FIELD AND CULTURE STUDIES OF A POPULATION OF ENDARACHNE BINGHAMIAE (PHAEOPHYTA) FROM SOUTHERN CALIFORNIA1

Abundances of the erect, blade phase of Endarachne binghamiae J. Ag. (Scytosiphonales, Phaeophyta) varied seasonally at a southern California rocky intertidal site. Blade cover and density were much greater in the fall through early spring; blades were mostly absent from quadrats during the summer. Blade abundances were negatively correlated with both seasonal variations in seawater temperature and photoperiod. Laboratory culture studies failed to provide evidence for sexual reproduction. The life history appears to be of the “direct” type with plurangia-produced zooids germinating into crustose disks. Most disks developed erect blade clusters under spring/fall (17° C) and winter (13° C) temperatures over the range of natural photoperiods employed (14:10, 12:12, 10:14 h LD). In contrast, cultures held under the summer temperature (21° C) produced almost entirely crustose growths regardless of photoperiod. Similar results were obtained for cultures grown at 100 and 200 μE · m^?2· s^?1. E. binghamiae blades were fertile throughout the year and produced viable zooids indicating that reproductive seasonality did not influence the seasonal pattern of blade abundance. Culture and field studies suggest that the initiation of new erect blade clusters from crustose disks is confined to the cooler months of the year (winter and spring). The summer reduction or absence of E. binghamiae blades appears to be due to increased mortality rates and temperature constraints on the development of new erect bladed thalli. Hypothetical causes of mortality are desiccation stress, sand burial, increased grazing activity and a genetically-based short life span.     

INTERSPECIFIC HYBRIDIZATION IN THE HAPLOID BLADE‐FORMING MARINE CROP PORPHYRA (BANGIALES,RHODOPHYTA): OCCURRENCE OF ALLODIPLOIDY IN SURVIVING F1 GAMETOPHYTIC BLADES1

We performed interspecific hybridization in the haploid blade‐forming marine species (nori) of the genus Porphyra, which have a heteromorphic life cycle with a haploid gametophytic blade and a diploid microscopic sporophyte called the “conchocelis phase.” The green mutant HGT‐6 of P. tenera var. tamatsuensis A. Miura was crossed with the wildtype HG‐1 of P. yezoensis f. narawaensis A. Miura; the F₁ heterozygous conchocelis developed normally and released numerous conchospores. However, almost all the conchospore germlings did not survive past the four‐cell stage or thereabouts, and only a few germlings developed into gametophytic blades. These results indicate that hybrid breakdown occurred during the meiosis, while the surviving F₁ gametophytic blades were considered a breakthrough in the interspecific hybridization of Porphyra. Organelle genomes (cpDNA and mtDNA) were found to be maternally inherited in the interspecific hybridization by molecular analyses of the organelle DNA. In particular, molecular analyses of nuclear DNA revealed that the surviving F₁ blades were allodiploids in the haploid gametophytic phase; however, there is a possibility of the occurrence of rapid chromosomal locus elimination and rearrangement in the F₁ conchocelis phase. Our findings are noteworthy to the breeding of cultivated Porphyra and will provide important information for understanding of the speciation of marine plants with high species diversity.     

Nutrient and productivity relations of the dune grasses Ammophila arenaria and Elymus mollis

Summary A comparative study of blade photosynthesis and nitrogen use efficiency was made on the dune grasses Ammophila arenaria and Elymus mollis. In the laboratory, an open system gas analysis apparatus was used to examine the gas exchange characteristics of blades as influenced by nitrogen supply. Plants were grown under near-ambient coastal conditions in a greenhouse near Bodega Bay, California, and given either high or low supplies of nitrogen in an otherwise complete nutrient solution. In the field, ¹⁴CO₂ uptake techniques were employed to measure the seasonal patterns of blade photosynthesis of plants growing in situ at Point Reyes National Seashore. Blades used in the lab and field studies were analyzed for total nitrogen content, thus allowing for calculations of photosynthetic nitrogen use efficiency (CO₂ fixed/unit of blade N.).Under laboratory conditions, the introduced Ammophila developed higher rates of light-saturated photosynthesis than the native Elymus, especially under the nitrogenlimited growth regime. Higher rates of photosynthesis and lower concentrations of blade N resulted in a significantly greater nitrogen use efficiency for Ammophila regardless of nutrient treatment. Low N availability induced qualitatively similar physiological responses in both species, including reductions in maximum net photosynthesis, mesophyll conductance, leaf conductance, dark respiration, and blade nitrogen content, and an increase in the CO₂ compensation point.Although the photosynthetic rates of Ammophila blades were higher in the lab, those of Elymus blades were consistently higher in the field. This could have resulted from differential effects of drought on the two species (i.e. Ammophila may have been more sensitive) or a higher photosynthetic capacity in Elymus that reflected the greater (1.2–1.5 X) nitrogen content of its blades. However, the nitrogen use efficiency of Ammophila blades was greater than that of Elymus throughout most of the sampling year, despite lower average rates of field photosynthesis.The results indicated that rates of photosynthesis perunit of blade area do not account for the greater aboveground productivity of Ammophila stands along the Pacific coast of North America. Instead, efficient nitrogen use in photosynthesis maycomplement other structural and physiological traits and thereby enhance long-term carbon gain in Ammophila relative to Elymus.     

PILAYELLA LITTORALIS F. RUPINCOLA FROM WASHINGTON: THE LIFE HISTORY IN CULTURE1

The life history of Pilayella littoralis f. rupincola from Washington was studied in culture using supplemented natural seawater media and various temperature, photoperiod, and light intensity regimes. Plants in nature exhibited characteristics typical for f. rupincola. Plants in culture, however, did not show the same morphological features, although they had a life history presumed typical for f. rupincola. Successive generations of plants in culture formed only unilocular sporangia. On the basis of morphological characters and the life history, Kylin elevated f. rupincola to species rank. Variation in morphology of both field collected and cultured specimens makes such recognition untenable. It is concluded that the type of life history alone is not adequate justification for the recognition of P. rupincola as a species, but the stability of the life history in various culture environments appears to warrant continued recognition of this taxon as a distinct form of P. littoralis, as originally proposed by J. E. Areschoug.     

CHIMERAS WITH MOSAIC PATTERN IN ARCHEOSPORE GERMLINGS OF PYROPIA YEZOENSIS UEDA (BANGIALES,RHODOPHYTA)1

In the marine crop Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi, it is known that conchospores from heterozygous conchocelis develop into sectored gametophytic blades (chimeras), but archeospores asexually released from haploid blades do not usually grow into chimeric blades. In this study, chimeras with mosaic pattern consisting of the green and wildtype colors were developed from archeospores that were released from a blade piece containing a cell cluster of green color induced by heavy‐ion beam irradiation. To make clear whether these archeospores were produced from the green‐colored cells or the wildtype‐colored cells, cell clusters of the green mutant, wildtype, and mosaic pattern were cut out from the grown chimera, and archeospores were released from each of the three blade pieces. Archeospores from the green‐mutant blade piece and from the wildtype blade piece developed into only green‐mutant blades and wildtype blades, respectively. In contrast, archeospores from the blade piece with mosaic pattern developed into green‐mutant blades, wildtype blades, and chimeric blades with mosaic pattern of the two colors, although the frequency of the chimeras was low. Because each gametophytic cell possesses a single plastid, it is difficult to explain the occurrence of the new chimeras as a mutation of the plastid DNA. Thus, the new chimeras are considered to be due to transposable elements in Pyropia.     

Morphological variability in a red seaweed: confirmation of co-occurring f. lessonii and f. chauvinii in Chondracanthus chamissoi (Rhodophyta,Gigartinales)

Variability in thallus morphology is common in red seaweeds. Two co-occurring forms have been described for Chondracanthus chamissoi based mainly on blade width. To determine whether two distinct forms or a range of intermediate morphologies occur in C. chamissoi, thalli were collected from three localities in southern Chile in autumn–winter, repeating the sampling in one locality in spring and in summer. In each occasion, individual sporophytic and male and female gametophytic clumps were collected, and the longest blade with intact apex from each clump was evaluated. Blade length, width, density of spines, axis curvature and thickness, and pinnule length and width were evaluated in each blade. Principal components analyses separated two groups of thalli, one group with narrow, thick, and curved (concavo-convex) blades, with few spines consistent with f. lessonii, and another with broad, thin, and flat blades, with many spines consistent with f. chauvinii. These variables also had bimodal frequency distributions. Pinnule measurements were mainly associated with differences among sporophytes and gametophytes. Age (length), phase of the life cycle, and sex were not related to the forms. Furthermore, thalli of both forms were collected side by side in the study sites and throughout the year so the occurrence of the two forms was not attributable to local environmental conditions. In this species, secondary basal disks are produced after attachment of apexes to the substratum. These disks may produce blades with a modified morphology in a way similar to proliferations and regenerations described for Schottera nicaeensis.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

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.     

