bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of soybean nodule phosphoenolpyruvate carboxylase in vivo
Authors: Wadham Carol , Winter Heike , Schuller Kathryn A.
Published: May 2006

The sensitivity of soybean (Glycine max L. Merr, cv. PS47) nodule phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) to inhibition by L‐malate in vitro increased when well‐nodulated plants were subjected to decapitation (shoot removal). There was no effect of decapitation on the apparent Km of the enzyme for its substrate PEP but the I50 (L‐malate) decreased from 4.2 to 1.7 mM. The total amount of PEP doubled and that of malate decreased by half in the nodules of decapitated plants relative to the control plants. This observation was consistent with a decrease in the activity of PEPC in vivo as a result of the increased malate sensitivity of the enzyme observed in vitro. Sucrose levels in the nodules declined in response to decapitation but there were no effects on the levels of glucose, fructose, pyruvate, 2‐oxoglutarate, glutamine or glutamate. The results are discussed in terms of the role of protein phosphorylation in the regulation of PEPC activity in legume nodules.
Short‐term aluminium uptake by tobacco cells: Growth dependence and evidence for internalization in a discrete peripheral region
Authors: Vitorello Victor A. , Haug Alfred
Published: May 2006

Short‐term uptake and initial localization of aluminium (Al) were investigated in cultured cells of Nicotiana tabacum L. cv. BY‐2. Graphite furnace atomic absorption spectrometry and an in vivo Al‐sensitive fluorometric assay, employing morin, yielded similar results in all experiments. Aluminium uptake was critically dependent on cell growth. As opposed to negligible uptake in stationary‐phase cells, Al uptake (20 μM AlCl3, pH 4.5, 23°C) by actively growing cells was detectable within 5 min, with an initial rate of 16 nmol Al (106 cells)−1 h−1. Increased CaCl2 levels (up to 20 mM), low temperature (4°C), and pre‐chelation of Al to citrate greatly reduced Al uptake (by 75–90%). A pH‐associated permeabilization of cells at pH 4.5, as monitored by trypan blue, was observed in some growing cells. Although permeability to trypan blue was not a requirement for Al uptake, enhanced membrane permeability at pH 4.5, relative to pH 5.6, may contribute to Al uptake. Aluminium was observed to localize mainly in a pronounced and discrete fluorescent zone at the cell periphery (2–30 μm wide), presumably in the cortical cytosol and/or the adjoining plasma membrane section, although the possibility cannot be excluded that some Al resided in the cell wall apposing this discrete region. However, as judged by the Al‐morin assay, there were no detectable Al levels in the remaining, larger portion of the cell wall. The potential of the Al‐morin method in Al toxicity studies is illustrated.
Functions of passage cells in the endodermis and exodermis of roots
Authors: Peterson Carol A. , Enstone Daryl E.
Published: May 2006

Passage cells frequently occur in the endodermis and exodermis but are not ubiquitous in either layer. Passage cells occur in the form of short cells in the dimorphic type of exodermis. In both layers, Casparian bands are formed in all cells, but the subsequent development of suberin lamellae and thick, cellulosic walls are delayed or absent in the passage cells. Available evidence suggests that passage cells of the endodermis are important for the transfer of calcium and magnesium into the stele and thus into the transpiration stream. They become the only cells which present a plasmalemma surface to the soil solution (and are thus capable of ion uptake) when the epidermis and central cortex die. This occurs naturally in some herbaceous and woody species and is known to be promoted by drought. Most evidence indicates that the development of suberin lamellae in both the endodermis and exodermis increases the resistance of the root to the radial flow of water. Passage cells thus provide areas of low resistance for the movement of water, and the position of these cells in the endodermis (i.e., in close proximity to the xylem) is explained in terms of function. Exodermal passage cells have a cytoplasmic structure suggesting an active role in ion uptake. This may be related to the tendency of the epidermis to die, leaving the passage cells as the only ones with their membranes exposed to the soil solution. Passage cells in the exodermis attract endomycorrhizal fungi while those in the endodermis do not. It is clear that passage cells of the endodermis and exodermis play a variety of roles in the plant root system.
Effective regulation of iron acquisition in graminaceous plants. The role of mugineic acids as phytosiderophores
Authors: Ma Jian Feng , Nomoto Kyosuke
Published: May 2006

Discovery of mugineic acids as phytosiderophores has shown that some graminaceous monocotyledonous plants have a different iron acquisition strategy (strategy II) from dicotyledonous and nongraminaceous monocotyledonous plants (strategy I). The process of iron acquisition by strategy II plants can be divided into four main steps: biosynthesis, secretion, solubilization, and uptake, all of which are effectively regulated by different systems. The biosynthesis of mugineic acids is controlled by an on‐off system which is operated under the control of iron demand in the plant. All mugineic acids share the same biosynthetic pathway from L‐methionine to 2′‐deoxymugineic acid, but the subsequent steps differ among plant species and even cultivars. The biosynthesis of mugineic acids is associated with the methionine recycling pathway. The secretion of mugineic acids shows a distinct diumal rhythm. Mugineic acids solubilize sparingly soluble inorganic iron by chelation and possess a high chelation affinity for iron, but not for other polyvalent ions such as Ca2+, Mg2+ and Al3+. The iron uptake process is regulated by a specific uptake system that transports the mugineic acid‐Fe(III) complex as an intact molecule. This system specifically recognizes the mugineic acid‐Fe(III) complexes, but not other mugineic acid‐metal or synthetic chelator‐Fe(III) complexes, suggesting that binding sites with strict recognition for stereostructure of the complex are located on the plasma membrane. All these regulatory systems are considered to represent an efficient strategy to acquire adequate amounts of iron and to avoid factors unfavorable for iron acquisition such as high pH, high concentrations of bicarbonate, Ca2‐ and Mg2+, microbial degradation, and uptake of other metals that are common in calcareous soils.
Auxin‐conjugate hydrolysis in Chinese cabbage: Characterization of an amidohydrolase and its role during infection with clubroot disease
Authors: Ludwig‐Müller Jutta , Epstein Ephraim , Hilgenberg Willy
Published: May 2006

Auxin conjugates play a role in the regulation of free indole‐3‐acetic acid (IAA) content in plants. Not much is known about the enzymes involved in either conjugate synthesis or hydrolysis. In this study we have isolated and characterized an auxin conjugate hydrolase from Chinese cabbage seedlings and investigated it during the development of both the Chinese cabbage plants and the clubroot disease. The hydrolase isolated from light‐ and dark‐grown seedlings accepted the amide conjugates indole‐3‐acetic acid‐alanine (IAAla), IAA‐phenylalanine (IAPhe), but not IAA‐aspartate (IAAsp) as substrates. We also found a substantial amount of hydrolysis of an ester conjugate (IAA‐glucose, IAGlu) in our enzyme preparation. The tentative reaction product IAA was identified by HPLC and subsequent GC‐MS analysis. The pH optima for the different substrates were not identical, suggesting several hydrolase isoforms. After gel filtration chromatography we found at least two peaks containing different hydrolase isoforms. The isoform, which converted IAGlu to IAA, exhibited a molecular mass of ca 63 kDa, and an isoform of ca 21 kDa converted IAAla and IAPhe. The increased free IAA content in clubroot‐diseased roots of Brassicaceae can be due to either de novo synthesis or release of IAA from conjugates. To answer this question free, ester‐ and amide‐bound IAA was measured in 24‐ and 30‐day‐old leaves and roots of healthy and Plasmodiophora brassicae‐infected Chinese cabbage, and the hydrolase activity with different substrates measured in the same tissues. The amide conjugates were dramatically enhanced in infected roots, whereas free IAA was only slightly enhanced compared to the control tissue. Hydrolase activity was also enhanced in clubbed roots, but the substrate specificity differed from that found in the seedlings. Especially, IAAsp hydrolysis was induced after inoculation with P. brassicae. We conclude that different auxin conjugates can be hydrolyzed at different developmental stages or under stress.
Interactions between respiration and inorganic phosphate uptake in phosphate‐limited cells of Chlamydomonas reinhardtii
Authors: Weger Harold G.
Published: May 2006

Phosphate addition to P‐limited cells of Chlamydomonas reinhardtii resulted in an immediate increase in the rate of respiratory O2 consumption. The respiration rate continued to increase for several minutes after the addition of P1. Similar patterns of P1 stimulation of respiratory O2 consumption were observed in the presence of cyanide (cytochrome oxidase inhibitor) and propyl gallate (alternative oxidase inhibitor). Stimulation of O2 consumption was accompanied by rapid changes in levels of glycolytic intermediates. These changes were consistent with activation of ATP‐dependent phosphofructokinase and pyruvate kinase. The adenylate pool exhibited only minor perturbations, P1, uptake resulted in extracellular acidification, which continued for several minutes after the exhaustion of added P1, whereas exhaustion of extracellular P1 resulted in a rapid decline in the O2 consumption rate. These results are consistent with control of respiration in P‐limited cells occurring largely at the level of glycolysis.
Interaction of elevated CO2and O3on growth, photosynthesis and respiration of three perennial species grown in low and high nitrogen
Authors: Volin John C. , Reich Peter B.
Published: May 2006

Seedlings of three species native to central North America, a C3tree,Populus tremuloidesMichx., a C3grass,Agropyron smithiiRybd., and a C4grass,Bouteloua curtipendulaMichx., were grown in all eight combinations of two levels each of CO2, O3and nitrogen (N) for 58 days in a controlled environment. Treatment levels consisted of 360 or 674 μmol mol‐1CO2, 3 or 92 nmol mol‐1O3, and 0.5 or 6.0 mMN. In situ photosynthesis and relative growth rate (RGR) and its determinants were obtained at each of three sequential harvests, and leaf dark respiration was measured at the second and third harvests. In all three species, plants grown in high N had significantly greater whole‐plant mass, RGR and photosynthesis than plants grown in low N. Within a N treatment, elevated CO2did not significantly enhance any of these parameters nor did it affect leaf respiration. However, plants of all three species grown in elevated CO2had lower stomatal conductance compared to ambient CO2‐exposed plants. Seedlings ofP. tremuloides(in both N treatments) andB. curtipendula(in high N) had significant ozone‐induced reductions in whole‐plant mass and RGR in ambient but not under elevated CO2.This negative O3impact on RGR in ambient CO2was related to increased leaf dark respiration, decreased photosynthesis and/or decreased leaf area ratio, none of which were noted in high O3treatments in the elevated CO2environment. In contrast,A. smithiiwas marginally negatively affected by high O3.
Effects of atmospheric CO2 enrichment and root restriction on leaf gas exchange and growth of banana (Musa)
Authors: Schaffer B. , Searle C. , Whiley A. W. , Nissen R. J.
Published: May 2006

The effects of atmospheric CO2 enrichment and root restriction on photosynthetic characteristics and growth of banana (Musa sp. AAA cv. Gros Michel) plants were investigated. Plants were grown aeroponically in root chambers in controlled environment glasshouse rooms at CO2 concentrations of 350 or 1 000 μmol CO2 mol‐1. At each CO2 concentration, plants were grown in large (2001) root chambers that did not restrict root growth or in small (20 1) root chambers that restricted root growth. Plants grown at 350 μmol CO2 mol‐1 generally had a higher carboxylation efficiency than plants grown at 1 000 μmol CO2 mol‐1 although actual net CO2 assimilation (A) was higher at the higher ambient CO2 concentration due to increased intercellular CO2 concentrations (Ci resulting from CO2 enrichment. Thus, plants grown at 1 000 μmol CO2 mol‐1 accumulated more leaf area and dry weight than plants grown at 350 μmol CO2 mol‐1. Plants grown in the large root chambers were more photosynthetically efficient than plants grown in the small root chambers. At 350 μmol CO2 mol‐1, leaf area and dry weights of plant organs were generally greater for plants in the large root chambers compared to those in the small root chambers. Atmospheric CO2 enrichment may have compensated for the effects of root restriction on plant growth since at 1 000 μmol CO2 mol‐1 there was generally no effect of root chamber size on plant dry weight.
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.
The effect of solar UV radiation on four plant species occurring in a coastal grassland vegetation in The Netherlands
Authors: Tosserams Marcel , de Sà Antonio Pais , Rozema Jelte
Published: May 2006

During the summer of 1992, growth and some physiological parameters of four native plant species occurring in a coastal grassland in The Netherlands, were studied after reduction of solar UV irradiance using different cut‐off filters. Biomass production, morphology and photosynthesis of all species tested were unaffected by the different treatments. Litter production of Plantago lanceolata was increased in the absence of the total UV waveband, indicating a possible role for this waveband in plant senescence. Depletion of the total UV waveband from sunlight resulted in alterations in biomass allocation in Calamagrostis epigeios and Urtica dioica while no changes were observed in P. Ianceolata and Verbascum thapsus. In C. epigeios an increase in the specific leaf area was observed, whereas in U. dioica root weight per total plant weight was decreased resulting in an increase in the shoot/root ratio. Both photosynthetic and UV‐absorbing pigment concentrations were altered by the different filter applications. When compared to control plants receiving full sunlight, depletion of UV‐B resulted in a significant increase in chlorophyll concentration in U. dioica leaves, this however did not affect photosynthetic rate. The presence of UV‐B radiation enhanced the UV‐absorbance of leaf extracts of all species except P. lanceolata. Optical characteristics of the leaves were also changed. Both the quantity (P. lanceolata and U. dioica) and the quality (all species) of radiation transmitted by the leaves was affected by the different treatments.
Identification of endogenous gibberellins, and metabolism of tritiated and deuterated GA4, GA9 and GA20, in Scots pine (Pinus sylvestris) shoots
Authors: Wang Q. , Little C. H. A. , Moritz T. , Odén P. C.
Published: May 2006

The application of gibberellin A4/7 (GA4/7) to the stem of previous‐year (1‐year‐old) terminal shoots of Scots pine (Pinus sylvestris) seedlings has been observed to stimulate cambial growth locally, as well as at a distance in the distal current‐year terminal shoot, but the distribution and metabolic fate of the applied GA4/7, as well as the pathway of endogenous GA biosynthesis in this species, has not been investigated. As a first step, we analysed for endogenous GAs and monitored the transport and metabolism of labelled GAs 4, 9 and 20. Endogenous GAs from the elongating current‐year terminal shoot of 2‐year‐old seedlings were purified by column chromatography and high‐performance liquid chromatography and analysed by combined gas chromatography‐mass spectrometry (GC‐MS). GAs 1, 3, 4, 9, 12 and 20 were identified in the stem, and GAs 1, 3 and 4 in the needles, by full‐scan mass spectrometry (GAs 1, 3, 4, 9 and 12) or selected‐ion monitoring (GA20) and Kovats retention index. Tritiated and deuterated GA4, GA9 or GA20 were applied around the circumference at the midpoint of the previous‐year terminal shoot, and metabolites were extracted from the elongating current‐year terminal shoot, the application point, and the 1‐year‐old needles and the cambial region above and below the application point. After purification, detection by liquid scintillation spectrometry and analysis by GC‐MS, it was evident that, for each applied GA, unmetabolised [2H2]GA and [3H]radioactivity were present in every seedling part analysed. Most of the radioactivity was retained at the application point when [3H]GA9 and [3H]GA20 were applied, whereas the largest percentage of radioactivity derived from [3H]GA4 was recovered in the current‐year terminal shoot. It was also found that [2H2]GA9 was converted to [2H2]GA20 and to both [2H2]GA4 and [2H2]GA1, [2H2]GA4 was metabolised to [2H2]GA1, and [2H2]GA20 was converted to [2H2]GA29. The data indicate that for Pinus sylvestris shoots (1) GAs applied laterally to the outside of the vascular system of previous‐year shoots not only are absorbed and translocated extensively throughout the previous‐year and current‐year shoots, but also are readily metabolised, (2) the GA metabolic pathways found are closely related to the endogenous GAs identified, and (3) GA9 metabolism follows two distinctly different routes: in one, GA9 is converted to GA1 through GA4, and in the other it is converted to GA20, which is then metabolised to GA29. The results suggest that the late 13‐hydroxylation pathway is an important route for GA biosynthesis in shoots of Pinus sylvestris, and that the stimulation of cambial growth in Scots pine by exogenous GA4/7 may be due to its conversion to GA1, rather than to it being active per se.
NADP+‐isocitrate dehydrogenase in germinating cucumber cotyledons: Purification and characterization of a cytosolic isoenzyme
Authors: Canino Stefania , Nieri Barbara , Pistelli Laura , Alpi Amedeo , De Bellis Luigi
Published: May 2006

The activity of NADP+‐dependent isocitrate dehydrogenase (ICDH, EC 1.1.1.42) was investigated during the post‐germinative growth of cucumber (Cucumis sativus L. cv. Marketmore) seedlings. Isoelectric focusing showed the presence of several isoenzymes, two of which represented 70–80% of the total NADP+‐ICDH activity in cotyledons of seedlings grown in the dark. They had pI values between 4.8 and 5.8. The isoenzyme with higher pI was purified to homogeneity by hydrophobic interaction, affinity, hydroxylapatite and anion exchange chromatography. The purified isoenzyme is a dimeric protein, consisting of two apparently identical 43‐kDa subunits. It is specific for NADP+, inhibited by ATP and by 2‐oxoglutarate, whereas it is not inhibited by citrate, succinate, and glyoxylate. The data indicate that NADP+‐ICDH from cucumber is structurally similar to ICDHs from other plants, but it shows some peculiar biochemical characteristics.
Electroporation‐mediated transient gene expression in isolated scutella of Hordeum vulgare
Authors: Hänsch Robert , Koprek Thomas , Heydemann Henrike , Mendel Ralf R. , Schulze Jutta
Published: May 2006

Electroporation was used to introduce DNA into excised scutella of immature embryos of Hordeum vulgare L. cvs Golden Promise and Delita. Using the firefly luciferase gene as reporter, parameters were analyzed for high transient gene expression while maintaining tissue viability. Enzymatic wounding was necessary for DNA uptake. The optimized protocol involves use of linearized DNA and addition of 15% (w/v) polyethylene glycol at a field strength of 950 V cm−1 and approximately 56 ms pulse length. A one‐day preculture was required for obtaining callus after electroporation. Transient gene expression was further demonstrated using the β‐glucuronidase gene. Blue spots were detected at the abaxial scutellar surface, indicating that cells competent for somatic embryogenesis are also amenable to transfection by electroporation.
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.
Nitrate reductase expression in maize leaves (Zea mays) during dark‐light transitions. Complex effects of protein phosphatase inhibitors on enzyme activity, protein synthesis and transcript levels
Authors: Redinbaugh Margaret G. , Huber Steven C. , Huber Joan L. , Hendrix Keith W. , Campbell Wilbur H.
Published: May 2006

The effects of cytoplasmic protein synthesis and protein phosphatase activity on NADH:nitrate reductase (NR) activity, protein and transcript were examined in maize (Zea mays L.) seedling leaves. A rapid increase in NR activity, measured in the presence of 5 mM Mg2+, was found upon exposure of excised leaves to light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]‐LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX), did not affect Mg2+ inhibition of NR activity during the dark‐to‐light transition. Vmax NR activity, measured in the presence of 5mM Mg2+, was found upon exposure of excised leaves to light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]‐LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX), did not affect Mg2+ inhibition of NR activity during the dark‐to‐light transition. Vmax NR activity, measured in the presence of Pi and EDTA, remained constant or increased slightly in maize leaves during the first 2 h of the light period. OKA, MC‐LR or CHX treatment caused a 40 to 50% reduction in Vmax NR activity during this time. Incorporation of 35S‐Met into NR protein was reduced more than 90% by CHX and 80% by OKA. The inhibition of NR protein synthesis by CHX and OKA correlated with a 50 to 60% decrease in 35S‐Met incorporation into total soluble protein over the treatment period. The increase in NR mRNA levels early in the light period was prevented by OKA and MC‐LR, but not by CHX. OKA had a similar effect on sucrose phosphate synthase mRNA levels, but did not affect Catalasel or Catalase3 mRNA accumulation. The data suggest that light‐induced decreases in Mg2+ inhibition of NR activity and transcript levels are independent of new protein synthesis. The effects of OKA and MC‐LR indicate that protein phosphatase activities could be involved, directly or indirectly, in the regulation of NR activity, protein synthesis and transcript accumulation.
Modulation of carbon and nitrogen allocation in Urtica dioica and Plantago major by elevated CO2: Impact of accumulation of nonstructural carbohydrates and ontogenetic drift
Authors: den Hertog J. , Stulen I. , Fonseca F. , Delea P.
Published: May 2006

Doubling the atmospheric CO2 concentration from 350 to 700 μ1 1−1 increased the relative growth rate (RGR) of hydroponically grown Urtica dioica L. and Plantago major ssp. pleiosperma Pilger only for the first 10–14 days. Previous experiments with P. major led to the conclusion that RGR did not respond in proportion to the rate of photosynthesis. The present paper is focussed on the analysis of the impact of changes in leaf morphology, dry matter partitioning, dry matter chemical composition and ontogenetic drift on this discrepancy.

Soon after the start of the treatment, carbohydrate concentrations were higher at elevated CO2: a reaction that was largely due to starch accumulation. An increase in the percentage of leaf dry matter and decreases in the specific leaf area (SLA) and the shoot nitrogen concentration were correlated with an increase in the total nonstructural carbohydrate concentration (TNC). A combination of accumulation of soluble sugars and starch and ontogenetic drift explains the decrease in SLA at the elevated CO2 level. A similar ontogenetic effect of elevated CO2 was observed on the specific root length (SRL). Other variables such as shoot nitrogen concentration and percentage leaf dry matter were not affected by correction of data for TNC levels. The net diurnal fluctuation of the carbohydrate pool in P. major was equal for both CO2 concentrations, indicating that the growth response to elevated CO2 may be ruled by variables other than photosynthesis, as for instance sink strength.

Elevated CO2 did not greatly influence the partitioning of nitrogen between soluble and insoluble, reduced N and nitrate, nor the allocation of dry matter between leaf. stem and root. The finding that the root to shoot ratio (R/S) was not affected by elevated CO2 implies that, in order to maintain a balanced activity between roots and shoot, no shift in partitioning of dry matter upon doubling of the atmospheric CO2 concentration is required. Our data on R/S are in good agreement with the response of R/S to high CO2 predicted by models based on such a theorem.
Time dependent K+ currents through plasmalemma of laticifer protoplasts from Hevea brasiliensis
Authors: Bouteau François , Bousquet Ulrike , Pennarun Anne‐Marie , Convert Monique , Dellis Olivier , Cornel Daniel , Rona Jean‐Pierre
Published: May 2006

The purpose of our work was to investigate the functioning of K+ channels in protoplasts of laticifers of Hevea brasiliensis Muell. Arg., anastomosed into a network devoid of large central vacuoles, after tapping stress. Physiological functions such as proton pump activity and uptake of sucrose (a rubber precursor) were maintained, when the voltage‐clamp method was used in vivo to record the whole‐cell K+ current during the stress response.

A time‐dependent inward current was induced in 50 mM KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K+ channel was not closely dependent on Ek. This would be coherent with the ‘valve model’ of Schroeder and Fang (1991, Proc. Natl. Acad. Sci. USA 88: 11583–11587) involving the activation of a H+‐pump accounting for the K+ uptake observed in laticiferous cells under stress. The activation half‐time of outward currents was clearly voltage dependent: from about 350 to 60 ms for 125 and 155 mV, respectively. Time‐dependent outward current sensitivity to 5 mM BaCl2 or CaCl2 or to 5 μM Erythrosin B showed that the K+ channels could be Ca2+‐dependent. Because of the positive values of the activation potential of the outward current, the possibility opens that an action potential exists, these cells being specialized for stress response.
Rhythms in magnesium ion inhibition and hysteretic properties of nitrate reductase in the CAM plant Bryophyllum fedtschenkoi
Authors: Lillo Cathrine , Smith Lucy H. , Nimmo Hugh G. , Wilkins Malcolm B.
Published: May 2006

Nitrate reductase (NR, EC 1.6.6.1) was tested in crude extracts of leaves from Bryophyllum fedtschenkoi plants growing under alternating light/darkness as well as in excised leaves kept in continuous light or darkness. In most extracts NR activity was inhibited 20–80% by 5 mM Mg2+ A light or darkness shift (30 min darkness) during the first part of the photoperiod gave an increase in the Mg2+ inhibition and a decrease in NR activity. Magnesium ion inhibition of NR also showed diurnal variations. Strongest inhibition was found in extracts made during the latter part of the photoperiod and start of the dark period. Pre‐incubation of crude extracts with ATP increased Mg2+ inhibition, indicating that phosphorylation of NR is involved in regulation of NR in Crassulacean acid metabolism (CAM) plants. In continuous light an increase in Mg2+ inhibition occurred after 20 h and 40 h, indicating a rhythm in the phosphorylation of NR. A delay in the production of nitrite in the assay (hysteresis) was generally seen in extracts susceptible to Mg2+ inhibition. The rhythms related to NR activity showed the same period length (20 h) as the rhythm in CO2 exchange. However, in contrast to the rhythm in CO2 exchange, NR rhythms were strongly damped in continuous light. In constant darkness the rhythms were even more damped. The results show that post‐translational modification of CAM NR is influenced by light/darkness and by an endogenous rhythm.
Cold hardiness and water relations parameters in Rhododendron cv. Catawbiense Boursault subjected to drought episodes
Authors: Anisko Tomasz , Lindstrom Orville M.
Published: May 2006

We determined whether increase in cold hardiness of Rhododendron cv. Catawbiense Boursault induced by water stress was correlated with changes in tissue water relations. Water content of the growing medium was either maintained near field capacity for the duration of the study or plants were subjected to drought episodes at different times between 15 July and 19 February. Watering during a drought episode was delayed until soil water content decreased below 0.4 m3m−3then watering was resumed at a level to maintain soil water content between 0.3 and 0.4 m3m−3. Cold hardiness was evaluated in the laboratory with freeze tolerance tests on detached leaves. Water relations parameters were determined using pressure‐volume analysis. Exposure to drought episodes increased cold hardiness during the cold acclimation stage in late summer and fall but not during the winter. When water‐stressed plants were re‐watered to field capacity, the previous gain in cold hardiness gradually disappeared. Water relations parameters correlating with seasonal changes of cold hardiness included dry matter content (r =−0.67). apoplastic water content (r =−0.60), and water potential at the turgor loss point (r = 0.40). Changes of cold hardiness in water‐stressed plants in reference to well‐watered plants were correlated with changes of all water relations parameters, except for osmotic potential at full turgor (r = 0.13). It is proposed that water stress reduced the hydration of cell walls, thereby increasing their rigidity. Increased rigidity of cell walls could result in a development of greater negative turgor pressures at subfreezing temperatures and therefore increased resistance to freeze dehydration.
A mathematical model that uses Gaussian distribution to analyze the germination of Manfreda brachystachya (Agavaceae) in a thermogradient
Authors: Orozco‐Segovia Alma , González‐Zertuche Lourdes , Mendoza Ana , Orozco Susana
Published: May 2006

Germination of nondormant seeds of Manfreda brachystachya (Agavaceae) was analyzed at temperatures ranging from 11–35°C. Maximum germination (95%) occurred at 25°C. An exponential sigmoid relationship was found between time and cumulative germination. Germination rate for every subpopulation (10–90% germination) was estimated by means of a normal distribution analysis. The kurtosis indicated die amplitude of the range of temperatures where the highest germination rates were concentrated, and the skew indicated sharply inhibitory temperatures in the range of temperatures used. Based on analysis of the normal distribution models for each subpopulation, we calculated a theoretical function which described germination rate over the temperature range considered: F(T,χ) = A × exp[−B(C−1)2], where A is the function that describes germination rate for each subpopulation (characterized by the percentage [χ] at optimal temperature); B is a shape parameter, 1/(σG2); and C is the ratio between each germination temperature (T) and the optimal germination temperature. The Gaussian curves were used to calculate thermal time, and base and ceiling temperatures. Germination thermal time ranged from 1 333 to 2 373°C h, and base and ceiling temperatures were 10.44 ± 0.7°C and 39.54 ± 0.7°C, respectively. There was a linear relationship between thermal time and cumulative percentage of germination of the subpopulations. Based on fitted curves for each subpopulation, the use of a general model for all the subpopulations has been proven: F8 = A × exp[−5.9437(C−1)2], where changes in the curves for each subpopulation depended on temperature only.
Polyamines in normal and auxin‐induced strawberry fruit development
Authors: Ponappa Tilak , Miller A. Raymond
Published: May 2006

