# Effects of Toxic Concentrations of Cadmium, Lead, or Zinc on Leaf Morphology, Anatomy and Calcium Oxalate Content in Metallicolous and Non-Metallicolous Ecotypes of Dianthus carthusianorum L

## TL;DR

This study shows how plants from metal-polluted areas adapt by producing more calcium oxalate to detoxify heavy metals.

## Contribution

The study identifies calcium oxalate as a key factor in metal detoxification in plants from polluted environments.

## Key findings

- Metal exposure caused mesophyll cell alterations and increased calcium oxalate in both ecotypes.
- The metallicolous ecotype accumulated nearly twice as much calcium oxalate as the non-metallicolous ecotype.
- Elevated calcium oxalate levels were observed in the metallicolous ecotype even without metal exposure.

## Abstract

Tolerance to metals develops independently across plant species and even among populations of the same species under strong environmental pressure. This study compares the morphology and leaf anatomy of Dianthus carthusianorum L. originating from a Zn–Pb waste dump (metallicolous ecotype, M) and from unpolluted areas (non-metallicolous ecotype, NM), exposed to toxic concentrations of Cd, Pb, or Zn under chronic (field) and acute (hydroponic) metal stress. The aim was to identify leaf anatomical adaptations that support growth of the M ecotype in metal-polluted environments and to assess structural changes induced by acute exposure in both ecotypes. In both ecotypes, metal exposure caused alterations of mesophyll cells and the formation of abundant calcium oxalate (CaOx) crystals. Two oxalate forms were determined: insoluble (CaOx crystals) and soluble oxalates, with the former predominating. Following metal treatment, the M ecotype accumulated nearly twice as much of both forms as the NM ecotype, indicating a key role of oxalates in metal detoxification via precipitation of excess metal ions as metabolically inactive CaOx. Interestingly, elevated CaOx levels were also observed in M ecotype leaves grown under control (no metal application) conditions, suggesting a genetically fixed adaptation to metal-rich environments.