Factors affecting germination and stand establishment ofphyllanthus Amarus (Euphorbiaceae)

Interest inPhyllanthus amarus (Euphorbiaceae) has been generated by reports of antiviral activity and wide usage in traditional medicine. Attempts at cultivation resulted in poor stands. The objectives of these studies were to determine the effects of light, storage temperature, age of seeds, time ofdehiscence, and a scarification procedure on the germination ofP. amarus. Seeds ofP. amarus require light to germinate, and thus should not be covered at sowing. Freezing did not significantly affect the germination of dry seeds compared to seeds stored at ambient room temperature or higher, but storage at 10°C was deleterious. Percent germination was typically less than 50% and significantly decreased with time. Germination of freshly harvested seeds was slower than older seeds. Seeds from the first capsules to dehisce had a higher percent germination. A scarification procedure rendered seeds inviable. These results helped explain poor stands seen infield plots. In a previously planted plot, the re-established stand by natural reseeding was equivalent to that following intentional reseeding procedures.     

Effect of light on seed germination and seedling growth ofMerremia species

The seeds ofMerremia aegyptia are indifferent to light conditions for germination, which becomes 100% in the first 24 hrs. On the contrary, inM. dissecta the highest percentage was found in red light within the first 24 hrs. This difference was lost later on except in far-red. The seedling growth of the two species was least in blue and red lights, respectively. However, the growth of hypocotyl in the former species was faster than the latter.     

Contribution to the ecology and seed germination ofCucumis callosus

Ecology and germination behaviour of the seeds of two categories ofCucumis callosus Cogn. has been studied here. The seeds were found to be rigid in their requirement of light and temperature for germination. Red and far-red lights were found to affect germination and a phytochrome system appeared to be present. Temperature was found to have a significant effect on seed germination.     

Dispersion,germination and growth of seedlings ofSagittaria lancifolia L.

Sagittaria lancifolia L. a perennial helophyte growing in shallow waters has asexual reproduction by rhizomes and sexual reproduction by achenes. We studied the morphological characteristics of achenes related to its dispersion, some factors affecting its germination and the development stages and growth of seedlings. This species produces many achenes, and disperses through epizoochory and hydrochory. Achenes germinate on light only. 100% germination was obtained at 25°C. Under conditions of inundation the germination period decreases, and the percentage of germination in creases when compared to achenes with or without imbibition. Achenes in anaerobic conditions have reduced germination. The growth of seedlings ofS. lancifolia was affected by the temperature: each organ of the seedlings grows differently in dependence upon this factor. For example, roots grow faster during the early stages of the seedlings.     

The effect of ethanol on germination of aleppo pine seeds (Pinus halepensis Mill.)

Ethanol can influence germination of seeds ofPinus halepensis. When supplied by the appropriate procedure, the anaesthetic is able to mimic light in stimulating seed germination. This action is interpreted in terms of changes in membrane properties.     

Contribution to the biology of germination of four species ofChenopodium album agg. under different condition

The study investigated various factors stimulating germination of seeds of four species ofChenopodium album agg.—C. album L. s. str.,C. ficifolium Sm.,C. strictum Roth,C. suecicum J. Murr. These factors were: storage in wet and cold, alternating temperature, nitrates mainly in combination with light and, to a lesser degree, the duration of chilling. Germination was inhibited by darkness, which was most marked with seeds ofC. strictum. The effect of alternating temperature was better on the germination ofC. ficifolium andC. suecicum than on that ofC. album andC. strictum. We also discussed several differences in specific reactions of the individual species to the factors under consideration.     

Atmospheric condition controlling the seed germination of an achlorophyllous orchid,Galeola septentrionalis

The aseptic seed germination ofGaleola septentrionalis was observed only in an airtight vessel at 30 C, germination being enhanced with increasing air pressure in the vessel up to the optimum of 1.8 atm. The presence of O₂ and CO₂ was essential for germination, and their optimum concentrations were 5 and 8%, respectively. The optimum pressure for germination (1.8 atm) was not influence by the composition of the air. Ethylene added at concentrations ranging from 2 to 8μl/l enhanced germination and its removal reduced the germination. The atmospheric condition required for the seed germination of this orchidin vitro was discussed with regard to that in its natural habitat.     

SUCCESSIVE PROCESSES INVOLVED IN THE GERMINATION RESPONSE OF NASTURTIUM SEEDS

1. The seeds ofNasturtium palustreDC. do not germinate, eitherin the light or darkness, at various constant temperatures,but require for their full germination a certain period of alow temperature (5°) applied immediately after light irradiation.These results indicate the existance of at least two processes,a light-dependent process and a low temperature-requiring process,in the initiation of germination ofNasturtiumseeds. Experimentalevidence indicated further that the light exposure causes twodifferent processes in the seed germination. 2. When a dark period at 23° was inserted between the lightirradiation and the low temperature treatment the germinationwas suppressed. The inhibitory effect of the inserted dark periodat 23° was eliminated by a short irradiation during thedarkness (light-break). 3. Prolonged exposure ofNasturtium seeds to any concentrationof gibberellin brought about no germination when exposure wasgiven in complete darkness. The germination was promoted onlywhen light irradiation was applied to the seeds. A short applicationof gibberellin at a fairly high concentration was, however,remarkably effective for the germination even in the darkness,and the germination was inhibited as the gibberellin applicationwas lengthened. It was considered that gibberellin could substitutefor the combined effect of light irradiation and low temperaturetreatment to induce the germination of Nasturtium seeds, andthat gibberellin was inhibitive toward the reactions followingthe above treatments which induced the germination (Received October 31, 1996; )     

Volatile and gaseous metabolites released by germinating seeds of lentil and maize cultivars with different susceptibilities to fusariosis and smut

The effect of volatile and gaseous metabolites released by germinating seeds of lentil cultivars more and less susceptible to fusariosis on the germination of spores ofMucor racemosus, Trichoderma viride, Verticillium dahliae andBotrytis cinerea was found to depend rather on the fungal genus than on the lentil cultivar. However, spores ofFusarium oxysporum reacted more sensitively during germination to the presence of exudates of both cultivars, when the more susceptible lentil displayed a stimulation, the less susceptible one an inhibition of spore germination. The greatest difference in the effect of exudates was observed in the more and less susceptible maize cultivars with respect to the germination of chlamydospores ofUstilago maydis, especially during the first hours of seed germination. Analysis of the exudates of germinating seeds showed the release of a greater amount of ethanol and methanol with acetaldehyde by the more susceptible cultivars of lentil and particularly maize.     

Germination and photo-induction of polarity in the spherical cells regenerated from protoplasm fragments ofBoergesenia forbesii

The processes of rounding (spheration) and cell wall formation of extracellular protoplasm fragments ofBoergesenia forbesii were examined. This spheration depended on the presence of Ca²⁺ in the medium, and was accelerated exponentially with increasing temperature up to 35 C. At 25 C the regenerated cell wall could be detected within 3 hr, after the release of protoplasm into Provasoli's ES-medium. Germination, the development of a protrusion from the round cell, had an optimal temperature of 30 C and was interrupted at temperatures below 17 C. The germination was promoted by red-light irradiation (a maximum around 625 nm). This promotion depended on both irradiation time and light intensity, and was diminished by DCMU. Therefore, it was concluded that this promotion was caused predominantly through photosynthetic activity. The rhizoidal protrusion developed on the shaded side of a unilaterally irradiated round cell. Blue light was most effective in inducing cell polarity with light of wavelengths longer than 600 nm being ineffective. This wavelength-dependency was similar to that observed for polarity induction ofFucus eggs or in phototropism ofAvena coleoptiles.     

Effects of storage on germination ofDioscorea composita (Dioscoreaceae) seeds

Effects of storage were tested on germination ofDioscorea composita (Dioscoreaceae) seeds. Freshly collected seeds and seeds stored at 25°C in paper bags from 1 to 11 mo or for 4 and 5 yr were used in most of the experiments. Seeds were tested for germination at 20, 25, 30, 35, 25–20, and 25–35°C in white light and in darkness. Initiation of germination was delayed in freshly harvested seeds, and dormancy was reduced in seeds stored for about 9 mo. Viability of the seeds decreased after 4 and 5 yr of storage.     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome     

The effect of growth retardants on phytochrome-induced lettuce seed germination

Experiments were carried out to explore the involvement of the plant hormone gibberellin (GA) in the light-induced germination of lettuce seeds. Three growth retardants known to be inhibitors of GA biosynthesis were tested for their effect on red-light-induced germination. Chlormequat chloride (CCC) and AMO-1618 had no effect, but ancymidol was strongly inhibitory. Moreover, the inhibition caused by ancymidol was completely overcome by GA₃. CCC and AMO-1618 inhibit the formation ofent-kaurene, while ancymidol blocks the oxidation ofent-kaurene toent-kaurenoic acid. Ancymidol also was found to inhibit GA-induced dark germination of lettuce seeds, and this inhibition was partially reversed by higher levels of GA. Therefore, the results suggest two possibilities for the relationship between phytochrome and GA in this system: first, the rate-limiting step in the germination of light-sensitive lettuce seeds, that which is regulated by phytochrome, is the oxidation ofent-kaurene toent-kaurenoic acid. Alternatively, red-light treatment may result in the release of active GAlike substances which, in turn, induce germination. In either case the results presented here support the view that phytochrome exerts its effect on lettuce seed germination by means of GA rather than via an independent pathway.     

Photosensibilité des graines depinus banksiana Lamb.

Germination ofPinus banksiana seeds is controlled by the photoreversible phytochrome reaction. The seeds, even unimbibed, are sensitive to red light. At 660 nm, the energy required to promote germination to the same order of magnitude is much higher for unimbibed seeds than for the imbibed ones. In both cases it is possible to reverse the effect of a single red light irradiation by applying far red light (730 nm).     

Effect of growth regulators on overcoming the light inhibition on germination ofCucumis anguria L.

The effects of some growth regulators on the dark-germinating seeds ofCucumis anguria have been investigated. GA₃, 6-BA and ethrel strongly promoted the germination of seeds kept in white light. GA₃ had no effect in counteracting the far red effect, but did counteract partially the blue light. Ethrel partially counteracted both the far red and blue light effect. No interaction could be found between red light and GA₃ or 6-BA.     

Identification ofEnterococcus sp. from midgut of silkworm based on biochemical and 16S rDNA sequencing analysis

Enterococcus sp. was isolated from the midgut of silkworm against the germination ofNosema bombycis spores. Identification was based on the biochemical characteristics, 16S rDNA sequences analysis and species-specific probes ofEnterococcus spp. The isolated strains fermented sorbitol and arabinose but did not ferment raffinose.Enterococcus sp. was clustered together withEnterococcus mundtii ATCC 43188 and 100% sequence homology was found by 16S rDNA sequences BLAST analysis and constructing the phylogenetic tree. Comparison of the sequences of the 16S rDNA species-specific probes ofEnterococcus spp. with the 16S rDNA sequence of isolate revealed similar segment to the species-specific probe ofE. mundtii. So, we can make conclusion the 16S rDNA segment ofEnterococcus sp. can hybridise with species-specific probe ofE. mundtii. Enterococcus mundtii was detected for the first time in the intestine of silkworm.     

光质、光强对入侵植物紫茎泽兰种子萌发及幼苗状态的影响

为了探讨紫茎泽兰种子需光萌发特性,对光质（不同颜色、红光/远红光）和光强对种子萌发率及幼苗状态进行了研究。研究发现：不同颜色光对发芽率影响显著,其中黄光、橙光和红光等波长在（591~750 nm）之间的光更有利于提高种子的萌发率（74.3%~83.3%）,而较短波长的光（<570 nm,紫光、蓝光和绿光）促进效果显著降低（62.3%~66.7%）（p<0.05）。光强对紫茎泽兰种子发芽和幼苗影响较光的颜色更具有规律性。黑暗条件下发芽率22%,随着光照提高,发芽率指数增加(r²=0.96),芽长指数下降(r²=0.99)、根长指数增加(r²=0.98),而鲜重呈现线性增加(r²=0.70)。适量红光（630 nm）和远红光（730 nm）照射能够打破和引起休眠,红光照射量与发芽率提高量成线性正相关（r²=0.98）,而远红光照射率与发芽率降低量呈线性正相关（r²=0.92）,说明紫茎泽兰需光萌发是一个光敏色素引起的过程。紫茎泽兰通常在裸地和人为干扰土壤上泛滥,这可能与其种子需光萌发有关。而对其生态学控制可以考虑从光强、特别是光质角度（如人工造林）控制种子萌发来实现。     

Reversal by Light of Ethylene-induced Inhibition of Spore Germination in the Sensitive Fern Onoclea sensibilis: An Action Spectrum

Spores of the fern Onoclea sensibilis L. normally germinate to produce two cells of unequal size. The larger cell divides to produce the familiar heart-shaped prothallus. The smaller cell elongates and differentiates into the rhizoid but normally does not divide again. Onoclea spores germinate in complete darkness. Dark germination can be completely inhibited by ethylene gas (10 microliters per liter is saturating). This inhibition can be reversed by light. Broad band colored light studies were designed to determine which area of the spectrum was most effective in overcoming ethylene inhibition. White light treatment resulted in 17% germination. Blue light treatment resulted in 1% germination. Red light treatment resulted in 15% germination. Red light, therefore, was most effective and accounted for most of the effects of white light. A detailed action spectrum was constructed using narrow band interference filters in the wavelength range from 350 to 764 nanometers. The action spectrum has only one major peak at 711 nanometers.     

光和不同打破种子休眠方法对紫茎泽兰种子萌发及幼苗状态的影响

紫茎泽兰是著名的外来入侵植物,作为入侵的第一步,发芽及其幼苗生长应该与其强入侵能力有关.基于此,通过不同光照强度处理和不同打破休眠方法的双因素实验,旨在探讨紫茎泽兰种子是否具有需光萌发特性以及低温、水杨酸、聚乙二醇,硝酸钾等常规打破休眠方法和光照如何共同影响其萌发、幼苗生长等问题.结果表明:在全光照条件下,不同处理的紫茎泽兰种子的萌发率均大于63％,铝箔纸覆盖的遮光条件(0.23％光照)萌发率均大于60％,而在完全黑暗条件下,其萌发率较低(均小于30％),这表明紫茎泽兰种子具有需光萌发的特性.有别于以往对其它植物种子的报道,低温处理、水杨酸处理、聚乙二醇处理和硝酸钾处理不能代替光照打破种子休眠,显示紫茎泽兰种子可能处于一种强迫休眠状态(种子静态).全光照与水杨酸处理、PEG处理对幼苗生长具有交互影响:黑暗下水杨酸处理浓度与幼苗生物量成正相关(P＜0.05),但全光照和加铝箔下不相关(P＞0.05);全光照下PEG处理浓度与根长显著正相关(P＜0.05),而加铝箔和黑暗下不相关(P＞0.05).紫茎泽兰种子需光萌发特征及其幼苗生长特点是人为破坏表土壤、深层土壤种子库地表化导致快速入侵的基础.结果也为通过引入适宜树种造林来控制光照因子对紫茎泽兰进行生态控制提供了理论依据.     

Paedogenetic conidiation inNeurospora crassa

Under conditions of growth limitation the germ tubes ofNeurospora crassa macroconidia may convert to functional conidiophores with developing chains of viable, new conidia. The induction of this paedogenetic conidiation in liquid culture does not require exposure to high temperature, as reported for conidia of some other ascomycetous fungi, but it is induced at normal growth temperatures within 12–15 h by germination of the conidia in a dilute, nutrient-poor incubation medium. The inoculum density, temperature of incubation, presence or absence of white light, and genetic strain ofN. crassa also influence the kinetics of conidium formation.