NADPH oxidase-dependent H2O2 production mediates salicylic acid-induced salt tolerance in mangrove plant Kandelia obovata by regulating Na+/K+ and redox homeostasis.

Salicylic acid (SA) is known to enhance salt tolerance in plants. However, the mechanism of SA-mediated response to high salinity in halophyte remains unclear. Using electrophysiological and molecular biological methods, we investigated the role of SA in response to high salinity in mangrove species, Kandelia obovata, a typical halophyte. Exposure of K. obovata roots to high salinity resulted in a rapid increase in endogenous SA produced by phenylalanine ammonia lyase pathway. The application of exogenous SA improved the salt tolerance of K. obovata, which depended on the NADPH oxidase-mediated H2O2. Exogenous SA and H2O2 increased Na+ efflux and reduced K+ loss by regulating the transcription levels of Na+ and K+ transport-related genes, thus reducing the Na+/K+ ratio in the salt-treated K. obovata roots. In addition, exogenous SA-enhanced antioxidant enzyme activity and its transcripts, and the expressions of four genes related to AsA-GSH cycle as well, then alleviated oxidative damages in the salt-treated K. obovata roots. However, the above effects of SA could be reversed by diphenyleneiodonium chloride (the NADPH oxidase inhibitor) and paclobutrazol (a SA biosynthesis inhibitor). Collectively, our results demonstrated that SA-induced salt tolerance of K. obovata depends on NADPH oxidase-generated H2O2 that affects Na+/K+ and redox homeostasis in response to high salinity.

Brassinosteroid enhances salt tolerance via S-nitrosoglutathione reductase and nitric oxide signaling pathway in mangrove Kandelia obovata.

Brassinosteroid (BR) has been shown to modulate plant tolerance to various stresses. S-nitrosoglutathione reductase (GSNOR) is involved in the plant response to environment stress by fine-turning the level of nitric oxide (NO). However, whether GSNOR is involved in BR-regulated Na+ /K+ homeostasis to improve the salt tolerance in halophyte is unknown. Here, we firstly reported that high salinity increases the expression of BR-biosynthesis genes and the endogenous levels of BR in mangrove Kandelia obovata. Then, salt-induced BR triggers the activities and gene expressions of GSNOR and antioxidant enzymes, thereafter decrease the levels of malondialdehyde, hydrogen peroxide. Subsequently, BR-mediated GSNOR negatively regulates NO contributions to the reduction of reactive oxygen species generation and induction of the gene expression related to Na+ and K+ transport, leading to the decrease of Na+ /K+ ratio in the roots of K. obovata. Finally, the applications of exogenous BR, NO scavenger, BR biosynthetic inhibitor and GSNOR inhibitor further confirm the function of BR. Taken together, our result provides insight into the mechanism of BR in the response of mangrove K. obovata to high salinity via GSNOR and NO signaling pathway by reducing oxidative damage and modulating Na+ /K+ homeostasis.

Genome-wide identification and characterization of aquaporins in mangrove plant Kandelia obovata and its role in response to the intertidal environment.

Aquaporins (AQPs) play important roles in plant growth, development and tolerance to environmental stresses. To understand the role of AQPs in the mangrove plant Kandelia obovata, which has the ability to acquire water from seawater, we identified 34 AQPs in the K. obovata genome and analysed their structural features. Phylogenetic analysis revealed that KoAQPs are homologous to AQPs of Populus and Arabidopsis, which are evolutionarily conserved. The key amino acid residues were used to assess water-transport ability. Analysis of cis-acting elements in the promoters indicated that KoAQPs may be stress- and hormone-responsive. Subcellular localization of KoAQPs in yeast showed most KoAQPs function in the membrane system. That transgenic yeast with increased cell volume showed that some KoAQPs have significant water-transport activity, and the substrate sensitivity assay indicates that some KoAQPs can transport H2 O2 . The transcriptome data were used to analyze the expression patterns of KoAQPs in different tissues and developing fruits of K. obovata. In addition, real-time quantitative PCR analyses combined transcriptome data showed that KoAQPs have complex responses to environmental factors, including salinity, flooding and cold. Collectively, the transport of water and solutes by KoAQPs contributed to the adaptation of K. obovata to the coastal intertidal environment.

Exploring the Mangrove Fruit: From the Phytochemicals to Functional Food Development and the Current Progress in the Middle East.

Nowadays, the logarithmic production of existing well-known food materials is unable to keep up with the demand caused by the exponential growth of the human population in terms of the equality of access to food materials. Famous local food materials with treasury properties such as mangrove fruits are an excellent source to be listed as emerging food candidates with ethnomedicinal properties. Thus, this study reviews the nutrition content of several edible mangrove fruits and the innovation to improve the fruit into a highly economic food product. Within the mangrove fruit, the levels of primary metabolites such as carbohydrates, protein, and fat are acceptable for daily intake. The mangrove fruits, seeds, and endophytic fungi are rich in phenolic compounds, limonoids, and their derivatives as the compounds present a multitude of bioactivities such as antimicrobial, anticancer, and antioxidant. In the intermediary process, the flour of mangrove fruit stands as a supplementation for the existing flour with antidiabetic or antioxidant properties. The mangrove fruit is successfully transformed into many processed food products. However, limited fruits from species such as Bruguiera gymnorrhiza, Rhizophora mucronata, Sonneratia caseolaris, and Avicennia marina are commonly upgraded into traditional food, though many more species demonstrate ethnomedicinal properties. In the Middle East, A. marina is the dominant species, and the study of the phytochemicals and fruit development is limited. Therefore, studies on the development of mangrove fruits to functional for other mangrove species are demanding. The locally accepted mangrove fruit is coveted as an alternate food material to support the sustainable development goal of eliminating world hunger in sustainable ways.

Metabolites with Anti-Inflammatory Activity from the Mangrove Endophytic Fungus Diaporthe sp. QYM12.

One new diterpenoid, diaporpenoid A (1), two new sesquiterpenoids, diaporpenoids B-C (2,3) and three new α-pyrone derivatives, diaporpyrones A-C (4-6) were isolated from an MeOH extract obtained from cultures of the mangrove endophytic fungus Diaporthe sp. QYM12. Their structures were elucidated by extensive analysis of spectroscopic data. The absolute configurations were determined by electronic circular dichroism (ECD) calculations and a comparison of the specific rotation. Compound 1 had an unusual 5/10/5-fused tricyclic ring system. Compounds 1 and 4 showed potent anti-inflammatory activities by inhibiting the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced RAW264.7 cells with IC50 values of 21.5 and 12.5 µM, respectively.

Comparative physiological and proteomic analyses of mangrove plant Kandelia obovata under cold stress.

Cold events had broadly affected the survival and geographic distribution of mangrove plants. Kandelia obovata, has an excellent cold tolerance as a true halophyte and widespread mangrove species. In this study, physiological characters and comparative proteomics of leaves of K. obovata were performed under cold treatment. The physiological analysis showed that K. obovata could alleviate its cold-stress injuries through increasing the levels of antioxidants, the activities of related enzymes, as well as osmotic regulation substances (proline). It was detected 184 differentially expressed protein spots, and of 129 (70.11%) spots were identified. These proteins have been involved in several pathways such as the stress and defense, photosynthesis and photorespiration, signal transduction, transcription factors, protein biosynthesis and degradation, molecular chaperones, ATP synthesis, the tricarboxylic acid (TCA) cycle and primary metabolisms. The protein post-translational modification may be a common phenomenon and plays a key role in cold-response process in K. obovata. According to our precious work, a schematic diagram was drawn for the resistance or adaptation strategy of mangrove plants under cold stress. This study provided valuable information to understand the mechanism of cold tolerance of K. obovata.

The First De Novo Transcriptome Assembly and Transcriptomic Dynamics of the Mangrove Tree Rhizophora stylosa Griff. (Rhizophoraceae).

Mangroves are salt-tolerant plant species that grow in coastal saline water and are adapted to harsh environmental conditions. In this study, we de novo assembled and functionally annotated the transcriptome of Rhizophora stylosa, the widely distributed mangrove from the largest mangrove family (Rhizophoraceae). The final transcriptome consists of 200,491 unigenes with an average length, and N50 of 912.7 and 1334 base pair, respectively. We then compared the genome-wide expression profiles between the two morphologically distinct natural populations of this species growing under different levels of salinity depending on their distance from the ocean. Among the 200,491 unigenes, 40,253 were identified as differentially expressed between the two populations, while 15,741 and 24,512 were up- and down-regulated, respectively. Functional annotation assigned thousands of upregulated genes in saline environment to the categories related to abiotic stresses such as response to salt-, osmotic-, and oxidative-stress. Validation of those genes may contribute to a better understanding of adaptation in mangroves species. This study reported, for the first time, the transcriptome of R. stylosa, and the dynamic of it in response to salt stress and provided a valuable resource for elucidation of the molecular mechanism underlying the salt stress response in mangroves and other plants that live under stress.

Uptake and concentration of heavy metals in dominant mangrove species from Hainan Island, South China.

By investigating three dominant mangrove species, namely Aegiceras corniculatum, Kandelia candel, Ceriops tagal and their rhizosediment in Mangrove wetlands in Hainan Island, this research analyzed absorption, concentration and distribution of heavy metals (Cr, Cu, Zn, As, Cd and Pb) in mangroves. The results found that the concentration of specific heavy metal differs in the different mangrove organs (leaf, stem and root). The content of heavy metals concentrated greatly in roots, but less in leaves and stems. The study also revealed that concentration capacity was weak in all three mangrove species (BCF0.02-0.91), with their organ ranking BCFroot > BCFstem > BCFleaf. Among three mangrove species, the transfer factors of leaves and stems in Ceriops tagal were highest, indicating a great distribution capability for heavy metals, followed by Kandelia candel. Transfer factors in Aegiceras corniculatum were the weakest. This ranking was opposite to bioconcentration factors of roots. This study can further reflect bioavailability of heavy metals in sediments, which provides scientific evidence on ecosystem protection and management in mangrove wetlands.

Copper and zinc differentially affect root glutathione accumulation and phytochelatin synthase gene expression of Rhizophora mucronata seedlings: Implications for mechanisms underlying trace metal tolerance.

Mangroves are susceptible to contamination due to their proximity to shores and human activities. Exposure to excessive trace metals can disturb their physiological functions and may eventually lead to death. Rhizophora mucronata is a common species growing in the mangrove forests of Thailand. Previous studies have shown that seedlings of R. mucronata are tolerant of trace metal and that they accumulate a large metal content in their root tissue. However, knowledge of their tolerance mechanisms is still lacking. To elicit the role of metal detoxification and sequestration by phytochelatins (PC) in the roots of R. mucronata seedlings, the impacts of Cu and Zn exposure were assessed on 1) physiological characteristics 2) the concentration of glutathione (GSH), a precursor of PC and 3) the level of the transcripts encoding phytochelatin synthase (PCS), the key enzyme for PC biosynthesis. Seedlings of R. mucronata were exposed to Cu and Zn in a hydroponic experiment (200 mg Cu or Zn/L in 1/4× Hoagland solution containing 8‰ NaCl, single addition). We found that both trace metals were largely accumulated in the roots. Only Cu-treated seedlings showed a decrease in the photosynthetic efficiency, in line with observed toxicity symptoms (i.e. bent stems and slight wilting of leaves). Metal accumulation, however, did not induce oxidative stress in the roots as indicated by similar level of total reactive species and lipid peroxidation across treatments. The GSH content in the roots exposed to Cu was significantly reduced while no change was observed in Zn-exposed roots. Coordinated semi-quantitative PCR and RT-qPCR revealed pcs down-regulation in Cu-treated roots, whereas Zn-treated roots showed a down-regulation on day 1 and a subsequent recovery on day 5. Failure of detoxification and sequestration of excess Cu due to GSH limitation and down-regulation of pcs may lead to the phytotoxic effects observed in Cu-treated plants. Our results suggest that both GSH and PC play an important role in trace metal tolerance in R. mucronata seedlings.

Expression, purification and molecular characterization of a novel transcription factor KcCBF3 from Kandelia candel.

Kandelia candel, a major species of mangrove in the tropical and subtropical area, is susceptible to low temperature in winter. K. candel was introduced into Zhejiang Province (the northern margin of South China) several decades ago, and suffered from low temperature causing growth retardation, in server cases, even death. To explore the molecular mechanisms of cold acclimation in K. candel, a novel C-repeat binding factor gene KcCBF3 (Genbank accession no. KF111715) of 729 bp open reading frame (ORF) encoding a protein of 242 amino acid residues was isolated, expressed, purified and characterized. Multiple sequence alignment analysis revealed that KcCBF3 contained a highly conserved AP2/EREBP DNA-binding domain which consisting of 79 amino acid residues, as well as two CBF signature sequences. Phylogenetic analysis indicated that KcCBF3 belonged to the A-1 subgroup of DREB subfamily based on the classification of AP2/EREBP transcription factors in Arabidopsis. Semi-quantitative RT-PCR showed that KcCBF3 transcripts were highly accumulated in roots and leaves, and could be induced by low temperature. Electrophoresis mobility shift assay (EMSA) demonstrated KcCBF3 could bind to the core sequence (CCGAC) of cis-acting element C-repeat (CRT)/dehydration-responsive element (DRE) in vitro. These results implied that KcCBF3 might participate in the adaptation of K. candel to low-temperature stress by binding to CRT/DRE element.

Phenolic metabolism and related heavy metal tolerance mechanism in Kandelia Obovata under Cd and Zn stress.

In the present study, a set of pot culture experiments was conducted to reveal how the metabolism process of phenolic compounds was affected by cadmium (Cd) and zinc (Zn) and to further uncover heavy metal tolerance mechanisms in Kandelia obovata. After 60d of treatment, the biomass and chlorophyll a content in the leaves were suppressed, but total phenolic compounds in roots and leaves were improved by the increasing gradient of Cd or Zn concentrations; Total phenolic compounds significantly increased by 3.6-44.6% in the roots, and by 0.4-126.6% in the leaves. At the meantime, the activity of Shikimate dehydrogenase (SKDH), cinnamyl alcohol dehydrogenase (CAD), and polyphenol oxidase (PPO) in the roots increased by 11.2-307.6%, 12.4-175.4% and - 2.7-392.8%, and the results were 3.4-69.5%, 1.7-40.0%, 16.0-99.7% in the leaves. Higher toxicity of Cd than Zn, as well as slight alleviating effect of 100 mg kg-1 Zn on 2.5 mg kg-1 Cd were found. Additionally, a significantly positive correlation coefficients for relationship between phenolic metabolism related enzyme activity and Cd/Zn contamination levels was found, and leaf SKDH, leaf CAD, and leaf PPO activities were moderately correlated with leaf Cd (r = 0.39, r = 0.43, and r = 0.57, respectively) and leaf Zn (r = 0.44, r = 0.41, r = 0.19, respectively) content, which indicate that Cd and Zn play a previously unrecognized but major role in phenolic compounds synthesis, transport, and metabolism in K. obovata. The results also provided evidence that the application of high levels of Cd and Zn was accompanied by three phenolic metabolism pathways participating in heavy metal tolerance process.

