Zinc‐induced vacuolation in root meristematic cells of Festuca rubra L.

. The effect of Zn on vacuole development in root meristematic cells was examined in three cultivars of Festuca rubra : a Zn‐tolerant cultivar (Merlin), a salt‐tolerant cultivar (Hawk) and a non‐tolerant cultivar (S.59) in order to determine whether or not vacuole development was related to Zn tolerance. Treatment with Zn greatly increased the percentage of cells in the apical meristem which were vacuolated in all three cultivars (7.01‐fold increase in Merlin, 3.61‐fold increase in Hawk and 5.39‐fold increase in S.59 over the range 0–0.5 μg Zn cm −3 ). Morphometric analyses on electromicrographs indicated that the percentage total vacuolar volume fraction of meristematic tissue was also increased by Zn treatment. Most of this increase was due to an increase in a particular component of the vacuole which was 0.2–0.5 μm in diameter, spherical or ovoid in outline and possessed a distinct amorphous electron dense matrix (Type A intravacuolar body). X‐ray microanalysis revealed that this matrix was rich in calcium and phosphorus in control plants. In Zn‐treated roots, elevated levels of Zn were found in the matrix in Merlin and Hawk, but not in S.59. In addition, intravacuolar membranous whorls or myelin bodies were more highly organized in Zn‐treated Merlin and Hawk but not S.59. Elevated Zn levels were not found in any other vacuolar component nor in nuclei, nucleoli, cell walls or ground cytoplasm. Control roots of Merlin possessed a greater type A vacuolar volume fraction than either Hawk or S.59 which may confer a greater capacity to compartmentalize Zn at the onset of exposure to toxic metals than the other cultivars. Predictably, the EM procedures resulted in loss of Zn from the roots to the fixative and dehydrating solutions. However, the rate of loss was the same (approximately 75–80%) regardless of cultivar. These findings are discussed in relation to their possible role in the mechanisms of Zn tolerance in these cultivars.