Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål.

BACKGROUND: Coastal land development has deteriorated the habitat and water quality for seagrass growth and causes the proliferation of opportunist macroalgae that can potentially affect them physically and biochemically. The present study investigates the morphological and biochemical responses of seagrass from the Hydrocharitaceae family under the macroalgal bloom of Ulva reticulata, induced by land reclamation activities for constructing artificial islands. METHODS: Five seagrass species, Enhalus acoroides, Thalassia hemprichii, Halophila ovalis, Halophila major, and Halophila spinulosa were collected at an Ulva reticulata-colonized site (MA) shoal and a non-Ulva reticulata-colonized site (MC) shoal at Sungai Pulai estuary, Johor, Malaysia. Morphometry of shoots comprising leaf length (LL), leaf width (LW), leaf sheath length (LSL), leaflet length (LTL), leaflet width (LTW), petiole length (PL), space between intra-marginal veins (IV) of leaf, cross vein angle (CVA) of leaf, number of the cross vein (NOC), number of the leaf (NOL) and number of the leaflet (NOLT) were measured on fresh seagrass specimens. Moreover, in-situ water quality and water nutrient content were also recorded. Seagrass extracts in methanol were assessed for total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radical cation scavenging activity (ABTS), and ferric reducing antioxidant power (FRAP). RESULTS: Seagrasses in the U. reticulata-colonized site (MA) had significantly higher (t-test, p < 0.05) leaf dimensions compared to those at the non-U. reticulata colonized site (MC). Simple broad-leaved seagrass of H. major and H. ovalis were highly sensitive to the colonization of U. reticulata, which resulted in higher morphometric variation (t-test, p < 0.05) including LL, PL, LW, and IV. Concerning the biochemical properties, all the seagrasses at MA recorded significantly higher (t-test, p < 0.05) TPC, TFC, and ABTS and lower DPPH and FRAP activities compared to those at MC. Hydrocharitaceae seagrass experience positive changes in leaf morphology features and metabolite contents when shaded by U. reticulata. Researching the synergistic effect of anthropogenic nutrient loads on the interaction between seagrasses and macroalgae can provide valuable information to decrease the negative effect of macroalgae blooms on seagrasses in the tropical meadow.

Variations of arsenic forms and the role of arsenate reductase in three hydrophytes exposed to different arsenic species.

In order to understand the mechanisms of arsenic (As) accumulation and detoxification in aquatic plants exposed to different As species, a hydroponic experiment was conducted and the three aquatic plants (Hydrilla verticillata, Pistia stratiotes and Eichhornia crassipes) were exposed to different concentrations of As(III), As(V) and dimethylarsinate (DMA) for 10 days. The biomass, the surface As adsorption and total As adsorption of three plants were determined. Furthermore, As speciation in the culture solution and plant body, as well as the arsenate reductase (AR) activities of roots and shoots, were also analyzed. The results showed that the surface As adsorption of plants was far less than total As absorption. Compared to As(V), the plants showed a lower DMA accumulation. P. stratiotes showed the highest accumulation of inorganic arsenic but E. crassipes showed the lowest at the same As treatment. E. crassipes showed a strong ability to accumulate DMA. Results from As speciation analysis in culture solution showed that As(III) was transformed to As(V) in all As(III) treatments, and the oxidation rates followed as the sequence of H. verticillata>P. stratiotes>E. crassipes>no plant. As(III) was the predominant species in both roots (39.4-88.3%) and shoots (39-86%) of As(III)-exposed plants. As(V) and As(III) were the predominant species in roots (37-94%) and shoots (31.1-85.6%) in As(V)-exposed plants, respectively. DMA was the predominant species in both roots (23.46-100%) and shoots (72.6-100%) in DMA-exposed plants. The As(III) contents and AR activities in the roots of P. stratiotes and in the shoots of H. verticillata were significantly increased when exposed to 1 mg·L-1 or 3 mg·L-1 As(V). Therefore, As accumulation mainly occurred via biological uptake rather than physicochemical adsorption, and AR played an important role in As detoxification in aquatic plants. In the case of As(V)-exposed plants, their As tolerance was attributed to the increase of AR activities.

