THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. III. INTERACTION OF CELL ELONGATION AND CELL DIVISION

Periodic cell divisions were induced in gametophytes of Pteridium aquilinum by daily irradiation with white light. In white-dark cycles, the rate of cell division was promoted by increased time in white light; cell elongation was not affected. The time of transition to two-dimensional growth (days to 5% 2-D) was closely associated with the mitotic rate. For white-red cycles, the rate of elongation was controlled by the intensity of red light (wavelengths over 550 nm). This increased elongation delayed the initiation of 2-D development. In both cases the rate of transition to 2-D growth was correlated with the amount of elongation per division.     

UNUSUAL DARK-GROWTH AND ANTHERIDIAL DIFFERENTIATION IN SOME GAMETOPHYTES OF THE FERN ONOCLEA SENSIBILIS

A fertile frond of O. sensibitis was found which yielded spores with unusual growth characteristics. About 25% of the gametophytes derived from the spores were able to undergo 2-dimensional development in darkness, in contrast to normal plants which are filamentous in darkness. When the aberrant spores were cultured in darkness under conditions of reduced ethylene concentration, the proportion of 2-dimensional plants rose to 75%, and, moreover, up to 50% of the gametophytes produced antheridia within 2 weeks. Under comparable conditions normal gametophytes produced no antheridia. The medium from antheridial cultures of the aberrant spores failed to induce the formation of antheridia in other plants.     

THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. II. KINETIC STUDIES ON PTERIDIUM AQUILINUM

Gametophytes of the fern Pteridium aquilinum were incubated 3 days in red light and then transferred to white light. The sequence of events occurring after the transfer was as follows: a swelling of the apical region within 1 hr; a reduction in cell elongation after 5 hr; a series of one-dimensional cell divisions between 10-25 hr; and the initiation of two-dimensional gametophytes after 25-50 hr. The percentage of two-dimensional gametophytes was proportional to the logarithm of the intensity of white light. The rate of elongation after 5 hr was inversely proportional to the logarithm of the intensity. The rates of cell divisions for one- and two-dimensional gametophytes were proportional to intensity up to 240 and 120 ft-c, respectively.     

ACTINOMYCIN D-INDUCED CHANGES IN GROWTH AND RIBONUCLEIC ACID METABOLISM IN THE GAMETOPHYTES OF BRACKEN FERN

Actinomycin D affected the morphological type of growth in the gametophytes of Pteridium aquilinum and the distribution of RNA and protein in their particulate fractions. Increasing concentrations of the drug progressively inhibited two-dimensional growth at the end of a period during which controls had formed typical two-dimensional plants. RNA was lost maximally from the nuclei-rich and ribosome-rich fractions of plants growing in a concentration of actinomycin D which inhibited two-dimensional growth. The magnitude of changes in protein content of the plants was less striking. Presence of actinomycin D in the medium also suppressed incorporation of uridine-H³ into cytoplasmic fractions of gametophytes. The possibility that two-dimensional growth in the gametophytes is under control of a newly synthesized messenger RNA, which is sensitive to actinomycin D, is discussed.     

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. II. INHIBITION OF CELL DIVISION

Ethylene, a natural product of sensitive fern (Onoclea sensibilis L.) gametophytes, has been demonstrated to inhibit cell division in light-grown prothallia. When plants were grown on Knop's solution plus 1 % sucrose under 300 ft-c or more of white light, all ethylene concentrations from 1–1000 μl/liter reduced the rate of increase of cell number by about one-half. The over-all rate of increase of cell number was regulated by various environmental and chemical factors, but regardless of the rate established in control cultures, ethylene treatment of 1–1000 μl/liter produced a relative 50 % depression of cell number. Ethylene was specific for inhibition of cell division and was not a general inhibitor of growth. The ethylene inhibition did not result from a reduction of photosynthesis or energy supply. Further demonstration of ethylene as the active gaseous component resulted when cultures were grown in small enclosed containers with an ethylene absorbent, mercuric perchlorate, and consequently the cell number of gametophytes was restored to the level of unenclosed controls.     

INTERPOPULATIONAL VARIATION IN THE GAMETOPHYTES OF PELLAEA ANDROMEDAEFOLIA

The development and mature morphology of the gametophytes from both sexual and apogamous populations of the fern Pellaea andromedaefolia were investigated. While most sexual examples were indistinguishable, some differences were noted. An insular collection was distinctive in its variability and irregularity of form. Although the latter was a representative of var. pubescens, other collections of the variety could not be distinguished from var. andromedaefolia on the basis of gametophytic characteristics. The apogamous gametophytes were decidedly more variable in development and often very different from sexual thalli. The mature asexual thalli tended to be more irregular in form and usually sharply divergent from the typical cordate type characteristic of the sexual populations. Each of the five apogamous samples was unique with respect to gametophyte development. The differences among the gametophytes of the various populations do not correlate with the sporophytic characteristics which differentiate the two varieties of the species.     

蕨类植物配子体发育的研究

研究了福建观音座莲、华南紫萁、粗齿紫萁、粗齿桫椤、溪边凤尾蕨、娱蚣草、狭翅铁角蕨、乌毛蕨等21种庆类植物的配子体发育过程。结果如下：(1)对孢子和配子体性状的UPG—MA法聚类分析结果表明,秦仁昌分类系统中亲缘关系近的种类在孢子和配子体性状方面相似性也高,但也有少数例外的情况;(2)蕨类植物的配子体发育有许多共性,但也存在许多不同点;(3)配子体发育中出现的某些性状是稳定的,可以作为分类的依据。     

THE GAMETOPHYTES OF OPHIOGLOSSUM PALMATUM L.

Gametophytes of the epiphytic species Ophioglossum palmatum L. are described for the first time, bringing the number of Ophioglossum species with known gametophytes to 11. Although somewhat unusual in terms of (a) degree of branching, (b) the marked expansion of the basically cylindrical axis in some cases, and (c) production of stout, papilla-like rhizoids, the gametophytes of O. palmatum are more similar to other Ophioglossum gametophytes than they are to the gametophytes of Botrychium or Helminthostachys. Gametophyte characters do not provide strong evidence for placing O. palmatum into a separate genus, viz., Cheiroglossa. The gametophytes of O. palmatum most closely resemble those of the other epiphytic species in the genus, O. pendulum. This similarity suggests a need for a revaluation of modern taxonomies which, in general, treat the two species as only distantly related.     

A MULTISPECIES LABORATORY ASSESSMENT OF RAPID SPOROPHYTE RECRUITMENT FROM DELAYED KELP GAMETOPHYTES1

Recent work suggests that the ability to delay reproduction as resistant haploid gametophytes may be important for seaweeds that experience unpredictable disturbances or seasonal periods of poor conditions that result in adult sporophyte absence. Further, delayed gametophytes of some kelp species (order Laminariales) may produce sporophytes more rapidly than if they had never experienced a delay, conferring a competitive advantage when conditions improve or after disturbance events. Here, it was determined that the gametophytes of the canopy‐forming kelp Macrocystis pyrifera (L.) C. Agardh could delay reproduction in a one‐ to two‐cell state (<50 μm) for at least 7 months when grown under nutrient‐limiting conditions. These stages retained reproductive viability and produced sporophytes within 5 d once nutrients were increased. This finding suggests that gametophytes could potentially promote recovery of M. pyrifera populations after extended periods of sporophyte absence. In addition, the time required for sporophyte production between gametophytes of the four most conspicuous kelp species in Southern California that had delayed reproduction and gametophytes that had not was compared. For these four kelp species, a delay of at least 30 d conferred a 40%–76% reduction in the time required for sporophyte production once nutrients were received. Fecundity did not decrease with delay duration, suggesting there is no apparent cost of delayed development for kelps as has been observed in other organisms. Thus, delayed development may be a viable strategy for surviving and initially dominating in environments with variable quality.     

岩蕨属植物配子体发育初报

本文为岩蕨属植物心岩蕨、岩蕨和耳羽岩蕨配子体个体发育和比较形态学初步研究。报道了用无机琼脂培养基由孢子培养配子体的方法。由孢子萌发到配子体成熟分四个时期:萌发期,原丝体发育期,过渡期和原叶体发育期。大多数原丝体发育到七个细胞,与顶端细胞相隔的原丝体细胞开始胞间细胞纵向分裂,进入过渡期。同时顶端细胞的横分裂受到抑制,直至原叶体顶端细胞形成开始原叶体发育期。岩蕨成熟配子体精子器盖细胞不分裂,耳羽岩蕨分裂为一个圆形细胞和一个镰刀形细胞,而心岩蕨两种情况兼而有之,配子体比较形态特征支持心岩蕨可能是以岩蕨和耳羽岩蕨为双亲的异源双二倍体的假设[5]。     

The DC1‐domain protein VACUOLELESS GAMETOPHYTES is essential for development of female and male gametophytes in Arabidopsis

In this work we identified VACUOLELESS GAMETOPHYTES (VLG) as a DC1 domain‐containing protein present in the endomembrane system and essential for development of both female and male gametophytes. VLG was originally annotated as a gene coding for a protein of unknown function containing DC1 domains. DC1 domains are cysteine‐ and histidine‐rich zinc finger domains found exclusively in the plant kingdom that have been named on the basis of similarity with the C1 domain present in protein kinase C (PKC). In Arabidopsis, both male and female gametophytes are characterized by the formation of a large vacuole early in development; this is absent in vlg mutant plants. As a consequence, development is arrested in embryo sacs and pollen grains at the first mitotic division. VLG is specifically located in multivesicular bodies or pre‐vacuolar compartments, and our results suggest that vesicular fusion is affected in the mutants, disrupting vacuole formation. Supporting this idea, AtPVA12 – a member of the SNARE vesicle‐associated protein family and previously related to a sterol‐binding protein, was identified as a VLG interactor. A role for VLG is proposed mediating vesicular fusion in plants as part of the sterol trafficking machinery required for vacuole biogenesis in plants.     

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. I. EFFECTS ON PROTONEMAL AND RHIZOIDAL GROWTH AND INTERACTION WITH AUXIN

Three responses resulted from the treatment with ethylene of dark-grown gametophytes of Onoclea sensibilis. Elongation of the filament was increased, elongation of the rhizoid was decreased, and cell division was inhibited. The optimal ethylene concentrations were between 0.01 and 0.1 ppm. Filament elongation was very tolerant of high ethylene concentrations, since up to 1,000 ppm did not inhibit growth below control levels. Enclosing cultures of gametophytes in chambers of limited volumes produced all the effects of treatment with ethylene, but the responses to sealing were eliminated if plants were enclosed in a chamber which contained a solution of mercuric Perchlorate. This evidence that gametophytes produced ethylene was substantiated by a direct gas chromatographic demonstration of ethylene formation. The growth-regulating effects of ethylene and auxin appeared to be independent in filament and rhizoid growth. Inhibition of elongation by supra-optimal auxin concentrations could not be attributed to an auxin-stimulated production of ethylene.     

INTERACTION OF LIGHT QUALITY AND NUCLEASES IN THE GROWTH OF THE GAMETOPHYTES OF ASPLENIUM NIDUS

Appropriate concentrations of ribonuclease A and B selectively inhibited initiation of two-dimensional morphology in the gametophytes of Asplenium nidus, grown under a photoperiod of 5½ hr white light. Filamentous growth was promoted in such sporelings, the individual cells of which were significantly longer than corresponding cells of the control. Higher concentrations of enzymes were required to inhibit two-dimensional growth in the gametophytes grown in blue light. Concentrations of ribonuclease A or B which inhibited two-dimensional growth in white light promoted growth in length of the protonema in red light. Growth modifications in the sporelings induced by deoxyribonuclease in different light conditions were similar to those induced by the ribonucleases. The results lend further support to the postulated role of RNA in the regulation of two-dimensional growth in fern gametophytes.     

东北蕨类植物配子体发育的研究X.岩蕨科

在室内培养条件下,详尽地比较观察了我国东北产的岩蕨科２属４种的配子体发育过程,了解该科在配子体发育上的特征,来说明建立岩蕨科的合理性和种属间的区别。     

Nuclear DNA level and life cycle of kelps: Evidence for sex‐specific polyteny in Macrocystis (Laminariales,Phaeophyceae)

Giant kelp, Macrocystis pyrifera (Linnaeus) C. Agardh, is the subject of intense breeding studies for marine biomass production and conservation of natural resources. In this context, six gametophyte pairs and a sporophyte offspring of Macrocystis from South America were analyzed by flow cytometry. Minimum relative DNA content per cell (1C) was found in five males. Unexpectedly, nuclei of all female gametophytes contained approximately double the DNA content (2C) of males; the male gametophyte from one locality also contained 2C, likely a spontaneous natural diploid variant. The results illustrate a sex‐specific difference in nuclear DNA content among Macrocystis gametophytes, with the chromosomes of the females in a polytenic condition. This correlates with significantly larger cell sizes in female gametophytes compared to males and resource allocation in oogamous reproduction. The results provide key information for the interpretation of DNA measurements in kelp life cycle stages and prompt further research on the regulation of the cell cycle, metabolic activity, sex determination, and sporophyte development.     

GAMETOPHYTES AND YOUNG SPOROPHYTES OF OPHIOGLOSSUM CROTALOPHOROIDES WALT.

The lens-shaped, dorsiventral gametophytes of Ophioglossum crotalophoroides are superficially different from the cylindrical gametophytes of other species of Ophioglossum. However, they have the same features as other Ophioglossum gametophytes (fundamentally axial organization, radially symmetrical apical meristem, radial distribution of gametangia) except that the cylindrical axis is reduced in length. Young sporophyte development is unique in the genus: all primary organs clearly arise from the embryo and develop simultaneously. The length of the life cycle of O. crotalophoroicles is considerably shorter than that of some other species in the Ophioglossaceae. A timetable for gametophyte and young sporophyte development is postulated. Spores germinate soon after they are released in the spring, and mature gametophytes develop by the next growing season. Fertilization occurs approximately one year after spore dispersal, and after two years, the photosynthetic first leaf of the young sporophyte emerges.     

THE INFLUENCE OF CULTURAL CONDITIONS ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Apogamous sporophytes formed on Pteridium gametophytes in response to concentrations of certain sugars which supported gametophytic growth. High osmotic concentration of the medium inhibited apogamy, while variations in the basic medium were not stimulatory. Agar, autoclaving, the ammonium ion, and dry media were not required for apogamy. Renewing the medium during an experiment enhanced the apogamous response. Changing the medium at set intervals facilitated the separation of apogamous plant development into gametophytic, initiative, and developmental phases, thus enabling testing of various factors at each of these stages. Apogamy was light-initiated, while the actual development of apogamous sporophytes was caused by light, succinic acid or sugar.     

ACTION OF PURINE AND PYRIMIDINE ANALOGS ON THE GROWTH AND DIFFERENTIATION OF THE GAMETOPHYTES OF THE FERN ASPLENIUM NIDUS

The purine analogs, 8-azaadenine, 8-azaguanine, 8-azaxanthine and 8-azahypoxanthine, and the pyrimidine analogs, 2-thiocytosine, 5-fluorouracil, 2-thiouracil and 6-azauracil, inhibited the induction of 2-dimensional growth in the gametophytes of the fern Asplenium nidus L. In contrast, thymine analogs such as 5-fluorodeoxyuridine, 2-thiothymine, 6-azathymine and 5-bromouracil caused non-specific growth inhibitions without suppressing 2-dimensional growth. Subinhibitory concentrations of 8-azaxanthine, 8-azahypoxanthine, and 2-thiouracil promoted both 1-dimensional and 2-dimensional phases of growth of the gametophytes. Inhibitory effects of the analogs were observed on treatment of the spores or of gametophytes of different ages. Gametophytes growing in the analogs for different periods of time recovered from inhibition on transfer to the basal medium.     

PHOTOCONTROL OF THE ORIENTATION OF CELL DIVISION IN ADIANTUM. III. EFFECTS OF METABOLIC INHIBITORS

5-Fluorouracil, 8-azaguanine and ethionine were tested on the orientation of cell division to see whether the two-dimensional development of the fern Adiantum gametophytes was due to newly synthesized protein(s). Using the system in which the orientation of cell division was controlled experimentally by sequential treatment with red light, white light and darkness and by the direction of irradiation, all the inhibitors decreased the rates of cell elongation and cell division of the gametophytes, but did not specifically affect the two-dimensional differentiation at all.     

GAMETOPHYTES AND SUBGENERIC CONCEPTS IN LYCOPODIUM

A critique of the Freeberg and Wetmore work on cultured Lycopodium gametophytes of L. selago, L. flabelliforme, and L. cernuum is presented. All three gametophytes are shown actually to be L. cernuum based on morphological and anatomical features of their sporophytes. A reassessment of characters in the genus demonstrates the taxonomic validity of the three groups proposed as subgenera within Lycopodium.