bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and characteristics of myrosinase in Brassica napus during early seedling growth
Authors: James David C. , Rossiter John T.
Published: May 2006

Myrosinase (β‐thioglucoside glucohydroase, E. C. 3.2.3.1) proteins with different physical, but similar kinetic characteristics exist in oilseed rape (Brassica napus L. cv. Bienvenu) seedlings. Two protein fractions have been described which are immunologically, and therefore likely to be structurally, related. Myrosinase I, a dimeric 156 kDa glycosylated protein was purified to apparent homogeneity, and polyclonal antibodies were raised against this protein. Myrosinase II, in comparison, was significantly less glycosylated. The native protein had a molecular weight of approximately 188 kDa, with subunit Mr's of mainly 62 kDa and also 68 kDa. Total ‘potential’enzyme activity (assayed in the presence of ascorbic acid activator) increased during early seedling growth. Immunoblot analysis of seedling proteins showed that this is directly related to an increase in the amount of myrosinase protein itself, predominantly myrosinase II proteins, which are not present in the dry seed. Myrosinase II protein is located exclusively in the cotyledons of 5‐day‐old seedlings, whilst myrosinase I is distributed throughout the seedling.
Na+/H+ antiport activity in tonoplast vesicles from roots of the salt‐tolerant Plantago maritima and the salt‐sensitive Plantago media
Authors: Staal Marten , Maathuis Frans J. M. , Elzenga J. Theo M. , Overbeek J. Hans M. , Prins Hidde B. A.
Published: May 2006

Plantago species differ in their strategy towards salt stress, a major difference being the uptake and distribution of Na+ ions. A salt‐sensitive (Plantago media L.) and a salt‐tolerant (P. maritima L.) species were compared with respect to Na+/H+ antiport activities at the tonoplast. After exposure of the plants to 50 mM NaCl for 6 days isolated tonoplast vesicles of P. maritima showed Na+/H+ antiport activity with saturation kinetics and a Km of 2.4 mM Na+, NaCl‐grown P. media and the control plants of both species showed no antiport activity. Selectivity of the antiport system for Na+ was high and was determined by adding different chloride salts after formation of a Δ pH in the vesicles. Specific tonoplast ATPase activities were similar in the two species and did not alter after exposure to NaCl stress.
Polyamine concentrations and arginine decarboxylase activity in wheat exposed to osmotic stress
Authors: Foster Sally A. , Walters Dale R.
Published: May 2006

The activity of L‐arginine decarboxylase (ADC: EC 4.1.1.19)and polyamine content were examine in intact wheat plants (Triticum aestivum L. cv. Sappo) exposed to osmotic stress (0.4 M mannitol) for 5 days. ADC activity was increased in first and second leaves and in roots of mannitol‐stressed plants. Concentrations of putrescine, cadaverine and spermine were generally increased in leaves and roots of plants exposed to mannitol, whereas spermidine was reduced in first leaves and roots of these plants. In an attempt to determine the localization of mannitol in stressed wheat. 14C‐mannitol was fed to plants grown in liquid culture. Most of the mannitol was detected in roots (84%), while small amounts were found in first (9%) and second (7%) leves.

Since it seemed possible that some of the effects on polyamine metabolism caused by exposure to mannitol could have been the result of water stress. polyamine metabolism was also studied in plants water stressed by exposure to 2% polyethylene glycol (PEG) 4000. ADC activity was not altered by exposure to PEG. but concentrations of putrescine, spermidine and spermine were generally reduced in leaves and roots of stressed plants. Cadaverine concentrations were not significantly affected by exposure to PEG. Spermidine and spermine concentrations were reduced in first and second leaves but remained unchanged in roots of plants exposed to PEG.
Ethylene effects on cambial activity and cell wall formation in hypocotyls of Picea abies seedlings
Authors: Ingemarsson Barbro S. M. , Eklund Leif , Eliasson Lennart
Published: May 2006

Ethylene regulation of cell division in the vascular cambium and cell wall formation was studied in hypocotyls of Norway spruce (Picea abies [L.] Karst.) seedlings. Cuttings from 6‐week‐old seedlings were placed in water culture to which compounds affecting the synthesis and action of ethylene were added. After a 3‐week treatment period, growth, ethylene production, morphology and cell wall composition of the hypocotyls were determined. Addition of high concentrations of the potent ethylene releasing agent 2‐chloroethylphosphonic acid (ethrel), which increased ethylene emission by more than twice compared to control plants, inhibited the expansion of xylem cells while stimulating the incorporation of cell wall material, especially cellulose. Addition of small amounts of ethrel, which slightly stimulated ethylene emission, led to increases in the size of xylem cells, the amount of phloem tissue and the number of intercellular spaces in the cortex, and thus to increased hypocotyl diameter. However, no significant change in cell wall composition was detected. When ethylene production was decreased by adding Co2+ to the nutrient solution, differentiation of new xylem was disturbed, but the rate of cell division was not affected. Although the incorporation of cell wall material was inhibited, the proportions of lignin and cellulose in the wall appeared to remain unchanged. Silver ions stimulated the expansion of both xylem and cortex cells, but had no significant effect on cell wall formation. We conclude that ethylene has a role in regulating the incorporation of wall carbohydrates.
In vitro‐selection of hydroxyproline‐resistant cell lines of wheat (Triticum aestivum): accumulation of proline, decrease in osmotic potential, and increase in frost tolerance
Authors: Tantau Hanny , Dörffling Karl
Published: May 2006

Five hundred hydroxyproline‐resistant cell lines were selected from cell cultures of wheat (Triticum aestivum L. cv. Koga II) after plating on 10 to 30 mM hydroxyproline (Hyp) containing solid Gamborg B 5 medium. All selected cell lines from 30 mM Hyp‐medium contained increased (up to 17‐fold) levels of free proline. Seventy‐four cell lines were transferred to Hyp‐free medium and subcultivated 25 times, for 12 months altogether, after which 80% still had increased proline levels. Fourteen cell lines with increased proline levels were further investigated in liquid media with regard to their frost tolerance, which was measured by means of electrolyte leakage. Ten of them showed increased fros tolerance, with LT 50 values as low as 2.7°C below that of the wild type (‐4.7°C). Besides increased proline levels and increased percentage dry weight, the Hyp‐resistant cell lines had lower osmotic potentials. Osmotic potentials correlated better than levels of free proline with the increase in frost tolerance.
Inorganic nitrogen regulation of glutamate uptake in the cyanobacterium Nostoc muscorum
Authors: Prakasham R. , Singh A. K. , Singh H. N. , Rai A. N.
Published: May 2006

In Nostoc muscorum (Anabaena ATCC 27893) glutamate was not metabolised as a fixed nitrogen source, rather it functioned as an inhibitor of growth. The latter effect was nitrogen source specific and occurred in N2‐fixing cultures but not in cultures assimilating nitrate or ammonium. NO3‐‐grown cultures lacked heterocysts and nitrogenase activity and showed a nearly 50% reduction in glutamate uptake rates, as well as in the final extent of glutamate taken up, compared to N2‐fixing or nitrogen‐limited control cultures. NH4+‐grown cultures showed a similar response, except that the reduction in glutamate uptake rates and the final exten of glutamate taken up was over 80%. The present results suggest a relation between nitrate/ammounium nitrogen‐dependent inhibition of glutamate uptake, probably via repression of the glutamate transport system, and glutamate toxicity.
Subcellular distribution of superoxide dismutase in leaves of ureide‐producing leguminous plants
Authors: Corpas Francisco J. , Sandalio Luisa M. , Palma José M. , Leidi Eduardo O. , Hernández José A. , Sevilla Francisca , Del Río Luis A.
Published: May 2006

The subcellular localization of superoxide dismutase (SOD; EC. 1.15.1.1) was studied in leaves of two ureide‐producing leguminous plants (Phaseolus vulgaris L. cv. Contender and Vigna unguiculata [L.] Walp). In leaves of Vigna and Phaseolus, three superoxide dismutases were found, an Mn‐SOD and two Cu, Zn‐containing SODs (I and II). Chloroplasts, mitochondria, and peroxisomes were purified by differential and density‐gradient centrifugation using either Percoll or sucrose gradients. The yields obtained in intact chloroplasts and peroxisomes from Vigna were considerably higher than those achieved for Phaseolus. Purified chloroplasts only contained the Cu, Zn‐SOD II isozyme, but in mitochondria both Mn‐SOD and Cu, Zn‐SOD I isozymes were present. In purified peroxisomes no SOD activity was detected. The absence of SOD activity in leaf peroxisomes from Vigna contrasts with results reported for the amide‐metabolizing legume Pisum sativum L. where the occurrence of Mn‐SOD was demonstrated in leaf peroxisomes (del Río et al. 1983. Planta 158: 216–224; Sandalio et al. 1987. Plant Sci. 51: 1–8). This suggests that in leaf peroxisomes from Vigna plants the generation of O2‐ radicals under normal conditions probably does not take place.
Carbohydrate metabolism during fruit development in sweet pepper (Capsicum annuum) plants
Authors: Nielsen Tom H. , Skjærbæ Helle C. , Karlsen Poul
Published: May 2006

Growth, accumulation of sugars and starch, and the activity of enzymes involved in sucrose mobilization were determined throughout the development of sweet pepper fruits. Fruit development was roughly divided into three phases: (1) an initial phase with high relative growth rate and hexose accumulation, (2) a phase with declining growth rate and accumulation of sucrose and starch, and (3) a ripening phase with no further fresh weight increase and with accumulation of hexoses, while sucrose and starch were degraded. Acid and neutral invertase (EC 3.2.1.26) were closely correlated to relative growth rate until ripening and inversly correlated to the accumulation of sucrose. Acid invertase specifically increased during ripening, concurrently with the accumulation of hexoses. Sucrose synthase (EC 2.4.1.13) showed little correlation to fruit development, and in periods of rapid growth the activity of sucrose synthase was low compared to the invertases. However, during late fruit growth sucose synthase was more active than the invertases. We conclude that invertase activities determine the accumulation of assimilates in the very young fruits, and a reactivation of acid invertase is responsible for the accumulation of hexoses during ripening. During late fruit growth, before ripening, sucrose synthase is transiently responsible for the sucrose breakdown in the fruit tissue. Results also indicate that pyrophosphate‐dependent phosphofructokinase (EC 2.7.1.90) and its activator fructose‐2,6‐bisphosphate (Fru2,6bisP) are involved in the regulation of the sink metabolism of the fruit tissue.
The tonoplast H+‐pyrophosphatase of radish seedlings: biochemical characteristics
Authors: Pugliarello Maria Chiara , Rasi‐Caldogno Franca , De Michelis Maria Ida , Olivari Claudio
Published: May 2006

The activity of the H+‐pyrophosphatase (H+‐PPase) was characterized in microsomes from 24‐h‐old radish (Raphanus sativus L., ev. Tondo Rosso Quarantino) seedlings, which are virtually devoid of the tonoplast H+‐ATPase. The H+‐PPase was localized to membranes which roughly comigrated with the plasma membrane in a sucrose density gradient, but clearly separated from plasma membrane when microsomes were partitioned in an aqueous dextran‐polyethylene glycol two‐phase system. The H+‐PPase activity was strictly dependent on Mg2+ and on the presence of a monovalent cation (K+=Rb+=NH3+Cs+≫Na+Li+) and was insensitive to anions such as Cl−, Br−, NO3− and SO42‐. It was inhibited by F−, imidodiphosphate and Ca2+. It had a pH optimum between pH 7.5 and 8.5 and was saturated by low concentrations of pyrophosphate (half saturation at 30 μM pyrophosphate). All of these characteristics are identical to those reported for the tonoplast H+‐PPase from various plant materials. The functional molecular weight of the H+‐PPase, measured with the radiation‐inactivation technique was 96 kDa.
Infection of tomato roots using callii of broomrape
Authors: Ben‐Hod Graham , Losner Dalia , Joel Daniel M. , Mayer Alfred M.
Published: May 2006

Parasitic weeds like members of the genera Orobanche and Striga cause heavy damage to grain, vegetables and other field crops. The germinating seedlings of the parasites attack the roots of their hosts, following a series of recognition events that control germination, seedling growth and attachment to the host root. An in vitro system has been developed that allows the production of partially differentiated callii of Orobanche aegyptiaca Pers. Protrusions of subcultures of these callii behaved like radicles of germinating seeds. Using this system normal infection of tomato roots was obtained in vitro. The infection process included haustorium formation and the development of young Orobanche plants under aseptic conditions. The system developed should now permit a study of biochemical events during infection of the host by Orobanche.
Changes in growth and photosynthetic capacity of rice with increased UV‐B radiation
Authors: Teramura Alan H. , Ziska Lewis H. , Sztein A. Ester
Published: May 2006

Sixteen rice (Oryza sativa L.) cultivars from 7 different geographical regions were grown in greenhouses at the Univ. of Maryland with and without supplemental ultraviolet‐B (UV‐B) radiation to determine alterations in biomass, morphology and maximum photosynthesis that would be anticipated from potential reductions in the stratospheric ozone column. A wide range of UV‐B effects were observed, with the Philippines cultivar Carreon (5993) and the Sri Lankan cultivar Kurkaruppan (15449) showing the greatest decrease and increase, respectively, in total biomass with supplemental UV‐B radiation. Approximately one‐third of all cultivars tested showed a statistically significant decrease in total biomass with UV‐B radiation. For these sensitive cultivars, leaf area and tiller number were also significantly reduced. Photosynthetic capacity as determined by oxygen evolution declined for some cultivars, but the correlation between changes in photosynthesis and biomass with increasing UV‐B was equivocal. Results from this experiment indicate that: (1) a number of rice cultivars are sensitive to potential increases in UV‐B radiation: and (2) the diversity exhibited by rice in response to increased levels of UV‐B suggests that selective breeding might be successfully used to develop UV‐B‐tolerant rice cultivars.
Symbiotic growth of indigenons white clover (Trifolium repens) with local Rhizobium leguminosarum biovar trifolii
Authors: Svenning Mette M. , Junttila Olavi , Solheim Bjørn
Published: May 2006

To study a possible adaptation of the symbiosis between white clover (Trifolium repens L.) and Rhizobium leguminosarum biovar trifolii with regard to light and temperature at northern latitudes, local seed populations of white clover and isolates of R. leguminosarum biovar trifolii from 3 different latitudes in Norway, 58°48'N, 67°20'N and 69°22'N, were used. The commercial cultivar Undrom was used as a reference plant. The experiments were done at 18 and 9°C under controlled conditions in a phytotron during the natural growing season at 69° 39'N. Growth of the plants was evaluated by number and size of leaves, dry matter production and total N‐content. At 18°C the white clover plants were harvested twice while at 9°C there was only one growth period. The results from first harvest at 18°C and total growth at 9°C, showed that white clover populations from northern Norway had a lower growth potential than the population from the south and cv. Undrom. This difference was not apparent in the second growth period at 18°C. Growth of the plants from seeds to first harvest was enhanced by mineral nitrogen compared to plants dependent on Rhizobium only. However, after a second growth period dry weight and total nitrogen content of the plants with nitrogen fixation were comparable to the plants receiving mineral nitrogen. Statistical analysis showed that the most important factor for the variation in dry matter production was the plant population. Within the populations at 9°C and at first harvest at 18°C, there were no significant differences in dry matter production with different Rhizobium inoculum. In the second growth period at 18°C, different inoculum gave significantly different amount of dry matter within a population. The results showed a significant interaction between plant population and Rhizobium inoculum, and the results indicated that plants from the north gave higher yield when nodulated by Rhizobium from the north than from the south.
The Glycine‐Glomus‐Bradyrhizobiun symbiosis. XI. Nodule gas exchange and efficiency as a function of soil and root water status in mycorrhizal soybean
Authors: Franson Raymond L. , Brown Milford S. , Bethlenfalvay Gabor J.
Published: May 2006

Soybean [Glycine max (L.) Merr. cv. Hobbit] plants were inoculated with a HUP− strain of Bradyrhizobium japonicum (Nitragin 61A118) and either colonized by the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol & Gerd.) Gerd. and Trappe or fertilized with KH2PO4 (nonVAM). They were grown for 50 days in a growth chamber and harvested over a 4‐day drought period during which available soil water decreased to 0. Nodule P concentrations and P‐use efficiency declined linearly with soil and root water content during the harvest period in both VAM and nonVAM plants. Nitrogenase activity, estimated from H2 evolution and C2H2 reduction data, was also a linear function of declining nodule P concentrations and CO2‐exchange rates and showed simular patterns in both treatments. Hydrogen evolution and the relative efficiency of N2 fixation, on the other hand, reacted differently to increasing drought in VAM and nonVAM plants. Differences in the responses of nodule activity in VAM and nonVAM plants to drought are interpreted in terms of demand for nodule P and carbohydrates and of the effects of dehydration on O2 diffusion through nodule tissue.
Structure‐function relationships and energy transfer in phycobiliprotein antennae
Authors: Holzwarth Alfred R.
Published: May 2006

The present understanding of how interactions between chromophore and protein as well as between chromophore and chromophore in different aggregation states influence the spectral and excited state kinetic properties of phycobiliprotein antenna pigments is discussed. Properties of isolated phycobiliproteins from both cyanobacteria and red algae as well as from cryptophytes and of intact phycobilisomes are covered. The experimental results are discussed in terms of general principles for chromophore coupling and energy transfer. Some controversial topics in this field are outlined.
Control of phloem unloading by action potentials in Mimosa
Authors: Fromm Jörg
Published: May 2006

In the sensitive plant, Mimosa pudica, action potentials arise when the leaves are touched and they trigger a sudden decrease in turgor of the pulvinar motor cells, which causes the leaf to close. These potentials may travel through the phloem and they appear to influence pulvinar phloem unloading after stimulation. Mature leaves were exposed to 14CO2 and phloem translocation was observed by autoradiography. In unstimulated pulvini, labeled photoassimilates were restricted to the phloem. However, after stimulation, the 14C‐label appeared to be concentrated in the extensor region of the motor cortex. Since stimulation elicits an action potential, it is suggested that it also triggers phloem unloading of sucrose in the pulvini.
Endogenous evolution of HCN during pre‐germination periods in many seed species
Authors: Esashi Yohji , Isuzugawa Kanji , Matsuyama Shinichi , Ashino Hiroki , Hasegawa Ryo
Published: May 2006

Both cyanogenic (Malus pumila Mill) and acyanogenic (Oryza sativa L., Hordeum vulgare L., Zea mays L., Glycine max Merr., Lactuca sativa L., and Xanthium pennsylvanicum Wallr. etc.) seeds evolve HCN gas during the early periods of water imbibition. All tested seeds contained reserve cyanogens which liberated HCN upon hydrolysis with H2SO4 and with β‐glucosidase and/or lipase. The amounts of liberated HCN were roughly comparable to those of unidentified cyanogens. It is thus conceivable that the cyanogens within seeds are available as precursors for free HCN evolved in the pre‐germination period. The amounts of HCN evolved in the acyanogenic seeds were only 0.002 to 1% of that in apple, but the contents of the cyanogenic compounds in rice and cocklebur increased temporarily during the pre‐germination period, then decreased and, finally, disappeared completely with the start of germination.
Aluminium effects on transmembrane potential in cells of fibrous roots of sugar beet
Authors: Lindberg Sylvia , Szynkier Krystyna , Greger Maria
Published: May 2006

The effect of aluminium (Al) on the electrical transmembrane potential of epidermal and outer cortical root cells of intact seedlings of sugar beet (Beta vulgaris L. cv. Monohill) was studied. The potential difference to the surrounding medium was recorded with microelectrodes inserted into the vacuoles (PDv) and cytoplasm (PDc) of intact roots. Both long‐term effects of AlCl3 (100, μM present during cultivation) and immediate effects of AlCl3 (10, 50, or 100 μM present in the assay medium), were measured. The effect of Al was measured at pH 4.0, 5.0 and 6.5 in order to obtain information on the toxicity of different Al forms existing at different pH values.

Low pH and/or the presence of AlCl3 during cultivation caused large depolarizations of the PDv. Since the immediate effect of 2,4‐dinitrophenol (DNP) on the resting potential of cells from Al‐cultivated plants was negligible, it is likely that Al affects the metabolic component of the transmembrane potential.

Aluminium also had an immediate effect on the PD in root cells of plants cultivated without Al. Addition of 10 or 50 μM Al to the assay medium caused hyperpolarization of PDv in the presence of 0.5 mM Ca2+ at all pH values studied, depolarization of PDc at pH 6.5, and hyperpolarization of PDc at lower pH. At 1 mM Ca2+, or in the presence of K+ (≥ 2 mM), however, the same Al concentrations had little effect on PDc.

The strongest depolarizing effects of 10 or 50 μM Al in short‐term treatments were obtained at pH 6.5, and were probably due to the soluble species Al(OH)3, which is more frequent at pH 6.5 than at a lower pH. Addition of 50 μM Al caused alkalinization of the root medium at pH 6.5, but not at pH 4.0. Therefore, it is possible that Al at pH 6.5 is bound to, or translocated across, the membrane without the accompanying hydroxide ions. It is likely that most of the Al is bound to the root cells, since removal of Al from the buffer surrounding the roots did not cause the changed PD values to return to the original values. Aluminium also interacts with effects of Ca2+ and K+ on the membrane potential, since changes in PD, induced by changes in concentrations of Ca2+ and K+ are different in the absence and presence of Al.
Ammonium‐assimilating enzymes and their regulation in wild and NADP‐glutamate dehydrogenase‐deficient strains of the ectomycorrhizal fungus Hebeloma cylindrosporum
Authors: Chalot Michel , Brun Annick , Debaud Jean Claude , Botton Bernard
Published: May 2006

Hebeloma cylindrosporum strain h 17 was grown on media containing either glutamate or ammonium as nitrogen source. Growth tests and in vitro activity measurements revealed that both glutamine synthetase (GS. EC 6.3.1.2) and NADP‐specific glutamate dehydrogenase (NADP‐GDH, EC 1.4.1.4) are fully functional in wild type mycelia grown on glutamate or ammonium as sole nitrogen source. However, NADP‐GDH appeared to be more active than GS in stationary growing mycelia. NADP‐GDH is also able to sustain adequate ammonium assimilation in methionine sulfoximine (MSX)‐treated mycelia since they grew as well as mycelia fed with ammonium alone. The NADP‐GDH also appeared to be L‐glutamate inducible whereas GS was repressed by ammonium. The NADP‐GDH deficient strain, when transferred from a glutamate containing medium to an ammonium containing medium, exhibited a derepressed GS, although this enzyme did not fully substitute for the deficiency of NADP‐GDH in ammonium assimilation. The low NADP‐GDH activity of the mutant strain exhibited a reduced mobility on a 6% constant polyacrylamide gel. By contrast, the two enzymes had identical molecular weights, estimated to be ca 295 kDa on gradient polyacrylamide gel. The involvement of NADP‐GDH and GS enzymes in nitrogen assimilation is discussed.
Betaines and free amino acids in salt stressed vitroplants and winter resting buds of Populus trichocarpa X deltoides
Authors: Bray L. , Chriqui D. , Gloux K. , Rudulier D. Le , Meyer M. , Peduzzi J.
Published: May 2006

Organic solutes, in particular glycine betaine and proline, have been detected as osmoprotective compounds in many microorganisms and herbaceous species. However, for woody plants, very little information is available on mechanisms of adaptation to salt stress. In the present study, effects of NaCI treatment on betaine and free amino acid contents in a clone of Populus trichocarpa X deltoides micropropagated vitroplants were analyzed using HPLC and silicate plate chromatography. The application during 12 days of 50 to 200 mM NaCI to viroplants cultured on Murashige and Skoog medium (Murashige and Skoog 1962. Physiol. Plant. 15: 473–497) led to a progressive decrease of growth, leaf senescence, abscission, and apical necrosis. Populus trichocarpa X deltoides was characterized by the absence of glycine betainc and/or proline accumulation. However, trigonelline was found to increase in vitroplants subjected to 100 mM NaCI. Trigonelline was also present in dormant buds harvested in natural conditions and missing in active buds. In vitroplants, the content of some amino acids was strongly modified by salt stress. A progressive accumulation of alanine and γ‐amino butyrate was particularly significant in roots, whereas the relative concentration of glutamine was strongly enhanced in leaves. Leaf content of glutamate and ornithine attained maximum in the presence of 100 and 150 mM NaCI concentrations, and then decreased. Arginine and serine pools were not significantly modified by salt treatment. The variations in vitroplants were of small amplitude compared to those observed in mature poplars where winter rest was associated with a very high arginine level and with a disappearance of nearly all other free amino acids. The results are discussed in relation to previous data obtained with herbaceous species and in relation to some metabolic pathways in poplars where trigonelline could be considered as a sensitive stress indicator.
Characterization of Na+ exclusion mechanisms of salt‐tolerant reed plants in comparison with salt‐sensitive rice plants
Authors: Matsushita Nobutoshi , Matoh Töru
Published: May 2006

Salt‐tolerant reed plants (Phragmites communis Trinius) and salt‐sensitive rice plants (Oryza sativa L. cv. Kinmaze) were grown in salinized nutrient solutions up to 50 mM NaCl, and growth, Na+ contents and kinetics of 22Na+ uptake and translocation were compared between the species to characterize the salt tolerance mechanisms operating in reed plants. When both plants were grown under the same salinity, Na+ contents of the shoots were lower in reed plants, although those of the roots were quite similar. The shoot base region of both species accumulated Na+ more than the leaf blades did. Sodium‐22 uptake and pulse‐chase experiments suggested that the lower Na+ transport rate from root to shoot could limit excessive Na+ accumulation in the reed shoot. There was a possibility that the apparently lower 22Na+ transport rate to the shoot of reed plants was due to net downward Na+ transport from shoot base to root.
The effects of auxin and antiauxin in an in vitro bioassay of flower regulatory activity in leaf exudate from tobacco plants
Authors: Hatori M. , Sakagami Y. , Marumo S.
Published: May 2006

An in vitro bioassay system for floral bud formation has been established using Nicotiana tabacum L. cv. MC, explants excised from floral stalks cultured on modified Murashige‐Skoog medium containing excess auxin and antiauxin. Three auxins. indolyl‐3‐acetic acid (IAA), 4‐chloroindolyl‐3‐acetic acid and 5,6‐dichloroindolyl‐3‐acetic acid, were tested for floral bud‐forming activity; IAA was most efficient. Three antiauxins. 5,7‐dichlorindolyl‐3‐isobutyric acid (5,7‐Cl2‐HBA), p‐chlorophenoxyiso butyric acid and 2,3,5‐triiodobenzoic acid, were tested for the ability to reverse the inhibition of floral bud formation caused by excess IAA. Only 5,7‐Cl2‐HBA was very effective. Leaf exudates from short day‐ and long day‐treated tobacco plants were added to the bioassay system which contained 1 µM 6‐benzylaminopurine, 5 µM IAA and 5 µM 5, 7‐Cl2‐HBA, Interestingly, only the leaf exudate from short day‐treated plants stimulated floral bud formation. Moreover, the buds produced grew into large. well‐developed ones with shapes similar to those of the natural floral buds of intact tobacco plants.
Photosynthetic responses of citrus trees to soil flooding
Authors: Vu Joseph C. V. , Yelenosky George
Published: May 2006

Continuous soil flooding reduced leaf photosynthetic rate, stomatal conductance to water vapor, chlorophyll concentration and activity of ribulose bisphosphate carboxylase‐oxygenase (Rubisco, EC 4.1.1.39) of sweet orange [Citrus sinensis (L.) Osbeck cv. Hamlin] trees, grafted onto rough lemon (RL; C. jambhiri Lush.) and sour orange (SO; C. aurantium L.) rootstocks. After 24 days of waterlogging, trees showed senescence, wilting and abscission of leaves, and these symptoms were more evident with flooded Hamlin/SO than Hamlin/RL. Reduction of leaf photosynthetic rate at day 24 was ca 94%, of stomatal conductance, 71%, of chlorophyll, 38% and of Rubisco, 62% for flooded Hamlin/SO, compared with 22, 5, 18 and 33%, respectively, for flooded Hamlin/RL. For both Hamlin/RL and Hamlin/SO, leaf photosynthetic rate and stomatal conductance to water vapor were closely correlated (r2= 0.87). Leaf internal CO2 concentration of flooded trees, however, was not decreased by reduced stomatal conductance. Dark respiration rates of fibrous roots of flooded trees were greatly reduced, but not in leaf tissues. Total nonstructural carbohydrate concentrations were higher in leaves (50 and 80% increases for Hamlin/SO and Hamlin/RL, respectively), but drastically reduced in roots (60 and 45% reductions for Hamlin/SO and Hamlin/RL, respectively), as a result of flooding. The data indicate that Hamlin grafted onto RL rootstocks was more tolerant to soil flooding than Hamlin grafted onto SO rootstocks.
The effect of water status and season on the incorporation of 14CO2 and [14C]‐acetate into resin and rubber fractions in guayule
Authors: Benzioni Aliza , Mills David
Published: May 2006

The effects of drought stress and season on both allocation of photosynthates to stems and leaves and potential for stem rubber synthesis were studied in guayule (Parthenium argentatum Gray USDA line 11604). Two‐year‐old plants grown under field conditions in the Negev desert of Israel were subjected to different irrigation regimes, and water status was assessed by measuring the relative water content (RWC). Undetached plant tips were exposed to a 1 h pulse of 14CO2, followed by a 24 h chase. 14C fixed and translocated to different plants parts and notably 14C incorporation into rubber and resin fractions was determined. The potential of detached branch slices to incorporate [14C]‐acetate into rubber was also studied. A higher percentage of fixed 14C was translocated from shoot tips in winter (28–30%) than in summer (15–18%). The percentage of [14C]‐acctate incorporated into the rubber fraction by stem slices was maximal in winter (20%) and minimal in summer (3–5%) in both cases in the absence of drought stress. In summer the translocation of photosynthates into stems was inversely related to plant RWC, dropping from 18% three days after irrigation to 3% 14 days later, and the potential of stems to synthesise rubber was high under drought conditions and low in well irrigated plants.
An oxygen electrode assay to determine autoclaved‐induced toxicity in tissue culture media
Authors: Hsiao Ke‐Cheng , Bornman Chris H.
Published: May 2006

An oxygen electrode was used to assay cyanide‐induced oxygen consumption of 8 sugars following autoclaving and the results correlated with the effects of the same sugars (reported by de Lange, S. Afr. J. Bol. 55, 1, 1989) on pollen germination and pollen tube growth. Of the sugars tested, fructose was the least stable, producing a degradation product that resulted in a 40‐fold higher consumption of oxygen than sucrose. The use of cyanide‐induced oxygen uptake makes it possible to control more carefully the conditions of preparation of sterile media by autoclaving.
Polyamines and ethylene in the removal of embryonal dormancy in apple seeds
Authors: Sińska Irena , Lewandowska Urszula
Published: May 2006

Putrescine (Put), spermidine (Spd) and spermine (Spm) were found in seeds of apple (Malus domestica Borkh. cv. Antonovka), in amounts that increased in the order given. The levels slowly decreased during 30 days of stratification. Exogenous polyamines (PAs) affected germination of isolated embryos in a way dependent on the type of polyamine, its concentration, and the state of the embryo dormancy. The effect of Put and Spd on germination was stimulatory, while that of Spm was inhibitory. Stimulation of germination was also observed when embryos were treated with arginine, ornithine and methionine. Canavanine inhibited germination, and this effect was reversed by arginine or Put. Ethephon, aminooxyacetic acid (AOA) and aminoethoxyvinylglycine (AVG) present during seed stratification had no effect on the levels of endogenous PAs. Put and Spd did not change ethylene production, neither during seed stratification nor during embryo germination, whereas Spm reduced ethylene evolution. The data suggest that Spm plays a role in the maintenance of dormancy by preventing ethylene production, while Put and Spd participate in dormancy removal, independently of ethylene.
Effect of mycorrhiza and nitrate nutrition on nitrate reductase activity in Scots pine seedlings
Authors: Sarjala Tytti
Published: May 2006

In vivo nitrate reductase (EC 1.6.6.1) activity was measured in seedlings of Scots pine (Pinus sylvestris L.) inoculated with Cenococcum geophilum (Sow.) Ferd. & Winge, Paxillus involutus (Batsch:Fr) Fr, Piloderma croceum Erikss, & Hjortst, and Suillus variegatus (Fr.) O. Kuntze. The activity was higher in the mycorrhizal pine roots than was previously found in the fungus symbiont alone, but lower than in the roots of nonmycorrhizal pine seedlings. The differences observed in a previous study between the fungal species under pure culture conditions were not found in the present work for mycorrhiza synthezised with the same fungal species. An increase in the nitrate concentration of the nutrient solution increased the proportion of the nitrate reductase activity in the needles. The mycorrhizal root tips had higher nitrate reductase activity than nonmycorrhizal root tips in the same root system.
Spectrophotometric characterization of phytochromes in dimorphic cocklebur seeds in relation to capacity for germination
Authors: Manabe Katsushi , Nakazawa Miki , Sato Yuuichi , Esashi Yohji
Published: May 2006

Phytochrome was measured spectrophotometrically in different tissues of the upper (positively photoblastic) and lower (negatively photoblastic) seeds of the cocklebur (Xanthium pennsylvanicum Wallr.). Axial parts of the seeds, in particular parts of the radicle, contained high levels of phytochrome, while cotyledonary parts contained only low levels. These results were consistent with the distribution of the light‐sensitive areas of the seeds that were associated with germination. Phytochrome levels in both types of dimorphic seeds increased gradually with increasing duration of dark imbibition for 4–8 h, then the rates of increase in levels of phytochrome accelerated. In both types of seed, some phytochrome was measurable even before imbibition. In the lower seeds, up to 20% of the phytochrome was occasionally observed as Pfr in samples imbibed in darkness for a short time (up to 12 h). A slight blue shift of the peak of PT in the difference spectrum of phytochrome was observed in the case of lower seeds imbibed for 0–2 h. These results suggest that, to some extent, the lower axes contain dehydrated Pfr or intermediate(s) in the photoconversion of phytochrome.

The dark reactions of Pfr were also examined in excised axes of both types of dimorphic seed after they had been pre‐imbibed for 16 h in darkness. Dark destruction of Pfr was observed in both types of seed. In addition, net increases in levels of Pr were observed in the dark controls and in the samples irradiated with red light after the level of Pfr diminished. No ‘inverse’ dark reversion from Pr to Pfr was detected. Thus, after 16 h of imbibition, there were no differences in terms of properties of phytochrome between the two types of seed, and the different responses to light of upper and lower seeds might depend mainly on a difference in the physiological state of the two types of seed rather than the properties of phytochrome.
Photosynthetic acclimation ofTradescantia albiflorato growth irradiance: Lack of adjustment of light‐harvesting components and its consequences
Authors: Chow W. S. , Adamson Heather Y. , Anderson Jan M.
Published: May 2006

The photosynthetic acclimation ofTradescantia albiflora(Kunth), a trailing ground species naturally occurring in the deep shade of rainforests, was studied in relation to growth irradiance (glasshouse; direct light and 1 to 4 layers of shade cloth, giving 100 to 1.4% relative growth irradiance). Contrary to other irradiance studies of higher plants grown in natural habitats or controlled light environments, the chlorophylla/bratios ofTradescantialeaves were low (∼2.2) and constant. Acclimation to growth irradiance caused no changes in the relative amounts of specific Chl‐proteins or the numbers of photosystem I (PSI) and PSII reaction centres on a chlorophyll basis, indicating that the light‐harvesting antenna sizes of PSII and PSI, as well as the photosystem stoichiometry, were independent of growth irradiance. However, the amount of cytochromefand ATP synthase on a chlorophyll basis increased with increasing the relative growth irradiance from 1.4 to 35%, showing acclimation of electron transport and photophosphorylation capacity. The photosynthetic capacity and ribulose 1, 5‐bisphosphate carboxylase (EC 4.1.1.39) activity also increased with increase of the growth irradiance to 35%. Beyond that, the inflexible PSII/PSI stoichiometry and shade‐type photosystem II/light‐harvesting units inTradescaniiaare a disadvantage for long‐term exposure to high irradiance since the leaves are more prone to photoinhibition.
Ethylene and in vitro rooting of hazelnut (Corylus avellana) cotyledons
Authors: González Aida , Rodríguez Roberto , Tamés Ricardo Sáchez
Published: May 2006

Ethylene may be one of the many factors that play a role in rooting. However, in some studies ethylene promoted rooting, while in others it was inhibitory or had no effect. Using cotyledons of hazelnut (Corylus avellana L. cv. Casina) observations were made of the effect of ethylene precursors on adventitious root formation. l‐methionine (Met) or 1‐aminocyclopropane‐1‐carboxylic acid (ACC) added to a standard indole‐3‐butyric acid (IBA)‐kinetin‐containing medium did not enhance rooting, while 2‐chloroethylphosphonic acid (CEPA) did. The ethylene inhibitor, aminoethoxyvinylglycine (AVG), inhibited root formation, but its effect was reversed by ACC when cotyledonary segments were transferred to rhizogenic medium plus ACC at day 10. Ethylene production by cotyledons cultured on rhizogenic medium or rhizogenic medium plus CEPA was high at the beginning of rooting. Thus, the wound‐induced ethylene is a key stimulatory factor in the formation of root primordia. The data support the hypothesis that ethylene plays a positive role in root formation.
Inhibition of early steps of de novo fatty‐acid biosynthesis by different xenobiotica
Authors: Focke Manfred , Feld Andrea , Lichtenthaler Hartmut K.
Published: May 2006

