Future onions leave the crying behind

For many, chopping onions is one of the cruelest cooking tasks due to the onion-induced tears. A New Zealand scientist has unlocked the key that is expected to bring tearless onions to market within a decade.

When an onion is sliced, it releases lachrymatory factor, which kicks off a crying jag for many people. About six years ago, Japanese researchers discovered the responsible gene, and using a technology developed in Australia, New Zealand’s Dr. Colin Eady has discovered a way to turn off that gene.

Pinpointing the cause

Until the group led by Shinsuke Imai at Japan’s House Foods Corporation isolated the lachrymatory factor synthase gene, the enzyme allinase was blamed for onions’ irritating effects. With that knowledge in hand, Eady and his team at the New Zealand Institute for Crop and Food Research in Christchurch applied a gene-silencing technology called RNAi, which was developed by Dr. Peter Waterhouse. Eady says that allowed him to reprogram the onion’s natural regulation system.

In general, onion is hard for scientists to work with because it has a large genome, slow generation time and little tolerance for adaptation. Eady selected Allium as a more researcher-friendly genus, and his study is thought to be the first gene silencing in the Allium genus. Previous work had focused on calibrating certain enzymes to enhance desirable traits and minimize the unwanted properties. An example is the Vidalia onion, which puts little or no stress on the eye. This variety was created by minimizing sulfur, which decreased the vegetable’s pungent aroma and taste, and positive health benefits.

Eady set out to make an impact on both the valued and undesirable properties. He wanted to reduce lachrymatory factor synthase (LFS) and prevent 1-propenyl sulfenic acid’s convertsion to lachrymatory factor (LF), putting an end to tears and enhancing the flavorful and healthful qualities. His theory was that this change would lead to the 1-propenyl sulfenic acid generating into thiosulfinate and thiosulfinate-derived sulfur compounds, the substances responsible for the desired pungency.

Studies proved Eady’s hypothesis, with LFS decreased by up to 1,544 times and sulfur compounds increased. These modifications make the new onion more akin to garlic, potentially yielding vegetables with enhanced health benefits.

Bumps along the road

One difficulty with ultimately bringing a tearless onion to market is the nature of the system used to silence the LFS gene. It is considered genetic engineering, requiring Eady to keep the plant under lock and key.

Late last year, New Zealand’s Environmental Risk Management Authority approved the institute’s application to field test genetically modified onions and other members of the Allium family. A test plot of up to 2.5 hectares (about 6 acres) will be established for 10 years.

A limited number of plants can be flowered and those must be confined to sturdy cages with a double layer of fine mesh. Those cages prevent escape of the laboratory-bred flies that will pollinate the onions. Because Alliums are insect-pollinated, the cages will ensure that flies don’t transport pollen to other plants. The insects will be killed before the cages are opened to avoid carrying pollen to other vegetation, a concern raised by neighboring growers. Close monitoring of the test plots by both institute staff and regulatory agencies will be required.

Assuming the trials are successful, the next hurdle will be gauging public acceptance of genetically modified onions. Consumer reaction to other altered foods has been mixed. Eady points out that he anticipates other benefits beyond the tearless quality, and citing the importance of onions as a dietary fiber source in many regions, he wants to ensure varieties into which the property is introduced will be hardy and easy to grow. The genesilencing technique can also aid in battling viruses and diseases, boosting the plant’s viability.

Beyond fiber, onions are loaded with beneficial compounds including thiosulfinates, fructans and flavonoids.

Along with their signature taste and aroma, thiosulfinates give the vegetables the ability to break up blood platelets, helping to prevent clots. Fructans are a type of dietary fiber that reduces the risk of colorectal cancers, and the flavonoids add antioxidant qualities.

U.S. research

Eady isn’t the only researcher trying to solve the onion problem. At the Agricultural Research Service (ARS), University of Wisconsin’s Dr. Michael Havey also attempted ending the vegetable’s adverse effect on eyes. Although it appears that Eady will develop the new form, Havey and other American scientists also are researching and releasing new varieties.

In late 2007, ARS announced three new onion releases. Inbred B8667 A&B relates to the production of red, long-day, well-storing hybrids. Havey developed the line, which is round, dark red with color extending through the internal rings of the bulb, firm, with good scale retention and excellent storage quality when produced on muck soils. B8667B is a F1MSMS2M3 from USDA Plant Introduction 262985 (“Noord Holland Bloodred”) crossed with B5361B (a red inbred developed by the late Dr. C.E. Peterson, but never released). It yielded in the top one-third of commercial and experimental hybrids evaluated over several years at the Kincaid Farm, Palmyra, Wis.

The long-day onion synthetic population Onion Haploid (OH) -1 serves as a responsive control for extraction of gynogenic haploids of onion. Bulbs of this synthetic population are yellow with good storage quality.

The long-day onion synthetic population Sapporo-Ki (SKI) -1 A&B is an open-pollinated population grown on the Japanese island of Hoikkaido. Bulbs of this synthetic population are yellow, early maturing in Wisconsin and have good storage ability.

Havey also is leading a study to better manage two major onion threats, thrips and the thrips-vectored iris yellow spot virus.

Based in Greensboro, N.C., the author writes articles about horticulture, landscaping and agriculture. She has been a contributor to Moose River Media publications for three years.