Comparative Proteomic Analysis Reveals the Regulatory Effects of H2S on Salt Tolerance of Mangrove Plant Kandelia obovata.

As a dominant mangrove species, Kandelia obovata is distributed in an intertidal marsh with an active H2S release. Whether H2S participates in the salt tolerance of mangrove plants is still ambiguous, although increasing evidence has demonstrated that H2S functions in plant responses to multiple abiotic stresses. In this study, NaHS was used as an H2S donor to investigate the regulatory mechanism of H2S on the salt tolerance of K. obovata seedlings by using a combined physiological and proteomic analysis. The results showed that the reduction in photosynthesis (Pn) caused by 400 mM of NaCl was recovered by the addition of NaHS (200 µM). Furthermore, the application of H2S enhanced the quantum efficiency of photosystem II (PSII) and the membrane lipid stability, implying that H2S is beneficial to the survival of K. obovata seedlings under high salinity. We further identified 37 differentially expressed proteins by proteomic approaches under salinity and NaHS treatments. Among them, the proteins that are related to photosynthesis, primary metabolism, stress response and hormone biosynthesis were primarily enriched. The physiological and proteomic results highlighted that exogenous H2S up-regulated photosynthesis and energy metabolism to help K. obovata to cope with high salinity. Specifically, H2S increased photosynthetic electron transfer, chlorophyll biosynthesis and carbon fixation in K. obovata leaves under salt stress. Furthermore, the abundances of other proteins related to the metabolic pathway, such as antioxidation (ascorbic acid peroxidase (APX), copper/zinc superoxide dismutase (CSD2), and pancreatic and duodenal homeobox 1 (PDX1)), protein synthesis (heat-shock protein (HSP), chaperonin family protein (Cpn) 20), nitrogen metabolism (glutamine synthetase 1 and 2 (GS2), GS1:1), glycolysis (phosphoglycerate kinase (PGK) and triosephosphate isomerase (TPI)), and the ascorbate-glutathione (AsA-GSH) cycle were increased by H2S under high salinity. These findings provide new insights into the roles of H2S in the adaptations of the K. obovata mangrove plant to high salinity environments.

Tolerance Mechanisms to Copper and Zinc Excess in Rhizophora mucronata Lam. Seedlings Involve Cell Wall Sequestration and Limited Translocation.

Rhizophora mucronata is a common mangrove growing in habitats subjected to heavy metal (HM) contamination. Understanding their physiological responses to copper (Cu) and zinc (Zn) excess and underlying tolerance mechanisms is crucial to assess impacts of metal pollution on mangrove community. Seedlings were treated with Cu or Zn (0, 50 or 100 mg per plant) by means of a single addition. At day 3 and 7, Cu and Zn accumulation, photosynthetic efficiency, superoxide dismutase and peroxidase activity, non-protein thiols, reactive oxygen species and lipid peroxidation in roots and leaves were measured. R. mucronata restricted Cu and Zn translocation, thus accumulated HM mainly in roots while kept the leaves unaffected. However, high root HM did not induce oxidative stress nor anti-oxidative defense as HM were largely deposited in cell wall. We concluded that HM tolerance strategies of R. mucronata seedlings are exclusion and restriction of translocation to the vital photosynthetic tissue.

Does ammonium nitrogen affect accumulation, subcellular distribution and chemical forms of cadmium in Kandelia obovata?

