bluuebunny/crossref_metadata_2025 huggingface dataset:
Lack of effect of photoperiod on metabolism of exogenous GA19 and GA1 in Salix pentandra seedlings
Authors: Olsen J.E. , Moritz T. , Jensen E. , Junttila O.
Published: May 2006

The effect of photoperiod on metabolism of 16,17‐[3H2]GA19, and 1.2‐[3H2]GA1 applied to intact seedlings of Salix pentandra, was investigated. No difference was found in conversion of 16,17‐[3H2]GA19 to 16,17‐[3H2]GA20, and 16,17‐[3H2]GA1, or in metabolism of 1,2‐[3H2]GA1 to [3H]GA8 between plants grown in continuous light and plants exposed for 14 days to a 12‐h photoperiod. Also, leaf discs from plants grown in long or short days, converted 16,17‐[3H2]GA19 both in light and darkness. These data on metabolism of 16,17‐[3H2]GA19, contrast with previous results, which have indicated a photoperiodic control of the metabolism of GA19 to GA20 in S. pentandra.

Presence of these applied labelled GAs and their metabolites in different parts of seedlings was recorded, after application to intact seedlings as well as to isolated plant parts. When 16,17‐[3H2]GA19 was applied through the roots of intact plants, the relative amounts of 16,17‐[3H2]GA1 present in leaves and shoot apices were higher than in roots and stems. In corresponding experiments with 1,2‐[3H2]GA1, relatively higher amounts of [3H2]GA8 were found in roots and stems than in leaves and shoot apices. Twenty‐four hours after application of 16,17‐[3H2]GA19 to isolated plant parts, 16,17‐[3H2]GA20 and 16,17‐[3H2]GA1 were found in leaves and roots, but not in internodes. Incubation of isolated plant parts with 1,2‐[3H2]GA1 for 24 h resulted in presence of [3H]GA8 in all parts.

The results mentioned above were obtained by monitoring metabolites by HPLC with on‐line radio counting. The conversions of 17‐[2H2]GA19 to 17‐[2H2]GA20 and 17‐[2H2]GA1 in shoot apices and whole seedlings, and of 17‐[2H2]GA8 in whole seedlings, were confirmed by GC‐MS.
Effects of defruiting on source‐sink relationship, carbon budget, leaf carbohydrate content and water use efficiency of apple trees
Authors: Wibbe Michael L. , Blanke Michael M.
Published: May 2006

Three‐year‐old apple (Malus domestica Borkh. cv. Golden Delicious) trees with ca 5 m2 leaf area each were grown in situ in lysimeters and defruited either in August. September or October. Net photosynthesis, dark respiration and water use efficiency were measured for 5 days prior to and after fruit removal. using tree canopy chambers and infrared gas analysis with a dedicated interface and software. Net photosynthesis of the tree canopy declined after defruiting. irrespective of the month of defruiting. The decline after fruit removal was 30‐40% in August or September and 57% in October. After defruiting in August or September, trees respired 50–60% slower in the dark, but 39% faster after defruiting in October. The excessive respiratory losses after fruit removal in October. when the tree lost more carbon than it assimilated. may have been induced by translocation of carbohydrates from the leaves to the perennial woody parts of the tree and by the onset of leaf senescence. Fruit removal in August or September increased water use efficiency by 31–41%. but decreased water use efficiency in October by 75%
Chronic photoinhibition in seedlings of tropical trees
Authors: Castro Yolanda , Fetcher Ned , Fernández Denny S.
Published: May 2006

Seedlings of five canopy species of tropical trees from Costa Rica and Puerto Rico were grown in full shade (midday range of photosynthetic photon flux density [PPFD], 100–140 μmol m−2 s−1), partial shade (midday PPFD, 400–600 μmol m−2 s−1) and full sun (midday PPFD, 1 500–1 800 μmol m−2 s−1) for 3 months. The species were Ochroma lagopus (Bombacaceae), a pioneer species; Inga edulis (Fabaceae), found in secondary forest; and Dipteryx panamensis (Fabaceae), Hampea appendiculata (Malvaceae), and Manilkara bidentata (Sapotaceae), three species characteristic of primary forest. After the plants were placed in the dark overnight, chlorophyll fluorescence characteristics were measured for recently expanded and mature leaves. The ratio of variable fluorescence to maximum fluorescence (Fv/Fm) was used to estimate the degree of chronic photoinhibition. Only individuals of one species, Dipteryx panamensis, showed significant depression of Fv/Fm after long‐term exposure to full sun. The depression was highly correlated with quantum yield of O2 evolution which also declined after exposure to full sun. The decline may have been related to foliar N concentration. Although all plants were supplied with ample nutrients, foliar N did not increase significantly for Dipteryx seedlings in full sun, whereas it did for Ochroma and Inga. Leaf age affected Fv/Fm only in the cases of Manilkara, where it was slightly lower in recently expanded leaves, and of Dipteryx where it interacted with the effects of light regime. We conclude that chronic photoinhibition is not common in seedlings of canopy trees of tropical rain forests except when availability of mineral nutrients may be limiting.
Inhibitory effects of auxins and related substances on the activity of an Arabidopsis glutathione S‐transferase isozyme expressed in Escherichia coli
Authors: Watahiki Masaaki K. , Mori Hitoshi , Yamamoto Kotaro T.
Published: May 2006

Glutathione S‐transferases (GSTs; EC 2.5.1.18) are encoded by a gene family. Some GSTs have the capacity to bind to indole‐3‐acetic acid (IAA), whereas the gene expression of other GSTs is regulated by auxin. In order to assess a possible physiological significance of the auxin binding of GST, we investigated effects of auxins on the activity of GST expressed in Escherichia coli. cDNA cloning was carried out for the fifth gene (GST5) of GST in Arabidopsis. Although the deduced amino acid sequence of GST5 was remotely related to that of the other Arabidopsis GSTs (less than 20% identical), the GST5 protein (GST5) expressed in E. coli showed GST activity. Apparent Km values of GST5 are 0.86 and 1.29 mM for glutathione (GSH) and 1‐chloro‐2,4‐dinitrobenzene, respectively. IAA, 2,4‐dichlorophenoxyacetic acid (2,4‐D), 1‐naphthaleneacetic acid (1‐NAA) and 2‐NAA inhibited the enzyme activity competitively with respect to GSH. The apparent Ki of IAA is 1.56 mM. Salicylic acid inhibited GST activity in a noncompetitive manner. 2,4‐D was the most inhibitory among the tested chemicals. GST5 bound to GSH‐immobilized agarose gel was effectively eluted by IAA. These results indicate that IAA and the related substances bind to GST5 at the GSH‐binding site, and exclude the possibility that the compounds could be substrates for GST5. Although the Ki value of IAA is too high for any physiological consequences, it might be assumed that GST activity is modulated in vivo by an auxin‐related substance(s). The steady‐state level of the GST5 mRNA was increased by wounding, heat shock, and spraying buffer on the plant, but was not influenced by auxin treatment.
Growth and photosynthetic response of three soybean cultivars to simultaneous increases in growth temperature and CO2
Authors: Ziska Lewis H. , Bunce James A.
Published: May 2006

Three soybean (Glycine max L. Merr.) cultivars (Maple Glen, Clark and CNS) were exposed to three CO2 concentrations (370, 555 and 740 μmol mol−1) and three growth temperatures (20/15°, 25/20° and 31/26°C, day/night) to determine intraspecific differences in single leaf/whole plant photosynthesis, growth and partitioning, phenology and final biomass. Based on known carboxylation kinetics, a synergistic effect between temperature and CO2 on growth and photosynthesis was predicted since elevated CO2 increases photosynthesis by reducing photorespiration and photorespiration increases with temperature. Increasing CO2 concentrations resulted in a stimulation of single leaf photosynthesis for 40–60 days after emergence (DAE) at 20/15°C in all cultivars and for Maple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO2 concentrations. Despite the season‐long stimulation of single leaf photosynthesis, elevated CO2 concentrations did not increase whole plant photosynthesis except at the highest growth temperature in Maple Glen and CNS, and there was no synergistic effect on final biomass. Instead, the stimulatory effect of CO2 on growth was delayed by higher temperatures. Data from this experiment suggest that: (1) intraspecific variation could be used to select for optimum soybean cultivars with future climate change; and (2) the relationship between temperature and CO2 concentration may be expressed differently at the leaf and whole plant levels and may not solely reflect known changes in carboxylation kinetics.
Stigmatic RNase in calamondin (Citrus reticulata var. austera x Fortunella sp.)
Authors: Roiz Levava , Goren Raphael , Shoseyov Oded
Published: May 2006

In calamondin. which is self‐compatible, ribonuclease (RNase) activity was found in the stigmatic diffusate. Tissue print experiments using calamondin styles demonstrated that most of the RNase is localized in the stigma. Stigmatic RNase activity was monitored at different developmental stages of the flower and was found to peak at anthesis. An SDS‐PAGE‐zymogram indicated the molecular mass of this RNase to be 24 kDa. In vitro germination of calamondin pollen showed a higher percentage of germination in the presence of diffusate from one stigma than in the control. However, diffusates from 3.5 and 7 stigmata per 100 μl aliquots of growth medium, exhibiting 15. 25 and 35 units ml−1 RNase activity, respectively, had successively stronger inhibition effects on the percentage of germination. Diffusate from 7 stigmata inhibited pollen tube elongation, as well as pollen germination. Both the 24‐kDa Stigmatic RNase and RNase TI significantly inhibited pollen germination and pollen tube elongation. In pollen tubes treated with either the 24‐kDa stigmatic RNase or RNase TI, considerable deposition of callose was observed, as compared to the control which had only a thin callosic cell wall.
Changes in the activity of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase in suspension‐cultured cells of Vitis
Authors: Suzuki Nao , Sakuta Masaaki , Shimizu Seki , Komamine Atsushi
Published: May 2006

3‐Deoxy‐D‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase (EC 4.1.2.15) is the first enzyme in the shikimate pathway, which leads to the biosynthesis of the aromatic amino acids. These amino acids are utilized as precursors for the synthesis of some secondary metabolites. The relationship between the accumulation of anthocyanin and the activity of DAHP synthase in suspension cultures of Vitis hybrid (Bailey Alicante A) was investigated. The activity of the plastidic isozyme, designated DS‐Mn, was very low throughout the culture of cells. However, the activity of the cytosolic isozyme, designated DS‐Co, increased transiently and then decreased after transfer of cells to fresh medium, reaching minimum levels during the logarithmic phase. Thereafter, the activity of DS‐Co increased rapidly prior to the accumulation of anthocyanin. When phosphate was removed from the culture medium, growth of cells was limited and rapid accumulation of anthocyanin occurred, coincident with the termination of cell division. The activity of phenylalanine ammonia‐lyase continued to increase from day 1 and the activity of DS‐Co in phosphate‐free culture also was 1.6‐fold greater than that in the control culture on day 1, while the activity of DS‐Mn was unaffected by this treatment. These results suggest a close correlation between the activity of DS‐Co and the biosynthesis of anthocyanin.
Regulation of anthocyanin biosynthesis in cell suspension cultures of Vitis in relation to cell division
Authors: Kakegawa Koichi , Suda Jun , Sugiyama Munetaka , Komamine Atsushi
Published: May 2006

Cell suspension cultures of Vitis produce anthocyanin in the dark after cessation of cell division. Production of anthocyanin was associated with increasing activities of phenylalanine ammonia‐lyase (PAL) and chalcone synthase (CHS) which followed transcript amounts. The level of endogenous phenylalanine, a precursor of anthocyanin, was also elevated before anthocyanin accumulated. Addition of phosphate to the medium at the early stationary phase induced cell division and completely inhibited the biosynthesis of anthocyanin. Activities of PAL and CHS did not increase in the stationary phase when phosphate was again added to the medium. The amount of phenylalanine decreased significantly after addition of phosphate. In contrast, when cells were inoculated into medium lacking phosphate, accumulation of anthocyanin was detected on day 2 and activities of PAL and CHS increased. The level of endogenous phenylalanine reached a maximum just before the initiation of anthocyanin synthesis.

When phenylalanine was added to the medium in mid‐logarithmic phase when the phenylalanine pool was lowest, the level of phenylalanine was immediately elevated and accumulation of anthocyanin was initiated. Enzymatic activity of CHS also increased by the addition of phenylalanine. Transcript level increased synchronously with changes in the amount of phenylalanine, after its addition.

We conclude that the induction of anthocyanin biosynthesis in cell suspension cultures of Vitis is triggered by high levels of endogenous phenylalanine following the cessation of cell division. Under these conditions, phenylalanine may be a signal that promotes transcription of genes of the anthocyanin biosynthetic pathway.
Seed dormancy in red rice. X. A 13C‐NMR study of the metabolism of dormancy‐breaking chemicals
Authors: Footitt Steven , Vargas David , Cohn Marc Alan
Published: May 2006

The metabolism of organic dormancy‐breaking chemicals is poorly defined and may provide clues to their mode of action. Therefore, hydrated, dormant seeds of red rice (Oryza sativa L.) were exposed to dormancy‐breaking treatments of propionate‐2‐13C (22 mW) or propanol‐1‐13C (75 mM) for 24 h at 30°C. Embryo extracts were analyzed by 13C‐nuclear magnetic resonance spectroscopy. Metabolism of propionate and propanol to 3‐hydroxypropionate, an intermediate of the modified β‐oxidation pathway, was detected after 2 and 4 h, respectively. This occurred prior to the onset of dormancy‐breaking which required 12 h of chemical exposure. Accumulation of 3‐hydroxypropionate was rapid and linear in the embryos of propionate‐treated seeds. In the embryos of propanol‐treated seeds, the level of 3‐hydroxypropionate reached a plateau at 4 h. Following 24 h of contact with propionate, labeled citrate was detected in the embryos. The decrease in tissue pH associated with the dormancy‐breaking process was fully accounted for by direct acid uptake and metabolic production of 3‐hydroxypropionate.
Adaptability of tomato and pepper leaves to changes in photoperiod: Effects on the composition and function of the thylakoid membrane
Authors: Dorais Martine , Carpentier Robert , Yelle Serge , Gosselin André
Published: May 2006

The adaptability of the thylakoid membrane to extended photoperiod (from natural to 24 h) was studied using a photoperiod‐sensitive species (Lycopersicon esculentum Mill. cv. Trend) and a non‐photoperiod‐sensitive species (Capsicum annuum L. cv. Delphin). Our results have shown that thylakoid membranes of both species adapt to an extended photoperiod by increasing their photosystem II to photosystem I ratio (PSII/PSI) in order to provide a more balanced energy distribution between both photosystems to improve quantum yield. In tomato plants, these results correspond with a lower chlorophyll (Chl) a/b ratio, a decrease in Chl associated with PSI light‐harvesting chlorophyll a/b protein complexes and with an increase in Chl associated with PSII light‐harvesting chlorophyll a/b protein complexes. In spite of these changes, the electron transport capacity through PSII and PSI per unit of Chl and the light saturation point of PSII remained unchanged. The inability of tomato plants to use supplemental light for an extended photoperiod is not the result of photoinhibitory conditions. In pepper plants a significant increase in electron transport capacity and in the light saturation point of PSII was found. There was a significant increase in CO2 assimilation when the light period was increased from 12 to 24 h. In contrast to tomato, pepper plants adapt to a 24‐h photoperiod by increasing their carboxylation capacity which is accompanied by an increase in electron transport capacity and the light saturation point.
Purification and partial characterization of an acidic ribosomal protein kinase from maize
Authors: Sepúlveda Gabriela , Aguilar Raül , Sánchez de Jiménez Estela
Published: May 2006

Phosphorylation and dephosphorylation of ribosomal proteins have been suggested to participate in the regulation of protein synthesis in eukaryotic organisms. The present research focuses on the purification and partial characterization of a protein kinase from maize ribosomes that specifically phosphorylates acidic ribosomal proteins. Ribosomes purified from maize axes were used as the enzyme source. Purification of ribosomes was performed by centrifugation through a 0.5 M sucrose, 0.8 M KCl cushion. A protein kinase activity present in this fraction was released by extraction with 1.5 M KCl and further purified by diethylaminoethyl cellulose column chromatography. A peak containing protein kinase activity was eluted around 400 mM KCl. Analysis of this fraction by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis showed one band of 38 kDa molecular mass, which cross‐reacted in a western blot with antibodies raised against proteins from the large ribosomal subunit. This enzyme specifically phosphorylates one of the acidic ribosomal proteins (P2). Its activity is inhibited by Ca2+ and Zn2+ and is activated by Mg2+, polylysine and spermine. The relevance of this protein kinase in reinitiating the protein synthesis process during germination is discussed.
Localized expression of a proline‐rich protein gene in juvenile and mature ivy petioles in relation to rooting competence
Authors: Sánchez M. C. , Smith Alan G. , Hackett W. P.
Published: May 2006

