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Can all plants make sugar?

Asked by: Clarida Marie Garcia
School: St. James Middle School
Grade: 6
Teacher: Mrs. Barnes

Answer from Karl Wilson

Professor of Biology, Binghamton University

Research area:  Biochemistry, degradation of proteins in plants; seed germination
Ph.D. school: University at Buffalo
Family: Wife (also a faculty member at Binghamton), daughter
Interests/hobbies:  Paleontology, photography, cooking
Web page address:  http://bingweb.binghamton.edu/~kwilson/home.htm

Clarida, your question leads to a number of interesting observations on plant biology!  All plants can use sugars, interconvert one sugar to another, and synthesize sugar polymers like cellulose and starch. Green plants synthesize sugars from the inorganic compounds water and carbon dioxide by photosynthesis, using the energy in light to drive the chemical reactions.  However, not all plant species are photosynthetic.  Some plants that can’t make their own sugar can get it from other plants. Such plants are called parasites. One example of this is the beechdrops (Epifagus americanum), a flowering plant lacking chlorophyll that is found under beech trees.  Beechdrops are root parasites, attaching to the roots of the beech tree, and drawing sugars directly from the tree.    Other non-photosynthetic plants are indirectly dependent on a photosynthetic plant.  At this point let us introduce the mycorrhizal fungus.  Many (if not most) plants form a symbiotic relationship with fungi that colonize the plant’s roots, and extend strands (hyphae) out into the soil.  In most cases this is what we call a mutualistic association where both the plant and the fungus benefit.  The fungus is effective in absorbing minerals such as phosphate from the soil, and passing the nutrients on to the plant through its roots.  The plant in turn supplies the fungus with sugars such as glucose and sucrose. Some non-photosynthetic plants have been able to tap into this system.  In our area the most common example is the Indian Pipe (Monotropa uniflora), a ghostly white plant often found sprouting up beneath trees in dense forests.  The Indian Pipe obtains its sugars by being a parasite on some species of mycorrhizal fungi. Thus, the Indian Pipe is really indirectly parasitic on the tree, with the flow of sugars going from Tree to Mycorrhizal Fungus to Indian Pipe.   You can find pictures of Beechdrops, Indian Pipe, and other parasitic plants on the internet at sites such as http://www.botany.org/parasitic_plants/

 

Last Updated: 9/18/13