bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Amaranthus caudatus seed germination by polyethylene glycol‐6000 and abscisic acid and its reversal by ethephon or 1‐aminocyclopropane‐1‐carboxylic acid
Authors: Kȩpczyński Jan
Published: May 2006

The effect of polyethylene glycol (PEG‐6000), abscisic acid (ABA), 2‐chloroethylphosphonic acid (ethephon) and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) on the germination of Amaranthus caudatus L. seeds was examined. Both PEG‐6000 and ABA inhibited the rate and percentage of seed germination. ABA potentiated the effect of PEG. Ethephon was highly effective in reversing the inhibitory effect of PEG and ABA or combinations of both. ACC relieved inhibition by ABA and the combined effect of ABA and PEG. Aminoethoxyvinylglycine (AVG) increased the inhibition of seed germination caused by ABA. The inhibition of seed germination by ABA seems to be related more or less to ethylene biosynthesis or is associated with a change of tissue sensitivity to ethylene. The possibility of ethylene control of water uptake by seeds is also considered.
Accumulation of agmatine in chayote (Sechium edule) leaves during development
Authors: Vansuyt Gérard , Zinsou Claude
Published: May 2006

Arginine, agmatine, putrescine and spermidine were found in the apical parts and leaves of chayote (Sechium edule Swartz) at various stages of development. The concentration of agmatine, the immediate decarboxylation product of L‐arginine, increased considerably in young leaves at the first emergence of floral buds. Young leaves always had a relatively higher content of agmatine than older ones. There was a decrease in the concentration of agmatine from the apical part to the basal leaves. Agmatine was the predominant amine in young leaves at every stage of development (50–90% of the whole amine pool). It was also predominant in mature leaves when the floral buds appeared (70% of the total amine content). An accumulation of agmatine could not be found in other Cucurbitaceae species.
Phaseshifting of the photoperiodic flowering response rhythm in Pharbitis nil by red‐light pulses
Authors: Lumsden Peter J. , Vince‐Prue Daphne , Furuya Masaki
Published: May 2006

The control by light of the flowering response rhythm in the short‐day plant Pharbitis nil Choisy cv. Violet was examined by giving a single pulse of light at various times between 1 and 6 h after a 24‐h light period. When the first circadian cycle of the rhythm was monitored, it was found that a pulse of red light given at 1, 2 or 3 h into a 72‐dark period caused a 1‐h delay of the phase of the response rhythm, while a pulse at 6 h caused a 2‐h delay. These results support the hypothesis that, when red‐light pulses are given at hourly intervals, they are as effective as continuous light in preventing the onset of dark timing because they repeatedly return the rhythm to the circadian time at which it is apparently suspended in continuous light. The perception of and response to continuous light and red‐light pulses are also briefly discussed.
Effect of different night temperature regimes on the assimilation, transport and metabolism of carbon in rose plants
Authors: Khayat Eli , Zieslin Naftaly
Published: May 2006

A decrease in CO2 uptake, an increase in leaf starch and sucrose content and a decrease in the content of reducing sugars were found in rose (Rosa hybrida cvs: Sonia and Golden Times) plants exposed to lower night temperature (12°C) in comparison with those grown at 18°C. These responses were not present when plants were grown under a night temperature regime of alternating temperature, 2 h at 18°C followed by 2 h at 12°C for 3 repetitive periods of a total of 12 h. The export of labelled carbon from the source leaves and translocation into the adjacent axillary buds were inhibited by lower night temperature, but not by the alternating temperature regime. The translocation of labelled carbon toward the basal plant parts was promoted by the lower temperature but not by alternating temperature. The partitioning of labelled carbon between the 2 uppermost lateral buds was also affected by the night temperature regime.
Effects of phospholipase A2 and alkaline pH on photosystem II particles isolated from spinach chloroplasts
Authors: Tuquet Christiane , Guillot‐Salomon Thérèse , Farineau Nicole
Published: May 2006

An O2‐evolving photosystem II fraction (PS II particles) isolated from spinach (Spinacia oleracea L.) chloroplasts by Triton X‐100 was treated by phospholipase A2 or by an alkaline pH. Phospholipase A2 depleted the particles of all phosphatidylcholine and of a part of phosphatidylglycerol containing trans‐hexadecenoic acid, and induced a parallel inactivation of the PS II activity. The protein pattern remained similar to that of the control particles. The addition of exogenous polar lipids from thylakoids could not reactivate PS II activity. Treatment of PS II particles by an alkaline pH, known to release the 33, 24 and 18 kdalton polypeptides and to inactivate PS II activity, did not affect the lipid composition. The involvement of lipids in PS II activity is discussed.
Effects of Ca2+/Mg2+ chelators, SKF 525‐A and rotenone on phytochrome‐mediated betacyanin formation in Amaranthus seedlings
Authors: Obrenović Sneẑana
Published: May 2006

The effects of EDTA, EGTA, SKF 525‐A (a selective inhibitor of cytochrome P‐450) and rotenone were studied in betacyanin induction by 6 h red and 5 min far‐red light, using etiolated, three‐day‐old Amaranthus caudatus L. half‐seedlings. With 0.1 mM EDTA, EGTA and rotenone, and with 10 μM SKF 525‐A, mainly the far‐red reversible betacyanin induction by red light was suppressed. Only in 0.1 mM rotenone was about 50% of that effect compensated by an increased far‐red irreversible betacyanin induction. An unspecific inhibition was obtained with 0.1 mM SKF 525‐A in both control and illuminated plants.

