GEOGRAPHIC VARIATION IN THERMAL TRAITS IN DIGENEA SIMPLEX AND CHAMPIA PARVULA (RHODOPHYTA) IN RELATION TO PRESENT AND GLACIAL TEMPERATURE REGIMES

Geographic variation in temperature responses (survival and growth) was investigated in two red algae: Digenea simplex (Wulfen) C. Agardh and Champia parvula (C. Agardh) Harvey. D. simplex has a tropical to warm temperate distribution; C. parvula extends from the tropics into the cold temperate zone. Ecoclinal variation was found in both species but was much stronger in C. parvula than in D. simplex. The former species showed variation in upper and lower tolerance limits as well as in the upper and lower limits for growth. The latter species showed variation mainly in its lower tolerance limit. Ecoclinal variation was related to the amount of present and glacial selection pressure along the climate gradient. In both species, isolates from the colder localities had insufficient cold tolerance to have survived low glacial winter temperatures, so these locations must have been colonized after the end of the glaciation. Eastern Mediterranean and Atlantic populations were probably isolated during the glaciation by a thermal barrier at the entrance of the Mediterranean. In C. parvula, evidence existed for a trade-off between the performance at high and at low temperatures, which would enhance selection pressure in opposite directions at either end of the climatic range. No evidence for such a trade-off was found in D. simplex.     

ASSESSING THE LIMITS OF RANDOM AMPLIFIED POLYMORPHIC DNAs (RAPDs) IN SEAWEED BIOGEOGRAPHY1

As judged by comparison with other molecular data sets, random amplified polymorphic DNA (RAPD) data are robust in identifying large-scale biogeographic populations that range from hundreds to thousands of kilometers apart. As the geographical scale is shifted downward, however, RAPD data often fail. This is because RAPD data are inherently “noisy” as a result of technical artifacts and reproducibility problems associated with non-independence of bands, “missing” bands, and the presence of de novo bands, all of which contribute to scoring errors in the data set. To estimate the contribution of these error factors in algal phylogeographic studies, segregation of RAPD bands in tetrasphorophytic and gametophytic parents, their natural and synthetic offspring, and self-cycled tetrasporophytes were compared in Lophocladia trichoclados (Mertens in C. Agardh) Schmitz and to a limited extent in Digenea simplex (Wulfen) C. Agardh. Wide-ranging biogeographic populations of D. simplex were compared as were mixed populations of tetrasporophytes and gametophytes. Results show that nested priming can lead to some nonindependence of bands but that this probably does not significantly contribute to scoring error. Southern analysis using individual RAPD bands as probes revealed that up to 16% of visually nondetectable bands are actually present but that the random distribution of the error contributes uniformly across the data set. Non-parental (de novo in offspring) and parental (not present in offspring) bands may contribute substantially to the scoring error in tetrasporophytes, gametophytes, and self-cycled tetrasporophytes. The presence of tetrasporophytes and gametophytes in a sample is not important in large-scale phylogeographic studies but does affect within-clade variation at smaller scales. We conclude that the overall level of error remains roughly constant at probably between 5 and 10%, which is not a problem at large biogeographic scales where the phylogenetic signal is strong. Finally, some unexpectedly large abberations in RAPD banding patterns among life stages in L. trichoclados were observed that cannot be explained by methodological artifacts alone due to comparisons with synthetic offspring controls. The possibility that carpospore amplification may not always involve a simple mitotic process is discussed.     

PROTOPLAST ISOLATION AND CELL DIVISION IN THE AGAR-PRODUCING SEAWEED GRACILARIA (RHODOPHYTA)1

Methods were developed for the isolation of large numbers of healthy protoplasts from two species of the agarophyte Gracilaria; G. tikvahiae McLachlan and G. lemaneiformis (Bory) Weber-van Bosse. This is the first report of protoplast isolation and cell division in a commercially important, phycocolloid-producing red seaweed, as well as for a member of the Florideophycidae. The optimal enzyme composition for cell wall digestion and protoplast viability consisted of 3% Onozuka R-10, 3% Macerozyme R-10, 1% agarase and 0.5% Pectolyase Y- 23 dissolved in a 60% seawater osmoticum containing 1.0 M mannitol. The complete removal of the cell wall was confirmed by several different methods, including electron microscopic examination, and the absence of Calcofluor White (for cellulose) and TBO (for sulfated polysaccharide) staining. Spontaneous protoplast fusion was observed on several occasions. Protoplast viability was dependent upon the strain and age of the parent material, as well as the mannitol concentration of the enzyme osmoticum. Cell wall regeneration generally occurred in 2-6 days; cell division in 5-10 days. Protoplast-produced cell masses up to the 16-32 cell stage have been grown in culture. However, efforts to regenerate whole plants have been unsuccessful to date.     

LITHIUM CHLORIDE EXTRACTION OF DNA FROM THE SEAWEED PORPHYRA PERFORATA (RHODOPHYTA)1

Lithium chloride facilitates the softening of cell walls resulting in a simple, quick (2 h) method for DNA extraction from the red seaweed Porphyra perforata J. Agardh. A 5-min treatment of tissues in Lid at 55°C extracts DNA that is relatively free of the viscous polysaccharides and proteins that are usually coextracted in large amounts from cell walls and cytoplasm. This protocol does not require grinding of tissues, hydroxyapatite binding, cetyl trimethyl ammonium bromide treatments, enzymatic treatments, phenol extraction, or CsCl-gradient centrifugation. The resulting DNA is of sufficient quality to be used as a template for polymerase chain reaction amplification.     

SPORELING COALESCENCE AND INTRACLONAL VARIATION IN GRACILARIA CHILENSIS (GRACILARIALES,RHODOPHYTA)1

This study evaluates the hypothesis that spore coalescence may cause intraclonal variation. Spore coalescence might allow the occurrence of unitary thalli that in fact correspond to genetically different, coalesced individuals. Plant portions simultaneously derived from these chimeric individuals may exhibit dissimilar growth responses even when incubated under similar abiotic conditions. Testing of the hypothesis included various approaches. Transmission electron microscopy observations of early stages of sporeling coalescence indicated that polysporic plantlets were formed by groups of spores and their derivatives. Even though adjacent cells in two different groups may fuse, these groups maintained an independent capacity to grow and form uprights. Laboratory-grown plantlets showed a significant correlation between the initial number of spores and the total number of erect axes differentiated from the sporeling. Construction and growth of bicolor individuals indicated the chimeric nature of the coalesced individuals. Coalesced, bicolor holdfasts had green and red cells, which subsequently produced green and red uprights, respectively. Individuals fronds were also chimeric, as indicated by the production of green and red branchlets from single, red uprights. The existence of mixed tissues was further substantiated by random amplified polymorphic DNA analysis. The banding pattern produced by branchlets of a unisporic thallus was consistently monomorphic, whereas the patterns produced by the polysporic thallus were polymorphic. Growth rates of polysporic thalli had larger data dispersal and variation coefficients than oligosporic or monosporic thalli. Therefore, all results support the original hypothesis and suggest that coalescence might be ecologically more important than previously thought.     

TWO SOLIERIACEAN ALGAE NEW TO THE MEDITERRANEAN: AGARDHIELLA SUBULATA AND SOLIERIA FILIFORMIS (RHODOPHYTA,GIGARTINALES)1

Two Atlantic species found in the Mediterranean Sea were ascribed to the family Solieriaceae on the basis of morphological features. In the extensive drifting beds of the Mar Piccolo basin (Taranto, Ionian Sea), Agardhiella subulata (C. Agardh) Kraft et Wynne and Solieria filiformis (Kützing) Gabrielson were the dominant species in summer. There were no attached populations, and perennation was ensured only by vegetative propagation. Characteristics of the outer cortex and chromatophores were useful for distinguishing the taxa at the species level and are recommended for recognition of sterile specimens.     

