Photosynthesis is a key natural process utilized by plants and is necessary for proper plant growth. Specifically, photosynthesis uses light to manufacture chemical compounds, including organic compounds—primarily carbohydrates—that are derived from carbon dioxide and a hydrogen source (such as water), most often with simultaneous liberation of oxygen. However, photosynthesis is relatively inefficient, and only a small portion of the available light is actually used to produce carbohydrates. Thus, scientists and farmers have been interested in enhancing the efficiency of photosynthesis, and thereby plant growth, through a variety of genetic engineering techniques. If these methods prove successful and safe, they could boost agricultural production and yield of some of the world's most important plants, including numerous food crops. See also: Agricultural science (plant); Biotechnology; Carbohydrate; Farm crops; Food; Genetic engineering; Genetically engineered plants; Genetically modified crops; Genetically modified organism (GMO); Genetics; Photosynthesis; Plant; Plant growth; Plant physiology
By employing genetic methodologies in tobacco (genus Nicotinia), researchers have modified one particularly inefficient operation, termed photorespiration, which occurs in many plants during photosynthesis. The results of this genetic manipulation have been remarkable, and the genetically altered tobacco plants increased their growth by more than 40% and added about 25% more biomass compared to unmodified wild-type tobacco plants. The genetically reprogrammed plants grew faster as well. See also: Biomass; Photorespiration; Tobacco
Photorespiration involves the fixation of oxygen (instead of carbon dioxide) during photosynthesis. When the reactions of photosynthesis use oxygen instead of carbon dioxide, a toxic compound called glycolate is formed, and carbon is lost from the photosynthetic pathway; this loss of carbon is directly responsible for much of the reduction (by 20–50%) in photosynthetic efficiency. Moreover, because the glycolate inhibits photosynthesis when allowed to accumulate in the plant, it must be removed. The reactions of photorespiration that break down the glycolate in the plant occur in multiple cell compartments, and the steps involved in these reactions require costly energy, further reducing the efficiency of photosynthesis. See also: Carbon dioxide; Oxygen; Toxicology
To conserve the amount of energy that is required to remove the toxic glycolate, researchers have altered the genetic makeup of tobacco plants. In particular, investigators inserted new genetic elements (derived from algae and pumpkin DNA) that contained alternate genetic information confining the glycolate to only one cell compartment (as opposed to passing through many cell compartments), where it would be transformed into useful carbon compounds. With the dramatic improvements in tobacco crop yields as a result of simplifying the metabolic breakdown of glycolate in field trials, scientists believe that they will be able to attain similar results in other important crops, including wheat, soybeans, potatoes, cowpeas, and rice. Still, it remains to be determined if these improvements in photosynthesis efficiency and growth will persist across plant generations, and if any of the genetically induced changes affect other physiological processes, such as the plant's ability to withstand certain stressors (for example, drought). See also: Deoxyribonucleic acid (DNA); Plant metabolism
