Anong Chirapart

Homogeneous population of the brown alga Sargassum polycystum in Southeast Asia: possible role of recent expansion and asexual propagation.

Southeast Asia has been known as one of the biodiversity hotspots in the world. Repeated glacial cycles during Pleistocene were believed to cause isolation of marine taxa in refugia, resulting in diversification among lineages. Recently, ocean current was also found to be another factor affecting gene flow by restricting larval dispersal in animals. Macroalgae are unique in having mode of reproduction that differs from that of animals. Our study on the phylogeographical pattern of the brown macroalga Sargassum polycystum using nuclear Internal Transcribed Spacer 2 (ITS2), plastidal RuBisCO spacer (Rub spacer) and mitochondrial cytochrome oxidase subunit-III (Cox3) as molecular markers revealed genetic homogeneity across 27 sites in Southeast Asia and western Pacific, in sharp contrast to that revealed from most animal studies. Our data suggested that S. polycystum persisted in single refugium during Pleistocene in a panmixia pattern. Expansion occurred more recently after the Last Glacial Maximum and recolonization of the newly flooded Sunda Shelf could have involved asexual propagation of the species. High dispersal ability through floating fronds carrying developing germlings may also contribute to the low genetic diversity of the species.

Growth and production of Thai agarophyte cultured in natural pond using the effluent seawater from shrimp culture

Growth rate determinations of the Thai agarophytes, Gracilaria fisheri (Xia et Abbott) Abbott, Zhang et Xia and G. tenuistipitata Chang et Xia var. liui Chang et Xia, were conducted by monoline method in natural earthen ponds (800 m2 in area) using shrimp pond effluents (P1) and ambient seawater (P2), from January 1998 to July 1999. Generally, plants of both species cultured in P1 showed a better growth rate and total production than those cultured in P2. Growth rates and total production of the Gracilaria cultured in P1 increased in the rainy months and reached a maximum value of 3.08 ± 1.14% d−1 for G. fisheri and 2.68 ±1.76% d−1 for G. tenuistipitata in January 1999. In contrast, growth of both species cultured in P2, projected a slight change in their growth rates, with a maximum value of 1.85 ± 1.00% d−1 for G. fisheri and 1.70 ± 0.49% d−1 for G. tenuistipitata attained in the rainy period (August 1998). All plants of G. tenuistipitata declined drastically in the following dry season. Total production of G. fisheri and G. tenuistipitata cultured in P1 showed the highest value of 1000 g wet wt and 961 g wet wt in January 1999, respectively. Plants of both species showed fluctuation in growth and total production, depending on specific cultured conditions of each pond, algal strain used, and on the season. The results suggest that G. fisheri can be grown all year round and is more suitable than G. tenuistipitata for earthen pond cultivation using shrimp pond effluents.

C6-Aldehyde formation by fatty acid hydroperoxide lyase in the brown alga Laminaria angustata

Some marine algae can form volatile aldehydes such as n-hexanal, hexenals, and nonenals. In higher plants it is well established that these short-chain aldehydes are formed from C18 fatty acids via actions of lipoxygenase and fatty acid hydroperoxide lyase, however, the biosynthetic pathway in marine algae has not been fully established yet. A brown alga, Laminaria angustata, forms relatively higher amounts of C6- and C9-aldehydes. When linoleic acid was added to a homogenate prepared from the fronds of this algae, formation of n-hexanal was observed. When glutathione peroxidase was added to the reaction mixture concomitant with glutathione, the formation of n-hexanal from linoleic acid was inhibited, and oxygenated fatty acids accumulated. By chemical analyses one of the major oxygenated fatty acids was shown to be (S)-13-hydroxy-(Z, E)-9, 11-octadecadienoic acid. Therefore, it is assumed that n-hexanal is formed from linoleic acid via a sequential action of lipoxygenase and fatty acid hydroperoxide lyase (HPL), by an almost similar pathway as the counterpart found in higher plants. HPL partially purified from the fronds has a rather strict substrate specificity, and only 13-hydroperoxide of linoleic acid, and 15-hydroperoxide of arachidonic acid are the essentially suitable substrates for the enzyme. By surveying various species of marine algae including Phaeophyta, Rhodophyta and Chlorophyta it was shown that almost all the marine algae have HPL activity. Thus, a wide distribution of the enzyme is expected.

Formation of Aldehyde Flavor (n-hexanal, 3Z-nonenal and 2E-nonenal) in the Brown Alga, Laminaria Angustata

Abstract2E-Nonenal and n-hexanal are the major and minor flavor compounds in the edible brown alga, Laminaria angustata, respectively. They are believed to characterize the flavor of this alga. However the metabolism of the two compounds is not precisely known. The pathways were clarified by elucidation of the intermediate structure through purification of the intermediate compounds from an enzymatic reaction and identification using HPLC and GC-MS techniques. Formation of n-hexanal, 3Z-nonenal and 2E-nonenal are proposed to be via two cascades from unsaturated fatty acids. They are C18:2(n-6), linoleic acid cascade and C20:4(n-6), arachidonic acid cascade through their hydroperoxides as intermediates by the lipoxygenase/fatty acid hydroperoxide lyase pathway.

Effects of partial acid hydrolysis on physical and chemical properties of agar from a newly reported Japanese agarophyte (Gracilariopsis lemaneiformis)

Physical and chemical properties of alkali-treated agar polymers extracted from Gracilariopsis lemaneiformis, newly reported Japanese agarophyte, were investigated after partial acid hydrolysis. The alkali-treated agar was hydrolyzed in boiling 0.1 N, 0.01 N, and 0.001 N sulfuric acid, oxalic acid, acetic acid, and citric acid solutions, for 1, 2, and 3 h at 100 °C. Partial acid hydrolysis of the agar polymers indicated strong effects on the physical properties. Different kinds of acid used for hydrolysis gave different agar properties. Gelling polymers were obtained from the agar hydrolysed in boiling 0.001 N acetic acid, oxalic acid, and citric acid solutions, and in 0.01 N acetic acid solution. High gel strength (715 ± 74.6 g cm-2) with low viscosity (2.47 cP) was obtained from 1 h treatment by 0.001 N acetic acid on hydrolysed agar. The results indicated that partial hydrolysis of agar under appropriate conditions probably improve agar quality and produce good grade agar from the Japanese agarophyte.

Transferring Gracilaria irregularis (Gracilariaceae, Rhodophyta) from Thailand to Gracilariopsis based on morphological and molecular analyses

Gracilaria irregularis, endemic to Thailand, was originally described from Ao Len, Trat peninsula, Thailand, and was characterized by a short, succulent thallus with irregular branching, verrucosa‐type spermatangia (a taxonomic criterion for Gracilaria) and the absence of nutritive filaments (a taxonomic criterion for Gracilariopsis). Due to the combination of characters diagnostic of both the genera Gracilaria and Gracilariopsis, the taxonomic status of this species is unclear. This present study reassesses the identity of G. irregularis based on morphological features and the large subunit of ribulose‐bisphosphate carboxylase/oxygenase gene sequences. Newly collected samples from the type locality and KU collection were investigated. Our morphological re‐examinations were relatively similar to the original type description, except that the male plants showed superficial chorda‐type spermatangia, an important characteristic recognized in Gracilariopsis. Molecular analysis placed G. irregularis in the Gracilariopsis clade, forming a well‐supported clade with Gracilariopsis bailiniae. Detailed morphology and molecular phylogenetic analyses clearly showed that G. irregularis is congruous with the generic concept of Gracilariopsis, and consequently the new combination of Gracilariopsis irregularis is proposed. We believe that in the original description a heterogeneous holotype was used. Our data also shows the problems that can occur when collections are made of multiple plants, of similar external morphology, to describe new species.

Fatty acid oxidizing activity in a red marine alga, Porphyra sp.

A crude enzyme solution prepared from fronds of Porphyra sp. showed rem arkable oxygen uptake activity when linoleic acid was added as a substrate. Fatty acid oxidizing activity was mainly present in the soluble fraction of the crude homogenate. The activity was purified 769- fold from mature fronds by ammonium sulfate fractionation, ion-exchange and hydrophobic chromatography. SDS-PAGE analysis of the purified proteins indicated that its subunit size was about 13 kDa. Gel filtration chromatography equipped with a photodiode array detector revealed that the activity was associated with a protein having a molecular weight of 12,500- 13,000. It eluted with a chromophore having the maximum absorbance at 417 nm, thus, the a protein was suggested to be a heme protein. The spectrophotometric property of the protein was highly similar to that of cytochrome c suggesting that it has heme c as a prosthetic group. The protein showed highest oxygenation activity against linoleic acid, and α-linolenic acid and arachidonic acid followed, but oleic acid could not be oxidized. From linoleic acid the protein form ed 9- and 13-hydroperoxides to the same extent, and both were shown to be racemic. These results showed that the oxidizing activity is accountable to a cytochrome, but not to a typical lipoxygenase.