bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phospholipids, free sterols and adenosine triphosphatase of plasma membrane‐enriched preparations from roots of citrus genotypes differing in chloride exclusion ability
Authors: Douglas Trevor John , Walker Robert Ronald 
Published: April 2006

Plasma membrane‐enriched preparations from fibrous roots of three citrus genotypes differing in their abilities for chloride exclusion, and grown in the presence of 0,50 or 100 mM NaCl for 4 weeks, were analysed for phospholipid and free sterol content and vanadate‐sensitive adenosine triphosphatase (ATPase) activity over a range of temperatures. The best chloride excluder, Rangpur lime (Citrus reticulaia Blanco var. austera hyb.?), had significantly higher maximal ATPase activity than both the moderate chloride excluder. Kharna khatta (Citrus kharna Raf.), and the worst chloride excluder, Etrog citron (Citrus medico L.), at all assay temperatures below 28°C. Salt treatment had no effect on maximal ATPase activity of either Rangpur lime or Etrog citron but resulted in increased activity of the enzyme in Kharna khatta at temperatures below 28°C.Arrhenius plots of ATPase activity from the three citrus genotypes showed that, in controls, the activation energy (E.,) of Rangpur lime ATPase was significantly lower than that of both Kharna khatta and Etrog citron. The thermotropic phase transition temperature (Tf) for Rangpur lime (27°C) was also lower than for the other citrus genotypes (31°C). Salt treatment resulted in increases in both Ea and T, for Rangpur lime, decreases in both parameters for Kharna khatta and no change of either parameter for Etrog citron.An inverse relationship between Ea and the phospholipid to free sterol ratio was evident for plasma membrane preparations from all three citrus genotypes in the presence and absence of salt treatment suggesting that changes in membrane fluidity, particularly those induced by free sterols, have the potential to influence active as well as passive ion transport processes and thus may play a significant role in the chloride exclusion mechanism.
Sexual differentiation in higher plants
Authors: Durand R. , Durand B. 
Published: April 2006

As in all organogenetic studies, sex differentiation implies three fields of research: the identification of macsomalecular markers specific for stamens or carpels }expression program); the analysis of the signals (such as phytohormones{ inducing them: and finally the knowledge of the regulator genes (sex detsrmination genes).In dioecious plants, sex determination (male and female genes or combinations of heterochromosomes) occurs at the fertilization stage. These regulators probably act early by means of inducers; their action is perceptible mainly when reproductive organs develop, and the existence of target cells able to respond to the inductive message is obvious. Experimental control of sex expression by phytohormones leads to the repression of the normal organogenetic program (induced by the presence of the sex genes) arrd to the induction of the opposite program (normally incompatible with these genes).Analogous mechanisms occur in monoecious plants, but here the male program is always expressed before the female one. Experimental control of sex expression suggests that the successive induction of first male and then the female program results from inverse gradients of male and female signals. Sex differentiation studies of monaeciousness are more difficult than studies on dioeciousness since, in all the cells. not only male and female programs co‐exist as in dioeciousness, but also male and female sex penes and signals.The present model has been tested in the dioecious Mercurialisannua (2n = 16) and some other species, and the results that have been established are described.
Changes in peroxidase, indolyl‐3‐acetic acid oxidase and amylase activities in a viable wheat hybrid and its antecedents
Authors: Chaturvedi Neera , Laloraya M. M. 
Published: April 2006

A viable wheat hybrid intermediate of the same height as the parents was obtained by crossing the female parent of tall variety NP4 with the male parent of the dwarf variety HD2160. Seeds of the hybrid and its parents were germinated and their growth pattern as well as the activities of peroxidase, indolyl‐3‐acetic acid oxidase and amylase in extracts made from them were studied at the early seedling stages i.e. up to 96 h.A positive correlation existed between the length of the axis at the early seedling stage and at mature plant height as far as the parental varieties are concerned but no such correlation was observed with the hybrid. Growth of the hybrid seedlings was less than of its parents. Light appeared to stimulate the longitudinal growth of the axis to different extents in the parents and hybrid. Higher activities of peroxidase, indolyl‐3‐acetic acid oxidase and amylase were observed in the hybrid as compared to both of its parents. Lethal wheat hybrid also exhibits increased activities of amylase, indolyl‐3‐acetic acid oxidase and peroxidase. Therefore, it appears that seedling growth and enzyme activities at the seedling stage are not always correlated with hybrid vigour.
Endopeptidase activity and nitrogen mobilization in senescing leaves of Nicotiana rustica in light and dark
Authors: Weckenmann Dieter , Martin Peter 
Published: April 2006

