bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endogenous elemental sulfur (S°) in dormant and aging α‐spores of Phomopsis viticola
Authors: Beffa Trello , Pezet Roger , Turian Gilbert 
Published: May 2006

Endogenous elemental sulfur (S°) was measured in dormant α‐spores of Phomopsis viticola Sacc. (ATCC 44940) from young (25‐day‐old) and aging (105‐day‐old) cultures grown on malt extract agar medium enriched with [35S]‐MgSO4. Endogenous S° from the mitochondrial fraction, and the lipid and aqueous cytoplasmic fractions of young and aging α‐spores were purified by column chromatography followed by thin‐layer chromatography. The purity of mitochondrial pellets were checked by the catalase (EC 1.11.1.6) and acid phosphatase (EC 3.1.3.1) activities. Activities of the mitochondrial enzymes NAD+‐isocitrate dehydrogenase (EC 1.1.1.41) and cytochrome c oxidase (EC 1.9.3.1) were also measured to determine the distribution of the endogenous S° between mitochondria and cytoplasm.In young dormant α‐spores, endogenous S° was mostly found in the cytoplasmic lipid reserves, which were mainly phospholipids. The mitochondrial fraction of these young α‐spores contained ca 10% of the total endogenous S°, whereas in aging α‐spores stored for 105 days the endogenous S° was mainly (ca 90%) localized in the mitochondrial fraction. This accumulation of S° in mitochondria of aging α‐spores was correlated with a sharp decrease in phospholipid reserves, endogenous and exogenous respiratory activities, ATP concentration, uptake of sulfate, and NAD+‐isocitrate dehydrogenase and cytochrome c oxidase activities. These metabolic changes were correlated with an irreversible loss of germination capacity which leads to the natural death of P. viticolaα‐spores.During the first min of the breaking of dormancy, the young α‐spores possess a 7.3‐fold capacity to reduce exogenous S° with production of hydrogen sulfide, as compared to the aging α‐spores. In young α‐spores the production of hydrogen sulfide was almost totally inhibited by 40 μM antimycin A (92%), and strongly inhibited by 2mM azide (75%) and by 15 μM 2,4‐dinitrophenol (63%).Our work suggests that endogenous S° plays a key role in the regulation of the dormancy and aging processes of α‐spores of P. viticola.
Properties of reformed prolamellar bodies from illuminated and redarkened etiolated wheat plants
Authors: Minkov Ivan N. , Ryberg Margareta , Sundqvist Christer 
Published: May 2006

Prolamellar bodies were isolated from etiolated leaves of wheat (Triticum aestivum L. cv. Walde, Weibull), which were illuminated for 4 h and then grown in darkness for 16 h. The inner etiochloroplast membranes were isolated by differential centrifugation, and prolamellar bodies and thylakoids were separated on a 10–50% continuous sucrose density gradient. The reformed prolamellar bodies contained phototransformable protochlorophyllide as the main pigment as shown by low temperature fluorescence spectra and high performance liquid chromatography. After illumination with 3 flashes of white light almost all of the protochlorophyllide was transformed to chlorophyllide. In the thylakoids, however, most of the protochlorophyllide was not phototransformed. The reformed prolamellar bodies and the thylakoids showed a fluorescence emission ratio 657/633 nm of 5.6 and 0.5, respectively. Both membrane systems contained also chlorophyllide and chlorophyll synthesized during the illumination. Polyacrylamide gel electrophoresis showed the main chlorophyllide oxidoreductasse.Teransmission and scanning electron micrographs indicated that the reformed prolamellar bodies are mainly of the “narrow” type and that the prolamellar body fraction had only a minor contamination with thylakoid membranes.The results obtained showed that reformed prolamellar bodies isolated from illuminated redarkened etiolated wheat leaves had features very similar to the prolamellar bodies isolated from etiolated leaves. This provides support for the idea that prolamellar bodies are an important natural membrane system which plays a dynamic role in the development of the etio‐chloroplasts in light.
Relation of light and nitrogen source to growth, nitrate reductase and glutamine synthetase activity of jack pine seedlings
Authors: Margolis H. A. , Vézina L. P. , Ouimet R. 
Published: May 2006

