Oil induces chlorophyll deficient propagules in mangroves.

In Australia, some trees of the mangrove, Avicennia marina, growing in a chronic oil polluted site, produce chlorophyll deficient (albino) propagules. We tested the hypothesis that albinism was due to an oil-induced mutant allele that controls photosynthesis. We determined whether there are genetic differences between normal and chlorophyll deficient propagules. Four gene regions (nuclear 18S-26S cistron; chloroplast - trnH-psbA, rsp16 and matK) were sequenced and analysed for normal and albino propagules. Mutations occurred in both nuclear (ITS) and coding chloroplast (matK) genes of albino propagules. There were 10 mutational differences between normal and albino propagules in the matK samples. Analysis of molecular variation (AMOVA) of the matK dataset indicated highly significant genetic differentiation between normal and albino propagules. Our study suggests for the first time that PAHs from a chronic oil polluted site resulted in mutations in both nuclear and chloroplast genes, resulting in the production of albino propagules.

The alleviation effect of iron on cadmium phytotoxicity in mangrove A. marina. Alleviation effect of iron on cadmium phytotoxicity in mangrove Avicennia marina (Forsk.) Vierh.

Cd has high activity and bioavailability and is a poisonous element to plants. As a critical ecosysterm, mangroves are subjected to serious Cd pollution. In this research, the hypothesis was presented that improving Fe bioavailability would alleviate Cd phytotoxicity to Avicennia marina (Forsk.) Vierh. To test this, we examined the effect of four exogenous Fe and three Cd concentrations on A. marina. The results showed that a significant positive correlation excited between moderate exogenous Fe concentration and Cd tolerance of A. marina. Moderate exogenous Fe concentration directly or indirectly promoted the formation of Fe plaque, which immobilised more Cd on the root surface and decreased Cd absorption in roots. Furthermore, an exogenous Fe application increased plant biomass and Fe accumulation in A. marina tissues. This improved the competition between Fe and Cd within the plants. Therefore, an Fe application facilitated a decrease in Cd toxicity within A. marina. Simultaneously, a moderate Fe concentration caused an increase in low-molecular-weight organic acid (LMWOA) secretion from the roots. Meanwhile, Cd can be chelated/complexed by LMWOAs. It also played a crucial role in Cd detoxification in A. marina. In conclusion, Fe application accelerated the growth and enhanced Cd tolerance of A. marina. Therefore, improving Fe bioavailability will protect mangroves from Cd contamination.

Ultrastructural and metabolic disorders induced by short-term cadmium exposure in Avicennia schaueriana plants and its excretion through leaf salt glands.

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.

Growth and antioxidative response of two mangrove plants to interaction between aquaculture effluent and BDE-99.

Mangroves are subject to contamination of polybrominated diphenyl ethers (PBDEs) due to waste and wastewater disposal, and aquaculture effluent (AE) from nearby aquaculture activities. However, the response of mangrove plants to these two stresses and their interaction has seldom been reported. A six-month microcosm study, planted with either Kandelia obovata (Ko) or Avicennia marina (Am), the two most dominant species in South China mangrove swamps, was conducted to investigate the effects of BDE-99, and the interactions of BDE-99 (one of the most abundant PBDE congeners) and AE on growth and physiological responses of these plants. In addition to mixed stressors, both stressors were also applied individually. Results showed that Avicennia was more tolerant to BDE-99 contamination than Kandelia, as reflected by the reduced biomass, but increased superoxide radical (O2-⁎) release and malondialdehyde (MDA) content in Kandelia. Addition of AE alleviated toxicity of BDE-99 in Kandelia by promoting biomass but lowering oxidative stress and MDA production. The hormesis model also demonstrated that the interaction between BDE-99 and AE on leaf and root MDA and O2-⁎ content in both Kandelia and Avicennia were mostly antagonistic. Activities of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) in both leaf and root of Kandelia were reduced by BDE-99. On the contrary, BDE-99 significantly enhanced the three enzyme activities in Avicennia root at month 3. Addition of AE also significantly enhanced root CAT, POD and SOD activities, and leaf SOD in both plant species to remove excess ROS produced under BDE-99 exposure. These results indicated that the tolerance of mangrove plants to oxidative stresses depended on antioxidative enzymes that were inducible.

