bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of nitrogenase to altered carbon supply in a Frankia‐Alnus incana symbiosis
Authors: Lundquist Per‐Olof , Huss‐Danell Kerstin
Published: May 2006

To study the effect of altered carbon supply on nitrogenase (EC 1.7.99.2), plants of Alnus incana (L.) Moench in symbiosis with the local source of Frankia were exposed to darkness for 2 days, and then returned to normal light/dark conditions. During the dark period nitrogenase activity in vivo (intact plants) and in vitro (Frankia cells supplied with ATP and reductant), measured as acetylene reduction activity, was almost completely lost. Western blots for both the Fe‐protein (dinitrogenase reductase) and the MoFe‐protein (dinitrogenase) showed that, in particular, the amount of MoFe‐protein was strongly reduced during darkness. Protein stained sodium dodecyl sulphate‐polyacrylamide gels of Frankia protein showed that the nitrogenase proteins were the only abundant proteins that clearly decreased during darkness. During recovery, studied for 4 days, nitrogenase activity in vivo recovered to the level before dark treatment but was still only half of control activity, Nitrogenase activity in vitro and the amount of MoFe‐protein, both expressed per Frankia protein, recovered and reached similar values in previously dark treated plants and in control plants. The rate of recovery was similar to the increase in activity of control plants, suggesting growth of Frankia in addition to synthesis of nitrogenase proteins during the recovery after carbon starvation.
The effect of excision on O2 diffusion and metabolism in soybean nodules
Authors: Sung L. , Moloney A. H. , Hunt S. , Layzell D. B.
Published: May 2006

Nitrogen‐fixing nodules of soybean [Glycine max (L.) Merr. cv. Maple Arrow inoculated with Bradyrhizobium japonicum USDA 16] were studied before and after excision from the root to determine the role the O2 regulation plays in the inhibition of nodule activity and the potential for using excised nodules nodules in studies of nodule metabolism. Relative nitrogenase (EC 1.7.99.2) activity (H2 evolution in N2:O2) and nodule respiration (CO2 evolution) were monitored first in intact nodulated roots and then in freshly excised nodules of the same plant to determine the time course of the decline in nodule metabolism. Folowing excision, nitrogenase activity and respiration declined rapidly in the first minute and then more gradually. After 40 min the rate of H2 evolution was only 14–28% of that in the intact plant. In some nodules activity declined steadily, and in others there was a partial recovery in activity ca 10 min after detachment. Infected cell O2 concentration (Oi), measured by a spectro‐photometric technique, also declined after nodule detachment with a time course similar to the declines in nitrogenase activity and respiration. Following excision, Oi levels declined rapidly from ca 21 nM in attached nodules to 8–12 nM at 4–10 min after excision and then more gradually to 2–3 nM O2 at 30–40 min after excision. These results show that the nodules' permeability to gas diffusion continued to be regulated for up to 40 min after detachement. At 40 min after detachment, when excised nodules displayed steady‐state rates of gas exchange, linear increases in pO2 from 20 to 100% at 4% min−1 resulted in recoveries of H2 and CO2 evolution, indicating that Oi limited nitrogenase activity durig this period, and that energy reserves were greatly in excess of the O2 available for respiration. When detached nodules were equilibrated for 12 h at 20, 30 and 50% O2, Oi values measured at supra‐ambient pO2 were greater than those at 20% O2 and were linked with a more rapid decline in nitrogenase activity. Also, increases in external pO2 (Oc) failed to stimulate nodule metabolism, suggesting that the nodules' energy reserves were no longer greatly in excess of their respiratory demands. It was concluded that soybean nodules could provide useful material for steady‐state studies of nodule metabolism between 40 and 240 min after detachment, but to attain metabolic rates equivalent to in vivo rates the nodules must be exposed to above‐ambient pO2.
Light regulates symplastic communication in etiolated corn seedlings
Authors: Epel Bernard L. , Erlanger Michael A.
Published: May 2006

The effect of light on symplastic communication in dark grown maize seedlings was tested using the symplastic probe carboxyfluorescein. Prior white‐light irradiation stimulated longitudinal transport of carboxyfluorescein in the mesocotyl stele of dark‐grown seedlings. The stimulation was multiphasic with a positive followed by a negative phase. Lateral transport from the stele into the mesocotyl cortex was inhibited by the prior white‐light irradiation. The inhibitory effect of prior white‐light irradiation on lateral transport was completely photo‐modulatable by terminal farred and far‐red/red irradiations, suggesting the involvement of phytochrome. The stimulatory effect of the prior white irradiation observed for the stele, however, was not photoreversible. It is suggested that environmental factors, such as light, might modulate growth and development, in part, by modulating symplastic cell to cell communication and thus the distribution of nutrients and growth regulators.
Regulation of glycolysis in heterotrophic cell suspension cultures of Chenopodium rubrum in response to proton fluxes at the plasmalemma
Authors: Hatzfeld Wolf‐Dieter , Stitt Mark
Published: May 2006

The present experiments were carried out to investigate the effect of increased fluxes of H+ across the plasmalemma on glycolysis in heterotrophic cell suspension cultures of Chenopodium rubrum L. (1) Increased H+ influx was produced by adding glucose, 6‐deoxyglucose, 2‐deoxyglucose, or sodium fluoride. The net influx decreased to zero after 3 min. This recovery was accompanied by an increase in the rate of O2 uptake, but not of dark CO2 fixation. When glucose or fluoride were added, the increase of O2 uptake occurred without a decrease in the ATP/ADP ratio, and was large enough to provide the ATP that would be needed for compensatory H+ extrusion via the plasmalemma H+‐ATPase. When 2‐deoxyglucose was added, the rise of respiration was restricted by sequestration of phosphate and depletion of phosphorylated metabolites, the ATP/ADP ratio declined, and a slow net H+ influx started again after 4 min. (2) Alkalinisation of the medium to induce an H+ efflux resulted in rapid activation of dark CO2 fixation, but not of O2‐uptake. (3) A stimulation of respiration or dark CO2 fixation was always accompanied by a decrease of phosphoenolpyruvate. This shows that the primary sites for regulation of glycolysis are pyruvate kinase and phosphoenolpyruvate carboxylase, respectively. (4) There was no consistent relation between glycolytic flux and triose‐phosphates or hexose‐phosphates. This shows that the reactions involved in carbohydrate mobilisation and the conversion of hexose‐phosphates to triose‐phosphates only have a secondary role in stimulation of glycolysis. (5) Phosphofructokinase will be stimulated as a consequence of the decrease in phosphoenolpyruvate. (6) The increase in glycolytic flux occurred independently of (in the case of 2‐deoxyglucose and fluoride), or before (in the case of glucose), any increase of fructose‐2,6‐bisphosphate. When fructose‐2,6‐bisphosphate did increase (after supplying glucose), this was accompanied by an increase of triose‐phosphate and fructose‐1,6‐bisphosphate, which otherwise remained very low. It is argued that fructose‐2,6‐bisphosphate increases as a consequence of the decrease of glycerate‐3‐phosphate, a known inhibitor of the synthesis of this regulator metabolite. However, activation of pyrophosphate fructose‐6‐phosphate phosphotransferase by fructose‐2,6‐bisphosphate does not play an obligatory role in the stimulation of glycolysis.
Molecular changes associated with tuberisation in Solanum tuberosum. Differential expression of α‐tubulin isotypes
Authors: Taylor M. A. , Davies H. V. , Scobie L. A.
Published: May 2006

Changes in gene expression that occur in the stolon tips of potato (Solanum tuberosum L.) cv. Record during tuberisation were investigated. Protein extracts from stolon tips at various stages in the tuberisation process were analysed by two‐dimensional gel electrophoresis. A number of quantitative and qualitative changes in polypeptide composition accompanied the very early stages of tuberisation. In vitro translation of RNA extracted from stolon tips also revealed quantitative and qualitative changes associated with tuberisation. Immunoblotting of protein extracts with monoclonal antibodies raised against α‐ and β‐tubulin showed quantitative changes in the relative level of β‐tubulin, but not α‐tubulin, as the stolon tips tuberised. Changes in the pattern of α‐tubulin isotype expression were shown to occur at early stages in the tuberisation process.
Subcellular localization of nuclease in barley aleurone
Authors: Holstein Susanne E. H. , Kobert Bettina , Hillmer Stefan , Brown Peter H. , Ho T.‐H. David , Robinson David G.
Published: May 2006

The intracellular localization of an endonuclease (nuclease I) in barley aleurone responding to gibberellic acid was investigated by subcellular fractionation and immunocytochemistry with monoclonal and polyclonal antibodies. Organelle separations were performed with aleurone layers and protoplasts; immunefixations were carried out on protoplasts only. Nuclease was detected in fractions from isopycnic sucrose density gradients which were enriched in either endoplasmic reticulum or Golgi apparatus membranes. These two organelles were also labelled by the indirect immunogold method on thin sections. Intensive labelling of protein and developing vacuoles was observed. Therefore, as noted in other plants nuclease in barley is essentially a vacuolar enzyme.
Photomorphogenic effects of UV‐B radiation on hypocotyl elongation in wild type and stable‐phytochrome‐deficient mutant seedlings of cucumber
Authors: Ballaré Carlos L. , Barnes Paul W. , Kendrick Richard E.
Published: May 2006

Hypocotyl elongation responses to ultraviolet‐B (UV‐B) radiation were investigated in glasshouse studies of de‐etiolated seedlings of a long‐hypocotyl mutant (lh) of cucumber (Cucumis sativus L.) deficient in stable phytochrome, its near isogenic wild type (WT), and a commercial cucumber hybrid (cv. Burpless). A single 6‐ or 8‐h exposure to UV‐B applied against a background of white light inhibited hypocotyl elongation rate by ca 50% in lh and WT seedlings. This effect was not accompanied by a reduction in cotyledon area expansion or dry matter accumulation. Plants recovered rapidly from inhibition and it was possible to stimulate hypocotyl elongation in plants exposed to UV‐B by application of gibberellic acid. In all genotypes inhibition of elongation was mainly a consequence of UV‐B perceived by the cotyledons; covering the apex and hypocotyl with a filter that excluded UV‐B failed to prevent inhibition. These results indicate that reduced elongation does not result from assimilate limitation or direct damage to the apical meristem or elongating cells, and strongly suggest that it is a true photomorphogenic response to UV‐B. The fact that UV‐B fluences used were very low in relation to total visible light, and the similarity in the responses of lh and wild‐type plants, are consistent with the hypothesis that UV‐B acts through a specific photoreceptor. It is argued that, given the weak correlation between UV‐B and visible‐light levels in most natural conditions, the UV‐B receptor may play an important sensory function providing information to the plant that cannot be derived from light signals perceived by phytochrome or blue/UV‐A sensors.
Quantitative analysis of protein changes during meristem intiation and bud development in protoplast‐derived Petunia hybrida callus
Authors: Renaudin Jean‐Pierre , Tournaire Colette , Teyssendier de la Serve Bernard
Published: May 2006

Small calluses from Petunia hybrida leaf protoplasts differentiated into meristems and then vegetative buds in the presence of high cytokinin concentrations. Total proteins from calluses grown at two cytokinin concentrations, of which only the highest induced bud formation, were analysed for molecular markers of cytokinin action by two‐dimensional electrophoresis. The protein patterns were also compared to those of differentiated shoots and roots and to those of calluses grown under various hormonal conditions. Five percent of the total proteins detected by this method varied significantly in their level of expression according to the treatment. Quantification by image analysis demonstrated the occurrence of five groups of polypeptides with different expression patterns. Polypeptides from group 1 marked the development of buds and were abundant in young photosynthetic organs from whole plants. Polypeptides from group 5 increased only in calluses grown on control medium, i.e. in the presence of the lowest cytokinin concentration. No protein increased specifically during meristem formation. The possible action of cytokinin on regeneration is discussed in relation to these results.
Translocation and cycling through roots of recently absorbed nitrogen and sulphur in wheat (Triticum aestivum) during vegetative and generative growth
Authors: Larsson C.‐M. , Larsson M. , Purves J. V. , Clarkson D. T.
Published: May 2006

15N‐Nitrate and 35S‐sulphate labelling experiments were performed with spring wheat (Triticum aestivum L. cv. Timmo) 44. 64, 79, 95 and 115 days after sowing (growth stages arbitrarily denoted I to V). Label was fed to the plants via a fraction of the root system, termed “donor root”, whereas the rest of the root (“receiver root”) was fed non‐labelled nutrient solution. Net uptake rates for both nitrate and sulphate per unit root weight changed little from growth stage I to IV, but were considerably lower at stage V. On a whole‐plant weight basis, uptake declined from stage I to IV, because root contribution to total plant weight declined. Between 80 and 95% of absorbed label was translocated to the shoot at all growth stages. At stage V, up to 30% of absorbed label was recovered in the ears. Labelling of the receiver root indicated that, at all growth stages, 10 to 17% of N and 12 to 32% of S translocated to the shoot was retranslocated to the root. This corresponds to between 35 and 85% of the label actually recovered in the roots. Analysis of 15N‐labelling of xylem sap collected from receiver roots at growth stages I to IV indicated that about half of the reduced N in the sap is derived from cycling through roots of recently assimilated N. Evidence of cycling was also obtained at stage V. Labelled sulphate was the only form of S cycled in the plant, but it accounted for only 1 to 7% of the sulphate in the xylem sap.
Distribution of NO3− reduction between roots and shoots of peachtree seedlings as affected by NO3− uptake rate
Authors: Gojon Alain , Bussi Claude , Grignon Claude , Salsac Louis
Published: May 2006

The distribution of NO3− reduction between roots and shoots was studied in hydro‐ponically‐grown peach‐tree seedlings (Prunus persica L.) during recovery from N starvation. Uptake, translocation and reduction of NO3−, together with transport through xylem and phloem of the newly reduced N were estimated, using 15N labellings, in intact plants supplied for 90 h with 0.5 mM NH4+ and 0.5, 1.5 or 10 mM NO3−. Xylem transport of NO3− was further investigated by xylem sap analysis in a similar experiment. The roots were the main site of NO3− reduction at all 3 levels of NO3− nutrition. However, the contribution of the shoots to the whole plant NO3− reduction increased with increasing external NO3− availability. This contribution was estimated to be 20, 23 and 42% of the total assimilation at 0.5, 1.5 and 10 mM NO3−, respectively. Both 15N results and xylem sap analysis confirmed that this trend was due to an enhancement of NO3− translocation from roots to shoots. It is proposed that the lack of NO3− export to the shoots at low NO3− uptake rate resulted from a competition between NO3− reduction in the root epidermis/cortex and NO3− diffusion to the stele. On the other hand, net xylem transport of newly reduced N was very efficient since ca 70% of the amino acids synthesized in the roots were translocated to the shoots, regardless of the level of NO3− nutrition. This net xylem transport by far exceeded the net downward phloem transport of the reduced N assimilated in shoots. As a consequence, the reduced N resulting from NO3− assimilation, principally occurring in the roots, was mainly incorporated in the shoots.
Effects of rapid changes in oxygen concentration on the respiration of carrot roots
Authors: Leshuk Jeffrey A. , Saltveit Mikal E.
Published: May 2006

Rates of CO2 production and O2 consumption from aged disks of carrot (Daucus carota L.) root tissues were measured for 4 h after they were transferred from 21% to 0, 1, 2, 4 or 8% O2 in gas mixtures. A transient peak in the rate of CO2 production started 5 to 7 min after transfer to 2% or lower O2 mixtures and peaked at 50 min. After the peaks in CO2 production from the 0, 1 and 2% O2 treatments and after the stable production from the 4 and 8% O2 treatments, the rate of CO2 production from all low O2 treatments started to decline at 50 min, reaching stable rates by 160 to 240 min. Concentrations of lactate and ethanol that were significantly higher than the 21% O2 controls had started to accumulate in disks between 10 and 50 min after exposure to atmospheres containing 2% or less O2. Production of CO2 started to increase 5 to 7 min after transfer to 0, 1 and 2% O2, while the initial decline and then rise in pH and the accumulation of ethanol did not occur until 30 min after the change in atmosphere. Ethanol accumulation paralleled the increase in pH; first at 0.4 μmol g−1 h−1 from 30 to 60 min as the pH shifted from 5.97 to 6.11, and then at 0.08 μmol g−1 h−1 from 60 to 100 min as the pH stablized around 6.12. The peak at 50 min in CO2 production roughly coincided with the shift from the rapid to the slow change in pH and ethanol accumulation.
A possible role for photosystem II in environmental perturbations of photosynthesis
Authors: Baker Neil R.
Published: May 2006

Photosystem II plays an especially important role in the response of photosynthesis in higher plants to environmental perturbations and stresses. The relationship between photosystem II and photosynthetic CO2 assimilation is examined and factors identified that may modulate photosystem II activity in vivo. Particular attention is given to non‐photochemical quenching of excitation energy, photoinhibition, state transitions, protein phosphorylation and biogenesis of photosystem II.
The inactivation of pectin depolymerase associated with isolated tomato fruit cell wall: implications for the analysis of pectin solubility and molecular weight
Authors: Huber Donald J.
Published: May 2006

An approach commonly employed to assess the potential role of the enzyme polygalacturonase (PG, EC 3.2.1.15) in tomato fruit cell‐wall pectin metabolism includes correlating levels of extractable PG with changes in specific characteristics of cell wall pectins, most notably solubility and molecular weight. Since information on these features of pectins is generally derived from analyses of subfractions of isolated cell wall, assurance of inactivation of the various isoforms of wall‐associated PG is imperative. In the present study, cell wall prepared from ripe tomato (Lycopersicon esculentum Mill. cv. Rutgers) fruit was examined for the presence of active PG and for the ability of phenolic solvents to inactivate the enzyme. Using pectin solubility and Mr (relative molecular mass) changes as criteria for the presence of wall‐associated PG activity, pectins from phenol‐treated and nonphenol‐treated (enzymically active) cell wall from ripe fruit incubated in 50 mM Na‐acetate, 50 mM cyclohexanetrans‐1,2‐diamine tetraacetic acid (CDTA), pH 6.5 (outside the catalytic range of PG), were of similar Mr and exhibited no change in size with incubation time. Wall prepared without exposure to the phenolic protein‐denaturants exhibited extensive pectin solubilization and depolymerization when incubated in 50 mM Na‐acetate, 50 mM CDTA at pH 4.5, indicating the presence of active PG. Based on the changes in the Mr of pectins solubilized in 50 mM Na‐acetate, 50 mM CDTA, pH 4.5, active PG was also detected in wall exposed during isolation to phenolacetic acid‐water (PAW, 2:1:1, w/v/v), a solvent commonly employed as an enzyme denaturant. Although the depolymerization of pectins in PAW‐treated wall was extensive, oligouronides constituted minor reaction products. Interestingly, PAW‐treated wall did not exhibit PG‐mediated pectin release when incubated under conditions (30 mM Na‐acetate, 150 mM NaCl, pH 4.5) in which nonphenol‐treated cell wall exhibited high autolytic activity. In an alternative protocol designed to inactivate PG, cell wall was exposed to Tris‐buffered phenol (BP). In contrast to pectins released from PAW‐treated wall, pectins solubilized from BP‐treated wall at pH 4.5 were indistinguishable in Mr from those recovered from BP‐treated wall at pH 6.5 Even when incubated at pH 4.5 at 34°C, conditions under which pectins from PAW‐treated wall underwent more rapid and extensive depolymerization, pectins from BP‐treated wall exhibited no change in Mr, providing evidence that active PG was not present in these wall preparations. The implications of this study in interpreting the solubility and Mr of pectin in cell wall from ripening fruit are discussed.
Effects of root hypoxia and a low P supply on relative growth, carbon dioxide exchange rates and carbon partitioning in Pinus serotina seedlings
Authors: Topa Mary A. , Cheeseman John M.
Published: May 2006

The present study was conducted to determine how 10 weeks of root hypoxia and a low P supply altered relative growth, and carbon acquisition and partitioning in a moderately flood tolerant pine. Pond pine (Pinus serotina Michx.) seedlings were grown in continuously flowing solution culture at 5 or 100 μM P, under aerobic or hypoxic solution conditions. Staggered harvests were used to ascertain changes in biomass allocation and relative growth over time. Carbon dioxide exchange rates (CER) were determined by infrared gas analysis, and needles were analyzed for inorganic P (Pi), sucrose, reducing sugars and starch. Although aeration treatment had no significant effect on shoot dry weight or shoot ontogeny, root dry weight of hypoxic seedlings was significantly lower than that of aerobic seedliings after 8 weeks, regardless of the P treatment. Mean relative growth rates (RGR) of roots in the high P treatment initially decreased under hypoxia, but recovered by the sixth week with the production of adventitious roots. Two weeks of hypoxic growth conditions decreased CER and stomatal conductances of seedlings in the high P treatment by more than 30% relative to their aerobic counterparts. Stomatal closure was not accompanied by a decrease in intracellular CO2, but was accompanied by an increase in starch accumulation. Recoveries of CER, stomatal conductance and carbohydrate metabolism coincided with the recovery of root growth. Low P growth conditions did not significantly affect shoot or root dry weight until the sixth week of treatment. However, differences in seedling RGR, particularly needle RGR, were discernable during the first 2 weeks. Low P treatment effects on CER paralleled changes in needle RGR, with needle RGR more affected than CER. After 6 weeks, CER of aerobically grown seedlings in the low P treatment were only 15% lower than CER of seedlings in the high P treatment, despite a 31% and 75% reduction in needle RGR and Pi concentrations, respectively. Increased starch concentrations of recently expanded needles at this time were probably a result of diminished growth. The inhibitory effect of a low P supply on shoot growth, more specifically on needle expansion and emergence of new fascicular needles, probably limited net carbon fixed per plant more than any direct effect of low P on CER per se.
Effects of oxygen level on metabolism and development of seedlings of Trapa natans and two ecologically related species
Authors: Menegus Faustino , Cattaruzza Liliana , Scaglioni Leonardo , Ragg Enzio
Published: May 2006

Seeds of the water plant Trapa natans L. (water chestnut) can germinate in strict anoxia. The seedlings show seminal roots growing upwards while shoot buds remain quiescent until O2 becomes available. Trapa seedlings are highly tolerant to anoxia. The rate of ethanol fermentation was 21.2 μmol (g FW)−1 h−1, while production of lactate was negligible and lower than that of succinate. The seminal root of Trapa compares better to the rice coleoptile rather than to the rice root, both functionally and as to the metabolic response to anoxia. The anaerobic germination of Nuphar luteum L. and Scirpus mucronatus L. was also characterized by a limited developmental program.
Cytokinin biochemistry in relation to leaf senescence. VII. Endogenous cytokinin levels and exogenous applications of cytokinins in relation to sequential leaf senescence of tobacco
Authors: Singh Santokh , Letham D. S. , Palni L. M. S.
Published: May 2006

The cytokinin complex in tobacco leaves of various maturities was characterized by radioimmunoassay and mass spectrometry. Zeatin was the major base, whereas zeatin riboside was identified as the main riboside. in leaves of all maturities studied. Relative to upper younger leaves, the basal yellow leaves had reduced levels of both cytokinin bases and ribosides. Exogenous applications of dihydrozeatin and zeatin to detached tobacco leaves in amounts sufficient to delay senescence, elevated cytokinin base and riboside levels 2–5 fold. Presenescent and senescent leaves of intact plants showed quantitatively similar changes in cytokinin content. which therefore appear to be of significance in control of senescence. When supplied exogenously, the principal cytokinin bases found to occur in tobacco leaves (zeatin and dihydrozeatin) were markedly more effective than auxins and gibberellic acid in retarding senescence. Localised application of cytokinins to leaf blades of detopped plants was much less effective than application to intact plants. The cytokinin induced senescence retardation in tobacco leaves was independent of effects on directed metabolite transport. Evidence that endogenous levels of active cytokinins in intact tobacco leaves are involved in control of sequential leaf senescence is discussed.
Comparison of growth and gibberellin concentrations in shoots from orchard‐grown standard and thermosensitive dwarf apple trees
Authors: Steffens G. L. , Hedden P.
Published: May 2006

Apple (Malus domestica Borkh.) trees were propagated by budding from selected fully grown hybrids that ranged in height from 1.5 to 8 m. The growth and development of the selected budded trees after 7 years in the orchard was similar to that of the parent trees. Additional grafting studies showed that the dwarfism was not associated with the roots. Differences in photosynthetic activity and associated processes were not related to the size difference between tissue culture‐propagated orchard‐grown standard cv. Golden Delicious and dwarf hybrid trees. Applications of GA3 did not stimulate elongation of shoots of dwarf trees. Shoots of both standard and dwarf trees started to develop in mid‐April when they contained nearly the same amounts of GA1, GA3 and GA8, but standard shoots contained higher concentrations of GA19, GA20 and GA29. On 2 June standard shoots were almost three times the length of dwarf shoots, but the number of leaves and area per leaf were nearly the same. The relative amounts of GAs on 12 May and 2 June for both plant types were similar to those on 20 April, except that GA19, GA20, GA1 and GA29 levels had declined. Gibberellin levels in standard shoots declined further between 2 and 22 June, after which there was no further shoot elongation or production of new leaves. Between 2 June and the end of the growing season, when summer temperatures were high, dwarf shoots continued to elongate slowly and to develop new leaves, which expanded little. During this time, the GA19 content of dwarf shoots nearly doubled, whereas the amounts of GA20, GA1, GA29 and GA8 declined. By the end of the season, standard shoots were 40 cm in length with 20 leaves and dwarf shoots were 28 cm in length, but with 36 leaves. High summer temperatures appear to induce loss of GA‐responsiveness in orchard‐grown dwarf trees and to cause a reduced rate of conversion of GA19 to GA20 in these genotypes.
Role of light in the in vivo and in vitro synthesis of spinach thioredoxin f
Authors: Carrasco José L. , Chueca Ana , Sahrawy Mariam , Hermoso Rosario , Lázaro Juan J. , Gorgé Julio López
Published: May 2006

Upon continuous illumination of dark‐grown spinach (Spinacia oleracea L. cv. Winter Giant) seedlings, the thioredoxin f (Td f) content (ELISA) showed a steep rise, which can be evaluated after 3 and 36 h illumination as 3 times and 10 times the dark value, respectively. These figures correspond to 0.03% and 0.1% of total soluble protein, which means a higher biosynthetic rate for Td f compared to the average of total proteins in the earlier steps of plant development. After 40‐50 h light the Td f level reached its highest value which remained stable for an additional 40 h and then decreased. Pulse‐chase in vivo experiments with [35S]‐methionine also showed this sharp increase of Td f in the dark‐light transition. From the pattern of decay of [35S]‐labelled Td f, a half‐life of 7 h was determined for this chloroplast protein. In vitro translation experiments with poly(A)‐mRNA isolated from illuminated young spinach seedlings, coupled to a wheat‐germ synthesizing system, showed the appearance of a labelled fraction of ca 19 kDa molecular mass, recognizable by a specific Td f antiserum. When intact spinach chloroplasts were added to the translation assay medium, and then illuminated, the 19 kDa band disappeared, with a parallel increase of an internalized 13 kDa labelled polypeptide, also recognized by the Td f antiserum. These results are good evidence for a nuclear‐coded synthesis of a Td f precursor, which travels through the chloroplast envelope, leaving the functional protein inside the organelle after the loss of a 6 kDa transit peptide.
Diurnal patterns of respiration in the leaves of four forest tree species
Authors: Collier Donald E. , Cummins W. Raymond , Villar Rafael
Published: May 2006

Respiration along the cyanide‐sensitive, cytochrome pathway and the cyanide‐in‐sensitive, alternative pathway was monitored over a 24‐h period in the leaves of Acerrubrum, Betula papyrifera, Populus tremuloides and Quercus rubra excised in the field. Populus displayed the greatest rate of total respiration, followed by Betula, Quercus and Acer. All species displayed the capacity for the alternative pathway as well as some engagement of the pathway, although the level of engagement in Acer was very low. In all species investigated there were no marked diurnal trends in any respiration variable measured. Leaf soluble sugar levels remained at a relatively constant level throughout the sampling period. It is concluded that respiration did not show diurnal fluctuations because substrate supply in the leaf was maintained at a constant level.
Mode of action of natural growth inhibitors in radish hypocotyl elongation – influence of raphanusanin on auxin‐mediated microtubule orientation
Authors: Sakoda Masako , Hasegawa Koji , Ishizuka Kozo
Published: May 2006

Raphanusanin is a plant growth‐inhibiting substance which plays an important role in light growth inhibition and phototropism of radish hypocotyls. We investigated the effect of raphanusanin on indole‐3‐acetic acid (IAA)‐mediated orientation of microtubules (MT) in the outer epidermal cells of radish hypocotyl segments using immunofluorescence microscopy. IAA‐mediated MT reorientation preceded cell elongation induced by IAA. A change of IAA‐mediated MT orientation from longitudinal to transverse started within less than 15 min after IAA treatment, while significant growth promotion induced by IAA was found within about 30 min. The IAA‐mediated transverse MT orientations were significantly inhibited by simultaneously added raphanusanin. We also investigated the effect of raphanusanin on the MT orientation of the segments pretreated with IAA. The change of MT orientation induced by raphanusanin preceded growth inhibition of the segments. Within about 60 min after its application, raphanusanin initiated inhibition of the steady‐state elongation pre‐induced by IAA, while IAA‐mediated transverse MT orientations started to change into longitudinal orientations within less than 30 min after application of raphanusanin. Based on these results, it is suggested that raphanusanin induces growth inhibition through interference with the auxin‐mediated MT orientations.
Supplemental manganese improves the relative growth, net assimilation and photosynthetic rates of salt‐stressed barley
Authors: Cramer Grant R. , Nowak Robert S.
Published: May 2006

Previous results in our laboratory indicated that a reduced Mn concentration in the leaves of barley was highly correlated with the reduced relative growth and net assimilation rates of salt‐stressed plants. If Mn deficiency limits the growth of salt‐stressed barley, then increasing leaf Mn concentrations should increase growth. In the present study, the effect of supplemental Mn on the growth of salt‐stressed barley (Hordeum vulgare L. cv. CM 72) was tested to determine if a salinity‐induced Mn deficiency was limiting growth. Plants were salinized with 125 mol m−3 NaCl and 9.6 mol m−3 CaCl2. Supplemental Mn was applied in 2 ways: 1) by increasing the Mn concentration in the solution culture and 2) by spraying Mn solutions directly onto the leaves. Growth was markedly inhibited at this salinity level. Dry matter production was increased 100% in salt‐stressed plants treated with supplemental Mn to about 32% of the level of nonsalinized controls. The optimum solution culture concentration was 2.0 mmol m−3, and the optimum concentration applied to the leaves was 5.0 mol m−3. Supplemental Mn did not affect the growth of control plants. Further experiments showed that supplemental Mn increased Mn concentrations and uptake to the shoot. Supplemental Mn increased the relative growth rate of salt‐stressed plants and this increase was attributed to an increase in the net assimilation rate; there were no significant effects on the leaf area ratio. Supplemental Mn also increased the net photosynthetic rate of salt‐stressed plants. The data support the hypothesis that salinity induced a Mn deficiency in the shoot, which partially reduced photosynthetic rates and growth.
Two dimensional gel electrophoresis patterns of total, in vivo labelled and in vitro translated polypeptides from orange flavedo during maturation and following ethylene treatment
Authors: Alonso José Miguel , García‐Martínez José Luis , Chamarro Jesús
Published: May 2006

Changes in the pattern of silver stained (SS), in vivo [35S]‐methionine labelled (IL), and in vitro poly(A+)RNA translated (IT) polypeptides from the flavedo of orange fruits [Citrus sinensis (L). Osbeck cv. Washington Navel] picked at three stages of maturity (mature‐green, turning and fully coloured) and treated with different doses of ethylene (0, 1 and 10 μl 1−1) were studied by two dimensional gel electrophoresis (using isoelectric focusing and nonequilibrium pH gradient as a first dimension). More than 500 SS, 300 IL, and 250 IT spots were detected in the gels. During maturation 32 SS, 2 IL and 2 IT spots decreased, whereas 2 SS, 3 IL and 2 IT spots increased. These results indicate that the maturation process is associated with a decrease of many accumulated flavedo proteins and with an increase of a reduced number of specific polypeptides, and that some of them may be regulated at the level of gene expression. All the spots which increased with maturity also increased with ethylene treatment, suggesting a role for this hormone in the maturation process. Ten IT spots which were not affected by maturity increased following ethylene treatment, while only 2 SS and 2 IL spots underwent this pattern of variation. Three spots recognized specifically by tobacco chitinase polyclonal antibodies remained essentially unaltered, whereas one spot whose intensity decreased significantly during maturation and ethylene treatment was identified as the large subunit of ribulose‐1,5‐bisphosphate carboxylase.
Production of transformed soybean plants by electroporation of protoplasts
Authors: Widholm Jack M. , Dhir Sarwan K. , Dhir Seema
Published: May 2006

Protoplasts obtained from immature seeds of Glycine max (L.) Merr. cv. Clark 63 (soybean) were electroporated with DNA carrying either the kanamycin or hygromycin resistance genes and the reporter genes, β‐glucuronidase or opine synthesis. Antibiotic resistance could be selected for at the frequency of about one colony from 2 000 electroporated protoplasts (0.05%) and the reporter genes were expressed in from 75 to 90% of the selected colonies. Antibiotic resistance and reporter gene expression were not found in untreated protoplasts. Shoots formed within about 5 months after a number of transfers of selected portions of the callus on the regeneration medium. The shoots have been rooted to form plants which express the reporter genes and contain the transforming DNA in their leaves as shown by Southern hybridization. The reporter genes are expressed (opine synthesis) in all leaves and roots and NPTII activity was present in all leaves, indicating that the transformed plants are not chimeral. We expect these plants to set seed since untransformed plants regenerated from protoplasts did. We can obtain shoots from several of the soybean genotypes we have used so far. Thus, we should have a method for the efficient production of nonchimeral, transformed plants of the important crop plant soybean.
Species‐specificity of the lytic activity of the cell wall in the genus Chlorella
Authors: Araki Naoko , Takeda Hiroshi
Published: May 2006

Cell wall lytic activity was compared among strains IAM C‐27, C‐87, SAG 211‐1c, ‐1d, ‐9a, ‐8b, ‐8c, ‐8l, ‐11f, ‐8k, ‐11g, and ‐11h/9 of the genus Chlorella. The optimal pH was alkaline in strains with glucosamine as the characteristic group of the rigid wall, and acidic in strains characterised by glucan groups. The lytic enzymes of strains in the former type of algae lyzed the cell wall mainly to soluble high molecular oligosaccharides. The lytic activity of the Chlorella cell wall thus appears species‐ and strain‐speicific.
Plant regeneration through somatic embryogenesis in Quercus suber
Authors: Bueno M. A. , Astorga R. , Manzanera J. A.
Published: May 2006

Cork oak (Quercus suber L.) zygotic embryos, endosperm and ovules were treated with different concentrations of 2,4‐D for induction of somatic embryos. Plant material was collected during the embryo development season, from June to September. Immature embryos proved to be the most reactive initial explant. Callus and somatic embryos developed a few weeks after the beginning of the 2,4‐D treatment. For embryo development experiments, different growth regulators and cold and desiccation treatments were tested. Cold storage of somatic embryos matured in vitro at 5°C was the best treatment for breaking dormancy.
Changes in carotenoids and fatty acids in photosystem II of Cudeficient pea plants
Authors: Ayala Matilde Barón , Gorgé Julio López , Lachica Manuel , Sandmann Gerhard
Published: May 2006

Photosystem II (PSII) from Cu‐deficient pea plants (Pisum sativumL., cv. Lincoln) has been investigated for electron transport activity, Cu content, and changes in some lipid components. Total fatty acid content was lower that in control plants, with an additional shift in the C18fatty acid patterns. Less α‐linolenic and more linoleic and oleic acids were found. PSII preparations from Cu‐depleted plants showed a decreased carotenoid content in light harvesting chlorophylla/bcomplex of photosystem II (LHCII) and additional variations in pigment composition of pigment‐protein complexes. In the green algaDunaliellathe effect of Cu deficiency on fatty acid composition was similar to that in pea plants, but the influence on the carotenoid pattern was much less pronounced.
Measurements of pH in the apoplast of sunflower leaves by means of fluorescence
Authors: Hoffmann Bernd , Flänker Rüdiger , Mengel Konad
Published: May 2006

A method was elaborated by which the pH in leaf apoplast can be measured. The technique is based on the pH dependent fluorescence of 5‐carboxyfluorescein (5‐CF) or fluorescein isothiocyanate (FITC). The fluorescein isothiocyanate is coupled with a macromolecular dextran molecule (FITC‐dextran). For eliminating the effect of the absolute dye concentration the dual excitation technique was applied. It was shown that the ratio of fluorescence excited by light of 491 nm and 463 nm was virtually independent of the concentration of 5‐CF and that this fluorescence ratio was related to the pH. The plasmalemma is practically impermeable to FITC‐dextran and in the test we carried out over a period of 6 h not the slightest indication was found that it may penetrate the plasma membrane. For 5‐CF this cannot be ruled out completely. It is possible that at pH values below 4.5 it may penetrate biological membranes at low rates.

Experiments with leaves of sunflower (Helianthus animuscv. Erika) perfused with 5‐carboxyfluorescein and supplied with different nitrogen forms showed that NH+4application resulted in a decrease and NO+3application in an increase of the leaf apoplast pH. Leaf spraying with fasicoccin was followed by a pH decrease, while leaf spraying with the protonophoresp‐trifluoromethoxy carbonytcyanide phenylhydra‐zon (FCCP) or nigericin resulted in neutral apoplastic pH. These results provide evidence that the method is well suited for measuring the response of the leaf apoplast pH to changing physiological conditions.
Chemical changes and O2˙− production in thylakoid membranes under water stress
Authors: Sgherri Cristima Luisa Maria , Pinzino Calogero , Navari‐Izzo Flavia
Published: May 2006

Sunflower seedlings (Helianthus annuus cv. Isabel) subjected to a moderate level of water stress showed a reduced growth and a 0. 1 MPa osmotic adjustment came into play. Thylakoid membranes isolated from stressed leaves showed decreased chlorophyll (Chl) and protein contents but the Chl al/Chlb and protein/Chl ratios were unchanged. Water stress caused a preferential hydrolysis in thylakoid proteins: the hydrophilic to hydrophobic protein ratio increased from 0. 8 in the control to 4. 5 in the stressed plants. However, the degree of unsaturation was unchanged and the electron spin resonance (ESR) measurements did not show an increased level of O2.‐radical production by photosynthetic membranes.
Petunia flower longevity: the role of sensitivity to ethylene
Authors: Porat R. , Reuveny Y. , Borochov A. , Halevy A. H.
Published: May 2006

Two petunia (Petunia hybrida L.) lines, differing in their flower longevity, were studied, Similar tendencies were found in the changes of corolla fresh weight, electrolyte leakage and membrane microviscosity over the life spans of the two lines. Ethylene production by flowers of the two lines showed a similar pattern, peaking at 3 nl flower−1 h−1. However, in flowers of the short‐lived line, ethylene production peaked at 6 days of age, but in the long‐lived line, the peak appeared at 10 days of age. A large difference was found in the responsiveness of the flower to ethylene, Flowers of the short‐lived line responded to a similar ethylene by immediate wilting, while those of the long‐lived line responded to a similar ethylene treatment only after two days. Differences in sensitivity to ethylene were also, observed when the flowers were treated continuosly with (aminooxy)acetic acid, which blocks ethylene synthesis. Flowers of both lines responded to ethylene treatment by increased ethylene production to a similar rate. Differential sensitivity to ethylene, independent of ethylene production, seemingly governs flower longevity in the two petunia lines studied.
Aluminum enhancement of plant growth in acid rooting media. A case of reciprocal alleviation of toxicity by two toxic cations
Authors: Kinraide Thomas B.
Published: May 2006

The generally rhizotoxic ion Al3+ often enhances root growth at low concentrations. The hypothesis that Al3+ enhances growth by relieving H+ toxicity was tested with wheat seedlings (Triticum aestivum L.). Growth enhancement by Al3+ only occurred under acidic conditions that reduced root elongation. Al3+ increased cell membrane electrical polarity and stimulated H+ extrusion. Previous investigations have shown that Al3+ decreases solute leakage at low pH and that the alleviation of H+ toxicity by cations appears to be a general phenomenon with effectiveness dependent upon charge (C3+>C2+>Cl+). Alleviation of one cation toxicity by another toxic cation appears to be reciprocal so that Al3+ toxicity is relieved by H+. It has been argued previously that this latter phenomenon accounts for the apparent toxicity of ALOH2+ and Al(OH)+2. Reduction of cell‐surface electrical potential by the ameliorative cation may reduce the cell‐surface activity of the toxic cation.
Genotype‐specific differences in chilling tolerance of maize in relation to chilling‐induced changes in water status and abscisic acid accumulation
Authors: Capell Bernd , Dörffling Karl
Published: May 2006

Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12‐h photoperiod with 200 μmol m−2 s−1 from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.
Degradation and solubilization of pectin by β‐galactosidases purified from avocado mesocarp
Authors: De Veau E. J. Ian , Gross Kenneth C. , Huber Donald J. , Watada Alley E.
Published: May 2006

Three β‐galactosidase (EC 3. 2. 1. 23) isozymes were purified from the mesocarp of ripe fruit of Persea americana Mill. cv. Lula. and their effects on pectin derived from mature‐green tomato fruit were investigated. The β‐galactosidases had pl values of 5. 0,5. 1 and 5. 2. and molecular weights of 41. 49 and 54 KDa. respectively. There was a partial degradation of pectin resulting in the release of monomeric galactose upon treatment with avocado β‐galactosidase. This degradation resulted in increased pectin solubility and decreased apparent average molecular size as determined by microfiltration and gel permeation by high‐performance liquid chromatography. The increase in solubility was due. in part. to an apparent decrease in the ability of pectin molecules to aggregate together.