ECOTYPIC VARIATION IN CYSTOCLONIUM PURPUREUM (RHODOPHYTA) SYNCHRONIZES LIFE HISTORY EVENTS IN DIFFERENT REGIONS1

Temperature and daylength responses were determined in culture for isolates of the red alga Cystoclonium purpureum (Hudson) Batters from Nova Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, France). Most isolates survived temperatures of –1.5°/–2° to 23°C, whereas 25°C was lethal. Only the RO-gametophytes died at 23°C. Optimal growth conditions were 10°–20°C in both long and short days for the NS isolates and 8°–15°C and 8°–18°C at daylengths of >12 h for the RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10°–20°C in long and short days within 5 months. At lower temperatures reproduction was limited or slow. The European isolates formed tetrasporangia at 10°–20°C (HE) or 5°–l8°C(RO), spermatangia at 5°–15°C (HE) or 5°–20°C (RO), and carpospores at 5°–15°C(HE) or 10°–15°C (RO). Short days either blocked or delayed reproduction of the European isolates. The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to form reproductive structures. In summer, tetra-and carpospores were shed followed by degeneration of the upright axes while branched holdfasts persisted. New upright axes and juvenile plants were formed in autumn, but these remained small during the winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observations correspond well with the results of the experiments. The life history of C. purpureum is regulated by temperature and daylength. In the eastern Atlantic, the limiting effect of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures alone bring about the same seasonal pattern. After plants have reproduced, uprights degenerate in spite of continuing favorable conditions.     

COMPARATIVE MORPHOLOGY AND TAXONOMIC STATUS OF GRACILARIOPSIS (GRACILARIALES,RHODOPHYTA)1

The vegetative organization and reproductive development of Gracilariopsis lemaneiformis (Bory) Dawson, Acleto et Foldvik [including Gracilaria sjoestedtii Kylin] were investigated. Our observations on spermatangial development and post-fertilization features establish that Gracilariopsis Dawson is distinct at the generic level from Gracilaria Greville, and ice propose the resurrection of Gracilariopsis Dawson as a result. Spermatangial parent cells of Gracilariopsis are superficial, initiated in pairs or groups of three by concavo-convex longitudinal and transverse divisions. Each spermatangial parent cell cuts off a single, colorless spermatangium distally by a transverse division. The female reproductive apparatus consists of a supporting cell that bears a two-celled carpogonial branch flanked by two sterile branches, as in Gracilaria. Likewise, up to six sterile cells fuse with the carpogonium after fertilization to produce a primary fusion cell that generates the gonimoblasts; however, a secondary fusion cell is absent. Inner gonimoblast cells unite with cytologically modified cells of the inner pericarp by means of secondary pit-connections. Tubular nutritive cells are absent. The gonimoblast consists of a central sterile tissue interconnected throughout by secondary pit-connections surmounted by a fertile layer composed of carposporangia aligned in straight chains. The distribution of Gracilariopsis is extended to Western Europe.     

ECOTYPIC VARIATION IN PHYLLOPHORA PSEUDOCERANOIDES (RHODOPHYTA) ENSURES WINTER REPRODUCTION THROUGHOUT ITS GEOGRAPHIC RANGE1

