A SURVEY AND PARTIAL CHARACTERIZATION OF ICE-NUCLEATING FLUIDS SECRETED BY GIANT-ROSETTE (LOBELIA AND DENDROSENECIO) PLANTS OF THE MOUNTAINS OF EASTERN AFRICA

Ice-nucleating activities of the fluids from east African giant lobeli as (13 samples from 10 taxa of Lobelia, Lobeliaceae) and giant senecio s (4 samples from 4 taxa of Dendrosenecio, Asteraceae) were determined using supercooling temperatures as the indicator. Variation in superc ooling temperatures of these fluids was found both within and between species. Fluids from L. gregoriana subsp. gregoriana, L. deckenii subs p. deckenii, L. telekii (Mount Kenya), D. brassiciformis, L. gregorian a subsp. elgonensis, L. rhynchopetalum, D. battiscombei, D. keniensis, and D. cheranganiensis subsp. dalei had the highest supercooling temp eratures and were assumed to contain the most effective ice-nucleators . The first four of these were chosen for more detailed examination. T he most effective ice-nucleating fluids contained either a polysacchar ide fraction composed primarily of uronic acid units or a pair of poly saccharide fractions containing little or no uronic acid. Polysacchari des isolated via 70% ethanol precipitation from fluids of L. gregorian a subsp. gregoriana, L. deckenii subsp. deckenii, and D. brassiciformi s gave the two fractions on DEAE-cellulose chromatography. Main fracti ons were composed primarily of neutral sugars (glucose, mannose, fucos e, rhamnose, and/or galactose); smaller amounts of galacturonic and gl ucuronic acids were also present. Fluid from L. telekii gave a single main fraction that chromatographed as an almost neutral polysaccharide although galacturonic acid was its principal sugar component. Superco oling temperatures of the isolated main fractions were lower than thos e of the original fluids except for that from L. gregoriana subsp, gre goriana, but all still exhibited ice-nucleating activities. Copyright (C) 1996 Elsevier Science Ltd