Two‐month‐old jack pine (Pinus banksiana Lamb.) seedlings were placed in a greenhouse where both nitrogen source and light level were varied. After 4 months, whole seedling biomass, leaf biomass and relative growth rate were greatest in seedlings grown with NH+4/NO/NO−3‐N and full light (FL) and least in seedlings grown with NO −3‐N and low light (LL). NO −3‐seedlings grown under full light and NH+4/NO−3‐seedlings grown under low light were approximately equal. This indicates that the extra carbon costs of assimilating only NO−3‐N were similar to the reduction of carbon fixation resulting from a 50% decrease in photon flux density. Percentage and total nitrogen content of needles were greater in seedlings grown under low light independent of nitrogen fertilization. Percentage and total nitrogen content of roots were higher under low light and lower when fertilized with NO−3.Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)−1 in needles, but not in roots. However, no nitrate was detected in the needles in any treatment. GS activity, on the other hand, was greater under low light in both needles and roots. GS activity in needles is most likely involved with the reassimilation rather than the initial assimilation of ammonium. Some implications of these shifts in enzymatic activity for ecological phenomena in forests are discussed.
The influence of oxygen deficiency on ethylene synthesis, 1‐aminocyclopropane‐1‐carboxylic acid levels and aerenchyma formation in roots of Zea mays
Authors: Atwell B J. , Drew M. C. , Jackson M. B. 
Published: May 2006

The relationship between ethylene production, 1‐aminocyclopropane‐l‐carboxylic acid (ACC) concentration and aerenchyma formation (ethylene‐promoted cavitation of the cortex) was studied using nodal roots of maize (Zea mays L. cv. LG11) subjected to various O2 treatments. Ethylene evolution was 7–8 fold faster in roots grown at 3 kPa O2 than in those from aerated solution (21 kPa O2), and transferring roots from aerated solution to 3 kPa O2 enhanced ethylene synthesis within less than 2 h. Ethylene production and ACC accumulation were closely correlated in different zones of hypoxic roots, regardless of whether O2 was furnished to the roots through aerenchyma or external solution. Both ethylene production and ACC concentrations (fresh weight basis) were more than 10‐fold greater in the distal 0–10 mm than in the fully expanded zone of roots at 3 kPa O2. Aerenchyma formation occurred in the apical 20 mm of these roots.Roots transferred from air to anoxia accumulated less than 0. 1 nmol ACC (mg protein)‐1 for the first 1.75 h; no ethylene was produced in this time. The subsequent rise in ACC levels shows that ACC can reach high concentrations even in the absence of O2, presumably due to a de‐repression of ACC synthase. The hypothesis was therefore tested that anoxia in the apical region of the root caused enhanced synthesis of ACC, which was transported to more mature regions (10–20 mm behind the apex), where ethylene could be produced and aerenchyma formation stimulated. Surprisingly, exposure of intact root tips to anoxia inhibited aerenchyma formation in the mature root axis. High osmotic pressures around the growing region or excision of apices had the same effect, demonstrating that a growing apex is required for high rates of aerenchyma formation in the adjacent tissue.
Mathematical approach to effects of repeated treatments in the study of very low fluence, low fluence and high fluence germination responses
Authors: De Petter E. , Van Wiemeersch L. , Dedonder A. , Rethy R. , Fredericq H. , De Greef J. A. 
Published: May 2006

Theoretical calculation of the germination response induced by repeated treatments, separated by a dark period long enough to enable fixation of the effect of the preceding treatment, is possible when defining the percentage germination induced by the first treatment as the responding proportion (p) of the total treated seed population. Consequently the germination response induced by a second treatment should be relative to the proportion (q) of the seed population not responding to the first treatment (q = 1 ‐ p).The fitting of these calculations with experimental data for the Very Low Fluence Response (VLFR) for germination of seeds of Kalanchoë blossfeldiana Poelln. cv. Vesuv, induced by repeated light pulses, suggests the independency of the effect of each treatment, i.e. the effect of the second treatment is neither positively nor negatively influenced by the first treatment.This hypothesis is not valid for calculation of the Low Fluence Response (LFR) for germination of Kalanchoë seeds induced by repeated light pulses, since the first light pulse does not result in a germination response. At least two irradiations are needed for an LFR while the third and following pulses increase the response much more than calculated with the proposed equation. It is suggested that the LFR in Kalanchoë, in contrast to the VLFR, includes the involvement of some pre‐existing far‐red absorbing form of phytochrome (Pfr) and the involvement of dark reactions are to be considered.The effect of long irradiation times (up to 2xl05 s) resulting in a (defined in this paper) high fluence response (HFR) for germination of Kalanchoë seeds is also discussed in terms of independently responding seed population fractions.
Effect of long‐term H2S fumigation on photosynthesis in spinach. Correlation between CO2 fixation and chlorophyll a fluorescence
Authors: Maas F. M. , van Loo E. N. , van Hasselt P. R. 
Published: May 2006

