A dynamic role for sterols in embryogenesis of Pisum sativum

Sterol profiling of aerial tissues from Pisum sativum indicate unusually high sterol concentrations, elevated isofucosterol and low stigmasterol levels in developing embryos. [Display omitted] ► GC–MS analysis of 25 steroids in Pisum sativum demonstrates dynamic sterol biosynthesis. ► Early stage embryos contain high sterol concentrations in comparison to other tissues. ► Isofucosterol levels are elevated while stigmasterol levels are low in young embryos. ► Coordinate transcript expression of sterol biosynthesis genes regulates sterol levels. Molecular roles of sterols in plant development remain to be elucidated. To investigate sterol composition during embryogenesis, the occurrence of 25 steroid compounds in stages of developing seeds and pods of Pisum sativum was examined by GC–MS analysis. Immature seeds containing very young embryos exhibited the greatest concentrations of sterols. Regression models indicated that the natural log of seed or pod fr. wt was a consistent predictor of declining sterol content during embryonic development. Although total sterol levels were reduced in mature embryos, the composition of major sterols sitosterol and campesterol remained relatively constant in all 12 seed stages examined. In mature seeds, a significant decrease in isofucosterol was observed, as well as minor changes such as increases in cycloartenol branch sterols and campesterol derivatives. In comparison to seeds and pods, striking differences in composition were observed in sterol profiles of stems, shoots, leaves, flowers and flower buds, as well as cotyledons versus radicles. The highest levels of isofucosterol, a precursor to sitosterol, occurred in young seeds and flower buds, tissues that contain rapidly dividing cells and cells undergoing differentiation. Conversely, the highest levels of stigmasterol, a derivative of sitosterol, were found in fully-differentiated leaves while all seed stages exhibited low levels of stigmasterol. The observed differences in sterol content were correlated to mRNA expression data for sterol biosynthesis genes from Arabidopsis. These findings implicate the coordinated expression of sterol biosynthesis enzymes in gene regulatory networks underlying the embryonic development of flowering plants.