bluuebunny/crossref_metadata_2025 huggingface dataset:
A morphological and cytological study of Petunia hybrida exposed to UV‐B radiation
Authors: Staxén Irina , Bornman Janet F.
Published: May 2006

The aim of this study was to investigate whether the cytoskeleton, and in particular the microtubular system, is affected by enhanced levels of ultraviolet‐B (280–320 nm, 9 kJ m−2 day−1 biologically effective UV‐B radiation) radiation in epidermal cells of Petunia x hybrida Vilm, isolated from leaves of plants grown under UV‐B radiation and visible light. In addition, morphological changes during development were monitored. In a previous study microtubules were depolymerized and delays in the different stages of the cell cycle were found when protoplasts of Petunia were irradiated with UV‐B radiation (Staxén et al. 1993. Protoplasma 173: 70–76). Thus it was of interest to ascertain whether the cytoskeleton would be similarly affected in an intact system. Assuming an effect of UV‐B radiation on the microtubular system, we wished to determine whether this could be correlated to concomitant changes in leaf morphology. Plants of Petunia hybrida were grown in greenhouse conditions in the presence or absence of UV‐B radiation. During the course of the experiment, samples were taken from young, expanding leaves and from older, fully expanded leaves and prepared for localization and analysis of microtubules from the adaxial epidermal cells. Morphology rather than the cytoskeleton was affected by UV radiation, despite the fact that the epidermal cytoskeleton would most likely be affected, since it is located in the cells which form the first intercepting layer for incident radiation.

Morphological changes under UV‐B radiation, as compared to those under control conditions, were reflected in earlier flowering and an increase in leaf number. Cell division was thus stimulated as was also evidenced from the increased leaf area. Our results indicate that the number of stomata differentiated on a leaf area basis was not altered although the number of stomata per epidermal cell was reduced.
Toxins of Pseudomonas syringae pv. syringae affect H+‐transport across the plasma membrane of maize
Authors: Di Giorgio Domenico , Camoni Lorenzo , Ballio Alessandro
Published: May 2006

The activity of some phytotoxic metabolites of Pseudomonas syringae pv. syringae Van Hall strains B359 and B301 on in vivo and in vitro systems of H+‐transport across the plasma membrane of maize (Zea mays L., hybrid Paolo) was investigated. In particular syringomycin, the first lipodepsinonapeptide isolated from Pss and already studied in plants and yeasts for its effects on several physiological systems, was compared with the recently described lipodepsipeptides with 22 or 25 amino acid residues, so called syringopeptins. The in vivo activity of the phytotoxins was tested on fusicoccin‐stimulated H−‐extrusion from cuttings of maize roots, which was inhibited by both types of toxins, with syringomycin more efficient than the syringopeptins. In vitro the H+‐ATPase activity of predominantly right‐side‐out plasma membrane vesicles purified by two‐phase partitioning was stimulated by 10 μM syringomycin and inhibited by higher levels, in agreement with the results of others with preparations of dicotyledons. Also the inhibition of the phosphohydrolytic activity of inside‐out vesicles of mung bean plasma membrane was confirmed for maize. In both types of vesicles the syringopeptirts were better inhibitors than syringomycin. The pH gradient formed on addition of ATP to predominantly (25% latency) inside‐out vesicles was immediately and completely collapsed by syringomycin and syringopeptins; H+‐pumping was prevented if the toxins were added before ATP. The inhibition was concentration dependent, but at very low concentrations the effect was inverted. The results of the present investigation, carried out with maize preparations, confirm and extend the evidence so far obtained with dicotyledons in favour of the plasma membrane as an important site of interaction of syringomycin with the plant cell. They also indicate that, except for some details, the effects of syringopeptins at the level of the plasma membrane are the same as those of syringomycin.
Photoactivation of the latent water‐oxidizing complex in photosystem II membranes isolated from dark‐grown spruce seedlings
Authors: Kamachi Hiroyuki , Tamura Noriaki , Yoshihira Takashi , Oku Tatsuo
Published: May 2006

Photosystem II membranes (D‐PSII) were isolated from dark‐grown spruce seedlings. All major PSII proteins except the 17‐ and 23‐kDa extrinsic proteins were present in D‐PSII. O2 evolution and Mn content in D‐PSII were negligible, while PSII‐donor activity showed a value comparable to that of NH2OH‐treated PSII membranes (NH2OH‐L‐PSII) from light‐grown seedlings. Light incubation of D‐PSII with 1 mM MnCl2, 50 mM CaCl2 and 100 μM DCIP at pH 5.3 resulted in activation of the latent water‐oxidizing complex. Accomplishment of photoactivation of PSII membranes from dark‐grown spruce seedlings clearly indicates that only ligation of Mn2+ to the apo‐water oxidizing complex is required for expression of O2 evolution, and that protein synthesis is not involved in the photoactivation process. There was no essential difference between ‘photoactivation’ of naturally Mn‐free PSII membranes and ‘photoreactivation’ of artificially Mn‐depleted PSII membranes on kinetics, pH dependence, Mn2+‐concentration dependence. However, kinetics and pH dependence of photoactivation were appreciably different in spruce PSII membranes and in PSII membranes of angiosperms such as wheat and spinach.
Effects of moderately enhanced levels of ozone on the acyl lipid composition of leaves of garden pea (Pisum sativum)
Authors: Carlsson Anders S. , Hellgren Lars I. , Selldén Gun , Sandelius Anna Stina
Published: May 2006

Plants of garden pea (Pisum sativum L.) were exposed to charcoal‐filtered air with or without addition of 65 ± 5 l−1 ozone. Plants were harvested daily for 9 days and lipids were extracted from the second‐oldest leaf. Visible injury of this leaf was evident from day 5 on, while the differences in lipids between ozone and control treatments were observed earlier. Ozone caused large decreases in the contents of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), a slower decrease in the content of phosphatidylcholine (PC), but an increase in the content of phosphatidylethanolamine (PE) per leaf area, compared with exposure to charcoal‐filtered air. The content of phosphatidylglycerol (PG) was unaffected by ozone. Compared with charcoal‐filtered air, fumigation with ozone resulted in a decrease in the proportion of linolenic acid (18:3) of the total lipid extract, with a concomitant increase in the proportion of linoleic acid (18:2). For individual lipids, ozone caused a similar pattern of decreased 18:3 and increased 18:2 in MGDG, SQDG, PC and PE, while the fatty acid composition of DGDG was unaffected. In PG, ozone decreased the proportions of 18:3 and trans‐Δ3‐decenoic acid (16:1trans), balanced by increased proportions of palmitic and oleic acids. The contents of chlorophylls and carotenoids were unaffected by ozone. Our results show that moderately elevated levels of ozone cause significant changes in the polar lipid composition of garden pea leaves and in the level of unsaturation of the lipid acyl groups and, furthermore, that ozone has different effects, which could be direct or indirect, on chloroplast lipids (MGDG, DGDG, SQDG, PG acylated with 16:1trans) and cytosolic membrane lipids.
Purification and some properties of starch branching enzyme (Q‐enzyme) from tuberous root of sweet potato
Authors: Nakayama Shigeki , Nakamura Yasunori
Published: May 2006

The pattern of isoforms of starch branching enzyme II or Q‐enzyme II in the tuberous root of sweet potato was distinct from those of other organs; altogether 7 isoforms of QEII were contained in the sweet potato plant. The QEIIf isoform, one of the two major QEII isoforms in the tuberous root, was purified to homogeneity by using a variety of HPLC columns. The purified QEIIf was a monomeric protein with a molecular mass of about 85 kDa. Western blot analysis showed that the polyclonal antibodies raised against the purified QEIIf was significantly reactive to the rice endosperm QEI, but not to the rice endosperm QEIIa. Furthermore, the sweet potato QEIIf reacted with the antiserum raised against the rice endosperm QEI, but not with that against the rice endosperm QEIIa. The results suggest that the sweet potato QEIIf is more similar to the rice endosperm QEI than to the rice endosperm QEIIa.
Using planar lipid‐bilayers to study plant ion channels
Authors: White P.J. , Tester M.
Published: May 2006

Ion channels are found in most plant membranes. They catalyse the rapid passive uniport of particular ions with varying selectivity. Planar lipid‐bilayer (PLB) techniques have been developed to study the electrical activities of single ion channels in well‐defined lipid and aqueous environments. They greatly facilitate both the biophysical and biochemical characterisation of ion channels and complement both conventional impaling electrode and membrane‐patch voltage‐clamping (patch‐clamping) electrophysiological techniques applied in vivo. Bilayers can be formed across the end of patch‐clamp pipettes or across apertures in specifically designed chambers. Ion channels in native membranes and purified, genetically altered or synthetic ion channels, proteins and peptides can all be studied in PLBs. The main applications of PLBs are (1) to study ion channels in membranes inaccessible to patch‐clamp electrodes, (2) to provide a functional assay system during channel‐protein purification and (3) to investigate the relationship between the molecular structure of ion channels and their conductance properties. In the present article we describe the techniques available for reconstitution and analysis of ion channels in PLBs and discuss how the PLB technique has been, and may be, useful to the study of plant ion channels.
A retrospective analysis of peer review at Physiologia Plantarum
Authors: Murphy Terence M. , Utts Jessica M.
Published: May 2006

An analysis of 134 reviews of manuscripts submitted to the North American Editorial Office of Physiologia Plantarum in 1993 compared personal/professional characteristics of the reviewers and the specificity of the interest and experience of the reviewers, relative to the reviewed paper, to the depth and tone of the reviews, the presence of constructive suggestions, and the recommendations for or against publication. There was no significant difference between the reviews from the reviewers of different ranks or degrees of seniority, of different employment sectors, of different degrees of interest and experience in the subject of the paper, or of other subgroups, except that reviewers whose interest and experience were very specific to the topic of the paper tended to give more constructive suggestions, and assistant professors tended to be less accepting of papers than editors more frequently than did reviewers in general. Recommendations regarding a manuscript were more similar than could be accounted for by chance, providing a positive indication of the reliability of the review‐system. Editors in their decisions tended to follow the recommendations of reviewers, but when reviewers took an extreme tone, either positive or negative, the editors tended to provide a balancing function. The data provide support for the reliability and lack of bias in a commonly used peer‐review system.
Stereoselectivity and structural determinants in molecular recognition by the ACC transport system in isolated maize mesophyll vacuoles
Authors: Saftner Robert A.
Published: May 2006

The ethylene precursor, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), is actively transported across the tonoplast of plant cells, impacting cellular compartmentation of ACC and ethylene biosynthesis. In the present study, the effects of ACC and amino acid analogs on ACC uptake into isolated maize (Zea mays L. cv. Golden Cross Bantam) mesophyll vacuoles were investigated to identify the stereospecific and structural features that are important in molecular recognition by the ACC transport system. Of the four stereoisomers of l‐amino‐2‐ethylcyclopropane‐l‐carboxylic acid (AEC), (1S, 2R)‐(–)‐AEC having a configuration corresponding to an L‐amino acid was the preferred substrate for the ACC transport system, competitively inhibiting ACC transport with a Ki of 18 μM. Of 11 neutral amino acid stereoisomers, L‐isomers were stronger inhibitors of ACC transport than corresponding D‐isomers. Neutral L‐amino acids with nonpolar side chains generally were more inhibitory than those with polar side chains, whereas several cationic and anionic L‐amino acids were ineffective antagonists of ACC transport. These observations suggest that the ACC transport system is stereospecific for relatively nonpolar, neutral L‐amino acids. This conclusion was supported by the observation that group additions, substitutions, or deletions at the carboxyl. α‐amino and the Pro‐ (R) methylene or hydrogen moieties (analogous to D‐amino acids) of ACC and other neutral amino acids and analogs essentially eliminated transport inhibition. In contrast, L‐amino acid analogs with variable substitutions at the distal end of the molecule remained antagonists. The relative activity of analogs was influenced by the length and degree of unsaturation of the side chain and by the location of side chain branching. Increasing the ring size of ACC analogs reduced antagonism whereas incorporating the α‐amino group into the ring structure as an L‐amino acid increased antagonism. The kinetics of L‐methoxyvinylglycine, L‐methionine. p‐nitro‐L‐phenylalanine and 1‐aminocyclobutane‐l‐carboxylic acid were competitive with Ki values of 3, 13, 16 and 19 μM, respectively. These results indicate that the ACC transport system can be classifie as a neutral L‐amino acid carrier having a relatively high affinity for ACC and other nonpolar amino acids. The results also suggest that the carrier interacts with the carboxyl, α‐amino and Pro‐(R) groups and with other less restricted side chain substituents of substrate amino acids.
Phytochrome‐mediated effects on extracellular peroxidase activity, lignin content and bending resistance in etiolated Vicia faba epicotyls
Authors: Casal Jorge J. , Mella R. Alejandra , Ballaré Carlos L. , Maldonado Sara
Published: May 2006

Etiolated Vicia faba seedlings were exposed to continuous red light to investigate whether changes in extracellular peroxidase activity were correlated in time and localization with changes in extension growth and/or lignin content in the subapical region of the epicotyl. Continuous red light: (a) increased extracellular peroxidase activity after a lag of ca 0.5 h, followed by a maximum peak after 2.5 h due to slightly acidic isoforms (pI = 6–6.5, according to isoelectrofocusing gels), a minimum after 4 h and a second maximum after 8 h due to acidic isoforms (pI=4–5), (b) increased lignin content and epicotyl resistance to bending after a lag of ca 4 h, i.e. simultaneously with changes in acidic extracellular peroxidase activity, and (c) reduced extension growth to a stable rate after a lag of ca 1 h, not coinciding with the kinetics of any of the extracellular peroxidase isoforms. These effects of continuous red light were at least partially mediated by phytochrome. Tissue printing and anatomical studies revealed red light effects on extracellular peroxidase activity and lignin content mainly in the outer cortical parenchyma. The results are consistent with the involvement of phyto‐chrome‐mediated effects on extracellular peroxidases (acidic isoforms) in the transduction chain leading to lignin responses to red light.
Photoinhibition, xanthophyll cycle and in vivo chlorophyll fluorescence quenching of chilling‐tolerant Oxyria digyna and chilling‐sensitive Zea mays
Authors: Koroleva Olga Y. , Brüggemann Wolfgang , Krause G. Heinrich
Published: May 2006

The relationship between susceptibility to photoinhibition, zeaxanthin formation and chlorophyll fluorescence quenching at suboptimal temperatures was studied in chilling‐sensitive maize and in non‐acclimated and cold‐acclimated Oxyria digyna, a chilling‐tolerant plant of arctic and alpine habitats. In maize, zeaxanthin formation was strongly suppressed by chilling. Zeaxanthin formed during preillumination at 20°C did not protect maize leaves from photoinhibition during a subsequent high‐light, low‐temperature treatment, as judged from the ratios of variable to maximal fluorescence, Fv/Fm. However, such preillumination significantly increased non‐photochemical quenching (qN) at low temperatures, mainly due to an enhancement of the fast‐relaxing qN component (i.e., of energy‐dependent quenching. qE). In O. digyna, cold‐acclimation resulted in an increased zeaxanthin formation in the temperature range of 2.5–20°C. Cold‐acclimation substantially decreased the susceptibility towards photoinhibition at 4°C, but qN remained nearly unchanged between 2 and 38°C, as compared to control plants. Effects of cold acclimation on photosynthesis, photochemical quenching and quantum efficiency of photosystem II were small and indicated a slight amelioration only of the function of the photosynthetic apparatus at suboptimal temperatures (2–20°Ct. I) is concluded, that the xanthophyll cycle is strongly influenced by cold acclimation, while effects on the photosynthetic carbon assimilation only play a minor role in O. digyna.
Respiratory energy requirements and rate of protein turnover in vivo determined by the use of an inhibitor of protein synthesis and a probe to assess its effect
Authors: Bouma T. J. , De Visser R. , Janssen J.H.J.A. , De Kock M.J. , Van Leeuwen P.H. , Lambers H.
Published: May 2006

Protein turnover is generally regarded as a major maintenance process, but experimental evidence to support this contention is scarce. Here we quantify the component of dark respiration rate associated with overall protein turnover of tissues in vivo. The effect of an inhibitor of cytosolic protein synthesis (cycloheximide, CHM) on dark respiration was tested on a cell suspension from potato (Solanum tuberosum L.) and quantified on leaf discs of expanding and full‐grown primary leaves of bean (Phaseolus vulgaris L.). The in vivo effect of CHM on protein biosynthesis was assessed by monitoring the inhibition of the induction of the ethylene‐forming enzyme (EFE) activity. The present method yields the energy costs of turnover of the total pool of proteins irrespective of their individual turnover rates. Average turnover rates were derived from the respiratory costs and the specific costs for turnover.

Inhibition of respiration by CHM was readily detectable in growing‐cell suspensions and discs of expanding leaves, The derived respiratory costs of protein turnover in expanding leaves were maximally 17–37% of total respiration. Turnover costs in full‐grown primary leaves of bean amounted to 17–21% of total dark respiration. The maximum degradation constants (i.e. Kd‐values) derived for growing and full‐grown leaves were up to 2.42 × 10−6 and 1.12 × l0−6 s−1, respectively.
Occurrence of polygodial in plant organs and tissue culture of Polygonum hydropiper
Authors: Hagendoorn Marc J.M. , Geelen Threes A.M. , van Beek Teris A. , Jamar Diaan C.L. , Tetteroo Frans A.A. , van der Plas Linus H.W.
Published: May 2006

Shoots of Polygonum hydropiper L. (waterpepper), especially in the leaves and flower‐heads, contain significant amounts of the sesquiterpenoid polygodial, a compound with a potential use as a natural pesticide. The polygodial content of the tepals is particularly high: up to 8.5% of the dry weight. Roots and seeds do not contain detectable amounts of polygodial. Polygodial containing organs e.g. leaves and tepals, were found to contain cavities. Fourier transform infra‐red (FTIR) microspectroscopy demonstrated that polygodial or its congeners are found in these cavities but not in other tissues or cells. Comparable cavities containing polygodial‐like compounds were absent in the closely related species Polygonum persicaria L.

Callus cultures and cell suspensions as well as root‐ and shoot cultures were initiated from mature P. hydropiper plants. Polygodial could be detected only in shoot cultures. Our results indicate that functioning plastids may be essential for polygodial production and cavities for its accumulation.
Ascorbic acid effect on the onset of cell proliferation in pea root
Authors: Citterio Sandra , Sgorbati Sergio , Scippa Stefania , Sparvoli Elio
Published: May 2006

The ability of ascorbic acid to induce cell proliferation of non‐cycling cells was investigated in quiescent embryo root of Pisum sativum L. cv. Lincoln, as well as in the active plantlet root meristem, where a minor portion of the cells is non‐proliferating. Quiescent embryo cells speeded up the G0–G1 transition during germination in the presence of ascorbic acid. In addition, proliferating cells present in the root tip of 3‐day‐old plantlets, arrested at the G1/S boundary by hydroxyurea, resumed the cycle earlier than the control, when treated with ascorbic acid. In contrast, ascorbic acid was unable to induce the proliferation of non‐cycling cells present in the active meristem. Therefore, these data suggest that the ability of ascorbic acid lo induce cell proliferation depends on the physiological status of the cell. In particular the data indicate that ascorbic acid is involved in cell proliferation as a factor necessary to enable already competent cells to progress through the cell cycle phases, but not as a factor able to induce non‐competent cells to overcome proliferation arrest.
Interaction of paclobutrazol and indole‐3‐butyric acid in relation to rooting of mung bean (Vigna radiata) cuttings
Authors: Wiesman Z. , Riov J.
Published: May 2006

Paclobutrazol (PB) only slightly stimulated the rooting of mung bean cuttings but, interestingly, the number of adventitious roots formed was dramatically increased when PB was used together with indole‐3‐butyric acid (IBA). Application of PB in the first phase of root formation, when root initials are induced, caused the greatest enhancement of the promotive effect of IBA on rooting. Investigation of the effect of PB on uptake, transport and metabolism of [5‐3H]‐IBA in mung bean cuttings revealed some changes in the rate of metabolism of IBA in comparison with control cuttings. PB was found to be involved in the partitioning of carbohydrates along the cuttings. Application of sucrose, like PB to the base of IBA‐treated cuttings enhanced the effect of IBA. The patterns of the effects of PB and IBA, separately and together, on rooting were similar in defoliated and intact cuttings, however the number of roots was much lower in the defoliated cuttings, which lacked a source of assimilates. PB counteracted the effect of GA3 in the upper regions of the cuttings and seemed to increase the sink capacity at the base of the cuttings. The results of the present study clearly demonstrated the enhancing influence of PB on IBA stimulation of the rooting of mung bean cuttings. It is suggested that PB may affect the rate of metabolism of IBA during rooting and the status of the local sink, in the base of the cuttings, thus partially contributing to the enhancement of the rooting‐promotive effect of IBA.
Identification and characterization of a nitrate reductase gene from bean (Phaseolus vulgaris) containing four introns
Authors: Jensen Poul E. , Hoff Tine , Møller Marianne G. , Stummann Bjarne M. , Henningsen Knud W.
Published: May 2006

A structural gene encoding nitrate reductase (NR) in bean (Phaseolus vulgaris) has been cloned and sequenced. The NR gene encodes a protein of 890 amino acids with a molecular mass of 100 kDa. Comparison to the other known NR gene from bean reveals 76% amino acid identity and comparison to NRs from other species shows amino acid identities ranging from 67 to 77%. At three positions the amino acid sequence displays differences from residues conserved in all other known NR proteins. The coding sequence is interrupted by four introns. Three of them are located at conserved positions in the region encoding the molybdenum cofactor‐binding domain. The fourth intron is located in the hinge region between the heme and the FAD domain. This is the only example in which more than three introns have been found in a higher plant NR gene. The mRNA cap site was identified as an adenosine 79 nucleotides (nt) upstream of the ATG translation start codon. Northern analysis shows that the gene is nitrate inducible and highly expressed in trifoliolate leaves of 20‐day‐old bean plants and only weakly expressed in roots. The gene is also induced by light and sucrose in leaves of dark‐adapted plants. The mRNA displays diurnal oscillation under the control of a circadian rhythm. Putative conserved GATA motifs in the promoter are discussed.
Stress‐induced factors involved in flower formation in Lemna
Authors: Takimoto Atsushi , Kaihara Sumiko , Yokohama Mineyuki
Published: May 2006

At a concentration equivalent to 0.3–1 μM, the norepinephrine solution in which the drought‐stressed plants of Lemna paucicostata 441 were immersed for 2 h, induced flowering in L. paucicosrata 151. Not only drought stress but also osmotic stress, 5 min on 0.5 M mannitol solution, and heat stress, 5 min on 45–55°C hot water, were effective in producing or releasing a factor capable of activating norepinephrine. Such a putative factor has been designated as factor C, The first supernatant obtained after immediate centrifugation of the homogenate of the plants had only weak factor C activity, hut the second supernatant, obtained after a 30‐min incubation of the suspension of the first pellet, showed high factor C activity. The water in which Lemna plants subjected to both drought and heat stresses had been immersed for 2 h. showed flower‐inducing activity even in the absence of added norepinephrine.
Effect of short‐chain fatty acids on the ethylene pathway in embryonic axes of Cicer arietinum during germination
Authors: Gallardo Mercedes , De Rueda Paloma Muñoz , Matilla Angel Jesús , Sánchez‐Calle Isabel Mariá
Published: May 2006

The effect of short‐chain saturated fatty acids (C5–C10) on the biosynthesis of ethylene in embryonic axes of chick‐pea (Cicer arietinum L.) seeds was investigated. The emergence of radicle and fresh weight of embryonic axes diminished with increasing number of carbons. The inhibition of germination caused by lower concentrations (1 mM) of fatty acids (C5–C10) was partially reversed by exogenous 1‐aminocyclopropane‐1‐carboxylic acid (ACC), whereas exogenous ethylene was able to overcome the inhibitory effect provoked by all concentrations (1–5 mM) of applied fatty acids (C5–C10). Ethylene production rates, and enzyme activities of ACC synthase and ACC oxidase decreased concomitantly with the molecular mass and increasing concentration of fatty acids. The inhibitory effect of these acids on ethylene production seems to result not only from a decreased ACC synthesis, but also from an enhancement of 1‐malonylamino)cyclopropane‐1‐carboxylic acid (MACC) synthesis.
Nitrogen reallocation and photosynthetic acclimation in response to partial shading in soybean plants
Authors: Pons T.L. , Pearcy R. W.
Published: May 2006

The first trifoliate of soybean was shaded when fully expanded, while the plant remained in high light; a situation representative for plants growing in a closed crop. Leaf mass and respiration rate per unit area declined sharply in the first few days upon shading and remained rather constant during the further 12 days of the shading treatment. Leaf nitrogen per unit area decreased gradually until the leaves were shed. Leaf senescence was enhanced by the shading treatment in contrast to control plants growing in low light. Shaded leaves on plants grown at low nutrient availability senesced earlier than shaded leaves on plants grown at high nutrient availability. The light saturated rate of photosynthesis decreased also gradually during the shading treatment, but somewhat faster than leaf N, whereas chlorophyll contents declined somewhat slower than leaf N.

Partitioning of N in the leaf over main photosynthetic functions was estimated from parameters derived from the response of photosynthesis to CO2. It appeared that the N exported from the leaf was more at the expense of compounds that make up photosynthetic capacity than of those involved in photon absorption, resulting in a change in partitioning of N within the photosynthetic apparatus. Photosynthetic nitrogen use efficiency increased during the shading treatment, which was for the largest part due to the decrease in leaf N content, to some extent to the decrease in respiration rate and only for a small part to change in partitioning of N within the photosynthetic apparatus.
Chitinase and β‐1,3‐glucanase activities in chickpea (Cicer arietinum). Induction of different isoenzymes in response to wounding and ethephon
Authors: Cabello Francisco , Jorrín Jesús V. , Tena Manuel
Published: May 2006

Chitinase and β‐1,3‐glucanase activities were assayed in roots, stems and leaves of 12‐day‐old chickpea (Cicer arietinum L.) plants. While glucanase activity was higher in roots than in the aerial parts of the plant, leaves had higher Chitinase activity. Both glucanase and chitinase activities were induced in roots and stems in response to wounding (excision into 1‐cm pieces), with activity increasing 6 h after treatment, reaching a maximum between 24 and 48 h, and thereafter remaining nearly constant up to 72 h. Ethephon treatment also induced β‐1,3‐glucanase and chitinase activities in stems but not in roots. Both enzymes occurred in root and stem tissues as a complex mixture of isoenzymes. At least four different peaks with glucanase and chitinase activities could be resolved by gel filtration chromatography on Sephacryl S‐200 and chromatofocusing on PBE 94 (pH 4–7). Following ammonium sulfate precipitation and ion exchange on CM‐ and DEAE‐Trisacryl, three β‐1,3‐glucanase and chitinase fractions, referred to as basic, neutral and acidic, were separated on the basis of their chromatographic behaviour. Most of the total protein (75%) of stem extracts was found in the acidic fraction, whereas the major glucanase (53%) and chitinase (62%) activities were in the basic and neutral fractions, respectively. While wounding resulted in an increase in the neutral glucanase and chitinase activities, the activities of the acidic fractions were promoted by ethephon.
Effects of exogenous gibberellins and paclobutrazol on floral stalk growth of tulip sprouts isolated from cooled and non‐cooled tulip bulbs
Authors: Rebers Mariken , Romeijn Gaea , Knegt Erik , van der Plas Linus H.W.
Published: May 2006

The involvement of gibberellins (GAs) in the regulation of floral stalk elongation and flower development has been studied in tulip. The biological activity of GA4 and GA9, both endogenous in tulip bulb sprouts, and GA1, was tested in vitro on sprouts of cooled and non‐cooled tulip bulbs (Tulipa gesneriana L. cv. Apeldoorn), in the presence or absence of the GA biosynthesis inhibitor paclobutrazol. At early starting dates of incubation, floral stalks from both cooled and non‐cooled bulbs hardly showed any elongation in the absence of exogenous GA. Paclobutrazol had no effect on floral stalk elongation, and the response to GAs of sprouts from cooled bulbs was greater than that of sprouts from non‐cooled bulbs. At later starts of incubation, considerable floral stalk elongation occurred without GA application. Paclobutrazol inhibited this floral stalk elongation, and the growth of sprouts from both cooled and non‐cooled bulbs was stimulated by GA application. The effect of paclobutrazol was reversed by simultaneous application of GA4 or GA9. Application of GA with and without paclobutrazol resulted in the same elongation of the floral stalk, indicating the absence of substantial side effects of the inhibitor. The isolated sprouts did not develop a full‐grown flower without the addition of GA. GA4 was more effective than GA9 in stimulating this flower development. The results demonstrate that both sprouts from cooled and non‐cooled bulbs are responsive to exogenous GAs in vitro, and may be a site of GA biosynthesis.
Interpreting changes in stem diameter in rose plants
Authors: Urban L. , Fabret C. , Barthélémy L.
Published: May 2006

Sixteen adult rose plants (Rosa hybrida cv. Sweet Promise) were grown in rockwool in a phytotron. Water uptake was estimated by computing the difference between the rate of nutrient solution supply and the rate of leaching, continuously measured using a high‐precision flowmeter. Transpiration was measured using a balance continuously recording the loss of weight in the entire system. Changes in stem diameter were recorded using linear variable differential transducers placed at the base of four developing shoots and on their corresponding basal stems. Changes in stem diameter were related to changes in the water content of 16 plants. The amplitude of shrinkage in daytime stem diameter and daily increase in stem diameter was lower in basal stems. Radial hydraulic resistance to water diffusion in stems seems to be very low and stem reservoirs appear to be very early sensors of water depletion. When the nutrient solution supply was suppressed, the amplitude of the daily increase in stem diameter and transpiration rates were reduced one and one‐and‐a‐half days later, respectively. When water depletion became more severe, stem diameter decreased from one day to another. The amplitude of daily stem shrinkage increased sharply for 6 days after watering was stopped, while the bulk modulus of elasticity of leaves decreased, probably as a result of damage to the cell wall.
Cadmium and copper change root growth and morphology of Pinus pinea and Pinus pinaster seedlings
Authors: Arduini Iduna , Godbold Douglas L. , Onnis Antonino
Published: May 2006

Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 μM CdSO4 or with 1 μM CdSO4 and 1 μM CuSO4 combined. In both species tap‐root elongation was drastically reduced in the 5 μM Cd2+ and in the (Cd2++ Cu2+) treatments. A supply of 0.1 or 1 μM Cd2+, however, enhanced root elongation in Pinus pinea without significantly influencing root elongation in Pinus pinaster. In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd2+ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd2+ concentrations and when Cd2+ and Cu2+ were combined. The data suggest that cell elongation is more sensitive to Cd2+ than cell division. The number and length of the lateral roots were also affected by Cd2+ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd‐ tolerance of the two species.
Nitrogen metabolism in cultured cotyledon explants of Pinus radiata during de novo organogenesis
Authors: Joy Richard W. , Bender Ludwig , Thorpe Trevor A.
Published: May 2006

