bluuebunny/crossref_metadata_2025 huggingface dataset:
Nutrient transfer between the root zones of soybean and maize plants connected by a common mycorrhizal mycelium
Authors: Bethlenfalvay Gabor J. , Reyes‐Solis Maria G. , Camel Susan B. , Ferrera‐Cerrato Ronald
Published: May 2006

The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular‐arbuscular mycorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean [Glycine max (L.) Merr.], were grown in association with a dwarf maize (Zea mays L.) cultivar in containers which interposed a 6‐cm‐wide root‐free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 μm) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N‐sufficient soybean plants through N2‐fixation or N‐fertilization on associated maize‐plant growth and nutrition were compared to those of an N‐deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N‐fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N‐deficient association. When maize was grown with nodulated soybean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N‐fertilized treatment. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N‐fertilized soybean plants was more advantageous to maize than was association with the N2‐fixing ones.
Physiological and enzymatic activity of pepper seeds (Capsicum annuum) during priming
Authors: Smith Patrick T. , Cobb B. Greg
Published: May 2006

Pepper (Capsicum annuum L. cv. Keystone Resistance Giant 3) seeds were monitored during priming to determine if seed treatments which accelerate the rate of germination could be correlated with specific physiological changes within the seeds. Pepper seeds primed with −0.90 and −1.35 MPa NaCl solutions at 23°C for 18 days did not completely equilibrate with the osmotic potential of the priming solution. Seed respiratory rates indicated that priming extends the lag phase of germination following imbibition. Soluble protein levels increased 115% in primed seeds, and the uptake and incorporation of [14C(U)] labelled amino acids into the acid insoluble fraction increased throughout the priming treatments. Alcohol dehydrogenase (EC 1.1.1.1, anaerobic metabolism), glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (EC 1.1.1.44, pentose phosphate pathway) activities remained stable throughout the priming treatment, but were higher after 6 days. than the water‐imbibed controls. Aldolase (EC 4.2.1.1. glycolysis) and isocitrate lyase (EC 4.1.3.1, glyoxylate cycle) activities increased with imbibition and were 61 and 56% (respectively) higher in primed seeds as compared to the water‐imbibed controls after 12 days. Treatment with the −0.90 MPa NaCl solution was more effective than the −1.35 MPa solution in improving the rate of germination, yet there were no significant differences between the protein concentrations or enzyme activities of the two priming treatments. However, the incorporation of labelled amino acids into pepper seeds was significantly higher in the −0.90 MPa priming treatment.
Gene expression associated with water‐stress adaptation of rice cells and identification of two genes as hsp 70 and ubiquitin
Authors: Borkird Chumpel , Simoens Chris , Villarroel Raimundo , Van Montagu Marc
Published: May 2006

We have isolated polyethylene glycol (PEG)‐adapted rice cells that can proliferate in a medium with 20% PEG as well as in a medium with 1% NaCl. The adapted‐cells overproduce a set of proteins whose roles may be associated with water‐stress adaptation. To isolate genes encoding these proteins, we differentially screened a cDNA library and obtained 5 cDNA clones which showed preferential hybridization to mRNA of adapted cells. The present paper describes the pattern of expression and the sequence analysis of these 5 genes. Sequence analysis of partial cDNAs indicates that two genes encode the 70 kDa heat shock protein and the ubiquitin but the identities of the other 3 are not known. The expression of all 5 genes fluctuates slightly during the growth cycle of the PEG‐adapted cells grown in the control or in the PEG‐containing medium. In contrast, gene expression in the parental cells fluctuates to a much greater extent and always begins with an enhanced expression during the first day after subculture. Sub‐lethal concentrations of PEG or NaCl have no immediate effect on gene expression in parental cells but NaCl may have a long term effect in enhancing the expression of two genes after 5 days. Abscisic acid (ABA) has no effect on the expression of 4 genes but suppresses the expression of one gene. The roles of these genes in water‐stress adaptation of plant cells are discussed.
Effects of anaerobiosis on ethylene production, respiration and flowering in iris bulbs
Authors: Marissen N. , Kanneworff W. A. , van der Plas L. H. W.
Published: May 2006

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30°C, production was 12–20 pmol C2H4 (kg fresh weight)−1 h−1. Higher temperatures (35°C, 40°C) enhanced the ethylene production; a treatment with 40°C for ca 7 days caused a 3 times higher ethylene production than at 30°.

During anaerobic storage (in 100% N2) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N2 was replaced by air, a burstlike ethylene production was observed. Twenty‐four h after the replacement, ethylene production was equal to control values again.

The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5‐norbornadiene (NBD), an ethylene antagonist.

Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity.

Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst‐like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering.
Role of cytokinin in Nicotiana genetic tumors — A working hypothesis
Authors: Kung S. D.
Published: May 2006

There are three prerequisites for the development of genetic tumors in Nicotiana; distantly related species must be crossed interspecifically, the hybrid plants must be exposed to stress conditions and an elevated level of cytokinin must be present. These events occur sequentially. First, the interspecific hybrid plants appear to produce a unique tumor‐inducing factor (Ti‐factor). Second, stress conditions trigger the synthesis signal molecule(s) which in turn stimulate synthesis of increased levels of cytokinin. Third, the elevated level of cytokinin acts upon the Ti‐factor to initiate uncontrolled growth. The predominant shooty/leafy morphology of genetic tumors reflects the high level of endogenous cytokinin, and this hormone appears to play a pivotal role in the development of these tumors.
Auxin metabolism and transport during gravitropism
Authors: Parker Karen E.
Published: May 2006

Auxins are endogenous, growth‐regulating compounds in plants: for decades investigators have hypothesized that plants change their growth rates and patterns in response to environmental signals by changing their transport of, metabolism of, or sensitivity to their endogenous auxins. The Cholodny‐Went hypothesis, for example, postulates that plants respond to tropic signals by changing the distribution of free indoleacetic acid within their tissues. This hypothesis was based on data from experiments investigating phototropism and gravitropism in oat (Avena sativa L.) and maize (Zea mays L.) coleoptiles. The results of recent experiments support the Cholodny‐Went hypothesis for maize coleoptile gravitropism. Recent experiments conducted on the gravitropisms of other developmental stages of grasses, and other species of plants, however, indicate that the Cholodny‐Went hypothesis may not adequately describe how all plants respond to gravity.
In vitro molecular weight increase in xyloglucans by an apoplastic enzyme preparation from epicotyls of Vigna angularis
Authors: Nishitani Kazuhiko , Tominaga Rumi
Published: May 2006

In order to gain insight into the mechanism of cell extension growth, enzymic processes involved in structural modification of cell wall xyloglucans were investigated, using an apoplastic enzyme preparation from epicotyls of dark grown Vigna angularis Ohwi et Ohashi cv. Takara and purified xyloglucans derived from cell walls of Vigna. The reaction of Vigna xyloglucan (mass average molecular weight=420 kDa) with the apoplastic enzyme preparation gave three fractions: (1) a waterinsoluble high molecular weight (820 kDa) xyloglucan fraction (WI), (2) a watersoluble low molecular weight (149 kDa) xyloglucan fraction (WS), and (3) an 80% ethanol‐soluble monosaccharide fraction (ES). WI and WS were chiefly composed of t‐galactosyl‐, t‐xylosyl‐, 2‐xylosyl‐, 4‐glucosyl‐ and 4,6‐glucosyl residues, whereas ES was composed of fucose, galactose, glucose and xylose monomers. The data indicate that WI is generated by the linking of xyloglucan molecules by some alkali stable linkages, probably of glycosidic nature. The optimal pH for the WI‐producing activity of the apoplastic enzyme preparation was 5.4. Higher WI‐producing activity was detected in the upper juvenile than in the lower non‐elongating regions of the epicotyl. Our data suggest the possible involvement of a transglycosylation reaction in the structural changes of the xyloglucans that are responsible for cell extension growth of the Vigna angularis epicotyl. The data are also consistent with the idea that the enzymic processes are regulated by hydrogen ions in the apoplastic space.
An evaluation of gene expression during somatic embryogenesis of two temperature‐sensitive carrot variants unable to complete embryo development
Authors: Schnall Jennifer A. , Hwang Cheol H. , Cooke Todd J. , Zimmerman J. Lynn
Published: May 2006

The synthesis of putative stage‐specific polypeptides during somatic embryogenesis of the carrot (Daucus carota L. cv. Danvers) was investigated in the temperature‐sensitive variants OB‐2 and OB‐3. These variants undergo normal embryo development to produce mature plantlets at the permissive temperature (24°C), but are arrested at the oblong stage to form elongated embryos without cotyledons at the restrictive temperature (33°C). Using two‐dimensional polyacrylamide gel electrophoresis of in vivo labelled polypeptides, the patterns of stage‐specific polypeptides in both lines were compared in: (1) oblong embryos grown at continuous 24°C vs oblong embryos exposed to 33°C during their temperature‐sensitive period (i.e. embryos of identical morphology but different developmental fates); and (2) heartshaped embryos grown at constant 24°C vs enlarged oblong embryos exposed to 33°C during their temperature‐sensitive period (i.e. embryos of the same age but different morphologies). The 22 putative stage‐specific, polypeptides observed in this study fall into four classes: (1) line‐specific, (2) age‐specific, (3) unsynchronized, and (4) synchronized polypeptides. Only the last class, which consists of 4 polypeptides, exhibits synthesis patterns which are consistent with the polypeptides being causally involved in somatic embryo development. It is concluded that stage‐specific behavior as assayed by PAGE analyses of simple ‘present or absent’ comparisons is insufficient to identify most of the polypeptides that may be relevant for somatic embryogenesis.
Cell wall changes in white spruce (Picea glauca) needles subjected to repeated drought stress
Authors: Zwiazek Janusz J.
Published: May 2006