Spinach plunts (Spinacia oleracea L. cv. Monosa) were exposed to air with and without 0.25 μl l‐1 H2S. Effects of H2S exposure for up to 18 days on photosynthesis, dark respiration and on chlorophyll a fluorescence were studied. Dark respiration was not affected by H2S fumigation. Photosynthetic CO2 fixation decreased linearly with time in both control and fumigated plants. The rate of decrease in CO2 fixation was faster in the fumigated plants; after 14 days of exposure the fumigated plants showed a decrease in CO2 fixation of 23%äs compared with the control plants. The H2S‐induced decrease in CO2 fixation was accompanied by a decrease in quenching of the chlorophyll fluorescence. The most characteristic change in chlorophyll fluorescence was a decreased difference between maximum and steady‐state fluorescence [(P‐T)/P), suggesting a reduced efficiency in the use of photochemical energy in photosynthesis. Differences in CO2 fixation were more pronounced whcn measured at high light intensity; the maximum rate of CO2 fixation at light saturation decreased significantly with time in the H2S‐exposed plants; after 14 days of H2S exposure a decrease of more than 70% was noted. The decrease in CO2 fixation could not be attributed to a decreased chlorophyll content; on the contrary, chlorophyll content even slightly increased during fumigation. The initial increase in CO2 fixation rate with increasing light intensity was also reduced by prolonged H2S fumigation, indicating an effect of H2S fumigation on photosynthetic electron transport.Finally, the phytotoxicity of H2S is discusscd in relation to the H2S‐induced changes in photosynthetic CO2 fixation and chlorophyll a fluorescence, and the effect of H2S on leaf development observed in earlier studies.
Conversion of the polygalacturonase isoenzymes from ripening tomato fruits
Authors: Knegt Erik , Vermeer Evert , Bruinsma Johan 
Published: May 2006

From pericarp tissue of ripening tomato (Lycopersicom esculentum Mill. cv. Sonato), two isoenzymes of polygalacturonase, PGl and PG2, can be extracted. With water hardly any polygalaeturonase activity is extracted; with 0.5 M NaCl predominantly PG2 is found and subsequent extraction with 1.25 M NaCI delivers mainly PGl. A partly purified PGl solution gradually decomposes into PG2. Conversion of PG2 into an isoenzyme that resembles PGl, but differs from it, can be brought about by a faetor (eonvertor) that occurs at low levels in free form in unripe and early‐ripe fruits as well as in leaves. Convertor (CV) ean be set free from PGl by a short treatment at 100°C, at which temperature the convertor activity itself also decreases.The in vitro activities and several characteristics of the isoenzymes and CV as found by us differ from that found by others, probably because of carefully optimized methods. It is suggested that the CV anchors PG2 onto the cell wall, forming PGl. Thus PGl would constitute the form that depolymerizes the peetins in the middle lamellae.
Cultivar differences in the rate of nitrate uptake by intact wheat plants as related to growth rate
Authors: Rodgers C. O. , Barneix A. J. 
Published: May 2006

Six Argentinian wheat (Triticum aestivum L.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3‐fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short‐term experiments, or by total N accumulation in the tissue during 8 days.No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is high.
Identification of a calmodulin‐stimulated (Ca2++ Mg2+)‐ATPase in a plasma membrane fraction isolated from maize (Zea mays) leaves
Authors: Robinson Curtis , Larsson Christen , Buckhout Thomas J. 
Published: May 2006

