bluuebunny/crossref_metadata_2025 huggingface dataset:
Pea seedling growth and development regulated by cotyledons and modified by irradiance
Authors: Veierskov Bjarke
Published: April 2006

Growth and development of hydroponically grown pea seedlings (Pisum sativum L. cv. Alaska) were measured using stem and root length as well as number of leaves and lateral roots. The growth was dependent on the presence of cotyledons and was modulated by the irradiance. All plants were grown in a full nutrient solution. If grown at low irradiance (73 μmol m‐2s‐1) they depended more and for a longer time on the cotyledons than plants grown at high irradiance (220 μmol m‐2s‐1). Low irradiance caused stem elongation but decreased root length and number of lateral roots as compared to plants grown at high irradiance. The dark respiration of the leaves was measured as oxygen uptake. In plants grown at the low irradiance, excision of the cotyledons caused the rate of oxygen uptake to increase by a factor of three, and the increase was sensitive to cyanide. Decotyledonized plants showed a high respiration rate and a diminished leaf growth for their entire life cycle. CO2 fixation also increased in decotyledonized pea seedlings grown at either irradiance. The mobilization of food reserves from the seeds was positively correlated to seed dry weight, but only if the plants were grown at 73 μmol m‐2s‐1. Increasing dry weight of the seed enhanced top growth, whereas root growth was depressed, so that top and root responds differently with regard to that part of growth which depends on mobilization of reserves from the seed.
Correlation between respiration and hydrogenase adaptation in Scenedesmus obliquus
Authors: Francis Kolandaiswamy , Senger Horst
Published: April 2006

Full activity of hydrogenase is induced in autotrophic or heterotrophic Scenedesmus obliquus [strain D3 (Gaffron)] cells after 2 h under anaerobic adaptation. Semi‐aerobic conditions allow only an induction of 20% activity. Hydrogenase is completely inactivated by oxygen in cell free preparations. Semi‐aerobic adaptation of hydrogenase is enhanced by glucose and inhibited by sodium azide. It is concluded that respiration enhances hydrogenase activation by creating an oxygen free microclimate and by providing energy in the form of ATP.
Characterization of a novel (±)‐abscisic acid metabolite
Authors: Tietz Dietmar
Published: April 2006

By application of (±)‐abscisic acid and (±)‐[1‐14C]‐abscisic acid to pea seedlings (Pisum sativumL. cv. Kleine Rheinländerin), a new abscisic acid metabolite (Pisumic acid, PISA) could be isolated and structurally characterized by combined gas chromatography‐mass spectrometry. From data of exact mass determination, it is suggested that the metabolite has the tentative structure of 4′‐dihydroabscisic acid with a hydroxylated methyl group at C‐6′. That this could be evidence for an alternative pathway of abscisic acid metabolism which was suggested earlier by Walton et al. [Planta 112: 87–90 (1973)] is discussed.
Comparison of phosphorus mobilization during monocarpic senescence in rice cultivars with sequential and non‐sequential leaf senescence
Authors: Mondal W. A. , Choudhuri M. A.
Published: April 2006

The senescence pattern of the three uppermost leaves of four rice (Oryza sativa L.) cultivars viz. Ratna, Jaya, Masuri and Kalojira was analysed in terms of decline of chlorophyll and by measuring [32P]‐phosphate retention and export from leaf to grains during the reproductive development. With the advancement of reproductive development, the cultivars Masuri and Kalojira showed a sequential mode of senescence, but the cultivars Ratna and Jaya showed a non‐sequential mode of leaf senescence where the flag leaf senesced earlier than the older second leaf. Foliar spraying with benzyladenine (0.5 mM) significantly delayed, and abscisic acid (0.1 mM) accelerated, leaf senescence. In untreated control plants, the second leaf had the highest export of labelled phosphate among the leaves at the grain formation stage (0–7 days) in Masuri and Kalojira. This was compensated by the flag leaf at the grain development stage (7–14 days), whereas export of [32P]‐phosphate was highest from the flag leaf of Ratna and Jaya at the grain development stage. Compared with the control, benzyladenine treatment caused higher retention of [32P]‐phosphate in the leaves and also export to the grains, but abscisic acid treatment gave lower retention and export of [32P]‐phosphate to the grains.

The amount of [32P]‐phosphate export from a mother to a daughter shoot developed in the axil of the second leaf of plants with the panicle removed, was less than that to panicles remaining on control plants of all cultivars. When the panicle had been excised, the greatest export of [32P]‐phosphate took place from the second leaf to the daughter shoot in all cultivars. Excision of the panicle delayed leaf senescence as compared with intact controls and maintained an age‐related leaf senescence pattern in all the four cultivars. The results presented here demonstrate that mobilization of phosphorus from leaf to grains, regardless of cultivar or age and position of the leaf, correlates well with the senescence of that leaf.
Water uptake and storage by rhizosheaths of Oryzopsis hymenoides: a numerical simulation
Authors: Bristow Caryn E. , Campbell G. S. , Wullstein L. H. , Neilson R.
Published: April 2006

Rhizosheaths (sheaths of sand grains that form around the roots of some grasses) are common in perennial grasses that colonise sandy substrates. It has been hypothesised that rhizosheaths increase water availability by increasing the efficiency of water absorption. Others have suggested that rhizosheaths act as storage reservoirs for water. In either case rhizosheaths undoubtedly play an important role in the water relations of these grasses.

In an attempt to evaluate the main function of rhizosheaths, we developed a finite element cylindrical water flow model which enabled us to simulate water uptake by Oryzopsis hymenoides (Roem, and Shult.) Ricker. This model allowed us to estimate total water uptake by root systems with and without rhizosheaths and to compare these values to the extra water stored within the rhizosheath. The results of this study suggest that the presence of rhizosheaths is more important in reducing the total resistance to water flow within the rhizosphere than in enhancing water storage.
Investigations into the possible regulation of negative gravitropic curvature in intact Avena sativa plants and in isolated stem segments by ethylene and gibberellins
Authors: Kaufman Peter , Pharis Richard P. , Reid David M. , Beall Frederick D.
Published: April 2006

Using Avena sativa L. cv. Victory oat seedlings and excised p‐1 stem segments (including the p‐1 and p‐2 internodes) the effect of exogenously supplied ethylene and the removal of ethylene on internodal extension and gravitropic bending was assessed. Similarly, the ability of the excised system to respond to gravistimulation was assessed in the presence of inhibitors of ethylene action (AgNO3) and ethylene synthesis (3,5‐diiodo‐4‐hydroxybenzoic acid and benzyl isothiocyanate; BITC). The production of ethylene from both intact and excised systems was also measured from 0 to 48 h after gravistimulation, relative to vertical controls.

Although gravitropic curvature is initiated, and indeed enters the most rapid phase of upward bending during the first 6 h, there is no difference in ethylene production between vertical and geostimulated plants during this period. The ethylene production of gravistimulated plants rises sharply to a maximum at 24 h, then decreases steeply to almost the control level by 48 h, at which time the rate of upward curvature is diminishing. Neither the addition nor removal of ethylene, nor the addition of inhibitors affecting ethylene‐action (AgNO3) or synthesis (DIHB) influence gravitropic bending or internodal extension in excised segments. Although the ethylene synthesis inhibitor BITC showed down the rate of upward bending, this effect could not be reversed by addition of ethylene. We conclude that the burst in ethylene production that develops in leaf‐sheath bases (pulvini) after they have started to curve upwards is not primary to the induction of curvature. We further suggest that ethylene has no major effect or role in the induction of upward bending after gravistimulation.

The metabolism of high specific activity gibberellin A1 ([3H]‐GA1) in the excised system was assessed during 1, 2 and 4 h of gravistimulation. Changes in endogenous GAs and GA metabolism have been shown previously to be correlated (at the later stages) with gravistimulated bending in intact Avena shoots. The excised segments ‘leaked’ free [3H]‐GAs and [3H]‐GA glucosyl conjugate‐like substances into the bathing medium, and this was a confounding factor. Nevertheless, gravistimulated stem segments, and especially the bottom half of the segment, were significantly less leaky then vertical segments. Thus, just 1 h after gravistimulation, bottom segment halves retained 22% more precursor [3H]‐GA1, 36% more free [3H]‐GA‐like metabolites, and 48% more [3H]‐GA glucosyl conjugate‐like metabolites than vertical segments. In contrast, the 1 h gravistimulated top halves retained slightly less (1–4%) precursor [3H]‐GA and free [3H]‐GA metabolites, but 21% more [3H]‐GA glucosyl conjugate‐like radioactivity than vertical segments.
Action spectrum for fruiting in the basidiomycete Schizophyllum commune
Authors: Yli‐Mattila Tapani
Published: April 2006

An action spectrum for fruit body formation was determined in the range 280–723 nm for a dikaryon of Schizophyllum commune Fr. Action maxima occurred at 280 and 340–360 nm (main peak), and there were minor peaks at 437 and 467 nm. The quantum effectiveness at 360 nm was ca seven‐fold compared to that of 437 nm light. Wavelengths longer than 500 nm were ineffective. Light also induced formation of brown pigment in the area producing fruit bodies. Wavelengths ranging from 260 to 300 nm injured aerial hyphae at the border of the colony. The possibility that a flavin or a pteridine may be the photoreceptor is discussed.
The physiological basis of seed dormancy in Avena fatua. VII. Action of organic acids and pH
Authors: Adkins S. W. , Simpson G. M. , Naylor J. M.
Published: April 2006

Citric, succinic, fumaric, malic, pyruvic and lactic acids induced germination in two genetically pure dormant lines of Avena fatua L. The sensitivity to these acids was low immediately after harvest and increased markedly after a period of dry after‐ripening. Because the acids could only overcome dormancy in partly after‐ripened caryopses, the mode of their action in these caryopses differed from that of another germination promotor, ethanol, and was similar to that of the germination promoter, sodium nitrate. The mode of action of the organic acids on the partly after‐ripened caryopses through lowering pH was indicated by the observation that other non‐metabolic weak acids could also break dormancy while neutral pH value salt solutions of some of the tested acids were inactive. The dose‐response curves of citric acid for the stimulation of germination and for oxygen uptake were similar, indicating that this organic acid may stimulate germination by promoting oxygen uptake. A time sequence study showed that citric acid stimulated oxygen uptake before the first visible signs of germination. Stimulation of germination and oxygen uptake over a range of pH values showed that those values of pH which stimulated germination also stimulated oxygen uptake, indicating that the ability to stimulate oxygen uptake was not confined to organic acids. The stimulation of both germination and oxygen uptake by citric acid was not inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration, therefore stimulation of both germination and oxygen uptake by citric acid does not require the operation of the alternative pathway of respiration. The function of weak acids as promoters of oxygen uptake is discussed with reference to the breakage of dormancy in partly after‐ripened caryopses and the involvement of various respiratory pathways is indicated.
Mechanism of parasitism by Cuscuta reflexa: Distribution of cytokinins in different regions of the parasite vine
Authors: Gupta Anjali , Singh Madhav
Published: April 2006

