Influence of temperature on cyanogenic polymorphisms

Abstract

CYANOGENIC glucosides occur widely in the plant kingdom, and in species which are polymorphic for their presence or absence they probably have ecological significance. The cyanogenic morphs may be relatively unpalatable to grazing animals^1–3 and consequently have an advantage where grazing pressure is significant⁴. Cyanogenic morphs of Trifolium repens and Lotus corniculatus are relatively rare at high altitudes, and in Europe their distribution correlates with the January 5 °C isotherm⁵. It has been inferred that where low temperatures and frost are frequent, cyanogenesis confers a reduced physiological fitness, but this aspect of the polymorphism has received less attention and has not been established experimentally. A marked difference between the morphs in their response to artificial cold treatment is shown by the data reported here, together with evidence that this difference is significant in natural conditions.