The time course of endopeptidase activity (digestion of azocasein at pH 4.6) in leaves of intact plants of Nicotiana rustica L. was studied and related to changes in the contents of chlorophyll, total nitrogen and soluble and insoluble protein nitrogen. Endopeptidase activity increased several fold during senescence. However, the course of protein degradation did not reflect the steep slope of azocaseolytic activity. When single mature leaves were darkened, senescence proceeded faster than in illuminated leaves but the amount of nitrogen mobilized and translocated did not differ greatly between darkened and illuminated leaves. However, in contrast to leaves in light, azocaseolytic activity did not increase.Gelatin zymograms obtained using isoelectric focusing of extracts of mature leaves showed several bands in the pH 4.0 to 6.5 region of the gels. During senescence in both light and dark the position and number of bands remained largely unchanged. In leaves in light, the activity of endopeptidases focusing in the range pH 4.1 to 5.0 increased greatly. In leaves in dark, however, no major changes in activity could be detected. The results suggest that in tobacco leaves endopeptidase activity normally increases considerably during senescence but this increase is not a prerequisite for an effective protein degradation.Separation and analysis of free amino acids showed that during senescence in light the levels of all amino acids decreased considerably. In leaves senescing in the dark there were large increases in the levels of glutamine and asparagine, concomitant decreases in glutamate and aspartate, and considerable increases in all other amino acids.
Oleic acid metabolism: A biochemical marker for studying photoregulation of epicotyl elongation in Vigna unguiculata
Authors: de March Ghislaine , Tréimolières Antoine , Lecharny Alain 
Published: April 2006

Oleic acid metabolism can be considered to be an indicator of growth photoregulation in cowpea (Vigna unguiculata Westphal cv. M53) epicotyls. Phosphatidylcholine and phosphatidylethanolamine are the two lipid classes concerned in the photoregulation of oleic acid accumulation. The incorporation of radioactive precursors in internodes of whole plants has shown that there is de novo synthesis of these phospholipids during the light dependent growth process.The variations in oleic acid content were used to study the photocontrol of elongation in segments excised from the apical part of the epicotyl. In this system, as in whole plants, oleic acid was the only fatty acid showing significant variation related to the light/dark treatments. Differences in photoresponse between excised intenode segments and internodes in whole plants are discussed.
Orientation nouvelle du métabolisme des acides hydroxycinnamiques dans les fruits de tomates blessés (Lycopersicon esculentum)
Authors: Fleuriet Annie , Macheix Jean‐Jacques 
Published: April 2006

A change in the metabolism of hydroxycinnamic acids in wounded tomato fruits (Lycopersicon esculentum).Healing of lesions in tomato fruits (Lycopersicon esculentum Mill. var. cerasiforme) is partly due to lignification of cells bordering the wounded zones. The pericarp of healthy fruits contains a high level of hydroxycinnamic derivatives but never shows lignification. Thus, the reaction of the fruit to wounding seems to be a change in the metabolism, leading to the formation of monomeric units of which lignins are constituted. Hydroxycinnamate:CoA ligase (EC 6.2.1.12; CL) and O‐methyltransferase (EC 2.1.1.6; OMT) appear to play an important role in this change. In wounded fruits CL acts preferentially on p‐coumarate and ferulate as compared to caffeate, and OMT is particularly active with 5‐OH ferulate as substrate. These changes lead to the formation of p‐coumaroyl CoA, feruloyl CoA and sinapate, which are incorporated into lignin. Phenylalanine ammonialyase (EC 4.3.1.5) and glucosyltransferase activities increase greatly after wounding, whereas the activity of hydroxycinnamoyl‐CoA:quinate hydroxycinnamoyl transferase decreases. These data complement those previously reported on peroxidases and suggest that, after the increase of enzyme activities, monomeric units are formed and then polymerized by some peroxidases specific for lignification.
Starch fermentation via a formate producing pathway in Chlamydomonas reinhardii, Chlorogonium elongatum and Chlorella fusca
Authors: Kreuzberg Karlheinz 
Published: April 2006

Starch degradation was investigated during anaerobic dark incubation in the algae Chlamydomonas reinhardii, Chlorogonium elongatum and Chlorella fusca. The pathway of algal formate fermentation was elucidated by determination of the relationship between substrate consumption and product accumulation. The fate of reducing equivalents was also determined. Investigations were done on dependence of pH, fermentation time, cell cycle, and after addition of H2, hypophosphite and inhibitors of protein synthesis.A mixed acid fermentation that produced formate, acetate and ethanol (2:1:1) with only small amounts of H2 and CO2 was shown for the algal strains used. The failure of inhibition with cycloheximide and chloramphenicol indicated the constitutive presence of all fermenting enzymes. Nevertheless, glycerol, D(–)lactate and stoichiometrical amounts of ethanol and CO2 were found additionally at extreme pH (pH 4.6 and 7.9), and after addition of H2 and hypophosphite (7 mM). During long‐term incubation (28 h) fermentation changed from mixed acid to ethanol production. The pathways of algal fermentation did not depend on cell cycle, and fermentation rate corresponded directly to the actual starch content of algal cells. The results gave evidence for synthesis of formate during anaerobic metabolism in algae by a thioclastic cleavage of pyruvate via the enzyme pyruvate formate lyase. This indicated an algal fermentation pathway thought to be present only in procaryotic organisms.
Nitrate reduction and compartmentation in tomato leaves. II. Nitrate loss by leaf sections in a gaseous atmosphere and the size of the metabolic nitrate pool
Authors: Mills David , Soares Ines M. M. , Cresswell Cristopher F. , Lips Herman S. 
Published: April 2006

Nitrate disappearance in tomato ((ycopersicon esculentum Mill. cv. Azes) leaf sections kept under a stream of gas (nitrogen or air) has been studied, using leaf sections from plants supplied with low (7.5 mM) or high (17.5 mM) nitrate levels in their nutrient solution. Cessation of nitrate loss occurred in leaf sections taken from plants irrigated with low (7.5 mM) nitrate‐containing nutrient solution. Resumption of nitrate disappearance occurred upon addition of exogenous nitrate by vacuum infiltration to leaf sections, suggesting that cessation of nitrate loss was due to exhaustion of the metabolic pool. We estimated that 53% of the total nitrate in leaf sections from low nitrate plants was located in a storage pool, probably the vacuole. The remainder was located in a pool, readily available for reduction (the metabolic pool). This pool is composed of nitrate in the free space as well as in the cytoplasm which was estimated to contain about 20% of the total nitrate.Either under air or nitrogen, less nitrite was accumulated than nitrate assimilated suggesting that nitrite accumulation was not an adequate parameter for the estimation of nitrate utilization. Anaerobic conditions inhibited nitrite reduction whereas nitrate assimilation was not blocked. Nitrate loss from endogenous pool in leaf sections placed under aerobic conditions is suggested as an adequate method for the estimation of the metabolic pool of nitrate.
Respiration of crop species under CO2 enrichment
Authors: Gifford Roger M. , Lambers Hans , Morison James I. L. 
Published: April 2006

Respiratory characteristics of wheat (Triticum aestivum L. cvs Gabo and WW15), mung bean (Vigna radiata L. Wilczek cv. Celera) and sunflower (Helianthus annuus L. cv. Sunfola) were studied in plants grown under a normal CO2 concentration and in air containing an additional 340 (or 250) μl l−1 CO2. Such an increase in global atmospheric CO2 concentration has been forecast for about the middle of the next century. The aim was to measure the effect of high CO2 on respiration and its components. Polarographic and, with wheat, CO2 exchange techniques were used. The capacity of the alternative pathway of respiration in roots was determined polarographically in the presence of 0.1 mM KCN. The actual rate of alternative pathway respiration was assessed by reduction in oxygen consumption caused by 10 mM salicylhydroxamic acid.Each species responded differently. In wheat, growth in high atmospheric CO2 was associated with up to 45% reduction in respiration by both roots and whole plants. Use of respiratory inhibitors in polarographic measurements on wheat roots implicated reduction in the degree of engagement of the alternative pathway as a major contributor to this reduced respiratory activity of high‐CO2 plants. No change was found in the total sugar content per unit wheat root dry weight as a result of high CO2. In none of the species was there an increase in the absolute, or relative, contribution by the alternative pathway to total respiration of the root systems. Thus the improved photosynthetic assimilate supply of plants grown in high CO2 did not lead to increased diversion of carbon through the non‐phosphorylating alternative pathway of respiration in the root. On the contrary, in wheat grown in high CO2 the reduced loss of carbon through that route must have contributed to their larger dry weight.
An effect of Na+ on K+ uptake in intact seedlings of Zea mays
Authors: Cheeseman John M. 
Published: April 2006

Models for the regulation of K+ uptake in higher plant roots have become more complex as studies have moved from the level of excised low‐salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.The uptake of K+ by low‐salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na+ concentration over a wide range. However, independence of Na+ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na+ in the uptake medium enhanced K+ uptake. In the presence of Na+, K+ uptake rates were similar in whole plants with high root K+ contents to rates in excised or intact, low‐salt roots.
Changes in catalase activity and hydrogen peroxide concentration in plants in response to low temperature
Authors: MacRae E. A. , Ferguson I. B. 
Published: April 2006

Taxicity of oxygen species such as free radicals and H2O2 has been invoked to explain a number of degradative processes in plants, most involving photo‐oxidation. Since catalase is a major protectant against accumulation and toxicity of H2O2, we examined alterations in catalase activity in several plant species (Pisum sativum L. cv. Greenfeast, Vigna radiata (L.) R. Wilcz, Cucumis sativus L. cv. Heinz Pickling, and Passiflora spp.) during chilling, and compared this change to change in H2O2 content. Catalase activity was reduced in a range of chilling sensitive and tolerant species by exposure to low temperature. This reduction in catalase activity correlated better with the onset of visible symptoms than with the treatment itself. Visible injury in turn was dependent on light and temperature differences. Hydrogen peroxide concentrations invariably decreased with low temperatures.Reduction in catalase activity therefore does not necessarily imply accumulation of H2O2 to damaging levels. The absence of a clear inverse relationship between catalase activity and H2O2 concentration suggests the continued activity of other reactions that remove H2O2 and these may be important in the tolerance of plants to oxidative attack. Loss of catalase activity may result from the inability of damaged peroxisomal membranes to transport catalase precursors into the peroxisome.
Methods to extract NAD+‐malate dehydrogenase efficiently from white spruce needles
Authors: Pitel J. A. , Cheliak W. M. 
Published: April 2006

The spectrophotometrically‐determined activity of NAD+‐malate dehydrogenase (MDH, EC 1.1.1.37) from white spruce [Picea glauca (Moench) Voss] needles was assayed with NADH and oxaloacetate. Activity was very low when extracted with only acetate buffer (pH 5.4), phosphate buffer (pH 6.8), or Tris‐HCl buffer (pH 8.0). However, activity increased from 1 to over 200 μmol (g dry weight)‐1 min‐1 with the addition of polymers such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) and the detergents, Tween 80, Tergitol 15‐S‐9 and Triton X‐100. Best activity was observed when extracted in a buffer at pH 6.8 and with 1% (v/v) for the three detergents and PEG, and 6% (w/v) for PVP.MDH activity decreased with age of the needles on the tree. Six‐year‐old needles contained only about one‐fifth of the activity of current year, fully‐expanded needles. The main decrease in enzyme activity was observed in one‐year‐old needles. Protein content obtained from needles extracted with just phosphate buffer (pH 6.8) was very low, but increased greatly when the above chemicals were added to the buffer. In contrast with needles, extracts of vegetative buds contained much higher levels of MDH and protein when extracted with only phosphate buffer (pH 6.8). Although MDH activity in needle extracts declined with storage of the extracts at 4°C in the dark for 6 days, the decrease was least for buffers containing a combination of different protective agents.
Nitrate and nitrite reduction in the plant fraction of alfalfa root nodules
Authors: Becana M. , Aparicio‐Tejo P. M. , Sanchez‐Diaz M. 
Published: April 2006

