bluuebunny/crossref_metadata_2025 huggingface dataset:
Translocation of phosphorus from nodal roots in two contrasting genotypes of white clover (Trifolium repens)
Authors: Chapman D. F. , Hay M. J. M.
Published: May 2006

Patterns of translocation of recently‐assimilated phosphorus (P) exported from‘young’ source roots (located 3–4 nodes from the stolon apex) and ‘old’ source roots (located near the base of the stolon) on the primary stolon of clonal plants of the forage legume white clover (Trifolium repens L.) were determined using 32P. Plants of a small‐leaved genotype and of a large‐leaved genotype were grown in sand culture at two notionally limiting or near‐limiting rates of P supply and one non‐limiting rate of supply. The small‐leaved genotype showed little response in growth rate to the full range of P treatments whereas growth of the large‐leaved genotype at the non‐limiting rate of P supply was 2. 4 times greater than at the two low rates of P supply. Source roots of both genotypes exported only 26–30% of the P they acquired to the shoot within 24 h when P supply was limited whereas at the high‐P rate 54% of recently‐assimilated P was exported. Patterns of translocation of exported P to specific sinks differed little between the genotypes and the P treatments; branches were the main sink, accounting for nearly 80% of the estimated amounts of P (μg day−1) exported from young and old roots combined. Translocation patterns from individual roots were determined largely by the modular structure of plants and by the location of the root relative to the major sinks, and were therefore consistent with the same source‐sink principles which govern carbohydrate translocation in clonally‐growing species. There were strong suggestions that storage of P in stolons and roots played a much greater role in the growth of the small‐leaved plants than of the large‐leaved plants.
Phytotropin‐induced root phototropism in maize
Authors: Geissler Art E. , Katekar Gerard F.
Published: May 2006

Phytotropins, even those not absorbing in the visible region of the spectrum, can induce a phototropic response in maize (Zea mays L. cv. PX‐75) roots when illuminated unilaterally with white light. The most active phytotropin, 2‐(1‐pyrenoyl) benzoic acid (PBA) can elicit a full response at 10 μM, while the other active molecules, 2‐carboxyphenyl‐3‐phenylpropane‐1,3‐dione (CPD), 2‐carboxyphenyl‐3‐phenyl‐1,2‐pyrazole (CPP), 1‐N‐naphthylphthalamic acid (NPA) and erythrosin elicit a full response at 100 μM. The less active phytotropins BBA and fluorescein give a reduced response. It is suggested that the observed effect cannot be explained solely on the basis of auxin transport inhibition. There is a photoreceptor in the extension zone of the root, which may be associated in some way with the receptor for NPA. The results are consistent with the proposal that the phototropic process may form part of the root gravitropic response mechanism.
The effect of handling on the yield of two populations of Lolium perenne selected for differences in mature leaf respiration rate
Authors: Kraus Edwin , Lambers Hans , Kollöffel Chris
Published: May 2006

Two populations of Lolium perenne L. S23 (perennial ryegrass), selected for differences in mature leaf dark respiration, were used in a non‐destructive indexing system for individual plants, to determine growth parameters. Population GL66, selected for high respiratory rates and low yield, responded strongly to the indexing treatment, when grown at low plant density. Dry weights of all plant parts decreased strongly, as did dry matter percentages of the leaf blades. At high density this population demonstrated the same trend, but additionally allocation to the shoot increased. In contrast, GL72, selected for low respiratory rates and a high yield, responded only at a high plant density. It is argued that there might be a relation between the dissimilar response of the two populations to mechanical influences and the presence of the genotypes of the low‐yielding population in the parent variety. The results also emphasize that non‐destructive growth analyses can only be used when their effects on the plants are known.
Chlorophyll breakdown in senescent leaves: demonstration of Mg‐dechelatase activity
Authors: Langmeier Monika , Ginsburg Samuel , Matile Philippe
Published: May 2006

The action of Mg‐dechelatase was brought to light by incubating senescent rape cotyledons or chloroplasts under conditions which prevented the oxidative cleavage of chlorophyll‐porphyrin. The accumulation of chlorophyllide and pheophorbide taking place under such conditions was considered as a measure of apparent activities of chlorophyllase and dechelatase, respectively. In excised cotyledons metal chelators such as 2,2′‐dipyridyl and o‐phenanthroline caused a marked accumulation of pheophorbide a, without affecting the apparent activity of chlorophyllase. Treatment of cotyledons with an inhibitor of cytoplasmic protein synthesis d‐2‐(4‐methyl‐2,6‐dinitroanilino)‐N‐methyl‐propionamide (d‐MDMP) caused a reduced accumulation of pheophorbide a in the presence of dipyridyl, suggesting that the appearance and maintenance of Mg‐dechelatase activity in senescent cotyledons requires continuous cytoplasmic protein synthesis. In isolated senescent chloroplasts (gerontoplasts) the cleavage of chlorophyll‐porphyrin requires the supplementation with glucose‐6‐phosphate (Glc6P). Upon the incubation of gerontoplasts in the absence of Glc6P, a conspicuous accumulation of pheophorbide a occurred. Much smaller pools of pheophorbide a were produced when porphyrin cleavage was allowed in the presence of Glc6P. These phenomena were not observed in pre‐senescent chloroplasts. In contrast to the apparent Mg‐dechelatase activity, chlorophyllase activity did not change in a senescent‐specific fashion. The lysis of gerontoplasts by freezing and thawing caused an enhancement of apparent chlorophyllase activity whereas the activity of Mg‐dechelatase was lower than in the intact organelles. In the pre‐senescent chloroplasts, lysis evoked a small apparent Mg‐dechelatase activity, suggesting that in a latent form this enzyme may be present even before the onset of foliar senescence.
Development of protein bodies in cotyledons of Fagus sylvatica
Authors: Collada C. , Allona I. , Aragoncillo P. , Aragoncillo C.
Published: May 2006

Electron microscopic analysis of cotyledons of beech (Fagus sylvatica) at different stages of seed maturation indicates that protein bodies originate by gradual subdivision of the vacuoles in which reserve proteins are deposited. The majority of protein bodies show a proteinaceous matrix and a number of globoid inclusions of different sizes. In a small number of cells, druse‐like inclusions were observed. Analysis by SDS‐PAGE of proteins extracted from isolated protein bodies shows that the majority correspond to beech seed storage globulins.
Effects of light and temperature on seed dormancy and gibberellin‐stimulated germination in Arabidopsis thaliana: studies with gibberellin‐deficient and ‐insensitive mutants.
Authors: Derkx M. P. M. , Karssen C. M.
Published: May 2006

Effects of light and temperature on gibberellin (GA)‐induced seed germination were studied in Arabidopsis thaliana (L.) Heynh. with the use of GA‐deficient (gal) mutants, mutants with a strongly reduced sensitivity to GA (gai) and with the recombinant gai/gal. Seeds of the gal mutant did not germinate in the absence of exogenous GAs, neither in darkness, nor in light, indicating that GAs are absolutely required for germination of this species. Wild‐type and gai seeds did not always require applied GAs in light. The conclusion that light stimulates GA biosynthesis was strengthened by the antagonistic action of tetcyclacis, an inhibitor of GA biosynthesis. In wild‐type, gal and gai/gal seeds light lowered the GA requirement, which can be interpreted as an increase in sensitivity to GAs. In gai and gai/gal seeds light became effective only after dormancy was broken by either a chilling treatment of one week or a dry after‐ripening period at 2°C during some months. The present genetic and physiological evidence strongly suggests that temperature regulates the responsiveness to light in A. thaliana seeds. The responsiveness increases during dormancy breaking, whereas the opposite occurs during induction of dormancy (8 days at 15°C pre‐incubation). Since light stimulates the synthesis of GAs as well as the responsiveness to GAs, temperature‐induced changes in dormancy may indirectly change the capacities to synthesize GAs and to respond to GAs. GA sensitivity is also directly controlled by temperature. It is concluded that both GA biosynthesis and sensitivity to GAs are not the primary controlling factors in dormancy, but are essential for germination.
Changes in water relation parameters under osmotic and salt stresses in maize and sorghum
Authors: Erdei László , Taleisnik Edith
Published: May 2006

A relatively drought tolerant cultivar of maize (Zea mays L. cv. Pioneer 3950) and a drought tolerant line of sorghum (Sorghum bicolor [L.] Moench cv. ICSV 112) were grown hydroponically for 11 days. Treatments for non‐ionic osmotic and salt stresses were started at the 8th day by addition of polyethylene glycol 6000 and NaCl, respectively, at 200 mOsm equivalent concentrations in the presence or absence of 0. 1 μM abscisic acid. Relative growth rate was depressed by both stress factors, more severely for maize than sorghum. Abscisic acid increased the growth rate and reverted the negative effect of NaCl in maize, while sorghum was only slightly affected. In general, sorghum had higher levels of K+ and lower levels of Na+ and the K+/Na+ ratio was further increased by abscisic acid treatment. From the pressure‐volume curves, osmotic potential, the water potential at turgor loss point, bulk elastic modulus and the water saturation deficit at initial turgor loss were estimated. Most significantly, sorghum had a higher elastic modulus than maize and it decreased under osmotic treatment, while in maize it increased under NaCl stress. The results suggest that bulk tissue turgor was not limiting growth under these conditions and underscores the possible implications of changes in the elastic condition of the cell walls in stress responses.
Chromium‐induced inhibition of ethylene evolution in bean (Phaseolus vulgaris) leaves
Authors: Poschenrieder Charlotte , Gunsé Benito , Barceló Juan
Published: May 2006

The influence of chromium concentration on ethylene production in bean plants (Phaseolus vulgaris L. cv. Contender) was investigated. A Cr ion‐induced inhibition of ethylene synthesis from endogenous 1‐aminocyclopropane‐1‐carboxylic acid (ACC) was observed within both leaf discs floated on 2 mM CrO2−4 or Cr3+ and leaf discs from plants cultured in nutrient solutions containing 10, 20 or 40 μM CrO2−4. However, Cr ions supplied either to plants with the nutrient solution or to discs with the incubation medium rather increased the conversion of exogenous ACC to ethylene. Primary leaves of plants exposed to CrO2−4‐containing nutrient solutions showed a statistically insignificant decrease of ACC‐synthase activity. In the trifoliolate leaves of plants exposed to 10 μM CrO2−4, in which a significant decrease of ethylene production from endogenous ACC was observed, a substantial increase of ACC synthase was found. These results indicate that Cr ion‐induced inhibition of ethylene production is not due to a breakdown of membrane integrity, which is necessary for ethylene forming enzyme activity, but caused by metabolic alterations leading to decreased ACC availability. Chromium ions may act by inhibiting ACC synthase activity or by diverting a metabolic step prior to the ACC synthase catalyzed reaction.
Control of the activity of plant plasma membrane MgATPase by the viscosity of the aqueous phase
Authors: Bérczi Alajos , Møller Ian M.
Published: May 2006

The activity of plant plasma membrane (PM) MgATPase (EC 3. 6. 1. 35) was studied in PM vesicles purified from spring wheat (Triticum aestivum L. cv. Drabant) roots, winter wheat (Triticum aestivum L. cv. Martonvásári‐8) roots, and soybean (Glycine max L. cv. Williams) hypocotyls by aqueous polymer two‐phase partitioning. MgATPase from spring wheat roots was assayed at 23°C (a) in the absence and presence of Triton X‐100, (b) in the presence of either 1 mM or 3 mM MgATP2−, and in the presence of increasing concentration of sucrose from 10 mM upto 1. 2 M. Activity of MgATPase in PM vesicles from winter wheat roots was measured at 21°C at sucrose concentrations of 15 mM–1. 1 M in the presence of 3 mM MgATP2− and absence of Triton X‐100 only. MgATPase activity from soybean hypocotyls was studied (a) in the absence and presence of Triton X‐100, (b) both at 21 and 31°C, in the presence of 3 mM MgATP2− and varying concentrations of sucrose between 10 mM and 1. 1 M. In all cases, independently of the assay conditions and the source of PM, the MgATPase activity decreased with increasing sucrose concentration. Latency of the MgATPase activity depended only slightly on the concentration of sucrose. The Q10 value for the MgATPase activity from soybean hypocotyls (and thereby the Arrhenius activation energy of the enzymatic reaction) was independent of the sucrose concentration and of the presence of Triton X‐100. At optimal assay conditions, the ATP‐hydrolyzing activity of plant PM MgATPase (v) was inversely proportional to the m‐th power of the viscosity of aqueous phase (η) as predicted by the modified Kramers'theory of enzymatic catalysis: v ∝ (1/η)m, where m is an empirical parameter between 0 and 1. For the activity of MgATPase in the three species studied, m varied between 0. 5 and 1. 1 in good agreement with the theory. We thus conclude that (a) the activity of integral membrane enzyme‐proteins may be controlled not only by the property(ies) of the membrane lipid phase but also by the viscosity of the aqueous phase in the vicinity of such enzymes, and (b) the determination of vesicle sidedness based on enzyme latency may need a minor revision. Our interpretation is in agreement with the molecular dynamics approach of enzymatic catalysis worked out for soluble enzymes.
Carbonic anhydrase in the plasma membranes from leaves of C3 and C4 plants
Authors: Utsunomiya Eiko , Muto Shoshi
Published: May 2006

Plasma membranes were isolated from green leaves of maize (Zea mays), spinach (Spinacia oleracea), Setaria viridis and wheat (Triticum aestivum cv. Omase) by aqueous two‐phase partitioning. Carbonic anhydrase activity was detected in these membranes. The activity was inhibited by specific inhibitors for carbonic anhydrase, acetazolamide and ethoxyzolamide. The carbonic anhydrase activity was markedly enhanced by the addition of Triton X‐100 to the plasma membranes. The highest activity was obtained in the presence of 0.015% detergent. The activity was scarcely affected when the plasma membrane vesicles were treated with proteinase K, but largely inactivated by the protease after treating the membranes with Triton X‐100. These results indicate that carbonic anhydrase faces the cytoplasmic side of the membrane since plasma membranes purified by aqueous two‐phase partitioning are tightly sealed vesicles of right side‐out orientation (apoplastic side‐out). With leaves of C4 plants, 20 to 60% of the total carbonic anhydrase activity was found in the microsomal fraction. By contrast, only 1 to 3% of the activity was found in the microsomal fraction from leaves of C3 plants. Western blot analysis showed that a polypeptide in the spinach plasma membrane cross‐reacted with an antiserum raised against spinach chloroplast carbonic anhydrase, and that the molecular mass of the plasma membrane enzyme was higher than that of the chloroplast carbonic anhydrase (28 and 26 kDa, respectively). This indicates the presence of different molecular species of carbonic anhydrase in the chloroplast and the plasma membrane.
Intracellular localization of sucrose‐Phosphate Phosphate in photosynthetic cells of lettuce (Lactuca sativa)
Authors: Echeverría Ed , Salerno Graciela
Published: May 2006

The intracellular localization of sucrose‐phosphate phosphatase (SPP) in photosynthetic cells of lettuce (Lactuca sativa) was investigated by using protoplasts isolated directly from leaf tissue. No SPP activity was detected in either vacuolar, chloroplast or mitochondrial preparations. The recovered activity of SPP was found in the cytosolic fractions at proportions parallel with those of the cytoplasmic marker alcohol dehydrogenase. Maximal activity was measured between pH 6. 0 and 7. 0. The data demonstrate a cytosolic location for SPP. Neither sucrose nor any other saccharide tested at 100 mM was a strong inhibitor of the enzyme, which was inactive in the presence of 35 mM ethylenediammetetraacetic acid.
Expression of a cytokinin synthesis gene from Agrobacterium tumefaciens T‐DNA in basket willow (Salix viminalis)
Authors: Vahala T. , Eriksson T. , Tillberg E. , Nicander B.
Published: May 2006

Willow cells transformed with an ipt gene from Agrobacterium tumefaciens grow in tissue culture as undifferentiated callus without shoot induction. We show that the transformed calluses contained high levels of the cytokinins 9‐β‐d‐ribofuranosyl zeatin and its monophosphate, demonstrating the presence of a functional isopentenyl transferase enzyme. The ipt gene was transcribed at different levels in different transformed callus lines. The absence of shoot differntiation is apparently not due to a lack of zeatin‐type cytokinins in the transformed callus.
Role of dark respiration in photoinhibition of photosynthesis and its reactivation in the cyanobacterium Anacystis nidulans
Authors: Shyam R. , Raghavendra A. S. , Sane P. V.
Published: May 2006

Photoinhibition of photosynthesis and its reactivation was studied in the cyanobaterium A. nidulans in the presence of the respiratory inhibitor sodium azide, the uncouplers carbonyl cyanide p‐(trifluoromethoxy)‐phenylhydrazone (FCCP) and carbonyl cyanide m‐chlorophenylhydrazone (CCCP) and the photosystem I elicitor phenazine methosulphate (PMS). Inhibition of dark respiration by azide increased the susceptibility of the cyanobacterium to photoinhibition. Both FCCP and CCCP also remarkably affected the process of photoinhibition in A. nidulans. The PMS at lower photoinhibitory light intensity partially protected A. nidulans from photoinhibition. The recovery from photoinhibition in the presence of azide or FCCP was slow and normal photosynthesis could not be resumed even after a longer period of incubation under suitable reactivating condition. Thus dark respiration has a key function in the process of photoinhibition of photosynthesis and its reactivation in the cyanobacterium A. nidulans.
Modulation of the blue light response of stomata of Commelina communis by CO2
Authors: Lascève Gérard , Gautier Hélène , Jappé Jocelyne , Vavasseur Alain
Published: May 2006

Effects of CO2 on stomatal movements of Commelina communis L. were studied with plants, epidermal strips and guard cell protoplasts. With plants, the stomatal response induced by a blue light pulse was studied for different ambient CO2 concentration ranging from CO2‐deprived air to 100 Pa in darkness or under red light. It was observed that the blue light response could be obtained not only under a red light background but also in darkness and CO2‐free air, the two responses being quite similar.

With epidermal strips, the effect of CO2 on ferricyanide reductase activity at the guard cell plasmalemma was studied by transmission electron microscopy. In the presence of ferric ions, reduced ferricyanide gives an electron dense precipitate of Prussian Blue. In darkness and air, no precipitate was observed. In darkness and CO2‐free air as well as under light and normal air, a precipitate was found along the plasmalemma of the guard cells, indicating a ferricyanide reductase activity. With guard cell protoplasts suspended in a medium either in equilibrium with air or in a CO2‐free medium the H+ extrusion induced by a blue light pulse added to a red light background was measured. A low CO2 content was obtained by adding photosynthetic algae to the suspension of guard cell protoplasts. In a CO2‐free medium the rate of H+ extrusion was enhanced.

The results are discussed on the basis of a possible competition for reducing power between CO2 fixation and a putative blue light dependent redox chain located on the plasma membrane.
Nodulation response of autoregulated or NH4+‐inhibited pea (Pisum sativum) after transfer to stimulatory (low) concentrations of NH4+
Authors: Waterer John G. , Vessey J. Kevin
Published: May 2006

It has been demonstrated previously that field pea (Pisum sativum L. cv. Express) grown in hydroponic culture on a complete nutrient solution with low NH4+ concentrations (<0.5 mM) will produce a larger than normal proliferation of nodules. Peas grown in the absence of mineral N in hydroponic culture have been shown to rapidly autoregulate nodulation, forming a static nodule number by 14 to 21 days after planting. The present study further characterizes the effect of NH4+ concentration in hydroponic culture on nodulation and nodule growth. Peas were grown continually for 4 weeks at NH4+ concentrations that were autoregulatory (0.0 mM), stimulatory (0.2 mM) or inhibitory (1.0 mM), or peas were transferred between autoregulatory or NH4+ inhibited and stimulatory solutions after 2 weeks. The peas nodulated as expected when grown under constant autoregulatory, stimulatory or inhibitory concentrations of NH4+. When peas were transferred from the inhibitory (1.0 mM) to the stimulatory solution (0.2 mM) a massive proliferation of nodule primordia over the entire root system was observed within 3 days of the transfer. When they were transferred from the autoregulatory (0.0 mM) to the stimulatory (0.2 mM) solution a 10‐day delay occurred before a proliferation in nodule primordia occurred at distal regions of the root system. These findings support our hypothesis that low concentrations (<1.0 mM) of NH4+ in hydroponic culture cause a suppression of autoregulation in pea. In addition, the temporal and spatial differences in nodule proliferation between transfer treatments demonstrate at a whole plant level that autoregulation and NH4+ inhibition suppress early nodule development via different mechanisms.
Purification and characterization of aconitase isoforms from etiolated pumpkin cotyledons
Authors: De Bellis Luigid , Tsugeki Ryuji , Alpi Amedeo , Nishimura Mikio
Published: May 2006

Although aconitase (EC 4.2.1.3) is involved in the glyoxylate cycle, which is localized in glyoxysomes, we detected very low aconitase activity in glyoxysomal fractions after sucrose gradient centrifugation of extracts prepared from etiolated pumpkin (Cucurbita sp.) colyledons. Two aconitase isoforms were purified to homogeneity, albeit in low yield, by hydrophobic interaction, hydroxylapatite and anion exchange chromatography. They were designated Aco I and Aco II; both were shown to be monomeric proteins of M1 100 000 or 98 000 by gel filtration and SDS‐PAGE analysis, respectively; isoelectric points were 5.0 and 4.8, respectively. Kinetic studies revealed similarities between Aco I and Aco II. A third aconitase isoform (Aco III) was revealed but not purified to homogeneity.
Photosynthetic acclimation to elevated atmospheric carbon dioxide and UV irradiation in Pinus banksiana
Authors: Stewart James D. , Hoddinott John
Published: May 2006

Pinus banksiana seedlings were grown for 9 months in enclosures in greenhouses at CO2 concentrations of 350 or 750 μmol mol−1 with either low (0.005 to 0. 3 W m−2) or high (0.25 to 0. 90 W m−2) ultraviolet‐B (UV‐B) irradiances. Total seedling dry weight decreased with high UV treatment but was unaffected by CO2 enrichment. High UV treatment also shifted biomass partitioning in favor of leaf production. Both CO2 and UV treatments decreased the dark respiration rate and light compensation point. High UV light inhibited photosynthesis at 350 but not at 750 μmol mol−1 CO2 due to a UV induced increase in ribulose‐1, 5‐bisphosphate carboxylase/oxygenase efficiency and ribulose‐1, 5‐bisphosphate regeneration. Stomatal density was increased by high UV irradiance but was unchanged by CO2 enrichment.
Control of development in plants and fungi by far‐UV radiation
Authors: Ensminger Peter A.
Published: May 2006

Far‐UV (200–320 nm) radiation regulates development in plants and fungi. Some of these responses are controlled by a chromophore which absorbs strongly near 260 nm, possibly a nucleic acid. Other responses are controlled by a chromophore(s). with maximal in vivo sensitivity near 295 nm. In plants. far‐UV induces genes in the phenylpropanoid pathway and the synthesis of phytoalexins and flavonoids. Far‐UV also regulates growth rate. controls curvature and taxis, and stimulates sexual and asexual morphogenesis of fungi. Some of these developmental responses may prevent damage by far‐UV radiation.
Dihydrofolate reductase and thymidylate synthase in plants: an open problem
Authors: Cella Rino , Parisi Bruno
Published: May 2006

This review deals with recent findings in the purification and characterization of dihydrofolate reductase (DHFR) and thymidylate synthase (TS) in plants. The few enzymes purified, which differ remarkably in regard to their structure. kinetic and molecular properties and subcellular location are described. The response of DHFRs to antifolic agents and the analysis of resistance mechanisms in isolated cell lines is also reported. Problems opened by recent studies of the enzymes isolated from plants are outlined.
Daylength and thermal time responses of budburst during dormancy release in some northern deciduous trees
Authors: Heide O. M.
Published: May 2006

Dormancy release and thermal time to budburst as affected by duration of chilling outdoors, followed by different flushing temperatures and daylengths in a phytotron, were studied in cuttings of several northern tree species. In Betula pubescens, B. pendula and Prunus padus vegetative buds were released from dormancy already in December, in Populus tremula in January, whereas in Alnus incana and A. glutinosa dormancy was not released until February. Thermal time (day degrees >0°C) to budburst decreased non‐linearily with increasing duration of chilling (i. e. duration outdoors), and the slope of this relationship differed among species. The estimated effective base temperature for accumulation of thermal time varied from + 1°C in P. tremula to −4°C in P. padus. The use of 0°C as base temperature is recommended. Long days reduced the thermal time to budburst at all flushing temperatures (9, 15 and 21°C) in all the above species and in Corylus avellana, whereas Sorbus aucuparia and Rubus idaeus showed no daylength response. Since the chilling requirement of all species was far exceeded even in a winter with January‐March temperatures 6.5°C above normal, it is concluded that under Scandinavian conditions, the main effect of climatic warming would be earlier budburst and, associated with that, a longer growing season and increased risk of spring frost injury.
Transient changes in length and growth of wheat coleoptile segments following treatments with osmotica and auxin
Authors: Bleiss W. , Ehwald R.
Published: May 2006

The dependence of elongation on the osmotic potential of the medium was investigated, using coleoptile segments (CS) of Triticim aestivum L. (cv. Hartri) and an optoelectronic device. The study aimed at separating the osmoelastic response from the irreversible growth response when an osmoticum (mannitol) was added, and to compare both processes in order to consider the possibility of growth‐induced reduction in turgor pressure.

The prompt inhibition of elongation registered just after addition of 50 mM mannitol as well as the subsequent resumption of the original elongation rate could be quantitatively explained by the extent and the kinetics of the osmoelastic relaxation. An initial reduction in the irreversible elongation component by mild osmotic stress could not be demonstrated.

Above a critical value, the irrevesible growth was insensitive to a further increase in water potential. The minimum turgor pressure required to drive steady growth was not far from zero in both the presence and absence of auxin.

The rate (r) of osmotically caused shortening per unit change of water potential
image

was determined from the kinetics of CS shortening induced by addition of mannitol at nearly isotonic concentration (300 mM). This parameter relates a fractional change in length to the difference in water potential between inside and outside, and was assumed to depend largely on the hydraulic resistance of the tissue and cuticle. It was found to be independent of IAA. The relatively low value of Γ suggests significant reduction of turgor at high growth rates. In accordance with this conclusion, the extent of osmoelastic shortening after a transfer to 300 mM mannitol (dependent on wall strain) was significantly decreased in the presence of IAA.

Addition of 100 μM IAA to CS growing at a constant rate induced pronounced oscillations in the rate of elongation, which may be connected with the change in elastic cell wall strain. Whereas the steady state growth rate before the addition of IAA was the same in the presence and in the absence of 50 mM mannitol, the maximum growth rate found after addition of IAA was substantially reduced in the mannitol variant.
A Cucumis sativus cell‐free translation system: preparation, optimization and sensitivity to some antibiotics and ribosome inactivating proteins
Authors: Rojo M. A. , Arias F. J. , Iglesias R. , Ferreras J. M. , Muñoz R. , Girbés T.
Published: May 2006

A cell‐free translation system was prepared from 3‐ to 5‐day‐old embryonic axes of gherkin (Cucumis sativus L.). The system was optimized for Mg2+, K+, NH+4, high speed supernatants, tRNA mixture from wheat germ, time and temperature. The system translates efficiently both endogenous mRNA (using a 30000 g supernatant) and polyuridylic acid (using either a 30000 g supernatant or a 100000 g supernatant supplemented with purified ribosomes). Translation by gherkin ribosomes was inhibited by several well‐known eukaryotic inhibitors, antibiotics and ribosome‐inactivating proteins. A translational inhibitory activity found in Cucumis sativus L. dry seeds acted on polypeptide synthesis carried out by cell‐free systems from several mammals and plants, including gherkin embryonic axes. Our results indicate that the inhibitor is located in the seed bark and cotyledons, and is either blocked or absent in the embryonic axes, thus allowing the isolation of active gherkin ribosomes. The presence of the putative inhibitor appeared to be unevenly distributed in developing plants.
Content of low‐molecular‐weight thiols during the imbibition of Pea seeds
Authors: Kranner Ilse , Grill Dieter
Published: May 2006

The metabolism of low‐molecular‐weight thiols was investigated in seeds of Pisum sativum L. cv. Kleine Rheinländerin during imbibition in water for 14 h. The amount of oxidized glutathione (GSSG) decreased from 319 nmol (g dry weight)−1 in dry seeds to 38 nmol (g dry weight)−1 within the first 14 h of imbibition. The decrease may have been due to the reduction of GSSG to reduced glutathione (GSH), catalyzed by the enzyme glutathione reductase (GR; EC 1.6.4.2). The enzyme activity was high in dry seeds [25 nkat (g dry weight)−1] and decreased to 20 nkat (g dry weight)−1 within 14 h of imbibition. The activity of glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49) decreased from 100 nkat (g dry weight)−1 in dry seeds to 67 nkat (g dry weight)−1 after 14 h of imbibition. Within 14 h the amount of γ‐glutamyl‐cysteine (γ‐GC) decreased from 135 to 38 nmol (g dry weight)−1, whereas the cysteine content rose from 81 nmol (g dry weight)−1 in dry seeds to a maximum of 170 nmol (g dry weight)−1 after 12 h of imbibition, which may be due to the degradation of γ‐GC into cysteine.
Foliar uptake of Cd by pea (Pisum sativum) and sugar beet (Beta vulgaris)
Authors: Greger Maria , Johansson Monica , Stihl Alvar , Hamza Karim
Published: May 2006

Pea (Pisum sativum L. cv. Fenomen) and sugar beet (Beta vulgaris L. cv. Monohill) were cultivated in nutrient media without or with 10 μM CdCl2. Leaves of the same size and stage of development, detached or still attached to the intact plants, were submerged into redistilled water containing 1 to 250 μM CdCl2. The uptake experiments were run for 1 to 8 h at pH 3.6 and 5.1. Cuticular transpiration rate, density of leaf and density of stomata were also measured. Percentage of open stomata was studied at different pH.

Foliar uptake of Cd into the leaf is evident since Cd is transported from the exposed part of the pea leaves, through the petioles and into the stipules, and since the Cd concentration of the leaves increases with time and external Cd concentration. The foliar uptake depends on the permeability of the cuticular membrane, which is increased by a high intrinsic Cd level, which in turn enhances the foliar uptake of Cd in sugar beet. Higher cuticular permeability in pea than in sugar beet is shown by a 2.5 times higher cuticular transpiration rate and a 4 times lower density of leaf for pea, which causes a 7 times higher foliar uptake in pea than in sugar beet. Low pH decreases the net uptake of Cd, probably by an exchange reaction in the cutin and pectin of the cuticular membrane. Stomata are not directly involved in the Cd uptake, and the differences in the sum total of stomatal aperture area per unit leaf area is not related to differences in foliar uptake of Cd. Percentage of open stomata, calculated as average of both sides of the leaves, was not affected by changes in pH: but especially at high pH. proportionally more stomata were open on the adaxial than on the abaxial side.
Oxygen influences benzyladenine and 2,4‐dichlorophenoxyacetic acid levels in cultured embryogenic tissue of Norway spruce
Authors: Kvaalen H. , Ernstsen A.
Published: May 2006

It is known that reducing the partial pressure of O2 influences the induction of somatic embryogenesis. We tested the hypothesis that O2 causes changes in the endogenous levels of exogenously supplied benzyladenine (BA) or 2,4‐dichlorophenoxyacetic acid (2,4‐D). Embryogenic tissue of Picea abies was incubated under reduced (2.5, 5 kPa) and ambient (21 kPa) levels of O2 for 1, 3, 7 and 11 days and the endogenous concentrations of BA and 2,4‐D were measured. For all treatments the concentration of BA in the tissue increased until the third day. At day 3, the ratio of BA in the tissue relative to the initial concentration in the medium, was 3.9, 2.8 and 1.9 for tissue incubated under 2.5, 5 and 21 kPa O2, respectively. The BA concentration then declined gradually. Uptake of 2,4‐D was inhibited at low O2 levels. However, 2,4‐D gradually accumulated in tissue grown under hypoxia, so that high levels were reached by day 11. These shifts in the BA and 2,4‐D levels also caused a transient increase in the BA to 2,4‐D ratio in tissue incubated under hypoxia. Although relevant for the previously reported effects of oxygen on induction of embryogenic tissue, it is unlikely that oxygen‐induced alterations in BA and 2,4‐D levels alone suffice to explain these findings.
ABA promotion of ethylene production in anther culture of Brussels sprouts (Brassica oleracea var. gemmifera) and its relevance to embryogenesis
Authors: Biddington Norman L. , Robinson Helen T. , Lynn James R.
Published: May 2006

Abscisic acid (ABA) inhibited embryogenesis in anther culture of Brussels sprouts. This was accompanied by enhanced ethylene production during the first half of the anther culture period followed by a reduction in ethylene during the latter half, when compared to anthers not treated with ABA. The enhancement of ethylene production by ABA 6 h and 48 h after the start of the culture period was counteracted by the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). Both AVG and the ethylene antagonist AgNO3 removed much of the ABA inhibition of embryogenesis, suggesting that at least part of the ABA effect on embryo production is mediated through increased ethylene biosynthesis.

ABA promotion of ethylene production was reduced by high temperature: less ethylene evolved from ABA‐treated anthers following a 24 h treatment at 35°C than from ABA‐treated anthers incubated continuously at 25°C. A high temperature treatment such as this is invariably necessary for embryogenesis in Brussels sprouts anther culture.
Preferential photoinactivation of catalase and photoinhibition of photosystem II are common early symptoms under various osmotic and chemical stress conditions
Authors: Streb Peter , Michael‐Knauf Andrea , Feierabend Jürgen
Published: May 2006

Activity of catalase (EC 1.11.1.6) and variable fluorescence (F) were measured in sections of rye leaves (Secale cereale L. cv. Halo) that were exposed for 24 h to moderately high irradiance under osmotic or chemical stress conditions (paraquat, DCMU, mannitol, NaCl, CdCl2, CuSO4, Pb(NO3)2, KNO2, or K2SO3). Changes of the chlorophyll content and of enzyme activities related to peroxide metabolism, such as glycolate oxidase, glutathione reductase, and peroxidase, were assayed for comparison. In the presence of the herbicides paraquat and low DCMU concentrations that exert only partial inhibition of photosynthesis, as well as after most treatments with osmotic or chemical stress factors, catalase markedly declined due to a preferential photoinactivation. At higher DCMU levels catalase did not decline. At low KNO2 concentrations catalase activity was preferentially increased. In general, photoinactivation of catalase was accompanied by a decline of the F/Fm ratio, indicating photoinhibition of photosystem II, while other parameters were much more stable. Inasmuch as both catalase and the D1 reaction center protein of photosystem II have a rapid turnover in light, their steady state levels appear to decline whenever stress effects either excessively enhance deleterious oxidative conditions and degradation (e. g. Paraquat, low DCMU), or inhibit repair synthesis. Photoinactivation of catalase and of photosystem II represent specific and widely occurring early symptoms of incipient photodamage indicating stress conditions where the repair capacity is not sufficient. During prolonged exposures, e. g. to NaCl and CuSO4, chlorophyll was bleached in light and the rate of its photodegradation increased in proportion as the catalase level had declined. The results suggest that the enhanced susceptibility of leaf tissues to photooxidative damage which is widely observed in stressed plants is related to the early loss of catalase.
Glutamine synthetase isozymes in germinating barley seeds
Authors: Marttila Salla , Saarelainen Ritva , Porali Ilkka , Mikkonen Anita
Published: May 2006

Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of ammonia assimilation in higher plants. In the present study the subunit composition and localization of GS in germinating barley (Hordeum vulgare) seed have been clarified. Analysis of the GS polypeptide composition by immunoblotting revealed two different polypeptides. A and B, with a molecular mass of 42 and 40 kDa, respectively. In the scutellum subunit A was already present in the ungerminated seed and remained unchanged, whereas subunit B appeared on day 2 and increased about 5‐fold during germination. Polypeptide B also appeared later during germination in the aleurone layer, roots and weakly in the etiolated shoots. By immunogold microscopy, GS was detected in the scutellum and the aleurone layer of barley seeds during germination. Subcellular localization of GS on ultrathin cryosections showed that a cytosolic isozyme was present in the scutellum. Our study confirms that only a cytosolic GS is expressed in barley seed, and its subunit composition changes during germination.
The effects of cadmium on photosynthesis of Phaseolus vulgaris – a fluorescence analysis
Authors: Krupa Zbigniew , Öquist Gunnar , Huner Norman P. A.
Published: May 2006

Bean plants (Phaseolus vulgaris L. cv. Scarlett), germinated in darkness for I week, were transferred to light (200 μmol m−2 s−1) and cultivated for I week in a complete nutrient solution. After this period, cadmium ions in the form of CdSO4 were added at the concentrations of 0.10.20 and 50 μM. The effects of this metal on the properties of photosystem II photochemistry were studied by means of modulated fluorescence analysis. Steady state photochemical quenching. non‐photochemical quenching and terminal fluorescence were determined in control and cadmiumtreated plants. We postulate that, during short term exposure of plants to cadmium in the early stages of growth, the Calvin cycle reactions are more likely than photosystem II to be the primary target of the toxic influence of cadmium. The reduced demand for ATP and NADPH upon Calvin cycle inhibition causes a down‐regulation of photosystem II photochemistry and of the yield of linear electron transport.
Biochemical and physiological responses of Gracilaria tenuistipitata uuder two different nitrogen treatments
Authors: García‐Sánchez María J. , Fernández José A. , Niell F. X.
Published: May 2006

The influence of nitrogen on ribulose‐1.5‐bisphosphate carboxylase/oxygenase (Rubisco. EC 4.1.1.39) content is poorly understood in macroalgae. N‐deficient Gracilaria tenuistipitata Zhang et Xia var. liui was cultivated in the laboratory under constant light intensity and temperature. Biochemical and physiological variables were monitored after a high (1 mM) or low (o. 1 mM) nitrate pulse. Rubisco content in crude extracts was estimated by SDS‐PAGE with the Coomassie Blue Staining procedure. Nitrate was consumed immediately in the low‐N treatment, but there was always an external nitrate source in the high‐N treatment. Total soluble proteins and phycobiliproteins decreased as internal nitrogen diminished in the low‐N treatment, but kept fairly constant in N‐sufficient conditions. However, Rubisco content increased until the 7th day and then started to decrease in both cases. Fresh weight increment showed a better correlation with Rubisco than with pigment content.
Occurrence of hydroxylated jasmonic acids in leaflets of Solanum demissum plants grown under long‐ and short‐day conditions
Authors: Helder Hans , Miersch Otto , Vreugdenhil Dick , Sembdner Günther
Published: May 2006

Under short‐day (SD) conditions both 11‐OH‐jasmonic acid (11‐OH‐JA) and a smaller quantity of 12‐OH‐JA occurred in leaflets of Solanum demissum Lindl. Plants which had formed tubers. This is the first time that 11‐OH‐JA has been detected as a native substance in higher plants. Under long‐day (LD) conditions no tubers were formed and none of these compounds were detectable. A positive correlation was found between the occurrence of 11‐OH‐JA and 12‐OH‐JA in leaflets of S. demissum and tuber formation, but a causal relation has yet to be proved. The (‐)‐JA content in leaflets was not significantly different under short and long days. Mild stress applied to detached SD and LD leaflets caused a rapid accumulation of JA in these leaflets. Upon this treatment an increase in the levels of hydroxylated JAs was detected in SD leaflets only.

JA was a potent promotor of tuber formation in vitro in S. demissum explants. Lipoxygenase (LOX: EC 1.13.11.12) is involved in the biosynthesis of JA. Under SD conditions, application of salicylhydroxamic acid (SHAM), an inhibitor of LOX activity, to the roots did not prevent tuber formation in vivo. It is suggested that daylength controls the hydroxylation of JA. The enzyme(s), responsible for the hydroxylation of JA, would only be effective under SD conditions.
TL‐DNA transformation decreases ABA level
Authors: Julliard Jacques , Pelèse Florence , Sotta Bruno , Maldiney Régis , Primard‐Brisset Catherine , Jouanin Lise , Pelletier Georges , Miginiac Emile
Published: May 2006

The endogenous levels of ABA were measured in Agrobacterium rhizogenes A4 Tl‐DNA transformed oilseed rape (Brassica napus L. var. oleifera cv. Brutor and cv. Drakkar), cabbage (Brassica oleracea). A4 transformed tobacco (Nicotiana tabacum cv. Xanthi) and their normal counterparts, using high performance liquid chromatography and enzyme‐liked immunosorbent assay. Measurements were made on different plant tissues (i. e. floral stem, terminal bud, young leaf, mature leaf, root and root tips) and ABA levels were compared in unstressed and osmotically stressed oilseed rape plants (cv. Brutor). In unstressed Plants. in each of the 5 independent transformation events studied, a significant reduction (about 65% of control) in ABA concentration was observed in all transformed plants. When subjected to an osmotic stress, TL transformed Brutor plants showed a higher ABA accumulation than untransformed plants. The change in ABA content as a consequence of TL‐DNA transformation is discussed with regard to phenotype, drought resistance and adaptability.
Effect of nitrogen supply on frost resistance, nitrogen metabolism and carbohydrate content in white clover (Trifolium repens)
Authors: Sandli Nina , Svenning Mette M. , Røsnes Kirsti , Junttila Olavi
Published: May 2006

Effects of mineral nitrogen (2, 4, 6 and 8 mM NH4NO3) and nodulation with Rhizobium on frost hardiness in seedlings of white clover (Trifolium repens) have been studied. Seedlings of a population from Bodø (67°N lat.) were grown in Leonard jars under controlled conditions in a phytotron. For induction of frost hardening, plants were first exposed to 12 h photoperiod conditions for 2 weeks at 18°C, then for 2 weeks at 6°C and finally for 2 weeks at 0.5°C. Frost hardiness after treatments at 6 and 0.5°C was significantly enhanced by increasing nitrogen supply and was positively correlated with total nitrogen content of the stolons. Frost hardiness of nodulated plants correlated to the tissue nitrogen concentration. Content of soluble proteins in stolons decreased during hardening at 6°C but did not change during treatment at 0.5°C. There were minor changes in total amount of free amino acids during hardening. Both absolute and relative amounts of proline and arginine increased, and those of asparagine decreased during hardening. Absolute amounts of all free amino acids increased with increasing nitrogen supply, but the changes during hardening were similar in all treatments. There was a significant increase in the content of soluble carbohydrates during hardening. However, this increase was inversely related to nitrogen supply.
Incorporation of 15N and 14C of methionine into the mugineic acid family of phytosiderophores in iron‐deficient barley roots
Authors: Kawai Shigenao , Itoh Kikukatsu , Takagi Sei‐ichi
Published: May 2006

The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15N‐ammonium sulfate, 14C‐amino acids, and [1‐14C, 15N]‐methionine to iron‐deficient barley roots (Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ‐amino butyric acid did not act as precursors of MAs. Carbon‐14 and 15N of methionine were incorporated into MAs. This specific incorporation of 14C and 15N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs.