RESUMO
Environmental cadmium (Cd) sources have increased in mangrove sediments in recent decades, inducing cellular damage to many plants. Avicennia schaueriana is abundant in mangrove sites and has been subject to Cd contamination. The possible effects of Cd toxicity and the structural and physiological disturbances to this plant were studied. Can this plant express early cellular tolerance mechanisms to such metal contamination? Seedlings of A. schaueriana were collected from sites of their natural occurrence, placed in plastic pots containing nutrient solution for 60 days, and subsequently exposed to increasing Cd concentrations for 5 days under experimental conditions. The anatomical, ultrastructural and physiological changes induced by Cd were analysed. Cd accumulated mainly in the root system and in pneumatophores, stems and leaves, induced differential accumulation of mineral nutrients, but did not induce necrosis or changes in leaf anatomy. However, there was a decrease in starch grains and an increase in deposited electron-dense material in the cortex and vascular bundles. Cd induced both increases in calcium (Ca) content in shoots and Ca oxalate crystal precipitation in leaf mesophyll and was detected in crystals and in the secretion of salt glands. Our observations and experimental results provide evidence of Cd tolerance in A. schaueriana. As a new feature, despite the clear cellular physiological disorders, this plant is able to eliminate Cd through leaf salt glands and immobilise it in Ca crystals, representing fast mechanisms for Cd exclusion and complexation in leaves in heavy metal coastal polluted marine ecosystems.
Assuntos
Avicennia/efeitos dos fármacos , Cádmio/toxicidade , Folhas de Planta/metabolismo , Avicennia/metabolismo , Avicennia/ultraestrutura , Cádmio/metabolismo , Cálcio/metabolismo , Microscopia Eletrônica de Transmissão , Raízes de Plantas/metabolismo , Caules de Planta/metabolismo , Plântula/efeitos dos fármacos , Plântula/metabolismo , Plântula/ultraestruturaRESUMO
Mangroves have been subject to more metal contamination, including cadmium (Cd). This study evaluated if a relatively short Cd exposure may induce metabolic, morphological and ultrastructural cell disturbance in Avicennia schaueriana. Cd induced evident constraints to seedlings since there was reduction in leaf gas exchanges and the plants did not survive for more than 10â¯days at a higher Cd exposure in controlled conditions. The highest Cd accumulation was observed in roots and gradually less in stem and leaves. Cadmium induced lignin deposition was observed in xylem cells of all vegetative organs. Intense sclerification in xylem cells, endoderm and change in the hypoderm organization were also detected. Cadmium clearly induced chloroplast deformities with ruptures of its membranes, thylakoids and core and provoked cytoplasm disorganization. These metal constraints under natural conditions for long term can lead to the accumulation of cellular and metabolic damages and jeopardize seedlings establishment and local biodiversity.
Assuntos
Avicennia/efeitos dos fármacos , Cádmio/toxicidade , Ecotoxicologia/métodos , Avicennia/metabolismo , Avicennia/ultraestrutura , Cádmio/farmacocinética , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Raízes de Plantas/química , Caules de Planta/efeitos dos fármacos , Plântula/efeitos dos fármacos , Áreas AlagadasRESUMO
Mangrove sites are constantly under tidal regimes, where there is variation of dissolved oxygen and saline content in water. This study evaluated the effects of varying salinity in Avicennia schaueriana, an abundant species in the sea-mangrove-river interface. Seedlings of A. schaueriana were harvested at the riverbank and placed in different saline and nutrient solutions in a greenhouse in order to simulate a saline flow. After 7 acclimatization days, plants were exposed to the following saline concentrations: 0, 50, 170 and 250mM NaCl, for a period of 30 days. After this, leaf gas exchange, chlorophyll a fluorescence, Falker chlorophyll index, leaf ultrastructure and micromorphology were evaluated. The highest saline concentration affected mainly the CO2 assimilation, internal CO2 concentration and the intrinsic efficiency of water use. The chlorophyll a fluorescence and Falker index were not significantly affected by any of the saline conditions, however chloroplast was damaged. Concomitantly, leaf salt glands clearly evidenced a higher salt secretion, when plants were submitted to the greatest saline concentration. The results indicated that A. schaueriana tolerates different salt concentration in the mangrove and excretes salt excess by salt gland, and this can attenuate the saline stress. However, when exposed to longer periods of higher salt fluxes the plant growth can be affected.
