bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt induced responses of chloroplast activities in species of differing salt tolerance. Photosynthetic electron transport in Aster tripolium and Pisum sativum
Authors: Wignarajah K. , Baker Neil R.
Published: April 2006

A comparative study was made of the effects of high concentrations of NaCl, KCl and MgCl2 on two electron transport reactions of thylakoids isolated from a mesophyte, Pisum sativum and a halophyte, Aster tripolium. The rate of photosystem I mediated electron transport from reduced N, N, N′, N′‐tetramethyl‐p‐phenylenediamine (TMPD) to methyl viologen was determined polarographically, and photosystem II mediated electron flow from water to 2,6‐dichlorophenolindophenol (DCPIP) was monitored spectrophotometrically. The response of photosystem II to increasing in vitro salt concentrations was similar for thylakoids isolated from both A. tripolium and P. sativum, but differences in the response of photosystem I to salinity changes were observed for the two species. Increasing NaCl, KCl and MgCl2 concentrations produced similar patterns of response of photosystem I activity in P. sativum thylakoids, whilst for A. tripolium KCl induced a completely different response pattern compared to NaCl and MgCl2. The salinity of the culture medium in which A. tripolium was grown also had an effect on both the absolute in vitro activities of photosystems I and II and their response to changes in salt concentration of the reaction media.
Adaptation of corn roots to exogenously applied auxin
Authors: Gougler Judy A. , Evans Michael L.
Published: April 2006

The ability of intact primary roots of corn (Zea mays L. Bear Hybrid WF 9 × 38) to adapt to growth‐inhibitory concentrations of auxin was studied using a highly sensitive position sensor transducer to measure growth. The timing, concentration dependence and temperature dependence of adaptation were studied as well as the time course of loss of adaptation upon removal of auxin. The rate of root elongation is inhibited 80% within 40 min after application of 10−7M IAA. Within 90 min growth rate begins to recover. For concentrations of IAA equal to or greater than 10−7M, recovery of growth rate (adaptation) is incomplete. Corn roots show a similar pattern of adaptation to the synthetic auxins NAA and 2,4‐D. The Q10 for adaptation is high (3.2) and comparable to that for root growth (3.3). Upon removal of exogenous IAA, loss of adaptation occurs with full sensitivity to the hormone regained within 20 min.

Based on the auxin specificity and the Q10 for adaptation it is concluded that adaptation occurs neither by a change in the auxin degradation capacity of the root nor by a diffusional redistribution of applied auxin. It is suggested that adaptation involves metabolic processes, perhaps a metabolically dependent alteration of the number or affinity of auxin binding sites.
The effect of kinetin on the indoleacetic acid level and indoleacetic acid oxidase activity in roots of young plants
Authors: Saleh Adirukmi Noor
Published: April 2006

Kinetin treatment increased the extractable IAA content in roots of young plants of Phaseolus vulgaris L., Zea mays L. and Avena sativa L. The highest increase was obtained with roots of beans and the lowest with oat roots. Maize was intermediate between these two species. Kinetin treatment decreased the activity of IAA‐oxidase but the correlation between the decrease of the activity of this enzyme and the increase in the level of IAA was not good. The decrease of the oxidase activity was greatest in oat roots where kinetin had very little effect on the IAA level, and was rather small in bean roots, where kinetin treatment significantly increased the IAA level.
Indole‐3‐acetaldehyde oxidase of pea seedlings
Authors: Miyata Susumu , Suzuki Yonezo , Kamisaka Seiichiro , Masuda Yoshio
Published: April 2006

Indole‐3‐acetaldehyde oxidase was partially purified from the epicotyl of Pisum satiyum seedlings by column chromatography using CM‐Sephadex and Sephadex G‐150. The enzyme was only active in the presence of molecular oxygen. The activity was maximal at pH 8.0, and the Km value for indole‐3‐acetaldehyde was 1.4 × 10−3M. The enzyme was inhibited strongly by p‐hydroxymercuribenzoate, cyanide and hydroxylamine, suggesting that it contains sulfhydryl group(s) and a metal component such as iron.
Elastic response of the roots of field crops
Authors: Whiteley G. M. , Dexter A. R.
Published: April 2006

The elasticity of root tips was investigated in experiments of the static clamped‐beam type. The response was non‐linear. The results were interpreted in terms of a generalized elastic modulus M, and two parameters, α and β, which account for the non‐linearity.

Seminal axes and primary lateral roots of 16 crop species grown in the laboratory show significant inter‐species differences but insignificant inter‐variety differences in the elastic properties. A smaller set of results for field‐grown roots with two tillage treatments shows that, in nearly all cases, the elastic modulus is smaller and the diameter is larger than with laboratory‐grown roots. Environmental factors such as water potential, and nutrition have significant influences on the diameters and elastic behaviour of roots.
Effects of moisture stress and senescence on the synthesis of abscisic acid in the primary leaves of bean
Authors: Eze J. M. O. , Dumbroff E. B. , Thompson J. E.
Published: April 2006

The capacity for ABA synthesis during moisture stress of primary leaves of bean (Phaseolus vulgaris cv. Kinghorn) was defined in terms of leaf age and associated changes in several physiological parameters. The leaves were fully expanded within 9 days after emergence. Fresh and dry weights per unit of leaf area fell during all 5 weeks of the study, from leaf expansion through advanced senescence. The most significant losses in weight occurred during the third and fourth weeks and coincided with a sharp drop in protein content that began immediately after full‐leaf. Chlorophyll concentrations declined rapidly during leaf expansion and then more slowly through the end of the fifth week when the leaves were ready to abscise. The ratio of chlorophyll a to b rose steeply over the first 4 weeks of the study.

Although a rapid loss of protein provided the most definitive indication of the early stages of leaf senescence, a marked decline in the ability to synthesize ABA was more closely associated with the termination of rapid leaf growth. This relationship between leaf expansion and the capacity for ABA synthesis during moisture stress remained unchanged when ABA content was expressed on a per unit chlorophyll, protein or dry weight basis.

A water deficit between 5 and 10% of fresh weight, representing a drop in water potential of less than 150 kPa, was sufficient to initiate accumulation of ABA in young leaves. Slightly more intensive levels of stress were required to stimulate ABA synthesis in senescent leaves, but total accumulation was less than one‐tenth of the amount recorded in the younger tissue.
Effects of varied nitrogen stress on growth and nutrition in three Salix clones
Authors: Ericsson Tom
Published: April 2006

The ability of Salix aquatica Smith, S. fragilis L. and S. viminalis L. to absorb nitrogen at varied growth rates was investigated in nutrient solutions. The effects of five nitrogen addition rates on growth rates, nitrogen contents of the plants, nitrogen concentration of the media, and dry matter distribution between roots, stems and leaves, were studied.

These clones are highly efficient in absorbing nitrogen at low concentrations in the root medium, independent of growth rate. Strong linear regressions were found between any two of the three factors: relative rate of nitrogen supply (RN), nitrogen content (plant), and relative growth rate (R). Dry matter production per unit nitrogen taken up and unit time (N‐productivity) and per unit nitrogen taken up independent of time (N‐efficiency) was closely correlated to the nitrogen status of the plant. Root development was favoured in the sub‐optimum treatments, and leaf development in the optimum treatments. With regard to their ability to absorb nitrogen, these Salix clones appear satisfactory for efficient short rotation energy forestry.
Purification and molecular properties of nitrite reductase from Anabaena sp. 7119
Authors: Mendez José M. , Vega José M.
Published: April 2006

Ferredoxin‐nitrite reductase (EC 1.7.7.1.) from the cyanobacteria Anabaena sp. 7119 has been purified 763‐fold with a specific activity of 21.5 units/nig protein (0.358 μkatals/mg). The enzyme has a molecular mass of 52,000 daltons with a Stokes radius of 3.09 nm and a sedimentation coefficient of 4.07 S. The cellular level of nitrite reductase activity gradually increases in response to the addition of increasing amounts of iron to the culture medium.

When partially purified nitrite reductase preparations are subjected to sucrose‐density‐gradient centrifugation there is a dose correspondence between nitrite reductase activity and absorbance at 400 nm. This suggests the association of a heme chromophore with the enzyme. Furthermore, the presence of an iron‐sulfur center is suggested by a close association of acid‐labile sulfide with nitrite reductase activity. Carbon monoxide inhibits nitrite reductase activity. The nature and kinetics of this reaction are comparable to other siroheme‐containing nitrite reductases.
Bacteroid distributions in alfalfa nodules upon dark‐induced senescence and subsequent partial rejuvenation
Authors: Paau Alan S. , Cowles Joe R.
Published: April 2006

Photosynthate availability directly controls the maturation, senescence and distribution of bacteroids (inoculum Rhizobium meliloti 102 F28) in alfalfa (Medicago saliva L. cv. Buffalo) nodules. Mature, dinitrogen‐fixing bacteroids were located principally in the middle section (region) of 6‐ to 8‐week‐old nodules in light‐grown alfalfa plants. Upon dark treatment of the plants, bacteroids in the middle region of a nodule were induced to senescence while those in the tip region began to mature faster. Senescence and deterioration of bacteroids in the basal region of a nodule also were more advanced in the dark‐treated plants. Sugar supplied exogenously during the dark period retarded the senescence process. Exposure of the dark‐treated plants to light partially restored nitrogenase activity. The distribution of bacteroids in the rejuvenated nodules was similar to that of the light‐grown plants.
Substances from cultured soybean cells which stimulate or inhibit acetylene reduction by free‐living Rhizobium japonicum
Authors: DeMoranville Carolyn J. , Kaminski Andrea R. , Barnett Neal M. , Bottino Paul J. , Blevins Dale G.
Published: April 2006

The effect of cultured soybean (Glycine max (L.) Merr. cv. Acme) cells and extracts thereof on acetylene reduction by Rhizobium japanicum 61A76 was determined under two culture conditions. In the first (submerged culture) Rhizobium growing on solid medium were submerged in an aqueous layer containing soybean cell suspension or extract; both soybean cells and crude cell extract inhibited free living rhizobial nitrogenase measured by acetylene reduction. In the second culture condition (surface culture) Rhizobium was grown on the surface of an agar medium which contained expressed soybean cell sap (7.4% v/v), which caused an increase in free living rhizobial nitrogenase activity. Larger concentrations (12.9 to 19.4% v/v) of soybean cell extract inhibited acetylene reduction also in surface culture, inhibition in submerged culture or surface culture was found after autoclaving of cells or extract, or treating the extract with pH extremes or with Streptomyces protease. Each of these treatments destroyed stimulatory activity of cell extract in surface cultures. Fractionation of the soybean cell extract on a Biogel P‐6 column showed that there are three inhibitory fractions and at least one stimulatory fraction. Using column data and the fact that stimulatory and inhibitory factors were dialysable against 0.1 M phosphate buffer, we estimated the molecular weights of the factors. The stimulatory factor has a molecular mass (Mr) between 6,000 and 14,000. The inhibitory factors have molecular masses less than 6,000. Crude extracts from cultured carrot (Daucus carota (L.) cv. Danvers) cells gave results similar to those seen with soybean cell extract Extracts from cultured winged bean (Psophocarpus tetragonolobus (L.) DS. cv. TPt2) cells gave inhibition but no stimulation.
Growth effects and metabolism of arginine in stationary and rapidly‐dividing sugarcane cell suspensions
Authors: Glenn Edward P.
Published: April 2006