Molecular Networking Leveraging the Secondary Metabolomes Space of Halophila stipulaceae (Forsk.) Aschers. and Thalassia hemprichii (Ehrenb. ex Solms) Asch. in Tandem with Their Chemosystematics and Antidiabetic Potentials.

The Red Sea is one of the most biodiverse aquatic ecosystems. Notably, seagrasses possess a crucial ecological significance. Among them are the two taxa Halophila stipulacea (Forsk.) Aschers., and Thalassia hemprichii (Ehrenb. ex Solms) Asch., which were formally ranked together with the genus Enhalus in three separate families. Nevertheless, they have been recently classified as three subfamilies within Hydrocharitaceae. The interest of this study is to explore their metabolic profiles through ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS/MS) analysis in synergism with molecular networking and to assess their chemosystematics relationship. A total of 144 metabolites were annotated, encompassing phenolic acids, flavonoids, terpenoids, and lipids. Furthermore, three new phenolic acids; methoxy benzoic acid-O-sulphate (16), O-caffeoyl-O-hydroxyl dimethoxy benzoyl tartaric acid (26), dimethoxy benzoic acid-O-sulphate (30), a new flavanone glycoside; hexahydroxy-monomethoxy flavanone-O-glucoside (28), and a new steviol glycoside; rebaudioside-O-acetate (96) were tentatively described. Additionally, the evaluation of the antidiabetic potential of both taxa displayed an inherited higher activity of H. stipulaceae in alleviating the oxidative stress and dyslipidemia associated with diabetes. Hence, the current research significantly suggested Halophila, Thalassia, and Enhalus categorization in three different taxonomic ranks based on their intergeneric and interspecific relationship among them and supported the consideration of seagrasses in natural antidiabetic studies.

Marine Seagrass Extract of Thalassia testudinum Suppresses Colorectal Tumor Growth, Motility and Angiogenesis by Autophagic Stress and Immunogenic Cell Death Pathways.

Marine plants have become an inexhaustible reservoir of new phytopharmaceuticals for cancer treatment. We demonstrate in vitro/in vivo antitumor efficacy of a standardized polyphenol extract from the marine angiosperm Thalassia testudinum (TTE) in colon tumor cell lines (RKO, SW480, and CT26) and a syngeneic allograft murine colorectal cancer model. MTT assays revealed a dose-dependent decrease of cell viability of RKO, CT26, and SW480 cells upon TTE treatment with IC50 values of, respectively, 175, 115, and 60 µg/mL. Furthermore, TTE significantly prevented basal and bFGF-induced angiogenesis in the chicken chorioallantoic membrane angiogenesis assay. In addition, TTE suppressed bFGF-induced migration of endothelial cells in a wound closure assay. Finally, TTE treatment abrogated CT26 colorectal cancer growth and increased overall organism survival in a syngeneic murine allograft model. Corresponding transcriptome profiling and pathway analysis allowed for the identification of the mechanism of action for the antitumor effects of TTE. In line with our in vitro/in vivo results, TTE treatment triggers ATF4-P53-NFκB specific gene expression and autophagy stress pathways. This results in suppression of colon cancer cell growth, cell motility, and angiogenesis pathways in vitro and in addition promotes antitumor immunogenic cell death in vivo.

Two novel diterpenes from the stems and leaves of tropical seagrass Enhalus acoroides in the South China sea.

Two novel diterpenes Enhoidin A (1) and Enhoidin B (2) featuring an unusual gibberellane skeleton were isolated from the stems and leaves of Enhalus acoroides. Their structures were elucidated on the basis of spectroscopic analysis including 1D and 2D NMR techniques and HR-ESI-MS. This is the first time that this type of lactone ring between C-18 and C-20 has been found among gibberellanes from the tropical seagrasses. Evaluation of the all compounds for cytotoxicity against four human cancer cell lines (MCF-7, HCT-116, HepG-2 and HeLa), and showed moderate cytotoxic activities.

Investigating the use of aquatic weeds as biopesticides towards promoting sustainable agriculture.

Aquatic weeds such as muskgrass (Chara spp.), water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), hydrilla (Hydrilla verticillate), filamentous algae (Lyngbya wollei), and duckweed (Lemna minor) thrive in farm canals within the Everglades Agricultural Area of South Florida. Their presence, particularly during the summer months is an environmental concern with regards to water quality, in addition to being a nuisance because of their ability to multiply and spread rapidly in open waters causing restricted drainage/irrigation flow and low dissolved oxygen levels. Chemical control is effective but can have undesirable off-target effects, so reduced herbicide use is desirable. Hence, need exists to discover ways in which these weeds could be best managed or utilized. The objective of this research was to evaluate the allelopathic effect of these weeds to determine their use as potential biopesticides. Six aqueous extracts were tested against 100 bacterial strains isolated from plants and soil to evaluate their antimicrobial activity. These extracts were also used to determine their insecticidal and antifeedant effects on fall armyworm (FAW, Spodoptera frugiperda). Both extracts and powder form of the aquatic weeds were tested for their herbicidal activity towards seed germination and growth of three common terrestrial weed species. At a dilution of 1:100 and 1:1,000, none of the aquatic weeds inhibited in-vitro growth of the bacterial strains, with one exception (filamentous algae extract at 1:100 reduced growth of one bacterial isolate by 54%). Water lettuce reduced the survival rate of FAW by 14% while hydrilla and duckweed caused 11% and 9% reduction of FAW growth, respectively. Powdered duckweed inhibited the growth of nutsedge by 41%, whereas filamentous algae powder and extract reduced germination of amaranth by 20% and 28%, respectively. Harvesting these weeds and converting them into useable compounds could not only eliminate the in situ farm canal and water quality problems but also result in development of new soil amendments or biopesticides.

Solid Sampling in Analysis of Various Plants Using Two-Jet Plasma Atomic Emission Spectrometry.

The possibility of two-jet plasma atomic emission spectrometry for analysis of different plants using solid sample preparation and unified calibration samples was investigated. The certified reference materials of wheat, maize, rice, potato, grass mix, birch leaves, and Elodea canadensis were used for analysis. On the basis of the behavior of these plants in the plasma, they were divided into two groups: starch-containing materials (cereal and root crops) and leaves/grass. It was found that the previous sample carbonization should be used for analysis of starch-containing plants while leaves and grass could be analyzed by the direct technique. Carbonization was only applied for determining low concentrations of trace elements in leaves and grass. The calibration samples based on graphite powder and simple sample preparation, dilution of powdered sample with a spectroscopic buffer, were used for both direct analysis and analysis after carbonization. Such an approach allowed estimation of B, Ba, Be, Cd, Co, Cr, Cu, Ga, Fe, Mn, Ni, Pb, Si, Sr, V, and Zn in different plants. The limits of detection (LODs) provided by the direct technique were at the level of (µg·g-1): n × 0.1 for Cd, Cu, and Mn; n for B, Ba, Co, Cr, Fe, Ga, Ni, Pb, Sr, V, and Zn; n × 10 for Si. Carbonization allowed improving LODs of elements several times depending on the thermal stability and mineral composition of plants. The LODs of elements in plants obtained after carbonization are the following (µg·g-1): n × 0.01 for Be, Cd, Cu, and Mn; n × 0.1 for Co, Cr, Fe, Ga, Ni, Pb, Sr, V, Zn; and n for Si. The techniques suggested are fast, easily workable, and do not require harmful chemical reagents. In some cases, the influence of variable matrices and different element species on analytical signal of elements was not completely suppressed; the deviation of element concentrations from the true values was discussed.

A comparative study of trace elements in Cymodocea nodosa from three semi-enclosed coastal areas in Tunisia.

The present study quantifies the levels of five trace elements (TEs) Zn, Cu, Ni, Pb, and Cd in the leaves and rhizomes of Cymodocea nodosa as well as the surficial sediments from three semi-enclosed coastal areas in Tunisia, in the south Mediterranean Sea. Samples were taken from the Bizerte and Ghar El Melh lagoons and from marina Cap Monastir. The TE ranking was found to be Zn > Cu > Pb > Ni > Cd in sediments and Zn > Cu = Ni = Pb = Cd in C. nodosa leaves and rhizomes. Except for Ni, levels of Zn, Cu, Pb, and Cd significantly differed between the sites. Translocation factors (TFs) were > 1 for all trace elements proving the high capacity of C. nodosa to accumulate TEs in its above-ground tissues. Results show that marina Cap Monastir's meadow exhibits higher TFs than the Bizerte and Ghar El Melh lagoons. This can be due to the presence of the non-indigenous species Halophila stipulacea. The present study highlights the need for further investigation on the effect of interspecific interaction on TE uptake by seagrasses.

Metal concentrations in seagrass (Halophila ovalis) tissue and ambient sediment in a highly modified estuarine environment (Sydney estuary, Australia).

Research into sediment-seagrass tissue metal relationships has been undertaken in Sydney estuary due to the recognized role contamination plays in threats to seagrass health. Seagrass (Halophila ovalis) leaf tissue concentrations are elevated in Cu, Pb and Zn and contain the highest reported root Cr concentrations. Seagrass metal concentrations were significantly different between species H. ovalis and Zostera capricorni; between root and leaf tissue; and between sampling locations. Greatest tissue enrichment was for Pb, however metals were not enriched in seagrass relative to surficial sediment. Fine and total sediment metal concentrations were temporally consistent between collection years 2013/15, whereas root tissue metals changed between years and sites and leaf metal contents were temporally inconsistent. Extractable metal concentrations in fine sediment (<62.5 µm) showed moderate significant correlation with root tissue and a weak significant relationship with leaf tissue, whereas total sediment metal showed no such relationships. Management implications are provided.

Hindering the formation and promoting the dispersion of medical biofilms: non-lethal effects of seagrass extracts.

BACKGROUND: Biofilms have great significance in healthcare-associated infections owing to their inherent tolerance and resistance to antimicrobial therapies. New approaches to prevent and treat unwanted biofilms are urgently required. To this end, three seagrass species (Enhalus acoroides, Halophila ovalis and Halodule pinifolia) collected in Vietnam and in India were investigated for their effects in mediating non-lethal interactions on sessile bacterial (Escherichia coli) and fungal (Candida albicans) cultures. The present study was focused on anti-biofilm activities of seagrass extracts, without killing cells. METHODS: Methanolic extracts were characterized, and major compounds were identified by MS/MS analysis. The antibiofilm properties of the seagrass extracts were tested at sub-lethal concentrations by using microtiter plate adhesion assay. The performance of the most promising extract was further investigated in elegant bioreactors to reproduce mature biofilms both at the solid/liquid and the solid/air interfaces. Dispersion and bioluminescent assays were carried out to decipher the mode of action of the bioactive extract. RESULTS: It was shown that up to 100 ppm of crude extracts did not adversely affect microbial growth, nor do they act as a carbon and energy source for the selected microorganisms. Seagrass extracts appear to be more effective in deterring microbial adhesion on hydrophobic surfaces than on hydrophilic. The results revealed that non-lethal concentrations of E. acoroides leaf extract: i) reduce bacterial and fungal coverage by 60.9 and 73.9%, respectively; ii) affect bacterial biofilm maturation and promote dispersion, up to 70%, in fungal biofilm; iii) increase luminescence in Vibrio harveyi by 25.8%. The characterization of methanolic extracts showed the unique profile of the E. acoroides leaf extract. CONCLUSIONS: E. acoroides leaf extract proved to be the most promising extract among those tested. Indeed, the selected non-lethal concentrations of E. acoroides leaf extract were found to exert an antibiofilm effect on C. albicans and E. coli biofilm in the first phase of biofilm genesis, opening up the possibility of developing preventive strategies to hinder the adhesion of microbial cells to surfaces. The leaf extract also affected the dispersion and maturation steps in C. albicans and E. coli respectively, suggesting an important role in cell signaling processes.

Effects of the decomposing liquid of Cladophora oligoclona on Hydrilla verticillata turion germination and seedling growth.

Excessive proliferation of filamentous green algae (FGA) has been considered an important factor resulting in the poor growth or even decline of submerged macrophytes. However, there is a lack of detailed information regarding the effect of decaying FGA on submerged macrophytes. This study aimed to investigate whether the decomposing liquid from Cladophora oligoclona negatively affects Hydrilla verticillata turion germination and seedling growth. The results showed that the highest concentrations of decomposing liquid treatments inhibited the turion germination rate, which was the lowest than other treatments, at only 84%. The chlorophyll a fluorescence (JIP test) and physiological indicators (chlorophyll a content, soluble sugars, Ca2+/Mg2+-ATPase and PAL activity) were also measured. The chlorophyll a content in the highest concentration (40% of original decomposing liquid) treatment group decreased by 43.53% than that of the control; however, soluble sugars, Ca2+/Mg2+-ATPase, and PAL activity increased by 172.46%, 271.19%, and 26.43% respectively. The overall results indicated that FGA decay has a considerable effect on submerged macrophyte turion germination and seedling growth, which could inhibit their expansion and reproduction. This study emphasized the need to focus on effects of FGA decomposition on the early growth stages of submerged macrophytes and offered technological guidance for submerged vegetation restoration in lakes and shallow waters.

Tape seagrass (Enhalus acoroides) as a bioindicator of trace metal contamination in Merambong shoal, Johor Strait, Malaysia.

Revealing the potential of seagrass as a bioindicator for metal pollution is important for assessing marine ecosystem health. Trace metal (111Cd, 63Cu, 60Ni, 208Pb, 66Zn) concentrations in the various parts (root, rhizome, and blade) of tape seagrass (Enhalus acoroides) collected from Merambong shoal of Sungai Pulai estuary, Johor Strait, Malaysia were acid-extracted using a microwave digester and analysed via inductively coupled plasma-mass spectrometry (ICP-MS). The ranges of trace metal concentrations (in µgg-1 dry weight) were as follows: Cd (0.05-0.81), Cu (1.62-27.85), Ni (1.89-9.35), Pb (0.69-4.16), and Zn (3.44-35.98). The translocation factor revealed that E. acoroides is a hyperaccumulator plant, as its blades can accumulate high concentrations of Cd, Cu, Ni, and Zn, but not Pb. The plant limits Pb mobility to minimize Pb's toxic impact. Thus, E. acoroides is a potential bioindicator of metal pollution by Cd, Cu, Ni, and Zn in estuarine environments.

Sulfated polysaccharides of seagrass Halophila ovalis suppresses tumor necrosis factor-α-induced chemokine interleukin-8 secretion in HT-29 cell line.

OBJECTIVES: The present study aims to investigate the anti-oxidant and anti-inflammatory properties of seagrass Halophila ovalis sulfated polysaccharide on HT-29 cell line. SUBJECTS AND METHODS: Monosaccharides composition was identified using liquid chromatography-mass spectrometry (LC-MS) and the functional groups were analyzed using Fourier transform-infrared (FT-IR) spectroscopy. The antioxidant and anti-inflammatory potential of crude extract and purified fractions was investigated in vitro. RESULTS: FT-IR spectra revealed that the presence of different functional groups and the presence of galactose (82.4%), xylose (7.6%), fructose (4.0%), mannose (2.0%), fucose (1.6%), glucose (1.2%), and arabinose (1.0%) was observed using LC-MS. Ho-SP and its fractions showed radical scavenging activity in hydroxyl, 2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid, and ferric reducing antioxidant power assay in a dose-dependent manner. Noticeable anti-inflammatory activity of purified fraction Ho FrIV (IC 50= 43.85 µg/ml) was observed in a noncytotoxic range of concentrations and inhibited the tumor necrosis factor-α (TNF-α)-induced interleukin-8 (IL-8) secretion (0.27 ng/ml) in HT-29 cell line. CONCLUSION: Overall, the results presented in this study suggest that purified fraction Ho FrIV of Ho-SP could suppress the TNF-α-induced secretion of IL-8 in HT-29 and thus could be used as a promising antioxidant and anti-inflammatory candidate with potential benefits.

Factors affecting palatability of four submerged macrophytes for grass carp Ctenopharyngodon idella.

Grass carp can weaken the growth and reproductive capacity of submerged macrophytes by consuming valuable tissues, but factors affecting palatability of submerged macrophytes for grass carp rarely are considered. In this study, relative consumption rate of grass carp with regard to submerged macrophytes was in the following order: Hydrilla verticillata > Vallisneria natans > Ceratophyllum demersum > Myriophyllum spicatum. Firmness of macrophytes was in the following order: M. spicatum > C. demersum > H. verticillata = V. natans, whereas shear force was M. spicatum > C. demersum > H. verticillata > V. natans. After crude extracts of M. spicatum were combined with H. verticillata, grass carp fed on fewer macrophyte pellets that contained more plant secondary metabolites (PSMs). This indicated that structure and PSMs affected palatability of macrophytes.PSMs do not contribute to reduction in palatability through inhibition of intestinal proteinases activity, but they can cause a decrease in the abundance of Exiguobacterium, Acinetobacter-yielding proteases, lipases, and cellulose activity, which in turn can weaken the metabolic capacity of grass carp and adversely affect their growth. Thus, the disadvantages to the growth and development of grass carp caused by PSMs may drive grass carp to feed on palatable submerged macrophytes with lower PSMs.

Decomposition characteristics of three different kinds of aquatic macrophytes and their potential application as carbon resource in constructed wetland.

Decomposition of aquatic macrophytes usually generates significant influence on aquatic environment. Study on the aquatic macrophytes decomposition may help reusing the aquatic macrophytes litters, as well as controlling the water pollution caused by the decomposition process. This study verified that the decomposition processes of three different kinds of aquatic macrophytes (water hyacinth, hydrilla and cattail) could exert significant influences on water quality of the receiving water, including the change extent of pH, dissolved oxygen (DO), the contents of carbon, nitrogen and phosphorus, etc. The influence of decomposition on water quality and the concentrations of the released chemical materials both followed the order of water hyacinth > hydrilla > cattail. Greater influence was obtained with higher dosage of plant litter addition. The influence also varied with sediment addition. Moreover, nitrogen released from the decomposition of water hyacinth and hydrilla were mainly NH3-N and organic nitrogen while those from cattail litter included organic nitrogen and NO3--N. After the decomposition, the average carbon to nitrogen ratio (C/N) in the receiving water was about 2.6 (water hyacinth), 5.3 (hydrilla) and 20.3 (cattail). Therefore, cattail litter might be a potential plant carbon source for denitrification in ecological system of a constructed wetland.

Permanently open stomata of aquatic angiosperms display modified cellulose crystallinity patterns.

