Biology Rewriting History

The mitochondria; primary function being producing ATP energy for the cell.  The mitochondria contains circular DNA which is only passed down from the mother.

In the news this past week I have come across two instances where biology has recently rewrote history.  The first and most publicized story has to do with the discovery of Great Britian's King Richard III  (Click for news story here).  Scientists, through the use of forensic skeletal evidence were able to show the skeleton in question had similar features to what history tells us about the king.  The final and most absolute evidence came in the form of mitochondrial DNA.  The mitochondria is an organelle within cells that produces ATP energy for running the cell.  The mitochondria contains a relatively small amount of DNA that is circular in shape.  This DNA is unique in that it is independent from DNA contained within the nucleus of the cell and that it is only passed down from the mother and not the father.  DNA in the nucleus is a combination of half coming from the father and half from the mother, so the offspring is a unique combination of DNA from both parents.  With DNA of the nucleus, every individual person has a unique combination of DNA, except in the case of identical twins which have identical DNA.  In mitochondrial DNA, all offspring have identical DNA to their mother, even if they have different fathers.  In the case of King Richard III, a direct match of mitochondrial DNA was found between the skeleton in question and a present day descendant of King Richard III's sister.  So to break this down, King Richard and his sister would have had identical mitochondrial DNA because they had the same mother.  Identical DNA would have then been passed down through the maternal side of all of King Richard's sisters descendants.  To find a direct match in mitochondrial DNA is undeniable evidence that two people are directly related to each other and that the skeleton must be King Richard III.

The second and far less publicized story has to do the Mary Ingalls, the sister of Laura Ingalls Wilder wrote the "Little House on the Prairie" books.  The question being asked about Mary Ingalls in this investigation was why really did Mary go blind (Click for news story here) .  In the books, Laura claims that Mary went blind as a result of scarlet fever.  With modern medicine we know that scarlet fever rarely causes blindness and if it does the blindness is only temporary.  So the idea that scarlet fever cause blindness is only a myth from the past.  A medical doctor examining this went through the many letters and writings of Laura Ingalls-Wilder in order to find what illness may have actually caused Mary's blindness.  In the letters, the doctor came across what appears to be Mary having spinal meningitis, which causes swelling of the central nervous system.  This swelling could have easily caused damage to the optic nerves and therefore causing blindness. 

Legumes: Self Fertilizing Plants

The green stem of the legume palo verde tree in the Sonoran Desert.

Determining how to fertilize a plant can be quite the difficulty.  You may have heard that most people over water their plants, but it is also true that most people over fertilize their plants.  Certain plants however never need to be fertilized simply because they have "figured" out a way to fertilize themselves.  Bean plants, also called legumes, form a symbiotic relationship with a bacterium known as rhizobium.  The air we breath is about 70 percent nitrogen, an essential nutrient for plant fertilization.  Atmospheric nitrogen however cannot be used by plants, it must be converted into a different form called ammonium.  Rhizobium bacteria has the ability to take nitrogen gas and convert it into ammonium.  This changing of nitrogen gas into ammonium is known as nitrogen fixation. 

Using legumes in the garden can be quite a useful way to fertilize your plants naturally.  Farmers in the Midwest will often alternate between corn and soybeans, taking advantage of the fact that soybeans naturally replenish the soil with nitrogen fertilizer that the corn can use.  In deserts, which have soils that are naturally deficient in nitrogen, plants must either be adapted to living in soils with low nutrients or have the ability to fix their own nitrogen.  For this reason, legumes are extremely common in desert ecosystems.  Legumes are not just your typical bean plant, they also grow into bushes and trees.  In the Sonoran Desert palo verdes, mesquites, ironwoods, and acacias are all small legume trees that form bean-like pods.  Typically, these legume trees will form islands of soil under their canopy that are rich in nutrients compared to soils beyond the canopy.  Because of the slightly richer soil many smaller plants will often be growing in this micro-environment. 

The darker growths on these plant roots are tumors infected with rhizobium bacteria.

Legumes and Rhizobium bacteria form their association with each other in the soil-root environment.  Rhizobium are naturally occurring soil bacteria but don't really do much if they haven't infected a legume.  When bean seeds germinate and begin to grow, rhizobium already present in the soil infects the new plants roots.  Points of rhizobium infection in the roots form into tumorous-like growths which are like little nitrogen fixing factories.  Typically we think of tumors as unhealthy but be assured, this type of plant tumor is very healthy and beneficial to not only the infected plant but also to the entire environment.  Legume plants that for some reason are not infected become extremely anemic with stunted growth and yellow coloration.