The importance of the early steps of de novo fatty‐acid biosynthesis is discussed in terms of rate‐limiting enzymic reactions with respect to their inhibition by xenobiotics. The inhibitory spectra of allicin as an inhibitor of the acetyl‐CoA‐synthase, two classes of graminicides (cyclohexane‐1,3‐diones and aryloxyphenoxypropionic acids) as inhibitors of acetyl‐CoA‐carboxylase, and the two antibiotics cerulenin and thiolactomycin, which affect the condensing step in fatty‐acid biosynthesis, are compared.
Leaf teeth, transpiration and the retrieval of apoplastic solutes in balsam poplar
Authors: Wilson T. P. , Canny M. J. , McCully M. E.
Published: May 2006

The rapid flow of the transpiration stream through major veins to leaf teeth was followed in leaves of Populus balsamifera L., using the tracer sulphorhodamine G (SR), which probes for cells with H+‐extrusion pumps. The tracer accumulated quickly in the hydathodes of the teeth. It was shown by freeze‐substitution and anhydrous processing that SR was taken up by phloem parenchyma and epithem cells of the hydathode. When 14C‐labelled aspartate was fed to the leaves in the transpiration stream, it also was taken up most strongly by the same phloem parenchyma and epithem cells. It is proposed that one function of the hydathodes in leaf teeth is the retrieval of solutes from the transpiration stream.
Abscisic acid and mannitol promote early development, maturation and storage protein accumulation in somatic embryos of interior spruce
Authors: Roberts Dane R.
Published: May 2006

Low levels of mannitol (2–6%) promoted the formation of globular embryos in embryogenic cultures of interior spruce (Picea glauca engelmanni complex). However, these concentrations of mannitol were inhibitory to the formation of cotyledonary embryos. A short (1 week) pulse of mannitol in combination with abscisic acid doubled the production of late cotyledonary somatic embryos compared with the standard abscisic acid treatment. Higher levels of mannitol (13 and 20%) were required to inhibit precocious germination of spruce somatic embryos. These concentrations of mannitol promoted the accumulation of storage proteins during cotyledon maturation, but were not as effective as abscisic acid. Furthermore, 13 and 20% mannitol treatments did not substitute for abscisic acid in promoting the formation of cotyledonary embryos. Pre‐treatment of late cotyledonary embryos with mannitol (13–25%) did not increase the frequency of germination compared with germination in non‐treated embryos (approximately 10% germinated) although dehydration with high relative humidity treatment increased germination to 83%.
Salinity effects on water relations in Lycopersicon esculentum and its wild salt‐tolerant relative species L. pennellii
Authors: Sánchez‐Blanco M. J. , Bolarín M. C. , Alarcón J. J. , Torrecillas A.
Published: May 2006

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P‐73 and its wild salt tolerant relative L. pennellii (Correll) D'Arcy accession PE‐47, were grown during spring‐summer 1989 under unheated plastic greenhouse conditions. Plants were submitted to two different salt treatments using 0 and 140 mM NaCI irrigation water. In both tomato species, salinity caused a proportionally larger reduction in leaf area than in leaf weight and, in L. esculentum, a proportionally larger decrease in stem weight than in leaf weight. Daily variations in leaf water potential (Ψ1) were fundamentally due to changes in the evaporative demand of the atmosphere. Reductions in Ψ1 due to salinity were consistent only in L. esculentum. In all the conditions studied, leaf turgor was maintained. Leaf conductance (g1)was higher in L. esculentum than in L. pennellii.Salinity induced a clear reduction in g1 levels in L. esculentum whereas, in L. pennellii, this reduction was noted only in May. In both species the Ψos (leaf osmotic potential at full turgor) levels were reduced by salinity. The bulk modulus of elasticity (E) and relative water content at turgor loss point (RWCtlp) were not affected by salinity. The RWCtlp values in L. pennellii seem to be controlled by E values.
Water relations of Picea abies. I. Comparison of water relations parameters of spruce shoots examined at the end of the vegetation period and in winter
Authors: Gross K. , Koch W.
Published: May 2006

Seasonal changes of some water relations parameters of Norway spruce shoots (Picea abies [L.] Karst.) were studied during two experiments using the pressure‐volume analysis. For each experiment only shoots of a single tree were used.

During the first study, the course of the turgor loss point (as bulk osmotic pressure when turgor first reaches zero, πp) of shoots developed in late 1986 vegetation period, were measured in 1987. The turgor loss point decreased temporarily from –2.5 MPa at the beginning of the year to –3.3 MPa at the end of March, but then increased to the original level for the rest of the year.

During the second study, water relations parameters were measured in late summer 1987 and in late winter 1988. Winter shoots at full water saturation contained up to 20% less water than in late summer. Accordingly, the bulk osmotic pressure at full water saturation (πp) decreased from –1.7 MPa in late summer to –1.9 MPa in winter, πp decreased also from –2.2 MPa to –2.8 MPa. However, the amount of osmotically active substances (mOsmol, N) remained unchanged. The relative amount of apoplastic water in the total shoot water content appeared to drop insignificantly from 17% to 15%.

The results show that the decrease in πo and πp in late winter is not due to an accumulation of osmotically active substances in the vacuoles but is due to a decrease in tissue water content. The temporary reduction of the symplastic volume by deposition of osmotically inert substances seems to be the most probable cause of this phenomenon.