Electron transport in Tradescantia leaves acclimated to high and low light: thermoluminescence, PAM-fluorometry, and EPR studies.

Using thermoluminescence, PAM-fluorometry, and electron paramagnetic resonance (EPR) for assaying electron transport processes in chloroplasts in situ, we have compared photosynthetic characteristics in Tradescantia fluminensis leaves grown under low light (LL, 50-125 µmol photons m-2 s-1) or high light (HL, 875-1000 µmol photons m-2 s-1) condition. We found differences in the thermoluminescence (TL) spectra of LL- and HL-acclimated leaves. The LL and HL leaves show different proportions of the Q (~ 0 °C) and B (~ 25-30 °C) bands in their TL spectra; the ratios of the "light sums" of the Q and B bands being SQ/SB ≈ 1/1 (LL) and SQ/SB ≈ 1/3 (HL). This suggests the existence of different redox states of electron carriers on the acceptor side of PSII in LL and HL leaves, which may be affected, in particular, by different capacities of their photo-reducible PQ pools. Enhanced content of PQ in chloroplasts of LL leaves may be the reason for an efficient performance of photosynthesis at low irradiance. Kinetic studies of slow induction of Chl a fluorescence and measurements of P700 photooxidation by EPR demonstrate that HL leaves have faster (about 2 times) response to switching on actinic light as compared to LL leaves grown at moderate irradiation. HL leaves also show higher non-photochemical quenching (NPQ) of Chl a fluorescence. These properties of HL leaves (faster response to light and generation of enhanced NPQ) reflect the flexibility of their photosynthetic apparatus, providing sustainability and rapid response to fluctuations of environmental light intensity and solar stress resistance. Analysis of time-courses of the EPR signals of [Formula: see text] induced by far-red (λmax = 707 nm), exciting predominantly PSI, and white light, exciting both PSI and PSII, suggests that there is a contribution of cyclic electron flow around PSI to electron flow through PSI in HL leaves. The data obtained are discussed in terms of photosynthetic apparatus sustainability of HL and LL leaves under variable irradiation conditions.

Limiting Effect of Self-Shading on the Height of Tradescantia fluminensis Mats.

Tradescantia fluminensis is an invasive plant species in New Zealand, Australia and parts of the USA. It reproduces vegetatively and can grow to form dense mats up to 60 cm deep. Growth is limited by available light, and shading is one of the few effective methods of control. In this paper, we develop a dynamic model of a vertical cross section of a T. fluminensis mat, capturing vertical variation in its biomass and internal light intensity. We measure both variables at different heights in experimental mats of the species and use these data to parameterize the model. The model produces realistic vertical biomass and light intensity profiles. We show that the mat grows to a steady-state biomass that depends only on: (i) the light absorption coefficient, which we estimate from experimental data and (ii) the ratio of photosynthesis to respiration rate. This steady state undergoes a transcritical bifurcation; when the ambient light intensity falls below a critical level, the biomass shrinks to zero and the mat cannot survive.

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.

The Tradescantia micronucleus assay is a highly sensitive tool for the detection of low levels of radioactivity in environmental samples.

Environmental contamination with radioactive materials of geogenic and anthropogenic origin is a global problem. A variety of mutagenicity test procedures has been developed which enable the detection of DNA damage caused by ionizing radiation which plays a key role in the adverse effects caused by radioisotopes. In the present study, we investigated the usefulness of the Tradescantia micronucleus test (the most widely used plant based genotoxicity bioassay) for the detection of genetic damage caused by environmental samples and a human artifact (ceramic plate) which contained radioactive elements. We compared the results obtained with different exposure protocols and found that direct exposure of the inflorescences is more sensitive and that the number of micronuclei can be further increased under "wet" conditions. The lowest dose rate which caused a significant effect was 1.2 µGy/h (10 h). Comparisons with the results obtained with other systems (i.e. with mitotic cells of higher plants, molluscs, insects, fish and human lymphocytes) show that the Tradescantia MN assay is one to three orders of magnitude more sensitive as other models, which are currently available. Taken together, our findings indicate that this method is due to its high sensitivity a unique tool, which can be used for environmental biomonitoring in radiation polluted areas.

The role of the mesophyll in stomatal responses to light and CO2.

