Effects of photooxidation on membrane integrity in Salix nigra seeds

ROQUEIRO GONZALO; FACORRO GRACIELA; HUARTE MONICA; RUBÍN DEL CELIS EMILIO; GARCIA FERNANDO; MALDONADO SARA; MARODER HORACIO

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2010 p. 1027 - 1034

0305-7364

Background and Aims– Salix nigra seeds are desiccation-tolerant, as are orthodox seeds, but lose viability in few weeks at room temperature. They also differ in that the chloroplasts of the embryo tissues conserve their chlorophyll and endomembranes. The aim of the present paper was to investigate the role of chlorophyll in seed deterioration. • Methods– Seeds were aged at different light intensities and atmospheric (air or nitrogen) conditions. Normal germination, total germination and mean germination time were evaluated, as well as the formation of free radicals, using electronic spin resonance spectroscopy, and changes in the fatty acid composition from phospholipids, galacolipids and triglycerides , with gas liquid chromatography. Free radicals and fatty acid composition on membrane integrity were studied by ESR Spin Probe techniques, electrolyte leakage and transmission electron microscopy. • Key Results Light and oxygen played an important role in free radical generation, causing a decrease in normal germination and an increase in mean germination time. Both indices were associated with a decrease in polyunsaturated fatty acids derived from membrane lipids as phospholipids and galactolipids, mostly from the lather. Consistent with decrease in both  type of lipids were damage detected in thylakoid membranes and the increase in plasmalema permeability. Triglycerides remain unchanged. Light induced damage began in outermost tissues and spreads inwards decreasing normal germination. Only at high light intensity damage reach apical meristem beginning the decrease total germination Conclusion–Salix nigra seeds result very susceptible to Photooxidation.. We assume that the thylakoid membranes would be the first target of the photooxidative process due to: a) galactolipids, an exclusive component of  thylakoid membrane, resulted the most degraded lipid and b) the contiguity of activated chlorophyll and lipids in the structure of that membrane,. The variations observed in normal germination and mean germination time could be explained by these processes. However, the role of light was limited to shortening the already brief period of viability that these seeds demonstrate in the dark.