Mathematical modularization of the contribution of β-cyanoalanine synthase and sulfurtransferase to cyanide assimilation in rice plants

Modeling the assimilation of biodegradable contaminants by plants is a smart option to simulate the efficiency of phytoremediation in a field trial. The involvement of β-cyanoalanine synthase (β-CAS) and sulfurtransferase (ST) in cyanide (CN−) assimilation in plants was evident. However, the contribution of both enzymes to CN− assimilation by plants is not defined. In this study, a rice completely mixed reactor model (RCMRM) combined with boundary conditions is developed to mathematically examine the fraction of β-CAS and ST involved in CN− conversion in rice plants. The modeling steps include: 1) estimation of CN− assimilation rates was based on the CN− in plant biomass and the solution; 2) inputs of the mass balance equations of CN− through either the β-CAS pathway or the ST pathway were calculated individually; 3) the boundary conditions refer to the condition, in which the expression levels of β-CAS and ST in the KCN treatments with application of exogenous 1-amino-cyclopropane-1-carboxylic acid (ACC) were higher than the KCN treatments without ACC addition. Results from the RCMRM suggested that CN− assimilation rates by rice seedlings followed an exponential kinetic (first order), which was linearly increased in the first 2 h before more gradual until equilibrium was reached at about 12 h. The catalytic efficiency of β-CAS activated in CN− conversion was higher than that of ST, and the fraction of both enzymes to CN− conversion is time-dependent rather than dose-dependent. Overall, this is the first attempt to mathematically describe the role of β-CAS and ST to exogenous CN− conversion in rice plants.