Cell division and root initiation of excised juvenile, mature and half‐expanded mature (My) leaf petioles of Hedera helix L. cultured in vitro were studied to determine whether these processes were correlated with localized expression of a proline‐rich protein (PRP) gene. Petioles of all three types showed cell divisions at day 5 of culture in auxin‐treated petioles but not in non‐auxin‐treated petioles. No cell division occurred in non‐auxin‐treated petioles even after day 9 of culture. Juvenile and one population of My auxin‐treated petioles formed root primordia after 9 days of culture. Mature petioles and another population of My petioles formed only callus in response to auxin. The spatial and temporal expression pattern of a gene encoding a PRP was analyzed by in situ hybridization. The PRP mRNA was not detectable in petioles of any developmental phase immediately after excision. In both juvenile and mature petioles the PRP mRNA preferentially accumulated in the phloem parenchyma, the inner cortex adjacent to the phloem, and in cells surrounding ducts. Cell division was not required for PRP gene expression since both auxin‐treated and non‐treated juvenile and mature petioles had expression. Steady state levels of PRP mRNA were much lower in juvenile relative to mature petioles cultured in vitro. Auxin treatment reduced the steady state levels of PRP mRNA in My petioles but not in mature or juvenile petioles. These data are consistent with an inverse relationship between competence to form adventitious roots and PRP mRNA levels in the specific cell types from which root primordia form. Alternatively, the PRP mRNA level may serve as a molecular marker for developmental plasticity for root initiation.
Multiple forms of nitrate reductase and their role in nitrate assimilation in roots of wheat at low temperature or high salinity
Authors: Kenjebaeva Saule , Rakova Natasha
Published: May 2006

NADPH‐, NADH‐, and KNO3‐eluted fractions of nitrate reductase (NR) were isolated from roots of winter wheat (Triticum aestivum L. cv. Mironovskaya 808) grown under low temperature or high salinity. All three fractions exerted activity with either NADPH or NADH as electron donor. The NADPH‐eluted fraction showed the highest activity with NADPH, whereas the NADH‐ and KNO3‐eluted fractions were most active with NADH. The NADH‐ and NADPH‐dependent activities in the NADH‐ and KNO3‐eluted fractions were the ones that changed the most in response to low temperature. The inhibitory effect of salt stress was the same for both activities in each of the NADH‐ and KNO3‐eluted fractions. The NADPH‐eluted NR was the one least affected by the growth conditions.
Regulation of K+ and NO3− fluxes in roots of sunflower (Helianthus annuus) after changes in light intensity
Authors: Casadesús Jaume , Tapia Luís , Lambers Hans
Published: May 2006

Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K+ and NO3− uptake by roots, both uptake of K+ and NO3− and secretion into the xylem of young sunflower plants (Helianthus annuus L.) were measured after changes in light intensity.

No close correlation was observed between the uptake of NO3− and that of K+; an increase in light intensity produced a much greater stimulation of NO3− uptake than of K+ uptake. On the other hand, secretion of NO3− into the xylem was tightly coupled to that of K+, and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K2‐malate shuttle on the regulation by the shoot of K+ and NO3− secretion in the xylem, which is linked to NO3− uptake, while K+ uptake is independent of this regulation mechanism.
Effect of 5‐aminolevulinic acid on the pigment content of darkgrown hypocotyls of Phaseolus vulgaris
Authors: Virgin Hemming I. , McEwen Birgitta
Published: May 2006

5‐Aminolevulinic acid (ALA)‐treatment of sections of dark‐grown hypocotyls of kidney beans from the hook and downwards resulted in an additional biosynthesis of the protochlorophyll(ide) complexes Pchl(ide)628‐633, and Pchl(ide)636‐642, approximately proportional to the concentration originally present. A short light pulse given to sections treated with ALA for 6 h phototransformed the Pchl(ide)650‐657 originally present to chlorophyllide.

When the sections were kept in light for 6 h without ALA, chlorophyll was formed and only traces of protochlorophyll(ides) were left. The pigment concentration (weight per fresh weight) in different sections of the hypocotyls was compared with their cell volume. The concentration decreased towards the roots and this decrease is mainly a dilution effect due to a gradual increase of the cell volume downwards, but a change of the pigment concentration per plastid also takes place.
Characterization of binding proteins that recognize oligoglucoside elicitors of phytoalexin synthesis in soybean
Authors: Côté François , Cheong Jong‐Joo , Alba Rob , Hahn Michael G.
Published: May 2006

We are studying the cellular signaling pathway leading to pterocarpan phytoalexin biosynthesis in soybean that is induced by a branched hepta‐β‐glucoside originally isolated from the mycelial walls of the phytopathogenic oomycete Phytophthora sojae. Our research has focused on the specific recognition of the hepta‐β‐glucoside elicitor by binding proteins in soybean cells. Elicitor‐binding proteins with properties expected of physiological receptors for the hepta‐β‐glucoside elicitor have been identified in soybean root membranes. These elicitor‐binding proteins co‐migrate with a plasma membrane marker (vanadate‐sensitive H+‐ATPase) on linear sucrose density gradients. Binding of a radio‐iodinated derivative of the hepta‐β‐glucoside elicitor by membrane‐localized elicitor‐binding proteins is specific, reversible, saturable, and of high affinity (Kd≅ 1 nM). After solubilization with the nonionic detergent, n‐dodecylsucrose, the elicitor‐binding proteins retain their high affinity (Kd= 1.8 nM) for the radiolabeled elicitor and their binding specificity for elicitor‐active oligoglucosides. A direct correlation is observed between the ability of oligoglucosides to displace labeled elicitor from the elicitor‐binding proteins and the elicitor activity of the oligosaccharides. Thus, the elicitor‐binding proteins recognize the same structural elements of the hepta‐β‐glucoside elicitor that are essential for its phytoalexin‐inducing activity, suggesting that the binding proteins are physiological receptors for the elicitor. Current research is directed toward the purification of the hepta‐β‐glucoside elicitor‐binding proteins by using ligand affinity chromatography. Purification and characterization of the hepta‐β‐glucoside binding proteins are among the first steps toward elucidating how the hepta‐β‐glucoside elicitor triggers the signal transduction pathway that ultimately leads to the synthesis of phytoalexins in soybean.
Germination and pH of intracellular compartments in seeds of Phacelia tanacetifolia
Authors: Espen Luca , Morgutti Silvia , Alisi Chiara , Pirovano Livia , Ragg Enzio , Cocucci Sergio M.
Published: May 2006

31 P nuclear magnetic resonance spectroscope (NMR) was used to study the response of Phacelia tanacetifolia seeds to dark and light conditions during the first 72 h of incubation. Changes in the chemical shifts (δ) of the pH‐dependent 31P‐NMR signals from the vacuolar and the cytoplasmic orthophosphate pools were correlated with the different incubation conditions. In the dark (favorable to germination), the cytoplasmic pH remained nearly constant over the whole period considered, while the vacuolar pH shitted to more acidic values after the 24th h of incubation. In the light (inhibiting germination), the values of cytoplasmic pH tended to become more acidic than in the dark after the 24th h of incubation, while the vacuolar pH remained practically constant. When seed germination was inhibited in the dark by butyric acid (BA). a permeant weak acid, the values of cytoplasmic and vacuolar pH were similar to those of the ungerminated seeds incubated in the light. When, vice versa, seed germination was promoted in the light by fusicoccin (FC), the values of cytoplasmic and vacuolar pH were similar to those of the dark‐germinated seeds. A progressive augmentation of P, metabolism occurred both in the dark and in the light up to the 24th h of incubation. Subsequently, light blocked any further evolution of this parameter. Treatment with butyric acid in the dark again mimicked the effect of light, while FC reversed the negative effect of light. The data show that in Phacelia tanacetifolia seeds germination is linked to a more alkaline cytoplasmic pH. The finding that the light‐dependent metabolic inhibition occurs after an early activation of metabolism, i.e. after the first 24 h. suggests that the effects of light on the cytoplasmic and vacuolar pH depend on the early metabolic processes involved in the control of the homeostasis of cell pH and/or on the inhibition of the reactivation of the transport mechanisms.
Vascular occlusion in stems of cut rose flowers exposed to air: Role of xylem anatomy and rates of transpiration
Authors: van Doorn Wouter G. , Reid Michael S.
Published: May 2006

Stems of cut rose flowers were exposed to air at 20°C and 60% relative humidity and then placed in water. The rate of water uptake in Frisco, Sonia, Madelon, and Cara Mia roses was maximally inhibited after 72, 36, 24, and 3 h of exposure to air. respectively. Anatomical observations showed no tyloses, gums, or deposition of hydrophobic material in the xylem conduits (tracheids and vessels) of any of the investigated cultivars. Frisco, Sonia, Madelon, and Cara Mia roses showed no difference in the number, the length, the wall thickness, or the diameter of the lumina of either the tracheids or the vessels. This indicates that differences in recovery are not related to capillary diameter or length.

During exposure to air the decrease in transpiration rate, fresh weight, and water potential was the same in Sonia, Madelon, and Cara Mia roses. Upon exposure to air Frisco roses lost less water than the other cultivars studied In Frisco roses stomatal conductance was similar to that of other cultivars, but the rate of cuticular transpiration was lower.

It is concluded that conservation of water through low cuticular transpiration is one of the reasons for the relatively slow development of the vascular occlusion in Frisco roses, but the differences between Sonia. Madelon and Cara Mia roses were not related to their rates of transpiration.
Promotion by 2,4‐D of 7‐glucosylation of benzyladenine in seed‐derived and shoot apex‐derived cell cultures of Dianthus zeyheri
Authors: Crouch N. R. , Van Staden J.
Published: May 2006

Cell suspension cultures derived from shoot apex or seed callus of the wild carnation Dianthus zeyheri were treated with [8−14]benzyladenine. The metabolism of applied cytokinin was evaluated with time (30 min. 6 h. 18 h. 48 h) in the presence of both low (2 mg l−1) and high (4 mg 1−1) levels of applied 2.4‐D. Both culture types metabolised BA to produce a qualitatively similar but quantitatively different array of metabolites. The 7‐glucoside of BA was the major metabolite produced by apex‐derived cultures, and the second largest product after the riboside in those cultures originating from seed. In both systems higher auxin application promoted 7‐glucosylation with a concurrent reduction in radioactivity associated with the‘active’ cytokinins. This suggests that cytokinin‐7‐glucosyl transferase is stimulated by the auxin 2.4‐D. and may, in part, explain the observed antagonistic interaction between these hormone classes.
The timing of maize leaf senescence and characterisation of senescence‐related cDNAs
Authors: Smart Catherine M. , Hosken Sally E. , Thomas Howard , Greaves John A. , Blair Bruce G. , Schuch Wolfgang
Published: May 2006

Leaf senescence was characterised in two Zea mays lines, earlier senescence (ES) and later senescence (LS). Loss of chlorophyll was delayed in LS compared with ES, but the decline in photosynthesis occurred simultaneously in the two lines. Western analysis detected transition points during senescence of both lines when major quantitative and qualitative changes occurred in a number of leaf proteins. Differences in the pattern of translatable mRNAs were apparent earlier than alterations in pigment or protein levels. A cDNA library was constructed using mRNA from ES leaves early in senescence and differential screening was employed to isolate senescence‐related clones. Two senescence‐enhanced cDNAs showed sequence homology with cDNAs for seed proteins ‐ a cysteine protease and a protein‐processing enzyme. These findings suggest that there are similarities between gene expression during seed maturation, germination and leaf senescence. Other senescence‐enhanced cDNAs were related to genes implicated in gluconeogenesis and chlorophyll breakdown.
Chlorophyll accumulation in cotyledons, hypocotyls and primary needles of Pinus pinea seedlings in light and dark
Authors: Ou Keli , Adamson Heather
Published: May 2006

Seeds of Pinus pinea L. were germinated and grown in darkness or under natural photoperiodic (day/night) conditions for 8 weeks. Samples were taken for analysis at frequent intervals and chlorophyll (Chl) and protochlorophyllide (Pchlide) contents of cotyledons, hypocotyls and primary needles determined spectrophotometrically alter separating the esterified from unesterified pigments by partitioning between ammoniacal acetone and petroleum ether. Chlorophyll accumulated in cotyledons, hypocotyls and primary needles of dark as Well as light grown seedlings. The maximum Chl concentrations achieved in darkness in these organs were approximately 60, 20 and 10% respectively, of concentrations achieved in light. The tinsel of rapid Chl accumulation by cotyledons in darkness coincided with the emergence of the radicle from the seed. Light had no effect on the timing of this process or on the duration of the lag period. However, it extended the exponential growth phase of cotyledons by at least a week and. once the seedlings were about 2 weeks old, enabled Chl to accumulate at a faster rate. Time courses of Chi and Pchlide accumulation by cotyledons in darkness were similar. Pchlide did not accumulate prior to the onset of Chi accumulation and Chl slopped accumulating once the Pchlide pool reached maximum size. The implications of these findings are discussed and a hypothesis to account for the inability of primary needles of smaller seeded pines to accumulate Chl in darkness is proposed.
Correlation of iron content, spectral forms of chlorophyll and chlorophyll‐proteins in iron deficient cucumber (Cucumis sativus)
Authors: Fodor Ferenc , Böddi Béla , Sárvári Éva , Záray Gyula , Cseh Edit , Láng Ferenc
Published: May 2006

Leaves and chloroplast suspensions of severely and slightly iron deficient cucumber (Cucumis sativusL.) plants were characterized by low‐temperature fluorescence emission spectroscopy and Deriphat polyacrylamide gel electrophoresis. The emission spectra of the chloroplast suspensions were resolved into Gaussian components and those changes induced by iron deficiency were related to the variations in the chlorophyll‐protein pattern. The symptoms described with these methods were also correlated with the iron content of the leaves. It was concluded that the lack of physiologically active iron caused a relative decrease of photosystem I (PSI) and light harvesting complex I (LHCI), together with the long wavelength fluorescence, especially the 740 nm Gaussian component, and. to a much lesser extent, of the photosystem II (PSII) core complexes (relative increase of 685, 695 nm components). However, the relative decrease in the amount of light harvesting complex II (LHCII) was followed by a relative increase in its fluorescence band at 680 nm, showing that energy transfer from LHCII to core complex II (CCII) was partly disturbed. Thus iron deficiency affected the photosynthetic apparatus in a complex way: it decreased the synthesis of chlorophylls (Chls) and influenced the expression and assembly of Chl‐binding proteins.
Long‐term drought stress alters nitrogenase activity and carbon translocation in split‐root cultured Alnus incana
Authors: Sundströom Karl‐Ragnar , Huss‐Danell Kerstin
Published: May 2006

Split‐root cultured grey alder, Alnus incana (L.) Moench., was grown in sand in cuvettes with a continuous supply of nutrient solution. During the drought treatment for up to 9 days the supply of solution was withheld from one of the split‐root halves. After 2–3 days of treatment, soil water became depleted and the unwatered root halves were at a constant drought stress, water potential (Ψnodules) = ‐1.1 to ‐1.6 MPa. Nitrogenase activity in the dry half decreased to about 70% of the initial value during the first 2–3 days and then stayed at this level. The water supply to the shoot from the wet root half was high and only a temporary slight decrease in photosynthesis and stomatal conductance was found in drought‐stressed split‐root plants. Labelling studies showed a reduced translocation of photoassimilates to the dry nodules. The fixation of CO2 in the nodules seemed to be more tolerant to drought than nitrogenase activity. During the drought treatment there was an osmotic adjustment from ‐0.9 to ‐1.7 MPa, but no change in the storage of starch in the nodules. In alders where parts of the root system is kept dry these roots acclimate and continue a persistent nitrogenase activity.
Ethylene effects on peroxidases and cell growth patterns in Picea abies hypocotyl cuttings
Authors: Ingemarsson Barbro S.M.
Published: May 2006

