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ozy ness
04-29-08, 12:17 PM
Using Genetic Engineering to Accomplish What Nature Already Does
Polyphenol oxidase (PPO) is an enzyme that plays a role in triggering a plant's defense mechanisms against sucking and chewing insects and plant diseases. It also controls the browning process in many fruits. Given the role of PPO in keeping plants healthy, scientists have for years looked for ways to increase the expression of PPO.

Breeders have often selected for varieties with enhanced disease and insect resistance by monitoring PPO levels.

In 2005 a team of Spanish scientists showed that organic grape production doubled the activity of PPO in grapes, linking the increase to the need for the organic vines to combat various bacterial and viral pathogens (Nunez-Delicado et al., 2005).

In 2008 scientists have genetically engineered (GE) tomato plants to force them to over-express PPO by a factor of 1.5 to 7.3-fold, offering the promise of improved resistance to insects and pathogens (Mahanil et al., 2008).

The differences in these two approaches to achieve the same goal are notable. The 2-X increase in PPO in organic grapes was achieved by creating a healthier, more balanced cropping environment, and letting plants rely on their own genetic potential in combating pests. Faced with the need to limit pest damage, the plants increased PPO levels on their own and at no added cost to the farmer.

But with the GE-tomatoes, the 1.5-X to 7.3-X increase in PPO comes at a considerable cost to the integrity of the plant's genome, and is triggered whether the plant needs to defend itself or not. Plus, it is very unlikely farmers will be able to buy tomato seeds genetically engineered to over-produce PPO at the same cost of conventional seeds.

One of the pillars of Integrated Pest Management is to save the big guns for when they are really needed. Engineering plants to continuously express an enzyme like PPO, regardless of need, makes as much sense as keeping one's foot on the gas pedal when the need arises to apply the brake.

Sources: E. Nunez-Delicado et al., "Effect of Organic Farming Practices on the Level of Latent Polyphenol Oxidase in Grapes," Journal of Food Science, Vol. 70, No. 1, 2005
S. Mahanil et al., "Overexpression of tomato polyphenol oxidase increases resistance to common cutworm," Plant Science, Vol. 174, No. 4, April 2008

PPARGammaGirl
04-30-08, 08:41 PM
Arrogant science thinks it trumps nature when it really doesn't.