bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of photoperiod and gibberellin on growth and photosynthesis of high‐latitude Poa pratensis
Authors: Heide O. M. , Bush M. G. , Evans L. T.
Published: April 2006

The relative growth rate of pot‐grown plants of Poa pratensis L. cv. Holt, origin 69s°N, was increased by 20–40% by photoperiod extension with low intensity incandescent light from 8 to 24 h at 9–21°C. The main increase occurred over the 14 to 18 h photoperiod range. The true photoperiodic nature of the response was demonstrated by the effectiveness of night interruption in stimulating growth. Fortnightly sprayings with gibberellic acid (GA3) (3 × 10‐6 to 3 × 10‐5M) mimicked all the effects of long days, whereas (2‐chloroethyl)‐trimethylammonium chloride (CCC) counteracted the effects of long days. Both growth substances exhibited pronounced interactions with photoperiod, GA3 being most effective in short days and CCC in long days. The growth stimulation, whether caused by long days or GA3, was exerted mainly through increases in individual and total leaf area. This was associated with a reduction in CO2, exchange rate and a parallel fall in specific leaf weight. Proportionally, however, the increase in leaf area was greater than the fall in CO2 exchange rate, resulting in a 38 to 118% increase in photosynthesis per leaf. No evidence was found of any direct and promotive effect of transition to long days on the CO2 exchange rate of already expanded leaves.
The effect of cold, anoxia and ethylene on the flowering ability of buds of Cichorium intybus
Authors: Joseph C. , Billot J. , Soudain P. , Côme D.
Published: April 2006

The apical bud and the axillary buds of Witloof chicory (Cichorium intybus L. cv. Tardive d'Anvers) remain in the vegetative state if they are left on the root and maintained at 18°C. Flowering occurs in long days of 16 h after a pretreatment of either 8 weeks at 3°C, 3 days in complete anoxia at 15°C, or 4 days in the presence of ethylene (1000 ppm) at 15°C. In contrast, the adventitious buds which spread out on the root after ablation of the collar flower in a photoperiod of 16 h without particular pretreatment. The grafting of apical buds onto roots after different treatments shows that cold and ethylene act on the root, whereas anoxia acts directly at the level of the bud. It seems that the inhibition of the flowering of preformed buds (apical and axillary) stems from the collar. A hypothesis is proposed to explain this inhibition and why it is broken by cold, anoxia and ethylene.
Mode of high temperature injury to wheat. II. Comparisons of wheat and rice with and without inflorescences
Authors: Kuroyanagi Toshiyuki , Paulsen Gary M.
Published: April 2006

High temperature injury to wheat (Triticum aestivum L.) during grain development is manifested as acceleration of senescence. Experiments were conducted to elucidate the mode of senescence and site of high temperature responses. Wheat (cv. Chris) and rice (Oryza sativa L. cv. Newbonnet), which have C3 photosynthesis but different temperature responses, were grown with and without inflorescences under three temperature regimes after anthesis. Plant growth and constituents associated with senescence were measured weekly until physiological maturity. Increasing temperatures from 25°C/15°C to 35°C/25°C day/night after anthesis decreased growth, leaf viability, chlorophyll and protein concentrations, and RuBP carboxylase activity and increased protease and RNase activities in wheat. Inflorescence removal increased vegetative weights and slowed most senescence processes more in wheat than in rice, but did not alter the course of high temperature responses. Results are interpreted as indicating that diversion of nutrients from roots by inflorescence sinks at normal temperatures and by increased respiration at high temperatures caused similar responses. Source and sink activities appeared to be regulated jointly, probably by cytokinins from roots, during senescence at normal and elevated temperatures.
Efficiency of respiration and energy requirements of N assimilation in roots of Pisum sativum
Authors: de Visser Ries
Published: April 2006

The function of alternative path respiration in roots was investigated in pea plants (Pisum sativum L. cv. Rondo). Plants were grown in symbiosis with Rhizobium leguminosarum (strain PF2), completely dependent on N2 fixation, or non‐nodulated, receiving nitrate or ammonium at the same rate as N2 was fixed in symbiosis. Under these conditions, relative growth rates of plants grown with N2, NO‐3 or NH+4 were the same. This facilitated interpretation of the effect of the N source on the efficiency of root respiration, as determined by the relative activity of the non‐phosphorylating alternative path. The ‘wasteful’ oxidation of carbohydrate via this pathway was defined as the glucose equivalent of the difference between the amounts of ATP (mol O2)‐1 produced in cytochrome and alternative path respiration. ‘Wasteful’ carbohydrate oxidation maximally amounted to 4% (N2), 15% (NO‐3) and 25% (NH+4) of the daily carbohydrate oxidation in the roots. It is concluded that the ‘wasteful’ oxidation of carbohydrate via the alternative path is of minor importance for the adaptation of root respiratory metabolism to different energy requirements of N assimilation. The total carbohydrate import by roots fixing N2 was ca 60 and 30% higher than the import by roots assimilating NO‐3 or NH+4, respectively. Two factors are shown to account for these differences: the high carbohydrate cost of N2 fixation, and the small contribution (30%) of the roots to NO‐3 reduction by the plant. The high carbohydrate requirements of roots fixing N2 were met by higher rates of photosynthesis as compared with plants utilizing NO‐3 or NH+4.
A rapid assay for aluminium phytotoxicity at submicromolar concentrations
Authors: Kinraide Thomas B. , Arnold Robert C. , Baligar V. C.
Published: April 2006

Investigations of Al phytotoxicity, including the identification of the Al species responsible for toxicity, require a rapid assay procedure employing very low concentrations of Al and a chemically simple rooting medium. Root elongation in newly germinated red clover (Trifolium pratense L. cv. Kenland) was inhibited by submicromolar concentrations of Al. Ca2+ at concentrations of at least 0.2 mM was essential for optimal elongation in control seedlings. Ca2+ also relieved Al toxicity with the net effect that maximum reduction of elongation by 1 μM Al was achieved at 0.2 mM Ca2+. Elongation in control seedlings was at least 90% of maximum from pH 4.5 to 5.7. Increases in pH relieved Al toxicity so that maximum sensitivity to 1 μM Al occurred at pH 4.7. As a consequence of these experiments and other considerations we chose for our basic assay a medium composed of 0.2 mM CaSO4 adjusted to pH 4.5 with H2SO4, variously supplemented with Al2(SO4)3.

Day‐old seedlings were incubated in this aerated medium in the dark at 23°C for one day. No additions of other solutes increased the sensitivity of the assay, but amelioration of Al toxicity was effected by Mg2+, F‐, phosphate and citrate. Increases in ionic strength per se had comparatively little effect on the toxic effects of Al. Two barley cultivars (Hordeum vulgare L. cv. Dayton and Kearney) and two wheat cultivars (Triticum aestivum L. cv. Hart and Thorne) known to differ in sensitivity to Al were reliably separated at submicromolar Al concentrations by the assay procedure, which was slightly modified. Suggestions for the improvement of the assay and for applications to future research are offered.
Comparative investigations on the distribution of sucrose synthase activity and invertase activity within growing, mature and old leaves of some C3 and C4 plant species
Authors: Claussen W. , Loveys B. R. , Hawker J. S.
Published: April 2006

Sucrose synthase (EC 2.4.1.13) activity in young growing leaves was highest in the leaf base in eggplants (Solanum melongena L.), cassava (Manihot esculenta Crantz), grapevine (Vitis vinifera L.), and in the leaf sheath of sugar cane (Saccharum of ficinarum L.) and maize (Zea mays L.). In addition, increasing sucrose synthase activity was measured towards the edge of growing eggplant leaves while the activity in mature leaves was highest in the midrib. The activity of acid and alkaline invertase was very low in the midrib but higher in the blade of fully expanded eggplant leaves. Highest invertase activities were found in younger growing leaves. It was concluded that in growing leaves a close relationship might exist between the activity of sucrose synthase and the import of sucrose from source leaves.

Detachment of mature eggplant leaves led to a 2‐ to 3‐fold increase of sucrose synthase activity in blade and midrib of these leaves. In contrast, invertase activity decreased after detachment in both leaf blade and midrib. It was concluded that the rise in sucrose synthase activity might have been caused by the observed increase of sucrose concentration in detached leaves and that sucrose synthase might have an important role in the regulation of sucrose content of the conducting tissue.
The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome
Authors: Badila P. , Lauzac M. , Paulet P.
Published: April 2006

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m‐2) promotes flowering, while far‐red (730 nm, 0.31 W m‐2) and irradiation with combined red + far‐red (0.20 + 0.41 W m‐2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m‐2, 12 min) at regular intervals, although these are counteracted by far‐red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.
Senescence in French‐bean nodules: Occurrence of different proteolytic activities
Authors: Pladys D. , Rigaud J.
Published: April 2006

A decline in nitrogenase activity (C2H2 reduction) of nodules of Phaseolus vulgaris L. cv. Contander was correlated with a decrease in their soluble protein including leghe‐moglobin. Concomitantly, two distinct proteolytic activities against leghemoglobin with acidic and alkaline pH optima were detected. The corresponding proteases were purified about 30‐fold by ammonium sulfate precipitation, gel filtration and hydroxy‐apatite chromatography. Both the acidic (pH optimum 3.5) and the alkaline (pH optimum 8.0) proteases were thiol enzymes. They were characteristic of senescing nodules, whereas only an acidic serine protease was present in functional nodules.
Effect of nicotianamine on iron uptake by the tomato mutant ‘chloronerva’
Authors: Scholz Günter , Schlesier Gisela , Seifert Karlheinz
Published: April 2006

In the tomato (Lycopersicon esculentum L.) mutant ‘chloronerva’ the biosynthesis of nicotianamine, a derivative of the amino acid azetidine‐2‐carboxylic acid, is blocked. Application of nicotianamine to leaves of seedlings of the mutant reduced the abnormally high iron content of the plants to the level of the wild‐type. In short‐term experiments nicotianamine decreased the amount of iron removed from the nutrient medium by isolated roots of both wild‐type and mutant. Addition of nicotianamine to the nutrient solution at 10−5M inhibited the excessive iron uptake by the mutant and wild‐type. This effect was more evident with 59Fe‐ethylenediamine‐N, N′‐bis‐(o‐hydroxyphenylacetic acid) than with 59FeCl3 as the iron source. It is concluded that nicotianamine plays a direct or indirect role as a regulator of iron uptake in plants.
Induction of nitrate assimilation in the cyanobacterium Anabaena variabilis
Authors: Avissar Yael J.
Published: April 2006

Filaments of Anabaena variabilis Kütz strain ATCC 29413 grown in the absence of nitrate contain nitrate reductase that is active in permeabilized filaments, but not in intact, living filaments until they have been incubated for about 40 min in the presence of nitrate. The delayed acquisition of the ability to reduce nitrate is insensitive to chloramphenicol. Thus, switching on of enzyme activity in the presence of nitrate does not involve protein synthesis and nitrate reductase activity is not regulated by the amount of enzyme present.
Effect of 2,5‐norbornadiene on abscission and ethylene production in citrus leaf explants
Authors: Sisler Edward C. , Goren Raphael , Huberman Mosche
Published: April 2006

Citrus (Citrus sinensis L. Osbeck) leaf explants completely abscise within 48 h when exposed to saturating amounts of ethylene at 25°C. When 2,5‐norbornadiene was added, 2000 μl 1−1 reduced abscission of explants also exposed to 2 μl 1−1 of ethylene to the level of the control, and 8000 μl 1−1 reduced abscission in explants exposed to 10 μl 1−1 of ethylene to the level of the control, but abscission was complete when 1 000 μl 1−1 of ethylene was used in the presence of 8 000 μl 1−1 of 2,5‐norbornadiene. When explants were exposed to 2 μl 1−1 of ethylene, 2000 μl 1−1 of 2,5‐norbornadiene prevented abscission if applied up to 10 h after exposure to ethylene. After 18 h, applied 2,5‐norbornadiene had little effect on abscission at 48 h. A Lineweaver‐Burk plot gave a 1/2 maximum value of 0.12 μl 1−1 for ethylene on abscission, 2,5‐Norbornadiene gave competitive kinetics with respect to ethylene with a K1 value of approximately 120 μl 1−1 of 2,5‐norbornadiene. The presence of 2,5norbornadiene stimulated ethylene production, which progressively increased as the 2,5‐norbornadiene concentration was increased from 250 to 8 000 μl 1−1 2,5‐Norbornadiene also suppressed the induction of cellulase and polygalacturonase by ethylene. Together, 2,5‐norbornadiene and 2,4‐dichlorophenoxyacetic acid were more effective than either alone in reducing abscission. 2,5‐Norbornadiene also was effective in preventing the reduction of indole‐3‐acetic acid transport induced by ethylene.
The effect of water stress on photosynthesis and related parameters in Pinus halepensis
Authors: Melzack R. N. , Bravdo B. , Riov J.
Published: April 2006

Net photosynthesis, transpiration, dark respiration rates and stomatal and mesophyll resistances were studied in young potted seedlings of Pinus halepensis Mill. under gradually decreasing soil and leaf water potentials. Stomatal resistance under non‐limiting xylem water potentials was 6–7 times higher than mesophyll resistance. Stomata started to close at threshold xylem water potentials of −0.8 MPa, whereas mesophyll resistance started to increase at about −1.4 MPa. Decreasing xylem water potentials increased the CO2 compensation point and decreased the water use efficiency (expressed by the photosynthesis to transpiration ratio) and dark respiration rate. It is concluded that at least part of the drought resistance characteristics of P. halepensis are associated with a sensitive stomatal mechanism which enables an efficient control of water loss.
Four major basic proteins of barley grain. Purification and partial characterization
Authors: Hejgaard J. , Bjørn S. E.
Published: April 2006

Four major basic proteins termed C, K, N and Q, which are synthesized very late in grain development, have been isolated from barley (Hordum vulgare L.) mutant Bomi 1508. Immunoelectrophoretic monitoring assured a high degree of purity after a few ion exchange and gel filtration steps. Charge microheterogeneity of two of the four antigenically distinct proteins was observed. Some physico‐chemical properties were determined, including molecular mass (C ∼ 28 000; K ∼ 30 000; N ∼ 11 000; Q ∼ 60000), isoelectric point(s) (C ∼ 9.7; K ∼ 10.1–10.3; N ∼ 9.3; Q ∼ 8.9–9.1 at 25°C), and amino acid composition. In total, the four proteins represent ∼ 5% of the salt‐soluble protein in grains of some cultivated barleys. The most basic protein K is rich in lysine (∼ 7.9 mol %) and may account for ∼1% of the grain lysine content in these barleys.
Response ofSuaeda aegyptiacato KCl, NaCl and Na2SO4treatments
Authors: Eshel A.
Published: April 2006

The response ofSuaeda aegyptiaca(Hasselq.) Zoh. to various salinity treatments was tested in sand culture. Growth was promoted by NaCl and by Na2SO4at all tested concentrations, but not by KCl. The effect of NaCl on growth was stronger than that of Na2SO4and it increased gradually up to a 125 eq. m−3optimum. Ion uptake was also affected by the different salts. Cl−was taken up in similar quantities from KCl and from NaCl solutions and the content of the respective cations was also similar to one another. The presence of Na+in the medium lowered the content of K+in the plants and at the same time increased growth by as much as 900%. Transpiration was reduced and water use efficiency increased by Na+‐salts. Highest water use efficiency was exhibited by plants which were treated with 125 eq. m−3NaCl. It is concluded that Na+at the macronutrient level has a specific promotive effect on the physiological processes ofS. aegyptiaca.This effect is not due to replacement of K+by Na+; neither can it be achieved by increasing the K+concentration. Cl−has an additional positive effect on growth of S.aegyptiaca.This effect is only expressed in the presence of Na+.
Is lipoxygenase involved in the formation of ethylene from ACC?
Authors: Kacperska Alina , Kubacka‐Zgbalska Maria
Published: April 2006

Freezing or desiccation of winter rape leaves (Brassica napus L. var. oleifera (cv. Górczanski) stimulated both lipoxygenase (EC 1.13.11.12) activity and ethylene formation during the post‐stress period. The effect depended on the degree of membrane injury. In tissues showing injury less than 50% (as checked with the electrical conductivity method) both activities increased according to the degree of stress‐induced damage. In leaves injured to a higher degree both activities decreased. Light and low temperature (5°C) inhibited the development of both lipoxygenase activity and ethylene formation in leaf disks stored for 20 h. Ethylene formation was also observed in a model system where soybean lipoxygenase was added to a mixture containing 1‐aminocyclopropane‐1‐carboxylic acid and linoleic or linolenic acid as substrate for lipoperoxide formation. Changes in pH and temperature conditions of the incubation mixture caused similar differences in the lipoxygenase activity and ethylene formation. We propose that the stimulation of lipoxygenase‐catalysed oxidation of polyunsaturated fatty acids (increasing free radical formation) leads to an increased ethylene production from ACC.
Light‐independent accumulation of chlorophyll a and b and protochlorophyllide in green barley (Hordeum vulgare)
Authors: Adamson Heather , Griffiths Trevor , Packer Nicolle , Sutherland Mark
Published: April 2006

Barley (Hordeum vulgare L. cvs Clipper, Procter, Astrix) seedlings were transferred from daylight to darkness and changes in chlorophyll a, chlorophyll b, protochlorophyllide and chlorophyllide (μ leaf−1) in either the first or second leaf determined spectrophotometrically after separating the esterified from unesterified pigments by partitioning between ammoniacal acetone and light petroleum ether. Chlorophyll a and b as well as protochlorophyllide accumulated in the dark. The ratio of chlorophyll to protochlorophyllide formed in the absence of light was 18:1. 5‐aminolevulinic acid (10 mM) promoted the synthesis of chlorophyll a and b and protochlorophyllide. Pigment synthesis and response to 5‐aminolevulinic acid addition was related to tissue age. Mature tissue in the apical third of the leaf accumulated most chlorophyll, but per μg chlorophyll present at the time of transfer to darkness, was less efficient than immature tissue towards the base of the leaf. Immature tissue was also most responsive to added 5‐aminolevulinic acid. Chlorophyll synthesis in the dark was accompanied by chloroplast development. Chloroplasts in immature leaf tissue increased in size and extent of thylakoid development when transferred from daylight to darkness. The results indicate that chlorophyll synthesis and chloroplast membrane development in light‐grown barley continue into the dark phase of the diurnal cycle. A light‐independent protochlorophyllide reductase in light‐grown barley seedlings is postulated.
The composition of the lipid globules of Ilex aquifolium leaves and its variability with the age of the leaf and with season
Authors: Niemann Gerard J. , Baas Wim J.
Published: April 2006

The cytoplasmatic globules of Ilex aquifolium L. mainly consist of fatty acid esters of the triterpenoid alcohols α and β‐amyrin. In very young leaves these are practically only palmitates. With increasing leaf age, increasing amounts of saturated and unsaturated C18 acids were found with comparatively high amounts of linoleic and linolenic acid in leaves of one year and older. Some accumulation of the triterpene precursor squalene was also observed with increasing age of the leaves. In addition to age effects, seasonal changes occur too. Independent of the age of the leaf, an increase in palmitic acid and a decrease in linoleic and especially linolenic acid was observed in the winter in mature leaves.
Induction and release of secondary seed dormancy in genetically pure lines of Avena fatua
Authors: Tilsner Heidy R. , Upadhyaya Mahesh K.
Published: April 2006

Induction and release of secondary dormancy in genetically pure dormant (AN‐51, Mont 73) and non‐dormant (CS‐40, SH‐430) lines of wild oat (Avena fatua L.) were studied. These lines differed with regard to the optimal period of anaerobiosis necessary for induction of dormancy, and/or the degree (% of seeds acquiring dormancy) and duration of the dormancy induced. Secondary dormancy could be induced more effectively in the after‐ripened seeds of dormant lines than in the non‐dormant lines, where only a short‐term dormancy could be induced (in 5–7 week‐old‐seeds). Higher anaerobiosis temperatures were more effective in inducing dormancy in all lines studied. Thus, as with primary dormancy, wild oat biotypes exhibit genetic variability in their secondary dormancy behaviour and factors like temperature can modify the expression of this trait.

The germination stimulants kinetin, isopentenyl adenine, sodium azide, potassium nitrate, ethanol and substituted phthalimides, which break primary dormancy in wild oats, stimulated germination of secondarily dormant seeds (line AN‐51). Since these chemicals are structurally diverse, primary and secondary dormancies appear to be similar in part in their regulation.

Salicylhydroxamic acid, an inhibitor of cyanide‐insensitive (alternative) respiration, did not inhibit: 1, spontaneous release of secondary dormancy in the line SH‐430; and 2, stimulation of germination of secondarily dormant AN‐51 seeds by various chemicals (except azide), suggesting that this respiratory pathway is not necessary for the release of induced dormancy.
Radioimmunoassay for determination of indole‐3‐acetic acid in fungi and plants
Authors: Madej Andrzej , Häggblom Per
Published: April 2006

A radioimmunoassay technique for indole‐3‐acetic acid is described. The method has successfully been used to measure extractable indole‐3‐acetic acid in fungal and plant materials and is able to detect as little as 0.3 pmol. As non‐radioactive antigen the methyl ester of indole‐3‐acetic acid is used and the radioactive antigen is tritiated. An acid‐catalyzed esterification of indole‐3‐acetic acid is used for conversion into methyl ester. The measuring range of the assay is 0.3–10 pmol. In the assay, separation of free and bound fractions is achieved by dextran‐coated charcoal, leaving the bound fraction in the supernatant.
Initiation and development of wound tissue and roots on hypocotyl cuttings of Pinus sylvestris in vitro
Authors: Grönroos Roland , von Arnold Sara
Published: April 2006

The rooting of hypocotyl cuttings from 20‐day‐old seedlings of Pinus sylvestris L. cultured in vitro is discussed. About 40% of the cuttings cultured on medium lacking activated charcoal produced roots during the first two months. When activated charcoal was added to the medium, either root formation (75% formed roots) or wound tissue growth (95% formed large wound tissues) was stimulated in different experiments. These large wound tissues did not develop any roots. The anatomical changes in the basal part of the cuttings were similar during the first two weeks in all the cuttings studied. A vascular cylinder composed of short tracheids with many pores developed. Thereafter the differentiation process became varied. The amount of wound tissue produced and the time for rooting differed among the cuttings. Tracheid nests which were in contact with the vascular system in the hypocotyl via short tracheids were observed after three weeks. Subsequently, roots developed from the tracheid nests. The longer root formation was delayed, the larger the wound tissue became.

Short tracheids were found close to the wound tissue surface. Their ability to adsorb nutrients and water is discussed.
A two‐step control of basic and acidic peroxidases and its significance for growth and development
Authors: Gaspar Thomas , Penel Claude , Castillo Federico J. , Greppin Hubert
Published: April 2006

A generalized two‐step and interdependent control of basic and acidic peroxidases (EC 1.11.1.7) is observed in plant responses to different physical and chemical stimuli. An interpretative model consisting of a pathway of reactions is presented on the basis of our own data and the literature. Stress‐induced membrane depolarization would generate different species of free radicals and peroxides, which in turn initiate lipid peroxidation. The degradation of cell membranes is suggested to bring about rapid changes in ionic fluxes (especially release of K+ which would result in an enhanced endogenous Ca/K ratio) and in leakage of solutes (among them electron donors such as ascorbic acid and phenolic substances). The increased intracellular relative calcium level results in: 1) activated secretion of basic peroxidases into the free space where, in association with the electron donors and maybe with the circulating indole‐3‐acetic acid (IAA), they eliminate the peroxides; and 2) facilitated binding of basic peroxidases to membrane structures allowing a role as 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐oxidases. The resulting IAA and ACC oxidase‐mediated changes in ethylene production would further induce (this time through the protein synthesis machinery) an increase in activity of phenylalanine ammonia‐lyase (EC 4.31.5) and acidic peroxidases. The resulting lignification and cell wall rigidification determines the growth and/or the developmental response to the initial stress.
Effects of UV‐C and UV‐B on cytomorphology and water permeability of inner epidermal cells of Allium cepa
Authors: Lichtscheidl‐Schultz Irene
Published: April 2006

Changes of cytomorphology and water permeability of inner epidermal cells of Allium cepa L. cvs Spartan and Keep Well were investigated with the light microscope after irradiation with UV‐C (254 nm) and UV‐B (280 and 310 nm). The sequence of the investigated changes of viscosity, protoplasmic streaming, organelle shape and water permeability was the same with 254 as with 280 nm. although a higher dose of 280 nm was needed to produce the same biologically equivalent effect. However, when calculated as a percentage of the lethal dose, the initial doses that produced the effects were the same for 254 and 280 nm. No changes could he observed at the cellular level after the cells were irradiated with 310 nm. The lethal dose depended upon the time between irradiation and observation. At 254 nm it was 1.1 kJ m−2 up to 1 h after irradiation and dropped to 860 J m−2 when measured 24 and 48 h later. At 280 nm a dose of 2.8 kJ m−2 killed the cells within I h while the dose needed after 24 and 48S h was 1.99 kJ m−2. The minimum doses which caused the different cytomorphological effects did not depend upon the observation time. Normal cell structure and functions that were altered immediately alter irradiation did not recover. Doses that were not immediately effective alter irradiation caused no later damage. Doses which increased water permeability were much higher than doses which influenced cytomorphological parameters of the cell.
Cytological and physiological behaviour of Euglena gracillis cells entrapped in a calcium alginate gel
Authors: Tamponnet Christian , Coslantino François. , Barbotin Jean‐Noel , Calvayrac Regis
Published: April 2006

The immobilisation of Euglena gracilis Z cells in a calcium alginate matrix maintained respiratory and photosynthetic activities and ultrastructural integrity. Moreover, immobilization did not prevent Euglena cells from greening inside the gel beads. Electron microscopy demonstrated that the immobilized cells were fixed in the same cellular state as they were when the immobilization occurred. This can he explained by simultaneous reaction of both Ca2+ and the alginate with the cells. Some hypotheses about the role of C2+ are discussed. In addition, long term storage (2 years) in calcium alginate has been performed permitting applications in algal storage.
Hardening, abscisic acid, proline and freezing resistance in two winter wheat varieties
Authors: Lalk Irmtraut , Dörffling Karl
Published: April 2006

Two varieties of winter wheat (Triticum aestivum L.) differing in freezing resistance (“Holme” from Sweden, freezing resistant, and “Amandus” from Germany, less freezing resistant) were hardened for five weeks by gradually reducing the day/night temperature from 20°C/15°C during the first week to 2° C/0° C during the fifth week and the photoperiod from 15 to 9 h. This treatment increased the freezing resistance of both varieties in comparison to unhardened control plants. Hardening caused an increase in osmolarity of cell sap and in the levels of proline and abscisic acid (ABA). Increase in osmolarity preceded the increase in ABA level, and proline levels increased later than ABA levels. Holme had higher values of osmolarity as well as higher levels of ABA and proline. but the differences between the two varieties were significant only for proline. Since the pressure potential remained constant or increased slightly during the hardening period, it is suggested that the accumulation of ABA is due to the hardening process and not to simple water stress caused by cold‐induced inhibition of water uptake by the root.

Spraying hardened plants with 10−4 M ABA 24 h before a freezing test increased freezing resistance in both varieties, but did not obliterate the differences in freezing resistance between the two varieties. Spraying hardened plants with an aqueous proline solution (10%, w/v) was without effect on freezing resistance. It is concluded that the hardening procedure causes an accumulation of ABA in winter wheat leaves and that ABA is involved in the chain of events leading to freezing resistance.
Nitrate metabolism in the cyanobacterium Anabaena cycadeae: Regulation of nitrate uptake and reductase by ammonia
Authors: Bagchi Suvendra N. , Rai Upendra N. , Rai Amar N. , Singh Hriday N.
Published: April 2006

Nitrogen regulation of nitrate uptake and nitrate reductase (EC 1.7.99.4) was studied in the cyanobacterium Anabaena cycadeae Reinke and its glutamine auxotroph. Development of the nitrate uptake system preceded, and was independent of, the development of the nitrate reductase system. The levels of both systems were several‐fold higher in the glutamine auxotroph lacking glutamine synthetase (EC 6.3.1.2) than in the wild type strain having normal glutamine synthetase activity. The nitrate uptake system was found to be NH4‐repressible and the nitrate reductase system NO3−‐inducible. NH4+ was the initial repressor signal for the uptake process which was involved in the control of the NO3−inducible reductase system.
Growth and development of winter rye at cold‐hardening temperatures results in thylakoid membranes with increased sensitivity to low concentrations of osmoticum
Authors: Huner N. P. A. , Hopkins W. G.
Published: April 2006

Chloroplasts developed at cold‐hardening (5°C) and non‐hardening temperatures (20°C) were compared with respect to the stability of photosynthetic electron transport activities, the capacity to produce and maintain a H+gradient and the capacity fat photophosphorylation as a function of resuspension in the presence or absence of osmoticum. The results for electron transport indicate that whole chain, photosystem I and pfaotosystem II activities in non‐hardened chloroplast thyalkoids were unaffected by resuspension in the presence of high or low osmoticum. In contrast, the same electron transport activities in cold‐hardened chloroplast thylakoids exhibited a 3‐ to 4‐fold decrease in activity when resuspended in the presence of low osmoticum. Impairment of electron transport through photosystem II of cold‐hardened thylakoids resuspended in the presence of low osmoticum was supported by room temperature fluorescence induction kinetics. Since the presence of Mn2+partially overcame this inhibition, it is concluded that this osmotically‐induced inhibition of PSII activity in cold‐hardened chloroplast thylakoids may, in part, be due to damage to the H2O‐splitting side of photosystem II. Both the initial rate and the maximum capacity for cyclic photophosphorylation were significantly inhibited in cold‐hardened as compared to non‐hardened thylakoids upon resuspension in the presence of low concentrations of osmoticum. This was correlated with an inability of the cold‐hardened chloroplast thylakoids to maintain a significant transrnembrane H+gradient. The results indicate that cold‐hardened thylakoid membranes required an osmotic concentration (0.8M) twice as high as non‐hardened thylakoids (0.4M) to produce the same initial rate of H+uptake. In addition, the capacity to produce a proton gradient in cold‐hardened thylakoids was less stable than that in non‐hardened thylakoids regardless of the osmotic concentration tested. It is concluded that development of rye thylakoid membranes at low temperature results in a differential sensitivity to low osmoticum and thus extreme caution should be exercised when comparing the structure and function of isolated thylakoids developed under contrasting thermal regimes.
Effect of nalidixic acid and novobiocine on the metabolism of suspension cultured carrot cells
Authors: Ciarrocchi Giovanni , Nielsen Erik , Cella Rino
Published: April 2006

Suspension cells of Daucus carota L. cv. Lunga di Amsterdam are extremely sensitive to both nalidixic acid and novobiocine. The synthesis of DNA, RNA and protein are inhibited within minutes of exposure even at concentrations less than 0.1 mM of both drugs. Moreover, uptake of deoxythymidine by cells is impaired more severely than by sodium azide. Reduction of oxygen consumption caused by the two drugs is slower than in the case of NaN3 and occurs a few minutes after the inhibition of macromolecular biosynthesis. This excludes the possibility that the block in oxidation is the primary cause of the observed inhibition of cellular functions and suggests that the inhibition of ATP synthesis, which is immediately affected in both cases, may be responsible for these effects. A possible interaction with other cellular targets may be secondary to the uncoupling effect. Cell growth is completely inhibited by 0.3 mM concentration of both drugs, but this inhibition is irreversible only in the case of novobiocine. The irreversibility of cell growth inhibition by novobiocine can be explained by the total disappearance of ATP from the cell.
Localization of nitrite and sulfite reductase in bundle sheath and mesophyll cells of maize leaves
Authors: Sclimutz Daniel , Brunold Christian
Published: April 2006

The distribution of nitrite reductase (EC 1.7.7.1) and sulfite reductase (EC 1.8.7.1) between mesophyll ceils and bundle sheath cells of maize (Zea mays L. cv. Seneca 60) leaves was examined. This examination was complicated by the fact that both of these enzymes can reduce both NO‐2 and SO2‐3 In crude extracts from whole leaves, nitrite reductase activity was 6 to 10 times higher than sulfite reductase activity. Heat treatment (10 min at 55°C) caused a 55% decrease in salfite reductase activity in extracts from bundle sheath cells and mesophyll cells, whereas the loss in nitrite reductase activity was 58 and 82% in bundle sheath cells and mesophyll cell extracts, respectively. This result was explained, together with results from the literature, by the hypothesis that sulfite reductase is present in both bundle sheath cells and mesophyll cells, and that nitrite reductase is restricted to the mesophyll cells. This hypothesis was tested i) by comparing the distribution of nitrite reductase activity and sulfite reductase activity between bundle sheath and mesophyll cells with the presence of the marker enzymes ribulose‐l, 5‐bisphosphate carboxylase (EC 4.1.1.39) and phosphoe‐nolpyruvate carboxylase (EC 4.1.1.32), ii) by examining the effect of cultivation of maize plants in the dark without a nitrogen source on nitrite reductase activity and sulfite reductase activity in the two types of cells, and iii) by studying the action of S2‐on the two enzyme activities in extracts from bundle sheath and mesophyll cells. The results from these experiments are consistent with the above hypothesis.
Metabolism of [14C]ss‐glucose and [14C]‐acetate by lettuce embryos during early germination
Authors: Raymond P. , Carre‐Nemesio A. M. , Pradet A.
Published: April 2006

The metabolism of [‘4C]‐labelled glucose and acetate has been investigated during the early germination ‐ before radicle emergence ‐ of lettuce (Lactuca sativa L., cv. Val d'Orge) embryos. Similar amounts of radioactivity from both substrates were evolved as C., or incorporated into organic acids, amino acids and proteins. A large part of the [14C]‐glucose was also incorporated into sucrose and polysaecharides, and a small part into the glycerol moiety of lipids. Acetate was massively incorporated into lipids, and only slightly into neutral compounds. These results show that both glucose and acetate can be utilized as respiratory substrates during early germination of lettuce embryos. Various biosynthetic pathways leading to amino acids, proteins, polysaecharides and lipids are active during this period.
Dual effect of 2, 4‐D on ethylene production and ripening of tomato fruit tissue
Authors: Vendrell Miguel
Published: April 2006

Tomato fruits (Lycopersicon esculentum Mill. cv. Indian River) were treated with aqueous solutions of 2, 4‐dichlorophenoxyacetic acid (2, 4‐D) and the effects on respiration, ethylene production, and ripening were examined. 10‐3 and 10‐5M 2, 4‐D solutions were used. Dipping treatment of whole fruit picked at the 74% stage of development, gave an increase in respiration and ethylene production, the effect being directly related to 2, 4‐D concentration. Ripening was advanced relative to control fruit.

Tomato disks cut from the pericarp tissue of fruit picked at the 81% stage of development were vacuum‐infiltrated with the same 2, 4‐D solutions. In these disks the increase in respiration continued longer compared to control disks. Ethylene production was considerably increased, and after an initial recovery the 2, 4‐D‐treated disks showed another increase at a much faster rate than controls. However, contrary to what could be expected from this increase in ethylene, ripening was delayed. Nevertheless, all disk samples showed advance ripening compared to whole fruit of the same age, indicating that they could not recover completely from the effect of cutting and treatment.

The results showed that 2, 4‐D causes a dual effect in tomato fruit tissue: an increase in ethylene production which promotes ripening, and a delay in ripening. This last effect, depending on the uniformity of the auxin distribution and its concentration, prevails.
Effect of CO2‐enrichnient on seedling physiology and growth of two tropical tree species
Authors: Oberbauer Steven F. , Strain Boyd R. , Fetcher Ned
Published: April 2006

Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la‐gopus Swartz, a fast‐growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower‐growing climax species, were grown under enriched atmospheric CO2 in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 μl 1−1 under photosynthetic photon flux densities of 500 μol m−2 s−1 and temperatures of 26°C day and 20°C night. Total biomass of both species increased significantly in the elevated CO2 treatment; the increase in biomass was greatest for the pioneer species, O. lagopus. Both species had greater leaf areas and specific leaf weights with increased atmospheric CO2. However, the ratio of non‐pho‐tosynthetic tissue to leaf area also increased in both species leading to decreased leaf area ratios. Plants of both species grown at 675 μl 1−1 CO2 had lower chlorophyll contents and photosynthesis on a leaf area basis than those grown at 350 μl 1−1. Reductions in net photosynthesis occurred despite increased internal CO2 concentrations in the CO2‐enriched treatment. Stomatal conductances of both species decreased with CO2‐enrichment resulting in significant increases in water use efficiency.
Localisation of translocated 14C in roots and root exudates of field‐grown maize
Authors: McCully M. E. , Canny M. J.
Published: April 2006

