Class Notes For BIO 410

Introductory Phycology

Division Charophyta


Traditionally members of the Chlorophyta
Considered separate from Chlorophytes based on ultrastructural studies
Now a single Class: Charophyceae
Worldwide distribution


Green Algal Traits of Charophytes

Chlorophylls A & B
Store starch
Aquatic habit- like Greens
Haploid cells with meiosis occurring in zygote


Unique Traits of Charophytes

Flagella attached laterally
Microtubular cytoskeleton and flagellar root system unique
Nuclear envelope breaks down during mitosis (open spindle)
Spindle microtubles form perpendicular to cell division plane ...


Cell Division:

Phycoplast (Green Algae) vs. Phragmoplast (Charophytes)


Division Charophyta
Class Charophyceae


Orders:


Klebsormidales

unbranched filaments


Coleochaetales

heterotrichous filaments


Charales

branching filaments


Zygnematales

filaments and unicells, no flagellated stages, sex by conjugation


Order Klebsormidales

Example species
Klebsormidium: filament looks like Ulothrix


Order Coleochaetales

species:

Coleochaete: epiphyte gowing as a flattened disc over the substrate. Possesses a number of advanced features...


Advanced features of Coleochaete
Only one zoospore per vegetative cell
Zygote remains on mother plant and becomes covered by surrounding vegetative cells (placenta)... a higher plant trait.


Charales

species:
Chara: Commonly called Stoneworts or Brittleworts grow in shallow alkaline lakes.
Up to 2 feet tall with whorls of short branches
May be encrusted with Calcium carbonate
Sterile cells surround sex organs...
Important organism as an evolutionary bridge between green algae and mosses

Nitella: Used in studies on cytoplasmic streaming.
Streaming rates up to 60 microns/sec.
Cytoplasmic streaming due to actin molecules moving along myosin filaments. ATP hydrolysis.


Zygnematales

Zygnema, Spirogyra
Reproduce by conjugation: two filaments come together, produce extensions, fuse.
Cell contents round up to form gametes
One gamete migrates to other and fuse to form a zygote.


The Desmids-unicellular Zygnematales

Unicells with elaborate shapes and divided into two semicells Reproduce by conjugation



The Land Plants likely arose from a Charophyte like Coleochaete



Euglenophyta

The Euglenoids

A Single Class:
Euglenophyceae


Euglenoid Characteristics

Single-celled flagellates living in freshwaters and marine environments

Chlorophylls A & B

Storage Storage product- paramylin (b1,3 glucan). Membrane bounded.

Cell wall without cellulose (pellicle)

No sexual reproduction reported (?)

Chromosomes permanently condensed

eyespots (separate from chloroplast)

1,2,4 flagella with fine hairs along length

flagella cross-section shows a paraflagellar rod

Euglenoid flagella emerge from anterior invagination of cell (the reservoir)

Heterotrophic euglenoids use reservoir in feeding


Euglenoid Eyespot: The Stigma

Collection of orange-red lipid drops

At anterior end of cell

Independent of chloroplast

Contains B-carotene & xanthophylls


Phototaxis:
Movement toward/away from Light

Euglenoids use stigma and flagella to orient toward (+ phototaxis) or away (- phototaxis) from light.

Usually orient toward dim light

Flagellar rod region acts as light shield to regulate phototaxis

Phototaxis: Mechanism in Euglenoids

Eyespot interacts with flagellar rod to sense light direction

As cell swims it rotates, causing the eyespot to shade flagellar swelling

In (+) phototaxis cell orients so to minimize shading

Mutant cells without flagellar rod do not respond to light, even with eyespot...?


Euglenoid Cell Wall: The Pellicle

Unique to the Division

Not cellulose- mostly protein (80%)

Made of spiral protein strips which overlap each other- making an alternating ridge/groove pattern

Metaboly: Euglenoid movement

Sliding of pellicle strips allows for a distinctive flowing movement (Metaboly)

Occurs when cells are not swimming

In Euglena gracilis cells are round in early light and elongate by mid-day

Metaboly rhythm is circadian (ie. controlled by an internal clock)


Other Circadian Rhythms in Euglenoids

Phototaxis: phototaxis only operative during the light period, light introduced during the dark period does nothing

Mitosis: cell division begins at start of dark period

Vertical movement in mud flats: rise to surface during low tide, go deeper as tide rises


Reproduction

Only by asexual reproduction... Longitudinal division

Nuclear envelope remains intact

Asexual thick-walled cysts may form during stress.

No sex reported...


Euglenoid Chloroplasts

Unusual in that they are surrounded by 3 membranes

Inner two from ancestry green algal plastid, outer membrane from euglenoid itself.


Classification: 3 Orders

Order Eutreptiales:

species with 2 emergent flagella (one forward, one dragging), show metaboly, not phagotrophic.

Examples: Eutreptia.


Order: Euglenales

Possess 2 flagella but only one (with swelling) emerges from reservoir

Includes green and colorless species

Examples:

Euglena, Trachelomonas, Astasia, Colacium

Astasia is a colorless form of Euglena.

Colacium libellae lives in winter in the warm(er) rectum of damselfly larvae

Colorless cells with a feeding apparatus

Take up and ingest food particles, other organisms

Examples: Peranema, Entosiphon.

Peranema cells may hunt in "packs" and rip away at prey cells,, tearing holes in them and "sucking" out cell contents.


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