The possible involvement of polyamines during strawberry (Fragaria×ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g−1 fresh weight at pollination to a minimum of 55 nmol g−1 fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g−1 fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re‐initiation of growth by application of 1 mMα‐naphtaleneacetic acid (α‐NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3‐fold in normally developing receptacles and in de‐achened, auxin‐treated receptacles 10 days after removal of achenes, but did not increase during this period in de‐achened receptacles not treated with exogenous auxin. α‐NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β‐NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de‐achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.
Recycling of CO2 during induction of CAM by drought in Talinum paniculatum (Portulacaceae)
Authors: Güerere Iraya , Tezara Wilmer , Herrera Cecilia , Fernández María Dolores , Herrera Ana
Published: May 2006

To investigate the possible induction of Crassulacean acid metabolism (CAM) by drought in Talinum paniculatum ([Jacq.] Gaertn.), a deciduous herb with succulent leaves and lignified stems, nocturnal acid accumulation and CO2‐exchange were studied in watered and droughted greenhouse‐grown plants. Watered plants had a typical C3 pattern of CO2‐exchange. When plants were subjected to drought, nocturnal acid accumulation increased significantly from 0.9 to 13.4 μmol H+ cm−2 after 21 days. Water deficit provoked a rapid reduction of daytime CO2 assimilation of as much as 92% and a slower increase in night‐time fixation. A maximum of 24% of the diel carbon gain was contributed by dark fixation in droughted plants. After 34 days of drought, only CO2 compensation and a small accumulation of acid (idling) was detected during the night. Relative recycling of respiratory CO2 was approximately 100% for most of the water deficit treatment, the amount of CO2 recycled showing a high positive correlation with nocturnal acid accumulation. A low rate of nocturnal loss of CO2 in watered plants did not explain the amount recycled nightly in droughted plants, implying that respiration increased with drought. Leaf lamina area was reduced by 49% during drought due to rolling. Leaf biomass remained unchanged during the water‐deficit treatment. Neither apparent quantum yield nor light‐saturated photosynthetic rate differed significantly between control and 14‐day water‐stressed plants rewatered for 20 h. Chlorophyll content did not change with drought. These results confirm that CAM is induced by drought in T. paniculatum; the carbon acquired through this pathway only contributes to maintain, but not to increase, leaf biomass; also, CAM is responsible for a high recycling of respiratory CO2 during the night. Recycling through CAM, plus the reduction of exposed leaf area during drought, may help explain the maintenance of chlorophyll, quantum yield and saturated photosynthetic rates in water‐stressed plants of T. paniculatum.
Aluminum resistance in wheat (Triticum aestivum) is associated with rapid, Al‐induced changes in activities of glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase in root apices
Authors: Ślaski Jan J. , Zhang Guichang , Basu Urmila , Stephens Julie L. , Taylor Gregory J.
Published: May 2006

We have investigated the effect of aluminum (Al) on the activity of glucose‐6‐phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) isolated from 5‐mm root apices of 4‐day‐old wheat (Triticum aestivum) cultivars differing in resistance to Al. Rapid increases in G6PDH and 6PGDH activities were observed in Al‐resistant cultivars (PT741 and Atlas 66) during the first 10 h of treatment with 100 μM Al, while no change in the activity of either enzyme was observed in Al‐sensitive cultivars (Katepwa and Neepawa) during a 24‐h exposure to Al. The Al‐induced increases in enzyme activities observed in the Al‐resistant PT741 appear to reflect an induction of protein synthesis since the increases were completely abolished by 1 mM cycloheximide. No differences in G6PDH and 6PGDH activities were observed between the Al‐sensitive and the Al‐resistant genotypes when Al was supplied in vitro. Under these conditions, an increase in Al concentration from 0 to 1.4 mM caused a gradual decrease in activity of both enzymes, irrespective of the Al‐resistance of whole seedlings. Aluminum‐sensitive and aluminum‐resistant cultivars also differed in the rate and extent of accumulation of slowly‐exchanging Al in 5‐mm root apices. During the first 6 h of Al treatment, Al accumulation was only 10% more rapid in Katepwa than in PT741. After 24‐h exposure, accumulation in the Al‐sensitive Katepwa, was two‐fold higher. A decline in Al accumulation in a slowly‐exchanging compartment as well as a decrease in activities of G6PDH and 6PGDH were found in the Al‐resistant PT741, when seedlings were transferred to Al‐free treatment solutions after 16‐h exposure to 100 μM Al. These results suggest that rapid induction of G6PDH and 6PGDH in the Al‐resistant line PT741 by Al may play a role in the mechanism of Al resistance, possibly by regulation of the pentose phosphate pathway.
Alterations in cell membrane structure and expression of a membrane‐associated protein after adaptation to osmotic stress
Authors: Chang Pi‐Fang Linda , Damsz Barbara , Kononowicz Andrzej K. , Reuveni Moshe , Chen Zutang , Xu Yi , Hedges Kathryn , Tseng Charles C. , Singh Narendra K. , Binzel Marla L. , Narasimhan Meena L. , Hasegawa Paul M. , Bressan Ray A.
Published: May 2006

