A survey of the polysaccharide reserves in geophytes native to the winter-rainfall region of South Africa

Abstract

Underground organs of 63 geophytic species, representing eight families of Monocotyledonae and five families of Dicotyledonae, native to the winter-rainfall region of South Africa, were analysed for their polysaccharide storage components. With respect to type of polysaccharide accumulated in the storage organs the species tested can be divided into three groups: 1) geophytes storing starch, II) geophytes storing fructan, III) geophytes storing both, fructan and starch. Most of the geophytes tested showed a capacity for storing large to massive amounts of polysaccharides. Starch and/or fructan contribute more than 40% to total dry mass of the underground storage organs. Within a family or a genus, species cannot naturally be placed in one group, e.g. members of the genus Ornithogalum or Lachenalia store either fructan or a combination of fructan and starch in the underground storage organs. However, all geophytes belonging to group III are members of the Monocotyledonae. In underground storage organs fructan was previously considered to be one alternative to starch: species rich in fructan do not accumulate more than traces of starch and vice versa. This survey demonstrates that this assumption can not be confirmed in the results for the underground storage organs of the South African geophytes. The majority of geophytes belonging to group III accumulated more than 20% of the total amount of polysaccharides as the minor component. In these geophytes fructan is accumulated in addition to and not as an alternative to starch.