By decreasing the expression of two genes encoding enzymes that regulate the fatty acid composition, the level of the healthy fatty acid (oleic acid) in the oil of the field cress seeds was increased from 11 to 84 percent. At the same time the unhealthy erucic acid was reduced from 20 percent down to 0.1 percent. The linolenic acid was decreased from 40 percent to 2.6 percent. Linolenic acid is a healthy polyunsaturated fatty acid, but it is unstable at high temperatures.
– This improved oil is suitable for food processing now, especially for frying, says Li-Hua Zhu, professor in plant breeding and biotechnology at SLU, who leads this research project.
She explains that we need to produce more oil from plants – to replace the fossil oil used, for instance, in the chemical industry, and to get more healthy oils for human consumption. There is no oil crop that could tolerate the cold winters in the north of Sweden today, but the field cress, after being completely domesticated, could be cultivated throughout Sweden, and other parts of the world as well in the future.
Field cress has the potential to become a crop that would be excellent in several respects. It is a biennial plant and can function as a catch or cover crop – it ”catches” the nutrient fertilizers from the field or cover the field during the winter when the arable land would otherwise be bare. Field cress can be cultivated together with for example barley or wheat. The plant has around 20 percent seed oil, but the oil quality in the wild type field cress is not useful for food consumption due to its high level of erucic acid.
Emelie Ivarson is a PhD-student in the research project.
– The field cress has a relatively high content of oil in the seeds, but the composition of fatty acids in the oil of the wild field cress is not suitable as foodstuff. Therefore, we have altered the oil composition, Emelie Ivarson explains.
The study shows the possibility to use the field cress for genetic engineering of oils as tailor-made for various end uses. Since fossil oil is environmentally non-sustainable and resources are depleting, it would be great if we could produce more plant oils for different purposes in our fields.
To develop the field cress into an economically viable crop, the researchers are now attempting to increase the oil content from 20 percent to levels around 30 percent. Winter oilseed rape is the major oilseed crop in Sweden and contains more than 40 percent seed oil, but it is only cultivated in southern Sweden due to its weak winter hardiness.
Ivarsson, E., Ahlman A., Lager I., & Zhu, L-H. 2016. Significant increase of oleic acid level in the wild species Lepidium campestre through direct gene silencing. Plant Cell Reports 35: 2055-2063
Researchers at SLU in Alnarp have developed lines of the plant species field cress (Lepidium campestre) that have a special trait – they produce wax esters in their seeds. The field cress got this trait when the researchers introduced three genes into its genome from another plant, jojoba (Simmondsia chinensis), known for having valuable wax esters in its seed oil.
Oils containing wax esters work very well as lubricating oils in the industry. Jojoba oil is also a popular ingredient in cosmetics. Jojoba is a perennial desert shrub that produces low seed yields, therefore the natural sources of plant-derived wax esters are limited and the oil is expensive. It is possible to produce wax esters synthetically, out of fossil oil, but this alternative is also expensive and results in poorer oil quality. Developing a new crop, like field cress, into a new industrial oil crop for wax ester production would be an interesting way to increase the supply. Unlike other oil crops, such as oilseed rape, field cress thrives in northern Sweden. So wax esters could become a new production branch for farmers in the north of Sweden in the future.
The researchers at SLU in Alnarp did this study in collaboration with researchers from Germany and the United States. The results indicate that it is indeed possible to produce wax esters in field cress, and the analysis also show what types of wax esters can be produced in the plant. Different wax esters have different properties depending on how long carbon chains of the molecules have and how unsaturated they are. Medium-length, monounsaturated chains are more stable against oxidation and have the best properties for lubricating purposes.
Ivarson E., Iven T., Sturtevant D., Ahlman A., Cai Y., Chapman K., Feussner I., & Zhu L-H. 2017. Production of wax esters in the wild oil species Lepidium campestre. Industrial Crops & Products 108: 535–542
Researchers have found variants of thirty important genes in the genome of the oilseed plant field cress (Lepidium campestre) and its relatives. Those genes determine for example the time of flowering, oil quality, and how easily the seeds fall of the plant when mature. The researchers will be using this knowledge to choose the right plants in the domestication of the wild plant.
The project to tame the field cress has been running for about 20 years at SLU. This plant would be suitable for our northern fields in Sweden. As a biennial oil crop, field cress could function as a catch crop as well, by taking up the nutrients in the soil that otherwise would leak out into the lakes and oceans. But the plant has a couple of ”wild” traits that are not fit for cropping, and it is the variation in those that the researchers have identified.
The interesting variation was found both within the field cress species and between species belonging to the genus Lepidium. The idea is that this knowledge about the genetic variation can help to speed up the domestication of the oilseed crop. The identification of this variation in the genes also reveals something about how the species within the genus Lepidium have changed during the evolution. Field cress is more closely related to Smith’s pepperwort (Lepidium heterophyllum)than to the pepperwort Lepidium hirtum.
– We studied the closely related pepperworts Lepidium heterophyllum and Lepidium hirtum in order to exploit some of their good qualities by crossing them with field cress, explains Cecilia Gustafsson, one of the researchers behind the study.
Field cress is also fairly closely related to the model plant thale cress (Arabidopsis thaliana), a species that is very well studied in terms of which genes that controls different traits. This was something that the researchers could make use of. They looked for genes in field cress that was similar to known genes in thale cress, and thereby they could identify the genes for venalization, florescence, pod shattering and quantity and quality of oil.
Gustafsson, C., Willforss, J., Lopes-Pinto, F., Ortiz, R. & Geleta, M. 2018. Identification of genes regulating traits targeted for domestication of field cress (Lepidium campestre) as a biennial and perennial oilseed crop. BMC Genetics 19:36 doi: 10.1186/s12863-018-0624-9
After extracting the oil from the field cress seeds, a protein-rich seed cake remains. The researchers thought that, just as with the rapeseed cake, you should be able to use the field cress seed cake as animal feed.
But first it is important to find out if this seed cake appeal to the animals’ taste buds and how it affects their health. In a pilot study, researchers at SLU in Ultuna mixed four, eight and twelve percent seed cake from field cress into a common cereal-based feed and gave it to growing pigs. It turned out that the pigs liked their new diet. The researchers did not want to give the pigs a higher proportion of field cress than twelve percent because in its wild form the plant contains relatively high amount of unhealthy glucosinolates.
The field cress seed cake also contains relatively high levels of insoluble fiber. This, together with the glucosinolate content, was found to result in a somewhat lower digestibility (how much of the nutrition the pig actually utilize) among the pigs eating the seed cake, but otherwise the researchers did not see any negative health effects of the new feed.
Because the digestibility of the field cress feed was lower among the young growing pigs, the researchers suggests that the field cress seedcake should perhaps be given to adult sows and ruminant animals, in which the slightly reduced digestion is less important. In any case until the scientists who domesticate the crop have managed to lower the glucosinolates.
One of the breeding goals is thus to reduce the content of glucosinolates in the seeds of the new crop. To succeed in this, the researchers at Alnarp is trying to stop the transport of the glucosinolates to the seeds, that is, to inhibit or eliminate the mechanism that controls the transport of the unhealthy substances into the seeds.
Arefaine, H., Rydhmer, L., Andersson, R., & Ivarsson, E. 2019. Lepidium cake as a feedstuff for pigs. Livestock Science 225:47-52
Arefaine, Hagos, 2016. Lepidium cake as a feed stuff to pigs.