The effect of 300 μM arginine on growth of sugarcane cell suspensions was studied. Cells transferred to defined media in the stationary growth stage showed a greater requirement for exogenous arginine than cells similarly transferred in the rapidly dividing stage. Cell arginine levels, rates of arginine synthesis, and enzymes of arginine synthesis all decreased in cells entering the stationary stage. It is concluded that stationary stage cells are deficient in their ability to synthesize arginine and are therefore dependent upon an exogenous supply to resume growth in fresh media.
The apparent viscosity of the protoplasm of subepidermal stem basis cells of Pisum sativum. Relation to aging, drought tolerance and water stress
Authors: Lee‐Stadelmann Ok Young , Hulme Dale A. , Stadelmann Eduard J.
Published: April 2006

Plants of Pisum sativum L. cv. Alaska wilt resistant were subjected to two different water stress regimes under controlled environment conditions: watering was stopped either on the 7th day (early stress) or on the 21st day (late stress) after planting. Plants under the early stress regime developed drought tolerance (adapted), while those under late stress did not. The apparent viscosity of the protoplasm of subepidermal stem basis cells was analyzed by the centrifugation and plasmolysis form method during the entire growth period.

The apparent viscosity of the subepidermal stem basis cells changed with plant age and was highest in 3‐week‐old plants. In controls the relation of apparent viscosity to age was the same when measured under full turgor and in relaxed state. Under early stress condition, however, the pattern of the viscosity changes with plant age was significantly different for turgescent and relaxed cells. In four week old plants, a higher apparent viscosity was measured in relaxed adapted cells than in relaxed control cells. It is suggested that the higher apparent viscosity is the result of a delayed cell aging.

Apparent viscosity was inversely proportional to soil moisture content and the osmotic potential of the cell sap for the cells of late stress plants, whereas no clear relation was found for the cells of early stress plants. This difference may indicate two mechanisms of viscosity changes: 1) osmotic dehydration of the protoplasm under water stress (passive viscosity change), 2) changes in the amount, hydration or architecture of macromolecules present in the cytoplasm (active viscosity change). Whereas differences in the apparent viscosity between control and stressed cells may not be the cause of drought tolerance, they seem to indicate the development of drought tolerance. Water stress history and plant age were the most critical factors controlling the apparent viscosity changes observed.
Distribution of ATPases in wheat root membranes separated by phase partition
Authors: Lundborg Tomas , Widell Susanne , Larsson Christer
Published: April 2006

The distribution of divalent cation stimulated ATPase activity in relation to the distribution of other enzyme activities was studied for membrane fractions from wheat roots (Tritium aestivum L. cv. Svenno). A homogenate from dark grown plants was fractionated by differential centrifugation at 1000 g, 10,000 g, 30,000 g and 60,000 g (1, 10, 30 and 60 KP fractions), followed by partition in an aqueous polymer two‐phase system, using polyethylene glycol 4000/dextran T500 concentrations of 5.7/5.7, 5.9/5.9, 6.1/6.1, 6.3/6.3 and 6.5/6.5% (w/w). The 30 KP fraction was also separated by counter‐current distribution id a 6.3/6.3% two‐phase system. Protein and activities of Ca2+, Mg2+, and Mn2+ stimulated ATPases. cytochrome oxidase, light induced absorbance change (LIAC) related to cyt b reductions, inosine diphosphatase and NADH dependent antimycin A insensitive cytochrome c reductase were measured.

The partition of ATPase activities stimulated by Ca2+, Mg2+ or Mn2+ was similar at all polymer concentrations tested, indicating: a low cation specificity of the dominating ATPases. The distribution of ATPases. agreed with different marker enzymes in different centrifuge fractions. Divalent cation stimulated ATPases were evidently related to several of the organelles. In the different fractions the distribution of ATPase activity should then follow that of the marker enzyme of the dominant organelle. From studies with different polymer concentrations the 6.3/6.3‐system was selected for further separation of the membranes in the 30 KP fraction by counter‐current distribution. By this method one fraction was obtained, which probably consisted of plasmalemma and was free from mitochondrial material. Indications for plasmalemma in this fraction were a) similar partition as protoplasts and b) high LIAC activity.
8‐14C‐Zeatin metabolites and their transport from leaf to phloem exudate of Yucca
Authors: Vonk C. R. , Davelaar E.
Published: April 2006

Transport and metabolism of 8‐14 C‐zeatin, applied to an attached de‐tipped one‐year‐old mature leaf of a Yucca plant bearing a bleeding inflorescent stalk, has been studied. Radioactive zeatin ribotide was found in the exudate of the bleeding inflorescence, which was collected over a period of 5 days. Radioactive zeatin ribotide was mainly extracted from the fed leaf. Minor conversion products in this leaf were zeatin ribotide, zeatin‐o‐β‐glucoside and zeatinriboside o‐β‐glucoside.

In not zeatin fed plants, zeatin‐o‐β‐glucoside was tentatively identified as the main endogenous cytokinin in one‐year‐old mature leaves. In the bleeding sap of not treated plants no free bases of zeatin or zeatin ribosides were found. After alkaline phosphatase treatment zeatin‐riboside was detected by combined gas chromatography‐mass spectrometry, indicating the presence of zeatin ribotide in the bleeding sap. High β‐glucosidase activity was found in the stern.

Results suggest that stared cytokinin glucosides from Yucca leaves are, converted by β‐glucosidase in leaves and stem, transported through the inflorescent stalk as zeatin nucleotides.
Nitrogen metabolism of Plantago major ssp. major as dependent on the supply of mineral nutrients
Authors: Stulen Ineke , Lanting Lineke , Lambers Huns , Posthumus Freek , van de Dijk Siebren J. , Hofstra Rinie
Published: April 2006

Various aspects of the nitrogen metabolism of Plantago major L. ssp. major, a grassland species from a relatively nutrient‐rich habitat, were investigated with plants that were grown in nutrient‐rich and nutrient‐poor culture solutions. In addition the influence of a change in the nutrient supply, both from high to low and from low to high nutrient conditions was studied. The data on P. major major showed that the activities of nitrate reductase (NR) and the reduced nitrogen content were all rather independent of the nutrient supply. These findings are in contrast with those of P. lanceolata, a grassland species from a relatively nutrient‐poor habitat, where both the activities of NR, GDH and GS and the reduced nitrogen content were correlated with the level of the nutrient supply. The rigidity of the nitrogen metabolism of P. major major may be of advantage if the nutrient supply is limited only for relatively short periods.
Respiratory changes with stratification of pear seeds
Authors: Alscher‐Herman R. , Musgrave M. , Leopold A. C. , Khan A. A.
Published: April 2006

Experiments on the stratification of seeds of pear (Pyrus communis cv. Bartlett) indicate that there is a progressive increase in respiratory capacity, with about a three‐fold increase developing during a 30‐day stratification period. Evidence is presented suggesting this increase in respiratory capacity occurs in the cytochrome oxidase pathway and not in the alternative pathway of respiration. The increase is much less pronounced if the seeds are held at 25°C rather than at 6°C. The seed coat serves as a barrier to the expression of the increased respiratory capacity.
Rapid scan spectrometry: oxidation of substrates by coupled potato mitrochondria
Authors: Ducet Gaston
Published: April 2006

By rapid scan spectrometry, spectral changes of redox components have been followed during the oxidation of substrates by coupled potato (Solanum luberosum L. cv. Bintje) mitochondria under different redox conditions. The redox changes of the b cytochromes, the changes in the base line level and in the slope of the spectra during aerobiosis appear to be connected with changes of the membrane potential. As the latter does not collaps at anaerobiosis, cytochrome o3 remains in an oxidized state. Collapse of the membrane potential by uncouplers induces partial oxidation of the b cytochromes and reduction of cytochrome a 3, so that toe resulting redox states derive from thermodynamic equilibrium with the redox conditions of the substrates. However, in aerobiosis as well as in anaerobiosis, the amplitude changes of the b cytochromes vary with the substrate oxidized as if these components were not always completely connected with the cytochrome oxidase complex. The b cytochromes become fuliy reduced only after dithionite reduction.
Inhibitors of chymotrypsin and microbial serine proteases in barley grains
Authors: Boisen S. , Andersen C. Yding , Hejgaard J.
Published: April 2006

Barley grains contain two imrnunochemically distinct inhibitors of chymotrypsin and microbial serine proteases. Both inhibitors are rich in lysine (9.5 and 11.5 g Lys/g protein). Hiproly high‐lysine barley contains twenty‐fold higher, high‐lysine mutant 1508 five‐fold higher amounts of these inhibitors than normally cultivated varieties. Inhibitors were extracted from Hiproly barley, and ammonium sulfate fractionation followed by gel filtration resulted in a neariy complete separation of the two inhibitors. No inactive protein impurities could be detected in a number of isoinhibitor preparations obtained in subsequent cation exchange chrotnatography steps. One inhibitor (CI‐1) was composed of at leas# 4 molecular forms with isoelecfric points in the range 4.75–5.55 and a monomer molecular size of about 9 000. Most of this inhibitor was apparently present as dimer forms in grain extracts. The other inhibitor (CI‐2) included at least 7 different molecular forms with isoelectric points in the range 6.05–7.90 and different molecular sizes in the range 6 500–9 000. Both dimer and monomer forms were present in grain extracts. In contrast to previously purified protease inhibitors of plant origin, the two barley inhibitors contain no cysteine. No interactions between the two inhibitors and trypsin were observed, but the inhibitors were immediately inactivated by pepsin at pH 2.0. Monospecific antibodies towards the two inhibitors were obtained after immunization with glutaraldehyde‐polymerized inhibitor.

Inhibitor CI‐1 is identical with an inhibitor of microbial alkaline proteases previously purified (Mikola and Suolinna 1971. Arch. Biochem. Biophys. 144: 566–575).
The role of darkness, GA and fusicoccin (FC) in breaking photodormancy in Phacelia tanacetifolia seeds
Authors: Cocucci S. , Ranieri A. M. , Morgiitti S. , Ciroli F.
Published: April 2006

The germination of the negatively photoblastic seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair) is promoted by gibberellic acid and fusicoccin. In the dark, or in the light in the presence of fusicoccin, seed germination is accompanied by an increase of gibberellic acid‐like substances. In these conditions, the inhibition of the synthesis of gibberellic acid‐like substances does not prevent seed germination, but it affects the growth and the survival of the seedlings. Seed germination, growth, and survival of seedlings are discussed in relation to phytochrome, fusicoccin, and gibberellic acid‐iite substances.
A tissue culture method for propagation and low temperature storage of Trifolium repens genotypes
Authors: Bhojwani Sant S.
Published: April 2006

Proliferating shoot cultures of Trifolium repens L. cv. Grasslands Huia have been established on Murashige and Skoog's medium containing 3% sucrose and 0.2 mg l−1 benzylamino purine. The shoots could be readily rooted on media without cytokinin and transferred to potting mix with 100% survival. The cultured shoots have been stored for 10 months, at 5°C in darkness without adversely affecting their potentiality for rapid multiplication. The significance of this approach for genotype storage is discussed.
Ptiotosynthetic activity and chloroplast membrane polypeptides in euploid cells of Ricinus
Authors: Timko M. P. , Vasconcelos A. C.
Published: April 2006

The possible effects of altered nuclear complement size on the poiypeptide composition and photochemical activity of chloroplasts in haploid, diploid, and tetraploid cells, of Ricinus communis L. have been evaluated. The electron transport capacity in isolated chloroplasts decreases with the increase in nuclear genome size. Both Photosystem II (DCPIP reduction) and Photosystem 1 oxygen uptake (TMPD to methyl viologen) activities were lower in plastid preparations from tetraploid individuals than in diploid and haploid cell preparations. Photosynthetic O2‐evolution and CO2‐fixation rates in leaf tissue from euploid individuals were also found to decrease with the increase in size of the nuclear genome. Specific activity levels of RuBP‐carboxylase were observed to increase with ploidy. Electrophoretic examination of the poiypeptide composition of thylakoid membranes from haploid, diploid, and tetraploid celis revealed no difference in the relative proportions of the constituent polypeptides of these membranes. The regulation of chloroplast development and the basis for altered plastid function in the presence of altered nuclear genome size are discussed.
Involvement of phytochrome in stomatal movement: Effect of blue and red light
Authors: Roth‐Bejerano Nurit , Itai Chanan
Published: April 2006

Blue and red light induce stomatal opening in Commelina comrnunis L. 3‐(3, 4‐di‐chlorophenyl)‐l, l‐dimethylurea (DCMU) slightly inhibits stomatal opening in blue light, while being strongly inhibitory in the presence of red light. Similar inhibition of red‐light‐induced opening is obtained by far red. Far red added to red light causes closure of open stomata almost to the degree obtained in darkness. Parallel to its effect on stomatal movement, far red increases 86Rb leakage from guard cells. The antagonism of red and far red possibly indicates the involvement of phytochrome. It is proposed that chlorophyll fluorescence in the far red region, increased by DCMU, is responsible for the inhibitory effect of red light. Similarly, the stimulatory effect of blue light may be due to its fluorescence in the red region.
Retardation of leaf senescence by inhibitors of RNA and protein synthesis
Authors: Yu Sheau Man , Kao Ching Huei
Published: April 2006

Effects of actinomycin‐D (ACT), cycloheximide (CH), rifampicin (RIF) and chloramphenicol (CAP) on senescence of soybean leaf discs were investigated. All inhibitors tested are effective in retarding senescence of soybean leaf discs. However, CH is more effective than ACT, RIF and CAP, suggesting that activation of preexisting, latent metabolic systems present in the cytoplasm piays predominant role in the initiating of leaf senescence. However, the possibility that events taking place in the nucleus or chloroplast are essential for the initiation of leaf senescence cannot be excluded.
Major nitrogen compounds transported in xylem vessels from roots to top in Citrus trees
Authors: Kato Tadashi
Published: April 2006

Four‐year‐old citrus trees (Citrus unshiu Marcovitch) were fed via the roots with (15NH4)2sO4 or K15NO3 as a nitrogen source. Nitrogenous compounds and their isotopic abundances in fine roots and xylem sap from trunks were assayed in order to obtain information on the species of nitrogen released by the root system into the ascending xyiem stream.

Arginine, asparagine, nitrate and proline in xylem sap accounted for 48, 21, 13 and 10%, respectively, of the total nitrogenous constituents tested in the sap. However, in the trees fed with labelled ammonium the main nitrogenous compound labelled with 15N in the xylem sap was asparagine and glutamine, which accounted for 79% and 18%, respectively, of total labelled nitrogen. In the xylem sap of trees fed with labelled nitrate, nitrate accounted for 94% of total labelled nitrogen. Nitrate and asparagine followed by glutamine showed the highest ratios of isotopic abundance in xylem sap as compared to fine roots. Proline and arginine had much lower ratios. These results indicate that nitrate, asparagine and glutamine are the main nitrogenous compounds released by the roots to the xylem stream, whereas arginine and proline are released into the xylern vessels by the trunk tissues. Furthermore, nitrate and asparagine are probably in steady movement upward in the trunk xylem, whereas glutamine is more easily taken up by the trunk tissues than nitrate and asparagine.
The effects of 2, 4‐dichIorophenoxyacetk acid altered chloroplast development on photosynthesis
Authors: McCracken Derek A. , Ort Donald R. , Nadakavukuren Mathew
Published: April 2006

We studied the changes in function and physical properties of isolated radish (Raphonus sativus L. cv. Sparkler) lamellar membranes 48 h after chloroplast development was altered by 2, 4‐(dichlorophenoxy)acet, tc acid. The number of chlorophyll molecules attendant to each electron transport chain was approximately 25% less in the chloroplasts from 2, 4‐(dichlorophenoxy)acetic acid‐treated plants than in chloroplasts from untreated plants. The maximal turnover rate of Photosystem I] in the treated chloroplasts was slightly less than half the turnover rate in normal chloroplasts. The efficiency of coupling between electron flux and ATP formation was not significantly different in the two chloroplast types. This hight efficiency of photophosphorylation in addition to normal membrane conductance to hydrogen ions indicates that the herbicide has not brought about a general deterioration of the membrane. A dramatic increase in the proton binding capacity of the lamellar membrane was observed in the treated chloroplasts. This increase in hydrogen ion buffering groups was largely accounted for by extrinsic membrane proteins bound to the exterior surface of the lamellar membrane. Although the addition of 2, 4‐(dichloro‐phenoxy) acetic acid to chloroplasts isolated from untreated plants caused concurrent uncoupling of ATP formation and inhibition of electron transport, our data show that these direct effects of the compound have little to do with its herbicidal action.
The influence of exogenous proline on the stomatal resistance in Vicia faba
Authors: Rajagopal Velamoor
Published: April 2006

Both the upper and lower stomata of Vicia faba responded to different concentrations of proline supplied either to the ‘detached’ leaves or sprayed to ‘intact’ leaves. The stomatal resistance of abaxial surfaces was increased more than that of the adaxial surfaces. A 1‐h treatment with 5 mM proline had greater influence than a prolonged treatment. The ‘young’ leaves responded more than the ‘mature’ ones to the exogenous proline. A relationship could be demonstrated between endogenous proline, which increased markedly due to exogenous supply, and stomatal resistance.
Effect of boron on stomatal opening in epidermal strips of Commelina communis
Authors: Roth‐Bejerano Nurit , Itai Chanan
Published: April 2006

Boron enhances stomalal opening in epidermal strips of Commelina communis L. under conditions conductive to opening, i.e. light and KCI. This effect is obtained when boron is given together or before KCI application. Since boron increases 86Rb net uptake in both illuminated epidermal strips and illuminated isolated guard cells, it is suggested that boron acts either by reducing potassium leakage or by increasing its uptake, thus leading to increased osmotic potential and, as a result, to stomatal opening.
The role of potassium in the vacuolization of plastids— An electron microanalysis study
Authors: Neumann Dietet , Jánossy Andras G. S.
Published: April 2006

Chloroplasts in leaf cuttings of Nicotiana rustica L. show swelling of the thylakoid system and formation of plastid vacuoles in the light. These ultrastructural changes may be caused by uptake of K+ and Cl‐ into the aqueous compartments between the thylakoid membranes. Ion changes arid ultrastructural alterations are reversible in darkness.
The effects of SAN 9789 and light on phytochrome and the germination of lettuce seeds
Authors: Widell Karl‐OIof , Sundqvist Christer , Virgin Hemming I.
Published: April 2006

Photoblastic seeds (akenes) of lettuce (Lactuca sativa (L.) cv. Grand Rapids) were treated with SAN 9789 [4‐chloro‐5‐(methylamine)‐2‐a, a, a,‐trifluoro‐m‐tolyl‐3‐(2H)‐pyridasinone]. The seeds weere placed in Petri dishes on filter paper soaked with water or SAN solution. The treatment increased the germination in darkness from 17% for water to 78% for SAN treated seeds. An irradiation with 5 min red light gave a germination of 98% both in water and in SAN. In water the effect of red irradiation could be reversed with a short irradiation (8 min) of far red light (17% germination), while in SAN solution the far red reversibility was poor (92% germination). If the far red light was given repeatedly (5 min per h) it had a slightly larger effect. If given continuously for 24 hours, the germination in water was decreased to 0.3% and in SAN solution to 9%. Possible mechanisms for the SAN effect are discussed.
Characterization and kinetics of soybean maturation and monocarpic senescence
Authors: Okatan Yener , Kahanak Gary M. , Noodén Larry D.
Published: April 2006

Daring monocarpic senescence in potted soybeans (Glycine maxi(L.) Merrill cv. Anoka) grown in controlled‐environment chambers, foliar chlorophyll, soluble protein nitrogen, total nitrogen, and starch decline (roughly in that order). All of these precede visible yellowing and, of course, abscission. The pattern of yellowing within a leaf is not uniform and is closely paralleled by starch loss. Unexpectedly, acid‐soluble nitrogen rises slightly before the total foliar nitrogen declines. Foliar fresh weight and total dry matter/cm2 of leaf surface decline little if at all before shedding. Preceding and even during the foliar yellowing, the seeds rapidly accumulate dry matter and nitrogen. Yellowing appears first in the radicle tip, then in the rest of the axis and the leaves and finally in the carpels. Ability to germinate is acquired at about the time the radicle + hypocotyl turns yellow. The relationship between these changes and their role in senescence is discussed.
The activity and interaction of brassinolide and gibberellic acid in mung bean epicotyls
Authors: Gregory Luis E. , Mandava N. Bhushan
Published: April 2006

