bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance and capacity in the thallus of Marchantia polymorpha
Authors: Paszewski A. , Bulanda W. , Dziubiñska H. , Trębacz K.
Published: April 2006

Calculations of the resistance r and capacity c of cell membrances and the resistancer 1 of cell interiors of a community of cells in Marchantia polymorpha L. thalli are presented. These parameters of a multicellular system were determined by the adaptation of methods employed for the calculation of the resistance and capacity of single cells. The obtained results indicate that such a procedure is justified. A generally accepted resistance‐capacity model of the cell was used as a basis for the determination of r, c, and r1 (representing membrane resistance, membrane capacity, and resistance of cell interior, respectively). The calculations were based on measurements of impedance and phase shift within the frequency range of 5 Hz‐1000 Hz. Stainless steel plates were employed as the measuring electrodes; polarization resistance and capacity were determined by separate measurements. The calculations confirmed the assumption that the parameters r, c, and r1 were constant within the investigated frequency range.

The calculations of resistance and capacity for 25 plants were constant within the investigated frequency range. The calculations of resistance and capacity for 25 plants were carried out by four different methods and they yielded results of the order of : r = 0.45 kΩ± 0.15 kΩ, r1= 1.0 kΩ± 0.45 kΩ, c = 11 μF ± 3.5 μF. Circular diagrams of impedance also confirmed the validity of the accepted model within the frequency range of 25–300 Hz.
Effect of triazinone on root growth and gravireaction
Authors: Ogawa Masami , Pilet Paul‐Emile
Published: April 2006

The effects of a synthetic growth promoter, 4‐ethoxy‐l‐(p‐tolyl)‐S‐triazine‐2,6 (1H, 3H)‐dione [TA], on growth and gravireaction of Zea mays L. (cv. LG 11) roots were investigated. In horizontal, intact roots, pretreatment with TA at 4 × 10−4M inhibited the gravireaction. If the pretreated roots were rinsed with a buffer solution before incubation, the TA effect was reduced, indicating that a continuous presence of TA was necessary for its maximal activity. On the other hand, the TA pretreatment (1×10−5, 1×10−4 and 4 × 10−4M) promoted the elongation of these roots. The TA effect was stronger for illuminated roots than for those kept in darkness. TA also decreased the lateral curvature of half‐decapitated roots maintained vertically in light. This indicates that the action of TA could be associated with some growth inhibiting substances produced or released in cap cells.
The effect of ergosterol, ergocalciferol and cholecalciferol on calcium‐controlled peroxidase secretion by sugarbeet cells
Authors: Kevers C. , Sticher L. , Penel C. , Greppin H. , Gaspar Th.
Published: April 2006

Provitamin D2 (ergosterol), vitamins D2 and D3 reduced the calcium‐mediated peroxidase secretion in three types of sugarbeet cells in suspension cultures. Vitamin D2 was the most effective in habituated non‐organogenic cells which were the less sensitive to calcium; provitamin D2 was the most effective in habituated organogenic cells, while normal non‐organogenic cells were equally sensitive to the three types of vitamin D. The calcium ionophore A23187 slightly restricted peroxidase release in all cases, except in the habituated organogenic cells in the presence of calcium where it exerted a promotive effect. The inhibiting effect of vitamin D2 was not counteracted by the ionophore except in this habituated organogenic cell line.
Chlorophyll(ide) forms after partial phototransformation of protochlorophyll(ide) in etiolated wheat leaves
Authors: Klockare Birgitta , Virgin Hemming I.
Published: April 2006

Dark‐grown wheat leaves (TriticumL. cv. Starke II Weibull) were illuminated repeatedly with light flashes giving partial phototransformation of protochlorophyllide to chlorophyllide. After short flashes (e.g. 15 ms red light, 250 W m−2), transforming only a minor part of the protochlorophyllide present, the first more stable chlorophyll(ide) measured ca 15 s after the phototransformation had its absorption maximum in the red around 672 nm. It stayed there during the following 30 min in darkness. After longer flashes (e.g. 125 ms), transforming a larger portion of the protochlorophyllide, the chlorophyll(ide) formed had its maximum absorption more towards 684 nm and shifted to 672 nm during a subsequent period in darkness. Thus, in this case a Shibata shift took place.

The conditions which produce the “stable” 672 nm form, without a Shibata shift, are discussed. The presence of large amounts of non‐transformed protochlorophyllide remaining after the phototransformation seems to be important. Under such conditions it is possible that the Shibata shift is completed within a very short time.

Also the possible existence of two kinds of phototransformable protochlorophyllide is discussed. According to this idea one of the two protochlorophyllide forms produces a chlorophyllide absorbing at 672 nm shortly after phototransformation without having passed a Shibata shift. The other protochlorophyllide form photo‐transforms to a chlorophyllide which proceeds through the Shibata shift.
Low density growth of cells derived from Nicotiana and Petunia protoplasts: Influence of the source of protoplasts and comparison of the growth‐promoting activity of various auxins
Authors: Muller J. F. , Missionier C. , Caboche M.
Published: April 2006

