BOT3015L Symbioses Presentation created by Danielle Sherdan All photos from Raven et al. Biology of Plants except when otherwise noted

Symbiosis Sym=together, bio=life parasitismcommensalismmutualism A continuum: A network of interactions among organisms on a continuum between beneficial and detrimental effects A major driving force behind evolution

A few examples Flowering plants and pollinating animals Humans and domesticated plants and animals Humans and bacteria in their digestive system Endosymbionts Origination of mitochondria and chloroplasts

Example of endosymbiosis Vorticella (protozoan) under compound light microscope One cell containing numerous autotrophic algal cells Scanning electron microscope ~5µ m

Basic Outline of (Primary) Endosymbiosis using the plastid as an example Some debate about origin of outer membranes of plastids The bulk of evidence indicates that all chloroplasts resulted from a single primary endosymbiotic event (=monophyletic origin of plastids) involving cyanobacteria. Modified from Outlaw lecture

A few examples Flowering plants and pollinating animals Humans and domesticated plants and animals Humans and bacteria in their digestive system Endosymbionts Origination of mitochondria and chloroplasts Plants and bacteria Rhizobia (also an example of endosymbiosis)

Symbioses between plants and bacteria BacteriaExample effect on plant physiology Many are parasitic, but Rhizobium is mutualistic

Rhizobia Symbioses between plants and bacteria Nitrogen Fixation Legumes (and a few other plants) form a symbiosis with a nitrogen-fixing bacterium. The bacterium enters the root and a nodule—part plant, part bacterium—is formed as a growth on the root. From Outlaw lecture

Rhizobia Symbioses between plants and bacteria Nitrogen Fixation Benefit to the plant: Source of usable nitrogen, which is limiting to growth. Benefit to the bacterium: Low O 2 environment (O 2 denatures nitrogenase) and source of reduced carbon. From Outlaw lecture

Liposaccharides Flavinoids Initiation of Rhizobium symbiosis at plant root Modified from Outlaw lecture

Initiation of Rhizobium symbiosis at plant root Rhizobia (arrows) attached to young root hair Bradyrhizobium on soybean (Glycine) Scanning electron micrograph ~5µ m

Initiation of Rhizobium symbiosis at plant root Root hair containing multiple infection threads (arrows) Bradyrhizobium on soybean (Glycine) Differential-interference contrast photomicrograph ~20µ m

Initiation of Rhizobium symbiosis at plant root Bradyrhizobium on soybean (Glycine) Scanning electron micrograph Infection thread with rhizobia ~1µ m

Initiation of Rhizobium symbiosis at plant root Bradyrhizobium on soybean (Glycine) Scanning electron micrograph Groups of bacteroids surrounded by membrane derived from infected root cell (uninfected cell in the above adjacent cell) ~2µ m

Rhizobium symbiosis in dicot root nodule Bradyrhizobium on soybean (Glycine) Compound light microscope Cross section of mature root nodule. Rhizobia- infected cells are stained dark. Arrows indicate vascular bundles ~500µ m

A few examples Flowering plants and pollinating animals Humans and domesticated plants and animals Humans and bacteria in their digestive system Endosymbionts Origination of mitochondria and chloroplasts Plants and bacteria Rhizobia (also an example of endosymbiosis) Humans and fungi Leafcutter ants and fungi Lichens

Symbiosis between fungus and population of unicellular or filamentous algal or cyanobacterial cells Interactions between lichens and animals exemplify the network nature of symbioses. Reindeer moss (Cladonia) (note the misnomer) Caloplaca

A few examples Flowering plants and pollinating animals Humans and domesticated plants and animals Humans and bacteria in their digestive system Endosymbionts Origination of mitochondria and chloroplasts Plants and bacteria Rhizobia (also an example of endosymbiosis) Humans and fungi Leafcutter ants and fungi Lichens Plants and fungi Mycorrhizae

Myco=fungus, rhiza=root Fungus gets carbohydrates from plant Plant gets better nutrient absorption Both have protective effects on the other Exposure to mycorrhizal fungi White pine (Pinus) __ +

Endomycorrhizae endo=within Branched fungal hyphae (arbuscules) invaginate the plasma membrane of sugar maple (Acer) root cells Scanning electron micrograph~10µ m

Endomycorrhizae Pawpaw and Glomales, an order of promiscuous endomycorrhizal fungi Fungi (stained blue to visualize) Plant cell wall The fungus does not penetrate the symplast. Modified from Outlaw’s lecture hypha arbuscules

Mycorrhizae dooryard observation Pawpaw (Asimina triloba) From Outlaw’s garden

Ectomycorrhizae Lodgepole pine (Pinus) Fungus surrounds roots and grows between intercellular regions Cross section of pine root with ectomycorrhizae Notice how much surface area is added by the fungus ~50µ m

Today Investigating mycorrhizae: Comparative study of mycorrhizae in local plants Work in groups of 2-3 to stain, observe, draw, and describe mycorrhizae in at least 3 different plant species Draw and describe lichen and nodules without magnification, then section them, then draw them as they appear under the dissecting scope at a high magnification.