Researches on Glucosides. The Physiological function of Salicin

The glucoside salicin, present in Salix purpurea and the greater part of the other Salix species, has the function of a reserve substance, which is hydrolyzed during sprouting by the enzyme salicase belonging to the emulsine complex. The two products are glucose and saligenin (ortho-oxybenz5'lalcohol); the former of which is used in metabolism, whilst the aglucon saligenin is quantitatively transmuted into pyrocatechol (orthodioxybenzol). This is proved by experiments with cut-off branches put in tapwater, which sprout in the dark. The decrease of salicin and the increase of pyrocatechol are in proportion of their molecular weights. The decrease of the glucoside salicin expressed in the quantity of this compound present before sprouting is always greater than the relative decrease of the total quantities of carbohydrates and proteins. This fact is an irrefutable proof of the reserve function. In absolute measure the decrease of the glucoside is however much smaller than that of the carbohydrates and the siginificance as lo a reserve material may be said to be in proportion to it. In the leaves of Salix purpurea the quantity of salicin increases in assimilating leaves, in which synthesis the pyrocatechol is used as well as the products of carbonassimilation. During the night, when transport of the products formed by assimilation is easily ascertainable, salicin decreases in the leaves, whilst pyrocatechol increases. The conclusion is, that during the night salicin is hydrolyzed by salicase; the formed glucose is transported whilst the aglucon is transmuted into pyrocatechol. Salicin has therefore not the function of a transport material, but may be regarded as a condensation product of glucose and the polyphenol pyrocatechol, which product by its non-diosmobility is a suitable accumulation product. The transmutation of saligenin into pyrocatechol forms a compound which according to several workers in this field of science sometimes together with a dehydrase and a polyphenolase forms an important oxidizing system. It is, in fact a question whether the production of different compounds as glucosides, alkaloides and benzolderivatives in the higher plants must always be of importance for the metabolism of the species, which contain them. Lately I maintained, that each genus of the higher plants has its own specific combination of these substances. The production of these compounds is to be regarded as a characteristic of the species or genus quite in the same way as its morphological or anatomical pecularities. A special significance for the metabolism or the struggle for existence of the species in question can no more be assigned to each of the chemical compounds than to each of these morphological or anatomical characteristics.