Plasma membranes were isolated from light‐grown, 14‐day‐old maize leaves (Zea mays L. cv. Golden Cross Bantam) using aqueous two‐phase partitioning. The plasma membrane (PM) fraction contained < 0.3% of the total chlorophyll, < 0.2% of the mitochondrial marker enzyme activity, minimal contamination by endomembranes and 34% of the total PM.A calmodulin‐stimulated (Ca2++ Mg2+)‐ATPase was identified in the PM‐enriched fraction. The Ca2++ calmodulin stimulation was dependent on Mg2+, saturated at ca 25 μM total Ca2+, had a pH maximum at 7.2 and was maximally stimulated by 600 nM bovine brain calmodulin. The stimulation was not greatly affected by the anion present and showed a divalent cation specificity of Ca2+ > Sr+2 ± Mn+2 > Co2+± Cu2+ > Ba2+. The napthalenesulfonamide W7, an antagonist of calmodulin action, completely inhibited the calmodulin stimulation at 175 μM, while the less active analogue W5 was ineffective at this concentration. La3+, an inhibitor of PM Ca2+ transport, showed a 50% inhibition of calmodulin‐stimulated ATPase activity at ca 200 μM. Taken as a whole, these data demonstrate the presence of a calmodulinstimulated, (Ca2++ Mg2+)‐ATPase on the cytoplasmic surface of the plasma membrane of maize leaf cells.
The role of calcium in exocytosis and endocytosis in plant cells
Authors: Steer M. W. 
Published: May 2006

The role of calcium in the individual cellular events leading to exocytosis is considered. Both vesicle movement processes and vesicle fusion at the cell surface require calcium for completion of specific events in this pathway. Our knowledge of these events is incomplete. In particular the movement of secretory vesicles by the cytoskeleton in response to added calcium is a key event that is beyond our comprehension at present. At the whole cell level, it is shown that external calcium, at the appropriate concentration, is required to elicit secretion at optimal rates. In both plant and animal cells secretion appears to be dependent on, or is triggered by, a rise in the level of internal free calcium ions from about 10‐7 to 10‐6M or even higher. In these eukaryotes internal organelles take up calcium and maintain a low level of calcium in the cell, offsetting the inflow of calcium from the plasma membrane. In some systems the inflow is restricted to a certain part of the plasma membrane, which then acts as a focus for exocytosis and, thereby, establishes a cellular polarity. In plant tissues there appears to be a requirement for some circulation of calcium within the apoplast, to sustain secretion.Recent papers on endocytosis have confirmed its occurrence in plant cells and made significant advances in isolating and characterising the clathrin coats of the coated vesicles involved in the uptake. There is no evidence, at present, for a direct role for calcium in these events. Indirectly, calcium stimulates exocytosis, and hence the delivery of excess membrane to the cell surface, which may be retrieved by an increase in the rate of endocytosis. Quantitative comparisons of the membrane flow occurring in these pathways are not available.Several plant cellular systems have been employed to study secretion and some of these may prove to be superior model systems for the investigation of certain aspects of the control of exocytosis and endocytosis by calcium ions.
Changes in the activity of enzymes involved with primary nitrogen metabolism due to ectomycorrhizal symbiosis on jack pine seedlings
Authors: Vézina L.‐P. , Margolis H. A. , McAfee B. J. , Delaney S. 
Published: May 2006