These results are consistent with the view that red light, but not far‐red, causes Ca2+ efflux from both mitochondria and cytoplasm, whereas Ca2+ uptake is indicated mainly after illumination. The resulting switch in the coupling of the mitochondrial electron transport to a Ca2+ dependent one in cytochrome P‐450 system via respiratory complex 1, appears to be responsible for the far‐red reversibility. However, the bulk of the high irradiance reaction seems to be related to another secondary messenger, alternative to Ca2+.
Polyamines in discrete regions of barley leaves infected with the powdery mildew fungus, Erysiphe graminis
Authors: Walters Dale R. , Wylie Moreen A.
Published: May 2006

The concentrations of putrescine, spermidine and spermine and the activities of arginine decarboxylase (ADC; EC 4.1.1.19) and ornithine decarboxylase (ODC: EC 4.1.1.17) were determined in discrete regions of barley leaves (Hordeum vulgare L. cv. Golden Promise) infected with the powdery mildew fungus (Erysiphe graminis f.sp. hordei Marchal). Polyamine concentrations and the activities of both enzymes were always greatest within the region surrounding the fungal pustule, with the lowest values always being found in the region furthest away from the pustule. Although the concentrations of the three amines and ADC and ODC activities within the fungal pustule were always less than values from the zone surrounding the pustule, these differences were never significant. Polyamine concentrations and ODC activity were not significantly reduced, and ADC activity remained unchanged in mildewed leaves with all surface fungal growth removed. It would appear therefore that not only does most of the increase in amines and ODC activity reside in the leaf itself, but that very little of this increase is due to fungal growth and sporulation. Furthermore, it seems possible that the increase in polyamines in mildewed barley could be involved in ‘green‐island’ formation, where regions around mildew pustules remain green and physiologically active while the rest of the leaf senesces.
Appearance of a reversible hydrogenase activity in Anabaena cylindrica grown in high light
Authors: Laczkó Llona
Published: May 2006

In vivo H2 evolution by Anabaena cylindrica Lemm. strain PCC 7122 grown in the presence of ammonia at low and high light intensities was studied. We found that after 2 h of anaerobic incubation, H2 evolution [at a rate of 0.5 μmol (mg dry weight)1 h−1] via reversible hydrogenase occurred in high light grown cells, while this kind of activity was not found in low light grown cells. H2 evolution was inhibited by 3‐(3′. 4′‐dichlorophenyl‐1, 1‐dimethylurea (DCMU). Illuminating the cells in the phycocyanin absorption region resulted in a higher rate of H2 evolution than illuminating the cells in the chlorophyll absorption region. The results indicate that reversible hydrogenase receives reducing equivalents from photosynthetic water photolysis and that both photosystem II and photosystem I participate in the H2 production. Hydrogenase activity was found in the soluble fraction after mild sonication in the case of low light grown cells. After this treatment high light grown cells retained 70% of their hydrogenase activity in the particulate fraction, but released it into the soluble fraction in the presence of 2% deoxycholic acid.

In vitro H2 evolution did not differ significantly in the low and high light grown cells. Hence, the differences in the in vivo H2 evolution reflect the different availability of endogenous reductants for hydrogenase in the two kinds of cells. On the basis of our results it is suggested that high light grown Anabaena cells eliminate part of the photosynthetically produced excess electrons via an induced reversible hydrogenase activity. This is the first report of H2 evolution associated with water photolysis and catalyzed by hydrogenase in cyanobacteria.
The physiological role of abscisic acid in the rooting of poplar and aspen stump sprouts
Authors: Blake Terence J. , Atkinson Susan M.
Published: May 2006

The better rooting performance of stump sprouts offers the means of mass‐producing rooted cuttings of many difficult‐to‐root genotypes. To study the physiological basis of rooting, stem cuttings were taken from stump sprouts of the more readily‐rooted hybrid poplar cultivar DN (P. deltoides × P. nigra) and the difficult‐to‐root aspen hybrid cultivar AE (P. alba × P. tremula). Seasonal variation in rooting percentage of both the AE and DN cultivars (higher in winter and lower in late summer and fall) of poplar was correlated with higher and lower levels of abscisic acid (ABA), respectively, in fractionated extracts of poplar. The presence of ABA in the purified inhibitory fraction was unequivocally confirmed by (i) co‐chromatography, (ii) gas chromatography‐electron capture detector and isomerization with UV light and (iii) combined negative chemical ionization‐mass spectrometry. Although ABA was identified in the inhibitory fractions of mung bean bioassays of both poplar and aspen extracts, exogenous ABA did not inhibit rooting when applied at physiological concentrations. Since ABA levels were higher in the more readily‐rooted hybrid poplar cultivar DN and were higher in February, close to the time of maximal rooting of cuttings, this suggests that ABA levels may possibly explain clonal and seasonal variation in rooting patterns of poplar stump sprouts. This interpretation is supported by the fact that lower, physiological concentrations increased rooting percentage, root number and root elongation when ABA was added to poplar and aspen cuttings.
Effects of tabtoxin on nitrogen metabolism
Authors: Turner John G. , Taha Rihab R. , Debbage Jill
Published: May 2006

Tabtoxin is a chlorosis‐inducing toxin produced by the plant pathogenic bacterium Pseudomonas syringae pv. tabaci. Previous studies have indicated that tabtoxin inhibits glutamine synthetase (EC 6.3.1.2) in vitro. We report here that tabtoxin also inhibits glutamine synthetase in vivo. The main evidence was that assimilation of exogenous 15NH3 into Asparagus sprengeri protein was rapidly inhibited in isolated cells exposed to tabtoxin. This was associated with an equivalent decline in glutamine synthetase activity in extracts of these cells and the accumulation of extracellular ammonia. Glutamine synthetase was also inhibited in leaves of Nicotiana tabacum L. cv. White Burley treated with tabtoxin and the affected tissue accumulated ammonia and became chlorotic. However, the development of symptoms and accumulation of ammonia was suppressed when the leaves were held in air containing 1% CO2 to reduce photorespiration. This indicates that the chlorotic symptom did not result from the inhibition of nitrogen assimilation but was a consequence of the interruption of the photorespiratory nitrogen cycle.
Interaction between a copper‐tolerant and a copper‐sensitive population of Silene cucubalus
Authors: Lolkema P. C. , Doornhof M. , Ernst W. H. O.
Published: May 2006

Interactions between copper‐tolerant and copper‐sensitive plants of Silene cucubalus (L.) Wib. were absent when grown in mixed culture in a nutrient solution with a normal Cu2+ concentration (0.5 μM). When grown in mixed culture in a nutrient solution with 40.5 μM CuSO4, however, the biomass production of the sensitive plants was less affected than when grown in monoculture. At 40.5 μM Cu2+, in the presence of tolerant plants, the concentration of copper in both roots and shoots of sensitive plants was significantly diminished in comparison to a monoculture without tolerant plants. At the same time the copper concentration in the roots of the tolerant plants was higher in the presence of sensitive plants. The possibility of external detoxification of the copper by tolerant plants as a mechanism of heavy metal resistance is discussed.
Comparison of chlorophyll fluorescence with several other techniques used to assess chilling sensitivity in plants
Authors: MacRae E. A. , Hardacre A. K. , Ferguson I. B.
Published: May 2006

Chilling tolerance in eight taxa was estimated from field and controlled environment observations and compared to tolerance estimated using a variety of techniques. The controlled environment observations suggested that the eight taxa could be ranked from chilling tolerant to chilling sensitive in the order: pea (Pisum sativum L. cv. Greenfeast), Passiflora edulis Sims., Passiflora ligularis Juss. and Passiflora quadrangularis L., pepino (Solanum muricatum L.) cultivars Comeraya, Suma, Miski, and mungbean [Vigna radiata (L.) R. Wilcz]; although the relationship between the passionfruit as a group and the pepinos was unclear.

The change in the variable component of chlorophyll fluorescence (FR) with time near 0°C in darkness was the most reliable method of ranking the plants according to relative chilling tolerance. It was also sufficiently sensitive to discriminate clearly between the closely related pepino cultivars. The Passiflora species and pea were not susceptible to short term reductions in FR, with or without a 20 min exposure to light. Exposure to light at temperatures near 0°C emphasised the reductions in FR in the more sensitive species. Pea was the only species capable of recovering a measurable FR after a 60 min exposure to white light.

Measurement of electrolyte leakage and ethylene evolution from leaf disks after a low temperature treatment could allow discrimination between closely related varieties, but not between genera. Catalase activity was reduced in all taxa in response to low temperature. However, both initial catalase levels and relative response to dark treatment at 20°C enabled the ranking of plants within the closely related subgroups according to susceptibility to chill injury.

No one method clearly distinguished chilling sensitivity over all taxa.
Nucleotide pools in leaf and root tissue of tobacco plants: Influence of leaf senescence
Authors: Meyer Reiner , Wagner Karl G.
Published: May 2006

The content of the different ribonucleotides, nucleoside diphosphate sugars, NAD+ and NADP+ was determined in the leaves and roots of single plants of Nicotiana tabacum L. cv. Samsun using a new procedure. The determination makes use of extraction with HClO4 followed by extract purification and separation by a combination of anion‐exchange and reversed phase high performance liquid chromatography. The largest pools were the adenine nucleotides and the uracil nucleotides with nucleoside diphosphate sugars as the main fraction. Leaf senescence was accompanied by a strong reduction of the nucleotide content of the leaves, but the adenine nucleotide‐derived energy charge remained at a high level and even increased at the later stages of senescence. This indicates a balanced metabolism also in the older leaves and excludes the possibility that leaf senescence is triggered by the energy charge.
Internode length in Pisum. The involvement of ethylene with the gibberellin‐insensitive erectoides phenotype
Authors: Ross John J. , Reid James B.
Published: May 2006

The gene lk in peas (Pisum sativum L.) confers the erectoides phenotype. This phenotype possesses much reduced internode and petiole lengths and is practically insensitive to applied GA1, compared with Lk plants. Application of the ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), resulted in increased internode elongation and increased GA‐sensitivity in lk plants, but not in the Lk line, L53. The ethylene‐releasing compound, ethephon, had the reverse effect when applied to the Lk line, L58, reducing internode length and GA‐sensitivity. Ethylene production was higher in lk segregates than in Lk segregates under the conditions used, and the shoot anatomy of lk segregates was consistent with these higher ethylene levels.

These results suggest that the phenotypic effects of gene lk may be due, at least in part, to increased ethylene production in erectoides plants. However, AVG application to lk plants did not produce true phenocopies of comparable lk plants and ethephon application to Lk plants did not produce the erectoides phenotype. Further work is therefore required to determine whether the effect of the gene lk on ethylene production is the primary action of this gene or merely a secondary consequence.
Transfer RNA pool sizes and half lives in wild‐type and cytokinin over‐producing strains of the moss Physcomitrella patens
Authors: Perry K. C. , Cove D. J.
Published: May 2006

