QUANTIFICATION OF CYANOGENIC GLYCOSIDES IN SEEDLINGS OF 3 MACADAMIA (PROTEACEAE) SPECIES

Members of the genus Macadamia contain cyanogenic compounds, which rel ease hydrogen cyanide (HCN) on hydrolysis. Concentrations of releasabl e cyanide were measured in tissues of mature nuts and seedlings of Mac adamia integrifolia Maiden & Betche, M. tetraphylla L.A.S. Johnson and M. ternifolia F.Muell. Root, cotyledon and leaf samples were assayed at several developmental stages from germination to maturation of the first leaves. All samples contained detectable levels of cyanide. Conc entrations were low (0.15 mu mol g(-1) fresh weight) in cotyledons of mature M. integrifolia and M. tetraphylla seeds, corresponding to the edibility of the seeds of these commercial species, and much higher (9 .6 mu mol g(-1)) in the inedible M. ternifolia seeds. Levels in cotyle dons of all three species rose dramatically during germination. Root c yanide concentrations of 6-23 mu mol g(-1) were measured. The immature first leaf of the commercial species contained the highest concentrat ions (38-77 mu mol g(-1)). Levels decreased with leaf maturity, correl ating with toughening of the leaf and possibly a consequent diminished requirement for cyanide as a herbivory deterrent. The significance of the results with respect to plant-insect interactions is discussed.