bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of nitrate assimilation between the root and shoot of legumes and a comparison with wheat
Authors: Wallace W.
Published: April 2006

Legumes of the Phaseoleae (Glycine maxL. Merr.,Phaseolus coccineusL.,P. vulgarisL.,Vigna radiataL. Wilczek andV. unguiculataL. Walp.), when grown on 10 mMnitrate, had a low in vitro nitrate reductase (NR) activity in the root compared to the shoot (<15%). In legumes of the Vicieae (Cicer aerietinumL.,Pisum sativumL. andVicia fabaL.), Genisteae (Lupinus albusL.) and Trifolieae (Medicago sativaL. andM. truncatulaGaertn.), 30–60% of their total NR activity was in the root. The Phaseoleae had a higher nitrate content in the shoot. Decreasing the nitrate supply increased the relative proportion of NR activity in the root of garden pea (Pisum sativum) and wheat but did not alter the predominantly leaf‐based assimilation of nitrate inPhaseolus vulgaris.When in vitro NR activity of the pea shoot was compared with the in vivo NR activity and the rate of accumulation of reduced N by this tissue, similar values were obtained. In vitro NR activity of the wheat shoot was 5 times its in vivo NR activity and 12 times its rate of accumulation of reduced N.
Effect of light‐dark transition on glutamine synthetase activity in tomato leaves
Authors: Cánovas Francisco M. , Avila Concepción , Botella José R. , Valpuesta Victoriano , de Castro Ignacio Núñez
Published: April 2006

The activities of glutamine synthetase (EC 6.3.1.2) and glutamate dehydrogenase (EC 1.4.1.2) appear to be inversely related in their distribution among the different tissues of 40‐day‐old tomato plants (Lycopersicon esculentum L. cv. Hellfrucht Frühstamm), glutamine synthetase activity being highest in the leaves and glutamate dehydrogenase activity in the root. Leaf glutamine synthetase activity decreases with plant growth and shows diurnal variation with a maximum in the light and a minimum in the dark. In vitro, the activity of purified glutamine synthetase increases with the energy charge of the assay medium and decreases with increasing concentrations of p‐chloromercuribenzoic acid. Glutamine synthetase activity in the plant may be regulated by physiological changes occurring during the light‐dark transition periods.
Cold tolerance in tomato. II. Early seedling growth of Lycopersicon spp.
Authors: Scott S. Jeffrey , Jones R. A.
Published: April 2006

Hypocotyl and root growth elongation of etiolated seedlings was measured non‐destructively for the wild tomato accessions LA 460 (Lycopersicon chilense Dun.), PI 126435, PI 127831 and PI 127832 (L. peruvianum Mill.) and controls PI 120256 and T3 (L. esculentum Mill.) on slant boards at 10, 15 and 20°C. Both hypocotyl and root elongation over time were fitted by a logistic growth function with three parameters estimated for each seedling by non‐linear least squares regression. Analysis of variance of these equation parameters indicated linear decreases of both hypocotyl and root growth rate parameters with temperature. All four wild accessions maintained greater hypocotyl growth rate parameters at 10°C than the fast‐germinating cultivated accession PI 120256, but not significantly greater than T3. Hypocotyl growth rates of the wild accessions were less inhibited at 10°C relative to 20°C than were either cultivated accession. These results suggest that these wild accessions have greater chilling tolerance than cultivated controls for early seedling growth, and may have potential use for genetically improving emergence times for tomatoes sown in cold soil.
Genetic differentiation and phenotypic plasticity in Plantago major ssp. major. II. The effect of differences in level of irradiance on Mg2+‐ and Ca2+‐stimulated ATPase activity from roots and shoot
Authors: Kuiper Daan , Staal Marten
Published: April 2006

Ca2+‐ and Mg2+‐stimulated ATPase activity of the microsomal fraction of shoots and roots and the temperature dependence of the Ca2+‐stimulated ATPase activity of the shoot of plants of two genotypes of Plantago major ssp. major L., one originating from an exposed and the other from a shaded habitat, were followed at two levels of irradiance. In addition the responses of these parameters were studied after transfer of the plants from one light condition to the other. The capacity and the optimum temperature of shoot ATPase activity were affected by irradiance during growth, in contrast to the root ATPase activity. Generally, no plastic adaptive response of the measured characteristics was observed after transfer of the plants. The remaining plasticity or stability of plant characteristics could not be interpreted as adaptive; the adaptive plastic responses were confined to the seedling stage of individuals of both genotypes. Possible mechanisms involved in plastic and adaptive responses and including phytochrome are discussed.
The effect of spermidine and putrescine on the senescence of cut carnations
Authors: Downs Chris G. , Lovell Peter H.
Published: April 2006

Blooms of Dianthus caryophyllus cv. Crowley Pink (carnations) were held under standard environmental conditions in a range of vase solutions. In the absence of preservative solution the senescence of the flower was characterized by a single sharp peak of ethylene production. Culture in preservative solution greatly extended the life of the bloom and also reduced the output of ethylene. In addition, there was great variability between individual blooms in the timing, the extent and the pattern of ethylene production. Instead of a single peak some blooms had two or even three small peaks which, in some cases, were separated by intervals of several days. Senescence of these flowers was also characteristic of blooms that were not producing ethylene in that the petals often did not inroll. Putrescine and spermidine, when added to the culture solutions, did not delay the onset of senescence, nor did they inhibit ethylene production. In fact, both additives resulted in the earlier production of ethylene and shorter longevity when applied in conjunction with preservatives. Their effects were similar, but less marked when they were applied alone. Although polyamines have been reported to delay senescence in a number of tissues, spermine and putrescine did not have a protective effect in carnation flowers; indeed, in some treatments they advanced senescence.
Benzyladenine effects on the development of the photosynthetic apparatus in Zea mays: Studies on photosynthetic activity, enzymes and (etio)chloroplast ultrastructure
Authors: Caers Marleen , Vendrig J. C.
Published: April 2006