Stomatal responses to light and CO(2) were investigated using isolated epidermes of Tradescantia pallida, Vicia faba and Pisum sativum. Stomata in leaves of T. pallida and P. sativum responded to light and CO(2), but those from V. faba did not. Stomata in isolated epidermes of all three species could be opened on KCl solutions, but they showed no response to light or CO(2). However, when isolated epidermes of T. pallida and P. sativum were placed on an exposed mesophyll from a leaf of the same species or a different species, they regained responsiveness to light and CO(2). Stomatal responses in these epidermes were similar to those in leaves in that they responded rapidly and reversibly to changes in light and CO(2). Epidermes from V. faba did not respond to light or CO(2) when placed on mesophyll from any of the three species. Experiments with single optic fibres suggest that stomata were being regulated via signals from the mesophyll produced in response to light and CO(2) rather than being sensitized to light and CO(2) by the mesophyll. The data suggest that most of the stomatal response to CO(2) and light occurs in response to a signal generated by the mesophyll.

Use of a bioindicator system in the study of the mutagenetical effects in the neighborhoods of deposits of radioactive waste.

The purpose of the research described in this paper was to analyze the biological mutational effects caused by low doses of ionizing radiation on biological samples placed nearby and around deposits of radioactive waste, as a way of monitoring the environment close to them. In order to do this, the plant Tradescantia pallida was chosen, and through micronuclei tests the sensitivity of the dose/response to bio-monitoring could be observed. The plants were exposed for a period of 24h in previously chosen sites around Brazil, within the proximity of nuclear waste deposits. In each location, three points were chosen for bio-monitoring. The results obtained at these locations showed a small increment in the frequency of micronuclei per cell of the biosensor. From these data, a scale of mutagenesis effects due to low-dose radiation was built up. T. pallida is a good alternative for environmental bio-monitoring in tropical climates, as it is an excellent alternative tool in the studies of the effects of ionizing radiation on the environment.

[The hormonal and genetic effects induced by an irradiation in small dozes at Tradescantia (a clone 02)].

The purpose of the present work was studying the possible interrelation of the hormonal status of plants and size of the genetic effects induced by an irradiation in small dozes. The frequency of somatic mutations in strings Tradescantia (a clone 02) at an irradiation in dozes up to 28 cGy was estimated. Influence radiations in a range from background up to 28 cGy on the maintenance in inflorescences Tradescantia (a clone 02) the basic groups of plant hormones is investigated: abscisic acid, cytokinin, auxin and gibberellin A3. It is shown, that small dozes of an irradiation cause extremely radical changes of hormonal balance in fabrics of inflorescences Tradescantia. Received results are discussed with attraction of the data on influence phytohormones on kinetics a cellular cycle.

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).

Toxicity to Tradescantia of technogenic radionuclides and their mixture with heavy metals.

The genotoxic effects on Tradescantia of (137)Cs, (90)Sr, and (236, 242)Pu, a heavy metal mixture [Cd, Cr(VI), Cu, Mn(II), Ni, Pb, Zn] and of a complex mixture of these toxicants were determined. The impact of radionuclides on plants subjected to ionizing radiation exposure was estimated. The number of somatic mutations and the quantity of nonviable stamen hairs were used as end points in the testing. An increase in the quantity of nonviable stamen hairs was observed with increasing internal exposure to (137)Cs, (90)Sr, and (236, 242)Pu; however, the number of somatic mutations was not observed to be dependent on ionizing radiation. The internal dose of individual radionuclides necessary to decrease the quantity of viable stamen hairs in Tradescantia by 50% can be arranged in the following sequence: (236, 242)Pu > (137)Cs > (90)Sr. Tradescantia died in the mixture of the radionuclides (90)Sr, (137)Cs, and (236)Pu (5 x 10(-2), 7 x 10(-5), and 4 x 10(-10) Gy, respectively) after 14 days, whereas the heavy metal mixture caused somatic mutations in 3% of the Tradescantia and nonviable stamen hairs in 7% but no mortality. However, the Tradescantia died in a combined mixture of these heavy metals and the radionuclides after 14 days. On the basis of all these observations, it can be concluded that the toxic effect of radionuclides was more significant than that of heavy metals.

[Comparative evaluation of early and long-term plant cell reactions under the combination of short-time and chronic impact of 232Th and Cd ]. / Sravnitel'naia otsenka rannikh i otdalennykh reaktsii kletok rastenii na kratkovremennoe i khronicheskoe sochetannoe vozdeistvie 232Th i Cd.

The short-time (30 hours) and chronic (30 days) 232Th and Cd combined effects on Tradescantia and Allium cepa plants were investigated. The 232Th ion concentration was equal to 0.18 mg/l and Cd ion--to 60 mg/l. The early response of both somatic and generative plant cells on Th and Cd combined action was shown to appear in synergic increase of cytogenetic damage frequency. The level of genotoxic and cytotoxic long-term effects turned out to be lower than of the additive one both under the chronic as under the short-time action. These similar in result responses occur on different biological organization levels: in the case of short-time action the effects observed are detected by the intracellular compensatory processes, and in the case of chronic action by the mass death of the most damaged buds in the inflorescence.

