Responses of free amino acids in rice seedlings during cyanide metabolism.

Responses of free amino acids to botanical assimilation of free cyanide were investigated. Young rice seedlings (Oryza sativa L. cv. XZX 45) were grown in nutrient solution amended with free cyanide (KCN). Cyanide was analyzed in solution as well as in plant materials to estimate the phyto-assimilation potential. Free amino acids in different parts of plants were also measured to determine metabolic responses to KCN exposure. Phyto-assimilation of KCN was obvious, and the rates were positively correlated to the concentration supplied. Although changes in total amino acid content in plant materials were negligible during KCN metabolism (p > 0.05), responses of different amino acids to KCN treatments were quite different. All treatments with KCN increased the content of proline (Pro) and isoleucine (Ile) in roots significantly compared with control (p < 0.05), while changes of aspartic acid, lysine, and histidine in roots were more evident at higher KCN treatments (p < 0.05). Results indicate that the content of Pro, Ile, and tyrosine showed pronounced increase in shoots of rice seedlings exposed to KCN at 1.44 mg CN/L or higher (p < 0.05). Other amino acids slightly changed in all plant materials exposed to KCN (p > 0.05). Results indicate that specific amino acids in rice seedlings showed positive response to non-toxic concentrations of exogenous KCN. These findings could provide additional insights into the inducible mechanisms underlying the involvement of amino acids in KCN metabolism.