Cytokinins in the different regions of Cuscuta reflexa Roxb. vine have been extracted and assayed using the Xanthium cotyledon bioassay with N6‐benzylaminopurine as the reference cytokinin. Maximum cytokinin level was found in the haustoria‐bearing region with the gradient decreasing towards the apex. The cytokinin content of the apex was less than 1% of that in the whole haustorial region. Interestingly, the concave half of the vine contained about forty times more cytokinin in the haustorial region than the corresponding convex half. The high concentration of cytokinin or cytokinin‐like substances in the haustoria‐bearing site in Cuscuta might be due either to a high RNase activity in the region or translocation from the host to parasite or both.
Effect of light and benzyladenine on dark‐treated growing rice leaves (Oryza sativa). I. Changes in chlorophyll content and catalase activity
Authors: Reddy K. P. , Kumar K. B. , Subhani S. M. , Khan P. A.
Published: April 2006

Light‐ and benzyladenine‐induced reversal of the changes in chlorophyll content and catalase activity were studied in the attached first leaf of Oryza sativa L. cv. Bala, kept in darkness for different periods before maturation. Dark treatment caused a decrease in chlorophyll content and catalase activity at all times. Light treatment of dark‐incubated seedlings at different periods before maturation reversed the dark‐induced effect on chlorophyll content, catalase activity and dry weight and also caused a further rise in chlorophyll content compared to initial values. In darkness, the application of benzyladenine replaced the light effect in maintaining catalase activity. Chlorophyll content was also maintained by initially applied benzyladenine. Benzyladenine did not promote the photoinduced maintenance and increase in chlorophyll content and catalase activity at any time. Treatment with hydrogen peroxide, glycolate and amizol resulted in an accelerated chlorophyll breakdown and had varied effects on catalase levels. Chlorophyll decrease due to peroxide accumulation was to some extent reversible by benzyladenine, but the hormone had no effect on the peroxide‐induced decrease in catalase activity. Development of catalase is light dependent. Benzyladenine stabilises the enzyme but has no effect on its synthesis.
Distribution of cytokinin‐like activity in different plant parts of the water hyacinth, Eichhornia crassipes
Authors: Nagar P. K. , Saha Shyamali
Published: April 2006

Cytokinin‐like activity in extracts of leaf laminae, petioles, shoots, roots and flowers of young plants of the water hyacinth, Eichhornia crassipes S. was analyzed following Sephadex LH‐20 column chromatography using the soybean callus bioassay. In all plant parts analyzed, two prominent peaks of cytokinin activity having elution volumes similar to zeatin and zeatin riboside were detected. Putative cytokinin gluco‐side‐like activity was detected only in leaves and flowers. The cytokinin complements of the leaves and the roots were qualitatively different. It would appear that cytokinins supplied by the roots are metabolized in the leaves or certain cytokinins are synthesized in the leaves themselves. The possible significance and distribution of cytokinins in different plant parts in relation to roots is discussed.
Nitrate and nitrite reduction by alfalfa root nodules: Accumulation of nitrite in Rhizobium melioti bacteroids and senescence of nodules
Authors: Becana M. , Aparicio‐Tejo P. M. , Sánchez‐Díaz M.
Published: April 2006

Addition of NO−3 rapidly induced senescence of root nodules in alfalfa (Medicago sativa L. cv. Aragon). Loss of nodule dry matter began at the lowest NO−3 concentration (10 mM) but degradation of bacteroid proteins was only detected when nodules were supplied with NO−3 concentrations above 20 mM.

Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate‐induced although substantial enzyme activities were present in the absence of NO−3 Typical specific activities for soluble NR and NiR of bacteroids under NO−3 free conditions were 1.2 and 1.4 μmol (mg protein)−1h−1, respectively. In the presence of NO−3, the specific activity of NR was considerably greater than that of NiR, thus causing NO−2 accumulation in bacteroids. Nitrite levels in the bacteroids were linearly correlated with specific activities of NR and NiR, indicating that NO−2 is formed by bacteroid NR and that this NO−2 in turn, induces bacteroid NiR. Accumulation of NO−2 within bacteroids also indicates that NO−2 inhibits nodule activity after feeding plants with NO−3
Plant seed lectins disrupt growth of germinating fungal spores
Authors: Brambl Robert , Gade Wayne
Published: April 2006

Plant seed lectins are well‐characterized proteins and glycoproteins whose natural function remains unknown. We found that eleven purified seed lectins (representing five groups of lectin sugar specificities) bound to the germ tubes of asexual spores of Neurospora crassa, Aspergillus amstelodami, and Botryodiplodia theobromae. The lectins caused several types of quantifiable growth disruption during germination of these seed‐ or soil‐borne fungal spores, including sensitivity to osmotic lysis, adventitious branching of the spore germ tubes, and inhibition of germ tube elongation. These anti‐fungal effects of purified lectins, which were reversible with the sugar hapten specific for each lectin, were partially duplicated by lectin‐like factors in the homologous crude seed extracts. The seed lectins may disrupt fungal growth by interfering with normal cell wall deposition and assembly.
Changes in steryl lipids of oat root cells as a function of water‐deficit stress
Authors: Liljenberg Conny , Karunen Pirjo , Ekman Rainer
Published: April 2006

Five‐day‐old seedlings of oat (Avena saliva L. cv. Seger) were subjected to water‐deficit stress for two and four periods, each of 24h duration with interjacent rewatering periods of 24 h. After two and tour stress periods the fresh weight/dry weight ratio of the roots was 73 and 74% of the control value, respectively. Two stress periods did not affect the amount or composition of free, esterified and glycosylated sterols (desmethylsterols) or methylsterols (mono‐ and dimethylsterols). After four stress periods the amount of tree sterols increased by 25% on a dry‐weight basis but that of free methylsterols only slightly. The most significant increase (by over 60%) occurred in esterified sterols and methylsterols. The amount of sterols bound as glycosides and acylaled glycosides decreased slightly (by 10%) after four stress periods. The amount of glycosylated methylsterols was negligible and did not respond to water‐deficit stress. Within all component groups the proportions of individual compounds remained unaffected after two and four stress periods. The increase of the sterol levels caused by the stress is discussed in terms of a hormone‐induced synthesis leading to a changed sterol/membrane acyl lipid ratio. This has implications for the chemo‐physical properties of the root cell membranes.
13C NMR determination of sugar levels in storage roots of carrot (Daucus carota)
Authors: Thomas T. H. , Ratcliffe R. G.
Published: April 2006

13C NMR was used to detect sugars in detached fibrous and storage roots of carrots (Daucus carota L. cv. Chantenay Red‐Cored). The relative amounts of sucrose, glucose and fructose in storage roots of two ages and in fibrous roots were similar to those detected by a destructive, enzymatic sugar determination method. In tap roots all three sugars were present with glucose being marginally predominant in 8‐week‐old roots and sucrose being the major sugar present in 12‐week‐old roots. Glucose was the major sugar present in fibrous roots with small amounts of sucrose and no fructose detected. The results indicate that with some instrumental modification, 13C NMR could be used as a non‐destructive method for measuring sugar levels in intact storage root systems during development.
Influence of genotype and culture medium on microspore callus induction and green plant regeneration in anthers of Oryza sativa
Authors: Reddy V. Siva , Leelavathi S. , Sen S. K.
Published: April 2006

Attempts to identify nutritional requirements of anthers of eight indica rice cultvars (Oryza sativa L. spp. Indica) for callus induction in vitro and green plant regeneration were made. The requirements varied with the genotype. Some cultivars, however, possessed a wide range of adaptability to diverse nutritional conditions. Indica rice is highly sensitive to the presence of NH+4, and MgSO4 in the medium. High sucrose concentration (11%) was deleterious for callus induction and green plant regeneration. Sucrose at 3 to 5% was optimal for growth. Auxins at high concentrations promoted regeneration of albino plants. The presence of 2,4‐dichlorophenoxyacetic acid (9.0 μM) supplemented with picloram (0,3 μM) and zcatin (0.5 μM) was effective for callus induction. A combined pretreatment of 35°C for 5 min followed by 10°C for 7 days was most suitable for callus induction and green plant regeneration.
Lipids of Cuscuta reflexa and changes in lipids of its host plants after infection
Authors: Sharma Shobha , Khanna Raj , Sanwal G. G.
Published: April 2006

The lipid level (fresh weight basis) of Cuscuta reflexa Roxb. was related to the lipid content of the host plants Meilicago saliva L., Helianthus annuus L., Pisum sativum L. and Lantana camara L. Parasitizing by the dodder significantly increased the total lipid level of the hosts. The increase was mainly due to enhancement in the neutral lipid fraction.

The level of phospholipid in the parasite was always higher than in its hosts. Phospholidyl choline and phosphatidyl ethanolamine constituted about 65% of the total phospholipid of Cuscuta. This was followed by phosphatidyl inositol (ca 20%) and phosphatidyl glycerol (ca 12%). Phosphatidic acid constituted only ca 3% of the phospholipids of Cuscuta. Although the total phospholipid levels of various host plants were not affected as a result of the infection by Cuscuta, a significant decrease occurred in the levels of phosphatidyl eholine and phosphatidyl ethanolamine as well as marked increases in phosphatidyl inositol and phosphatidic acid. The infected tissue showed an increase in phospholipase D activity as compared with the controls. The results have been discussed in relation to changes in permeability of the infected tissue.
Photosynthesis of Coffea arabica after chilling
Authors: Bauer H. , Wierer R. , Hatheway W. H. , Larcher W.
Published: April 2006

Net photosynthetic CO2 exchange of 1‐year‐old plants of Coffea arabica L. was studied after the above‐ground parts had been exposed once or repeatedly to night temperatures in the chilling range. Chill‐reduced rates of CO2 uptake (measured at 24°C and at natural CO, level) were observed after a 12 h night exposure to about 6°C. After exposure to 4°C, activity was reduced to less than half of that of the controls, and after exposure to 0.5°C the leaves suffered visible necrotic injury and were no longer able to take up Co2 If the leaves were not lethally injured, net photosynthesis recovered completely within 2 to 6 days. About 25% of chill‐induced reduction of CO2 uptake was due to reduced stomatal aperture and 75% to impairment of carboxylation efficiency.

Chilling on successive nights at 4–6°C reduced CO, uptake progressively on each day following treatment. After 10 nights, activity was decreased to less than 10% of initial performance. Conditioning at temperatures slightly above the chilling level (e.g. 15/I2°C) for 2 weeks led to almost complete impairment of photosynthetic activity without additional chilling stress instead of improving chilling tolerance.
Fruit growth and abscission in Macadamia imtegrifolia
Authors: Sakai William S. , Nagao Mike A.
Published: April 2006

Growth in diameter of fruits (follicles) of five cultivate of Macadamia integrifolia Maiden and Betche followed a single sigmoidal pattern. A rapid increase in fruit diameter began 2 to 3 weeks after anithesis and continued until weeks 14 to 16. No further increase in size was observed after 16 weeks. Growth in fresh weight of the two cnltivars observed also followed a single sigmoidal pattern. A rapid increase in fresh weight began 5 to 6 weeks after anthesis and continued until weeks 15 to 18. No further increase in fresh weight was evident after 18 weeks. Abscission of flowers and fruits occurred continuously from anthesis through fruit maturity and could be separated into three periods. The first period of abscission occurred in the first 2 weeks after anthesis and commonly involved over 90% of the flowers. The second period of abscission occurred from 3 to 8 weeks after anthesis and commonly involved over 80% of the initial set of small fruit. This period of abscission occurred prior to and concurrent with the rapid increase in growth. The third period of abscission was gradual and occurred from 9 weeks after anthesis until maturity at 28 to 30 weeks. Measurement of ethylene evolution by fruits showed a peak during weeks 3 and 4. This was prior to the peak in relative abscission rate at week 5. The fruit removal force increased from anthesis through week 12 and decreased from week 24 through maturity.
A fluorescent compound in oat root plasma membrane
Authors: Møller Ian M. , Lundborg Tomas
Published: April 2006

Homogenates of 7‐day‐old oat (Avena sativa L. cv. Brighton) roots were highly fluorescent (excitation and emission maxima around 360 and 440 nm, respectively). Less than 1/10 as much fluorescence per g fresh weight was found in oat shoots or in wheat (Triticum aestivum L. cv. Drabant) roots or shoots. Most of the fluorescence of oat roots was found in the soluble fraction (150 000g supernatant). However, some could be detected in the plasma membrane fraction (excitation and emission maxima 365 and 417 nm, respectively), which contained a 3‐fold higher fluorescence per mg protein than the homogenate.

Growth of oat or wheat in a medium containing, 10‐−5M scopoletin (6‐methoxy‐7‐hy‐droxy coumarin), a fluorescent compound previously reported to be present in both wheat and oat roots, caused the disappearance of scopoletin from the medium (proportional to the amount of roots) and the appearance of increased fluorescence in the root homogenates but not in the shoot homogenates. In both oat and wheat roots ail of the extra fluorescence was recovered in the soluble fraction and at least in wheat it consisted of unconverted scopoletin. The concentration of scopoletin in wheat roots grown in 10‐−5M scopoletin was around 50 nmol (g fresh weight)−1, or about five times the concentration in the growth medium. Scopoletin in the growth medium (10‐−5M) or in the assays (up to 10‐−4M) did not affect Mg2+‐, Mg2++K+‐ or Ca2+‐ATPase activities in wheat or oat roots.

The fluorescence properties of the oat plasma membrane were different from those of authentic scopoletin. Either the surroundings modify the fluorescence of membrane‐associated scopoletin or the endogenous fluorescent compound is not scopoletin but a glycoside‐derivative of scopoletin or some completely unrelated compound.
Extra‐ and intracellular measurements of action potentials in the liverwort Conocephalum conicum
Authors: Zawadzki T. , Trębacz K.
Published: April 2006

Action potentials induced by electrical stimuli were recorded from the thalli of tfie liverwort, Conocephalum conicum L. An analysis of an equivalent circuit of Conocephalum conicum thallus in situ has shown that the multiphasic time course of extracellular recordings is caused by a branching of extracellular conduction layers and by an overlapping of action currents. As compared to the velocity of excitation propagation without short‐circuiting, more than 10 times higher rates of action potential conduction have been recorded when the plants are immersed in a low resistaace solution. Furthermore, simultaneous extra‐ and intracellular recordings from thalli in situ are presented.
Regulation of nitrate and nitrite reduction in barley leaves
Authors: Soares M. Inês M. , Lips S. Herman , Cresswell Cristopher F.
Published: April 2006

Reduction of nitrate and accumulation of nitrite were studied in barley (Hordeum vulgare L. cv. Gars Clipper ex Napier) leaf sections in the dark and in the light, under aerobic (air and mixtures of O2 and N2) or anaerobic (N2) conditions. Oxygen prevented nitrite accumulation but had no effect on accumulated or infiltrated nitrite. Most of the nitrite accumulated under dark‐anaerobic conditions was in the “cytoplasmic” (the cell section between the plasma lemma and the tonoplast) fraction of the tissue. Reduction of nitrate was stimulated by 2, 4‐dinitrophenol in tissue under dark‐air and by 3‐(3′, 4′‐dichlorophenyl)‐l, l‐dimethyl urea (DCMU) and carbonyl cyanide m‐chlorophenylhydrazone (CCCP) in tissue under all environmental conditions studied. Nitrite accumulated in the light in DCMU‐treated tissue under N2 or under aerobic conditions in the presence of CCCP. On its own, CCCP did not promote accumulation of nitrite in leaf sections under light‐air. A model for the reduction of nitrate and nitrite is proposed.
Evidence on the mechanism of enhanced sucrose uptake at low cell turgor in leaf discs of Phaseolus coccinius
Authors: Daie Jaleh , Wyse Roger E.
Published: April 2006

Plants often tolerate water deficits by lowering the osmotic potential of their cell sap. This may be achieved by accumulation of solutes which results in the maintenance of a positive turgor potential. In this study, the effect of water deficit on sugar uptake was investigated in leaf discs of Phaseolus coccinius L. (cv. Scarlet). Evidence is presented that cell turgor affects the kinetics of sugar transport at the membrane level. Uptake kinetics of sucrose, glucose and 3‐O‐methyl glucose by tissues equilibrated in solutions of relatively high (200–400 mOsm) osmotic concentration consisted of a sat‐urable and a linear component. Low external osmotic concentration i.e., high cellular turgor inhibited the saturating component of sucrose uptake, resulting in a linear uptake profile. However, high cell turgor had no effect on glucose or 3‐O‐methyl glucose uptake kinetics. The effect of turgor versus osmotic component of water potential was differentiated by comparing responses to non‐penetrating (manmtol) or polyethylene glycol, (3350) and penetrating (ethylene glycal) osmotica. Changes in sucrose uptake rates and kinetics were due to changes in cellular turgor and not osmotic potential. Furthermore, at low cellular turgor, a net increase in sucrose uptake occurred as a consequence of enhanced influx rates and not as a result of reduced efflux rates. The data are consistent with previous findings that sugar uptake rates are enhanced under low turgor. We present first evidence indicating that the mechanism by which higher rates of sucrose uptake are maintained underwater deficit conditions is by the activation of the saturable transport system. This mechanism supports previous suggestions that changes in cell turgor are sensed and manifested at the membrane level.
Chloroplast protection in greening leaves
Authors: Gillham D. J. , Dodge A. D.
Published: April 2006

Changes in photosynthetic activity, leaf pigments and the activities of enzymes that scavenge damaging oxygen species in chloroplasts were followed during the greening of 8‐day‐old etiolated pea (Pisum sativum L. cv. Meteor) seedlings. Accumulation of chlorophyll and carotenoids was accompanied by development of photosynthetic activity. Carotenoids present in etiolated leaves, and the high ratio of carotenoid to chlorophyll detected during the early hours of greening are suggested to provide important protection against singlet oxygen. Superoxide dismutase, ascor‐bate peroxidase and glutathione reductase, which scavenge superoxide and hydrogen peroxide in chloroplasts, are present at high activities in etiolated leaves and throughout greening. The mechanisms by which developing chloroplasts may generate damaging oxygen species, and the role of these scavengers during greening is discussed.
Short term 22Na+ and 42K+ uptake in intact, mid‐vegetative plants
Authors: Cheeseman John M. , Bloebaum P. D. , Wickens Linda K.
Published: April 2006

Spergularia marina (L.) Griseb. is. a rapidly growing, annual, coastal halophyte. Because of its small size, it is suitable for isotope studies of ion transport well beyond the seedling stage. The purpose of this report is to establish the similarities and differences between 22Na+ and 42K+ uptake in S. marina and in more commonly used mesophytic crop species. Vegetative plants were used 18 days after transfer to solution culture. Plants were grown either on Na+‐free medium or on 0.2 × sea water. 22Na+ uptake was linear with time for several hours. The rate was relatively insensitive to external concentration between 1 and 180 mol Na+ m−3, particularly in Na+‐free plants. Transport to the shoot accounted for 40 to 70% of the total uptake, dependent on salinity but largely independent of time. 42K+ uptake decreased with increasing salinity in Na+‐free plants and increased in 0.2 × sea water plants. Both uptake and transport to the shoot were non‐linear with time, upward concavity suggesting recovery from a manipulative and/or osmotic injury. Steady state root contents were compared with predicted contents based on cortical cell electrical potentials using the Nernst equation. Reasonable agreement was found in all cases except Na+ content of 0.2 × sea water plants, in which active efflux was indicated. Uptake studies conducted in the presence of chemical modifiers (dicyclohexylcarbodiimide, dinitrophenol and fusicoccin) showed responses of 42K+ uptake as expected from studies on agronomic species, and implied the presence of a similar active uptake here despite the appearance of equilibrium. Active Na+ uptake was suggested at low Na+ levels. We conclude that S. marina is a promising experimental system combining the rapid nutrient acquisition strategy of agionomically important annuals with a high degree of salt tolerance.
Phototransformation of oat phytochrome with millisecond and submillisecond flashes: The level of the photostationary Pfr/Ptot ratio is modified by photoreversible intermediates
Authors: Scheuerlein Robert , Sundqvist Christer , Haupt Wolfgang
Published: April 2006

Photoconversion of the red‐absorbing form of phytochrome (Pr) to the far‐red‐absorbing form of phytochrome (Pfr) and vice versa has been measured spectrophotometrically at 10°C in immobilized and soluble phytochrome (118 kdalton), prepared from 5‐day‐old etiolated oat seedlings (Avena saliva L. cv. Sol II). The photostationary equilibrium φ= PfrPtot (with Ptot= total amount of phytochrome Pr+ Pfr) for red light depends on whether it is established by repetitive pulses (≥ 5 s) or by repetitive flashes (≥ 4 ms). In the wavelength region around 660 nm, a lower φ is reached with flashes as compared to that with pulses. This difference becomes negligible if the wavelength is shortened to the 600 nm region, and it also disappears if the fluence of each individual flash is reduced. In contrast, in long‐wavelength red light and short‐wavelength far‐red light, a higher φ is reached with flashes than with pulses.

