Ventilation and respiration in roots of one-year-old seedlings of grey mangrove Avicennia marina (Forsk.) Vierh.

Avicennia marina (Forsk.) Vierh. was grown from seed for 12 months in artificially tidal tanks providing a range of duration and depth of inundation. Plant growth characteristics were measured at harvest. Root aerenchyma development was estimated by pycnometry, root respiration rates by manometry, and the oxygen supply capacity of the above-ground portions of the plant was determined using oxygen electrode chambers. The mass per plant at harvest was influenced by the extent of inundation during growth with maximal growth at intermediate-length (1.5 to 6.5 h per tide) inundation periods. Those plants that had been submerged the longest (8.5 h per tide) had the least root tissue. The oxygen conductance of the stem base plus any pneumatophores showed a maximum in plants grown under intermediate inundation. Oxygen demand and internal gas space per unit dry weight of root were independent of extent of inundation. During high tide the plants grown at inundation periods of more than about 3–5 hours per tide were likely to become anaerobic. This may constitute a physiological limit for this species at the bottom of the tidal range.     

Aerenchyma tissue development and gas-pathway structure in root of Avicennia marina (Forsk.) Vierh.

The aerenchyma differentiation in cable roots, pneumatophores, anchor roots, and feeding roots of the mangrove plant, Avicennia marina (Verbenaceae) was analyzed using a light microscope and scanning electron microscope. In all types, cortex cells were arranged in longitudinal columns extending from the endodermis to the epidermis. No cells in the cortex had intercellular spaces at the root tip (0–150 m), and aerenchyma started developing at 200 m from the root apex. The aerenchyma formation was due to cell separation (schizogeny) rather than cell lysis. The cell separation occurred between the longitudinal cell columns, forming long intercellular spaces along the root axis. During aerenchyma formation, the cortex cells enlarged longitudinally by 1.8–3.9 times and widened horizontally by 2.2–2.9 times. As a result, the aerenchyma had a pronounced tubular structure that was radially long, elliptical or oval in cross section and that ran parallel to the root axis. The tube had tapering ends, as did vessel elements, although there were no perforated plates. The interconnection between neighboring tubes was made by abundant small pores or canals that were schizogenous intercellular spaces between the wall cells. All aerenchyma tubes in the root were interconnected by these small pores serving as a gas pathway.     

Microsatellite analysis of genetic structure in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

The level of genetic variation throughout the entire worldwide range of the mangrove species Avicennia marina (Forsk.) Vierh. was examined using microsatellite markers. Three microsatellite loci detected high levels of allelic diversity (70 alleles in total), essential for an accurate estimation of population genetic parameters. The informativeness of the microsatellite loci tended to increase with increasing average number of repeats. The levels of heterozygosity detected for each population, over all loci, ranged from 0.0 to 0.8, with an average of 0.407, indicating that some populations had little or no genetic variation, whereas others had a large amount. Populations at the extremes of the distribution range showed reduced levels of heterozygosity, and significant levels of inbreeding. This is not unexpected as these populations may be subject to founder effects and environmental constraints. The presence of genetic structure was tested in A. marina populations using three models: (i) a single panmictic model; (ii) the discrete subpopulation model; and (iii) the isolation by distance model. The discrete subpopulations model was supported by the overall measures of population differentiation based on the infinite alleles model (F-statistics), and the stepwise mutation model (R statistics). In addition, an analysis of molecular variance (AMOVA), using both theoretical models, found that most of the variation was between populations (41-71%), and within individuals in the total population (31-49%). There was little variation among individuals within populations (0-10%). There was no significant isolation by distance. The high levels of genetic differentiation observed among populations of A. marina may be due to environmental and ecological factors, particularly past sea level and climatic changes.     

Isolation and characterization of 10 new compound microsatellite markers for a mangrove tree species,Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

Avicennia marina is an ecologically important mangrove tree species. We isolated 10 polymorphic microsatellite loci from this species using an improved technique. Our isolated loci provided compound microsatellite markers with polymorphism of two to six alleles per locus. The observed and expected heterozygosities ranged from 0.025 to 0.625 and from 0.096 to 0.767, respectively. These markers would be the useful tools for researching on the genetic diversity and population genetic structure of A. marina.     

Low salinities adversely affect photosynthetic performance of the mangrove,Avicennia marina

Photosynthetic performance of the highly salt tolerant mangrove, Avicennia marina, was compared at two sites differing insubstrate soil salinities. Carbon dioxide exchange and chlorophyll fluorescence weremonitored at a high salinity site in Durban Bay (35) and at a low salinitysite in Beachwood (< 12). Mean CO₂ exchange, conductanceand transpiration were consistently higher at the high salinity site. Carbondioxide response curves indicated that carboxylation efficiency was higherand stomatal limitation lower at the Durban Bay site. PSII quantum yield,electron transport rates (ETR) and intrinsic PSII efficiency(F_v/F_m) were significantly higher at the high salinity site.Quenching analysis indicated a higher degree ofphotoinhibition/photoprotection in leaves at the low salinity site. Predawnand midday leaf water potentials were –1.6 and –3.1 MPa at Beachwood,compared to –2.6 and –3.8 MPa, respectively, at Durban Bay. Leafconcentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺,Cl^- and N were significantly higher at Durban Bay. Photosyntheticperformance is apparently impaired at the low salinity site in Beachwood asa result of K⁺ and N deficiencies in the leaves.     

Growth and establishment of mangrove (Avicennia marina) on the coastlines of Kuwait

Mangrove (Avicennia marina) communities constitute an importantcomponent of the renewable natural vegetation resources of the coastalzones of the Arabian Gulf south of Kuwait. Attempts to introduce themangrove into the intertidal zones of the coastline of Kuwait are underwaybecause of the expected favorable environmental impact of this plant, andbecause of its moderating influence on the local climate and enhancementof the aesthetic and recreational value of the coastlines and fisheryresources. Propagules were collected from natural stands of mangrove inBahrain and the United Arab Emirates. Silvicultural practices were followedto produce healthy plants after growing of propagules in the greenhouse.Observations indicated that there is a positive correlation betweenpropagule weight and the length of the seedling stem. Outplanting wasdone in two sites in the intertidal zone around the Sulabikhat Bay, Kuwait.Data on plant survival showed that the most suitable level for successfulestablishment of mangrove was around or below the 3-meter contour tidalline. After 7 years of growth, plants reached a mean height of 250 cm,which is close to the height of their parent trees in Bahrain. The U.A.E.stock plants reached 288 cm after 5 years of growth in Kuwait. Plantsflowered and produced viable seeds. The biological feasibility ofestablishing mangrove plantations in the intertidal flats of Kuwait's coastlineswas documented from the field observation of the experimental plantations.Studies to document the environmental impact of the introduction areunderway.     

Characterisation and analysis of microsatellite loci in a mangrove species, Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

An enriched microsatellite library of the mangrove species Avicennia marina was constructed, in which 85.8% of the clones contained microsatellite sequences. Of the microsatellite repeat sequences isolated, 55.0% were di-nucleotides, 34.2% were tri-nucleotides, 50.0% were perfect, 24.2% were imperfect, and 15.0% were compound. Four different di-nucleotide repeats were isolated with repeat lengths ranging from 5 to 33; ten different tri-nucleotide repeats were isolated with repeat lengths ranging from 3 to 25. The most common di-nucleotide was the AC/TG repeat; the most common tri-nucleotide was the CCG/GGC repeat. Sixteen microsatellite sequences were selected for primer design, and 6 primers were selected to investigate the polymorphism detected among 15 individuals of A. marina from three natural populations in Australia. A total of 40 alleles were detected at 6 microsatellite loci. The number of alleles per microsatellite locus ranged from 5 to 13. On average, 7 alleles were detected per locus. All microsatellite loci showed high levels of gene diversity (heterozygosity), with values ranging from 0.53 to 0.88; the mean value of gene diversity was 0.70. Microsatellite loci were also tested for conservation across Avicennia species. There was a decline in amplification success with increasing divergence between Avicennia species. The results indicate that microsatellites are abundant in the Avicennia genome and can be valuable genetic markers for assessing the effects of deforestation and forest fragmentation in mangrove communities, which is an important issue for mangrove conservation and afforestation schemes. Received: 8 June 1999 / Accepted: 21 September 1999     

Isolation of several anti-stress genes from a mangrove plant Avicennia marina

In order to isolate anti-stress genes from mangrove plants, a cDNA library of Avicennia marina was constructed and screened for anti-stress genes by a functional expression screening with Escherichia coli cells. Several stress-related gene homologues, such as chaperonin-60, clpP protease of the clp/Hsp 100 family of chaperones, ubiquitin, eEF1A, drought-induced AtDi19 gene of Arabidopsis thaliana, and secretory peroxidase, were successfully isolated.     

Molecular cloning and characterization of betaine aldehyde dehydrogenase gene from Suaeda liaotungensis and its use in improved tolerance to salinity in transgenic tobacco

cDNA encoding betaine aldehyde dehydrogenase (BADH) from the halophyte Suaeda liaotungensis has been cloned, sequenced and expressed in tobacco (Nictiana tabacum 89). The full-length cDNA is 1506 base pairs (bp) long and encodes a 502 amino-acid polypeptide. The cDNA fragment coding for the mature enzyme was cloned into vector pCAMBIA-1301 for expression in tobacco. Southern blotting analysis showed that that the Badh gene was integrated into the genome of tobacco. Tobacco expressing BADH survived on MS medium containing 200 mM NaCl, whereas the untransformed plants turned yellow after about 20 d and died.     

Thermo-osmotic gas supply not detected in Avicennia marina seedlings

Ethane was used as tracer gas to assess the likelihood of thermo-osmotically induced mass-flow in the aerenchyma of Avicennia marina seedlings without pneumatophores. Ethane movement was measured in darkness and with illumination at approximately 600 µ mol m^–2s^–1 provided to the leaves and stem, with the expectation that leaf warming under illumination would provide for thermo-osmotic flow. In some seedlings the flow increased with illumination, and in others it either decreased or remained unchanged. Overall, there was no statistically significant difference in the conductance to ethane between darkened illuminated plants, and the rates of ethane movement were consistent with an average diffusive conductance to oxygen down the stem of 0.22 × 10^–19m³ s^–1. it was concluded that there was no evidence for thermo-osmotically induced in this case.     

Water relations determine short time leaf growth patterns in the mangrove Avicennia marina (Forssk.) Vierh.

High‐resolution leaf growth is rarely studied despite its importance as a metric for plant performance and resource use efficiency. This is in part due to methodological challenges. Here, we present a method for in situ leaf growth measurements in a natural environment. We measured instantaneous leaf growth on a mature Avicennia marina subsp. australasica tree over several weeks. We measured leaf expansion by taking time‐lapse images and analysing them using marker tracking software. A custom‐made instrument was designed to enable long‐term field studies. We detected a distinct diel growth pattern with leaf area shrinkage in the morning and leaf expansion in the afternoon and at night. On average, the observed daily shrinkage was 37% of the net growth. Most of the net growth occurred at night. Diel leaf area shrinkage and recovery continued after growth cessation. The amount of daily growth was negatively correlated with shrinkage, and instantaneous leaf growth and shrinkage were correlated with changes in leaf turgor. We conclude that, at least in this tree species, instantaneous leaf growth patterns are very strongly linked to, and most likely driven by, leaf water relations, suggesting decoupling of short‐term growth patterns from carbon assimilation.     

Comparative analysis of genetic diversity in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae) detected by AFLPs and SSRs

Avicennia marina is an important mangrove species with a wide geographical and climatic distribution which suggests that large amounts of genetic diversity are available for conservation and breeding programs. In this study we compare the informativeness of AFLPs and SSRs for assessing genetic diversity within and among individuals, populations and subspecies of A. marina in Australia. Our comparison utilized three SSR loci and three AFLP primer sets that were known to be polymorphic, and could be run in a single analysis on a capillary electrophoresis system, using different- colored fluorescent dyes. A total of 120 individuals representing six populations and three subspecies were sampled. At the locus level, SSRs were considerably more variable than AFLPs, with a total of 52 alleles and an average heterozygosity of 0.78. Average heterozygosity for AFLPs was 0.193, but all of the 918 bands scored were polymorphic. Thus, AFLPs were considerably more efficient at revealing polymorphic loci than SSRs despite lower average heterozygosities. SSRs detected more genetic differentiation between populations (19 vs 9%) and subspecies (35 vs 11%) than AFLPs. Principal co-ordinate analysis revealed congruent patterns of genetic relationships at the individual, population and subspecific levels for both data sets. Mantel testing confirmed congruence between AFLP and SSR genetic distances among, but not within, population comparisons, indicating that the markers were segregating independently but that evolutionary groups (populations and subspecies) were similar. Three genetic criteria of importance for defining priorities for ex situ collections or in situ conservation programs (number of alleles, number of locally common alleles and number of private alleles) were correlated between the AFLP and SSR data sets. The congruence between AFLP and SSR data sets suggest that either method, or a combination, is applicable to expanded genetic studies of mangroves. The codominant nature of SSRs makes them ideal for further population-based investigations, such as mating-system analyses, for which the dominant AFLP markers are less well suited. AFLPs may be particularly useful for monitoring propagation programs and identifying duplicates within collections, since a single PCR assay can reveal many loci at once. Received: 3 October 2000 / Accepted: 19 February 2001     

The population dynamics of the mangrove Avicennia marina; demographic synthesis and predictive modelling

Population dynamics of the widespread mangrove Avicennia marina was studied over the complete life-history from zygotes through to adults in southeastern Australia. Zygote survival, propagule dispersal, seedling establishment, seedling recruitment and sapling recruitment were examined by demographic censuses over a range of spatial and temporal scales. Hypotheses about factors regulating survival were tested by manipulative field experiments. Life table statistics for survival and fecundity were used to calculate transition probabilities and their variance for seven stages of life history. These parameters were used as the basis of a stochastic model that predicts population structure after small and large scale perturbations.     

Trace metals complexation behavior with root exudates induced by salinity from a mangrove plant Avicennia marina (Forsk.) Vierh

This study investigated the characteristics of exudates from mangrove plant Avicennia marina seedling roots under 0, 200 and 600?mM NaCl treatments and their complexation behavior with trace metals using excitation emission matrix (EEM) fluorescence spectrometry. Two fulvic-like fluorescence peaks, namely peak A (Em = 440?nm, Ex = 250?nm, UV fulvic-like compounds) and peak B (Em = 440?nm, Ex = 340?nm, visible fulvic-like compounds) were identified. The fluorescence intensities of peak A and peak B were enhanced by increasing salinity. Furthermore, the fluorescence of both peaks could be quenched by the ions of copper (Cu²⁺), manganese (Mn²⁺) and cadmium (Cd²⁺). Conditional stability constant (logK_a) exhibited that binding capacity of both peak A and peak B with trace metals are Cu²⁺?>?Mn²⁺?>?Cd²⁺ in the range from 2.21 to 4.01. Besides, Hill coefficient (n) >1 for Cu²⁺ but n?<?1 for Mn²⁺ and Cd²⁺. The results of high n and high logK_a for Cu²⁺ rather than Mn²⁺ and Cd²⁺ indicate that the fulvic-like compounds in root exudates of A. marina have maximum potential for Cu²⁺ complexation compared to Mn²⁺ and Cd²⁺, suggesting the fulvic acids in root exudates of A. marina have strong complexation with Cu²⁺ rather than Mn²⁺ and Cd²⁺.     

Zinc distribution and excretion in the leaves of the grey mangrove,Avicennia marina (Forsk.) Vierh