Dosimetric assessment of radon in a vegetable system.

An alpha-dose calculation due to radon uptake in anthers of Tradescantia, clone 4430, has been performed. Probability distribution density of the dose in the pollen mother cells was calculated by means of a model that simulates the interaction of separate alpha-particles with these cells. It is shown that alpha-radiation from either radon or its decay products surrounding the buds does not reach pollen mother cells because of the short-range alpha-particles. However, it is suggested that radon diffuses through the gap structure of the bud to the anther from which a radon-gas adsorption process takes place. Absorbed-dose calculations in the anther are discussed as well as their relationship to the experimental results of micronucleus induction in pollen mother cells. The radon concentration interval used (0.85 kBq m(-3)-98.16 kBq m(-3)) is equivalent to the exposure to an average environmental radon concentration (40 Bq m(-3)) for 2.3 months or 22.1 years, respectively. The lowest radon concentration to induce micronuclei was 12.1 kBq m(-3), which is 15 times in excess of that adopted for old buildings in Canada.

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.

Some results of radiobiological studies performed on Cosmos-110 biosatellite.

The experiment carried out on the Cosmos 110 biosatellite is a step further in radiobiological investigations performed in outer space and differs appreciably from flight experiments conducted on board the Vostok and Voskhod spacecraft. The difference lies, firstly, in the integral dose of cosmic radiation. According to the onboard dosimeter readings, it was 12 rad at an average dose rate of 500 mrad/day during the biosatellite flight, whereas in previous biological flight experiments, as is well known, the total dose was below 80 mrad (on a five-day flight of Vostok 5) at a dose rate of 80 to 20 mrad/day. Secondly, during the biosatellite mission, cosmic radiation originated not from the primary cosmic radiation as was the case in the Vostok and Voskhod flights but mainly from the Earth's radiation belts. Thirdly, the duration of the Cosmos 110 flight was far longer than that of any previous mission: the effect of weightlessness lasted for about 22 days. The paper presents results of investigations performed on E. coli K-12 lambda lysogenic bacteria, Tradescantia microspores, dry seeds of higher plants, different Chlorella strains and an intact plant of Tradescantia paludosa. The biological effect of space flight factors was evaluated by various physiological, cytogenetic, genetic and microbiological techniques. Similar to previous experiments carried out on board the Vostok 3-6 spacecraft, tests with lysogenic bacteria revealed a statistically significant induction of moderate bacteriophage. The induction value was shown to lag behind the mission duration dependence level. This seems to be related to a change of inducibility properties of lysogenic bacteria and a reduction of the yield range of phages per bacterial cell. Other tests (duration of the latent period, formation pattern of phage components) indicated no significant differences between test and control objects (N.N. Zhukov-Verezhnikov, N.I. Rybakov, V.A. Kozlov et al.). A study of protective properties of chemical compounds of different types in relation to the bacteriophage induction demonstrated that preparations of the aminothiolic group produced a high antimutagenic effect (V.A. Kozlov, N.I. Rybakov et al.). A postflight cytological analysis of Tradescantia paludosa microspores indicated their changes of three types: chromosome aberrations, mitotic disturbances and disorders of growth processes in the cell. Examinations of dry seeds of wheat, barley, pine and other plants, as well as of Allium cepa bulbs, gave evidence of a diverse effect of space flight factors on both physiological processes and hereditary structures of the objects. In some cases an increased percentage of seed germination, stimulation of their growth and a significant increase of aberrations were found. An investigation of the occurrence frequency of visible mutations in reaction cell cultures of different Chlorella strains (LARG-1, LARG-3 and others) showed no significant differences between the test and control material. Some cultures taken under a more detailed study indicated a delay with which cells entered the first sporulation and a greater amount of cells that divided into a lesser than usual number of autospores. In addition, test variants of the strains showed a slightly reduced survival of Chlorella cells. The reduction appeared to be statistically significant for the LARG-3 strain only (E.N. Vaulina et al.). A postflight examination of the appearance of the Tradescantia paludosa plant showed that it retained good turgor; its leaves were dark green and several bright flowers bloomed. No signs of its inhibition or etiolation were noted. As compared to the control, the test plant grew noticeably and the stem became crooked. Certain problems of biological indications of outer space are discussed.