摘要:

AbstractSelenium (Se) has chemical properties similar to sulfur, but slight differences can lead to altered tertiary structure and dysfunction of proteins and enzymes, if selenocysteine is incorporated into proteins in place of cysteine.In some areas of California with irrigation agriculture elevated Se concentration in drainage and shallow groundwaters caused bioaccumulation of Se in wetlands and Se toxicity to wildlife. Among higher plants Se accumulators are tolerant to high Se concentrations whereas non‐accumulators are Se‐sensitive. Algae show a requirement of Se for growth and development, but no Se essentiality has been demonstrated for higher plants, possibly with the exception of Se accumulators. Higher plants take up Se preferentially as selenate via the high affinity sulfate permease. Contents of Se in agricultural crops are usually below 1 mg kg−1DW, and hence such crops are considered safe for human and animal consumption even when grown on moderately high Se soils. Sulfate salinity inhibits uptake of selenate by many plant species.Assimilation of selenate by non‐accumulators leads to synthesis of selenocysteine and selenomethionine; Se‐cysteine is readily incorporated into proteins. High Se can interfere with S and N metabolism in non‐accumulators. In contrast, Se accumulators sequester Se mainly in non‐protein selenoamino acids. Among several selenoenzymes identified in bacteria and mammals, Se‐dependent glutathione peroxidase which catalyses the reduction of organic peroxides and H2O2has been demonstrated convincingly in algae; in higher plants, however, the experimental evidence regarding its occurrence is controversial. All organisms including higher plants contain Se‐cysteyl‐tRNAs that decode UGA. Selenocysteine is proposed to function as 21st proteinaceous amino acid and thus is suggested to have a biological role in higher plants.Biogeochemical cycling of Se involves significant volatilization of methylated selenides such as dimethyl selenide to the atmosphere from higher plants as well as freshwater algae, but Se exchange between oceans and the atmosphere appears to proceed as net

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00774.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA method for enzymatic isolation of protoplasts from the unicellular green algaEremosphaera viridisfor patch‐clamp measurements is described. Viable protoplasts with “patch‐clean” plasma membranes could only be isolated when combining high enzyme concentrations and long incubation times.In whole‐cell recordings the protoplasts exhibited electrical properties similar to those measured in intact cells. Taken together with the protoplasts' ability for rapid deplasmolysis after transfer into hypotonic solution, this indicates the viability of the isolated pr

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00775.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractEuglena gracilisgreen cells were dark‐starved for four months. After this period almost the entire population died, while a few giant, viable cells appeared in the culture. The giantism was maintained after repeated subcultures in growth medium in light or dark conditions. However, the phenomenon was not permanent, and the morphological characteristics of the wild‐typeEuglenawere gradually restored.In giant cells nuclei enlarged greatly, DNA content increased and the Golgi apparatus greatly proliferated. Chloroplasts and mitochondria increased in number and size and often presented structural modifications when compared with normalEuglena. Importantly, in the giant cells that were maintained in darkness in resting or growth conditions chloroplasts persisted as structured organelles which appeared red‐fluorescent under UV illumination.Whether giantism is a phenotypic or a genotypic change is still debated. In our case, the evolution of this phenomenon, chiefly the enhanced DNA content, suggests that teratism is a multiploid mutation with the possibility of a return to the normoploid condition. Constitutive chloroplasts are present in most algae, except for a few species, among which isEuglena gracilis. The persistence of differentiated plastids in darkness in giantEuglenais considered to be a return to an ancestral condition and may, therefore, be phylogenetically impo

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00776.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractHomocontinuous cultures of the cyanobacteriumAnacystis nidulans(syn.Synechococcussp. PCC 6301) were grown at white light intensities of 2 and 20 W/m2, and supplied with 0.03 and 3 % CO2enriched air. The mutual influence of these growth factors on the development of the photosynthetic apparatus was studied by analyses of the pigment content, by low temperature absorbance and fluorescence spectroscopy, by analyses of oxygen evolution light‐saturation curves, and by SDS PAGE of isolated phycobilisomes.The two growth factors, light and CO2, distinctly affect the absorption cross section of the photosynthetic apparatus, which is expressed by its pigment pattern, excitation energy distribution and capacity. In response to low CO2concentrations, the phycocyanin / allophycocyanin ratios were lower and one linker polypeptide L30R, of the phycobilisomes was no longer detectable in SDS PAGE. Apparently, low CO2adaptation results in shorter phycobilisome rods. Specifically, upon adaptation to low light intensities, the chlorophyll and the phycocyanin content on a per cell basis increase by about 50% suggesting a parallel increase in the amount of phycobilisomes and photosystem core‐complexes. Low light adaptation and low CO2adaptation both cause a shift of the excitation energy distribution in favor of photosystem I. Variations in the content of the “anchor” polypeptides L60CMand L75CMare possibly related to changes in the excitation energy transfer from phycobilisomes to the photosystem II and photosystem I core‐

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00777.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPollen ofCrocus biflorusMiller subsp.biflorusfrom natural habitats of Tusculum (Frascati, near Rome, Italy) has been studied in order to compare its structure and physiology to pollen of otherCrocusspecies belonging to theCrocus sativusgroup. Mature pollen grains are rounded, 60 μm in diameter, in‐aperturate (but with surface incisions where exine is lacking). DAPI staining reveals a spindle‐shaped generative nucleus which is intensely fluorescent, and vegetative nucleus which is less fluorescent, and is elongated with numerous lobes. At anthesis the pollen is bicellular, but about 2% of tricellular grains occur among the pollen grains released from the anthers as well as on both naturally or handpollinated stigmas.Pollen germination is lowin vitro, but higherin vivo. The pollen tubes are of normal shape. An electron‐dense surface coat is sometimes visible on the exine, which in many cases, is detached from the exine. The vegetative cytoplasm is very rich in glycolipid bodies surrounded by endoplasmic reticulum. The generative cell has a lobed cell wall and is surrounded by the vegetative n

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00778.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA continuous 15 month study of the floral ecology of four syntopic understorey palm species ofGenomawas conducted in Amazonian Peru lowland rainforest.The spicate inflorescences ofG. macrostachys, G. acaulisandG. gracilisare strictly protandrous and the plants are functionally dioecious. Data suggest that inG. macrostachysandG. acaulispollination is based on a mimicry system, the pistillate flowers mimicking the staminate ones in colour, shape and scent. Pollen‐collecting meliponine bees (Hymenoptera, Apidae, Meliponinae) and pollen‐feeding syrphid flies (Diptera, Syrphidae) which visit inflorescences during both sexual stages are the pollinators ofG. macrostachys. Geonoma acaulisis pollinated by small pollen‐feeding weevils (Coleoptera, Curculionidae, Derelomini) that visit male and female spikes.Additionally, inG. macrostachysanother pollinator type,viz. euglossine bees (Hymenoptera, Apidae, Euglossinae), which are attracted and rewarded by both types of flowers may account for long‐distance pollination.The palmG. gracilisshows a very distinct pollination system. Although opportunistic insect visitors are attracted to the inflorescences of this species it seems to be mainly anemophilous because pollen becomes powdery during an thesis.The branched inflorescences ofG. interruptaare also protandrous, but unlike the other species ofGeonomaobserved, staminate and pistillate anthesis of individual flowers are, for the most, overlapping. A broad spectrum of visitors is attracted (bees, wasps, flies, and beetles), which all may act as pollinators. Outcrossing is especially encouraged during the purely female phase at the end of the flowering cycle when there are no more staminate flowers in the inflorescence.Effects on the reproductive biology and population structure of different pollination systems and breeding system are di

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00779.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe pollination biology ofNorantea brasiliensis(Marcgraviaceae) was studied in the rain forest of southeastern Brazil. This plant presents bizarre, brush‐type racemous inflorescences bearing numerous flowers and extrafloral cup‐shaped nectaries. Flower anthesis is diurnal, nectar production is continuous and copious, and the sticky pollen is readily removed by visitors during the first morning hours. The ruby‐coloured inflorescences were visited by eight species of hummingbirds (Trochilidae), and 10 species of passerine birds (three Coerebidae and seven Thraupidae). Hummingbirds hovered while probing for nectar and touched flowers occasionally, whereas passerine birds perched and made contact with flowers habitually. Due to differences in flower‐visiting and general foraging behaviour, perching birds act as better pollen vectors than hovering birds. The inflorescence ofNorantea brasiliensisseems well fitted for pollination by passerine birds, and the hexose‐dominated nectar supports this idea. Pollination syndrome trends within Marcgraviaceae may stem from insect‐pollinated, condensed and spike‐like inflorescences which would give rise to bird‐pollinated, brush‐type inflorescences. From the same basic condensed inflorescence, bat‐pollinated umbelliform inflorescence may be derived from bird‐pollinated, pendulous and corymb‐like inflorescences. These postulated inflorescence types are found among the extant sp

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00780.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00781.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1993.tb00782.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY