Studies on the anhydrous fixation of dry seeds of lettuce ( Lactuca saliva L.)

summary A number of fixation techniques were used on cubes of dry cotyledonary tissue of lettuce seed to develop a satisfactory technique for the anhydrous fixation of dry seed material for electron microscopy. Fixation with formaldehyde or acrolein vapours in combination with Spurr's resin embedding produced satisfactory sections, while protocols involving the use of osmium tetroxide vapours resulted in brittle specimens that were difficult to section. The use of glycerol as a vehicle for anhydrous aldehyde fixation, followed by subsequent aqueous processing, introduced artifacts in membrane infrastructure. When model phospholipid systems, known to exist in the hexagonal phase, were prepared for electron microscopy and compared with anhydrously fixed cotyledonary tissue, the results suggested that dry seed membranes exist in a lamellar phase. It is proposed that leakage from imbibing seeds may be the result of physical/molecular changes in the membranes rather than of a phase change from the hexagonal to the lamellar state.