bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
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.
Changes in carbohydrates and mineral elements in Citrus leaves during flowering and fruit set
Authors: Sanz A. , Monerri C. , González‐Ferrer J. , Guardiola J. L. 
Published: May 2006

Mineral elements and metabolizable carbohydrates in Citrus leaves [Citrus sinensis (L.) Osbeck cv. Washington navel] have been determined from bud sprouting until the end of the June drop and related to fruitlet growth and abscission. Mineral elements in old leaves decreased during the spring flush of growth and reached minimum values at flower opening, coinciding with a peak in abscission. This was followed by a rapid recovery in potassium and nitrogen to the initial values, with little change afterwards. Old leaves accumulate carbohydrates until flowering, and lose them during post‐anthesis at a constant rate for more than 4 months; this rate of export is unaltered by the presence of a nearby growing fruit. Inflorescence leaves accumulate carbohydrates and mineral elements during post‐anthesis; during the June drop there is an interruption in the accumulation of nitrogen and a net loss of phosphorus, potassium and carbohydrates from these leaves, coinciding with the attainment of the maximum growth rate of the fruit.The two main periods of abscission coincide with minima in the amount of reserves in leaves, suggesting that a limitation in metabolite supply may be the primary cause of drop. There is a closer relationship of the fruit with inflorescence leaves than with old mature ones; however, the regulation of carbohydrate levels in the inflorescence leaves cannot be simply explained in terms of source‐sink relationships with the nearby growing fruit, and the smaller size of inflorescence leaves vs. vegetative ones is not due to the presence of the flower during leaf development.
Isolation of root hairs from seedlings of Pisum sativum. Identification of root hair specific proteins by in situ labeling
Authors: Röhm Mechthild , Werner Dietrich 
Published: May 2006

A procedure was developed which allows the large‐scale isolation of root hairs from seedlings of Pisum sativum. L. cvs. Kleine Rheinländerin and Rosa Krone. The method may yield up to 50 g fresh weight of root hairs per 3.104 seedlings. In a modified form considerable amounts of root hair material may be harvested, even after incubation of the roots in aqueous solutions. Thus, detailed biochemical studies on the root hair system have become feasible.The occurrence of specific proteins in membrane fractions of P. sativum root hairs was demonstrated as follows: Incubation of root hairs in situ with 3‐azidonaphthalene‐2,7‐disulfonate – a strongly anionic, photoactivated fluorescent marker – followed by gel electrophoresis of membrane fractions showed the presence of root‐hair specific proteins which, since the system was intact, suggests that they are on the outer surface of the cells.
Chlorophyll synthesis in green leaves and isolated chloroplasts of barley (Hordeum vulgare)
Authors: Dehesh Katayoon , Kreuz Klaus , Apel Klaus 
Published: May 2006

The photoreduction of protochlorophyllide was studied in leaves and isolated chloroplasts of barley. Leaves of plants which had been preilluminated for varying lengths of time were incubated with [14C]‐δ‐ aminolevulinic acid for 2 h in the dark. The subsequent photoreduction of [14C]‐protochlorophyllide was analyzed by high performance liquid chromatography of pigments extracted from illuminated leaves and plastids. The plastids used in this study were isolated in the dark from leaves at the end of the 2 h labelling period. Three major results were obtained:

The extent of protochlorophyllide reduction in vivo was rapidly reduced as a function of the preillumination period. In 24 h preilluminated plants only a small fraction of the radioactively labelled protochlorophyllide was reduced during the subsequent light period.
The amount of NADPH‐protochlorophyllide oxidoreductase (EC 1.6.99.‐) present in plastids of fully‐green plants was drastically reduced relative to levels in plastids of dark‐grown plants as estimated by the methods of immunoblotting of plastid proteins and immunogold labelling of ultrathin sections of the leaf tissue.
In etiolated plants light seemed to affect the reduction of protochlorophyllide directly through the excitation of protochlorophyllide. In fully green plants, however, light also affected chlorophyll formation indirectly by the supply of NADPH via photosynthetic electron transport.
Germination uniformity of Fraxinus excelsior controlled by seed water content during cold treatment
Authors: Van de Walle Claude 
Published: May 2006

The seeds of Fraxinus excelsior L. are dormant after harvest, since they need a period of chilling for germination. Moist treatment at 20°C for 2–3 months followed by stratification at 4°C for 7 months breaks dormancy. We observed that germination occurred during stratification and was spread over a period of 3 months. Germination at low temperature was temporarily inhibited by a moderate reduction of the seed water content initiated after the third month of stratification. This allowed the afterripening process to continue.The following procedure was developed to suppress dormancy and to induce uniform germination:

Imbibition of the seeds and moist treatment at 20°C for 2–3 months;
stratification for 3 months;
treatment at low temperature and low water potential for at least 4 months, this treatment should not exceed 6 months;
complete rehydration of the seeds at 16°C.
The effects of exogenously applied plant growth substances on the physiological plasticity in Plantago major ssp. pleiosperma: Responses of growth, shoot to root ratio and respiration
Authors: Kuiper Daan , Staal Marten 
Published: May 2006

Growth rates, shoot to root ratios and root respiration were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) at two regimes of mineral nutrition. The responses of plants transferred from one condition to the other were compared with similarly transferred plants supplied with a plant growth substance and also with plants permanently grown at the same nutritional level.The effect of an addition of benzyladenine (BA) depended on the concentration. Changes in the relative growth rates, shoot to root ratios and root respiration as a response to a lowered mineral supply were strongly retarded by 10−8M BA. These effects of BA were very obvious in the first period of 7 days after the transfer of the plants. During the second period of 7 days the hormonal effects disappeared due to limitation of mineral nutrients. Daily spray with abscisic acid or with indoleacetic acid did not significantly affect the measured characteristics. The results from the experiments with BA addition are discussed in relation to a possible regulatory role of cytokinins in physiological plasticity upon mineral nutrition.
Preparation of extracts from mature spruce needles for enzymatic analyses
Authors: Weimar Maria , Rothe Gunter M. 
Published: May 2006

It was possible to extract simultaneously several active enzymes involved in the carbohydrate or the amino acid metabolism from spruce needles [Picea abies (L.) Karst.] when a) a 100 mM Na‐Pi buffer of pH 7.5 containing 5% PVPP and 0.5% Triton X‐100 was used and when b) the resulting crude extracts were freed from lowmolecular‐weight compounds by gel‐chromatography using the separation medium Fractogel TSK HW‐40. Besides Triton X‐100, Triton X‐305, Myrij‐52 and Brij‐35 were tested, but 0.5% Triton X‐100 brought about the most active enzyme extracts. In crude extracts prepared from spruce needles during the early summer a high increase in absorbance at 334 nm was observed when the co‐substrate NADP+ was added, thus making reliable spectrophotometric assays impossible. The interfering low‐molecular‐weight substances could be eliminated by gel chromatography. As separation media Bio‐Gel P‐6 DG, Sephadex G‐25 m, Trisacryl GF 05 and Fractogel TSK HW‐40 (F) were tested, with Fractogel yielding the highest activities.With the methods described in this paper the activities of the following enzymes were determined: glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49), 6‐phosphogluconate dehydrogenase (EC 1.1.1.44), glucose‐6‐phosphate isomerase (EC 5.3.1.9), shikimate dehydrogenase (EC 1.1.1.25), NAD+‐malate dehydrogenase (EC 1.1.1.37), glutamate dehydrogenase (EC 1.4.1.2), aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2). The activities estimated for NAD+‐malate dehydrogenase and 6‐phosphogluconate dehydrogenase are in the range of those published for the needle enzymes of white spruce and Scots pine, respectively.
Photosynthesis and stomatal characteristics of Striga hermonthica in relation to its parasitic habit
Authors: Shah N. , Smirnoff N. , Stewart G. R. 
Published: May 2006

Photosynthesis and stomatal characteristics of the angiosperm parasite Striga her‐monthica (Del.) Benth. have been compared with those of Antirrhinum majus L. cv. Suttons Yellow Rust Resistant, a related, non‐parasitic species. The concentration of photosynthetic pigments in S. hermonthica leaves was less than 40% of those of A. majus leaves. Light saturated CO2 assimilation rate of S. hermonthica was less than 40% that of A. majus on a chlorophyll basis and under 20% than of A. majus on a leaf area basis.Stomata of Striga showed only partial closure in darkness, remained open in water stressed leaves and showed little response to exogenously applied abscisic acid. Stomatal conductance and transpiration were considerably higher in Striga compared with Antirrhinum. The high transpiration and low photosynthetic rates of S. hermonthica resulted in a low water use efficiency. The water relations of Striga leaves, while seemingly inappropriate for growth in drought prone environments, do appear to maximise nutrient and water acquisition from the host and as such may be an adaptation to the parasitic habit.
Changes in K+, Cl− and P contents in stomata of Zea mays leaves exposed to different light and CO2 levels
Authors: Lascève G. , Couchat P. , Vavasseur A. , Bossy J. P. 
Published: May 2006

Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO2 partial pressure. The K+, Cl− and P contents were then determined by X‐ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling.In normal air, the K+ and Cl− contents in guard cells only rose from a light threshold of about 300 μmol m−2 s−1 at which stomata were already largely open. At 600 μmol m−2 s−1, the K+ and Cl− levels in guard cells attained values that were 3‐ and 8‐fold greater, respectively, than the values observed in darkness. The K+ and Cl− contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO2‐free air in darkness induced a significant K+ influx towards guard and subsidiary cells. Under light and in CO2‐free air, the K+ and Cl− contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO2‐free air, the K+ and Cl− contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl−/K+ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K+ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K+ and Cl−, to be practically independent of stomatal aperture.