Poaceae Terminology
DNA Sequencing Technology

Poaceae Terminology

Tiller

Culm

Node

Internode

Intercallary meristem

Sheath

Open sheath

Closed sheath

Blade

Ligule

Auricle

Stolon

Rhizome

Inflorescence

Spike

Panicle

Panicle branch

Spikelet

Floret

Glume

Lemma

Palea

Rachilla

Rachis

Lodicule

Filament

Anther

Stigma

Caryopsis

DNA Sequencing Technology

Types of DNA:
There are three types of DNA that may be studied in plants, chloroplast DNA (cDNA), mitochondrial DNA (mDNA) and nuclear DNA (nuclear chromosomes).

Nuclear DNA comprises the chromosomes of organisms. Each chromosome consists of one long, double-stranded DNA molecule with many genes located along its length. It tends to be highly repetitive, meaning there are many segments that are repeated many times throughout the chromosomes. Because most plants are polyploids, there also may be several copies of each chromosome present in every cell. Also, there may be segments of DNA that are never expressed in the plant.

Chloroplast DNA is found in chloroplasts only. Chloroplasts may represent an ancient symbiotic relationship between photosynthetic bacteria and eukaryotic cells. Chloroplasts have a small amount of DNA, similar to that of bacteria, and replicate themselves through a fission process. Chloroplast DNA is highly conserved. This means that it doesn't have a high rate of mutation or change. Inversions and other rearrangements are uncommon in flowering plant chloroplast DNA. Chloroplast DNA is not as highly repetitive as nuclear DNA. Chloroplast DNA is also useful for study because it is small compared to nuclear DNA. The chloroplast genome is about 134 kb in grasses (134,000 bases long).

Mitochondrial DNA is found in mitochondria only. Mitochondria also probably represent ancient symbiosis between respiratory bacteria and eukaryotic cells. Mitochondrial DNA is similar to chloroplast DNA in size and rate of change.

Polymerase Chain Reaction (PCR) Technology:
This process is used to increase amounts of DNA for further study. Very small amounts of DNA can be turned into larger amounts for various types of studies. DNA is extracted from the plant. It is heated to separate the two strands of the double helix. The single-stranded DNA is cooled with materials necessary for production of complementary strands. The enzyme DNA polymerase is added together with all of the necessary bases and complimentary strands of DNA form along both single strands of DNA at the same time. Once replication is complete, the mixture is heated to separate the two strands of the new DNA, then the process is repeated. Each heating/replication cycle doubles the number of copies of the DNA segment.

Specific primers can be added to initiate replication at specific base sequences. The resulting double-stranded DNA fragments can be separated on electrophoretic gels where they migrate at rates according to their size.