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Recent studies indicated that coastal green belts could not provide proper protection from extreme coastal flooding. Recent studies recommend employing a compound defense system of natural and artificial structures for extreme hazards. In this study, we introduce a new compound defense system consisting of coastal mangrove trees combined with reef ball modular structures. A series of laboratory experiments were conducted to investigate drag force reduction through the hybrid defense system. The hybrid defense system was subjected to a surge-type flow generated by a quickly lifting gate in a laboratory water tank. Within the experimental framework, the hydrodynamics of coastal flooding were described by the characteristics of the surge bore and the absorbed drag force. The obtained results show that the hybrid system effectively enhanced the absorbed bore drag forces and significantly improved the flow-damping performance. [ABSTRACT FROM AUTHOR]

The present study evaluated the potentials of phytoremediation and the biomonitoring of potentially toxic metals (PTMs) (Zn, Ni, Fe, Pb, and Cu) in the mangrove leaves of Rhizophora apiculata from the tropical mangrove ecosystem in the Sepang Besar River and Lukut River, Peninsular Malaysia. Overall, the present studies concluded that (a) the levels of essential Fe, Cu, and Zn in lamina are significantly (p < 0.05) higher than in MP, (b) the levels of Pb and Ni in MP are significantly (p < 0.05) higher than in lamina, (c) the lamina has better potential as a phytoremediator of Cu, Zn, and Fe, while MP is a better potential phytoremediator of Pb and Ni, (d) lamina is a potential biomonitoring agent of potentially toxic metals based on better correlation coefficients with the surface sedimentary geochemical fractions, and (e) metal uptake in the mangrove leaves and comparative levels of metals is low with reported studies. Specifically, based on bioconcentration factors (BCF), their most obtained values were considered low (<1), suggesting that R. apiculata can be considered as a low-efficiency plant for the bioaccumulation of PTM. However, the present findings also suggested that R. apiculata may be classified as a potential phytoremediator for Zn, Cu, Pb, and Ni in the leaves, as indicated by higher metal accumulation in the MP, with BCFEFLE values > 1.0; BCFAR > 1.0 for Cu, Pb, and Ni. The mangrove leaves are potential biomonitors of PTMs since positive correlations of PTMs were found between the leaves and their habitat surface sediments. Having been identified as a potential phytoremediator and biomonitor of PTMs, the present study emphasized the possibility of establishing a framework for managing the coastal aquatic ecosystems along the mangrove ecosystems of Sepang and Lukut. [ABSTRACT FROM AUTHOR]

Salinity reduces the growth and productivity of crop plants worldwide. Mangroves have evolved efficient ion homeostasis mechanisms to survive under their natural saline growth habitat. Information obtained from them may be utilized for increasing the salt tolerance of crop plants. We identified and characterized a high-affinity potassium transporter gene (AoHKT1) from Avicennia officinalis. The expression of AoHKT1 was induced by NaCl mainly in the leaves. Functional study by heterologous expression of AoHKT1 in Arabidopsis T-DNA insertional mutants athkt1–1 and athkt1–4 revealed that it could enhance the salt tolerance of the mutant plants. This was accompanied by an increase in K+ accumulation in the leaves. AoHKT1 was localized to the plasma membrane in Arabidopsis, and when expressed in yeast, it could complement the functions of both Na+ and K+ transporters. An attempt was made to identify the upstream regulator of AtHKT1 , a close homolog of AoHKT1. Using chromatin immunoprecipitation, luciferase assay and yeast one-hybrid assays, WRKY9 was identified as the main transcription factor in the process. Furthermore, this was corroborated by the observation that AtHKT1 levels were significantly reduced in the atwrky9 seedlings. These findings revealed a part of the molecular regulatory mechanism of HKT1 induction in response to salt treatment in Arabidopsis. Our study suggests that AoHKT1 is a potential candidate for generating crop plants with increased salt tolerance. • Salt-responsive AoHKT1 was characterized from the mangrove Avicennia officinalis. • AoHKT1 increases salt tolerance in Arabidopsis by maintaining high shoot K+/Na+. • AoHKT1 transports both K+ and Na+ when expressed in yeast. • In Arabidopsis, AtHKT1 expression is reduced when AtWRKY9 is mutated. • WRKY9 transcription factor regulates HKT1 expression in plants. [ABSTRACT FROM AUTHOR]

