About Erysimum cheiranthoides L.
Erysimum cheiranthoides L. is an annual herbaceous plant that visually resembles many other mustard species. It grows an erect stem between 15 and 100 cm (5.9 to 39.4 in) tall, rarely reaching 150 cm. Its leaves are lanceolate to elliptic, measuring 2 to 11 cm long and 0.5 to 1 cm across, with margins ranging from smooth to coarsely toothed. It blooms in summer, between June and August. Its flowers are bright yellow, 5 to 12 mm in diameter, and arranged in an erect inflorescence. After blooming, it produces a slender cylindrical capsule 1 to 3 cm long, rarely reaching 5 cm, that holds several small pale brown or dark brown seeds. This species is native to temperate regions of Europe and Asia. Within its native Asian range, it occurs in China’s Heilongjiang, Jilin, Nei Monggol, and Xinjiang provinces, as well as Japan, Korea, Mongolia, and Siberia. In Europe, it is native to Eastern Europe (Belarus, Estonia, Latvia, Lithuania, Moldova, and Ukraine), Central Europe (Austria, Belgium, the Czech Republic, Germany, Hungary, the Netherlands, Poland, Slovakia, and Switzerland), Northern Europe (Denmark, Finland, Norway, Sweden, and the United Kingdom), and Southeastern Europe (Bosnia and Herzegovina, Bulgaria, Croatia, France, Romania, Serbia, and Slovenia). It is also widely naturalized outside of its native range, occurring in New Zealand, additional parts of Europe, North America including parts of Canada, and Tierra del Fuego, Argentina. It grows in disturbed areas, fields, and dry stream beds, and is typically found at altitudes from 0 to 3,000 m (0 to 9,843 ft) above sea level. Like other species in the genus Erysimum, E. cheiranthoides produces two main classes of defensive chemicals to protect against herbivory: glucosinolates, which are characteristic of the mustard family Brassicaceae, and cardiac glycosides called cardenolides, a compound class produced by at least twelve different plant families. The glucosinolates found in this species include glucoiberin, glucoerucin, glucocheirolin, and glucoiberverin. Cardenolides detected in E. cheiranthoides seeds include strophanthidin, digitoxigenin, cannogenol, erychroside, erysimoside, erycordin, cheiranthoside, glucoerysimoside, and glucodigifucoside. Grafting experiments and genetic crosses show that cardenolides are produced in the species’ leaves and then transported to other plant tissues. Some specialist insect herbivores that feed exclusively on crucifers do not readily feed or oviposit on E. cheiranthoides. The orange tip butterfly Anthocharis cardamines, which normally oviposits on almost all crucifer species, avoids this plant. Similarly, the specialist crucifer-feeding white cabbage butterfly Pieris rapae is deterred from feeding and ovipositing on E. cheiranthoides. However, the related pierid species Pieris napi oleracea (green veined white butterfly) is less sensitive to exogenously added cardenolides than P. rapae in oviposition trials, and readily oviposits on E. cheiranthoides leaves. For P. rapae, oviposition experiments using E. cheiranthoides extracts sprayed onto cabbage (Brassica oleracea) identified both oviposition attractants and deterrents in the plant: 3-methylsulfinylpropyl glucosinolate and 3-methylsulfonylpropyl glucosinolate stimulated oviposition, while the cardenolides erysimoside and erychroside from E. cheiranthoides extracts acted as deterrents. Another cardiac glycoside from the plant, erycordin, showed no deterrent activity in this assay. P. rapae tarsal sensilla respond to both glucosinolates and cardenolides, meaning the insects detect these compounds on the leaf surface before laying eggs. Consistent with their deterrent effect on oviposition, cardenolides from E. cheiranthoides leaf extracts also act as feeding deterrents for P. rapae caterpillars. However, adult P. rapae readily lay eggs and caterpillars feed on mutant E. cheiranthoides plants that do not produce cardenolides. Predatory paper wasps (Polistes dominulus) took longer to consume Pieris napi caterpillars that had fed on E. cheiranthoides than caterpillars that had fed on cabbage. This slower consumption is attributed to the extra time wasps need to selectively remove the caterpillars’ guts, which contain plant material. Because Erysimum belongs to Brassicaceae, researchers have proposed that the extensive genetic resources already developed for the well-studied model organism Arabidopsis thaliana can be adapted for genetic analysis of Erysimum, making the genus particularly useful for studying the cardenolide biosynthetic pathway. E. cheiranthoides itself is diploid with a relatively small genome of approximately 200 Mbp arranged across 8 chromosomes. It can be grown from seed to mature seed production in as little as 10 weeks, and grows well under laboratory conditions. The genome of E. cheiranthoides variety Elbtalaue has been fully sequenced. Due to its close genetic similarity to A. thaliana, genetic modification and research techniques developed for A. thaliana are expected to work for E. cheiranthoides. Mutant strains of E. cheiranthoides with altered cardiac glycoside content have already been identified. Cardiac glycosides, which are abundant in E. cheiranthoides, are used to treat heart disease and other ailments in both traditional and modern medicine, but E. cheiranthoides is not a common commercial source of these compounds. Despite this, it has been used as an herbal remedy in traditional Chinese medicine. Sixteenth-century European herbalists used the plant to treat insect and animal bites. Its common name, wormseed wallflower, comes from its historical use to treat intestinal worms.
