Tetraspore Germination Research Articles

Shell powder as source of calcium in the development of Gelidium floridanum (Rhodophyta, Gelidiales) tetraspores and explants

This work aimed to improve the techniques for cultivating the species Gelidium floridanum, testing different sources of calcium. Tetraspores and explants were grown in the laboratory for 20 days with seawater enriched with 50% von Stosch solution and oyster or mussel shell powder (252 mg L-1 and 336 mg L-1), or calcium chloride (147 mg L-1 and 295 mg L-1). Tetraspores or explants cultivated with no calcium salts or shell powder were used as control. Tetraspore germination rate and morphology, and germling morphology, average length, and growth rate were evaluated. Besides, the morphology, upright axes formation and growth rate of explants were also evaluated. There was no difference in tetraspore germination among treatments and control. Treatments with shell powder impaired tetraspore viability, indicated by a greenish color, cellular disorganization, and delay in germ tube development. Germlings cultivated with CaCl2 show better initial development but with no improvement compared to control. Concerning explants, those cultivated with mussel shell powder showed the highest growth rate (3.92 and 4.28% day-1, according to concentration) in relation to other treatments. In particular, those cultivated with 252 mg L-1 mussel shell powder had a significant formation of upright axes (10.15 ± 0.85 upright axes) compared to the control (5.18 ± 0.42 upright axes). Based on these results, we recommend using mussel shell powder at a concentration of 252 mg L-1 to optimize explant cultivation.

Evaluation of salinity effects on the release, adhesion, and germination of the tetraspores of Gelidium floridanum (Rhodophyta, Florideophyceae)

The release, adhesion, and germination of tetraspores determine the successful development of the red seaweed Gelidium floridanum. The aim of this study was to investigate the effects of salinity on the initial development of G. floridanum tetraspores. To accomplish this, tetraspores were released and allowed to germinate under salinity of 24, 28, 32, 36, and 40 psu for a period of 6 to 24 h. Samples were processed for light, confocal, and transmission electron microscopy to analyze the ultrastructural characteristics, as well as analyses of the cell viability (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)) and quantification of photosynthetic pigments. At 32 psu, tetraspores exhibited normal characteristics with germ tube formation after 6 h and rhizoid formation after 24 h. Under hyposalinity of 24 psu, tetraspores did not form a germ tube after 6 h, and no development at all occurred after 24 h. Thus, the development of tetraspores was inhibited, resulting in nonviable cells or disorganized cytoplasmic contents. Tetraspores cultivated in hypersaline conditions (40 psu) showed a delay in development. After only 6 h of culture, samples in both hyposaline and hypersaline conditions showed differences in photosynthetic pigments, and such pigments tend to stabilize after 24 h. Based on these results, we can conclude that this species has only limited tolerance to salinity in the range of 28 to 36 psu and that salinity above or below these values is sufficient to change the pattern of development of G. floridanum tetraspores.

Effects of brefeldin A on the endomembrane system and germ tube formation of the tetraspore of Gelidium floridanum (Rhodophyta, Florideophyceae).

Gelidium floridanum W.R. Taylor tetraspores are units of dispersal and are responsible for substrate attachment. This study aimed to examine evidence of direct interaction between germ tube formation and Golgi activity during tetraspore germination of G.floridanum. After release, the tetraspores were incubated with brefeldin A (BFA) in concentrations of 4 and 8μM over a 6h period. The controls and treatments were analyzed with light, fluorescence (FM4-64 dye) and transmission electron microscopy. In the control samples, the Golgi bodies were responsible for germ tube formation. In contrast, BFA-treated samples were observed to inhibit spore adhesion and germ tube formation. These tetraspores also showed an increase in volume (≥30μm width). BFA treatment also resulted in the disassembly of Golgi cisternae and the formation of vesiculated areas of the cytoplasm, blocking the secretion of protein and amorphous matrix polysaccharides. When stained with FM4-64, the control samples showed fluorescence in the apical region of the germ tube, but the treated samples showed an intense fluorescence throughout the cytoplasm. From these results, we can conclude that the germ tube is formed by the incorporation of vesicles derived from Golgi. Thus, vesicle secretion and Golgi organization are basic processes and essential in adhesion and tube formation. By blocking the secretion of protein and amorphous matrix polysaccharides, BFA treatment precluded tetraspore germination.

Effects of UV-B radiation on Gelidium floridanum (Rhodophyta, Gelidiales): germination of tetraspores and early sporeling development

The increased incidence of UV-B radiation, particularly in southern South America, has sparked more interest in its effects on marine organisms. Here we describe the effects of UV-B on the early life stages of Gelidium floridanum, an agar-producing species abundant on rocky coasts in southern Brazil. Treated samples were submitted to 0.12 W m−2 of artificial UV-B radiation for 2 h per day over a 15-day period. UV-B exposure induced impairment of tetraspore germination and germling development. We observed a delay in germination, a reduced growth rate of tetrasporelings, and morphological changes, such as a different length-to-width ratio, twisted thallus, loss of pigmentation, and differentiation of more than one apical cell, all leading to a different growth pattern in sporelings that survived treatment. Results indicated a great susceptibility of early-developing Gelidium to UV-B, even at low irradiance and short exposure time.

The morphogenesis of gametophyte of <I>Kappaphycus alvarezii</I>

The formation,release and germination of tetraspores,together with the morphogenesis of gametophyte of Kapphycus alvarezii were investigated in Lian Bay,Hainan Province,China from November,2007 to April 2009.The results showed the brown Kappaphycus alvarezii,originally gained from Phillippines in 1985,were tetrasporophytes and the tetraspores were mainly formed and released from April to October.Both tetraspore germination and embryogenesis could be induced artificially in the laboratory and great variations of embryos in color from brown red,yellow-green,olivine green to olivine-brown chimera were observed.Rhizoids were formed and then disappeared during the embryogenesis period.The germination rate of tetraspores was about 87.1% ± 7.2% and the mean specific growth rate of embryos was about 6.3% ± 1.1 % /d for indoor dish culture.After 160 days indoor cultivation,the germinated tetraspores developed to young gametophytes.Then,20 young gametophytes were cultured on the soften raft in the sea.The average specific growth rate measured was over 10% /d in the first month culture in the sea,and the highest specific growth rate for young gametophytes was over 21.2 % /d.However,the specific growth rate gradually reduced accompanied with the frond increase in size in the following cultivation.Four types of gametophytes with different morphology,density of branches and growth rate were obtained as follows:TypeⅠ shows thick buds,cylinder-shaped trunk,taper terminal,and sparse branches.Type Ⅱ shows thin buds,cylinder-shaped trunk,blunt terminal,sparse branches.Type Ⅲ shows thin buds,cylinder-shaped trunk,taper terminal,and dense branches.Type Ⅳ shows thin buds,cylinder-shaped trunk,oblate terminal stem,taper terminal,and dense branches.During our experimental period,a large scale of ice-ice disease broke out,and the vitality and resistance to the ice-ice disease in some strains of the gametophytes improved significantly compared to their parent plants.

Germination and survival of tetraspores of Kappaphycus alvarezii var. alvarezii (Solieriaceae, Rhodophyta) introduced in subtropical waters of Brazil

SUMMARYThe carrageenophyte Kappaphycus alvarezii was introduced in 1995 and vegetatively propagated in Ubatuba, São Paulo State, Brazil, for the purpose of commercial cultivation. This species produces tetraspores mainly in the austral summer and fall. Tetraspore germination and survival were studied under different conditions of temperature, photon flux density, and photoperiod in the laboratory. Field experiments were also carried out. Although tetraspores of K. alvarezii germinated, they had low survival rates, most dying after 20 days. Recruitment of K. alvarezii tetraspores did not occur in experiments conducted in the field. The results indicated that the establishment of K. alvarezii via spore production in the natural environment of the south‐east coast of Brazil is rather remote.

Callus induction and micropropagation improved by colchicine and phytoregulators in Kappaphycus alvarezii (Rhodophyta, Solieriaceae)

Tissue culture techniques were applied for micropropagation of the red alga Kappaphycus alvarezii in order to select the best strain and experimental system for in vitro culture. Five strains were tested: brown (BR), green (GR) and red (RD) tetrasporophytes, brown female gametophyte (BFG), and a strain originating from tetraspore germination (“Edison de Paula”, EP). The effects of three culture media were tested on callus formation, regeneration from explants and from callus in the three tetrasporophytic and EP strains: seawater enriched with half-strength of von Stosch’s (VS 50) and Guillard & Ryther’s (F/2 50) solutions, plus synthetic ASP 12-NTA medium, with or without gelling agent. Explants of the EP strain were treated with glycerol and the phytoregulators indole-3-acetic acid (IAA); 2,4-diclorophenoxyacetic acid (2,4-D); and benzylaminopurine (BA), alone or in combination. The effects of colchicine (0.01%) during 24, 48, 72 hours and 14 days were analyzed in the BFG and EP strains. The EP strain showed the highest percentage of explants forming callus and regeneration from explants in VS 50, indicating its high potential for micropropagation in comparison to the other strains. Regeneration from callus was very rare. Treatments with glycerol and IAA:BA (5:1 mg L−1) stimulated the regeneration from explants. Significant differences were observed in the percentages of regeneration of EP strain explants treated with colchicine for 14 days. Our results indicate that IAA and BA stimulated the regeneration process, and that colchicine produced explants with high potential for regeneration, being useful for improving the micropropagation of K. alvarezii.

Ultrastructure of tetraspore germination in the agar-producing seaweed Gelidium floridanum (Gelidiales, Rhodophyta)

Z.L. Bouzon, L.C. Ouriques and E.C. Oliveira. 2005. Ultrastructure of tetraspore germination in the agar-producing seaweed Gelidium floridanum (Gelidiales, Rhodophyta). Phycologia 44: 409–415.Spore germination is a crucial step in the dispersion and establishment of algae. Here we describe for the first time the ultrastructure of the initial stages of the tetraspore germination of Gelidium floridanum, a species considered to be of potential economical value in Brazil. The stages of the germination process of G. floridanum tetraspores were studied under light and transmission electron microscopy. When released, the spores had no cell walls and were surrounded by a mucilage envelope that enabled primary attachment of the spore to the substratum. Following spore release, numerous tubular invaginations of the plasma membrane became apparent. These structures appeared to be connected to the endoplasmic reticulum and may play a role in the transport of cell wall material. Small vesicles with fibrillar content, although abundant in the tetraspores, were no longer seen in the sporelings, suggesting that these vesicles contain the precursors of the cell wall material that accumulates during sporogenesis. We observed that, soon after attachment, cellulose deposition began at one pole of the cell and gradually extended over the spore surface in a thin layer. As germination proceeded, a germ tube formed, to which most of the cytoplasmic content of the spore migrated. A cell division and the production of a cross wall separating the tube from the original spore followed. Subsequently, the germ tube elongated and underwent a series of transverse and diagonal septations, producing cells of various sizes. We can conclude that germination of tetraspores in G. floridanum depends on a basic process consisting of: attachment, cell wall deposition, activation of dictyosomes, mobilisation of starch accumulated during sporogenesis, polarised vacuolation, germ tube formation, and cell division.

Morphology, reproduction and development of Hypoglossum hypoglossoides (Stackhouse) Collins & Hervey (Ceramiales, Rhodophyta) from the south and southeastern Brazilian coast

Hypoglossum hypoglossoides (Stackhouse) Collins & Hervey is reported for the first time from the infralittoral of Sao Paulo and Santa Catarina states. The species was already reported to the states of Rio de Janeiro, Espirito Santo and Bahia as Hypoglossum tenuifolium (Harvey) J. Agardh var. carolinianum Williams. A detailed description of the morphology and reproduction is given based on field-collected material. Unialgal cultures were initiated from tetraspore germination, and growth rates of gametophytes were determined under different conditions of temperature, photoperiod and irradiance. Gametophytes grew well between 15 to 30 oC, 14L:10D and 10L:14D photoperiods and irradiance from 20 to 120 µmol photons.m-2.s-1, but presented low percentage of fertile plants in low temperature (15 oC). Gametophytes cultured in laboratory developed only male reproductive structures. Physiological responses of H. hypoglossoides indicate that the species is well adapted to temperature and light variations which could explain its range of vertical (6-26 m depth) and latitudinal distribution (from Fernando de Noronha to Santa Catarina) as well as the absence of sexual reproduction in the southern limit of its distribution.

Histórico de vida de espécimens selvagens e variantes cromáticas de Gracilaria birdiae (Gracilariales, Rhodophyta)

(Gracilariales, Rhodophyta) e uma macroalga marinha de coloracao vermelha (vm) comum na costa Nordeste do Brasil e amplamente coletada para a extracao de agar. O objetivo deste estudo foi completar o historico de vida de especimens selvagens (coloracao vermelha) e variantes cromaticas. Duas variantes foram isoladas, alem dos especimens selvagens coletados na praia de Paracuru, Ceara: i, marrom-esverdeada (me), encontrada em uma populacao natural da praia de Paracuru; e ii, verde (vd), obtida espontaneamente in vitro a partir de um ramo tetrasporofitico. As condicoes gerais de cultivo tanto para gametofitos quanto para tetrasporofitos foram: meio de cultura von Stosch 25%; fotoperiodo 14L:10E (luz: escuro); irradiância 100 µm.m-2.s-1 e aeracao a cada 30 min. Tetrasporofitos das tres coloracoes e gametofitos verdes foram cultivados tambem em 10L:14E. O historico de vida foi completado in vitro em 498 (vm), 523 (me) e 861 (vd) dias, mostrando-se do tipo Polysiphonia. Tetrasporofitos produziram tetrasporos apenas em fotoperiodo 10L:14E. Gametofitos femininos verdes desenvolveram cistocarpos apenas em fotoperiodo 14L:10E. No entanto, a diferenciacao de conceptaculos do tipo verrucosa em gametofitos masculinos verdes e a liberacao de espermacios ocorreu em ambos os fotoperiodos. Gametofitos masculinos vermelhos apresentaram conceptaculos espermatangiais do tipo henriquesiana, enquanto gametofitos masculinos marrom-esverdeados apresentaram os tipos verrucosa e henriquesiana. Nao foram verificadas diferencas quanto ao habito de especimens de uma mesma coloracao, independentemente do estadio reprodutivo analisado. Verificou-se em todos os tetrasporofitos a germinacao de tetrasporos in situ.

No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta)

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7°C±0·73 (SD) to 21°C±1·19. Monthly mean biomass in 25×25 cm quadrats (n=3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27°C. Tetrasporangia, gametangia and cystocarps were formed at 19°C and above, but not at 13 or 16°C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21°C) yet...

No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta)

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7°C±0·73 (SD) to 21°C±1·19. Monthly mean biomass in 25×25 cm quadrats (n=3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27°C. Tetrasporangia, gametangia and cystocarps were formed at 19°C and above, but not at 13 or 16°C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21°C) yet only three plants with tetrasporangial branches were found in the field. In September the biomass of C. okamurae declined sharply following severe storm damage. Thus, the absence of reproductive organs in field populations of C. okamurae may occur because they inhabit a seasonally stressful habitat, in which typhoon damage removes branches before the water temperature becomes favourable for reproduction.

CULTIVATION STUDIES OF GIGARTINA SKOTTSBERGII IN SOUTHERN CHILE

In Chile, the demand for carrageenophytic algae has increased significantly in recent years. The preferred species is Gigartina skottsbergii, with landings of 26,181 tons in 1998. To avoid a possible overexploitation the development of cultivation technologies is needed. In this study we present a critical view of published and new information to propose the best culture strategy for this species. The results indicate that viable spores are seasonally available only during winter, with tetraspore germination rates of ca. 40%. Germination of carpospospores is lower than 20%. Growth in tanks can be as high as 1% day−1 and high nutrient concentrations (N and P) must be added. Gigartina also present a high and unique regeneration capacity. Field experiments indicate that Gigartina can be cultured in rope systems, where the inoculum can be tissue fragments. These results indicate that vegetative propagation techniques can be used for the massive culture of Gigartina, but selection of a high growing strain remains as one of the future challenges.

The life history of a Santa Catalina Island population of Liagora californica (Nemaliales, Rhodophyta) in the field and in laboratory culture

The gametangial phase of Liagora californica Zeh has a life span rarely exceeding 10 mo at Santa Catalina Island, California. Gametophytes reached maximal cover during late summer and autumn, periods of longer photoperiods and warmer sea temperatures, before declining sharply in abundance by late winter. Field-collected gametophytes were both dioecious and monoecious. Carpospores developed in culture into filamentous tetrasporophytes that produced irregular, cruciate tetrasporangia within 45 d. No monosporangia were detected in either gametophytes or tetrasporophytes. 4′,6-diamidino-2-phenylindole (DAPI) fluorescence of the nuclei of gametophyte vegetative cells was half that of vegetative sporophyte cells, suggesting that meiosis occurs during tetrasporogenesis. The magnitude of tetrasporangial production varied between two clones but occurred under all nine photoperiod (14: 10, 12: 12, and 10: 14 h L: D) and temperature combinations (13, 17, and 21°C); best tetraspore production occurred in both clones under ‘summer’ conditions (14: 10 h L:D; 21°C). Germination of tetraspores into uniseriate, filamentous gametophytes and the production of erect gametophyte axes from bud-like initials also occurred under all photoperiod-temperature conditions. Greatest production of young, uniseriate gametophytes occurred under 13 and 17°C; best growth and development of erect, multiaxial gametophyte fronds occurred under the combination of longer day and warmer temperature conditions. On the basis of field and laboratory data, we hypothesize that small, prostrate, uniseriate gametophytes are the overwintering stage of L. californica at Santa Catalina Island. Enhanced tetrasporogenesis and the growth and development of erect gametophyte axes under longer days and warmer temperatures may be adaptations that evolved at lower latitudes and not ones optimally suited for year-round maintenance of L. californica gametophytes at temperate Santa Catalina Island, the northern distributional limit of this species in the eastern North Pacific.

A review of the life history, reproduction and phenology of Gracilaria

The basic life history of the red alga Gracilaria is of the three-phase Polysiphonia type but a number of species show deviations. Plants can bear both gametangia and tetrasporangia, either on separate parts of the thallus or on the same. Explanations include the in situ germination of tetraspores (allowing gametophytic thalli to be epiphytic on tetrasporophytes), the coalescence of spores or developing discs (resulting in chimaeras), mitotic recombination during cell division in the mature diploid thallus (resulting in patches of diploid male and female cells on the tetrasporophyte), a mutation eliminating the repression of female expression allowing haploid male plants to be bisexual and initial failure of cell walls to form during the development of tetraspores. Polyploids can be produced from plants with diploid gametangia. The sexes and phases are usually morphologically identical but gametophytes or their parts may be smaller. The growth rates of the sexes may differ and diploid juveniles may survive better than haploid. Neither polyploidy nor hybridization results in superior growth. The sex ratio is probably 1:1 but females may appear to be more abundant. Diploid and haploid phases are usually either about equal or diploids predominate, often depending on the type of substratum. At high latitudes reproduction peaks in late summer whereas in the tropics it may be high all year. In temperate regions growth rate is fastest and biomass highest in late summer; in the tropics peak biomass is mainly in the winter. Spermatia are effective for only a few h. Spores vary in size around 25 \m, diploid ones usually being larger. Cystocarps or tetrasporangia in the field may not currently be releasing spores. In the laboratory spore release shows a diurnal rhythm, peaking during the night or day according to the species. All the above attributes are potentially important in planning and executing Gracilaria cultivation.

Life history and reproductive potential of the agarophyte Gelidium robustum in California

The reproductive potential of the tetrasporangial phase of Gelidium robustum was studied for 16 months at two sites off Santa Barbara, California. In all samples tetrasporangial thalli were always more abundant than gametangial ones. Tetratrasporangial sori were present throughout the duration of the study but relative fecundity was highest [300–400 sori g−1 (w. wt)] in spring/summer samples of consecutive years, as a result of increasing numbers both of tetrasporangial branchlets per plant and of sori per branchlet. On the other hand, laboratory experiments showed that tetraspore release per sorus was highest (150–250 spores sorus−1 d−1) in winter. Inferring from these field and laboratory data plants released up to ± 34 000 tetraspores g−1 (w. wt) d−1 in the spring/summer of the second study year. Tetraspore germination, under defined culture conditions, also showed a marked seasonality increasing sharply from less than 10% in winter up to almost 60% in spring/summer, thus coinciding with the period of maximal spore output per plant. These results suggest that although relatively high numbers of tetraspores may be released by G. robustum plants all year round these might not always have the potential to germinate and recruit.

Life history and physiology of the red alga, Gelidium coulteri, in unialgal culture