White spruce [Picea glauca (Moench) Voss] seedlings were preconditioned by subjecting them to 3 cycles of a mild drought stress. After 1 week of stress relief their water status, soluble carbohydrate content and cell wall composition in newly formed needles were examined and compared with those in control seedlings. Both preconditioned and control seedlings were subsequently subjected to a severe drought stress and again analyzed. Preconditioning treatment both before and during subsequent stress exposure lowered osmotic potentials at full hydration, and after the loss of turgor, decreased lignin content and increased hemicellulose content of the cell walls. Severe drought had similar but more drastic effects on seedling water relations, sugar accumulation and cell wall hemicellulose content; it also decreased cell wall pectin levels. The decrease in pectin levels was accompanied by a loss of galactose and glucose from pectic substances. Little change in cellulose content was observed as a result of preconditioning and severe drought.
Increased resistance to copper‐induced damage of the root cell plasmalemma in copper tolerant Silene cucubalus
Authors: De Vos C. H. R. , Schat H. , De Waal M. A. M. , Vooijs R. , Ernst W. H. O.
Published: May 2006

The relation between copper tolerance and the sensitivity of plants with respect to the effect of copper on the plasmalemma of root cells was studied using plants from one copper sensitive and two copper tolerant populations of Silene cucubalus Wib. In each population, the external copper concentration needed to induce ion leakage (a measure of damage to the permeability barrier) was similar to the highest no‐effect‐concentration of copper for root growth in that population. At higher concentrations, the degree of root growth inhibition paralleled the rate of ion leakage, the degree of trypan blue staining (a measure of plasmalemma integrity) and the accumulation of lipid peroxidation products. The amount of copper taken up by the plants was inversely related to their level of copper tolerance. Compared to copper sensitive plants, copper tolerant plants showed no increased resistance to either the sulfhydryl reagent N‐ethylmaleimide or the free radical‐producing compound cumene hydroperoxide.

These results indicate that damage to the permeability barrier of root cells constitutes the primary effect of copper toxicity in both sensitive and tolerant plants, and that copper tolerance is coupled to the ability of the plants to prevent such damage. This ability might depend on exclusion of copper by the root cell plasmalemma.
Stimulation of bicarbonate incorporation by ammonium in nonphotosynthetic cell suspension cultures of Acer pseudoplatanus
Authors: Goodchild Jonathan A. , Givan Curtis V.
Published: May 2006

Ammonium supplied to Acer cells incubated in Tricine buffer raised net dark incorporation of 14C‐bicarbonate by 1.5 to 3.3 fold; this stimulation was not abolished by prior inhibition of glutamine synthetase by methionine sulphoximine. With cells in phosphate buffer, ammonium gave a smaller 1.15 to 1.3 fold stimulation which was abolished when glutamine synthetase was inhibited. Ammonium had no direct effect on the activities of phosphoenolpyruvate carboxylase and pyruvate kinase assayed in partially purified extracts or on the enzymes catalysing release of label.
Gibberellin‐enhanced transcription by isolated nuclei from cucumber hypocotyls
Authors: Sechley Konrad A. , Srivastava Lalit M.
Published: May 2006

Nuclei isolated from apical 1 cm (gibberellin‐responsive region) of dark grown cucumber (Cucumis sativus L. cv National Pickling) hypocotyls and purified on Percoll step gradients were capable of in vitro transcription; however, only nuclei from the upper regions of the gradient gave GA4‐enhanced transcription. Addition of GA4 altered the transcriptional activity in favor of RNA polymerase II, from 50% in control to more than 90% in GA4‐treated nuclei. The GA4‐enhanced transcription was rapid and did not require extraction of nuclei in a medium with exogenous GA4 or preincubation of nuclei in GA4. Addition of [3H]GA4‐binding cytosolic protein to nuclei increased the overall transcription but did not affect the GA4‐enhanced transcription. Receptor‐binding assay indicated that these nuclei contain [3H]GA4‐binding sites which are heat‐labile and bound to nuclear matrix. Also, the nuclei seem to contain an inhibitor of GA4‐enhanced transcription which is sensitive to heat and removed by repeated washings. Nuclei from the non‐ responsive basal region of the hypocotyl or from the apical region of cucumber hypocotyls grown at 34°C did not show GA4‐enhanced transcription.
Activation of the non‐electrochromic component in the 518 nm absorbance change by photosystem I
Authors: Ooms Jaap J. J. , Versluis Wilma , Vredenberg Wim J.
Published: May 2006

The flash‐induced absorbance change measured at 518 nm (P515) in intact chloroplasts consists of at least 4 kinetically different components. Here the non‐electrochromic component, either called phase d or reaction 3, is studied in some detail. The effect of DCMU, DQH2 and DBMIB on the amplitude of reaction 3 and the turnover of cytochrome f and P700 have been monitored, suggesting an involvement of photosystem 1 in the activation of the non‐electrochromic absorbance change. This is confirmed by the parallel oscillation pattern found in P700 rereduction and the amplitude of reaction 3.
Ethanol in the stems of trees
Authors: MacDonald Robert C. , Kimmerer Thomas W.
Published: May 2006

Acetaldehyde and ethanol are usually thought to be produced in plant tissues as a mechanism to tolerate hypoxic conditions. We have found acetaldehyde and ethanol to be common in the vascular cambium and in the transpiration stream of trees. In nonflooded trees, acetaldehyde and ethanol concentrations averaged 130 and 40 μM in the cambium and 130 and 50 μM in the xylem sap, respectively. Ethanol concentrations in the transpiration stream and the cambium increased to as much as 5 mM upon flooding. Ethanol concentrations in the vascular cambium of Populus deltoides could not be eliminated by placing logs from nonflooded trees in a pure oxygen environment for as long as 96 h, but increased by almost 3 orders of magnitude when logs were exposed to low external partial pressures of O2. These results suggest that the vascular cambium was not hypoxic, despite the presence of acetaldehyde, ethanol and the enzymes for their synthesis.
Levels of endogenous indole‐3‐acetic acid and indole‐3‐acetylaspartic acid during adventitious root formation in pea cuttings
Authors: Nordström Ann‐Caroline , Eliasson Lennart
Published: May 2006

Levels of endogenous indole‐3‐acetic acid (IAA) and indole‐3‐acetylaspartic acid (IAAsp) were monitored in various parts of leafy cuttings of pea (Pisum sativum L. cv. Marma) during the course of adventitious root formation. IAA and IAAsp were identified by combined gas chromatography—mass spectrometry, and the quantitations were performed by means of high performance liquid chromatography with spectrofluorometric detection. IAA levels in the root forming tissue of the stem base, the upper part of the stem base (where no roots were formed), and the shoot apex remained constant during the period studied and were similar to levels occurring in the intact seedling. A reduction of the IAA level in the root regenerating zone, achieved by removing the shoot apex, resulted in almost complete inhibition of root formation. The IAAsp level in the shoot apex also remained constant, whereas in the stem base it increased 6‐fold during the first 3 days. These results show that root initiation may occur without increased IAA levels in the root regenerating zone. It is concluded that the steady‐state concentration is maintained by basipetal IAA transport from the shoot apex and by conjugation of excessive IAA with aspartic acid, thereby preventing accumulation of IAA in the tissue.
Extracellular proteins and early embryo development in Citrus nucellar cell cultures
Authors: Gavish Hanna , Vardi Aliza , Fluhr Robert
Published: May 2006

Highly efficient synchronous embryogenesis was induced in suspension cultures of sour orange (Citrus aurantium L.) by a change in the carbon source of the growth medium from sucrose to glycerol. In liquid culture the embryos developed into globular structures during a three week period. Embryo development showed an absolute requirement for the continued presence of glycerol. The embryo cell cultures turned green in the light, but light did not affect the course of development. The profiles of soluble cellular protein extracts of embryo and proembryogenic (PEM) cells were very similar as judged by two‐dimensional polyacrylamide gel electrophoresis. However, major differences were detected in the profiles of extracellular proteins. PEM cells accumulated extracellular glycoproteins of 53–57 kDa mass. Upon subculture in glycerol containing medium, the accumulation of these proteins ceased within two days. Developing embryos accumulated at least 4 new extracellular polypeptides of 41–42 kDa mass. In addition to these polypeptides, stage specific peroxidases and proteases were found. The relatively extended duration and synchrony in which these early developmental events take place make Citrus cultures an especially useful system for the study of early events in plant embryogenesis.
High frequency regeneration of plantlets from the leaf‐bases via somatic embryogenesis and comparison of polypeptide profiles from morphogenic and non‐morphogenic calli in wheat (Triticum aestivum)
Authors: Rajyalakshmi K. , Grover A. , Maheshwari N. , Tyagi A. K. , Maheshwari S. C.
Published: May 2006

High frequency regeneration via somatic embryogenesis was achieved in the leaf‐base cultures of wheat (Triticum aestivum L. cv Sonalika) by optimizing the concentration of the hormone, 2,4‐dichlorophenoxy acetic acid, and selecting for the appropriate part of the leaf base as explant. It was possible to distinguish compact (morphogenic) and friable (non‐morphogenic) calli by the naked eye, after about 60 days of culture on medium enriched with 2,4‐dichlorophenoxy acetic acid. The fact that the compact calli are morphogenic, while the friable ones are not, was evident from the observation that only the former formed plantlets after transfer to the basal medium. The morphogenic and non‐morphogenic cultures showed substantial difference in soluble protein content on a fresh weight basis. A comparison of silver‐stained profiles of soluble polypeptides from morphogenic and non‐morphogenic calli revealed many polypeptides specifically associated with either type of calli.
Evaluation of somatic embryos of interior spruce. Characterization and developmental regulation of storage proteins
Authors: Flinn Barry S. , Roberts Dane R. , Taylor Iain E. P.
Published: May 2006

Storage proteins of interior spruce (Picea glauca engelmanii complex) somatic embryos were compared to those of zygotic embryos by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and immunoblotting. Somatic embryos contain the same storage proteins as zygotic embryos based on similarities of molecular weight, isoelectric variants, solubility characteristics and disulfide linkages. Storage protein levels varied among different somatic embryo genotypes; however, all genotypes tested accumulated significant amounts of storage proteins. Zygotic and somatic embryos display a similar developmental accumulation of storage proteins. The 22, 24, 33 and 35 kDa proteins appear in early stage embryos, while the 41 kDa protein begins to accumulate during mid cotyledon development. The 22, 24 and 41 kDa proteins accumulate continuously during cotyledon development in somatic embryos cultured on abscisic acid. In contrast, zygotic embryos display a more rapid and transient accumulation of these proteins.
Membrane fluidity changes in embryogenic and non‐embryogenic cultures of Asclepias and Daucus in response to auxin removal
Authors: Wilson K. J. , Stillwell W. , Maxam T. , Baldridge T.
Published: May 2006

Significant differences in membrane fluidities, expressed as fluorescence anisotropies, are demonstrated between embryogenic (E) and non‐embryogenic (NE) cell lines when cells in suspension culture are removed from auxin. Cells of an E and NE cell line of Asclepias tuberosa were grown for 21 days either with or without 2, 4‐dichlorophenoxy acetic acid (2,4‐D), cultures were sampled at various intervals and protoplast membrane (hydrophobic interiors) was labeled with 1, 6 diphenyl‐1, 3, 5‐hexatriene (DPH). No differences between cultures with and without 2,4‐D were detected in the NE line. In contrast the E line rapidly developed differences in membrane fluidity over time. Such clear differences in the responses of E and NE lines in membrane fluidity indicated that this parameter could be a good predictor and marker for embryogenesis. Eight suspension cell lines of Asclepias and 2 of Daucus carota were tested. After 2 days on medium without auxin, every E cell line exhibited a positive change in anisotropy and became embryogenic, whereas NE cell lines exhibited much lower positive changes or even negative changes in anisotropy and never underwent embryogenesis. Such changes have been consistent in all cell lines tested and represent a marker for embryogenicity in suspension cell lines before morphological change becomes apparent after removal from auxin. Basic molecular membrane changes in embryogenesis are likely to be common among different culture systems and understanding them could be a major step in removing barriers to regenerating plants from cultured material.
Higher plant responses to environmental nitrate
Authors: Redinbaugh Margaret G. , Campbell Wilbur H.
Published: May 2006

Nitrate is the most common N source used by higher plants and is the ‘substrate inducer’ of nitrate and nitrite reductase activities. However, environmental nitrate also has other effects on higher plants, which include the induction of a high affinity nitrate transport system. changes in root morphology, and increased root respiration. Nitrate induces nitrate and nitrite reductase activities by altering gene expression, mainly by enhancing transcription of the respective genes. We have begun to view these responses of higher plant tissues to environmental nitrate in the context of a model for signal transduction. In our model, nitrate is a signal for developmental changes in the physiology of the plant, which are expressed in a hierarchy. The primary responses include induction of genes for nitrate and nitrite reductases, nitrate uptake and translocation systems, and DNA regulatory proteins required for expression of the secondary response gene systems. The secondary responses include more complex phenomena such as proliferation of the root system, enhancement of respiration and other changes in the physiology of the plant.
Protochlorophyll forms in roots of dark‐grown plants
Authors: McEwen Birgitta , Virgin Hemming I. , Böddi Béla , Sundqvist Christer
Published: May 2006

Protochlorophyll was found in roots of dark‐grown plants of seven species investigated. It was identified by absorbance and fluorescence spectra of acetone and ether extracts. Chlorophyll was also found in roots of one pea species. The concentration of protochlorophyll was usually highest in young root tips and decreased upwards along the roots. The maxima of the in vivo absorbance spectra of the species studied varied between 634 and 638 nm. Low temperature in vivo fluorescence emission spectra had two maxima, one at ca 633 and the other at ca 642 nm, when the wavelengths of the excitation light were 440 and 460 nm, respectively. In vivo fluorescence excitation spectra displayed a shift of the excitation maximum from 438 to 445 nm, when emission varied from 620 to 647.5 nm. Deconvolution of these three types of spectra into Gaussian components made it possible to identify two spectral forms of protochlorophyll: protochlorophyll629–633 and protochlorophyll638–642.
Interaction of divalent metal ions with the NADP+‐malic enzyme from maize leaves
Authors: Drincovich María Fabiana , Iglesias Alberto A. , Andreo Carlos S.
Published: May 2006

The effect of several metal ions on NADP+‐malic enzyme (EC 1.1.1.40) purified from Zea mays L. leaves was studied Mg2+, Mn2+, Co2+ and Cd2+ were all active metal cofactors. The malic enzyme from maize has a moderately high intrinsic preference for Mn2+ relative to Mg2+ at pH 7.0 and 8.0 Negative cooperativity detected in the binding of Mg2+ at pH 7.0 and 8.0 and in the binding of Mn2+ at pH 7.0 suggests the existence of at least two binding sites with different affinity. All of the activating metal ions have preference for octahedral coordination geometry and have ionic radii of 0.86–1.09 Å. The ions that act as inhibitors are outside this range and/or are incapable of octahedral coordination. Ba2+, Sr2+, Cd2+, Ca2+, Be2+, Ni2+, Cu2+, Zn2+, Co2+, Hg2+ showed mixed‐type inhibition. The reciprocal of their K1 values follow the order of their apparence in the Irving‐Williams series of stability that derives in part from size effects. It is suggested that the size of the ions may play a partial role in determining the strength of the metal interaction.
Free fatty acids, neutral and polar lipids in Hordeum vulgare exposed to long‐term fumigation with SO2
Authors: Navari‐Izzo Flavia , Quartacci Mike F. , Izzo Riccardo
Published: May 2006

Three 9‐day‐old cultivars of Hordeum vulgare L. (Barberousse, Gerbel and Panda) were exposed to low levels of SO2 fumigation (40 ± 5 and 117 ± 20 ppb). After 48 days of treatment the seedlings were harvested for lipid analysis. In comparison to the control (plants exposed to charcoal‐filtered air), the total lipid content of fumigated seedlings declined at 40 ppb SO2 and even more so at 117 ppb in all three cultivars. A large reduction in diacylglycerols. polar lipids and free sterols was also observed after fumigations at both SO2 concentrations, whereas the treatments resulted in an increase in triacylglycerols and free fatty acids. The percentage composition of total fatty acids and that of each lipid class were changed by the fumigations. resulting in an increase in the degree of unsaturation. No changes in the percentage composition of sterols occurred in the fumigated leaves. These results suggest that even if SO2 may not directly oxidize unsaturated fatty acids at the low concentrations used here (which do not cause visible injury). it may alter lipid metabolism. This alteration. which was particularly evident in the polar lipids and sterols, could affect the functions associated with membrane stabilization, in which lipids plus sterols play a key part.
Activities of chlorophyllase, phosphoenolpyruvate carboxylase and ribulose‐1,5‐bisphosphate carboxylase in the primary leaves of soybean during senescence and drought
Authors: Majumdar Sonali , Ghosh Sibdas , Glick Bernard R. , Dumbroff Erwin B.
Published: May 2006

The effects of senescence and drought on the levels and activities of chlorophyllase (EC 3.1.1.14), phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) and ribulose‐1,5‐bisphosphate carboxylase (Rubisco, EC 4.1.1.39) in the intact primary leaves of soybean (Glycine max L. cv. Jackson) were monitored. Plants were grown either (1) for 2 to 8 weeks and the primary leaves harvested every week or (2) for 2 weeks and the plants subjected to drought stress and compared to control plants that were watered daily. In the senescence experiment, chlorophyllase activity changed in parallel with water content, leaf chlorophyll and total protein per unit dry weight of leaf tissue, with all factors increasing in concert during expansion of the primary leaves in the first 4 to 5 weeks of seedling development. Thereafter, all factors, including chlorophyllase activity, declined reaching markedly reduced values at weeks 7 and 8 when the primary leaves were yellow and ready to abscise. PEPC and Rubisco activities peaked in the third week, i.e. well before full leaf expansion, and then declined. In contrast to its response during senescence, chlorophyllase activity per unit leaf dry weight did not change during drought stress, but the specific activity of the enzyme rose and showed an inverse relationship to total leaf chlorophyll and protein content. Rubisco activity was highly sensitive to drought, with decrements observed in the activity and in levels of the large subunit within 2 days of withholding water and before significant changes in leaf water content were detected.
Germination behaviour of Dactyloctenium aegyptium from two localities in Nigeria
Authors: Okusanya O. T. , Sonaike A. A.
Published: May 2006

The germination response of Dactyloctenium aegyptium (L.) Beauv from two localities in Nigeria to the effects of some environmental factors was determined experimentally. The two populations (Otta and University) germinated equally well in alkaline medium, but in acidic medium the Otta population germinated significantly better than the University of Lagos population. They germinated to the same extent in light and dark and equally well in humic soil. The Otta population had significantly better germination in the red earth and sand than the University population, even though germination in both populations in sand was significantly poorer than in humic soil and red earth. Under the various soil moisture contents tested, they both showed an increase in germination as soil moisture content decreased. The populations exhibited the usual pattern of minimum, optimum and maximum germination in response to the constant temperatures tested. The University population had a salinity tolerance range of 20% sea water with the percentage germination decreasing with increase in salinity, while the Otta population had a range of 100% with maximum germination in up to 50% sea water. The results are discussed in relation to the ecology of the species and the habitats of the populations as well as the need to state not only the place and date of seed collection but also the environmental factors prevailing in the locality.
Effects of drought on water relations and nonstructural carbohydrates in cladodes of Opuntia ficus‐indica
Authors: Nerd Avinoam , Nobel Park S.
Published: May 2006

Nocturnal acid accumulation, water content, osmotic pressure (π), and nonstructural carbohydrates were determined in the chlorenchyma and the water‐storage parenchyma of Opuntia ficus‐indica (L.) Miller for well‐watered plants and those subjected to drought for 15 weeks. During the 15‐week drought, total cladode water content decreased by 57%, the water‐storage parenchyma losing a greater fraction of water than the chlorenchyma, which most likely helped maintain nocturnal acid accumulation in the latter tissue. Despite the preferential water loss from the water‐storage parenchyma, it had a lower π than the chlorenchyma over the 15 weeks of drought, suggesting a substantial decrease in osmotically active solutes in the water‐storage parenchyma. Also, the measured π increases of both tissues were much less than those predicted based on the loss of water during drought and the initial content of osmotically active solutes under well‐watered conditions. A decrease in the amount of soluble sugars (glucose. fructose and sucrose) occurred in plants subjected to drought. accounting for 46% and 81% of the difference between the measured and the predicted increases in π of the chlorenchyma and the water‐storage parenchyma. respectively. The decrease in soluble sugars was associated with an equivalenl increase in polysaccharides, presumably starch, in the water‐storage parenchyma. but not in the chlorenchyma.
Cloning and light‐dependent expression of the gene coding for the P‐protein of the glycine decarboxylase complex from peas
Authors: Kim Younghee , Shah Ketan , Oliver David J.
Published: May 2006

The glycine decarboxylase multienzyme complex (EC 2.1.2.10) is located in the mitochondrial matrix and catalyzes a key reaction of the photorespiratory C‐2 cycle of plants. The light‐dependent control of the synthesis of the P‐protein of this complex in pea (Pisum sativum cv. Alaska) leaves was studied using a partial (0.7 kb) cDNA clone. The size of the P‐protein mRNA detected by this probe was 3.5 kb. When the mRNA hybrid selected by this probe was translated in vitro, a protein that migrated in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) with an apparent molecular mass of 114 kDa was formed. This protein could be immunoprecipitated with the P‐protein‐specific antibody. The mass of the mature P‐protein on SDS‐PAGE is 100 kDa. This suggests the presence of a presequence used to direct the protein to the mitochondrial matrix. Analysis of the concentration of P‐protein mRNA showed an approximately 5‐fold increase in the abundance of this transcript in light‐grown as compared to dark‐grown pea seedlings. The time course for the production of P‐protein mRNA following exposure of dark‐grown peas to white light was compared to that for the H‐protein of glycine decarboxylase, the small subunit of ribulose bisphosphate carboxylase/oxygenase, and the chlorophyll a/b binding protein. All 4 mRNAs accumulated with similar kinetics where they remained low during the first 3 h of illumination, increased about 5‐fold during the next 8 h, and then maintained a steady state over the next 12 h.
Investigations of proliferative and senescent callus of soybean
Authors: Keese Renee J. , Rupert Earlene A. , Carter George E.
Published: May 2006

Different explant sources from several Giycine max (L.) Merr. cultivars and several G. soja F. J. Herm Plant Introductions were tested for calluas production. Embryo axis explants produced callus most readily; hence, they were selected for media response studies and microscopic evaluation. Two callus types, proliferative and senescing, were identified and characterized by light and scanning electron microscopy (SEM). Proliferative callus was composed of chloroplast‐containing cells interspersed with colorless meristematic areas, while senescing callus contained mostly large, vacuolate cells without chloroplasts. In SEM preparations a furry, layered, mucilaginous coating was seen on the outer surface of the senescing callus, while proliferative callus cells had uncoated, smooth or wrinkled surfaces. The mucilage contained glucose and galactose.
Changes in the structure of ovary tissues and in the ultrastructure of mesocarp cells during ovary senescence or fruit development induced by plant growth substances in Pisum sativum
Authors: Vercher Yolanda , Carbonell Juan
Published: May 2006

Structural changes of tissues in unpollinated ovaries of Pisum sativum L. cv. Alaska after treatment with different plant growth substances (gibberellic acid, 2,4‐dichlorophenoxyacetic acid, and 6‐benzyladenine) or decapitation of the plant were studied. All the treatments resulted in the prevention of cellular disorganization associated with ovary senescence. They effected the enlargement of mesocarp cells and the differentiation of endocarp cells in very similar patterns, suggesting a similar induction of the structural processes involved in fruit development. Ultrastructural changes in mesocarp cells after treatment with gibberellic acid showed that rapid enlargement of mesocarp cells was sustained mainly by a reorganization of the membrane systems directed to the sysnthesis of primary cell wall. Early changes in the subcellular components in mesocarp cells were observed as the first symptoms in ovary senescence.
Priming relieves dormancy in lettuce seeds independently of changes in osmotic constituents
Authors: Weges Roelf , Koot‐Gronsveld Elly , Karssen Cees M.
Published: May 2006

The relationship was studied between germination and dormancy of lettuce seeds (Lactuca sativa L. cv. Musette) and both soluble amino nitrogen metabolism and osmotic potential. Germination at 15°C in darkness coincided with a rise in the levels of free amino acids and total soluble amino nitrogen compounds and in the activity of glutamine synthetase (GS, EC nr. 6.3.1.2). In further experiments GS activity was used as indicator of soluble amino nitrogen metabolism. GS activity increased after the start of growth indicated by an increasing intolerance to desiccation. At 30°C seeds did not germinate, unless dormancy was broken beforehand during incubation at 2° or 15°C (priming). The alleviation of dormancy occurred much earlier than the rise in the activity of GS. Priming at 15°C in polyethylene glycol instead of water retarded the breaking of dormancy and at –1.28 MPa even stimulated the induction of secondary dormancy, but did not prevent a continued rise in the activity of GS. GS activity was also not reduced during induction of secondary dormancy by dehydration of primed seeds, which antagonized the beneficial effect of priming. Psychrometric measurements showed that osmotic potential (Ψπ) of the seeds remained constant during prolonged priming in polyethylene glycol at 15°C. During incubation in water, Ψπ increased both prior to and after the moment of germination to less negative values. It is concluded that changes in the level of dormancy in lettuce seeds occur independently of soluble amino nitrogen metabolism and of changes in Ψπ.
Steady‐state kinetics of the plasma membrane H+‐ATPase from red beet (Beta vulgaris): its inhibition by vanadate and inorganic phosphate
Authors: de La Vara Luis E. González , Medina Guadalupe
Published: May 2006

The intial velocity vs ATP concentration curves obtained with the plasma membrane H+‐ATPase from red beet (Beta vulgaris L.) did not follow classical Michaelis‐Menten kinetics. A rate equation containing second‐order terms in ATP concentration in both the numerator and the denominator was used to obtain a significantly better fit to the data. The observed deviations from Michaelis‐Menten kinetics were more pronounced in the presence of potassium ions. The inhibition caused by inorganic phosphate was partial. i.e. the ATPase activity extrapolated at an infinite phosphate concentration was not zero. In contrast, the inhibition produced by orthovanadate was nearly total. The inhibitions caused by both phosphate and vanadate were uncompetitive with respect to ATP and enhanced by potassium ions and high concentrations of dimethyl sulfoxide. a solvent used to lower the water activity of the reaction medium. The ATP‐dependent proton transport was stimulated by potassium ions and was inhibited by phosphate only at high ATP concentrations. A kinetic mechanism, in which the H+‐ATPase can adopt two conformations during its catalytic cycle and can form a ternary enzyme‐ATP‐phosphate complex able to hydrolyze bound ATP. is proposed to explain those results.
The role of ice nucleation active bacteria in supercooling of citrus tissues
Authors: Constantinidou H. A. , Menkissoglu O. , Stergiadou H. C.
Published: May 2006

The frost sensitivity of Citrus sinensis in relation to the presence of biogenic ice nuclei was studied. In commercially managed citrus groves the ice nucleation active (INA) bacterium Pseudomonas syringae reached 6 × 104 colony forming units (CFU) leaf−1, a population sufficiently high to catalyze ice formation. However, a transient loss of bacterial nucleation activity was noticeable at subzero field temperatures, followed by resumption as temperatures rose. This loss was apparently due to a temporary transition of INA to ice nucleation inactive (INI) bacteria. Field application of Bordeaux mixture, copper hydroxide, streptomycin, and 2‐hydroxypropylmethanethiolsulfonate (HPMTS), resulted in reduction of INA bacterial populations to detectability (≤ 102 CFU leaf−1) limits. However, the corresponding reduction in ice nucleation events in treated samples as compared to controls at nucleation temperature ≥−3°C was not as dramatic. It ranged from approximately 7% in samples treated with the bactericide HPMTS, to 35% in samples treated with chemicals possessing combined bactericidal ‐ fungicidal action (coppers). Since a quantitative relationship exists between ice nucleation events on individual leaves and the INA bacterial populations harbored by these leaves, these results suggest the co‐existence of a bacterial and a proteinaceous, yet non‐bacterial ice nucleating source in citrus, both active at ≥−3°C.
Phototropic stimulation does not induce unequal distribution of indole‐3‐acetic acid in maize coleoptiles
Authors: Togo Shigenori , Hasegawa Koji
Published: May 2006

Distribution of endogenous diffusible auxin into agar blocks from phototropically stimulated maize coleoptile tips was studied using a bioassay and a physicochemical assay, to clarify whether phototropism in maize coleoptiles involves a lateral gradient in the amount of auxin. At 50 min after the onset of phototropic stimulation, when the phototropic response was still developing, direct assay of the blocks with the Avena curvature test showed that the auxin activity in the blocks from the shaded half‐tips was twice that of the lighted side, at both the first and second positive phototropic curvatures. However, physicochemical determination following purification showed that the amount of indole‐3‐acetic acid (IAA) was evenly distributed in the blocks from lighted and shaded coleoptile half‐tips at both the first and second positive phototropic curvatures. The even distribution of the IAA was also confirmed with the Avena curvature test following purification by HPLC. These results indicate that phototropism in maize coleoptiles is not caused by a lateral gradient of IAA itself and thus cannot be described by the Cholodny‐Went theory. Furthermore, the lower auxin activity in the blocks from the lighted half‐tips suggests the presence of inhibitor(s) interfering with the action of auxin and their significant diffusion from unilaterally illuminated coleoptile tips.
Phytochrome and photoperiodic induction
Authors: Thomas Brian
Published: May 2006

The photoreceptor phytochrome has been extensively characterized at the chromophore, protein and gene level. It consists of a family of red/far‐red reversible molecules and the genes for three members have been sequenced. Phytochromes are chromoproteins, which probably exist as dimers in vivo. Photoperiodism in higher plants involves the interaction of phytochrome with an endogenous timekeeping system. The interaction is complex, and several distinct actions of light can be distinguished. The possible involvement of different phytochromes in different actions of light in both long‐day plants and short‐day plants is discussed. Potential roles for different members of the phytochrome family and homo‐and hetero‐dimers of phytochrome are proposed.