Abscisic Acid-Induced Cellular Alterations During the Induction of Freezing Tolerance in Bromegrass Cells

Abstract

Cellular alterations in bromegrass (Bromus inermis Leyss cv Manchar) cell suspension cultures were characterized at different hardiness levels using fluorescence and transmission electron microscopy. After one day, when cells treated with abscisic acid (ABA) were 5 °C hardier than control cells, the hardier cells exhibited greater numbers of vacuoles and lipid bodies. However, no changes were observed in cell-wall thickness or cell size. Vacuole size in ABA-treated cells were equally distributed among three size classes, whereas control cells had a higher proportion of large vacuoles. Conversely, the lipid bodies in cells exposed to ABA treatment were consistently smaller than those in control cells. After 7 treatment days when hardiness had increased to -28 °C, the walls of ABA treated cells were significantly thicker than the control cells. The differences observed in lipid bodies after one day were accentuated in the hardier ABA treated cells after 7 days. The size of lipid bodies decreased and their numbers increased by a factor of ten. Osmiophilic granules and golgi apparati became more prevalent near the plasma membrane in the more frost tolerant cells. Cell-wall and protoplasm autofluorescence increased in response to ABA treatment and were quenched by methanol: chloroform extraction. These results show that ABA treatments at room temperature elicit ultrastructural changes associated with hardiness that are similar to those reported after low temperature acclimation.