Gelidium coulteri Harv., an agarophyte of commercial importance, was grown in unialgal culture in natural seawater under various environmental conditions. Growth rate, reproductive status, morphology and agar production for whole plants under each condition were determined over 2-month periods. Reproduction could be induced in these plants by (1) limiting them for nutrients, then relieving the limitation with addition of Provasoli's enrichment, or (2) increasing photon flux densities (PFD) from <50 μE m −2 s −1 to 150 μE m −2 s −1. The sexual life history was completed in 2 months. Red light inhibited tetraspore germination vs. white light, but blue and green light did not. Vegetative tetrasporophytes and gametophytes showed no differences in their growth responses to environmental changes. Growth rates increased with increasing PFD and were optimal at 150–250 μE m −2 s −1. Growth inhibition and bleaching were seen at 400 μE m −2 s −1. Agar yield on a dry weight basis increased with increasing PFD to 32–35% at 150 μE m −2 s −1 and remained constant at higher PFDs. Plants grown at PFD<50 μE m −2 s −1 were linear with little branching. Increasing PFD to 150 μE m −2 s −1 stimulated branching within 1 week. Growth rate increased with increasing temperature to a maximum at 20–27°C. Temperatures above 31°C were lethal. Agar yield was constant at 32–35% dry weight with respect to temperature to 31°C, at which agar yields increased to 40%. Growth was optimal at pH 7.5–8.5. Tissue necrosis and cell death occurred at pH below 7.0. Plants formed superficial carbonate deposits at pH above 9.0. Agar yields were constant from pH 6.0 to 9.0. Plants grown in unfortified seawater showed declines in chlorophyll content and growth rate to nearly zero after 3 weeks. Phycobiliprotein levels decreased to zero after 12 days. Agar yields of these plants were 40–60% higher than in plants grown with nutrient supplementation. Subsequent 0.36 mM nitrate addition led to a recovery of chlorophyll and phycobiliprotein in 2–3 days.

ULTRASTRUCTURE OF TETRASPOROGENESIS IN THE CORALLINE ALGAHALIPTILON CUVIERI(RHODOPHYTA)1

ABSTRACTTetrasporogenesis begins with the formation of the tetra‐sporocyte, an elongate, apparently wall‐less, cell containing few organelles. The tetrasporocyte rapidly elongates and a distinctive cell wall forms before the onset of meiosis. During this elongation phase there is also an increase in the number of plastids and mitochondria. The meiotic tetrasporocyte is characterized by extensive development of perinuclear endoplasmic reticulum (PNER) and peripheral endoplasmic reticulum (PER) and during the latter stages of sporogenesis by internuclear endoplasmic reticulum. Immediately next to the nuclear envelope the inter‐cisternal spaces of the PNER are filled with very electron dense material and the PNER cisternae are quite narrow, while further away from the nucleus the PNER cisternae dilate. Throughout meiosis there is continued replication of plastids and mitochondria as well as synthesis of starch and the formation of Golgi‐derived vesicles with very osmiophilic contents. Cytokinesis begins with the formation of striated thickenings on the inside of the tetrasporocyte wall, at the sites where the cleavage furrow, produced by infurrowing of the plasmalemma, will be formed. Early in cytokinesis the PER disappears and is replaced by osmiophilic vesicles and mitochondria. Tubular plasmalemma invaginations of 27–30 nm width also appear during the early stages of tetraspore wall formation. The ultra‐structure of the early stages of tetraspore germination is also described.

The life history of Halosaccion ramentaceum

The complete life history of Halosaccion ramentaceum has been determined. It is very similar to that of Palmaria palmata, consisting of haploid male and female gametophytes alternating with a diploid tetrasporophyte. As for P. palmata, there is no carposporophyte. Male and female gametophytes attain sexual maturity almost a generation apart. Whereas male plants require approximately 1 year's growth before producing spermatia, female gametophytes are microscopic and reach sexual maturity only a few days after tetraspore germination. The diploid tetrasporophyte initiates its development on the female, but almost immediately forms an independent holdfast on the substratum beside the female. The first diploid fronds arise from that holdfast after it is well established.The existence of a complete sexual cycle was proven by demonstrating: fertilization of trichogynes by spermatia; meiosis in tetrasporangia, with a chromosome number of n = ~24 in gametophytes and 2n = ~48 in tetrasporophytes; and by documenting the Mendelian transmission of a mutant phenotype from the male parent to the F1 gametophytes.

Studies on Gracilaria. 5. In vitro life history of Gracilaria sp. from the Maritime Provinces

The life history of Gracilaria sp. was completed in culture demonstrating a typical Polysiphonia-type life history. Carpospores released by plants collected in nature developed into tetrasporophytes and subsequent release and germination of tetraspores gave rise to a gametophytic generation morphologically similar to the tetrasporophyte. Development of tetrasporophytes from carpospores released by the carposporophytic generation completed the life history. A male to female ratio of 1:1 was found for plants originating from tetraspores and only female plants grown in the presence of male plants formed fertile cystocarps. Detached plants showed the greatest reproductive potential; reproductive maturation of these plants occurred in 8–10 weeks after spore germination. Vegetative propagation through rapid regeneration of adventitious branches from wound tissue was observed.