bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short‐term effects of boron, germanium and high light intensity on membrane permeability in boron deficient leaves of sunflower
Authors: Cakmak Ismail , Kurz Hannes , Marschner Horst 
Published: May 2006

The effects of varied boron (B) supply (0.01–50 μM and light intensity (100–580 μpmol m−2 s−1) on plant growth, leaf symptoms and membrane permeability of leaves were studied in sunflower plants over a 10‐day‐period of growth in nutrient solution. Membrane permeability was measured by incubating isolated young leaves in aerated distilled water. Additional experiments showed the effect of short‐term supply (20 min to 2 h) of B and germanium (Ge) on membrane permeability of B‐deficient leaves incubated in distilled water. Low supply of B decreased shoot and root growth and caused brown‐purple pigmentation of young leaves, particularly under high light intensities. Leakage of K‐ from leaves increased with severity of B deficiency whereas, in B‐sufficient leaves, leakage of solutes was low. Also leakage of phenolics, amino acids and sucrose was enhanced by B deficiency. Compared to B‐sufficient leaves, the leakage from B‐deficient leaves was 35‐fold higher for K+, 45‐fold higher for sucrose and 7‐fold higher for phenolics and amino acids. Increases in solute leakage were marked in leaf areas with brown‐purple pigmentation and particularly pronounced by increasing light intensity or by exposure of leaves to continuous light. In severely B‐deficient leaves grown under high light intensity, treatment with B and Ge up to 1 000 μMM for 20 min resulted in an immediate decrease in K+ efflux to about the same levels as in B‐sufficient leaves. Similar rapid decreases in K+ efflux were also found in B‐deficient leaves when exposed to darkness for 16 h or 30 h before the leakage measurement.The results demonstrate a particular role for B in maintaining the integrity of plasma membranes. Boron presumably stabilizes the structure of the plasma membrane by complexing membrane constituents. It also has a protective effect on membrane constituents by complexing phenolics, so that oxidation of phenolics to highly toxic quinones and oxygen free radicals is prevented or limited. In these functions, boron seems to be to a large extent replaceable by germanium.
Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?
Authors: Johnsson Anders , Brown Allan H. , Chapman David K. , Heathcote David , Karlsson Christina 
Published: May 2006

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time.Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g‐stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided Plants at two stages of coleoptile development were tested. Plant responses were obtained using time‐lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g‐doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g‐doses, chiefly because the data were more variable.It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm× 1), with m‐values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well‐defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.
A procedure for quantification of cytokinins as free bases involving scintillation proximity immunoassay
Authors: Wang J. , Letham D. S. , Taverner E. , Badenoch‐Jones J. , Hocart C. H. 
Published: May 2006

Cytokinins occur in a diversity of forms and determination of their individual levels requires extensive purification. However, determination of the total level of each major base in free, riboside and nucleotide forms would often be adequate. Hence, a methanolysis procedure which releases cytokinin bases from 9‐ribosyl derivatives was developed and applied to plant extracts. A simple procedure, involving low pressure column chromatography, for purification of the cytokinin bases in treated extracts, and a scintillation proximity immunoassay for their quantification, were developed. The total level of each cytokinin base [N6‐(2‐isopentenyl)adenine, zeatin and dihydrozeatin] in free and ribosylated forms determined by these methods is reported for several plant tissues and the results are compared with those obtained after additional purification by HPLC. Values for zeatin were not changed by HPLC but isopentenyl‐adenine and dihydrozeatin levels were usually reduced indicating the presence of unknown compounds which cross‐react in the immunoassay. Modifications to the above purification method to quantify O‐glucosyl cytokinins are also described.The methods described facilitate the quantification of the total amount of each cytokinin base in forms closely associated with cytokinin action, and the detection of cytokinin biosynthesis by labelled precursor incorporation.
A device to estimate the light gradients relevant to phototropism in the laboratory and the field
Authors: Firn Richard D. , Digby John 
Published: May 2006

An apparatus has been devised to measure the irradiance falling on a central point from each of 48 points of the compass. The apparatus has been used to estimate the magnitude and spatial distribution of light gradients in a variety of situations which are known to cause phototropism.Measurements show that the typical laboratory treatments used to induce phototropism produce extreme light gradients which are not typical of the light gradients likely to be experienced by seedlings growing in the natural environment. Diffuse light which is always present in the natural environment, ensures that all flanks of seedlings will be subject to potentially physiologically significant light stimulation. Such findings need to be taken into account when devising and testing models of phototropic detection in plants.
Characterisation of a Ca2+‐dependent ATP hydrolysis associated with the vacuolar membrane of wheat roots
Authors: Allen Gethyn J. , Morais Francisco , Muir Shelagh , Wyn Jones R. Gareth , Leigh Roger A. 
Published: May 2006

Microsomal fractions from wheat tissues exhibit a higher level of ATP hydrolytic activity in the presence of Ca2+ than Mg2+. Here we characterise the Ca2+‐dependent activity from roots of Triticum aestivum lev. Troy) and investigate its possible function. Ca2+‐dependent ATP hydrolysis in the microsomal fraction occurs over a wide pH range with two slight optima at pH 5.5 and 7.5. At these pHs the activity co‐migrates with the major peak of nitrate‐inhibited Mg2+. Cl‐ATPase on continuous sucrose gradients indicating that it is associated with the vacuolar membrane. Ca2+‐dependent ATP hydrolysis can be distinguished from an inhibitory effect of Ca2+ on the plasma membrane K+, Mg2+‐ATPase following microsomal membrane separation using aqueous polymer two phase partitioning. The Ca2+‐dependent activity is stimulated by free Ca2+ with a Km of 8.1 μM in the absence of Mg2+ ([CaATP] = 0.8 mM). Vacuoiar membrane vacuolar preparations contain a higher Ca2+‐dependent than Mg2+‐dependent ATP hydrolysis, although the two activities are not directly additive. The nucleotide specificity of the divalent ion‐dependent activities in vacuolar membrane‐enriched fractions was low. hydrolysis of CTP and UTP being greater than ATP hydrolysis with both Ca2+ and Mg2+ The Ca2+‐dependent activity did discriminate against dinucleotides, and mononucleotides. and failed to hydrolyse phosphatase substrates. Despite low nucleotide specificity the Mg2+‐dependent activity functioned as a bafilomycin sensitive H+‐pump in vacuolar membrane vesicles.Ca2+‐dependent ATP hydrolysis was not inhibited by the V‐, P‐, or F‐type ATPase inhibitors bafilomycin. vanadate and azide, respectively. nor by the phosphatase inhibitor molybdate, but was inhibited 20% at pH 7.5 by K+. Possible functions of Ca2+‐dependent hydrolysis as a H+‐pump or a Ca2+‐pump was investigated using vacuolar membrane vesicles. No H+ or Ca2+ translocating activity was observed under conditions when the Ca2+‐dependent ATP hydrolysis was active.
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.
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.
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.
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.
Platanetin and 7‐iodo‐acridone‐4‐carboxylic acid are not specific inhibitors of respiratory NAD(P)H dehydrogenases in potato tuber mitochondria
Authors: Roberts Thomas H. , Rasmusson Allan G. , Møller Ian M. 
Published: May 2006

Progress in understanding the role of NAD(P)H oxidation in plant respiration is restricted by the lack of access to specific inhibitors of each of the unknown number of NAD(P)H dehydrogenases in the inner mitochondrial membrane. Platanetin (3,5,7,8‐tetrahydroxy‐6‐isoprenyl flavone) is known to be an inhibitor of extermal NADH oxidation by plant mitochondria, while 7‐iodo‐acridone‐4‐carboxylic acid (IACA) is an inhibitor of an internal, rotenone‐insensitive NAD(P)H dehydrogenase isolated from yeast mitochondria.Here we show that platanetin inhibits external NAD(P)H oxidation by intact potato (Solanum tuberosum L. cv. Bintje) tuber mitochondria, deamino‐NADH oxidation by Complex I assayed using inside‐out submitochondrial particles from these mitochondria, and rotenone‐insensitive NAD(P)H oxidation by these submitochondrial particles. IACA was found to inhibit the oxidation of external NADH and succinate by intact mitochondria with similar efficiency. However, IACA also inhibited NADPH and duroquinol oxidation by intact mitochondria as well as deamino‐NADH and NAD(P)H oxidation by inside‐out submitochondrial particles. This indicates that IACA has several sites of inhibition in the electron transport chain. The lack of specificity of both platanetin and IACA prevents these inhibitors from being used to shed more light on the identity of the NAD(P)H dehydrogenases in plant mitochondria.
The influence of enriched rhizosphere CO2 on N uptake and metabolism in wild‐type and NR‐deficient barley plants
Authors: Cramer M. D. , Savidov N. A. , Lips S. H. 
Published: May 2006

Positive influences of high concentrations of dissolved inorganic carbon (DIC) in the growth medium of salinity‐stressed plants are associated with carbon assimilation through phosphoenolpyruvate carboxylase (PEPc) activity in roots; and also in salinity‐stressed tomato plants, enriched CO2 in the rhizosphere increases NO−3uptake. In the present study, wild‐type and nitrate reductase‐deficient plants of barley (Hordeum vulgare L. cv. Steptoe) were used to determine whether the influence of enriched CO2 on NO−3 uptake and metabolism is dependent on the activity of nitrate reductase (NR) in the plant. Plants grown in NH4+and aerated with ambient air, were transferred to either NO3− or NH4+ solutions and aerated with air containing between 0 and 6 500 μmol mol−1 CO2. Nitrogen uptake and tissue concentrations of NO3− and NH4+ were measured as well as activities of NR and PEPc.The uptake of NO−3 by the wild‐type was increased by increasing CO2. This was associated with increased in vitro NR activity, but increased uptake of NO3− was found also in the NR‐deficient genotype when exposed to high CO2 concentrations; so that the influence of CO2 on NO3− uptake was independent of the reduction of NO3− and assimilation into amino acids. The increase in uptake of NO3− in wild‐type plants with enriched CO2 was the same at pH 7 as at pH 5, indicating that the relative abundance of HCO3− or CO2 in the medium did not influence NO3− uptake. Uptake of NH4+ was decreased by enriched CO2 in a pH (5 or 7) independent fashion. Thus NO3− and NH+4 uptakes are influenced by the CO2 component of DIC independently of anaplerotic carbon provision for amino acid synthesis, and CO2 may directly affect the uptake of NO3− and NH4+ in ways unrelated to the NR activity in the tissue.
Growth and pigment production in two subarctic grass species under four different UV‐B irradiation levels
Authors: Gwynn‐Jones Dylan , Johanson Ulf 
Published: May 2006

The aim of the experiment was to test the sensitivity of grasses from a subarctic region to a range of different ultraviolet‐B (UV‐B, 280–320 nm) levels. Seedlings of Calama‐grostis lapponica and tillers of Calamagrostis purpurea were grown for 50 days in a greenhouse at 4 different levels of UV‐BBE radiation (no UV‐B, ambient UV‐B, UV‐B corresponding to 15 and 25% ozone depletion, respectively, at 68°N, northern Sweden on July 27th).In C. purpurea total plant dry weight was significantly reduced at the 15% level compared to all other treatments, whilst tiller number was reduced when compared to the non UV‐B treatment only. Reduced growth at the 15% level was accompanied by significant increases in shoot to root ratio (S:R), leaf area ratio (LAR) and leaf weight ratio (LWR), which were due to changes in both specific leaf area (SLA) and root growth. Similarly, in C. lapponica there were reductions in total dry weight at the 15% level, although differences in partitioning were only observed in LWR which was significantly greater than in the non UV‐B treatment.There was a difference in tiller number in C, lapponica between all treatments. A reduced number of tillers was observed with increasing UV‐B exposure from zero UV‐B to the 15% level, whilst tiller number was significantly higher at the 25% level than in all other treatments.In C, lapponica, differences were apparent in the amount of UV absorbing pigments. Plants exposed to ambient UV‐B and the 15% level had significantly more UV‐B absorbing compounds than those in the 25% and non UV‐B treatments.All these results suggest that the 15% ozone depletion level was the most harmful to plant growth and few damaging effects were observed at the higher 25% ozone depletion level.
Light enhances differentiation of the vascular system in the fruit of Actinidia deliciosa
Authors: Biasi R. , Altamura M. M. 
Published: May 2006

Light is recognized as crucial in determining high quality of fleshy fruits, for example, kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson]. Among the possible mechanisms through which light improves the quality of kiwifruit berry, there may be a direct morphogenic role on the differentiation of the fruit's vascular system, though this has not yet been investigated.The present study's aim was to determine (1) whether light positively affects the differentiation of the vascular system of the fruit and/or the pedicel, and, if so, (2) which component (xylem, phloem, or both) is more affected, and (3) in which period of the berry's development the improvement of the vascular differentiation (if any) occurs. To this end, fruit morphogenesis of kiwifruit was studied in two developmental environments (i.e., in full sunlight and in paper bags that reduced the full sunlight to 10%), and in two phases of fruit development (i.e., 1 and 5 months [harvest] after anthesis). During the growth period, the type of environment did not affect the differentiation pattern of the vascular system in the three types of bundles present in the fruit. However, in comparison with shade, light improved the vasculature in the fruit pericarp and pedicel, inducing a consistently higher extent of the xylary component in the main bundles of the fruit and pedicel, principally due to an increase in the number of xylem elements. The phloic component was also increased by light, but to a much lesser extent than that of the xylary. During the entire period of development, light‐grown fruits contained higher concentrations of calcium and magnesium, as compared with shade‐grown fruits.In conclusion, in the berry of Actinidia deliciosa, light enhances the differentiation of the vascular system, in particular the xylary component. The hypothesis that fruit quality is improved through a more efficient translocation of specific mineral nutrients (e.g., calcium) via the xylem is presented.