Subhyaline (0/5/10/0)
to pale yellow with green tint (0/5/20/0). Most spores extracted from active
pot cultures are a very pale yellow.
SHAPE:
Mostly globose, subglobose.
SIZE DISTRIBUTION: 80-120 µm, mean = 99 µm (n=86).
SPORE WALL: Two
layers (L1 and L2), the outer layer continuous with the wall of the neck of
the parent sporiferous saccule and the inner layer synthesized locally with
onset of spore formation.
L1: Hyaline, 0.4-0.8 µm thick when intact, degrading to form
a granular coating or sloughing completely.
L2: A layer consisting of very fine and adherent sublayers
(or laminae) that often are difficult to discern; very pale yellow (0-0-10-0)
in color, and 1.8-3.2 µm thick (mean of 2.4 µm). At maturity, the spore detaches
form the saccule and is sessile. It is essentially an 'endospore' in that it
separates completely from the parent saccule neck and the spore wall has no
break or opening in the region of attachment to the saccule neck.
GERMINAL WALLS:
Two hyaline flexible inner
walls (gw1 and gw2) are formed sequentially in spores after the spore wall has
completed differentiation and the spore has ceased expansion (see sequence below,
from left to right).
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GW1:
May be bi-layered as is the case for other Acaulospora species, but
only one layer is visible, 0.5-0.8 µm thick.
GW2: Consisting of two layers (L1 and L2) that are tightly
adherent. The surface of L1 is uniformly covered with granular
excrescences (or "beads") that tend to dislodge with applied pressure
or become invisible after the specimen is mounted in PVLG for several months
or longer; 0.6-0.8 µm thick when freshly mounted. L2 is 0.6-1.9
µm thick; usually stains light pink (0-5-0-0) to a slightly darker pink (0-10-20-0)
in Melzer's reagent, occasionally showing no reaction.
CICATRIX:
This
scar is a remnant of the connection between the spore wall and the wall of the
parent hypha (forming the sporiferous saccule)during spore synthesis; diameter
is 6.5-9.6 µm (mean = 7.8 µm).
COLOR:
Hyaline.
SHAPE:
Mostly globose.
SIZE DISTRIBUTION:
70-80 µm, mean = 78.2 µm.
SACCULE WALL:
One layer, smooth surface, 0.6-1.4 µm thick.
DISTANCE FROM SACCULE TO SPORE:
60-100 µm.
Arbuscules and intraradical hyphae stain with considerable variation in intensity with trypan blue, although vesicles and hyphae generally stain darkest. Infection units appear to be patchily distributed with oblong to irregular vesicles often forming in small clusters. Hyphae forming coils are up to 7 µm in width; hyphae growing parallel to the root axis range from 2-4 µm wide.
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GERMINATIONA germination "orb" has been observed in only a few spores, and they were old with spore contents coalesced so that fragile structure was detectable. It spanned most of the diameter of the spores, was circular with a simple inward spiral, with a smooth outer margin.
This species is one of only a few in which the inner layer (L2) of the innermost germinal (gw2) wall stains light pink or not at all in Melzer's reagent. Dark red-brown to dark red-purple are common reactions in most other species of Acaulospora and Entrophospora.
Walker, C., C. M. Pfeiffer, and H. E. Bloss. 1986. Acaulospora delicata sp. nov. -- an endomycorrhizal fungus from Arizona. Mycotaxon 25:621-628.
