Plant Cloning
A recent edition of the Sacramento Bee, October 11, 2002, has an article titled “Clippings for clone; Group seeks copies of the world’s oldest tree.”
A few weeks ago, we described our visit to the White Mountains of California to visit the world’s oldest trees – maybe the world’s oldest organisms. The bristlecone pine occurs in a very arid, harsh environment, generally at elevations above 10,000 feet.
Members of the Michigan-based Champion Tree Project International, with the cooperation of the U. S. Forest Service, went to the location of the oldest known bristlecone pine, the gnarled, 4,768 year-old tree called Methuselah.
They removed new growth, needles and cones which they hope will provide live vegetative cells which can produce exact copies of this tree. They also took samples from “the Patriarch”, the largest known bristlecone. They loaded their material onto ice and delivered it to the University of California for their cloning laboratory.
The Champion Tree Project International has cloned more than 70 of this country’s largest trees, known as “national champion trees”. These trees are so designated because of their great circumference, height, and crown spread. The Project’s goal is to clone the champions of more than 800 U. S. tree species. The Project’s sponsors claim many benefits to cloning these trees. It is like saving the best genetic material and it helps scientists understand the reason for the longevity of the Earth’s oldest living things.
The University of California’s cloning laboratory will place the buds in a starchy medium with plant growth hormones. Certain cells of the bud, known as parenchyma, have full genetic potential, like human stem cells, to divide and divide and in the proper environment to differentiate into a complete functional organism. Roots and stems may come out of those buds’ cells, and these plants can be set out in a pot or bed for additional growth before they are set out in natural conditions.
The undifferentiated parenchyma cells may be found in flower parts, leaf parts, fruits, and in stems and roots. Root and stem tips are mostly composed of these kinds of cells. Regardless of where they are found, they have the capability in tissue culture or under the right conditions to produce exact copies (clones) from whence they came. This summer we removed branches from a beautiful tuberous begonia that we were growing outside. We placed them in water and now they are forming roots. That means that the parenchyma cells at the base of the stem cuttings have divided and differentiated into roots which contain specialized root cells. Those roots still contain hundreds of parenchyma cells. We know that leaves from jade plants, African violet plants, and others contain those cells that can form both stem and root cells and from this make complete new plants.
Any means that is vegetative reproduction, without the production of gametes (sperm and egg) results in the production of clones or exact genetic copies.
We have seen the National Forest Service locate a good healthy specimen of a tree, remove branches from the tree with high-powered rifles and root the branches and establish a nursery full of clones of that tree. Many species do require rooting hormones like Indole-butyric acid (IBA) for good rooting. This rooting hormone is readily available in garden shops.
Some plants even under supposed ideal conditions, and even with added rooting hormones may not form roots. Some of my botany students and I failed after many attempts to successfully root cuttings from a suspected blight-resistant American chestnut located at the corner of Hunter Street and Riverside Drive.
Some years ago, we invited local landowners who were removing wood lots for farming purposes to allow us to come to the wood lot and remove and transfer rare or special plants to other permanent locations. I located a very rare specimen in one such wood lot and transferred it to my back yard for safe- keeping. It was a common spring wild flower known as Rue Anemone. All the reproductive parts of the plant were modified petals. It was sterile. When it was in full flower it was very beautiful with numerous white petal-like structures and very fragile ferny leaves. We were studying how to clone the plant when we sadly discovered that someone had removed it without any trace. There went my fortune!
It is a guiding principle that when any kind of rare or unusual plant or desirable fruit or flower is found, the safest way and perhaps the only way in some cases to reproduce it is by cloning techniques.
A new delightful rose may be bred or discovered that can only be faithfully reproduced by grafting buds or stems from that plant onto other rootstock.
A Golden Delicious apple was discovered many years ago in Clay County, West Virginia. It was apparently a cross between Grimes Golden and another variety whose name I can’t remember. The owner of that orchard recognized the potential value of the cross. It sold that apple tree to Stark Fruit Company. All of the present Golden Delicious apples are from that original stock. It has been cloned by grafting onto other root stock. If a Golden Delicious tree, produces seeds, even though both the male and female gametes are from that same tree, those seeds would not produce the Golden Delicious trees, but would produce many variations of a tree similar to a Golden Delicious tree.
So many plants by fortuitous sightings such as Naval Oranges, are with us today because plants contain parenchyma cells, which make it possible to clone exact copies. We can now buy thousands of plants of a desired type, all of which are exact copies and all of which may have originated from the parenchyma cells from one plant.
– Percy