BIOLOGY 3404FEVOLUTION OF PLANTS

Fall 2008Lecture 8October 14

Chapter 15, Part II:Rhodophyta & Chlorophyta

Rhodophyta (red algae):

• Few unicellular, few freshwater; most are marine seaweeds

• Some are coralline (covered in calcium carbonate) – important in coral reefs

• Life cycles include alternation of generations (sporic meiosis)

Rhodos, II• Source of both important edible species (dulse [Rhodymenia = Palmaria] in Canada and western Europe; nori [Porphyra] in Japan)

• Source of chemicals used in food, pharmaceutical and industrial applications (agar and agarose from Gelidium; carageenan predominantly from “Irish moss”, Chondrus crispus – also good for making chocolate seaweed pudding

Marine: Bonnemaisonia. Phycobilins make them red

Marine: coralline red algae in a tide pool

Marine: crustose red alga from coral reef, Porolithon

Marine: Irish moss, Chondrus crispus

Freshwater: Batrachospermum, from cold lakes and streams

Chlorophyta (green algae):

• Very large group (17,000 described species, probably many more inconspicuous ones), ranging from unicellular to colonial forms and large seaweeds, and a few are calcified like the coralline red algae

• Many are not really green but orange, red or pink because of photoprotective pigments; “strawberry snow” (especially common on glaciers, but also common here in Ontario on late winter snow) is a species of Chlamydomonas that forms the base of an unusual snow-surface food chain

Chlorophyta II

• Photosynthetic and wall chemistry as well as DNA sequences link chlorophyta to true plants

• Skip ultrastructural details• Refer to Lab 1 for the groups of Green algae that we cover: – Chlorophyceae (Chlamydomonas, Volvox, Hydrodictyon)

– Ulvophyceae (Ulva, Cladophora, Acetablularia)

– Charophyceae (Spirogyra, desmids, Coleochaetales: Coleochaete, Charales: Chara).

Chlorophyta III

• The Charophyceae include the closest existing organism to the probable ancestor of embryophytes (land plants): Coleochaete

• Zygotes of Spirogyra and Chara form thickened walls containing sporopollenin, also found in spores (or pollen) of true plants

• Life cycles may have zygotic meiosis (like fungi; Chlamydomonas) or sporic meiosis (Ulva)

Red, or watermelon, snow caused by Chlamydomonas nivalisAlso green snow, orange snow, … Carotenoids protect the photosynthetic machinery from high sunlight of alpine areas.

Zygotic meiosis in life cycle of Chlamydomonas

Colonial Chlorophyceae: Gonium, Pandorina, Eudorina

Colonial Chlorophyceae: Volvox

Colonial Chlorophyceae: Hydrodictyon

Ulvophyceae: branched filaments of Cladophora

Sporic meiosis and alternation of generations in the life cycle of Ulva, the sea lettuce

“Siphonous” Ulvophyceae (means they are coenocytic): Codium

Siphonous Ulvophyceae: Ventricaria

Siphonous Ulvophyceae: Acetabularia, which we saw in lab

Placobranchus, a sea slug (nudibranch) containing cloroplasts of siphonous Ulvophyceae such as Codium. Chloroplasts survive in their respiratory chambers, and may make the slugs net oxygen producers

Charophyceae: Spirogyra, showing conjugation of two haploid filaments and formation of diploid zygospores; life cycle has zygotic meisois

Desmids: Xanthidium, Euastrum, and Micrasterias, showing cell division on right

Coleochaete (Charophyceae), the closest we have to a common ancestor to higher green plants (embryophytes)

Charophyceae: Chara, a stonewort (hardened by calcium carbonate)On the right you can see gametangia: oogonium above antheridium