G01015: Food safety implications of secondary metabolites produced in response to biotic and abiotic stress by genetically modified potatoes

Study Duration: June 1999 to October 2002

Contractor: National Institute of Agricultural Botany

This project is studying the effect that transgenes have on the production of secondary metabolites by potatoes when they are placed under a series of biotic and abiotic stresses.

The populations of potatoes being studied include potatoes with one transgene, potatoes with two stacked transgenes, and control potatoes (some of which have undergone the transformation process but do not contain a transgene). The project aims to find out if the presence of transgenes effects the production of secondary metabolites such as glycoalkaloids and sesquiterpenoids during stress resulting from pathogenic attacks from an array of pathogens, as well as from environmental factors such as drought.

Genetic manipulation of carbohydrate metabolism and pathogen resistance may lead to changes in the profile of plant defence compounds in the organs of potato plants, including tubers. Reasons for this are unclear, but include direct effects due to changes in the sugar pool and/or indirect effects due to changes in susceptibility of the plants to infection/infestation. The effects of genetically transforming potatoes on levels of toxic metabolites were assessed using different combinations of transgenes and a range of biological and non-biological stresses. In most cases, effects resulting from external stresses were greater than differences between gentically modified (GM) and non-GM plants. The results support the need to assess transgenes and GM crops on a case by case basis as part of the mandatory pre-market assessment.

In this project lines of potatoes with one transgene (either antisense invertase or maize-RIP), two stacked transgenes (both antisense invertase and maize-RIP) and controls (potatoes which have undergone the transformation process but do not contain transgenes), were selected. These lines were then exposed to biotic and abiotic stresses such as blight, potato leaf roll virus, slugs and mechanical damage, in order to determine the effects of genetically transforming potatoes on levels of glycoalkaloids and sesquiterpenes (toxic metabolites that function as plant defense compounds).

A consistent pattern was observed in the antisense invertase material, which tended to have lower potato glycoalkaloid (PGA) levels than non-GM controls. The maize-RIP lines were less consistent, being either unchanged or having elevated levels of PGAs and sesquiterpenes in some lines. Few conclusions can be drawn about the behaviour of the stacked lines due to the limited number generated.

Tuber blight, gangrene and Erwinia sp. (wet rot) were stresses that were most likely to lead to differences between the various lines.

Differences observed between the various GM and non-GM lines were in most cases smaller than effects caused by stress alone. Tuber blight, gangrene and Erwinia sp. infection generally led to elevated levels of PGAs compared to the uninfected material. In some instances the observed levels of PGAs in infected material were more than three times acceptable levels.

Antisense invertase lines

Glycoalkaloid levels: All GM antisense invertase lines had significantly lower levels of PGAs than non-GM controls following infection with Erwinia sp. There were no differences observed between the GM antisense invertase and non-GM lines following the other stresses. Another effect was that when potatoes (GM or non-GM) were subjected to tuber blight, gangrene, physical damage or slug infestation, the levels of PGAs were significantly higher than in the unstressed material.

Sesquiterpene levels: Significant differences in sesquiterpene levels between antisense invertase and control material were only observed in material infected with gangrene, where two of the GM lines showed increased levels of these compounds compared to the non-GM controls. In addition where GM and non-GM plants were subjected to gangrene, Erwinia sp. or tuber blight, significantly higher levels of sesquiterpene levels were observed in infected material in comparison to the uninfected controls.

Maize-RIP/stacked lines

Glycoalkaloid levels: Lines transformed with the maize-RIP constructs were less consistent in their response to stress than the antisense invertase lines. Whilst most showed no significant differences from the controls for most treatments, several GM lines showed elevated PGA levels in response to gangrene and tuber blight. Again material infected with gangrene and tuber blight contained higher levels of PGAs than uninfected material regardless of its GM status.

Sesquiterpene levels: Significant differences in sesquiterpine levels were observed between GM and non-GM material following gangrene infection, with a number of GM lines having elevated levels of these compounds. Material infected with gangrene had significantly higher levels of sesquiterpenes as compared to uninfected material regardless of its GM status.

This study suggests that it is possible that genetic manipulation of carbohydrate metabolism and pathogen resistance can lead to changes in the profile of plant defence compounds present in the organs of potato plants including tubers. The direction of this change depends on the transgene used. The mechanisms behind the changes observed are not clear but may include direct effects due to changes in the sugar pool and/or indirect effects on the susceptibility of the plants to infection and infestation.

The potato plants used in this project were all experimental lines. No GM potatoes have been approved for commercial cultivation or food use in the EU. However, the findings of this project show that it is essential for the regulatory process to consider each GM potato line as an individual entity in any pre-market assessment.

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk