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 samplcd. 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 inde- pendently 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.

Isolation and characterization of a cone snail protease with homology to CRISP proteins of the pathogenesis-related protein superfamily

The pathogenesis-related (PR) protein superfamily is widely distributed in the animal, plant, and fungal kingdoms and is implicated in human brain tumor growth and plant pathogenesis. The precise biological activity of PR proteins, however, has remained elusive. Here we report the characterization, cloning and structural homology modeling of Tex31 from the venom duct of Conus textile. Tex31 was isolated to >95% purity by activity-guided fractionation using a para-nitroanilide substrate based on the putative cleavage site residues found in the propeptide precursor of conotoxin TxVIA. Tex31 requires four residues including a leucine N-terminal of the cleavage site for efficient substrate processing. The sequence of Tex31 was determined using two degenerate PCR primers designed from N-terminal and tryptic digest Edman sequences. A BLAST search revealed that Tex31 was a member of the PR protein superfamily and most closely related to the CRISP family of mammalian proteins that have a cysteine-rich C-terminal tail. A homology model constructed from two PR proteins revealed that the likely catalytic residues in Tex31 fall within a structurally conserved domain found in PR proteins. Thus, it is possible that other PR proteins may also be substrate-specific proteases.

Solubility of selected esters in supercritical carbon dioxide

The solubility of ethyl propionate, ethyl butyrate, and ethyl isovalerate in supercritical carbon dioxide was measured at temperature ranging from 308.15 to 333.15 K and pressure ranging from 85 to 195 bar. At the same temperature, the solubility of these compounds increases with pressure. The crossover pressure region was also observed in this study. The experimental data were correlated by the semi-empirical Chrastil equation and Peng-Robinson equation of state (EOS) using several mixing rules. The Peng-Robinson EOS gives better solubility prediction than the empirical Chrastil equation. (C) 2002 Elsevier Science B.V. All rights reserved.