Jack pine (Pinus banksiana Lamb.) seedlings were inoculated with either one of the ectomycorrhizal (ECM) fungi, Laccaria bicolor (Maire) Orton or Pisolithus tinctorius (Pers.) Coker and Couch, and grown for 16 weeks in a growth chamber along with non‐ECM controls. Five enzymes involved with the assimilation of nitrogen or the synthesis of amino acids were measured in the 3 jack pine root systems as well as in the pure fungal cultures. Pisolithus tinctorius in pure culture had no detectable activity of nitrate reductase (NR. EC 1.6.6.1), glutamate dehydrogenase (GDH. EC 1.4.1.2), glutamate decarboxylase (GDCO. EC 4.1.1.15) or glutamate oxoglutarate aminotransferase (GOGAT, EC 1.4.1.13) but did have some glutamine synthetase (GS, EC 6.3.1.2) activity. Laccaria bicolor in pure culture had no NR activity, small levels of GDCO activity, and high GS, GDH and GOGAT activity. The high levels of enzymatic activity present in L. bicolor indicate that it may play a greater role in the nitrogen metabolism of its host plant than P. tinctorius.ECM infection clearly altered the enzymatic activity in jack pine roots but the nature of these changes depended on the fungal associate. Non‐ECM root systems had higher specific activities than ECM root systems for NR, GS, GDH and GDCO but GOGAT activites were the same for both the ECM and non‐ECM roots. Root systems infected with L. bicolor had significantly greater NR and GDCO activity than those infected with P. tinctorius. Differences in the GS activity of the two fungi in pure culture corresponded to the GS activity of jack pine roots in symbiotic association with these fungi. While the free amino acid profiles in roots were significantly affected by ECM infection, the profile of free amino acids exported to the stem was the same for all treatments. High asparagine and low glutamine in roots infected with P. tinctorius indicates that asparagine synthetase (EC x.x.x.x) activity should be higher within this symbiotic association than in the L. bicolor association or in the non‐mycorrhizal roots.
Influence of low temperature on regulation of Rb+ and Ca2+ influx in roots of winter wheat
Authors: Erlandson A. Gunvor I. , Jensén Paul 
Published: May 2006

Influx of Rb+(86Rb+) and Ca2+(45Ca2+) was determined in roots of winter wheat (Triticum aestivum L. cv. Weibulls Starke II) after 14 days at 16°C/16 h light, after 1 and 8 weeks of cold acclimation (2°C/8 h light) and at intervals after deacclimation (16°C/16 h light) for up to 14 days. The plants were cultivated at 3 ionic strengths: 100, 10 and 1% of a full strength nutrient solution, containing 3.0 mM K+ and 1.0 mM Ca2+.K+ concentrations in roots and shoots increased during cold treatment, while Ca2+ in the roots decreased. In the shoots Ca2+ concentrations remained the same. Influx of Rb+ as a function of average K+ concentration in the roots of 14‐day‐old, non‐cold‐treated plants was high at a certain K+ level in the root and decreased at higher root K+ levels (negative feedback). The pattern for Ca2+ influx versus average concentration of Ca2+ in the root was the reverse. Independent of duration of treatment (1–8 weeks), cold acclimation partly changed the regulation of Rb+ influx, so that it became less dependent upon negative feedback and more dependent on the ionic strength of the cultivation solution. After exposure to 2°C, Ca2+ influx increased at high Ca2+ concentrations in the root as compared with influx in roots of 14‐day‐old non‐cold‐treated plants. Under deacclimation, Ca2+ influx gradually decreased again, and reached the level observed before cold treatment within 7–14 days at 16°C; the number of days depending on the exposure time at 2°C. It is suggested that Rb+(K+) influx became adjusted to low temperature and that abscisic acid (ABA) may be involved in this mechanism. It is also suggested that extrusion of Ca2+ was impaired and/or Ca2+ channels were activated at 2°C in roots of plants grown in the full‐strength solution and that extrusion was gradually restored and/or Ca2+ channels were closed under deacclimation conditions.
Abscisic acid physiology and biosynthesis in higher plants
Authors: Creelman Robert A. 
Published: May 2006

Abscisic acid (ABA) has been postulated to modulate several aspects of plant growth and development. While it is tempting to attribute changes in growth and development to a specific hormone such as ABA, the reality is that these processes are complex and poorly understood. Since there is so little known about basic biochemical events that occur during growth and development, it is difficult ot unambiguously assign a role for ABA in any process. Becuse of this, many of the cited effects of ABA on growth and development have not been conclusively demonstrated. Howver, it is clear that ABA has a function in ameliorating water‐stress and preventing vivipary. The roles of ABA in bud dormancy and growth still remain unclear. With the use of biosynthesis inhibitors and mutants which block ABA accumulation, it has been shown that ABA does not play a role in gravitropism.Knowledge of how the levels of any particular growth regulator are modulated is essential for the understanding of its physiology. The use of mutants, inhibitors and heavy isotopes suggests that ABA may be derived from a carotenoid rather than directly from farnesyl pyrophosphate (FPP), and that the cleavage of a carotenoid is the rate limiting step. However, the relative contribution of each pathway (and the role of xanthoxin) in ABA biosynthesis remain unknown.