bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative rates of delivery of xylem solute to shoot tissues: Possible relationship to sequential leaf senescence
Authors: Neumann Peter M. , Stein Zipporah
Published: April 2006

The rates of delivery of regulatory solutes such as cytokinins and mineral ions from the roots to competing shoot tissues can influence rates of metabolism and development. A 15 min pulse of a synthetic xylem mobile and phloem‐immobile solute, acid fuchsin, was used to quantify relative rates of solute delivery to competing organs on excised transpiring bean shoots (Phaseolus vulgaris L. cv. Contender) at different stages of development. Stem, flower and fruit tissues received comparatively low rates of solute delivery. The relative rate of solute delivery to newly opened leaves was initially low, but increased during rapid leaf expansion and then declined progressively as the leaves exceeded 70% of their final area.

The relative rate of solute delivery to tissues of the basal primary leaves declined progressively from 2 weeks onwards. This decline appeared to be caused by progressive internally regulated increases in both stomatal resistances and hydraulic resistances to xylem flow up to and into the leaf blade. Thus combined abaxial and adaxial stomatal resistance values in the primary leaves (Rs) increased from 3 to ≥ 7 s cm−1 between 2 and 5 weeks. Similarly, mean values for the connection resistances (Rc) to hydraulic flow into the primary leaves rose from 7 to 13 TPa · s · m−1 between 2 and 4 weeks. In the same period pathway resistance from stem to primary leaf petioles (Rp), as determined by direct pressure flow assay, increased from 7 to 15 TPa · s · m−1.

Senescence‐associated declines in protein and chlorophyll levels in the primary leaves were initiated in parallel with, or after, declines in relative rates of solute delivery. The provision of extra illumination at the basal leaf level between 2 and 5 weeks did not prevent declines in chlorophyll and soluble protein or increases in stomatal resistance. We suggest that internally programmed changes in the hydraulic architecture of the plant progressively divert xylem‐transported root supplies of nutrients and cytokinins from basal to more apical leaves and thus regulate the progressive senescence of leaves from the base upwards.
The effect of bacterial strain and temperature changes on the nitrogenase activity of Lotus pedunculatus root nodules
Authors: Pankhurst C. E. , Layzell D. B.
Published: April 2006

After 40 days of growth at 25°C, Lotus pedunculatus cav., cv. Maku plants infected with Rhizobium loti strain NZP2037 displayed similar relative growth rates but had twice the nodule mass and only one third the whole plant dry weight of plants infected with Bradyrhizobium sp. (Lotus) strain CC814s. In the NZP2037 symbiosis, the rate of CO2 evolution (per g dry weight of nodulated root) was 1.6 times as high as that in the CC814s symbiosis while the rate of C2H2 reduction (per g dry weight of nodule) was only 48% of that in the CC814s symbiosis. Studies of the effect of short term temperature changes on the gas exchange characteristics (CO2 and H2 evolution, C2H2 reduction) of these symbioses revealed wide differences in the optima for C2H2 reduction. Nodules infected with NZP2037 displayed maximal C2H2 reduction rates [157 μmol (g dry weight nodule)−1 h−1] at 12°C, whereas nodules infected with CC814s were optimal at 30°C [208 μmol (g dry weight nodule)−1 h−1]. These short term studies suggested that differences in temperature optima for N2 may have partially accounted for the poorer effectivity, at 25°C, of strain NZP2037 when compared with strain CC‐814s.

The relative efficiency [RE = 1 – (H2 evolution/C2H2 reduction)] of N2 fixation varied widely with temperature in the two symbioses, but there was a general trend toward higher RE with lower temperatures. The ratio of CO2 evolution: C2H2 reduction (mol/mol) in nodulated roots infected with CC814s was constant (ca 10 CO2/C2H2) between 5°C and 30°C, whereas in plants infected with NZP2037 it reached a minimal value of 3.3 CO2/C2H2 at 10°C and was 19 CO2/C2H2 at the growing temperature (25°C).
Anion‐sensitive ATPase activity and proton transport in isolated vacuoles of species of the CAM genus Kalanchoë
Authors: Jochem Petra , Rona Jean‐Pierre , Smith J. Andrew C. , Lüttge Ulrich
Published: April 2006

Vacuoles were isolated from leaves of Kalanchoë daigremontiana Hamet et Perrier de la Bathie, and the ionic sensitivity of the vacuolar ATPase was studied in vacuole homogenates desalted on Sephadex G‐25. The ATPase activity was dependent on the presence of divalent cations (Mg2+≥ Mn2+≥ Ca2+, Co2+; Zn2+ had no effect). Mg2+‐dependent ATPase activity was stimulated by anions (Cl− > malate2+, HCO−3), with maximal stimulation at concentrations above 50 mM. Mg2+‐Dependent activity was inhibited by NO−3 above 2 mM, but no saturation was observed up to 100 mM. No stimulation by K+ or Na+ was detected; stimulation by NH+4 was abolished by 0.01% (w/v) Triton X‐100, suggesting that the NH+4 effect was due to the permeability of vacuolar membrane vesicles to NH3.

Trans‐tonoplast electrical potentials (Δψ) and intra‐vacuolar pH were measured with glass microelectrodes and antimony covered glass micro‐pH‐electrodes, respectively. Free vacuofes isolated from Kalanchoë tubiflora (Harv.) Hamet were slightly positive with respect to the suspension medium. This Δψ was insensitive to the protonophore FCCP and depolarized by about 4 mV on addition of 50 mM KCl, still remaining about +5 mV. Upon addition of 7 mM Mg‐ATP, vacuoles showed an FCCP‐sensitive increase of Δψ from +9.2 ± 2.8 (13) to +17.8 ± 3.7 (12) mV [given as x̄± sd (n)] and an internal acidification from pH 5.4 ± 0.2 (11) to pH 4.3 ± 0.4 (12). Mg‐ADP and ATP without Mg2+ had no effect on Δψ.

It is concluded that the H4 pumping at the tonoplast is due to the functioning of the anion‐sensitive vacuolar ATPase and that this is an essential part of the mechanism of nocturnal acid accumulation in CAM.
Triadimefon reduces transpiration and increases yield in water stressed plants
Authors: Fletcher R. A. , Nath V.
Published: April 2006

Two‐week‐old wheat (Triticum aestivum L. cv. Fredrick), peas (Pisum sativum L. cv. Little Sweetie) and soybean (Glycine max L. cv. Hodgson) seedlings were transferred to paper cups containing various concentrations of triadimefon [1‐(4‐chlorophenoxy)‐3,3 dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone] a fungicide. Twelve days after treatment, triadimefon (20 μg ml−1) significantly reduced transpiration in wheat, peas and soybeans by 40, 29 and 19%, respectively. The reduction of transpiration prevented the leaves from wilting and becoming senescent. In another experiment, triadimefon was applied as a soil drench after the initiation of flowers in soybeans and peas and after swelling in radish (Raphanus sativus L. cv. Cherry Belle) roots. After treatment the water level was maintained at half field capacity. In all three species, the treated plants were shorter, more compact and had thicker and greener leaves than the control plants. In the case of radish, the treatment also prevented flowering. Triadimefon significantly increased the seed yield of soybeans and peas and the root to shoot ratio in radish. Hence root application of triadimefon reduces transpiration, protects plants, and increases yield under water stress conditions.
Capacity of cytochrome and alternative path in coupled and uncoupled root respiration of Pisum and Plantago
Authors: Blacquière Tjeerd , de Visser Ries
Published: April 2006

The control of electron flow through the cytochrome and alternative pathways was studied in intact roots of Plantago lanceolata L., P. major L. ssp. major and Pisum sativum L. cv. Rondo, grown either on nitrate or on ammonium. Root respiration in these species was highly resistant to 0.2 mM cyanide and sensitive to 25 mM salicylhydroxamate (SHAM). The uncoupler carbonyl cyanide‐m‐chlorophenyl‐hydrazone (CCCP) stimulated root respiration to the same extent in nitrate‐ and ammonium‐grown plants. In the presence of SHAM, root respiration was not stimulated by CCCP. It is, therefore, suggested that in the presence of SHAM the cytochrome path operates at a rate determined by the Vmax of at least one of its carriers. The sum of the capacities of the alternative and the cytochrome pathways, as determined with 0.2 mM KCN and 25 mM SHAM respectively, was less than the uncoupled rate of root respiration. It is therefore suggested that part of the root oxygen uptake is sensitive to both KCN and SHAM. With increasing age the activity of the alternative path decreased in both Plantago species.
The effect of brassinosteroid and 2,4‐D‐L‐amino acid conjugates on ethylene production by etiolated mung bean segments
Authors: Arteca Richard N. , Schlagnhaufer Carl
Published: April 2006

Brassinosteroid (BR) an analogue of brassinolide was tested in combination with thirteen 2,4‐dichlorophenoxyacetic acid‐L‐amino acid conjugates for its possible synergistic effects on ethylene production by etiolated mung bean (Vigna radiata L. Rwilcz cv. Berken) hypocotyl segments. When BR was used in combination with 2,4‐D‐L‐amino acid conjugates the degree of enhanced ethylene production varied with the conjugate tested. In fact, the activity of the conjugate alone was directly related to its activity with BR.
Inhibition of IAA‐induced ethylene production in etiolated mung bean hypocotyl segments by 2,3,5‐triiodobenzoic acid and 2‐(p‐chlorophenoxy)‐2‐methyl propionic acid
Authors: Tsai De‐Sheng , Arteca Richard N.
Published: April 2006

The effect of two auxin antagonists, 2,3,5‐triiodobenzoic acid (TIBA) and 2‐(p‐chlorophenoxy)‐2‐methyl propionic acid (CMPA) on IAA‐induced ethylene production in etiolated mung bean hypocotyl (Vigna radiata L. Rwilcz cv. Berken) segments was studied. Both TIBA and CMPA inhibited IAA‐induced ethylene production and CO2 production at concentrations from 0.001 mM to 0.1 mM and 0.01 mM to 1.0 mM, respectively. The optimum concentration for inhibition of ethylene production by TIBA was 0.05 mM and CMPA was 0.5 mM. At the optimum concentration of TIBA and CMPA, there was a significant decrease in IAA‐induced ethylene production without a decrease in respiration rates below control levels. After 18 h, mung bean hypocotyl segments treated with 0.05 mM TIBA for 6 h or 0.5 mM CMPA for 8 h showed a maximum inhibition of IAA‐induced ethylene production. Treatments longer than 8 h caused no further inhibition. The uptake of [14C]‐naphthaleneacetic acid by mung bean segments was greatly reduced by the addition of either TIBA (0.05mM) or CMPA (0.5 mM) to the incubation media. The results of treatment sequences showed that TIBA needed to be applied prior to IAA in order to inhibit IAA‐induced ethylene production, but CMPA caused the same inhibitory effect whether applied before or after IAA treatment. These findings provide evidence that TIBA inhibits auxin‐induced ethylene production in etiolated mung bean hypocotyl segments by blocking auxin movement into the tissue whereas CMPA may work on both auxin transport and action.
Protease activities in non‐embryogenic and embryogenic carrot cell strains during callus growth and embryo formation
Authors: Carlberg Irene , Söderhäll Kenneth , Glimelius Kristina , Eriksson Tage
Published: April 2006

Embryogenic and non‐embryogenic cell strains of Daucus carota L. were examined for their protease activity using a wide range of chromogenic synthetic peptides as substrates. High arginine‐specific activity was present in all strains, but no protease activity “specific” for embryogenic or non‐embryogenic strains could be detected with the substrates tested. The specific protease activity was 5–10 times higher in the non‐embryogenic as compared to the embryogenic strain for most tested substrates, and this difference was not due to release of proteases in the latter. All strains showed a decrease in protease activity when cultured in media without 2,4‐dichlorophenoxyacetic acid, but the embryos had high protease activity in comparison with the nondifferentiated cell aggregates. In the latter aggregates, hydrolyzing activity towards three of the substrates (H‐D‐Phe‐Pip‐Arg‐p‐nitroanilide, Suc‐Ala‐Pro‐Phe‐p‐nitro‐anilide and Bz‐Phe‐Val‐Arg‐p‐nitroanilide) was absent, whereas the embryos were able to hydrolyze them.
Purification and properties of the germination‐inducing factor in the ectomycorrhizal fungus Leccinum aurantiacum (Boletaceae)
Authors: Bjurman Jonny , Fries Nils
Published: April 2006

A diffusion gradient bioassay on agar strips was developed for determination of the germination‐inducing activity of exudates from mycelium of Leccinum aurantiacum (Bull.) S. F. Gray on basidiospores of the same species. The taxon‐specific germination‐inducing factor, GIF, present in the active exudates, was non‐volatile, diffusible, soluble in water, methanol and ethanol, resistant to boiling of short duration, and stable after lyophilization if preserved at −20°C. Gel filtration and adsorption experiments contributed to the chemical and physical characterization of GIF. Passage of an exudate through a Sep‐Pak C18 minicolumn removed 99.5% of concomitant substances including germination inhibitors. GIF could then be eluted from the column with methanol without loss of activity.
The hydraulic architecture of balsam fir (Abies balsamea)
Authors: Ewers F. W. , Zimmermann M. H.
Published: April 2006

Leaf‐specific conductivities (LSCs – hydraulic conductivity per dry weight of supplied leaves). Huber values (transverse sapwood area per dry weight of supplied leaves), specific conductivity (hydraulic conductivity per transverse sapwood area) and tracheid diameters were measured throughout the trunk and crown of 20‐year‐old trees of Abies balsamca (L.) Mill. Measured specific conductivity was proportional to the radius to the fourth power of tracheids. LSCs, which indicate the relative water availability to different plant parts, are much higher in the trunk than in first order branches, and lowest in second order branches. The structural basis for this “hydraulic hierarchy” lies both in Huber values and in tracheid diameters. For similar diameter stem segments, there was no statistically significant difference for trunks versus branches in specific conductivity. However, in old parts of the tree, trunks are wider than supported branches and producer wider tracheids resulting in greater specific conductivities than in branches. In vigorous trees with strong apical control, Huber values were 12.0 times greater in the trunk than in similar diameter branch segments. In slow‐growing trees with weak apical control, Huber values were 2.2 times greater in the trunk versus similar branch segments.
Correlations between net auxin and secondary xylem development in young Populus deltoides
Authors: DeGroote David K. , Larson Philip R.
Published: April 2006

Stems of cottonwood (Populs deltoides Bartr. ex Marsh.) plants grown under different conditions were examined to determine the relation between net endogenous auxin yields and the acropetal advance of the primary‐secondary vascular transition zone (TZ). In all treatments, the internode yielding maximum net auxin activity, as determined by the Avena curvature bioassay, closely corresponded with the internode in which the TZ occurred. Under short‐day (SD) dormancy‐inducing conditions, auxin yield declined steadily while the maximum auxin peak and the TZ shifted toward younger internodes. Auxin yields from these plants were extremely low after 5 weeks of SD compared with those from long‐day (LD) plants. The only consistent auxin yield was obtained from internodes subtending young leaves beneath the apical bud. Plants placed in SD for 3 weeks and then returned to LD conditions showed an immediate increase in auxin yield in the stem, and the progressive acropetal advance of the TZ under SD was reversed. Therefore, within 7 LD the positions of the TZ and peak auxin yield corresponded to those observed before the imposition of SD Fully dormant plants placed in LD showed a dramatic rise in auxin yields during the first 2 weeks of renewed growth. Although low levels of auxin were found in the newly developing shoots after 6 LD, yields increased rapidly after 9 and 14 LD. The position of the TZ corresponded with the peak of net auxin activity after 9 and 14 LD.
Purification and characterization of soybean nodule nitrite reductase
Authors: Hunter William J.
Published: April 2006

