Relationships among cold hardiness, water-soluble protein, anthocyanins, & free sugars in Hedera helix L.

It has been much disputed whether seasonal variations in proteins or in sugars are better related to cold hardiness changes in certain over-wintering plants (for example, 1, 2, 3, 8, 12, 14). But proteins have been difficult to study, since they are not easily extracted from such plants as our native winter-hardy trees. This is because such proteins are often precipitated by vacuolar substances during tissue homogenation. The inner bark of black locust (Robinia pseudoacacia L.) is one of the few tree species which yields substantial amounts of water-soluble protein (6,10,14). As a result, much work on the concept of protein relationships to hardiness is based on work with this species. It, therefore, seemed of interest to find another plant that would yield sufficient watersoluble protein and would also be easy to study for cold hardiness. A survey of a number of evergreen woody plants showed that English ivy (Hedera helix L.) yielded large amounts of water-soluble protein. Protein determinations (13) as well as sugar analyses (5) have been previously made on this species, but no concomitant studies of these changes with cold hardiness in English ivy have been made. Closely related to sugar changes is the question of whether the reddening or purpling of evergreen leaves in autumn is any measure of their cold hardiness. Since this is a visual observation easily made in the field it is of much interest to foresters and horticulturalists. There appears to be some connection between cold resistance and the red coloration in some species (16, 18) but to our knowledge this has never been clearly demonstrated. Anthocyanins as well as free sugars were, therefore, studied in English ivy.