bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid modulation of nitrate reductase in leaves and roots: Indirect evidence for the involvement of protein phosphorylation/dephosphorylation
Authors: Kaiser W. M. , Spill D. , Glaab J. 
Published: May 2006

Nitrate reductase activity (NRA; NADH‐nitrate reductase, E. C. 1.6.6.1) has been measured in extracts from leaves of spinach (Spinacia oleracea L.) in response to rapid changes in illumination, or supply of CO2 or oxygen. Measured in buffers containing magnesium, NRA from leaves decreased in the dark and increased again upon illumination. It decreased also, when CO2 was removed in continuous light, and was reactivated when CO2 was added. Nitrate reductase (NR) from roots of pea (Pisum sativum L.) was also rapidly modulated in vivo. It increased under anaerobiosis and decreased in air or pure oxygen. The half time for inactivation or reactivation in roots and leaves was 5 to 30 min.When spinach leaves were harvested during a normal day/night cycle, extractable NRA was low during the night, and high during daytime. However, at any point of the diurnal cycle, NR could be brought to a similar maximum activity by preincubation of the desalted leaf extract with AMP and/or EDTA. Thus, the observed diurnal changes appeared to be mainly a consequence of enzyme modulation, not of protein turnover. In vivo, the reactivation of the inactivated enzyme from both leaves and roots was prevented by okadaic acid, and inhibitor of certain protein phosphatases. Artificial lowering of the ATP‐levels in leaf or root tissues by anaerobiosis (dark), mannose or the uncoupler carbonyl cyanide m‐chlorophenyl hydrazon (CCCP), always brought about full activation of NR.By preincubating crude leaf or root extracts with MgATP, NR was inactivated in vitro. Partial purification from spinach leaves of two enzymes with molecular masses in the 67 kD and 100 kD range, respectively, is reported. Both participate in the ATP‐dependent inactivation of NR.Alltogether these data indicate that NR can be rapidly modulated by reversible protein phosphorylation/dephosphorylation, both in shoots and in roots.
On the inducibility of nitrate transport by tobacco cells
Authors: Guy Micha , Heimer Yair M. 
Published: May 2006

The question as to whether the nitrate transport system is induced by nitrate was addressed using a cell suspension of the XD line ofNicotiana tabacumL. cv. Xanthi as an experimental system. The cells were grown on area as the sole nitrogen source, and tungstate was used to render nitrate reductase non‐functional. To avoid shock due to vacuum filtration, the cells, were harvested by gravity filtration. Nitrate uptake by cells, which were harvested, transferred to fresh medium, and immediately exposed to nitrate (freshly harvested cells), displayed a lag period of about 3 h.In cells which were given incubation periods in fresh medium before exposure to nitrate (preincubated cells), the lag period was considerably shortened. After 3 h of preincubation in the absence of nitrate (recovered cells), the lag period was almost completely eliminated. Cycloheximide inhibited nitrate uptake by recovered cells within minutes, and prevented the development of nitrate uptake in freshly harvested cells. Cycloheximide did not affect uptake of α‐aminoisobutyric acid (AIB) within the first 2 h after its addition. Recovery of the membrane potential from a low value just after the harvest of the cells to a maximal value 3 h later, was observed using the lipophilic cation methyltriphenylphosphonium (MTPP+), supplied at low concentrations, as a probe. Depolarization of the membrane potential by MTPP+, at the millimolar range, caused a rapid inhibition of nitrate uptake by recovered cells. The results indicate that nitrate transport by the XD cells depends on the membrane potential and on protein components with short half life. In addition, it requires a continuous protein synthesis. The effects of physical manipulation on nitrate uptake are discussed.
Inorganic carbon fixation and metabolism in maize roots as affected by nitrate and ammonium nutrition
Authors: Cramer M. D. , Lewis O. A. M. , Lips S. H. 
Published: May 2006

The effects of NO−3 and NH+4 nutrition on the rates of dark incorporation of inorganic carbon by roots of hydroponically grown Zea mays L. cv. 712 and on the metabolic products of this incorporation, were determined in plants supplied with NaH14CO3 in the nutrient solution. The shoots and roots of the plants supplied with NaH14CO3 in the root medium for 30 min were extracted with 80%; (v/v) ethanol and fractionated into soluble and insoluble fractions. The soluble fraction was further separated into the neutral, organic acid, amino acid and non‐polar fractions. The amino acid fraction was then analyzed to determine quantities and the 14C content of its individual components.The rates of dark incorporation of inorganic carbon calculated from H14CO−3 fixation and attributable to the activity of phosphoenolpyuvate carboxylase (EC 4.1.1.31), were 5‐fold higher in ammonium‐fed plants than in nitrate‐fed plants after a 30‐min pulse of 14C. This activity forms a small, but significant component of the carbon budget of the root. The proportion of 14C located in the shoots was also significantly higher in ammonium‐fed plants than in nitrate‐fed plants, indicating more rapid translocation of the products of dark fixation to the shoots in plants receiving NH+/sp4 nutrition.Ammonium‐fed plants favoured incorporation of 14C into amino acids, while nitrate‐fed plants allocated relatively more 14C into organic acids. The amino acid composition was also dependent on the type of nitrogen supplied, and asparagine was found to accumulate in ammonium‐fed plants. The 14C labelling of the amino acids was consistent with the diversion of 14C‐oxaloacetate derived from carboxlyation of phosphoenolpyruvate into the formation of both asparatate and glutamate. The results support the conclusion that inorganic carbon fixation in the roots of maize plants provides an important anaplerotic source of carbon for NH+4 assimilation.
Inhibition by 2,4‐D of somatic embryogenesis in carrot as explored by its reversal by difluoromethylornithine
Authors: Nissen Per , Minocha Subhash C. 
Published: May 2006

The development of somatic embryos is, in many plants, inhibited by 2,4‐dichlorophenoxyacetic acid (2,4‐D) and other auxins. The finding that difluoromethylornithine (DFMO) can counteract this inhibition has been used to test some of the hypotheses for the mechanism of inhibition.Inhibition of somatic embryogenesis in carrot (Daucus carota L.) by exogenous ethylene (from ethephon), antioxidants (ascorbic acid and glutathione), ethanol/acetaldehyde and abscisic acid was not counteracted by DFMO, indicating that the inhibitory effect of 2,4‐D is not manifest through the formation of these compounds. Embryogenesis was abolished by micromolar concentrations of the polar auxin transport inhibitors 2, 3, 5‐triiodobenzoic acid (TIBA), N‐1‐naphthylphthalamic acid (NPA) and 9‐hydroxyfluorene‐9‐carboxylic acid (HFCA). This inhibition was counteracted to a considerable extent by DFMO. Inhibition by relatively high concentrations of the antiauxin 2‐(p‐chlorophenoxy)‐isobutyric acid (CPIB), which does not affect polar auxin transport, was in contrast not counteracted by DFMO. These findings indicate that exogenous auxins may inhibit embryogenesis by interfering with the ability of postglobular embryos to set up internal auxin gradients necessary for polarized growth.
Gibberellin‐enhanced sugar accumulation in growing subhooks of etiolated Pisum sativum seedlings. Effects of gibberellic acid, indoleacetic acid and cycloheximide on invertase activity, sugar accumulation and growth
Authors: Miyamoto Kensuke , Ueda Junichi , Kamisaka Seiichiro 
Published: May 2006

The possible involvement of invertase in the action of gibberellic acid (GA) on stimulating sugar accumulation in growing subhooks of Alaska pea (Pisum sativum L. cv. Alaska) was studied. GA and indoleacetic acid (IAA) stimulated elongation growth to a similar extent. GA, in contrast to IAA, increased the amount of soluble sugars in the subhook. GA substantially increased invertase activity whereas IAA did not. These results suggest that the mode of action of GA and IAA differs, although both stimulate pea subhook growth.Cycloheximide (CH) inhibited the effect of GA on invertase activity, accumulation of soluble sugars, and elongation growth. Good correlations were found between invertase activity, the amount of soluble sugars and growth. The results suggest that GA‐induced enhancement of sugar accumulation in the subhook cells is dependent on increased invertase activity. The sugar accumulated in the subhook may be involved in growth promotion by GA.
Responses of soybean to ammonium and nitrate supplied in combination to the whole root system or separately in a split‐root system
Authors: Chaillou Sylvain , Rideout James W. , Raper C. David , Morot‐Gaudry Jean‐François 
Published: May 2006

To address the questions of whether allocation of carbohydrates to roots is influenced by ionic form of nitrogen absorbed and whether allocation of carbohydrates to roots in turn influences proportionality between NH4+ and NO3− uptake from mixed sources, NH4+ and NO3− were supplied separately to halves of a split‐root hydroponic system and were supplied in combination to a whole‐root system. Dry matter accumulation in the split‐root system was 18% less in the NH4+‐fed axis than in the NO3−‐fed axis. This, however, does not indicate that partitioning of carbohydrate between the two axes was different. Most of the reduction in dry matter accumulation in the NH4+‐fed axis can be accounted for by the retransport of CH2O equivalents from the root back to the shoot with amino acids produced by NH4+ assimilation. Uptake of NH4+ or NO3− by the respective halves of the split‐root system was proportional to the estimated allocation of carbohydrate to that half.When NH4+ and NO3− were supplied to separate halves of the split‐root system, the cumulative NH4+ to NO3− uptake ratio was 0.81. When supplied in combination to the whole‐root system, the cumulative NH4+ to NO3− uptake ratio was 1.67. Thus, while the shoot may affect total nitrogen uptake through the export of carbohydrates to roots, the shoot (common for halves of the split‐root system) apparently does not exert a direct effect on proportionality of NH4+ and NO3− uptake by roots. For whole roots supplied with both NH4+ and NO3−, the restriction in uptake of NO3− may involve a stimulation of NO3− efflux rather than an inhibition of NO3− influx. While only the net uptake of NH4+ and NO3− was measured by ion chromatography, monitoring at approximately hourly intervals during the first 3 days of treatment revealed irregularly occurring intervals of both depletion (net influx) and enrichment (net efflux) in solutions. In the case of NH4+, numbers of net efflux events were similar (21 to 24 out of 65 sequential sampling intervals) whether NH4+ was supplied with NO3− to whole‐root systems or separately to an axis of the split‐root system. In the case of NO3−, however, the number of net efflux events increased from 8 when NO3− was supplied to a separate axis of the split‐root system to between 19 and 24 when NO3− was supplied with NH4+ to whole‐root systems.
Effects of gamma irradiation on the plasma membrane of suspension‐cultured apple cells. Rapid irreversible inhibition of H+‐ATPase activity
Authors: Dong Chang‐Zhi , Montillet Jean‐Luc , Triantaphylidès Christian 
Published: May 2006

The effects of ionizing radiation, used in post‐harvest treatment of fruit and vegetables. were investigated on cultured apple cells (Pyrus malus L. cv. Royal Red) on a short‐term period. Irradiation (2 kGy) induced an increase of passive ion effluxes from cells and a decrease of cell capacity to regulate external pH. These alterations are likely due to effects on plasma membrane structure and function and were further investigated by studying the effects of irradiation on plasma membrane H+‐ATPase activity. Plasma membrane‐enriched vesicles were prepared and the H+‐ATPase activity was characterized. Irradiation of the vesicles induced a dose dependent inhibition of H+‐ATPase activity. The loss of enzyme activity was immediate, even at low doses (0.5 kGy), and was not reversed by the addition of 2mM dithiothreitol. This inhibition may be the result of an irreversible oxidation of enzyme sulfhydryl moieties and/or the result of changes induced within the lipid bilayer affecting the membrane‐enzyme interactions. Further analysis of the H+‐ATPase activity was carried out on vesicles obtained from irradiated cells confirming the previous results. In vivo recovery of activity was not observed within 5 h following the treatment, thus explaining the decrease of cell capacity to regulate external pH.This rapid irreversible inhibition of the plasma membrane H+‐ATPase must be considered as one of the most important primary biochemical events occurring in irradiated plant material.
Development of auxin autotrophy in Nicotiana tabacum callus cultures
Authors: Szabó M. , Köves E. , Somogyi I. 
Published: May 2006

Changes of auxin and ethylene metabolism of Nicotiana tabacum var. Xanthi callus were investigated in relation to auxin‐independent growth. During the habituation process, changes occur progressively in hormone metabolism in auxin‐heterotrophic tissues: the potential for the destruction of indoleacetic acid (IAA) increases, the IAA level in the cultures rises slightly, and the auxin sensitivity of the callus becomes modified. Preceding the onset of habituation, ethylene production is enhanced although the tissues retain their ability to undergo regeneration.Gradual changes in auxin metabolism and ethylene production confirm the epigenetic character of the habituation process.
Enhancement of extractable ethylene at light/dark transition in primary leaves of paclobutrazol‐treated Phaseolus vulgaris seedlings
Authors: Tari Irma , Nagy Maria 
Published: May 2006

Paclobutrazol [(2RS,3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1,2,4‐triazol‐1‐yl)pentan‐3‐ol], a triazole growth retardant, increased the 1‐aminocyclopropane‐1‐carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum‐extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum‐extraction of primary leaves of treated plants and the ethylene deficiency of retardant‐treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl‐ACC.It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol‐treated bean plants, but under special environmental conditions in vivo it may reach that of the control.
Relationship between banding and photosynthetic activity in Chara corallina as studied by the spatially different induction curves of chlorophyll fluorescence observed by an image analysis system
Authors: Plieth Christoph , Tabrizi Hamed , Hansen Ulf‐Peter 
Published: May 2006

Image analysis was applied for studying the kinetics of chlorophyll fluorescence in the alkaline and acid zones of internodal cells of Chara corallina Klein ex Willd., in order to test the hypothesis that in the acid bands an outward proton current yields a conversion of HCO3− ions to CO2, thus facilitating inward diffusion of CO2.The analysis of the responses of chlorophyll fluorescence induced by changes in light intensity from 0.15 W m−2 to 2.0 W m−2 (λ <580 nm) revealed different kinetic behaviour. In the alkaline zones, the amplitude of the variable components of fluorescence was smaller than in the acid zones. Curve fitting by a sum of exponentials showed that the 4 time constants of about 2, 22, 48 and 140 s were not significantly different between the alkaline and acid zones. In contrast the related amplitude factors were smaller in the alkaline zones. by a factor of about 1.6 to 2.0 in old calcified cells and by a factor of about 1.2 in young cells without acrustations.The interpretation of these results in terms of a better supply of carbon dioxide in the acid zones was supported by investigations on leaves of tobacco. Lowering the CO2 concentration of an artificial atmosphere below 20 ppm resulted in a similar reduction of the variable component of chlorophyll fluorescence as found in the alkaline zones of Chara.
Integration of nuclear‐encoded proteins into pea thylakoids with different pigment contents
Authors: Dahlin Clas , Timko Michael P. 
Published: May 2006

The in vitro membrane integration of the light‐harvesting protein of photosystem II (LHCP), the Rieske FeS protein of the cytochrome (Cyt) blf‐complex, and the NADPH:protochlorophyllide oxidoreductase (Pchlide reductase) into pea thylakoids with different pigment composition was studied. Pea plants (Pisum sativum L. cv. Kelvedon Wonder) with different contents of chlorophyll (Chl) and carotenoids were obtained by growing the seedlings in a greenhouse or in weak red light with or without the herbicide Norflurazon, an inhibitor of carotenoid biosynthesis. Chloroplasts from untreated and Norflurazon‐treated plants grown in weak red light contained approximately 29 and 14% of Chl compared to chloroplasts from untreated plants grown in the greenhouse. The corresponding carotenoid contents were 66 and 5%. Following an integration reaction using LHCP precursor protein and chloroplast lysate, thylakoids from untreated and Norflurazon‐treated plants grown in weak red light contained approximately 30 and 5% of protease‐protected LHCP, respectively, compared to thylakoids of untreated plants grown in a greenhouse. In contrast to LHCP, the in vitro assembly of the Pchlide reductase was only sligthly reduced in chloroplast lysates of plants grown in weak red light compared to greenhouse‐grown plants. In chloroplast lysates of Norflurazon‐treated plants, however, the amount of membrane associated, protease‐protected Pchlide reductase was reduced to 32% of the amount in untreated plants grown under the same light conditions. In contrast, the integration of the Rieske FeS protein occurred to almost similar levels irrespective of light conditions and herbicide treatments.Reconstitution assays where stroma from Norflurazon‐treated plants was added to thylakoids from untreated plants, showed that the herbicide did not affect any stromal component(s) vital for the insertion reaction. Removal of samples during the integration reaction of LHCP showed that no degradation of the protein occurred during the assay. Neither was the assembled protein degraded up to 24 h after the termination of the assay. This indicates that growing plants in weak red light, with or without Norflurazon treatment, mainly affected the primary step in thylakoid assembly of LHCP, i.e. the insertion reaction into the membrane. The results further indicate that proteins normally bound to pigments also require pigments for membrane recognition or integration.
Light quality beneath field‐grown maize, soybean and wheat canopies – red:far red variations
Authors: Sattin M. , Zuin M. C. , Sartorato I. 
Published: May 2006

Using artificial canopies, several authors have shown that horizontally propagated and overall propagated radiation beneath the canopy differ substantially in spectral distribution in the red (R) and far red (FR) wavelengths. Given the lack of information about light quality under real crop canopies, the R:FR ratio of vertical and horizontal radiation beneath field‐grown maize, soybean and wheat was monitored until leaf area index (LAI) reached 4, 2.5 and 6.9, respectively.A Li‐Cor 1800 spectroradiometer with a remote cosine receptor fitted with a quartz fibre‐optic light‐guide was used. To isolate radiation coming from a given direction, a black coated tube was fitted to the cosine receptor. The viewing angle was 15°. In open conditions, the values of R:FR from the upper hemisphere were between 1.07 and 1.20. For vertically and horizontally‐propagated light, average values were 1.22 and 0.75 respectively.Beneath the canopy, both R:FR and photosynthetic photon flux density (PPFD) from the entire upper hemisphere decreased in relation to LAI and crop height. R:FR of the horizontal component were found to be generally much lower than the vertical, which decreased significantly only in the later measurements.The lowest R:FR values were recorded under wheat and soybean canopies. Even the very low LAIs present at early development stages were enough to cause a sharp decrease of R:FR in the horizontal fluxes. Referring to the entire upper hemisphere, PPFD transmittance and R:FR as a percentage of the external references appeared well correlated.
Changes in spectral properties of ageing and senescing maize and sunflower leaves
Authors: Masoni Alessandro , Ercoli Laura , Mariotti Marco , Barberi Paolo 
Published: May 2006

The objective of this study was to determine the differences between maize (Zea mays L.) and sunflower (Helianthus annuus L.) in the pattern of leaf chlorophyll content and spectral properties occurring with leaf ageing and senescence.Chlorophyll accumulation and leaf spectral properties were determined in growing and senescing leaves of field‐grown maize and sunflower hybrids. Measurements were taken at intervals of 3–4 days during the rapid stem elongation phase on leaf 11 for maize and leaf 17 for sunflower. Reflectance (R) and transmittance (T) spectra of adaxial surfaces of attached leaves were measured using a LI‐COR 1800 hand‐held spectroradiometer with an external integrating sphere, over the wavelength range from 400 to 100 nm. Absorptance (A) was computed as: A = 100‐(R + T).In the growing leaf, chlorophyll content increased until full leaf expansion, while no changes in A and T were recorded. After full leaf expansion was reached, chlorophyll dropped from 514.3 to 328.0 μmol m−2 in maize and from 527.2 to 164.1 μmol m−2 in sunflower. Absorptance in the PAR region declined about 5% in maize and about 11% in sunflower and T increased about 1% in maize and 7% in sunflower. Within the PAR region, variations in A and T were recorded only in the green band (520–600 nm) for maize and in the green and red (630–690 nm) bands for sunflower. There were differences between maize and sunflower in the relative timing of the decrease in chlorophyll content and A in senescing leaves: maize retained chlorophyll longer than sunflower and A declined more slowly in maize as a result of the different length of leaf maturity and senescing stages.