A nodule cytosol nitrite reductase was isolated from soybean [Glyine max (L.) Mer. cv. Tracy] grown in the presence of nitrate. Enzyme activity increased when increased amounts of nitrate were supplied to the plant. A purification procedure involving ammonium sulfate precipitation, gel filtration, DEAE Sephadex and Blue Sepharose chromatography resulted in an activity capable of forming 6.7 μmol ammonia (mg protein)−1 min−1. This represented a 235‐fold increase in specific activity. The molecular weight, estimated by gel filtration, was 55 000. The pH optimum for activity was 7.1. Ammonia formed stoichiometrically as nitrice was consumed. From Lineweaver‐Burk plots, Km values of 0.5mM for nitrite and 0.2mM for methyl viologen were calculated. Spectral data suggest the association of a heme chromophore with the enzyme.
Effects of nitrogen nutrition and root medium water potential on growth, nitrogen uptake and osmotic adjustment of rice
Authors: Yambao E. B. , O'Toole J. C.
Published: April 2006

The effects of nitrogen (N) nutrition on growth, N uptake and leaf osmotic potential of rice plants (Oryza sativa L. ev. IR 36) during simulated water stress were determined. Twenty‐one‐day‐old seedlings in high (28.6 × 10 −4M) and low (7.14 × 10 4M) N levels were exposed to decreased nutrient solution water potentials by addition of polyethylene glycol 6000. The roots were separated from the solution by a semi‐permeable membrane. Nutrient solution water potential was −0.6 × 105 Pa and was lowered stepwise to −1 × 105, −2 × 105, −4 × 105 and −6 × 105 Pa at 2‐day intervals. Plant height, leaf area and shoot dry weight of high and low nitrogen plants were reduced by lower osmotic potentials of the root medium. Osmotic stress caused greater shoot growth reduction in high N than in low N plants. Stressed and unstressed plants in 7.14 × 104M N had more root dry matter than the corresponding plants in 28.6 × 104M N. Dawn leaf water potential of stressed plants was 1 × 105 to 5.5 × 105 Pa lower than nutrient solution water potential. Nitrogen‐deficient water‐stressed plants, however, maintained higher dawn leaf water potential than high nitrogen water‐stressed plants. It is suggested that this was due to higher root‐to‐shoot ratios of N deficient plants. The osmotic potentials of leaves at full turgor for control plants were about 1.3 × 105 Pa higher in 7.14 × 10−4M than in 28.6 × 10−4M N and osmotic adjustment of 2.6 × 105 and 4.3 × 105 Pa was obtained in low and high N plants, respectively. The nitrogen status of plants, therefore, affected the ability of the rice plant to adjust osmotically during water stress.

Plant water stress decreased transpiration and total N content in shoots of both N treatments. Reduced shoot growth as a result of water stress caused the decrease in amount of water transpired. Transpiration and N uptake were significantly correlated. Our results show that nitrogen content is reduced in water‐stressed plants by the integrated effects of plant water stress per se on accumulation of dry matter and transpiring leaf area as well as the often cited changes in soil physical properties of a drying root medium.
Effect of plant density on the uptake and distribution of 14C in the field bean, Vicia faba
Authors: Crompton Hilary J. , Hill‐Cottingham D. G. , Hudd G. A. , Lloyd‐Jones C. P.
Published: April 2006

Whole bean plants, ev. Cockfield, grown in pots crowded or well‐spaced (50 or 10 plants m2, respectively) were treated with 14CO2 at the pod‐fill stage (25 modes) and the radioactivity in each leaf was determined after 30 min. With spaced plants the uptake was greatest in the mid‐stem leaves and was proportional to leaf area. In contrast, 70% of the total assimilation took place in the upper six leaves of crowded plants and there was a steady decrease down the stem.

When 14CO2 was fed to single leaves of similar crowded plants the resultant distribution of labelled assimilates varied with the position of the treated leaf. After 6 h, 67% of the 14C fixed by a mid‐stem leaf (node 13) was recovered from the beans, whereas 76% of that from an upper leaf (node 23) had accumulated along the stem. Due to the shading of mid‐stem leaves at the higher planting densities, seed yield becomes increasingly dependent upon re‐distribution of assimilates from stem to beans.
Starch in prasinophycean algae
Authors: Bressler Steven L. , Meeuse B. J. D.
Published: April 2006

Reserve products isolated from three species of prasinophycean algae: Pyramimonas parkeae Norris and Pearson, Pyramimonas amylifera Conrad and Platymonas tetrathele West were compared. Three pieces of experimental evidence indicate that the reserve product of each of the species analyzed is a true starch. (I) There is no essential difference between the light absorption curve for the complex formed between corn starch and iodine and the corresponding curves for the algal products. (2) The β‐amylase breakdown limit of these compounds is very close to that of corn starch. (3) The X‐ray diffraction diagrams produced by the reserve material from Pyramimonas parkeae and Platymonas tetrathele is a so‐called A‐spectrum characteristic of cereal starches while the diagram produced by grains from Pyramimonas amylifera corresponds to the B‐spectrum typical for tuber starches. The dissimilarity between the X‐ray diagrams produced by the starches from the Pyramimonas species suggests that a re‐examination of the taxonomy of these species is warranted.
Photoinhibition of respiratory CO2 release in the green alga Scenedesmus
Authors: Scherer Siegfried , Stürzl Erwin , Böger Peter
Published: April 2006

