Most people are familiar with the unappetizing browning of apples shortly after they’re cut or bitten into. The good news is that molecular biologists have devised a clever way to prevent it. The bad news is that organizations that represent apple growers are implacably opposed to the improved fruit.
And therein lies a cautionary tale.
The biology of apples is complicated but fascinating. Almost all commercial apple varieties are grafted onto hardy root stocks that have dwarfing genes to keep the trees on apple plantations short and easier to harvest. Therefore, the DNA of the roots is different from the DNA of the fruit tree.
Apples’ blossoms are self-incompatible with respect to fertilization so they must be cross-pollinated by insects (primarily bees) in order to develop fruit. Special pollinating trees are found in most orchards as a source of pollen for the fruit tree blossoms. These pollinating trees (often crab apples) have still different DNA. Once the pollen fertilizes the apple blossom the fruit can develop.
The pollen DNA mixes with the flower ovum DNA and the resulting hybrid seed embryo grows and produces a hormone that directs other parts of the flower (which contains only flower DNA) to develop into the fruit. Thus, the DNA in the fruit itself is different from the DNA in the seeds.
This difference in DNA between the fruit and the seeds is why different varieties of apples can be grown in close proximity and yet maintain their differences. Because the DNA in the fruit is only from the flower, not the pollen, Granny Smith apples growing next to Golden Delicious growing next to Red Delicious all produce apples with their own unique DNA.
A Canadian company has petitioned both the U.S. and Canadian federal regulatory authorities to permit the sale of a new variety called Arctic® Apple that contains a commercially significant trait. It is highly resistant to the unappetizing browning that occurs when an apple is cut or bruised. The biology that made this possible is elegant and intriguing.
Enzymatic browning is caused by the apple’s chemical reaction to cell injury, such as when the fruit is bitten or sliced, which ruptures the cells and triggers a chemical reaction between an enzyme called polyphenol oxidase (PPO) and chemicals in the apple that cause the apple flesh to turn brown. A family of four genes controls the majority of PPO production, so scientists turned off those genes—and lo and behold, Arctic Apples don’t manifest enzymatic browning.
Ordinarily, this development of another new apple variety would be a nonevent—except, perhaps, for apple growers and retailers who would, one would expect, relish a new product with additional appeal to consumers—but the seeds of discontent have sprouted: Because the shutoff of the four genes was done with recombinant DNA technology, there have been objections and consternation.
Simply because this highly precise and predictable methodology was used, some apple growers are worried that this new variety could constitute a threat to other apple crops. The U.S. Apple Association (USApple), the industry’s trade group, says that it “supports advancements from technology and genetics and genomics research,” and that “benefits can include attributes such as quality…”—which would certainly include nonbrowning apples—but, paradoxically, USApple has also come out firmly against the introduction of the Arctic Apple.
USApple has emphasized that its objections are “not based on any concern about human health and safety,” but “consumers like their apples and are not calling for these new ‘nonbrowning’ cultivars.” How lame. Are consumers clamoring for apple cultivars that are more resistant to predation by insects, viruses, or fungi?
There are several reasons why their concerns are unfounded.
First, as described, farmers and plant breeders have been creating new varieties of apples for millennia. The new molecular techniques for accomplishing this are far more precise, predictable, and conservative.
Second, there is vast experience in both cultivation and in our diets with recombinant DNA-modified varieties of various crops. Farmers in three dozen countries have cumulatively cultivated more than 1.25 billion hectares (about 3.75 billion acres) of them, and North Americans alone have consumed more than 3 trillion servings of food or ingredients from recombinant DNA-modified plants. There has never been a single documented case of disruption of an ecosystem or harm to a person.
Extensive global scientific research has identified no unique health risks associated with recombinant DNA-modified crops or food, and the apple growers associations (except perhaps the organic growers, who often seem to reside in a parallel universe) have no concerns about the safety of this nonbrowning apple.