Nicotiana tabacum (cv. Xanthi), N. plumbaginifolia Viviani, N. sylvestris Speg. and Comes and Petunia axillaris× (P. axillaris × P. hybrida) (cv. Mitchell) mesophyll protoplast‐derived cells were able to grow at low densities in chemically‐defined media. Protoplasts of different origins (mesophyll, epidermis, pith, suspension culture) also gave rise to protoplast‐derived cells that were able to grow at low densities. When auxin requirements at low densities were compared for different sources of auxins, IAA was found to be efficient in the same range of concentrations as NAA. This was unexpected since tobacco mesophyll protoplasts cannot be induced to divide when plated at high density in the presence of IAA. Optimal 2,4‐D concentrations for low density growth were higher and clearly pH‐dependent. On the contrary, picloram induced low density growth over a wide range of concentrations suggesting a distinct mechanism of action. These results confirm and extend previous observation on the tobacco mesophyll protoplast and show that the low‐density growth technique has a potential use for the study of the action of phytohormones.
Validity of the multiphasic concept of ion absorption in plants
Authors: Nissen Per , Nissen Øivind
Published: April 2006

Borstlap (Naturwissenschaften 68: 41–43, 1981; Plant Cell Environ. 4: 189–195, 1981) has alleged that the concept of multiphasic uptake of solutes in plants is invalid. This claim is considered in detail and shown not to be justified. Contrary to Borstlap, the concentration‐dependence of uptake cannot be adequately represented by the sum of two Michaelis‐Menten terms and a linear term, or by similar continuous functions, if sufficiently detailed and precise data are used. Published evidence for the multiphasic concept, including the existence of discontinuities and separate uptake and transition sites, remains valid.
The effect of potassium and calcium on cotyledon expansion and ethylene evolution induced by cytokinins
Authors: Green Jerome
Published: April 2006

In the cucumber (Cucumis sativus L. cv. Straight Eight) cotyledon expansion assay, cytokinin‐stimulated ethylene production was separated from cytokinin‐stimulated growth through the use of potassium and calcium salts. Low concentrations of KC1, which dramatically promoted growth induced by cytokinin, inhibited ethylene evolution, while CaCl2 at a concentration that had no effect on growth, strongly promoted the cytokinin‐induced ethylene evolution. In contrast to the growth response, stimulation of ethylene production was not directly related to the presence of potassium or calcium but to their relative concentrations. Concentrations of KCl and CaCl2 which promoted ethylene evolution singly, strongly inhibited it when mixed together. Low rates of exogenous ethylene had no effect on the growth response. Both the growth and ethylene responses were found to be general cytokinin phenomena. Cotyledon respiration was promoted by KC1, CaCl2 and cytokinin, but its stimulation was not correlated with either growth or ethylene production. In the presence of KClm cytokinin‐induced respiration sharply lowered the content of certain sugars during the large growth response and followed KCl uptake. Analysis of KCl uptake showed that its growth promoting synergism with cytokinin was not due to osmotic effects.
Indole‐3‐methanol as an intermediate in the oxidation of indole‐3‐acetic acid by peroxidase
Authors: Sabater Francisco , Acosta Manuel , Sánchez‐Bravo José , Cuello Juan , del Rio José A.
Published: April 2006

During oxidation of indole‐3‐acetic acid catalyzed by horseradish peroxidase, indole‐3‐aldehyde and 3‐hydroxymethayloxindole cease to be produced a few minutes after initiation of the reaction even though IAA is still being consumed. At the same time an increased accumulation of indole‐3‐methanol is observed and the ratio of oxygen to indole‐3‐acetic acid consumed becomes less than unity. Indole‐3‐niethanol can be a substrate for horseradish peroxidase provided that H2O2 is present. In this reaction, indole‐3‐aldehyde but not 3‐hydroxymethyloxindole is formed. H2O2 is not merely an activating agent for the enzyme but also a true oxidant because it is consumed stoichiometrically (1 mol of H2O2 per mol of indole‐3‐methanol) and the reaction is independent of the presence of oxygen. Indole‐3‐methanol is proposed as an intermediate in the process of oxidation of indole‐3‐acetic acid into indole‐3‐al‐denyde, the second step of which requires peroxide as an oxidant.
Enhanced inflorescence development in tomato by growth substance treatments in relation to 14C‐assimilate distribution
Authors: Leonard Maggy , Kinet Jean‐Marie , Bodson Monique , Bernier Georges
Published: April 2006

Inflorescence development in tomato plants (Lycopersicon esculentum Mill., cv. King Plus) grown under a low‐light regime is promoted by exogenous applications of a mixture of N6‐benzyladenine (BA) and gibberellins A4+7 (GA) directly on the inflorescence. The photosynthetic rate of the young mature leaf, which feeds the developing inflorescence, and the proportion of 14C‐assimilates exported from the source leaf are not affected by the growth substance treatment, but the pattern of 14C‐assimilate distribution is altered. Assimilate supply to the treated inflorescence increases concomitantly with a decrease in the 14C import into the apical shoot, reflecting a competition between these two plant parts. The increased assimilate accumulation in the treated inflorescence is apparent 1 day after the first application of BA+GA, and precedes any morphological changes in the reproductive structure. These results are discussed in relation to nutritional hypotheses that regard assimilate supply as limiting for reproductive development.
Induced pore formation in membranes of cortex cells in excised Sorghum roots: its effect on membrane potential and nucleotide leakage
Authors: Lerner H. R. , Denti A. Ballarin , Pradet A.
Published: April 2006

Measurements of membrane potentials were used for screening various molecules capable of inducing pore formation in cellular membranes for their ability to penetrate into excised roots of Sorghum bicolor (L.) Moench.

Poly‐l‐lysine (30 000 MW) and amphotericin B did not affect cortical cells even though they affected epidermal cells; the lysine polymer and the amphotericin B micelle were apparently too large to diffuse into the roots. Polymyxins and filipin depolarized the epidermal cells as well as the cells of the cortex. Depolarization of cortical cells by filipin was slower than that by polymixins.

Leakage of adenylate nucleotides was measured to obtain information concerning the size of the pores induced by polymyxins. Incubation with 200 μg/ml polymyxin B caused leakage of ATP from root segments. Leaked nucleotides were found in the medium; however, with time they were dephosphorylated, presumably by cell wall phosphatases. In situ ATP formation was observed when root segments were incubated with polymyxin, ADP, Pi, succinate and glucose, confirming that the induced pores were larger than the size of a nucleotide.
Kinetics of indole acetic acid‐induced growth in hypocotyl sections of Vigna mdiata
Authors: Bouchet Marie‐Hélène , Prat Roger , Goldberg Renée
Published: April 2006

The kinetics of auxin‐induced elongation of segments from Vigna radiata (L.) Wilczek hypocotyls have been investigated using auxanometer measurements. Doseresponse curves were established for several well‐defined parameters of the growth response. The experimental data revealed that different kinetic parameters were affected differently by increasing auxin concentrations. The dose‐response curves are slightly sigmoid for fresh weight, nearly bell‐shaped for total elongation or maximal elongation rate, and nearly linear for maximal growth acceleration. The effects of auxin concentration on regulation of growth orientation are discussed.

A biphasic response is observed mainly with segments taken from the middle of the hypocotyl (‘C’) which exhibit maximal growth rates. Segments from other levels, with lesser growth potentials, exhibit a very weak response. The two successive phases may then require different maturation states. Kinetics of the acceleration curves are very similar all along the hypocotyl and remain very homogeneous with increasing IAA concentrations.
Long‐term effects of low levels of SO2 on bean plants (Phaseolus vulgaris). I. Immission‐response pattern of net photosynthesis and transpiration during life‐long, continuous measurements
Authors: Saxe Henrik
Published: April 2006

The immission‐response effect of five low levels of sulfur dioxide on net photosynthesis and transpiration was studied during continuous measurements in near‐complete life cycles of whole bean plants (Phaseolus vulgaris L. cv. Processer) grown in a controlled environment. Sixteen plants were grown in individual water cultures in each of five 100 1 glass assimilation chambers with a new type of exposure system with separate root aeration. SO2 immission ranged from 10 μg m−3 to 950 μg m−3 during 12‐h day‐time exposure periods, five days a week, while a low, natural background of NOx was accepted.

The SO2‐induced photosynthetic reductions were in the short term, but in particular on the long‐term level very closely related with stomatal conductance (significance level better than 0.0005). However, a causal coherence was not inferred. Physiological inhibitions were composed of: (1) A reversible component (night and week‐end recovery) and (2) an irreversible component (related to reduced green leaf area). The pattern of leaf growth was studied, with the conclusion that SO2 reduced leaf area by promoting senescence, rather than by interfering with leaf emergence and development.
Adventitious root formation ‘in vitro’ in apple rootstocks (Malus pumila) I. Factors affecting the length of the auxin‐sensitive phase in M.9
Authors: James David J.
Published: April 2006

The length of the auxin‐sensitive phase of root initiation ‘in vitro’ in the apple rootstock M.9 (Malus pumila Mill.) has been determined using the auxins indol‐3yl‐acettc acid (IAA) at 2.8 × 10−5M and indol‐3yl‐butyric acid (IBA) at 1.5 × 10−5M in the presence and absence of 10−3M phloroglucinol (PG). PG synergised IBA‐induced rooting after 4 days exposure, but contact times exceeding 8 days decreased root number. In contrast, PG consistently synergised IAA‐induced rooting in the dark for contact periods up to 13 days with the highest rooting being recorded at 9 days. An irradiance of 20 W m−2 from fluorescent lamps halved IAA‐induced rooting irrespective of the presence or absence of PG. The culture of shoots at temperatures of 22,25 and 29°C during the root initiation phase (auxin present) and the root emergence phase (auxin absent) produced no difference in rooting response. In the presence of PG the use of liquid culture in place of agar‐solidified culture during the auxin‐sensitive phase reduced root number but not rooting percentage.
Adventitious root formation ‘in vitro’ in apple rootstocks (Malus pumila) II. Uptake and distribution of indol‐3yl‐acetic acid during the auxin‐sensitive phase in M.9 and M.26
Authors: James David J.
Published: April 2006

During the auxin‐sensitive phase of root initiation, rates of 3‐indolyl‐ [2‐14C] acetic acid (IAA) uptake into the 1 cm bases of shoots of the apple rootstock M.9 (Malus pumila Mill.) ‘in vitro’ were not significantly affected by the presence of 10−3M phloroglucinol (PG) using either liquid or agar‐solidified media. The use of a liquid medium did however reduce rates of uptake over a 10‐day period of auxin application. The distribution of labelled IAA between the 1‐cm base and the shoot remainder was not affected by PG.

Exposure of shoots of the difficult‐to‐root M.9 and the easy‐to‐root M.26, to 2.8 × 10−5M IAA containing [2‐14C] IAA revealed no positive correlation between the amount of label taken up by the 1‐cm base and rooting performance. M.9 bases absorbed almost twice as much label as M.26 after 9 days but had produced only one‐third as many roots. Measurements of label distribution between the 1‐cm base and the shoot remainder showed that less than 10% of the label moved to the shoot remainder over a 6‐day period of auxin application. Dose‐response curves of IAA and rooting over the range 1 × 10−5M and 3 × 10−3M showed that root number in M.9 was at an optimum at 1 × 10−3M IAA after 6 days whilst M.26 required only 1 × 10−4M for a similar response. These data support the hypothesis that differences in rooting of the two rootstocks reflect differences in the endogenous metabolism of exogenous IAA and not differences in its rates of uptake or distribution in the shoots.
A cytokinin complex from the developing fruits of Aegle marmelos
Authors: Ghosh A. K. , Nagar P. K. , Sircar P. K.
Published: April 2006

Following ion‐exchange, Sephadex LH‐20 and paper chromatography of the methanolic extracts of young, developing fruits of Aegle marmelos Correa, cytokinin‐like activity in the soybean callus assay was detected in six fractions. Of the four butanol‐soluble compounds, two were tentatively identified as zeatin and zeatin riboside, and the others as zeatin glucoside and zeatin riboside glucoside. The major cytokinino of the butanol‐insoluble fraction is probably zeatin nucleotide. The levels of compounds with cytokinin‐like activity were high during the early phase, and low in the subsequent period of fruit growth. The activity resembling that of cytokinin glucoside increased with maturation of the fruit. The content of free cytokinins in the fruits was more than that released from the tRNA.
Characterization of ferric reducing activity in roots of Fe‐deficient Phaseolus vulgaris
Authors: Bienfait H. F. , Bino R. J. , van der Bliek A. M. , Duivenvoorden J. F. , Fontaine J. M.
Published: April 2006

Iron‐deficient bean plants (Phaseolus vulgaris L. cv. Prélude) exhibited a ferric reducing activity in the roots, with kinetics characteristic for matrix‐bound enzymes: the reaction rate was proportional to substrate (Fe‐EDTA) concentration until 100 μM, and at higher concentrations it leveled off to a maximum; the Lineweaver‐Burk plot yielded a non‐linear relationship between rate −1 and substrate −1. The Arrhenius plot yielded apparent activation energies which were dependent on substrate concentration. No evidence was obtained for the secretion by roots of a low molecular weight metabolite involved in the reduction of iron prior to its uptake. The results are interpreted to indicate that the ferric reducing activity in the roots of iron‐deficient bean plants is located in an enzyme in the plasmalemma of the cortex or epidermis cells.
Further studies in flood tolerance of Betula papyrifera seedlings
Authors: Tang Z. C. , Kozlowski I. T.
Published: April 2006

Flooding of soil for 60 days drastically reduced height growth, cambial growth, dry weight increment, and relative growth rate of 150‐day‐old Betula papyrifera Marsh. seedlings. Comparisons of responses to flooding of 150‐day‐old and 230‐day‐old seedlings indicated important differences between the two age classes. Whereas the younger seedlings produced abundant adventitious roots on submerged portions of stems, the older seedlings did not. Flooding also induced much more leaf abscission in the older seedlings. Flooding generally reduced root‐shoot ratios of both age classes, largely as a result of inhibition of growth and decay of root systems. However, root‐shoot ratios were altered appreciably by formation of adventitious roots in the younger seedlings and by extensive leaf abscission in the older seedlings.
Thylakoid differentiation in endocyanelles
Authors: Marten Sabine , Stamm Reinhard , Brandt Peter
Published: April 2006

Cyanophora paradoxa Korshikov synchronized autotrophically in a light‐dark regime of 14 h light and 10 h dark divides in the last two hours of the dark period. The division rate of the free‐living blue‐green alga, Synechococcus leopoliensis Raciborski, at identical culture conditions (24°C; 32 W m−2) is only slightly lowered in the light period. The comparison of thylakoid differentiation in the endocyanelles of Cyanophora paradoxa and in Synechococcus leopoliensis during the light‐dark regime yields (1) the same ensemble of pigment‐protein complexes in both organisms, (2) comparable syntheses of chlorophyll and phycobilins of Cyanophora paradoxa grown under 32 W m−2 and of Synechococcus leopoliensis grown under light intensities below 9.2 W m−2, and (3) identical photosynthetic oxygen evolution during the light period of the light‐dark regime with minima at the beginning, in the middle (6th–7th h), and at the end of the light period. In both organisms this stage‐specific oxygen evolution is inhibited by treatment with chloroamphenicol. Cycloheximide, however, causes no significant alterations. Results are discussed in view of the endosymbiotic theory.
Effect of fertilization level on some physiological, morphological and growth characteristics of Ficus benjamina
Authors: Ceulemans R. , Gabriëls R. , Impens I.
Published: April 2006

Young Ficus benjamina L. (weeping fig) plants were grown in perlite under low photon flux density regime in the greenhouse. Influence of seven fertilization levels – ranging from nutrient deficiency to saline conditions – on photosynthetic, morphological and growth characteristics was studied. The compensation point for photosynthetic photon flux density was minimal and the quantum efficiency of photosynthesis was maximal at a fertilization level with an electrical conductivity of 1.75 mS. Dark respiration was not affected by the level of fertilization. Chlorophyll content per unit leaf area increased while stomatal conductance slowly decreased with increasing fertilization level. Growth expressed in terms of either height, total dry weight or total leaf area attained an optimum at 1.75 mS, i.e. at the level where the compensation point for photon flux density and the quantum efficiency of photosynthesis were optimal. Leaf size and visible quality decreased at higher fertilizer levels.
Growth, photosynthesis and assimilate partitioning in Lolium temulentum exposed to chilling temperatures
Authors: Pollock Christopher J. , Lloyd Eric J. , Stoddart John L. , Thomas Howard
Published: April 2006

Vegetative plants of Lolium temulentum L, grown at 20°C with an 8 h photoperiod were transferred to either 5 or 2°C (8 h photoperiod) at 4th leaf maturity. Measurement of dry weight gain indicated a marked decline in relative growth rate below 5°C, with growth being reduced as much between 5 and 2°C as between 20 and 5°C. This reduction was not associated with increased mortality and was reversible if plants were returned to 20°C. Tissue explants from cold‐treated plants retained the ability to extend if returned to 20°C Rates of extension in explants were less temperature sensitive than the relative growth rates observed in intact plants. Measurements of photosynthetic capacity, and of the patterns of accumulation of reserve carbohydrate in plants exposed to different temperatures, suggested that the inhibition of growth caused by chilling is not caused by an inability of the plants to fix sufficient carbon.
Effects of agar brand and concentration on the tissue culture medium
Authors: Debergh P. C.
Published: April 2006

In tissue‐cultured Cynara scolymus L. (globe artichoke) vitrification (hyperhydric transformation) can only be overcome by increasing the concentration of agar. However, with increasing concentrations of Difco Bacto agar (8–15 g/I) the availability of labelled kinetin is decreased. There is some evidence for postulating that cytokinins under inductive conditions of low agar concentration or high matrix potential are evocators of vitrification.

Both the brand and concentration of agar also affect the chemical and physical characteristics of a culture medium.

Impurities introduced with the agar are responsible for significant differences in the concentration of an element in comparable media with different levels of agar, and are easily detected by conductance.

Penetrometer measurements also show large ranges in solidity of media with increasing concentrations, not only within the type of agar, but also for the same concentration within different brands.
The relationship between Rb+ influx and K+‐stimulated Mg2+‐ATPase activity in oat roots of different K+ status flexible coupling?
Authors: Lundborg Tomas , Jensen Paul , Kylin Anders
Published: April 2006

The relationship between Rb+ influx and microsomal ATPase activity stimulated by K+ and Mg2++ K+ was investigated for roots of 7‐day‐old seedlings of oat (Avena sativa L., cv. Brighton). Different concentrations of K+ in the roots, K+root were produced by cultivating plants in complete nutrient solutions of different dilutions and dFifferent K+ concentrations at various temperatures. Experiments were performed in both light and darkness. The range of the influx/ATPase ratios was large with a factor of 5 or more between the highest and lowest values. In most cases, the highest ratios were obtained at low K+root and at high temperatures, and the lowest at high K+root and at low temperatures. At high temperatures (20 and 25°C) in the light, the influx/ATPase ratio was constant, independently of K+root, if K+ in the medium was kept constant but the bulk of the nutrient solution diluted. If K+ was varied and the other components of the medium kept constant, the normal relation of decreasing influx/ATPase ratio at increasing K+root was found; thus, Rb+ influx appears regulated by both the internal and external potassium conditions. Also in darkness, at 15°C and with K + in the medium varied, the influx/ATPase ratio was independent of K+root but in the corresponding light experiments, ratio and K+root had the normal, inverse relationship. The difference between light and dark conditions appears to indicate that growth rate is of importance for the relationship between energy input and transport. Our data lead to the concept of “flexible coupling” between transducers) of energy and ion carrier. Without excluding other possibilities, this may be one of the mechanisms for ecological adaptation to variations in the root medium.
Calmodulin dependent formation of membrane potential in barley root plasma membrane vesicles: A biochemical model of aluminum toxicity in plants
Authors: Siegel Neal , Hang Alfred
Published: April 2006

Micromolar concentrations of aluminum ions interfere with calmodulin‐stimulated, membrane bound ATPase activity which plays a role in the maintenance of the transmembrane potential of plasma membrane enriched vesicles isolated from barley roots. Calmodulin appears to be the major target for aluminum interaction resulting in pronounced changes in the exposure of a large, hydrophobic surface on this protein as determined with a fluorescent, hydrophobic surface probe. At a molar ratio of 3:1 [aluminum]/[calmodulin], the calmodulin stimulated enzymatic activity, probably associated with a Ca2++ Mg2+ATPase, is about 95% inhibited. Aluminum induced changes in calmodulin structure are reflected in reduced formation of the membrane potential when assayed with a fluorescent potential probe, oxonol VI. We hypothesize that the aluminum caimodulin complex represents a primary lesion in toxic responses of plants to this metal.
Effect of temperature on drought resistance and growth of cotton plants
Authors: Loffroy O. , Hubac C. , Vieira da Silva J. B.
Published: April 2006

In cotton plants (Gossypium hirsutum L. cv. B.J.A.) the temperature of the roots affected both root and shoot growth, as did the temperature of the shoot. Drought resistance increased when the temperature imposed on roots (27°C) was lower than that imposed on shoots (17°C); the result was a decrease in both transpiration and flow of root sap. Stomatal characteristics as measured by density, index and resistance, depended only on shoot temperature. Differences in drought resistance, depended only on shoot temperature. Differences in drought resistance seem to be a result of changes in transpiration flow modulated by the amount of absorbed water.
Current concepts on the role of potassium in stomatal movements
Authors: Outlaw W. H.
Published: April 2006

A stoma opens when the surrounding guard cell pair increases in turgidity. The increase results from active accumulation of potassium in the guard cell vacuole. The intracellular compartmentation of potassium evokes compensatory accumulation of a yet‐unidentified solute in the guard cell cytoplasm. The source of potassium is other epidermal cells; this indicates that stomatal movements in situ are under control of these cells also. Presumably, guard cell potassium uptake, which is from the apoplast, is mediated by a proton ‐extruding ATPase on the guard cell plasmalemma. The energy source is. oxidative phosphorylation and, to a lesser extent, photosynthetic electron transport. Except for high flux capacity and different responses to applied chemicals, potassium uptake by guard cells is similar to potassium uptake by other plant cells.
Electrical activity of the liverwort Conocephalum conicum: The all‐or‐nothing law, strength‐duration relation, refractory periods and intracellular potentials
Authors: Dziubińska H. , Paszewski A. , Trębacz K. , Zawadzki T.
Published: April 2006

The characteristics of the potential changes caused by excitation of the thallus of Conocephalum conicum L. were investigated and compared with the basic criteria of an action potential. Electrical stimulation (square DC pulses) was applied, and extraand intracellular potentials were recorded. The all‐or‐nothing law, strength‐duration relation, refractory periods, and general characteristics of the changes of transmembrane potential difference were examined. The electrical phenomena occurring during the excitation of Conocephalum fulfil the basic criteria of an action potential. The results contribute additional evidence for the hypothesis that action potentials occur both in plants and in animals.
Influence of spectral quality on the growth response of intact bean plants to brassinosteroid, a growth‐promoting steroidal lactone. I. Stem elongation and morphogenesis
Authors: Krizek Donald T. , Mandava N. Bhushan
Published: April 2006

The growth response of bean (Phaseolus vulgaris L. ‘Pinto′) plants treated with 5 μg of brassinosteroid (BR) in the bean second‐internode assay was measured in a controlled environment under 3 radiation sources: cool white fluorescent (CWF), far‐red (FR) fluorescent and incandescent (INC) lamps. Growth comparisons were made under equal levels (90 μmol s‐1 m‐2) of photosynthetic photon flux density provided by CWF or INC lamps and equal levels of far‐red (28 W m‐2, 700–800 nm) radiation provided by the same INC or FR lamps. Treatment of the second internode with BR produced a sequential increase in elongation, curvature, and swelling under normal bioassay conditions (CWF lamps), as observed previously with brassins. In addition, BR induced marked splitting of the treated internode provided that ample photosynthate was available. Spectral quality had a differential effect on internodal elongation. Under CWF lamps, internodes, 6 days after BR‐treatment, were 2–3 times longer than those of controls; under INC or FR lamps they were 30–60% shorter than those of controls. In all cases, BR‐treatment greatly stimulated accumulation of photosynthate in the treated internode, as indicated by fresh and dry weights and stem diameter measurements. This suggests a possible mobilization role for BR in the intact plant. Brassinosteroid also partially overcame the natural inhibitory effects of CWF radiation on stem elongation.
Highly purified intact chloroplasts from mesophyll protoplasts of the C4 plant Digitaria sanguinalis. Inhibition of phosphoglycerate reduction by orthophosphate and by phosphoenolpyruvate
Authors: Hallberg Mats , Larsson Christer
Published: April 2006

Purified mesophyll protoplasts from the C4 plant Digitaria sanguinalis were used to prepare intact mesophyll chloroplasts with low cytoplasmic contamination. The procedure involved breakage of protoplasts, differential centrifugation, partition in a dextran‐polyethylene glycol two‐phase system, and Percoll density gradient centrifugation. The final chloroplast preparation contained about 80% intact chloroplasts with a phosphoenolpyruvate carboxylase contamination of 0.2–1% of the original protoplast activity, corresponding to 1–6 μmol 14CO2 fixed/mg Chl h. The purified chloroplasts showed substrate‐dependent oxygen evolution in the range of 40–150 μmol substrate reduced/mg Chl h, with phosphoglycerate or oxaloacetate as substrate. Both reactions were stimulated 1.5 fold by pyruvate and further by addition of the other substrate. These measurements indicated that phosphoglycerate reduction was limited by substrate transport across the chloroplast envelope. Without added substrate, the chloroplasts consumed oxygen via pseudo‐cyclic electron transport in the light. Also this reaction was stimulated by pyruvate.

Phosphoglycerate‐dependent oxygen evolution was inhibited by Pi and by phosphoenolpyruvate to about the same extent with purified chloroplasts, but only by Pi with protoplast extracts. This suggests that phosphoglycerate, Pi and phosphoenolpyruvate share a common carrier, similar to the Pi‐translocator in C3 chloroplasts, and that the lack of inhibition obtained with phosphoenolpyruvate and unpurified chloroplasts is artefactual, possibly due to oxaloacetate formation from added phosphoenolpyruvate and concomitant stimulation of oxygen evolution by oxaloacetate reduction. Furthermore, the results suggest that phosphoenolpyruvate is transported with a Km similar to that of Pi in C4 mesophyll chloroplasts.
Studies of diurnal variations of nitrate reductase activity in barley leaves using various assay methods
Authors: Lillo Cathrine
Published: April 2006