The growth rate of mung bean epicotyls was used for evaluating the effect of brassinolide on cell elongation. Growth above that of control plants was observed at 10−10M and above. Gibberellic acid showed an additivity relationship with low concentrations (10−9–10−8M) of brassinolide in this test system and the two growth promoters may therefore act independently at the cellular level. Because of relative ease of operation, great sensitivity and the short time required for assessing biological activity, this assay could be used in conjunction with the bean second internode bioassay for evaluating the activity of brassinolide and its analogs, as well as of other growth promotors.
The nature and localization of superoxide dismutase in fronds of Lemna gibba L. and the effect of copper and zinc deficiency on its activity
Authors: Vaughan D. , DeKock P. C. , Ord B. G.
Published: April 2006

Superoxide dismutase (SOD) is present in the fronds of Lemna gibba L. Differential centrifugation showed that ca. 90% of the enzyme is present in the 140,000 g soluble cell fraction. Lemna SOD is sensitive to cyanide and is probably a Cu‐Zn metallo‐protein. Gel filtration showed the SOD to have a mass of 31,000 daltons. In Zn‐defizient culture media, the activity of Lemna SOD was less than in fronds grown in complete nutrient media whereas in Cu‐deficient media little change was found in the enzyme activity. The SOD activity in Zn‐deficient plants could be partly restored to the level of Zn‐sufficient fronds by adding Zn2+ to the enzyme assay solution.
Indirect effect of abscisic acid on the induction of secondary dormancy in lettuce seeds
Authors: Karssen C. M.
Published: April 2006

During temporary incubation at 25°C in buffered solutions (pH 4.0) of abscisic acid (ABA) seeds of lettuce (Lactuca sativa L. cv. Olof) lost the red‐light initiated ability to germinate in buffer. The development of secondary dormancy required an inhibitory ABA content in the seeds during a number of days. A temporary incubation in ABA during 24 h met these requirements only if the solution was about 100‐fold more concentrated than during continuous incubation. Studies with 2‐14C‐ABA showed that the amount of ABA which had penetrated in 24 h was reduced by a factor 100 within 3 to 4 days during subsequent incubation in buffer. Both leaching and metabolic changes were involved in the reduction process. The nature of the metabolic products remained obscure. A shift to 2°C after incubation in ABA prevented the induction of secondary dormancy, but inhibited ABA metabolism. ABA did not interfere with the induction rate of secondary dormancy, and it was not required to maintain the state of dormancy. The sole function of ABA was the non‐specific inhibition of germination, which indirectly facilitated the development of an ABA independent secondary dormancy. – The level of endogenous ABA was compared to the amount of ABA found in the embryo during and after incubation in ABA solutions marked with 2‐14C‐ABA. The level of endogenous ABA in air‐dry seeds (0.11 ng/mg dry weight) corresponded to the minimal level at which penetrated ABA inhibited germination. This level had to be present at least during 4 to 5 days to inhibit the effect of red light. Since endogenous ABA was quickly reduced upon imbibition, a regulatory function of endogenous ABA in the inhibition of red light induced germination can be ruled out. A function in the temporary inhibition of dark germination and, consequently, in the development of secondary light irresponsiveness cannot be excluded, however.
Direct evidence for the presence of a rotenone‐resistant NADH dehydrogenase on the inner surface of the inner membrane of plant mitochondria
Authors: Møller Ian M. , Palmer John M.
Published: April 2006

Submitochondrial particles (SMP) were produced from Jerusalem artichoke (Helianthus tuberosus L.) mitochondria by sonication and differential centrifugation. The SMP were about 50% inside‐out as measured by the access of reduced cytochrome c to cytochrome c oxidase. Uncoupled NADH oxidation (1 mM NADH) by the SMP was 120 nmol O2 min−1mg−1, which was reduced to 98 nmol O2 min−1 (mg mitochondrial protein)−1 in the presence of EGTA. In contrast, the oxidation of NADH by intact mitochondria was completely inhibited by EGTA (from 182 to 14 nmol O2 min−1mg−1). The EGTA‐resistant NADH oxidation by the SMP is ascribed to the NADH dehydrogenase(s) on the inside of the inner membrane and exposed to the medium in the inside‐out SMP. In the presence of EGTA it could be shown that two NADH dehydrogenase activities were present in the SMP. One had an apparent Km of 7 μM for NADH, a Vmax of 80 nmol NADH min−1mg−1, and was rotenone‐sensitive. This dehydrogenase is equivalent to the mammalian Complex I NADH dehydrogenase. The other dehydrogenase, which was rotenone‐resistant, had a Km of 80 μM and a Vmax of 131 nmol NADH min−1mg−1; it is probably responsible for the rotenone‐resistant oxidation of organic acids often observed in plant mitochondria. The redox poise of the pyridine nucleotides had only a small effect on the relative rates of the two internal dehydrogenases. Electron flow through these dehydrogenases appears, therefore, to be regulated mainly by the concentration of NADH in the matrix of the mitochondria.
Photosynthetic responses to low temperature in Betula pubescens and Betula tortuosa
Authors: Hällgren Jan‐Erik , Sundbom Erik , Strand Martin
Published: April 2006