The plant fraction of alfalfa (Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH‐NR from the cytosol of nodules not treated with NO3‐ was about 30 nmol (mg protein)‐1‐h‐1 and was not basically affected by NO3 addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein)‐1h‐1 using methyl viologen as electron donor. This activity strongly increased with NO3 concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein)‐1h‐1 at 50 to 200 mM NO3.Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO2 accumulating in the cytosol upon NO3, supply, and the different response to NO3 of bacteroid and cytosolic NRs support the concept that most of this NO2 comes from the bacteroids.
Isolation and characterization of a DCMU (3–(3,4–dichlorophenyl)‐1,1–dimethylurea) resistant strain of a marine alga, Dunaliella bioculata
Authors: Grizeau D. , Jeanne N. , Calvayrac R. 
Published: April 2006

A DCMU‐resistant strain was isolated from cell cultures of a wall‐less alga, Dunaliella bioculata (Butcher 19/4 CCAP). This variant strain is essentially characterized by its ability of grow autotrophically in the presence of 4 μM DCMU and by the stability of this property even after numerous subcultures in the absence of the herbicide.Chloroplastic structures and photosynthetic activities of whole and fragmented cells of the wild and the variant strains were compared for their respective sensitivities towards DCMU. The DCMU‐resistant strain was also insensitive to other photosynthetic inhibitors such as chloroxuron, but not to atrazine. The results suggest that the DCMU‐resistance could be due to some modified plastid property.
Temperature‐induced absorbance changes in developing barley chloroplasts
Authors: Singh Bal Ram , Singhal Gauri S. 
Published: April 2006

Absorbance changes on cooling and heating of barley (Hordeum vulgareL. cv. IB65) chloroplasts greened for 12, 48 and 72 h were investigated to understand the structural changes during biogenesis of chloroplast membranes. Upon cooling the chloroplast suspension from 24 to 8°C, a positive absorbance change occurred at 678, 435 and 495 nm in 12, 48 and 72 h greened chloroplasts. During heating from 24 to 45°C negative absorbance changes were observed with some shifts in positions in different chloroplast preparations and a simultaneous increase in absorbance between 690 and 735 nm. For chloroplasts developed for 12, 48 and 72 h the changes in absorbance on cooling were 3.8, 3.3 and 1.9% at 678 nm, and on heating, 8.9, 8.3 and 4.1% at 680 nm.The differences in absorbance changes are considered as an indication of variations in the structural organization and composition of developing chloroplasts. The reversibility of the absorbance changes was maximum in chloroplasts greened for 72 h and minimum in chloroplasts greened for 12 h. This would suggest that fully developed chloroplasts have more flexibility towards temperature‐induced changes in the membranes.
Methanol production from lignin‐related substances by Phanerochaete chrysosporium
Authors: Ander Paul , Eriksson Mats E. R. , Eriksson Karl‐Erik 
Published: April 2006

Methanol production resulting from the demethoxylation of lignin‐related substances by Phanerochaete chrysosporium K‐3 was studied in the presence or absence of glutamic acid in order to determine if methanol formation involved the ligninolytic system of the fungus. The general pattern was that methanol formation, calculated as percentage of theoretical yield, decreased in the order guaiacyl > syringyl > veratryl (3,4‐dimethoxy) compounds. Methoxyhydroquinone and vanillic acid were most easily demethoxylated, while methanol production decreased with increasing molecular weight for the same type of structure (i.e. guaiacyl). Glutamic acid inhibited the demethoxylation of many of the compounds tested. The demethoxylation of the 4‐methoxy group of veratric acid was particularly inhibited by glutamic acid suggesting a participation of the ligninolytic system, while the 3‐methoxy group was influenced to a lesser extent.The demethoxylating enzyme acting on lignin‐related phenols is probably a peroxidase, while the identity of the enzyme demethoxylating dimethoxy compounds is not known with certainty, although a peroxidase type of enzyme reaction is anticipated also here.