Germination of Epiphytic Bromeliads in Forests and Coffee Plantations: Microclimate and Substrate Effects

This study explores whether differences in germination ability shape habitat distributions among closely related epiphytic species, particularly in the context of the ability to colonize disturbed habitats. We compared the germination of three epiphytic bromeliad species differing in their ability to colonize secondary arboreal vegetation in natural forests, and in old and young coffee plantations. We asked if germination is related to their distribution within the canopy and between habitats, and the extent to which the substrate (branch) or microclimate affects germination success. Tillandsia viridiflora, a species that is largely restricted to closed forests, had highest germination success in natural forests, Tillandsia juncea, a pioneer species, germinated best in young coffee plantations, and Tillandsia heterophylla, an intermediate species, equally in forests and young plantations. Surprisingly germination rates of all three species were lowest in old plantations. Bryophyte cover on branches had a positive effect on germination of T. viridiflora and T. heterophylla, but T. juncea germination rates were largely independent of climate and substrate. These results show that germination can limit the ability of species to colonize disturbed habitats and also contributes to within‐canopy distribution. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Does proximity to a mature forest contribute to the seed rain and recovery of an abandoned agriculture area in a semiarid climate?

Proximity to forests contributes to the recolonisation of anthropogenic‐disturbed areas through seed input. We evaluated the role of proximity to a mature forest in the recolonisation of an agricultural area that has been abandoned for 18 years and is currently a young forest. Seed rain was monitored at fixed distances from the mature forest. The type of surface recolonisation (germination versus resprouting) and the reproductive season were measured in both forests. The majority of plants recolonising the young forest originated from seed germination. Proximity to the mature forest contributed to the seed rain in the young forest; however, 18 years has not provided sufficient time for the recolonisation of 80 species present in the mature forest. Some species shared between forests differed in their fruiting season and seed dispersal. The seed rain had a total species richness of 56, a total density of 2270 seeds·m^?2·year^?1 and predominance of self‐ and wind dispersal. A significant reduction in seed rain with increasing distance from the mature forest was observed. The young forest contained 35 species not observed in the mature forest, and the floristic similarity between the two forests was 0.5, indicating that the two forests are floristically distinct.     

Seed of Cercis siliquastrum L (Leguminosae,Caesalpinioideae): Reserves and their Utilization after Germination

An ultrastructural study on the reserves stored in cotyledons and endosperm and on their utilization after germination has been carried out in Cercis siliquastrum seeds. The observations have shown that all the cotyledonal reserves of proteins and lipids are used during seedling growth. However, inside the endosperm cells only the protein reserves are depleted, and large quantities of lipids remain undigested. In both cell walls and intercellular spaces of the endosperm cells huge masses of polysaccharide reserves are stored. However, only the polysaccharides inserted in the cell walls are dismantled, while those located in the intercellular spaces are not attacked by the lytic enzymes. Some hypotheses regarding the possible roles of those endospermic non-nutritional materials in the strategies of seed germination and seedling growth are suggested.     

Drought tolerance of germinating seeds and young seedlings of Anastatica hierochuntica L.

Summary Drought tolerance of germinating seeds and young seedlings of Anastatica hierochuntica L. was studied under controlled conditions. When seeds at various stages of germination were air-dried, or alternatively were desiccated over CaCl₂ to the same or a lower water level than in the air-dried seeds, and after various periods of storage were rewetted, they readily continued germination or growth. Similarly, 60% of dried young seedlings with rootlets 4–6 mm long that had been dehydrated for one week, renewed their growth 8 h after wetting, their shrivelled, dried rootlets imbibing water. Recovery was adversely affected by both longer periods of germination prior to the dehydration, or by the longer duration of storage of the redried seeds/seedlings. The higher rate of dehydration also reduced recovery. It is argued that despite this tolerance of seedlings to drought, the Rose of Jericho cannot be considered a resurrection plant. Compared with other desert annuals, this behavior is specific for Anastatica. However, it may occur also in other annual species of populations sequestered within the driest of desert habitats.     

Dry mass changes in germinating spores of Diplodia maydis

Summary The dry mass of two-celled Diplodia maydis spores was measured both before and after germination by quantitative interference microscopy. The dry mass of spores declined approximately 50% during germination. However, the dry mass of germinating spores plus the dry mass of their germ tubes was greater than the dry mass of spores before germination. We conclude that the germinating spores absorbed nutrients released from non-germinating spores.The dry mass of fungal spores can be estimated by weighing large numbers of spores and determining the mean from sample spore counts. Mumford and Pappelis(4) determined the total dry mass of individual spores of Fusarium roseum and the contained lipid bodies before and after spores germinated using quantitative interference microscopy. The mean spore dry mass before germination was 57 pg. Lipid bodies accounted for about 61% of that mass and decreased as spores germinated. The total dry mass of the spore and germ tube 24 hr later greatly exceeded that of the spore before germination. Quantitative interference microscopy has been used to measure the dry mass of various types of cells. Kulfinski and Pappelis (3) recently reviewed how this technique has been applied to plant cells. Technical aspects of interference microscopy have been described by Ross (6).The purpose of this study was to examine the dry mass changes in Diplodia maydis (Berk.) Sacc. with and without germ tubes through the use of interference microscopy.     

A new aspect of the life cycle ofCandida tropicalis

The life cycle ofCandida tropicalis has been elucidated by nuclear staining. We were able to distinguish 5 stages: (1) the sexually active unstable haplophase which either can mutate directly to (2) the sexually inactive haplophase, or is converted to (3) the diplophase by “autoploidization”. The unstable diplophase changes into the sexually inactive haplophase, which is stable, by “budding meiosis’. Chlamydospores (4), which are possibly formed by sexually inactive haploid cells, are true resting spores, and during their germination only mitosis takes place. The buds formed during germination may develop into either the sexually active, or the inactive haplophase. During budding meiosis in the diplophase, multinucleate giant cells (5) may occur. The authors do not consider the latter to be metabasidia. Instead, they might in some way be homologus with asci, and their daughter nuclei might be comparable with the nuclei of ascospore initials. These new nuclei migrate successively into new buds which process results in a short chain of haploid cells. True ascospores have not been found. From these findings it is likely thatC. tropicalis is closely related to the ascomycetes rather than to the Hemibasidiomycetes.     

MACROCYSTS IN THE LIFE CYCLE OF THE DICTYOSTELIACEAE. II. GERMINATION OF THE MACROCYSTS

Macrocyst germination was demonstrated in the five species of the Dictyosteliaceae known to produce these structures. The morphological changes that occurred during germination appeared to be identical in all of the strains examined, showing the following stages: (1) swelling of the dark, contracted content of the dormant cysts, (2) gradual loss of color and reappearance of cells within what previously appeared as a homogeneous protoplasmic mass, and (3) rupture of the heavy cellulosic cyst wall to liberate the myxamoebae. The age of the macrocyst appeared to be the most critical factor in determining whether or not germination would occur, since the cysts in many of the strains needed to age for several weeks or months before germination could be demonstrated. In Dictyostelium mucoroides strain DM-7, upon which the current study was centered, light was necessary to stimulate germination of young macrocysts—a requirement that gradually diminished as the cysts aged. The rate of germination and the temperature permitting germination were also age dependent: older macrocysts germinated more rapidly and at considerably higher temperatures than did young cysts. Although light was not essential for germination in every strain, the results obtained with strain DM-7 seem to be generally applicable to the germination process.     

Germination and physiological properties of Frankia spores

Spores from four Frankia strains were isolated and purified to homogeneity. The purified spores were biochemically and physiologically characterized and compared to vegetative cells. Frankia spores exhibited low levels of endogenous respiration that were at least ten-fold lower than the endogenous respiration rate of vegetative cells. The macromolecular content of purified spores and vegetative cells differed. One striking difference among the Frankia spores was their total DNA content. From DAPI staining experiments, only 9% of strain ACN1^AG spore population contained DNA. With strains DC12 and EuI1c, 92% and 67% of their spore population contained DNA. The efficiency of spore germination was correlated to the percentage of the spore population containing DNA. These results suggest that the majority of strain ACN1^AG spores were immature or nonviable. The presence of a solidifying agent inhibited the initial stages of spore germination, but had no effect once the process had been initiated. The optimal incubation temperature for spore germination was 25°C and 30°C for strains DC12 and EuI1c, respectively. A mild heat shock increased the efficiency of spore germination, while root extracts also stimulated spore germination. These results suggest that strains DC12 and EuI1c may be suitable strains for further germination and genetic studies.     

Selective autophagy in the aid of plant germination and response to nutrient starvation

Selective autophagy, mediated by Atg8 binding proteins, has not been extensively studied in plants. Plants possess a large gene family encoding multiple isoforms of the Atg8 protein. We have recently reported the identification of two new, closely homologous Arabidopsis thaliana plant proteins that bind the Arabidopsis Atg8f protein isoform. These two proteins are specific to plants and have no homologs in nonplant organisms. The expression levels of the genes encoding these proteins are elevated during carbon starvation and also during late stages of seed development. Exposure of young seedlings to carbon starvation induces the production of a newly identified compartment decorated by these Atg8-binding proteins. This compartment dynamically moves along the endoplasmic reticulum membrane and is also finally transported into the vacuole. Enhanced or suppressed expression of these Atg8-binding proteins respectively enhances or suppresses seed germination under suboptimal germination conditions, indicating that they contribute to seed germination vigor.     

Cytology of Spore Germination in Clostridium pectinovorum

The process of spore germination in Clostridium pectinovorum has been followed by phase-contrast and electron microscopy. Unlike most other Bacillaceae, germination of this species takes place within the sporangium. Under phase-contrast, the spore darkens and swells slightly, and then the vegetative rod slips out through the end opposite the collar-like extension of the sporangium. In thin sections, a spore from an early stage in germination consists of a central protoplast, core membrane, germ cell wall, cortex, and two coats. Within a short period, the cortex disintegrates and the young cell develops. It possesses a large fibrillar nucleoplasm and several mesosomes. Subsequently, the young cell elongates, becomes somewhat deformed, and then emerges through a narrow aperture in the inflexible coats of the spore, finally rupturing the sporangium. Free vegetative cells of C. pectinovorum resemble in their structure other gram-positive rods.     

Regulation of Gene Expression in Developing Zea mays Embryos: Protein Synthesis during Embryogenesis and Early Germination of Maize

Polypeptides synthesized in dissected embryos of Zea mays at different stages of embryogenesis and early germination have been characterized by their migration in two-dimensional gel electrophoresis. This analysis has been carried out with in vivo labeled polypeptides from excised embryos and with proteins synthesized in vitro in the rabbit reticulocyte system directed by poly(A⁺) RNA isolated from the different developmental stages. We have identified three main sets of expressed polypeptides: (a) embryonic set: this group of polypeptides is synthesized in young and mature embryos but not in early germination; (b) maturation set: this group of polypeptides is not present in young embryos and appears during the maturation period. Some of these polypeptides are still present in early germination while others disappear from stored mRNAs in dry embryos. One particular group from this set can be induced prematurely in young embryos by incubation with abscisic acid; and (c) germination set: this group of polypeptides is not expressed in the maturation period and appears after brief imbibition of the dry embryos.     

ULTRASTRUCTURAL INVESTIGATIONS ON THE TWO-NUCLEATE POLLEN GRAIN OF TILLANDSIA CAPUT-MEDUSAE MORR. (BROMELIACEAE)

The fine structure of the pollen grain of Tillandsia caput-medusae Morr. (Bromeliaceae) prior to germination has been studied. The development, after the first mitosis, is here schematized in three stages which are in accordance with the main steps described in angiosperms. The ultrastructural modifications occurring in the generative and vegetative cells are discussed in view of their different destiny. The results obtained are compared with the data known about tropical orchids and epiphyteic plants like Tillandsia. The following differences have been observed: a large vacuole in the vegetative cell; rapid thinning of the wall between the generative and vegetative cells; great quantity of ribosomes and rough endoplasmic reticulum surrounding the vacuoles in the generative cell. The above-listed ultrastructural features may have a meaning, considering the peculiar environmental conditions in which the epiphytism of Tillandsia is achieved.     

The life cycle of Gyrodinium instriatum (Dinophyceae) in culture*

The life cycle events of an unarmored dinoflagellate Gyrodinium instriatum Freudenthal et Lee has been investigated using clonal cultures. After the inoculation of vegetative cells into fresh medium, clumping of gametes was observed after a period of 10 days. In the clumps, a number of gametes were observed to be swimming in close contact with each other, pairing successively and then forming a plano-zygote. This clumping behavior is considered to be useful in the performance of sexual reproduction, particularly in the event of low cell density, because it increases the chance of fusion. Gametes of this species were most often isogarnous, although apparent amsogamous fusions were occasionally observed. When planozygotes were isolated and placed in fresh medium, they enlarged their size and finally divided into two cells. The daughter cells continued to multiply by binary fission and produced vegetative cells. Thus, G. instriatum has an alternative cycle between vegetative cells and zygotes without a hypnozygote stage. However, cysts of this species were transformed from large motile cells (pre-cyst cells) which are oblong and dorso-ventrally flattened in shape. These mottle pre-cyst cells have two longitudinal flagella, which may indicate that cysts of this species are of zygote origin. On the basis of these results, the relationship between zygotes and pre-cysts of G. instriatum is discussed. Excystment was enhanced by dark and cold treatments prior to the incubation for germination experiments with a germination success rate of 26–64%. Encystment was greatly inhibited by the lack of dark and cold treatments.     

Discovery of sporothecae in adult femaleTrochometridium Cross,with notes on analogous structures inSiteroptes Amerling (Acari: Heterostigmata)

Adult female mites of the genusTrochometridium Cross possess a pair of internal sacs between the bases of legs III and IV, which are adapted for carrying spores, apparently ascospores, of an undetermined fungus. A three-way symbiotic relationship exists between the mite, the fungus, and various bees (and possibly other holometabolous insects) which nest in relatively dry alkaline soils. The mite transports spores of the fungus to suitable sites for germination — cells of ground-nesting bees containing a bee egg or young larva which dies as a result of development of the fungus and mite. The mite may also stimulate mycelial growth, possibly by killing the young bee or by secreting a substance when feeding. The fungus provides the preferred mycelial substrate on which the mite feeds and undergoes its life cycle. This mutualistic association between the mite and fungus is at the expense of the bee, which transports the other two entities to favorable sites for their development — its newly made and provisioned cells. The sporothecae and specialized association ofTrochometridium mites with a fungal pathogen or saprophyte of another host organism are compared with those ofSiteroptes mites, which are considerably better understood.     

Infection Process of Botrytis cinerea on Eucalypt Leaves

This study aimed to elucidate the infection process of Botrytis cinerea on eucalypt leaves. Tests were conducted to evaluate the influence of leaf side (adaxial or abaxial), leaf age and luminosity on conidial germination, appressorium formation and grey mould (GM) severity. The adaxial and abaxial surfaces of detached eucalypt leaves were inoculated with a conidial suspension of B. cinerea and kept under constant light or dark. Subsequently, the adaxial surface of young and old leaves was inoculated and kept in the dark. To evaluate the percentage of conidia germination and appressorium formation, leaf samples were collected 6 hours after inoculation (hai), clarified (alcohol and chloral hydrate) and evaluated under a light microscope. The severity of GM was assessed 10 days after inoculation. For scanning electron microscopy analysis, samples were collected from 2 to 168 hai. A higher percentage of conidia germination (92%) and GM severity (21%) occurred on the adaxial surfaces of leaves kept in the dark. There was no statistical difference between the surfaces of young and old leaves for conidia germination. No appressorium was formed by B. cinerea. The GM severity on young leaves (17.3%) was 34 times higher than on old leaves (0.5%). The micrographs showed germinating conidia emitting 1–4 germ tubes in samples at 4 hai. The fungus penetration occurred through intact leaf surfaces, and both extra‐ and intracellular colonization of the mesophyll cells by the hyphae of the pathogen were observed at 120 hai. Sporulation occurred on the adaxial and abaxial surfaces (macronematous conidiophores) and below the epidermis (micronematous conidiophores).     

