|Plants & Human Affairs (BIOL106) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; firstname.lastname@example.org; http://www.employees.csbsju.edu/ssaupe|
II. Characteristics of the Bean Family
A. Leaves - compound (dissected)
The fruit type is called a legume. These fruits are 1-several seeded and splits open along two sides to release the seeds. Note that modern cultivars are selected to remain closed.
The flower structure depends on the specific type. One characteristic group of legume plants has "papillonaceous" flowers (butterfly shaped, Papilio - recall the film "Papillion"?). These flowers have five petals - the uppermost petal is largest and called the banner (or standard), there are two side petals (wings) and two lower petals (keel petals) that are fused into a canoe-like structure (keel). There are 10 stamens that are fused together. The flowers are designed for bee pollination.
The roots are nodules that contain bacteria (Rhizobium) that can fix nitrogen.
III. Nitrogen Fixation
Points to consider:
forms of nitrogen in the environment are: N2 (air is
comprised of 80% nitrogen), ammonia (NH4), nitrate (NO3),
& nitrite (NO2). The latter three are mostly dissolved
is used in many molecules in plants and other organisms especially in
proteins and nucleic acids (DNA)
fixation - converts nitrogen gas into ammonia.
This is the result of the action of:
(a) aquatic microbes like Anabaena and Nostoc, which
are types of blue-green algae that are better called cyanobacteria; (b)
electrical discharges ("the grass is always greener after a thunder
storm"), (c) free-living soil microbes (Azotobacter); and (d)
symbiotic nitrogen-fixing bacteria (Rhizobium) in nodules on the
roots of legumes (called poor-persons meat, rich in protein cause they fix
nitrogen) and a few other plants.
absorb ammonia (conifers, grasses) or nitrate (most others).
- conversion of ammonia to
nitrate by soil microbes (Nitrosomas converts ammonia to nitrite; Nitrobacter
converts nitrite to nitrate). Favored
by warm temperature and neutral pH.
and decayed organic materials decomposed by another set of bacteria into
ammonia - called ammonification. Various
microbes are responsible, favored by cool temperatures, all pH's.
- closes the cycle. Returns
nitrogen to the atmosphere. Conversion
of nitrate, nitrite, and/or ammonia back to nitrogen gas by other microbes.
heavy reliance on microbes for the function of this cycle.
plants can usually out compete others in nutrient poor soil
fixation is "expensive" - it requires a lot of energy (high
are excellent green manure because they have high levels of nitrogen.
Nitrogen in many systems is usually in short supply so legumes are valuable
Fertilizers rated by the nitrogen (N) - phosphorus (P) - potassium (K) amounts or abbreviated, NPK. For example, Osmocote, a slow release pelletized fertilizer is 14 - 14 - 14, which means it has a nitrogen content of 14%, phosphorus content of 14% and potassium content of 14%.
IV. Uses of Legumes
seeds (e.g., lima beans, navy beans, kidney beans, peanuts) and/or pods (snow peas) eaten for food
sprouts (e.g., alfalfa or mung beans)
forage crop (e.g., alfalfa)
nitrogen fertilizer (green manure)
erosion control (many grow quickly and good at stabilizing soil and adding nitrogen - Crown vetch is a good example)
ornamental plants (for example, honey locust trees are widely planted on campus)
wood pulp (Leucaena trees are an important global source of wood pulp for the paper industry)
dyes (indigo comes from a legume plant)
flavoring (carob comes from the pod of a legume plant)
insecticide (rotenone is obtained from the roots of a legume plant)
V. Limitations as a food source.
Although legumes provide an excellent source of protein in the diet, there are limitations to using legumes for food. These include:
VI. A Quick Bean Survey
A. Soybean (Glycine max)
rich source of commercially important oil (cooking, margarine, paint, lubricants, soaps). The oil is expressed
food (soy sauce, tofu, sprouts, soy milk)
Tofu is prepared by soaking → rinse → crush → heat → a. liquid (soymilk, used as beverage or can make cheese) → salt → curd; or b. solid → okara
Soy sauce: okara + wheat + fungi (Aspergillus oryzae) → salt (18%) → age year
domesticated in NE China about 7000 ybp
B. Peanut (Arachis hypogaea)
C. Lentils (Lens culinaris)
D. Peas (Pisum sativum)
E. Broad Bean or Horse Bean (Vicia faba)
F. Chick pea or Garbanzo (Cicer arietinum)
G. Phaseolus Beans (Phaseolus sp.)
These are New World beans. There are several common species:
H. Vigna Beans (Old World)
Last updated: 01/07/2005 / � Copyright by SG Saupe / URL:http://www.employees.csbsju.edu/ssaupe/index.html