Assuntos
Aclimatação/efeitos dos fármacos , Avicennia/efeitos dos fármacos , Fotossíntese/efeitos dos fármacos , Folhas de Planta/efeitos dos fármacos , Cloreto de Sódio/farmacologia , Áreas Alagadas , Animais , Avicennia/crescimento & desenvolvimento , Avicennia/fisiologia , Clorofila/metabolismo , Clorofila A , Cloroplastos/efeitos dos fármacos , Cloroplastos/metabolismo , Relação Dose-Resposta a Droga , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/fisiologia , Rios/química , Salinidade , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimento , Plântula/fisiologiaRESUMO
In Brazil, some mangrove areas are subjected to air pollution by particulate iron from mining activities. However, the effect of this pollutant on mangrove plants is not well known. This study aimed to comparatively analyze the morphoanatomy, histochemistry, and iron accumulation in leaves of Avicennia schaueriana, Laguncularia racemosa, and Rhizophora mangle. Samples were collected from five mangrove sites of Espírito Santo state, each of which is exposed to different levels of particulate iron pollution. The amount of particulate material settled on the leaf surface was greater in A. schaueriana and L. racemosa, which contain salt glands. High iron concentrations were found in leaves of this species, collected from mangrove areas with high particulate iron pollution, which suggests the foliar absorption of this element. None of the samples from any of the sites showed morphological or structural damage on the leaves. Scanning electron microscopy (SEM) coupled to X-ray diffraction rendered a good method for evaluating iron on leaves surfaces. A histochemical test using Prussian blue showed to be an appropriate method to detect iron in plant tissue, however, proved to be an unsuitable method for the assessment of the iron bioaccumulation in leaves of A. schaueriana and R. mangle. So far, this study demonstrates the need of evaluating the pathway used by plants exposed to contaminated particulate matter to uptake atmospheric pollutants.
Assuntos
Avicennia/efeitos dos fármacos , Combretaceae/efeitos dos fármacos , Poluição Ambiental/análise , Ferro/metabolismo , Material Particulado/farmacologia , Folhas de Planta/metabolismo , Rhizophoraceae/efeitos dos fármacos , Avicennia/metabolismo , Brasil , Combretaceae/metabolismo , Monitoramento Ambiental/métodos , Microscopia Eletrônica de Varredura , Rhizophoraceae/metabolismo , Difração de Raios XRESUMO
The effects of copper toxicity on the photosynthetic activities of Avicennia germinans was investigated using two CuSO4 concentrations (0.062 and 0.33 M) added in Hoagland's solution in an aerated hydroponic system. Photosynthesis and chlorophyll fluorescence were measured after 30 h of copper stress. Results obtained in this study show that increasing levels of Cu(+2) of 0.062 and 0.33 M Cu(+2) resulted in a general reduction of the stomatal conductance (28 and 18%, respectively) and 100% of inhibition of net photosynthesis. Additionally, at these concentrations of Cu(+2), reductions of chlorophyll fluorescence parameters were also observed. These changes suggested that the photosynthetic apparatus of Avicennia germinans was the primary target of the Cu(+2) action. It is concluded that Cu(+2) ions causes a drastic decline in photosynthetic gas exchange and Chlorophyll fluorescence parameters in A. germinans leaves.