Primary leaf segments from 8‐day‐old dark‐grown, and from 4‐ and 8‐day‐old light‐grown seedlings of Zea mays L. cv. Fronica, were treated with 10‐bM benzyladenine (BA) in the dark for 14 h. The segments were then studied after an exposure to light for 14 h. Photosynthetic activity (O2 evolution and CO2 fixation) and chlorophyll accumulation were stimulated by BA in dark‐grown leaf segments with etioplastids in the earliest stage of development. In these segments BA stimulated the activities of ribulose‐1,5‐bisphosphate carboxylase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (EC 4.1.1.31), NADP+‐malic enzyme (EC 1.1.1.40) and pyruvate, orthophosphate dikinase (EC 2.7.9.1). In segments taken from 4‐ and 8‐day light‐grown seedlings, BA did not enhance the photosynthetic activity nor the chlorophyll accumulation. The activity of the enzymes mentioned above, was significantly enhanced by the BA‐treatment.

BA mainly affected grana stacking in mesophyll cell chloroplasts in primary leaf segments taken from 3‐ to 5‐day light‐grown seedlings. Stroma thylakoid development was stimulated only in leaf segments from 3‐day‐old plants. At the same time BA accelerated grana loss in chloroplasts of bundle sheath cells, a typical phenomenon of development in such chloroplasts. Stroma thylakoid length in these chloroplasts increased by a BA treatment in segments from 3‐ and 4‐day light‐grown plants. A significantly higher number of chloroplasts was only observed with segments taken from 8‐day light‐grown seedlings and treated with BA.

The etiochloroplast number in segments taken from 8‐day etiolated plants was significantly higher in BA‐treated segments after 26 h illumination. In etiochloroplasts from both mesophyll and bundle sheath cells, BA enhanced grana stacking after illumination for 4 h or more, whereas stroma membrane length was significantly higher only after 26 h light.

It is concluded that the effects of BA depend on the developmental stage. BA accelerates the development of mesophyll and bundle sheath cell (etio)chloroplasts, but does not affect the ultrastructure of mature chloroplasts.
The subcellular localisation of absorbed copper in Fucus
Authors: Smith Kim L. , Hann A. C. , Harwood John L.
Published: April 2006

The localisation of absorbed copper in the brown seaweeds Fucus vesiculosus L. and Fucus serratus L. was studied by X‐ray microanalysis in the electron microscope. The metal was localised in the physodes of the photosynthetic and inner non‐photosyn‐thetic cells. No significant copper was found in the cell walls of these algae, which had been collected from sites which were continually polluted by run‐off from old copper mines.
Rhizobium trifolii mutants deficient in exopolysaccharide production
Authors: Deryto Mieczyslawa , Skorupska Anna , Bednara Józef , Lorkiewicz Zbigniew
Published: April 2006

Spontaneous mutants of Rhizobium trifolii 24AR5 which did not produce exopoly‐saccharide were isolated. The non‐mucoid mutants formed small white and ineffective nodules on both red and white clover. These nodules contained infection threads, but only a small number of bacteria were released into nodule cells, and bacteroids were rarely observed. The non‐mucoid phenotype was not complemented by the symbiotic plasmid (pJB5JI) of Rhizobium leguminosarum.
Sodium ion transport in Neurospora crassa
Authors: Ortega María D. , Rodríguez‐Navarro Alonso
Published: April 2006

Na+ influx and efflux in Neurospora crassa RL21a can be studied separately to calculate net Na+ movements. In the absence of external K+, Na+ influx was independent of the K+ content of the cells, but when K+ was present, the inhibition of Na+ influx by external K+ was higher the higher the K+ content. Efflux depended on the K+ and Na+ content, and on the history of the cells. Efflux was higher the higher the Na+ and K+ contents, and, in low‐K+ cells, the efflux was also higher in cells grown in the presence of Na+ than when Na+ was given to cells grown in the absence of Na+. Addition of K+ to cells in steady state with external Na+ resulted in a net Na+‐loss. In cells grown without Na+ this loss was a consequence of the inhibition of Na+ influx. In Na+‐grown cells, addition of K+ inhibited Na+ influx and increased Na+ efflux.
The influences of calcium and magnesium ions on the exchange of monovalent cations in Neurospora crassa
Authors: Sancho Enrique D. , Rodríguez‐Navarro Alonso
Published: April 2006

Low‐K+, high‐Na+ cells of strain RL21a of Neurospora crassa, in steady state with 25 mM Na+, were used to study K+/Na+ exchanges in the presence or absence of Ca2+ and Mg2+. In the presence of Ca2+ and Mg2+, a low concentration of K+ (0.3 mM) triggered a rapid exchange, but in the absence of the divalents, a high K+ concentration (30 mM) was required to initiate the exchange at a rapid rate. In the absence of Ca2+ and Mg2+, K+ uptake did not occur at low K+ concentration, internal K+ did not regulate Na+ influx in the presence of external K+, and the efflux of Na+ proceeded at maximum activity at very low‐K+ contents.
The effect of the seed coat, embryonic axis and aeration conditions on starch degradation hi cotyledons of Lens culinaris
Authors: Revilla M. Angeles , Fernández‐Tárrago Jorge
Published: April 2006

The influence exerted by the seed coat, the embryonic axis and aeration conditions on starch degradation and a‐amylase activity (EC 3.2.1.1) in lentil (Lens culinaris Medik cv. Castellana) cotyledons was studied over twelve days of seedling growth. The presence of the seed coat influenced starch degradation and amylase activity negatively. The starch content in attached cotyledons decreased with time; however, in detached cotyledons starch degradation was very slow. These differences were in accordance with the variations in dry weight. The axis exerted a promotive effect on amylase development during the first days of growth if aeration conditions were restricted. Moreover, in the last days, similar levels in attached and detached cotyledons were reached. When the detached cotyledons were placed under improved aeration conditions, the amylase levels reached were greater than under any other conditions.

The low rates of starch degradation in detached cotyledons in spite of high amylase activity was not due to feed‐back inhibition of the enzyme system, but may have been due to osmotic stress.
Hypocotyl growth of Pinus pinaster seedlings. Changes in osmotic potential and cell wall composition
Authors: Lorences E. P. , Zarra I.
Published: April 2006

The changes in osmotic potential and cell wall composition of hypocotyl cell walls from different hypocotyl regions were investigated during growth of etiolated seedlings of Pinus pinaster Aiton. The osmotic potential in the subapical 5 mm part was minimum when hypocotyl growth rate was low, and increased when the fast growth phase began. The main non‐cellulosic sugars of the cell wall from pine hypocotyl were arabinose, galactose, xylose, glucose and uronic acids, although their relative proportions were different from those found for angiosperm cell walls. Non‐cellulosic glucose was the sugar showing the most important changes during hypocotyl growth as well as along the hypocotyl, suggesting that a glucose‐rich polysaccharide is involved in a very active turnover during growth. A partial degradation of a xyloglucan during growth is suggested.
Effect of phytochrome activation followed by prolonged dark incubation on chloroplast development in etiolated cucumber cotyledons
Authors: Cohen Lila , Arzee Tova
Published: April 2006

The inhibitory effect of a short red light pulse followed by prolonged dark incubation on chlorophyll accumulation in etiolated cucumber cotyledons (Cucumis sativus L. cv. Elem) was reflected in the development of the internal membrane system of the mesophyll plastids. Dark incubation for 24 h after phytochrome activation produced the characteristic accelerating effect OB chlorophyll synthesis and chloroplast development. However, longer intervening dark periods (48, 72 and 96 h) before white light exposure resulted not only in a diminished capacity to concentrate chlorophyll, but also in an impaired ability to form grana. The absence of stacking was consistent with a high chlorophyll a to chlorophyll b ratio.
Effects of stabilizing solutes on salt activation of phosphoenolpyruvate carboxylase from various plant sources
Authors: Shooter‐Ilan Adiva , Waisel Yoav
Published: April 2006

Phosphoenolpyruvate carboxylase (PEP carboxylase EC 4.1.1.31) was extracted from various halophytic, semi‐halophytic and glycophytic plant species. When the enzyme of those extracts was substrate protected, and in the presence of 1.6 mM PEP in the reaction mixture, the activity of PEP carboxylase was increased by 100 mM NaCl, and the activity range in the presence of NaCl was expanded. No correlation could be established between the response of the enzyme to ions and various plant characteristics, such as taxonomic status, salt tolerance or carbon fixation pathways. Salt activation of PEP carboxylase was substrate (PEP) dependent, but the minimal substrate concentration varied in different species.

Effects of the stabilizing solutes PEP, betaine, proline and glycerol on the kinetic properties of PEP carboxylase from Zea mays (L.) cv. Hazera were analyzed. In the absence of NaCl the slope of the Hill plot (nIt) tended to rise in the presence of these solutes. Stabilization of the enzyme with betaine or glycerol caused a decrease in K′. while K′ and VTO increased in the presence of PEP. NaCl (100 mM) caused an increase in both K′ and Vmax in the protected as well as in the unprotected enzyme, except for PEP protection, where K′ decreased somewhat. In the presence of the protectants, glycerol and PEP, the effect of NaCl on Vmax, was 2–4 times higher than its effect on the non‐protected enzyme.
Effect of rootstock on apple (Malus domestica) tree water relations
Authors: Olien W. C. , Lakso A. N.
Published: April 2006

The effects of rootstock on mid‐season water relations, under orchard conditions of non‐limiting soil moisture, were determined for bearing ‘Empire’ apple trees (Malus domestica Borkh.) on the clonal rootstocks M9, M26, M7, MM106, and MM104 (most to least dwarfing) in their sixth and seventh growing seasons. Stem water potentials (ψstem) of trees on M9 and M26 were more negative at midday, under warm, sunny conditions, than were the trees on the other three rootstocks. However, change in ψstem per change in stem distance through the canopy (water potential gradient) did not vary among rootstocks at midday. There was no rootstock effect on diurnal variation in transpiration or stomatal conductance. Differences in water storage capacitance, relative to tree size, were determined in a separate study but did not account for the differences observed in ψstem. Calculated hydraulic conductivities of xylem water transport suggest that rootstocks differ in their ability to conduct water to the scion, but hydraulic conductivity of the scion was not affected by rootstock. Root‐stock differences in hydraulic conductivity were not accounted for by differences in tree size.
Free amino acids and total nitrogen during shoot development in Scots pine seedlings
Authors: Gezelius Kerstin
Published: April 2006

The concentration of free amino acids and total nitrogen was studied in needles, stems and roots of seedlings of Pinus sylvestris L. for five weeks during the second growth period (“summer”). In one group of seedlings the source/sink relation was disturbed through removal of the terminal buds. The seedlings were cultivated in artificial year‐cycles in a climate chamber.

