Hexitols in coconut milk: Their role in nurture of dividing cells

Abstract

The growth-stimulating qualities of coconut milk toward phloem explants from carrot root is due to the interactions of an "active fraction", "neutral fraction", and "nitrogenous fraction," the latter being replaceable in the culture medium by non-specific sources of reduced N, such as casein hydrolysate. The active fraction, obtained by adsorption on activated charcoal and elution with aqueous acetic acid, represents about 0.1% of the total dry weight, is effective at about 10 ppm, and is a very complex mixture of substances which induce cell division. The neutral fraction, not retained by ion exchange resins or by charcoal, represents about 85% of the dry weight, consists largely of carbohydrates, and is effective at about 250 ppm. When recombined, active fraction and neutral fraction reproduce the major portion of the growth response induced by whole coconut milk. Crystalline sorbitol, myo-inositol, and scyllo-inositol were isolated from the neutral fraction and critically identified. Their approximate concentrations''in coconut milk solids are: sorbitol, 30%; scyllo-inositol, 1%; and myo-inositol, 0.2%. Myo-inositol was also isolated from similarly prepared neutral fractions from an extract of immature corn (Zea) grains and from the liquid endosperm of immature horsechestnut fruits, representing over 10% of the total dry weight in the latter. Of a number of sugars and sugar alcohols tested as a C source for the growth of the carrot tissue cultures, sucrose and glucose were most effective and sorbitol is ineffective. In factorially designed growth experiments, the various interactions of active fraction, neutral fraction, casein hydrolysate, indoleacetic acid, sorbitol, and the inositols are described. Much of the activity of the neutral fraction can be attributed to the hexitols present, with myo-inositol playing the key role.