bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyamines, both common and uncommon, under heat stress in rice (Oryza sativa) callus
Authors: Roy Malabika , Ghosh Bharati
Published: May 2006

Enhanced production and accumulation of free and conjugated polyamines as well as increased activities of their biosynthetic enzymes in plants have been associated with heat stress. Perchloric acid‐soluble free, as well as conjugated polyamines, and their metabolic enzymes were studied under 45°C heat stress in callus raised from heat‐tolerant and ‐sensitive rice cultivars. The levels of free and conjugated polyamines, as well as arginine decarboxylase (EC 4.1.1.19) and polyamine oxidase (EC 1.4.34) activities were higher in tolerant than in sensitive callus under non‐stressed conditions. Heat stress caused greater accumulation of free and conjugated polyamines in callus of the heat‐tolerant cultivar N22 than in that of the heat‐sensitive cultivar IR8. In particular, the uncommon polyamines norspermidine and norspermine were detected in cv. N22, which increased appreciably during stress, but they were not detected in callus of cv. IR8. Arginine decarboxylase and polyamine oxidase activities increased to a larger extent in N22 than in IR8 callus during stress, activities that were well correlated with the increased levels of common and uncommon polyamines. Increased levels of transglutaminase activity indicated the high titre of conjugated polyamines.
Extension rate and respiratory activity in the growth zone of wheat roots: Time‐course for adjustments after defoliation
Authors: Bingham I. J. , Panico A. , Stevenson E. A.
Published: May 2006

The time‐course for adjustments in the rate of extension of wheat (Triticum aestivum L. cv. Alexandria) roots, and the activity and capacity of respiratory pathways in the root apex, were determined after pruning the shoot to the ligule of the first leaf. Leaf pruning reduced the extension rate of both seminal and lateral roots. The onset of the response occurred within 1 h of pruning for laterals and between 2 and 3 h for seminals. The reduction in rate appears to be the result of a decrease in carbohydrate availability because (1) in seminal roots it was preceded by a decrease in soluble sugar content of the apical part of the growth zone (0–5 mm behind the root apex) and (2) supplying glucose (50 mM) to the roots of plants defoliated 24 h earlier led to a steady increase in extension rate of both seminal and lateral roots compared to non‐fed controls. Supplying 3‐O‐methyl glucose had no effect. The reduction in extension rate of seminal roots was accompanied (or slightly preceded) by a reduction in respiratory O2 uptake in the apical part of the growth zone (0–5 mm). Changes in respiratory activity in the basal part of the growth zone (5–10 mm) only occurred several hours later. At the time root extension rate was reduced, the rate of O2 uptake could be stimulated with FCCP, which indicates that respiration was under the fine control of adenylates. From these results we suggest the following sequence of events occurs after defoliation. Firstly, defoliation reduces the supply of sugars to the root apex, this leads to a reduction in rate of extension through some form of coarse control by carbohydrates on cell division and expansion, which in turn reduces the rate of respiratory O2 uptake because of a smaller demand for ATP. The results also indicate that there is a rapid (<1.5 h) reduction in respiratory capacity in the root apex after defoliation which occurs before any change in the overall rate of respiration.
Transient expression of a reporter gene in bulbscales and immature embryos of three Lilium species is affected by 5’upstream sequences and culture conditions
Authors: Tsuchiya Takao , Takumi Shigeo , Shimada Takiko
Published: May 2006

In Lilium, a transformation system has not yet been developed. For efficient selection of cells expressing transferred genes following particle bombardment, the effects of 5’upstream regions on the transient expression of the β‐glucuronidase gene (gusA) were estimated in bulbscales and immature embryos of lily. When four plasmids having the gusA gene under the control of the cauliflower mosaic virus (CaMV) 35S, maize alcohol dehydrogenase gene and rice actin gene (Actl) promoters, and the castor bean catalase introm were introduced by particle bombardment, the patterns of transient expression in the bulbscales showed differences among three Lilium species, L. x formolongi, L. dauricum and L. japonicum. In immature embryos of L x formolongi, transient expression was significantly influenced by age of embryos after self‐pollination, duration of culture before bombardment, and culture conditions. Moreover, the transient gusA expression driven by six different 5’upstream regions, including the maize ubiquitin gene promoter and a modified CaMV 35S promoter were compared in both bulbscales and immature embryos. Use of the Actl and modified CaMV 35S promoters resulted in the greatest number of cells that transiently expressed gusA in both types of tissue of L. x formolongi. These two promoters are efficient for use in lily transformation.
Alleviation of salt stress by arbuscular‐mycorrhizal Glomus species in Lactuca sativa plants
Authors: Ruiz‐Lozano J. M. , Azcón R. , Gómez M.
Published: May 2006

Improved salt tolerance of mycorrhizal plants is commonly attributed to their better mineral nutrition, particularly phosphorus. However, the effect of arbuscular‐mycorrhizal (AM) fungi on salt tolerance may not be limited to this mechanism. We investigated the possibility that non‐nutritional effects of AM fungi, based on proline accumulation or increased photosynthesis and related parameters, can influence the tolerance of lettuce (Lactuca sativa L.) to salinity. Three levels of salt (3, 4 and 5 g NaCl kg‐1 dry soil) were applied and plants were maintained under these conditions for 7 weeks. The salt‐treated AM plants produced greater root and shoot dry weights than unfertilized or P‐fertilized non‐AM controls. With increasing salinity, both shoot and root dry weights were reduced, but this decrease was greater in uninoculated plants. In particular, shoot dry weight was not reduced in G. fasciculatum‐colonized plants as a consequence of salt, whereas in uninoculated plants it was reduced by about 35% at the highest salt level. Proline accumulation was considerably lower for P‐amended non‐AM and for AM plants except for G. mosseae‐colonized plants than was the case for unamended plants. Transpiration, carbon dioxide exchange rate (CER), stomatal conductance and water use efficiency (WUE) were higher in mycorrhizal plants. At 5 g NaCl kg‐1, both photosynthesis and WUE increased by more than 100% in mycorrhizal treatment relative to uninoculated plants. The contents of phosphorus of P‐fertilized non‐AM plants was similar to or higher than those of G. mosseae‐ and G. fasciculatum‐colonized plants. Plants colonized by G. deserticola had the highest P‐content regardless of salt level. Hence, the effect of G. mosseae and G. fasciculatum on salt tolerance in this experiment could not be attributed to a difference in the P content. The mechanisms by which these two fungi alleviated salt stress appeared to be based on physiological processes (increased CER, transpiration, stomatal conductance and WUE) rather than on nutrient uptake (N or P).
Development and accumulation of ABA in fluridone‐treated and drought‐stressed Vicia faba plants under different light conditions
Authors: Popova Losanka P. , Riddle Kimberly A.
Published: May 2006

The effects of fluridone on guard cell morphology, chloroplast ultrastructure and accumulation of drought stress‐induced abscisic acid (ABA) were studied in Vicia faba L. plants grown under different light conditions. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. The appearance of defective and undeveloped stomata, and chloroplasts with a destroyed thylakoid membrane system was found in fluridone‐treated plants grown at a photosynthetic photon flux (PPF) of 600 μmol m‐2 s‐1. Plants grown at a PPF of 40 μmol m‐2 s‐1 had diminished levels of ABA after imposition of dehydration. Fluridone treatment reduced the level of ABA in both unstressed and dehydrated leaves. Accumulation of ABA in the control plants was considerably reduced when they were exposed to dark periods of 24, 48 and 72 h just before imposition of the stress. Twenty‐four hours after the dark treatment dehydration of the leaves resulted in a 3‐fold decrease in the level of stress‐induced ABA, and 72 h after dark treatment the amount of stress‐induced ABA approximated the prestressed values. Fluridone‐treated plants failed to accumulate ABA under water stress. In addition to functionally active chloroplasts, well‐developed and functional stomata are required for drought stress to elicit a rise in ABA.
Inhibitory effects of ambient levels of solar UV‐A and UV‐B radiation on growth of cucumber
Authors: Krizek Donald T. , Mirecki Roman M. , Britz Steven J.
Published: May 2006

The influence of solar UV‐A and UV‐B radiation at Beltsville, Maryland, on growth and flavonoid content in four cultivars of Cucumis sativus L. (Ashley, Poinsett, Marketmore, and Salad Bush cucumber) was examined during the summers of 1994 and 1995. Plants were grown from seed in UV exclusion chambers consisting of UV‐transmitting Plexiglas, lined with Llumar to exclude UV‐A and UV‐B, polyester to exclude UV‐B, or cellulose acetate to transmit UV‐A and UV‐B. Despite previously determined differences in sensitivity to supplemental UV‐B radiation, all four cultivars responded similarly to UV‐B exclusion treatment. After 19–21 days, the four cultivars grown in the absence of solar UV‐B (polyester) had an average of 34, 55, and 40% greater biomass of leaves, stems, and roots, respectively, 27% greater stem height, and 35% greater leaf area than those grown under ambient UV‐B (cellulose acetate). Plants protected from UV‐A radiation as well (Llumar) showed an additional 14 and 22% average increase, respectively, in biomass of leaves and stems, and a 22 and 19% average increase, respectively, in stem elongation and leaf area over those grown under polyester. These findings demonstrate the extreme sensitivity of cucumber not only to present levels of UV‐B but also to UV‐A and suggest that even small changes in ozone depletion may have important biological consequences for certain plant species.
Both phytochrome A and phytochrome B are required for the normal expression of phototropism in Arabidopsis thaliana seedlings
Authors: Janoudi Abdul‐kader , Konjevic Radomir , Whitelam Garry , Gordon William , Poff Kenneth L.
Published: May 2006

The role of phytochrome A (phyA) and phytochrome B (phyB) in phototropism was investigated by using the phytochrome‐deficient mutants phyA‐101, phyB‐1 and a phyA/phyB double mutant. The red‐light‐induced enhancement of phototropism, which is normally observed in wild‐type seedlings, could not be detected in the phyA/phyB mutant at fluences of red light between 0.1 and 19 000 μmol m−2. The loss of phyB has been shown to have no apparent effect on enhancement, while the loss of phyA resulted in a loss of enhancement only in the low fluence range (Janoudi et al. 1997). The conclusions of the aforementioned study can now be modified based on the current results which indicate that phototropic enhancement in the high fluence range is mediated by either phyA or phyB, and that other phytochromes have no role in enhancement. First positive phototropism was unaffected in phyA‐101 and phyB‐1 However, the magnitude of first positive phototropism in the phyA/phyB mutant was significantly lower than that of the wild‐type Landsberg parent. Thus, the presence of either phyA or phyB is required for normal expression of first positive phototropism. The time threshold for second positive phototropism is unaltered in the phyA‐101 and phyB mutants. However, the time threshold in the phyA/phyB mutant is about 2 h, approximately six times that of the wild type. Finally, the magnitude of second positive phototropism in both phyA‐101 and phyB‐1 is diminished in comparison with the wild‐type response. Thus, phyA and phyB, acting independently or in combination, regulate the magnitude of phototropic curvature and the time threshold for second positive phototropism. We conclude that the presence of phyA and phyB is required, but not sufficient, for the expression of normal phototropism.
Slow wave potentials in cucumber differ in form and growth effect from those in pea seedlings
Authors: Stahlberg Rainer , Cosgrove Daniel J.
Published: May 2006

A positive hydraulic signal in the form of a xylem pressure step was applied to the roots of intact seedlings of Cucumis sativus L. and Pisum sativum L. Surface electrodes at three positions along the epicotyl/hypocotyl recorded a propagating depolarization which appeared first in the basal, then the central and sometimes the apical electrode positions and fitted the characteristics of a slow wave potential (SWP). This depolarization differed between pea and cucumber. It was transient in cells of pea epicotyls but sustained in cucumber hypocotyls. It was not associated with a change in cell input resistance in pea epicotyls but preceded an increase in the input resistance of cucumber hypocotyl cells. With the increased xylem pressure the growth rate (GR) of cucumber hypocotyls and pea epicotyls underwent a transient increase, peaking after 5 min. If the depolarization reached the growing upper region, it preceded a sustained decrease in the GR of cucumber hypocotyls but only a transient decrease in the GR of pea epicotyls. A temperature jump in the root medium (heat treatment) induced a steep pressure spike in the xylem of the cucumber hypocotyl which showed similar electric and growth effects as the previously applied, non‐injurious pressure steps. We suggest that the observed differences in the electric and growth responses between the species were caused by the closure of ion channels in depolarized cells of cucumber but not pea seedlings.
2,4‐Dichlorophenoxy acetic acid and indoleacetic acid partially counteract inhibition of organogenesis by difluoromethylornithine
Authors: Davis David G.
Published: May 2006

Difluoromethylornithine (DFMO) is a well known inhibitor of putrescine biosynthesis that has been reported to interact in varying ways with auxins such as indoleacetic acid (IAA) and 2,4‐dichlorophenoxy acetic acid (2,4‐D). In the present report DFMO is shown to inhibit root formation in isolated hypocotyl segments of Euphorbia esula L. (leafy spurge) grown in the dark on solidified nutrient media in Petri dishes. Shoot formation was only slightly inhibited by DFMO and only on media with salts and vitamins diluted 10‐fold. 2,4‐D inhibited both root and shoot formation in full strength or diluted media. Simultaneous application of both compounds resulted in partial reversal of root inhibition, but only at 450 nM 2,4‐D, the highest concentration used. In both media IAA also partially reversed DFMO effects on root formation. The effects of DFMO, 2,4‐D or IAA on root (or shoot) formation do not appear to be closely related to endogenous content of the polyamines determined by high performance liquid chromatography.
Carbohydrate supplements to the callus culture medium modify the growth of potato tuber moth larvae feeding on Lycopersicon chmielewskii callus
Authors: Steinitz Benjamin , Navon Amos , Berlinger Menachem J. , Mazor Michal
Published: May 2006

Lycopersicon esculentum and L. chmielewskii are respectively susceptible and resistant to the potato tuber moth (Phthorimaea operculella Zeller) in the field. Feeding bioassays were conducted with the herbivore caterpillars reared on callus derived from both tomato species and grown in vitro, and the influence of carbohydrate supplements to the callus culture medium, on the insect's feeding behavior was investigated. Newly‐hatched larvae fed with L. esculentum or L. chmielewskii callus raised on a medium with 88 mM sucrose, reached a weight of 12–15 mg and 1.5–3.0 mg, respectively, within 9 days. Restriction of larval weight increase in insects reared on L. chmielewskii callus, disappeared when the host tissue was transferred 24 h prior to the callus‐insect assay to a medium supplemented with 264 mM of either sucrose, glucose, fructose or mannose. The capability of L. chmielewskii callus to restrict growth of larvae was restored in host tissue retransferred from a medium with 264 mM sucrose to a 24‐h incubation on one supplemented with 264 mM of either mannitol, sorbitol, glycerol or myo‐inositol, before the callus‐insect bioassay. The larval growth response remained unaltered by callus incubated on a medium with 264 mM xylose. The ameliorating effect on insect growth of high sucrose in the callus medium was not due to sucrose as an ingredient of the insect's diet. The diverse response of L. chmielewskii callus, and its dependence on the type of carbohydrate in the medium, rule out effects of these substances as nonspecific medium osmotica. The swift callus responses to carbohydrates (within hours of a change in medium composition), as reflected in the insect's growth, were not accompanied by visible morphological variations in the host tissue. We suggest that suppression by high levels of exogenously applied saccharides and derepression by exogenous polyols and myo‐inositol of the impedement to growth of the potato tuber moth larva, reflect the existence in L. chmielewskii of a carbon metabolic control mechanism of gene expression whose products affect insect growth.
Growth inhibition of pollen tubes by blocking the aromatic or branched‐chain amino acid pathways of biosynthesis
Authors: Grabe Annett , Kristen Udo
Published: May 2006

Pollen tubes of Nicotiana sylvestris growing in vitro were used to study growth inhibitory effects of glyphosate, which interferes with the biosynthesis of aromatic amino acids, and of metsulfuron methyl, which reduces the production of the branched‐chain amino acids valine, leucine and isoleucine. Using the pollen tube growth test, i.e., photometric quantification of pollen tube growth in vitro, both herbicides were found to inhibit tube growth poorly in the suspension medium but strongly when the medium was replaced by a fresh one 30 min after suspension of pollen. We suggest that the enhanced sensitivity of the suspended pollen resulted from the removal of released amino acids, because addition to the fresh medium of aromatic amino acids or branched‐chain amino acids significantly reduced the inhibitory effect of glyphosate or metsulfuron methyl, respectively. Different amino acid compositions were used to analyze the inhibitory concentrations of the herbicides. The data indicated that growing pollen tubes were able to synthesize aromatic or branched‐chain amino acids via the shikimate/chorismate pathway or via the acetolactate synthase reaction, respectively.
Isolation and characterization of an auxin‐binding protein gene from radish, and its expression in insect cells
Authors: Anai Toyoaki , Takai Ryota , Miyata Momo , Uchida Hidenobu , Kosemura Seiji , Yamamura Shosuke , Ishizaki Ryotaro , Hasegawa Koji
Published: May 2006

Auxin‐binding protein (ABP1) is a putative receptor for auxin in the plasma membrane. We isolated a full‐length cDNA encoding ABP1 from radish by screening a cDNA library with its partial cDNA fragment generated by the reverse transcriptase‐polymerase chain reaction (RT‐PCR) method. Radish abpl mRNA was highly expressed in cotyledons, hooks and hypocotyls, and less so in roots of radish seedlings. The deduced amino acid sequence of radish abpl consisted of conserved auxin‐binding motifs, a signal peptide and ER‐retention signal, and contained two potentially N‐linked glycosylation signals. To analyze the biochemical properties of the radish abpl product, this cDNA was expressed in insect cells by the baculovirus vector system. The result of tunicamycin‐treatment showed that the signal peptide was cleaved and that the radish abpl product was glycosylated at both target sites in insect cells.
Effects of abiotic stresses on the turnover of the D1 reaction centre II protein
Authors: Giardi Maria T. , Masojídek Jiri , Godde Doris
Published: May 2006

In the 1990's, evidence has accumulated that various unfavourable environmental conditions substantially affect the turnover of the D1 protein of reaction centre II, the psb A gene product. Biochemical, molecular and physiological studies in higher plants indicate that alterations of D1 protein turnover occur under drought, nutrition deficiency, heat, chemical stress, ozone fumigation as well as UV‐B and visible photo‐stresses. The behaviour of photosystem II under these various stress conditions indicates that the response of D1 protein turnover can be interpreted as a general adaptive response to environmental extremes.
The aromatic cytokinins
Authors: Strnad Miroslav
Published: May 2006

After the discovery of kinetin (Miller et al. 1956, J. Am. Chem. Soc. 78: 1345–1350) there was a flurry of syntheses that led to the finding of 6‐benzylaminopurine (BA), an active and easily obtainable cytokinin. Much research into cytokinin physiology was subsequently done with this substance. Further, the isolation and unequivocal identification of natural BA and the high biological activity of its meta‐hydroxylated analogues stimulated the search for other natural aromatic cytokinins. Screening was accomplished by ELISA of HPLC fractions using antisera against ortho‐ and meta‐hydroxybenzyladenosine. Subsequent isolation and decisive identification by mass spectrometry led to discovery of a broad spectrum of endogenous plant growth substances structurally similar to a highly active compound, meta‐topolin (6‐[3‐hydroxybenzyl‐amino]purine), and to its less active analogue, ortho‐topolin (6‐[2‐hydroxybenzyl‐amino]purine). The structures of such aromatic cytokinins suggest considerably different biosynthetic pathways from that of zeatin and related isoprenoid cytokinins. From a physiological viewpoint, aromatic cytokinin metabolism can be classified under four main headings analogous to isoprenoid cytokinins: interconversion, hydroxylation, conjugation, and oxidative degradation. This review attempts to put into context what is known about 9‐alkyl‐BAs and compares their metabolism in regard to the practical use of cytokinins in agriculture and biotechnology. The recently discovered unusual specificity of additionally C2,N9‐disubstituted aromatic cytokinins toward cell cycle kinases, suggests that these cytokinin‐derived growth regulators may selectively inhibit certain steps of the cell cycle. The functional overlap of the aromatic cytokinins with those of their isoprenoid counterparts and cytokinin inhibitors, in relation to growth and developmental processes in plants, has yet to be determined.
Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. I. Interactions between photosynthetic acclimation and photoinhibition during simulated canopy gap formation
Authors: Tognetti Roberto , Johnson Jon D. , Michelozzi Marco
Published: May 2006

Natural regeneration of European beech (Fagus sylvatica L.) establishes under shade, but sudden exposure to high irradiance may occur due to openings in the canopy. To elucidate ecophysiological mechanisms associated with survival of European beech seedlings, the gas exchange, chlorophyll concentrations, and chlorophyll a fluorescence parameters of two different beech populations were studied under changing light conditions. Plants were grown both in a growth chamber and at a natural site (one population) where the seedlings were raised in containers placed in understory and in simulated canopy gaps. Upon exposure to high light in the growth chamber, photosynthetic rates of shade‐acclimated leaves of seedlings from both populations increased severalfold and then decreased over several days to the rates of the low‐light control seedlings. High‐light seedlings always had the highest photosynthetic rates. Initial fluorescence displayed a trend opposite that of photosynthesis; it increased over time, and relative fluorescence and half‐time rise declined continuously until the end of experiment to very low values. Exposure to high light of shade‐acclimated seedlings resulted in a shift in chlorophyll concentrations to levels intermediate between high‐light and low‐light seedlings. The light treatment effects were statistically greater than population effects; however, seedlings from the Abetone population were found to be more susceptible to changing light conditions than seedlings from Sicily. Reciprocal light treatments on plants growing at the natural site confirmed the results obtained in the growth chamber experiment. Overall, beech seedlings grown in the field appeared to have a fairly large acclimation potential achieved by plasticity in the photosynthetic apparatus. The lack of pronounced acclimation to high light in seedlings grown in the growth chamber was ascribed to a threshold‐type relationship between the acclimation capacity and the level of damage. These observations on the limited potential for acclimation to high light in leaves of European beech seedlings which show a clear capability to exploit sunflecks, are discussed in relation to regeneration following canopy gap formation and reinforce the view of the central role of gap formation in forest dynamics. We conclude that small forest gaps (in which sunflecks play a major role) may present a favorable environment for survival and growth of beech because of their limited ability to acclimate to a sudden increase in irradiance and because of the moderate levels of light stress found in small gaps.
Hormonal regulation of α‐amylase gene expression in germinating wheat (Triticum aestivum) grains
Authors: Appleford N. E. J. , Lenton J. R.
Published: May 2006

The diffusion of GA1and GA3from the embryo, and the decline in ABA content of endosperm, were associated with the induction of α‐amylase (EC 3.2.1.1) gene expression in aleurone of intact wheat (Triticum aestivum L. cv. Maris Huntsman) grains germinated at 25°C. The scutellum appeared to be the main site of de novo GA biosynthesis based on (1) the abundance of transcripts of a cloned wheat GA 20‐oxidase. (2) the increase in content of GAs belonging to the early 13‐hydroxylation GA pathway, and (3) the accumulation of ent‐kaurene in grains imbibed in the presence of an ent‐kaurene oxidase inhibitor. Again, the initiation of GA biosynthesis in the scutellum was closely associated with the induction of α‐amylase gene expression in scutellar epithelium, although the two events may not have been causally linked. The embryo was required to be present for 36 h from the start of imbibition in order to induce α‐amylase activity in aleurone, and the response could be replicated by low doses of GA1applied to de‐embryonated grains. After‐ripened wheat aleurone was relatively unresponsive to applied ABA in terms of suppression of GA‐induced α‐amylase production. Subtle differences were observed in the temporal pattern of α‐amylase gene expression between intact germinated grains and de‐embryonated grains challenged with GA1. It appears that endogenous GAs are an important component of the embryo stimulus initiating α‐amylase gene expression in aleurone of germinating wheat grain, as originally proposed for barley. Their role in the synthesis of α‐amylase in scutellar epithelium remains to be clarified.
Low temperature enhances petunia flower pigmentation and induces chalcone synthase gene expression
Authors: Shvarts M. , Borochov A. , Weiss D.
Published: May 2006

Flower coloration is controlled by internal and external factors, including temperature. The aim of the present work was to examine the effect of temperature on anthocyanin synthesis and chalcone synthase gene (chs) expression in petunia flowers. A moderate‐low temperature enhanced both anthocyanin accumulation and chs expression in the corollas. However, the effect on chs expression was not always correlated with that on anthocyanin content, suggesting a post‐translational effect. The effect was local and required the exposure of corollas, but not the whole plant, to the ambient temperature. The response of chs to moderate‐low temperatures did not coincide with its expression during flower development. Moderate‐low temperatures only slightly affected gibberellic acid (GA3)‐induced chs expression in the light, but activated chs expression under non‐inducing conditions, i.e. in the absence of GA3 in the dark. The results of this study suggest that moderate‐low temperatures do not simply enhance the developmental regulation of anthocyanin biosynthetic gene expression; they act as a specific and separate signal.
Auxin metabolism and rooting in young and mature clones of Sequoia sempervirens
Authors: Blažková Alena , Sotta Bruno , Tranvan Hoa , Maldiney Régis , Bonnet Magda , Einhorn Jacques , Kerhoas Lucien , Miginiac Emile
Published: May 2006

The capacity of young and mature Sequoia sempervirens clones to produce roots in vitro was studied after wounding and indole‐3‐butyric acid (IBA) treatments. Rooting was not observed in mature or in young cuttings cultivated for 30 days in medium without IBA. The presence of 25 μM IBA in the medium resulted in the appearance of roots at the base of the cuttings. More roots appeared and grew faster on cuttings of the young than on the mature clone. This difference in rooting capacity between young and mature cuttings may be related to differences in the hormone levels at the base of the 5 mm long cuttings during the first 4 days of the root inductive period. After HPLC fractionation. IAA. IBA and related compounds, including indole‐3‐aspartic acid (IAAsp) and IBA‐glucose ester (IBA‐GE), were determined by MS and MS‐MS and their levels measured by ELISA. Another immunoreactive compound was also found and determined to be N,N‐dimethyltryptophan (DMT), a compound previously reported to inhibit auxin‐enhanced ethylene production. Wounding of the stem without IBA treatment revealed a transient increase in IAA, IAAsp and DMT levels in young cuttings while a dramatic increase in the levels of DMT was observed in mature cuttings. Following IBA treatment. IAA levels increased in both clones, but higher levels were measured in the young than in the mature clone. IBA and IBA‐GE were also found but in higher levels in the mature clone. Thus, the difficult‐to‐root mature clone differs from the young clone in its auxin metabolism.
Chelator used in pectin extraction triggers ethylene production by tomato fruit
Authors: Plank David W. , Tong Cindy B.
Published: May 2006

In our search for an endogenous ethylene trigger from tomato (Lycopersicon esculentum Mill. ev. Rutgers) fruit cell wall alkaline soluble pectin (ASP), we purified an active component using DEAE‐Sepharose chromatography followed by elution on Bio‐Gel P‐100 or Superose 12. The purified active fraction produced a single band on silver‐stained SDS‐PAGE of approximately Mr 20000. Using two‐dimensional proton‐proton and proton‐carbon correlation spectroscopy, we identified the repeating sub‐unit as trans‐1,2‐diamino‐cyclohexane‐ N,N,N′,N′‐tetraacetic acid (CDTA), a chelator used to extract ASP. Although the ASP undergoes extensive dialysis during its extraction which should remove CDTA, the CDTA apparently forms a large molecular weight polymer which does not diffuse out of the dialysis tubing. Infiltration of commercially prepared CDTA into mature green tomato fruit stimulated ethylene production. The ethylene stimulatory effect of CDTA was not affected by the presence of equimolar amounts of CaCl2, or nmol g‐1 amounts of the calcium channel blockers, nifedipine or verapamil. EDTA, EGTA, and diethylenetriaminepentaacetic acid, other divalent cation chelators, also stimulated ethylene production when they were infiltrated into tomato fruit. Neither the purified material nor commercial CDTA stimulated ethylene production when they were infiltrated into leaf tissue.
Purification and characterization of a calcium‐regulated protein kinase from beet root (Beta vulgaris) plasma membranes
Authors: Baizabal‐Aguirre Victor M. , González de la Vara Luis E.
Published: May 2006

A calcium‐regulated protein kinase (CRPK) associated with the plasma membrane of beet root cells was purified by deoxycholate extraction of plasma membrane proteins followed by chromatography in DEAE‐ and phenyl‐Sepharose columns. This procedure rendered a purified CRPK preparation with a specific activity higher than 2.2 μmol mg‐1min‐1 using histone III‐S as substrate. The molecular mass of CRPK, estimated by SDS‐PAGE, was 58 kDa. Gel filtration and glycerol gradient centrifugation indicated that the native enzyme is a monomer. Phosphorylation of histone by CRPK displayed a broad pH optimum between 7.0 and 8.2, Syntide‐2, a CaM‐kinase II substrate, was phosphorylated much more efficiently than kemptide, Ac‐MBP (4–14), CKII substrate or poly‐(Glu, Tyr) 4:1. The kinetics of this enzyme can be described by a steady‐state ordered mechanism in which four bound Ca2+ ions are required for the phosphorylation of the peptide substrate. After Ca2+ binding, the affinity of the enzyme for ATP was not affected while that for syntide‐2 or histone decreased. Curves of kinase activity vs ATP at different syntide‐2 concentrations indicated that the Km values for ATP or syntide‐2 increased with increasing cosubstrate concentrations. Similar curves of kinase activity vs ATP at different histone concentrations indicated that the apparent affinities of CRPK for ATP or histone were not affected by the cosubstrate concentration. The purified CRPK was not recognized by antibodies against soybean or Arabidopsis calcium‐dependent protein kinase (CDPK). These results suggest that CRPK and CDPKs could be different enzymes, although they show some similar properties.
The peribacteroid membrane
Authors: Whitehead Lynne F. , Day David A.
Published: May 2006

The objective of this review is to summarise current knowledge about the structure and function of the peribacteroid membrane from the root nodules of leguminous plants. The information is presented in terms of development of this symbiotic membrane from its origin, through proliferation and in the mature state. There are clear indications that the peribacteroid membrane has a distinct structure and function at each developmental stage. The mature peribacteroid membrane has been the most intensively studied. The lipid and protein content of the mature peribacteroid membrane is discussed with particular emphasis on genetic and functional studies of the proteins. The mechanism and control of peribacteroid membrane biogenesis is also discussed. There is evidence for a specific biogenetic pathway for this membrane which requires both symbiotic partners for its correct functioning.
Protein import into chloroplasts
Authors: Lübeck Jens , Heins Lisa , Soll Jürgen
Published: May 2006

Most chloroplastic proteins are encoded in the nucleus, synthesized on cytosolic ribosomes and subsequently imported into the organelle. In general, proteins destined for the chloroplast are synthesized as precursor proteins with a cleavable N‐terminal presequence that mediates routing to the inside of the chloroplast. These precursor proteins have to be targeted to the correct organellar membrane surface after their release from the ribosome and furthermore they have to be maintained in a conformation suitable for translocation across the two envelope membranes. Recognition and import of most chloroplastic precursor proteins are accomplished by a jointly used translocation apparatus. Different but complementary studies of several groups converged recently in the identification of the outer envelope proteins OEP86, OEP75, OEP70 (a Hsp 70‐related protein), OEP34, and of the inner envelope protein IEP110 as components of this translocation machinery. None of these proteins, except for OEP70, shows any homology to components of other protein translocases. The plastid import machinery thus seems to be an original development in evolution. Following translocation into the organelle, chloroplastic proteins are sorted to their suborganellar destination, i.e., the inner envelope membrane, the thylakoid membrane, and the thylakoid lumen. This structural and evolutionary complexity of chloroplasts is reflected by a variety of routing mechanisms by which proteins reach their final location once inside the organelle. This review will focus on recent advances in the identification of components of the chloroplastic protein import machinery, and new insights into the pathways of inter‐and intraorganellar sorting.
Production of several isoforms of β‐1,4‐glucanase by the cyanolichen Peltigera canina
Authors: de los Ríos Asunción , Ramírez Rosalía , Estévez Pilar
Published: May 2006

Lichen cellulase may participate in the degradation of the external substrata and/or modification of the photobiont cell wall. To promote a better understanding of the roles of cellulases in lichens, a cyanolichen was chosen because of the absence of cellulose in its symbionts. Freshly‐collected thalli of Peltigera canina (L.) Wild, produce β‐1,4‐glucanase (EC 3.2.1.4, β‐1,4‐D‐glucanohydrolase). This enzyme's activity was detected in the soluble and cell wall fractions and it was found to be secreted to the incubation medium when thalli were floated on water or on cellobiose. Several forms of the enzyme were detected by isoelectrofocusing. In preparative isoelectrofocusing, a single peak was obtained in each fraction, characterized by pls of 5.05, 5.25 and 4.75 in the soluble, cell wall and medium fractions, respectively. These differences were in agreement with the different pattern of bands obtained in slab‐isoelectrofocusing, where the most acidic band (pl of 4.45) was present only in the soluble fraction and the band with higher pl (6.17) was more intense in the cell wall fraction. Since both symbionts in a cyanolichen lack cellulose, cellulases cannot participate in the modification of their cell wall; the presence of cellulase in Peltigera canina must therefore be related to the degradation of the tissues of the moss substratum.
Protein accumulation potential in barley seeds as affected by soil‐ and peduncle‐applied N and peduncle‐applied plant growth regulators
Authors: Foroutan‐pour Kayhan , Ma Bao Luo , Smith Donald Lawrence
Published: May 2006

Although much investigated, the factors constraining cereal grain protein accumulation are not well understood. As a result of the development of a new technique, new approaches to this question are now possible. A peduncle perfusion system was used to deliver a range of plant growth regulators (PGRs) and/or N solutions into barley (Hordeum vulgare) plants during the grain‐filling period. The perfusion technique floods the peduncle interior with a treatment solution for periods of weeks to months, allowing the plant to take up administered substances from the perfused solution. The objectives of the present work were to determine: (1) whether some PGRs could alter the overall pattern of N allocation within barley plants, perhaps leading to higher protein accumulation in the seeds, (2) whether the addition of N through the peduncle could increase the seed N concentration even when the concentration of N in the rooting medium was high, and (3) whether or not PGR‐stimulated elevations in grain protein levels and peduncle‐added N increases in grain protein levels were additive. Three experiments were conducted to determine the physiological effects of (1) peduncle‐administered PGRs (2) combinations of soil‐ and peduncle‐applied N and (3) selected combinations of soil‐ and peduncle‐administered N, and peduncle‐applied PGRs on photosynthetic rate, dry matter partitioning and N accumulation of barley plants during grain filling. The first experiment tested four PGRs: abscisic acid (ABA), kinetin, gibberellic acid (GA3), and 2,4‐dichlorophenoxy acetic acid (2,4‐D) each at three concentrations. The second experiment tested three levels of soil N (NH4NO3) fertility, and two concentrations of peduncle‐added N (urea). The third experiment tested four PGRs: ABA, kinetin, GA3, and 2,4‐D with two soil N concentrations and two concentrations of peduncle‐added N. ABA and 2,4‐D decreased total seed weight of the perfused spike. The addition of peduncle‐perfused N increased seed protein concentration and content under conditions of high soil N fertility, suggesting that seed protein accumulation is more limited by the ability of roots to take up N from the soil than by the seed to take up N from the rest of the plant. The effects of the PGRs on N allocation among plant parts varied with the amount of N available to the plant. Because it resulted in less protein stored in the flag leaf and more in the seeds, GA3 perfusion caused an overall change in the allocation of N among plant parts. Peduncle perfusion of kinetin and ABA affected some aspects of photosynthetic physiology.
Dehydrins: A commonalty in the response of plants to dehydration and low temperature
Authors: Close Timothy J.
Published: May 2006