The acclimation of the net flux density of CO2 to temperature, and the effects of freezing‐stress on the functional integrity of photosynthesis were compared for Betula tortuosa and Betula pubescens. Single expanded leaves of B. tortuosa had a higher rate of net photosynthesis and a greater capacity to acclimate to a low growth temperature regime than had leaves of B. pubescens. At low temperatures, stomatal conductances were higher for B. tortuosa than for B. pubescens. In neither species were the stomatal conductances determining the decrease of the rate of net photosynthesis at low temperatures. There was a marked difference between leaves of the two species in their ability to withstand freezing, as revealed by measurements of changes in temperature‐induced variable fluorescence. The chloroplast thylakoids of B. tortuosa were better able to maintain their functional integrity at sub‐zero temperatures than were those of B. pubescens.
The effect of a day at low irradiance of a maize crop. II. Photosynthesis, transpiration and respiration
Authors: André M. , Massimino J. , Daguenet A. , Massimino D. , Thiery J.
Published: April 2006

The kinetics of daily photosynthesis, transpiration and dark respiration of shoots of maize plants (Zea mays L.) were studied in a growth chamber. After one or two days of reduced light intensity, the photosynthesis and the transpiration returned immediately to a level higher than expected. Respiration, which was reduced by at least 50%, returned slowly for over 2 days towards the initial level. These results suggest the existence of reserves of assimilation products which are used up while maintaining the growth of the aerial part in spite of the lack of assimilation. The prolonged reduction of the respiration shows that it is not strongly correlated to photosyntheis or to growth but rather to the amount of available reserves of assimilate.
Mode of action of glyphosate in relation to metabolism of indole‐3‐acetic acid
Authors: Lee T. T.
Published: April 2006

Studies were conducted with radio‐labeled indole‐3‐acetic acid ([2‐14C] IAA) and tobacco callus culture (Nicotiana tabacum L. cv. White Gold) to investigate the mode of action of the herbicide glyphosate (N‐phosphonomethylglycine). The tissue was first grown with or without glyphosate for 1 to 14 days and then incubated with [2‐14C] IAA for 4 h. Metabolism of [2‐14C] IAA in the tissue was studies by solvent fractionation, high performance liquid chromatography and liquid scintillation counting. The tissue grown with 0.2 mM glyphosate had low level of free [2‐14C] IAA and high levels of other fractions containing metabolites and conjugates of the labeled IAA. After 1 day of glyphosate treatment the free [2‐14C] IAA level in the tissue was reduced by 77% compared to that of the control; after 10 days of treatment the decrease was 96%. The decrease in the free [2‐14C] IAA level was not due to inhibition of IAA uptake, but due to enhanced rates of oxidation and conjugate formation of IAA. The increased oxidation of IAA in the treated tissue was not due to a direct effect of glyphosate on IAA‐oxidase since glyphosate was inactive on IAA oxidation in a cell‐free system in vitro. The glyphosate‐induced growth inhibition was partially overcome by addition of 1 μM 2,4‐dichlorophenoxyacetic acid to the medium. The results lead to the conclusion that glyphosate inhibits growth by depletion of free IAA through rapid acceleration of both conjugate formation and oxidative degradation of IAA.
Field studies of water relations and photosynthesis in Scots pine.
Authors: Hillerdal‐Hagströmer Karin , Mattson‐Djos Erkki , Hellkvist Jerk
Published: April 2006

Needle water potential at noon and diurnal variation in needle water potential was measured with a pressure chamber during the growth seasons (1974, 1975 and 1976) in a 20‐year‐old stand of Scots pine (Pinus sylvestris L.), subjected to daily irrigation and nutrient treatments at Jädraås, in central Sweden (60°50′N).

In unstressed conditions there was little difference in water potential amongst the treatments. However, during a dry spell in 1976 the diurnal curves of water potential in the control and combined irrigated and fertilized treatment diverged by up to 6 bar in the middle of the day. Irrigation alone resulted in higher midday water potentials (Ψn) than in the controls only during this period. At other times in 1974, 1975 and early 1976, the values of Ψn in the irrigated treatment were similar to the controls. Fertilization alone resulted in higher Ψn than in the controls in both 1975 and 1976 during both wet and dry periods. However, the largest difference between treatment and control occurred in the combined, irrigated and fertilized treatment during the dry spell in 1976.

Several possible explanations for the effect of fertilization on leaf water potential are discussed, including changes in hydraulic conductivity and water storage. The most likely explanation is a reduced transpiration rate as a result of more effective stomatal control of water loss.
Physiological significance of indoleacetic acid and factors determining its level in cotyledons of Lupinus albus during germination and growth
Authors: Elkinawy Mahasen
Published: April 2006

The results demonstrate the profile of the endogenous indole‐3‐acetic acid (IAA) in the cotyledons of Lupinus albus L. (L. termis Forssk.) during germination and seedling growth. The auxin level increases markedly after seed hydration, especially during the time of radicle emergence 24 h after the onset of imbibition. This rise is accompanied by a minimal IAA‐oxidase activity, formation of indoleacetylaspartic acid (IAAsp) and an increase in the endogenous tryptophan and tryptophan‐carboxyl‐14C degradation, though the latter cannot account for the high IAA level detected during early stages of germination. It is believed that cotyledons are a source of IAA to the developing embryonic axis. – The auxin level drops in the cotyledons during seedling growth, 2–18 days after sowing. This is true also for IAAsp and tryptophan‐degrading activity of enzyme extracts. Conversely, endogenous tryptophan is increasingly liberated up to day 14, and IAA‐oxidase activity climbs to a peak detected on day 12, prior to the appearance of senescence in the cotyledons. – The physiological significance of IAA and the factors regulating its level in the cotyledons during germination and growth are discussed.