Seed dormancy and germination of five selected NATURA-2000 plant species from Croatia showing different germination strategies

Abstract

NATURA-2000, the ecological network of protected areas in the European Union that has been included in the Croatian legislation, defines Community important plant species with imperative on their conservation ex/in situ. In the Botanical Garden of the Faculty of Science, University of Zagreb, five NATURA-species have been selected as research subjects for germination study to shed light on the topic of their seed ecology and consequently advance their conservation efforts: Degenia velebitica, Scilla litardierei, Klasea lycopifolia, Ligularia sibirica and Genista holopetala. The freshly matured seeds of each species were exposed to cold or warm stratification in duration of four to sixteen weeks, and their germination was investigated through different regimes of incubation parameters, i.e. illumination (light/dark) and temperature (5, 15/6, 23?°C). All species had higher germination values after cold stratification, with the exception of G. holopetala. We concluded that D. velebitica, K. lycopifolia and presumably L. sibirica seeds has non-deep physiological dormancy while S. litardierei has deep complex morphophysiological dormancy and G. holopetala has physical dormancy. The observed patterns in seeds’ behaviour are consistent with the conditions in their natural habitats in Croatia and the knowledge of these patterns is vital for successful conservation strategies in the future.     

OBSERVATIONS ON THE CHARACTERISTICS OF THE LEMMA AND PALEA OF THE LATE CENOZOIC GRASS PANICUM ELEGANS

Scanning electron microscopy (SEM) was used to study the surface features of the anthoecia (fertile lemma and palea) of Panicum elegans Elias from the Late Cenozoic deposits in Ellis County, Kansas. Examination of the lemma revealed a well developed germination lid, irregularly arranged, simple, rounded papillae and a crescent-shaped scar of attachment. The presence of a germination lid indicates that this structure has been present in some members of the Gramineae since at least the Late Miocene-Early Pliocene. Evidence is presented which contradicts current ideas regarding the distribution of the germination lid in extant Gramineae. The surface of the palea is characterized by simple, rounded papillae spaced in regular rows. The arrangement and form of these papillae are like that present in some modern Dichanthelium. Both the epidermises of the lemma and palea are composed entirely of long cells with strongly sinuous, interlocking cell walls. The pattern of cells on the lemma indicates that the systematic placement of Panicum elegans is correct.     

Seed and cone diversity and seed germination of Pinus pinea in Strofylia Site of the Natura 2000 Network

Variation in cone size, seed number per cone, seed potential, seed efficiency, seed morphology and seed germination behavior of Pinus pinea and its relation to stand conditions was analyzed. Data were collected from P. pinea forest in Strofylia, southern Greece, a forest that belongs to the Natura 2000 European network and the RAMSAR convention and is characterized by the absence of regeneration for many decades. The pine stands found in the area were distinguished into five categories according to a previous study and our observations, regarding stand age, canopy cover and the degree of stress by human pressure. The categories are: (I) young artificial, (II) closed-mature, (III) open-mature, (IV) over-mature stands and (V) highly degraded stands. Cones were collected from all stand types and their morphological characteristics as well as their seed production were measured. Seeds were extracted from the collected cones, measured and their germination behavior was tested. The findings showed that the over-mature and the high degraded stands and to a lesser extent, the closed-mature stands, produced significantly smaller cones with a lower seed potential, a lower number of filled seeds per cone, a greater number of not fully developed seeds and reduced seed morphological characteristics than the young and open-mature stands. However, the seed germination behavior of fully developed seeds was only slightly affected by the stand type.     

Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: an Experimental Test

Endozoochory and fire are crucial ecological factors determining germination success and recruitment in many plant species. Fire is a well‐known germination trigger while endozoochory may allow seed dispersal along with an increase in germination. Their interaction has rarely been addressed, however, even though both factors are pervasive in human‐transformed ecosystems like most Neotropical Dry Forests (NDF). For three common Mesoamerican tree species (Acacia pennatula, Enterolobium cyclocarpum, and Guazuma ulmifolia), we used feeding trials to assess the preference of cattle, which are their main seed dispersal agent. We also experimentally tested the interaction between gut passage and fire as triggers of germination. The fruits of the three species were eaten by cattle, but the small seeds of G. ulmifolia were ingested 10‐fold more than those of the other species. While gut passage did not have any effect on germination, heat‐shocks above 90 °C increased the number of germinating seeds by 15 percent. These results suggest that cattle may be a key dispersal vector in NDF, but that fire may be an important germination trigger. Physical dormancy in these species may have been selected for by extinct megaherbivores because it was a key trait ensuring seed survival after gut passage. However, in light of the recent expansion of cattle‐ranching and fire occurrence in NDF, it has become a useful exaptation facilitating the colonization of disturbed areas.