COMPARISON OF HEXAMETHYLDISILAZANE (HMDS), PELDRI-II, AND CRITICAL-POINT DRYING METHODS FOR SCANNING ELECTRON-MICROSCOPY OF BIOLOGICAL SPECIMENS

Three different drying methods, critical-point drying (CPD), Peldri II , and hexamethyldisilazane (HMDS), were compared using representative animal (rat kidney, trachea, duodenum, lung, and red blood cells) and plant (leaves from ten species of monocotyledons and dicotyledons) spe cimens. All three drying methods produced identical results with anima l specimens. Plant specimens showed signs of shrinkage regardless of w hich drying method was employed. The order of preservation quality fro m best to worst for leaves was CPD > Peldri II > HMDS, with the CPD me thod providing substantially better results in all but one case. Postf ixation of leaves with osmium tetroxide resulted in poorer preservatio n in all instances. Peldri II caused complete extraction of leaf cutic ular wax, while both both CPD and HMDS showed minimal extraction compa red with samples air dried directly from acetone. These results indica te that HMDS provides a time-saving and inexpensive alternative to CPD for animal specimens. Plant specimens, particularly those containing cells with large central vacuoles, are adequately preserved only with the CPD method. In addition, postfixation with osmium should be avoide d when processing plant specimens for scanning electron microscopy. (C ) 1993 Wiley-Liss, Inc.