Nitrogen metabolism was investigated under shoot‐forming (SF) and non‐shoot‐forming (NSF) conditions in cultured cotyledon explants of Pinus radiata by following the incorporation of [14C]‐l,2‐acetate into various metabolites. Early in culture, the lipid fraction contained the most 14C; however, this percentage decreased in favor of increased label in the amphoteric fraction. Label in the amphoteric fraction of SF cultures decreased by day 21 but plateaued in NSF cultures at this time. Radioactive labeling of the principle nitrogen metabolites, glutamate and glutamine, which made up the majority of the amphoteric fraction, paralleled labeling patterns in the amphoteric fraction. Percentage label in glutamate remained at similar levels throughout the 21‐day culture period for both SF and NSF cultures. Specific activity of glutamate (kBq mg‐1) was significantly greater during promeristemoid formation in SF compared to that in NSF tissues. Glutamine labeling increased during shoot bud initiation in SF cultures, but dropped to lower levels during shoot bud development. In contrast, in NSF cultures, there was a continual and substantial increase in glutamine labeling throughout the 21‐day culture period. These trends were similar when the specific activities of glutamine were determined, as there was a continual decrease from culture initiation to the end of shoot bud differentiation in SF cultures. In NSF cultures, in contrast, specific activity of glutamine increased substantially from day 5 to 21 relative to that in SF cultures. The nitrogen assimilation enzymes glutamate synthase and glutamine synthase increased in activity from day 0 to 21 for both SF and NSF tissues. Enzyme activities for glutamate dehydrogenase were similar in both treatments to day 10 in culture but subsequently diverged, with activities in NSF cultures being substantially greater than those of SF cultures by day 21. Taken together, labeling and enzyme data indicate that nitrogen metabolism is enhanced during culture, especially in SF tissues at the time of promeristemoid formation, and in non‐organ‐forming tissue senescence‐like metabolism was exhibited later in culture.
Ecotypes of the fungus Bipolaris oryzae with various responses of the mycochrome system
Authors: Kihara J. , Kumagai T.
Published: May 2006

Two types of fungi based on the light required for induction of conidiophore formation are known as ‘photo‐induced’ and ‘non‐photo‐induced’ sporulators. Conidial development in a ‘photo‐induced’ strain of Bipolaris oryzae (formerly, Helminthosporium oryzae) is controlled by antagonistic action of blue and near‐UV radiation mediated through the ‘mycochrome’ system at two developmental stages: conidiophore induction and conidiophore maturation. Otherwise, conidial development in a ‘non‐photo‐induced’ strain of B. oryzae, unlike that in the ‘photo‐induced’ strain, is controlled by antagonistic action of blue and near‐UV radiation at the conidiophore maturation stage alone. In this study, we collected fungi, B. oryzae, from brown lesion spots on rice leaves cultivated in paddy fields, and investigated the possible existence of a new ecotype different from known ‘photo‐induced’ and ‘non‐photo‐induced’ sporulators. We also investigated the sensitivity of conidial development of each isolate to blue and near‐UV radiation.

The isolates were identified as B. oryzae by morphology of hyphae and conidia and the symptomatic brown lesion spots on rice leaves caused by each isolate. There was no distinction between ‘photo‐induced’ and ‘non‐photo‐induced’ strains on rDNA base. Moreover, the existence of a new type of ‘non‐photo‐induced’ sporulator different from the one presently known was confirmed. In this newly identified sporulator, conidial development was not affected by light irradiation. Among 153 isolates, one isolate belonged to a previously known ‘non‐photo‐induced’ sporulator, five isolates belonged to a new ‘non‐photo‐induced’ sporulator ecotype, and over 95% of the isolates were “photo‐induced” sporulators. Among ‘photo‐induced’ strains, there were several subtypes having different sensitivities to near‐UV radiation required for inducing conidiophore formation.
Comparative studies of coupled assays for phosphoenolpyruvate carboxylase
Authors: Wedding Randolph T. , Kline Katie
Published: May 2006

Phosphoenolpyruvate carboxylase (PEPC) from higher plants is usually assayed by using malate dehydrogenase (MDH) as a coupling enzyme. To avoid erroneous readings caused by metal ions, which convert oxaloacetate (OAA) to pyruvate, lactic dehydrogenase can be included. Reporting the total NADH used by both coupling enzymes gives the total OAA production. Microbial PEPC has been assayed by employing citrate synthase (CS) as a coupling enzyme which detects the reaction of CoA with Ellman's reagent. Comparable Km values for MgPEP are found with the two assays. When MDH alone is used as the coupling system, the Vmax value is about 60% larger than the one found with the CS assay. However, when MDH is added to the CS assay without the NADH cofactor, Vmax is brought back to the same level as that with the NADH‐coupled enzyme. Malate inhibition of PEPC assayed with the CS coupling system is blocked by low concentrations of citrate in the range produced in the assay. High concentrations of citrate inhibit PEPC. Glucose‐6‐phosphate in concentrations higher than 1 mM blocks the response of PEPC to added MDH in the CS assay.
Involvement of putrescine in the inductive rooting phase of poplar shoots raised in vitro
Authors: Hausman Jean‐François , Gevers Claire , Gaspar Thomas
Published: May 2006

Micropropagated poplar shoots rooted 100% on a rooting medium (A) containing NAA, but they did not root in the absence of auxin (NA). Putrescine, but not spermidine and spermine, promoted rooting up to 42% when added to the NA medium. Cyclohexylamine (CHA), an inhibitor of spermine synthase, also promoted (up to 36%) rooting in the absence of auxin. The inhibitors of polyamine biosynthesis DFMA (α‐difluoromethylarginine) and DFMO (α‐difluoromethylomithine), aminoguanidine (AG) and methylglyoxal‐bis‐guanylhydrazone (MGBG), inhibited rooting when applied in the presence of auxin and had no effect in its absence.

The rooting inductive phase (in the presence of auxin) was determined by periodical transfer of shoots from A to NA medium, and by changes in peroxidase activity, to be 7 h. Putrescine (not spermidine and spermine) accumulated to a maximum during the inductive phase. Both putrescine and CHA promoted rooting on NA medium when applied during the first 7 h. In contrast DFMA and AG inhibited rooting during this period. The results point to the involvement of putrescine and its Δ1‐pyrroline pathway, in the inductive phase of rooting in poplar shoots.
Ultraviolet absorption and epidermal‐transmittance spectra in foliage
Authors: Day T. A. , Howells B. W. , Rice W. J.
Published: May 2006

We examined the UV absorption spectra and the epidermal‐transmittance spectra (280–350 nm) of foliage from 42 plant species. Sun foliage was sampled from naturally growing individuals of seven species in each of six life forms comprising two evergreen groups (gymnosperms and angiosperms) and four deciduous angiosperm groups (trees, shrubs and vines, herbaceous dicotyledons and grasses). There were large differences in absorption spectra of whole‐leaf extracts among species. While absorbance declined with increasing wavelength in most woody species, there was a trough in absorbance around 300 nm in many herbaceous species. Absorption spectra were negatively correlated with epidermal‐transmittance spectra in 31 of the 42 species. Relationships between absorbance and transmittance did not follow the theoretical exponential function. Species rankings of UV‐screening effectiveness were similar when we assessed it by using epidermal transmittance at single wavelengths (300 or 320 nm) or different UV‐action spectra to weight epidermal‐transmittance spectra and estimate the levels of biologically effective UV reaching the mesophyll. Thus, differences in absolute epidermal transmittance among species appeared to overshadow spectral differences. Nevertheless, the differences we found in the internal UV spectral regime in foliage suggest that whole‐plant action spectra will differ among species. While species rankings of UV‐screening effectiveness were similar when different action spectra were used, the absolute amounts of biologically effective UV reaching the mesophyll of species varied considerably when different action spectra were used.
Superoxide dismutases of chestnut leaves, Castanea sativa: Characterization and study of their involvement in natural leaf senescence
Authors: Longa M. Angeles , del Río Luis A. , Palma Josè M.
Published: May 2006

Superoxide dismutases (SOD; EC 1.15.1.1) in chestnut (Castanea sativa Mill., cv. 431) leaves were characterized by native polyacrylamide gel electrophoresis. The three molecular forms of SOD were distinguished from each other by their different sensitivity to cyanide and H2O2 Three CuZn‐containing SODs were detected (CuZn‐SOD I, II. and III), and all the isozymes had a molecular mass of 33 kDa. CuZn‐SOD III was the most abundant isozyme. whereas CuZn‐SOD II was present in a minor amount. In leaves showing typical symptoms of senescence increases of 2.5‐. 7‐ and 4‐fold in the specific activities of CuZn‐SODs I, II, and III. respectively, were found. In addition, the pattern of the three isozymes was modified by the age of leaves, a rise in the CuZn‐SOD II and a decrease in the CuZn‐SOD 1 percentages being found in senescent leaves compared to green leaves. As to other activated oxygen‐related enzymes, an increase in the superoxide‐generating xanthine oxidase activity and a decline in both catalase and peroxidase activities during natural senescence of chestnut leaves were observed. Results obtained suggest that in natural senescence of chestnut leaves activated oxygen species are involved, and an overproduction of hydrogen peroxide and superoxide radicals probably takes place.
Purification and characterization of an anionic peroxidase from sycamore maple (Acer pseudoplatanus) cell suspension cultures
Authors: Dean Jeffrey F. D. , Sterjiades Raja , Eriksson Karl‐Erik L.
Published: May 2006

A 42 kDa anionic peroxidase (EC 1.11.1.7) having a pl of 3.6 was purified from suspension cultures of cells of sycamore maple (Acer pseudoplatanus L.) grown in the dark by a combination of lectin‐affinity, anion‐exchange and gel permeation chromatography. The enzyme had an amino acid composition similar to that found for other anionic plant peroxidases, but the protein was blocked to amino‐terminal protein sequencing. Commercially available antibodies against horseradish peroxidase were shown to cross‐react with the sycamore maple enzyme on immunoblots. The purified peroxidase displayed differences in its affinity for each of the three monolignols, and these differences were compared to those found for a commercial preparation of horseradish peroxidase, as well as a laccase (p‐diphenol:O2 oxidoreductase: EC 1.10.3.1) purified from sycamore maple cell suspension cultures. These results are discussed with respect to the role played by peroxidases in lignin deposition and host‐pathogen response.
Increased level of cytokinin ribosides in jasmonic acid‐treated potato (Solanum tuberosum) stem node cultures
Authors: Dermastia Marina , Ravnikar Maja , Vilhar Barbara , Kovač Maja
Published: May 2006

Cytokinin free bases, ribosides and 9‐glucosides were measured in stem node cultures of potato (Solanum tuberosum L. cv. Ulster Sceptre) in the presence or absence of 1 μM jasmonic acid (JA) to examine whether or not their changed levels were part of the JA‐induced growth response. The enhanced growth response in JA‐treated plantlets included: expanded root systems, extended leaf areas, increased number of nodes, and enlarged stem diameters. The protein analysis revealed a substantial decrease in a 62‐kDa polypeptide. On a dry weight basis, the levels of ribulose‐1,5‐biphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) and chlorophylls a and b were constant. The total concentration of endogenous cytokinins remained virtually the same in control and treated plantlets; but in JA‐treated plantlets the amount of cytokinin free bases and cytokinin 9‐glucosides decreased. In addition, the level of cytokinin ribosides was elevated. The ratio between active and inactive cytokinins increased from 1.2 to 2.1, which correlates with the enhanced growth of potato plantlets grown on 1 μM JA. Thus the observed growth and developmental changes may be a consequence of the measured altered cytokinin level. However, significant morphological alterations of the potato plantlets treated with JA may also be a result of the changed critical cytokinin concentration or critical ratios of cytokinins to auxins and JA, rather than their absolute concentrations.