CYANOGENESIS - A PERSONAL PERSPECTIVE

The past 35 years have provided much new knowledge of the process of cyanogenesis in higher plants. In 1958, when the first studies establishing the biosynthetic origin of the aglycone of a cyanogenic glycoside from a protein amino acid were published, only a dozen cyanogenic glycosides had been described. Fewer than half of those had been rigorously characterized, although the list included linamarin, first isolated from Linum. Today, more than 60 cyanogenic glycosides have been reported and at least 2500 plant species are known to be cyanogenic. Although the biosynthesis of cyanogenic glycosides was examined vigorously in our laboratory for 20 years, important details of the biosynthetic sequence are still being sorted out by others in 1993. One surprising observation made during our biosynthetic work was the metabolism of HCN released from cyanogenic glycosides to form -cyanoalanine and asparagine. This detoxification process retains the nitrogen atom of the cyanogenic glycosides in metabolites that lead to ammonia. In this way, the nutritionally significant nitrogen atom is conserved and returned to the plant's nutrition as ammonia.

Compartmentalization of cyanogenic glycosides away from their catabolic enzymes is self evident. Some details of that process were first described in 1980 for sorghum leaves. Studies in other species, including cassava, followed. The situation in seeds of Prunus serotina has recently been documented in exquisite detail. This type of information is essential when attempting to understand how cyanogenic glycosides can be transferred between tissues within the same plant. This older knowledge on biosynthesis and compartmentation of cyanogenic glucosides will be related to the theme of this workshop.