Total nitrogen increased in needles and sterns of intact seedlings in the beginning of the “summer” and decreased during shoot growth. In seedlings, from which the buds had been removed, nitrogen remained at high levels in the primary needles and accumulated in steins and roots. The results are consistent with utilization of nitrogen in older needles and in the stem during shoot elongation.

The pool of free amino acids increased in the beginning of the “summer” and decreased after bud break in primary needles, stems and roots. Arginine and glutamine, in the roots also asparagine, were the dominating amino acids (amides included). Together, these compounds (plus glutamate and aspartate) contributed about 90% of the nitrogen in the amino acid pool in all organs. In primary needles and in the stem, arginine predominated at the end of hardening (75–85% of the amino acid nitrogen). Free amino acids contributed at most ca 10% of the total nitrogen in primary needles, where the ratio of free amino acid nitrogen: total nitrogen was highest at the end of dormancy and in the early “summer”. Free amino acids accumulated after bud removal in primary needles and especially in stems and roots. Glutamine became relatively more dominant than arginine in the different organs.

The observations are consistent with the role of arginine and glutamine for storage and transport of nitrogen in conifers. Because of the low concentrations of amino acid nitrogen in the primary needles, arginine is not considered a major nitrogen reserve in needles of Scots pine seedlings.
Mitochondria from Zea mays leaf tissues: Differentiation of carbon assimilation and photorespiratory activity between mesophyll and bundle sheath cells
Authors: Petit Patrice , Cantrel Catherine
Published: April 2006

A procedure was developed to obtain intact and purified mitochondria from mesophyll and bundle sheath tissues of Zea mays L. cv. I.N.R.A. 180, an NADP+‐malic enzyme type C4 plant. There was little cross‐contamination between the two mitochondrial fractions.

Both types of mitochondria oxidized NADH, succinate and malate with respiratory control. In mesophyll mitochondria malate oxidation was highly sensitive to KCN (85–90% inhibition of first state 3) and showed good respiratory control. In bundle sheath mitochondria malate oxidation was less sensitive to cyanide (75‐80% inhibition) and showed poor respiratory control. Malate and NADH appeared to be the best substrates for respiratory activity. Mesophyil mitochondria could not oxidize glycine, whereas bundle sheath mitochondria could.

The results indicate that mesophyll and bundle sheath mitochondria of Zea mays are differentiated, not only with respect to the decarboxylation of malate but also with respect to the decarboxylation phase of photorespiration.
Short‐term effects of two aphid species on plant growth and root respiration of three leguminous species
Authors: Hawkins C. D. B. , Aston M. J. , Whitecross M. I.
Published: April 2006

The short‐term effects of cowpea aphids (Aphis craccivora Koch) and pea aphids (Acyrthosiphon pisum Harris), both Homoptera: Aphididae, on plant growth and respiration of excised, intact roots of cowpea [Vigna unguiculata (L.) Walp. cv. Caloona], broadbean (Vicia faba L. cv. Aquadulce) and garden pea (Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant‐aphid combinations were used. Plant and root mean relative growth rates were significantly reduced within 10 days in the infested plants. Rates of total root respiration were was also significantly reduced in all infested plants within 10 days, presumably because of the reduced availability of translocate to the roots. The contribution of the cytochrome pathway to root respiration was significantly greater in control than in infested plants. The activity and engagement of the alternative respiratory pathway was also greater in control plants, and was absent in infested plants after 10 days infestation in all cases but one. These data indicate that the roots of aphid‐infested plants were more efficient, in terms of energy conversion, than their respective controls.
Effects of the barley mutants Risø 1508 and 527 high lysine genes on the cellular development of the endosperm
Authors: Klemsdal S. S. , Kvaale A. , Olsen O.‐A.
Published: April 2006

The dry grain weight of the Risø barley (Hordeum vulgare L. var. disticum) high lysine mutants 1508 and 527 at maturity was 32 and 37% lower, respectively, than the grains of the cultivar Bomi. Dry grain weight of the double mutant 527/1508 was reduced by 57%. Total number of endosperm nuclei from cv. Bomi, mutants 1508, 527 and 527/1508 at 24 days after anthesis was 173 000,156 000,121 000 and 111 000, respectively. Transverse mid‐grain sections from mutants 1508 and 527 contained fewer aleurone cells and approximately the same number of starchy endosperm cells as cv. Bomi. The cellular organization of the endosperm of the double mutant deviated substantially from the normal. Cell volume in the central starchy endosperm of cv. Bomi, mutants 1508 and 527 at 33 days after anthesis averaged 390 000, 270 000 and 180 000 um5, respectively. Cell volume in the double mutant was smaller than in 527, but could not be accurately estimated due to the irregular shape of the cells. The mean section area of individual large starch granules in the central endosperm of mutants 1508, 527 and 527/1508 at 33 days after anthesis was 30, 48 and 72% smaller, respectively, than those of cv. Bomi. The average aleurone cell volume in cv. Bomi at 33 days after anthesis was 6 200 μm3.
Which cells respond to gravitropic stimulus in the lentil root?
Authors: Darbelley Nicole , Perbal Patrick , Perbal Gérald
Published: April 2006