Most floating aquatic plants have stomata on their upper leaf surfaces, and usually their stomata are permanently open. We previously identified 3 distinct crystallinity patterns in stomatal cell walls, with angiosperm kidney-shaped stomata having the highest crystallinity in the polar end walls as well as the adjacent polar regions of the guard cells. A numerical bio-mechanical model suggested that the high crystallinity areas are localized to regions where the highest stress is imposed. Here, stomatal cell wall crystallinity was examined in 4 floating plants from 2 different taxa: basal angiosperms from the ANITA grade and monocots. It appears that the non-functional stomata of floating plants display reduced crystallinity in the polar regions as compared with high crystallinity of the ventral (inner) walls. Thus their guard cells are both less flexible and less stress resistant. Our findings suggest that the pattern of cellulose crystallinity in stomata of floating plants from different families was altered as a consequence of similar evolutionary pressures.

Thalassiolin D: a new flavone O-glucoside Sulphate from the seagrass Thalassia hemprichii.

Thalassiolin D, a new flavone O-glucoside sulphate along with three flavonoids, two steroids, p-hydroxybenzoic acid, 4,4'-dihydroxybenzophenone and nitrogen compound, octopamine were isolated from the seagrass Thalassia hemprichii, collected from the Saudi Red Sea coast. By extensive spectroscopic analysis including 1D and 2D NMR and MS data, the structure of the new compound was elucidated as diosmetin 7-O-ß-glucosyl-2″-sulphate. The new compound displayed moderately in vitro antiviral HCV protease activity with IC50 value 16 µM.

Real-time in-situ Simultaneous Monitoring of Dissolved Oxygen and Materials Movements at a Vicinity of Micrometers from an Aquatic Plant by Combining Deflection of a Probe Beam and Fluorescence Quenching.

It is desirable to be able to monitor the intake or release of the components at different organs of aquatic plants in real time and in-situ. Here, we report a novel optical detection system that allows for real-time in-situ simultaneous monitoring of the dissolved oxygen and material movements at a vicinity of micrometers from the aquatic plant surface. A blue semiconductor diode-laser was used as the light source of both the probe beam and excitation light for fluorescence. The laser light reflected by a dichroic mirror was focused to a vicinity of the plant/water interface in a culture dish by an objective lens. The distance between the focused laser beam and the plant surface was adjusted by an X-Y-Z micro-stage. Deflection of the probe beam was detected by a position sensor, and fluorescence from the vicinity was monitored by a PMT. A commercial fluorescent DO sensor, which simultaneously monitored temperature, was immersed into the culture dish at about 1 cm away from the aquatic plants. A white-light LED was used to illuminate the aquatic plants in the dish in photosynthesis process. A Ru-complex (tris (2,2'-bipyridyl)ruthenium(II) chloride) was used as a fluorescent probe, and Egeria densa Planch. was used as a model aquatic plant. The DO-quenched fluorescence and material movement-induced deflection signals are compared at different distances from the aquatic plant surface. The results show that the optical detection system can monitor DO and the material movements at a vicinity of the aquatic plants not only much more sensitively, but also much more closely to real time than analytical methods that monitor concentration changes at a bulk solution.

Phytochelatin 2 accumulates in roots of the seagrass Enhalus acoroides collected from sediment highly contaminated with lead.

Phytochelatins (PCs), the heavy metal-binding peptides of plants, play a main function in heavy metal detoxification. In this study, Enhalus acoroides samples collected at six distinct seagrass beds from the coast of Khanh Hoa province, Viet Nam, were evaluated for their PCs. The contents of different PCs in each organ including leaf, rhizome, and root were determined by using HPLC analysis. Significant differences of PC2 contents among specific organs and their relation were tested by ANOVA, Tukey test, and Pearson's correlation. The results showed that higher PC2, appearance of PC3 and a strong correlation between PC2 and Pb concentration were found in the root organ collected from a Pb contaminated area. We conclude that high Pb in the sediment induce high PC2 and PC3 production in the root. This first report on in situ detection of PCs of seagrass encourages future investigation on the ability to use seagrass for phytoremediation and as a bioindicator of heavy metals based on PC contents.