We relate the differences in φ for flash and pulse irradiation to photochromic systems between Pr and photoreversible intermediates in the phototransformation pathway Pr→ Pfr. Thus, light absorption by phytochrome intermediates can be limiting for the quantitative relationship between light signal and Pfr formed.
Genetic differentiation and phenotypic plasticity in Plantago major ssp major. I. The effect of differences in level of irradiance on growth, photosynthesis, respiration and chlorophyll content
Authors: Kuiper Daan , Smid Albert
Published: April 2006

Growth, root respiration, photosynthesis, dark respiration, chlorophyll content and chlorophyll alb ratio were followed in two genotypes of Plantago major L. ssp major L., originating from an exposed and a shaded habitat, respectively, at two levels of irradiance. In addition, responses of these processes to a transfer of plants from one light condition to the other were studied. Genetic differentiation between the two genotypes was reflected in growth rate, photosynthetic activity, dark respiration and chlorophyll content. Individuals of the genotype originating from a shaded habitat were less inhibited by low irradiance: growth was less depressed at low irradiance, while the genotype of the exposed habitat seemed to be more restricted to exposed conditions. The adaptive plastic response of growth and physiological parameters upon an alteration in irradiance was very small. The shoot to root ratio was a stable plant characteristic in these experiments. Plants of both genotypes were probably damaged after a transfer from the low to the high level of irradiance; the growth of these plants was not stimulated by high irradiance, and the photosynthetic activity was even decreased. Plants, which were transferred to the low level of irradiance, showed an immediate effect of the change and no adaptive response was observed. Obviously, the ability to perform adaptive plastic responses, which was demonstrated in the non‐transferred plants after pretreatment, had been lost during the experiment and was confined to the seedling stage of individuals of the two genotypes.
Esters hydroxycinnamiques et induction photopériodique florale in vitro chez Cichorium intybus
Authors: Badila P. , Paulet P.
Published: April 2006

Hydroxycinnamic acid esters and photoperiodic flowering induction in vitro of Cichorium intybus.

In root tissues of Cichorium intybus L. cv. Witloof cultured in vitro, the photoinductive period occurs between the 8th and the 16th day after the start of the culture. The promotive light conditions are either long days (16 h photoperiod) or daily cycles of 9 h white + 15 h red light applied during the photoinductive period in an otherwise short day treatment. During the photoinductive period and under suitable irradiation conditions, the endogenous hydroxycinnamic acid esters (especially chlorogenic acid) show a regular development as from the 8th day, reaching a maximal level by the 16th day. The amount of these molecules then decreases rapidly, preceding the external expression of floral induction. When we apply non‐inductive conditions [short days (9 h) or daily cycles of 9 h white + 15 h (far‐red + red) light supplied from the 8th to the 16th day in otherwise short day conditions], the metabolic changes indicate the same pattern during the inductive period as mentioned above. However, a fundamental difference exists between the inductive and non‐inductive conditions, so that the production of hydroxycinnamic acid esters is particularly high towards the end of the second week of in vitro development in the induced state. This increase is not primarily due to increased photosynthetic activity in long day conditions, since it occurs both in the long day treatments and in the treatments with daily cycles of 9 h white + 15 h red light, thus revealing the morphogenetic action of light via phytochrome. This accumulation of hydroxycinnamic acid esters is correlated with floral induction, which appears to be ineffective unless there is a certain minimum amount of these molecules in the tissues.
Effect of far‐red light on malate and potassium contents in cotton leaves: Relation to drought resistance
Authors: Hubac Camille , Guerrier Danièle , Bousquet Ulrike
Published: April 2006

Long‐ or short‐term far‐red light given before a dark treatment modified the water status and the potassium and malate contents in cotton (Gossypium hirsutum L. cv. Bou) leaves. Upon a long‐term treatment, the leaf water content and the leaf water and osmotic potentials were lower whereas stomatal resistance was greater with a decrease in daily transpiration. There was a parallel increase in potassium and malate, but the calcium content was not significantly changed. This resulted in better water economy with an increase in drought resistance. Upon a short‐term treatment, the accumulation of potassium and malate was reversible and the drought resistance was modified accordingly. There was a positive correlation between the ability of a plant to resist water stress and the content of potassium and malate.
Effect of nigericin on the H+‐translocating adenosine triphosphatase from tonoplast of Hevea latex
Authors: Marin B.
Published: April 2006

