24 research outputs found
Morphological changes induced by heavy metals in dandelion (Taraxacum officinale Web.) growing on mine soils.
Purpose Heavy metal accumulation produces significant
physiological and biochemical responses in vascular plants.
Plants growing on abandoned mine sites are of particular
interest, since they are genetically tolerant to high metal
concentrations. In this work, we examined the effect of heavy metals (HMs) on the morphology of T. officinale growing in pots with mine soils, with the following objectives: (1) to determine the evolution of HM concentration in leaves and roots over 3 years of cultivation; (2) to highlight possible
damage at anatomical and cytological level.
Materials and methods Wild specimens of Taraxacum
officinale Web., with their soil clod, were gathered from three
sites with different contamination levels by heavy metals (Cd,
Cr, Cu, Fe, Pb, Zn) in the abandoned Imperina Valley mine
(Northeast Italy). A control plant was also gathered from a
non-contaminated site nearby. Plants were cultivated in pots at the botanical garden of the University of Florence (HBF), and appeared macroscopically not affected by toxic signals (reduced growth, leaf necrosis) possibly induced by soil HM
concentration. Leaves and roots taken at the same growing
season were observed by light microscopy and transmission
electron microscopy. Results and discussion Light microscopy observations show a clear difference in the cellular organisation of noncontaminated and contaminated samples. The unpolluted samples present a well-organised palisade tissue and spongy photosynthetic parenchyma. Samples from contaminated sites, instead, present a palisade parenchyma less organised, and a reduction of leaf thickness proportional to HM concentration.
The poor structural organisations, and the reduced
foliar thickness of the contaminated plants, are related to soil
contamination. Differences in root micromorphology concern
the cortical parenchyma. Moreover, all the samples examined
present mycorrhiza. Ultrastructure observations of the parenchyma cells show mitochondrial structure alteration, with
lacking or reduced cristae of the internal membrane at increasing metal content. Instead, chloroplast organisation does not present significant differences, particularly in number and compartmentalization of thylakoids.
Conclusions Although macromorphology does not present
evidence of phytotoxicity, the recorded observations of the
micromorphological characteristics of leaves and roots, show
a suffering state of the plants, strictly related to HM content.
Leaching reduced partly the HM content of the soil, therefore
decreasing their phytotoxic effect. A gradual restoration of
leaf organisation suggests that somewhat resilience occurred
in plants. Moreover, the presence of stress-tolerant mycorrhizal fungi could contribute to reduce metal toxicity