Quantification of cyanogenic glycosides in white clover (Trifolium repens L.) from horse pastures in relation to equine grass sickness

As a preliminary step in testing the hypothesis that ingestion of cyanogenic glycosides in white clover (Trifolium repens L.) may be one of the risk factors for equine grass sickness (EGS, or equine dysautonomia), the cyanogen content of clover leaves collected from fields (n = 16) soon after an occurrence of EGS was compared with that of (i) control white clover samples (n = 10) collected from the same fields out of the disease period and (ii) control clover samples (n = 54) collected sequentially from three control fields. Clover samples from EGS fields were highly cyanogenic, with a median cyanide potential of 497 (range 307–1786) mg kg dry matter^?1. Furthermore, clover collected from EGS fields soon after an occurrence of EGS had significantly higher concentrations of the cyanogenic glycosides linamarin and lotaustralin than control samples. While these findings indicate that horses grazing EGS fields may ingest significant quantities of cyanogenic glycosides, the design of the study does not facilitate investigation of any potential association between cyanogens and EGS. Further study is therefore required to determine whether cyanogens are a risk factor for EGS or whether these findings simply reflect variations in plant metabolism unrelated to disease pathogenesis.     

A study of dominance at the locus controlling cyanoglucoside production in Trifolium repens L.

Summary The Ac allele for cyanoglucoside production in white clover has been shown to be incompletely dominant and a dosage effect is indicated at this locus. The recessive allele, ac, when homozygous gives rise to absence of cyanoglucosides in the leaf tissue, whereas in heterozygous plants it has been shown to reduce the level of cyanoglucoside, to a level less than half the value found in Ac Ac plants.     

Linamarin content and genetic stability of cassava plants derived by somatic embryogenesis

A protocol was established for high frequency cyclic somatic embryogenesis for different varieties of cassava. An efficient plant regeneration system was developed for the high cyanogenic variety PRC60a. Linamarin content and linamarase activity were determined in various tissues of secondary somatic embryos and regenerated plants of PRC 60a. Both linamarin and linamarase activity were not detected in embryogenic callus, roots induced from callus and somatic embryo tissues. The stems and leaves of regenerated plants (in vitro) and storage roots and leaves of mature plants (in vivo), however, contained variable amounts of linamarin and linamarase activity whereas in the non storage root tissues (in vitro) only linamarin was detected. The present study suggested that the linamarin biosynthetic pathway may be absent or not switched on in the embryogenic callus and somatic embryos. The ploidy level and somatic chromosome number of the regenerated plants were found to be same as the source plants. The availability of this regeneration system would be useful not only for investigating cyanogenesis but also for genetic manipulation in cassava. This revised version was published online in July 2006 with corrections to the Cover Date.