bluuebunny/crossref_metadata_2025 huggingface dataset:
Permeability of the Chara cell membrane for ethylene glycol, glycerol, meso‐erythritol, xylitol and mannitol
Authors: Kiyosawa Keitaro
Published: May 2006

The permeability of internodal cells of Chara australis R. Brown for polyol molecules was determined by using a turgor balance to measure the increase in the osmotic pressure of an internodal cell incubated in artificial pond water containing one of the polyol compounds tested. The permeabilities for ethylene glycol, glycerol, meso‐erythritol, xylitol and mannitol were (4. 39 ± 0. 52) × 10−9, (1. 49 ± 0. 40) × 1010, (4. 92 ± 0. 27) × 10−10 (9. 9 ± 3. 4) × 1011 and (7. 6 ± 4. 8) × 10−12 m s−3, respectively. The permeability for glycerol was slightly smaller than that for meso‐erythritol, whose molecular weight is larger than that of glycerol in this homologous series: but the reason for this is not clear.
Polyamine levels in pollinated and auxin‐induced fruit of tomato (Lycopersicon esculentum) during development
Authors: Egea‐Cortines Marcos , Coben Ephraim , Arad Shoshana (Malis) , Bagni Nello , Mizrahi Yosef
Published: May 2006

The changes taking place during fruit development in the concentration of the 3 polyamine fractions, i.e. free, perchloric acid‐soluble conjugates and perchloric acid‐insoluble bound polyamines, were analyzed in tomato fruits (Lycopersicon esculentum Mill, cv. F121) induced to set by either pollination or auxin application. Before the onset of cell division, total polyamines were 50% higher in auxin‐treated fruits than in pollinated ones, most of the polyamines being found as perchloric acid‐soluble conjugates in both fruit set treatments. At the onset the level of polyamines in both fruit types was 100 times higher than during cell expansion or ripening. The highest polyamine found during cell division was perchloric acid‐soluble conjugated spermidine in both fruit set treatments. After cell division, polyamine concentration was similar in both fruit set treatments. The concentration of polyamines in the jelly was similar in pollinated and auxin‐induced fruits during cell expansion but not during ripening. At the onset of ripening there was an increase of one order of magnitude in the concentration of perchloric acid‐insoluble bound putrescine in the jelly of pollinated fruits. Polyamines were more than 5‐fold higher in unpollinated ovaries than in fruits induced to set by either pollination or auxins. It is suggested that pollinated and parthenocarpic fruits differ in their polyamine metabolism during the initial stages of development, but not after cell division. It is also suggested that polyamines undergo rapid turnover during cell division. Perchloric acid‐insoluble bound putrescine might play a role in seed formation in tomatoes.
Drought resistance of mycorrhizal pepper plants independent of leaf P concentration ‐ response in gas exchange and water relations
Authors: Davies F. T. , Potter J. R. , Linuerman R. G.
Published: May 2006

Pepper (Capsicum annuum L.) plants with and without the VA‐mycorrhizal fungus Ghmus deserticola Trappe. Bloss and Menge (VAM and NVAM. respectively), were drought acclimated by four drought cycles (DA) or kept well watered (NDA). All plants were then subjected to an additional drought followed by a 3‐day irrigation recovery period. Measurements of water relations, gas exchange and carbohydrates were made at selected intervals throughout the drought cycles and recovery. To equalize growth and avoid higher P in VAM plants. NVAM plants received higher P fertilization. Consequently, similar transpirational surface and shoot mass were achieved in all treatments, but NVAM had a higher tissue P concentration than VAM plants. Plants that were either VAM or DA, but especially the VAM‐DA plants, tended to be high in net photosynthetic flux (A), A per unit of tissue P concentration (A/P), stomatal conductance (g) or leaf turgor (Ψp) during high environmental stress or recovery from stress. During this time, NVAM‐NDA plants had low A. A/P and leaf chlorophyll, but high soluble carbohydrate concentrations in their leaves. All VAM and DA plants had some osmotic adjustment compared to the NVAM‐NDA plants, but VAM‐DA plants had the most. Osmotic adjustment was not due to accumulation of soluble carbohydrate. The high turgor, A and g in the VAM‐DA plants during and following environmental stress indicated superior drought resistance of these plants; however, osmotic adjustment was only apparent during recovery and cannot account for the observed drought resistance during environmental stress. Drought resistance of VAM‐DA plants was not attributable to high leaf P concentration or confounded by differences in plant transpirational surface.
Cellular responses of two rapid‐cycling Brassica species, B. napus and B. carinata, to seawater salinity
Authors: He Tie , Cramer Grant R.
Published: May 2006

Cellular responses of two rapid‐cycling Brassica species. B. napus and B. carinata, to seawater salinity were characterized to determine whether callus showed a tolerance similar to that of whole plants. Callus was initiated from the leaves of 7‐day‐old seedlings of B. napus and B. carinata and then subcultured with two different levels of seawater salinity (2.3 and 5.2 g l−1 Instant Ocean. Aquarium Systems, Inc. Mentor. OH, USA) for 14 days. Callus growth of both species was reduced by seawater salinity. Based on the percentage of the reduction in the relative fresh weight gain. B. napus was more salt‐tolerant than B. carinata. consistent with the response of whole plants of the same species to seawater salinity. Seawater salinity caused changes in the concentrations of Na, K. Ca, Mg and Cl in both B. napus and B. carinata. The growth expressed as the percentage of control was significantly (P = 0.05) positively correlated with the concentration of Ca. and K/Na and Ca/Na ratios. It was also negatively correlated (P= 0.01) with the concentrations of Na. Cl and Mg. In comparison with B. carinala. the salt‐tolerant species, B. napus, showed a small reduction in the concentrations of Ca and K in the salt‐stressed plants relative to the control.
Possible role of adenylates in the engagement of the cyanideresistant pathway in nutrient‐starved Catharanthus roseus Cells
Authors: Hoefnagel Marcel H. N. , Van Iren Frank , Libbenga Kees R. , Van der Plas Linus H. W.
Published: May 2006

In Cathuranthus roseus (L.) G. Don cells the cyanide‐resistant pathway is engaged after phosphate or nitrogen starvation. Re‐addition of these nutrients disengaged it again. Re‐addition of phosphate leads to a transient disengagement which becomes only permanent after a second addition of phosphate. Disengagement after re‐addition of nitrogen is slow: it takes 9 days before the activity has disappeared. In this system the mechanism of engagement of the cyanide‐resistant pathway was studied. Addition of phosphate to phosphate‐starved cells induced cell division within 24 h. The disengagement of the cyanide‐resistant pathway was probably only an indirect effect of phosphate because the cellular P, content, which increased rapidly after addition, was low again before the cyanide‐resistant pathway was disengaged. A better correlation was observed between high ADP and adenylate content of the cells and disengagement of the cyanide‐resistant pathway. In addition it appeared that the engagement of the cyanide‐resistant pathway was not the result of a limited carrier capacity of the cytochrome pathway. It is tentatively concluded that the engagement of the cyanide‐resistant pathway in phosphate‐starved cells was the result of a limited adenylate content.

After nitrogen addition to N‐starved cells, it took 5 days until the first growth occurred. Before the cyanide‐resistant pathway was disengaged, its activity increased with the increased respiration rate which preceded growth. Within 72 h a higher ADP content was observed, which was still high after 10 days. The stimulation of the cytochrome pathway by uncoupler was small and more or less the same with and without added nitrogen, as long as the cyanide‐resistant pathway was engaged. After disengagement the stimulation by uncoupler was significantly larger. It is suggested that the engagement during N‐starvation was the result of a limited carrier capacity of the cytochrome pathway.

Stimulation of the metabolism by re‐addition of phosphate, nitrogen or sucrose resulted in a rapid increase in the levels of uracil nucleotides and uridine diphosphoglucose (UDPG) which are involved in sucrose metabolism.
Effect of light and gibberellic acid on photosynthesis during leaf senescence of alstroemeria cut flowers.
Authors: Jordi W. , Pot C. S. , Stoopen G. M. , Schapendonk A. H. C. M.
Published: May 2006

The functioning of the photosynthetic apparatus during leaf senescence was investigated in alstroemeria cut flowers by a combination of gas‐exchange measurements and analysis of in vivo chlorophyll fluorescence. Chlorophyll loss in leaves of alstroemeria cut flowers is delayed by light and by a treatment of the cut flowers with gibberellic acid (GA3). The maximal photosynthesis of the leaves was approximately 6 μmol CO2 m−2 s−1 at I 350 μmol m−2 s−1 (PAR) which is relatively low for intact C3 leaves. Qualitatively the gas‐exchange rates followed the decline in chlorophyll content for the various treatments, i.e. light and GA3‐treatment delayed the decline in photosynthetic rates. However, when chlorophyll loss could not yet be observed in the leaves, photosynthetic rates were already strongly decreased. In vivo fluorescence measurements revealed that the decrease in CO2 uptake is (partly) due to a decreased electron flow through photosystem II. Furthermore, analysis of the fluorescence data showed a high nonphotochemical quenching under all experimental conditions, indicating that the consumption of reducing power in the Calvin cycle is very low. The chlorophyll, remaining after 9 days incubation of leaves with GA3 in the dark should be considered as a ‘cosmetic’ pigment without any function in the supply of assimilates to the flowers.
Cytokinins modulate stress response genes in isopentenyl transferase‐transfornied Nicotiana plumbaginifolia plants
Authors: Harding S. A. , Smigocki A. C.
Published: May 2006

The effects of transiently elevated cytokinin levels on gene expression following stress were examined in transgenic Nicotiana plumbaginifolia plants. Plants were transformed with a bacterial gene encoding isopentenyl transferase (ipt) cloned behind the heat shock (HS) protein 70 promoter from Drosophila melanogaster. Following a l‐h, 45°C HS of whole plants, the ipt transcript levels in leaves increased 30‐ to 40‐fold. Analysis of in vitro translation products of leaf messenger RNA showed rapid isopentenyl transferase‐dependent changes in gene expression. A subset comprising 1 to 2% of resolvable translation products was specifically up‐regulated in heat shock ipt‐inducible (HS‐ipt) plants. Several cDNA clones were isolated which correspond to mRNAs that are up‐regulated 2‐ to 4‐fold in HS‐ipt plants. Two of the cDNAs encode stress‐related polypeptides. one a member of a class of small heat shock polypeptides (HSP) and the other, a wound‐inducible glycine‐rich protein. Benzylaminopurine feeding experiments show that the HSP transcripts are up‐regulated by other treatments including watering but that cytokinins strongly accelerate or amplify the response. These data are the first to show altered modulation of stress‐induced genes in intact plants transformed with the cytokinin biosynthesis gene ipt.
Turgor‐dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points
Authors: Patrick J. W.
Published: May 2006

Key physiological characteristics of turgor‐dependent efflux of photosynthates were examined using excised coats and cotyledons of developing Phaseolus vulgaris (cv. Redland Poineer) and Vicia faba (cv. Coles Prolific) seed during the linear phase of seed fill. Exposure to solutions of high osmotic potential inhibited net uptake of [14C]sucrose by cotyledons at developmental stages less than 60% of their final dry weight. The effect could not be fully reversed by transferring cotyledons to solutions set at lower osmotic potentials. The inhibition became apparent at osmotic potentials that were higher than those that caused stimulation of efflux from seed coats. Net [14C]sucrose uptake by cotyledons at more advanced stages of development was unaffected by external osmotic potential. Specified tissue layers were removed from seed coats by pretreatment with pectinase. Efflux studies with the pectinase‐modified coats of Phaseolus and Vicia seed demonstrated that the cellular site of turgordependent efflux was the ground parenchyma and thin‐wall parenchyma transfer cells, respectively. Coats subjected to long‐term (hours) incubations, under hypo‐osmotic conditions, exhibited the capacity for turgor regulation. This was mediated by turgor‐dependent efflux of solutes. The solutes exchanged were of nutritional significance to the developing embryo. The relationship between efflux and coat turgor was characterised by a turgor‐independent phase at low turgors. Once turgor exceeded a minimal value (set point), efflux increased in proportion to the magnitude of the turgor deviation (error signal) from the set point. For coats of sink‐limited seed of Vicia and Phaseolus, efflux exhibited apparent saturation at turgors above 0.25 and 0.5 MPa respectively. The putative turgor set point and slope of the turgor‐dependent component of efflux varied with seed development, the prevailing source/sink ratio and genetic differences in seed growth rate. The nature of these kinetic variations was compatible with the competitive ability of the seed. A turgor homeostat model is proposed that incorporates the observed functional attributes of turgor‐dependent efflux. Operationally, the model provides a mechanistic basis for the integration of assimilate demand by the cotyledons with assimilate import into and unloading from the seed coat.
Characterization of the protein kinase activity in beet root plasma membranes
Authors: Baizabal‐Aguirre VíActor M. , González de la Vara Luis E.
Published: May 2006

Two protein kinase activities were found in plasma membrane‐enriched preparations from red beet (Beta vulgarix L.). The kinases in these preparations produced the phosphorylation of several membrane polypeptides. These kinases also phosphorylated histone III‐S and casein. The activities of two different kinases could be distinguished: one was half‐maximally stimulated by 1 μM free Ca2+ phosphorylated histone III‐S better than casein, showed half‐maximal activity at an ATP concentration of 0.071 mM. had an optimum pH of 7, and was poorly inhibited by GTP, CTP or UTP. Another, much lower, kinase activity that phosphorylated casein was also observed; it was Ca2+ independent, showed half‐maximal activity at ATP concentrations of 0.017 and 0.287 mM, exhibited a broad pH optimum about pH 7 and was inhibited by GTP, CTP, UTP or GDP to a greater extent than the calcium‐stimulated activity. When plasma membrane proteins were solubilized with lysophosphatidyicholine and treated with [γ‐32P]ATP at several dilutions, a 125‐kDa polypeptide was autophosphorylated in the absence of Ca2+, while 77‐, 71‐ and 65‐kDa polypeptides were autophosphorylated in its presence. Autophosphorylation in gels after electrophoresis showed a Ca2+‐stimulated phosphoprotein band at 64 kDa.
Implication of persimmon fruit hemicellulose metabolism in the softening process. Importance of xyloglucan endotransglycosylase
Authors: Cutillas‐Iturralde Antonio , Zarra Ignacio , Fry Stephen C. , Lorences Ester P.
Published: May 2006

Hemicellulosic polysaccharides from persimmon fruit (Diospyros kaki L.) pericarp were extracted from depectinated cell walls with 0.5, 1 and 4 M KOH at different stages of development: (I) maximal growth corresponding to the first sigmoidal growth phase; (II) cessation of growth corresponding to the lag between the first and the second sigmoidal phases; (III) maximal growth corresponding to the second sigmoidal phase; and (IV) cessation of growth when the fruit had reached its maximum size and the change in colour (green to red) had taken place. During fruit development the amount of total hemicelluloses per unit dry mass cell wall decreased twofold. Xyloglucan was present in the three hemicellulosic fractions, and also decreased with fruit age, although its amount relative to other hemicelluloses increased. The amount of xyloglucan was especially high in the hemicelluloses extracted with 4 M KOH, representing more than 50% at stages III and IV. The average molecular mass of xyloglucan increased from stage I through stage II (0.5 M hemicellulosic fraction) or through stage III (I and 4 M hemicellulosic fractions) and decreased after that. The xyloglucan endotransglycosylase (XET: EC 2.4.1.‐) activity was measured as the incorporation of [3H]XXXGol (reduced xyloglucan heptasaccharide labelled at position 1 of the glucitol moiety) into partially purified persimmon fruit xyloglucan. XET specific activity increased greatly between stages I and II. The importance of this enzyme during fruit ripening is discussed.
Increasing growth temperature reduces the stimulatory effect of elevated CO2 on photosynthesis or biomass in two perennial species
Authors: Ziska Lewis H. , Bunce James A.
Published: May 2006

We examined how anticipated changes in CO2 concentration and temperature interacted to alter plant growth, harvest characteristics and photosynthesis in two cold‐adapted herbaceous perennials, alfalfa (Medicago sativa L. cv. Arc) and orchard grass (Dactylis glomerata L. cv. Potomac). Plants were grown at two CO2 concentrations (362 [ambient] and 717 [elevated] μmol mol−1 CO2) and four constant day/night temperatures of 15, 20, 25 and 30°C in controlled environmental chambers. Elevated CO2 significantly increased total plant biomass and protein over a wide range of temperatures in both species. Stimulation of photosynthetic rate, however, was eliminated at the highest growth temperature in M. sativa and relative stimulation of plant biomass and protein at high CO2 declined as temperature increased in both species. Lack of a synergistic effect between temperature and CO2 was unexpected since elevated CO2 reduces the amount of carbon lost via photorespiration and photorespiration increases with temperature. Differences between anticipated stimulatory effects of CO2 and temperature and whole plant single and leaf measurements are discussed. Data from this study suggest that stimulatory effects of atmospheric CO2 on growth and photosynthesis may decline with anticipated increases in global temperature, limiting the degree of carbon storage in these two perennial species.
Changes in protein ubiquitination and the expression of ubiquitin‐encoding transcripts in daylily petals during floral development and senescence
Authors: Courtney S. E. , Rider C. C. , Stead A. D.
Published: May 2006

The occurrence of ubiquitin‐protein conjugates and the expression of ubiquitin genes during floral development and senescence of Hemerocallis fulva (daylily) is reported. Daylily petal proteins were extracted at various stages of floral development and the abundance of ubiquitinated proteins determined by western blotting with affinity purified antibody to ubiquitin. Up to 100 ubiquitin conjugates in the molecular mass range 22–220 kDa were detected within the petals during bud development through to flower opening. The intensity of several of the ubiquitinated protein bands changed markedly during flower opening and/or senescence. Ubiquitinated proteins of apparent molecular masses 160, 105 and 29 kDa were intense in the daylily bud, but rapidly disappeared after flower opening, whereas ubiquitinated proteins of apparent molecular masses 26 and 15.5 kDa increased in intensity as the flowers senesced. Treatment of daylily buds with a 1‐h pulse of cycloheximide as the flowers commenced opening prevented these changes; this treatment also delayed the onset of visual signs of senescence by 5–6 days. Analysis by northern blotting demonstrated differential expression of ubiquitin transcripts by the multi‐ubiquitin gene family during floral development and senescence. Inhibition of petal senescence by treatment with cycloheximide resulted in the accumulation of several ubiquitin‐encoding transcripts and the down‐regulation of a 3.4 kb transcript. Overall, these studies suggest that ubiquitin is involved in the degradation of many petal proteins during floral development and senescence and that, during senescence, this selective degradation is occurring against a background of net proteolysis.
Genetic study of resistance to inhibitory effects of UV radiation in rice (Oryza sativa)
Authors: Sato Tadashi , Kang Hye Sook , Kumagai Tadashi
Published: May 2006

Genetic analysis of resistance to the inhibitory effects of UV radiation on growth of rice (Oryza sativa L.) cultivars was carried out. Some experimental plants were grown in visible radiation supplemented with UV radiation containing a large amount of UV‐B and a small amount of UV‐C in a phytotron, while others were grown without UV radiation. The degree of resistance to UV radiation was estimated in terms of the degree of reduction caused by supplemental UV radiation in the fresh weight of the aboveground plant parts and the chlorophyll content per unit fresh weight. Fresh weight and chlorophyll content in F2 plants generated by reciprocally crossing cv. Sasanishiki, a cultivar more resistant to UV radiation, and Norin 1, a cultivar less resistant to such radiation exhibited a normal frequency distribution. The heritabilities of these two properties in F2 plants were low under conditions of non‐supplemental UV radiation. Under elevated UV radiation, the F2 population shifted to the lower range of fresh weight and chlorophyll content, and the means were close to those of Norin 1. The heritabilities of these two properties were the same in the reciprocal crosses, indicating that maternal inheritance was not involved. Inheritance of chlorophyll content per unit fresh weight was further determined in F3 lines generated by self‐fertilizing F2 plants of Sasanishiki and Norin 1. The results showed that the F3 population was segregated into three genotypes, namely, resistant homozygotes, segregated heterozygotes and sensitive homozygotes, with a ratio of 1:65:16.

It was thus evident that the resistance to the inhibitory effect of elevated UV radiation in these rice plants was controlled by recessive polygenes.
Stem extension‐growth responses to blue light require Pfr in tomato seedlings but are not reduced by the low phytochrome levels of the aurea mutant
Authors: Casal J. J.
Published: May 2006

The effects of blue light (B) on stem extension growth were investigated in wild‐type (WT) and aurea (au) mutant seedlings of tomato. The au mutant has reduced phytochrome levels. Etiolated seedlings were grown under background red light (R) or far‐red light (FR) with or without B. Hypocotyl growth was inhibited by B added to R but not by B added to FR, both in WT and au seedlings. The levels of B and/or R reaching the stem of fully de‐etiolated seedlings grown in a glasshouse were reduced by means of collars around it. Both in WT and au‐mutant seedlings the responses to B were larger at high than at low R/FR quantum ratios. In etiolated and light‐grown au seedlings, changing the levels of phytochrome‐absorbable radiation did not cause the same effect as changing B levels, indicating the action of specific BL/UV‐A photoreceptor(s) (BAP). The responses to B are reduced by the low calculated levels of Pfr established by light treatments but not by the low levels of phytochrome present in the au mutant. The au mutant appears to be deficient in a phytochrome pool that is not essential for the interdependent co‐action observed between phytochrome and BAP in the control of stem extension growth in tomato.
Influence of irradiance on in vitro growth and proliferation of Vaccinium corymbosum (highbush blueberry) and subsequent rooting in vivo
Authors: Noè Nicola , Eccher Tommaso
Published: May 2006

The effects of light on in vitro proliferation and subsequent in vivo rooting and acclimatisation of Vaccinium corymbosum were investigated. The shoots were exposed in vitro to different irradiances (total radiation ranging from 55 to 240 μmol m−2 s−1) for 7 to 60 days. In vitro growth and proliferation and the possible consequences on in vivo rooting were observed.

As compared to the control treatment (55 μmol m−2 s−1), higher irradiances improved proliferation and rooting ratios only with short applications (7 days). Short but high (210 μmol m−2 s−1) exposures applied at the end of the proliferation phase increased in vivo growth and rooting of the shoots. The shoots treated with strong light for longer times (14 and 28 days) showed both inhibition of growth and red colour of leaves and sprouts, and were less vigorous when transferred in vivo.
The stimulating effect of a cold dark‐pretreatment on the etioplast/chloroplast transformation of angiosperms. III. Involvement of the excision factor and of cold‐retarded aging processes?
Authors: Schönbohm Ekkehard , Babbel Ute , Czeska‐Werner Ulrike , Zellner Sebastian , Zwicker Hans‐Georg
Published: May 2006

Our question is whether the stimulating effect of a cold dark‐pretreatment on the process of de‐etiolation in primary leaves of wheat seedlings under subsequent continuous white light is essentially mediated by the retarding effect of highly lowered temperatures on the following processes: aging and/or senescence, realization of the so‐called excision factor in detached leaves, decrease of the cytokinin level in detached leaves. The strong stimulating effect of a cold dark‐preatreatment remains inspite of progressive aging in parts of the leaves and a strong decrease of the capability of chlorophyll accumulation in detached in contrast to attached leaves. The strong stimulatory effect of a cold dark‐pretreatment is not diminished by application of cytokinin or gibberellic acid. The stimulating effect of a cold dark‐pretreatment is detectable over several days under continuous light, but it is lost during a warm dark‐phase of a few hours duration between the cold dark‐pretreatment and the white light phase.
Regulation by light of chlorophyll synthesis in the cotyledons of Scots pine (Pinus sylvestris) seedlings
Authors: Drumm‐Herrel Helga , Mohr Hans
Published: May 2006

Seedlings of gymnosperms, unlike angiosperms, synthesize chlorophyll(ide) (Chl) in darkness (D). In Scots pine cotyledons (Pinus sylvestris L.) Chl accumulation ceases in D at a low level but Chl accumulation is strongly increased by light, red light (R) being more effective than blue light (B), whereas in Pinus maritima Chi synthesis is almost light‐independent. In Scots pine the capacity to form Chl can be increased by R pulses, fully reversible by far‐red light, demonstrating the involvement of phytochrome. However, when B‐ or R–grown seedlings were transferred to D, Chl accumulation stopped immediately irrespective of the level of Pfr (far‐red light absorbing form of phytochrome), indicating that the conversion of protochlorophyllide (PChl) is light‐dependent. Dose response curves in R and B and simultaneous irradiation with R and B show that R and B are perceived by separate photoreceptors. The immunodetected NADPH‐dependent protochlorophyllide oxidoreductase (POR, EC 1.6.99.1), assumed to regulate light‐dependent Chl synthesis in angiosperms, is not correlated with the capacity of gymnosperm Chi accumulation in darkness. While two FOR bands could be separated in extracts from dark grown material (38 and 36 kDa) of Pinus sylvestris and P. maritima, only the 38 kDa band disappeared consistently in the light. However. the significance of the more light resistant 36 kDa band for chlorophyll synthesis remains unclear as well.
Phytochrome‐mediated closure of Albizzia lophantha leaflets as affected by sorbitol, mannitol and fusicoccin
Authors: Moysset Luisa , Llambrich Esther , Simón Esther
Published: May 2006

The effect of sorbitol and mannitol and their interaction with the effect of fusiccocin has been investigated in phytochrome‐mediated nyctinastic closure of Albizzia lophantha leaflets. Treatments were commenced 2 h into the photoperiod. Pairs of leaflets were excised, floated on test solutions, and transferred to darkness immediately after red or far red irradiation. Leaflet angles were measured in darkness for 3 h. Fusicoccin (1 to 100 μM) inhibited nyctinastic closure and enhanced reopening in the presence of Pft (far‐red‐absorbing form of phytochrome). Fusicoccin effects on far red treated leaflets were not constant and whichever fusicoccin concentration was applied, the effects were small. These results confirm the role of the plasma membrane proton pump in extensor cells during opening. Sorbitol and mannitol (25–100 mM) increased nyctinastic closure for about 2 h and then enhanced reopening in the presence of Pfr. When sugar alcohols were applied together with fusicoccin, sorbitol and mannitol enhanced the fusicoccin inhibition of closure and a marked synergistic effect was observed. These results indicate that both fusiccocin and the reduction of external osmotic potential caused by sorbitol and mannitol supply may stimulate the activity of the extensor H+ pump promoting the reopening.
Phosphatidylinositol metabolism in low temperature‐affected winter oilseed rape leaves
Authors: SmoleńAska‐Sym Gabriela , Kacperska Alina
Published: May 2006

The aim of the present experiments was to find out whether low temperature may put into operation the phospholipase C‐inositolphospholipid signaling cascade in tissues of chilling‐tolerant plants. Therefore, the effects of a short and a rapid exposure of non‐acclimated (NA) and cold‐acclimated (CA) winter oilseed rape (Brassica napus L. var. oleifera L. cv. Jantar) leaves to chilling (> 0°C) or freezing (‐5°C, ‐7°C) temperatures on the inositolphospholipid (PI, PIP and PIP2) contents and [2‐3H]‐inositol incorporation into phosphoinositides and inositol phosphates (IP3, IP2, and IP) were studied. LiCl (50 mM) was used to arrest inositol phosphate hydrolysis on the IP level. Cold acclimation resulted in increased contents of PI and PIP2 in the leaves. Rapid exposure of NA leaves to 0°C and CA leaves to ‐7°C (temperature of ice nucleation in the tissue) increased the amount of radioactivity in inositol phosphates and decreased the radioactivity in PIP2 and PIP. The data indicate that low temperature induced phospholiphase C activity in winter rape leaves, the effectiveness of the treatment being dependent on the state of plant acclimation to cold. Mechanisms engaged and some biological implications of the responses observed for cold acclimation of plants are discussed.
Polypheolic auxin protectors in buds of juvenile and adult chestnut
Authors: Mato M. C. , Méndez J. , Vázquez A.
Published: May 2006

Both qualitative and quantitative estimates of the relative amounts of several poly‐phenols in buds of juvenile and adult plants of chestnut (Castanea sativa x C. crenata) were carried out. In buds of both types of plants, chesnatin, crenatin, cretanin and (+)‐catechin were identified. Crenatin and cretanin showed inhibitory activity of peroxidase‐catalysed indoleacetic acid oxidation. Auxin protection capacity was greater in extracts of the juvenile tissues which also were richer in active phenols. The phenolic content and its possible relationship to the easier establishment in vitro of juvenile tissue is discussed.
Comparison of endogenous polyamine content in hazel leaves and buds between the annual dormancy and flowering phases of growth
Authors: Rey Manuel , Díaz‐Sala Carmen , Rodríguez Roberto
Published: May 2006

Variations of endogenous polyamine levels were determined in leaves and buds of mature hazelnut trees (Corylus avellana). Results indicated specific correlations between high spermidine and spermine levels with rapid shoot growth and leaf expansion. Conversely, low spermidine and spermine, along with increasing putrescine levels, may be associated with the imposition of shoot‐bud dormancy. In previous studies on the morphogenic ability in hazel, and taking into account that hazel explants can be easily established in vitro during dormancy imposition, we observed that high levels of putrescine and increasing putrescine to polyamines ratios could be related to a higher morphogenic potential in this species, showing in adult tissues the typical behaviour of juvenile tissues in vitro. Genotypic differences affecting the morphogenic potential could account for the observed differences in the polyamine levels of the cultivars. The data obtained could also be correlated with seasonal changes of other endogenous growth regulators in hazel.
The consequences of freezing temperatures followed by high irradiance on in vivo chlorophyll fluorescence and growth in Picea abies
Authors: Welander N. T. , Gemmel P. , Hellgren O. , Ottosson Birgitta
Published: May 2006

Picea abies (L.) Karst. plants, propagated by cuttings, were subjected to one night of freezing temperatures (‐5°C), high irradiance (1 200 or 1 800 μmol m−2 s−1), or freezing temperatures followed by high irradiance. The treatments were applied at bud burst, at time of shoot elongation, and when the shoots had ceased to elongate. The maximum quantum yield of photosynthesis, Fv/Fm, dry weight of branches and needles, and length and survival of shoots were measured. Fv/Fm and growth decreased after a night of freezing temperatures followed by high irradiance, at the time of bud burst and shoot elongation. High irradiance alone influenced Fv/Fm, but not growth. Freezing temperatures affected Fv/Fm, and growth at the time of shoot elongation. F0 increased after a night of freezing temperatures and decreased with age of the current‐year needles. It was concluded that the use of short‐term measurements of chlorophyll fluorescence induction to predict changes in growth after a night of frost and subsequent high light was not a reliable method.
The effect of aluminium on respiration of wheat roots
Authors: de Lima Maria L. , Copeland Les
Published: May 2006

The effects of aluminium ions on respiration of excised root apices from wheat (Triticum aestivum L. cv. Vulcan) and on isolated mitochondria have been investigated. Addition of 75μ M aluminium to the growth medium of 4‐day‐old seedlings inhibited O2 uptake by excised root apices by 23 and 35% after 12 and 24 h, respectively. This decreased rate of respiration was initially caused by inhibition of the cytochrome pathway of mitochondrial electron transport. The cyanide‐insensitive, alternative pathway was inhibited only after more prolonged exposure to aluminium. Mitochondria isolated from roots of aluminium‐treated seedlings had reduced oxidative capacity with substrates that supply electrons to Complexes I and II, compared with mitochondria from roots of untreated control seedlings. The state 3 and state 4 rates of O2 uptake and the uncoupled rates with these substrates were also inhibited when aluminium was added directly to reaction mixtures containing mitochondria isolated from untreated plants. In contrast, when aluminium was added to reaction mixtures oxidizing exogenous NADH, state 4 O2 uptake was stimulated, whereas no effect was observed on the state 3 rate or the rate in the presence of uncoupler. The results suggest that aluminium initially affects electron flow through Complexes I and II, and that after more prolonged exposure, aluminium may also interact with other sites in mitochondria.
Carbohydrate metabolism enzymes in CO2‐enriched developing rice grains of cultivars varying in grain size
Authors: Chen C. L. , Li C. C. , Sung J. M.
Published: May 2006

The increased supply of photosynthate from maternal tissue is known to promote grain growth in several crop species. However, the effect of increasing photosynthate supply on grain growth receives little attention in rice. This study was aimed at evaluating the effect of increasing photosynthate supply through CO2 enrichment (650 μl I‐1) on grain growth in three rice cultivars differing in grain size. CO2 enrichment was applied to the pot‐grown plants between anthesis and final harvest. The results indicated that high CO2 treatment enhanced the CO2 exchange rate of leaf tissue, and subsequently increased the sucrose level of peduncle exudate, but it did not promote starch accumulation in the developing grains. This phenomenon was linked to the poor CO2 responses for the grain activities of sucrose synthase, UDP‐glucose pyrophosphorylase. ADP‐glucose pyrophosphorylase, and starch synthases involved in the conversion of sucrose to starch. Significant cultivar differences also existed for the activities of sucrose to starch conversion enzymes with larger grain size cultivars tending to have higher enzymes activities (expressed on a grain basis), resulting in a greater carbohydrate accumulation.
Trehalose and trehalase in root nodules from various legumes
Authors: Müller Joachim , Xie Zhi‐Ping , Staehelin Christian , Mellor Robert B. , Boller Thomas , Wiemken Andres
Published: May 2006

Nitrogen‐fixing (effective) nodules from various legume‐Rhizobiumcombinations were analyzed for trehalose and other soluble carbohydrates using gas chromatography and for trehalase activity using biochemical assays. Whereas the bacterial disaccharide trehalose was present only in the minority of the nodules, trehalase activity was found in all of them. Extracts from determinate nodules had a higher trehalase activity than extracts from indeterminate nodules. More detailed studies were done on soybean nodules formed in interactions with two effective and 5 ineffectiveBradyrhizobium japonicumstrains. Only in effective soybean nodules colonized by the strain 61‐A‐101 was trehalose a major soluble carbohydrate. Irrespective of the wildtype strains used. effective soybean nodules contained about 10 nkat trehalase g−1fresh weight, whereas the ineffective nodules colonized by mutant strains derived from these wildtype strains contained 2 to 30 times less trehalase. However, a clear correlation between trehalose content and trehalase activity could not be established.
Drought and chlorophyll fluorescence in field‐grown potato (Solanum tuberosum)
Authors: Jefferies R. A.
Published: May 2006

Light interception, stomatal conductance and chlorophyll fluorescence were measured in potato (Solanum tuberosum L.) grown either irrigated, or droughted from the time of plant emergence. Compared with the irrigated treatment, drought reduced both light interception and stomatal conductance. In both treatments, the yields of variable fluorescence in the dark‐ and light‐adapted states (Fy/Fm and F′v/F′m, respectively) were negatively correlated with photosynthetic photon flux density (PPFD) and mirrored daytime changes in PPFD. Photochemical quenching was positively correlated with PPFD, but the dominant effect of F′v/F′m resulted in a decrease in the quantum yield of photosystem II (PSII) electron transport with increasing PPFD.

Drought had no significant effect on the functioning of PSII and the balance between photochemical and non‐photochemical quenching was unaffected. Non‐photochemical quenching was not increased by drought and the quantum yield of PSII electron transport was unaffected. It is concluded that, in leaves of droughted plants, excess energy, resultant of stomatal limitation of photosynthesis, was dissipated by photochemical quenching such as increased photorespiration.
The effects of low root‐zone temperature stress on two soybean (Glycine max) genotypes when combined with Bradyrhizobium strains of varying geographic origin
Authors: Lynch D. H. , Smith D. L.
Published: May 2006

In areas with short growing seasons, poor early vegetative growth of soybean (Glycine max [L.] Merr.) is often attributed to the restrictive effect of cool soil conditions on nodulation and N2‐fixation by this subtropical grain legume. However, there are few studies regarding potential genetic variability of soybean and Bradyrhizobium japonicum genotypes for nodulation at cool root‐zone temperatures (RZT). Experiments were conducted to (1) test for a threshold temperature for low RZT inhibition of soybean nodulation and (2) ascertain whether this threshold temperature response depends mainly on the micro‐ or macrosymbiont. In experiment 1 soybean seedlings (Glycine max [L.] Merr. cv. Maple Arrow) were inoculated with 1 ml of a log phase culture of B. japonicum strain 532C, H8 or H15 (the latter two strains were isolated from cold soils of Hokkaido, northern Japan) and maintained at either 16, 17.5, 19 or 25°C RZT. In experiment 2 seedlings of cv. Maple Arrow and a cold‐tolerant Evans isoline were combined with strain 532C and two Hokkaido strains (H5, H30) at both 19 and 25°C RZT. Results indicated that N2‐fixation at 44 days after inoculation was substantially reduced (30–40%) by RZT as high as 19°C, due to development of less nodule mass and to a delay in the onset of N2‐fixation and a small decrease in the number of nodules formed. However, the number of nodules formed was sharply reduced and the time required for the first appearance of nodules was significantly delayed below an RZT of 17.5°C. Differences between cultivars for nodulation and N accumulation were apparent at 25°C, but were abolished by growth at 19°C, indicating that, in spite of differences in growth potential between the cultivars under optimum RZT, both cultivars were equally limited by low RZT. Differences between B. japonicum strains were consistent across temperatures and were largely attributable to higher rates of specific nodule activity recorded for strain 532C, which seemed well adapted to low RZT. These results suggest that the host plant mediates the sensitivity of N2‐fixation under low RZT and that inoculation with B. japonicum strains from cold environments is unlikely to enhance soybean N2‐fixation under cool soil conditions.
Myosin in onion (Allium cepa) bulb scale epidermal cells: involvement in dynamics of organelles and endoplasmic reticulum
Authors: Liebe Susanne , Quader Hartmut
Published: May 2006

Studied with the fluorochrome 3,3‐dihexyloxacarbocyanine iodide [(DIOC6(3)], the dynamic system of the endoplasmic reticulum (ER) in epidermal cells of onion bulb scales consists of long, tubular strands moving together with organelles in the deeper cytoplasm, and of a less mobile network composed of tubular and lamellar elements at the cell periphery. Treatment with the sulfhydryl‐reagent N‐ethylmaleimide (NEM) inhibited organelle and ER movement, and caused the fusion of ER‐tubules into flat sheets. Fixed, long, tubular ER strands were formed by lowering the cytosolic pH of NEM‐treated cells. Both these observations indicate the involvement of myosin in the dynamics of organelles and ER. Using a monoclonal antibody against murine skeletal muscle myosin (known to cross‐react with plant myosin; Tang et al. 1989, J. Cell Sci. 92: 569–574), myosin was identified by immunofluorescence microscopy. Mapping the distribution of myosin, actin filaments, ER, and organelles in different phases of recovery after centrifugation of epidermal cells, co‐localization of myosin with ER and organelles but not with actin filaments was observed, supporting the hypothesis that a membrane bound motor protein exists in onion epidermal cells, which translocates organelles and the endoplasmic reticulum along actin filaments.
Factors influencing the phycobilisome rod composition of the cyanobacterium Synechococcus sp. PCC 7942: Effects of reduced phycocyanin content, lack of rod‐linkers, and over‐expression of the rod‐terminating linker
Authors: Bhalerao Rishikesh P. , Gustafsson Petter
Published: May 2006

Four novel mutants with altered phycobilisomes were constructed in the cyanobacterium Synechococcus 7942 to study factors influencing the rod length and composition. These mutants show (1) reduced phycocyanin content, (2) reduced phycocyanin content combined with loss of the 33 kDa linker, (3) loss of the 30 kDa rod‐linker and (4) overexpression of the 9 kDa rod terminating linker. For these mutants we determined the 33 to 27 kDa and 30 to 27 kDa linker ratios in the isolated phycobilisomes and compared these ratios with those in the wild type. The 30 kDa linker can be incorporated into the rods in absence of the 33 kDa linker. The incorporation of the 30 kDa linker is lower in absence of the 33 kDa linker. When the 30 kDa linker is missing, an increase in the level of the 33 kDa linker is seen, indicating that there could be an excess of the 33 kDa linker in the cells. Our results also show that a reduction in the phycocyanin content causes a decrease in the rod length simultaneously with a reduction of the 30/27 linker ratio, without altering the 33/27 ratio. Reduced phycocyanin content and absence of the 33 kDa linker cause a dramatic reduction in the incorporation of the 30 kDa linker into the rods in the mutant B2SMIKM. Over‐expression of the 9 kDa linker results in a decreased incorporation of both the 33 and 30 kDa linkers into the rods, the effect being more pronounced for the 30 kDa linker. This result indicates that the level of the 9 kDa linker relative to those of the 33 and the 30 kDa linkers may be an important determinant of the phycobilisome rod length.
Respiratory responses of higher plants to atmospheric CO2 enrichment
Authors: Wullschleger Stan D. , Ziska Lewis H. , Bunce James A.
Published: May 2006

Although the respiratory response of native and agricultural plants to atmospheric CO2 enrichment has been reported over the past 75 years, only recently have these effects emerged as prominent measures of plant and ecosystem response to the earth's changing climate. In this review we discuss this rapidly expanding field of study and propose that both increasing and decreasing rates of leaf and whole‐plant respiration are likely to occur in response to rising CO2 concentrations. While the stimulatory effects of CO2 on respiration are consistent with our knowledge of leaf carbohydrate status and plant metabolism, we wish to emphasize the rather surprising short‐term inhibition of leaf respiration by elevated CO2 and the reported effects of long‐term CO2 exposure on growth and maintenance respiration. As is being found in many studies, it is easier to document the respiratory response of higher plants to elevated CO2 than it is to assign a mechanistic basis for the observed effects. Despite this gap in our understanding of how respiration is affected by CO2 enrichment, data are sufficient to suggest that changes in leaf and whole‐plant respiration may be important considerations in the carbon dynamics of terrestrial ecosystems as global CO2 continues to rise. Suggestions for future research that would enable these and other effects of CO2 on respiration to be unravelled are presented.
Evidence for two pathways of phloem loading
Authors: Eschrich Walter , Fromm Jörg
Published: May 2006

The minor veins of small leaf discs, punched out of mature leaves and incubated in 14C‐sucrose solution, appear labeled in macro‐ and microautoradiographs. Discs with a labeled vein pattern and with labeled sieve tubes in microautoradiographs were found in Beta vulgaris, Vicia faba, Gomphrena globosa and Antirrhinum majus. However, in several other plant species, minor veins appeared unlabeled in macroautoradiographs when the discs were incubated in 14C‐sucrose. Mesophyll cells (Acer pseudoplatanus, Juglans regia, Fagia, sylvatica, Syringa vulgaris, Laburnum anagyroides), bundle‐sheath cells of major veins (Salix viminalis, Robinia pseudoacacia, Commelina communis) or epidermal layers (Ginkgo biloba, Chlorophytum comosum) appeared labeled. Lack of radioactivity in sieve tubes of this latter group was confirmed by microauto‐radiography. Using 14C‐glucose instead of 14C‐sucrose, leaf discs of Beta vulgaris showed no labeled vein pattern and in microautoradiographs the sieve tubes appeared unlabeled. In view of the by‐pass phloem loading, this study provides evidence for two pathways of phloem loading.