bluuebunny/crossref_metadata_2025 huggingface dataset:
Microsomal polypeptides in sunflower (Helianthus annum). Comparison between normal type before and after cold‐induction, and a high oleic acid mutant
Authors: Sarmiento Cristina , Mancha Manuel , Garcés Rafael
Published: May 2006

Differences in high‐resolution two‐dimensional gel electrophoresis patterns of micro‐somal proteins from developing normal sunflower (Helianthus annuus L.) seeds before and after cold‐induction, and also from normal and a high oleic sunflower mutant have been studied in order to detect the polypeptides associated with the microsomal Δl2‐desaturase activity and its regulation by temperature. Proteins were obtained from developing seeds of two isogenic sunflower lines HA‐89 (normal) and HA‐OL9 (high oleic) which greatly differed in linoleic acid content and “in vitro” oleate desaturase activity. In the high oleic mutant, four polypeptides of about 32 kDa and two of 33 kDa were found to change in position, to the same extent, toward a lower isoelectric point in the high oleic mutant. Also, two polypeptides, of 32 and 49 kDa each, appeared in the mutant. Quantitative differences between cold‐induced seeds (10°C, 24 h) and their non‐induced controls were found. One polypeptide of 43 kDa decreased in the cold‐treated seeds and two others, of 30 and 32 kDa each, increased markedly after cold induction. Some of these polypeptides could be related to oleate desatnrase activity or its regulation by temperature.
Chitinase activities are induced in Eucalyptus globulus roots by ectomycorrhizal or pathogenic fungi, during early colonization
Authors: Albrecht Catherine , Asselin Alain , Piché Yves , Lapeyrie Frédéric
Published: May 2006

A comparative study of root chitinase activities induced by the ectomycorrhizal basidimycete Pisolithus tinctorius Coker and Couch and the pathogenic fungus Phytophthora cinnamomi, has been carried out. Two chitinases were constitutively present in Eucalyptus globulus ssp. bicostata (Maid et al.) Kirkp. roots. When 7‐day‐old seedlings were challenged with the ectomycorrhizal fungus, root chitinase activity was stimulated already after 6 h, during the very early stages of ectomycorrhizal colonization. Comparing chitinase electrophoretic patterns induced by symbiotic strains more or less compatible with Eucalyptus, a strong stimulation of chitinase activity indicated a successful interaction, which evolved quickly towards root infection and mature mycorrhizae formation. Root chitinase activity remained constant over 7 days during the establishment of the symbiosis. No new chitinase band was induced by the pathogen, when compared with the symbiotic fungi. Chitinase activity was only stimulated quantitatively after pathogenic infection. Root chitinase activities were also stimulated by fungal cell extracts applied in vitro. Such stimulation mimicked precisely the stimulation by living fungi. The intensity of the plant response to fungal extracts was related to fungal strain aggressiveness.
Evidence for a glucose 1‐phosphate translocator in storage tissue amyloplasts of potato (Solanum tuberosum) suspension‐cultured cells
Authors: Kosegarten Harald , Mengel Konrad
Published: May 2006

Transport of glucose 1‐phosphate (G1P) and highly purified triose phosphate into storage tissue amyloplasts was studied. Isolated amyloplasts from potato (Solanum tuberosum L., dihaploid stock, HH 258) were transport‐functional and metabolically active in starch synthesis. Fourty percent of the amyloplasts were intact and there was only a small degree (0–1.6%) of contamination by other cellular compartments. G1P showed a clear uptake pattern paralleled by starch synthesis. Uptake of triose phosphates was virtually nil. Uptake of GIP was pH dependent with a sharp maximum at pH 5.7 and showed Michaelis‐Menten kinetics with an apparent Km of 0.5 mM. Temperature influenced the rate of uptake, the highest rate being at 25°C. Fructose l‐phosphate, ADP‐glucose, glucose, and inorganic phosphate inhibited the uptake of G1P. Uptake was also inhibited by DIDS (1–25 μM) and by Phloretin (45–750 μW). It is therefore concluded that the transport of GIP across the inner amyloplast membrane is mediated by a hexose phosphate translocator selective for phosphate and glucose moieties of the molecule. Considering the low pH maximum for G1P uptake it is possible that the uptake of G1P, and eventually starch synthesis, is regulated by an acidification of the intermembrane space by proton pumps of the inner amyloplast membrane.
Cytokinin oxidase: Biochemical features and physiological significance
Authors: Hare P. D. , van Staden J.
Published: May 2006

The catabolism of cytokinin in plant tissues appears to be due, in large part, to the activity of a specific enzyme, cytokinin oxidase. This enzyme catalyses the oxidation of cytokinin substrates bearing unsaturated isoprenoid side chains, using molecular oxygen as the oxidant. In general, substrate specificity is highly conserved and cytokinin substrates bearing saturated or cyclic side chains do not serve as substrates for most cytokinin oxidases tested to date. Despite variation in molecular properties of the enzyme from a number of higher plants, oxygen is always required for the reaction. Cytokinin oxidases from several sources have been shown to be glycosylated. Cytokinin oxidase activity appears to be universally inhibited by cytokinin‐active urea derivatives. Auxin has been reported to act as an allosteric regulator which increases activity of the enzyme.

