Scutellospora scutata

(reference accession BR243)

Whole Spores

Sparkling white translucent spheres brown small circle on surface

 

Size distribution graph variable left tail some right skewCOLOR: Hyaline/white in most recently formed spores to yellow-brown (0-5-40-0) in older spores (especially those from field soils).

SHAPE: Globose, subglobose, often elliptical or strongly oblong.

SIZE DISTRIBUTION: 340-640 µm (mean = 494, n = 66)

Subcellular Structure of Spores

SPORE WALL: Two permanent adherent layers (L1 and L2). Both layers differentiate together.

L1: A single hyaline layer < 1µm thick with a smooth surface.

L2: A rigid layer consisting of fine tightly adherent sublayers (or laminae), 3.5-16 µm thick, white to pale yellow (0-0-10-0) in color.

L3 (?): To see this layer the region of attachment between spore wall and sporogenous cell wall must be intact, and this is extremely difficult to obtain in broken spores. It is assumed to be there because it is present in other related Scutellospora species (most obvious in S. cerradensis).

Spores mounted in PVLG
PVIG smashed spore with germination shieldSpore wall gw1 2 and 3 light curved linesL1 and L2 of wall gw1 and 2 as darker linesL1 L2 wall light lines gw1 2 and 3 light thin lines

 

Spores mounted in PVLG and Melzer’s reagent (1:1 v/v)
Melzers germination shield dark irregular over gw2 and 3Melzers L1 and 2 of gw 1 2 and 3 very thin linesMelzers wall gw 1 2 3 germination shield over gw3Melzers L1 L2 gw1 2 and 3 distinct curved lines


GERMINAL WALLS: Three bi-layered flexible hyaline inner walls (gw1, gw2, and gw3) are present that are completely separate from the spore and sporogenous cell walls. Interpretation of germinal walls can be difficult in broken spores because of difficulties in obtaining a “clean” squash and walls tend to stick together (appearing as one) or fold over each other. Wall number and structure were ascertained most confidently from close examining of inner wall structure at the edges of germination shields (which are always positioned on the innermost germinal wall).

GW1: Two layers (L1 and L2) that usually are adherent; occasionally separable near the broken edge (see photo at right in immature spore in which only gw1 has formed) or with deep folding. L1 is < 0.5 µm thick; L2 is 4-9 µm thick (some of this may be due to swelling with applied pressure). Neither layer reacts in Melzer’s reagent.


Melzers spore walldarker L2 wall lighter L1 L2 gw1 similar


GW2: Two layers (L1 and L2) that also usually are adherent, although they separate more frequently than those of gw1. L1 is < 0.5 µm thick, not reactive in Melzer’s reagent. L2 is slightly plastic, 3-6 µm thick, often producing a pink to light brownish-pink reaction in Melzer’s reagent.

GW3: Two layers (L1 and L2) that usually are adherent, separating when spores are severely crushed. L1 is 3-5 µm thick; slightly reactive in Melzer’s reagent, producing a light pink reaction. L2 is more plastic (or “amorphous”) in newly-mature healthy spores, staining red-purple (20-80-20-0) to dark red-purple (40-80-60-0) in Melzer’s reagent; becoming more rigid with concomitant reduction in staining intensity (to a dark red-brown color) with age and senescence; thickness is highly variable because of this plasticity, ranging from 4.0-18.0 µm thick when amorphous, 3-6 µm thick when more rigid.

Subtending Hypha

Sporogenous cell darkpouch at end of dark line


WIDTH OF SPOROGENOUS CELL: 47-90 µm (mean = µm).

SPOROGENOUS CELL WALL: Two layers (L1 and L2) probably are present (continuous with the two layers of the spore wall), but only L2 is discernible under the compound microscope.

L2: Brownish yellow (0-20-80-0), 3-12 µm thick near the spore and then thinning to 1-3 µm beyond the sporogenous cell.

OCCLUSION: Closure by a plug concolorous with the wall of the sporogenous cell.

Germination

COLOR: Dark yellow-brown (0-30-100-0)

SHAPE: Circular, occassionally more oval-shaped, with multiple lobes; formed on gw3.

SIZE: 240-325×208-302 µm

GERMINATION SHIELD
Germination shield 9 circles around edgeGermination shield short lines edges longer lines extend across surfaceSide germination shield between gw1 and gw3 germ tube emergingGermination shield dark shape within GW1 2 and 3

Auxiliary Cells

Auxilary cells pale brown hyphae dark brown cluster

Aggregate (1-12) cells borne on coiled light brown (0-40-80-0) hyphae, thin-walled (< 1 µm thick), pale brown (0-40-80-0) to dark brown (0-60-100-10) in transmitted light, each cell with shallow swellings < 1-2 µm high and 6-10 µm wide.

Mycorrhizae

Intraradical arbuscules and hyphae consistently stain darkly in roots treated with trypan blue. Arbuscules with many fine tips from a swollen trunk. Hyphae often with knobs or projections, usually densely coiled near entry points. Auxiliary cells and external hyphae often amass around the root, with the former most abundant in pot cultures just prior to spore formation and declining thereafter. External hyphae are brown.

Arbuscules in corn roots
Inraradical hyphae dark blue worm like branching external hypha grayArbuscule one stemmed bush like hyphal structure in cellBlue stained arbuscule indistict

 

Other mycorrhizal structures in corn
Inraradical hyphae dark blue worm like branching external hypha grayScutellospora scutataCoiled hyphae external and internal stained black brown arbuscules indistinct dark patchesCoiled intracellular hyphae brown dark blue looped lines within cell

Notes

Walker and Diederichs (1989) only describe two germinal walls in spores of S. scutata. Given the difficulty in crushing such large spores and the resultant jumble of flexible inner wall structures, such a conclusion is not surprising. We have had this fungus in culture for almost a decade and have mounted numerous spores to find some that gave a clear picture of germinal wall organization.

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High Resolution Images

Sparkling white translucent spheres brown small circle on surface
Spores
PVIG tranparent with lines
In PVLG
Germination shield brown in PVLG
In PVLG
PVIG smashed spore with germination shield
In PVLG
Melzers germination shield irregular shape within layers
In Melzer's Reagent
Germination shield 9 circles around edge
Germination Shield

Reference

  • Walker, C. and C. Diederichs. 1989. Scutellospora scutata sp. nov., a newly described endomycorrhizal fungus from Brazil. Mycotaxon 35:357-361.