Role of cyanogenic glycosides in the seeds of wild Lima bean, Phaseolus lunatus: Defense, nutrition or both?

Authors: CUNY, MAXIMILIEN - Neuchatel University - Switzerland; LA FORGIA, DIANA - Gembloux Agricultural University; DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); GLAUSER, GAETAN - Neuchatel University - Switzerland; BENREY, BETTY - Neuchatel University - Switzerland

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2019
Publication Date: 6/25/2019
Citation: Cuny, M.A., La Forgia, D., Desurmont, G., Glauser, G., Benrey, B. 2019. Role of cyanogenic glycosides in the seeds of wild Lima bean, Phaseolus lunatus: Defense, nutrition or both?. Planta. 250, 1281-1292. https://doi.org/10.1007/s00425-019-03221-3.
DOI: https://doi.org/10.1007/s00425-019-03221-3

Interpretive Summary: Plants produce a wide range of toxic compounds to defend themselves against herbivores. Some of these compounds can also be used to store nitrogen, which can help plant's growth. Here we investigated the functions of cyanogenic glycosides (CNGs), a class of chemical compounds known for their anti-herbivores proprieties, in the lima bean. We used different populations of lima bean that have low and high levels of CNGs in their seeds and a caterpillar with a broad host range as a model herbivore. Results showed that these compounds protect lima bean plants against caterpillars when seedlings are very young (cotyledon stage) but do not seem to play to promote plant growth.

Technical Abstract: Wild lima bean plants contain cyanogenic glycosides (CNGs) that are known to defend the plant against leaf herbivores. However, seed feeders appear to be unaffected despite the high levels of CNGs in the seeds. We investigated a possible role of CNGs in seeds as nitrogen storage compounds that influence plant growth, as well as seedling resistance to herbivores. Using seeds from four different wild lima bean natural populations that are known to vary in CNG content we tested two non-mutually exclusive hypotheses: 1) seeds with higher CNG levels germinate better and produce plants that exhibit better growth, and 2) seeds with higher CNG levels produce seedlings that are more resistant against generalist herbivores. Seed CNG content did not correlate with germination rates, nor with seedling growth. However, CNG concentrations increased significantly soon after germination and seeds with the highest CNG concentrations produced seedlings with a higher CNG content in cotyledons and secondary leaves. Moreover, the growth rate of the generalist herbivore Spodoptera littoralis was lower on cotyledons with high CNG content. We conclude that CNGs in Lima bean seeds do not play a role in plant growth, but they may contribute seedling defense. To our best knowledge, this is the first study that examines the potential dual role of cyanogenic glycosides in defense and early plant development in wild lima bean.