Root activities and arsenic translocation of Avicennia marina (Forsk.) Vierh seedlings influenced by sulfur and iron amendments.

Sulfur and iron are abundant and have close, complex interactions with the biogeochemical cycle of arsenic (As) in mangrove ecosystems. A hydroponic experiment was conducted to investigate the influences of variable SO42- and Fe2+ supplies on radial oxygen loss (ROL), iron plaque formation and As translocation in Avicennia marina upon exposure to As(III). The results indicate that A. marina is an As-tolerant plant, the application of iron and sulfur not only showed positive growth effects but also induced much higher amounts of ROL-induced iron plaque formation on root surfaces. The presence of iron plaque remarkably improved the proportion of As sequestration near this area but consequently reduced the proportion of As translocation in root. Therefore, it is concluded that iron plaque may act as a barrier for protection against As, and iron and sulfur play important roles in controlling the growth and translocation of As in A. marina seedlings.

Effects of different humic substances concentrations on root anatomy and Cd accumulation in seedlings of Avicennia germinans (black mangrove).

Mangrove areas are among most threatened tropical ecosystems worldwide. Among polluting agents Cadmium is often found in high concentrations in mangrove sediments. Humic substances, complex biomolecules formed in soil and sediments during animal and plant residuals decomposition, have a known biostimulant activity and can be adopted to counteract various plant stresses. This study explores, in controlled conditions, the effect of humic substances on Avicennia germinans seedlings, with or without cadmium contamination. Humic compounds significantly changed plant root architecture, and, when coupled with cadmium, root anatomy and Cortex to Vascular Cylinder diameter ratio. These modifications led to lower Cd uptake by humic substances-treated plants. Humic substances amendment could be effective, depending on their concentrations, on improving plant health in mangrove areas, for forest recuperation and/or dredged sediments phytoremediation purposes.

Short-term cadmium exposure induces gas exchanges, morphological and ultrastructural disturbances in mangrove Avicennia schaueriana young plants.

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 10 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.

A combined effect of polybrominated diphenyl ether and aquaculture effluent on growth and antioxidative response of mangrove plants.

Mangrove wetland receives nutrient-rich aquaculture effluent (AE) from nearby farming activities and polybrominated diphenyl ethers (PBDEs) from the production and usage of flame retardants. The effects of BDE-209 (the most common PBDE congener), AE and their combination on two true mangrove species, namely Kandelia obovata and Avicennia marina, were compared in a 6-month microcosm study. Results showed that K. obovata was more sensitive to these contaminants than A. marina, as reflected by its enhanced production of leaf superoxide (O2-∗) by BDE-209 and root malondialdehyde (MDA) by the combined BDE-209 and AE treatment. The hormesis model showed that the combined effects of BDE-209 and AE on the production of MDA, O2-∗ and catalase (CAT) activity in K. obovata and A. marina were antagonistic except root O2-∗ in A. marina, but the effects on leaf superoxide dismutase (SOD) activity in K. obovata, and root SOD and peroxidase (POD) activities in A. marina were synergistic. The defense mechanisms differed between treatment and species. The activities of SOD and POD were the main mechanisms to defend K. obovata and A. marina against BDE-209, but CAT in K. obovata and POD in A. marina were more important in defending the combined BDE-209 and AE treatment.

Exogenous phosphorus enhances cadmium tolerance by affecting cell wall polysaccharides in two mangrove seedlings Avicennia marina (Forsk.) Vierh and Kandelia obovata (S., L.) Yong differing in cadmium accumulation.

Phosphorous (P) is an essential element that mediates various stresses in plants. In this study, the effects of P on polysaccharides in the root cell walls of two hydroponically cultivated mangrove seedlings (A. marina and K. obovata) that differ in Cd accumulation ability were examined in the context of Cd stress. The results showed that A. marina exhibited a higher degree of tolerance to Cd than K. obovata. In both mangrove seedlings, pectin and hemicellulose 1 increased significantly with increasing P levels, the effects of which were greater in A. marina under Cd stress. In addition, cell wall pectin methylesterase (PME) activity was markedly increased in the presence of Cd and P compared with Cd alone. These effects were more pronounced in A. marina than in K. obovata. Taken together, the results of this study provide further insight into the mechanisms of P-mediated alleviation of Cd stress in mangrove seedlings.

The retention and distribution of parent, alkylated, and N/O/S-containing polycyclic aromatic hydrocarbons on the epidermal tissue of mangrove seedlings.

The polycyclic aromatic hydrocarbons (PAHs) located on the epidermal tissues showed distinctive toxic effects to root, while the retention and distribution of PAHs on mangrove seedlings poorly understood. Our results confirmed that the partition coefficients (Kf) of the PAHs retained on the epidermal tissue of mangrove roots, such as Kandelia obovata, Avicennia marina and Aegiceras corniculatum, were much higher than the Poaceae plants roots, for example wheat and maize (Wild et al., 2005). Moreover, to the parent and alkyl PAHs, a well negative correlation was observed between the surface polarity of these three species of mangrove root and the Kf values (p < 0.05). To the N/O/S containing PAHs, these relationships were not obviously due to existing of the π-π, n-π interactions and hydrogen bonding between the N/O/S-containing PAHs and epidermal tissues. The PAHs retained on these three species of mangrove root epidermal tissues formed larger clusters than that of on Poaceae plants, such as wheat and maize (Wild et al., 2005) due to the limitation of the suberization of the root exodermis and endodermis. After exposure of 30 d, rhizo- and endophytic bacteria degraded parts of the N/O/S-containing PAHs to medium-lifetime fluorescence substances. To our knowledge, this is the first time to assess the retention of PAHs on the epidermal tissue of mangrove root, which will improve our understanding of the root uptake PAHs process.

Different salt concentrations induce alterations both in photosynthetic parameters and salt gland activity in leaves of the mangrove Avicennia schaueriana.

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.

Phosphorus mediation of cadmium stress in two mangrove seedlings Avicennia marina and Kandelia obovata differing in cadmium accumulation.

Mangrove ecosystems are vulnerable to environmental threats. In order to elucidate the effect of phosphorus (P) on cadmium (Cd) tolerance and physiological responses in mangroves under Cd stress, a mangrove specie with salt exclusion Kandelia obovata and a specie with salt secretion Avicennia marina were compared in a hydroponic experiment. The results showed that most Cd was accumulated in mangrove roots and that P addition induced Cd immobilisation in them. Cd stress significantly increased malonaldehyde content, whereas P significantly decreased malonaldehyde in mangroves. Phosphorus positively regulated the photosynthetic pigment, proline content and synthesis of non-protein thiols, glutathione and phytochelatins in the leaves under Cd stress conditions. The results suggest different adaptive strategies adopted by two mangroves in a complex environment and A. marina showed a stronger Cd tolerance than K. obovata. The study provides a theoretical basis for P mediated detoxification of Cd in mangrove plants.

The effects of CO2 and nutrient fertilisation on the growth and temperature response of the mangrove Avicennia germinans.

In order to understand plant responses to both the widespread phenomenon of increased nutrient inputs to coastal zones and the concurrent rise in atmospheric CO2 concentrations, CO2-nutrient interactions need to be considered. In addition to its potential stimulating effect on photosynthesis and growth, elevated CO2 affects the temperature response of photosynthesis. The scarcity of experiments testing how elevated CO2 affects the temperature response of tropical trees hinders our ability to model future primary productivity. In a glasshouse study, we examined the effects of elevated CO2 (800 ppm) and nutrient availability on seedlings of the widespread mangrove Avicennia germinans. We assessed photosynthetic performance, the temperature response of photosynthesis, seedling growth and biomass allocation. We found large synergistic gains in both growth (42 %) and photosynthesis (115 %) when seedlings grown under elevated CO2 were supplied with elevated nutrient concentrations relative to their ambient growing conditions. Growth was significantly enhanced under elevated CO2 only under high-nutrient conditions, mainly in above-ground tissues. Under low-nutrient conditions and elevated CO2, root volume was more than double that of seedlings grown under ambient CO2 levels. Elevated CO2 significantly increased the temperature optimum for photosynthesis by ca. 4 °C. Rising CO2 concentrations are likely to have a significant positive effect on the growth rate of A. germinans over the next century, especially in areas where nutrient availability is high.

Mangrove propagule size and oil contamination effects: Does size matter?

Three mangroves species with differential propagule size, Avicennia marina (2.5±0.3cm), Bruguiera gymnorrhiza (16±2cm) and Rhizophora mucronata (36±3cm), were subjected to oil contamination. In a series of glasshouse and field experiments, the sediment, propagules, leaves and stems were oiled and growth monitored. Oiling of the propagules, leaves, internodes or sediment reduced plant height, leaf number, leaf chlorophyll content index and induced growth abnormalities, leaf abscission and mortality, with effects being greatest in A. marina, intermediate in R. mucronata and least in B. gymnorrhiza. The results suggest that the greater susceptibility of A. marina to oil is due to early shedding of the protective pericarp and rapid root and shoot development after detachment from the parent tree and not to propagule size. After seedling emergence, micromorphological factors such as presence of trichomes, salt glands and thickness of protective barriers influence oil tolerance.

Influence of the phenols on the biogeochemical behavior of cadmium in the mangrove sediment.

Phenols exert a great influence on the dynamic process of Cd in the soil-plant interface. We investigated the influence of phenols on the biogeochemical behavior of cadmium in the rhizosphere of Avicennia marina (Forsk) Vierh. All combinations of four levels of cadmium (0, 1, 2 and 4 mg/kg DW) and two levels of phenol (0 and 15 mg/kg DW) were included in the experimental design. We found that phenols facilitated increasing concentrations of exchangeable cadmium (Ex-Cd), acid volatile sulfide (AVS) and reactive solid-phase Fe (II) in sediments, and iron in plants, but inhibited Cd accumulation in iron plaque and roots. The concentrations of AVS and reactive solid-phase Fe (II) were significantly positively correlated with Cd treatment. As for the biogeochemical behavior of Cd in mangrove sediments, this research revealed that phenols facilitated activation and mobility of Cd. They disturbed the "source-sink" balance of Cd and turned it into a "source", whilst decreasing Cd absorption in A. marina. Additionally, phenols facilitated iron absorption in the plant and alleviated the Fe limit for mangrove plant growth.

Effect of heavy metals on the carbon and nitrogen ratio in Avicennia marina from polluted and unpolluted regions.

The accumulation of heavy metals and its impact on the C/N ratio of Avicennia marina of the Patalganga and Amba estuaries were studied. Vadinar was selected as a relatively uncontaminated location for comparison. Cd was accumulated in leaves of the Patalganga and Amba estuarine mangroves; however, at Vadinar it was accumulated and arrested only in roots and stems. Negative correlation of Cr, Cd, Pb and Zn with C in the mangroves suggested that their accumulation may lead to lowered C content in the mangroves. The average C/N ratios in mangroves of the inner Patalganga estuary, Patalganga mouth, and Amba estuary were found to be 80.1 ± 7.3, 105.8 ± 12.5 and 52.4 ± 3.4 respectively, whereas at Vadinar it was well within the expected range (26.4 ± 2.8). The results of the present study suggest: (i) metal accumulation, leading to less carbon content in plants; (ii) heavy metal enrichment in the root zone sediment, affecting the uptake of nitrogen by plants and resulting in altered C/N ratio.

Molecular cloning of class III chitinase gene from Avicennia marina and its expression analysis in response to cadmium and lead stress.

Mangrove species have high tolerance to heavy metal pollution. Chitinases have been widely reported as defense proteins in response to heavy metal stress in terrestrial plants. In this study, a full-length cDNA sequence encoding an acidic and basic class III chitinase (AmCHI III) was cloned by using RT-PCR and RACE methods in Avicennia marina. AmCHI III mRNA expression in leaf of A. marina were investigated under Cd, Pb stresses on using real-time quantitative PCR. The deduced AmCHI III protein consists of 302 amino acids, including a signal putative peptide region, and a catalytic domain. Homology modeling of the catalytic domain revealed a typical molecular structure of class III plant chitinases. Results further demonstrated that the regulation of AmCHI III mRNA expression in leaves was strongly dependent on Cd, Pb stresses. AmCHI III mRNA expressions were significantly increased in response to Cd, Pb, and peaked at 7 days Cd-exposure, 7 days Pb-exposure, respectively. AmCHI III mRNA expression exhibited more sensitive to Pb stress than Cd stress. This work was the first time cloing chitinase from A. marina, and it brought evidence on chitinase gene involving in heavy metals (Cd(2+) and Pb(2+)) resistance or detoxification in plants. Further studies including the promoter and upstream regulation, gene over-expression and the response of mangrove chitinases to other stresses will shed more light on the role of chitinase in mangrove plants.

The influence of flavonoid amendment on the absorption of cadmium in Avicennia marina roots.

Flavonoid is a key factor for the tolerance to cadmium in plants. Concentration-dependent kinetics experiment was conducted to investigate the influence of flavonoid amendment on the Cd(2+) uptake in Avicennia marina (Forsk) Vierh. roots. We found that compared with the control, saturation concentration and maximal absorption rate of Cd was higher under flavonoid amendment (p<0.05). When roots were exposed to ion transport inhibitor (LaCl3), flavonoid amendment also facilitated Cd transport in roots. Flavonoids had no influence on Cd(2+) uptake in root cell walls. In conclusion, flavonoids enhance the tolerance to Cd and have a significant stimulative effect on symplasm transport of Cd in A. marina roots. Ca(2+)-channel was not the unique means of symplasm transport for Cd(2+) absorption.

Effect of pollution by particulate iron on the morphoanatomy, histochemistry, and bioaccumulation of three mangrove plant species in Brazil.

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.

The effect of atmospheric carbon dioxide concentrations on the performance of the mangrove Avicennia germinans over a range of salinities.

By increasing water use efficiency and carbon assimilation, increasing atmospheric CO2 concentrations could potentially improve plant productivity and growth at high salinities. To assess the effect of elevated CO2 on the salinity response of a woody halophyte, we grew seedlings of the mangrove Avicennia germinans under a combination of five salinity treatments [from 5 to 65 parts per thousand (ppt)] and three CO2 concentrations (280, 400 and 800 ppm). We measured survivorship, growth rate, photosynthetic gas exchange, root architecture and foliar nutrient and ion concentrations. The salinity optima for growth shifted higher with increasing concentrations of CO2 , from 0 ppt at 280 ppm to 35 ppt at 800 ppm. At optimal salinity conditions, carbon assimilation rates were significantly higher under elevated CO2 concentrations. However, at salinities above the salinity optima, salinity had an expected negative effect on mangrove growth and carbon assimilation, which was not alleviated by elevated CO2 , despite a significant improvement in photosynthetic water use efficiency. This is likely due to non-stomatal limitations to growth at high salinities, as indicated by our measurements of foliar ion concentrations that show a displacement of K(+) by Na(+) at elevated salinities that is not affected by CO2 . The observed shift in the optimal salinity for growth with increasing CO2 concentrations changes the fundamental niche of this species and could have significant effects on future mangrove distribution patterns and interspecific interactions.