Phenotypic Characteristics as Predictors of Phytosterols in Mature Cycas micronesica Seeds

Abstract

The relationship between mature Cycas micronesica K.D. Hill seed sterol concentration and content and plant or seed phenotypic characteristics was established by multiple regression. Combined models were significant for free but not glycosylated sterols. Reduced models revealed leaf number as the only significant predictor. Free and glycosylated sterol concentrations were unaffected throughout the range of several predictors: tree height (1.7 to 5.8 m), seed fresh weight (48 to 120 g), seed load (one to 76 seeds per plant), and estimated tree age (32 to 110 years). The free and glycosylated sterol phenotypes were also not dependent on the presence/absence of developed embryos in mature seeds. The significant response to leaf number was subtle with an increase of 43 leaves associated with a 0.1-mg increase in free sterol per gram seed fresh weight. This is the first report for any cycad that discusses reproductive or physiological traits in the context of allometric relations. Results indicate a highly constrained phenotypic plasticity of Cycas gametophyte sterol and steryl glucoside concentration and seed content in relation to whole plant and organ size variation.

Distribution of free and glycosylated sterols within Cycas micronesica plants

“…We have also begun determining distribution of cycad seed sterols at larger spatial scales to reveal that concentration differences among seeds within a plant is less variable than among plants within a location or among locations throughout Guam (Marler et al, 2005b, 2007). Individual seed size, total seed load per plant, developmental stage of the embryo, and plant size were not significant predictors of megagametophyte sterol concentration (Marler and Shaw, 2009b). In contrast, seed age strongly influenced sterol relations, with a non-linear decline in concentration (Marler et al, 2006) accompanied by a linear increase in bioaccumulation (Marler and Shaw, 2009a).…”