bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endocytosis in plants
Authors: Robinson David G. , Milliner Stefan 
Published: May 2006

Endocytosis in animal cells has been heavily documented. Both fluid‐phase and receptor‐mediated modes of uptake have been frequently studied, and the endocytic pathway is well defined. This contrasts markedly with the situation in plants where our knowledge of this process is still rudimentary. Partly responsible for this situation has been the view, widely held among plant physiologists, that because of turgor, endocytosis cannot occur in plant cells. As discussed below, the case against endocytosis is no longer water‐tight.Endocytosis is a fact in protoplasts. It can be demonstrated with electron‐dense tracers as well as with membrane impermeant dye Lucifer Yellow CH. The latter has also been used with success on both suspension‐cultured and tissue cells of higher plants, suggesting that fluid‐phase endocytosis is also a feature of cells with walls. Through the application of fluorescently labelled elicitor molecules, which specifically bind to the cell surface of suspension‐cultured cells, it has also been possible to provide convincing evidence for the operation of receptor‐mediated endocytosis in plants. A number of studies on protoplasts and cells clearly indicate that endocytosis in plants can be mediated by coated pits in the plasma membrane. At least one of the organelles that lie on the endocytic pathway in plants has a structurally similar counterpart in animal cells: the multivesicular body. The first recipient of internalized molecules is the partially coated reticulum, although its relationship to the Golgi apparatus and Golgi function remain to be clarified. The final target for endocytosis in plants appears to be the vacuole.
Hybrid genes in the analysis of transformation conditions: II. Transient expression vs stable transformation—analysis of parameters influencing gene expression levels and transformation efficiency
Authors: Negrutiu I. , Dewulf J. , Pietrzak M. , Botterman J. , Rietveld E. , Wurzer‐Figurelli E. M. , Ye De , Jacobs M. 
Published: May 2006

Reports on direct gene transfer have dealt with either the obtention of stable transformants and transgenic plants, or described the use of reporter genes to analyse different aspects of gene expression in plant protoplasts and conditions for their use in transient gene expression assays.In this paper we present comparisons between several transformation techniques, show species‐specific differences in efficiencies of stable transformants and in the levels of transient gene expression, and report on the identification of major parameters responsible for DNA uptake as judged from transient chloramphenicol acetyl transferase (CAT) expression levels and from efficiencies of transformation based on kanamycin‐resistance. The described procedures have been simplified, optimized and standardized and should allow routine use with a great variety of plant species.
Polysome formation and incorporation of new ribosomes into polysomes during germination of the embryonic axis of maize
Authors: Dommes Jacques , Van de Walle Claude 
Published: May 2006

Isolated axes of Zea mays L. cvs CiV2 and CUZCO were imbibed for different periods of time, and free polysomes were extracted and analysed by centrifugation in a sucrose gradient. The amount of rRNA per axis was determined at different moments of germination. Polysome reassembly was practically completed by 8 h and 54% of the preformed ribosomes were found in the polysome fraction. An increase in the proportion of large polysomes was also observed during this period of germination. During the following period, the polysome content and the distribution of the various classes of polysomes remained unchanged.The time of appearance of newly synthesized ribosomes into the polysomes was investigated using axes germinated in the presence of [3H]‐uridine. Centrifugal analysis of EDTA‐dissociated polysomes and gel electrophoretic analysis of polysomal RNA showed that new ribosomes appeared into polysomes a few hours after completion of the initial polysome assembly. When released into the cytoplasm, the new ribosomes were preferentially incorporated into polysomes rather than stored as free ribosomes.
Diffusible IAA and dominance phenomena in fruits of apple and tomato
Authors: Gruber J. , Bangerth F. 
Published: May 2006

The relationships between indole‐3‐acetic acid (IAA) diffusing out of the fruit and competition among fruits, and between fruits and shoot tips were investigated using apple (Malus domestica Borkh. cv. Jonagold) and tomato (Lycopersicon esculentum Mill.) plants. Dominant fruits always had more diffusible IAA than subordinated, inhibited fruits. Alterations in dominance – by fruit‐ or shoot tip removal – led to significant changes in diffusible IAA by the remaining fruits. This change could be detected one day after dominance modification.It is suggested that diffusible IAA is involved in the correlative signal regulating dominance relationship between fruits, and between fruits and shoots in apple and tomato.
Synergistic effect of 1‐aminocyclopropane‐1‐carboxylic acid and ethylene during senescence of isolated carnation petals
Authors: Overbeek J. H. M. , Woltering E. J. 
Published: May 2006

The effects of ethylene (C2H4), (2‐chloroethyl)phosphonic acid (ethefon) and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers (Dianthus caryophyllus L. cv. White Sim) were investigated.Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N‐malonyl‐ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene‐forming enzyme (EFE), thereby making the tissue receptive to ACC.In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.
Study on nutrient stress tolerance of nine Taraxacum microspecies with a contrasting mineral ecology by cultivation in a low nutrient flowing solution
Authors: Hommels C. H. , Kuiper P. J. C. , Telkamp G. P. 
Published: May 2006

Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO−3, H2PO−4, K+, Mg2+ and Ca2+ were investigated.The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum. These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites. T. nordstedtii, a microspecies of infertile sites, was most efficient in absorbing NO−3, H2PO−4 and K+. T. sellandii and T. eudontum, both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum, internal N concentration appeared to limit growth. Efficiencies in N use, at sub‐optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii, from infertile sites, and T. sellandii, from fertile sites, were established as high and low extremes, respectively.
A role for young leaves in vernalization of cauliflower: I. Analysis of leaf development during curd induction
Authors: Williams C. A. , Atherton J. G. 
Published: May 2006

Growth analysis techniques are used to test the hypothesis that chilling induces curd (flower) initiation in the cauliflower (Brassica oleracea Botrytis L. cv. Perfection) through inhibiting leaf growth, thereby increasing the availability of growth factors to the stem apex and enabling differentiation of the curd. Effects of chilling on leaf growth and curd induction are compared in juvenile and mature, vegetative plants. Chilling at 5°C reduced dry matter accumulation in the total leaf complement by ca 60% in juvenile plants and 40% in mature plants, compared to control plants growth at 20°C. Juvenile plants showed slower rates of leaf initiation than mature plants. Leaf initiation was retarded by chilling in both plant types with the most marked effect seen in the juvenile plants. This was consistent with dry matter availability to the stem apex limiting differentiation more severely in juvenile plants than in mature plants. The rate of dry matter accumulation in existing leaves, however, was faster in juvenile plants than in mature plants at 20°C. Plants that were juvenile during chilling produced an average of 43 leaves below the curd whereas those that were mature produced 25.Dry matter accumulation in younger leaves was more markedly inhibited by chilling than in older leaves. Chilling also reduced the rate at which enlarging leaves became positionally more remote from the stem apex. Possible roles for such leaves in regulating apical development are considered.
Soret absorption of intermediate(s) in protochlorophyllide to chlorophyllide photoreduction trapped at low temperature
Authors: Dujardin Esther , Kahn Albert , Mathis Paul 
Published: May 2006

Absorption spectra at ca 100 K from 400 to 750 nm and fluorescence emission spectra at 77 K from 600 to 750 nm were obtained from: 1) etiolated leaves of the H‐ordeum vulgare L. (barley) mutant albozonata 2 and SAN 9789‐treated Avena sativa L. (oat) with low levels of carotenoids, and 2) preparations of protochlorophyllide holo‐chrome from Phaseolus vulgaris L. cv. Commodore (bean).This allowed clear resolution for the first time of the Soret bands of the green pigments before and after light‐induced accumulation of intermediate(s) in protochlorophyllide to chlorophyllide photoreduction and after conversion of the intermediate(s) to chlorophyllide by warming the samples to 233 K in darkness. Although the intermediate(s) differ(s) in absorption and fluorescence in the red wavelength region from both protochlorophyllide and chlorophyllide, the extinction in the Soret band is not distinguishable from that of chlorophyllide. These observations indicate that the C7‐C8 double bond in ring IV of protochlorophyllide has been altered in intermediate(s) accumulated at low temperature in intense light, such that the transition state exhibits the character of a π complex.
Induction and repression of phenylalanine ammonia‐lyase and chalcone synthase enzyme proteins and mRNAs in carrot cell suspension cultures regulated by 2,4‐D
Authors: Ozeki Yoshihiro , Komamine Atsushi , Tanaka Yoshiyuki 
Published: May 2006

Changes in the amounts of enzyme proteins and mRNAs for phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) and chalcone synthase (CHS, EC 6.‐.‐.‐) were investigated in suspension cultures of carrot (Daucus carola L. cv. Kurodagosun), in which anthocyanin synthesis was induced and repressed in the absence and presence of 2,4‐dichrolophenoxyaeetic acid (2,4‐D), respectively. The amounts of enzyme proteins were measured using anti‐PAL and anti‐CHS sera. In a medium lacking 2,4‐D, enzyme proteins and mRNAs for both PAL and CHS were induced 5 days after transfer, when the anthocyanin synthesis was induced. They all increased coordinately during days 5‐7 after transfer, when anthocyanin was rapidly synthesized, and then they decreased. In contrast, in a medium containing 2,4‐D, the amount of enzyme protein and mRNA for CHS were below detectable levels throughout the culture time. As regards PAL, however, whether 2,4‐D was present or not, both enzyme protein and mRNA rapidly increased after the transfer of cells to fresh medium, and then decreased and remained at low levels in a medium containing 2,4‐D. The addition of 2,4‐D to cells cultured for 6 days in a medium lacking 2,4‐D caused an immediate decrease in the amounts of enzyme proteins and mRNAs for both PAL and CHS.All the results obtained here indicate that the induction and suppression of the synthesis of PAL and CHS were probably due lo increase and decrease, respectively, in the amounts of their mRNAs. Thus, it is suggested that the induction and suppression of anthocyanin in this system may be regulated at the transcriptional level by 2,4‐D.
Leaf morphology and water status changes in Triticum durum under water stress
Authors: Rascio A. , Cedola M. C. , Toponi M. , Flagella Z. , Wittmer G. 
Published: May 2006

Water relations, leaf morphology and the chemical composition of cell walls in irrigated and unirrigated plants of three durum wheat eultivars were measured at two growth stages (booting and flowering). Plant response to water stress differed at the two stages: cell wall elasticity increased at booting and osmotic potential values decreased at flowering; this may be due to the changes in stress history, leaf development and plant growth stage between the two harvests. Leaf tissue characteristics were modified by water stress only at flowering: accumulation of fibrous constituents and hemicellulose in the cell walls, reduction of acid detergent fiber (ADF) per unit of leaf area, increase in specific leaf weight (SLW), decrease in turgid weight/dry weight ratio (TW/DW) and alteration in mesophyll cell morphology (cell area / ceil perimeter ratio) were observed.Generally, cv. Valforte (the less drought‐resistant cultivar) had the greatest mesophyll cell area and perimeter and it had greater values of neutral detergent fiber (NDF) at the booting stage than cv. Appulo. Reactivity to water stress differed in the eultivars: Valforte showed the greatest increase in hemicellulose content and decrease in cell dimensions under drought at flowering.No significant relationships between osmotic potential and mesophyll cell characters were observed; there were no correlations among cell wall elasticity, cell morphology and the chemical components of leaf tissue. The total fiber content and the hemicellulose per unit of leaf area were correlated with the TW/DW ratio at flowering. This parameter decreased more in plants subjected to water stress owing to accumulation of hemicellulose. Correlations between leaf structural constituents and $$ suggest that the absorptive capacity of the cell wall may significally affect the osmotic volume of the cell.
Function of the polygalacturonase convertor in ripening tomato fruit
Authors: Knegt Erik , Vermeer Evert , Pak Caroline , Bruinsma Johan 
Published: May 2006

In extracts from pericarp tissue of ripening tomato (Lycopersicon esculentum Mill. cv, Sonato) fruits, two isoenzymes of polygalacturonase (E.C. 3.2.1.15), PG1 and PG2, are usually found. Also in such extracts, or as part of PG1, a convertor (CV) occurs. Incubation of PG2 with this CV gives rise to PG1 or a different isoenzyme, PGx, that is also stable at 65°C but differs in pH optimum and size from PG1. It appears that CV has two affinity sites that can bind with PG2 or with a polydextran. PG1 is an extraction artifact, consisting of one molecule of CV and two molecules of PG2. PGx is made up of one molecule of CV and one molecule of PG2. It is the CV part of PGx that binds to polydextrans such as Blue Dextran 2000, Sephadex G‐100, and cell wall preparations. In this last form PGx is the physiologically active form of the enzyme, solubilizing demethylated pectin.On Sephacryl S‐300, CV appears to have a molecular weight of 81 kDa, but because of its heat stability and partial leakage through a 10 kDa cut‐off membrane, it might be a much smaller, rod‐like molecule. The polygalacturonase convertor might be a lectin without intrinsic enzyme activity, with a function to immobilize, stabilize and activate enzymic proteins in the cell wall.
Protein synthesis in mitochondria purified from roots, leaves and flowers of sugar beet
Authors: Lind Christina , Halldén Christer , Møller Ian M. 
Published: May 2006

Highly purified, intact and functional mitochondria were isolated from roots and leaves of a number of fertile and male‐sterile lines of sugar beet (Beta vulgaris L.). Intact and functional mitochondria were successfully isolated from the flowers of fertile plants, but not from the flowers of male‐sterile plants. Several alternative methods for the homogenization of male‐sterile flowers were tried. Their failure suggests that the mitochondria from male‐sterile flowers are more sensitive to mechanical damage than mitochondria from fertile, or other organs of male‐sterile, plants.In organello protein synthesis was optimized with respect to the total concentration of amino acids, the concentration of [35S]‐methionine, pH and respiratory substrate. Inhibitor experiments showed that the mitochondrial preparations contained mitochondrial translational activity only. With the exception of one band, no processing or proteolytic breakdown in either root or leaf mitochondrial protein synthesis products could be detected in pulse‐chase experiments. Submitochondrial fractionation experiments showed the presence of two soluble polypeptides, whereas all other polypeptides were membrane bound.The polypeptide patterns of root, leaf and flower mitochondria were very similar with the exception of 4 polypeptides involved in glycine oxidation. These 4 polypeptides were present in large amounts in leaf mitochondria and just detectable in flower mitochondria. The patterns of polypeptides syntesized in mitochondria isolated from roots, leaves and flowers also showed a number of organ‐specific differences. Six qualitative and 6 quantitative differences were found between mitochondria isolated from these three organs. No unique polypeptides were found to be synthesized either by flower mitochondria or by mitochondria from roots and leaves of male‐sterile plants compared to their male‐fertile counterparts.
Effects of prohexadione (BX‐112) and gibberellins on shoot growth in seedlings of Salix pentandra
Authors: Junttila Olavi , Jensen Einar , Ernstsen Arild 
Published: May 2006

Effects of gibberellins A1, A4/7, A9, A19 and A20 and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth‐retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX‐112), which is suggested to block 3β‐hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA1, but not GA19 and GA20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA19, GA20 and GA1 are native in S. pentandra, and the results are compatible with the hypothesis that GA1 is active per se in shoot elongation, and that the effect of GA19 and GA20 is dependent on their conversion to GA1.A mixture of GA4 and GA7 was as active as GA1 in promoting shoot elongation in seedlings treated with prohexadione, while GA9 showed slight activity only when applied at high doses.
β‐Glucosidase activities and HCN liberation in unimbibed and imbibed seeds, and the induction of cocklebur seed germination by cyanogenic glycosides
Authors: Esashi Yohji , Matsuyama Shinichi , Ashino Hiroki , Ogasawara Maria , Hasegawa Ryo 
Published: May 2006

In many seed species, the major source of HCN evolved during water imbibition is cyanogenic glycosides. The present investigation was performed to elucidate the role of endogenous cyanogenic glycosides in the control of seed germination and to examine the involvment of β‐glucosidase in this process. All seed species used here contained some activities of β‐glucosidase already in the dry state before imbibition. in the decreasing order of Malus pumila, Daucus carota, Hordeum vulgare, Chenopodium album and so on. β‐Gluosidase activity in upper and lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.) decreased with imbibition, and in lower seeds the activity disappeared when they germinated. On the contrary, in caryopses of rice (Oryza sativa L. cv. Sasanishiki) β‐glucosidase increased during imbibition, and this increase continued even after germination. β‐Glucosidase in cocklebur seeds was more active in the axial than in the cotyledonary tissue. Amygdalin, prunasin and linamarin could all serve as substrattes for the β‐glucosidase(s) from both cocklebur and rice.Amygdalin, prunasin and linamarin as well as KCN, were effective in stimulating the germination of upper cocklebur seeds. The seeds evolved much more free HCN gas when they were exposed to the cyanogenic glycosides than when the glycosides were absent. Moreover, the application of the cyanogenic glycosides or of KCN caused accumulation of bound HCN in the seeds. Carbon monoxide, which stimulated cocklebur seed germination only slightly, did not cause accumulation of bound HCN. We suggest that a balance between the cytochrome and the alternative respiration pathways, which is adequate for germination (Esashi et al. 1987. Plant Cell Physiol. 28: 141–150), may be brought about by the action of endogenous HCN; a large portion of which is liberated from cyanogenic glycosides via the action of β‐glucosidase. In addition to the partial suppression of the cytochrome path and unlike carbon monoxide, the HCN thus produced may act to supply cyanide group(s) to unknown compounds necessary for germination.