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, harve sted in 1992 and 1976, respectively) were studied by the EPR method wi th 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 membra ne integrity. Spin-labeled derivatives of stearic acids, 5-doxylsteara te I(12.3) and 16-doxylstearate I(1.14), were used to monitor the chan ges in structural characteristics of embryo cell membranes. The EPR sp ectra of these spin labels represent the superpositions of at least tw o signals from the molecules located in domains characterized by diffe rent fluidity. The comparison of the EPR spectra from I(12.3) in embry o 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 localiz ed 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 molecule s located in cell membranes of nonviable seeds is more rigid, as compa red with that in the membranes of the viable cells. The study of dehyd ration-rehydration effects has demonstrated that the loss of water cau ses the restriction of spin label mobility in embryo cells from both k inds of seeds.