NEW 17 - Plant Evolution and Colonization of Land

where did the plasmids in archaeplastids arise from?

primary endosymbiosis

Where did red algae diverge from?

Red algae (rhodophyta) diverged from the green algae and plants over one billion years ago

Where did terrestial plants diverge from?

green algae (charohyptes) about 500 million years ago

What are algae?

term for photosynthetic eukaryotic protists

• polyphyletic group

• unicellular microalgae

• multicellular macroalgae

What does macroalgae anatomically consist of?

Holdfast: root-like structure that attaches algae to a hard surface

Stipe: stem-like structure 

lamina/blade: leaf-like structure

How are algae taxonomically categorized?

based on color of the thallus (stipe/lamina)

What is a plant?

• historically, “plants” included organisms that photosynthesize, have cell walls, spores, and sedentary behavior

• Contained a variety of microscopis organisms, all of the algae, and the more familiar plants that live on land 

OR 

• evaluate the evolutionary history of life and to use that history to delimit the groups of life 

What are the different “plant” groups?

• Viridiplanta/chlorobionta

• Embryophytes

• Tracheophytes

What is viridiplantae/chlorobionta?

united by chloroplast containing organisms 

• includes both aquatic “green algae”

What are embryophytes?

plants that live in terrestial environments

• have waxy cuticle to protect from drying out

• specialized gametangia that protect developing egg and sperm 

• alternation of generations 

What are tracheophytes?

plants that have vascular tissue 

• composed of 3 distinct groups: 

1. Seedless vascular plants 

2. Gymnosperms 

3. Angiosperms 

What did land plants evolve from?

algae

What is Zygnema?

an alga closely related to terrestrial plants

What key ancestral traits to land plants share with charophytes?

1. Rings of cellulose-synthesizing complexes → makes a cell wall, outer layer external to plasma membrane; structure makes peptioglycan that makes cell wall

(WONT TALK ABOUT:)

1. structure of flagellated sperm

2. The polymer sporopollenin 

3. High similarities between nuclear, chloroplast, and mitochondrial DNA sequences

What does the structure of plants living on land look like and what are their functions?

Leaf: performs photosynthesis

Cuticle: reduces water loss 

Stomata: allow gas exchange 

Stem: supports plant (and may perform photosynthesis) 

Roots: anchor plant, absorb water and minerals from the soil (aided by mycorrhizal fungi) 

What does the structure of plants in water look like and what are their functions?

Whole alga:

• performs photosynthesis, absorbs water, CO2, and minerals from the water

Holdfast: anchors the alga

• surrounding water supports the alga 

What are the benefits to moving onto land?

• unfiltered sunlight

• more plentiful CO2

• nutrient-rich soil 

• few herbivores/pathogens

What are some challenges to living on land:

• less water and lack of structural support against gravity

What allowed plants to thrive on land?

• Plants diversified as they evolved adaptations to survive on land - such as waxy leaves, roots, vascular tissue, and seeds

What are mycorrhizae? Where did they come from/what’s their origin?

• earliest land plants (about 500 million years ago) 

• acted as the first roots of land plants before they evolved their own true roots 

• as plants evolved on land, their symbiotic relationships also diversified - meaning new kinds of partnerships formed over time

• —> when pinacease (pine trees) species formed (about 180 million years ago) they developed ectomycorrhizal fungi - fungi that live around their roots, helping them absrobs nutrients and grow in tough soils

Which 4 key traits are in nearly all land plants but are absent in what?

1. Alternation of generations 

2. Apical meristems 

3. Multicellular gametangia 

4. Walled spores in sporangia 

• multicellular gametangia and walled spores in sporangia are reproductive structures designed to live on dry lands → designed to keep gametes from drying up

What is alternation of generations?

the life ctycle of all land plants alternates between 2 generations of distinct multicellular organisms

• Gametophyte (haploid, n) 

• Sporophyte (diploid, 2n) 

• haploid sperm + haploid egg = zygote → mitosis → sporophyte (makes spores) → develop strong structure (resists drying out to protect developing spores) 

• each generation gives rise to the other (hence alternation) 

What are gametophytes?

