Land Plants Flashcards by Janessa Haaksma

When did land plants arrive

500mya

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Major events that changed earths atmosphere to allow for land plants

2.8-2.2 mya: first oceans formed and atmosphere was full of nitrogen and methane. Cyanobacteria in oceans produced oxygen to transform air.
650mya: snowball earth: green house gases used up by photo-synthesizers, resulting in more oxygen and extreme low temperatures.
500mya: trilobites, mollusks, sea stars and urchins arrive as well as early plants.

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How did the transition from water to land happen..

Algae moved to end of water, and had to adapt to dessication=poikilohydric

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The flagellated cells of Charophyceae are distinct from other classes because…

Why is this important for land plants?

Asymmetrical flagellar root system of microtubules that anchor flagellum

Multilayered structure (MLS) is associated with one of the flagellar roots

Flagellated root system of Charophyceae with its MLS is very similar to that found in the sperm of bryophytes and some vascular plants. Therefore Charophyceae green algae are considered closest relative to bryophytes and vascular plants.

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Two orders of early land plants

Charales

Coleochaetales -surface or submerged rocks or plants; uninucleate cells, one large chloroplast with embedded Pyrenoid

Similar chloroplasts and Pyrenoids found in hornworts

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Coleochaete

Reproduction

Sexual reproduction is oogamous

Zygotes retained on female mat (gametophyte), similar to other embryophytes such as Chara and land plants

Protected by layer of somatic cells that grow around them

Develop placenta that enables material distribution to its gametes, that consists of cells secretory cells (transfer cells) similar to the placenta that connects the sporophyte and gametophyte generations of land plants

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Charales

Reproduction

-eggs borne in enclosed Oogonia, positioned in a position analogous to seedless plants
-close resemblance with sperm of bryophytes

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Charales characterisitc

-calcification of Oogonia with calcium carbonate provides good fossil record
-apical growth
-attached to the sediment with branching underground rhizoids

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Embryophyta

-constitute the terrestrial or land plants
-first representatives around 450mya
-shared with all terrestrial plants is retention of the embryo by the parent organism.

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Embryo coverage of coleochaete, Charales and terrestrial paints

Coleochaete: covers the embryo (but not around the ovule until it is fertilized)

Charales and all terrestrial plants cover both the ovule (before fertilization) and the embryo

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Modern embryophytes share the following traits with ancestors:

-a life cycle with alternation of generations
-apical cell growth
-cuticle
-multicellular antheridia and archegonia

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General features of bryophytes

-eukaryotic
-have chlorophyll a and b, xanthophylls and carotenoid pigments
-store starch
-pectin-cellulose walls
-mitosis is open (nuclear membrane disappears in mitosis)
-cytokinesis is by formation of a cell plate along a phragmoplast

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All bryophytes have a _____ life cycle that is ______

Sporuc
Oogamous

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_____, _______ and ______ are very similar to each other and fundamentally similar to flowering plants

Hepatophytes
Anthocerophytes
Bryophytes

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Rhizosphere

Volume of soil influenced by the root
-contains over 1000 microbial cells per gram of soil with over 30,000 microbial species

Roots and root hairs support intense chemical and biological activity in narrow area surrounding young roots

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Mycorrhizosphere

Rhizosphere with symbiotic mycorrhizal fungi associate with roots

Why is mycorrhizal associations so important to plants?

Important to the acquisition of phosphorous from soul
-hyphae access inorganic nutrients from soil beyond the Rhizosphere
-scavenging role and active transport of low soluble forms of phosphorous (P) and Zn2+, Cu2+ and NH4+

Symbiotic sharing of carbohydrates (fructose and glucose) from plant

Endomycorrhizae (arbuscular mycorrhiza)

Ectomycorrhizae

-Form symbiosis with 90% of vascular plants
-Fungal hyphae penetrate surface cells of roots (primary cortex)
-zygomycota

-High taxonomic diversity
-form symbiosis with 3% of plants (shrubs and trees=woody)
-large, fruiting bodies
-grows mantle around root but does not penetrate root with hypahe
-hyphae penetrate between root cells
-Basidiomycota and ascomycota

In addition to the enhances nutrient uptake, different categories of mycorrhizae may protect roots against….

Pathogens, produce plant hormones and translocates carbohydrates between plants

Mycorrhiza infection area occurs only on the….

Smallest order of secondary roots. These are the root tips that are still growing, elongating and increasing in girth. That is the only part of the root system that will absorb water and minerals.

-Very small part of root system of a plant which will be infected by the mycorrhizal fungus
-in all mycorrhizae only the cortical cells of the root are invaded by the fungus. (Between epidermis and vascular tissue)

Species with _______ root hairs and _____ root hairs are not as dependent on mycorrhizae as species with _______ roots

Fine
Many

Taproot

We’re terrestrial plants first to have mycorrhizal associations?

Nope, aquatic

Mycorrhizal associations can also occur with plants without____

Roots (mosses and liverworts)

Endo-mycorrhizae: arbuscualr mycorrhizae

How it works

-aseptate mycelium penetrates root and develops thick-walled, multi-nucleate vesicles
-hyphae fork repeatedly to form an arbuscule
-plant and fungal membranes remain separated by an apoplastic space (periarbuscular space)
-exchange of nutrients and water across periarbuscular space

Chlamydospores

Large, Resting, asexual spores Contain energy reserves (lipid, glycogen and proteins) Survive in soil for many years Only sexual reproduction known for this group Important elements of soil food web Reproducing and resting fungal spores to establish new mycelium ENDO-mycorrhizae

How do hyphae penetrate root cell walls in Endo-mycorrhizae

Hypahe penetrate root cell walls by mechanical pressure or cell-wall-degrading enzymes Plant membrane extends to encase fungus branches—> fungus is surrounded by the cell membrane

Metabolic activity and cytoplasm volume is higher in root cells with ______

Arbuscules Periarbuscular space is highly acidic: ATPases in plasma memebranes of both partners set up protein gradient for active uptake of sucrose (fungus) and mineral nutrients (plant)

Vesicular arbuscular mycorrhizae

Vesicles: thick walled oval structures contain large amounts of lipids and often numerous nuclei. I’m dead root fragments, vesicles can be infective propagules and re-grow hyphae to infect new roots.

What type of mycorrhizae is more recent

Ecto-mycorrhizae

Ecto-mycorrhizae facilitate ______ and _____ transfer across individuals in a forest

Carbon Nutrient Survival of young trees enhanced when connected to a network of old trees

Hartig net

Complex of fungal hyphae found in the intracellular spaces between the cortical cells of a root in ecto-mycorrhizae

What other job do ecto-mycorrhizal fungal do

Decomposers Fungal sheaths that form around the secondary root tips, accumulate minerals from the decomposing litter, before they are able to pass into the deeper mineral layers of the soil

Infected ecto-mycorrhizae roots have what appearance

Short, pairs of branches

Orchid mycorrhizae

-endomycorrhizae (mostly basidiomycota) -all orchids infected with mycorrhizal fungus -orchid seeds have small food reserve for the embryo and it is depleted by the time that the first few cell divisions of the embryo have occurred, therefore they depends on mycorrhizae. -most orchid seeds do not germinate until the fungus symbiont penetrates seed coat of the seed. -fungus supplies minerals and organic compounds to orchid like carbohydrates

Many orchids are epiphytes meaning they live on plants rather than soil. How does mycorrhizal fungus work around this?

Fungus acts as a parasite upon the plant which the orchid is growing -> food is transferred by the fungus, from the tree, on which the orchid is growing, to the orchid.

Ericaceous mycorrhizae

-formed by ascomycota fungi and plants in the family epacridaceae, ericaceae, pyrolaceae -

Ericoid mycorrhizae

Ericoid mycorrhizae have evolved in association with plants that are continually stressed by factors within the soil Soul is typically extremely acidic, low in available minerals because of mineralization is inhibited. Plants with Ericoid mycorrhizae have high tolerance to these stresses

Where does Endo and ecto mycorrhizae go in a root

Endo-into epidermis-cortical cells-inside cortical cells Ecto-into epidermis-inbetween cortical cells

Arbuscular mycorrhizae are _______ mutualists

Obligate Need partner plant root to germinate