Heavy metals and nutrients are commonly found in mangrove sediments, but the effect of nutrients on heavy metals in mangrove plants is not clear. A study quantifying the effects of ammonium nitrogen (NH4+-N) on the accumulation, subcellular distribution and chemical forms of cadmium (Cd) in Kandelia obovata seedlings were conducted. The experiment consisted of four levels of NH4+-N (0, 10, 50 and 100 mg L-1) in each of which consisted of four Cd levels (0, 1, 5 and 10 mg L-1). The results showed that NH4+-N magnified the Cd toxicity due to reduced plant biomass, especially with 10 mg L-1 Cd and 100 mg L-1 NH4+-N supply. NH4+-N, especially at 100 mg L-1, enhanced the concentration and accumulation of Cd in root but its role on Cd translocation from root to stem and leaf was limited, probably due to low translocation factor. At subcellular level, Cd mainly accumulated in root cell wall but its fractionation depended on Cd levels. Under the stress of 1 and 5 mg L-1 Cd, 50 mg L-1 NH4+-N supply improved transfer of Cd from root cell wall into cell, and increased pectate and protein integrated forms of intracellular Cd to alleviate Cd toxicity. Under the stress of 10 mg L-1 Cd, NH4+-N supply promoted the deposition of Cd on root cell wall to restrain its transfer to root cell, which was verified by the reduced levels of pectate and protein integrated forms of Cd in root cell. Thus, NH4+-N supply improved immobilization of Cd in roots and alleviated Cd toxicity through integration with pectate and protein as well as cell wall combinations in root of K. obovata.

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.

A multilevel investigation to discover why Kandelia candel thrives in high salinity.

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.

Massive turnover rates of fine root detrital carbon in tropical Australian mangroves.

Dead fine roots are the major component of organic carbon (C) stored in mangrove forests. We measured the mass and decomposition of fine root detritus in three mangrove forests along an intertidal gradient in tropical Australia to provide the first integrated estimates of the rate of turnover of fine root detritus. The grand mean dry masses of dead fine roots in the forests decreased in the order mid-intertidal Rhizophora (mean 28.4 kg m(-2)), low-intertidal Rhizophora (16.3 kg m(-2)) and high-intertidal Ceriops (mean 8.9 kg m(-2)), and were some of the highest on record. The first-order decay coefficients (day(-1)) for dead fine roots in the low Rhizophora, mid Rhizophora and high Ceriops forest sites were 0.0014, 0.0017 and 0.0007, respectively, and were the lowest on record. The estimated mean fluxes of C via decomposition of dead fine roots were very high in all forests, decreasing in the order mid Rhizophora (18.8 g C m(-2) day(-1)), low Rhizophora (8.4 g C m(-2) day(-1)) and high Ceriops (2.5 g C m(-2) day(-1)). There were relatively low levels of uncertainty in these estimates when all sources of error were considered. The fluxes of C for the two Rhizophora sites integrate all losses from saprophytic decay and leaching of dissolved C and were 50-200 % higher than the estimated total annual loss of C derived by summing rates of bacterial metabolism and export via groundwater and surface waters in these forests. The significant difference reflects both the very high dead root masses and the incorporation of the impact of fungi in our estimates.

[Tree above-ground biomass allometries for carbon stocks estimation in the Caribbean mangroves in Colombia]. / Ecuaciones alométricas de biomasa aérea para la estimación de los contenidos de carbono en manglares del Caribe Colombiano.

The distribution of carbon in "Blue Carbon" ecosystems such as mangroves is little known, when compared with the highly known terrestrial forests, despite its particular and recognized high productivity and carbon storage capacity. The objective of this study was to analyze the above ground biomass (AGB) of the species Rhizophora mangle and Avicennia germinans from the Marine Protected Area of Distrito de Manejo Integrado (DMI), Cispatá-Tinajones-La Balsa, Caribbean Colombian coast. With official authorization, we harvested and studied 30 individuals of each species, and built allometric models in order to estimate AGB. Our AGB results indicated that the studied mangrove forests of the DMI Colombian Caribbean was of 129.69 ± 20.24 Mg/ha, equivalent to 64.85 ± 10.12 MgC/ha. The DMI has an area of 8 570.9 ha in mangrove forests, and we estimated that the total carbon potential stored was about 555 795.93 Mg C. The equations generated in this study can be considered as an alternative for the assessment of carbon stocks in AGB of mangrove forests in Colombia; as other available AGB allometric models do not discriminate mangrove forests, despite being particular ecosystems. They can be used for analysis at a more detailed scale and are considered useful to determine the carbon storage potential of mangrove forests, as a country alternative to support forest conservation and emission reduction strategies. In general, the potential of carbon storage from Colombian Caribbean mangrove forests is important and could promote the country leadership of the "blue carbon" stored.

