Seed ecology of dust seeds in situ: a new study technique and its application in terrestrial orchids

A method is described by which seeds of terrestrial orchids are sown and retrieved in the field under almost natural conditions. For the first time it is possible to conduct a quantitative study of orchid germination in situ and observe seasonal growth and mortality of seedlings. The technique has also enabled us to investigate the relation between the site where the seeds are sown, the availability of an appropriate fungus to infect the seeds, and seedling establishment in the soil. Five local species were studied. Corallorhiza odontorhiza, Goodyera pubescens, and Galearis spectabilis all began to germinate in May–June, after 23-30 weeks in the soil. These species differed in their dependency on infection at germination time, but none of the seedlings developed beyond the point of rupturing the testa except when infected. Seeds of Liparis lilifolia and Tipularia discolor did not germinate within the first 12 months of the experiment. The implications and potential uses of this field sowing technique for further studies and for other kinds of minute seeds are discussed.     

In vitro germination of some Western European orchids

Several germination factors were studied in 23 Western European orchids in order to obtain a germination percentage which approximates the maximum percentage of coloured embryos after an adaptation of the tetrazolium test. The duration of seed pretreatment with Ca(OCl)₂+ Tween-80 was one of the most important factors controlling the germination of Western European orchids. Best germination occurred in continuous darkness at 23°C on dilute media. The nitrogen source had a species related influence. The best results were obtained with casein hydrolysate, although it could nearly be replaced by one amino acid, L-glutamine. A cytokinin was required by Cypripedium calceolus and Epipactis hellborine but was not necessary for Lisiera ovata and Dactylorhiza maculata.
Experiments with 3 species have shown that the objective, to obtain a germination percentage, which approximated the maximum percentage of coloured embryos, was achieved. This has led to the elaboration of a basic sowing method for European orchids. The application of this method gave good germination responses with 21 of the 23 species tested.     

Cryopreservation of seeds and protocorms of rare temperate orchids

The efficiency of cryopreservation of seeds of five rare and endangered species of temperate orchids belonging to Platanthera and Dactylorhiza genera followed by their asymbiotic culture in vitro, as well as of in vitro cultured D. fuchsii protocorms (specific stage of orchid embryo development after release from the seed coat) was investigated. Germination rates of seeds after their exposure to liquid nitrogen were species-depended and could be either higher or lower than in the unfrozen control. There was no significant difference between growth rates of protocorms of the same species obtained from seeds collected in various Russia regions and cultured for 5 months. After vitrification, 9% of D. fuchsii protocorms with a larger diameter of 1200 μm survived cryopreservation; however, their growth was retarded for three months when compared to control protocorms.     

Ecology of germination of weed seeds

Summary Merremia gangetia Linn. (Cuf) is one of the most important weeds invading cultivated lands of India. Temperature, both high (45° C) and low (15° C) exhibit a definite role in development of the weed, particularly during germination. Higher tempeeratures (45° C) during dry storage appeared to be the main factor in laboratory experiments as well as in nature. Low temperature induced secondary dormancy and its removal by incubation at 35° C helps to explain the ecological mechanism through which the weed endures winter conditions. Germination of buried seeds confirm that the atmospheric conditions were found to be more effective in upper layers of soil. Ecological adaptations of this weed via germination requirements are assessed in the paper.     

Synchronization of germination of celery seeds

The effects of osmotic pre-treatments on the germination response of celery seeds were studied in a series of experiments designed to optimize that treatment. The experimental variables were different osmotica (polyethylene glycol (PEG) or a mixture of potassium nitrate and tri-potassium orthophosphate), levels of osmotic potential, temperature and duration of treatment. The rate and synchronization of germination were very significantly improved by many of these pre-treatments but the maximum effects on cv. Lathom Blanching were obtained by treating the seeds with a solution of the salt mixture of c.–10 bars potential at 15 °C for 21 days. This treatment resulted in 50 % germination of the viable seeds within 1–4 days at a temperature of 20 °C compared with 13-7 days from the untreated seeds. There were indications that the optimum pre-treatment may vary somewhat between varieties and seed stocks. The results showed that the effects of the two osmotica on germination response were similar, thus enabling a technique to be developed for treating, with the salt solution, larger quantities of seed and germinating them prior to fluid drilling in the field.     

Treatment of cotton seeds for germination

Summary Effects of H₂SO₄, H₂O₂, C₂H₅OH and of acetone on germination of cotton seeds and on the growth of seedling root were studied under laboratory conditions. H₂SO₄ or H₂O₂ hastened germination but decreased the ultimate number of seeds germinated. Higher temperature (27°C) hastened germination and increased the number of seeds germinated. Root length remained unaffected by treatments at room temperature while H₂SO₄ or H₂SO₄/H₂O₂ substantially decreased it at 27°C.     

