bluuebunny/crossref_metadata_2025 huggingface dataset:
The phytotoxin syringomycin elicits Ca2+‐dependent callose synthesis in suspension‐cultured cells of Catharanthus roseus
Authors: Kauss Heinrich , Waldmann Thomas , Jeblick Wolfgang , Takemoto Jon Y.
Published: May 2006

Deposition of the 1,3‐β‐glucan callose onto the cell wall represents one of the defence reactions of plants against pathogens. This process can be induced in suspension cells of Catharanthus roseus by subtoxic concentrations of the bacterial phytotoxin syringomycin and is associated with a slight increase in Ca2+ uptake and some K+ release. Under these conditions callose formation can be prevented by complexing external Ca2+, indicating that some Ca2+ uptake is essential as a signal. However, higher syringomycin concentrations elicit increased Ca2+ uptake without increasing callose formation, although the potential for callose synthesis is not exhausted – as shown using digitonin as an additional elicitor. These results suggest that, superimposed on Ca2+, another, yet unknown signal is also involved in the regulation of callose synthesis.
The greening process in cress seedlings. I. Pigment accumulation and ultrastructure after application of 5‐aminolevulinate and complexing agents
Authors: Kittsteiner Ursula , Mostowska Agnieszka , Rüdiger Wolfhart
Published: May 2006

A reduced rate of greening after continuous illumination was observed in dark‐grown cress seedlings (Lepidium sativum L.) incubated with 5‐aminolevulinate (ALA) or the complexing agents 2,2′‐bipyridyl, 8‐hydroxyquinoline or 1,10‐phenanthroline. This effect cannot be explained merely by photodynamic damage caused by chlorophyll precursors which are accumulated in the dark under these conditions. Flash light experiments revealed that photoconversion of protochlorophyll(ide) to chlorophyllide was not influenced by chelator treatment. The next step in the chlorophyll pathway, the esterification of chlorophyllide, however, was inhibited. Simultaneously applicated ALA and complexing agents did not result in a synergistic reponse; on the contrary, ALA seemed to render cress plants less susceptible to the treatment with complexing agents upon subsequent irradiation. Ultrastructural studies demonstrated that grana formation in light was inhibited after pretreatment with ALA or complexing agents.
Purification and properties of α‐1,4‐glucan phosphorylase from the red seaweed Gracilaria sordida (Gracilariales)
Authors: Yu Shukun , Pedersén Marianne
Published: May 2006

α‐1,4‐Glucan phosphorylase (EC 2.4.1.1) from the red seaweed Gracilaria sordida(Harv.) W. Nelson was adsorbed onto starch‐Sepharose 6B and Sephacryl S‐300 under specified conditions. The algal enzyme was purified to homogeneity by these two steps. A molecular weight of 97.4 kDa was observed on SDS‐polyacrylamide gel electrophoresis under reducing conditions, while the native molecular weight was 240 kDa asrevealed by 8‐25% native gradient gel electrophoresis or 245 kDa by gel filtration. The pI of the enzyme was 5.4. It had a Km of 227, 264, 285, and 453 μg ml‐1, respectively, towards glycogen, amylopectin, amylose, and maltodextrin. The enzyme activity was inhibited by cyclohexaamylose, ADP‐glucose, and UDP‐glucose. In contrast to other plant sources, cell‐free extracts of G. sordida contained only one form of phosphorylase.
Effects of water stress on growth, osmotic potential and abscisic acid content of maize roots
Authors: Ribaut Jean‐Marcel , Pilet Paul‐Emile
Published: May 2006

Under water stress conditions, induced by mannitol solutions (0 to 0.66 M) applied to the apical 12 mm of intact roots of Zea mays L. (cv. LG 11), a growth inhibition, a decrease in the osmotic potential of the cell sap and a significant accumulation of abscisic acid (ABA) were observed. When the roots were placed in a humid atmosphere after the stress, the growth rate increased again, even if elongation had been totally inhibited. Under a stress corresponding to an osmotic potential of ‐1.09 MPa in the solution, growth was totally inhibited, which means that the root cell turgor pressure was reduced to the yield threshold. These conditions led to the largest accumulation of ABA. The effect of water stress on the level of ABA was studied for three parts of the root. The greatest increase in ABA (about 10 fold) was obtained in the growth zone and this increase was apparently independent of the hydrolysis of the conjugated form. With a mannitol treatment of 1 h equivalent to a stress level of ‐1.39 MPa, a 4‐fold increase in ABA efflux into the medium was obtained. These results suggest that there are interactions between water stress, root growth, osmotic potential and the ABA level. The growth under conditions of stress and the role of endogenous ABA in the control of plant metabolism, specially in the growth zone, are discussed.
The effects of mineral nutrition and benzyladenine on the plasmalemma ATPase activity from roots of wheat and Plantago major ssp. pleiosperma
Authors: Kuiper Daan , Sommarin Marianne , Kylin Anders
Published: May 2006

There is an increasing awareness of the possibilities of mineral nutrition as regulator of growth substance action and vice versa. The present paper focuses on the effects of mineral nutrition and benzyladenine at the level of the plasma membrane. Seedlings of wheat (Triticum aestivum L. cv. Drabant) and juvenile plants of Plantago major L. ssp. pleiosperma (Pilger) were grown hydroponically at different mineral levels with or without benzyladenine. Purified plasmalemma preparations from roots of wheat and P. major ssp. pleiosperma were obtained by the two phase partitioning method, using 6.5% (w/w) of each of Dextran T‐500 and polyethylene glycol 3350. The Mg2+ and (Mg2++ K+) dependent ATPase activities of the root plasmalemma in both species and the (Mg2++ Cl−) one in P. major ssp. pleiosperma increased with increasing mineral levels, but the ionic strength did not influence the substrate specificity, the sensitivity to inhibitors or the pH optima.

The addition of 10−8M benzyladenine to a nutrient solution increased the ATPase activities. The pH optima and the sensitivity to several inhibitors were not affected by benzyladenine, but the substrate specificity for ATP decreased, except for the K+ stimulation. In conclusion, benzyladenine mimics the effects of a higher mineral level than actually applied. Data from this and previous experiments indicate that benzyladenine exerts its effects by increasing the endogenous cytokinin concentrations and by modulating membrane components.
Increase in nitrate uptake by soybean plants during interruption of the dark period with low intensity light
Authors: Raper C. David , Vessey J. Kevin , Henry Leslie T.
Published: May 2006

Diurnal patterns of net NO−3 uptake by nonnodulated soybean [Glycine max (L.) Merr. cv. Ransom] plants growing in flowing hydroponic culture at 26 and 16°C root temperatures were measured at hourly intervals during alternate days of a 12‐day growth period. Ion chromatography was used to determine removal of NO−3 from the culture solution. Day and night periods of 9 and 15 h were used during growth. The night period included two 6‐h dark periods and an intervening 3‐h period of night interruption by incandescent lamps to effect a long‐day photoperiod and repress floral initiation. At both root temperatures, the average specific rates of NO−3 uptake were twice as great during the night interruption period as during the day period; they were greater during the day period than during the dark periods; and they were greater during the dark period immediately following the day period than during the later dark period that followed the night interruption. While these average patterns were repetitious among days, measured rates of uptake varied hourly and included intervals of net efflux scattered through the day period and more frequently through the 2 dark periods. Root temperature did not affect the average daily specific rates of uptake or the qualitative relationships among day, dark and night interruption periods of the diurnal cycle.
The greening process in cress seedlings. II. Complexing agents and 5‐aminolevulinate inhibit accumulation of cab‐mRNA coding for the light‐harvesting chlorophyll a/b protein
Authors: Kittsteiner Ursula , Brunner Harald , Rüdiger Wolfhart
Published: May 2006

Dark‐green cress seedlings were treated with 5‐aminolevulinate (ALA) or the metal complexing agents 2,2′‐bipyridyl and 8‐hydroxyquinoline. The subsequent induction of cab‐mRNA coding for the light‐harvesting chlorophyll a/b protein (LHCP) by white or far‐red light was investigated. Pretreatment with ALA 48 h after sowing yielded increased levels, the same pretreatment 72 or 96 h after sowing decreased levels of cab‐mRNA. The strongest inhibition of light induction of cab‐mRNA was found by pretreatment with 2,2′‐bipyridyl. Less inhibition was obtained by pretreatment with 8‐hydroxyquinoline. Steady‐state levels of transcripts which are not light‐regulated (actin, psbA) were only slightly decreased by pretreatment with ALA or the metal chelators, whereas no decrease was found for mRNA coding for NADPH: protochlorophyllide oxidoreductase. Run‐off transcription with isolated nuclei showed that the transcription rate was reduced by pretreatment of intact plants with the metal chelator 2,2′‐bipyridyl. The results are discussed in the context of current proposals for the role of transition metals. ALA, and chlorophyll precursors in light‐induction of gene expression.
Effects of sodium, potassium and calcium on salt‐stressed barley
Authors: Cramer Grant R. , Epstein Emanuel , Läuchli André
Published: May 2006

We grew barley (Hordeum vulgare L. CM 72) for a 28‐day period and sequentially harvested plants every 3 or 4 days. Plants were salt‐stressed with either NaCl or KCl (125 mM) with or without supplemental Ca (10 or 0.4 mM final concentration, respectively). We determined tissue concentrations of Na, Ca, Mg, K. S, P, Fe, Mn, Cu and Zn for each harvest date by inductively coupled plasma spectrometry. Uptake (specific absorption rate) was calculated from the element content and growth rates. Salinity had significant effects on the uptake and concentrations of most elements. Mg and Mn concentrations declined with time. The concentrations of all other elements determined increased over time. Element uptake on a root dry weight basis declined with time. Three variables were significantly affected by salinity and correlated with growth; 1) the Ca concentration, 2) the total sum of the cation concentration (TC), and 3) the Mn concentration of the shoot. Salinity reduced Ca uptake and concentrations. Supplemental Ca increased Ca concentrations and was positively correlated with growth during salt stress. Salinity doubled TC, which was negatively correlated with relative growth rate (RGR). Relative growth rate declined at TC values above 150 mM. Salinity reduced the uptake and concentration of Mn. Manganese concentrations in the shoot were highly correlated with RGR. Relative growth rate declined at Mn concentrations below 50 nmol (g fresh weight)−1.
Photoinhibition and recovery of photosynthesis in intact barley leaves at 5 and 20°C
Authors: Greer D. H. , Ottander C. , Öqust G.
Published: May 2006

Photoinhibition of photosynthesis and its recovery were studied in intact barley (Hordeum vuigare L. cv. Gunilla) leaves grown in a controlled environment by exposing them to two temperatures, 5 and 20°C, and a range of photon flux densities in excess of that during growth. Additionally, photoinhibtion was examined in the presence of chloramphenicol (CAP, an inhibitor of chloroplast protein synthesis) and of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU). Susceptibility to photoinhibition was much higher at 5 than at 20°C. Furthermore, at 20°C. CAP exacerbated photoinhibition strongly, whereas CAP had little additional effect (10%) at 5°C. These results support the model that net photoinhibition is the difference between the inactivation and repair of photosystem II (PSII); i.e. the degradation and synthesis of the reaction centre protein, Dl. Furthermore, the steady‐state extent of photoinhibition was strongly dependent on temperature and the results indicated this was manifested through the effects of temperature on the repair process of PSII. We propose that the continuous repair of PS II at 20°C conferred at least some protection from photoinhibition. At 5°C the repair process was largely inhibited, with increased photoinhibition as a consequence. However, we suggest where repair is inhibited by low temperature, some protection is alternatively conferred by the photoinhibited reaction centres. Providing they are not degraded, such centres could still dissipate excitation energy non‐radiatively, thereby conferring protection of remaining photochemically active centres under steady‐state conditions.

A fraction of PS II centres were capable of resisting photoinhibition when the repair process was inhibited by CAP. This is discussed in relation to PS II heterogeneity. Furthermore, the repair process was not apparently activated within 3 h when barley leaves were transferred to photoinhibitory light conditions at 20°C.
Effects of spermidine on the synthesis of α‐amylase in cotyledons of mung bean seedlings
Authors: Koizuka Nobuya , Tanaka Yoshiyuki , Morohashi Yukio
Published: May 2006

When cotyledons of mung bean [Vigna radiata (L.) Wilczek] were treated with spermidine (3 mM) during the first 6 h of imbibition, the development of α‐amylase activity in cotyledons during the following 3 days was severely inhibited (75%) This inhibition was due to a slower accumulation of α‐amylase protein, which in turn resulted from an inhibition of α‐amylase synthesis. The rise in the level of α‐amylase mRNA in cotyledons was also inhibited by spermidine treatment. However, the degree of inhibition of mRNA accumulation (40%) was not so marked as that of the activity of α‐amylase synthesis (80%). These results are discussed in relation to the mode of action of spermidine on α‐amylase expression.
Characterization of hexose kinases from camellia and lily pollen grains
Authors: Nakamura Norio , Shimizu Minoru , Suzuki Hiroshi
Published: May 2006

Extracts from Camellia japonica, Lilium longiflorum and L. lancifolium pollen grains showed a far higher kinase activity with fructose than with glucose. Fructokinase (EC 2.7.1.4) and hexokinase (EC 2.7.1.1) preparations were obtained by partial fractionation of the extracts by DEAE‐cellulose chromatography; the former was practically inactive with glucose. All had a pH optimum at 7.0–8.0 and required Mg1+ ions for activity with optima at 0.5‐1 mM and 1‐2 mM for fructokinase and hexokinase activities, respectively. Fructokinases had Km of 0.2‐0.4 mM for fructose and similar affinities for ATP and UTP, and were inhibited by fructose above 1 mM. Hexokinases had a higher affinity for glucose than for fructose and a lower affinity for UTP compared to ATP. In camellia pollen most of hexose kinase activities were found to be due to fructokinase. These results are discussed in relation to stimulation of camellia pollen tube growth by oligosaccharides susceptible to invertase (EC 3.2.1.26).
Effects of temperature and photoperiod on flowering in Hyptis brevipes
Authors: Zaidan Lilian B. P. , Dietrich Sonia M. C. , Schwabe W. W.
Published: May 2006

Few tropical species have been tested for their flowering response under controlled conditions. Hyptis brevipes Poit, is an annual herb, commonly found in wet margins of streams and ponds, being considered a weed for some perennial plantations in Brazil. Under experimental glasshouse conditions, this species proved to be an obligate short‐day plant. Flowering was delayed when photoperiods longer than 8 h were given, the critical photoperiod being between 12 and 13 h. When both temperature and photoperiod were controlled, at 20°C a longer protoperiod (by almost 1 h) is still inductive compared to 25 and 30°C. The number of short‐day cycles required for full induction is relatively high and dependent upon temperature; at 20°C or above, 10 cycles are adequate, but at 15°C, more short‐day cycles are needed. The number of inflorescences formed as well as the floral index vary according to daylength × temperature × inductive cycle number, allowing flowering to be assessed quantitatively. Long days are inhibitory to flowering, either suppressing it completely (when symmetrically intercalated among 24 inductive cycles) or preventing the floral index from increasing.
Effect of indole‐3‐acetic acid (IAA) and sucrose on vessel size and density in isolated stem segments of oak (Quercus robur)
Authors: Zakrzewski Jacek
Published: May 2006

The effects of several concentrations of indole‐3‐acetic acid (IAA) and sucrose on xylogenic cambial activity and secondary xylem differentiation were investigated in isolated stem segments of Quercus robur L. supplied with liquid medium in aseptic conditions. After 5 weeks of culture auxin controlled cambial cell division and the number and size of vessel elements even without sugar in the medium. Sucrose modified these IAA effects, although little cambial activity occurred without auxin. The xylem increment correlated with changes of auxin concentration with the optimum at 28.5 μM IAA. The formation of wide vessels was correlated with the optimal concentration of auxin. The frequency of vessel differentiation increased with auxin concentration. High concentrations of sucrose (0.24 M and 0.96 M) reduced both the number of vessels and their diameter. The frequency of vessel formation was inhibited more than the vessel size by changes of sugar concentration. The vessels formed under low concentrations of IAA were circular in transverse section. With increase in IAA concentration the shape of the vessel cross‐section changed to oval with the largest dimension in the radial direction.
Increase in lodging safety factor of thigmomorphogenically dwarfed shoots of mulberry tree
Authors: Tateno Masaki
Published: May 2006

The lodging safety factor of mechanically stimulated shoots of mulberry tree (Morus bombycis Koidz. cv. Kenmochi) was measured to test the hypothesis that thigmomorphogenic dwarfing increases mechanical stability of plants. The lodging safety factor, an indicator of mechanical stability of erect shoots, has been defined as the ratio of critical lodging load to leaf fresh weight. Two‐year‐old shoot cuttings of mulberry tree were rubbed, brushed, and shaken every day. During the experimental period, the lodging safety factor of the control shoots remained at about 5. while the safety factor of the thigmomorphogenically dwarfed ones was ca 1.6 times larger, which supports the hypothesis. The mechanical stimulation reduced the stem elongation rate, but did not greatly change the partitioning of dry matter between leaves and stem. Therefore, it is concluded that the reduction of stem elongation rate was the main cause of the increase in the lodging safety factor of the stimulated shoots.
Electroporation: Mechanism and transient expression, stable transformation and biological effects in plant protoplasts
Authors: Joersbo Morten , Brunstedt Janne
Published: May 2006

The present state of knowledge about the mechanistic and theoretical aspects of electroporation is summarized. Parameters affecting the efficiency of transient expression and stable transformation of electroporated plant protoplasts are rewieved. Biological effects of electroporation on plant protoplasts are described.
The molecular genetics of seed maturation in maize
Authors: McCarty Donald R. , Carson Christian B.
Published: May 2006

The maturation phase of seed formation involves coordinated expression of multiple developmental pathways. These processes include abscisic acid regulated responses associated with the arrest of embryo development and induction of anthocyanin synthesis in embryo and aleurone tissues. Studies of the maturation defective vivaparous mutants of maize suggest that one gene, viviparous‐1 (vpl), regulates both of these pathways in the developing seed. Mutations at vpl reduce the sensitivity of the developing embryo to abscisic acid. In addition, Vpl is required for expression of Cl, a regulatory gene for the anthocyanin pathway. This interaction is consistent with the idea that Vpl and Cl function as part of a regulatory hierarchy controlling seed development. Molecular studies of vpl mutations which separate control of embryo arrest and anthocyanin synthesis suggest that these functions map to discrete domains in the Vpl protein. Therefore, coordinate control of diverse maturation processes may be achieved through expression of a functionally complex regulatory molecule.
Repetitive proline‐rich proteins in the extracellular matrix of the plant cell
Authors: Marcus Abraham , Greenberg Jonathan , Averyhart‐Fullard Vera
Published: May 2006

Several classes of hydroxyproline‐rich proteins have been found in the cell walls of plants. Monomeric forms of the proteins can be solubilized from the walls, but the majority of the proteins are insolubilized by as yet unidentified crosslinks. The proteins have repeated sequences and are often rich in basic amino acids. The repeat proline‐rich region may be serving to generate an elongated rod‐like structure while the regularly spaced lysines probably interact with the acidic pectins. Several of the genes coding for these proteins have been isolated, and their expression has been found in some cases to be tissue specific and in others inducible by hormones and various types of stress.
The controls of late dicot embryogenesis and early germination
Authors: Galau Glenn A. , Jakobsen Kjetill S. , Hughes D. Wayne
Published: May 2006

During seed formation, the embryo appears to be germinable as soon as cell division is completed; however, it continues development on the plant. This review describes the stages of development after cell division and provides a summary of important observations and recent use of molecular markers as they apply to the regulation of dicot seed formation. Genetic evidence suggests that abscisic acid may help initiate late embryogenesis, although no evidence firmly establishes that abscisic acid controls any other aspect of late dicot development. Previous studies utilizing cultured embryos have implicated abscisic acid and water potential as endogenous promoters of late embryogenesis and inhibitors of germination. However, these embryo culture experiments have been misinterpreted. The experiments show that both immature and mature embryos respond to environmental water stress by expressing a developmental program that is normally induced in late embryogenesis by abscission of the vascular connection. This postabscission program probably prepares the embryo for its forthcoming desiccation during normal development and is predicted to be important in protecting the embryo from water stress during germination.
mRNA levels in the developing aleurone and starchy endosperm in wild type and a high lysine (lys 3a) mutant of barley
Authors: Jakobsen Kjetill S. , Kalvenes Catherine , Olsen Odd‐Arne
Published: May 2006

We have analysed the effects of the lys 3a mutation on mRNA levels in the developing aleurone and starchy endosperm. The objective was to investigate whether the increase in non‐hordein gene mRNA is a compensation for decreased hordein mRNA levels or if the increase is a result of a selective transcriptional or posttranscriptional regulation of specific genes. Our results show that protein Z and β‐amylase which are downregulated by the lys 3a mutation are affected only in the starchy endosperm. In contrast, mRNA levels for the chymotrypsin inhibitors (CI‐1, CI‐2) are enhanced in the aleurone as well as in the starchy endosperm. The two isoform inhibitor genes of CI‐1 (CI‐1A, CI‐1B) are differentially affected in the aleurone by the lys 3a mutation. The lys 3a gene enhances mRNA levels of two aleurone‐specific genes. Together, these findings suggest that the lys 3a gene encodes or affects a regulatory factor which specifically modulates mRNA levels of several genes in different seed tissues.
Flowering responses to light‐breaks in photomorphogenic mutants of Arabidopsis thaliana, a long‐day plant
Authors: Goto Nobuharu , Kumagai Tadashi , Koornneef Maarten
Published: May 2006

Flowering response and plant form of photomorphogenic mutants (hy1, hy2, hy3, hy4 and hy5) of Arabidopsis thaliana (L.), a long‐day plant, were examined in long and short days. There were only slight differences among genotypes including Landsberg wild type with respect to the flowering time under long days. The effect of 1 h light‐(night)‐breaks of far‐red, red, blue and white light given in the middle of the dark period of plants grown under short days, was studied. Effects of far‐red light applied at the end or the beginning of the main photoperiod on flowering and plant form were also examined. The light‐breaks with all the above mentioned light qualities promoted floral initiation of all the genotypes including the wild type in terms of both the flowering time and the number of rosette leaves. In general, far‐red light was most effective. It is possible to classify the hy‐mutants into 3 groups by their responses to light‐breaks under short day conditions: (a) Mutants hy2 and hy3, which have a reduced number of rosette leaves, and flower early. Red light is as effective as far‐red light. The wavelength of light‐breaks is relatively unimportant for flowering response. (b) Mutants hy4, hy5 and Landsberg wild type, which have a greater number of rosette leaves, and flower relatively late. The effectiveness of light‐breaks is in the following order, far‐red, blue, and red light, which is in reverse order to the transformation of phytochrome to the Pfr form. (c) Mutant hy1, which behaves anomalously with respect to relations between flowering time and number of rosette leaves; late flowering with reduced number of rosette leaves. Red, blue and far‐red light are effective, but white light is ineffective for reducing the number of rosette leaves.

When far‐red light was given in the middle of the night or at the end of the main photoperiod, it markedly reduced the number of rosette leaves compared to those grown under short days for all the genotypes, while when applied at the beginning of the main photoperiod far‐red light did not affect the number of rosette leaves. Different effects on the plant form dependent on the time of treatment with far‐red light‐breaks are also discussed.
Thermal stability and kinetic properties of NADP+‐malate dehydrogenase isomorphs in two populations of the C4 weed species Echinohloa crus‐galli (Barnyard grass) from sites of contrasting climates
Authors: Simon Jean‐Pierre , Vairinhos Franklin
Published: May 2006

The thermal stability and kinetic properties of purified NADP+‐malate dehydrogenase (NADP+‐MDH; EC 1.1.1.82) isomorphs were analyzed from plants of two populations of Barnyard grass from contrasting thermal environments. Plants from Québec (QUE) and Mississippi (MISS) were acclimated under controlled conditions at 26/20°C and 14/8°C (day/night). While the enzyme from QUE showed one isomorph, 3 isomorphs were detected in all plants from MISS, suggesting the presence of gene duplication and fixed heterozygosity for the expression of this dimeric enzyme. This findig raises the possibility that the enhanced acclimatory potential of NADP+‐MDH from MISS plants, as found from previous studies with the partially purified and unfractioned enzyme, may result from differential kinetic properties of isomorphs which would allow for the proper modulation of catalysis over a wide temperature range. The thermal stability of the QUE isomorph was significantly higher than that of any of the MISS isomorphs. The apparent activation energy of the QUE isomorph was within the range of values found for the 3 MISS isomorphs which were similar to each other. The Michaelis‐Menten constants (Km) for oxalacetic acid were not significantly different among isomorphs or between thermoperiods, but Km (NADP+) values for the QUE isomorph were significantly higher than those of two of the MISS isomorphs over the 15–25°C assay range Vmax/Km ratios for OAA and NADP+ were not significantly different among isomorphs or between thermoperiods. Our data indicate that, under highly purified conditions, the single NADP+‐MDH isomorph of QUE plants possesses good acclimatory potential for maintaining catalytic efficiency under a wide range of temperature conditions. In vitro thermal and kinetic data do not support the hypothesis that the the multiple NADP+‐MDH isomorphs found in MISS plants may have been selected to optimize the thermal and catalytic efficiency of NADP+‐MDH under warm temperature conditions.
In vivo labelling of the proteins in the first leaf of intact oat plants (Avena sativa)
Authors: Klerk H. , Tophof S. , van Loon L. C.
Published: May 2006

In order to label the primary leaves of intact oat plants (Avena sativa L. cv. Victory) for studying protein turnover using two‐dimensional polyacrylamide gel electrophoresis, the following methods were tested: growth of seedlings on 35S‐sulfate‐containing Knop medium, labelling with 35S‐methionine by vacuum infiltration of the leaf, injection into the leaf base or into the seed near the embryo, or wiping the surface of the leaf with ethanol followed by incubation in the labelled solution. A specific activity of 1.6 kBq per 20 μg of leaf protein applied was minimally necessary to obtain a well‐resolved fluorogram of the gels. This level of labelling was reached only upon the treatment with ethanol, which did not require more than 0.55 MBq of 35S‐methionine per leaf. The method may be useful locally to apply compounds to intact plants.
Effect of wounding on ethylene biosynthesis and senescence of detached spinach leaves
Authors: Philosoph‐Hadas Sonia , Meir Shimon , Aharoni Nehemia
Published: May 2006

Parameters of senescence and ethylene biosynthesis pathway were screened simultaneously in detached spinach leaves and leaf discs. Senescence was enhanced by application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and was retarded by amino‐ethoxyvinylglycine (AVG). Evidence is presented showing that the bursts of both wound‐ and climacteric‐like ethylene promoted senescence of detached leaves and leaf discs. This ethylene‐enhanced leaf senescence was dependent on: (a) ethylene production rates in the tissue; (b) the degree of wounding. Wounding resulted in elevated levels of 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (MACC), which declined in advanced stages of senescence. The results suggest that wounding might be regarded as one of the primary events in the induction of the senescence syndrome in detached leaves and leaf discs, while ethylene is implicated as a regulator of the rate of the process.
Photoregulation of seed germination of wild‐type and of an aurea‐mutant of tomato
Authors: Lercari B. , Lipucci di Paola M.
Published: May 2006

Seed germination of an aurea mutant of tomato (Lycopersicon esculentum Mill.) is promoted by continuous irradiation with red, far‐red or long‐wavelength far‐red (758 nm) light as well as by cyclic irradiations (5 min red or 5 min far‐red/25 min darkness). Far‐red light applied immediately after each red does not change the germination behaviour. Seed germination of the isogenic wild‐type, cv. UC‐105, is promoted by continuous and cyclic red light while it is inhibited by continuous and cyclic far‐red light and by continious 758 nm irradiation. Far‐red irradiation reverses almost completely the promoting effect of red light. The promoting effect (in the aurea mutant) and the inhibitory effect (in the wild‐type) of continuous far‐red light do not show photon fluence rate dependency above 20 nmol m−2 s−1. It is concluded that phytochrome controls tomato seed germination throgh low energy responses in both the wild type and the au mutant. The promoting effect of continuous and cyclic far‐red light in the au mutant can be attributed to a greater sensitivity to Pfr.
Differentiation of circular vessels in isolated segments of Fraxinus excelsior
Authors: Kurczyńska E. U. , Hejnowicz Z.
Published: May 2006

The differentiation of circular vessels was studied in stem segments which had passed winter dormancy and were stimulated by application of auxin in vitro. The circular vessels differentiated near the basal end of internodes. The prevailing form of circular vessels was a pair of cells connected by two perforations. Two‐cell vessels never had only one perforation. The occurrence of two perforations strongly supports the view that auxin flux is a stimulus for vessel differentiation and not the very presence or concentration of auxin; the circular vessels developed as a results of a circular flux. In general, the circular vessels appeared in contact with rays. Their formation was delayed in comparison with that of normal vessels.
Differences in osmoacclimation between sporophytes and gametophytes of the brown alga Ectocarpus siliculosus
Authors: Thomas David N. , Kirst Gunter O.
Published: May 2006

The osmoacclimation of Ectocarpus siliculosus isolates known to have different salt tolerances was investigated. Included were isolates originating from 5 different locations in the northern hemisphere, and sporophyte and gametophyte phases of different ploidy from two of the locations were compared. The effect of salinity treatment (8–64%0) on inorganic ions (K+, Na+, Mg2+, Cl−, SO2−4, phosphate) and the low molecular weight carbohydrate mannitol was measured, together with complimentary measurements of cell viability. Very different responses between isolates were obtained, both between isolates of different geographic origin and between sporophytes and gametophytes from the same parent material. A similarity in response between haploid and diploid gametophytes, and diploid and triploid sporophytes indicates that physiological differences between gametophyte and sporophyte generations are not necessarily based on ploidy changes alone. There were no identifiable differences in the responses of male and female gametophytes. K+ is the major osmolyte within the species, and differences in the regulation of K+ largely account for the observed variation in osmoacclimation, both between life history phases and between isolates from different localities. Isolates with broader salt tolerances had the higher concentrations of mannitol. There were differences between isolates in the amounts and regulation of Cl− and phosphate, the latter being present in unusually high concentrations. There were also isolate differences in the concentrations of Mg2+ and SO2−4, although these divalent ions were present only in low concentrations.
Stability of salt tolerance at the cell level after regeneration of plants from a salt tolerant tobacco cell line
Authors: Watad A. A. , Swartzberg D. , Bressan R. A. , Izhar S. , Hasegawa P. M.
Published: May 2006

Plants were regenerated from both the wild type and a stable NaCI‐tolerant line of tobacco cells (Nicotiana tabacum/gossii). The regeneration process was much more difficult in the case of the NaCI‐tolerant line and was only successful in the absence of NaCI. These plants differed morphologically from those regenerated from the wild type cell line, exhibiting abnormally short internodes, small leaves and reduced growth. Cell suspension cultures derived from plants regenerated from the stable NaCI‐tolerant line retained a high level of tolerance to salt. The NaCI‐concentration required to reduce fresh and dry weight gain by 50% was about twice that observed in the case of the cells obtained from wild type plants.

The results presented here, together with those of Watad et al. (1985), indicate that resistance to salt is operating and stable at the cellular level before and after plant regeneration. When the regenerated plants were grown in increasing levels of salt their growth response was not clearly different from that of the plants regenerated from the wild type cell line. However, the survival of plants on high concentrations of NaCI tended to be higher in the case of plants regenerated from the NaCI‐tolerant cell line.
Regulation of plant plasma membrane H+‐ATPase activity
Authors: Palmgren Michael Gjedde
Published: May 2006

The plant plasma membrane H+‐ATPase plays a central role in plant physiology. This enzyme belongs to the P type family of cation‐translocating pumps and generates the proton‐motive force that drives nutrient uptake across the plasma membrane. It also determines the extracellular acidification associated with elongation growth. The activity of the plasma membrane H+‐ATPase is rapidly altered after exposure of plant tissues to plant growth factors such as plant hormones, light and pathogens. However, very little is known about the mechanisms that regulate plasma membrane H+‐ATPase activity in the intact cell. The recent identification of an auto‐inhibitory domain in the C‐terminus of the plant plasma membrane H+‐ATPase implies that there are several possible means by which the enzyme could be regulated. The inhibitory interaction between the inhibitory domain and the catalytic site and/or a proton binding site may thus be regulated by a variety of means, such as the binding of effector molecules, phosphorylation, partial proteolysis, or removal of the inhibitory domain at the gene level. In addition, proton pumping across the plasma membrane could be regulated by changes in the transcriptional activity of H+‐ATPase genes or by differential expression of pump isoforms varying in their C‐terminal domain.
Coordination of stomatal, hydraulic, and canopy boundary layer properties: Do stomata balance conductances by measuring transpiration?
Authors: Meinzer Frederik C. , Grantz David A.
Published: May 2006

A striking coordination is observed in sugarcane between prevailing levels of stomatal opening and the hydraulic capacity of the soil, roots and stem to supply the leaves with water. This coordination of vapor phase and liquid phase conductances is associated with decreases in stomatal conductance on a leaf area basis that compensate for increasing leaf area during canopy development, causing transpiration to approach a maximum value on a per plant or ground area basis rather than increase linearly with leaf area. The resulting balance between water loss and water transport capacity maintains leaf water status remarkably constant over a wide range of plant. sizes and growing conditions. These changes in stomatal conductance during development are determined by changes in the composition of the xylem sap rather than by changes in leaf properties. Changes in boundary layer conductance resulting from non‐developmental changes in canopy structure such as loding cause additional changes in stomatal conductance mediated by altered humidity at the leaf surface. These maintain a constant level of total canopy vapor phase conductance (stomatal and boundary layer in series) and a constant level of canopy transpiration. These patterns indicate that stomata exert an active role in regulating transpiration even in dense canopies. This control function is consistent with stomatal metering of transpiration, mediated by fluxes of root‐derived materials in the xylem sap.
ATP‐dependent Ca2+ transport in wheat root plasma membrane vesicles
Authors: Olbe Malin , Sommarin Marianne
Published: May 2006

Plasma membrane preparations of high purity were obtained from roots of dark‐grown wheat (Triticum aestivum L. cv. Drabant) by aqueous polymer two‐phase partitioning. These preparations mainly contained sealed, right‐side‐out vesicles (ca 90% exposing the original outside out). By subjecting the preparations to 4 freeze/thaw cycles the proportion of sealed, inside‐out (cytoplasmic side out) vesicles increased to ca 30%. Inside‐out and right‐side‐out plasma membrane vesicles were then separated by partitioning the freeze/thawed plasma membranes in another aqueous polymer two‐phase system. In this way, highly purified, sealed, inside‐out (>60% inside‐out) vesicles were isolated and subsequently used for characterization of the Ca2+ transport system in the wheat plasma membrane. The capacity for 45Ca2+ accumulation, nonlatent ATPase activity and proton pumping (the latter two markers for inside‐out plasma membrane vesicles) were all enriched in the inside‐out vesicle fraction as compared to the right‐side‐out fraction. This confirms that the ATP‐binding site of the 45Ca2+ transport system, similar to the H+‐ATPase, is located on the inner cytoplasmic surface of the plant plasma membrane. The 45Ca2+ uptake was MgATP‐dependent with an apparent Km for ATP of 0.1 mM and a high affinity for Ca2+ [Km(Ca2+/EGTA) = 3 μM]. The pH optimum was at 7.4–7.8. ATP was the preferred nucleotide substrate with ITP and GTP giving activities of 30–40% of the 45Ca2+ uptake seen with ATP. The 45Ca2+ uptake was stimulated by monovalent cations; K− and Na+ being equally efficient. Vanadate inhibited the 45Ca2+ accumulation with half‐maximal inhibitions at 72, 57 and 2 μM for basal, total (with KCI) and net K+‐stimulated uptake, respectively. The system was also highly sensitive to erythrosin B with half‐maximal inhibition at 25 nM and total inhibition at 1μM. Our results demonstrate the presence of a primary Ca2+ transport ATPase in the plasma membrane of wheat roots. The enzyme is likely to be involved in mediating active efflux (ATP‐binding sites on the cytoplasmic side) to the plant cell exterior to maintain resting levels of cytoplasmic free Ca2+ within the cell.
Phytohormonal changes in greening and senescing intact cotyledons of oilseed rape and pumpkin: influence of the growth retardant BAS 111 ˙˙ W
Authors: Grossmann Klaus , Kwiatkowski Jacek , Häuser Christiane
Published: May 2006

The triazole growth retardant BAS 111‥W delayed senescence in cotyledons of pumpkin (Cucurbita maxima L. cv. Gelbe genetzte Riesenmelone) and stimulated chlorophyll synthesis in greening cotyledons of oilseed rape (Brassica napus L. cv. Petranova) seedlings. In both cases, changes of phytohormone‐like substances in the cotyledons were analyzed on a fresh weight basis by immunoassay.

After soil treatment with increasing retardant concentrations, a close correlation was observed in senescing cotyledons of pumpkin between a reduced loss in total chlorophyll and increasing levels of dihydrozeatin riboside (DZR) and trans‐zeatin riboside (ZR)‐type cytokinins. In contrast, the levels of isopentenyladenosine (IPA)‐type cytokinins, 3‐indoleacetic acid (IAA) and gibberellin (GA) did not change significantly. The levels of abscisic acid (ABA) were slightly elevated at low retardant concentrations but dropped considerably below those of controls at higher doses. Consequently, the molar ratio of total cytokinin to ABA content changed from approximately 1:40 in controls (50% of initial chlorophyll) to 1:3 in cotyledons treated with 3 mg BAS 111‥W plant−1 (85% of initial chlorophyll). These changes, together with the known reduction of ethylene production by plants treated with nitrogen‐heterocyclic retardants, can explain the delayed senescence in pumpkin cotyledons. Likewise, when etiolated, BAS 111‥W‐treated seedlings of oilseed rape were exposed to light, the stimulation of chlorophyll synthesis in the cotyledons was accompanied by an accumulation of DZR‐ and, particularly, ZR‐type cytokinins and IAA. In contrast, GA and ABA contents decreased slightly. We conclude that the influence of BAS 111‥W on cytokinin levels might be involved in the stimulation of greening.
Seawater‐resistant, non‐spherical protoplasts from seagrass leaves
Authors: Arai Masayoshi , Pak Jun Yong , Nomura Koji , Nitta Takeshi
Published: May 2006

Two distinct types occurred among enzymatically isolated protoplasts from leaves of eelgrasses (Zostera marina L., Z. japonica Ascherson and Phyllospadix iwatensis Makino). Spherical protoplasts with a smooth cell membrane were obtained only from young leaf tissues at the basal portions of blades protected from seawater by tightly enclosing sheaths. Non‐spherical protoplasts had a highly invaginated cell membrane and were obtained from mature leaf blades, where the cells also in situ have this type of membrane. The protoplasts from mature leaves were rather rigid in shape and resistant to wide ranges of osmotic potential and salinity without change in their non‐spherical shape, while the spherical protoplasts were rapidly destroyed in seawater. Detergents lysed the spherical protoplasts but not the non‐spherical ones, suggesting that the highly invaginated enclosing structures of the non‐spherical protoplasts contained detergent‐resistant materials. Thus, the seagrass leaf cells develop seawater resistance, and this change alters the nature of the enclosing structures during the growth of the leaf blades. The non‐membranous enclosing structures and their characteristic materials in the mature leaf cells remain to be defined.
Characterization of the early events of potato tuber development
Authors: Hannapel David J.
Published: May 2006

The early events of potato (Solanum tuberosum L. cv. Superior) tuberization were examined by using a model system of axillary bud tuber development from petiole‐leaf single‐node cuttings. Both fresh weight and starch accumulation were monitored to establish a developmental framework for morphological changes. Fresh weight and starch content began to increase in axillary buds after 2 days. Visible changes in bud morphology could be detected 4 days after the start of incubation. Substantial increases in both total protein and total RNA were observed at the onset of tuber morphology. Immunoblot analysis showed that the major tuber protein, patatin, could be initially detected in day 4 buds and that a 22‐kDa proteinase inhibitor could be initially detected at day 8. Northern blot analysis corroborated this pattern of accumulation at the RNA level for both protein types. Substantial accumulation of the two proteinase inhibitor mRNAs occurred later than patatin mRNA accumulation. The results of this study showed that there is considerable accumulation of both protein and mRNA occurring during the early stages of tuber development prior to the substantial accumulation of the major tuber storage proteins.
Further studies on the effects of different auxins and cytokinins on flower formation in thin cell layers of Nicotiana tabacum: The effects of zeatin riboside, dihydrozeatin and dihydrozeatin riboside
Authors: Heylen Christine , Vendrig Jan C.
Published: May 2006

Organogenesis in thin cell layers of Nicotiana tabacum L. was studied in relation to the effects of natural and synthetic auxins in combination with various cytokinins. All cytokinins tested, benzyladenine (BA), kinetin, zeatin (Z), zeatin riboside (ZR), N6‐Δ2‐isopentenyl) adenine (IPA), dihydrozeatin [(diH)Z] and dihydrozeatin riboside [(diH)ZR], seem to be active in flower bud formation. In addition to the initiation of flower buds, vegetative buds or roots were also formed on the explants in the presence of BA, Z or IPA as exogenous cytokinins. Only dihydrozeatin and its riboside stimulated the initation of flower buds alone (as is known for kinetin), especially if supplemented with indole‐3‐acetic acid (IAA) as exogenous auxin. A high number of explants with flower buds was also found with high cytokinin/2,4‐D ratios. In these conditions the presence of (diH)Z yielded the higest number of flower buds per explant.