THE LIFE CYCLE OE SARGASSUM HORNERI (PHAEOPHYTA) IN LABORATORY CULTURE1

The life cycle of the large dioecious alga Sargassum horneri (Turner) C. Agardh was completed in unialgal culture by controlling photoperiod in relation to the phase of growth. Embryos isolated from a naturally grown female thallus gave rise to early germlings that rapidly formed blades under both short-day (9 h L) and long-day (15 h L) conditions at 20° C Shoot elongation, which followed early blade formation, occurred under the short-day conditions hut not under the long-day conditions. Functional female and male receptacles developed when thalli 8–14 cm long grown under the short-day conditions were transferred to the long-day conditions; gamete fusion occurred when male and female thalli were grown together. Fertilized oospores gave rise to normal thalli in a manner similar to that for in situ plants. Thus, the life cycle of S. horneri was completed in laboratory culture.     

MORPHOLOGY AND TAXONOMY OF HIMANTOTHALLUS (INCLUDING PHAEOGLOSSUM AND PHYLLOGIGAS), AN ANTARCTIC MEMBER OF THE DESMARESTIALES (PHAEOPHYCEAE)1

The sporophyte of Himantothallus develops according to a closed pattern in which the number and position of the blades is determined by the location of trichothallic meristems in a filamentous germling. Expansion of the miniature juvenile to the massive adult thallus is accomplished by diffuse secondary growth and involves a change from filamentous rhizoids to a hapteroid holdfast, flattening of the stipe, and enormous increases in length, breadth, and thickness of both stipe and blade. The axis usually bears 1–8 lateral blades, often paired, and terminates in a flattened stub. Phaeoglossum is interpreted as a growth form of Himantothallus in which a terminal blade develops to the exclusion of lateral blades, the latter being represented by a single spine. Phyllogigas clearly falls within the morphological spectrum of Himantothallus, the lack of twisting being related to physical factors in the environment. Sporangia, interspersed with an equal or somewhat larger number of two-celled paraphyses, are borne in slightly elevated sori scattered over both surfaces of the blade. Zoospore germination was not observed, nor were gametophytes, either in culture or in the field. Haptera apparently originate from the meristoderm in the lower part of the maturing stipe and lack a filamentous medulla. The mature stipe and the mature blade are anatomically similar, being composed of a superficial meristoderm, a cortex of parenchyma-like cells, and a filamentous medulla. The meristoderm is usually a single layer of plastid-containing cells that divide anticlinally to accommodate (or effect) expansion and periclinally to produce cortical tissue inward. Cortical cells are in radial files and increase in diameter towards the interior. They usually are densely packed with physodes. The medulla is uniquely distinguished by the presence of sheathed trumpet hyphae. Cells of the trumpet hyphae have perforate end walls with callose deposits and probably function in conduction as do the sieve filaments in Laminariales. Sheathing cells are filled with plastids. Sheathing filaments form connections among themselves and with nearby unsheathed filaments. The sheathed trumpet hyphae and their matrix of unsheathed filaments form a plexus, which in the mature blade is flattened and may be stripped intact from the other tissues. Development of the embryonic sporophyte is very similar to that in Desmarestia, as is the anatomy of the adult thallus and the sporangia. From these considerations, Himantothallus is assigned to the Desmarestiaceae (Desmarestiales).     

LIFE HISTORY AND GROWTH OF LAURENCIA BRACHYCLADOS (RHODOPHYTA,CERAMIALES)1

Laurencia brachyclados Pilger from Hawai'i completed a “Polysiphonia-type” tri-phasic life history in 21 weeks in laboratory culture. Tetraspores developed into gametophytes in a nearly 1:1:1 ratio of females: males: non-reproductive. Carpospores were released as early as 21 days after mixing virgin female and male gametophytes. Cultured thalli showed a “guerilla type” growth form. Other Hawaiian Laurencia species in culture had longer maturation times or remained non-reproductive. Variation in life history schedules may influence Laurencia species coexistence and algal community structure.     

Defense mechanisms of sargassacean species against the epiphytic red alga Neosiphonia harveyi

Flora diversity and abundance of epiphytes are specific to their basiphyte species and may relate to variations in the defensive abilities of basiphytes. Thus, investigating the interactions between epiphytes and basiphytes is useful for a better understanding of the biological impact of epiphytism and the survival strategies of basiphytes. We examined the epiphyte density on five sargassacean species at six locations between two study sites, which showed that the epiphytic red alga Neosiphonia harveyi was remarkably less abundant on Sargassum siliquastrum at all locations. To assess its defense mechanism against N. harveyi, we performed bioassays of phlorotannins, which are considered effective in deterring fouling, by culturing sargassacean blades with N. harveyi carpospores and observed the process by which sargassacean blades remove epiphytes. When the carpospores were incubated with various concentrations of dissolved phlorotannins, settlement and germination were inhibited only at the highest concentrations (>0.1 g · L^?1), and this effect did not significantly differ among the five sargassacean species. When the carpospores were combined with blades from the five species, many of the spores attached and germinated on every blade. Because N. harveyi penetrated rhizoids into basiphyte tissues, cuticle peeling observed in all five sargassacean species could not remove this epiphyte after germination. However, in S. siliquastrum, the blade tissues around the germlings became swollen and disintegrative, and were removed together with the germlings. The spores normally grew on the dead blades, suggesting that the tissue degradation of S. siliquastrum is triggered by the infection of N. harveyi.     

Selection of age classes of<Emphasis Type="Italic"> Sasa</Emphasis> leaves by caterpillars of the skipper butterfly<Emphasis Type="Italic"> Thoressa varia</Emphasis> using albo-margination of overwintered leaves

A blade of the bamboo grass Sasa veitchii var. hirsuta (Koidzumi) typically has a lifespan of 2–4 years. After winter, the edge of the blade dies and a white margin is drawn on the blade. Such an albo-marginated blade is thought to be of relatively low quality as food for insects. Caterpillars of the skipper butterfly Thoressa varia (Murray) (Lepidoptera: Hesperiidae) that fed on blades of S. veitchii almost always utilized current-year blades. The mechanism by which they discriminate between age classes of blades was studied. The caterpillars did not choose albo-marginated blades, but they chose overwintered blades whose margins had been removed. This indicates that they use albo-margination as evidence of the age of a blade.     

Somatic meiosis in the life history of Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniales,Rhodophyta) from the Iberian peninsula

Carpospores isolated from Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniaceae, Rhodophyta) and grown in culture developed into their respective ‘Hymenoclonium’ prostrate phases. In both species, young gametophytes were initiated directly on the prostrate phase from tetrasporangia-like protuberances. Comparison of the relative fluorescence area (rfa) of nuclear DNA over the sequence of life-history stages indicated that the lowest ploidy levels (1–2C) occurred in the gametophytes, whereas the lowest ploidy levels in the prostrate phases were 2–4C. Rfa data demonstrated that meiosis occurred in the tetrasporangia-like protuberances where 1C values were recorded. The present observations establish that B. asparagoides and B. clavata have a heteromorphic diplohaplontic life history, which involves a haploid gametophyte produced directly on a diploid prostate phase after somatic meiosis. We conclude that the life history of these taxa corresponds to the Lemanea-type. This indicates that the life history of several Bonnemaisoniales with a ‘Hymenoclonium’ phase but lacking tetrasporangia requires re-investigation.     

Photoperiodic regulation of receptacle induction in Sargassum horneri (Phaeophyceae) using clonal thalli

We developed a clonal culture of Sargassum horneri to investigate the effect of photoperiod on reproduction in this species. Regenerated vegetative thalli were obtained using lateral branches excised from a thallus grown from a single embryo under short‐day conditions (SD = 10:14 h light : dark cycle). Lateral branches excised from the SD‐regenerated thallus became vegetative thalli that remained in that phase as long as they were cultured under SD. When an excised lateral branch was cultured under long‐day conditions (LD = 14:10 h light : dark cycle), it began to enter the reproductive phase while still less than 50 mm long. Induction of the reproductive phase was accompanied by a distinctive morphological change – suppression of blade formation at the apical region of the branch; elongation of branches without blades was then followed by differentiation of receptacles bearing conceptacles on their surface. Apices of receptacles were able to interconvert between reproductive and vegetative phases, as blades resprouted upon transfer from LD to SD. The critical day length for induction of receptacle formation was between 13 and 14 h; receptacle formation was also induced under SD conditions with night breaks (NBs). These results strongly suggest that reproductive regulation of S. horneri is a photoperiodic long‐day response. NBs with blue and green light were effective for reproductive induction but not with red light. This suggests that blue‐ and/or green‐light photoreceptors are involved in the photoperiodic reproductive response of S. horneri.     

The Knotted leaf blade is a mosaic of blade,sheath, and auricle identities

The dominant Knotted-1 mutations in maize alter development of the leaf blade. Sporadic patches of localized growth, or knots, and fringes of ectopic ligule occur along lateral veins of mutant leaf blades. In addition, bundle sheaths do not completely encircle lateral veins on mutant leaf blades. We have compared mutant leaf blades with wild-type leaves to determine the precise nature of the perturbed regions. Our analysis includes characterization of epidermal cell shapes, localization of photosynthetic proteins and histology of the leaf. We show that mutant leaf blades are a mosaic of leaf organ components. Affected regions of mutant leaf blades resemble either sheath or auricle tissue in both external and internal features. This conversion of blade cells represents an acropetal shift of more basal parts of the leaf blade region and correlates with previously identified ectopic expression of the Knotted-1 protein in the leaf blade. We propose that inappropriate expression of Kn1 interferes with the process of establishment of cell identities, resulting in early termination of the normal blade development program or precocious expression of the sheath and auricle development programs. © 1994 Wiley-Liss, Inc.     

Developmental Studies in Porphyra Vietnamensis: a High-Temperature Resistant Species from the Indian Coast

Porphyra vietnamensis Tanaka & Pham-Hoang Ho (Bangiales, Rhodophyta) is a tropical seaweed collected from the west coast of India. Thalli of the blade phase are found growing only during the rainy season between July and September. They grow on rocky intertidal or subtidal substrata or as epiphytes on other seaweeds such as Enteromorpha flexuosa and Chaetomorpha media. The gametophytic thallus is monostromatic and covered with spines at the base. The species is monoecious. Male gametangia are found in patches that are distributed in the upper part of the thallus. Archeospores are found at the thallus margins and give rise to the blade phase after one week of germination even at 30 ^∘ C. Zygotospores germinated at 25 ^∘ C into conchocelis within three days from the date of their inoculation. Conchospores were released at 30 ^∘ C. The young blades grew at 32 ^∘ C in the laboratory.     

Translocation of C in Macrocystis pyrifera (Giant Kelp)

The pattern of import and export of ¹⁴C-labeled assimilates in Macrocystis pyrifera (L.) C. A. Agardh in southern California was studied by labeling single blades on fronds, in situ, with [¹⁴C]NaHCO₃ for 24 hours. The pattern was found to be similar to that known in dicotyledons: actively growing tissue imported and did not export. As a blade reached maturity it began to export, at first only acropetally to the apex which formed it, later also down the frond to sporophylls and frond initials at the base of the frond, and into the apical regions of juvenile fronds; finally there was a phase of declining export, late in the life of the blade, when transport was only downward. Young fronds imported from older fronds until they were approximately 3 meters long, by which time they had developed mature, upward exporting blades. No translocation was found from a younger frond to an older frond, nor was there transport upward from a blade on a frond lacking the apical region.     

CULTURE AND HYBRIDIZATION STUDIES ON GIGARTINA PAPILLATA (RHODOPHYTA)1

The foliose red alga Gigartina papillata (C. Ag.) J. Ag. was studied in culture to determine its life history and possible relationship to the life history of Petrocelis middendorffii (Ruprecht) Kjellman. Carpospores cultured from individual female plants gave rise to either crustose Petrocelis-like plants that reproduced by tetraspores, or to another generation of foliose female (cystocarpic) plants that reproduced by carpospores. Apices cultured from blades of individual field-collected female plants produced either papillae with many procarps that developed cystocarps only when crossed with male plants, or papillae with few procarps that produced cystocarps in the absence of male plants. The results are interpreted to demonstrate that two types of life history occur in G. papillata: one, a sexual life history involving a crustose tetrasporophyte; the other, a possibly apomictic life history involving only cystocarpic plants. Hybridization experiments demonstrated, that G. papillata is interfertile with Gigartina-phase gametophytes cultured from tetraspores of P. middendorffii. Sexual plants of G. papillata are postulated to represent the naturally-occurring gametophyte of P. middendorffii in California. The possible relationships of the sexual and apomictic plants of G. papillata are discussed.