Cytokinin oxidase activity is subject to tight regulation. Levels of the enzyme are controlled by a mechanism sensitive to cytokinin supply. The up‐regulation of cytokinin oxidase expression in response to exogenous application of cytokinin suggests that the metabolic fate of exogenously applied cytokinins may not accurately mimic that of the endogenous compounds.

Cytokinin oxidase is believed to be a copper‐containing amine oxidase (EC 1.4.3.6). Considerable evidence strongly supports a common mechanism for amine oxidases. It is possible that advances in understanding of other amine oxidases could be extrapolated to increase our understanding of cytokinin oxidase at the molecular level. This is discussed with reference to what is currently known about the catalytic mechanism of the enzyme. The possibility of pyrroloquinoline quinone, or a closely related compound, as a redox cofactor of cytokinin oxidase is considered, as are the implications of the glycosylated nature of the enzyme for its regulation and compartmentalisation within the cell.
Roles of osmotic adjustment and turgor potential in leaf area expansion
Authors: Feng Yongsheng , Li Xiaomei , Boersma Larry
Published: May 2006

We examined the roles of turgor potential and osmotic adjustment in plant growth by comparing the growth of spring wheat (Triticum aestivum cv. Siete cerrors) and sudangrass (Sorghum vulgare var. Piper) seedlings in response to soil water and temperature stresses. The rates of leaf area expansion, leaf water potential and osmotic potential were measured at combinations of 5 soil water potentials ranging from −0.03 to −0.25 MPa and 6 soil temperatures ranging from 14 to 36°C. Spring wheat exhibited little osmotic adjustment while sudangrass exhibited a high degree of osmotic adjustment. However, the rate of leaf area growth for sudangrass was more sensitive to water stress than that of spring wheat. These results were used to evaluate the relationship between growth and turgor potential. The modified Arrhenius equation based on thermodynamic considerations of the growth process was evaluated. This equation obtains growth rate as a function of activation energy, enthalpy difference between active and inactive states of enzymes, base growth rate and optimum temperature. Analyses indicate that the modified Arrhenius equation is consistent with the Lockhart equation with a metabolically controlled cell wall extensibility.
Potato cold hardiness development and abscisic acid. I. Conjugated abscisic acid is not the source of the increase in free abscisic acid during potato (Solanum commersonii) cold acclimation
Authors: Ryu Stephen B. , Li Paul H.
Published: May 2006

Free and conjugated abscisic acid (ABA) levels in stem‐cultured plantlets of potato (Solanum commersonii Dun, PI 458317) during cold acclimation were measured. The levels of free and conjugated ABA were measured by an enzyme immunoassay (EIA) with rabbit anti‐ABA‐serum. The use of immunoglobulin G fraction purified from rabbit antiserum and the methylated form of ABA resulted in an improved measuring range (0.01 to 10 pmol ABA) and precision (slope of logit‐log plot, −1.35) of EIA, compared to the use of antiserum and free ABA. Estimates of the EIA were consistent with those resulting from a commercial EIA. Under a 4/2°C (day/night) temperature regime, the potato plantlets increased cold hardiness from −5°C (warm‐grown control) to −10°C by the 7th day. During the same period, there were two transitory increases in free ABA, the first one three‐fold from 1.5 to 5.3 nmol (g dry weight)−1 on the 2nd day and the second one five‐fold from 1.5 to 7.6 nmol (g dry weight)−1 on the 6th day. Each increase in ABA concentration was followed by an increase in cold hardiness. There was no significant change in conjugated ABA content (4.2±0.6 nmol [g dry weight]−1) throughout the cold acclimation period. The lack of an interrelationship between levels of free and conjugated ABA suggested that the transitory increase in free ABA during cold acclimation was not a result of the conversion of conjugated ABA. The increase in free ABA due to biosynthesis of ABA during potato cold acclimation is discussed.
Potato cold hardiness development and abscisic acid. II. De novo synthesis of proteins is required for the increase in free abscisic acid during potato (Solanum commersonii) cold acclimation
Authors: Ryu Stephen B. , Li Paul H.
Published: May 2006

During cold acclimation of potato plantlets (Solanum commersonii Dun, PI 458317), there are two transitory increases in free ABA content corresponding to a three‐fold increase on the 2nd day and a five‐fold increase on the 6th day (Ryu and Li 1993). During this period, plantlets increased in cold hardiness from −5°C (killing temperature, control grown at 22/18°C, day/night) to −10°C by the 7th day of exposure to 4/2°C (day/night). This increase in free ABA was not found when cycloheximide (CHI), an inhibitor of cytoplasmic protein synthesis, was added to the culture medium 6 h before exposure to low temperatures. Plantlets treated with CHI did not acclimate to cold, maintaining a hardiness level (−5°C) similar to that of the 22/18°C‐grown plantlets. When the CHI‐treated plantlets were exposed to low temperatures for 3 days, transferred to CHI‐free culture medium and grown at low temperatures, the plantlets showed a transitory increase in free ABA 2 days later. This increase was followed by the development of cold hardiness (−8°C). Application of CHI to the culture medium after 3 days of cold acclimation, when the first ABA peak and a partial development of cold hardiness (−8°C) had occurred, blocked the second transitory increase in free ABA and resulted in no further development of cold hardiness. These results suggest that de novo synthesis of proteins is required for these transitory increases in free ABA during cold acclimation of potato plantlets.
Carbohydrate and mineral nutrition of orange fruitlets in relation to growth and abscission
Authors: Ruíz R. , Guardiola J. L.
Published: May 2006

Carbohydrate and mineral nutrition was studied in relation to abscission in fruitlets from leafy inflorescences of the Washington navel orange (Citrus sinensis [L.] Osbeck). Differences in the growth rate of the fruitlets permitted to predict abscission several weeks in advance. This allowed characterization of early differences in composition and behaviour of persisting and abscising fruitlets.

Inflorescences with persisting fruitlets accumulated more mineral elements than inflorescences with abscising fruitlets, and for the phloem‐mobile elements the excess accumulation was allocated to the fruitlets. Starch accumulated in the inflorescence leaves during early fruitlet growth, and this accumulation was enhanced by the persisting fruitlets despite their higher growth rate and mobilizing ability. The relations between the fruitlets and the inflorescence leaves cannot be explained totally in terms of source sink relationships; a hormonal regulation of the leaves by the fruitlets is postulated.

Acid invertase activities and hexose concentration in the pericarp were higher in the abscising fruitlets. The lower early growth rate of these fruitlets is thus not caused by a limitation in carbohydrate supply. It seems more related to carbohydrate utilization, probably hormonally mediated, as demonstrated by the higher dependence on hormone supply for the growth in vitro of the endocarp explants.
Glycosidase activities in grapefruit flavedo, albedo and juice vesicles during maturation and senescence
Authors: Burns Jacqueline K. , Baldwin Elizabeth A.
Published: May 2006

Glycosidases were extracted from grapefruit (Citrus paradisi Macf. cv. Ruby Red) flavedo, albedo, and juice vesicles harvested at five periods throughout the season. Flavedo β‐galactosidase activity was high at the September harvest and then significantly declined by November. Thereafter, no further changes occurred in β‐galactosidase activity. Flavedo α‐galactosidase activity was low and unchanged throughout the study. α‐Mannosidase, initially low in flavedo, steadily increased with advanced maturity. Trends in glycosidase activities of albedo were similar but attenuated. Juice vesicle β‐galactosidase did not change through the study period, whereas α‐galactosidase activity decreased 70% after the initial harvest period. α‐Mannosidase was initially high and then decreased to 50% of the original activity. A second peak of activity was measured in March, followed by a second decline. Extractability differences of the glycosidases suggest differences in compartmentation and function. Two isozymes of α‐mannosidase were separated in flavedo and one in juice vesicles, and characteristics were determined at an early and late harvest period. The results suggest that changes in the three glycosidases could be used to further define maturity and senescence in grapefruit.
Vascular occlusion in cut flowering rose stems exposed to air: role of the xylem wall pathway for water
Authors: van Doorn Wouter G.
Published: May 2006

Upon exposure to air at 20°C and 60% relative humidity (RH), an occlusion to water uptake developed in the basal stem segment of cut, flowering Sonia roses. The development of the occlusion was delayed by removing the leaves before storage, indicating an effect of transpiration. Placing the stem ends at 100% RH during exposure to air had no effect, which shows that water loss through the cut end is not the cause. Scanning electron microscopy did not show plant gums or tyloses in the water conducting elements.

The hypothesis by Scholander et al. (1955) that water uptake into stems held in air and then placed in water occurs through conduit walls rather than the lumen was tested by using stems of which the cut surface was covered with laboratory grease and a ring of bark was removed (girdling). Girdled stems placed in water remained fully turgid when the girdled area was about 60 mm2 or more. Water uptake was strongly inhibited when the girdled stems were exposed to air for 24–36 h, as in non‐girdled controls exposed to air for the same period. Inclusion of a surfactant (nonylphenoxypolyethoxy ethanol) in the vase water, however, facilitated water uptake after dry storage of normal cut flowering stems but did not improve water uptake into the girdled stem system, which is inconsistent with the hypothesis.

It is concluded that the vascular occlusion developing upon exposure to air cannot be explained by decreased flow in the wall pathway for water.
Abscisic acid controls dormancy development and bulb formation in lily plantlets regenerated in vitro
Authors: Kim Kwang‐Soo , Davelaar Evert , De Klerk Geert‐Jan
Published: May 2006

Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA‐synthesis, applied during culture in vitro, inhibited the swelling of the petioles and promoted leaf formation. At high fluridone concentrations (10 or 33μM), swelling was completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and resulted in plantlets with scales only. When applied simultaneously with fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlets regenerated in vitro on scale explants at 20 or 25°C were harvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve rapid emergence after planting in soil. Fluridone added during the culture in vitro prevented the development of dormancy, and the bulblets did not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of culture at 20°C had not yet developed dormancy. Bulblets regenerated at 15°C were only slightly dormant. In both types of bulblets, it is unlikely that the lack of dormancy was due to low ABA‐levels since addition of ABA did not affect the dormancy status. These data indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of dormancy.
Changes in protein kinase and protein phosphatase properties during the cycle of asparaginase activity in Leptosphaeria michotti
Authors: Jerebzoff‐Quintin Simonne , Jerebzoff Stéphan
Published: May 2006

Regulation of the cyclic activity of asparaginase (obtained as a purified protein complex) by a reversible auto‐phosphorylation process has been previously reported in the fungus Leptosphaeria michotii (West) Sacc.

In the present study, the protein complex was purified in the presence of either a mixture of 3 protein phosphatase inhibitors (fluoride, vanadate and molybdate) or EGTA, during the cycle of asparaginase activity, and the protein kinase and protein phosphatase activities characterized. (I) At the phase of increasing asparaginase activity, a Ca2+/calmodulin‐dependent kinase activity was identified by (a) its inhibition by calmidazolium, reversed by calmodulin, and its inhibition by EGTA, but not by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole or polylysine (b) an increasing level of calmodulin bound to the complex, as estimated by enzyme‐linked immunosorbent assay (ELISA). (2) At the phase of decreasing asparaginase activity, the Ca2+‐calmodulin‐dependent kinase activity disappeared and a little calmodulin remained associated with the complex: phosphorylation of the complex was increased several‐fold by 1 nM okadaic acid and 25 nM inhibitor‐2, and was not affected by EGTA, indicating a protein phosphatase‐2A‐like activity. (3) When asparaginase activity was low, a little calmodulin was bound to the complex. The kinase could phosphorylate casein and phosvitin. was inhibited by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole and heparin, stimulated by polylysine and not affected by calmidazolium or EGTA, just as a casein kinase 2. A Ca2+‐dependent but calmodulin‐independent protein phosphatase activity, not affected by okadaic acid and inhibitor‐2. was then identified.

We postulate the presence in the complex, of (a) only one protein kinase and one protein phosphatase, whose properties could change during the cycle of asparaginase activity: (b) two Ca2+/‐binding proteins: first calmodulin, which could bind to Ca2+ and the casein kinase‐2 form to give a Ca2+/calmodulin‐dependent kinase, which could become Ca2+/calmodulin‐independent following an auto‐phosphorylation process: second a protein homologous to calmodulin, able to bind to the protein phosphatase‐2A catalytic subunit to give a protein phosphatase‐2B catalytic subunit.
Metabolism of [14C]trans‐zeatin and [14C]benzyladenine by letached yellow, green and variegated leaves of Schefflera
Authors: van Staden J. , Upfold S. J. , Altman A.
Published: May 2006

[8‐14C]Benzyladenine (BA) and [8‐14C]trans‐zeatin (tZ) were fed through the petiole to mature, detached green, yellow and variegated leaves of Schefflera arboricola. Recovery of radioactivity from the plant material ranged between 4.2 and 22.1%. More radioactivity was recovered when tZ was applied compared to BA. Green leaves or the green parts of variegated leaves yielded more radioactivity than the yellow leaf material. BA was metabolized much faster than the endogenous cytokinin tZ. It would appear that while lower amounts of radioactivity were present in yellow leaves, as well as in yellow parts of variegated leaves, the rate of cytokinin metabolism was nevertheless faster. Metabolites that were formed to a greater extent in these yellow parts were the nucleotides of both cytokinins. Currently it is not known whether or not cytokinins influence chlorophyll and other pigment development in chimeric variegated leaves.
Oscillations in the electrical resistance of Nitellopsis obtusa nodes
Authors: Tokarska Malgorzata , Śpiewla Edward
Published: May 2006

Oscillatory changes of the electrical resistance across the nodal complex of Nitellopsis obtusa (Desv. in Lois) J. Gr. were observed in experiments performed for 40–150 min with the use of external electrodes and microelectrodes. Three main patterns of node resistance oscillations were similar to those found for membrane potential and resistance. The presented findings indicate an oscillatory behaviour of the plasmodesmata system at the node, which may be connected with e.g. pulsatile variations in the number of open plasmodesmata.
Catabolism of putrescine and spermidine in embryogenic and non‐embryogenic callus lines ofPicea abies
Authors: Santanen Arja , Simola Liisa Kaarina
Published: May 2006

The oxidation of putrescine and spermidine were studied in embryogenic and nonembryogenic cell cultures ofPicea abies(L.) Karst., with [1,4‐14C]‐putrescine and [1,4‐14C]‐spermidine as substrates. Activities of putrescine and spermidine oxidation varied at every developmental stage in both cultures. Putrescine was oxidized ca 5 times as fast both in embryogenic and non‐embryogenic tissue as spermidine. Diamine and especially polyamine oxidase activity increased markedly in both tissues towards the end of the culturing. In maturing embryos and in ageing non‐embryogenic cultures, enzyme activities were lower than in non‐differentiated embryogenic calli. Aminoguanidine (1 mM) inhibited di‐ and polyamine oxidation in non‐embryogenic tissue by >60% and >30%, respectively. The pH optimum for putrescine oxidation was 8.0, but in non‐embryogenic tissue spermidine was degraded even more actively at pH 5.0. [14C]‐Spermidine was catabolized to [14C]‐putrescine. Pyrroline dehydrogenase activity was observed in non‐embryogenic spruce tissue cultures.
Direct and indirect inhibition of single leaf respiration by elevated CO2 concentrations: Interaction with temperature
Authors: Ziska Lewis H. , Bunce James A.
Published: May 2006

Two herbaceous perennials, alfalfa (Medicago sativa L. cv. Arc) and orchard grass (Dactylus glomerata L. cv. Potomac), were grown at ambient (367 μmol mol−1) and elevated (729 μmol mol−1) CO2 concentrations at constant temperatures of 15, 20, 25 and 30°C in order to examine direct and indirect changes in nighttime CO2 efflux rate (respiration) of single leaves. Direct (biochemical) effects of CO2 on nighttime respiration were determined for each growth condition by brief (<30 min) exposure to each CO2 concentration. If no direct inhibition of respiration was observed, then long‐term reductions in CO2 efflux between CO2 treatments were presumed to be due to indirect inhibition, probably related to long‐term changes in leaf composition. By this criterion, indirect effects of CO2 on leaf respiration were observed at 15 and 20°C for M. sativa on a weight basis, but not on a leaf area or protein basis. Direct effects however, were observed at 15, 20 and 25°C in D. glomerata; therefore the observed reductions in respiration for leaves grown and measured at elevated relative to ambient CO2 concentrations could not be distinguished as indirect inhibition. No inhibition of respiration at elevated CO2 was observed at the highest growth temperature (30°C) in either species. CO2 efflux increased with measurement and growth temperature for M. sativa at both CO2 concentrations; however, CO2 efflux in D. glomerata showed complete acclimation to growth temperature. Stimulation of leaf area and weight by elevated CO2 levels declined with growth temperature in both species. Data from the present study suggest that both direct and indirect inhibition of respiration are possible with future increases in atmospheric CO2, and that the degree of each type of respiratory inhibition is a function of growth temperature.
Phytohormonal changes in intact shoots of wheat and oilseed rape treated with the acylcyclohexanedione growth retardant prohexadione calcium
Authors: Grossmann Klaus , König‐Kranz Susanne , Kwiatkowski Jacek
Published: May 2006

The effects of the acylcyclohexanedione‐type growth retardant prohexadione calcium on seedling growth and endogenous levels of immunoreactive phytohormone‐like substances in shoots of wheat (Triticum aestivum L. cv. Kanzler) and oilseed rape (Brassica napus L. ssp. napus cv. Lirajet) were studied. After treatment of seedlings with increasing retardant concentrations in hydroponics, plant height and fresh weight of shoots were reduced by up to 40%. Concomitantly, the amount of immunoreactive gibberellins decreased, on a fresh weight basis, when compared with levels in the shoots of control plants. In contrast, the levels of abscisic acid and dihydrozeatin riboside and isopentenyladenosine‐type cytokinins were considerably elevated by the growth retardant. The content of 3‐indoleacetic acid decreased slightly. These results suggest that, in addition to its effect on gibberellin content, prohexadione calcium also influences the levels of endogenous abscisic acid and cytokinins.
Alternative and cytochrome pathway respiration during shoot bud formation in cultured Pinus radiata cotyledons
Authors: Winkler Michele N. , Mawson Bruce T. , Thorpe Trevor A.
Published: May 2006

Respiration rates for excised cotyledons of Pinus radiata cultured in the presence (shoot‐forming) and absence (non‐shoot‐forming) of N6‐benzyladenine (BA) over a 21‐day period were measured using a Clark‐type oxygen electrode. The capacities and activities of cytochrome and alternative pathways of respiration were determined from titrations with KCN (1‐10 mM) and salicylhydroxamic acid (2–20 mM) individually and in combination. Respiration accounted for by alternative (AP) and cytochrome (CP) pathways varied with both culture treatment and age in culture. Rates of total respiration, CP respiration and AP activity rose concurrent with key developmental events of shoot bud formation. The greatest AP capacity was measured at day 3 in shoot‐forming tissue. In contrast, for cotyledons cultured under non‐shoot‐forming conditions, no AP activity was observed after day 3 despite relatively constant AP capacity throughout the culture period. Although initial increases in cotyledon respiration during the culture period may be related to wounding and introduction to a tissue culture environment, later differences in respiratory patterns between shoot‐forming and non‐shoot‐forming cotyledons appear to be associated with the cytokinin‐induced developmental changes which give rise to shoot primordia in cultured radiata pine cotyledons.
Delay of tomato fruit ripening by an oligosaccharide N‐glycan. Interactions with IAA, galactose and lectins
Authors: Yunovitz Hermona , Gross Kenneth C.
Published: May 2006

The unconjugated N‐glycans Manα1→6(Manα→3)Manα1→6(Manα1→3)‐Manβ1→4GlcNAc (Man5GlcNAc) and Manα1→6(Manα1→3)(Xy1β1→2)‐Manβ1→4GlcNAcβ1→4(Fucα1→3)GlcNAc were shown to stimulate and delay ripening of mature green tomato fruit (Lycopersicon esculentum Mill. cv. Rutgers) at 1 and 10 ng (g fresh weight)−1, respectively (Priem and Gross 1992, Plant Physiol. 98: 399–401). Also, the occurrence and structure of 10 unconjugated N‐glycans, including Man5GlcNAc, in tomato fruit were recently reported (Priem et al. 1993, Plant Physiol. 102: 445–458). In this work, we studied the potential interaction between Man5GlcNAc and several compounds by using a system that allowed pericarp discs to be kept up to 14 days after excision. Studies were performed to determine the effect of Man5GlcNAc, indole‐3‐acetic acid (IAA), concanavalin A and tomato lectin on ripening as defined by red coloration of the skin. Ripening in pericarp discs, unlike that in intact fruit, was unaffected by 1 ng (g fresh weight)−1 Man5GlcNAc. However, discs showed delayed ripening with 10 ng (g fresh weight)−1, and the delay of coloration was galactose dependent. Man5GlcNAc at 10 ng (g fresh weight)−1 inhibited the stimulation of coloration induced by 100 μ IAA in the presence of 40 μg (g fresh weight)−1 galactose. Man5GlcNAc lost biological activity in the presence of the two lectins. These results support the possible interaction of IAA and various oligosaccharides during plant growth and development, and for the first time suggest a physiological significance for tomato lectin.
Gravitropically‐stimulated seedlings show autotropism in weightlessness
Authors: Chapman David K. , Johnsson Anders , Karlsson Christina , Brown Allan , Heathcote David
Published: May 2006

In a spaceflight experiment, autotropism by oat (Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter‐reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter‐reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter‐reactions in the absence of gravitropic stimulation is discussed.
The effect of the gaseous state on bud induction and shoot multiplication in vitro in eastern white cedar
Authors: Nour Katy A. , Thorpe Trevor A.
Published: May 2006

The effect of vessel type and the gaseous phase on the morphogenic response of Thuja occidentalis L. explants in vitro was studied. Explants were cultured in container types that varied in their degree of gas exchange. Traps for ethylene and CO2 were employed. During shoot bud induction from embryonic explants, the number and elongation of shoot buds improved significantly when gastight, serum‐capped flasks were used compared to the foam bung‐capped flasks or the regularly used Petri dishes. Elimination of the two gases from the headspace of the flasks either singly or together reduced shoot bud induction and especially elongation of shoots. A similar response was seen during axillary bud development from cultured shoots. Ethylene and CO2 accumulation promoted development and elongation of axillary shoots. An increase in the zeatin concentration in the medium produced a greater number of axillary shoots and higher levels of ethylene in the culture vessels. Removal of CO2 caused gradual death of the shoots, while removal of ethylene alone reduced axillary shoot lengths significantly. Inclusion of aminoethoxyvinylglycine in the medium combined with ethylene traps produced an effect similar to the use of ethylene traps alone.
Influences of soil volume and an elevated CO2 level on growth and CO2 exchange for the Crassulacean acid metabolism plant Opuntia ficus‐indica
Authors: Nobel Park S. , Cui Muyi , Miller Patsy M. , Luo Yiqi
Published: May 2006

Effects of the current (38 Pa) and an elevated (74 Pa) CO2 partial pressure on root and shoot areas, biomass accumulation and daily net CO2 exchange were determined for Opuntia ficus‐indica (L.) Miller, a highly productive Crassulacean acid metabolism species cultivated worldwide. Plants were grown in environmentally controlled rooms for 18 weeks in pots of three soil volumes (2 600, 6 500 and 26 000 cm3), the smallest of which was intended to restrict root growth. For plants in the medium‐sized soil volume, basal cladodes tended to be thicker and areas of main and lateral roots tended to be greater as the CO2 level was doubled. Daughter cladodes tended to be initiated sooner at the current compared with the elevated CO2 level but total areas were similar by 10 weeks. At 10 weeks, daily net CO2 uptake for the three soil volumes averaged 24% higher for plants growing under elevated compared with current CO2 levels, but at 18 weeks only 3% enhancement in uptake occurred. Dry weight gain was enhanced 24% by elevated CO2 during the first 10 weeks but only 8% over 18 weeks. Increasing the soil volume 10‐fold led to a greater stimulation of daily net CO2 uptake and biomass production than did doubling the CO2 level. At 18 weeks, root biomass doubled and shoot biomass nearly doubled as the soil volume was increased 10‐fold; the effects of soil volume tended to be greater for elevated CO2. The amount of cladode nitrogen per unit dry weight decreased as the CO2 level was raised and increased as soil volume increased, the latter suggesting that the effects of soil volume could be due to nitrogen limitations.
Membrane‐bound glucosamine acetyltransferase in coleoptile segments of Avena sativa
Authors: Piro G. , Buffo M. , Dalessandro G.
Published: May 2006

The in vivo metabolism of D‐[U‐14C]glucosamine and the in vitro properties of glucosamine acetyltransferase (EC 2.3.1.3), the first committed enzyme in the metabolism of exogenously supplied D‐glucosamine, were studied in coleoptile segments of Avena sativa L. cv. Sole II. D‐[U‐14C]glucosamine was taken up by oat coleoptile segments and sequentially metabolised to radioactive N‐acetylglucosamine, N‐acetylglucosamine 6‐P, N‐acetylglucosamine 1‐P, UDP‐N‐acetylglucosamine and UDP‐N‐acetylgalactosamine. In addition, N‐acetylglucosamine residues were incorporated into glycoproteins and glycolipids of the cells. All glucosamine acetyltransferase activity was found to be membrane‐bound. The enzyme was solubilized by either digitonin or CHAPS. The specificities and the kinetics of the membrane‐bound and soluble glucosamine acetyltransferase were determined. The effects of ions, nucleotides, nucleoside diphosphate amino sugars, coenzymes and group‐specific chemical probes on the rate of membrane‐bound and CHAPS‐solubilized enzyme were investigated. Our data indicate that UDP‐N‐acetylglucosamine and UDP‐N‐acetylgalactosamine do not exert a feed‐back control on the glucosamine acetyltransferase either in vivo or in vitro. Further, some nucleotides and the metal ions Cu2+, Zn2+, Fe2+, Fe3+ and Co2+ affect the activity of the enzyme in vitro.
Effects of NaCl on the carboxylating activity of Rubisco from Tamarix jordanis in the presence and absence of proline‐related compatible solutes
Authors: Solomon A. , Beer S. , Waisel Y. , Jones G. P. , Paleg L. G.
Published: May 2006

The effects of NaCl on the carboxylating activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) were investigated in the presence of two proline‐related analogues found in Tamarix jordanis. N‐methyl‐L‐proline ameliorated the inhibition of the activity of Rubisco by NaCl. Full amelioration was reached at 200 mM of this protectant. Protection by N‐methyl‐trans‐4‐hydroxy‐L‐proline was less effective. Significant differences in the Rubisco protein content from different populations of Tamarix jordanis were observed. Moreover, higher carboxylation rates were obtained for Rubisco preparations from plants that had been grown in saline media. These results are discussed with respect to the adaptation strategies of Tamarix jordanis to saline conditions.
Effects of simulated microgravity on the germination and elongation of protonemata of Adiantum capillus‐veneris
Authors: Kasahara Hirokazu , Takeuchi Yuichi , Yamashita Masamichi , Yamada Mitsuhiro
Published: May 2006

Germination of spores and elongation of protonemata of Adiantum capillus‐veneris L., which can be controlled by light irradiation, were examined under various gravitational conditions including microgravity simulated by a three‐dimensional clinostat. The elongation of protonemata that had been irradiated from below and grew downwards was greater than that of protonemata growing horizontally or upwards. Under microgravity, protonemata were shorter than the controls. Germination of spores, direction of growth, and cell division were not affected by gravitational conditions.
Leaf age effects on photosynthetic rate, transpiration rate and nitrogen content in a tropical dry forest
Authors: Sobrado M. A.
Published: May 2006

This study examines the effect of leaf age on photosynthesis, transpiration and nitrogen concentration in four deciduous (DC) and two evergreen (EG) species coexisting in a tropical dry forest of Venezuela. Leaf age was characterized on the basis of leaf chorophyll, nitrogen content, and construction and maintenance costs. The mean leaf area‐based nitrogen concentration (N) in EG was about twice that in DC species. A leaf age effect was observed in both DC and EG species, with largest N concentration in mature leaves. Fractional leaf N allocation to chlorophyll was higher in the DC than in the EG species. Differences in the construction costs of leaf mass between the youngest and the oldest leaves averaged from 2.14 to 1.55 g glucose g−1 dry weight. Although variation in area‐based leaf maintenance and construction costs between DC and EG species existed, they were, nevertheless, positively correlated. Individual data sets, for each species, indicated that leaf N and maximum rate of photosynthesis (Amax) were linearly related. Nitrogen use efficiency (NUE) and water use efficiency (WUE) tended to be higher in mature leaves than in expanding and old leaves. Moreover, DC species always had higher NUE than EG species. Intercellular to ambient pressures of CO2 (Pi/Pa) were related to WUE in a negative manner. Higher Pi/Pa values were observed in expanding and old leaves. Leaf age effect on photosynthesis was, therefore, due to greater decline of carbon fixation capacity by mesophyll tissue relative to the decline in stomatal conductance in youngest and oldest leaves.
Molecular characterization of UV‐treated sugar beet somaclones using RFLP markers
Authors: Levall Mats W. , Bengtsson Karina , Nilsson Nils‐Otto , Hjerdin Annika , Halldén Christer
Published: May 2006

Sugar beet plants regenerated from UV‐treated calluses were examined by restriction fragment length polymorphism (RFLP) analysis to determine the extent of somaclonal variation occurring at the DNA level. In total, 50 random sugar beet DNA sequences were used to screen 42 somaclones for genetic alterations. Three polymorphisms were detected among the 7 644 alleles analysed. From these data a mutation frequency of 0.03 ± 0.02% per allele was estimated. This frequency is in agreement with similar studies of somaclonal DNA variation using molecular markers and lies in the upper range of the spontaneous gene mutation frequencies found in plants. The two probegenotype combinations showing independent polymorphisms, were further analysed using the restriction enzymes Bam HI, Eco RI, Eco RV and Hind III. Both polymorphisms are likely to result from structural rearrangements rather than from point mutations. Differences in methylation among 10 of the investigated somaclones were tested for by comparing Hpa II and Msp I generated RFLP patterns. The somaclones showed extensive methylation, but no differences in their degree of methylation. Cytological analysis revealed 34 diploid, 8 tetraploid, but no aneuploid plants.
The role of hormones in apical dominance. New approaches to an old problem in plant development
Authors: Cline Morris G.
Published: May 2006

The role of hormones in apical dominance has been under investigation with traditional ‘spray and weigh’ methods for nearly 5 decades. Even though the precision of hormone content analyses in tissue has greatly improved in recent years, there have been no significant breakthroughs in our understanding of the action mechanism of this classical developmental response. Auxin appears to inhibit axillary bud outgrowth whereas cytokinins will often promote it. Conclusive evidence for a direct role of these or other hormones in apical dominance has not been forthcoming. However, promising new tools and approaches recently have begun to be utilized. The manipulation of endogenous hormone levels via the use of transgenic plants transformed with bacterial genes (iaaMandiptfromAgrobacterium tumefaciensandiaaLfromPseudomonas syringaepv.savastanoi) has demonstrated powerful effects of auxin and cytokinin on axillary bud outgrowth. Also, possible auxin and cytokinin involvement ofrolBandCgenes fromAgrobacterium rhizogeneswhose activity is associated with reduced apical dominance in dicotyledons has received considerable attention. The characterization of unique mRNAs and proteins in non‐growing and growing lateral buds before and after apical dominance release is helping to lay the groundwork for the elucidation of signal transduction and cell cycle regulation in this response. The use of auxin‐deficient, and auxin/ethylene‐resistant mutants has provided another approach for analyzing the role of these hormones. The presumed eventual employment of molecular assay systems (SAUR/GH3 promoters fused with GUS reporter gene) which are presently being developed for analyzing auxin localized in lateral buds will hopefully provide a critical test for the direct auxin inhibition hypothesis.
The role of sugar, vitrification and membrane phase transition in seed desiccation tolerance
Authors: Sun Wendell Q. , Irving Thomas C. , Leopold A. Carl
Published: May 2006

In a search for the mechanism of desiccation tolerance, a comparison was made between orthodox (desiccation‐tolerant) soybean (Glycine max [L.] Merrill) and recalcitrant (desiccation‐intolerant) red oak (Quercus rubra L.) seeds. During the maturation of soybean seeds, desiccation tolerance of seed axes is correlated with increases in sucrose, raffinose and stachyose. In cotyledons of mature oak seeds, sucrose levels are equal to those in mature soybeans, but oligosaccharides are absent. By using the thermally stimulated current method, we observed the glassy state in dry soybean seeds during maturation. Oak cotyledons showed the same phase diagram for the glass transition as did mature soybeans. By using X‐ray diffraction, we found the maturation of soybeans to be associated with an increased ability of membranes to retain the liquid crystalline phase upon drying, whereas the mature oak cotyledonary tissue existed in the gel phase under similar dry conditions. These findings lead to the conclusion that the glassy state is not sufficient for desiccation tolerance, whereas the ability of membranes to retain the liquid crystalline phase does correlate with desiccation tolerance. An important role for soluble sugars in desiccation tolerance is confirmed, as well as their relevance to membrane phase changes. However, the presence of soluble sugars does not adequately explain the nature of desiccation tolerance in these seeds.
Effect of atmospheric ammonia on the nitrogen metabolism of Scots pine (Pinus sylvestris) needles
Authors: Pérez‐Soba M. , Stulen I. , van der Eerden L. J. M.
Published: May 2006

Four‐year‐old seedlings of Scots pine (Pinus sylvestrisL.) were exposed to filtered air (FA), and to FA supplemented with NH3(60 and 240 μg m−3) in controlled‐environment chambers for 14 weeks. Exposure to the higher NH3concentration resulted in an increased activity of glutamine synthetase (GS, EC 6.3.1.2), and an increase in the concentrations of soluble proteins, total nitrogen, free amino acids and leaf pigments in the needles. The GS activity (μmol g−1fresh weight h−1) in the needle extract increased to levels 69% higher than in FA and the soluble protein concentration to levels 22% higher. Total nitrogen concentration in the needles was 42% higher than in FA, while the free amino acid concentration was 300% higher, which was caused by an increase in arginine, glutamate, aspartate and glutamine. Chlorophylla, chlorophyllband carotenoid concentrations were 29, 38 and 11% higher, respectively. Neither the glutamate dehydrogenase (GDH, EC 1.4.1.2) activity nor the concentrations of free NH4+and glucose in the needles were affected by exposure to NH3. After NH3fumigation at 240 μg m−3the starch concentration decreased by 39% relative to the FA. The results indicate that the metabolism of Scots pine acclimates to concentrations of NH3which are 3 to 10 times higher than the average concentration in areas with intensive stock farming. The possible mechanisms underlying acclimation to NH3are discussed.
Influence of selenium on uptake and toxicity of copper and cadmium in pea (Pisum sativum) and wheat (Triticum aestivum)
Authors: Landberg Tommy , Greger Maria
Published: May 2006

The detoxifying effect of selenium on animals toxicated with heavy metals is well known. In this study we examine if there is a similar effect in plants. Wheat (Triticum aestivum L. cv. Sunny) and pea (Pisum sativum L. cv. Fenomen) were grown for 21 days on a nutrient solution based on the nutrient proportions in healthy plants. Nutrients along with cadmium, copper, selenite, selenate or selenite and selenate in combinations with copper or cadmium were supplied in small amounts with a daily incremental increase of 0.12 (wheat) and 0.20 (pea). The metal and selenium uptake and distribution in the plants as well as the effects on growth were investigated.

The results show that selenium does not reduce the toxicity of heavy metals to plants. Instead, selenium enhances metal uptake and toxicity, especially in peas grown in the presence of metal and selenate. Selenite increased cadmium concentrations of pea roots up to 300% and selenate that of wheat shoots up to 50%.