Tensor decomposition reveals concurrent evolutionary convergences and divergences and correlations with structural motifs in ribosomal RNA

Evolutionary relationships among organisms are commonly described by using a hierarchy derived from comparisons of ribosomal RNA (rRNA) sequences. We propose that even on the level of a single rRNA molecule, an organism's evolution is composed of multiple pathways due to concurrent forces that act independently upon different rRNA degrees of freedom. Relationships among organisms are then compositions of coexisting pathway-dependent similarities and dissimilarities, which cannot be described by a single hierarchy. We computationally test this hypothesis in comparative analyses of 16S and 23S rRNA sequence alignments by using a tensor decomposition, i.e., a framework for modeling composite data. Each alignment is encoded in a cuboid, i.e., a third-order tensor, where nucleotides, positions and organisms, each represent a degree of freedom. A tensor mode-1 higher-order singular value decomposition (HOSVD) is formulated such that it separates each cuboid into combinations of patterns of nucleotide frequency variation across organisms and positions, i.e., "eigenpositions" and corresponding nucleotide-specific segments of "eigenorganisms," respectively, independent of a-priori knowledge of the taxonomic groups or rRNA structures. We find, in support of our hypothesis that, first, the significant eigenpositions reveal multiple similarities and dissimilarities among the taxonomic groups. Second, the corresponding eigenorganisms identify insertions or deletions of nucleotides exclusively conserved within the corresponding groups, that map out entire substructures and are enriched in adenosines, unpaired in the rRNA secondary structure, that participate in tertiary structure interactions. This demonstrates that structural motifs involved in rRNA folding and function are evolutionary degrees of freedom. Third, two previously unknown coexisting subgenic relationships between Microsporidia and Archaea are revealed in both the 16S and 23S rRNA alignments, a convergence and a divergence, conferred by insertions and deletions of these motifs, which cannot be described by a single hierarchy. This shows that mode-1 HOSVD modeling of rRNA alignments might be used to computationally predict evolutionary mechanisms.     

Temperature regulation of germination in crimson clover seeds

Seeds of Dixie crimson clover (Trifolium incarnatum cv. Dixie) completed germination in 36 hours at 20 C. At 10 C germination was delayed by 24 hours. At 30 C only 20% germinated and the rest remained viable for a long time but not germinable. Different patterns of adenylate energy state and zymograms of acid phosphatase and esterase were observed from seeds grown under the three temperatures for 24 hours. Varied specific activities of protease, α-amylase, ATPase, RNase, acid phosphatase, glutamine synthetase, and fumarase were also found. Protein-synthesizing ability was proportional to temperature. These data indicate that temperature regulates seed germination at multiple sites.     

徐长卿种子生活力检测及发芽生物学特性观察

对徐长卿[Cynanchum paniculatum(Bge．)Kitag．]种子生活力与发芽生物学特性进行了观察。结果表明：秋收徐长卿种子贮藏至次年3和4月,生活力分别为87％和80％;种子表面用1％H2O2除菌预处理,有利于正常发芽,发芽率达82％,发芽时间提前1d,第3日出现发芽高峰。温度从15℃至30℃,发芽率逐渐升高;25℃时,种子第2天即开始发芽,出现最短发芽持续时间(5d)和最高发芽势(75％),因此,25℃是徐长卿种子发芽的最适温度。     

Isoenzyme changes accompanying germination of wheat seeds

Electrophoretic patterns of soluble proteins and enzymes during development from dry seed to first leaf were studied in wheat by means of disc electrophoresis. The patterns considered were those of alcohol dehydrogenase (ADH), peroxidase, and nonspecific esterases. Multiple forms (isoenzymes) were found for all these enzymes in dry seeds. The ADH pattern did not change during development. Esterases and peroxidase patterns changed both qualitatively and quantitatively. Increase in the number of peroxidase bands was marked.Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission.     

Volatile metabolites controlling germination in buried weed seeds

Velvetleaf (Abutilon theophrasti Medic), morning glory (Ipomoea purpurea [L.] Roth), and wild mustard (Brassica kaber [D.C.] L. C. Wheeler) seeds exhibited decreased germination with increased planting depth in soil. Flushing the soil for 2 minutes each day with air overcame the inhibition. A sealed in vitro system was used to sample the volatile components produced by weed seeds. Inhibition of seed germination was accompanied by decreased O₂ levels and production of volatile metabolites identified as acetaldehyde, ethanol, and acetone. The effectiveness of these compounds in reducing germination was dependent on O₂ levels.     

