bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca2+‐ATPase is expressed differentially in phosphate‐starved roots of tomato
Authors: Muchhal Umesh S. , Liu Chunming , Raghothama K. G.
Published: May 2006

The expression of Ca2+‐ATPase (LCA1) and H+‐ATPase (LHA1) genes was analyzed in tomato (Lycopersicon esculentum) plants subjected to phosphate (Pi) starvation. The amount of LCA1 transcript increased significantly in tomato roots after 5 days of Pi starvation, whereas the transcript levels remained constant during this period in leaves. The LCA1 transcript level decreased when the Pi‐starved plants were resupplied with phosphate. Our data suggest that the accumulation of LCA1 transcripts in roots is a response specific to Pi starvation. The levels of LHA1 transcript remained relatively constant even after 7 days of Pi starvation in both roots and leaves of tomato plants.
Plasma membrane ATPase activity during pepino (Solanum muricatum) ripening
Authors: Heyes J. A. , Sealey D. F. , de Vré L. A.
Published: May 2006

Plasma membrane‐enriched samples were extracted from pepino fruit (cv. El Camino) by phase partitioning. H+‐ATPase (EC 3.6.1.35) activity in these samples increased during late fruit development (immediately before the onset of ripening) and western blotting confirmed there was an increase in enzyme abundance at this time. H+‐ATPase activity decreased during early ripening and then increased again in the final phase of ripening. Immunolocalisation showed the plasma membrane H+‐ATPase was most abundant in the outer cell layers of the fruit, which are considered to have a major role in determining fruit texture. Fruit softening was not accelerated by harvest and there was no stimulation of H+‐ATPase activity by harvest. An in vitro tensile test using fruit rings showed tissue softening proceeded faster at low apoplastic pH (4.5) than at pH 6.5; and tissue buffered at pH 6.5 softened less than unbuffered rings. Erythrosin B, an inhibitor of the plasma membrane H+‐ATPase, also retarded softening in vitro. These data suggest that plasma membrane H+‐ATPase activity may contribute to the onset of pepino softening through a reduction in apoplastic pH.
Purification of an antifungal PR‐5 protein from flower buds of Brassica campestris and cloning of its gene
Authors: Cheong Na Eun , Choi Yeon Ok , Kim Woe Yeon , Kim Sun Chang , Cho Moo Je , Lee Sang Yeol
Published: May 2006

An antifungal pathogenesis‐related (PR) group 5 protein with a molecular mass of 27 kDa (BFTP) was purified from flower buds of Brassica campestris. BFTP exhibits antifungal activity against Neurospora crassa, causing rapid release of cytoplasmic material at the hyphal tips of the fungus. BFTP immuno‐cross‐reacts with antiserum raised against the tobacco osmotin‐like PR‐5 protein. Using a PCR product generated with the help of two degenerate PCR primers for (1) the N‐terminal amino acid sequence of the protein and (2) the conserved peptide domain that appears in all PR‐5 proteins, we were able to isolate from a flower‐bud cDNA library a cDNA (933 bp) that encodes this protein (pBFTP). The deduced amino acid sequence shows high similarity to PWIR2 from wheat (43%) and thaumatin II from Thaumatococcus daniellii Benth (40%). It contains the 16 cysteine residues that are conserved in all PR‐5 proteins at their invariant positions. The cDNA predicts the synthesis of a preprotein which is subsequently processed into the mature protein by removal of an N‐terminal signal peptide. The mRNA is predominantly expressed in flower buds, with a moderate level of transcripts detected in stems. Very low levels of the mRNA are present in root and leaf tissue. The gene is a member of a small multigene family in the genome of B. campestris.
Promoter switches specific for abscisic acid (ABA)‐induced gene expression in cereals
Authors: Shen Qingxi , Ho Tuan‐Hua David
Published: May 2006

Abscisic acid (ABA) has been shown to regulate many physiological and developmental processes which are often mediated by the induction and suppression of gene expression. Herein, we review the progress made in the understanding of gene expression regulated by ABA, with the emphasis on cis‐ and trans‐acting elements controlling gene expression. Promoter sequences containing an ACGT‐core have been shown by several groups to be necessary for the ABA‐induced gene expression. However, similar ACGT‐core‐containing sequences are also necessary for responses to a variety of environmental and physiological cues. To address the question what determines the response specificity, we have studied two barley ABA inducible genes and defined the modular nature of ABA response complex (ABRC), the promoter unit necessary and sufficient for ABA induction of gene expression. ABRCs of these genes consist of a 10‐bp element with an ACGT‐core (ACGT‐box) and a coupling element (CE1 or CE3). These ABRCs function in both seed and vegetative tissues. Genetic analysis has led to the cloning of genes, such as maize Viviparous 1 (VP1), involved in the regulation of sensitivity of plants to ABA. In seeds, ABA induction of the ABRC containing CE3, but not the ABRC with CE1, is enhanced in the presence of the transcription regulator, encoded by the VP1 gene, indicating these two ABRCs are mediated by different ABA signal transduction pathways. Other potential signal transduction components mediating ABA signal transduction pathways are also discussed.
Ethylene in seed dormancy and germination
Authors: KeÇpczyński Jan , KeÇpczyńska Ewa
Published: May 2006

The role of ethylene in the release of primary and secondary dormancy and the germination of non‐dormant seeds under normal and stressed conditions is considered. In many species, exogenous ethylene, or ethephon – an ethylene‐releasing compound ‐ stimulates seed germination that may be inhibited because of embryo or coat dormancy, adverse environmental conditions or inhibitors (e.g. abscisic acid, jasmonate). Ethylene can either act alone, or synergistically or additively with other factors. The immediate precursor of ethylene biosynthesis, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), may also improve seed germination, but usually less effectively. Dormant or non‐dormant inhibited seeds have a lower ethylene production ability, and ACC and ACC oxidase activity than non‐dormant, uninhibited seeds. Aminoethoxyvinyl‐glycine (AVG) partially or markedly inhibits ethylene biosynthesis in dormant or non‐dormant seeds, but does not affect seed germination. Ethylene binding is required in seeds of many species for dormancy release or germination under optimal or adverse conditions. There are examples where induction of seed germination by some stimulators requires ethylene action. However, the mechanism of ethylene action is almost unknown.

The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied.
Senescence mechanisms
Authors: Noodén Larry D. , Guiamét Juan J. , John Isaac
Published: May 2006

Senescence in plants is usually viewed as an internally programmed degeneration leading to death. It is a developmental process that occurs in many different tissues and serves different purposes. Generally, apoptosis refers to programmed death of small numbers of animal cells, and it shows some special features at the cell level. Some senescing plant cells show some symptoms typical of apoptosis, while others do not. This review will focus primarily on leaf senescence with ultimate aim of explaining whole plant senescence (i.e., monocarpic senescence). Traditionally, the ideas on senescence mechanisms fall into two major groupings, nutrient deficiencies (e.g., starvation) and genetic programming (i.e., senescence‐promoting and senescence‐inhibiting genes). Considerable evidence indicates that nutrient deficiencies are not central senescence program components, while increasing evidence supports genetic programming. Because chlorophyll (Chl) and chloroplast (CP) breakdown are so prominent, leaf senescence is generally measured in terms of Chl loss. Although CP breakdown may not be the proximate cause of leaf cell death, it certainly is important as a source of nutrients for use elsewhere, e.g., for developing reproductive structures in monocarpic plants, and this loss limits assimilatory capacity. The CP is dismantled in an orderly sequence. Individual protein complexes seem to be taken out all at once, not one subunit at a time. Removal of any component, e.g., Chl, seems to destabilize the whole complex. It is of special interest that senescing CPs secrete Chl‐containing globules indicating that some CP components are broken down outside the CP. Senescence appears to be imposed on the CP by the nucleus, and all the known senescence‐altering genes except one, cytG in soybean, are nuclear. Only the d1d2 mutation(s) in soybean prevents a broad range of leaf senescence processes. Exactly, what causes cell death is unclear; however, the selective thiol protease inhibitor, E‐64, does delay death, and this suggests that proteases play a key role.
Multiple effects of salinity on photosynthesis of the protist Euglena gracilis
Authors: González‐Moreno Sergio , Gómez‐Barrera Juan , Perales Hugo , Moreno‐Sánchez Rafael
Published: May 2006

The effect of NaCl in the culture medium on growth, photosynthesis and cell content of chlorophyll, K+, Na+, Ca2+ and Mg2+ in Euglena gracilis was studied. O2 production, quantum yield of photosystem II (PSII), the non‐photochemical quenching of chlorophyll fluorescence (qN) and the chlorophyll alb ratio all diminished by 0.2 M NaCl. Respiration and chlorophyll a and b increased, whereas the photochemical quenching (qp) of chlorophyll fluorescence was not affected by 0.2 M NaCl. Salt stress also induced an increase in cell volume and in K+ and Na+ concentrations, but decreased the concentrations of Ca2+ and Mg2+. Except for a protective effect on O2 production, additional Ca2+ in the culture medium did not attenuate the salt effect on the parameters measured. The addition of HCO3− restored the PSII quantum yield of O2 production in cells grown in high salt. Salt stress promoted a decrease in the apparent rate of quinone A (QA) reduction and an apparent obstruction of QB reduction, which were not prevented by excess HCO3−; the addition of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) did not increase chlorophyll fluorescence in salt‐grown cells. These results indicate that photosynthesis in Euglena grown under salt stress exhibits: (1) diminution of the HCO3− dependent water‐splitting activity of PSII; (2) inhibition of the electron transfer at the quinone pool level; (3) probable increase in thylakoid stacking (as indicated by the effect on the chlorophyll alb ratio); and (4) dissipation of the H+ gradient across the thylakoid membranes (as indicated by the decrease of qN).
Changes in ascorbic acid levels in apoplastic fluid during growth of pine hypocotyls. Effect on peroxidase activities associated with cell walls
Authors: Sánchez María , Queijeiro Eva , Revilla Gloria , Zarra Ignacio
Published: May 2006

The apoplastic fluid of pine (Pinus pinaster Aiton) hypocotyls contains ascorbic acid (AA) and dehydroascorbic acid (DHA). The amounts of ascorbic and dehydroascorbic acids were in the nmol (g fresh weight)−1 range and decreased with the hypocotyl age as well as along the hypocotyl axis. The ratio AA/(AA+DHA) also decreased with the hypocotyl age and along the hypocotyl. Both ascorbic oxidase and peroxidase activity against ascorbic acid showed very low activity not only in the apoplastic fluid but also in the fractions ionically and covalently bound to the cell walls. However, the peroxidase activity in the three abovementioned fractions was strongly increased in the presence of ferulic acid. That stimulation effect increased with the hypocotyl age and from the apical towards the basal region of the hypocotyls of 10‐day‐old seedlings. Furthermore, the oxidation of ferulic acid by apoplastic and ionically‐ and covalently‐bound peroxidases was inhibited by ascorbic acid as long as ascorbate was available. A regulatory role of apoplastic ascorbic acid levels in the formation of dehydrodiferulic bridges between wall polysaccharides catalysed by cell wall peroxidases and thus in the cell wall stiffening during plant growth is proposed.
Ultraviolet‐B radiation causes shade‐type ultrastructural changes in Brassica napus
Authors: Fagerberg Wayne R. , Bornman Janet F.
Published: May 2006

Cell and chloroplast structural changes in palisade cells from mature leaves of Brassica napus L. cv. Paroll were quantified following exposure of plants to enhanced ultraviolet‐B (280–320 nm; 13 kJ m−2 day−1 biologically effective UV‐B) radiation at two different levels of photosynthetically active radiation (PAR, 400–700 nm; 200 and 700 μmol m−2 s−1). Short‐term changes in leaf ultrastructure after 30 min and longer term changes after one day and one week were analyzed using stereological techniques incorporating light and electron microscopy and mathematical reconstruction of a mean cell for each sample.

Ultraviolet‐B together with either relatively high or low PAR resulted in cell structural changes resembling those typical of plants under shade conditions, with the most marked response occurring after 30 min of UV‐B radiation. The ultrastructural changes at the cellular level were generally similar in both the relatively high and low PAR plus UV‐B radiation treatments. The surface areas of all three thylakoid types, the appressed, non‐appressed and margin thylakoids increased in the palisade tissue under supplemental UV‐B irradiation.

Although the appressed and non‐appressed thylakoids increased in surface area, they did not increase equally, leaving open the possibility that the two thylakoid types have independent regulatory systems or different sensitivity to UV‐B radiation. Increased thylakoid packing (mm2 thylakoid membrane per mm2 leaf surface) in UV‐B‐exposed plants may increase the statistical probability of photon interception. An increased level of UV‐absorbing pigments after one week of supplemental UV‐B radiation did not prevent or significantly ameliorate UV effects. Our data supported the assumption that UV‐B radiation may have a regulatory role besides damaging effects and that an increased UV‐B environment will likely increase this regulatory influence of UV‐B radiation.
Blue light‐promoted stomatal opening in abaxial epidermis of Commelina benghalensis is maximal at low calcium
Authors: Parvathi K. , Raghavendra A. S.
Published: May 2006

The requirement for calcium in blue light‐promoted stomatal opening, in comparison with that in red light, was studied in epidermal strips of Commelina benghalensis L. Blue light promoted stomatal opening in the presence of a low level of calcium, whereas in red light opening was relatively tolerant to calcium. Stomatal opening under blue light was restricted by external calcium (above 5 μM) or abscisic acid. When present in the incubation medium, EGTA increased the extent of stomatal opening under blue light. Verapamil (a calcium‐channel blocker) and trifluoperazine (TFP, a calmodulin antagonist) reduced the stimulation of stomatal opening by blue light. Lanthanum, an external calcium‐channel antagonist, had no significant effect on stomatal opening under either blue or red light. These observations indicate that blue light‐promoted stomatal opening preferentially occurs at low levels of calcium, and modulation by calmodulin is strongly suggested. We conclude that a fine‐tuning of the calcium level within guard cells is essential during the transduction of the blue light signal.
Ubiquitin metabolism in Chlamydomonas reinhardtii following cold shock
Authors: Ligr Martin , Malek Ladislav
Published: May 2006

The present work characterizes parameters of ubiquitin turnover in Chlamydomonas reinhardtii Dangeard growing under constant temperature conditions and after an exposure to cold shock. The ratio of free and conjugated ubiquitin to total protein and the rate constant of ubiquitin synthesis and conjugation increased about 2‐fold during the first 4 h after cold treatment, whereas the rate constant of ubiquitin degradation reached its maximum 8 h after treatment. The half‐life of ubiquitin calculated from the constant of degradation decreased from 6 h to 3.5 h during the first 4 h after completion of the cold treatment. The rate constant of ubiquitin deconjugation did not change after cold treatment. The ratio of free to conjugated ubiquitin decreased temporarily to approximately 8 immediately after cold treatment and increased back to its original value of about 11 at 2 h after cold treatment. These observations raise questions regarding the regulatory mechanisms of ubiquitin synthesis and degradation.
Effects of manganese toxicity on leaf CO2assimilation of contrasting common bean genotypes
Authors: González Alonso , Lynch Jonathan P.
Published: May 2006

Parameters related to leaf photosynthesis were evaluated in three genotypes of common bean (Phaseolus vulgarisL.) with contrasting tolerance to Mn toxicity. Two short‐term studies in solution culture were used to assess the effect of excess Mn on CO2assimilation in mature and immature leaves. Mn toxicity decreased total chlorophyll content only in immature leaves, with a consequent reduction of leaf CO2assimilation. Mature leaves that showed brown speckles characteristic of Mn toxicity, did not suffer any detriment in their capacity to assimilate CO2, at least in a 4‐day experiment. Stomatal conductance and transpiration were not affected by the presence of high levels of Mn in leaf tissue. Lower stomatal conductance and transpiration rates were observed only in leaves with advanced chlorosis. Differences among genotypes were detected as increased chlorosis in the more sensitive genotype ZPV‐292, followed by A‐283 and less chlorosis in the tolerant genotype CALIMA. Since CO2assimilation expressed per unit of chlorophyll was not different between high‐Mn plants and control plants, we conclude that the negative effect of Mn toxicity on CO2assimilation can be explained by a reduction in leaf chlorophyll content.
Role of oxygen limitation and nitrate metabolism in the nitrate inhibition of nitrogen fixation by pea
Authors: Kaiser Brent N. , Layzell David B. , Shelp Barry J.
Published: May 2006

The impact of nitrate (5–15 mM, 2 to 7 days) on nitrogenase activity and nodule‐oxygen limitation was investigated in nodulated, 21‐day‐old plants of a near‐isogenic nitrate reductase‐deficient pea mutant (A3171) and its wild‐type parent (Pisum sativum L. cv. Juneau). Within 2 days, 10 or 15 mM nitrate, but not 5 mM nitrate, inhibited the apparent nitrogenase activity (measured as in situ hydrogen evolution from nodules of intact plants) of wild‐type plants; none of these nitrate levels inhibited the apparent nitrogenase activity of A3171 plants. Nodule‐oxygen limitation, measured as the ratio of total nitrogenase activity to potential nitrogenase activity, was increased in both wild‐type and A3171 plants by all nitrate treatments. By 3 to 4 days the apparent nitrogenase activity of A3171 and wild‐type plants supplied with 5 mM nitrate declined to 53 to 69% of control plants not receiving nitrate. By 6 to 7 days the apparent nitrogenase activity of A3171 plants was similar to the control value whereas that of the wild‐type plants continued to decline. From 3 to 7 days, no significant differences in nodule‐oxygen limitation were observed between the nitrate (5 mM) and control treatments. The results are interpreted as evidence for separate mechanisms in the initial (O2 limitation) and longer‐term (nitrate metabolism) effects of nitrate on nitrogen fixation by effectively nodulated pea.
Localized and internal effect of nitrate on symbiotic dinitrogen fixation
Authors: Blumenthal Jürg M. , Russelle Michael P. , Vance Carroll P.
Published: May 2006

Alfalfa (Medicago sativaL.) is a deeply rooted perennial legume which, under field conditions, may be exposed to varying NO3−concentrations with depth. Our objective was to characterize the effect of localized (deep vs shallow) exposure of alfalfa root systems to NO3−on symbiotic N2fixation and NO3−‐N uptake. Cuttings of a single alfalfa plant were grown in vertical split root systems in a controlled environment chamber. The split root system was a rigid acrylic tube (5 cm diam. by 60 cm long) filled with silica sand and divided into upper and lower sections at the 30‐cm depth by a 5‐mm‐thick wax layer. Roots penetrated the wax layer, but mixing of nutrient solutions between the sections was prevented. Nodulation was restricted to the upper section. The plants were subjected for 10 days to the following treatments: both sections of the split root system received nutrient solution containing either 0.5, 5.25, or 10 mMNO3−; the upper section received 0.5 mMNO3−while the lower section received 10 mMNO3−; or the upper section received 10 mMNO3−while the lower section received 0.5 mMNO3−. Increasing supply of NO3−in the nutrient solution to both sections resulted in higher NO3−‐N uptake, lower nodule mass and lower specific nitrogenase activity. Although NO3−‐N uptake did not differ, plants exposed to 10 mMNO3−for 10 days in the upper, nodulated section of the root system had a 20% lower nodule mass than plants exposed to the same NO3−concentration in the lower, non‐nodulated section of the root system. Specific nitrogenase activity was not different between these two treatments. Therefore, we conclude that: (1) nodule mass was dependent on two factors, the amount of NO3−‐N taken up and the concentration of NO3−within the nodulated root zone; and (2) specific nitrogenase activity was little affected by the concentration of NO3−surrounding the nodules, but was strongly inhibited by NO3−‐N taken up.
Ammonium assimilation in bryophytes. l‐glutamine synthetase from Sphagnum fallax
Authors: Kahl Stefan , Gerendás Jóska , Heeschen Volker , Ratcliffe R. George , Rudolph Hansjörg
Published: May 2006

Cytosolic and plastidic l‐glutamine synthetase (EC 6.3.1.2) isoenzymes from Sphagnum fallax Klinggr. (Klinggr. clone 1) were separated by size‐exclusion and ion exchange chromatography. The cytosolic enzyme (GS1) was purified to apparent electrophoretic homogeneity. The native enzyme had a molecular mass of 390 ± 20 kDa as estimated by gel filtration and was apparently composed of 8 subunits with molecular masses of 48 kDa. GS1 activity could be measured from pH 6.8 to 8.6 in 50 mM imidazole buffer, with a broad optimum between pH 7.2 and 8.0. The Km values were 2.5 mM, 0.5 mM and 0.5 mM for l‐glutamate, ammonium and ATP, respectively. The enzyme was inhibited by more than 10 mM ammonium or glutamate. The incorporation of 15NH4+ into amino acids was observed in vivo using 15 NMR. Label from ammonium was first detected in the amide N of glutamine, and only subsequently in the amino N of glutamate. Moreover, no assimilation was detected in the presence of the specific GS inhibitor methionine sulfoximine. These observations are consistent with a dominant role for GS in the assimilation of ammonium in Sphagnum.
Chlorophyll synthesis modulates retention of apoproteins of light‐harvesting complex II by the chloroplast in Chlamydomonas reinhardtii
Authors: Park Hyoungshin , Hoober J. Kenneth
Published: May 2006

Localization of apoproteins of the major light‐harvesting complex (LHCII) in Chl b‐less cells of Chlamydomonas reinhardtii cbn 1–113 was determined by immunoelectron microscopy. In dark‐grown cells, a low amount of apoproteins was detected in cytoplasmic vacuoles. The amount in vacuoles, and in the cytosol, increased dramatically when the rate of protein synthesis was enhanced in the dark by raising the temperature to 38°C. After exposure of cells to light, the apoproteins accumulated also in the chloroplast. Mature‐sized apoproteins were recovered in an alkali‐soluble fraction of cellular proteins commensurate with accumulation in the cytoplasm. At 25°C, content of apoproteins in the chloroplast of pale‐green cells grown in medium lacking acetate was one‐half of the amount in cells grown with acetate, yet the total amount remained similar. Cytoplasmic vacuoles, which were nearly filled with immunoreactive, electron‐opaque material, were more abundant in cells grown without acetate as compared with cells grown with acetate. Accumulation of apoproteins outside of the chloroplast suggested that translocation into the organelle of a portion of the apoproteins, apparently synthesized in excess of the amount accommodated by Chl synthesis, was aborted after processing of precursors. These results suggested that assembly of LHCII was required for retention of apoproteins by the chloroplast.
Characterization of phytochelatin synthase from tomato
Authors: Chen Jianjun , Zhou Jianmin , Goldsbrough Peter B.
Published: May 2006

The enzyme that synthesizes Cd‐binding phytochelatins (PCs), PC synthase, has been studied in tomato (Lycopersicon esculentum) cell cultures and plants. This enzyme transfers γ‐GluCys from GSH or PC to either GSH or an existing polymer of (γ‐GluCys)nGly. PC synthase from tomato requires GSH or PCs as substrates but cannot utilise γ‐GluCys or GSSG. PC synthase is activated both in vivo and in vitro by a variety of heavy metal ions, including Cd2+, Ag+, Cu2+, Au+, Zn2+, Fe2+, Hg2+ and Pb2+. In crude protein extracts from tomato cells the enzyme has an apparent Km of 7.7 mM for GSH in the presence of 0.5 mM Cd2+, and exhibits maximum activity at pH 8.0 and 35°C. PC synthase is present in tomato cells grown in the absence of Cd. The level of enzyme activity is regulated during the cell culture cycle, with the highest activity occurring 3 days after subculture. Cadmium‐resistant tomato cells growing in medium containing 6 mM CdCl2 have a 65% increase in PC synthase activity compared to unselected cells. PC synthase is also present in roots and stems of tomato plants, but not in leaves or fruits. The distribution of the enzyme in tomato plants and regulation of PC synthase activity in tomato cells indicate that PC synthase, and PCs, may have additional functions in plant metabolism that are not directly related to the formation of Cd‐PC complexes in response to cadmium.
Effects of increasing inorganic carbon supply to roots on net nitrate uptake and assimilation in tomato seedlings
Authors: Gao Z. F. , Lips S. H.
Published: May 2006

We investigated the influence of an increased inorganic carbon supply in the root medium on NO−3 uptake and assimilation in seedlings of Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were pre‐grown for 4 to 7 days with 0 or 100 mM NaCl in hydroponic culture using 0.2 mM NO−3 (group A) or 0.2 mM NH+4 (group B) as nitrogen source. The nutrient solution for group A plants was aerated with air or with air containing 4 800 μumol mol−1 CO2. Nitrate uptake rate and root and leaf malate contents in these plants were determined. The plants of group B were subdivided into two sets. Plants of one set were transferred either to N‐free solution containing 0 or 5 mM NaHCO3, or to a medium containing 2 mM NO−3 and 5 mM NaHCO3. Both sets of group B plants were grown for 12 h in darkness prior to 2 h of illumination, and were assayed for malate content and NO−3 uptake rate (only for plants grown in N‐free solution). The second set of group B plants was labeled with 14C by a 1‐h pulse of H14CO−3 which was added to a 5 mM NaHCO3 solution containing 0 or 100 mM NaCl and 0 or 2 mM NO−3, and 14C‐assimilates were extracted and fractionated.

The roots of group B plants growing in carbonated medium accumulated twice as much malate as did control plants. This malate was accumulated only when NO−3 was absent from the root medium. Both a high level of root malate and aeration with CO2‐enriched air stimulated NO−3 uptake. Analysis of 14C‐assimilates indicated that with no NO−3 in the medium, the 14C was present mainly in organic acids, whereas with NO−3, a large proportion of 14C was incorporated into amino acids. Transport of root‐incorporated 14C to the shoot was enhanced by NO−3, while the amino acid fraction was the major 14C‐assimilates in the shoot. It is concluded that inorganic carbon fixed through phosphoenolpyruvate carboxylase (EC 4.1.1.31) in roots of tomato plants may have two fates: (a) as a carbon skeleton for amino acid synthesis; and (b) to accumulate, mainly as malate, in the roots, in the absence of a demand for the carbon skeleton. Inorganic carbon fixation in the root provides carbon skeletons for the assimilation of the NH+4 resulting from NO3 reduction, and the subsequent removal of amino acids through the xylem. This ‘removal’ of NO−3 from the cytoplasm of the root cells may in turn increase NO−3 uptake.
Molecular cloning and characterization of cDNAs coding for ferredoxin‐dependent glutamate synthase fromVitis vinifera
Authors: Loulakakis Konstantinos A. , Roubelakis‐Angelakis Kalliopi A.
Published: May 2006

Activity of ferredoxin‐dependent glutamate synthase (Fd‐GOGAT, EC 1.4.7.1), an enzyme with a central role in the assimilation of ammonia in higher plants, was detected in all grapevine (Vitis viniferaL.) tissues examined. Two cDNA clones, encoding the carboxy‐ and near to amino‐terminal sequences of the Fd‐GOGAT, respectively, were isolated from a grapevine cell suspension library. The deduced amino acid sequence of the grapevine enzyme is significantly identical to the respective sequences of other known plant Fd‐GOGATs and shows homology to the alfalfa nodule NADH‐dependent GOGAT and to the large subunit of theEscherichia coliNADPH‐dependent GOGAT. DNA blot analysis suggested the existence of two Fd‐GOGAT genes in grapevine. In northern blots both clones hybridized to a 5.7‐kb transcript which was abundant in leaf and root tissues. Both, the Fd‐GOGAT mRNA and the enzymic activity increased upon illumination of leaves of dark‐grown plants suggesting that grapevine Fd‐GOGAT gene expression is regulated by light. In cell cultures, Fd‐GOGAT transcript level responded differently to the external nitrogen source, showing higher levels in the presence of nitrate and lower levels in the presence of ammonium.
The Agrobacterium rhizogenes rolB and rolC promoters are expressed in pericycle cells competent to serve as root initials in transgenic hybrid aspen
Authors: Nilsson Ove , Tuominen Hannele , Sundberg Björn , Olsson Olof
Published: May 2006

Expression of the Agrobacterium rhizogenes rolB and rolC promoters was studied in transgenic hybrid aspen (Populus tremula L. ×P. tremuloides Michx.) lines containing a chimeric fusion of either the rolB or the rolC promoter and the reporter gene uidA. The resultant GUS activity was monitored by histochemical analysis in aerial tissues as well as in developing roots. Both the rolC and rolB promoters were shown to be expressed in the phloem and in the root tips, which is similar to the expression pattern previously described for annual plants. However, a strong expression of the rolB promoter in the rays of the phloem and the cambial zone of the stem, and of the rolC promoter in groups of pericycle cells prior to and during lateral root initiation was unique for hybrid aspen. In both stem and root tissues, the expression of the rolB and rolC promoters was localised primarily in a subset of cells competent to form adventitious or lateral roots, suggesting that these cells might serve as the target for A. rhizogencs infection. The biological significance of the cell‐specific rol gene expression in establishing the hairy root disease is discussed.
Getting to the root: The role of the Agrobacterium rhizogenes rol genes in the formation of hairy roots
Authors: Nilsson Ove , Olsson Olof
Published: May 2006

Agrobacterium tumefaciens and A. rhizogenes are the causative agents of the crown gall and hairy root diseases, respectively. The pathogenicity of both species is caused by an inter‐kingdom transfer of DNA from the bacteria to wounded plant cells. This ‘transfer‐DNA’ (T‐DNA) contains oncogenes whose expression transforms the plant recipient cell into a rapidly dividing tumour cell. In the case of A. tumefaciens, three of these oncogenes have been shown to encode enzymes catalyzing the biosynthesis of the plant growth hormones auxin and cytokinin. Therefore, the unorganized cell division in the crown gall tumour can be largely explained by an unregulated overproduction of these plant growth regulators. In contrast, the hairy root disease is characterized by a massive growth of adventitious roots at the site of infection. Because of the similarities of the infection processes, and because A. rhizogenes and A. tumefaciens are very closely related, it has been suggested that the most important A. rhizogenes oncogenes, the so called rol genes, are also encoding proteins involved in the regulation of plant hormone metabolism. However, recent data indicate that this is not the case. Thus the rol genes have functions that most likely are different from producing mere alterations of plant hormone concentrations. This review summarizes recent results concerning the expression and function of the rol genes, and presents a model for the role of these genes, especially rolB and rolC, in the A. rhizogenes infection process.
Signalling gates in abscisic acid‐mediated control of guard cell ion channels
Authors: Blatt Michael R. , Grabov Alexander
Published: May 2006

Multiple signalling pathways and their messengers – entailing changes in cytosolic‐free Ca2+([Ca2−]). pH (pH) and protein phosphorylation – underpin K+and anion channel control during stomatal movements. This redundancy is wholly consistent with the ability of the guard cells to integrate the wide range of environmental and hormonal stimuli that affect stomatal aperture. Signal redundancy effects a spectrum of graded responses by linking pathways to gate signal transmission, and so boosts or mutes the final ‘integrated signal’ that reaches each ion channel. All evidence supports a role for the AB11 protein phosphatase and protein kinase elements in gating K+channel sensitivity to pH and ABA. Changes in [Ca2+]I. in turn, are demonstrably sensitive to pH1. Because each of these signal elements modulate and, in turn, are influenced by the activity of different sets of ion channels, the additional couplings engender a remarkably complex network, layering positive and negative controls with the ion channels that facilitate ion fluxes for stomatal movement.
Cytokinins as regulators of gene expression
Authors: Schmülling Thomas , Schäfer Silke , Romanov George
Published: May 2006

Plant gene expression can be markedly altered in response to cytokinins, leading to an increase or decrease in the abundance of specific transcripts. Cytokinins control gene expression at the transcriptional level as well as posttranscriptionally. Their influence on transcript abundance can be rapid but also includes long‐term changes. The observed alterations are for the most part quantitative, sometimes with only subtle differences and rarely include qualitative changes such as a complete repression of gene expression. Relatively small differences in the endogenous cytokinin concentration can change the steady‐state mRNA levels of genes. Cytokinin control of gene expression can be cell‐type specific. Protein phosphorylation plays a role in the transmission of the cytokinin signal. Cytokinin specific cis‐elements and trans‐acting factors have not yet been described. Cytokinin target genes are frequently regulated by additional stimuli, such as light or auxin. The products of the regulated genes play a role in diverse biological processes, such as cell division, photosynthesis, chloroplast development, disease resistance and nutrient metabolism. This spread reflects the variety of cytokinin responses in plants. The isolated genes present valuable tools to dissect cytokinin signal transduction pathways and to understand the functional mechanism of this hormone. Rapid progress in this field will be instrumental for a deeper insight in the molecular mechanisms of cytokinin activity.
Gibberellin mutants
Authors: Ross John J. , Murfet Ian C. , Reid James B.
Published: May 2006

Research on gibberellin (GA) mutants is reviewed, focusing on reports, published since 1993. The mutants have usually been identified via a shoot elongation screen. This screen exposes mutations influencing GA synthesis, deactivation and reception, and also those acting further down the elongation pathway. Mutations blocking synthesis lead to a dwarf. GA‐responsive phenotype. Numerous such mutations are now known. For some steps homologous mutations are known across 4 to 6 model species. Examples include the early step, geranylgeranyl diphosphate to copalyl diphosphate, and the activation step, GA26to GA1. Several GA‐synthesis mutations have now been characterised at the molecular level and all are in structural genes. It is now clear some steps are controlled by gene families with distinct tissue specificity. Further, some enzymes control more than one step in the biosynthetic pathway. The only mutation known to block deactivation. sin in pea, leads to an elongated phenotype.

The GA response mutants are less well understood and are a more diverse group. They include elongated mutants with a constitutive GA response (spy in arabidopsis. la cry‐s in pea and sln in barley) or an enhanced GA response (phyB in arabidopsis. lv in pea and Ih in cucumber). Short response mutants include at least three types. One group accumulates GAs and are mostly unresponsive to applied GA (gai in arabidopsis. D8 in maize. Rht3 in wheat). A recently identified group, exemplified by Igr in pea and gas in barley, have a short stature and reduced response but attain full responses with very high doses of exogenous GA. How close these mutations act to GA reception remains to be determined. Lastly, a number of mutants with short stature and reduced GA response differ in overall phenotype from GA‐deficient plants and cannot be made to mimic wild type even at high GA application rates. These mutations act beyond GA reception and some have already proved useful in elucidating other pathways that affect shoot elongation. For example, the lk and lkb mutations in pea appear to block brassinolide synthesis and this in turn prevents normal GA‐mediated elongation responses.
Molecular mechanisms of ethylene regulation of gene transcription
Authors: Deikman Jill
Published: May 2006

Ethylene‐regulated gene transcription has been studied in the context of plant defense, carnation flower petal senescence, and tomato fruit ripening. This review summarizes what is known about the molecular mechanisms of this process. Activation of plant defense genes in response to ethylene involves a promoter element called the GCC box, which interacts with ethylene‐responsive element‐binding proteins (EREBPs). Genes expressed in response to ethylene during petal senescence and fruit ripening use different promoter elements. For fruit ripening genes, two cooperative promoter elements are required for ethylene‐responsive transcription. DNA‐binding proteins of carnation and tomato that interact with ethylene‐responsive promoter elements have been studied, and in some cases cDNAs encoding such proteins have been isolated. The immediate goal of this work is to determine which DNA‐binding proteins are involved in mediating ethylene‐responsive gene transcription, and how they interact with other components of the ethylene signaling pathway. This work will lead to a more complete understanding of ethylene signal transduction.
Enzymes involved in jasmonic acid biosynthesis
Authors: Mueller Martin J.
Published: May 2006

(+)‐7‐epi‐Jasmonic acid has attracted much attention as an inducible plant signal that stimulates the expression of an array of wound‐inducible and defence‐related genes as well as playing a role in various developmental responses. This review focuses on the enzymology of jasmonate biosynthesis and addresses open questions with respect to the regulation and subcellular localisation of the jasmonic acid pathway. The apparent analogy of jasmonate biosynthesis from a‐linolenic acid in plants with that of the arachidonate‐derived signalling molecules of the leukotriene‐ and prostaglandin‐type in animals make the jasmonic acid cascade one of general biological interest.
Polyamine metabolism and its regulation
Authors: Tiburcio Antonio F. , Altabella Teresa , Borrell Antoni , Masgrau Carles
Published: May 2006

Data obtained in bacteria and mammals have revealed the existence of transcriptional, translational and/or post‐translational mechanisms controlling polyamine metabolism. In plants, most of the genes encoding polyamine biosynthetic enzymes have recently been isolated and antibodies to some are available. These tools have been used to initiate the study of the regulatory mechanisms controlling cellular polyamine levels in plants, as well as to attempt the alteration of polyamine metabolic fluxes in transgenic plants. The transgenic approach has increased our understanding of how polyamines might function and how this could be used for achieving beneficial biotechnological applications. The aim of this review is to cover both of these basic and applied aspects.
Recent progress in brassinosteroid research
Authors: Sasse Jenneth M.
Published: May 2006

