Seminars Archive

CdS quantum dots and CdSO4 salts behave as different types of stressors on A. thaliana w.t.

Abstract
Plants of A. thaliana (L. erecta) w.t., were tested in vitro at three times of growth (15, 30, 45 d.) with three concentrations of either CdSQDs or CdSO4. The contaminants were supplemented in agarized MS medium respectively as water-soluble nanoparticles or as salts at concentrations corresponding to 0, 1/3 MIC, 2/3 MIC (MIC = minimum concentration for growth inhibition, already calculated in previous experiments). Plants were analysed for total Cd concentration and main oxidative stress non-enzymatic parameters: chlorophylls and carotenoids content in leaves, leaf respiration, total phenolics, ABTS, DPTH, total H2O2, GSH redox state, AsA redox state, Lipid peroxidation. These measures were utilised in a multivariate statistic approach to understand the impact of type and time of treatment on the plants oxidative stress level. Factor reduction statistics was instrumental to identify physiological descriptors for nanoparticle-induced oxidative stress. ESEM/EDX was used to observe leaf and roots without sample treatment, at low-vacuum and high humididty, with magnification from 1000 to 3000x to detect morphological changes at the level of organ and tissues such as: main root thickness and length, lateral roots number and morphology, hairy roots density, root cap shape, aberrations in leaf trichome number and brancing, stomata number, adaxial wax deposition, reproductive organs development. Microanalysis was performed to verify Cd uptake from the roots, root-shoot translocation and identify possible sinks for Cd storage for all types of treatments. These parameters were used to establish a correlation between the oxidative stress response of the plants to CdS QDs or to Cd salt, at different concentrations and treatment time. Taking into account the natural senescence process of A. thaliana (particularly evident after 45 days), we evidenced substantial differences in the response of the plants to the two types of contaminants. CdS QDs caused slow increase in oxidative stress which the plant cells were able to counter in the first stages of the treatment with non-enzymatic antioxidants. However on the long term, oxidative stress, respiration and photosynthesis depletion reached toxic levels. After 45 days, CdSQDs caused gross roots morphology aberration, reduced trichome brancing, decrease in stomata number. Cd salt toxicity was evident in the short term, after 30 days ROS production was causing cell redox state imbalance, drop in photosynthesis and respiration, induction of thin, hairless roots, trichome and stomata death, adaxial wax deposition.