USE OF LOW-TEMPERATURE SEM TO LOCATE FREE-WATER IN FROZEN, HYDRATED SEED TISSUES OF GLYCINE-MAX (LEGUMINOSAE)

Low temperature field emission electron microscopy was used to determi ne the location of free water in soybean seeds. Frozen, hydrated soybe an seeds were fractured, the water etched from the fractured surface, and then part of the etched surface was refractured. The resulting sur face, which contained a freeze-fractured face as well as a freeze-etch ed face was coated with platinum and viewed on the cryostage of a low temperature field emission electron microscope. Two surfaces could be viewed simultaneously to determine the location of water in the seed t issue. Viewing the fractured surface gave an indication of the extent of hydration of the tissue. Viewing the etched surface detailed the ma cro- and microanatomy of the tissue. Viewing the intersection between the fractured and etched surfaces allowed observation of the environme nt of partially etched cells and organelles. The technique avoids arti facts associated with chemical fixation, dehydration, and critical-poi nt drying, procedures that affect the water content of the seed. The t echnique does not affect the degree of hydration of the seed and can b e used to localize water in the inter- and intracellular environment o f the seed. This technique could find wide application in studies of w ater relationships of seeds during development, maturation, and imbibi tion.