Nigeria as a country use to be the highest producer of oil palm in the world, just before the period of oil boom in the 70s. I would say we are one of the most blessed countries in the world in terms of natural resources, biodiversity and of course human resources. However, after the discovery of crude oil, things have gone south since then; partly due to the withdrawal of attention on other sector of the economy and partly due to mismanagement and corruption from the government. Agriculture which use to be the mainstay of the Nigerian economy suffered great neglect simply because the crude oil was bringing in a lot of revenue, to the extent that our leaders considered money not to be a problem, but how to spend it is ^^.
The neglect of the agricultural sector made other countries to overtake us in agricultural production. Of particular interest is the oil palm plant which happens to be native to tropical vegetation like ours. A closer look at the oil palm production now sees Indonesia at the top closely followed by Malaysia and my dear country, where oil palm plant is native to is lying at number 5.
Basically, what countries like Indonesia and Malaysia did was to get few oil palm seeds or seedlings from the plant's nativity. History actually has it that Malaysian envoys came to take few seedlings of the oil palm plant from Nigeria and established it in their country. How then were they able to assume the position as the top producers of oil palm ahead of Nigeria? The answer lies in what my today's write-up is based; plant tissue culture.
What is plant tissue culture?
Simply put, plant tissue culture is the technique of generating plants by culturing of plant's organs such as leaves, stems, fruits and so on. Just as micro-organisms are grown on synthetic media under asceptic conditions, plant organs can also be cultured under strict aseptic/sterile conditions to generate what is known as callus or to generate plantlets. The plantlets in this case are clones of the original plant. This method of propagating plants is widely known as micropropagation.
In tissue culture, a small organ of a desired plant can be used to generate thousands or even millions of plant through cloning. It has a host of advantages over propagation of plants from seeds or other asexual method. Exact copies of plant with desirable traits such as sweet fruits, big leaves etc. can be produced without fear of been modified during propagation process. In addition, multiple plants can be produced in the absence of seeds or pollinators to produce fertile seeds. The mehod is useful in testing the outcome of genetic modification of plants, whether succesful or not. Since the method is carried out asceptically, clean stocks are produced at the end of the process thereby limiting the chance of spread of pathogens on the field.
Steps involved in plant tissue culture
Basically, there are four main steps involved in carrying out plant tissue culture. These are;
- Inoculation of the desired plant's organ
- Incubation of inoculated medium
- Sub-culturing
- Tranplantation of plantelets to the field.
Inoculation involves the act of cutting the parts of the tissue from which plantlets are to be generated and placing such on a previously prepared growth medium. The part of the plant being inoculated is generally referred to as explant. Like I said earlier, the whole process must be under asceptic conditions. Therefore the portion of tissue to be inoculated must be disinfected using appropriate medium before being excised for inoculation. The whole process is usually done under the hood of the lamina flow in the laboratory.
The medium to be used for inoculation depends on the plant. The necessary conditions for optimum growth and morphogenesis may vary from plant to plant. However, tissue culture media should generally contain the following in addition to specific plant requirement; macro and micronutrients, vitamins, nitrogen-based supplements, carbon source, organic supplements, plant growth regulators and solidifying agents in form of agar, agarose or gellan plum. The compositions are mixed according to pre-determined proportion and then sterilized in an autoclave after which it is poured in the petri dish and allowed to set/solidify before inoculation the tissue is made.
After inoculation, the culture is then incubated in a culture room or in an incubator designed for such purpose. Depending on the specific requirement of the plant, conditions such as temperature, humidity, light and some other conditions might need to be altered to achieve the desired result. However, extreme conditions can cause the medium to dry up or water-logged or even cause the death of the plant tissue itself.
Did I forget to state it that plant tissue culture can be done to generate callus or plantlets? No, I did not. To explain it further, when tissue culture is done to specifically generate callus to detect the expression of genes that have been introduced into the plant through genetic manipulations, it is called callus culture. The manipulation of the two plant hormones, auxin/cytokinin ratio defines the kind of morphogenesis that would take place. A high auxins to cytokinins in the medium will lead to embryogenesis, callus initiation, and root initiation while a low auxin/cytokinnin ratio would favour axillary and shoot proliferation.
Hence, if the focus is to generate plantlets from the tissue culture, the initial medium is first enriched with high auxin/cytokinnin ratio to initiate root formation in the growing cells after which the entire cell is asceptically sub-cultured unto a fresh medium with high cytokinnin/auxin ratio to initiate shoot formation. Thereafter, the plantlets generated are carefully transferred into the field and closely monitored till they are full established. It is advisable to first transplant them to an environment where abiotic conditions can be controlled to suit the growth requirement of the plantlets in order for them to get acclimatized before being transferred to natural field.
Tissue culture and genetically modified plants
Tissue culture is quite important for analysis of genetically modified plants. Plants are genetically modified by introducing foreign deoxyribonucleic acid carrying some specific traits into the genome or genetic composition of the plant. The introduction of the DNA can be done in several ways including;
- Gene gun or particle bombardment
- lipofection
- electroporation
- Ti-plasmid mediated transfection
- direct injection of naked ssDNA by microinjection
Gene gun or particle bombardment involve using the DNA containing the desired traits to be introduced to coat the surface of small metal particles and bombarding the cells of the plant with the DNA containing particles. Lipofection, also known as liposome transfection involves the injection of DNA with the desire genes into the cells of the plant through the liposome. The liposome is quite functional for the purpose because it is made up of phospholipid bilayer, hence, it can easily merge with the cell membrane because of their chemical similarity.
Electroporation method involves the application of electrical field to the cells of the plant in order to make them more permeable to the introduction of the DNA fragments containing the desired genes. The Ti-plasmid mediated method of DNA introduction involves the use of organisms such as viruses and bacteria which tranfer their small circular DNA (plasmids) into host cells as normal part of their life cycle. The DNA containing the gene of interest is tranfered into the genome of the organisms which eventually becomes incorporated into the genome. The genome of the organism which now contains the new DNA is then transferred into the genome of the cells of the plants. The most common organism used by scientist for this purpose is Agrobacterium tumefaciens.
On some rare occassions, the process of DNA transfer into cells to generate genetically modified cells for tissue culture can actually hapen in nature. Example of this is found in sweet potato, Ipoemea batatas which contain DNA sequences that were transferred by Agrobacterium bacteria thousands of years ago.
After successful incorporation of the DNA containing the desired genes into the cells of the plant, there is need to test if the traits will be expressed in the cells of plants in which they were introduced. This is dues to the fact that the DNA sequence containing the desired gene is randomly inserted into the genome of the cells of the plant and may or may not end up expressing the desired traits. Therefore, the genetically modified cells are cultured asceptically using the plant tissue culture method to either generate culture or plantlets by modification of auxin/cytokinnin ratio in the culture medium. The generated callus is tested for the presence of specific proteins encoding the genes introduced while the plantlets can be grown on the field and observed for the desired traits.
In conclusion
So basically, the Malaysian envoys came to my dear country and, took few seedlings of oil palm plant and used the technological advancement in form of plant tissue culture to produce millions of plantlets and plant them on a large scale to produce palm oil. All these happened while the Nigerian leaders were busy with money from crude oil, neglecting agriculture in the process. The result? Malaysia is now one of the highest producers of palm oil and Nigeria is lavishing some ways behind. I am just a common scientist, not a politician.
Thank you for reading.
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