The halophilic mangrove species Kandelia candel is an excellent model for understanding why halophytes thrive in high salinity. Preliminary transcriptomic analyses revealed that genes involved in diverse functions, such as in phenylpropanoid and amino acid metabolisms, and those in DNA replication and damage repair were highly responsive to salt stress. Proteomic analyses revealed that the proteins involved in light reaction of photosynthesis, amino acid and carbohydrate metabolisms, secondary metabolite biosynthesis and posttranslational modification showed increased levels in response to salt stress. The metabolisms of phenylpropanoids and amino acids under salt stress were systematically examined based on the preliminary omics analyses. The activities of phenylpropanoid biosynthetic enzymes and the contents of phenols, flavonoids, anthocyanins and lignins were significantly increased under salt stress. In the free amino acid pool, glutamate was the most abundant. Together with γ-aminobutyric acid, glutamate levels further increased, while proline levels remained unchanged in response to salt stress. These findings point to the potential importance of phenylpropanoids and free amino acids in salt tolerance of K. candel that have been observed, but not systemically investigated at the levels of gene expression, enzyme activity and metabolite accumulation in glycophytes and non-tree halophytes. [ABSTRACT FROM AUTHOR]

We analyzed nuclear and chloroplast microsatellite makers to assess genetic diversity and examine genetic structure of two mangrove tree species, Bruguiera gymnorrhiza and Kandelia obovata recovered from nine major river basins of Iriomote Island of the Ryukyu Archipelago, Japan. The average number of alleles per nuclear locus per population was 2.6 in B. gymnorrhiza and 1.7 in K. obovata. Bayesian clustering analysis using InStruct identified two genetic clusters in B. gymnorrhiza and three clusters in K. obovata. Chloroplast microsatellites revealed two dominant haplotypes from B. gymnorrhiza and three haplotypes from K. obovata. The overall result suggests low genetic diversity for both species. AMOVA for nuclear microsatellites showed 9.3 % of population variation in B. gymnorrhiza. Although genetic differentiation between several populations was significant in this species, F suggested low to moderate level of differentiations between most of the populations. Distribution of genetic clusters and chloroplast haplotypes also suggested weak differentiations among B. gymnorrhiza populations. In K. obovata, population variation was, however, relatively high (27.8 %). The high differentiation between K. obovata populations was also suggested from the F and genetic clusters from nuclear microsatellites, and chloroplast haplotypes. A significant correlation between chloroplast genetic distances and coastline distances as well as haplotype distributions for both species suggest that propagules from each species mostly disperse to the neighboring river basins. While significant F and higher percentage of admixed clusters from nuclear microsatellites suggested inbreeding, continual gene exchange by propagule dispersal among populations especially among neighboring populations was suggested for both species from maternally inherited chloroplast microsatellites analyses. [ABSTRACT FROM AUTHOR]

Volume equations were constructed for five species of mangrove treeson volcanic high islands of Micronesia in the north Pacific Ocean, where islands that span a distance of more than 3000km from east to west are characterized by a gradient of rainfall from 080 to 5250mm/year and a range of typhoon frequency from less than one per century to several per decade. We also calculated mean annual increments for a subset of the trees. The inclusion of very large trees in the data setmakes these volume equations unique. For the five most common species, separate volume equations were calculated for each of the two easternmost islands (Kosrae and Pohnpei), the remaining islands (`WesternIslands', including Chuuk, Yap, and Palau), and all the islands together (Micronesia). Tree structure differed significantly among the three island groupings and for two species, between Kosrae and Pohnpei,which are only 560km apart. Mean annual diameter increments for Sonneratia alba and Bruguiera gymnorrhiza indicated significantly faster growth on Kosrae (0.96 and 0.44cm/year, respectively) than on Pohnpei(0.33 and 0.26cm/year, respectively). Frequency distributions of diameter size classes on these two islands demonstrated a more even distribution of sizes and more large trees on Kosrae (e.g., up to 3.2m indiameter for S. alba). Differences in diameter distributions may be attributed to a typhoon that devastated Pohnpei, but not Kosrae, in 1905, but differences in growth rates cannot yet be explained. [ABSTRACT FROM AUTHOR]