X-ray structure investigations of winter wheat membrane systems. I. Influence of phytohormones on phospholipid orientation in non- and embryogenic cells

Abstract

Changes in surface structure of liposomes in aqueous solutions obtained from phospholipids of plasmalemma of winter wheat cells were analysed by small-angle X-ray scattering (SAXS) method. Winter wheat cells were obtained from immature inflorescences and cultured in Murashige and Skoog medium supplemented with auxin (non-embryogenic calli, NE) or without phytohormones (embryogenic calli, E). Measurements were performed in the fully hydrated liposomal dispersions in pure water:methanol (100:1 v/v) buffer or in buffer supplemented by auxins (IAA and its chemical analogue melatonine) or cytokinins (kinetin and its analogue mercaptopurine). Both types of liposomes (NE and E) were different in the hydrophilic and hydrophobic phase. The higher amount of PE in comparison to PC as well as the higher content of unsaturated fatty acids, especially 18:2 and 18:3, were observed in E membranes. The SAXS curves from NE and E liposomes indicate the possibility of bilayer formation by these phospholipids. Changes in distance distribution functions derived for NE and E phospholipid liposomes could be explained by changes of bilayer thickness. All investigated hormones were affected only E liposomes and did not have an influence on NE liposomes. These changes of the bilayer size of E membranes after phytohormone treatment were in the range of those detected for NE membranes. This was observed especially for IAA and its chemical analogue. Kinetin influenced bilayer thickness in a lesser degree and inconsiderable differences were noticed for its chemical analogue—mercaptopurine. Thus we suggest that removal of auxins from winter wheat culture media is necessary to maintain structure of membranes characteristic for embryogenic cells.