Identification of zinc‐containing globules in roots of a zinc‐tolerant ecotype of Deschampsia caespitosa

Abstract

In previous work on Zn‐tolerant and non‐tolerant ecotypes of Deschampsia caespitosa root elongation was shown to be a sensitive parameter of Zn toxicity. Laser microprobe mass analysis of small volumes in thin sections from freeze substituted root tips of seedlings grown on nutrient solutions containing high levels of Zn, showed the sporadic presence of Zn. This Zn seemed to be associated with particles, but the optical resolution of the method was insufficient to establish the nature of the intracellular Zn distribution. Subsequent electron probe X‐ray microanalysis showed the presence of Zn in globular bodies of about 1 μm diameter, which were frequent in the inner cortical cells of the elongation zone of root tips of the Zn‐tolerant ecotype. The globules were located within the cytoplasm in small vacuoles, and, within each treatment, contained stable proportions of Zn, Mg, and K with relatively large amounts of P. It is suggested that their properties are similar to the globoid crystals of phytate which are known to store minerals in seeds.

Key words:

• Electron probe X‐ray microanalysis
• globoid crystals
• intracellular zinc distribution
• laser microprobe mass analysis
• phytin
• vacuolar compartmentation
• zinc tolerance