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Bernard J. Mulligan
§ * Corresponding author Financial support:
Ministry of Science, Research and Technology of Iran.
One of the features of programmed cell death process is the breakdown of chromosomal DNA in animal cells. This phenomenon occurs in apoptosis and has been discovered to happen in some types of cell deaths in plants. In this research, the intactness of chromosomal and organellar DNA (mitochondria and chloroplast) of senescing rice suspension cultures was investigated using two methods. One method was the amplification of specific fragments of DNA called polymerase chain reaction PCR and the other was Southern blotting. In PCR, two small pieces of DNA, template DNA, a thermostable enzyme for DNA amplification, DNTPs and a buffer are mixed in a small tube and placed on an apparatus for the amlification of DNA fragments. In Southern blooting, the target DNA is cut into pieces by specific enzymes obtained from microorganisms. Then the cut DNA is mounted on a membrane and a radiolabeled piece of DNA which is thought to match with a piece of the target DNA is transferred into a glass tube containing a buffer and the membrane. After about 12 hours the membrane is taken out, washed and exposed on an X-ray film. The black signals picked on the film indicate that the radiolabeled DNA has matched with our target DNA. A mitochondrial
gene (COXII), a chloroplast gene (PSAa) and a nuclear
DNA marker (RG64) were employed to examine the intactness of
DNA of rice cell cultures during senescence. In this respect, PCR showed
no changes in mitochondrial DNA, but showed some changes in chloroplast
and nuclear DNA. Southern blot analysis revealed that mitochondrial
and nuclear DNA contents declined but chloroplast DNA remained relatively
the same. It seems that using cell cultures and the two approaches described
above, were applicable in studying the intactness of DNA, but however,
for further investigation, more genes would be required. |
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