The progress of investigations in recent years of the occurrence, analysis, structure/activity relationships, physiology, role in stress responses, and applications of brassinosteroids is reviewed. Their inclusion in the category of plant hormones is now widely accepted, and much more research into the effects of brassinosteroids can be expected in future.
Infrared microspectroscopy: Sampling heterogeneity in plant cell wall composition and architecture
Authors: McCann M. C. , Chen L. , Roberts K. , Kemsley E. K. , Sene C. , Carpita N. C. , Stacey N. J. , Wilson R. H.
Published: May 2006

The use of probes such as monoclonal and polyclonal antibodies to specific cell wall components, at both the light and electron microscope levels, has demonstrated the diversity in cell wall composition between species, between tissues, between different regions of the cell surface, and even within a single wall. Traditional methods of cell wall analysis have provided valuable information on wall composition and architecture, but, by having to rely on the use of bulk samples, have averaged out this intrinsic heterogeneity. Fourier Transform Infrared (FTIR) microspectroscopy addresses this problem by providing chemical information from an area as small as 10×10 μm of a single cell wall fragment or area of a tissue section that has been imaged with a microscope accessory.

We have used FTIR microspectroscopy as a powerful and extremely rapid assay for wall components and putative cross‐links in muro. The spectra are sensitive to polymer conformation, and the use of polarisers in the microscope accessory allows the orientation of particular functional groups to be determined, with respect to the long axis of elongating cells. The spectra constitute species and tissue‐specific ‘fingerprints’, and the use of classical discriminant analysis may provide the opportunity for correlating spectral features with chemical, architectural or rheological wall properties. Spectral mapping of an area of a specimen allows the morphological features resulting from cell growth and differentiation to be characterised chemically at the single cell level.
Removal of the pericarp and testa of seeds of japonica and indica rice (Oryza sativa) at various oxygen concentrations has opposite effects on germination
Authors: Miyoshi Kazumitsu , Sato Tadashi
Published: May 2006

The germination of intact, dehusked, and peeled seeds (caryopses) of the japonica rice cultivar Sasanishiki, harvested 30, 40, 47 and 60 days after anthesis, and of the indica rice cultivar Assam IV, harvested 14 and 28 days after anthesis, was examined. Dehusking strongly inhibited germination of Sasanishiki seeds, with the exception that seeds harvested 30 days after anthesis gave minimal germination percentages even when left intact. Peeling (removal of the pericarp and testa) restored or enhanced germination, and 60–100% of seeds germinated after 10 days. By contrast, the rank order of germination of Assam IV seeds was intact, dehusked, and peeled seeds, with peeled seeds yielding germination percentages of 100%. In Sasanishiki, inhibition of germination of peeled seeds was observed at reduced oxygen concentrations (1–4% oxygen). This inhibition might explain the inhibitory effects of dehusking on germination of seeds from the japonica cultivar. It is possible that the testa and pericarp, which cover the embryos of dehusked seeds, acted as a barrier to the diffusion of oxygen to the embryo.
Immunolocalization of integrin‐like proteins in Arabidopsis and Chara
Authors: Katembe W. Jira , Swatzell Lucinda J. , Makaroff Christopher A. , Kiss John Z.
Published: May 2006

Integrins are a large family of integral plasma membrane proteins that link the extracellular matrix to the cytoskeleton in animal cells. As a first step in determining if integrin‐like proteins are involved in gravitropic signal transduction pathways, we have used a polyclonal antibody against the chicken β1 integrin subunit in western blot analyses and immunofluorescence microscopy to gain information on the size and location of these proteins in plants. Several different polypeptides are recognized by the anti‐integrin antibody in roots and shoots of Arabidopsis and in the intemodal cells and rhizoids of Chara. These cross‐reactive polypeptides are associated with cellular membranes, a feature which is consistent with the known location of integrins in animal systems. In immunofluorescence studies of Arabidopsis roots, a strong signal was obtained from labeling integrin‐like proteins in root cap cells, and there was little or no immunolabel in other regions of the root tip. While the antibody stained throughout Chara rhizoids, the highest density of immunolabel was at the tip. Thus, in both Arabidopsis roots and Chara rhizoids, the sites of gravity perception/transduction appear to be enriched in integrin‐like molecules.
The role of the glutathione system during dehydration of Boea hygroscopica
Authors: Navari‐Izzo F. , Meneguzzo S. , Loggini B. , Vazzana C. , Sgherri C. L. M.
Published: May 2006

Plants of Boea hygroscopica F. Muell were subjected to dehydration for 25 days until the relative water content was 23%. The rate of water loss was very slow during the first 12 days of dehydration while it dramatically increased during the last 3 days of the treatment. On day 12 of dehydration total glutathione content was reduced to 24% of the control level and was mainly present in the oxidized form. At that time an oxidation of the sulfhydryl groups of soluble proteins was observed. A protection of glutathione against oxidation of the sulfhydryl groups of soluble proteins was established only after 22 days of desiccation, at the same time as glutathione began to accumulate. During the whole desiccation period enzyme activities related to glutathione utilization and regeneration and the activity of NADP+‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.12), which contains essential sulfhydryl groups, were maintained. The results of the present experiment suggest that during dehydration of Boea hygroscopica glutathione has above all, a primary role in the protection of the sulfhydryl groups of the thylakoid proteins, which were maintained in the reduced form during the whole dehydration period.