Assuntos
Avicennia/efeitos dos fármacos , Clorofila/metabolismo , Cobre/toxicidade , Fotossíntese/efeitos dos fármacos , Estresse Fisiológico/efeitos dos fármacos , FluorescênciaRESUMO
The effect of heavy metal stress on the cell viability and leakage of electrolytes of Avicennia germinans leaf discs was investigated by the tissue tolerance test. Foliar discs were incubated with different Cd2+ or CU2+ concentrations for 24 h; thereafter, the cell membrane stability of the tissue was assayed by the cell viability Evans blue and leakage electrolytes methods. The results indicated that electrolyte leakage of the leaf discs increased 24 h after exposure to heavy metal stress, as shown by a reduction of the cell viability by 30% in discs exposed to higher doses of Cd2+ (0.546 M) and Cu2+ (0.7 M), respectively. Additionally, the histological analysis of the leaf discs exposed to heavy metal stress revealed that at higher Cd2+ and/or Cu2+ concentrations an increase in the intercellular spaces and destruction of mesophyll cells was observed 24 h after exposure. In summary, the biochemical and structural changes observed in foliar tissues of A. germinans suggest that higher cadmium and copper concentrations may result in structural changes and altered physiological characters in leaves.
Assuntos
Avicennia/citologia , Sobrevivência Celular/efeitos dos fármacos , Eletrólitos/metabolismo , Metais Pesados/farmacologia , Avicennia/efeitos dos fármacos , Avicennia/metabolismo , Cádmio/farmacologia , Cobre/farmacologia , Folhas de Planta/citologia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Sementes/efeitos dos fármacos , Sementes/metabolismoRESUMO
Alterations in the glutathione antioxidant system and lipid peroxidation in Avicennia marina were studied under laboratory and field conditions. The activity of glutathione peroxidase (GPx) was found to respond to Zn exposure, and a significant positive relationship between leaf Zn concentration and GPx activity was observed after 96 h and 8 weeks. Lipid hydroperoxides increased proportionally with increasing leaf Zn concentration after 2 and 8 weeks, while no changes in total glutathione were observed. Induction of GPx at 96 h predicted effects at the individual level at a later time interval (reduced biomass at 8 weeks). Results from the field revealed that increasing leaf metal concentration (Zn, Cu or Pb) produced a proportional increase in GPx activity whereas lipid hydroperoxides and total glutathione were not affected. The utility of GPx as an early warning biomarker is suggested, since GPx activity increases in a dose-dependant fashion in response to accumulated leaf metals, and is predictive of later effects on growth.
Assuntos
Antioxidantes/metabolismo , Avicennia/efeitos dos fármacos , Avicennia/metabolismo , Glutationa/metabolismo , Poluentes Químicos da Água/toxicidade , Zinco/toxicidade , Austrália , Avicennia/química , Biomarcadores , Monitoramento Ambiental , Sedimentos Geológicos/química , Metais Pesados/toxicidade , Folhas de Planta/química , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismoRESUMO
To evaluate the role of phytochelatins and metallothioneins in heavy metal tolerance of black mangrove Avicennia germinans, 3-month-old seedlings were exposed to cadmium or copper for 30 h, under hydroponic conditions. Degenerate Mt2 and PCS primers were synthesized based on amino acid and nucleotide alignment sequences reported for Mt2 and PCS in other plant species found in GenBank. Total RNA was isolated from A. germinans leaves and two partial fragments of metallothionein and phytochelatin synthase genes were isolated. Gene expression was evaluated with reverse transcripatase-polymerase chain reaction (RT-PCR) amplification technique. Temporal analysis showed that low Cd2+ and Cu2+ concentrations caused a slight (but not significant) increase in AvMt2 expression after a 16 h exposure time, while AvPCS expression showed a significant increase under the same conditions but only after 4h. Results strongly suggest that the rapid increase in AvPCS expression may contribute to Cd2+ and Cu2+ detoxification. Moreover, we found that A. germinans has the capacity to over-express both genes (AvMt2 and AvPCS), which may constitute a coordinated detoxification response mechanism targeting non-essential metals. Nonetheless, our results confirm that AvPCS was the most active gene involved in the regulation of essential metals (e.g., Cu2+) in A. germinans leaves.
