EVALUATION OF FIXATIVE COMPOSITION, FIXATIVE STORAGE, AND FIXATION DURATION ON THE FINE-STRUCTURE AND VOLUME OF ROOT-CELL NUCLEOLI

The effect of various combinations of three fixative compositions (glu taraldehyde buffered in veronal acetate, cacodylate, and piperazine-N, N'-bis[2-ethanesulfonic acid]-PIPES), two fixative storage times (fres h vs 6 weeks), and two fixation durations (3 h vs 9 days) on nucleolar fine structure and nucleolar volume in three root cell-types of oat s eedlings (Avena sativa L, cv Seger) were evaluated. All fixatives show overall good preservation of fine structure. Nucleolar components are distinct and well delineated in cells fixed in solutions buffered wit h either cacodylate or veronal acetate; the components are more conden sed when preserved in fixative buffered with PIPES. Nucleolar volume i s greatest in cells fixed in the cacodylate fixative, and smallest in those preserved in the PIPES fixative. Among the treatments tested, th e PIPES fixative evidently best maintains nucleolar volume. Distractin g particulate deposits are abundant on nuclei and nucleoli in cells pr eserved in the veronal-acetate fixative. Contrary to common assumption s, aging of buffered fixative at room temperature for 6 weeks seems to affect neither the general quality of cellular preservation nor the p H of the fixatives, although nucleolar volume is reduced by such treat ment. Long-period fixation (9 days) results in destruction of membrane integrity (mitochondria, plastids, ER), and shrinkage of organelles f rom the cytoplasm. Nucleolar volume is reduced with prolonged fixation .