Responses to temperature and daylength were determined in laboratory culture for isolates of the red alga Phyllophora pseudoceranoides (Gmelin) Newroth et A.R.A. Taylor from Nova Scotia, Iceland, Roscoff (France), and Helgoland (Germany). All isolates grew from 3° to 25° C and survived from -2° or 0° C to 27° C but not 30° C. Reproductive requirements differed between life history phases and isolates. Isolates from Helgoland and Roscoff formed sporangial sori at 3°-20° C, tetraspores at 3°-12° C, and procarps at 10°-20° C, irrespective of daylength. Spermatangia developed at 10°-23° C but only in long days. As the other European isolates, the isolate from Iceland formed tetrasporangia at 3°-12° C, but it had an additional requirement for short days. The Nova Scotian isolate formed sori at 10°-20° C and sporulated at 10°-18° C. When grown plants were transferred from noninductive to inductive conditions, sori were formed after 4 months and tetraspores developed and were shed (1-)3 months later. Procarps formed 1(-3) months after transfer. The phenology of P. pseudoceranoides was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. Plants were perennial, forming new blades from October to June, which degenerated between August and February. In June, reproductive structures (sori, spermatangia, and procarps) started to appear on the new blades. From October to April, mature cystocarps were found. Mature tetrasporangia were observed only in February. The life history of P. pseudoceranoides is regulated by temperature and daylength. Differential effects on the different life history phases all serve to confine the production of spores (both carpospores and tetraspores) to the winter season. Differences in response between isolates from different geographic regions bring about the same effect: spores are shed only in winter. The nature of the geographic boundaries of P. pseudoceranoides is discussed.     

WATER MOTION AND MORPHOLOGY IN CHONDRUS CRISPUS (RHODOPHYTA)1

Morphological variability of intertidal Chondrus crispus Stackh. fronds along a small open rocky coast was related to wave exposure and emersion. Cluster analysis revealed two well-defined morphologies: filiform and planiform, named the N morphotype and B morphotype, respectively. We propose a rapid method of classifying fronds based on the morphology of the cross section at half the height on the thallus. The N morphotype is characterized by fewer dichotomies per unit length, a circular cross section with a large inner cortex, and narrow fronds. It is abundant at low intertidal and exposed sites. The B morphotype is characterized by more dichotomies, smaller sizes, a subelliptical or flattened cross section, and broad fronds. It is abundant at high intertidal sites in sheltered areas. Regression analysis revealed a major effect of water movements on frond morphology with respect to tidal level, which was more evident at high intertidal levels. No relationships were observed between morphology and life history phases.     

TAXONOMY OF THE FLATTENED SOLIERIACEAE (RHODOPHYTA) IN BRAZIL: AGARDHIELLA AND MERISTIELLA1

Taxonomic studies of an extensive collection of flattened members of the Solieriaceae considered by many authors to be species of Agardhiella, Eucheuma, Meristotheca, and Meristiella lead us to conclude that they represent only two genera in Brazil: Agardhiella, including A. ramosissima (Harvey) Kylin and A. floridana (Kylin) Gabrielson ex Guimarães et Oliveira, and Meristiella, with only one species, M. gelidium (J. Agardh) Cheney et Gabrielson. Accordingly, we propose that 1) Meristotheca gigartinoides Joly et Ugadim be synonymized with Agardhiella floridana, and 2) Meristiella echinocarpa (Areschoug) Cheney et Gabrielson and M. schrammii (P. et H. Crouan) Cheney et Gabrielson be synonymized with Meristiella gelidium.     

ULTRASTRUCTURE OF TETRASPOROGENESIS IN PALMARIA PALMATA (RHODOPHYTA)1

The tetrasporangial initial in Palmaria palmata (L.) O. Kuntze (formerly Rhodymenia palmata (L.) Greville) arises from a cortex cell which enlarges and deposits a protein-rich wall layer. This cell undergoes mitosis to form a tetrasporocyte and a stalk cell. Synaptonemal complexes are formed in the sporocyte nucleus while in the cytoplasm floridean starch is deposited in association with ER or with particles presumed to be ribosomes. Microbody-like structures become numerous between the nuclear envelope and perinuclear ER, and clusters of non-membranous, spherical structures also are associated with the nucleus. Chromatin condensation is reversed following pachytene and a prolonged diffuse stage ensues, when dictyosomes and ER produce vesicles which deposit mucilage rich in sulfated and acidic polysaccharides around the tetrasporocyte. A conspicuous lenticular thickening of the mucilage sheath develops at the apical end of the sporangium. Dictyosomes are frequently associated with mitochondria which may be associated with chloroplasts. Following nuclear divisions the tetrasporocyte is cleaved into four spores by sequentially initiated, but simultaneously completed periclinal and anticlinal furrows. When mucilage deposition ceases, the dictyosomes begin to produce vesicles with glycoprotein-rich contents. These vesicles are abundant in released tetraspores, and they probably contain adhesive material aiding in the attachment of the liberated spores.     

SALINITY TOLERANCE,BILIPROTEINS, AND FLORIDOSIDE CONTENT OF COMPSOPOGON COERULEUS (RHODOPHYTA)1

The freshwater red alga Compsopogon coeruleus (Balbis) Montague is capable of growing and reproducing in salinities up to 35 ppt. Increased accumulation of floridoside (D-galactopyranosyl glycerol) parallels increase in salinity. Compsopogon phycobilisomes contain an unusual B-phycoerythrin completely lacking in phycourobilin chromophores, but with a pigmented γ subunit. The α, β, and γ subunits of this phycoerythrin all carry phycoerythrobilins. These results suggest that C. coeruleus is secondarily adapted to freshwater from marine habitats.     

TRACKING DISPERSAL ROUTES: PHYLOGEOGRAPHY OF THE ARCTIC-ANTARCTIC DISJUNCT SEAWEED ACROSIPHONIA ARCTA (CHLOROPHYTA)1

Phylogenetic relationships in the Arctic-Antarctic disjunct seaweed species Acrosiphonia arcta (Dillwyn) J. G. Agardh (Acrosiphoniales, Chlorophyta) were examined using restriction fragment-length polymorphism analysis of the fast-evolving nuclear ribosomal intergenic spacer (IGS) region and random amplified polymorphic DNA (RAPD) markers. Twenty-two isolates collected from 10 different locations in both hemispheres were compared. Five IGS length classes were identified among the 10 locations. Throughout the North Atlantic, IGS regions were found to be extremely homogeneous whereas RAPD patterns revealed subdivided populations that suggest founder effects. Acrosiphonia arcta populations found in the Arctic and North Atlantic oceans are hypothesized to be of Pacific origin. Extensive differences found between Arctic Greenland populations and those in the North Atlantic suggest that colonization of Arctic Greenland occurred as an independent event. Recolonization of the Antarctic peninsula from Southern Chile is favored, whereas the directionality of transequatorial passage along the western coast of the Americas could be in either direction.     

REGENERATION AND SEXUAL DIFFERENTIATION OF GRIFFITHSIA JAPONICA (CERAMIACEAE,RHODOPHYTA) THROUGH SOMATIC CELL FUSION1

Hybrid cells were obtained from somatic cell fusion among male, female, and tetrasporangial plants in Griffithsia japonica Okamura by a wound-healing process. Isolated fusion cells regenerated new mature plants with mixed reproductive structures. The plants regenerated from hybrid cells between male and female plants developed into 1) spermatangiate, 2) carpogonial, 3) bisexual with spermatangia and carpogonial branches, 4) mixed-phase with spermatangia and tetrasporangia, or 5) bisexual/mixed-phase plants with spermatangia, carpogonial branches, and tetrasporangia. About 70% of the plants regenerated from hybrid cells between male and female plants produced tetrasporangia that were always formed with spermatangia on a single cell. Some of those tetrasporangia released tetraspores, six of which gave rise to mature plants. The plants regenerated from hybrid cells between male and tetrasporangial plants developed into spermatangiate, tetrasporangiate, or mixed-phase plants with spermatangia and tetrasporangia. The plants regenerated from hybrid cells between female and tetrasporangial plants developed into carpogonial, tetrasporangiate, or mixed-phase plants with carpogonial branches and tetrasporangia. All types of reproductive structures we re functional.     

DISTRIBUTION AND SYSTEMATICS OF FRESHWATER CERAMIALES (RHODOPHYTA) IN NORTH AMERICA1

Twenty-five freshwater populations of Ceramiales were collected in North America, 24 of which were from the tropical rainforest region of Central America and the Caribbean. The streams tended to be moderate in mean current velocity (X?= 23.3 cm·S^?1) and maximum width (X?= 6.3 m) but high in temperature (X?= 23.1°C), pH (X?= 7.9), and specific conductance (X?= 320 μS·cm^?1). Three Bostrychia species were restricted to the Caribbean islands: B. moritziana (Sonder ex Kütz.) J. Ag. (syn. B. cornigera Mont. and B. radicans f. moliforme Post), with ecorticate indeterminate axes, monosiphonous ultimate branches, and cladohaptera; B. radicans (Mont.) Mont. (syn. B. leprieurii Mont and B. rivularis Harv.), with ecorticate and polysiphonous axes throughout and cladophaptera; and B. tenella (Lamour.) J. Ag., with corticate indeterminate axes, monosiphonous ultimate branches, and peripherohaptera. Ballia prieurii Kütz. was found in Belize and Costa Rica and was characterized by rebranched determinate laterals, opposite branching, and long apical cells (X?= 61 μm) and axial cells (X?= 43 μm). Caloglossa leprieurii (Mont.) J. Ag. was localized in Puerto Rico while. C. ogasawaerensis Okam. was collected only in Costa Rica. The two species were separated by site of branching (midrib vs. margin) and blade width (X?= 384 vs. 861 μm). Polysiphonia subtilissima Mont. from Florida and Jamaica had four pericentral cells, no cortication, rhizoids arising from pericentral cells, and branches initiated at trichoblast scars.     

LIFE HISTORY AND HYBRIDIZATION STUDIES ON GIGARTINA STELLATA AND PETROCELIS CRUENTA (RHODOPHYTA) IN THE NORTH ATLANTIC1

Fourteen isolates of the crustose marine red alga Petrocelis cruenta J. Agardh from various localities in the British Isles, France (including the type locality), Spain and Portugal gave rise in culture to dioecious foliose plants identifiable as Gigartina stellata (Stackhouse) Batters although two isolates formed only sterile foliose blades. A total of 145 isolates of Gigartina stellata were also grown in culture from various localities in the U.S.A. (Maine), the British Isles, Iceland, Denmark, France, Spain and Portugal using both carpospores and vegetative blade apices. Two basic types of life history were found among these isolates: a direct-type life history involving the formation of further foliose plants from carpospores, some isolates of which also form spermatangia on the same papillae as the cystocarps; and a heteromorphic-type in which only crustose plants resembling Petrocelis cruenta are formed from carpospores. Only heteromorphic-type life histories were found from Spain and Portugal. Both life history types were found in plants from the U.S.A., the British Isles and northern France. Only direct-type life histories were found in plants from Iceland and Denmark. Some Petrocelis-like crusts derived from field collected G. stellata carpospores and Petrocelis crusts of hybrid progeny formed tetrasporangia in 8:16 h LD, 10° C but not in 8:16 h LD, 15° C; 16:8 h LD 10° C or 15° C; and 10:6.5:1: 6.5 h LDLD, 10° C. The spores thus formed were viable and produced normal dioecious male and female gametophytes. Short day and low temperature conditions appear necessary for tetrasporogenesis. The results from crossing experiments with 32 male and 27 female isolates of the heteromorphic-type derived from both G. stellata and P. cruenta showed that two virtually non-interbreeding populations with a high degree of geographical separation exist in the north-eastern Atlantic. Morphological differences between plants from each population are described. On the basis of culture and crossing results, Petrocelis cruenta J. Agardh is placed in synonymy with Gigartina stellata (Stackhouse in Withering) Batters.     

