'Stressed' tomatoes hold key to a healthy old age

Scientists at the John Innes Centre​ (JIC) and Institute of Food Research (IFR)​ in Norwich identified the gene - HQT - as the producer of the antioxidant chlorogenic acid (CGA).

By increasing the activity of HQT, CGA levels in the tomato fruits were lifted, helping to protect them against attack from bacterial disease. CGA could also protect humans eating the tomatoes against degenerative, age-related diseases, the scientists purport.

"CGA is the main polyphenol in this category in tomatoes. Now we have identified the gene for the enzyme that produces it, we can look for genes that produce similar compounds in other plants, with benefits for agriculture and for human nutrition,"​said Dr Tony Michael, project deader at IFR.

"For us the excitement is that this adds to our understanding of how plants naturally protect themselves against stress and diseases, but in the long term it may be that this discovery leads to fruits that are better for us,"​ added Dr Cathie Martin, project leader at JIC.

Tomatoes are known to contain the health-boosting antioxidant lycopene, a carotenoid that has attracted significant attention in recent years as it has been linked in some research to reduced risk for cancers, especially prostate cancer. New findings also suggest that it could have a protective effect on heart disease, the cause of more deaths among women than any other disease.

The lycopene market is expanding significantly, with growth rates forecast at over 100 per cent in a recent report on the carotenoids market from Frost & Sullivan. The report values the ingredient at $34 million in 2003, and with growing demand, new sources of the nutrient will attempt to lift this figure further.

Having unveiled the biochemical pathway that plants use to make CGA the UK scientsts were able to isolate one of the key genes (called HQT) for making CGA. When they suppressed the activity of the HQT gene (using gene silencing) they found that CGA levels in developing tomato fruits fell. The reverse happened when they increased the activity of HQT.

Antioxidants are important compounds that help protect plants and animals against the effects that stress (from disease or the environment) has on their biology and a wide range of chemicals has antioxidant properties.

Some of the most important are phenol compounds, such as chlorogenic acid, which accumulates to high levels in some plants. In plants where CGA production is reduced, the cells in the mature leaves die more quickly than when CGA is present. In animals CGA has a high bioavailability - meaning it is readily absorbed and used by the body.

To test whether higher levels of CGA gave added protection, the scientists infected the high CGA tomatoes with bacteria that cause tomato blight (Pseudomonas syringae​). In the high CGA plants the effect and spread of the disease was significantly less than in the unmodified plants.

Similarly, when the plants were tested for resistance to oxidative stress the high CGA plants were more resistant to stress damage than the unmodified plants.

Full findings of the UK study are published online in Nature Biotechnology​ and in the June 2004 hard copy of the journal.