Mangroves are important as primary producers in estuarine food chains. Zinc is often a major anthropogenic contaminant in estuarine ecosystems and has potential ecotoxicological consequences for mangrove communities. Accumulation, distribution and excretion of zinc in the leaf tissue of the grey mangrove, Avicennia marina was studied using SEM X-ray microanalysis and Atomic Absorption Spectroscopy. The first leaves of A. marina grown in 500 μg Zn as ZnCl₂ per g of dry soil were found to accumulate 106.3±18.5 μg Zn per g dry tissue, significantly higher than control plants, after a 7-month period. Washings from first leaves contained significantly higher amounts of zinc (0.30±0.14 μg/cm² Zn) than control plants after 1 month, suggesting excretion of zinc from glandular trichomes. SEM X-ray microanalysis revealed salt crystals exuded from glandular tissue on the adaxial surface of first leaves to be composed of alkaline metals and zinc in zinc treated plants. SEM X-ray microanalysis of seedlings dosed with 4 g/l Zn as Zn Cl₂ revealed a decreasing Zn gradient from xylem tissue, through photosynthetic mesophyll, to hypodermal (water) tissue. A subsequent increase in Zn concentration was observed in glandular tissue. Cell wall Zn concentrations were consistently higher than intracellular Zn concentrations.     

Growth responses of the mangrove Avicennia marina to salinity: development and function of shoot hydraulic systems require saline conditions

Background and Aims Halophytic eudicots are characterized by enhanced growth under saline conditions. This study combines physiological and anatomical analyses to identify processes underlying growth responses of the mangrove Avicennia marina to salinities ranging from fresh- to seawater conditions.Methods Following pre-exhaustion of cotyledonary reserves under optimal conditions (i.e. 50 % seawater), seedlings of A. marina were grown hydroponically in dilutions of seawater amended with nutrients. Whole-plant growth characteristics were analysed in relation to dry mass accumulation and its allocation to different plant parts. Gas exchange characteristics and stable carbon isotopic composition of leaves were measured to evaluate water use in relation to carbon gain. Stem and leaf hydraulic anatomy were measured in relation to plant water use and growth.Key Results Avicennia marina seedlings failed to grow in 0–5 % seawater, whereas maximal growth occurred in 50–75 % seawater. Relative growth rates were affected by changes in leaf area ratio (LAR) and net assimilation rate (NAR) along the salinity gradient, with NAR generally being more important. Gas exchange characteristics followed the same trends as plant growth, with assimilation rates and stomatal conductance being greatest in leaves grown in 50–75 % seawater. However, water use efficiency was maintained nearly constant across all salinities, consistent with carbon isotopic signatures. Anatomical studies revealed variation in rates of development and composition of hydraulic tissues that were consistent with salinity-dependent patterns in water use and growth, including a structural explanation for low stomatal conductance and growth under low salinity.Conclusions The results identified stem and leaf transport systems as central to understanding the integrated growth responses to variation in salinity from fresh- to seawater conditions. Avicennia marina was revealed as an obligate halophyte, requiring saline conditions for development of the transport systems needed to sustain water use and carbon gain.     

Effect of salt stress on the metabolism of ethanolamine and choline in leaves of the betaine-producing mangrove species Avicennia marina

Glycinebetaine synthesis from [methyl-14C]choline and [1,2-14C]ethanolamine in leaf disks of Avicennia marina, was increased by salt stress (250 and 500 mM NaCl). After 18 h incubation with [methyl-14C]choline, phosphocholine and CO(2) were found to be heavily labelled. Phosphocholine contained 39% of the total radioactivity taken up by non-salinised (control) leaf disks and 15% of the total for salinised leaf disks stressed with 500 mM NaCl. Eighteen and 49% of the radioactivity absorbed by control and salinised disks, respectively, were released as CO(2). Metabolic studies of [1,2-14C]ethanolamine revealed that the radioactivity taken up by the leaf disks was recovered as the following compounds after 18 h: phosphorylated compounds (mainly phosphoethanolamine, phosphodimethylethanolamine and phosphocholine) (40-50%); choline (1-2%); glycinebetaine (3-5%); lipids (20-28%); CO(2) (6-10%). Unlike glycinebetaine, incorporation into phosphorylated compounds and lipids were reduced by salt stress. Incorporation of [methyl-14C]S-adenosyl-L-methionine (SAM) into choline, phosphocholine and glycinebetaine in leaf disks was stimulated by salt stress. In vitro activities of adenosine kinase and adenosine nucleosidase, which are implicated in stimulating the SAM regeneration cycle, increased after the leaf disks were incubated with 250 and 500 mM NaCl for 18 h. Changes in metabolism involving choline and glycinebetaine due to salt stress are discussed.