REVEALING GENETIC MARKERS IN GELIDIUM VAGUM (RHODOPHYTA) THROUGH THE RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) TECHNIQUE1

The recently developed random amplified polymorphic DNA technique was evaluated as a method for characterizing isolates of the agarophyte Gelidium vagum Okamura. Reaction conditions for single primer polymerase chain reaction were optimized to obtain a high degree of reproducibility of the amplified bands generated from purified G. vagum DNA. A total of 165 primers, including both (A + T)- and (G + C)-rich sequences, was screened for DNA amplification using template DNA from a single Gelidium isolate. None of the 45 (A + T)-rich primers was positive (i.e. band-producing). Of the (G + C)-rich primers, 47 were positive, generating a total of 322 prominent amplification products for DNA from 13 different G. vagum isolates. Polymorphic DNA loci were detected by 37 of the primers. Unweighted pair-group arithmetic average cluster analysis (UPGMA) of these loci was used to group the G. vagum isolates and thereby determine which were most similar. G. latifolium, used as an out-group for the UPGMA analysis, showed a high degree of dissimilarity.     

GROWTH AND DIFFERENTIATION OF AXIAL AND LATERAL FILAMENTS IN BATRACHOSPERMUM SIRODOTII (RHODOPHYTA)1

Development of the vegetative gametophyte of Batrachospermum sirodotii Skuja was examined with light and both transmission and scanning electron microscopy. Patterns of wall growth were followed using the Calcofluor White ST pulse-chase method. Thallus structure was analysed in terms of the pattern of development of the apical, periaxial and pleuridial initials that generate the axial and whorled lateral filaments characteristic of Batrachospermum. Apical cells of axial filaments elongate initially by tip growth with the nucleus maintaining a distal position. Nuclear division is horizontal. One daughter nucleus migrates basipetally and a thin, convoluted annular septum and perforate-occluded pit connection are then formed. Elongating axial cells subsequently extend by wall deposition at the base of the cell. Periaxial cells are initiated laterally and elongate primarily by tip growth while the nucleus remains within the axial cell. The nucleus then migrates to the boundary between the initial and the axial cell, divides, and one daughter nucleus moves into the initial and the other back into the axial cell. A slightly irregular annular septum and simple-occluded pit connection are then formed. Pleuridial cell initials begin as terminal to subterminal protuberances on periaxial or pleuridial cells. They first extend by tip growth and later by bipolar band growth. The nucleus remains within the parent cell as the pleuridial initial expands and a narrow septal ring is formed between the two cells. It then migrates through the septal ring into the initial and divides transversely. One nucleus passes back into the parent cell and a thick, flat septum and perforate-occluded pit connection are formed. It is concluded that the potentially indeterminate axial filaments and the determinate lateral pleuridia represent distinct developmental types in Batrachospermum.     

LIGHT ACCLIMATION IN PORPHYRIDIUM PURPUREUM (RHODOPHYTA): GROWTH,PHOTOSYNTHESIS, AND PHYCOBILISOMES1

Acclimation to three photon flux densities (10, 35, 180 μE.m^?2.s^?1) was determined in laboratory cultures of Porphyridium purpureum Bory, Drew and Ross. Cultures grown at low, medium, and high PPFDs had compensation points of <3, 6, and 20 μE-m^?2.s^?1, respectively, and saturating irradiances in the initial log phase of 90, 115, 175 μE.m^?2.s^?1 and up to 240 μE.m^?2.s^?1 in late log phase. High light cells had the smallest photosynthetic unit size (phycobiliproteins plus chlorophyll), the highest photosynthetic capacity, and the highest growth rates. Photosystem I reaction centers (P700) per cell remained proportional to chlorophyll at ca. 110 chl / P700. However, phycobiliprotein content decreased as did the phycobilisome number (ca. 50%) in high light cells, where as the phycobilisome size remained the same as in medium and low light cells. We concluded that acclimation of this red alga to varied PPFDs was manifested by the plasticity of the photosystem II antennae with little, if any, effect noted on photosystem I.