"You still don't understand what you're dealing with, do you? The perfect organism. Its structural perfection is matched only by its hostility. I admire its purity. A survivor … unclouded by conscience, remorse, or delusions of morality." - Ash to Ripley (Alien, 1979)
Orchids are widely distributed across
the world with 25,000 to 35,000
species except for Antarctica . Orchid’s lifecyle begins after pollination
with the shivering of its petal and sepals. Then, it begins to form a seed; The
maturation period of the seed is unique to each orchid species. Next, the seed germinates into a seedling
resulting in the flowering of orchid and the process begins again. Since orchids’ seeds lack endosperm, they use
resources from fungus to complete the germination process .
fungi provide energy and nutrients to orchids, from familyOrchidaceae. The fungi in the orchid mycorrhiza fulfill
the role of endosperm in orchid seed . During
the non-photosythentic phase of the orchid’s lifecycle, the fungi provide the
orchid with energy and carbon compounds . After the non-photosynthetic phase, the fungi
can also increase the nutrients and mineral intake of the orchid through the
roots. The fungi form pelotons that are
like the host cell. These pelotons are surrounded by a membrane similar to
plasma membrane. An infect orchid has altered microtubules and cell wall
microfibrils . All these
alterations caused by the fungi help the orchid to absorb inorganic nutrients
and trace elements from the soil. The
fungi also benefits from these interactions by receiving some of the
photosynthesized carbohydrates . Thus, the relationship between
orchid and orchid mycorrhiza is mutualistic.
Some orchid mycorrhiza have evolved to be specific based on the species
of the orchid therefore, can serve to be pathogenic to other orchid species .
Cost and Benefit
As stated above, both the orchid and
fungi benefit from this relationship.
The fungi gains carbohydrates from the orchid while the orchid receives nutrients
The orchid does not spend a
lot of energy in developing its roots in order to increase its volume of
nutrients and minerals absorption from the soil. Instead, the fungi fulfill that role. The fungi are not limited to the roots alone. They can explore other cavities and compounds
that are not near the roots.
Even though fungal infection can be
pathogenic to the orchid, the orchid is able to control the infection. The orchid has defense genes and compounds
such as orchinol that can control the fungal infection . These defense mechanisms does not significantly
affect the reproductive success of the fungus.