Transfer RNA metabolism in developmentally‐abnormal ove strains of Physcomitrella patens (Hedw.) Br. Eur. which produce more than 100 times the wild‐type level of cytokinin, was analysed. tRNA from ove and wild‐type strains of P. patens was extracted and characterised and tRNA metabolism in these strains was compared. No differences large enough to account for the observed levels of cytokinin production by ove strains were found. The amount of cellular tRNA and the rate of cytokinin degradation were similar in ove and wild‐type strains suggesting that the cause of over‐production in the mutants may be due to changed control of a biosynthetic route independent of tRNA.
Glutamate dehydrogenase isoforms in lupine roots and root nodules. Immunological studies
Authors: Ratajczak L. , Koroniak D. , Mazurowa H. , Ratajczak W. , Prus‐Glowacki W.
Published: May 2006

In roots of the lupine (Lupinus luteus L. cv. Ventus) glutamate dehydrogenase (EC 1.4.1.2–4) was present in a single, electrophoretically homogeneous form (GDHR), while in root nodules eight forms of the enzyme (GDHN) were detected. Highly purified fractions of glutamate dehydrogenase from roots and nodules were used to prepare antisera in rabbits. The two antisera recognized extracts of glutamate dehydrogenase from both roots and nodules. Low concentrations of the antiserum raised against nodule glutamate dehydrogenase precipitated GDH from the nodule extract (the homologous antigen) effectively but decreased the activity of GDH from the root extract only slightly. At high concentrations, however, the antiserum totally precipitated both enzyme extracts. Ouchterlony's double diffusion test showed that seven forms of root nodule glutamate dehydrogenase arose as the result of random association of two subunits in a hexameric complex, while the eighth form probably consisted of totally distinct subunits. The question of whether the new glutamate dehydrogenase forms, present exclusively in root nodules, can be classified as nodulins, is discussed.
Effect of fusicoccin and gibberellic acid on primary dormant Avena fatua caryopses
Authors: Foley Michael E.
Published: May 2006

Fusicoccin induced germination in dormant and partially afterripened dormant caryopses of Avena fatua L. The rate of caryopsis germination was slower and final percentage germination lower in the highly dormant inbred line M73 at a given concentration of fusicoccin than in the dormant caryopses of line AN265. Gibberellic acid was more effective than fusicoccin in breaking dormancy in both lines. Promotion of germination of dormant caryopses by fusicoccin was inhibited by a 6‐day pretreatment with (2‐chloroethyl)trimethylammonium chloride.

The basal rate of proton efflux from embryos isolated from dormant and fully afterripened line AN265 caryopses was similar. Addition of fusicoccin increased the rate of proton efflux from the isolated embryos of dormant and afterripened caryopses by nearly 400%. Gibberellic acid had no effect on the rate of proton extrusion. The uptake of 86Rb+ in dormant and afterripened A. fatua embryos was similar after a 2 h uptake period. The addition of fusicoccin to the medium doubled the uptake of 86Rb4 by dormant and afterripened embryos. Gibberelleic acid had no effect on the uptake of 86Rb+ by isolated embryos from either dormant or afterripened caryopses. The experimental results indicate that gibberellic acid is more versatile in its action than fusicoccin, and gibberellic acid may facilitate dormant A. fatua caryopsis germination by stimulating mechanisms other than the direct H+ efflux and K+ uptake at the membrane level.
Partial floral evocation by exogenous cytokinin in the long‐day plant Sinapis alba
Authors: Havelange A. , Bodson M. , Bernier G.
Published: May 2006

A single application of benzyladenine (BA) at 4.3 × 10−5M to the shoot apex of vegetative plants of Sinapis alba L. causes an increase of the import of [14C]‐assimilates in the apical bud and of the starch content. BA also produces the breakdown of the vacuoles into smaller vacuolar units and an increase of the mitotic index leading to nearsynchronization of the meristem cell population in G1. All these changes normally occur in the meristem of Sinapis plants during the transition to flowering (full evocation). Other events normally associated with full evocation are not caused by BA which thus produces only partial evocation. The part of evocation produced by BA is different from that caused by high irradiance.
Isolation of plasma membrane and tonoplast fractions from spinach leaves by preparative free‐flow electrophoresis and effect of photoinduction
Authors: Auderset Guy , Sandelius Anna Stina , Penel Claude , Brightman Andrew , Greppin Hubert , Morré D. James
Published: May 2006

A membrane fraction enriched in plasma membrane and tonoplast vesicles was isolated from green leaves of Spinacia oleracea L. and subjected to subfractionation by free‐flow electrophoresis. The most electronegative membrane vesicle fraction collected after the free‐flow electrophoretic separation was identified as derived from tonoplast, while the least electronegative fraction was identified as derived from plasma membrane. The identification of the fractions was based on membrane morphology, and on the presence or absence of biochemical markers. The plasma membrane fraction was enriched in thick (9–11 nm) membranes which bound N‐1‐naphthylphthalamic acid (NPA), and reacted with phosphotungstic acid at low pH on thin sections for electron microscopy. The tonoplast fraction was enriched in vesicles with 7–9 nm thick membranes that neither bound NPA nor reacted with phosphotungstic acid at low pH. Both the plasma membrane and the tonoplast fraction were about 90% pure, with a cross‐contamination of not more than 2%. Membrane vesicles originating from dictyosomes, endoplasmic reticulum, mitochondria, plastids, or peroxisomes contaminated the plasma membrane and the tonoplast fractions by a few % only. In leaves of photoinduced plants (24 h light period), the plasma membranes were thicker than in control leaves (8 h light, 16 h dark). The plasma membrane fraction obtained from photo‐induced leaves by free‐flow electrophoresis retained this increase in thickness, showing not only that photoinduction alters plasma membrane structure, but also that this change is stable to isolation.
Stimulation of ATPase activity in barley (Hordeum vulgare) root plasma membrane after treatment of intact tissues and cell free extracts with triacontanol
Authors: Lesniak Andrew P. , Haug Alfred , Ries Stanley K.
Published: May 2006

Ca2+‐ and Mg2+‐dependent ATPase activity (EC 3.6.1.3) in a plasma membrane‐enriched fraction increased rapidly after in vivo application of physiologically active concentrations of triacontanol (TRIA) to the roots of barley (Hordeum vulgare L. cv. Conquest) seedlings. Ca2+‐ and Mg2+‐dependent ATPase activity was 64 and 85% higher, respectively, in the roots of seedlings germinated in the presence of growth‐promoting concentrations of TRIA compared to controls. The increase in vivo was concentration dependent, with the greatest increase obtained at 2.3 nM TRIA. Maximal stimulation of ATPase activity of excised tissue treated with TRIA coincided with the temperature at which the barley was grown. At this temperature the plasma membrane is primarily in a mixed gel/liquid crystalline state. Pretreatment of barley roots with cyclohexamide did not alter ATPase stimulation by TRIA. Two to three times more [14C]‐TRIA (mg membrane protein)−1 was found associated with plasma membrane‐enriched vesicles treated with TRIA than with vesicles enriched for mitochondrial membranes or for vesicles enriched for tonoplast, Golgi and rough endoplasmic reticulum. Both Ca2+‐ and Mg2+‐dependent ATPase activity increased by 40–60% within 30 min of the addition of 2.3 nM TRIA to cell‐free extracts of barley roots. The addition of octacosanol, the C28 analogue of TRIA, to cell‐free extracts did not affect metal‐dependent ATPase activity. Consistent with many studies in the green‐house, simultaneous additions of equimolar amounts of TRIA and octacosanol to cell‐free extracts resulted in inhibition of ATPase stimulation by TRIA. TRIA may directly affect plasma membrane function in barley roots.
Accumulation of phytoene in plastoglobuli of SAN‐9789 (Norflurazon)‐treated dark‐grown wheat
Authors: Dahlin Clas , Ryberg Hans
Published: May 2006

Grains of wheat (Triticum aestivum L. cv. Starke II) were treated with SAN‐9789 (Norflurazon), and grown in darkness for 6 days. The SAN treatment resulted in an inhibition of the carotenoid synthesis at the level of phytoene. The plastids of SAN‐treated plants contained enlarged and non‐osmiophilic plastoglobuli, compared to the plastoglobuli of the control. The plastoglobuli were isolated and purified by means of a flotation technique, and their lipid composition was determined. Efforts were made to avoid contamination of epicuticular soluble lipids in the plastoglobuli suspension during isolation. The most suitable method was found to be a mechanical removal of the lipids from the surface of the intact leaves prior to homogenization. Membrane lipids, i.e. galacto‐, phospho‐ and sulpholipids could not be detected in plastoglobuli from either SAN‐treated or control plants, indicating that contamination with membranes was negligible. In plastoglobuli of SAN‐treated plants, large amounts of phytoene and, to a lesser extent, phytofluene accumulated. The proportion of triacylglycerols to quinones was lower than in the control. The main lipids in control plastoglobuli were triacylglycerols, plastoquinones and α‐tocopherol. The possible function of plastoglobuli in etioplasts is discussed.
Characteristics of β‐galactosidase purified from cell suspension cultures of carrot
Authors: Konno Haruyoshi , Yamasaki Yoshiki , Katoh Kenji
Published: May 2006

Five glycosidase activities from cell homogenate of carrot (Daucus carota L. cv. Kintoki) cell cultures were assayed after extraction successively by phosphate buffer (pH 7.0) and the buffer plus 2 M NaCl. A β‐galactosidase (EC 3.2.1.23) was isolated in a highly purified state from the buffer‐soluble protein fraction by ammonium sulfate fractionation and chromatography on CM‐Sephadex C‐50, DEAE‐Sephadex A‐50 and Sephadex G‐200. The molecular weight of this enzyme was ca 104 000 and the isoelectric point was pH 7.8. The optimal activity occurred at pH 4.4 with McIlvaine buffer. The Km and Vmax values were 1.67 mM and 201 units (mg protein)−1, respectively, for p‐nitrophenyl β‐d‐galactopyranoside. The enzyme activity was strongly inhibited by Zn2+, Cu2+, Hg2+ and d‐galactono‐1,4‐lactone. The enzyme acted on the β‐1,4‐linked galactan prepared from citrus pectin in an exo‐fashion. Furthermore, the enzyme was slightly involved in the hydrolysis of the pectic polymer and cell walls purified from carrot cell cultures.
Membrane lipid changes in root cells of rape (Brassica napus) as a function of water‐deficit stress
Authors: Svenningsson Helén , Liljenberg Conny
Published: May 2006

Rape seedlings (Brassica napus L. cv. Brink) were exposed to repeated water‐deficit stress. The water‐stress program started after 19 days of growth and consisted of three 24 h stress periods interspersed with 24 h rewatering periods. After the third stress period the seedlings were harvested and the membrane lipids of the roots were extracted, isolated and quantified. The stress caused an increased ratio of dry weight roots/shoot. Furthermore, the total amount of acyl lipids as well as phospholipids decreased drastically. However, the relative distribution of individual phospholipids was constant and independent of stress. Free and esterified sterols showed only a small decrease in response to water stress. As a consequence the ratio free sterols/phospholipids increased from 0.07 in the control root cells to 0.15 in the stressed cells. The lipid changes are discussed in relation to membrane activity.
Salicylhydroxamic acid‐stimulated NADH oxidation by purified plasmalemma vesicles from wheat roots
Authors: Møller Ian M. , Bérczi Alajos
Published: May 2006

Purified, right side‐out plasmalemma vesicles were isolated from 7‐day‐old roots of dark‐grown wheat (Triticum aestivum L. cv. Drabant) by aqueous polymer two‐phase partitioning. The oxygen consumption by these vesicles at pH 6.5 in the presence of 1 mM NADH [12–29 nmol (mg protein)−1min−1] was 66% inhibited by 1 mM KCN and ca 40% by 1 mM EDTA. It was unaffected by rotenone, antimycin A, carbonyl cyanide trifluoromethoxyphenylhydrazone (FCCP), mersalyl, chlorotetracycline + Ca2+, and EGTA. Salicylhydroxamic acid (SHAM) and its analogue, m‐chlorobenzhydroxamic acid, stimulated the rate of oxygen consumption 10–20 fold in the presence of 1 mM NAD(P)H with an apparent Km (SHAM) of ca 40 μM (with NADH). The dependence of O2 consumption on NADH concentration in the presence of SHAM (2 mM) was sigmoidal, possibly due to endogenous catalase activity, and half‐maximal rate was obtained at 1.5 mM. In the absence of SHAM the rate increased with increasing acidity and no pH optimum was detectable between pH 4.5 and 8.5. In the presence of SHAM an optimum was observed at pH 6.5 and 0.8 mol of H2O2 was produced for every 1 mol O2 consumed. Endogenous catalase converted this H2O2 to O2 and after complete conversion the stoichiometry was 2 mol NADH consumed for every mol O3. SHAM was not consumed in the reaction. The possible involvement of a cytochrome P‐450/420 system is discussed.
Intracellular localisation of some peptidases and α‐mannosidase in cotyledons of resting kidney bean, Phaseolus vulgaris
Authors: Mikkonen Anita , Begbie Robert , Grant George , Pusztai Arpad
Published: May 2006

Cotyledons of resting kidney beans (Phaseolus vulgaris, L., cv. “Processor”) contain high activities of two alkaline peptidases, an aminopeptidase (EC 3.4.11) acting on Leu‐Tyr and Leu‐Gly‐Gly and a dipeptidase (EC 3.4.13) hydrolysing Ala‐Gly together with low activities of neutral naphthyiamidases (marker substrate Leu‐β‐NA) and of acid carboxypeptidases (EC 3.4.16; marker substrate Z‐Phe‐Ala). The intracellular localisation of these peptidases and that of α‐mannosidase (EC 3.2.1.24) was studied by subcellular fractionations in different media. In density gradient centrifugations in non‐aqueous glycerol‐potassium iodide media the alkaline peptidases remained mainly in the application zone suggesting localisation in the cytosol. The carboxypeptidase and α‐mannosidase activities banded mainly in the protein body zone, but about 15–30% of each activity was found in the cell wall zone. Results obtained by short centrifugation in glycerol or high‐density sucrose solutions (65/70%) and by the isolation of essentially pure cell wall fractions confirmed these assignments. The results are in accordance with previous suggestions that the abundant alkaline peptidases may play a role in the mobilization of reserve proteins in germinated seeds by hydrolysing peptides which are produced initially within the protein bodies by acid proteinases and carboxypeptidases and which subsequently leak out or are transported from the autolyzing protein bodies to the cytosol.
Effects of calcium ions on responses of two jute species under water‐deficit stress
Authors: Roy Chowdhury S. , Choudhuri M. A.
Published: May 2006

Water‐deficit stress (–1.0 MPa through polyethylene glycol 6000 for 2 h) decreased the relative water content (RWC) and leaf water potential (LWP) in the two jute species Corchorus capsularis L. (cv. JRC 212) and C. olitorius L. (cv. JRO 632), more so in the latter. Pretreatment of seeds with 5 mM CaCl2 improved the water uptake capacity without altering stomatal movement, whereas foliar spraying with 0.01 mM ABA reduced transpiration through the reduction of stomatal aperture. A combination of both treatments, i.e. seed treatment followed by foliar spraying, additively improved the water status under water‐deficit stress. Efflux of K+ from the guard cells followed by stomatal closure was more rapid in C. capsularis than in C. olitorius under water‐deficit stress. Uptake of [32P]‐phosphate under water‐deficit stress decreased more in C. olitorius than in C. capsularis and treatment of seeds with Ca2+ counteracted this decrease more markedly in the former species. These findings indicate that C. olitorius is more susceptible than C. capsularis to water‐deficit stress.
Anion uptake in maize roots: Interactions between chlorate and nitrate
Authors: McClure Peter R. , Omholt Thomas E. , Pace Gary M.
Published: May 2006

Effects of nitrate, chloride and chlorate ions upon nitrate and chlorate uptake by roots of maize (Zea mays L., cv. B73) seedlings were examined. Net nitrate uptake, 36ClO3− influx and 36Cl− influx (the latter two in a background of 0.5 mM KNO3) displayed similar pH profiles with optima at pH 5.5 and below. External, non‐labeled chloride had little effect on the accumulation of 36ClO3− (both in 5 h and 20 min uptake assays), while nitrate and chlorate had almost identical, marked inhibitory effects. Nitrate pretreatment caused an apparent induction of both 36ClO3− and 15NO3− uptake activities. After 5 h of treatment in nitrate, the uptake activities of chloride‐ and chlorate‐pretreated plants increased to that of nitrate‐pretreated plants. During 6 h exposure to chlorate, 36ClO3− uptake activity of nitrate‐pretreated plants decreased to that of chlorate‐ and chloride‐pretreated plants. The results support the existence of a shared nitrate/chlorate transport system in maize roots which is not inhibited by external chloride, and which is induced by nitrate, but not by chlorate or chloride. The suggestion is made that selection of chlorate‐resistant mutants of maize can identify nitrate uptake as well as nitrate reductase mutants.
Relation between the diameter of the growing shoot and the mature size of leaves and flower head of sunflower
Authors: Pieters George A.
Published: May 2006

Helianthus annuus L. cv. INRA 6501 plants were cultivated at irradiances of 15, 30 and 60 W m−2 (400–700 nm) at 20°C and a relative humidity of 60% on a gravel culture subirrigated with Hoagland's nutrient solution. From 10 days after the opening of the cotyledons the diameter of the growing shoot increased linearly with time at a rate dependent on the irradiance. These measurements were continued until the flower bud became visible. By extrapolation of this linear growth to the day of anthesis the diameter of the stem below the flower head was predicted. This stem diameter had a constant ratio (9.7) to the measured diameter of the flower head. In the early stages of development of the plant it is proposed that the diameter of the growing shoot, supported by its vascular system, is a determinant of the size of the mature leaves. Later in the development the diameter of the growing shoot is a determinant of the diameter of the flower head. This change of function is caused by localised activity of the cambial cells which results in tangential growth in the vascular cylinder and ultimately in a hollow stem.
Protochlorophyll(ide) accumulation and degradation in the dark and photoconversion to chlorophyll in the light in pigment mutant C‐2A’ of Scenedesmus obliquus
Authors: Senger Horst , Brinkmann Gerd
Published: May 2006

Pigment mutant C‐2A’ of Scenedesmus obliquus accumulates only traces of chlorophyll, when grown heterotrophically in the dark. Immediately upon transfer of cells into fresh medium protochlorophyllide and protochlorophyll are formed, which accumulate to their maximum concentrations within 8 to 12 h. Subsequently, this protochlorophyll(ide) is degraded in the dark, but not transformed into chlorophyll. After 6–8 days of dark growth no protochlorophyll(ide) can be detected any more. The protochlorophyll(ide) pool of cultures, which contain reduced concentrations, can be reestablished either by addition of glucose or illumination with blue light; both increase the rate of respiration.

By low temperature spectroscopy in vivo and by absorption and fluorescence emission spectroscopy of pigment extracts it is shown that the protochlorophyllide accumulated in freshly inoculated cultures can be converted to chlorophyll in light.

From the action spectrum for chlorophyll formation after addition of glucose it can be seen that protochlorophyllide 636 and 649 are present and are photoconvertible in this mutant.
Osmoregulation, growth and sucrose accumulation in germinated Trigonella foenum‐graecum (fenugreek) seeds treated with polyethylene glycol
Authors: Spyropoulos Caroline G.
Published: May 2006

Germinated seeds of Trigonella foenum‐graecum L. (fenugreek) were grown in water or in polyethylene glycol (PEG) solutions. After endosperm removal, the water relations, growth, dry weight, sucrose and reducing sugar content of the embryo were determined. Under water sstress conditions, water content and osmotic potential (π0) at saturation, growth and dry weight were lower than in non‐stressed controls. The reduction in dry weight indicated a lower uptake of solutes from the endosperm and the decrease in π0 was not accompanied by an increase in the amount of the accumulated solutes. It is suggested that embryos of stressed fenugreek seeds control osmotic potential by reduction of water uptake and that this results in reduction of growth. Embryos isolated from germinated seeds (“naked” embryos) were grown in water or in PEG solutions, with or without galactose (as an external solute source substituting for the endosperm). The results indicate that a decrease in the external solute did not account for growth reduction under conditions of water stress, and that decreased solute transport to the embryo may be important. The sucrose contents of “naked” embryos and of embryos from whole seeds were higher after PEG treatment, while reducing sugar contents were lower compared to non‐stressed controls. The increased sucrose accumulation may be due to decreased sucrose hydrolysis.
The interaction of thylakoid lipids with everted photosystem II membranes
Authors: Rochester C. P. , Andersson B.
Published: May 2006

Spinach (Spinacia oleracea L. cv. Viking II) thylakoid membranes enriched in photosystem II were disrupted by incubation at 35°C for 5 min followed by sonication. This treatment caused the loss of manganese and the release of extrinsic photosystem II proteins of 16, 23 and 33 kdaltons, resulting in retention of only 12–18% of the oxygen‐evolving activity. Prior addition of exogenous digalactosyldiacylglycerol to the membranes afforded protection against the release of manganese and extrinsic proteins and enabled the retention of up to 47% of the activity. Monogalactosyldiacylglycerol was less effective in both respects and enabled retention of only 30% of the activity. Addition of charged thylakoid lipids had a severely damaging effect on photosystem II.
Putative role of ethylene in Datura metel microspore embryogenesis
Authors: Babbar Shashi B. , Gupta Shrish C.
Published: May 2006

The role of ethylene in microspore embryogenesis was analyzed by studying the effect of cobalt ions, silver ions, methionine and Ethrel on the androgenic response of in vitro cultured anthers of Datura metel L. Cobalt and silver ions, provided in the form of cobalt chloride and silver nitrate, respectively, decreased the average number of embryos/plantlets developed per anther, at all the concentrations tested. In contrast, methionine (10−5–10−3M) and Ethrel (10−6 and 10−5M) stimulated embryo formation. The optimal enhancement was recorded at 10−5M of both methionine and Ethrel.
Growth synchrony and cellular parameters of the unicellular nitrogen‐fixing marine cyanobacterium, Synechococcus sp. strain Miami BG 043511 under continuous illumination
Authors: Mitsui A. , Cao S. , Takahashi A. , Arai T.
Published: May 2006

A marine unicellular aerobic nitrogen‐fixing cyanobacterium Synechococcus sp. strain Miarni BG 043511 was pretreated with different light and dark regimes in order to induce higher growth synchrony. A pretreatment of two dark and light cycles of 16 h each yielded good synchrony for 3 cell division cycles. Longer dark treatments decreased the degree of synchrony and shorter dark treatments caused irregular cell division. Once synchronous culture was established, distinct phases of cellular carbohydrate accumulation and cellular carbohydrate degradation were observed even under continuous illumination. Changes in carbohydrate content were repeated in a cyclic manner with approximately 20 h intervals, the same as the cell division cycle. This change in carbohydrate metabolism provided a good index of growth synchrony under nitrogen‐fixing conditions.

Photosynthetic oxygen evolution and nitrogen fixation capabilities and their activities in near, in situ, culture conditions were measured in well synchronized cultures of this strain under continuous illumination. Distinct oscillations of both photosynthetic oxygen evolution and nitrogen fixation capabilities with ca 20‐h intervals, similar to the interval of the cell division cycle, were observed for three cycles. However, the activities of photosynthetic oxygen evolution were inversely correlated with those of nitrogen fixation. During the nitrogen fixation period, net oxygen consumption was observed even in the light under conditions approximating in situ culture conditions. The phase of temporal appearance of nitrogenase activity during the cell division cycle coincided with the phase of carbohydrate net degradation. These data indicate that this unicellular cyanobacterium can grow diazotrophically under conditions of continuous illumination by the segregation of photosynthesis and nitrogen fixation within a cell division cycle.
Protein synthesis and phosphorylation of light‐harvesting apoproteins in normal and chlorophyll b‐deficient Chlamydomonas reinhardii
Authors: Michel Hanspeter , Boschetti Arminio
Published: May 2006

Phosphorylation of polypeptides in whole cells and in chloroplasts of different strains of Chlamydomonas reinhardii was studied. Phosphorylation in vivo was strongly reduced when cytoptasmic protein synthesis was inhibited either by anisomycin or by cycloheximide. In isolated chloroplasts these two inhibitors had no effect on labelling. The incorporation of [32P]‐phosphate into one of the apoproteins of the light‐harvesting chlorophyll a/b‐protein complex (LHC 2) was also studied in relation to its synthesis. In vivo, in a chlorophyll b‐deficient mutant and in its parent strain we found a pronounced relationship between synthesis and phosphorylation of this LHC 2‐apoprotein. Our results suggest that LHC 2‐apoproteins, newly synthesized in the cytoplasm, are preferentially phosphorylated after synthesis. Together with the observation that phosphorylation still occurs in isolated chloroplasts we conclude that in vivo at least two levels of phosphorylation of the LHC 2‐apoproteins have to be clearly differentiated. One level involves the phosphorylation of existing and the other of newly synthesized polypeptides. The biological significance of phosphorylation of the LHC 2‐apoproteins in vivo and probably also of other thylakoid polypeptides is complex and not restricted to regulation of energy distribution between photosystems 1 and 2.
Effect of auxin on the mitotic cell cycle in cultured leaf segments at different stages of development in wheat
Authors: Wernicke Wolfgang , Milkovits Lydia
Published: May 2006

Young leaves of Triticum timopheevi Zukh. show a defined gradient of development. One‐mm‐long sections from such leaves were cultured in vitro. At a low concentration of exogenous auxin, cells in the most basal, highly meristematic explants divided readily in culture, but in the absence of auxin they soon ceased dividing and were arrested in G1 and G2 of the mitotic cell cycle. In the region adjoining the meristem, where most cells were arrested in G1, very high concentrations of auxin had to be applied to reinitiate cell division, i.e. stimulate transitions from G1 to S‐phase and from G2 to mitosis. Above this potentially auxin‐responsive region, which represented less than 50% of the total leaf length, there followed tissue, which, when excised, showed nuclear DNA replication in a number of cells in the absence of auxin. However, the cells did not complete the mitotic cycle, either in the absence or presence of exogenous auxin. We suggest this loss of responsiveness is correlated with an uncoupling of auxin from the control of the cell cycle.
UDP‐Glucose level as a limiting factor for IAA‐induced cell elongation in Avena coleoptile segments
Authors: Inouhe Masahiro , Yamamoto Ryoichi , Masuda Yoshio
Published: May 2006

The effects of galactose on IAA‐induced elongation and endogenous level of UDP‐glucose (UDPG) in oat (Avena sativa L. cv. Victory) coleoptile segments were examined under various growth conditions to see if there was a correlation between the level of UDPG and auxin‐induced growth. The following results were obtained:

Galactose (10 mM) inhibited the auxin‐induced cell elongation of oat coleoptile segments after a lag of ca 2 h. Determinations of cell wall polysaccharides and UDP‐sugars indicated that galactose, when inhibiting the cell wall polysaccharide synthesis, decreased the level of UDPG but caused an increase in the levels of Gal‐1‐P and UDP‐Gal.

When coleoptile segments treated with IAA and galactose were transferred to galactose‐free IAA‐solution, the segment elongation was restored and the amounts of cell wall polysaccharides increased. During this period, the amount of UDPG increased and the levels of Gal‐1‐P and UDP‐Gal slightly decreased or leveled off. The UDP‐pentoses changed similarly as UDPG did.

Addition of sucrose (30 mM) enhanced IAA‐induced cell elongation and removed growth inhibition by 1 mM galactose. Sucrose increased the amounts of the cell wall polysaccharides and the level of UDPG in the presence or absence of IAA and also counteracted the decrease in UDPG caused by galactose.

These results indicate that the level of UDPG is an important limiting factor for cell wall biosynthesis and, thus, for auxin‐induced elongation.