Nigericin stimulated the ATPase activity of tightly‐sealed membrane vesicles prepared from Hevea brasiliensis Müll.‐Arg. lutoïds in the presence of K+. This stimulation required a functioning membrane since it was membrane‐bound and since it was not observed for the ATPase activity solubilized from the tonoplast by dichloromethane. The extent of nigericin‐induced stimulation of tonoplast ATPase was proportional to the ΔpH collapsed by the ionophore in the presence of K+.
Ion supply capacity of roots in relation to rejuvenation of primary leaves in vivo
Authors: Neumann Peter M. , Stein Zipporah
Published: April 2006

Removal of the shoot above the primary node (detopping) of 3‐week‐old bean plants (Phaseolus vulgaris L. cv. Contender) altered the metabolism and development of the remaining leaves. An increase in levels of chlorophyll, protein, stomatal opening, photosynthesis and growth, i.e. rejuvenation of primary leaves, was established within 7 days of detopping. These levels were maintained while the primary leaves of equivalent intact plants senesced.

The flux of xylem solution (mineral ions, cytokinins and water) into leaves is related to the leaf area to be supplied and root supply capacity; it has been suggested that detopping leads to an increased availability of root‐supplied solutes and hence rejuvenation of the remaining leaves. This assumes however that root output of solutes is not decreased by the defoliation treatment.

We found that root output of ions (electrical conductivity of passive xylem exudate) in detopped plants was 30% lower than in intact plants after 24 h and 60% lower after 7 days. The output of Ca2+, Mg2+ and K+ were similarly reduced 7 and 14 days after detopping as were fresh and dry weights of roots. Furthermore, neither the calculated xylem flux of ions nor directly measured levels of Ca2+, Mg2+ and K+ were significantly increased in leaves of detopped plants during their rejuvenation. We therefore conclude that root output is tightly coupled to shoot demand and that the apparent rejuvenation of primary leaves caused by detopping bean plants is not a consequence of increased xylem flux of mineral ions into the leaves.
Primary and secondary induction requirements for flowering in Alopecurus pratensis
Authors: Heide Ola M.
Published: April 2006

The critical temperature for primary induction of flowering in two Norwegian eco‐types of meadow foxtail (Alopecurus pratensis L.) was about 21°C, with 6 weeks induction period. Inflorescence primordia were initiated with increasing effectiveness as the temperature was reduced below this level in both short days (SD) and long days (LD), although SD was the more effective photoperiod at all temperatures above 6°C. The degree of primary induction was closely negatively correlated with the length of basal leaves. Culm elongation and heading (secondary induction) were promoted by LD and high temperature and inhibited by the combination of SD and low temperature. The relationship between SD primary induction and vernalization is discussed in the light of these and other results.
The role of ethylene during flooding of Phaseolus vulgaris
Authors: Schravendijk H. Wadman‐van , van Andel O. M.
Published: April 2006

Wilting symptoms in Phaseolus vulgaris L. cv. bruine Noord‐Hollandse were observed after a few hours of flooding. They were well correlated with an accumulation of ethylene. The ethylene level in the leaves started to increase after 2 h of flooding and reached a 3–4 fold rise after 4–6 h. From then on throughout the next two days it gradually returned to control values. On the day when plants were flooded, a positive correlation was found between the ethylene concentration and the degree of wilting. During this day the time course of abscisic acid (ABA) level, diffusion resistance and water potential was measured. The effect of ethylene on stomatal aperture was investigated by spraying Ethrel on the leaves. In control plants, Ethrel treatment had no influence on the diffusion resistance. Spraying plants with ABA resulted in a significant, dose‐dependent increase in diffusion resistance. When Ethrel was added to the ABA‐containing solutions only 62% of this increase was observed. Ethrel (pre‐) treatment of plants that were to be flooded had a similar effect; the increase in diffusion resistance was only 70% of what was observed in untreated flooded plants. It is concluded that ethylene may interfere with the regulation of stomatal aperture by abscisic acid.
Uptake of chlorate and other ions in seedlings of the nitrate‐uptake mutant B1 of Arabidopsis thaliana
Authors: Scholten H. J. , Feenstra W. J.
Published: April 2006

The accumulation of labelled ions was measured in seedlings of Arabidopsis thaliana (L.) Heynh. grown in submerged cultures. Genotypes used were wild type and the nitrate‐uptake mutant B1, which is altered in the uptake of nitrate and chlorate from concentrations above 1 mM when grown under normal conditions. At low and high concentrations of chlorate, chloride, and K+, significantly less radioactivity was accumulated in seedlings of B1 than in seedlings of wild type. The influx of sulphate did not decrease in B1. The results indicate that the effect of the mutation in B1 is restricted to the uptake of monovalent ions.
Ethylene and ethane release during tobacco protoplast isolation and protoplast survival potential in vitro
Authors: Cassells Alan C. , Tamma Lakshmi
Published: April 2006

Studies on stress ethylene and ethane during protoplast isolation from water‐stressed and waterlogged donor plants Nicotiana tabacum L. xanthi‐nc, show a correlation between ethane, but not ethylene, release and protoplast survival in vitro. Ethane release shows a high negative correlation with protoplast survival potential from donor plants subjected to both stresses. Ethylene showed a high negative correlation with protoplast survival potential in tissues from water‐stressed but not from long‐term waterlogged plants. The absence of correlation in the latter may be related to decreased ability to produce ethylene in hyperstressed plants.

The results are discussed in relation to the use of stress ethane release as a parameter of the physiological status of the plant.