17 - Plant Colonization of Land and Early Diverging Lineages

Supergroup- archaeplastids

• plastids in this group arose through primary endosymbiosis

Algae

• informal term for photosynthetic eukaryotic protists: polyphyletic group, unicellular microalgae + multicellular macro algae

macroalgae

• anatomically consists of:

• holdfast- root-like structure that attaches algae to a hard surface

• stipe - stem-like structure

• lamina/blade - leaf-like structure

• taxonomically categorized based on color of the thallus (lamina)

What is a plant?

• historically plants include organisms that photosynthesize, have cell walls, spores, and sedentary behavior

• second way to answer- evaluate the evolutionary history of life and use to delimit the groups of life

Plant groups

• viridiplantae/chlorobionta - united by chloroplast containing organisms

• embryophytes - plants that live in terrestrial environments

• tracheophytes -plants w vascular tissue

evidence that land plants evolved from algae

1. rings of cellulose synthesizing complexes similar

2. structure of flagellated sperm

3. the polymer sporopollenin

4. high similarities btwn nuclear chloroplast and mitochondrial DNA sequences

Land living

• benefits: unfiltered sunlight, more CO2, nutrient rich soil, few herbivores/pathogens

• challenges: scarcity of water and lack of structural support

mycorrhizae

• earliest land plants (~500 mya)

• acted as the first roots of land plants

• associated w fungi that produced mycorrhiza like structures

Four traits that appear in nearly all land plants but absent in charophytes

1. alternation of generations

2. apical meristems

3. multicellular gametangia

4. walled spores in sporangia

Alternation of Generations - multicellular gametangia

• life cycle of all land plants alternates btwn gametophytes (n) and sporophytes (2n)

• each generation gives rise to the other

• gametophyte - produce haploid gametes by mitosis and fuse to form diploid zygotes

Sporophyte

• spore-producing plant

• meiosis produces haploid spores

• mitotic division of spore cell produces new multicellular gametophyte

apical meristems

• location where plants sustain continual growth

• functions to extend the body

primary meristems

• exist throughout the plant body

• initiated during embryogenesis

• remain meristematic for some time before beginning to differentiate into specific cells types in the primary tissues

parenchyma tissue

• solid mass in the apical meristem region

• resemble unspecialized, undifferentiated cells of actively dividing meristematic tissue

• enabled plants to alter growth in response to environment

cuticle

waxy covering of the epidermis that reduces water loss

stomata

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

gametophytes

• larger and longer-living than sporophytes

• produce flagellated sperm

byrophytes

• not a monophyletic group

• highly dependent on water for survival and reproduction

• lack vascular tissue

• have flagellated sperm

• life cycle dominated by gametophyte generation

what does vascular tissue in recently evolved plants allow for

increased height

• xylem - undirectional movement of water

• phloem - bi-directional movement of sugar and solutes

evolution of roots

• allowed for more adaptive advancements enabling much more efficient water and mineral acquisition and conduction

• permitted the evolution of plants in more extreme habitats

why were leaves essential for newly evolved vascular plants

• increased plant surface area - which allowed for the increased capture of solar energy for photosynthesis

microphylls

evolved as outgrowths of stems (410 mya) having a single mid vein

megaphylls (370 mya)

evolved as webbing between flattened branches, have a highly branched vascular system

seedless vascular plants

• life cycle dominated by sporophyte

• first group to have vascular tissue

• developed true roots that absorb water and nutrients from the soil

• still reproduce w spores and need a film of water for sperm to swim through