Cation localization and related biological responses in the liverwort Conocephalum conicum L. Dum exposed to environmentally relevant concentrations of Zn, Cu, Cd and Pb.
(1) Department of Biology, University of Naples Federico II, Naples, Italy; (2) CeSMA, University of Naples Federico II, Naples, Italy; (3) ISPRA, Italian National Institute for Environmental Protection and Research, Rome, Italy.
In the present study we assessed the tissue localization, oxidative stress, ultrastructural alterations and photosynthesis efficiency in the gametophyte of the thallose liverwort Conocephalum conicum exposed in-vitro to a mix of Zn, Cu, Cd and Pb. For the exposure mixture we choose environmentally relevant concentrations detected in different impacted areas of Savone river. First, we investigated the accumulation and conduction pattern of the selected metals in the epidermis, photosynthetic parenchyma and hyaline parenchyma through X-ray microanalysis and the bulk metal concentrations in the whole thalli through ICP-MS. The results showed the heavy metals bioaccumulation in C. conicum was dependent by its concentration in the contaminated water. X-ray microanalysis evidenced that non-essential metals (Cd and Pb) accumulated mainly in the central portion of the thallus (nerve) and specifically in the hyaline parenchyma, whilst essential metals (Zn and Cu) were more homogeneously distributed between the tissues. After, we investigated ultrastructural alterations, oxidative stress biomarkers (ROS, CAT, SOD, GST), and photosynthetic efficiency through PAM imaging in the both nerves and wings tissues. At the ultrastructural level, the exposure to the mix caused alterations of the fine structure of the cells, inducing marked alterations of the chloroplast structure. Accordingly, an enhancement of CAT, SOD and GST activities was observed. The PAM imaging shown that the lowest photosynthetic efficiency was localized in the central tissue, in accordance with the ultrastructural alteration observed in the chloroplasts of the photosynthetic parenchyma of the nerve. All these responses were higher in the nerve than the wing tissues of C. conicum thalli.
Keywords: Conocephalum conicum; environmental pollution; heavy metals; photosynthesis; tissue localization; ultrastructure.