Novel and conserved miRNAs in the halophyte Suaeda maritima identified by deep sequencing and computational predictions using the ESTs of two mangrove plants.

BACKGROUND: Although miRNAs are reportedly involved in the salt stress tolerance of plants, miRNA profiling in plants has largely remained restricted to glycophytes, including certain crop species that do not exhibit any tolerance to salinity. Hence, this manuscript describes the results from the miRNA profiling of the halophyte Suaeda maritima, which is used worldwide to study salt tolerance in plants. RESULTS: A total of 134 conserved miRNAs were identified from unique sRNA reads, with 126 identified using miRBase 21.0 and an additional eight identified using the Plant Non-coding RNA Database. The presence of the precursors of seven conserved miRNAs was validated in S. maritima. In addition, 13 novel miRNAs were predicted using the ESTs of two mangrove plants, Rhizophora mangle and Heritiera littoralis, and the precursors of seven miRNAs were found in S. maritima. Most of the miRNAs considered for characterization were responsive to NaCl application, indicating their importance in the regulation of metabolic activities in plants exposed to salinity. An expression study of the novel miRNAs in plants of diverse ecological and taxonomic groups revealed that two of the miRNAs, sma-miR6 and sma-miR7, were also expressed in Oryza sativa, whereas another two, sma-miR2 and sma-miR5, were only expressed in plants growing under the influence of seawater, similar to S. maritima. CONCLUSION: The distribution of conserved miRNAs among only 25 families indicated the possibility of identifying a greater number of miRNAs with increase in knowledge of the genomes of more halophytes. The expression of two novel miRNAs, sma-miR2 and sma-miR5, only in plants growing under the influence of seawater suggested their metabolic regulatory roles specific to saline environments, and such behavior might be mediated by alterations in the expression of certain genes, modifications of proteins leading to changes in their activity and production of secondary metabolites as revealed by the miRNA target predictions. Moreover, the auxin responsive factor targeted by sma-miR7 could also be involved in salt tolerance because the target is conserved between species. This study also indicated that the transcriptome of one species can be successfully used to computationally predict the miRNAs in other species, especially those that have similar metabolism, even if they are taxonomically separated.

Hydrogen isotope response to changing salinity and rainfall in Australian mangroves.

Hydrogen isotope ratios ((2) H/(1) H, δ(2) H) of leaf waxes covary with those in precipitation and are therefore a useful paleohydrologic proxy. Mangroves are an exception to this relationship because their δ(2) H values are also influenced by salinity. The mechanisms underlying this response were investigated by measuring leaf lipid δ(2) H and leaf and xylem water δ(2) H and δ(18) O values from three mangrove species over 9.5 months in a subtropical Australian estuary. Net (2) H/(1) H fractionation between surface water and leaf lipids decreased by 0.5-1.0‰ ppt(-1) for n-alkanes and 0.4-0.8‰ ppt(-1) for isoprenoids. Xylem water was (2) H depleted relative to surface water, reflecting (2) H discrimination of 4-10‰ during water uptake at all salinities and opportunistic uptake of freshwater at high salinity. However, leaf water (2) H enrichment relative to estuary water was insensitive to salinity and identical for all species. Therefore, variations in leaf and xylem water δ(2) H values cannot explain the salinity-dependent (2) H depletion in leaf lipids, nor the 30‰ range in leaf lipid δ(2) H values among species. Biochemical changes in direct response to salt stress, such as increased compatible solute production or preferential use of stored carbohydrates, and/or the timing of lipid production and subsequent turnover rates, are more likely causes.