• gamete-producing plant 

• produce haploid gametes (eggs and sperm) by mitosis 

• Fuse (fertilization) to form diploid zygote 

What are sporophytes?

• spore-producing plant 

• meiosis in mature sporophyte produces haploid 

→ reproductive cells that can develop into a new haploid organisms without fusing with another cell 

• Mitotic division of spore cell produces new multicellular gametophyte 

What are apical meristems?

• special regions in plants where growth happens 

• Apex = tip

• undifferentiated cell (blank slate) where stem cells can develop into everuthing into the body (organs tissue)

• plants sustain continual growth in their apical meristems

• cells from the apical meristems differentiate

• found at the tips of all roots and stems, functions to extend the plant body

What do apical meristems produce? what were they initiated by?

produce primary meristems (protoderm, ground meristem, procambium) 

• were all initiated during embryogenesis 

What do primary meristems produce?

primary tissues

What is development?

• coordination of growth and differentiation of a single cell into tissues and organs

What is growth?

• irreversible increase in mass due to division and enlargement of cells 

What are growth and development a reponse to?

response to the environment 

What are development and growth both characterized by a high degree of…

plasticity

• adjusts development and growth to respond to changes in the environment 

• necessary for plants to survive because as sessile organisms they cannot escape from adverse conditions 

In animals, most adult organs are already present in the….

embryo

• in animals, organogenesis mostly occurs during embryogenesis

When are organs formed in plants?

most organs are formed after embryogenes is finishes

What do meristems contain?

a population of undifferentiated (can’t become a specific type of cell yet) self-renewing ‘stem cells’ (keep making more stem cells) 

Where are meristems found?

found at the shoot and root apices, leaf axils, and also along the vascular system

Where are stem cells found?

in the center of meristem

What is a key to plant adaptability?

• post-embryonic organ development

What does animal capacity for location allow?

the fight or flight response when confronted with a stressor

What does it mean it plants are sessile organisms?

need to deal with environmental challenges in a fixed location

What is apical meristem?

• all land plants grow by rapid cell divisions at the apex of the stem, shoot, and root 

Where did cells derive from in land plants? what does it allow plants to do?

apical meristem region form a solid mass of parenchyma tissue

• most resemble unspecialized, undifferentiated cells of actively dividing meristematic tissue

• enabled plants to alter growth in response to environment

What are some additional derived traits of plants?

Cuticle: waxy covering of the epidermis that reduces water loss

Stomata: pores that facilitate gas exchange between the outside air and internal plant tissues 

What is the problem with cuticles?

plant can no longer move CO2 and O2 across cells, its sealed itself in

How does alternation of generations helps us classify plant groups?

alternation of generation helps us classify plant groups based on which stage dominates the life cycle 

• Mosses → gametophyte dominant 

• Ferns → both visible 

• Seed → sporophyte dominant 

• over time sporophytes become more dominant (larger) while gametophyte becomes reduced in higher plants 

What is a spore? What is its function?

Hard exterior, genetic info inside (haploid) 

Function: disperse

What is flagellation (gametophyte generation)

sperms always goes to egg (remember in bio, whichever is bigger doesn’t move)

• swims through water -→ cannot have movement/fertilization without water

What is multicellular gametangia?

• have protected tissues to protect inside of the gametes (sperm and egg) they are going to produce

What is a gametophyte generation (alternation of generations)?

• haploid stage of a plant’s cycle

• grows from a spore, makes gametes (eggs and sperm) and after fertilization, gives rise to the sporophyte generation 

What is the sporophyte generation

• diploid phase that grows from the zygote and makes haploid spores by meosis, which them grows into gametophytes