Knee Roots in Avicennia marina (Forsk.) Vierh.

The occurrence of knee roots in Avicennia marina (Forsk.) Vierh.is reported and specimens at various stages of development aredescribed Knee roots arise from horizontal roots in a mannersimilar to pneumatophores but anatomically they resemble horizontalroots After re-entering the soil the knee root reverts to ahorizontal position and gives rise to further pneumatophoresand anchoring roots.     

Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.)

The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg^–1 s^–1for cable roots and 3·27±0·12 µmolkg^–1 s^–1 for fine roots. The Q₁₀ for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m^–3 and 3·4mol m^–3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma     

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.     

Recalcitrant Seeds: Short-term Storage Effects in Avicennia marina (Forsk.) Vierh. may be Germination-associated

When recalcitrant propagules (seeds) of Avicennia marina werestored in a dry air stream there was no significant change intheir moisture content for 10 days, after which it declinedrapidly. Seed viability remained high during this 10-d period,only then declining. Ultrastructural changes in embryonic rootprimordium cells during the 10-d storage period were similarto those characterizing germination. It is suggested that thecontinuation of germination processes after shedding may beresponsible for the deterioration in stored recalcitrant seeds. Avicennia marina, recalcitrance, seed storage, germination     

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.     

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.     

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.     

Horizontal Structures on Pneumatophores of Avicennia marina (Forsk.) Vierh.--A New Site of Oxygen Conductance

Conductance of pneumatophores of the grey mangrove, Avicenniamarina, to oxygen depended on lenticel number up to about 25functional lenticels per pneumatophore, and probably on cross-sectionalarea of the gas space in pneumatophores with over 25. The dependenceon lenticel number was far from perfect, because of a substantialnon-lenticellular component of conductance. This non-lenticellularconductance was attributed to 'horizontal structures' on themost recently formed part of the pneumatophore. These were thoughtto result from persistent portions of the root cap which remainedattached to the surface of the pneumatophore, and around whichbreaks in the surface of the periderm developed. Following flooding,the lenticels dried and resumed full conductance within aboutthree minutes. Non-lenticellular conductance imputed to thehorizontal structures took about ten times as long to recoverafter flooding. Nevertheless, these horizontal structures arelikely to represent a significant pathway for admission of oxygen,especially in rapidly growing roots where the tip region lackslenticels. A name, 'subrisules', for these horizontal structuresis proposed.Copyright 1994, 1999 Academic Press Avicennia marina (Forsk.) Vierh., Avicenniaceae, grey mangrove, pneumatophore, lenticel, conductance, oxygen electrode, aerenchyma, subrisule     

Genetic variation of Avicennia marina (Forsk.) Vierh. (Avicenniaceae) in Vietnam revealed by microsatellite and AFLP markers

Genetic variation of Avicennia marina in the costal area of Vietnam was examined using microsatellite and AFLP markers. By using five microsatellite loci a total of 21 alleles were detected. The average number of alleles per locus per population ranged from 1.667 to 3.000. The observed heterozygosity varied from 0.180 to 0.263, with an average of 0.210 indicating relatively low level of genetic variation comparing to the previous studies on A. marina in the worldwide range. The expected heterozygosity was larger than the observed heterozygosity leading to positive inbreeding coefficients in all the six populations. Highly significant departures from Hardy-Weinberg Equilibrium were detected in four populations. AFLP analysis revealed a total of 386 loci, of which 232 (60.1%) were polymorphic. In congruent with microsatellite markers relatively low levels of genetic variation were detected at both gene and nucleotide levels (H = 0.086; pi = 0.0054). Reduced level of genetic variation was found in the central population, and in the southern populations. Both microsatellite and AFLP markers revealed large genetic differentiation (F(ST) = 0.262 and 0.338, respectively) indicating strong genetic structure among regional populations. Pairwise genetic distance by AFLP showed two populations in the north and the other two in the south are closely related each other.     