The in vitro and various modifications of the in vivo assay for nitrate reductase have been compared in order to elucidate their usefulness in studies of diurnal variations of enzyme activity in barley leaves (Hordeum vulgare L. cv. Herta). Generally, activity was low in the morning and increased rapidly during the first hours of the photoperiod. In the in vivo assay the leaf tissue was vacuum‐infiltrated, whereafter either N2 was bubbled through the assay buffer (anaerobic assay), or no N2 was used (aerobic assay). Activity was 2–25 times higher in the anaerobic than in the aerobic assay. Anaerobiosis enhanced activity most during the dark period when the nitrate reductase level was low. Aerobic in vivo activity usually showed a more rapid decrease towards the end of the light period than did anaerobic activity. Addition of glucose and/or nitrate to the in vivo assay buffer usually stimulated activity more in the aerobic than in the anaerobic assay. In the morning, at the end of the dark period, these additives stimulated activity by 20–400% depending on growth and assay conditions. Later in the day stimulation was usually less, and even a slight inhibition was observed when only nitrate (0.1 M) was added. The effect of these additives on the activity patterns determined was to dampen the oscillations. The additives were therefore not advantageous when testing diurnal variations. However, when the plants were grown under relatively poor light conditions it was necessary to add nitrate and glucose to the aerobic in vivo assay buffer since activity was otherwise too low to be measured. The in vitro assay gave about 5 times higher activity than the anaerobic in vivo assay. During the last part of the dark period in vivo activity (without glucose and KNO3 in the assay buffer) decreased while in vitro activity remained constant.
Differences in phytochrome action on the formation of carotenoids and quinones during chloroplast development in seedlings of barley (Hordeum vulgare)
Authors: Kleudgen H. K. , Grumbach K. H.
Published: April 2006

The influence of phytochrome on the light induced formation of carotenoids and quinones was investigated using etiolated seedlings of barley (Hordeum vulgare L. cv. Villa). The biosynthesis of both the quinones and the carotenoids was enhanced by active phytochrome, but the formation of the individual carotenoids and quinones was influenced by quite different thresholds. In both younger and older plants the biosynthesis of β‐carotene, lutein and violaxanthin was promoted by a low Pfr threshold. The formation of plastoquinone‐9, plastohydroquinone‐9, α‐tocoquinone and phylloquinone was also influenced by a low Pfr threshold. The biosynthesis of zeaxanthin and neoxanthin required a much higher amount of Pfr. Only antheraxanthin‐likeα‐tocopherol, desmethylphylloquinone and, in older leaves, α‐tocoquinone exhibited a complete reversibility of the phytochrome action in their biosynthesis. The effect of phytochrome on the biosynthesis of carotenoids and quinones was different in seedlings of different age.
Kinetics of the reactivation of the Hill reaction in CO2‐depleted chloroplasts by addition of bicarbonate in the absence and in the presence of herbicides
Authors: Snel Jan E. H. , van Rensen Jack J. S.
Published: April 2006

In isolated broken chloroplasts photosynthetic electron transport requires the presence of CO2 and/or bicarbonate. This bicarbonate effect on electron flow was measured in a medium containing 100 mM sodium formate. In this medium a dark incubation time with bicarbonate is required for the reactivation of the Hill reaction. We have measured the kinetics of the reactivation of electron flow by varying the dark incubation of CO2‐depIeted pea (Pisum sativum L., cv. Rondo) chloroplasts with bicarbonate. The half‐time of this reactivation appears to be 25 s when 2 mM bicarbonate is added.

The dinitrophenol herbicide, i‐dinoseb, is shown to be a competitive inhibitor of the bicarbonate dependent Hill reaction with an inhibitor constant (Ki) of 31 nM. In the presence of 100 nM i‐dinoseb or 100 nM DCMU the half‐time of the reactivation by 2 mM bicarbonate appears to increase to about 58 s. We provide an explanation for these phenomena by analyzing the bicarbonate‐thylakoid interaction on the basis of a simple reaction scheme. The binding of bicarbonate to the thylakoids appears to be a second order reaction with pseudo‐first order kinetics. According to our analysis, any inhibitor, which is competitive with respect to the bicarbonate stimulation of the Hill reaction, should increase the half‐time of the reactivation of the Hill reaction.
Three‐phase extraction and partitioning with the aid of dialysis – a new method for purification of indolyI‐3‐acetic and abscisic acids in plant materials
Authors: Liu Si‐jiu , Tillberg Elisabeth
Published: April 2006

A three‐phase partitioning method to separate indolyl‐3‐acetic acid (IAA) and abscisic acid (ABA) from a crude plant extract was developed and evaluated. The aqueous phase at pH 2.7 of a methanolic plant extract constituted the 1st phase, from which IAA and ABA were transferred via diethyl ether, the 2nd phase, to a 3rd phase consisting of an alkaline buffer, enclosed in a dialysis tube. Partitioning of the free forms of the two hormones among the three phases in one container were carried out simultaneously and efficiently. The method also proved to be satisfactory when used as a combined step for both extraction and partitioning, at which the plant homogenate in buffer at pH 2.7 constituted the 1st phase. The content of IAA and ABA in kernels of Zea mays and in hypocotyls of Beta vulgaris were tested with the new method. The method presented is reliable and time‐saving, and the demand for chemicals is less than for most of the conventional procedures used.
Action spectra for the blue and near ultraviolet reversible photoreaction in the induction of fungal conidiation
Authors: Kumagai Tadashi
Published: April 2006