Comparative reproductive biology reveals two distinct pollination strategies in Neotropical twig-epiphyte orchids

Members of Oncidiinae are widely known for their interactions with oil-collecting bees that explore lipophilic secretions on flowers. They may also be pollinated through food deception and the offering of nectar. Although data on breeding systems are available for many Oncidiinae orchids, little is known about the reproductive strategies in Rodriguezia, a neotropical genus of ca. 55 species. In this paper, we explore the reproductive biology of two species of Rodriguezia with distinctive morphologies: R. decora and R. lanceolata. Floral features, spectral reflectance, pollinators and pollination mechanisms, and breeding systems were studied. Both species are scentless and produce nectar as a reward. Floral nectar is secreted by a gland at the base of the labellum and stored into the sepaline spur. Rodriguezia decora reflects mainly in the blue and red regions of the light spectrum, while R. lanceolata reflects in the red region. Rodriguezia decora is exclusively visited and pollinated by butterflies, while Trochilidae hummingbirds are the pollinators of R. lanceolata. Pollinaria attach to the upper third of the proboscis of butterflies (R. decora), and to the bill of hummingbirds (R. lanceolata), during the collection of nectar from the spur. Both Rodriguezia species are self-sterile. Flower features and floral reflectance support the occurrence of psychophily in R. decora and ornithophily in R. lanceolata.     

Underdeveloped embryos and germination in Aristolochia galeata seeds

Aristolochiaceae have been described as having seeds with underdeveloped embryos and morphological or morphophysiological dormancy. Aristolochia galeata is a native climber found in the Cerrado biome, associated with road and gallery forest edges. The aims of this study were to investigate: embryo growth rate, morphology and seed germination parameters under different treatments. Embryos were excised to obtain embryo length at four stages: initial, seeds after coat rupture, radicle tip protrusion and cotyledon emergence from the seed coat. Germination tests were conducted at 30 °C under three nitrate concentrations (1, 10 and 20 mM), fluctuating temperature (27/20 °C) and light and dark conditions. We found that seeds have underdeveloped embryos, which take about 301 ± 178 h (±SD) to achieve seed coat rupture, another 205 ± 126 h to reach radicle protrusion and 176 ± 76 h more to the final stage of cotyledon emergence. Germinability was above 52% in all treatments, except in the dark (15%). For all treatments, average germination time was above 290 ± 123 h. Potassium nitrate increased germinability to >87%. No particular treatment was required for embryo development, but seeds in the population that continued to germinate after 1 month were probably in various states of non-deep, simple morphophysiological dormancy. Increased germinability in nitrate treatments and light requirement for germination could prevent germination under unsuitable environmental conditions and be a strategy to increase seedling establishment in the cerrado.     

Involvement of cytokinins in the germination of chick-pea seeds

Eight cytokinins detected in germinated chick-pea (Cicer arietinum L. var. Castellana) seeds were first present in the embryonic axes but appeared in the cotyledons after 12h of germination. The cytokinins detected in the cotyledons originate in the embryonic axes, but no passage of these substances from the cotyledons to the axes was detected, except when the seeds were treated with red light.It is concluded that the role played by the embryonic axis in mobilizating the main reserves of the cotyledons is mainly effected through these cytokinins. Both natural and synthetic cytokinins exert an important regulatory role in the hydrolysis of reserve proteins and calcium could be involved as an intermediate.Abbreviations BA benzyladenine - cot. cotyledon - (diH)Z dihydrozeatin - (diH)ZR dihydrozeatin riboside - GZR glycosyl zeatin riboside - 2iP 277-1 - iPA 277-2 riboside - Kin kinetin - Z zeatin - ZG zeatin glucoside - ZR zeatin riboside     

Physical forces in dormancy and germination of xanthium seeds

The germination of seeds of Xanthium pensylvanicum Wallr. occurs in 2 phases, an initial passive phase of water uptake followed by an active phase of growth. These 2 phases have been separated experimentally, and shown to occur similarly in isolated cotyledons and embryonic axes. Measurements of the physical thrust generated by the entire seed and its separate components of cotyledon and axis reveal that non-dormant Xanthium seeds develop more than twice the thrust of dormant seeds, and that this difference develops principally in the second phase of enlargement of the axis. Measurement of the forces required for piercing the testa of these seeds establishes that whereas the thrust developed by non-dormant seed is adequate to cause testa rupture, that developed by dormant seeds is not. It is concluded that the dormancy of Xanthium involves an inadequacy in the embryo for rupture of the testa.