Cultured tobacco cells (Nicotiana tabacum L. cv. Wisconsin 38) adapted to NaCl exhibited significant morphological and physiological changes. Adapted cells remained smaller and more isodiametric at maturity than unadapted cells. The vacuole increased in size relative to the cytoplasm and an extensive network of transvacuolar membrane strands developed. These changes altered the surface contact area between the cytoplasm and the vacuole substantially. In addition, the network of Hechtian strands that anchor the cortical structure to the cell wall became more extensively branched possibly facilitating surface contact of the cytoplasm to the extracellular matrix. Many changes in membrane proteins could also be identified after NaCl adaptation. In particular, a 50‐kDa protein that is associated with the plasma membrane and tonoplast was induced during adaptation. Immunocytochemical localization indicated that this 50‐kDa protein is associated with Golgi vesicles. By immunoscreening using anti‐50‐kDa antibody, a 1.71‐kb cDNA clone (p50C) was isolated from a λ‐ZAP cDNA expression library. The sequence of p50C did not show any significant identity with other genes. Because of the very low abundance of the p50C message, quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) was used to analyze p50C gene expression. Immunoblot and quantitative RT‐PCR analyses indicated that the expression of this gene is regulated developmentally since the mRNA and protein increased with age in salt‐adapted cells but decreased with age in unadapted cells. Also in tobacco plants, p50C mRNA was more abundant in younger leaves than in older leaves. The gene was responsive to NaCl in tobacco cells and to ABA in tobacco seedlings.
Transformation efficiencies and progeny analysis after varying different parameters of direct gene transfer of Nicotiana tabacum protoplasts
Authors: Jarl Carin I. , Rietveld Ellen M.
Published: May 2006

Nicotiana tabacum protoplasts were transformed by polyethylene glycol (PEG)‐mediated uptake and electroporation, with circular and linear DNA, and with or without X‐ray irradiation. We investigated the influence on the transient expression by these parameters as well as on the frequencies for stable transformation. Plants were regenerated and selfed, and the progenies of the transformed plants were analysed and used to compare the pattern of gene integration by these different variations in transformation methods. The results from the transient expression as judged by glucuronidase (GUS) activity, showed electroporation to give higher and more reproducible results than PEG‐mediated uptake. Using linear instead of circular DNA increased the rate of stable transformation about 3 times. Including a mild X‐ray treatment gave an increase in the same range. When the inheritance of the transferred trait was investigated, it was found that protoplasts transformed with linear DNA resulted in the highest number of plants with single‐copy insertions. Protoplasts transformed with circular DNA showed the highest incidence of losing the trait, while plants in which the transformation included an X‐ray treatment, had the highest frequency of multicopy insertion events.
Conservation of the alternative oxidase and enhancement of cyanide‐resistant respiration in suspension‐cultured pear fruit cells by inhibitors of macromolecular synthesis
Authors: Gallerani Giovanni , Romani Roger J.
Published: May 2006

The contribution of the alternative pathway to the respiration of suspension‐cultured pear (Pyrus communis cv. Passa Crasanne) cells was enhanced, often severalfold, within 2 to 4 days following the addition of cycloheximide, actinomycin D, or 2‐(4‐methyl‐2,6‐dinitroanalino)‐N‐methyl propionamide (D‐MDMP). Concomitant inhibition of cellular protein synthesis by cycloheximide and actinomycin D was transient and incomplete. However, inhibition by D‐MDMP was virtually complete (>97%) and persisted over several days. [35S]‐labelling and polyacrylamide gel separation indicated that cycloheximide precluded the appearance of discernable new proteins in mitochondria. Probes with monoclonal antibodies revealed a conservation of alternative oxidase protein levels in the mitochondria of inhibitor‐treated cells. The data, appraised within the complexities of cell‐culture dynamics, lead to the conclusion that the observed increases in capacity for cyanide‐resistant respiration are the consequence, likely indirect, of inhibited protein synthesis with resultant retention and activation of constitutive alternative oxidase.