Ribulose diphosphate carboxylase (Rubisco) is a key enzyme in the dark fixation of CO2 Modification of Rubisco to reduce photorespiration (Osmond 1981) by elimination of oxygenase activity would increase-the C02 fixation rate. The enzyme has two sub units and is known to be coded by seven genes. If these genes could be altered, resulting in the changed Rubisco, it will increase the photosynthetic efficiency.
(d) Nitrogen fixation:
The roots of leguminous plants normally possess nitrogen fixing nodules, induced by various strains of Rhizobiumm. As a result; leguminous plants require little or no nitrogen fertilizer.
Arable crops require about 100 kg of nitrogen per hectare. If this can be replaced by N2 fixing genes, it would lead to a lot of saving in terms of fertilizer cost. Nitrogen fixation is catalyzed by the ATP dependent electron reduction of dinitrogen to ammonia by nitrogenase. If it is possible to introduce the gene to higher plants, it would bring about a revolution in agriculture.
This may be achieved by one of the following ways. 1. Transfer of nitrogen fixing gene (nif) from the living bacteria like Klebsiella, Azatobacter etc., to higher plants.
This would enable the plants to fix the N2 directly. This is still in the experimental stage, as the nitrogenase, produced by the nif gene, is highly oxygen Habile and gets degraded in higher organisms. 2. Expansion of host range of symbiosis to crops other than legumes.
At present non leguminous plants do not have symbiosis with Rhizobium. If it is possible to expand the host range for the bacteria, a lot more plants will have the capacity of N2 fixation. 3. Increasing the efficiency of symbiotic bacteria to N2 fixation. By gene manipulation, it may be possible to increase the N2 fixing capacity of the symbiotic bacteria, which will benefit the plants.
(e) Herbicide resistance, disease resistance etc:
By gene manipulation, it will be possible to introduce this character into plants. In conclusion it may be said, that genetic engineering is a highly potential tool by which man can alter the macromolecule of inheritance and thereby change the biological environment to his choice. But the new technique has to be used judiciously; otherwise it can also create untold harm to human society, if unscrupulous scientists use it to create destructive genes. A few of the specific applications of genetic engineering are discussed below in some detail.