Friday, April 27, 2012

Orchids and Orchid mycorrhiza

            Orchids are widely distributed across the world with 25,000 to 35,000 species except for Antarctica [1].  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 [2]

Description of the Relationship
Intracellular hyphal peloton [7]
            Basidiomycetes fungi provide energy and nutrients to orchids, from family Orchidaceae.  The fungi in the orchid mycorrhiza fulfill the role of endosperm in orchid seed [3].   During the non-photosythentic phase of the orchid’s lifecycle, the fungi provide the orchid with energy and carbon compounds [4].  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 [3].  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 [5]. 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 [3].

Cost and Benefit Analysis
            As stated above, both the orchid and fungi benefit from this relationship.  The fungi gains carbohydrates from the orchid while the orchid receives nutrients and energy.  

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[5]
            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 [3].  These defense mechanisms does not significantly affect the reproductive success of the fungus.


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