Chemotaxonomy in marine algae: Secondary metabolite synthesis by Laurencia in unialgal culture

The application of chemistry to taxonomy assumes that the secondary metabolites of an organism used in chemotaxonomic investigations are quantitatively constant and independent of the continually changing physical and chemical factors experienced in nature. To determine the extent to which chemical changes occur with varying environmental conditions in marine algae, we have investigated the haloterpenoids of Laurencia snyderae Dawson, L. subopposita (J. Agardh) Setchell, and L. pacifica Kylin. Gas chromatographic and thin-layer chromatographic comparisons were made of the haloterpenoid components from both natural populations and from cultured algae grown under varying conditions of temperature and photoperiod. In addition, L. spectabilis Postels and Ruprecht, L. gardneri Hollenberg, L. undulata Yamada, L. nipponica Yamada, L. intermedia Yamada and L. okamurai Yamada were cultured and, where appropriate, their secondary metabolites compared to those reported in the literature. It was found that normal secondary metabolites synthesis occurs in culture and is largely unaffected by modification of the culture conditions. Furthermore, the chemical compounds produced are both qualitatively and quantitatively identical to those produced in the natural populations. In order to study the effect of genetic variables on secondary metabolites, we have investigated sympatric populations of L. pacifica that are morphologically similar but chemically distinct. These populations were intrafertile, but not interfertile in culture. The unique secondary metabolites of the populations and their reproductive isolation probably reflect genetic differences.     

The reproductive structures of the Mediterranean alga Laurencia pelagosae (Ceramiales,Rhodophyta)

Reproductive structures of Laurencia pelagosae are described for the first time. Tetrasporangia, in parallel arrangement, are cut off from the mother cells adaxially; antheridial branches, which are unramified, are inserted in depressions lacking a row of axial cells on their bases; cystocarps are sessile and subspherical. The occurrence of secondary pit-connections between epidermal cells and of lenticular thickenings in the walls of medullary cells is documented. The species is included in the new section Pelagosae within the subgenus Laurencia.     

A new species of Laurencia, L. omaezakiana (Ceramiales, Rhodophyta), from Japan

Laurencia omaezakiana Masuda, sp. nov. (Ceramiales, Rhodophyta) is described from Japan. It is characterized by the following set of features: (i) the production of four periaxial cells from each vegetative axial cell; (ii) a shift in branching from distichous to spiral; (iii) the presence of projecting superficial cortical cells near the apices of branches; (iv) the presence of longitudinally oriented secondary pit-connections between contiguous superficial cortical cells; (v) the presence of lenticular thickenings in the walls of medullary cells; (vi) the occurrence of 1–2 corps en cerise in each superficial cortical cell and a single corps en cerise in each trichoblast cell; and (vii) a parallel arrangement of tetrasporangia. Furthermore, it produces a characteristic triterpenoid (enshuol), which has not been detected in other species of Laurencia, as a major halogenated secondary metabolite. A synoptical key to the 23 species of Laurencia growing in Japan is given. Laurencia ceytanica J, Agardh and Laurencia heteroclada Harvey are excluded from the Japanese marine algalflora. The latter is a distinct species from Laurencia filiformis (C. Agardh) Montagne.     

Additional analysis of chemical diversity in Laurencia nipponica (Ceramiales, Rhodophyta)

The red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) is known to contain several chemical races, each of which is characterized by a particular, major halogenated secondary metabolite. Both field-collected and cultured plants of a population of this species found recently at Shikanoshima Island, Fukuoka Prefecture, southern Japan, produced C₁₅ bromoethers, (3E)-laureatin and (3E)-isolaureatin, and sesquiterpenoids, 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene and 2,10-dibromo-3-chloro-α-chamigrene. Laurencia nipponica can be referred to as a further chemical race that is characterized by the production of two C₁₅ bromoethers, (3E)-laureatin and (3E)-isolaureatin, and a sesquiterpenoid, 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene as major compounds.     

Composition of Gigartina carrageenan in relation to sporophyte and gametophyte stages of the life cycle

Total carrageenan levels (55–88% of plant dry weight) of four Gigartina species showed little variation between male, female and tetrasporic plants. However whereas male and female gametophyte plants gave carrageenans with K: λ ratios usually ranging from 1·0 to 4·0, with one species in the range 0·3–0·8, tetrasporophyte carrageenans gave very low K: λ ratios, 0·02–0·1, indicative of a virtual absence of K-carrageenan from plants of this stage of the life cycle.     

<Emphasis Type="Italic">Remalcis</Emphasis> and <Emphasis Type="Italic">Epiphyton</Emphasis> as different stages in the life cycle of calcareous algae

Although the calcareous algae Renalcis and Epiphyton, which were main reef-constructors at the end of the Late Proterozoic, beginning of the Cambrian, and, partially, in the Devonian, long attracted the attention of scientists, their nature long remained enigmatic. Numerous revisions inclined to the opinion that Renalcis only existed and considered Chabakovia, Shuguria, Izhella, and even Epiphyton as synonyms of the former genus. However, convincing proofs for this conclusion were lacking. I propose a new morphological interpretation of the Renalcis group, based on Gemma with its unique preservation of monospores within the colony, which overgrew outside the colony first in Korilophyton and then in Epiphyton. It was concluded that the life cycle of Epiphyton included heteromorphous stages of Renalcis (Izhella), Chabakovia (Shuguria), Gemma, and dendroid Korilophyton.     

HETEROMORPHIC LIFE-HISTORY STRATEGIES IN THE BROWN ALGA SCYTOSIPHON LOMENTARIA (LYNGB.) LINK1

The adaptive significance of a life-history strategy, expressed as divergent morphological forms, was examined for the heteromorphic alga Scytosiphon lomentaria. Successional studies were performed by physically clearing mature, temporally-constant intertidal communities on San Clemente I., California. At week six, after clearing, complanate thalli dominated the successional plots (mean cover = 23.5%) and began to decline as the cylindrical form became abundant. The latter attained its peak cover (82.3%) at week 13, whereupon it too began a precipitous reduction. The crustose ralfsioid form appeared surprisingly early (4–13 wks) in trace amounts but did not achieve its greatest cover (85.0%) until week 43. The ranking from high to low primary productivity (cylindrical form = 8.1 mg C · g dry. wt^-1·h^-1, complanate form = 6.5 mg, crustose form = 0.5 mg) corresponded closely with the data for photosynthetic vs. structural components (cylindrical = 92.3% pigmented, complanate = 65.3%, crustose = 32.0%). This finding indicates that selection in the crust form, which is more readily accessible to epilithic grazers, has tended to increase allocation of materials to nonpigmented structural tissue at the expense of photosynthetic tissue and reduced production rates. The results for thallus losses to urchin grazing over 48 h were complanate form = 82.7% lost, cylindrical = 81.4% and crustose = 16.2%, which correlates with the calorific contents of the three forms (i.e. complanate = 4.97 kcal · ash-free g dry wt.^-1, cylindrical = 4.46 kcal and crustose = 3.55 kcal). The crustose form had tougher thalli (26 g · mm^-2 to penetrate thallus) than either the complanate form (12 g) or the cylindrical form (15 g). It is likely that opposing selective factors have resulted in the evolutionary divergences observed in algae with heteromorphic life histories. Previous work may have overemphasized the selective role of grazing because the crustose form is also adapted to withstand physical forces (sand-scouring, burial and wave-shearing) or as an overwintering stage under physiologically stressful conditions.