Orchid mycorrhizae

1. Man, Microbes and
Environment

2. Orchid Mycorrhizae

3. ORCHIDS
● The Orchidaceae is one of the largest plant families with close to
35,000 species and a circum-global distribution.
● It is also one of the most advanced plant families with many
adaptations enabling long-term survival.
● A reliance on mycorrhizal interactions is an important adaptive
mechanism that has allowed orchids to persist in less than ideal
habitats and has led to their occurrence worldwide.
● Orchids lacking chlorophyll, called achlorophyllous
mycoheterotrophs, will retain their fungal symbionts their entire lives,
relying on the fungus for carbon.
● The debate over whether fungal symbiosis is necessary for the
orchid is an old one, as Noel Bernard first proposed orchid
symbiosis in 1899. Although epiphytic orchids grow on other plants
they may produce chlorophyll in their leaves, stems, and roots.

4. ORCHID MYCORRHIZAE
● Orchid mycorrhizae are symbiotic relationships between the roots
of plants of the family Orchidaceae and a variety of fungi.
● All orchids are myco-heterotrophic at some point in their life cycle.
● Orchid mycorrhizae are critically important during orchid
germination, as an orchid seed has virtually no energy reserve and
obtains its carbon from the fungal symbiont.
● The symbiosis starts with a structure called a protocorm. During
the symbiosis, the fungus develops structures called pelotons
within the root cortex of the orchid.
● The pelotons of orchid mycorrhiza are intensely coiled dense
fungal hyphae that are often more extensive in comparison to
endomycorrhizal structures of arbuscular mycorrhiza.
● Many adult orchids retain their fungal symbionts throughout their
life, although the benefits to the adult photosynthetic orchid and
the fungus remain largely unexplained.

5. SEED GERMINATION
Orchids have several life stages.
a. The first stage is the non-germinated
orchid seed,
b. The next stage is the protocorm, and
c. The following stage is the adult orchid.

6. ORCHID SEED
● Orchid seeds are very small (0.35mm to 1.50mm long),
spindle-shaped, and have an opening at the pointed end.
● Each seed has an embryo that is undifferentiated and lacks
root and shoot meristems.
● An orchid seed does not have enough nutritional support to
grow on its own.
● Instead, it gets nutrients needed for germination from fungal
symbionts in natural settings.

7. PROTOCORM
When the orchid seeds germinate they form intermediate
structures called protocorms, young plants which have
germinated but lack leaves and which consist mainly of
parenchyma cells. Infected protocorms tend to develop an
active meristem within a few days.
ADULT ORCHID
In the adult stage, many orchids have a small amount of
thick unbranched roots which results in a root system with
a small surface area that is favorable to potentially
mycotrophic tissue.

8. FUNGAL ENTRY INTO ORCHID
● Mutualistic fungi can enter at various orchid life stages.
● Fungal hyphae can penetrate the parenchyma cells of
germinated orchid seeds, protocorms, late-staged seedlings,
or adult plant roots
● The fungal hyphae that enter the orchid have many
mitochondria and few vacuoles, thus increasing their metabolic
capacity when paired with an accepting symbiont.
● In the protocorm stage hyphae enter the chalazal (top) end of
the embryo, however in terrestrial orchids fungal entry into
adult plant roots happens mainly through root hair tips which
then take on a distorted shape.
● The symbiosis is typcally maintained throughout the lifetime of
the orchid because they depend on the fungus for nutrients,
sugars and minerals.
● However, some orchids have been found to switch fungal
partners during extreme conditions.

9. FUNGAL PELOTONS AND ORCHID
ROOT CORTEX
● Shortly after the fungus enters an orchid, the fungus produces
intracellular hyphal coils called pelotons in the embryos of
developing seedlings and the roots of adult plants.
● The formation of pelotons in root cortical cells is a defining
anatomical structure in orchid mycorrhiza that differentiate it
from other forms of fungi. The pelotons can range in size and
in the arrangement and density packaging of their hyphae.
● Pelotons are separated from the orchid's cytoplasm by an
interfacial matrix and the orchid's plasma membrane.
● Orchid cells with degenerating pelotons lack starch grains,
whereas the newly invaded orchid cells contain large starch
grains, suggesting the hydrolysis of starch resulting from the
fungal colonization.

10. ● There is an enlargement of the nucleus in infected
orchid cortical cells and in non-infected cortical cells near
an infected area as a result of increased DNA content.The
increased DNA content has been correlated with the
differentiation of parenchymal cells suggesting its role in
orchid growth.
● As pelotons of live fungal hyphae age and are
eventually disintegrated, or lysed, they appear as brown
or yellow clumps in the orchid cells.
● The cortical cells of older roots tend to have more lysed
pelotons than young pelotons.
● Although pelotons are lysed, new pelotons continue to be
formed, which indicates a high amount of new hyphal
activity.

11. FUNGI FORMING ORCHID MYCORRHIZAE
● The main group of fungi inhabiting orchid roots is
Basidiomycetes, these fungi come from a range of taxa
including
■ pathogenic Rhizoctonia .
■ Sebacina,
■ Tulasnella (a genus of effused (patch-forming) fungi)
■ Russula species.
● Though rare in orchids, Ascomycete associations have been
documented in several orchid species. The European
terrestrial orchid Epipactis helleborine has a specific
association with ectomycorrhizal ascomycetes in the
Tuberaceae.

12. NUTRIENT EXCHANGE:
● Orchid mycorrhizas are different from other types of mycorrhizae in
the nature of the nutrient exchange. After establishment of a
mycorrhiza, organic carbon and minerals are passed from the
fungus to the seed. Because a symbiotic germination requires
sugars, amino acids and vitamins, it is assumed that these are also
obtained from the fungus.
● The fungus continues to supply the protocorm with all its organic
energy until such times as the plant starts to photosynthesis. Even
then, it appears that the fungus does not gain significant supplies of
carbon from the photosynthetic partner.
● The organic materials surrounding the plant may also provide
nutrients to mycorrhizal fungi. Mycorrhizal fungi have the potential to
solubilize complex carbohydrates, including cellulose. The fungi
translocate trehalose in the hyphae and hexose is made available at
the interface.
● Thus the fungus acquires, translocates and transfers organic energy
to and from the plant. This role is significant even in adult plants,
especially epiphytes that exist in shadows of the canopy.

13. CONTROL OF COLONIZATION
● The interaction between plant and fungus is highly regulated by the
plant. The plant releases orchinol, a phytoalexin that causes the
pelotons to collapse.
● The degree of colonization changes over the season, indicating that
the orchid is controlling uptake of nutrients while preventing
parasitism by the fungus.
● Some terrestrial orchids have an annual cycle, whereby a period of
growth is followed by loss of leaves and/or roots. The orchid then is
maintained below ground until conditions become suitable for further
growth.
● The fungus is commonly excluded from the orchid during these
periods of dormancy.
● The roots of epiphytic orchids are colonized only in zones that are in
contact with organic substrate.
● Like terrestrial orchids, epiphytic orchids may have periods where
they are poorly colonized. In the absence of mycorrhiza, the
fungus may be retained in the velamen of the root, or the
organic substrate.

14. Animals Fermenters
&
Microorganisms

15. ANIMAL FERMENTERS
● The co-evolution of animals and microbes led to the
development of mutualistic relationships between hosts and
their microbial colonizers, accounting for an expansion of the
host's metabolic traits.
● Thus, animals across the phylogenetic tree have, to varying
degrees, a portion of the gastrointestinal tract adapted to
accommodate fermenting microbes, which assist in the
digestive process.
● In these enlarged gut regions, dense communities of
microorganisms form a close ecological unit with the host,
having a vital role in the nutrition, physiology and immunology of
the host animal.
● In the gut microbial chambers, microbial extracellular enzymes
catalyze the hydrolysis of the refractory dietary plant fiber that
otherwise could not be degraded by the animal's enzymes.

16. ● Although the specialized teeth of herbivores effectively shred and
grind the cell walls of plant tissues and release their content, only
certain enzymes can digest cellulose. Most mammals however, do
not produce cellulolytic enzymes so they rely on the symbiotic
microorganism breakdown and metabolize the cellulose so it can be
used by mammal host. Ungulates have evolved 2 different systems
for breaking down cellulose:
■ Hindgut fermentation
■ Foregut fermentation (rumination)
So ungulates can be classified into foregut or hindgut fermenters, based
on the characteristics of their digestive fermentation sites.
● By definition, a foregut fermenter has a pre-gastric fermentation
chamber. Ruminants include cattle, sheep, goats, buffalo, deer, elk,
giraffes and camels.
● Whereas a hindgut fermenter has enlarged fermentation
compartments in the cecum and/or colon where fermentation takes
place long after the initial gastric digestion in the stomach. Examples
of hindgut fermenters include proboscideans and large odd-toed
ungulates such as horses and rhinos, as well as small animals such
as rodents, rabbits and koalas.

17. HINDGUT FERMENTATION
Hindgut fermentation is a digestive process seen in monogastric
herbivores, animals with a simple, single-chambered stomach. Cellulose
is digested with the aid of symbiotic bacteria The microbial fermentation
occurs in the digestive organs that follow the small intestine:
■ The large intestine and
■ Cecum.
● Hindgut fermenters masticate food as the eat, initiating digestion
with salivary glands.
● Digestion continues by enzymatic activity within the simple stomach
and food they move rapidly into the small intestine as new food is
eaten.
● Hindgut fermenters do not regurgitate their food. Nutrients are
absorbed in the small intestin.
● Finely grounded food pass from small intestine to cecum and larger
food particles pass to large intestine. Among the hindgut fermenters
the colon act as the principal fermentation chamber for the larger
species while cecum fulfils this function in small species.

19. FOREGUT FERMENTATION
● Rumination also known as foregut fermentation is typified by
artiodactyl.
● Foregut fermenters possess a complex, multi-chambered stomach
with cellulose digesting microorganism.
● After food is procured by cropping or grazing, it is immediately
passed into the first and the largest camber of this network Rumen.
Here food is moistened and kneaded which mix it throughly with
microorganism that ferment the food.
● Large particles of food floats on the top of rumen fluid and pass to
the second chamber Reticulum which is a blind end sac with honey
comb partition in its walls. The reticulum id where the softened mass
called cud is formed.
Fermentation occurs both in rumen and reticulum, and both absorb main
products of fermentation, short chain fatty acids.

20. ● When animal is at rest, this softened mass is regurgitated
allowing the animals to chew the cud.
● At this time the mass is further broken by potent enzyme,
salivary amylase.
● The food is swolled a second time and enter the third
chamber omasum where muscular walls knead it further.
● The fourth and final chamber the abomasum is the true
stomach. Here digestive enzyme that kill any escaping
microorganism are secreted and protein digestion is
completed.
● Digestive material is then passes into the small intestine,
where food is absorbed.
● Some additional fermentation and absorption takes place
in cecum.

22. CELLULOSE DIGESTION IN ANIMALS
MICROBIAL CELLULOSE DIGESTION IN ANIMALS
A diverse group of microbes live within the digestive systems of ruminants.
Ruminants include cloven-hoofed animals with plant-based diets such as cows,
sheep, deer, and goats that degrade plant materials in a specialized foregut
organ, the rumen. The microbes allow the animals to break down complex plant
materials such as amino acids, cellulose, starch, and sugars into simpler
products that can then be broken down by the animal’s own metabolism.
Attachment and enzymatic activity
The degradation of cellulose occurs when the β-1,4 linkages are hydrolyzed
by cellulase enzyme. Degradation is made possible by large, multienzyme
complexes known as cellulosomes. The attachment of the complex to the
cellulose substrate is coordinated in part by noncellulolytic microbes.
Cellulose-binding proteins within the cellulase enzyme complex are thought
to direct the attachment of the complex onto the crystalline cellulose structure.
Scaffoldin or cellulosome-integrating proteins, large glycosylated proteins,
can facilitate enzyme attachment, cellulose binding, or anchoring to the
bacterial cell surface. These proteins have separate sections for binding and
cleavage of polysaccharide bonds.