Genetic variations in plants have been made possible through many conventional methods since many years. The biotechnological approach for the desired plant was achieved by genetic engineering. Transgenes refers to gene or genes which are not native of an organism and are introduced by many methods. Transgenic plants refer to plants having one or more transgenes. This technique of involving plants to produce various chemical commodities and pharmaceuticals is known as phytofermentation.
A variety of biochemicals such as proteins, lipids and carbohydrates are obtained from plants. Production of transgenic plants has resulted in generating modified biochemical production in plants.
A reasonable amount of interest has been developed in the field of bioplastic as a result of increased concern about non degradability of plastics and environmental hazards. Bioplastic have been known to be produced by various means including vegetable fats, cornstarch etc
The role of biotechnology in the field of bioplastic has been accounted mainly to the presence of the property of biodegradation by naturally occurring polyhydroxy- alkanoates(PHAs). These are naturally occurring polyesters produced by bacterial fermentation. Polyhydroxybutyrate(PHB) is a form of PHA. It is produced in the bacterial cell as a result of physiological stress in the form of energy storing molecules. These PHAs are metabolized and used up by such bacteria when none of the other forms of energy source is available under conditions of stress. The properties of PHB include non toxic, water insoluble, high oxygen permeability and ultra violet resistance, thermostable and biocompatible.
Bacterial fermentation of Alcaligenes eutrophus produces polyhydroxy alkanoates.
The organism is cultured under normal conditions to attain stable growth. The conditions of the medium are then altered so that the bacterium induces production of PHA. This is usually induced in deficiency conditions of macro elements, oxygen etc or due to the excess presence of carbon sources in the medium. Acetyl-coA serves as a precursor in the production of polyhydroxy alkanotaes. The microbial fermentation of Alcaligenes for the production of PHAs is not favourable as the yield is very low. The cost involved in such mechanisms is substantially higher.
Though plants do not produce PHB naturally, they can be programmed to do so. For the production of PHBs by genetic engineering, the two genes involved in the production of enzymes namely, aceto-acetyl-CoA reductase (phbB) and PHB synthase (phbC) are isolated. These two enzymes are pivotal in the PHB synthesis from its precursor. The genes responsible are transferred and expressed in Arabidopsis thaliana plant. These two genes are so targeted so that they are expressed in plastids of plant. The PHB gets accumulated in leaves and can be extracted easily.
Thus synthesis of polyhydroxyl butyrate is a classic example of application of biotechnology in the production of goods of commercial value. Transgenic trees producing phbB and phbC are also produced where the PHB are synthesised in the leaves which can be extracted. Studies shows that plant produce PHB 20 -40% of their dry mass.
This method of production involves many advantages like;
(i) Upstream production (the production of biomass from which the biochemical has to be isolated) costs are much lower than microbial fermentation.
(ii) The post translation modification system of proteins in a plant cell is as advanced as in the animal cell. As a result the PHB which is formed undergo appropriate modification so that when extracted they do not require any further modification.
(iii) The plant seeds of transgenic plants can be stored and transported easily. These seeds could be used to produce transgenic plants to synthesize bioplastic when required.
(iv) Since animal system is not used, it does not face any concerns regarding to ethical issues.
(i) The production levels do not rise to the expected levels.
(ii) The increased level of trangenes in a plant genome results in accumulation of transgenic product. This can effect the plant growth and stability.
Several studies involving production of PHB in corn, potato etc has been initiated. Transgenic tobacco plants have also been extensively studied for PHB production. It is also estimated that potatoes can be a good source of PHB production from which PHB can be easily obtained and the resulting yield is also proposed to be higher is such ‘plastic potatoes’. If successful, it will be he most cost effective method involved.