The structural differences between the embryos of viable and nonviable wheat seeds as studied with the EPR spectroscopy of lipid-soluble spin labels.

Dried and hydrated embryos of wheat seeds (viable and nonviable, harvested in 1992 and 1976, respectively) were studied by the EPR method with the use of the spin-labeling technique. Spin label Tempone was used for testing the plasmalemma integrity. It has been demonstrated that the loss of seed viability correlates with the loss of external membrane integrity. Spin-labeled derivatives of stearic acids, 5-doxylstearate I(12.3) and 16-doxylstearate I(1.14), were used to monitor the changes in structural characteristics of embryo cell membranes. The EPR spectra of these spin labels represent the superpositions of at least two signals from the molecules located in domains characterized by different fluidity. The comparison of the EPR spectra from I(12.3) in embryo cells and model systems (total fraction of lipids and purified seed oil) indicates that the majority of spin label molecules is located in the lipid surroundings, while the minor portion of I(12.3) is localized in so-called lipid bodies which contain seed oil. The embryo cells of viable and nonviable seeds differ in the sizes of these 'solid' and 'fluid' intracellular domains. The environment of spin label molecules located in cell membranes of nonviable seeds is more rigid, as compared with that in the membranes of the viable cells. The study of dehydration-rehydration effects has demonstrated that the loss of water causes the restriction of spin label mobility in embryo cells from both kinds of seeds.