摘要:

Developing embryos of barley (Hordeum vulgareL. cv. Bomi) detached 21–27 days after anthesis took up 1 mM [14C]‐glutamine at pH 5 and 30°C at a rate of about 20 nmol embryo−lh−1(5 μol g−1h−1). The uptake was inhibited by about 50% by di‐nitrophenol and by about 80% by 300 mMunlabelled glutamine or alanine. The bulk of the uptake appeared, therefore, to be due to carrier‐mediated active transport. The pH optimum of the uptake was 4.5. Leucine, proline, lysine, arginine and as‐paragine were taken up at approximately similar rates as glutamine, and they also inhibited the uptake of glutamine. This, suggests that the uptake of glutamine was at least partly due to an unspecific carrier(s) also shared by other amino acids. The embryos also took up the dipepti.de glycykarcosine; the rate was about 6 nmol embryo−1h−1(1.5 μol g−1h−1) (2 mM glycylsarcosine, pH 4.5, 30°C). The uptake was inhibited by about 70% by dinitrophenol or by 300 mMglycylglycine. This indicates that the bulk of the uptake was due to carrier‐mediated active transport. The pH optimum of the uptake was about 4.5.The rates of glutamine and glycylsarcosine uptake increased during the early and middle stages of embryo development (until day 28 after anthesis), but decreased towards the end of the maturation of the grain. These changes, as well as the relatively high activities, suggest that carrier‐mediated active uptake of amino acids, and possibly also that of peptides, plays a role in the n

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08657.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Seedlings of two tree species from the Atlantic lowlands of Costa Rica,Ochroma la‐gopusSwartz, a fast‐growing pioneer species, andPentaclethra macroloba(Willd.) Kuntze, a slower‐growing climax species, were grown under enriched atmospheric CO2in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 μl 1−1under photosynthetic photon flux densities of 500 μol m−2s−1and temperatures of 26°C day and 20°C night. Total biomass of both species increased significantly in the elevated CO2treatment; the increase in biomass was greatest for the pioneer species,O. lagopus. Both species had greater leaf areas and specific leaf weights with increased atmospheric CO2. However, the ratio of non‐pho‐tosynthetic tissue to leaf area also increased in both species leading to decreased leaf area ratios. Plants of both species grown at 675 μl 1−1CO2had lower chlorophyll contents and photosynthesis on a leaf area basis than those grown at 350 μl 1−1. Reductions in net photosynthesis occurred despite increased internal CO2concentrations in the CO2‐enriched treatment. Stomatal conductances of both species decreased with CO2‐enrichment resulting in significant incr

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08658.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Published data for the most widely used bioassays for auxins as. well as other auxin‐induced responses, have been analyzed to determine whether the response is ultrasensitive, hyperbolic or subsensitive, i.e. whether the change from 10 to 90% of maximal response requires less than, equal to or more than an 81‐fold increase in external auxin concentration. Auxin‐dependent callus growth is most often ultrasensitive. Other responses, including the curvature ofAvenacoleoptiles, may show simple Mi‐chaelis‐Menten kinetics. In the majority of cases, however, the response is sub‐sensitive, often very markedly so. The finding of subsensitive responses is consistent with the proposal by A. J. Trewavas that plant development is regulated by changes in the sensitivity to plant growth substances.Detailed data for subsensitive dose responses, particularly auxin‐induced inhibition of root growth, can often be precisely represented by bi‐ or multiphasic isotherms, with the phases separated by sharp transitions. The relationship to auxin uptake and the relationship, if any, between carriers and receptors for auxins remain t

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08659.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Subcultured explants ofMagnolia soulangeanaSoul, were incubated in tissue culture containers fitted with different types of closures. Type of closure affected the CO2concentration, with levels as high as 14% CO2being detected. The ethylene concentration increased gradually with time, to as much as 2–3 ppm after 9 weeks. There was a large variation in the composition of the atmosphere within the containers of any one type. The way by which a container was closed influenced exchange of the inner gas phase with the surrounding atmosphere and was important in determining the development of the cultured tissue

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08660.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The roots of a mature, field‐grown maize plant are dimorphic: the primary root and those from the oldest nodes are bare with a heavily lignified cortex arid sloughed epidermis; those from younger nodes, except for a bare elongation zone, have an intact epidermis surrounded by a persistent soil sheath. Sheathed roots consistently have more layers of cortical cells, but the ratio of volumes of cortex to stele (ca 4) and the cross‐sectional area of phloem (ca3× 10−2mm2) are similar in each type. Assimilated carbon (from14Capplied to a small area of one leaf) was translocated to all roots and actively metabolized in cortex and stele of both types. After 1 to 2 days the proportion of14C exuded from a given length of mature root into its soil sheath, or into the adjacent unattached soil in the case of bare roots, was the same (5%) in both root types when compared with the ethanol‐soluble14C in the tissues of this length. Up to 75% of the ethanol‐soluble label in the roots was in a cationic fraction (amino acids and unidentified compounds), ca 1% was in an anionic fraction and the remainder was in a neutral fraction (sugars). Approximately equal amounts of soluble14C were found in the stele, cortex an

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08661.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Changes in photosynthetic activity, leaf pigments and the activities of enzymes that scavenge damaging oxygen species in chloroplasts were followed during the greening of 8‐day‐old etiolated pea(Pisum sativumL. cv. Meteor) seedlings. Accumulation of chlorophyll and carotenoids was accompanied by development of photosynthetic activity. Carotenoids present in etiolated leaves, and the high ratio of carotenoid to chlorophyll detected during the early hours of greening are suggested to provide important protection against singlet oxygen. Superoxide dismutase, ascor‐bate peroxidase and glutathione reductase, which scavenge superoxide and hydrogen peroxide in chloroplasts, are present at high activities in etiolated leaves and throughout greening. The mechanisms by which developing chloroplasts may generate damaging oxygen species, and the role of these scavengers during greening is disc

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08662.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Nocturnal acidity increases of the Crassulaceae acid metabolism succulentAgave salmianaOtto ex Salm. ssp.crassispina(Trel.) Gentry were determined for various photosynthetically active radiation (PAR) levels in the field and various day/night temperatures and soil water potentials in the laboratory. When a particular factor was optimal for nocturnal acid accumulation, it was assigned an index value of unity. The product of the three indices was termed the environmental productivity index (EPI), which summarizes the effect of PAR, temperature, and water status on nocturnal acid accumulation. A monthly value for EPI was determined using microclimatic conditions at the field site near Salinas de Hidalgo, San Luis Potosf, Mexico. EPI was highly correlated with the number of leaves unfolding monthly from plants in the field (r2= 0.95), where monitoring of such leaf unfolding is a non‐destructive technique for assessing plant productivity. By using the measured leaf area index for four groupsof A. salmianaand a relationship between acid accumulation and net CO2up‐take, the EPI acidity data were converted to dry weight gain per unit ground area. This measure of productivity closely agreed with the 1.05 kg m−2year−1determined by conventional harvesting techniques. The productivity is also in agreement with studies on other desert agaves, but about 10‐fold higher than that generally considered for desert e

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08663.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A procedure is described by which the ribosome assemblies isolated from the buds of Scots pine (Pinus sylvestrisL.) as well as the ribosome and polysome fractions purified by sucrose density gradient centrifagation can be prepared for study by scanning electron microscopy. The technique has also been used to illustrate ribosomes extracted froai leaves and roots ofNicotiana tabacumL., from roots ofTuiipa gesnerianahybr. and from commercial wheat germ. The sample under study is spread on a piece of coverslip', frozen and dried at room temperature. The coverslip, with attached material, is taken through the critical point drying procedure, glued on a specimen retainer aod coated with gold‐palladium. The coverslip serves as a sufficiently stable specimen support to allow the study of ribosomes at magnifications of several hundred thousand. Use of the method makes it possible to study the structure of polysomes, to check the purity of fractioned samples and to investigate differences in the ribosome assembly of the developing plant tissue

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08664.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The ribosome assemblies isolated from buds of Scots pine (Pinus sylvestrisL.) containing microsporangiate strobili varied both quantitatively and qualitatively in samples collected from October to April. The seasonal fluctuation in the amount of ribosonnes was more evident in the cytosolic fraction than in the smaller membrane‐bound fraction. The profiles obtained after sucrose density gradient centrifugation were of two types. One type was commonly obtained from samples collected late in the autumn and early in the spring, and this type was characterized by a relatively high peak for the large subunits, a low or negligible peak for the dimers, and an even or ascending series of peaks for the polymers. The other type was obtained from samples collected during the winter, and was characterized by small peaks for both subunits, a moderate to large peak for the dimers and a descending series of peaks for the polymers. However, the scanning electron microscope investigations indicated that the winter‐time samples did not lack polysomes and clusters of ribosomes. They did not become visible in the polysome profiles because they pelleted too tightly at the bottom of the centrifuge tubes to be removed with gradient fractionation. The au‐toradiographic analyses suggested that the cells were capable of synthesizing mRNA throughout the winter, whereas rRNA synthesis was arrested. On the basis of the above results, we postulate that the synthesis of the enzyme proteins needed for the maintenance of winter‐time metabolism takes place in the cytosolic ribosome fraction. The possible existence of winter‐time polysome stores is also po

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08665.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The role of phyto chrome and flavins in blue light induction of betacyanin formation was studied in etiolated, three‐day‐oldAmaranthus caudatusL. seedlings, using the criterion of far‐red reversibility and exogenously applied riboflavin and KCN. The effect of riboflavin was studied using high fluence rate blue light (42.7 :nmol m−2s−1nm−1at 450 nm). When present in the incubation medium during illumination, riboflavin promoted the far‐red reversibility with short light treatments and suppressed the inductive action of continuous illumiaation. If added after light treatments, it promoted betacyanin formation. The filtration of blue light through the riboflavin solution caused profound changes in light quality without affecting the far‐red reversibility after 30 mm illumination. The effect of 1 mM KCN was tested with 70′% lower fluence of blue light. Cyanide caused the suppression of the inductive effect with 5 min blue light, which was accompanied by an enhancement of betacyanin induction by the terminal far‐red light pulse. With 30 min blue light, however, it caused the appearance of far‐red reversibility. The inductive effect of continuous blue illumination was slightly promoted by this Inhibitor. These results demonstrate that the effect of blue light on the pbyto chrome system is complex, whereas the physiological (inductive) action of the flavin triplet state is limited to low fluence, short

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1985.tb08666.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY