bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular weight distribution of hemicellulosic polysaccharides of the cell wall of tall and dwarf rice cultivars, and the effect of GA3
Authors: Revilla Gloria , Zarra Ignacio , Masuda Yoshio
Published: May 2006

Growth rate, osmotic potential of the cell, cell wall mechanical properties, sugar composition and molecular weight (MW) distribution of water‐soluble hemicellulosic polysaccharides of the second leaf sheath of one tall (Oryza sativa L. cv. Nihonbare) and two dwarf (Oryza sativa L. cvs. Tan‐ginbozu and Waito C) cultivars of rice were compared. The effect of gibberellic acid (GA3) on the above‐mentioned parameters was also studied using the tall (Nihonbare) and one of the dwarf (Waito C) cultivar. The minimum stress‐relaxation time (T0) was higher in the cell wall from the two dwarfs than in the tall cultivar. Furthermore, in the water‐soluble hemicellulosic polysaccharides the mass‐average MW of β‐glucan was higher and that of arabinoxylan was lower in the tall cultivar than in the dwarf ones. Thus, dwarfism of cvs Tan‐ginbnozu and Waito C might be correlated with the different MW distributions of β‐glucan and arabinoxylan. GA3 induces growth in the dwarf Waito C cultivar, decreases the T0 value of the cell wall, and also decreases the average MW of water‐soluble hemicelluloses. Changes in β(1–3)(1–4)glucan or arabinoxylan or in both are proposed as part of the cell wall loosening mechanism induced by gibberellin.
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.
Cold acclimation of Ilex aquifolium under natural conditions with special regard to the photosynthetic apparatus
Authors: Rütten Dorothea , Santarius Kurt A.
Published: May 2006

Frost resistance of leaves of holly (Ilex aquifolium L.) increased from about −9°C in late summer to −24°C in mid‐winter. The gradual rise in cold hardiness occurred when the minimum air temperature dropped to 0°C or below and was closely related to increase in the cellular sap concentration. Predominantly, the decrease in the osmotic potential of the cellular sap was caused by sugar accumulation, mainly of sucrose. The capacity of net photosynthesis of the leaves, as well as the total lipid and protein content and the proportion of individual lipids of the thylakoid membranes, did not significantly change during cold acclimation. The gradual shift towards desaturation in the fatty acids of the thylakoid lipids during the hardening period was neither correlated with alterations in the frost resistance nor did it affect the potential efficiency for various light‐induced chloroplast membrane reactions such as linear photosynthetic electron transport, photophosphorylation and the proton gradient (ΔpH). It is suggested that in holly leaves reduction in cell volume changes during freeze‐thawing and cryoprotection by sugars could play a dominant role for the increase in frost resistance. Seasonal changes in the degree of unsaturation of polar lipids of the thylakoids could contribute to maintain optimal functional efficiency of the membranes at low temperatures rather than to avoid freezing damage.
The effect of abscisic acid and K+ on xylem exudation from excised roots of Lupinus luteus
Authors: Van Steveninck Reinhard F. M. , Van Steveninck Margaret E. , Läuchli André
Published: May 2006

External application of abscisic acid (ABA) induces a relatively high rate of xylem exudation in excised roots of Lupinus luteus L. cv. Weiko III. The response is relatively slow with a lag period of ca 1 h. It is also slowly, but reversibly, abolished by application of 3.6 or 36 μM cycloheximide (CHX). Contrary to expectation, K+ is not a significant factor in maintaining flow rates in lupin roots as no response was measured after adding K+ to root systems, from which K+ had been withheld for periods ranging from 3 h to several days. In fact, excised roots obtained from seedlings raised in the absence of K+ failed to respond to added K+. Total depletion of K+ is difficult to achieve, because of initial seed reserves, and prolonged exudation in lupins can be maintained utilising only a small proportion of the K+ originally present in the root tissue. Nevertheless, the data cast doubt on the general applicability of the concept that volume flow is maintained by an osmotic gradient with K+ as the principal mineral ion.
Salt tolerance of the reed plant Phragmites communis
Authors: Matoh Toru , Matsushita Nobutoshi , Takahashi Eiichi
Published: May 2006

Reed plants (Phragmites communis Trinius) were grown at NaCl concentrations up to 500 mM and their growth, mineral contents and leaf blade osmotic potential were determined. Addition of NaCl up to 300 mM did not affect growth significantly. Sucrose, Cl‐and Na+ concentrations in the shoots increased with the salinity of the medium and the shoot water content decreased. K+ always contributed most to the leaf osmotic potential. Even in the presence of 250 mM NaCl in the rooting medium, the leaf blade contained only 50 mM Na+, suggesting that the plants have an efficient mechanism for Na+ exclusion. 22Na+ uptake experiments suggested that the retranslo‐cation of absorbed Na+ from shoots to the rooting medium lowered the uptake of Na+.
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.
Changes of monoterpene concentrations in needles of pollution‐injured Picea abies exhibiting montane yellowing
Authors: Jüttner F.
Published: May 2006

Terpenes were analyzed in needles of pollution injured Picea abies (L.) Karst. of the Southern Black Forest (SW Germany) showing symptoms of montane yellowing. Compared to a set of healthy trees, a set of injured trees showed increased terpene hydrocarbon concentrations relative to needle fresh weight. This difference was even more pronounced when the terpene concentrations of green, healthy and yellowing, injured needles from the same internode of individual injured trees were compared. Increased terpene concentrations were observed in the basal parts of injured needles, while their distal parts exhibited a loss of terpenes. In addition, an alteration in the pattern of terpene occurrence was observable. Most striking was the changed ratio of α‐pinene to β‐pinene. with marked increase of the latter, in injured needles. As indicated by ultratrace analysis of isolated mesophyll. vascular tissue and resin ducts of the needles, mono‐ and sesquiterpenes were found exclusively in resin ducts. The other tissues were virtually free of terpenes. Isolated resin from a single resin duct contained all terpenes (monoterpene hydrocarbons, alcohols and ketones, and sesquiterpene hydrocarbons) that are typical for the needle. An individual response to air pollution of each separate short resin duct in the needle may be deduced.
Germination of seeds of annual and biennial celery (Apium graveolens)
Authors: Pressman Etan , Shaked Rachel , Negbi Moshe
Published: May 2006

Seeds of 4 annual cultivars of celery (Apium graveolens L. No. 15, 16, 17 and 143) were able to germinate in the dark, under high temperature, in relatively high concentrations of NaCl solutions and in the presence of relatively high concentrations of the inhibitors of the biosynthesis of gibberellin, paclobutrazol and ancymidol. Seeds of two biennial cultivars [Florida and Earlibell (EB)] showed very low germinability, or failed to germinate under the same conditions. These results are discussed in terms of endogenous gibberellin levels, which may be higher in the seeds of annual cultivars as compared to biennial ones.
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.
Changes in levels of peroxidases and phenolics during root formation in Vitis cultured in vitro
Authors: Mato M. C. , Rúa M. L. , Ferro E.
Published: May 2006

Root formation in vine (Vitis vinifera L. cv. Albariño) was accompanied by at first a rise and then a fall in total peroxidase (EC 1.11.1.7) activity in the explant. These variations ran parallel to similar changes in the amount of the three cathodic isope‐roxidases detected, the most abundant of which, C2, also exhibited IAA oxidase activity. The anodic isoperoxidase bands detected were very weak and underwent no variation during rooting. Changes in the opposite direction (a fall followed by a rise) were shown by certain endogenous phenolics, including monoferuloyl, monocaffeoyl and mono‐ρ‐coumaroyl tartaric acids, some of which may act as auxin protectors.
Phospholipid composition and fatty acid peroxidation during ageing of Acer platanoides seeds
Authors: Pukacka Stanislawa , Kuiper Pieter J. C.
Published: May 2006

Seeds of Norway maple (Acer platanoides L.) differing in water content (10, 20 and 30%) were stored for 6 weeks at 20 to 30°C. During this period changes in phospholipids and fatty acids as well as in seed viability and germination capacity were studied. A considerable decrease in the phospholipid content was observed, which depended on the water content in the seeds and was related to the decrease of the seed germination capacity. The level of linoleic (18:2) and linolenic (18:3) acids in the phospholipid fraction decreased considerably in the course of the accelerated seed ageing. The results obtained suggest that phospholipid degradation and peroxidation of unsaturated fatty acids, followed by membrane destruction, play a considerable role in maple seed ageing.
Isolation and characterization of xanthine dehydrogenase from Chlamydomonas reinhardtii
Authors: Pérez‐Vicente Rafael , Pineda Manuel , Cárdenas Jacobo
Published: May 2006

Xanthine dehydrogenase (XDH, EC 1.2.1.37) of Chlamydomonas reinhardtii (Sager) 6145c wild strain has been isolated and characterized for the first time in a unicellular green alga. The enzyme has an Mr of 330 kDa, and FAD, molybdenum and iron are cofactors required for its activity as deduced from results obtained using specific inhibitors, 59Fe‐labelling experiments, activity protection by FAD, physiological responses in vivo to iron and molybdenum deficiencies in the culture medium and work with mutants lacking molybdenum cofactor. Xanthine dehydrogenase exhibited Mi‐chaelian kinetics typical for a bisubstrate enzyme with apparent Km values for NAD +, hypoxanthine and xanthine of 35, 160 and 70 μM, respectively. Under phototrophic conditions enzyme activity was repressed by ammonium, but xanthine was not required for the enzyme to be induced, since high levels of enzyme activity were found in cells grown on ammonium and transferred to either N‐frec media or media containing either of the nitrogen sources adenine, urea, urate, xanthine, hypoxanthine and guanine.
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.
Changes of fatty acids and sterols in apple buds during bud break induced by a plant bioregulator, thidiazuron
Authors: Wang S. Y. , Faust M.
Published: May 2006

The effects of N‐phenyl‐N'‐l,2,3,‐thidiazol‐5‐ylurea (thidiazuron; Dropp; SN 49537) on fatty acids of membrane lipids and sterol content in apple (Malus domestica Borkh cv. Golden Delicious) buds associated with bud break and bud development were determined. The predominant fatty acids in the membrane lipids of apple buds were palmitic acid (C16:0), linoleic acid (C18:2) and linolenic acid (C18:3). β‐Sitosterol and sitosteryl ester were the predominant sterols. An accumulation of unsaturated polar membrane fatty acids started after thidiazuron treatment. A decrease in the percentage of the sitosterol was accompanied by an increase in campesterol and stigmasterol at the beginning of rapid growth. An increase in the ratio of campesterol and stigmasterol to sitosterol and a decrease in the ratio of free sterols to membrane lipids upon breaking of dormancy also occurred in apple buds induced by thidiazuron.
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.
Circumnutation in Phaseolus vulgaris. I. Growth, osmotic potential and cell ultrastructure in the free‐moving part of the shoot
Authors: Millet Bernard , Melin Daniel , Badot Pierre‐Marie
Published: May 2006

Circumnutation of Phaseolus vulgaris L. cv. Blanc de Juillet twining shoots was examined at the cellular level. Cell growth was monitored inside the free‐moving part of the shoot as a function of time and position with respect to the terminal bud. Complete elongation of epidermal cells required >7 days. A 60% increase in length of the cells in the bending zone was observed. Scanning and transmission electron microscopy studies showed the elasticity of cell walls, the extent of plasmodesmata and endoplasmic reticulum of epidermal cells. The osmotic potential in epidermal cells of the bending zone displayed significant differences only between the concave and convex sides. The pattern of cell growth in twining shoots is discussed. Circumnutation could be seen as a consequence of periodic turgor changes inducing periodic growth.
Establishment, graft union characteristics and growth of Prunus micrografts
Authors: Gebhardt K. , Goldbach H.
Published: May 2006

A micrografting technique for use on shoots derived by shoot‐tip culture is described. Autografts of Prunus domestica cv. Hauszwetsche as well as heterografts of several sour cherry cultivars (Prunus cerasus L. cvs Schattenmorelle, Weiroot 158, Köröser) were established. Successful graft formation in vitro was confirmed by translation of 86Rb+ from the stock root into growing scion tissues. A mechanically strong graft union was formed during the course of a 3‐week subculture of micrografts in a liquid medium without the addition of growth regulators. In the case of graft rejection, 86Rb+ was mainly attracted to new developing shoots from lateral meristems of the stock plant. Histological examination of the graft union revealed callus formation, cytodifferentiation and xylogenesis leading to the formation of vascular connections. Stem elongation after micrografting was related to vigour of the stock and scion genotypes. Early stem elongation could be used as a criterion for preselection of growth vigour in graft combinations. Micrografts were transferred to soil and grown in the greenhouse.
Physiological effects of Na2SO4 and NaCl on callus cultures of Brassica campestris (Chinese cabbage)
Authors: Paek Kee Yoeup , Chandler Stephen F. , Thorpe Trevor A.
Published: May 2006

Hypocotyl‐derived callus cultures of Brassica campestris L. ssp. pekinensis cv. Kim‐jung (Chinese cabbage) were grown on Murashige and Skoog medium containing no additional salt, NaCl or Na2SO4. Na2SO4 was more than twice as inhibitory in comparison to the same concentration of NaCl when growth and fresh:dry weight ratios of established callus were measured. Levels of protein, starch, sucrose and α‐amino nitrogen were not significantly altered in salt‐grown callus. Concentrations of reducing sugars and chlorophyll were 2–3 times greater in callus grown on either salt. Proline concentration increased 15–20 fold on the highest levels of salt. Final concentrations (reached in 20–24 days) were closely correlated to the initial Na+ concentration of the medium, regardless of salt type. The osmotic potential in callus transferred to NaCl or Na2SO4 reached a maximum negative value after 16 days. For both salts, subsequent increases were correlated to increases in fresh:dry weight and growth. On both salts, turgor remained relatively constant (0. 6–0.75 MPa). Changes in Na+, K+, Mg2+ and Ca2+ content were correlated to initial Na+ concentration in the medium, not salt type. Accumulation of Na+ was accompanied by loss of K+ and Mg2+. Six to seven times less sulfate was measured in callus grown on Na2SO4 than chloride in callus grown on similar concentrations of NaCl.
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.
Accumulation of di‐n‐butylphthalate in plants and its effect on pigment and protein content
Authors: Virgin Hemming I.
Published: May 2006

Seedlings of radish (Raphanus salivas L. cv. Cherry Belle) and wheat (Triticum aestivum L. cv. Starke II, Weibull) placed in air containing vapour of di‐n‐butyl‐phthalate accumulate phthalate to a concentration that is 106 times that of the surrounding air within 3 days. Particularly high accumulation is found in the cuticular and wax layers. Plants earlier found not to respond to di‐n‐butylphthalate (wheat) show toxic symptoms (carotenoid and chlorophyll deficiency in strong light, conco‐mittant with chloroplast destruction and swollen mitochondria) when the phthalate concentration is further increased by addition to the nutrient medium. Phthalate‐affected, white leaves lack the protein moieties normally belonging to the light harvesting complex.
Dose responses of gibberellins
Authors: Nissen Per
Published: May 2006

To determine the response type, published data for the most widely used bioassays for gibberellins have been analyzed by means of a computer program for estimating sensitivity parameters, or by interpolation. The dose response data are almost uniformly subsensitive, i. e. more than an 81‐fold increase in external gibberellin concentration is required for a change from 10 to 90% of maximal response (S90/S10). Data for the interaction of gibberellins with artificial membranes are, in contrast, markedly ultrasensitive (S90/S10± 10). This difference further strengthens the view that lipid structures do not function as receptors for gibberellins. Most of the subsensitive dose responses for gibberellins can be quite precisely represented by cooperative isotherms. However, available data are insufficiently detailed for an unequivocal choice among cooperative, multiphasic or more complex kinetics.
Reality of P‐680 chlorophyll protein – Identification of the site of primary photochemistry in oxygenic photosynthesis
Authors: Satoh Kimiyuki
Published: May 2006

Until recently nearly all available experimental evidence seemed to indicate that the largest subunit of about 50 kDa in the photosystem II core complex (psbB gene product) is the site of primary photochemistry, and thus the name “P‐680 apoprotcin” has been given to this subunit. The notion, however, has also been challenged on the basis of deduced amino acid sequence homology between the proteins in the photosystem II and those of the purple bacterial reaction center. The actual preparation of a functionally active photosystem II reaction center completely devoid of the psbB gene product, but consisting of D‐1 and D‐2 proteins and cytochrome b‐559, has now been achieved.
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.
Proteinase activities in quiescent and germinating seeds of xHaynaldoticum sardoum
Authors: Galleschi Luciano , Capocchi Antonella , Giannoni Paola , Floris Carlo
Published: May 2006

Breakdown of gliadin during germination of xHaynaldoticum sardoum Meletti et Onnis seeds is correlated with the appearance in the endosperms of a proteinase activity, which is absent in the quiescent seed. This activity is optimal at pH 4 and has a maximum stability at pH 4–5. Gel filtration of proteinase activity extracted from quiescent seeds indicates a molecular weight of 60–100 kDa. The proteinase can hydrolyze hemoglobin but not gliadin and is inhibited by pepstatin A and, to a lower extent, by p‐chloromercuribenzoic acid (p‐CMB). Gel filtrations of crude extracts from germinating seeds reveal two peaks (molecular weight 66 and 21 kDa) of activity against hemoglobin and a shoulder and a peak (molecular weight 21 kDa) of activity on gliadin. The first peak of activity against hemoglobin is inhibited by pepstatin A and p‐CMB; the second one is inhibited by p‐CMB and leupeptin. As for the gliadin‐eluted activity the shoulder is mainly inhibited by pepstatin A and p‐CMB, whereas the peak is inhibited by p‐CMB and leupeptin. Estimations of the ratios of total nitrogen to α‐amino nitrogen, suggest that the enzyme preparations mainly contain proteinases. It is concluded that the proteinases present in the quiescent seeds of xH. sardoum, in particular aspartic proteinases (EC 3.4.23), could play a role as initiator endoproteases or participate in the digestion of modified proteins during the mobilization of reserve proteins. The cysteine proteinases (EC 3.4.22) appearing during the germination seem to account for the hydrolysis of the most abundant class of protein reserves, the prolamins.
The chloroplast nucleoids of the bundle sheath and mesophyll cells of Zea mays
Authors: Lindbeck A. G. C. , Rose R. J. , Lawrence M. E. , Possingham J. V.
Published: May 2006

Dimorphic chloroplasts of Zea mays L. cv. GH5004 from bundle sheath and mesophyll cells contained similar amounts of DNA, while bundle sheath chloroplasts contained twice the number of nucleoids compared to mesophyll chloroplasts. On average bundle sheath nucleoids were half the size of mesophyll nucleoids and contained half as much DNA. Electron microscope autoradiography of the chloroplasts showed that the nucleoid DNA is associated with the thylakoids and in the case of mesophyll chloroplasts preferentially with the grana. These observations suggest that the differences in nucleoid distribution may be due to differences in membrane morphology, with the small nucleoids of agranal bundle sheath chloroplasts being widely dispersed.
Characteristics of the light‐induced generator potentials in the liverwort Conocephalum conicum
Authors: Trȩbacz K. , Tarnecki R. , Zawadzki T.
Published: May 2006

Light‐induced generator potentials were examined in the liverwort Conocephalum conicum L. by applying sub‐threshold light stimuli (400–750 nm). The fluenceresponse dependence was determined for various wavelengths. At low values of quantum flux density (less than 1 μmol m−2 s−1) the plant reacts to the light pulses with hyperpolarization which, with a rise in the pulse intensity, is masked by the depolarization of the transmembrane potential. The action spectrum of depolarization shares many features with the absorption specturm of photosynthetic pigments. Application of inhibitors and electron donors showed a predominant role of photosystem II in the formation of the generator potential. No significant Emerson enhancement was observed after simultaneous illumination with light beams of 650 and 700 nm.
The effects of ionic channel inhibitors and factors modifying metabolism on the excitability of the liverwort Conocephalum conicum
Authors: Trȩbacz K. , Tarnecki R. , Zawadzki T.
Published: May 2006

Changes in the excitability of the liverwort Conocephalum conicum L. caused by inhibitors of ionic channels and phosphorylation uncouplers, were examined. Action potentials were triggered by electrical and light stimuli. Tetraethylammonium chloride, an inhibitor of K+ channels, completely blocked the ability to generate action potentials. Excitability also disappeared under the influence of MnCl2 and LaCl3, inhibitors of Ca2+ channels. The participation of Ca2+ and K+ in the electrogenesis of action potentials in C. conicum is discussed. Treatment with phosphorylation uncouplers induced a gradual disappearance of the metabolic component of the resting potential. It was accompanied by some series of excitations, numbering from several to over a dozen impulses characterized by decreasing amplitudes, after which the organism became totally unexcitable. Dicyclohexylcarbodiimide an inhibitor of H+‐ATPase, also caused depolarization of the transmembrane potential and disappearance of excitability. The results indicated the participation of a metabolic component in the generation of action potentials in C. conicum.
Purine nucleotide and RNA synthesis in suspension cultured cells of carrot
Authors: Ashihara Hiroshi , Nygaard Per
Published: May 2006

Purine nucleotide and RNA synthesis have been investigated at the different growth stages of carrot (Daucus carota L.) cells grown in suspension cultures. At the early growth stages an increase in the content of RNA was observed, although at later stages RNA was degraded. The highest rates of incorporation of [14C]‐labelled adenosine into ATP and GTP were observed at the late growth sttages. This indicated that purine slavage was more importnt at the late growth stages, while de novo synthesis was dominant during the initial growth stages. This pattern was also reflected by increased levels, in the cell dividison phase, of theenzymes glycinamide ribonucleotide synthetase (EC 6.3.1.3.) and phosphoribosylpyrophosphate amido‐transferase (EC 2.4.2.14) involved in de novo purine synthesis. The activities of the purine salvage enzymes varied little during growth. Cells in the stationary phase, that were starved for sucrose and phosphate, showed a dramatic increase in cellular metabolism, as judged from a rapid uptake and incorporation of [32P]‐labelled phosphate into nucleotides and RNA, when incubated in fresh medium.
Relationship between autoregulation and nitrate inhibition of nodulation in soybeans
Authors: Day David A. , Carroll Bernard J. , Delves Angela C. , Gresshoff Peter M.
Published: May 2006

Ten of 11 supernodulating mutants of soybean [Glycine max (L.) Merr.] cv. Bragg, in which nodulation was far in excess of that in the wild type, showed pronounced tolerance of nodulation to applied nitrate. Mutant nts (nitrate‐tolerant symbiosis) 1116 had an intermediate nodulation response and also showed some inhibition by nitrate. Mutant 1029, a revertant of nts382 (an extreme supernodulator), showed a wild‐type nodulation pattern and was equally sensitive to nitrate as cv. Bragg. Grafting experiments with cv. Bragg and nts382 indicated that both supernodulation and tolerance of nodulation to nitrate were dependent on shoot factors. Total leaf nitrate reductase (EC 1.6.6.1 and EC 1.6.6.2) activity of the supernodulating mutants was similar to that in cv. Bragg. We conclude from these results that the inhibitory effect of nitrate on nodule initiation and development in soybean depends on an interaction between nitrate and the autoregulation singal. In the supernodulating mutants, the autoregulation signal is either altered or absent and cosequently nodulation in these mutants is not sensitive to nitrate.
Influence of blue light on the activity of phosphofructokinase in Chlorella kessleri
Authors: Grotjohann Norbert , Kowallik Wolfgang
Published: May 2006

In crude extracts of Chlorella kessleri Fott and Novákóva cells grown autotrophically in white light the activity of phosphofructokinase (PFK, EC 2.7.1.11) is 62.9 ± 1.5 nmol (mg protein)−1 min−1 under optimized test conditions. It is greatly increased in red [88.3 ± 1.8 nmol (mg protein)−1 min−1], but somewhat decreased [57.0 ± 0.5 nmol (mg protein)−1 min−1] in blue light of equal productivity. Mixtures of blue and red light yield the low activity as long as blue light represents at least 35% of the total quantum fluence rate. The rough wavelength dependence of the counteracting effect of short wavelength light on the increasing effect of red light exhibits a broad peak at 460 nm, reminiscent of action spectra of the blue/UV photoreceptors(s). Upon transfer of red light‐grown cells to blue light, the decrease develops slowly within 72 h; it cannot be prevented by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea (DCMU). Since there is less carbohydrate in blue than in red light‐exposed cells, correlations between biosynthesis of PFK and level of carbohydrate are discussed, based on the assumption that red light decreases and/or blue light increases the transport of metabolites across the chloroplast envelope.
Leaf development in Lolium temulentum: plastid membrane polypeptides in relation to assembly of the photosynthetic apparatus and leaf growth
Authors: Davies T. G. Emyr , Ougham Helen J. , Thomas Howard , Rogers Lyndon J.
Published: May 2006

Cellular and compositional changes related to tissue growth and assembly of the photosynthetic apparatus were established with reference to the developmental gradient along the expanding fourth leaf of Lolium temulentum L. Ba 3081. The number of cells and the fresh weight per leaf segment fell with increasing cell age (distance from the leaf base). Components of the photosynthetic apparatus increased in concentration towards the more mature part of the leaf. Appreciable levels of chlorophyll and carotenoid could be detected in basal tissue enclosed in the sheaths of previous leaves prior to emergence into full light. The distributions of NADPH‐protochlorophyllide oxidoreductase (PCR. EC 1.6.99.1) and cytochrome f along the age gradient were visualized by Western blotting. Leaf base tissue contained two forms of PCR, 41 and 39 kDa, the smaller of which diminished with increasing cell age and proximity to full light. Cytochrome f comprised a 52 kDa species, which also declined with distance from the base, and a group of polypeptides at around 30–33 kDa which greatly intensified with tissue maturity. The significance of multiple forms of plastid proteins and the role of the light gradient penetrating the leaf sheath in regulating growth and plastid assembly processes are discussed.
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.
Diurnal and temporal changes in the chemical profile of xylem exudate from Vitis rotundifolia
Authors: Andersen Peter C. , Brodbeck Brent V.
Published: May 2006

Positive root pressure in Vitis rotundifolia Michx. cv. Noble was employed to quantify diurnal and temporal changes in the chemical profile of xylem exudate. Xylem fluid osmolarity (7.2 to 16.8 mM), water flux (8.2 to 18.5 ml h−1) and solute flux (0.7 to 2.2 mmol h−1) from a cut spur exhibited a diurnal pattern with maxima during midday and minima at night. Total osmolarity was similar to the sum of all organic and inorganic entitites quantified, indicating that the major solutes have been identified. Total amino acid and organic acid concentration were about equal (2 to 7 mM), and sugars accounted for a minor fraction of the total profile (<0.2 mM). Glutamine represented ca 80% of the organic N and 70% of the total N transported in the xylem fluid. A circadian rhythm in water flux and net flux of most organic and inorganic entities was observed with maxima during midday and minima at night. The increase in xylem fluid osmolarity occurring during midday was primarily a consequence of increased organic acid (oxalic, citric, tartaric, malic and succinic acids) and ion (NH4+, No3−, P and Ca) concentration. A diurnal cycle in amino acid concentration was less clear. The concentration of individual organic and inorganic entities varied asynchronously with time. Xylem solute was comprised of 80% organic and 20% inorganic components when collected 5 min to 2 h after the commencement of bleeding, but the ratio of organic to inorganic components fell to about 50% after 7 days.
Internode length in Pisum. Two further gibberellin‐insensitivity genes, lka and lkb
Authors: Reid James B. , Ross John J.
Published: May 2006

Two further internode length genes are identified in Pisum sativum L. and named lka (identified from line NGB5865) and lkb (from NGB5862). These genes result in a similar phenotype, which includes reduced stem elongation, peduncle length and basal branching, and ‘banding’ of the stem. These effects are similar to, but less severe than, those of gene lk. Genes lka and lkb influence gibberellin (GA) sensitivity, since mutants NGB5865 and NGB5862 possess similar levels of endogenous GA‐like substances to the wild‐type parental cultivar Torsdag and respond less to applied GA1 than do wild‐type plants or GA‐synthesis mutants of a similar stature. The action of genes lka and lkb is localised in the young apical tissue but is not thought to involve GA‐perception, since plants possessing genes lka and lkb are not true phenocopies of GA‐deficient plants. The genetic interaction of genes lka and lkb is examined and the action of gene lkb on a le gene background determined.