Cyanogen Metabolism in Cassava Roots: Impact on Protein Synthesis and Root Development

Abstract

Cassava (Manihot esculenta Crantz), a staple crop for millions of sub-Saharan Africans, contains high levels of cyanogenic glycosides which protect it against herbivory. However, cyanogens have also been proposed to play a role in nitrogen transport from leaves to roots. Consistent with this hypothesis, analyses of the distribution and activities of enzymes involved in cyanide metabolism provides evidence for cyanide assimilation, derived from linamarin, into amino acids in cassava roots. Both β-cyanoalanine synthase (CAS) and nitrilase (NIT), two enzymes involved in cyanide assimilation to produce asparagine, were observed to have higher activities in roots compared to leaves, consistent with their proposed role in reduced nitrogen assimilation. In addition, rhodanese activity was not detected in cassava roots, indicating that this competing means for cyanide metabolism was not a factor in cyanide detoxification. In contrast, leaves had sufficient rhodanese activity to compete with cyanide assimilation into amino acids. Using transgenic low cyanogen plants, it was shown that reducing root cyanogen levels is associated with elevated root nitrate reductase activity, presumably to compensate for the loss of reduced nitrogen from cyanogens. Finally, we overexpressed Arabidopsis CAS and NIT4 genes in cassava roots to study the feasibility of enhancing root cyanide assimilation into protein. Optimal overexpression of CAS and NIT4 resulted in up to a 50% increase in root total amino acids and a 9% increase in root protein accumulation. However, plant growth and morphology was altered in plants overexpressing these enzymes, demonstrating a complex interaction between cyanide metabolism and hormonal regulation of plant growth.

Improving Cassava Quality for Poultry Feeding Through Application of Biotechnology

“…With reference to cassava plant, the use of biotechnology involves the exploitation of biological processes, especially the genetic manipulation of microorganisms for the production of hormones and enzymes, and manipulation of genes with the aim of producing disease-resistant varieties, improving the nutrient composition, as well as eliminating any ANF inherent in cassava crop. Several studies have shown the efficacy of biotechnologically targeted processing methods in improving the feed value of cassava for both humans and animals, for instance, in a study to ascertain the feasibility of enhancing root cyanide assimilation into protein, optimally overexpressed Arabidopsis CAS and NIT4 genes in cassava roots resulted in up to a 50% increase in root total amino acids and a 9% increase in root protein accumulation [88]. It has been hypothesised that cyanogen toxicity in cassava foods can be accelerated by cyanogenesis and cyanide volatilization during food processing [89].…”

HCN Regulates Cellular Processes through Posttranslational Modification of Proteins by S-cyanylation

“…Hydrogen cyanide (HCN) is a gaseous acid produced in nature by a wide variety of microorganisms such as fungi, bacteria, and algae (Knowles, 1976), as well as in cyanogenic plant food such as almonds (Prunus dulcis), millet sprouts (Panicum miliaceum), cassava roots (Manihot esculenta), or lima beans (Phaseolus lunatus), which are capable of accumulating significant amounts of cyanide, produced by the hydrolysis of cyanogenic glycosides (Hanschen et al, 2014;Baskar et al, 2016;Zidenga et al, 2017). Noncyanogenic plant species also produce cyanide as a byproduct of some metabolic processes, such as during camalexin and ethylene biosynthesis (Peiser et al, 1984;Yip and Yang, 1988;Böttcher et al, 2009).…”

Review on Mineral Malabsorption and Reducing Technologies

“…Several methods are used for the quantitative determination of anti-nutritional factors in foods based on reports by different authors. These are: trypsin inhibitor activities are determined according to these studies [6,15,17,[25][26][27][28].…”

“…The bioavailability of the essential nutrients in plant foods could be reduced by the presence in these plants of some anti-nutritional factors such as oxalates and cyanogenic glycosides [28]. Too much of soluble oxalate in the body prevents the absorption of soluble calcium ions as the oxalate binds the calcium ions to form insoluble calcium oxalate complexes.…”

“…Cyanogenic glycosides are classified as phytoanticipins. Their general function in plants is dependent on activation by b-glycosidase to release toxic volatile HCN as well as a ketones or aldehydes to fend off herbivore and pathogen attack [28]. Excessive intake of required nutrients can also result in them having an anti-nutrient action.…”