Ectopic expression of pigeonpea cold and drought regulatory protein (CcCDR) in yeast and tobacco affords multiple abiotic stress tolerance

Pigeonpea (Cajanus cajan L.) cold and drought regulatory protein encoding gene (CcCDR) has been introduced into yeast and tobacco for its functional validation. In yeast, expression of CcCDR imparted marked tolerance against abiotic stresses exerted by PEG and NaCl. Transgenic tobacco lines, expressing CcCDR under the control of CaMV35S and rd29A promoters, when subjected to mannitol, NaCl and cold (4 °C) stress, developed into healthy plants with profuse root system, increased biomass, root length and chlorophyll content in contrast to the weak-stunted wild-type plants. Transgenic plants also showed increased levels of proline, reducing sugars and endogenous abscisic acid (ABA) content. Exogenous ABA treatment resulted in increased hypersensitivity and decreased stomatal aperture size of transgenic plants compared to wild type. Localization studies confirmed that CcCDR could enter the nucleus as revealed by intense fluorescence, indicating its plausible interaction with various nuclear proteins. The overall results amply demonstrate the intrinsic effect of CcCDR in bestowing multiple abiotic stress tolerance at cellular and whole plant levels. Accordingly, the multipotent CcCDR seems promising as a prime candidate gene to fortify crop plants with abiotic stress tolerance.     

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     

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⁺.     

Nitrogen Fixation Associated with the New Zealand Mangrove (Avicennia marina (Forsk.) Vierh. var. resinifera (Forst. f.) Bakh.)

Nitrogenase activity in mangrove forests at two locations in the North Island, New Zealand, was measured by acetylene reduction and ¹⁵N₂ uptake. Nitrogenase activity (C₂H₂ reduction) in surface sediments 0 to 10 mm deep was highly correlated (r = 0.91, n = 17) with the dry weight of decomposing particulate organic matter in the sediment and was independent of light. The activity was not correlated with the dry weight of roots in the top 10 mm of sediment (r = −0.01, n = 13). Seasonal and sample variation in acetylene reduction rates ranged from 0.4 to 50.0 μmol of C₂H₄ m⁻² h⁻¹ under air, and acetylene reduction was depressed in anaerobic atmospheres. Nitrogen fixation rates of decomposing leaves from the surface measured by ¹⁵N₂ uptake ranged from 5.1 to 7.8 nmol of N₂ g (dry weight)⁻¹ h⁻¹, and the mean molar ratio of acetylene reduced to nitrogen fixed was 4.5:1. Anaerobic conditions depressed the nitrogenase activity in decomposing leaves, which was independent of light. Nitrogenase activity was also found to be associated with pneumatophores. This activity was light dependent and was probably attributable to one or more species of Calothrix present as an epiphyte. Rates of activity were generally between 100 and 500 nmol of C₂H₄ pneumatophore⁻¹ h⁻¹ in summer, but values up to 1,500 nmol of C₂H₄ pneumatophore⁻¹ h⁻¹ were obtained.     

Generation and analysis of expressed sequence tags from the salt-tolerant mangrove species Avicennia marina (Forsk) Vierh

Salinization poses an increasingly serious problem in coastal and agricultural areas with negative effects on plant productivity and yield. Avicennia marina is a pantropical mangrove species that can survive in highly saline conditions. As a first step towards the characterization of genes that contribute to combating salinity stress, the construction of a cDNA library of A. marina genes is reported here. Random expressed sequence tag (EST) sequencing of 1,841 clones produced 1,602 quality reads. These clones were classified into functional categories, and blast comparisons revealed that 113 clones were homologous to genes earlier implicated in stress responses, of which the dehydrins are the most predominant in this category. Of the ESTs analyzed, 30% showed homology to previously uncharacterized genes in the public plant databases. Of these 30%, 52 clones were selected for reverse Northern analysis: 26 were shown to be up-regulated and five shown to be down-regulated. The results obtained by reverse Northern analysis were confirmed by Northern analysis for three clones.     

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 demography of the temperate mangrove [Avicennia marina (Forsk.) Vierh.] at its southern limit in New Zealand

An expanding monoculture of the mangrove Avicennia marina var. resinifera growing at its southern limit in New Zealand was modelled using a Leslie matrix technique which assumed exponential population growth. The predictions from the model were partially verified from sequential aerial photographs of the population. The results add to a growing body of practical experience in the application of matrix techniques to plant demography. Modelling indicates that survivorship of the young tree size class is the main determinant of the population growth rate; annual seed production is relatively unimportant. Avicennia trees produce relatively few large viviparous propagules, each of which has a high probability of establishment. Seedlings are retained in a ‘seedling bank’ for several years. The λ value of 1.2228 reflects the colonizing ability of the species, and is compared with published values for other species.     

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.