14CO2 evolution of prelabeled Scenedesmus obliquus Kütz, has been followed in the dark and in the light. In the light, no carbon dioxide is evolved. Addition of unlabeled NaHCO, leads to 14CO2 release attaining 20 to 30% of the dark rate. Double‐reciprocal plots of NaHCO3 concentrations vs 14CO2 release results in a straight line, indicative of competition between exogenously supplied bicarbonate and endogenously evolved carbon dioxide. With this method, it is possible to measure CO2 evolved by respiration in the light and to show that true photoinhibition of respiration occurs in Scenedesmus. In the light. DCMU substantially increases 14CO2 evolution; in the presence of the uncoupler carbonyl cyanide‐m‐chlorophenylhydrazone. 14CO2 evolution is comparable to that in the dark. 14CO2 release and oxygen uptake in the dark are only slightly affected by cyanide, indicative of a cyanide‐resistant respiration and/or fermentation as the essential CO2‐yielding processes in the presence of cyanide. These results, compared with concurrent ATP levels, lead us to assume that energy charge is not the only factor responsible for photoinhibition of respiration.
Leaf expansion as related to plant water availability in a wild and a cultivated sunflower
Authors: Sobrado M. A. , Rawson H. M.
Published: April 2006

This study aimed to determine if two species of sunflower, Helianthus annus L. cv. Hysun 31 (cultivated, single‐stemmed genotype) and Helianthus petiolaris Nuttall ssp. fallax (wild, many‐hranched genotype) differed in the response of leaf growth to water deficits. Earlier published studies, concerned only with H. annuus, failed to reveal differences in the response of sunflowers to water stress. Plants of the two species were paired in large containers of soil and grown under high radiation in a glasshouse. One batch of plants was irrigated and the other allowed to dry so that predawn leaf water potentials declined at an average of 0.072 MPa day−1. The dry batch was rewatered when predawn leaf water potentials reached −0.85 MPa.

The stress imposed was sufficient to curtail leaf growth so that plants in the dry treatment had only 60% of the leaf area of irrigated plants at the onset of rewatering. Both species were affected by stress to the same relative extent, though their leaf areas at this stage differed 7‐fold. Both genotypes also recovered to the same degree in the long term, finally having leaf areas and gross dry matter distribution patterns which were indistinguishable from plants which were irrigated throughout. However, water stress resulted in different distribution patterns of leaf area: H. annuus produced larger leaves at the top of its single stem which compensated for the reduced area in lower leaves, whereas H. petiolaris compensated in the leaves on its branches. Leaves which emerged after the time of stress were most able to compensate in area subsequently. For example, those leaves of H. annuus which emerged one week after stress‐relief were more than three times larger than comparable leaves on plants irrigated continuously. Leaf expansion rates were affected earlier in the stress cycle than leaf conductance in H. annuus, but not in H. petiolaris. But as with other plant responses to water stress, the differences between the two species were small.
A model for cation content of plants based on surface potentials and surface charge densities of plant membranes
Authors: Bérczi Alajos , Møller Ian M. , Oláh Zoltán , Lundborg Tomas , Erdei László
Published: April 2006

The model presented takes into account the interaction between the negatively charged membranes and macromolecules and the cations. A central postulate is that a constant average surface charge density (σ) as well as a constant average surface potential (Ψ) is conserved under different ionic conditions. The model makes it possible to predict the size of σ and Ψ from measurements of Na, K, Mg and Ca content in plant tissues of the same age but grown under two different ionic conditions (e.g. high and low K+). Assumptions were made about the relative amounts of free and bound Ca2+ and σ and Ψ were calculated from values in the literature. In all cases σ (and Ψ) are predicted to be higher for shoot (−29 to −96 mC m−2) than for root membranes (−14 to −27 mC m−2). In most cases the predicted σ falls within the range determined experimentally for biological membranes.
Net uptake and partitioning of nitrogen and potassium in cultivars of barley during ageing
Authors: Perby Harald , Jensén Paul
Published: April 2006

Experiments were carried out with barley cultivars (Hordeum vulgare L.) grown in both pot‐ and water‐culture. Net uptake of NO3− and K+ in the roots was followed in two barley cultivars grown on water‐culture for 85 days. After an initial period of low net uptake of both ions, uptake increased until a maximum was reached after 30 to 45 days. Thereafter, net uptake of NO3− and K+ steadily decreased. In the pot experiments, effects of different mineral supply on day 4 to 18 upon the development of five barley cultivars of various earliness were investigated. The effect of earliness on fresh weight production was largest when mineral supply on day 4 to 18 was limited. The influence of limited mineral supply on day 4 to 18 on K‐economy was independent of earliness of the cultivars. The maximal N‐content was reached at the same time as maximal fresh and dry weight in fairly late cultivars; in early cultivars maximum N‐level was reached later than maximum fresh and dry weight. Overall, maximal N‐content was higher in the fairly late cultivars than in the early cultivars. The highest rate of 15N‐transport was attained later in two of three fairly late cultivars than in early cultivars. Partitioning of dry weight, N and K in the shoots changed during ageing, ears being an important sink. Varietal differences in partitioning depended on the earliness of the cultivars. The largest fraction of recently supplied 15N, supplied as nitrate, and K+ (86Rb) were found in the stems. In the oldest plants of the early cultivars the transport to the ears of these isotopes was gradually impaired, reflecting the decreasing function of the long distance transport system.
Cytokinin‐induced retention of chlorophyll in senescing barley leaves: Complexity of dose response
Authors: Schistad Ingvard J. , Nissen Per
Published: April 2006

Detailed dose‐response curves were obtained for cytokinin‐induced retention of chlorophyll in detached leaves of barley, Hordeum vulgare L. cv. Møyar, over a wide range, 10−10– 2.5 × 10−4M, of external concentrations of benzyladeninc or kinetin. The over‐all shape of the curves was log‐linear and the response was subsensitive. Benzyladenine was somewhat more effective than kinetin. In the curves there were pronounced local minima and maxima both at low, intermediate (10−7– 10−5M) and high concentrations. At low and high concentrations these deviations from the best smooth curves were reproducible, statistically significant and occurred at the same concentrations for benzyladenine and kinetin. In the intermediate range the deviations from the log‐linear line were marked and statistically highly significant in some but not all experiments. The cause of the complexities in the dose response curve is not known, but multiphasic uptake of the cytokinins may be involved.
Development of pH sensitivity of sucrose uptake during ageing of Vicia faba leaf discs
Authors: Lemoine Remi , Delrot Serge , Auger Evelyne
Published: April 2006

Uptake of [U‐14C]‐sucrose (40 mM) by fresh and aged peeled leaf discs of broad bean (Vicia faba L. cv. Aguadulce) has been studied. In fresh discs, uptake was nearly insensitive to external pH, whereas the pH response of absorption in discs aged for 12 h was bell‐shaped, with an optimum between pH 5 and 6. At this pH, uptake was nearly twice that in fresh tissue. The passive (insensitive to carbonyl cyanide m‐chlorophenylhydrazone and to cold treatment) uptake was the same in fresh or aged discs. The development of pH sensitivity of absorption did not appear when ageing was performed in the presence of 10−HM cycloheximide or 5.7 × 10−5M actinomycin D. Similarly, when the tissues were treated with 10−3M spermidine for 2 h after excision and then aged for 10 h, the development of the pH‐sensitive uptake system was inhibited. Ca2+ (10−2M) supplied together with spermidine prevented the inhibiting effect of spermidine. The appearance of the pH‐sensitive system was also markedly reduced if ageing took place in the presence of 10−3M aminoethoxyvinylglycine. Autoradiographs from fresh discs and from discs aged with or without the inhibitors suggest that pH sensitivity developed more intensively in the parenchyma than in the veins.

The results suggest some caution when using excised leaf discs for studies on sucrose uptake and phloem loading. Development of pH sensitivity of uptake may require the synthesis of both DNA‐dependent RNA and protein and could be related to ethylene metabolism.
Phosphorus nutrition of barley, buckwheat and rape seedlings. II. Influx and efflux of phosphorous by intact roots of different P status
Authors: Schjørring Jan K. , Jensén Paul
Published: April 2006

Seedlings of barley (Hordeum vulgare L. cvs Salka and Zita), buckwheat (Fagopyrum esculentum Moench) and rape (Brassica napus L. ssp. napus cv. Line) were raised at 8 or 10 different extenral P concentrations in the range 0–2000 μM. Apart from P, the nutrient solutions were complete. Phosphate influx in roots of different P status was determined by use of a nutrient solution containing 0.1 mM32P‐labelled phosphate. A double labelling technique was used for simultaneous determination of influx (33P) and efflux (32P) of phosphorus by roots of barley and rape with three selected P levels. Flux determinations were also done in presence of a metabolic uncoupler (2,4‐dinitrophenol) and a protein synthesis inhibitor (cycloheximide). Influx of phosphate was maximal at a certin optimal P level of the roots and decreased at both lower and higher P levels. Maximum phosphate influex [μmol (g root)‐−1 h−1] were: rape 4,4, buckwheat 2.2, barley cv. Salka 1.6, barley cv. Zita 1.5. Both Hill plots and plots of the untransformed decreasing phosphate influx vs root P concentrations above the optimal were linear and had high correlation coefficients. The Hill coefficient varied between ‐3.1 and ‐4.2. The decrease of phosphate influx from the maximum to the lowest value at the highest P concentration of the root was 60–70%. Hence, phosphate influex appeared to be regulated through negative feedback by the internal level of phosphorous in the roots. The regulation mechanism seems bascially similar for the three species and may be of an allosteric type. P efflux from roots of low and optimal (with regard to P influx) P status was 15–20% of the simultaneous P influx. Contary to P influx, P efflux increased at high P status and almost eliminated (barley) or halved (rape) net P uptake. 2,4‐Dinitrophenol reduced both P influx and P efflux by low P roots and gave linearly increasing P efflux with increasing root P status. This indicates that P efflux partly occurred by counter transport and ion exchange at the uptake sites, partly by passive P efflux along an electrochemical potential gradient. Phosphate influx was not affected by inhibition of barley root growth with cycloheximide, but P efflux increased considerably.
The role of the chloroplast coupling factor in the inactivation of thylakoid membranes at low temperatures
Authors: Santarius Kurt A.
Published: April 2006

Thylakoids isolated from spinach leaves (Spinacia oleracea L. cv. Monatol) were exposed to variable low temperatures under non‐freezing conditions. After incubation, changes in the activities of several photochemical reactions and physical properties of the membranes were measured at room temperature.

Cyclic photophosphorylation was strictly dependent on the temperature and the electrolyte concentration: decrease in temperature and increase in NaCl concentration enhanced membrane damage. Inactivation of photophosphorylation was accompanied by stimulation of non‐cyclic electron transport, increase in proton permeability and decrease in δpH. When dicyclohexylcarbodiimide was added, the proton gradient became completely restored. The temperature‐ and salt‐dependent breakdown of photophosporylation was closely related to the release of the chloroplast coupling factor (CF1) from the membranes. The addition of Mg2+, very low concentrations of ATP or ADP, or higher concentrations of low‐molecular‐weight polyols prior to temperature treatment prevented thylakoid damage.

The data indicate that inactivation of photophosphorylation of thylakoids at low temperatures is determined to a considerable extent by the cold lability of the CF1. As a consequence, it must be concluded that damage of biomembranes caused by freezing is not due solely to changes resulting from the ice formation but additionally by temperature‐dependent alterations of cold‐labile proteins. Moreover, the data explain the mechanism of non‐colligative cryoprotection of isolated thylakoid membranes.
Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress
Authors: Wample Robert L. , Thornton Robert K.
Published: April 2006

Wample, R. L. and Thornton, R. K. 1984. Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress.

Comparison of drought‐ and flood‐stressed sunflower plants (Helianthus annuus L. hybrid 894) showed some similarities in response but differences in the mechanisms responsible for the responses to stress. Drought–stressed plants showed typical reductions in leaf water potential with increasing stress accompanied by increased leaf resistance. Photosynthesis declined while photorespiration increased after 48 and 96 h of drought stress. A primary reason for reduced photosynthesis in drought‐stressed plants was increased stomatal resistance. No significant 0change in leaf water potential or in leaf resistance in flooded plants was found in this study. However, photosynthesis declined in a manner similar to that in drought‐stressed plants and photorespiration showed only a transient increase at 48 h. Dark respiration was significantly higher at 48 and 96 h but the magnitude of the increase cannot account for the reduction in photosynthesis. Since the photosynthetic rate of flooded plants declined while stomata remained open, an effect at a more fundamental level is suggested and is thought to be related to disruption of carbohydrate transport.
Effect of manganese ions on benzyladenine‐induced growth and chlorophyll synthesis in excised cucumber cotyledons
Authors: Mudliar Anita , Bharti Sudhakar
Published: April 2006

The behaviour of endogenous Mn2+ was studied by electron spin resonance spectro‐scopy during benzyladenine‐induced growth of excised cucumber (Cucumis sativis L. cv. Long green) cotyledons. The level of endogenous Mn2+ was decreased by ben‐zyladenine treatment, most pronounced after 96 h. MnCl2 applied alone promoted chlorophyll synthesis at relatively low concentrations but in the presence of ben‐zyladenine higher concentrations of MnCl2 were required for stimulation of chlorophyll synthesis. A pronounced increase in growth was observed when Mn2+ was applied with benzyladenine at 96 h, when the decline in the endogenous level of paramagnetic Mn2+ was maximal.
Growth and root nodule nitrogenase activity of Pisum sativum as influenced by transpiration
Authors: Visser Ries de , Poorter Hendrik
Published: April 2006

The influence of shoot transpiration on the rates of growth and nitrogen fixation was investigated in Pisum sativum L. cv. Rondo. In short term experiments, rates of transpiration and acetylene reduction of intact plants were measured simultaneously, using air‐tight perspex vessels enclosing the basal part of the nodulated root. In long term experiments, accumulation of dry matter and reduced nitrogen in the plant were determined as well. Transpiration rate changed diurnally and was varied by manipulating the vapour saturation deficit or the flow rate of the air in the growth cabinet. The rate of acetylene reduction declined after subjecting intact plants to high transpiration rates. This decline was accompanied by a desiccation of the root nodules. Dry matter and reduced nitrogen accumulation were not affected by transpiration rate. At low transpiration rate reduced nitrogen content of the root nodules was higher than at high transpiration rate. However, in these nodules the rate of acetylene reduction was not significantly affected. It is concluded that the nitrogenase activity of pea root nodules is insensitive to changes in the flow rate and the organic N concentration of the xylem sap within a wide range of transpiration conditions under the applied growth conditions.
Effect of storage, photoperiod and mechanical scarification on seed germination in Ocimum americanum
Authors: Amritphale Dilip , Mukhiya Y. K. , Gupta J. C. , Iyengar Shamanta
Published: April 2006

Seeds of Ocimum americanum L. display an absolute light requirement for germination. The minimal length of the daily photoperiod required to induce a high germination decreased with increasing seed age, but the length of the photoperiod under potential control of terminal far‐red light inhibition remained unchanged. There was a gradual escape from the far‐red inhibition with increase in the length of the photoperiod. Seeds developed flash photosensitivity after the first 13 h photoperiod. Scarification treatment did not allow the seeds to bypass the light requirement, but it enhanced the germination considerably. Under conditions of natural day length in the field, weakening of the testa by sand may abolish the need for a second exposure to light for most of the seed population, thus rendering them non‐photoperiodic.
Influence of the axis on the development of mitochondrial activity in imbibed black gram cotyledons
Authors: Morohashi Yukio , Matsushima Hisashi
Published: April 2006

The respiration rate of mitochondria from detached Vigna mungo L. cotyledons (without the embryonic axis) doubled during the first day after imbibition, whereas that of mitochondria from attached ones increased by only 50%. Contrary to the respiration rate, the respiratory control ratio was higher in attached cotyledons. The activities of enzymes in the mitochondrial fraction from detached cotyledons increased by about 30% during the first day, while those in mitochondria from attached ones changed little. Cycloheximide did not inhibit the development of mitochondrial respiration in either attached or detached cotyledons, although it almost completely inhibited the incorporation of [14C]‐leucine into mitochondrial proteins. Cycloheximide did not retard the increase in the activities of mitochondrial enzymes in detached cotyledons. It is inferred that the development of mitochondria in black gram cotyledons is brought about by repair or activation of mitochondria present in dry seeds and that the axis affects this repair process.
Effects of nitrate on influx, efflux and translocation of potassium in young sunflower plants
Authors: Pettersson Sune
Published: April 2006