When roots of lentil (Lens culinaris L., cv. Large blonde) were placed in horizontal position for 2 h, their upper side elongated faster than their lower side, and also faster than vertical controls. The length of the cortical cells was greater in the upper half than in the lower half of roots which had been horizontally stimulated for 2 h. The zone of curvature extended from the distal part of the meristem to the proximal part of the cell elongation zone. The curvature in the meristem was due to early differentiation of the cells of its upper part. In the proximal part of the cell elongation zone, bending took place due to inhibition of cell growth in the lower half of the root. The results obtained are in agreement with the hypothesis of lateral transport of an inhibitor in gravistimulated roots. This inhibitor should be present in greater amounts in the lower side of the stimulated root and in lower amounts in its upper side than in the vertical controls.
Effect of light on photosynthetic capacity during cold acclimation in a cold‐sensitive and a cold‐tolerant potato species
Authors: Steffan Kenneth L. , Palta Jiwan P.
Published: April 2006

The effect of low temperature acclimation at various light levels on the photosynthetic capacity of Solanum species was examined. Two species, Solanum tuberosum L. cv. Red Pontiac and Solanum acaule Bitt., which differ significantly in degree of frost‐tolerance and in their ability to acclimate to low temperature stress, were compared. Acclimation conditions included 5/2°C (day/night) temperatures, and either moderate (400 · mol · m−2· s−1) or low (40 · mol · m−2· s−1) photosynthetic photon flux densities. Several parameters of photosynthesis were measured in tissue pieces during acclimation treatments including chlorophyll content, chlorophyll a/b ratios and carbon dioxide‐saturated photosynthetic oxygen evolution during light‐limited and light‐saturated assays.

Most measured photosynthetic parameters of low temperature‐grown plants of both species showed greater declines under the moderate light than the low light conditions. Chlorophyll a/b ratios were unchanged after low temperature exposures in both light level treatments. At low temperatures, the cold‐sensitive S. tuberosum demonstrated a greater inhibition of photosynthetic capacity in light‐ and carbon dioxide‐saturated assays than S. acaule at all light levels. In addition to a pronounced inhibition at the higher light level, S. tuberosum demonstrated a very strong inhibition of photosynthetic capacity at very low light levels. Our results suggest a correlation between ability to maintain essential metabolic processes during low temperature stress in the presence of moderate light levels and the ability to increase cold tolerance.
Proteolysis of ribulose‐1,5‐bisphosphate carboxylase/oxygenase in Citrus leaf extracts
Authors: García‐Martínez José L. , Moreno Joaquín
Published: April 2006

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) has been purified from orange [Citrus sinensis (L.) Osbeck cv. Washington Navel] leaves using sucrose gradient centrifugation in a fixed angle rotor. Following sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), two major bands corresponding to the two subunits of RuBP carboxylase were found. The large subunit coincided with the polypeptide band that has been previously reported to be preferentially mobilized during the spring and summer flush periods.

The degradation of RuBP carboxylase during autodigestion of Citrus leaf extracts, investigated by SDS‐PAGE, occurred mainly at acidic (2.5‐5.5) pH. The two subunits showed differences in the rate of degradation, the smaller being more rapidly hydrolyzed than the larger. At least four proteolytic activities were identified by means of inhibitor experiments: 1) a pepstatin A‐sensitive activity that acts on both RuBP carboxylase subunits, 2) a mercurial (p‐hydroxymercuribenzoate and p‐chloromercuriphenylsulfonate)‐sensitive activity that degrades only the small subunit, 3) an EDTA‐sensitive activity that hydrolyzes both the large and small subunits, and 4) a mercurial‐stimulated activity that acts only on the large subunit. It is suggested that the last two proteases may be responsible for the degradation of RuBP carboxylase observed in vivo during the periods of mobilization of leaf protein in Citrus.
Lack of correlation between effects of tentoxin on chloroplast coupling factor and chloroplast ultrastructure
Authors: Lax Alan R. , Vaughn Kevin C.
Published: April 2006

The mediation of tentoxin‐induced chlorosis through inhibition of chloroplast coupling factor 1 (CF1) ATPase activity was investigated through an examination of the effects of tentoxin on electrophoretically‐separated CF1 ATPases from sensitive and insensitive Nicotiana species. Sensitive species exhibited three major ATPases, only one of which was inhibited at some concentrations of tentoxin. Insensitive Nicotiana species showed the same three “isozymes”upon electrophoresis but none of the isozymes were tentoxin sensitive. CF1 isolated from Zea mays L. cv. Pioneer 3541, which is insensitive to tentoxin in vivo based on lack of chlorosis, exhibited two ATPases, one of which was sensitive to tentoxin. The concentration/activity relationships between tentoxin and ATPase inhibition of the sensitive isozyme did not correlate well with the chlorosis induced at similar levels of tentoxin in vivo. Both Oenothera hookeri Torr. & Gray and the CF1‐deficient I iota mutant derived from it are sensitive to tentoxin as determined by loss of chlorophyll and ultrastructural changes typical of the tentoxin syndrome. These results support a mechanism of action different from inhibition of CF1 for tentoxin‐induced chlorosis.
Morphological differentiation and occurrence of thiophenes in leaf callus cultures from Tagetes species: Relation to the growth medium of the plants
Authors: Ketel David H.
Published: April 2006

The morphology, and the number and concentration of thiophene‐like compounds were studied in leaves, roots and calli of Tagetes species grown with different nutrient solutions. The type of nutrient solution exerted no effect on the number of thiophene‐like compounds, but altered the type of morphological differentiation and thiophene content of calli. Calli of T. minuta L. showed little differentiation and resulted in suspensible callus after two passages. Calli of T. erecta L. cv. Rose d'Inde differentiated rapidly and turned dark brown after one passage. The morphology of calli from T. patula L. cv. Nana furia was intermediate. Tertiary callus of T. patula contained more thiophene‐like compounds and higher concentrations than did the corresponding calli of T. minuta. The content of thiophene‐like compounds decreased after various callus passages, but the relative decrease varied between species.
Abscisic acid and cessation of apical growth in Salix pentandra
Authors: Johansen Liv G. , Odén Per‐Christer , Junttila Olavi
Published: April 2006

Effects of exogenous abscisic acid (ABA) on growth and transpiration in seedlings of two ecotypes of Salix pentandra L. were studied in phytotron experiments. Application of ABA resulted in increased stomatal resistance, reduced transpiration and reduced growth rate. ABA did not induce cessation of apical growth in seedlings grown under a 24‐h photoperiod. The content of endogenous ABA in seedlings grown under 24‐h (LD) or 12‐h (SD) photoperiods was analysed from purified methanol extracts using gas chromatography and electron capture detection. No significant differences were found in the ABA contents of LD‐ and SD‐grown plants. SD‐induced cessation of apical growth was not associated with increased stomatal resistance or reduced transpiration rate.
Increase in glutamate synthase (NADH) activity in maize seedlings in response to nitrate and ammonium nitrogen
Authors: Singh Rana P. , Srivastava H. S.
Published: April 2006

Roots and leaves of Zea mays L. cv. Ganga Safed‐2 seedlings grown with nutrient solution containing either 10 mM KNO3 or NH4Cl or 5 mM NH4NO3 had considerably higher glutamate synthase (NADH, EC 1.4.1.14) activity than the corresponding organs from seedlings grown without any nitrogen. The supply of inorganic nitrogen for a short time, i.e. 3 h, to roots and leaves excised from seedlings grown without nitrogen also increased the enzyme activity in these organs. This increase was more pronounced with nitrate than with ammonium nitrogen. When excised roots and leaves from NH4NO3‐grown seedlings were incubated in a minus nitrogen medium for 24 h, the enzyme activity declined considerably. This decline was inhibited to some extent by nitrogen, especially by nitrate. Inorganic nitrogen prevented similarly the decline in in vitro enzyme activity during 24 h storage at 25°C, more regularly for the root than for the leaf enzyme. The experiments demonstrate the role of inorganic nitrogen in the regulation of glutamate synthase activity.
Internode length in Pisum. Two further mutants, lh and ls, with reduced gibberellin synthesis, and a gibberellin insensitive mutant, lk
Authors: Reid James B. , Potts Wendy C.
Published: April 2006

Three further internode length mutants in peas (Pisum sativum L.), lh, ls and lk, were examined to determine if they influenced gibberellin synthesis or sensitivity. Two mutants, lh and ls, showed pronounced elongation in response to applied GA1 and extracts from their shoots contained little gibberellin‐like activity when assayed on the rice seedling (cv. Tan ginbozu) bioassay compared with similar extracts from essentially isogenic Lh and Ls plants. The third mutant, lk, was almost insensitive to applied GA1 and at no dose rate did it become a phenocopy of normal Lk plants. Extracts from the shoots of lk and Lk segregants contained similar levels of gibberellinlike substances. All three mutants influenced growth in both the light and the dark, although only the effect of genes Lh and Ls were graft transmissible. These results suggest that lh and ls are mutants with reduced gibberellin synthesis, while lk is the first gibberellin‐insensitive dwarfing gene identified in peas.
Metabolism of benzyladenine by excised embryos of Picea abies
Authors: Van Staden J. , Forsyth C. , Bergman L. , von Arnold S.
Published: April 2006

Isolated embryos of Picea abies (L.) Karst. were pulsed with either distilled water, cold benzyladenine (BA) or [8‐14C]‐BA for 3 h under sterile conditions, whereafter they were transferred to cytokinin‐free media for a further 24 h. Embryos of each treatment were then analysed for cytokinin activity. The embryos themselves yielded very little cytokinin activity. Analysis of the [14C]‐BA‐treated material revealed that some residual BA was present even after 27 h of treatment but that the total radioactivity recovered from the embryos at this time was less than 10% of that recovered after the 3 h treatment. Apart from BA, the embryos contained other radioactive peaks, the major ones apparently being of a nucleotide nature. The BA‐containing medium in which the embryos were incubated initially was also analysed and again, apart from residual BA, the major metabolite(s) appeared to be BA‐nucleotide. However, two radioactive peaks were found in the medium which were absent from the embryos themselves and chemical tests indicated that these could be 7‐ and 9‐glucosides of BA. As the major metabolite resulting from the BA‐pulse was of a nucleotide nature and was found to be biologically active, it is postulated that the action of the BA may be mediated via the nucleotide.
Mass selection for salt resistance in Rhodes grass (Chloris gayana)
Authors: Malkin E. , Waisel Y.
Published: April 2006

High salt stresses were exerted upon seedlings of the common variety of Rhodes grass (Chloris gayana Kunth.) in order to select a salt resistant strain and to ascertain the characteristics which differentiate between the original parent population and the currently selected one. Five generations of seedlings were grown on sand culture and irrigated with NaCl solutions up to 0.7 M. The most successful survivors of each generation were selected and grown to maturation and seed production. Plants of the F5‐selected population showed a marked improvement in their survival and regeneration capabilities after harvesting. Some effects of selection were found in seed germination and in water use. No apparent differences between the parent and the F5 populations were found in growth of unclipped plants, ion content or protein synthesis. The data presented indicate that the capability to survive through salt stresses can be raised in Rhodes grass by mass selection. Fundamentally this is achieved by improving the regeneration capability of the plants after multiple clippings.
Induction of flowering in the duckweed Lemna paucicostata under non‐inductive photoperiods by tannic acid
Authors: Khurana J. P. , Maheshwari S. C.
Published: April 2006

Flowering in Lemna paucicostata 6746 could be induced by tannic acid under strictly non‐inductive photoperiods. This polyphenol completely abolished the photoperiodic sensitivity of strain 6746 as flowering could also be obtained under continuous light (nearly 80% flowering was recorded in the plants supplied with 10−5 tannic acid). Though its mode of action is unknown, tannic acid is unlikely to act as a gibberellin‐antagonist in its effect on flowering in strain 6746.
Cytoplasmic and mitochondrial localization of the glutamate dehydrogenase induced by senescence in barley (Hordeum vulgare)
Authors: Calle Florentina , Martín Mercedes , Sabater Bartolomé
Published: April 2006

The subcellular localization of NAD+‐dependent glutamate dehydrogenase (GDH; EC 1.4.1.4) in leaves of barley (Hordeum vulgare L. cv. Hassan) was studied during leaf senescence induced by detachment and incubation in the dark. GDH strongly increased in the cytoplasmic fraction isolated by differential centrifugation during senescence. It also showed a retarded and low increase in the mitochondrial fraction. No GDH was detected in the chloroplast fraction. The marker of the cytoplasmic fraction glucose‐6‐phosphate dehydrogenase (G‐6‐P dehydrogenase; EC 1.1.1.49) rapidly decreased after the induction of senescence. The effects of kinetin, gibberellic acid, abscisic acid and ethylene on the levels of GDH and G‐6‐P dehydrogenase were, in general, in agreement with the known hormonal effects on other senescence symptoms.
Products of photosynthetic 14CO2 fixation and related enzyme activities in fruiting structures of chickpea
Authors: Singal H. R. , Sheoran I. S. , Singh Randhir
Published: April 2006

Fruiting structures of a number of legumes including chickpea are known to carry out photosynthetic CO2 assimilation, but the pathway of CO2 fixation and particularly the role of phosphoenolpyruvate carboxylase (EC 4.1.1.31) in these tissues is not clear. Activities of some key enzymes of the Calvin cycle and C4 metabolism, rates of 14CO2 fixation in light and dark, and initial products of photosynthetic 14CO2 fixation were determined in podwall and seedcoat (fruiting structures) and their subtending leaf in chickpea (Cicer arietinum L.). Compared to activities of ribulose‐1,5‐bisphosphate carboxylase (EC 4.1.1.39) and other Calvin cycle enzyme, viz. NADP+‐glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.13), NAD+‐glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.12) and ribulose‐5‐phosphate kinase (EC 2.7.1.19), the levels of phosphoenolpyruvate carboxylase and other enzymes of C4 metabolism viz. NADP+‐malate dehydrogenase (EC 1.1.1.82), NAD+‐malate dehydrogenase (EC 1.1.1.37), NADP+ malic enzyme (EC 1.1.1.40), NAD+‐malic enzyme (EC 1.1.1.39), glutamate oxaloacetate transaminase (EC 2.6.1.1) and glutamate pyruvate transaminase (EC 2.6.1.2), were generally much higher in podwall and seedcoat than in the leaf. Podwall and seedcoat fixed 14CO2 in light and dark at much higher rates than the leaf. Short‐term assimilation of 14CO2 by illuminated fruiting structures produced malate as the major labelled product with less labelling in 3‐phosphoglycerate, whereas the leaf showed a major incorporation into 3‐phosphoglycerate. It seems likely that the fruiting structures of chickpea utilize phosphoenolpyruvate carboxylase for recapturing the respired carbon dioxide.
Volume changes of Commelina communis guard cell protoplasts in response to K+, light and CO2
Authors: Fitzsimons Peter J. , Weyers Jonathan D. B.
Published: April 2006

The effects of K+ concentration, light intensity and CO2 levels on the volume of Commelina communis L. guard cell protoplasts were studied. Two degrees of swelling response were observed, both dependent on an external supply of K+, but not necessarily on the supply of a permeant anion. The presence of K+ itself, independent of light or CO2 level, stimulated swelling at a relatively slow rate. When K+, light and low CO2 conditions were supplied together, the swelling was relatively rapid and of high magnitude. The rapid swelling was specific for K+ and Rb+ giving a half maximal effect after 2 h at a KCl concentration of about 18 mmol m−3. The addition of CaCl2 at 1 mol m−3 inhibited K+‐dependent swelling under all conditions tested. The response to light and low CO2 levels by Commelina guard cell protoplasts is thought to reflect a high degree of physiological integrity.
Potassium ion uptake by swelling Commelina communis guard cell protoplasts
Authors: Fitzsimons Peter J. , Weyers Jonathan D. B.
Published: April 2006

Commelina communis L. guard cell protoplasts were induced to swell under low CO2 conditions in the light while incubated in media containing KCl. Precise measurements of changes in the volume of the protoplasts were made including estimates of protoplast non‐osmotic volume by Boyle‐van't Hoff analysis. The amount of K+ which accumulated during the treatment was measured. The observed changes in osmotic volume could be accounted for by the uptake of K+ which appeared to be balanced by an anion or anions with an effective mean charge of – 1.63. The K+ flux rates occurring in guard cell protoplasts were sufficient to explain guard cell turgor regulation in vivo.
Rhizobium induces marked root hair curling by redirection of tip growth: a computer simulation
Authors: van Batenburg F. H. D. , Jonker R. , Kijne J. W.
Published: April 2006

Computer simulation shows that Rhizobium can induce marked curling in legume root hairs by growth induction. Essential elements are: a) the attachment of one inducing principle (e.g. one bacterium or a group of bacteria), preferably within the growth area of the root hair; b) translocation of the inductor along the growing root hari tip; and c) redirection of the original plant‐driven tip growth. Also other root hair deformations, for example root hair branching and infection thread growth, can be explained with the proposed model.
A comparison of inhibition of French‐bean and soybean nitrogen fixation by nitrate, 1% oxygen or direct assimilate deprivation
Authors: Wasfi Mirghani , Prioul Jean‐Louis
Published: April 2006

Inhibition by NO−3 of acetylene reduction in bean (Phaseolus vulgaris L. cv. Contender) and soybean (Glycine max L. cv. Amsoy 71) was measured in parallel with nodule carbohydrate and nitrate metabolism. In bean the onset of inhibition of C2H2 reduction (6 h) coincided with decreased import of assimilates and a lowering of carbohydrate pools (sucrose, glucose and starch). Nitrate reductase (EC 1.6.6.1) activity was induced in all plant organs after 3 h but no nitrite was detected in the nodules. In soybean, nodule carbohydrate concentrations and import of assimilates into the nodules increased markedly between 6 to 24 h after supply of nitrate when the nitrogenase (EC 1.7.99.2) was progressively inhibited. High nitrate reductase activity was observed in the nodules and nitrites accumulated because of insufficient nitrite reductase activity. The nitrate‐induced inhibition of nitrogenase was compared with the inhibition observed with low oxygen around the roots (1% O2) or with direct assimilate deprivation (girdling or decapitation). Soybean and bean appeared equally sensitive to these treatments as regards to acetylene reduction. The results are discussed in relation to the current hypotheses explaining nitrate‐induced inhibition of dinitrogen fixation: assimilate deprivation or nitrite poisoning. Present data are in favour of the first for bean and of the second for soybean.
Effects of carbanilates on the growth and development of cell suspension cultures of Acer pseudoplatanus
Authors: Macherel David , Nurit Françoise , Lescure Anne‐Marie , Tissut Michel
Published: April 2006

The effects of three isopropyl carbanilate derivatives (propham, chlorpropham, 3,4‐diCl isopropyl carbanilate) were studied on Acer pseudoplatanus L. cell suspension cultures (Lamport's strain). At 0.1 mM, three types of effects were observed: the 3,4‐diCl derivative rapidly killed the cells; chlorpropham inhibited mitosis, but the cells remained alive without any significant increase in fresh or dry matter; and propham strongly inhibited mitosis, but not cell growth.

Ultrastructural analysis indicated that no observable changes in mitochondrial or plastid density occurred during the cytoplasmic expansion in the presence of propham. Size increase was also accompanied by vacuolar expansion and morphological changes of the nuclei. In Acer cell cultures, isopropyl carbanilates clearly show selective inhibition of mitosis only when the phenyl ring is not substituted by chlorine.
Effect of one night with “low light’on uptake, reduction and storage of nitrate in spinach
Authors: Steingröver Eveliene , Siesling Johan , Ratering Pieter
Published: April 2006

During the night, shoot nitrate concentration in spinach (Spinacia oleraceaL. cv. Vroeg Reuzenblad) increased due to increased uptake of nitrate by the roots. When the plants were subjected to a one night “low light’period at 35 μmol m−2s−1, the shoot nitrate concentration did not increase and was reduced by 25% compared to control plants in the dark. The major contribution to this decrease was located in the leaf blades, where the nitrate concentration was decreased by 60%, while the petiole nitrate concentration decreased by only 9%. Nitrate accumulated in the leaf blade vacuoles during a dark night, but this was not the case during the “low light’period. This decrease in vacuolar nitrate concentration, compared to control plants in the dark, was not caused by increased amounts of leaf blade nitrate reductase (NR; EC 1.6.6.1). During a “low light’night period, the cytoplasmic soluble carbohydrate concentration was increased compared to the control plants in the dark. Calculations showed in situ NR activity to be higher than in the control plants in the dark. This increase in NR activity, however, was not large enough to account for the total difference found in the shoot nitrate concentration. Net uptake of nitrate by the roots was increased during the initial hours of the dark night, while vacuolar nitrate concentration in the leaf blades increased at the same time. During the “low light’night period, however, net uptake of nitrate by the roots did not increase, and vacuolar nitrate concentration did not change. We conclude that nitrate uptake by the roots and vacuolar nitrate concentration in the leaf blades are tightly coupled. The decreased shoot nitrate concentration is mainly caused by a reduction in net uptake of nitrate by the roots. During the “low light’night period, carbohydrates and malic acid partly replaced vacuolar nitrate. A “low light’period one night prior to harvest provides a valuable tool to reduce shoot nitrate concentrations in spinach grown in greenhouses in the winter months.