The effect of 2‐chloroethylphosphonic acid (ethrel) on cell growth patterns and per‐oxidase activity (EC 1.11.1.7) and location in young Norway spruce cuttings (Picea abies [L.] Karst.) was investigated. The peroxidase activity in a fraction containing soluble and membrane bound enzymes show a diurnal variation, with decreased activity during the light period and a corresponding increase during the following dark period. The decrease during the day could to some extent be counteracted by treatment with ethrel. It appears that ethrel affects only peroxidases in the isolated membrane fraction, since peroxidases bound to the cell wall were not affected by ethrel. In vitro experiments indicated that the hydrophobicity of soluble peroxidases was increased by treatment with ethylene. Cytochemical localization of peroxidase activity in differentiating tracheids revealed a clear ethrel‐induced increase in the tonoplast. It appears that ethylene affects soluble peroxidases in vivo in such a way that they are directed to a more hydrophobic environment, like the tonoplast. Treatment with ethrel also changed the appearance of the rough endoplasmic reticulum (ER) and Golgi apparatus. Dilated ER cisternae were observed on electron micrographs, as a result of treatment with ethrel. The number of vesicles produced by the Golgi apparatus and also the amount of vesicles fusing with the plasma membrane in secondary‐wall‐forming tracheids increased considerably. The results clearly indicate that the stimulatory effect of ethylene in spruce seedlings on lignification and cell wall formation, is due to a general stimulation on both synthesis, transport and secretion of cell wall material and not on a stimulation of peroxidase activity as reported for other species.
Gaba shunt in developing soybean seeds is associated with hypoxia
Authors: Shelp Barry J. , Walton Craig S. , Snedden Wayne A. , Tuin Lucie G. , Oresnik Ivan J. , Layzell David B.
Published: May 2006

In the present study we investigated the proposal that the γ‐aminobutyrate (Gaba) shunt in developing soybean (Glycine max [L.] Merr.) seeds is associated with hypoxia. The ontogeny and pH profile of enzymes associated with glutamate metabolism (glutamate decarboxylase [EC 4.1.1.15]. Gaba transaminase [EC 2.6.1.19], succinic semialdehyde dehydrogenase [EC 1.2.1.16], glutamate dehydrogenase [EC 1.4.1.2], glutamate:oxaloacetate transaminase [EC 2.6.1.1], glutamate:pyruvate transaminase [EC 2.6.1.2] and 2‐oxoglutarate dehydrogenase complex [EC 1.2.4.2]) and hypoxia (alcohol dehydrogenase [ADH, EC 1.1.1.1] and pyruvate decarboxylase [PDC, EC 4.1.1.1]) were determined in cotyledons, nucellus and seed‐coat tissues. Gaba‐shunt enzymes were ubiquitous in the developing seed. Activities of enzymes catalyzing glutamate‐C entry into the Krebs cycle via 2‐oxoglutarate were generally greater than those of Gaba‐shunt enzymes. In cotyledons, the activity of ADH increased throughout seed development (up to 72 days after anthesis [DAA]), whereas PDC was static during early development, then increased. In contrast, the activities of ADH and PDC in maternal tissues (nucellus and seed coat) were initially high, then declined dramatically after 37 DAA. The adenylate energy charge (AEC) = ([ATP]+0.5 [ADP])/ ([ATP] + [ADP] + [AMP]) of soybean seeds from fruits (37 DAA) frozen in situ was low (0.67±0.01) compared to the AEC of adjacent pod tissue (0.82 ± 0.04) and cotyledons exposed to air (0.84 ± 0.01). A 60‐min time‐course study showed that the rate of [U‐14C]‐glutamate catabolism by an intact excised cotyledon at 37 DAA was markedly lower at 8 and 0% O2 than at 21%; the pool size of [14C]‐Gaba was unaffected. The data indicated that: (1) Gaba‐shunt activity is not a response to limited glutamate deamination/transamination: (2) the soybean seed is hypoxic; and (3) the relative partitioning of glutamate‐C through glutamate decarboxylase is increased by hypoxia.
Inhibition of ethylene‐induced cellular senescence symptoms by 1‐methylcyclopropene, a new inhibitor of ethylene action
Authors: Serek M. , Tamari G. , Sisler E. C. , Borochov A.
Published: May 2006

Ethylene is known to accelerate flower senescence, but the sequence of events that links its interaction with the tissue and the final senescence symptoms is still obscure. Recently, 1‐methylcyclopropene (1‐MCP) was found to inhibit ethylene‐induced wilting in flowers. This work was carried out in order to investigate the effects of 1‐MCP on cellular senescence symptoms in petunia flowers following expossure to ethylene. Cut petunia (Petunia hybrida) flowers that were exposed to ethylene for 12 h at concentrations of 1–12 ppm wilted sooner than their untreated counterparts. This effect was abolished by a 6‐h pre‐treatment with 1‐MCP. Immediately following the ethylene treatment, decreases in petal fresh weight and total protein content were measured, along with higher electrolyte leakage, and lower membrane lipid fluidity and protein content. When applied alone, 1‐MCP had relatively little impact on these parameters. However, when the flowers were treated with 1‐MCP prior to the ethylene treatment, ethylene had no effect. These results indicate that while ethylenes effects on wilting were obvious 3 days after the treatment, cellular parameters were affected already at the end of the treatment. Since 1‐MCP repressed these early ethylene effects, it was concluded that it interferes with ethylene action in petunia flowers at a rather early stage, long before apparent wilting.
Thidiazuron‐induced somatic embryogenesis in intact seedlings of peanut (Arachis hypogaea): Endogenous growth regulator levels and significance of cotyledons
Authors: Murthy B. N. S. , Murch Susan J. , Saxena Praveen K.
Published: May 2006