Influx, efflux and translocation of K+(86Rb) were studied in the roots of sunflower seedlings (Helianthus annuus L. cv. Uniflorus) treated with 0–4.0 mM NO3− during a 9 day growth period or a 24 h pretreatment period. Roots treated with high levels of NO3− absorbed and translocated more K+(86Rb) than seedlings treated with low levels of NO3−. The content of K+ in the shoots was, however, higher in seedlings treated with low levels of NO3−, indicating a low rate of retranslocation of K+ in those plants. K+(86Rb) efflux was highest into the low‐NO3− solutions. All effects on K+(86Rb)‐fluxes were more obvious in high‐K plants than in low‐K plants. The results are discussed in relation to the Dijkshoorn‐Ben Zioni hypothesis for K++ NO3−‐uptake and translocation in plants.
Effect of 2,4‐dichlorophenoxyacetic acid on polysomal profiles and polyadenylated RNA in excised tuber tissue of Jerusalem artichoke (Helianthus tuberosus)
Authors: Minocha Subhash C. , Minocha Rakesh , Kahl Günter
Published: April 2006

Dormant tuber tissue of Jerusalem artichoke (Helianthus tuberosus L.) can be stimulated by wounding to initiate RNA and protein synthesis. No DNA synthesis or cell divisions occur unless an auxin is provided. Changes in polysomal profiles and levels of Poly(A)+‐RNA in response to wounding and auxin treatment were studied. Polysomes were isolated at various times after excision and incubation of tissue in the presence or absence of 10−5M 2,4‐dichlorophenoxyacetic acid. Polysomal profiles were studied by sucrose density gradient centrifugation. Dormant tissue contained ribosomes mainly in monosome form. Within 4 h of excision, a significant increase in the polysomal fraction was observed both in control and auxin‐treated tissue. Increases in polysomes continued during the next 20 h. Poly(A)+‐RNA was isolated from total polysomal RNA by oligo(dT)‐cellulose column chromatography. There was a large increase in the amount of poly(A)+‐RNA within 4 h of excision. During the first 43 h of incubation, levels of total polysomal RNA as well as poly(A)+‐RNA in tissue treated with 2,4‐dichlorophenoxyacetic acid were significantly higher than those in controls.
Nutrient translocation pattern and accumulation of free amino acids in rice coleoptile elongation under anoxia
Authors: Menegus Faustino , Brambilla Ida , Bertani Alcide
Published: April 2006

Comparing nutrient translocation to the rice (Oryza sativa L. var. Arborio) shoot during anoxia with the aerobic situation, it was found that anoxia reduced the translocation of K+, phosphorus, Mg2+ and Ca2+ with progressive intensity; Ca2+ translocation was practically zero in the absence of oxygen. The translocation of K+ and phosphorus under anoxia was still considerable and contributed to the maintenance of a high osmotic potential while the blocking of Ca2+ translocation caused a decrease in its concentration in the anoxic coleoptile, possibly favouring high cell wall plasticity in that organ. As anoxia proceeded, amino acids, no longer employed in protein synthesis, accumulated in the coleoptile, reaching spectacular levels [51 mmol kg of tissue‐water)−1] and, after 48 h of anoxia, their contribution to the osmotic potential was 80% of that of K+, as against less than 20% in all aerobic treatments. Anoxia caused a reduction in soluble hexose concentrations which, however, were more than compensated osmotically by the accumulation of amino acids.
Circadian rhythmicity of nitrate reductase activity in barley leaves
Authors: Lillo Cathrine
Published: April 2006

Nitrate reductase (EC 1.6.6.1) activity showed circadian rhythmicity in the first leaf of 8–11 days old barley (Hordeum vulgare L. cv. Herta) plants. Circadian rhythms were found using both the in vitro and in vivo method for testing the enzyme activity. When the light intensity was reduced from 65 to 20 W m−2, the amplitude was smaller and the oscillations were damped sooner. In continuous darkness nitrate reductase activity decreased in a two step process. Three different light qualities were tested which all gave the same results.
Hormone‐like effect of vascular tissue on starch accumulation in stem explants of kale, Brassica oleracea
Authors: Luŝtinec J. , Kaminek M. , Beneŝ K. , Conrad K.
Published: April 2006

Explants of stem pith of kale (Brassica oleracea L. var. medullosa cv. Krasa), cultured for several days on agar medium containing sucrose, accumulate starch. Application of streptomycin, 5‐fluorouracil and other inhibitors indicates that starch accumulation depends on protein synthesis on 80 S ribosomes. If explants derived from plants grown under natural long‐day conditions contained vascular tissue, including cambium, in addition to pith parenchyma, the amount of starch formed in the pith tissue increased up to seven fold when compared with explants without vascular tissue. Similar increase of starch content as caused by vascular tissue was achieved by the addition of kinetin or trans‐zeatin (10 μ) in the presence of 5 μ indole‐3‐acetic acid or 1‐naphthaleneacetic acid. A further three‐fold increase in starch accumulation could be achieved by application of cytokinin and auxin to explants containing vascular tissue. When explants were derived from plants grown under natural short‐day conditions cytokinins and auxins had little or no effect, but vascular tissue enhanced starch formation significantly. The spreading of starch inducing stimulus from vascular tissue (probably from its meristematic region) to the pith parenchyma up to a distance of at least 20 mm was demonstrated. It was concluded that a hormone‐like factor other than cytokinin and auxin was involved in the stimulatory action of vascular tissue. The effects of this factor on protein accumulation and growth in the explants and its possible production by meristematic tissues in vivo are discussed.