bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein synthesis in mitochondria purified from roots, leaves and flowers of sugar beet
Authors: Lind Christina , Halldén Christer , Møller Ian M.
Published: May 2006

Highly purified, intact and functional mitochondria were isolated from roots and leaves of a number of fertile and male‐sterile lines of sugar beet (Beta vulgaris L.). Intact and functional mitochondria were successfully isolated from the flowers of fertile plants, but not from the flowers of male‐sterile plants. Several alternative methods for the homogenization of male‐sterile flowers were tried. Their failure suggests that the mitochondria from male‐sterile flowers are more sensitive to mechanical damage than mitochondria from fertile, or other organs of male‐sterile, plants.

In organello protein synthesis was optimized with respect to the total concentration of amino acids, the concentration of [35S]‐methionine, pH and respiratory substrate. Inhibitor experiments showed that the mitochondrial preparations contained mitochondrial translational activity only. With the exception of one band, no processing or proteolytic breakdown in either root or leaf mitochondrial protein synthesis products could be detected in pulse‐chase experiments. Submitochondrial fractionation experiments showed the presence of two soluble polypeptides, whereas all other polypeptides were membrane bound.

The polypeptide patterns of root, leaf and flower mitochondria were very similar with the exception of 4 polypeptides involved in glycine oxidation. These 4 polypeptides were present in large amounts in leaf mitochondria and just detectable in flower mitochondria. The patterns of polypeptides syntesized in mitochondria isolated from roots, leaves and flowers also showed a number of organ‐specific differences. Six qualitative and 6 quantitative differences were found between mitochondria isolated from these three organs. No unique polypeptides were found to be synthesized either by flower mitochondria or by mitochondria from roots and leaves of male‐sterile plants compared to their male‐fertile counterparts.
Effects of prohexadione (BX‐112) and gibberellins on shoot growth in seedlings of Salix pentandra
Authors: Junttila Olavi , Jensen Einar , Ernstsen Arild
Published: May 2006

Effects of gibberellins A1, A4/7, A9, A19 and A20 and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth‐retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX‐112), which is suggested to block 3β‐hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA1, but not GA19 and GA20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA19, GA20 and GA1 are native in S. pentandra, and the results are compatible with the hypothesis that GA1 is active per se in shoot elongation, and that the effect of GA19 and GA20 is dependent on their conversion to GA1.

A mixture of GA4 and GA7 was as active as GA1 in promoting shoot elongation in seedlings treated with prohexadione, while GA9 showed slight activity only when applied at high doses.
Evidence for the involvement of jasmonic acid in the control of the stem‐growth habit of soybean plants
Authors: Koda Yasunori , Yoshida Koichi , Kikuta Yoshio
Published: May 2006

Soybean plants show diversity in stem‐growth habit which ranges from the determinate type to the indeterminate type. Stem growth of determinate plants abruptly terminate near the beginning of flowering. The possible involvement of jasmonic acid (JA) in the control of the stem growth‐habit was examined in indeterminate and determinate isolines of soybean [Glycine max (L.) Merril cv. Harosoy]. JA‐like activities in leaves of both isolines were very low 20 days before the commencement of flowering. The activity increased rapidly thereafter and reached a maximum near the time of flowering. Although the activities in leaves of both isolines fluctuated in a similar manner, the activity in the determinate isoline was much higher than that in the indeterminate isoline after flowering. The presence of JA in the leaves of the determinate isoline was confirmed by purification by high‐performance liquid chromatography and by mass spectrometry. Exogenous application of JA to cultured shoot apices of the indeterminate isoline strongly inhibited growth. These results suggest that jasmonic acid is a major endogenous factor that controls the growth habit of soybean plants.
β‐Glucosidase activities and HCN liberation in unimbibed and imbibed seeds, and the induction of cocklebur seed germination by cyanogenic glycosides
Authors: Esashi Yohji , Matsuyama Shinichi , Ashino Hiroki , Ogasawara Maria , Hasegawa Ryo
Published: May 2006

In many seed species, the major source of HCN evolved during water imbibition is cyanogenic glycosides. The present investigation was performed to elucidate the role of endogenous cyanogenic glycosides in the control of seed germination and to examine the involvment of β‐glucosidase in this process. All seed species used here contained some activities of β‐glucosidase already in the dry state before imbibition. in the decreasing order of Malus pumila, Daucus carota, Hordeum vulgare, Chenopodium album and so on. β‐Gluosidase activity in upper and lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.) decreased with imbibition, and in lower seeds the activity disappeared when they germinated. On the contrary, in caryopses of rice (Oryza sativa L. cv. Sasanishiki) β‐glucosidase increased during imbibition, and this increase continued even after germination. β‐Glucosidase in cocklebur seeds was more active in the axial than in the cotyledonary tissue. Amygdalin, prunasin and linamarin could all serve as substrattes for the β‐glucosidase(s) from both cocklebur and rice.

Amygdalin, prunasin and linamarin as well as KCN, were effective in stimulating the germination of upper cocklebur seeds. The seeds evolved much more free HCN gas when they were exposed to the cyanogenic glycosides than when the glycosides were absent. Moreover, the application of the cyanogenic glycosides or of KCN caused accumulation of bound HCN in the seeds. Carbon monoxide, which stimulated cocklebur seed germination only slightly, did not cause accumulation of bound HCN. We suggest that a balance between the cytochrome and the alternative respiration pathways, which is adequate for germination (Esashi et al. 1987. Plant Cell Physiol. 28: 141–150), may be brought about by the action of endogenous HCN; a large portion of which is liberated from cyanogenic glycosides via the action of β‐glucosidase. In addition to the partial suppression of the cytochrome path and unlike carbon monoxide, the HCN thus produced may act to supply cyanide group(s) to unknown compounds necessary for germination.
Influence of aluminium on phosphorus and calcium localization in roots of beech (Fagus sylvatica)
Authors: Asp Håkan , Bengtsson Bengt , Jensén Paul
Published: May 2006

Beech plants (Fagus sylvatica L. provenance Maramures) were grown in nutrient solution at low pH (4.2) and exposed to different concentrations of AlCl3. Uptake and leakage of Ca2+(45Ca2+) and H2PO4‐(32P) were studied. A high external aluminium concentration (1.0mM) reduced the uptake and export to the shoot of both calcium and phosphate, while 0.1 mM Al increased the phosphorus level in the roots. To determine the impact of aluminium on the localization of calcium and phosphate, leakage of the elements from both intact plants and plants frozen prior to the leakage experiment was studied. The leakage of Ca2+ from intact plants was not affected by prior exposure to 0.1 mM Al. Freezing of the beech plants before the leakage experiment increased leakage of calcium slightly more from roots of control plants than for roots exposed to 0.1 mM Al, indicating that even low concentrations of alminium may impede the influx of calcium across the plasma membrane in the roots. The patterns of Ca2+ leakage from roots previously exposed to 1.0 mM Al indicated that very little Ca2+ was located extracellularly. The extracellular fraction of phosphate increased with increasing Al concentration in the nutrient solution. Low Al concentration (0.1 mM) only reduced the intracellular phosphate concentration to a minor extent, while 1.0 mM Al profoundly decreased it. It is concluded that 0.1 mM AlCl3 has a limited effect upon the localization of Ca2+ and phosphate in the roots. At higher levels of Al, 0.1–1.0 mM, there is a more dramatic change in nutrient localization in the free space and uptake over the plasma membrane.
Light‐quality and irradiance effects on pigments, light‐harvesting proteins and Rubisco activity in a chlorophyll‐ and light‐ harvesting‐deficient soybean mutant
Authors: Eskins Kenneth , Jiang Cai Zhong , Shibles Richard
Published: May 2006

Soybean (Glycine max [L.] Merrill) plants, normal green (Clark L1) and mutant yellow (Clark y9y9), were grown in (1) full‐spectrum solar irradiation; (2) either red plus far‐red or blue plus far‐red; (3) either red or blue light with no far‐red light. Young leaves harvested from first (1TF) trifoliolate or fifth (5TF) trifoliolate stages of development showed that the mutant plants express pigment and protein deficiencies as a direct function of irradiance. Response of the mutant to light quality indicates that blue light slightly enhances expression of the mutation at higher irradiances. Direct response of light‐harvesting proteins of photosystem 2 (LHCP2) and light‐harvesting protein of photosystem 1 (LHCP1) to light quality increases the ratio of LHCP1/LHCP2 in blue light compared to that in red or red/far‐red light. Rubisco proteins and Rubisco activity (leaf area basis) are directly related to irradiance level but are enhanced in blue light over equal irradiance red. This enhancement is not shown in the presence of far‐red light.
The cleavage of cyanogenic lipids by esterases
Authors: Selmar Dirk
Published: May 2006

A method for the determination of esterases responsible for the cleavage of cyanogenic lipids is described. The cyanogenic esterase of Ungnadia speciosa seeds was examined. This enzyme was found exclusively in the lipid phase of homogenates, where also all cyanogenic lipids were located. The esterase exhibited maximum activity at pH 4.4.
Characterization of ATPase activities in rice root plasmalemma vesicles isolated by two‐phase partitioning
Authors: Ros R. , Sanz A. , Segura J. , Picazo I.
Published: May 2006

Plasma membrane vesicles were isolated from the roots of 7‐day‐old rice plants (Oryza sativa L. cv. Bahía) by utilizing an aqueous polymer two‐phase system with 6.2%:6.2% (w/w) Dextran T500 and polyethylene glycol 3350 (PEG) at pH 7.6. Plasmalemma vesicles of high purity were obtained as indicated by the vanadate‐sensitive K+, Mg2+‐ATPase activity that was 18 times higher in the upper (PEG‐rich) phase than in the lower (Dextran‐rich) phase and by specific staining with sodium silicotungstate. Two peaks of ATPase activity were found. One showed a pH optimum at 6.0 in the presence of 150 mM KCl and 3 mM ATP with apparent Km (ATP) and Vmax of 0.75 mM and 79 μmol (mg protein)−1 h−1, respectively. With 50 mM KCl and 7 mM ATP a pH optimum of 6.5, an apparent Km (ATP) of 6.3 mM and Vmax of 159 μmol (mg protein)−1 h−1 were determined. Both activities were specific for ATP, unspecific for monovalent cations, sensitive to sodium vanadate and Ca2+ but insensitive to azide and nitrate.
Continuous shoot growth monitoring in hydroponics
Authors: Smolders Erik , Merckx Roel , Schoovaerts Frans , Vlassak Karel
Published: May 2006

A weighing apparatus for automatic recording of fresh weight of shoots of spinach plants (Spinacia oleracea L., cv. Subito) growing in nutrient solution is described. The system was tested for 17 days in a controlled environment and enabled the determination of the relative growth rate (RGR) of the shoot fresh weight. Results from three consecutive growth experiments demonstrated diurnal fluctuations in the relative growth rate of the shoot fresh weight. In general, relative growth rates were between 0.32 and 0.36 day−1 16 days after sowing and decreased to between 0.11 and 0.18 day−1 during the 12 following days. The variance between three replicate growth curves was compared with the variance of a growth function fitted through destructively obtained spinach shoot weight data.
Seasonal changes in photosynthetic capacity of leaves of kiwifruit (Actinidia deliciosa) vines
Authors: Buwalda J. G. , Meekings J. S. , Smith G. S.
Published: May 2006

The seasonal trend of photosynthetic capacity of leaves of kiwifruit (Actinidia deliciosa var. deliciosa) vines growing in the field was examined, by measuring the response of net photosynthesis (A) to irradiance (PAR) at monthly intervals for leaves that emerged at different stages of the growing season. A climate controlled minicuvette system was used, to ensure constant environmental conditions, apart from the controlled changes in leaf irradiance. Responses of A to irradiance were described using asymptotic exponential curves, providing estimates of the radiation saturated rate of A (Asat), and the reponse of A to increasing incident PAR at low PAR levels (ϕi). The change in photosynthetic capacity with leaf age was similar for leaves emerging 1, 2, 3 or 4 months after bud burst. At 1 month after leaf emergence, when leaves were fully expanded, Asat was 9–11 μmol CO2 m−2 s−1. Maximum photosynthetic capacity was not attained until 3–5 months after leaf emergence, when Asat was 16–17 μmol CO2 m−2 s−1. The increasing photosynthetic capacity during 3–5 months after leaf emergence was closely related to concomitant changes in leaf N and chlorophyll contents. The possibility that N import to the leaf was a significant factor limiting the development of photosynthetic capacity is discussed.
Hydrolysis of lipid and protein reserves in loblolly pine seeds in relation to protein electrophoretic patterns following imbibition
Authors: Groome Maralee C. , Axler Seymour R. , Gifford David J.
Published: May 2006

The correlation between changes in seed protein electrophoretic patterns and the hydrolysis of lipid and protein reserves of loblolly pine (Pinus taeda L.) seed was studied. Seeds were incubated at 30°C for up to 12 days following stratification, then megagametophytes and embryos were assayed for lipid and protein content after each day of imbibition. The megagametophyte of mature seed was found to contain 20% lipid and 12% storage protein on a fresh weight basis. The embryo contained 26% lipid and 15% protein. Both lipid and protein reserves were depleted constantly following imbibition. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble and insoluble protein fractions showed a 60 kDa protein that was representative of crystalloid‐like proteins. These crystalloid‐like proteins comprised 85% of the insoluble protein storage reserves. A small number of insoluble storage proteins, including a 47 kDa protein, were distinct in that they were unaffected by 2‐mercaptoethanol treatment. The soluble fractions from both tissues were labelled with [35S]‐methionine, and incorporation was visualized by two‐dimensional electrophoresis. Proteins were found to belong to one of three categories, those synthesized constitutively (comprising the bulk of newly synthesized proteins), those synthesized during germination or those synthesized after radicle emergence. Accompanying seed reserve hydrolysis were developmental shifts in protein pattern and synthesis, suggesting the possibility that control of hydrolysis is at the level of enzyme accumulation.
Seasonal, diurnal and rehydration‐induced variation of pressure‐volume relationships in Pseudotsuga menziesii
Authors: Kubiske Mark E. , Abrams Marc D.
Published: May 2006

Seasonal and diurnal variation and rehydration effects of pressure‐volume parameters in Pseudotsuga menziesii (Mirb.) Franco from a plantation in central Pennsylvania, USA, were evaluated during May‐September, 1989. Predawn elastic modulus was lowest in overwintering and newly expanded shoots in May and June, respectively, whereas predawn osmotic potentials at full and zero turgor were lowest in May and in early September, following an August drought. Seasonal variation in predawn relative water content at zero turgor was highly correlated with increases and decreases in elastic modulus and osmotic potential. Diurnal osmotic adjustment resulted in nearly constant turgor pressure, despite decreases in bulk shoot water potential. Elastic modulus decreased diurnally on 1 August and increased on 3 September. Decreases in osmotic potential and/or elastic modulus on 24 June and 1 August lowered the relative water content at zero turgor. Plateaus in pressure‐volume data caused by excess apoplastic water, were present in 67% of naturally rehydrated shoots and in all of the shoots artificially rehydrated for 3, 6, 12 and 24 h, and they increased in volume with rehydration time. Plateaus represented 80–95% of the excess apoplastic water lost during pressure‐volume analysis. Correcting for plateaus via linear regression had no significant effect on osmotic potential at full turgor; however, uncorrected elastic modulus and relative water content at zero turgor were often significantly lower than the plateau‐corrected values, particularly in artificially rehydrated shoots. Plateau‐corrected osmotic potential at full turgor and osmotic potential at zero turgor were significantly higher in most artificially rehydrated shoots than in those naturally rehydrated as the result of loss of symplastic solutes. Corrected elastic modulus decreased following 12 and 24 h of rehydration and corrected relative water content at zero turgor increased in as little as 3 h of rehydration. These results indicate that seasonal and diurnal patterns of tissue‐water parameters in Pseudotsuga menziesii vary with plant phenology and drought conditions, and that the length of rehydration period is an important consideration for pressure‐volume studies.
Plantlet morphology and the regulation of net water loss in tissue‐cultured Douglas‐fir
Authors: Mohammed Gina H. , Vidaver William E.
Published: May 2006

Tissue‐culture plantlets of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] were highly susceptible to detrimental water loss upon removal from culture in vitro. Control of net water loss was related to shoot and root morphology. Relative water content after 3 h of atmospheric water stress was positively correlated to root number, root surface area, and the length of the longest root, and was inversely correlated to the ratio of needle surface area/root surface area. High relative water content apparently was a result of a higher rate of water uptake among plantlets with beneficial morphological features. It is recommended that, to improve the ability of a plantlet to withstand water stress during acclimatization, beneficial root system features be focused upon during plantlet production.
Direct and indirect effects of Cd2+on photosynthesis in sugar beet (Beta vulgaris)
Authors: Greger Maria , Ögren Erling
Published: May 2006

Sugar‐beet plants (Beta vulgarisL. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μMCdCl2to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μMCdCl2to the assay media. The photosynthetic properties were characterized by measurement of CO2fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO2‐dependent O2evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd2+impeded CO2fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd2+was applied through the culture medium the capacity for, and the maximal quantum yield of CO2assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd2+‐cultivated plants showed an increased rate of dark respiration.
Partial deglycosylation of an anionic isoperoxidase from peach seeds – effect on enzyme activity, stability and antigenicity
Authors: Tigier Horacio A. , Quesada Miguel A. , Heredia Antonio , Valpuesta Victoriano
Published: May 2006

An anionic isoperoxidase (EC 1.11.1.7) purified from peach seeds (Prunus persica L. Batsch cv. Merry) was partially deglycosylated by glycopeptidase F (EC 3.2.2.18) treatment. A 40% deglycosylation resulted in an activity loss of 50% when assayed with o‐dianisidine. 60% with guaiacol and 78% with 2,2′‐azino‐bis(3‐ethyl)benzethiozoline‐6‐sulfonic acid (ABTS) as substrate. The indole‐3‐acetic acid oxidase activity loss was close to 55%. The partially deglycosylated isoperoxidase also showed a higher Km value for H2O2 and higher values for Arrhenius activation energy and enthalpy of activation. There was a decrease in enzyme stability at 4°C after deglycosylation. Native and partially deglycosylated isoperoxidase reacted equally well in an enzyme‐linked immunosorbent assay (ELISA) with rabbit polyclonal antibodies raised against the native enzyme. The carbohydrate moiety of this peach seed isoperoxidase appears to be important for enzyme activity and stability.
Stimulation by 2,4‐dichlorophenoxyacetic acid of betacyanin accumulation in suspension cultures of Phytolacca americana
Authors: Sakuta Masaaki , Hirano Hiroshi , Komamine Atsushi
Published: May 2006

2,4‐Dichlorophenoxyacetic acid (2,4‐D) strongly promoted betacyanin accumulation in suspension cultures of Phytolacca americana L. The betacyanin accumulation attained a maximum at 5 μM 2,4‐D, when betacyanin content per cell reached 252% as compared to the control (2,4‐D free). 2,4‐D elevated the level of free tyrosine, which is the precursor of betacyanin. The addition of 1 mM tyrosine to the medium partially reversed the reduction of betacyanin accumulation caused by the removal of 2,4‐D. Tracer experiments using labelled tyrosine showed that 2,4‐D activated the biosynthetic pathway from tyrosine to betacyanin. These results indicate that a sufficient supply of tyrosine and the activation of biosynthesis of betacyanin from tyrosine by 2,4‐D elevate the level of betacyanin.
Comparison among the isozyme profiles associated with ethrel treatments of leaves, and with senescence and plum pox virus infection in Chenopodium foetidum
Authors: Visedo Guillermo , Fernández‐Piqueras José , García Juan A.
Published: May 2006

Changes in the isozyme profiles of peroxidases (POX, EC 1.11.1.7), glutamate oxaloacetate transaminase (GOT, EC 2.6.1.1) and esterases (EST, EC 3.1.1.1) have been studies in leaves of Chenopodium foetidum S. treated with ethrel. Different systems for administration of the ethrel led to different responses. In intact plants, treatment of the complete surface of leaves or local administration by pricking the leaves induced senescence and wilting as well as quick changes, characteristic of ageing, in the isozyme patterns of the treated leaves. Isolated leaves treated with ethrel in vitro also showed a senescence response, but this was followed by a necrosis that displayed an isozyme pattern highly similar to that of necrotic lesions induced by plum pox virus (PPV) infection. An accelerated senescence process seems to be involved in the induction of changes in the isozyme patterns of expression during the hypersensitive response of Chenopodium foetidum to PPV infection, and ethylene could participate in this process. However, other factors may also be required for necrotization.
Peroxidase isozyme analysis of factors involved in development of symptoms in Nicotiana clevelandii infected by plum pox virus
Authors: Visedo Guillermo , Fernández‐Piqueras José , García Juan A.
Published: May 2006

Isozyme profiles of peroxidases (POX, EC 1.11.1.7) have been determined in leaves at different developmental stages as well as in other tissues of Nicotiana clevelandii. Modifications of the POX profiles associated with infection by plum pox virus and their relationship to senescence and wounding have also been determined. Systemically infected leaves displaying symptoms of infection showed a pattern highly similar to that of old leaves. Extensive alterations in the POX profile were observed in the inoculated leaves, and both ageing and wounding seemed to contribute to these transformations. The isozyme profile of POX after ethrel treatments suggested that ethylene could be involved in the senescence reaction produced by the virus infection.
Developmental changes in tomato fruit composition in response to water deficit and salinity
Authors: Mitchell J. P. , Shennan C. , Grattan S. R.
Published: May 2006

Processing tomato (Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na2SO4/CaCl2) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (Ψ) and soluble solids content were determined throughout development. Fruit Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in Ψ of stressed fruits. Mineral ions (Na+, K+, Ca2+, Mg2+, Cl− and SO2‐4) contributed –0.31 MPa to Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K+ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit Ψ, but were independent of fruit K+. Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits.
Biosynthesis of cyclic carotenoids: Biochemistry and molecular genetics of the reaction sequence
Authors: Sandmann Gerhard
Published: May 2006

Cyclic carotenids are found in the photosynthetic apparatus of higher plants. The biosynthesis of these pigments has been under investigation for two decades. Especially with in vitro systems from chromoplasts and unicellular cynaobacteria. new information has been obtained on the enzymatic reactions in carotenogenesis. Very recently, progress in the identification and cloning of several genes from the carotenogenic pathway has been made with bacteria, cyanobacteria and fungi. The new developments in biochemistry and molecular biology of cyclic carotenoids are reviewed, and the consequences of the results obtained by molecular genetics on the general understanding of the biosynthetic pathway of carotenoids are discussed, especially the desaturation and isomerization reactions.
Current perspectives on plasmodesmata: structure and function
Authors: Beebe Dwight U. , Turgeon Robert
Published: May 2006

Recent studies on plasmodesmata have shown that these important intercellular passages for communication and transport are much more sophisticated in both structure and regulatory abilities than previously imagined. A complex, but not well understood, substructure has been revealed by a variety of increasingly reliable ultrastructural techniques. Proteinaceous particles are seen within the cytoplasmic sleeve surrounding the desmotubule. Dye‐coupling studies have provided experimental evidence for the physical pathway of solute movement, supporting conclusions about substructural dimensions within plasmodesmata drawn from the ultrastructural studies. Calcium has been identified as a major factor in the regulation of intercellular communication via plasmodesmata. Evidence from studies on virus movement through plasmodesmata suggests a direct interaction between virallycoded movement proteins and plasmodesmata in the systemic spread of many viruses. There is increasing evidence, albeit indirect, that in some plant species phloem loading may involve transport of photoassimilate entirely within the symplast from mesophyll cells to the sieve element‐companion cell complexes of minor veins.
Cytochemical and X‐ray microanalytical studies of calcium in the extending zone, particularly in the rhizodermis of Zea mays roots
Authors: Jaunin Françoise , Rouelle‐Rossier Viviane Boutinard , Hofer Rose‐Marie
Published: May 2006

Calcium was detected in CaCl (10 mM)‐pretreated roots of Zea mays L. (cv. LG 11) by means of electron probe X‐ray microanalysis with energy‐dispersive spectrometry (EDS) using embedded samples, fixed by the antimonate staining procedure. A high level of calcium was found where large amounts of antimonate precipitates were observed by light or transmission electron microscopy. In the elongation zone, after 20 h in humid air following a 2 h CaCl2 pretreatment, the level of calcium was higher in trichoblasts than in atrichoblasts. In these cells it was detected mainly in the walls and nucleus, and antimonate staining was observed in the walls. Abundant precipitates containing calcium were associated with the nucleus, vacuoles, mitochondria and endoplasmic reticulum of non‐differentiated cells, whereas they were confined to the walls of these cells just after the CaCl2 pretreatment. The involvement of calcium in the formation of root hairs is discussed.
GTP‐specific pyrophosphorylation of thiamin in dark‐grown soybean (Glycine max) seedling axes
Authors: Howle Patrick K. W. , Fites Roger C.
Published: May 2006

ATP:thiamin pyrophosphotransferase (TPT: EC 2.7.6.2) was purified 5 900‐fold from 48 h dark‐grown soybean [Glycine max (L.), Merr. cv. Ransom II] seedling axes. TPT activity was monitored during purification by measuring the formation of thiamin pyrophosphate (TPP) from [2‐14C]‐thiamin at optimal pH (7.3). Although other nucleoside triophosphates were active as pyrophosphate donors (apparent Kms from 21 to 138 mM), GTP was the preferred nucleotide with an apparent Km of 0.021 mM. TPT activity was extremely sensitive to TPP formation, suggesting product feedback inhibition of TPT activity in vivo. Sulfhydryl, H+ and Mg2+ concentrations, either independently or in concert, were found to affect TPT activity.
Effects of boron on growth of tomato cell suspensions
Authors: Seresinhe P. S. J. W. , Oertli J. J.
Published: May 2006

The effects of various B levels in the culture medium on the biomass production and B concentrations of cells were studied using tomato (Lycopersicon esculentum Mill. cv. Rodeo) cell suspensions in three separate experiments. In the initial study, no increase in cell biomass was observed after day 4 in the absence of B in the medium. These cells had lost their viability by day 6. Cells grown at a B level of 0.09 or 0.55 mM in the medium had the highest biomasses (doubled by day 6). Cells grown at 0.92 or 1.85 mM B had lower biomasses (doubled by day 8). In the other two studies, both under low (0.005–0.07 mM) and high (2.30–4.15 mM) concentrations of B in the media, there was only a slight increase in biomass and the cultures failed to double their biomasses even by day 10. Cells grown with 3.70 or 4.15 mM in the medium showed a black discolouration by day 6 and were no longer viable. Except in the high B study, the B concentrations in the cells did not vary after day 2. With increasing B levels in the medium, the B concentrations of cells were in near equilibrium with the media B. Due to increasing toxicity which may have altered the membrane properties of the cell, this relationship did not continue with B levels of 1.85 mM or higher. These results indicate that B enters the tomato cells through passive transport and that a passive equilibrium exists between B concentrations in the cells and in the media.
Water stress, carbon dioxide, and light effects on sucrosephosphate synthase activity in Phaseolus vulgaris
Authors: Vassey Terry L. , Quick W. Paul , Sharkey Thomas D. , Stitt Mark
Published: May 2006

The characteristics of sucrose‐phosphate synthase (SPS; EC 2.4.1.14) activity in leaves of Phaseolus vulgaris L. cv. Linden was studied in plants subjected to water stress and various CO2 and light treatments. When water was withheld for 3 days causing mild water stress (–0.9 MPa), the activity of SPS measured in crude extracts was reduced ca 50%. The effect of water stress was most evident when the enzyme was assayed with saturating amounts of its substrates fructose 6‐phosphate and UDP glucose. Placing a water‐stressed plant in an atmosphere containing 1% CO2 reversed the effect of water stress on SPS activity over 5 h even though the water stress was not relieved. Holding unstressed leaves in low CO2 partial pressure reduced the extractable activity of SPS. After 1 h of low CO2 treatment the effect of low CO2 could be reversed by 20 min of 5% CO2. However, after 24 h of low CO2 treatment, less SPS activity was recovered by the 20 min treatment. The cytosolic protein synthesis inhibitor cycloheximide prevented the slow recovery of SPS activity, but did not affect the rapid recovery of SPS. We conclude that the effect of water stress on SPS activity was a consequence of the inhibition of photosynthesis caused by stomatal closure. Responses of Phaseolus vulgaris SPS to light were similar to the response to low CO2 in that the effects were most pronounced under Vmax assay conditions. This is the first report of this type of light response of SPS in a dicotyledonous species.
Regulation of acid hydrolysis of sucrose in acid lime juice sac cells
Authors: Echeverria Ed
Published: May 2006

The sucrose content of acid lime [Citrus aurantifolia (Christm.) Swing.] juice tissue was measured at time 0 and at various times following incubation at 15.5, 26.6 and 37.7°C. The decline in sucrose content in fruit stored at 15.5°C paralleled the expected values for a sucrose solution at pH 2.1. At higher temperatures, the in vivo sucrose content decreased at significantly lower rates than the expected values. In fruit stored at 26.6 and 37.7°C, the vacuolar pH increased 0.11 and 0.23 units, respectively. When sucrose hydrolysis was recalculated at the increased vacuolar pH of juice cells stored at 26.6 and 37.7°C, the calculated values were similar to the measured values obtained in vivo. It is concluded that within the limits of the experimental conditions, the rates of sucrose acid hydrolysis are regulated by changes in the vacuolar H+ concentration.
Sodium and potassium relations of Spergularia marina following N and P deprivation: results of short‐term growth studies
Authors: Wickens Linda K. , Cheeseman John M.
Published: May 2006

In this, we consider the coordination of plant growth and ion acquisition, reporting the short‐term adjustments of growth and K+ and Na+ relations which follow when plants are subject to a sudden deprivation of N and P. The plant used for the experiments, Spergularia marina (L.) Grieseb., is a small coastal halophyte, and the growth medium was 0.2 × modified seawater. By considering nutrients whose availability has not been changed, we report on an aspect of organismal integration which has received little attention either experimentally or in mathematical models. The studies are limited to the first 60 h after N and P deprivation in order to consider changes that, if they are not primary responses, are not temporally remote, passive adjustments.

For growth analyses, plants were used approximately 30 days after germination and 16 days after transfer to solution culture. Random harvests were made at hourly invervals, and after 12 h, one‐half of the plants were transferred to cultures without N or P. Tissue analyses were used to calculate relative growth rates, relative accumulation rates and net uptake rates. For comparison, isotope uptake studies using 42K+ and 22Na+ were conducted at 12, 36 and 60 h after deprivation.

The effects on growth and biomass allocation were very rapid, detectable within 13 h. K+ transport also responded quickly, and from the beginning of the study, there was essentially no net translocation of K+ to the shoot. Isotope studies confirmed the responsiveness, with translocation reduced 33 and 90% after 12 and 36 h, respectively. Though Na+ adjustments were slower, they were coordinated with growth such that tissue concentrations in the N and P‐deprived plants were comparable to those in the controls. We conclude that N and C are insufficient elements on which to build mathematical models useful to environmental physiologists. At a minimum, the incorporation of K+ relations in growth models would both allow the development of the osmotic potential needed to drive cell expansion, and provide a means to probe –experimentally as well as mathematically – the coordinating mechanisms of plant growth and resource management.
Strongly reduced levels of endogenous abscisic acid in developing seeds of tomato mutant sitiens do not influence in vivo accumulation of dry matter and storage proteins
Authors: Groot Steven P. C. , van Yperen Ingrid I. , Karssen Cees M.
Published: May 2006

The role of endogenous abscisic acid (ABA) in seed development was studied with the use of the ABA‐deficient sitw (sitiens) mutant of tomato (Lycopersicon esculentum Mill. cv. Moneymaker). The sitw mutation causes a strong reduction of the endogenous ABA level in the developing seed. Reciprocal crosses of wild‐type and the sitw mutant show a dual origin of ABA. The genotype of the mother plant regulates the ABA content present in the testa, which shows a peak half‐way through seed development. The genotype of the embryo and endosperm is responsible for a second ABA fraction, present in these tissues. This second fraction reaches its peak during the second half of seed development. The strong reduction of endogenous ABA level in the developing sitw/sitw seed does not change the final fresh and dry weights of the seed nor the accumulation and composition of storage proteins.
Effect of phenolic compounds on abscisic acid‐induced stomatal movement: Structure – activity relationship
Authors: Purohit Sadhna , Laloraya Man Mohan , Bharti Sudhakar
Published: May 2006

Application of abscisic acid (ABA) brings about stomatal closure within 30 min in epidermal peels of Vicia faba. A number of phenolic compounds antagonise the effect of ABA. Derivatives of benzoic acid, cinnamic acid, coumarin and flavonoids have been studied in order to establish structure – activity relationship. Derivatives of benzoic acid reverse the ABA effects. Coumarin, esculetin and three hydro derivatives of cinnamic acid fail to show the anti‐ABA activity. Thus, the presence of parahydroxyl group and double bond in the side chain is necessary for anti‐ABA activity.
Isolation and sugar uptake characteristics of protoplasts from maize endosperm suspension cultures
Authors: Felker Frederick C. , Thomas Paul A. , Crawford C. Gerald
Published: May 2006

The isolation and sugar uptake characteristics of protoplasts from maize (Zea mays L.) endosperm‐derived suspension cultures are described. In contrast with protoplasts from intact developing endosperm, which by virtue of their large size and high starch content are too fragile for sugar uptake experiments, suspension cultures yielded protoplasts capable of withstanding the necessary handling and centrifugations. Intactness of the protoplasts was demonstrated by dye exclusion or accumulation and latency of malate dehydrogenase activity. Uptake of radioactivity from [3H]‐inulin did not increase with time, but that from [14C]‐sugars increased over a wide range of external concentrations. Kinetics of fructose, glucose and sucrose uptake were biphasic, and the saturable components of uptake were eliminated by p‐chloromercuribenzene sulfonate (PCMBS). Rates of uptake of sucrose and 1′‐fluorosucrose were similar, confirming that hydrolysis by cell wall invertase contributes to sucrose uptake by the suspension cultures. The isolation of protoplasts from this tissue source will enable experimental access to plasma membrane sugar carriers which may exist in the intact maize endosperm.
Translocation and metabolism of glycine betaine in nodulated alfalfa plants subjected to salt stress
Authors: Pocard Jean‐Alain , Bernard Théophile , Le Rudulier Daniel
Published: May 2006

The fate of radioactive glycine betaine was investigated in 31‐day‐old alfalfa (Medicago sativa L. cv Europe) plants nodulated by Rhizobium meliloti 102 F 34. Radioactive [methyl‐14C]‐ or [1,2‐14C]glycine betaine was fed for 6 h to plants subjected or not to stress by 0.2 M NaCl. A 36% decrease in glycine betaine uptake was observed in salinized plants. No loss of radioactivity in the gas phase or the growth medium was ever observed from either stressed or unstressed plants, even after a 4‐day chase period. Glycine betaine catabolism was negligible in shoots of both control and salinized plants, but it was important in roots and even more significant in nodules of unstressed plants. In unstressed nodules, 52% of the labelled betaine was metabolized after 4 days, and the half‐life of glycine betaine was estimated at ca 4 days. On the contrary, catabolism was dramatically reduced in stressed roots and, particularly, nodules in which the half‐life of glycine betaine increased to at least 16 days. Analysis of the redistribution of radioactivity among plant organs during the chase period shows that glycine betaine was translocated from the roots to the nodules of salinized plants, so that during this period salinization resulted in a 91% increase in nodule radioactivity, whereas a 34% decrease was observed in control plants. Altogether, reduced catabolism and increased translocation of glycine betaine to stressed nodules favored its accumulation in these organs. The high level of glycine betaine might contribute to maintain a better water status in the nodule and, thus, protect the nitrogen fixation activity against the deleterious effects of elevated osmolarity in the nutrient solution.
Rejuvenation of a 100‐year‐old Sequoiadendron giganteum through in vitro meristem culture. I. Organogenic and morphological arguments
Authors: Monteuuis Olivier
Published: May 2006

True‐to‐type cloning of mature trees, especially when they do not sprout from their base, remains problematic. Special attention is focused on the shoot apical meristem, since it is an obvious choice for vegetative propagation. In Sequoiadendron giganteum a meristem removed during budbreak from a 100‐year‐old tree regenerated a truly rejuvenated line that exhibited the same juvenile characters as the juvenile clone used as control, especially in regard to morphological traits and organogenic capacity, and as manifested by the ability to produce adventitious roots in vitro. This rejuvenation has been maintained for 3 years in both in vitro and ex vitro conditions. This result is discussed in terms of inhibitory correlative systems acting within the donor tree in situ, especially as concerns miniaturization of the explant.
Rejuvenation of a 100‐year‐old Sequoiadendron giganteum through in vitro meristem culture. II. Biochemical arguments
Authors: Bon Marie‐Claude , Monteuuis Olivier
Published: May 2006

The phenomena of phase change and rejuvenation are characterized mainly by morphological and physiological criteria. Thus far, biochemical assessments have been relatively limited. In Sequoiadendron giganteum, techniques of sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and miniaturized two‐dimensional gel electrophoresis were applied to a meristem‐derived line from a 100‐year‐old tree to attest the basic origin of the resulting rejuvenation observed from morphological and organogenic standpoints in vitro as well as after acclimation in outdoor conditions. The membrane‐associated protein J16, which characterizes the juvenile status was detected in both the juvenile control and the rejuvenated line, while in the original mature form it was totally lacking. In addition, two‐dimensional electrophoretic analysis of protein patterns of single meristems belonging to the mature and the rejuvenated form suggested that rejuvenation might involve a drastic modification of the protein content within the meristem itself.
Changes in the metabolism of nucleic acids during the growth and senescence of tobacco callus
Authors: Tan Bao‐Cai , Liang Hou‐Guo
Published: May 2006

Changes in DNA and RNA metabolism, DNA composition and RNA species in callus of tobacco (Nicotiana rustica L. cv. Gansu Yellow Flower) were investigated during the growth and senescence. DNA and RNA contents remained almost unchanged during the callus growth period, but started to decrease synchronously at the time that callus senescence was initiated. Synthesis of DNA and RNA, as measured by incorporation of [3H]‐labelled precursor, increased during the growth period and did not decrease until late in senescence. The activities of DNase and RNase (pH 4.5) increased during the early senescence period in accordance with the decrease in the levels of DNA and RNA, but appeared to decrease during late senescence. These results suggest that the decrease in the levels of DNA and RNA in senescing tobacco callus may stem from the increase in the hydrolytic activities of DNase and RNase (pH 4.5) in the early stage of senescence, and that the slowdown of synthesis in the late senescence period may also be a cause. DNA and RNA electrophoresis showed that a low‐molecular‐weight satellite DNA band disappeared after the onset of senescence and that the nuclear main band DNA gradually decreased, whereas the high‐molecular‐weight satellite DNA seemed to undergo no significant changes during the senescence period tested. Of the RNA species, 4–5S RNA was far more susceptible to damage during senescence than 25S and 18S rRNA. This suggests different susceptibilities of different DNA and RNA components to damage during the senescence of tobacco callus or alternatively a highly sequenced degradation of DNA and RNA molecules.
The role of light reactions in the regulation of anthocyanin synthesis in Petunia corollas
Authors: Weiss David , Halevy Abraham H.
Published: May 2006

The role of light reactions in anthocyanin synthesis was studied in both attached and detached corollas of Petunia hybrida (cv. Hit Parade Rosa), the latter grown in vitro in media containing 150 mM sucrose and 50 μM gibberellic acid (GA). Light was essential for the synthesis of anthocyanin in detached corollas, whereas in intact corollas its effect was only to enhance anthocyanin synthesis. Continuous white light at a fluence rate of at least 20 μmol m−2 s−1 was needed for anthocyanin synthesis in detached corollas. Blue light was more effective than red or green, and far‐red was ineffective. Pigmentation of detached corollas exposed to light was inhibited by the photosynthetic inhibitor 3‐(4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU). The chloroplast uncoupler NH4Cl did not affect anthocyanin synthesis, which was, however, inhibited by the blocking of ATP synthesis in both the chloroplast and the mitochondria by dicyclohexylcarbodiimide (DCCD). Sucrose uptake in vitro was inhibited by DCMU and by darkness, and was promoted equally by blue and red light. The activity of phenylalanine ammonialyase (EC 4.3.1.5) was inhibited in detached corollas grown in the dark or in the light in the presence of DCMU. The activity of chalcone isomerase (EC 5.5.1.6) was not affected by light. These findings suggest that at least two different light reactions are involved in the regulation of anthocyanin synthesis in petunia corollas, namely the high irradiance reaction (HIR) and photosynthesis.