The regulatory role of thidiazuron (TDZ) and explant factors in imparting somatic embryogenic potential was assessed in relation to endogenous growth regulator levels in peanut (Arachis hypogaea L. cv. Tango). TDZ induced somatic embryogenesis over a range of concentrations (0.5 to 10 μM). Culture of seedlings for just 2 days on TDZ‐supplemented medium was sufficient to induce somatic embryogenesis. Seedling age and retention or removal of cotyledons during culture influenced morphogenic potential significantly. The younger the seedlings, the better was the embryogenic response to TDZ treatment. The embryogenic potential of seedlings was limited for explants with no cotyledons and they did not respond to increasing levels of TDZ. In contrast, retention of at least one or both the cotyledons resulted in increased response to TDZ. Endogenous levels of cytokinins, auxins and abscisic acid were influenced by TDZ treatment, while TDZ itself was detected only in the cotyledons. The cytokinin N6‐(2‐iso‐pentenyl)adenine (2iP) fluctuated on a 10‐day cycle in the cotyledons; TDZ treatment suppressed this change and caused an overall decrease in the pool of available 2iP in the tissue. It appeared that TDZ induced somatic embryogenesis in peanut by influencing endogenous levels of both auxin and cytokinins.
Effect of an increased sink demand on the carbon metabolism and export of a maize source leaf
Authors: Jeannette Emmanuelle , Rocher Jean‐Paul , Prioul Jean‐Louis
Published: May 2006

The sink demand was increased on a source maize leaf (Zea mays L. cv. F7F2) by darkening all the leaves except the fourth, which was maintained under the prevailing irradiance conditions. The parameters of carbon metabolism were measured precisely during the first hours, and then daily during one week. The ambient photosynthetic activity and the maximum photosynthetic capacity were not altered by the treatment but the soluble carbohydrate and starch contents diminished, while ADP‐glucose pyrophosphorylase (EC 2.7.7.27) activity increased. The carbon export rate, evaluated by the rate of disappearance of radioactivity after a 1‐min 14CO2 pulse, was faster than in control leaves. A compartmental analysis of the time course of 14C export further indicated that the sucrose pool providing the export flux was largely increased by the dark treatment. The darkened leaf 5, taken as an example of the darkened sources, was completely depleted of its carbohydrate content after one day in the dark and remained devoid of carbohydrates during the following week.
Endo‐β‐mannanases in the endosperm of germinated tomato seeds
Authors: Nonogaki Hiroyuki , Nomaguchi Masako , Morohashi Yukio
Published: May 2006

Three forms of galactomannan‐hydrolyzing enzymes (dyed galactomannan as substrate) were partially purified from germinated tomato [Lycopersicon esculentum (L.) Mill.] seed. Two of the enzymes were of the same molecular mass, 38 kDa, as judged by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), but the points of elution from a CM‐Toyopearl column by a pH‐gradient were different between the two (pH 5.15 and 5.45. respectively). The molecular mass of the third form was slightly less (37.5 kDa) than that of the other two. These 3 enzymes showed no α‐galactosidase (EC 3.2.1.22) or β‐mannosidase (EC 3.2.1.25) activity. Thin‐layer chromatography (TLC) revealed that the products of the reaction were oligosaccharides and that free galactose and mannose were not released. These results indicate that the 3 galactomannan‐hydrolyzing enzymes are endo‐β‐mannanases (EC 3.2.1.78). Polyclonal antibodies raised against the 37.5‐kDa polypeptide cross‐reacted with the two 38‐kDa polypeptides, indicating that the 3 endo‐β‐mannanases are immunologically homologous. Activity staining and immunoblotting of native PAGE of endosperm extracts revealed that only two (38‐kDa. elution point pH 5.15 and 37.5‐kDa proteins) of the 3 forms were major endo‐β‐mannanases present in the endosperm of germinated tomato seeds.
Boron mobility in plants
Authors: Shelp Barry J. , Marentes Eduardo , Kitheka Alice M. , Vivekanandan Pathmanathan
Published: May 2006

Boron (B) is a micronutrient essential for the normal growth of monocots, dicots. conifers, ferns and several diatom species. Boron deficiency causes many anatomical, physiological and biochemical changes, making it difficult to identify a primary role for it: however, evidence does indicate that B is involved at the membrane level. Whatever the role(s). it likely involves the complexation of B with compounds containing cis‐hydroxyl groups. Boron deficiency in crops is more widespread than deficiency of any other micronutrient. Nutritional disorders in vegetables include brown heart in rutabaga, turnip and radish roots, and hollow stem in cauliflower and broccoli. The occurrence of these disorders even when B is in ample supply suggests that they are physiological in nature and related to the mobility of B in the plant. The distribution of B is related to the loss of water from shoot organs, suggesting that it is primarily xylem‐mobile with limited retranslocation in phloem. However, research has shown that B is present in the phloem, albeit at low concentration, and that it is generally retranslocated in the phloem to satisfy the demands of sink organs that do not readily transpire. Further progress into the mechanism(s) of B retranslocation will be facilitated by insights into the role and metabolism of B in plants.
The contribution of ozone to forest decline
Authors: Schmieden Ursula , Wild Aloysius
Published: May 2006

More than 10 years of intensive research into forest decline in Germany has ascertained that the full extent of the visible damage cannot be explained by just one of the current hypotheses on forest decline. One of the prominent hypotheses is that chronic exposure of forest trees to ozone is probably one of the primary causes of forest decline. The aim of this paper is the critical review of a number of recent results dealing with the ozone hypothesis from a plant physiological point of view. The synopsis focusses on the effects of ozone on conifers because the most extensive data are available for coniferous trees, especially for spruce (Picea sp.) and pine (Pinus sp.) trees.