Eighteen Ultrastructural Forms of Zoospores are Produced in this Order:
Our research has discovered 18 distinct zoospore forms in Rhizophydiales, each of which corresponds to a molecularly-based clade (Letcher et al. 2008b). Each zoospore form in Rhizophydiales is defined on the basis of having a unique suite of ultrastructural character states (listed below). We analyze these characters and look for concordance with gene-based phylogenetic hypotheses to delineate taxa.
Ultrastructural Characters and Character States in the Rhizophydiales (click here to see detailed illustrations of character states):
1. Microbody-lipid globule cisterna:
0=absent; 1=simple; 2=inconspicuously fenestrated;
3=conspicuously fenestrated.2. Kinetosome-associated structure:
0=absent; 1=a solid spur; 2=a laminated spur; 3=a shield.
3. Number of lipid globules:
0=predominantly one; 1=multiple.
4. Vesiculated region adjacent to kinetosome:
0=absent; 1=present.
5. Fibrillar bridge between kinetosome and non-flagellated centriole:
0=perpendicular to the two structures; 1=diagonal between the two structures.
6. Microtubular root:
0=absent; 1=present.
7. Number of mitochondria in longitudinal section:
0=one; 1=multiple.
8. Granular cylinder in core of kinetosome and/or non-flagellated centriole:
0=absent; 1=present.
9. Perpendicular zone of convergence in fibrillar bridge between
kinetosome and non-flagellated centriole:
0=absent; 1=narrow (0.010-0.025 µm); 2=wide (~0.075 µm).10. Close association of a lobe of a mitochondrion with kinetosome:
0=absent; 1=present.
11. Close association of a lobe of a microbody with kinetosome:
0=absent; 1 = present
12. Location of nucleus:
0-outside the ribosomal mass; 1=embedded in the ribosomal mass.
13. Microbody morphology:
0=simple; 1=lobed.
14. Endoplasmic reticulum ramifying through the ribosomal mass:
0=absent; 1 = present
References:
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- Barr DJS. 1980. An outline for the reclassification of the Chytridiales, and for a new order, the Spizellomycetales. Can J Bot 58: 2380-2394.
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- Letcher PM, Powell MJ, Churchill PE, Chambers JG. 2006. Ultrastructural and molecular phylogenetic delineation of a new order, the Rhizophydiales (Chytridiomycota). Mycol Res 110: 898-915.
- Letcher PM, Powell MJ, Viusent MC. 2008a. Rediscovery of an unusual chytridiaceous fungus new to the order Rhizophydiales. Mycologia 100: 325-334.
- Letcher PM, Velez CG, Barrantes ME, Powell MJ, Churchill PF, Wakefield WS. 2008b. Ultrastructural and molecular analyses of Rhizophydiales (Chytridiomycota) isolates from North America and Argentina. Mycol Res 112: 759-782.
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- Powell MJ, Roychoudhury S. 1992. Ultrastructural organization of Rhizophlyctis harderii zoospores and redefinition of the type I microbody-lipid globule complex. Can J Bot 70: 750-761.
- Roychoudhury S, Powell MJ. 1992. Precise flagellar configuration of the Rhizophlyctis harderii zoospore. Can J Bot 70: 762-771.
This research is supported through NSF REVSYS: Phylogenetics and Taxonomic Revision of the Rhizophydium Clade (Chytridiomycota) DEB-0516173.
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