Acclimation of shade-tolerant and light-resistant Tradescantia species to growth light: chlorophyll a fluorescence, electron transport, and xanthophyll content.

In this study, we have compared the photosynthetic characteristics of two contrasting species of Tradescantia plants, T. fluminensis (shade-tolerant species), and T. sillamontana (light-resistant species), grown under the low light (LL, 50-125 µmol photons m-2 s-1) or high light (HL, 875-1000 µmol photons m-2 s-1) conditions during their entire growth period. For monitoring the functional state of photosynthetic apparatus (PSA), we measured chlorophyll (Chl) a emission fluorescence spectra and kinetics of light-induced changes in the heights of fluorescence peaks at 685 and 740 nm (F 685 and F 740). We also compared the light-induced oxidation of P700 and assayed the composition of carotenoids in Tradescantia leaves grown under the LL and HL conditions. The analyses of slow induction of Chl a fluorescence (SIF) uncovered different traits in the LL- and HL-grown plants of ecologically contrasting Tradescantia species, which may have potential ecophysiological significance with respect to their tolerance to HL stress. The fluorometry and EPR studies of induction events in chloroplasts in situ demonstrated that acclimation of both Tradescantia species to HL conditions promoted faster responses of their PSA as compared to LL-grown plants. Acclimation of both species to HL also caused marked changes in the leaf anatomy and carotenoid composition (an increase in Violaxanthin + Antheraxantin + Zeaxanthin and Lutein pools), suggesting enhanced photoprotective capacity of the carotenoids in the plants grown in nature under high irradiance. Collectively, the results of the present work suggest that the mechanisms of long-term PSA photoprotection in Tradescantia are based predominantly on the light-induced remodeling of pigment-protein complexes in chloroplasts.

Evaluation of toxic and genotoxic effects of low-level 137Cs ionising radiation on plants.

The aim of this study was to evaluate the impact of low internal exposure to 137Cs on L. sativum meristem cells and Tradescantia stamen hair cells. It also compared the impact of 137Cs internal and external irradiation of similar level on the plant seed germination and root growth. Compared to control, the tested internal (0.0007 mGy to 0.7 mGy) and external (0.04 mGy to 5.5 mGy) 137Cs ionising radiation doses stimulated the elongation of L. sativum roots by 11% to 12% and 24% to 33%, respectively. Internal 137Cs exposure (0.0003 mGy to 0.5 mGy) for 14 days caused 1.2% to 1.6% of somatic mutations and 19% to 87% of non-viable stamen hair in Tradescantia.

A Tradescantia como bioindicador vegetal na monitoração dos efeitos clastogênicos das radiações ionizantes / Use of Tradescantia to monitor the clastogenic effects of ionizing radiation

A influência de agentes químicos e físicos (em especial a radiação) sobre a freqüência de mutações tem sido amplamente estudada por meio da análise de alterações observadas na Tradescantia, uma planta utilizada como bioindicador dessas alterações. A avaliação das alterações genéticas da Tradescantia pode ser feita tanto pela detecção de mutações somáticas quanto de aberrações cromossômicas induzidas por mutágenos presentes no ar, solo e água. Os resultados apresentados por diversos estudos estimulam o uso da Tradescantia na avaliação dos efeitos das radiações ionizantes. Estudos futuros de mutagenicidade e aberrações cromossômicas também podem ser feitos, por meio da comparação com os efeitos produzidos por outros tipos de radiações, avaliação do efeito da associação da radiação com drogas ou outros agentes químicos, além da biomonitoração de ambientes de alto risco.

The influence of chemical and physical agents (specially radiation) on the frequency of mutations has been widely studied by means of the analysis of changes observed in Tradescantia, a plant used as a bioindicator. The evaluation of these genetic changes may be performed both by detection of somatic mutations or chromosome abnormalities induced by mutagens that are present in the air, soil, or water. The results obtained from several studies support the use of Tradescantia for monitoring the effects of ionizing radiation. Studies of mutagenicity and chromosomal abnormalities may be carried out in future to compare the effects of other types of radiation, evaluation of the effects of the combined use of radiation and drugs or other chemical agents, and to monitor high risk environments.

Genotoxic effects of extremely low frequency (ELF) magnetic fields (MF) evaluated by the Tradescantia-micronucleus assay.

Extremely low frequency (ELF) electric fields (EF) and magnetic fields (MF) are generated during the production, transmission, and use of electrical energy. Although epidemiology studies suggest that there is a cancer risk associated with exposure to ELF-MF, short-term genotoxicity assays with bacteria and mammalian cells have produced inconsistent results. In the present study, we investigated the possible genotoxicity of ELF-MF by using the Tradescantia-micronucleus (Trad-MN) assay, a sensitive, reproducible, well-standardized assay for genotoxicity testing. A 50 Hz ELF-MF was generated by a laboratory exposure system consisting of a pair of parallel coils in a Helmholtz configuration. Exposure of Tradescantia (clone # 4430) inflorescences to the ELF-MF, at a flux density (B) corresponding to 1 mT, for 1, 6, and 24 h resulted in a time-dependent increase in MN frequency. The results indicate that a 50 Hz MF of 1 mT field strength is genotoxic in the Trad-MN bioassay and suggest that this assay may be suitable as a biomonitor for detecting the genotoxicity of ELF-MF in the field.

The study of the effects of low-level exposure to ionizing radiation using a bio-indicator system.

The object of the present study was to apply the high sensitivity of a botanical mutagenicity test (Tradescantia stamen-hair mutation bioassay), in "in situ" bioassays to determine the responses induced by the exposure to low levels of ionizing radiation. Mutagenesis was evaluated during 28 days, in an environment that presented gamma radiation exposure rates of 1.6 (control), 25.0 and 75.0 microR min(-1). From the results we observed that there was no linear response throughout the exposure time when compared mutagenic events and gamma radiation exposure rates were compared. The results obtained in the second week of exposure of Tradescantia showed that after exposure to 25.0 and 75.0 microR min(-1) there was a significant increase (p<0.05) in the mutation levels in Tradescantia stamen-hair. In the third and fourth week after exposure 25.0microR min(-1), the plants demonstrated a mutation rate that was not significantly different from the control (p>0.05).

Antimutagenic property of an herbal medicine, Polygonum multiftorum Thunb. detected by the Tradescantia micronucleus assay.

The root extracts of a Chinese herb, Polygonum multiflorum Thunb., have been used for centuries as an internal medicine to improve liver and kidney functions. In this study, we evaluated the antimutagenic property of this drug with the Tradescantia micronucleus (Trad-MCN) assay. The Trad-MCN bioassay is a well-established test for chromosome damage induced by physical or chemical agents in terms of micronuclei (MCN) frequency. Inflorescences of the Tradescantia plant cuttings were first exposed to 0.35 Gy soft X-rays (80 kV, 5 mA, 1 mm Al filter, dose rate around 0.50 Gy/min), followed by drug treatments at 1, 3, and 6% concentrations of the aqueous solution for a total recovery period of 24 hours. The positive (X-rays), negative (nutrient solution), and drug control (3% drug solution) groups were maintained in each of the three series of repeated experiments. Flower buds of the treated and control groups were fixed in aceto-alcohol (1:3 ratio) in preparation for slides to score MCN frequencies in the early tetrads of the meiotic pollen mother cells. The mean MCN frequencies (MCN/100 tetrads +/- SE) of the positive control (irradiated) was 26.68 +/- 2.49; the negative control was 2.93 +/- 0.50; the PM solution control was 2.06 +/- 0.39, and the 0.35 Gy X-ray plus 6% PM drug treated was 18.76 +/- 1.69. A 45% reduction in chromosome damage was observed. Antimutagenic effects were relatively decreased at lower concentrations of PM. This antimutagenic effect could be attributed to the antioxidant action of PM, enhancement of DNA repair, or the radical elimination from the irradiated plant cells.