Among proteins that accumulate in plants in response to dehydrative forces or low temperature, dehydrins (late embryogenesis abundant [Lea] D11 family) have been the most commonly observed. Dehydrins are composed of several typical domains joined together in a few characteristic patterns, with numerous minor permutations. These domains include one or more putative amphipathic a‐helix forming consensus regions, a phosphorylatable tract of Ser residues, and an N‐terminal consensus sequence. Lesser conserved domains are also present at various positions, particularly between the putative a‐helix forming domains, where they may occur as tandem repeats. This medley of permutations is mirrored by a wide size range of dehydrin polypeptides from less than 100 to nearly 600 amino acid residues. As of yet, the fundamental biochemical mode of action of dehydrins has not been demonstrated, but a number of immunolocalization and cell fractionation studies have established that dehydrins can be located in the nucleus or cytoplasm. Furthermore, it appears that these proteins associate with macromolecules ranging from nucleoprotein complexes in the nucleus to an endomembrane sheath in the cytoplasm. At present, all observations are consistent with a hypothesis that dehydrins are surfactants capable of inhibiting the coagulation of a range of macromolecules, thereby preserving structural integrity.
Antifreeze proteins in winter rye
Authors: Griffith Marilyn , Antikainen Mervi , Hon Wai‐Ching , Pihakaski‐Maunsbach Kaarina , Yu Xiao‐Ming , Chun Jong Un , Yang Daniel S. C.
Published: May 2006

Six antifreeze proteins, which have the unique ability to adsorb onto the surface of ice and inhibit its growth, have been isolated from the apoplast of winter rye leaves where ice forms at subzero temperatures. The rye antifreeze proteins accumulate during cold acclimation and are similar to plant pathogenesis‐related proteins, including two endoglucanase‐like, two chitinase‐like and two thaumatin‐like proteins. Immunolocalization of the glucanase‐like antifreeze proteins showed that they accumulate in mesophyll cell walls facing intercellular spaces, in pectinaceous regions between adjoining mestome sheath cells, in the secondary cell walls of xylem vessels and in epidermal cell walls. Because the rye antifreeze proteins are located in areas where they could be in contact with ice, they may function as a barrier to the propagation of ice or to inhibit the recrystallization of ice. Antifreeze proteins similar to pathogenesis‐related proteins were also found to accumulate in closely‐related plants within the Triticum group but not in freezing‐tolerant dicotyledonous plants. In winter wheat, the accumulation of antifreeze proteins and the development of freezing tolerance are regulated by chromosome 5. Rye antifreeze proteins may have evolved from pathogenesis‐related proteins, but they retain their catalytic activities and may play a dual role in increasing both freezing and disease resistance in overwintering plants.
Cellular origin and ultrastructural changes of regenerating shoots from tobacco (Nicotiana tabacum) internodes cultured in vitro
Authors: Arai M. , Saito T. , Kaneko Y. , Matsushima H.
Published: May 2006

Ultrastructural changes were studied during shoot formation from tobacco internode slices cultured on Murashige and Skoog's (MS) basal medium plus 0.54 μM naphthaleneacetic acid, 0.44 μM 6‐benzyladenine, 3% (w/v) sucrose and 0.8% (w/v) agar. Dramatic structural changes were observed in cortical cells below the internodal epidermis, especially those immediately centripetal to the stomata, by light and scanning electron microscopy. Transmission electron microscopic investigation revealed conspicuous structural changes to plastids at each stage during shoot regeneration. To confirm the significance of the cortical cells in shoot regeneration, protoplasts were isolated from them and shoots regenerated successfully. The ability of single cortical cell protoplasts to differentiate into shoots was demonstrated.
Growth, membrane potential and endogenous ion currents of willow (Salix viminalis) roots are all affected by abscisic acid and spermine
Authors: Fromm Jörg , Meyer Andreas J. , Weisenseel Manfred H.
Published: May 2006

Growth measurements of hormone‐treated roots from willow cuttings were combined with electrophysiological recordings to study hormone‐induced changes in membrane potential and in endogenous ion currents. The mean growth rate of roots was 10 ± 2 μm min−1 in regular nutrient solution. It increased to 13 ± 2 μm min+1 after application of spermine and decreased to 0.07 ± 0.01 μm min−1 after treatment with abscisic acid (ABA). Transient depolarizations were elicited in root cortex cells by spermine, while ABA caused a transient hyperpolarization. All changes in membrane potential were accompanied by transient responses of the endogenous current. These responses suggest that first anions, then cations leave the root during spermine‐induced depolarizations. From the changes of the endogenous current an apparent efflux of anions (presumably Cl−) and cations (presumably K+) of 200 to 700 pmol cm−2 per depolarization was calculated.

To further investigate a possible relation between endogenous ion currents, growth and the growth regulators ABA and spermine, long‐lasting extracellular vibrating‐probe measurements were performed. Control roots showed an inward current of about 1.5 μA cm−2 at the apical elongation zone and an outward current with a maximum density of 1.3 μA cm−2 at the central and basal elongation zone. The addition of ABA and spermine (final concentration 0.1 mM) to the bathing medium affected the endogenous current in opposite ways: ABA caused a reduction of inward and outward current, while spermine stimulated both. Since protons are a major component of the endogenous current, and sucrose can be taken up by root cells from the apoplast via symport with H+, a role of the endogenous current in growth regulation is indicated.