bluuebunny/crossref_metadata_2025 huggingface dataset:
In suspension cultures of Catharanthus roseus the cyanide‐resistant pathway is engaged in respiration by excess sugar in combination with phosphate or nitrogen starvation
Authors: Hoefnagel Marcel H. N. , van Iren Frank , Libbenga Kees R.
Published: May 2006

Suspension cultured cells of Catharanthus roseus were used to study the effects of excess sugar, and phosphate or nitrogen starvation on growth and respiration. Excess sugar resulted in a higher dry weight but the cell number was not significantly higher than in the controls. After inoculation in phosphate‐free medium almost no growth was observed, whereas in medium without nitrogen some growth still occurred, indicating that the medium contains more than enough nitrogen and only a limited amount of phosphate. The maintenance respiration in the nitrogen‐free medium was lower than in the control, probably as a result of a lower protein production. In phosphate‐free medium, however, the maintenance respiration was higher, because the cyanide‐resistant pathway was engaged and the P/O ratio was decreased. In Catharanthus roseus cells the cyanide‐resistant pathway is engaged upon phosphate or nitrogen starvation in combination with excess sugar, while excess sugar, as such, does not engage the cyanide‐resistant pathway. In the presence of excess sugar the rate of glycolysis is adenylate‐controlled. It is only in combination with mineral starvation that the rate of glycolysis does not match the capacity of the cytochrome pathway, resulting in an overflow via the alternative pathway. After combination of mineral starvation with a low sugar supply the rate of glycolysis is controlled by both the substrate supply and the adenylates, and the cyanide‐resistant pathway is not engaged.
An excision and squash technique for analysis of the cell cycle in the root quiescent centre of maize
Authors: Múller Mathias L. , Pilet Paul‐Emile , Barlow Peter W.
Published: May 2006

The quiescent centre of primary roots of Zea mays L. (cvs LG 11 and Golden Bantam) consists of a population of slowly cycling diploid cells. These metabolically inactive cells may be triggered to synthesise DNA under specific conditions and constitute a good model for studying the regulation of the cell cycle. An excision and squash technique is described for the quiescent centre which, when coupled with Feulgen and fluorochrome staining, allows nuclear DNA contents to be determined by microdensitometry in less than a day. This technique was coupled with experiments in which excised quiescent centres were placed on solid culture medium into which hormones and radioactive DNA precursors were incorporated. In complementary and control experiments [methyl‐3H]thymidine was supplied to intact roots (with or without root caps) by means of fibre‐glass cubes as donors.

Progression of the cell cycle was followed by microdensitometry and autoradiography. Distribution of DNA content was similar in excised and squashed quiescent centres and in histological sections. Labelling experiments showed that the quiescent centre is made up of cells that differ in their cycle time. While some labelled cells had reached mitosis after 8 h, others were still in G2 after 16 h of continuous labelling. Excision and culture of the quiescent centre resulted in a dramatic activation of the cell cycle as shown by the labelling index that increased from 15% in intact roots fed during 16 h with [methyl‐3H]thymidine to 31% in excised quiescent centres to which radioactive precursor was supplied during the same time. Supplying hormones (50 μM abscisic acid [ABA], 0. 1 μM zeatin, 1 μM zeatin riboside) to quiescent centres via the culture medium restored their inactivity (labelling indices dropped to 1% after ABA. and to 11% after zeatin and zeatin riboside treatments. respectively).
Effect of temperature on the growth of individual cucumber fruits
Authors: Marcelis Leo F. M. , Hofman‐Eijer Lutske R. Baan
Published: May 2006

In order to study the effect of temperature on the growth of individual fruits in cucumber (cucumis sativus L. cv. Corona), fruits were grown at 17. 5. 20,25 and 30°C continuously or the fruit temperature was changed from 17. 5 to 27.5°C or vice versa. Fruit development appeared to be closely related to the temperature sum. When the growth of a fruit was not constrained by assimilate supply, a decrease in growing period with increasing temperature was more than compensated for by a strong increase in growth rate, resulting in an increase in final fruit weight. However, when the growth of a fruit was constrained by assimilate supply, the increase in growth rate with increasing temperature was small and did not compensate for the decrease in growing period, resulting in a decrease in final fruit weight. Determinations of cell number and size showed that the effect of temperature on fruit growth was due to effects on cell expansion rather than on cell division. When growth was not constrained by assimilate supply. However, when assimilate supply did constrain fruit growth the number of cells per fruit decreased with increasing temperature, while the effect on cell size was negligible. In all stages of fruit development, the growth rate of a cucumber fruit responded within one day to a change in temperature. It was not irreversibly impaired by a low temperature (17. 5°C) during the early development of a fruit. A high temperature treatment (27. 5°C), however, had a great effect on the growth rate of a fruit after the temperature treatment had terminated. At all stages of fruit development (even before anthesis) a period of four days at 27. 5°C resulted in a pronounced stimulation of the growth rate afterwards at 17. 5°C.
Import of nuclear‐encoded proteins into carotenoid‐deficient young etioplasts
Authors: Dahlin Clas
Published: May 2006

Young etioplasts with different carotenoid contents were assayed for their ability to import in vitro synthesized nuclear‐encoded proteins. The plastids were isolated from the basal 1. 5cm of dark‐grown wheat seedlings developed from seeds imbibed with 4 different concentrations of Norflurazon. an inhibitor of the carotenoid biosynthesis. Plastids isolated from plants treated with the two highest concentrations. 2. 8 and 28 mg l−1, of Norflurazon contained approximately 10 and 5% of the carotenoid contents, respectively, compared to the control. The total amounts of proteins in these plastids were approximately 68 and 60% compared to control plastids. Translocation assays employing the precursors of the small subunit of ribulose 1. 5‐bisphosphate carboxylase/oxygenase (pSS), and the non‐Photosynthetic heat‐shock protein 21 (pHSP21), showed that the rate of protein import was considerably lower in plastids with low carotenoid contents. The amounts of imported, processed SS were 11 and 10% after 2. 8 and 28 mg 1−1, respectively, compared to the control, whereas the amounts of HSP21 at these herbicide concentrations were 20 and 18%, respectively. The low apparent import in plastids of Norflurazon‐treated leaves was not an effect of intraorganellar degradation of imported proteins, nor were there any differences in the amounts of processed, protease‐protected protein when Norflurazon was added to the import reaction using control plastids. The low import capabilities are therefore discussed in relation to the possible role of the carotenoids in the translocation of cytosolically synthesized proteins into the plastidic compartment.
Use of lysophosphatidylethanolamine, a natural lipid, to retard tomato leaf and fruit senescence
Authors: Farag Karim M. , Palta Jiwan P.
Published: May 2006

We studied the influence of lysophosphatidylethanolamine (LPE) on the pattern and rate of ethylene production and respiration of tomato (Lycopersicon esculentum cv. H7155) leaflets and fruit. Leaflets that had been senescing on the plant showed a climacteric‐like rise in ethylene production but not in respiration rate which decreased continuously with leaf age. Detached leaflets had a climacteric‐like pattern in respiration whether they were incubated in complete darkness or in light. Detached leaflets incubated in the dark had higher rates of ethylene production and CO2 evolution than did light‐incubated leaves. There was no change in the pattern of ethylene production or CO2 evolution as a result of LPE treatment. However, LPE‐treated attached and detached leaflets had consistently lower rates of CO2 evolution. The reduction in CO2 evolution by LPE was most pronounced at the climacteric‐like peak of the detached leaves. LPE‐treated leaflets had a higher chlorophyll content and fresh weight and lower electrolyte leakage than the control. LPE‐treated fruits had lower rates of ethylene and CO2 production than did the control. LPE‐treated fruits also had higher pericarp firmness and lower electrolyte leakage than the control. The results of the present study provide evidence that LPE is able to retard senescence of attached leaves and detached leaves and tomato fruits. Several recent studies suggest that lysolipids can act in a specific manner as metabolic regulators. Our results suggest a specific role of lysolipid LPE in aging and senescence
Oxygen‐induced recovery from short‐term nitrate inhibition of N2 fixation in white clover plants from spaced and dense stands
Authors: Faurie Olivier , Soussana Jean‐François
Published: May 2006

Nitrogenase (N2ase; EC 1.18.6.1) activity (H2 evolution) and root respiration (CO2 evolution) were measured under either N2:O2 or Ar:O2 gas mixtures in intact nodulated roots from white clover (Trifolium repens L.) plants grown either as spaced or as dense stands. The short‐term nitrate (5 mM) inhibition of N2‐fixation was promoted by competition for light between clover shoots, which reduced CO2 net assimilation rate. Oxygen‐diffusion permeability of the nodule declined during nitrate treatment but after nitrate removal from the liquid medium its recovery parallelled that of nitrogenase activity. Rhizosphere pO2 was increased from 20 to 80 kPa under N2:O2. A simple mono‐exponential model, fitted to the nodule permeability response to pO2, indicated NO−3 induced changes in minimum and maximum nodule O2‐diffusion permeability. Peak H2 production rates at 80 kPa O2 and in Ar:O2 were close to the pre‐decline rates at 20 kPa O2. At the end of the nitrate treatment, this O2‐induced recovery in nitrogenase activity reached 71 and 82%; for clover plants from spaced and dense stands, respectively. The respective roles of oxygen diffusion and phloem supply for the short‐term inhibition of nitrogenase activity in nitrate‐treated clovers are discussed.
Nitrogen assimilation and transport in carob plants
Authors: Cruz C. , Lips S. H. , Martins‐Louçαo M. A.
Published: May 2006

Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata) is localised in the roots. The nitrate concentration in the leaves is relatively low compared to that in the roots, suggesting that nitrate influx into the leaf may be a major factor limiting the levels of nitrate reductase in the shoot. Transport of nitrate from root to shoot appears limited by the entrance of nitrate into the xylem. In order to study this problem, we determined the nitrate concentrations and nitrate reductase activities along the roots of nitrate‐grown plants, as well as the composition of the xylem sap and the nitrate levels in the leaves. Some of the the bypocotyl, in order to bypass the loading of nitrate into the xylem of the roots. The results show that the loading of nitrate into the xylem is a limiting step.

The cation and anion concentrations of nitrate‐ and ammonium‐fed plants were similar, showing almost no production of organic anions. In both nitrate‐ and ammonium‐fed plants, the transport of nitrogen from root to shoot was in the form of organic nitrogen compounds. The nitrate reductase activity in the roots was more than sufficient to explain all the efflux of OH− into the root medium of nitrate‐fed plants. In carob plants the K‐shuttle may thus be operative to a limited extent only, corresponding to between 11 and 27%; of the nitrate taken up. Potassium seems to be the cation accompanying stored nitrate in the roots of carob seedlings, since they accumulate nearly stoichiometric amounts of K+ and NO−3.
Uptake of ammonium and nitrate by carob (Ceratonia siliqua) as affected by root temperature and inhibitors
Authors: Cruz C. , Lips S. H. , Martins‐Loução M. A.
Published: May 2006

Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for 5 weeks, with or without nitrogen at different root temperatures (10, 16, 22, 30, 35 or 40deg;C) and with the air temperature kept between 20 and 24°C. The nitrogen was given as either ammonium or nitrate. At all root temperatures studied, nitrogen‐depleted plants developed higher net uptake rates for nitrogen than plants grown in the presence of nitrogen. Temperature affected the kinetic parameters of nitrate uptake more than those of ammonium uptake. With increasing root temperature, the Km of ammonium uptake decreased, but to a lesser extent than the Km for nitrate. The increase in Vmax of ammonium uptake with temperature was also less noticeable than that for nitrate uptake. Ammonium and nitrate uptakes were inhibited in a similar way by respiratory or protein synthesis inhibitors. It may be noted that ammonium uptake in the presence of inhibitors at 40°C was higher than uptake at 10°C without inhibitors. Some similarities between the transport mechanisms for nitrate and ammonium are underlined in the present work. Components of both transport systems displayed saturation kinetics and depended on protein synthesis and energy. The following components of nitrate uptake were distinguished: (a) a passive net influx into the apparent free space; (b) a constitutive active uptake and (c) active uptake dependent on protein synthesis. We may similarly define three ammonium uptake systems: (a) a passive influx into the apparent free space; (b) passive diffusion uptake at high temperature and (c) active uptake dependent on protein synthesis. The possible role of the ratio between mechanism (c) and mechanism (b) as determinant of ammonium sensitivity is discussed.
Effect of inhibitors on ammonium assimilation in Chlorella sorokiniana in light and darkness
Authors: Rigano Carmelo , Rigano Vittoria Di Martino , Vona Vincenza , Esposito Sergio , Martino Catello Di
Published: May 2006

In N‐sufficient cells of Chlorella sorokiniana Shihira and Krauss strain 211/8K (CCAP of Cambridge University), assimilation of ammonium was strictly dependent on light and CO2, and was severely inhibited by 100 μM atrazine or 10 μM 3‐(3,4‐dichlorophenyl)‐1, l‐dimethylurea (DCMU). In N‐limited cells, assimilation of NH4+ took place at similar rates in both light and darkness, which were 1.6‐fold higher than the rate of light‐dependent assimilation by N‐sufficient cells. Assimilation by N‐limited cells was inhibited by l‐methionine‐dl‐sulfoximine (MSX), but not by atrazine or DCMU.

The rate of photosynthetic O2 evolution was 2.9±0.9 mmol ml−1 packed cell volume (PCV) h−1 in N‐sufficient cells, and 0.64±0.12 mmol ml−1 PCV h−1 in N‐limited cells. In the latter resupply of ammonium resulted in a rapid activation by 22%;, followed by a time‐dependent increase of the photosynthetic O2 evolution, which after 12 h reached the same rate as in N‐sufficient cells.

Respiratory consumption of oxygen in darkness in N‐sufficient and N‐limited cells was 0.10±0.03 and 0.11±0.02 mmol ml−1 PCV h−1, respectively. Addition of ammonium was without effect on respiration of N‐sufficient cells, but resulted in a 4‐fold stimulation of respiration of N‐limited cells. Such stimulation took place also in cells treated with DCMU, atrazine, or MSX, and it was also promoted by methylammonium. The stimulation of respiration lasted for several hours.
Purification and characterization of a nitrilase from Brassica napus
Authors: Bestwick Lara A. , Grønning Line M. , James David C. , Bones Atle , Rossiter John T.
Published: May 2006

In germinating seedlings of Brassica napus glucosinolate levels decrease and are potentially degraded to nitriles by a myrosinase. Little is known about the metabolism of glucosinolate aglycone products and the objective of this work was to investigate nitrilase activity and carry out a purification of the enzyme from seedlings of B. napus. A nitrilase capable of converting phenylpropionitrile to phenylpropionic acid was purified to apparent homogeneity from seedlings of B. napus. The protein has a molecular mass of approximately 420 kDa made up of 38 kDa subunits. The pI of the native protein was found to be 4.6. Under denaturing conditions on an isoelectric focusing (IEF) gel a major and minor protein was observed with pI in the range of 5.4‐5.9, suggesting the presence of isoforms. Apart from the potential role of the nitrilase in indole‐3‐acetic acid (IAA) synthesis a developmental study with seedlings indicates that the increase in activity observed may be linked to the in vivo degradation of glucosinolates.
Genetic basis of sodium exclusion and sodium tolerance in yeast. A model for plants
Authors: Haro Rosario , Bañuelos María A. , Quintero Francisco J. , Rubio Francisco , Rodríguez‐Navarro Alonso
Published: May 2006

A yeast strain carrying disruptions in TRK1 and ENA genes was very sensitive to Na+ because uptake discriminated poorly between K+ and Na+, and Na+ efflux was insignificant. Transformation with TRK1 and ENA1 restored discrimination, Na+ efflux and Na+ tolerance. Increasing external Ca2+ increased Na+ tolerance almost in the same proportion in TRK1 enal cells and in trkl ENAI cells, suggesting an unspecific effect of this cation. By using a vacuolar ATPase mutant, the role of the vacuole in Na+ tolerance was also demonstrated. The yeast model of Na+ exclusion and Na+ tolerance may be extended to plants.
Superoxide dismutase in vesicular arbuscular‐mycorrhizal red clover plants
Authors: Palma José M. , Longa M. Angeles , del Río Luis A , Arines Justo
Published: May 2006

The isoenzymatic pattern of Superoxide dismutase (SOD; EC 1.15.1.1) was studied in the symbiosis of Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe‐Trifolium prarense L A Cu.Zn‐SOD (M, 40500) was found in spores of G. mosseae. while one Mn‐SOD (Mn‐SOD I) and two Cu.Zn‐SODs (Cu.Zn‐SOD 1 and Cu.Zn‐SOD II) were present in both roots and leaves of T. pratense. Molecular masses for Cu.Zn‐SOD I and Cu.Zn‐SOD II were 31000 and 34300. respectively. However, when T. prateme and G. mosseae were associated, mycorrhizal roots showed two new iso‐zymes, Mn‐SOD II and mycCu.Zn‐SOD, which have relative molecular masses of 37 800 and 33 300, respectively. The mycCu.Zn‐SOD was found to be specific for this association, whereas Mn‐SOD II was also present in nodules of Rhizobium‐T. pra‐tense. Results suggest that both enzymes are induced in the T. praiense roots in response to invasion by mycorrhizal fungi, perhaps as a result of an increase in the generation of O‐2 radicals in plant roots.
Extraction and biochemical characterization of 1‐aminocyclopropane‐1‐carboxylic acid oxidase from pear
Authors: Vioque Blanca , Castellano José María
Published: May 2006

Activity and biochemical characteristic of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) oxidase from pear (Pyrus communiscv. Blanquilla) was determined. The enzyme showed a low Km(57.5 μM) for ACC and was dependent on O2(Km0.44% in atmosphere). It had an absolute requirement for Fe2+, ascorbate and CO2and was inhibited by α‐aminoisobutyric acid (AIB: K14.2 mM) and cobalt. ACC oxidase has an optimum pH of 6.7 and temperature maxima at 28 and 38°C and it is concluded that the activity of ACC oxidase from pear resembles authentic in vivo activity.
Seed and fruit abortion as a process of self organization among developing sinks
Authors: Ganeshaiah K. N. , Uma Shaanker R.
Published: May 2006

Fruit and seed abortion in plants have been traditionally attributed to limiting factors such as resources or to chemically mediated dominance hierarchy among the developing sinks. These hypotheses however do not satisfactorily explain the observed patterns of seed and fruit abortion and have also not withstood the test of critical experimentation. In this paper, we propose an alternative model based on the process of self organization used in physics to explain the flow of liquids etc. As proposed here, the model assumes one simple rule, that the probability of any given sink getting a resource molecule is a function of (a) the sink‐drawing ability of each unit of the tissue and (b) the amount of resource molecules already moved to that sink. Accordingly, any resource molecule moving to a sink, autocatalytically increases the probability of the latter getting further resources.

We show that starting from a set of identical sinks, all with equal sink‐drawing ability, the differential development of sinks and thence their abortion might occur purely as a consequence of the autocatalytic or feedback movement of the resource molecules to the developing sinks. We also show that, such a process can lead to abortion even under resource‐abundant conditions, though resource limitation aggravates the extent of abortion. Further, the extent of abortion is shown to be highly dependent on the sink‐drawing ability of the species. We offer the test of this prediction in two ways: (a) in Derris indica the extent of abortion increases with the sink drawing ability of the fertilized ovules and (b) treatments involving growth regulators that increase the sink‐drawing ability result in increased abortion of seeds and fruits. Based on these, we argue that self organization could be the basic process regulating resource flow to sinks and factors such as resource limitation and chemical inhibition might be additionally aggravating the asymmetry among the developing sinks.
The effects of drought stress on free amino acid accumulation and protein synthesis in Brassica napus
Authors: Good Allen G. , Zaplachinski Steven T.
Published: May 2006

Changes in the concentrations of free amino acids and specific organic acids were analysed during the induction of drought stress in Brassica napus. Most of the amino acids showed a characteristic linear increase with the induction of drought stress in Brassica leaves, increasing an average of 5.9‐fold over control levels, followed by a reduction in concentration upon rehydration of the plants. Pyruvate concentrations doubled after 4 days of drought stress whereas 2‐oxoglutarate concentrations remained relatively constant. The activities of two of the enzymes involved in amino acid biosynthesis, alanine aminotransferase (EC 2.6.1.2) and aspartate aminotransferase (EC 2.6.1.1), were also measured. Neither enzyme showed any increase in activity, except when the plants were rehydrated. This suggests that the increase in both alanine and aspartate levels results from the increase in their precursors pyruvate and glutamate and may not require increased enzyme activity. The effect of drought stress upon changes in protein synthesis was analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. We found that there was an overall decrease in protein synthesis with the induction of drought stress, followed by a resumption of synthesis upon rehydration. In addition, the synthesis of a number of specific polypeptides was found to decrease upon water loss in the leaves.
Isolation of plasma membranes from mung bean hypocotyl sections by two‐phase partitioning: suitability of the technique for ageing tissues
Authors: Stallaert V. M. , Cooke D. T. , Geuns J. M. C.
Published: May 2006

This paper discusses the application of a particular two‐phase partitioning system to the isolation of plasma membranes from heterogeneous starting material, differing in physiological age. Plasma membranes were isolated from hypocotyl segments of mung beans (Vigna radiata L. Wilczek) on four successive days in order to examine the variation caused by ageing of the seedling. Additionally, the segments were cut at different positions of the hypocotyl to measure variation caused by position‐related ageing. To assess purity and degree of contamination of the plasma membrane‐enriched preparations, a series of membrane enzyme markers were screened for all isolated fractions. Glucan synthetase II activities were enriched in the plasma membrane fractions, but enrichment and recovery became less pronounced with increasing age. Plasma membrane ATPase activity affected by VO43‐, Ca2+ and K+ was similar in all segments throughout the time‐course of the experiment (4 days). However, control ATPase activity varied with segment origin: the physiologically oldest segments showed only 75% activity compared to the youngest ones. Km and Vmax values indicated a smaller proportion of active enzyme but higher substrate affinity as the age of the segments increased. Contamination by intracellular membranes was minimal and unrelated to tissue age.
The effect of phosphate deficiency on carbohydrate metabolism in bean roots
Authors: Rychter Anna M. , Randall Douglas D.
Published: May 2006

Bean plants (Phaseolus vulgaris) grown in phosphate‐deficient (–P) medium display deficiency symptoms after about 2 weeks of culture. A decrease in inorganic phosphate level in roots was observed after 10 days of culture, and after 17 days it was more than 30 times less than control. The dry weight of the shoots of phosphate‐deficient plants was lower whereas the dry weight of the roots was higher as compared to the control roots. After 2 weeks of culture, the sucrose level in –P roots almost doubled compared to control roots. An increase in glucose and fructose was observed earlier than that of sucrose, and after 10 days of culture in phosphate‐deficient medium the glucose level in –P roots was about 3 times higher than that in +P roots. At the same time, a decrease in hexose‐phosphate level was observed. This decrease may reflect a higher drain from the hexose phosphate pool, or it may be due to the lower capacity for hexose phosphorylation of phosphate‐deficient plants, as judged by the lower hexokinase and fructokinase activities. The ratio of non‐phosphorylated to phosphorylated sugars in –P roots was about 5 times higher as compared to control roots. We propose that glucose and fructose accumulation in phosphate‐deficient roots represents a non‐metabolic, probably vacuolar pool which is not utilized for growth and metabolism of the roots.
Changes in free amino acids and osmotic adjustment in leaves of water‐stressed bean
Authors: Raggi Vittorio
Published: May 2006

Bean (Phaseolus vulgaris L. cv. Topcrop) plants were raised in a growth chamber in small pots or flower boxes and kept at full water regime until the full development of primary leaves (14–16 days). Both potted and flower box‐grown plants were subjected to a gradually increased water stress of about 60–70 kPa day−1 leaf water potential (stressed plants) or full water regime (control). The water potential, osmotic potential and turgor pressure in freshly detached primary leaves and osmotic potential at zero turgor were calculated using pressure/volume curves. Changes in free amino acids and amides were also measured in parallel trials. Water relation parameters documented that in the stressed leaves there was moderate osmotic adjustment, which was more evident in the potted plants. If considered 0% ionised, the accumulation of free amino acids and amides (μmol g−1 H2O) accounts for a van't Hoff's value of about 10.2 kPa in the small pot‐grown and 5.5 kPa in the box‐grown plants. The values are twice as high if considered 100% ionised. Proline accumulation accounted for about 6.4% of the pool enlargement in the potted plants and 22.3% in the flower box plants.
Photorespiratory ammonium assimilation in chloroplasts of Chlamydomonas reinhardtii
Authors: Ramazanov Ziyadin , Cárdenas Jacobo
Published: May 2006

The effect of CO2 concentration on the rate of photorespiratory ammonium excretion and on glutamine synthetase (GS) and carbonic anhydrase (CA) isoenzymes activities has been studied in Chlamydomonas reinhardtii cw‐15 mutant (lacking cell wall) and in the high CO2‐requiring double mutant cia‐3/cw‐15 (lacking cell wall and chloroplastic carbonic anhydrase). In cw‐15 cells, both the extracellular (CAext) and chloroplastic (CAchl) CA activities increased after transferring cells from media bubbled with 5% CO2 in air (v/v, high‐Ci cells) to 0.03% CO2 (low‐Ci cells), whereas in cia‐3/cw‐15 cells only the CAext was induced after adaptation to low‐Ci conditions and the CAchl activity was negligible. During adaptation to low‐Ci conditions in the presence of 1 mM of l‐methionine‐D,L‐sulfoximine (MSX), a specific inhibitor of GS activity, both mutant strains excreted photorespiratory ammonium into nitrogen free medium. In addition, the ammonium excretion rate by cw‐15 in the presence of MSX was lower in cells grown and kept at 5% CO2 than in high‐Ci cells adapted to 0.03% CO2. The double mutant cia‐3/cw‐15 excreted photorespiratory ammonium at a higher rate than did cw‐15. Total GS activity (GS‐1 plus GS‐2) increased during adaptation to 0.03% CO2 in both strains of C. reinhardtii. However, only the activity GS‐2, which is located in the chloroplast, increased during the adaptation to low CO2, whereas the cytosolic GS‐1 levels remained similar in high and low‐Ci cells. We conclude that: (1) cia‐3/cw‐15 cells lack chloroplastic CA activity; (2) in C. reinhardtii photorespiratory ammonium is refixed in the chloroplasts through the GS‐2/GOGAT cycle; and (3) chloroplastic GS‐2 concentration changes in response to the variation of environmental CO2 concentration.
Photosynthetic induction of dual phosphate uptake kinetics inPorphyra umbilicalis
Authors: Fernández José A. , García‐Sánchez Maria J.
Published: May 2006

The rates of phosphate uptake and photosynthesis were simultaneously determined in order to investigate the relationship between phosphate use and photosynthesis.Porphyra umbilicalis(L.) Kützing exhibited two different phosphate uptake kinetics. The first one followed a saturation model and was observed in light (maximum phosphate uptake rate. Vmax= 94 ± 30 nmol P1m−2s−1: semisaturation constant. S15= 4.0 ± 3.4 μM: phosphate compensation point. PCP = 0.3 ± 0.4 μMγ: the seeraid one was linear and worked at high external phosphate concentrations in the dark. Inhibition of photosynthesis by removing the inorganic carbon from the medium produced the same effect aa darkness on phosphate uptake. Successive bicarbonate additions produced increments of photosynthesis rate and the recovering of the phosphate uptake pattern observed in light. The results showed thatPorphyra umbilicalis, at the typical phosphate concentrations in its natural habitat, takes up phosphate in the light through the operation of a photosynthetically controlled active system.
Studies on vacuole regeneration in evacuolated tobacco mesophyll protoplasts. Protein analysis by one‐ and two‐dimensional microgel‐electrophoresis
Authors: Hoffmann E. M. , Hampp R.
Published: May 2006

Evacuolated protoplasts, P(–), have been prepared from mesophyll protoplasts. P(+), of Nicotiana tabacum L. (cv. Samsun) by centrifugation in an iso‐osmotic Percoil gradient. In comparative analyses performed with these two types of cells, vacuole proteins should appear in P(+) extracts, but be absent from freshly isolated P(–). Such differences were detectable in total protein extracts after two‐dimensional electrophoresis. Four spots were located that are likely to represent soluble vacuolar proteins. They have low molecular mass (around 20 kDa) and slightly acidic isoelectric points. In culture, evacuolated tobacco protoplasts regenerated a vacuole de novo. The vacuolation process as observed microscopically correlated welt with the reappearance of vacuolar marker enzymes. Likewise, the protein spots that were missing in the P(–)‐pattern immediately after evacuolation reappeared within the first days of protoplast culture. By immunoblotting the same behaviour was demonstrated for the well‐known vacuolar protein, tonoplast ATPase.
Tissue‐specific expression of multiple forms of cyprosin (aspartic proteinase) in flowers of Cynara cardunculus
Authors: Cordeiro Maria C. , Pais M. Salomé , Brodelius Peter E.
Published: May 2006

Three heterodimeric aspartic proteinases (cyprosin 1, 2 and 3) with milk‐clotting activity have previously been purified from flowers of Cynara cardunculua and partly characterized (U. Heimgartner et al. 1990, Phytochemistry 29: 1405–1410). These proteinases have now been further studied. Isoelectric focusing has revealed a micro‐heterogeneity of the apparently pure cyprosins. Three isozymes with close isoelectric points around 4.0 have been found. Reversed‐phase high performance liquid chromatography of electrophoretically purified large subunits of cyprosin has also shown a microheterogeneity. Peptide mapping of cyprosins 2 and 3 by trypsin or BrCN cleavage indicate that they are derived from common procyprosin(s). Studies on the organspecific accumulation of the enzyme were carried out using flower buds and flowers at different stages of development and styles and corollas from open flowers, leaves and seeds. Immunostained western blots revealed the presence of cyprosin in very young flowers in low amounts. The amount of enzyme increased towards later stages of development and it was mostly present in the violet parts of styles and corollas. The enzyme could not be detected in leaves or seeds. Proteolytic and milk‐clotting activities correlate well with these findings. The enzyme was localized by immunolabelling in the epidermal cell layer of styles. Mature flowers collected at 8 different locations in Portugal showed some variation in proteolytic activity while the milk‐clotting activity was essentially the same for all extracts.
Molecular analysis of natural leaf senescence in Arabidopsis thaliana
Authors: Lohman Karin N. , Gan Susheng , John Manorama C. , Amasino Richard M.
Published: May 2006

We have analyzed macromolecular changes that are associated with natural leaf senescence in Arabidopsis thaliana. The loss of chlorophyll that is characteristic of leaf senescence is accompanied by a specific pattern of decline of total RNA and protein levels. We have constructed two cDNA libraries representing mRNAs from Arabidopsis leaves at different senescence stages. Six cDNA clones corresponding to mRNAs that substantially increase in abundance during senescence were isolated. The levels of these mRNAs remain elevated into the late stages of senescence when most of the chlorophyll and protein of the leaf has been degraded. Sis cDNA clones that correspond to mRNAs that exhibit contrasting behavior were also identified: the levels of these mRNAs decrease to undetectable levels during senescence. The changes in the levels of these specific mRNAs during the course of senescence are presented. The results indicate that major changes in gene expression occur in Arabidopsis leaves during the process of senescence.
The epidermis of barley leaves is a dynamic intermediary storage compartment of carbohydrates, amino acids and nitrate
Authors: Dietz Karl‐Josef , Hollenbach Beate , Hellwege Elke
Published: May 2006

Sugars, amino acids and nitrate were measured in the epidermis of barley seedlings and compared with whole leaf levels. I. Under all conditions, concentrations of glucose and fructose were lower in the epidermis than in the remaining leaf tissues; levels were lowest at the end of the dark period (0.2–1.4 mM) and increased under conditions of inhibited assimilate export (3–6 mM). 2. Epidermal sucrose concentrations were very low (« 0.2 mM) even in excised leaves which had accumulated assimilates. 3. Similar to the sugars, amino acids were also less concentrated in the epidermis than in whole leaf extracts. However, the amino acid profiles showed cell type‐specific differences. 4. Nitrate was accumulated in the epidermis. The epidermal pool decreased during nitrate starvation. Since no nitrate reductase activity was associated with the epidermis, nitrate was mobilised from the epidermis and metabolized presumably in the mesophyll. These results suggest that the epidermis functions as a regulated intermediary storage compartment of the leaves and that stored substances are readily available for remobilisation.
Secretion of basic and acidic chitinases from salt‐adapted and ‐unadapted winged bean cells
Authors: Esaka Muneharu , Toyota Akie , Hayakawa Hiromi
Published: May 2006

Six specific proteins are secreted from salt‐adapted winged bean (Psophocarpus tetragonolobus) cells. A protein, designated S AP3, with molecular mass of 37 000 was secreted abundantly by suspension cultures of winged bean callus adapted to 0.5% (86 mM) or 1.0% (171 mM) NaCl. When the amino acid sequence of the amino‐terminal part (16 amino acid residues) of SAP3 was determined, a significant homology was found between the amino‐terminal amino acid sequence of SAP3 and that of basic chitinase from kidney bean, Arabidopsis, tobacco and pumpkin. SAP3 had chitinase activity, suggesting that basic chitinase is secreted specifically from salt‐adapted winged bean cells. A protein with molecular mass of 29000 was exclusively secreted into the culture medium at the later stage (20–30 days) of both salt‐adapted and ‐unadapted cultures. The protein was purified from the medium at day 30. One‐step ammonium sulfate fractionation was sufficient for purification to homogeneity. The protein had chitinase activity. The amino‐terminal amino acid sequence (17 amino acid residues) of the protein suggested that it was acidic chitinase. Thus, acidic chitinase with a molecular mass of 29000 is exclusively secreted at the later stage of culture of salt‐adapted and ‐unadapted winged bean cells, in contrast to pumpkin (Cucurbita) cell suspension cultures where basic chitinase with a molecular mass of 32 000 is secreted abundantly at the early culture stage.
Growth analysis of UV‐B‐irradiated cucumber seedlings as influenced by photosynthetic photon flux source and cultivar
Authors: Krizek Donald T. , Mirecki Roman M. , Kramer George F.
Published: May 2006

A growth analysis was made of ultraviolet‐B (UV‐B)‐sensitive (Poinsett) and insensitive (Ashley) cultivars of Cucuumis satives L. grown in growth chambers at 600 μmol m−2 s−1 of photosynthetic photon flux (PPF) provided by red‐ and far‐red‐deficient metal halide (MH) or blue‐ and UV‐A‐deficient high pressure sodium/deluxe f HPS/DX) lamps. Plants were irradiated 6 h daiiy with 0.2 f‐UV‐B) or 18.2 C+UV‐B) kJ m−2 day−1 of biologically effective UV‐B for 8 or 15 days from time of seeding. In general, plants given supplemental UV‐B for 15 days showed lower leaf area ratio (LARs, and higher specific leaf mass (SLM) mean relative growth rate (MRGR) and net assimilation rate (NAR) than that of control plants, but they showed no difference in leaf mass ratio (LMR), Plants grown under HPS/DX lamps vs MH lamps showed higher SLM and NAR. lower LAR and LMR. hut no difference in MRGR. LMR was the only growth parameter affected by cultivar: at 15 days, it was slightly greater in Poinsett than in Ashley. There were no interactive effects of UV‐B. PPF source or cultivar on any of the growth parameters determined, indicating that the choice of either HPS/DX or MH lamps should not affect growth response to UV‐B radiation. This was true even though leaves of UV‐B‐irradiated plants grown under HPS/DX lamps have been shown to have greater chlorosis than those grown under MH lamps.
Isolation of the rotenone‐sensitive NADH‐ubiquinone reductase (complex I) from red beet mitochondria
Authors: Rasmusson Allan G. , Mendel‐Hartvig Janet , Møller Jan M. , Wiskich Joseph T.
Published: May 2006

Complex 1 of the respirator) chain (EC 1.6.531, measured as NADH‐duroquinone and NADH‐ubiquinone, reductase activities, was isolated from purified red beetroot (Beta vulgaris L.I mitochondria. The mitochondria were disrupted by freeze‐thawing and inner membrane vesicles were pelleted. After solubilization of the vesicles with Triton X‐100, the enzyme complex was purified 11‐fold (compared to the activity in the inner membrane vesicles) by size‐exclusion chromatography on a Sephacryl S‐400 HR column and then by ion‐exchange chromatography on a DEAE‐Sepharose CL‐6B column. Triton X‐100 was present throughout the purification procedure. Tire purified complex showed approximately 30 bands on SDS‐PAGE and about 15 polypeptides including those at 80. 54, 53. 51. 27. 25 and 22 kDa cross‐reacted with polyclonal antibodies raised against complex I from Neurospora crassa. This is similar lo the pattern obtained with complex I from Neurospera crassa.

Analysis by nativc‐SDS 2‐dimensional PAGE revealed the existence of several molecular mass forms of the purified complex.

After reconstitution of the purified complex into phosphatidylcholine vesicles, the NADH‐ubiquinone reductase activity had a Km (NADH) of about I μM and was inhibited by both rotenone and dicyclohexylcarbodiimide.
Is the release of phytosiderophores in zinc‐deficient wheat plants a response to impaired iron utilization?
Authors: Walter Andrea , Römheld Volker , Marschner Horst , Mori Satoshi
Published: May 2006

The effect of zinc nutritional status on the time course of phytosiderophore release, and uptake of iron and translocation of iron to the shoot, was studied in nutrient solution cultures for two cultivars of wheat (Triticum aestivum. cv. Aroona: T. durum, cv. Duratit) differing in their susceptibility to zinc deficiency. In the zinc‐efficient cultivar Aroona, under zinc deficiency translocation of iron from roots to shoot was significantly decreased in 13‐ and 15‐day‐old plants, whereas release of phytosiderophores was enhanced when the plants were 16 days old. As zinc deficiency became more severe in older plains, translocation of iron to the shoot was further decreased and release of phytosiderophores was further enhanced. Resupplying zinc in nutrient solution to zinc‐deficient plants significantly increased the translocation of iron to the shoot after 48 and 72 h. Concomitantly the release of phytosiderophores was repressed. The other cultivar Durati classified as zinc‐inefficient in field observations differed from cv. Aroona by showing a lower rate of phytosiderophore release under Zinc deficiency, and a less impaired translocation of iron to the shoot. Foliar application of iron citrate to zinc‐deficient Aroona plants repressed the release of phytosiderophores and increased iron concentrations in shoot and roots. Application of 55Fe to the leaves demonstrated that retranslocation of iron from the shoot to the roots was not affected by the zinc nutritional status. It is concluded that enhanced release of phytosiderophores in zinc‐deficient wheat plants was induced primarily by impaired trans‐location of iron lo the shoot.
Gibberellic acid promotes growth and cell wall synthesis in Avena internodes regardless of the orientation of cell expansion
Authors: Montague Michael J.
Published: May 2006

Segments cut from the next‐to‐last (peduncular‐1) internode of Avena sativa L. cv. Victory (oat) shoots elongate as much as 10‐fold in response to gibberellic acid (GA3). The objective of the present investigation was to differentiate the effects of GA3 on growth from its effects on wall synthesis (measured gravimetrically and through the incorporation of [14C]‐glucose) by using several cell wall synthesis inhibitors with widely varying mechanisms of action. Four compounds, viz. monensin, cycloheximide, lanthanum, and galactose. caused (1) relatively little inhibition of either cell wall synthesis or elongation in segments without GA3, (2) roughly proportionate, dose‐dependent inhibition of elongation and wall synthesis in GA3‐treated segments and (3) generally greater inhibition of GA3‐promoted uptake of radioactivity than of wall incorporation or elongation. Two other compounds, colchicine and 2,6‐dichlorobenzonitrile (DCB). (1) inhibited GA3‐induced elongation considerably more than cell wall synthesis and (2) caused swelling (radial expansion). especially of GA3‐treated segments. DCB‐treated internodal cells apparently compensated for inhibited cellulose synthesis by greater synthesis of matrix polysaccharide (beginning between 3 and 6 h). While normal cellulose synthesis was not required for short‐term (up to 6 h) GA3‐induced elongation or for long‐term hormone‐promoted radial expansion, it was required for sustained GA3‐induced elongation. These results indicate that GA3‐promoted cell wall loosening (manifested as radial expansion) and cell wall synthesis in Avena internodes occur at least partially independently of any hormonal effect on the orientation of microtubules and microfibrils.
Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds
Authors: Edelstein Menahem , Ben Tal Yossi , Wodner Maria , Kigel Jaime
Published: May 2006

The effect of the plant growth retardants ancymidol. mefluidide and uniconazole on germination of two melon accessions differing in their ability to germinate at 14°C was examined. The accessions were the cold sensitive Noy Yizre'el and the cold tolerant Persia 202. The three growth retardants were able to delay the germination of intact Noy Yizre'el seeds, but did not affect that of intact Persia 202 seeds. On the other hand germination of decoated seeds of both accessions was unaffected by these inhibitors at normal oxygen concentration, but was inhibited at 5% oxygen. When gibberellin‐like activity was measured by a dwarf rice biological assay following HPLC fractionation, it was found that seeds of Persia 202 contained much more gibberellin‐like activity than Noy Yizre'el seeds. Among the extracted compounds several endogenous gibberellins were identified by combined gas chromatography‐mass spectrometry (GC‐MS). They included GA4, GA20, GA1 and GA3 in Noy Yizre'el and GA34, GA20, GA1 and GA8 in Persia 202. It is suggested that the better germination of intact Persia 202 seeds, compared to Noy Yizre'el seeds at low temperature and low oxygen concentration, is due to a higher endogenous level of GA and a better seed coat permeability to oxygen.
Dual induction control of flowering in Leucanthemum vulgare
Authors: Heide O. M.
Published: May 2006

The perennial herb Leucanthemum vulgare (oxeye daisy) has a dual induction requirement for flowering. The primary induction is a typical low temperature vemalization response. Temperatures up to 15°C are effective, and the optimum is 6–9°C. Short days (SD) during low temperature exposure enhanced primary induction, but SD could not fully substitute for low temperature in primary induction. At optimum temperatures about 6 weeks exposure were required for 100% flowering, but the flowering response increased with increasing exposure up to 12 weeks, especially at higher temperatures. Seedling have a short juvenile phase of about 4 weeks. Populations with origin ranging from 59 to 69°N in Norway did not vary in their primary induction requirements. Long days (LD) were required for inflorescence initiation and stem elongation at 9°C. At 21 and 15°C some plants initiated and developed inflorescences in SD, but the inflorescences were sessile and their development strongly delayed. More than 16 LD cycles were required for normal stem elongation (bolting).