Oomycota
See web page:
http://www.ucmp.berkeley.edu/chromista/oomycota.html
Characterisitics (see table for orders)
Zoospore: biflagellate with one flagellum tinsel and the other whiplash
Coenocytic hyphae
Cell walls composed primarily of B-glucans, hydroxyproline, and small amount of cellulose, rarely chitin (in Leptomitales , Achyla, and Saprolegnia)
Mitochrondia with tubular cristae
Golgi bodies with flattened cristate
No sporocarp
Ooogamous, Oospores (one or many), Gametic meiosis
No true male gametes
Gametangial copulation
DAP lysine synthesis
Zoosporangia or vesicles
Diplanetic zoospores
Biochemistry
Synthesis of thiamine
Utilization of nitrates and sulfates
Can synthesize sterols: fuscosterol
Storage compound: mycolaminarin
Absence of sugar alcohols
|
Orders |
Leptomitales |
Lagenidiales |
||
|
Primary zoospores |
+ |
- |
in some |
+ |
|
Secondary zoospores (see fig. 27.2, 27.5 in handout) |
+; dimorphic |
+; monomorphic in Pythium, Phytophthora. |
Mostly; about morphic |
+? About morphic |
|
Sporangia differentiation |
none |
well |
similar to saprolegniales |
well |
|
Vesicles see fig. 27.4 in handout) |
no |
in some (Pythium; Phytopthora; not in Albugo |
no |
present |
|
#oospheres/oogonium |
several |
1 |
1 |
1 |
|
synthesis of thiamine |
+ |
- |
+ |
? |
|
utilize nitrates |
- |
+ |
- |
? |
|
utilize sulfates |
- |
+ |
+ |
- |
|
special features |
variation in genera where secondary zoospores are produced; sporangial proliferation; gemmae |
mostly obligate parasites of animals or plants (downy mildews, white blister rust, potato blight) |
contrction, plugged with cellulin (mixture of chitin and glucan; function?); Aqualiderella (high co2, low to no O2; on debris in clear water or in stagnant ponds |
holocarpic, endobiotic, parasitic in algae and roots of vascular plants. |
Saprolegniales
Where secondary zoospores produced: Saprolegnia (outside of sporangia); Achlya (at tip of sporangium, kept together by hooks); Dictyuchus (in sporangium); Aphanomyces (long, nematosporangium)
Life cycle of Saprolegnia (see figure 23-17; pg. 705 in Alexopoulos).
Sexual reproduction and hormone (steroids: antheridiol and oogoniol; production in Achlya (see previous handout, figure 10-5 in Biology of Fungi)
Peronosporales
Features: reniform zoospores; distinct sporangia; gametic meiosis; obligate parasites.
Pythiaceae: sporangiophores indistinct from mycelium; determinate in growth
Pythium: causes various kinds of wilts and damping off; has oval vesicles (see life cycle fig. 23-21, pg. 714 in textbook)
Phytophthora: zoospores in lemon-shaped sporangium that can function as a conidium if conditions are correct; sporangiophores are cross-shaped; causes late blight of potato and port orford root disease (see life cycle, fig. 23-25 on pg. 720 of textbook)
Albuginaceae (Albugo) (blister rust of crucifers): sporangia globose and in chains; subepidermal; sporangiophores undeterminate and unbranched
Peronosporaceae (downy mildews): branched sporangiophores; determinate.
See Fig. 23-26 on page 725 to distinguish between different genera. Life cycle of Plasmopara viticolas, causative agent of downy mildew of grapes (Fig. 23-26, pg. 727)
Leptomitales: sporangia resemble those of the Saprolegniales; see chart.
Aqualiderella has not cystochrome system; obligately fermentative; indicator of pollution.
Lagenidiales: holocarpic, endobiotic, parasite of algae. See chart.