Dhurrin: An endogenous turnover n-source for early seedling growth in sorghum

Authors: Emendack, Yves; Sanchez, Jacob; LAZA, HAYDEE - Texas Tech University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2025
Publication Date: 5/7/2025
Citation: Emendack, Y., Sanchez, J.V., Laza, H.E. 2025. Dhurrin: An endogenous turnover n-source for early seedling growth in sorghum. Frontiers in Plant Science. 16. https://doi.org/10.3389/fpls.2025.1558712.
DOI: https://doi.org/10.3389/fpls.2025.1558712

Interpretive Summary: The economic value of sorghum as a forage crop will be greatly enhanced if prussic acid poisoning could be prevented in cattle grazing or foraging on sorghum. Dhurrin, the precursor of prussic acid is found in all vegetative tissues of sorghum, acting as herbivore repellent, osmoprotectant, nitrogen storage, and with anti-fungal activity. Breeding for low or non-prussic acid sorghum has led to the creation of dhurrin-free mutants. However, research on the importance of dhurrin as a nitrogen source for early seedling growth is limited. Through collaborative work, scientists from USDA-ARS and Texas Tech University, evaluated the importance of dhurrin in early sorghum seedling growth using high-and low-dhurrin level lines grown in the presence or absence of nitrogen fertilization in soil and play sand. They reported that, dhurrin was the primary source for early seedling fresh biomass accumulation, particularly in the absence of nitrogen fertilization. Thus, the use of dhurrin knocked-out mutants may affect field germination and stand establishment particularly under low nitrogen input conditions. Also, this finding is critical, considering that the cultivation of sorghum in most regions, particularly in sub-Sahara Africa and Asia, where grain sorghum is a staple, is usually in low input environments, where nitrogen fertilization is minimal at best and lacking at worst.

Technical Abstract: Dhurrin is a cyanogenic glucoside found in all vegetative tissues of Sorghum bicolor, functioning as herbivore repellant, antifungal activity, osmoprotectant, and nitrogen storage. Dhurrin concentration is usually highest in young seedlings where it rapidly accumulates following germination, after which its biosynthesis decreases and its turnover increases as the seedling ages. To avoid prussic acid poisoning from dhurrin catabolism in cattle grazing or foraging on sorghum, numerous research now focuses on breeding for dhurrin-free or acyanogenic sorghum mutants. However, there has been limited and conflicting research investigating the role dhurrin plays as a potential nitrogen source in sorghum early seedling growth. It is plausible that the presence of background mutations in dhurrin-free sorghum mutants could mask or confound how the absence of dhurrin affects early seedling growth. Using a naturally occurring (non-mutant) ultra-low dhurrin genotype and known low and high dhurrin genotypes, the current research investigated the importance of dhurrin as a potential endogenous nitrogen source for early seedling growth in simulated non-marginal (N-available) and marginal (N-deficient) media. Dhurrin was identified to be the primary source for nitrogen in early seedling growth, when plants are subjected to N-deficient or N-limiting environments. While acyanogenic sorghum will be great in expanding sorghum economic value, the use of dhurrin knocked-out mutants may affect field germination and stand establishment particularly under low N-input conditions. Also, this finding is critical, considering that the cultivation of sorghum in most regions, particularly in sub-Saharan Africa and Asia, where grain sorghum is a staple, is usually in low input environment, where fertilization is minimal at best and lacking at worst.