Induction of conidiation in Alternaria tomato (Cke.) Weber and Helminthosporium oryzae V. Breda de Haan was repeatedly controlled by ulternating doses of near ultraviolet light and blue light. These fungi did not form conidia in total darkness. However, when dark‐grown colonies were exposed to near altraviolet light, conidiophore formation was induced, and conidia were then produced upon return to darkness. Conidiation was inhibited by blue light applied immediately after near ultraviolet light. Furthermore, the final response depended on the last kind of light received. The action spectrum for induction of conidiation showed a peak near 300 nm with a shoulder between 310 nm and 330 nm, as is common in photoconidiation of various fungi. The action spectrum for the reversion of induction of conidiation showed a peak near 447 nm with a shoulder between 400 nm and 440 nm, one minor peak around 478 nm and another one near 385 nm. This is very similar to the spectrum for the ubiquitous blue light receptor (cryptochrome).
Iron phosphate precipitation in Murashige and Skoog media
Authors: Dalton C. C. , Iqbal K. , Turner D. A.
Published: April 2006

Murashige and Skoog revised medium, a standard plant tissue culture medium, precipitated on keeping because iron was ineffectively chelated. Most of the precipitate formed after two days and analysis indicated that it was predominantly iron phosphate. It was found that, after precipitation, the supernatant medium had lost c. 45% of its original iron, 20% zinc and 13% phosphate. The following modifications prevented precipitation: lowering the pH to below 3.2, increasing to 3 the molar ratio of EDTA:Fe or preparing the stock solution of FeEDTA with inadequate heating. Most of these modifications had a deleterious effect on the growth and greening of Ocimum basilicum suspension cultures. However, when an increase in the molar ratio of EDTA:Fe was achieved by reducing the iron concentration to one‐third, there was no inhibitory effect on growth or greening of these suspension cultures.
Analysis of the response of leaf extension to chilling temperatures in Lolium temulentum seedlings
Authors: Thomas Howard
Published: April 2006

Lolium temulentum L. plants were grown at 20°C and transferred to 2°C or 5°C at 21, 28 or 35 days after sowing, when leaves 3, 4 and 5, respectively, were at mid‐expansion and leaves 4, 5 and 6 were just emerging. Leaves of plants exposed to 2°C for 7 or 14 days before their date of emergence at 20°C failed to appear at all during the course of the experiment. Transfer to 2°C at emergence resulted in a delay of about 40 days before expansion was detected and subsequent growth was extremely slow. By contrast, although leaves of seedlings exposed to 5°C at or prior to emergence were significantly smaller and slower‐growing than the same leaves of plants maintained at 20°C, the difference in vegetative development and tillering between 2°C and 5°C was much less marked than between 5°C and 2°C, implying the existence of a rather sharp threshold for growth between the latter temperatures. Leaves transferred to 2°C at mid‐expansion attained a final size not very different from leaves exposed to 5°C at the same time, but expension rates were only 20–30% of those at 5°C, and the time taken to achieve full expansion a corresponding 3 to 5 times longer. These responses were quantified by fitting Richards functions to measurements of leaf extension and determining, from the parameters of the curves, asymptotic maximal lengths, mean relative and absolute extension rates, inflexion points and durations of growth. The potential usefulness of Lolium temulentum as a model species for studying the relationship between temperature and growth in the Granmineae is discussed.
Free and bound abscisic acid in relation to water potential in aging cotyledons of Lupinus albus
Authors: Elkinawy Mahasen
Published: April 2006

To evaluate the capacity for biosynthesis of abscisic acid (ABA) in the cotyledons of developing plants of Lupinus albus L. (=L. termis Forssk.) cv. Giza 1, and the physiological role which the compound may perform during senescence, the levels of free and bound forms of ABA have been estimated in conjunction with the natural changes in the water potential of the tissues during a period of 18 days after sowing. In the cotyledons of the dry seeds, the bound form of ABA is about three times as abundant as the free form. Peaks of the free ABA occur on days 3 and 8, when the water potential reaches minimum values of –1060 and –950 kPa respectively. Since the concentration of the bound ABA does not drop during days 1–8, it is suggested that the peaks of free ABA are due to synthesis in the expanding cotyledons in response to the two water potential minima. During the post expansion period (days 9–18), free ABA appears to be released from a bound form as a consequence of decreased synthetic activity and increased tissue deterioration. The remarkable increase in the rate of the dry weight loss which immediately follows each peak of ABA suggests the involvement of ABA in the senescence of the cotyledons by speeding up the translocation of nutrients to the developing axis.
α‐Aminoisabutyric acid, propyl gallate and cobalt ion and the mode of inhibition of ethylene production by cotyledonary segments of cocklebur seeds
Authors: Satoh Shigeru , Esashi Yohji
Published: April 2006

Using cotyledonary segments of cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the inhibitory effect of α‐aminoisobutyric acid (AIB) on ethylene production was compared with that of propyl gallate and CoCl2. Of these inhibitors only AIB was effective in causing the accumulation of endogenous free 1‐aminocyclopropane‐l‐carboxylic acid (ACC) in the tissue. The degree of inhibition of ethylene production by AIB decreased markedly with increasing concentrations of pre‐loaded ACC, while the inhibition by propyl gallate and CoCl2 changed little. Kinetic analysis showed that AIB competitively inhibited the conversion of pre‐loaded ACC to ethylene, but propyl gallate and CoCl2 did not. Short‐chain organic acids and analogues of AIB, such as acetic, propionic, butyric and cyclopropanecarboxylic acids, did not inhibit ethylene production by the segments. Thus, additional support for the competitive mode of inhibitory action of AIB on the conversion of free ACC to ethylene was provided.

A conjugated hydrolysable ACC was found to be present in abundance in cotyledons of this seed. However, its content in the tissue was hardly affected by treatment with the three inhibitors and by administration of exogenous ACC, suggesting that the conjugated ACC was not directly involved in ethylene production.