The roots of a mature, field‐grown maize plant are dimorphic: the primary root and those from the oldest nodes are bare with a heavily lignified cortex arid sloughed epidermis; those from younger nodes, except for a bare elongation zone, have an intact epidermis surrounded by a persistent soil sheath. Sheathed roots consistently have more layers of cortical cells, but the ratio of volumes of cortex to stele (ca 4) and the cross‐sectional area of phloem (ca3× 10−2 mm2) are similar in each type. Assimilated carbon (from 14C applied to a small area of one leaf) was translocated to all roots and actively metabolized in cortex and stele of both types. After 1 to 2 days the proportion of 14C exuded from a given length of mature root into its soil sheath, or into the adjacent unattached soil in the case of bare roots, was the same (5%) in both root types when compared with the ethanol‐soluble 14C in the tissues of this length. Up to 75% of the ethanol‐soluble label in the roots was in a cationic fraction (amino acids and unidentified compounds), ca 1% was in an anionic fraction and the remainder was in a neutral fraction (sugars). Approximately equal amounts of soluble 14C were found in the stele, cortex and laterals.
Effect of riboflavie and cyanide on blue light induction of betacyanin formation in Amamnthus caudatus seedlings
Authors: Gbrenović Snežana
Published: April 2006

The role of phyto chrome and flavins in blue light induction of betacyanin formation was studied in etiolated, three‐day‐old Amaranthus caudatus L. seedlings, using the criterion of far‐red reversibility and exogenously applied riboflavin and KCN. The effect of riboflavin was studied using high fluence rate blue light (42.7 :nmol m−2s−1nm−1 at 450 nm). When present in the incubation medium during illumination, riboflavin promoted the far‐red reversibility with short light treatments and suppressed the inductive action of continuous illumiaation. If added after light treatments, it promoted betacyanin formation. The filtration of blue light through the riboflavin solution caused profound changes in light quality without affecting the far‐red reversibility after 30 mm illumination. The effect of 1 mM KCN was tested with 70′% lower fluence of blue light. Cyanide caused the suppression of the inductive effect with 5 min blue light, which was accompanied by an enhancement of betacyanin induction by the terminal far‐red light pulse. With 30 min blue light, however, it caused the appearance of far‐red reversibility. The inductive effect of continuous blue illumination was slightly promoted by this Inhibitor. These results demonstrate that the effect of blue light on the pbyto chrome system is complex, whereas the physiological (inductive) action of the flavin triplet state is limited to low fluence, short blue light treatments.
Vitamin D3 affects growth and Ca2+ uptake by Phaseolus vulgaris roots cultured in vitro
Authors: Vega Manuel A. , Santamaria Eduardo C. , Morales Alfonsina , Boland Ricardo L.
Published: April 2006

Vitamin D3 at low concentration (10−9 M) inhibited the growth of Phaseolus vulgaris L. (cv. Contrancha) roots in vitro as measured by elongation (14 h) and [3H]‐leucine incorporation into protein (2 h), and increased their labelling with 45Ca2+ (2 h). Cycloheximide and puromycin (50 u.M) blocked vitamin D3 stimulation of root 45Ca2+ labelling, indicating that it is mediated by de novo protein synthesis. The calcium ionophore X‐537A (10−5JW) induced similar changes both in root elongation and 45Ca2+ uptake (14 h). This may indicate that the inhibitory effects of the sterol on root growth are mediated by changes in Ca2+ fluxes. However, this interpretation should be further strengthened by additional studies as the ionophore may have acted on root growth, affecting physiological processes other than Ca2+ transport.
The metabolism of [14C]‐tMdiaziiroii in callus tissues of Phaseolus lunatus
Authors: Mok Machteld C. , Mok David W. S.
Published: April 2006

The metabolism of [14C]‐thidiazuron (N‐phenyl‐N'‐l,2,3‐tbiadiazol‐5‐ylurea), a compound with extremely high cytokinin activity, was examined in callus cultures of Phaseolus lunatus L. cv. Kingston. No appreciable metabolism of the compound was detected in short‐term studies (up to 48 h). When tissues were grown on medium containing [14C]‐thidiazuron for longer periods (12 to 33 days), several major metabolites were isolated. The array of radioactive metabolites was the same using [14C]‐thidiazuron with the label in the phenyl ring, the urea bridge or the thiadiazol ring, indicating no degradation of the thidiazuron molecule. Enzyme digestion followed by HPLC and TLC analyses was used to identify major metabolites. α‐Gtacosidase degraded two of the metabolites to thidiazuron and a third was converted to N‐p‐hydroxyphenyl‐N2‐l,2,3‐thiadiazol‐5‐ylurea. Limited tests of the O‐glycosyl derivatives for cytokinin activity indicated that they are much less active than the parent compound. Bioassays involving hydroxylated derivatives of thidiazuron indicated that the p‐hydroxyphenyl derivative was 10000 limes less active than the parent compound, and the oetho‐ and mete‐derivatives had 1000 and 100 times lower activity, respectively, than thidiazuron. These results suggest that thidiazuron itself is the active compound and that metabolism of thidiazuron in Phaseolus tissues only involves modification of the intact structure, yielding metabolites that are less cytokinin‐active.