Free sugar profile in cycads

Abstract

The sugars fructose, glucose, maltose, and sucrose were quantified in seven tissues of Zamia muricata Willd. to determine their distribution throughout various organs of a model cycad species, and in lateral structural roots of 18 cycad species to determine the variation in sugar concentration and composition among species representing every cycad genus. Taproot and lateral structural roots contained more sugars than leaf, stem, female strobilus, or coralloid roots. For example, taproot sugar concentration was 6.4-fold greater than stem sugar concentration. The dominant root sugars were glucose and fructose, and the only detected stem sugar was sucrose. Sucrose also dominated the sugar profile for leaflet and coralloid root tissue, and fructose was the dominant sugar in female strobilus tissue. Maltose was a minor constituent of taproot, leaflet, and female strobilus tissue, but absent in other tissues. The concentration of total free sugars and each of the four sugars did not differ among genera or families. Stoichiometric relationships among the sugars, such as the quotient hexoses/disaccharides, differed among organs and families. Although anecdotal reports on cycad starch have been abundant due to its historical use as human food and the voluminous medical research invested into cycad neurotoxins, this is the first report on the sugar component of the non-structural carbohydrate profile of cycads. Fructose, glucose, and sucrose are abundant in cycad tissues, with their relative abundance highly contrasting among organs. Their importance as forms of carbon storage, messengers of information, or regulators of cycad metabolism have not been determined to date.

Axial and Radial Spatial Patterns of Non-Structural Carbohydrates in Cycas micronesica Stems

“…40 mg·g −1 reported for Zamia muricata Willd. stems [ 22 ] was much less than that of C. micronesica stems. Although the same methods were used among these studies, the limited number of species do not enable an interpretation of these contrasting results for the two genera.…”

Seed Ontogeny and Nonstructural Carbohydrates of Cycas micronesica Megagametophyte Tissue

“…Our results indicate that this may be a severe under estimation of Cycas megagametophyte starch content, as the starch content of C. micronesica megagametophyte was 65% at maturity. Marler and Lindstr€ om (2014) reported the sugar profile of an entire Zamia muricata Willd. megastrobilus was 65% fructose.…”

Carbohydrates, pollinators, and cycads

“…Our recent report of fructose, glucose, and sucrose content in cycad tissues 3 sets the stage for designing continued research on how non-structural carbohydrates are involved in cycad pollination biology. Moreover, cycad horticulturists routinely harvest, store, and ship pollen prior to its use for successful pollination.…”

“… 2 As a result, we studied various aspects of free sugar content and reported that fructose, glucose, and sucrose were abundant in tissues from species representing every described cycad genera, and sugar content and stoichiometry varied greatly among organs. 3 The importance of these carbohydrates as forms of carbon storage, components of signaling, or regulators of cycad metabolism have not been determined to date.…”