Assuntos
Aminoaciltransferases/efeitos dos fármacos , Avicennia/efeitos dos fármacos , Cádmio/toxicidade , Cobre/toxicidade , Metalotioneína/efeitos dos fármacos , Poluentes da Água/toxicidade , Sequência de Aminoácidos , Aminoaciltransferases/biossíntese , Aminoaciltransferases/genética , Avicennia/genética , Avicennia/metabolismo , Sequência de Bases , Cádmio/metabolismo , Cobre/metabolismo , Exposição Ambiental , Expressão Gênica/efeitos dos fármacos , Metalotioneína/biossíntese , Metalotioneína/genética , Dados de Sequência Molecular , Folhas de Planta/química , Reação em Cadeia da Polimerase , Alinhamento de Sequência , Fatores de Tempo , Poluentes da Água/metabolismoRESUMO
The toxic effects of cadmium on the photosynthetic apparatus of Avicennia germinans were evaluated by means of the chlorophyll fluorescence transient O-J-I-P. The chlorophyll fluorescence transients were recorded in vivo with high time resolution and analyzed according to the OJIP-test that can quantify the performance of photosystem II. Cadmium-treated plants showed a decrease in yield for primary photochemistry, TR0/ABS. The performance index of photosystem II (PSII), PI(ABS), decreased due to cadmium treatment. This performance index is the combination of the indexes of three independent parameters: (1) total number of active reaction centers per absorption (RC/ABS), (2) yield of primary photochemistry (TR0/ABS), and (3) efficiency with which a trapped exciton can move an electron into the electron transport chain (ET0/TR0). Additionally, the F0/Fv registered the highest sensitivity to the metal, thus indicating that the water-splitting apparatus of the oxidizing side of PSII is the primary site of action of cadmium. In summary, cadmium affects several targets of photosystem II. More specifically the main targets of cadmium, according to the OJIP-test, can be listed as a decrease in the number of active reaction centers and damage to the activity of the water-splitting complex.
Assuntos
Avicennia/fisiologia , Cádmio/toxicidade , Fotossíntese/efeitos dos fármacos , Complexo de Proteína do Fotossistema II/efeitos dos fármacos , Avicennia/efeitos dos fármacos , Relação Dose-Resposta a Droga , Cinética , Fotossíntese/fisiologia , Teoria Quântica , Espectrometria de FluorescênciaRESUMO
We have studied the interactive effects of salinity and light on Avicennia germinans mangrove seedlings in greenhouse and field experiments. We hypothesized that net photosynthesis, growth, and survivorship rates should increase more with an increase in light availability for plants growing at low salinity than for those growing at high salinity. This hypothesis was supported by our results for net photosynthesis and growth. Net daily photosynthesis did increase more with increasing light for low-salinity plants than for high-salinity plants. Stomatal conductance, leaf-level transpiration, and internal CO(2) concentrations were lower at high than at low salinity. At high light, the ratio of leaf respiration to assimilation was 2.5 times greater at high than at low salinity. Stomatal limitations and increased respiratory costs may explain why, at high salinity, seedlings did not respond to increased light availability with increased net photosynthesis. Seedling mass and growth rates increased more with increasing light availability at low than at high salinity. Ratios of root mass to leaf mass were higher at high salinity, suggesting that either water or nutrient limitations may have limited seedling growth at high salinity in response to increasing light. The interactive effects of salinity and light on seedling size and growth rates observed in the greenhouse were robust in the field, despite the presence of other factors in the field--such as inundation, nutrient gradients, and herbivory. In the field, seedling survivorship was higher at low than at high salinity and increased with light availability. Interestingly, the positive effect of light on seedling survivorship was stronger at high salinity, indicating that growth and survivorship rates are decoupled. In general, this study demonstrates that environmental effects at the leaf-level also influence whole plant growth in mangroves.