bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchrony induced by double phosphate starvation in a suspension culture of Catharanthus roseus
Authors: Amino Shin‐ichi , Fujimura Tatsuhito , Komamine Atsushi
Published: April 2006

A synchronous cell division system was established using the double phosphate starvation method, based on the observation that one of the limiting factors in the growth of a suspension culture of Catharanthus roseus (L.) G. Don cells in the medium of Murashige and Skoog was phosphate. In the system, an increase in cell number took place in a short period of only 4 h, while the cell number remained almost constant during other periods of the cell cycle. The synchrony of the culture was confirmed by changes in mitotic index, which increased sharply prior to the increase in cell number. The S phase was determined by measuring incorporation of [3H]‐thymidine into the DNA fraction during the cell cycle and synchrony of DNA synthesis was verified likewise. Synchronization by phosphate starvation is discussed in relation to the function of phosphate as a nutrient. The synchronous system thus established will be useful in biochemical studies of the cell cycle in higher plants.
Effects of activated charcoal in anther cultures
Authors: Johansson Lars
Published: April 2006

Embryogenesis in anther cultures of Anemone Canadensis L., Anemone hupehensis Lemoine and Nicotiana tabacum L. was shown to be inhibited by abscisic acid added to the medium. However, this inhibition was reduced in the presence of activated charcoal (AC).

The presence of AC in the culture medium strongly promoted embryogenesis in anther cultures of Anemone Canadensis compared with other media combinations. Treatment of the agar medium with AC, which was removed before inoculation of the anthers, also stimulated embryogenesis, but treatment of the water constituent did not.

The number of embryos produced in anther cultures of Anemone Canadensis and Nicotiana tabacum was shown to be positively related to the length of lime of incubation on medium supplemented with AC. In the case of Anemone Canadensis the stimulating effect of AC was most pronounced when the first visible embryos had emerged.

The presence of anther‐derived embryos from Anemone Canadensis in anther cultures of Anemone Canadensis and Nicotiana tabacum was shown to inhibit embryogenesis. It was also demonstrated that embryos from anther cultures of Anemone canadensis, Papaver setigerum DC and Clematis viticella L. produced phenolic substances, and that the concentration of these substances was higher in culture medium lacking AC. Treatment of such medium with AC could reduce the concentration of phenolic substances by more than 80%.
Source of electrons for extracellular Fe(III) reduction in iron‐deficient bean roots
Authors: Sijmons P. C. , Bienfait H. F.
Published: April 2006

Iron‐deficient Phaseolus vulgaris L. cv. Prelude developed a high reducing capacity for extracellular Fe(III) at the root surface. This reduction was competitively inhibited by Nitro‐Blue Tetrazolium salt (Nitro‐BT) which was deposited as a blue precipitate within the epidermis cells of the youngest root parts. Root respiration was not influenced by Nitro‐BT. The intracellular reduction of Nitro‐BT could largely be prevented by excess extracellular Fe(III)EDTA. Iron‐sufficient control plants reduced both extracellular Fe(III)EDTA and intracellular Nitro‐BT at a much slower rate. A role of cytosolic NADH or NADPH as direct electron donors for the enhanced Fe(III) reduction at the plasmalemma is indicated. NAD+‐3‐phosphate dehydrogenase activity was higher in preparations from iron‐deficient root parts than in preparations from control root parts. Ferricyanide, dichlorophenolindophenol and phenazine methosulfate were also reduced at an increased rate by iron‐deficient roots. We conclude that a trans‐plasma membrane electron transfer, mediated by a membrane‐bound reductase, is responsible for the reduction of extracellular Fe(III).
Imbibition conditions and seed dormancy of Arabidopsis thaliana
Authors: Cone J. W. , Spruit C. J. P.
Published: April 2006

The optimal combinations of temperature in the range of 0 to 20°C and duration (1 to 14 days) of imbibition for the induction of germination of Arabidopsis thaliana (L) Heynh., ecotype “Landsberg‐erecta”, by red light were investigated. At 2°C, 10 days of imbibition are needed tor loss of dormancy, whereas at higher temperatures, e.g 15°C, it is already lost after 1 or 2 days. It is proposed that the development of light‐inducible germination is governed by two temperature‐dependent processes‐the loss of primary or innate dormancy and the simultaneous induction of secondary dormancy. Data are discussed in terms of the availability of phytochrome, the availability of an unknown factor X and changes in sensitivity of the process of germination induction by the far‐red absorbing form of phytochrome (Pfr).
The pathway of betalain biosynthesis: Effect of cytokinin on enzymic oxidation and hydroxylation of tyrosine in Amaranthus tricolor seedlings
Authors: Elliott Daphne C.
Published: April 2006

The effect of exogenously added tyrosine or l‐3‐(3,4‐dihydroxyphenyl) alanine on the accumulation of betacyanin in response to cytokinin in Amaranthus tricolor (L.) var. tricolor half‐seedlings depends on the age of the seedlings and the treatment of the seedlings prior to induction of pigment by benzyladenine. Neither extracted polyphenol oxidase, peroxidase or tyrosine hydroxylase activity, nor in vivo tyrosine hydroxylation is increased in response to exposure of seedlings to cytokinin. However a small percentage of the polyphenol oxidase activated or unmasked by Triton X‐100 treatment of membrane fractions is increased after cytokinin treatment of half‐seedlings for 22 h. It is concluded that cytokinin control may be on a multi‐enzyme membrane‐located complex involving part of the polyphenol oxidase activity of the tissue (possibly an isoenzyme), and that the majority of the polyphenol oxidase activity in Amaranthus is a constitutive membrane enzyme which is not involved in betacyanin synthesis.

Although cytokinins do not affect in vivo tyrosine hydroxylation, this activity follows closely the accumulation of betacyanin which is first detectable about 6.5 h after the application of cytokinin. Only a very low level of in vivo hydroxylation can be demonstrated in half‐seedlings treated for 6 h either with or without cytokinin but it begins to increase shortly after this time. A large increase in this activity by 16 h (independent of cytokinin) can be almost completely (79%) prevented by chloramphenicol (300 μM) although the drug increases accumulation of betacyanin. At this concentration about 30% of the protein synthesis in inhibited. In vitro tyrosine hydroxylation is, however, not reduced in half‐seedlings treated with chloramphenicol during 16 h induction nor is extractable polyphenol oxidase reduced. It is concluded that chloramphenicol is inhibiting the synthesis of some protein essential for in vivo hydroxylation other than the activity measured during in vitro hydroxylation and that the inhibition of synthesis of 79% in vivo hydroxylation still leaves enough activity for maximum betacyanin synthesis.
Effects of di‐n‐butyl phthalate on growth and photosynthesis in algae and on isolated organelles from higher plants
Authors: Melin Christina , Egnéus Hans
Published: April 2006

Di‐n‐butyl phthalate (DBF) is widely used as a plasticizer and has been found in all types of ecosystems. It inhibits growth and photosynthesis of green algae (Chlorella emersonii CCAP strain 211/8 h and Selenastrum capricornutum CCAP strain 278/4) at concentrations higher than 10‐5M. The IC50 value for CO2‐dependent oxygen evolution in algae was 3 × 10‐4M. The CO2‐reduction in isolated protoplasts prepared from barley (Hordeum vulgare L. cv. Simba) was also inhibited by phthalate. The IC50 value was 2 × 10‐4M. The electron transport in isolated thylakoids prepared from spinach was inhibited with an IC50 value of 3 × 10‐4M. The IC50 value for uncoupled electron transport extrapolated to zero chlorophyll concentration was 2.5 × 10‐5M. The effect of di‐n‐butyl phthalate was localized to reactions in photosystem II. Di‐n‐butyl phthalate could thus be a pollutant which affects growth and photosynthesis of plants. The reported IC50 values may be underestimated since di‐n‐butyl phthalate can attach to surfaces. The results are discussed in relation to observed effects of di‐n‐butyl phthalate on other organisms.
Lipid changes during natural aging of soybean seeds
Authors: Priestley David A. , Leopold A. Carl
Published: April 2006

When soybean seeds [Glycine max (L.) Merr. cv. Wayne] were stored at approximately 4°C and low humidity for 44 months (“natural aging”) there was a marked decline in vigor and viability which was associated with a decrease in the proportion of the polyunsaturated fatty acids. Other lipid parameters showed little change. Seeds subjected to high humidity at 40°C for several days (“accelerated aging”) experience a comparable decline in vigor and viability, but without the change in fatty acid polyunsaturation. These results indicate that accelerated aging may cause loss of vigor in a manner quite different from natural aging. The accelerated aging treatment is therefore of limited usefulness in investigations of the mechanism of natural seed aging.
Changes in protein composition of the shoot meristem during floral evocation in Sinapis alba
Authors: Lyndon R. F. , Jacqmard A. , Bernier G.
Published: April 2006

Shoot apical meristcms of vegetative and induced plants of Sinapis alba L. were labelled with [35S] methioninc for 2 h and the proteins were then separated by isoelectric focussing and polyacrylamide gel electrophoresis. Quantitative and possibly qualitative changes in the complement of proteins being synthesised during evocation were detected in the meristem, distal to the primordia, 50 to 52 h after the beginning of the inductive long day. This was before morphological changes in the meristem, and before the initiation of flower bud primordia.
Isolation from sugarcane cultures of variants resistant to antimetabolites
Authors: King John , Maretzki Andrew
Published: April 2006

Variants resistant to antimetabolites are useful for investigating metabolic regulation and biochemical genetics in organisms. In this study, suspensions of mutagenized sugarcane (Saccharum sp.) cells, originating from a stalk parenchyma explain of the Hawaiian variety 50–7209, were used to investigate the feasibility of isolating variants resistant to l‐canavanine, glyphosate [N‐(phosphonomethyl)glycine], ophiobolin A and orthovanadate. Rigorous retesting of clones which grew on selection media led to the identification of three cell lines, two of which were resistant to glyphosate and one to orthovanadate. No variants were isolated which showed a persistent resistance either to l‐canavanine or ophiobolin A.

The results demonstrate that resistant variants do occur, or can be induced, in sugarcane cell suspensions and that they can be rescued and cultivated.
Calcium and magnesium effects on symbiotic nitrogen fixation in the alfalfa (M. sativa) –Rhizobium meliloti system
Authors: Miller Richard W. , Sirois Jean Claude
Published: April 2006

An investigation of the roles of calcium and magnesium ions in symbiotic nitrogen fixation by legumes has shown that alfalfa plants (Medicago sativa L. cv. Saranac and Apollo) deficient in either cation were poorly nodulated and retarded in growth on nitrogen‐free media. This effect was reversed by supplementation with normal levels of these cations. After recovery, the calcium deficient seedlings showed continuing effects of early mineral deficiencies but recovered to 75% of the nitrogenase activity and had nearly the same yield as control plants. Magnesium deficient plants recovered nitrogenase activity to the same degree but grew to only about 50% of the weight of controls. Supplementation of non‐deficient seedlings grown on N‐free media with varying amounts of Ca2+ and Mg2+ resulted in the identification of an optimal ratio of calcium and magnesium near 2 when neither cation was growth limiting. A highly significant positive correlation was obtained between yield of dry matter and the fraction of total expressed nitrogenase activity that was actually available for dinitrogen reduction (nitrogen reducing equivalent). Bacteroids isolated from root nodules and freed of plant cytoplasmic components required high magnesium levels for maximal utilization of externally supplied ATP and dithionite. Ca+ was antagonistic to this activity but complemented Mg2+ in stimulating the respiration‐supported nitrogenase activity of intact bacteroids which had been treated with a chelating agent. The effects of calcium and magnesium on the nitrogenase system of intact bacteroids may be due to binding of the Ca2+ ions to the bacteroid membrane.
Induction and suppression of RNase activity by growth regulators in senescing ragi leaves
Authors: Kumar K. B. , Khan P. A.
Published: April 2006

Activity of RNase was studied in attached and detached leaves of 7‐day‐old ragi (Eleusine coracana Gaertn. cv PR 202) plants during senescence using crude enzyme extracts. The RNase activity was relatively constant in attached leaves. In excised leaves incubated in the dark there was a rapid rise in enzyme activity up to 48 h, followed by a decline. No such decrease was observed in the light. Benzimidazole and gibberellic acid suppressed the activity of RNase up to 48 h in the dark and 96 h in the light. Both the growth regulators also prevented the post‐48 h decline in RNase activity of dark incubated excised leaves. Decline in the levels of chlorophyll and RNA in the illuminated excised leaves was not affected by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyIurea, but the inhibitor prevented the photo‐induced rise in RNase activity. Cycloheximide and actinomycin D could completely prevent both detachment (increase in enzyme activity after the leaf is excised) and photo‐induced rise in RNase activity. Benzimidazole and gibberellic acid prevented the rise in the activity of RNase on one hand and maintained it on the other by their influence on its biosynthesis. Photoinduction of RNase and photo‐induced retardation of senescence are concluded to be two different processes.
Characteristics of ATPase from sugarcane protoplast and vacuole membranes
Authors: Thom M. , Willenbrink J. , Maretzki A.
Published: April 2006

Characteristics of membrane‐associated ATPase from commercial Hawaiian varieties of sugarcane (Saccharum spp. hybrids) were investigated in preparations from sugarcane cell suspension culture and from stalk tissues of the intact plant. In order to examine comparable preparations, protoplasts and vacuoles, in turn, were obtained from both sources. ATPase from preparations of crude protoplast membranes and tonoplast had a pH optimum of 6 to 6.5. The relative effectiveness of divalent cations in stimulating ATPase was Mg2+ > Mn2+≥ Co2+ > Ca2+≥ Zn2+. Enzyme activity was not stimulated by K+, nor by other monovalent cations. Protoplasts and vacuoles from both sources showed significant acid phosphatase activity. Acid phosphatase activity was inhibited by molybdate, but ATPase activity was unaffected. Membrane preparations from protoplasts contained inorganic pyrophosphatase, but enzyme activity was low or not present in tonoplast preparations. Cell suspension and stalk tissue preparations hydrolyzed a large number of nucleoside di‐ and triphosphates. The hydrolysis is most likely due to a series of enzymes rather than a single enzyme. ATPase from protoplast and tonoplast preparations was inhibited 30–50% by diethylstilbestrol and sodium ortho‐vanadate and was unaffected by ionophores. This study illustrates the complexity of phosphohydrolase activities in membrane preparations from sugarcane. The study, however, also illustrates substantial similarity in the behavior of these enzymes, whether they are derived from the plant itself or from cell cultures originating from comparable tissues of the plant.
Pollen dimorphism in relation to pollen plant formation
Authors: Rashid A.
Published: April 2006

Induction of haploid plants from pollen grains on culture of anthers has been possible in a number of angiosperms but it is not yet understood why only a fraction of pollen responds to form haploids. Noteworthy in this connection are the recent experiments on anther culture of barley, tobacco and wheat, where it has been pointed out that pollen populations are basically dimorphic. Pollen capable of forming haploids occur in a low frequency, arc smaller, and different from the majority of pollen destined to form gametes. Particularly in tobacco it has been possible to increase the frequency of pollen capable of forming embryos by subjecting plants to low temperature prior to flowering, and to achieve differentiation of embryogenic pollen by subjecting young buds from such plants to a prolonged cold treatment. On selective isolation, from the rest of the pollen, the embryogenic pollen from such buds readily form embryos at high frequency on a simple mineral‐sucrose medium. The embryogenic pollen are repressed for gametophytic differentiation and in culture they differentiate to produce embryos. These experiments provide evidence that only certain pollen are capable of forming haploids.
Effects of a brassinosteroid on growth and electrogenic proton extrusion in maize root segments
Authors: Romani G. , Marriè M. T. , Bonetti A. , Cerana R. , Lado P. , Marrè E.
Published: April 2006

In apical or subapical root segments of maize (Zea mays L. cv. Dekalb XL640), 10−7–10−5M 24‐epibrassinolide (BR), a physiologically active synthetic epimer of the pollen hormone brassinolide, induces a significant stimulation of root growth, associated with an increase of acid secretion. The increase in acid secretion is enhanced by the presence of K+ in the medium and is accompanied by an early, significant hyperpolarization of the transmembrane electric potential (PD), which is completely suppressed by the addition of the protonophore uncoupler FCCP. Similar effects of BR have earlier been reported for shoots, and also for IAA in shoots. Contrariwise, 10−8–10−7M IAA inhibits acid secretion and depolarizes the PD in the maize root segments. This suggests different pathways for the action of the two different hormones on the proton pump.
Response to directional light by leaves of a sun‐tracking lupine (Lupinus succulentus)
Authors: Vogelmann Thomas C. , Björn Lars Olof
Published: April 2006

Experiments were done to examine the phototrophic response of sun‐tracking leaves of Lupinus succulentus Dougl. to fixed beams of white and broad band light. Upon irradiation with 15 W m−2 white light that struck the laminae at an angle of 45°, there was a 45–60 min lag period prior to leaf movement. The greatest rate of movement was 15° h−1, and reorientation ceased when leaves attained a position within 15° of perpendicular to the light beam. Laminar movement was largely pulvinar, and a 60 min inductive light treatment was sufficient to activate a maximum pulvinar response in subsequent darkness. Light striking the lamina at angles between 20 and 70° induced similar maximum pulvinar responses and only light that struck the upper (adaxial) leaf surface was effective. Leaf tracking was fully activated by blue light but not by red or yellow light.
Organogenesis and fine structure in megagametophyte callus lines of Picea abies
Authors: Simola Liisa Kaarina , Honkanen Jarmo
Published: April 2006

Differentiation and fine structure were studied in 63 callus lines originating from the haploid megagametophyte of Picea abies (L.) Karst. Developing cones were collected from 27 trees growing in 13 localities in Finland. Vernalization of cones for 12–42 days at 4°C was optimal for callus initiation from the immature megagametophyte (primary endosperm). Five combinations of media based on the macronutrient elements of Chu et al. (1975; Sci. Sin. 18: 659–668) and the micronutrient elements and vitamins of Murashige and Skoog were tested for callus induction, growth and differentiation. Only about 1.5% of the megagametophytes produced subculturable callus (which may be partly due to the high frequency of lethal genes), although in certain mother trees callus production was as high as 20%. In most of the trees sampled, polyamines could not replace casein hydrolysate and glutamine in induction of megagametophyte callus. About half of the originally haploid, diploid and mixoploid callus lines were able to differentiate. A combination of three polyamines (putrescine 0.25, spermidine 0.1 and spermine 0.025 mM) favoured development of roots. In five callus lines shoots and roots developed in the same piece of callus, but these organs usually had no connection with each other. The fine structure of the callus cells was normal, but their starch stores were rather abundant. Mesophyll cells of needles differentiated from originally haploid callus had chloroplasts with fairly well‐developed grana. Secondary metabolites were observed in the vacuoles of some callus cells and in organ initials. Plasmodesmata were very rare in callus cells but they were characteristic of those of the needles. The electron microscope observations showed that the poor capacity for differentiation of P. abies callus cultures was not due to cytological instability.
Isolation and photosynthetic characteristics of mesophyll cells from developing leaves of soybean
Authors: Cosio Eric G. , Servaites Jerome C. , McClure Jerry W.
Published: April 2006

Mesophyll cells were isolated from developing sink leaves (25 to 30 mm in length) of soybean, Glycine max (L.) Merr. cv. Will. Leaf strips were incubated for two h in a buffered medium containing osmoticum and 0.2% Pectolyase Y‐23. Gently stirring the leaf strips released from 7 to 16% of the total leaf mesophyll cells. Other pectinase enzymes, effective in releasing cells from mature source leaves (70 to 75 mm in length), did not release cells from sink leaves. Sink and source cell preparations were about 50 and 95% intact, respectively, based on the exclusion of Evans Blue dye. Intact cells could not be separated from broken cells on Ficoll or metrizamide density gradients. Total protein and catalase, glyceraldehyde‐3‐phosphate dehydrogenase, glycolate oxidase, phosphoenolpyruvate carboxylase, and ribulose 1,5‐bisphosphate carboxylase activities on a chlorophyll basis were about 50% lower in sink mesophyll cells than in sink leaf homogenates indicating that broken sink cells lost soluble protein to the medium. Source cells and source leaf homogenates had comparable amounts of protein and enzymatic activities. Enzymatic activities on a chlorophyll basis were similar in source and sink leaves with the exception of phosphenolpyruvate carboxylase, which was two times higher in sink leaves. This enzyme was also exceptionally low in source and sink cells being only 61 and 23%, respectively, of whole leaf activities. Sink cell rates of 14CO2 fixation were only 7% of source cell rates and sink cells did not show light‐dependent O2 evolution. Both cell preparations had photosystem II activiteis which were comparable to rates of 14CO2 fixation at satuarating light and CO2 concentration. It was concluded that the reduced photosynthetic rate of sink cells was limited by the low photochemical capacity rather than a limitation of Calvin cycle enzymes.
Internode length in Pisum. IV. The effect of the Le gene on gibberellin metabolism
Authors: Ingram T. J. , Reid J. B. , Potts W. C. , Murfet I. C.
Published: April 2006

The highly active, polar gibberellin‐like substance found in the apical region of shoots of tall (genotype Le) peas (Pisum sativum L.) is shown by combined gas chromatography‐mass spectrometry (GC/MS) to be GA1. This substance is either absent or present at only low levels in dwarf (le) plants. Multiple ion monitoring (MIM) tentatively suggests that GA8 may also be present in shoot tissue of tall peas. Gibberellin A1 is the first 3 β‐hydroxylated gibberellin positively identified in peas, and its presence in shoot tissue demonstrates the organ specificity of gibberellin production since GA1 has not been detected in developing seeds. Application of GA1 can mask the Le/le gene difference. However, whilst Le plants respond equally to GA20 and GA1, le plants respond only weakly to GA20, the major biologically active gibberellin found in dwarf peas. These results suggest that the Le gene controls the production of a 3 β‐hydroxylase capable of converting GA20 to GA1. Further support for this view comes from feeds of [3H] GA20 to Le and le plants. Plants with Le metabolise [3H] GA20 to three major products whilst le plants produce only one major product after the same time. The metabolite common to Le and le plants co‐chromatographs with GA29. The additional two metabolites in Le peas co‐chromatograph with GA1 and GA8.
The localization of magnesium‐protoporphyrin and protochlorophyllide in separated prolamellar bodies and prothylakoids of wheat treated with 8‐hydroxyquinoline and δ‐aminolevulinic acid
Authors: Ryberg Margareta
Published: April 2006

Dark‐grown leaves of wheat (Triticum aestivum L. cv. Starke II, Weibull) were treated in darkness with 8‐hydroxyquinoline and δ‐aminolevulinic acid in order to accumulate magnesium‐protoporphyrin and/or magnesium‐protoporphyrin monomethylester. Prolamellar bodies and prothylakoids were separated from the treated leaves by sucrose density gradient centrifugation. About 90% of the recovered magnesium‐protoporphyrin/magnesium‐protoporphyrin monomethylester and about 75% of the recovered protochlorophyllide was found in the prothlakoid fraction. The significance of the distribution pattern of the chlorophyll precursors between the prolamellar bodies and the prothylakoids is discussed. The results indicate that the prothylakoids are the site for synthesis of membrane‐bound chlorophyll precursors and that phototransformable protochlorophyllide is a constituent of prolamellar bodies as well as of prothylakoids.
The effect of 1‐β‐d‐ribofuranosyl‐ 1,2,4‐triazole‐3‐carboxamide on bud and shoot formation in tobacco petiole cultures
Authors: Cassells A. C. , Long R. D.
Published: April 2006

Ribavirin (1‐β‐d‐ribofuranosyl‐ 1,2,4‐triazole‐3‐carboxamide) increases starch accumulation in explants of Nicotiana tabacum L. ev. Xanthi nc and increases the number of meristematic zones; adventitious bud and shoot formation is significatntly increased. It overcomes auxin inhibition of bud and shoot formation in this system but studies on interaction with exogenous auxin and triiodobenzoic acid do not support the hypothesis that ribavirin acts directly on auxin metabolism. The results are discussed in relation to the induction and maintenance of permissive or receptive cell states in tobacco explant culture.
Seasonal variation of nitrogenous compounds in the xylem sap of Citrus
Authors: Moreno Joaquín , García‐Martinez José L.
Published: April 2006

Samples of tracheal sap of Citrus sinensis (L.) Osbeck cv. Washington Navel were taken from field trees throughout the year and the nitrogen composition of the sap was determined. The nitrogenous fraction of the sap was composed mainly of free amino acids (92–97% of total nitrogen) and nitrates throughout the year. Proline was the most abundant amino acid during almost the entire cycle, and its concentration was especially high during the autumn and winter period. Nevertheless, a significant part (40–60%) of the total organic nitrogen was transported as arginine. Total nitrogen as well as amino acids and nitrates were maximal at spring flush. At spring flush and summer flush there was also a diversification of α‐amino nitrogen among different amino acids. During the spring flush, nitrates, asparagine and γ‐aminobutyric acid in the xylem sap seemed to have a radicular origin, whereas glutamic acid and arginine were released from the surrounding parenchyma. The results suggest a metabolic transformation in the wood parenchyma of nitrogenous compounds coming from the roots (including reduction of nitrates) and a turnover of different nitrogen metabolites between the xylem and surrounding cells.
Morphogenesis in dormant embryonic shoots of Picea abies: Influence of the crown and cold treatment
Authors: Jansson Eva , Bornman Chris H.
Published: April 2006

Retention of the crown, a plate of homogeneously thickened collenchymatous cells at the base of the embryonic shoot of Picea abies (L.) Karst., has marked effects on the induction of adventitious buds from the needle primordia. These effects were observed on embryonic shoots of three clones which were cold‐treated at 4 ± 1°C for nil, two, four and six months; and then excised either with or without the crown, before subculturing either directly on a medium lacking plant growth regulators or after application of 125 μM benzyladenine (BA) as a 3‐h pulse. Embryonic shoots retaining the crown and treated with BA responded reproducibly better than those lacking it. This was true both for the number of shoots that produced adventitious buds and for the numbers of adventitious buds per shoot. Differentiation of as many as five adventitious buds in a single needle primordium was observed, with development occurring nearly twice as early (7 as compared with 12 weeks) in the presence as in the absence of the crown. The response decreased progressively with increasing exposure to cold treatment.

A number of anatomical changes occurred during culture in vitro. After 3 to 4 weeks a band of sclerenchymatous cells commenced differentiation at the centre of the crown. In embryonic shoots without the crown, a tissue which was identified as a wound periderm formed at the excision surface. Vascular unions were observed between the tissues of the newly — formed shoots induced from the needle primordia and those of the original shoot explants.
Effects of a brassinosteroid on growth and electrogenic proton extrusion in Azuki bean epicotyls
Authors: Cerana R. , Bonetti A. , Marrè M. T. , Romani G. , Lado P. , Marrè E.
Published: April 2006

Brassinolide, a plant hormone newly isolated from pollen, promotes growth of the stem of a number of plant species. Similar effects are induced by a brassinosteroid (BR), the synthetic 24‐epibrassinolide. In this paper the effects of BR on acid secretion and transmembrane electrical potential difference in Azuki bean (Vigna angularis, Ohwi and Ohashi cv. Takara) epicotyls were determined in short term experiments and compared with the effects on growth. At concentrations between 10‐7 to 10‐5M, BR stimulates, similarly to indole‐3‐acetic acid (IAA), growth and H+ extrusion and hyperpolarizes the transmembrane electric potential (PD). These effects of BR, as well as those of IAA, are suppressed by inhibitors of RNA and protein synthesis. All these effects of BR and IAA appear roughly additive, even when both hormones are present at their optimal concentrations. The data are interpreted as showing that the action of BR on growth is at least in part mediated by its capability to activate electrogenic proton extrusion. The additivity of the effects of BR and IAA suggests that the primary mechanism of action of the two hormones is different.
Breakdown of photosynthetic pigments and lipids in spinach leaves with ozone fumigation: Role of active oxygens
Authors: Sakaki Takeshi , Kondo Noriaki , Sugahara Kiyoshi
Published: April 2006

In spinach (Spinacia oleracea L. cv. New Asia) plants fumigated with ozone in light, destruction of chlorophylls and carotenoids and formation of malondialdehyde (MDA), an indicator of lipid peroxidation, were observed. Chlorophyll a and carotenoids in leaves started to be broken down 6–8 h after the commencement of 0.5 ppm ozone fumigation, whereas MDA formation in leaves increased linearly for the initial 8 h of fumigation followed by a more rapid increase. In leaf discs excised from 6‐h fumigated plants, destruction of chlorophyll a and carotenoids and MDA formation proceeded in the light but were almost completely suppressed under an anaerobic condition. Effects of exogenously applied scavengers of active oxygen species suggest that active oxygens, especially superoxide radical (O2‐), participated in both the destruction of chlorophyll a and carotenoids and the formation of MDA. Ozone fumigation reduced the levels of endogenous scavengers of O2‐, superoxide dismutase (SOD) and L‐ascorbate, in leaves to one‐half the initial levels each by 3.5 and 8 h fumigation, respectively. The results indicate that the photosynthetic pigments and lipids were broken down by active oxygens accumulated in leaves as a result of the ozone‐induced destruction of physiological defense against oxygen toxicity.

Activity of polyphenol oxidase in chloroplast membranes of 4‐h fumigated leaves increased to 240% of the initial level, suggesting that the thylakoid membranes had been affected severely before the pigment destruction. The relations between the pigment destruction and the disintegration of thylakoids are discussed.
Inhibition by mevinolin of plant growth, sterol formation and pigment accumulation
Authors: Bach Thomas J. , Lichtenthaler Hartmut K.
Published: April 2006

To obtain information on the importance of a functional mevalonate synthesis for plant growth and development, we investigated the effect of mevinolin, a highly specific inhibitor of 3‐hydroxy‐3‐methylglutaryl (HMG) coenzyme A reductase (the mevalonate‐producing enzyme) on growth, sterol accumulation and pigment formation of radish seedlings (Raphanus sativus L. cv. Saxa Treib) and in part also wheat seedlings (Triticum aestivum L. cv. Kolibri). Mevinolin applied during germination inhibits root elongation and development of lateral roots in etiolated and light‐grown radish seedlings. This effect cannot be overcome by exogenous GA3, but by addition of mevalonic acid, the product of the internally inhibited reaction. This emphazises the specifity of the mevinolin effect and indicates that the biosynthesis of mevalonic acid is a mandatory requirement for root growth. In light‐grown radish seedlings mevinolin also affects hypocotyl length‐growth and inhibits sterol accumulation, but has little effect on the chlorophyll and carotenoid accumulation in the chloroplasts of the cotyledons. This indicates the possible presence of an independent mevalonate synthesizing pathway within the plastids and suggests a low transport rate of mevinolin from the radish roots to the cotyledons. When mevinolin is directly applied to the leaves at higher concentrations, it also reduces the light‐induced chlorophyll and carotenoid accumulation as has been shown with etiolated primary leaves of wheat. This inhibition is age‐dependent and proceeds to a higher extent in older than in younger etiolated leaf tissue. From our results we conclude that plastids possess an independent HMG‐CoA reductase.

In the cotyledons of radish, mevinolin seems to induce a senescence retardation and sun‐type growth response, as has been evaluated by measuring the fast and slow chlorophyll fluorescence induction kinetics (Kautsky effect). These responses may be due to inhibitor‐induced changes in the intracellular phytohormone balance.
Induction of embryogenic pollen grains in situ and subsequent in vitro pollen embryogenesis in Nicotiana tabacum by treatments of the pollen donor plants with feminizing agents
Authors: Heberle‐Bors Erwin
Published: April 2006

Tobacco plants (Nicotiana tabacum L., var. Badischer Burley) were treated with chemicals (sprays and soil drenches) known to affect sex expression in other species. Their effect was tested on sex balance, pollen sterility, embryogenic pollen grain (P‐grain) formation in situ, and on pollen plant formation in anther and pollen cultures after anther preculture. Napthalene acetic acid (NAA) increased the length of pistils and stamens and shifted sex balance towards femaleness when the plants were raised in long or short days at 24 or 15°C. In parallel, pollen sterility, P‐grain frequency in situ and pollen plant production from anther and pollen cultures were increased by NAA. Alar 85 redueed the length of pistils and stamens and shifted sex balance towards femaleness when the plants were raised in long days at 24°C, but shifted it towards maleness in short days and/or at 15°C. In parallel, pollen sterility, P‐grain frequency in situ, and pollen plant production in vitro were increased when plants in long days at 24°C were treated with Alar 85, but decreased when plants in short days and/or at 15°C were treated. Ethrel, Cycocel, and GA3 applied in a similar manner, were ineffective. Water sprays and nitrogen starvation shifted sex balance towards femaleness in long days at 15°C and increased pollen sterility, P‐grain frequency in situ and pollen plant production in vitro. At 24°C, water sprays and nitrogen starvation had no effect.
Rb+ uptake by isolated pea mesophyll protoplasts in light and darkness
Authors: Rahat Michaela , Reinhold Leonora
Published: April 2006

Rb+ uptake into protoplasts isolated from the mesophyll of Pisum sativum L. cv. Dan has been followed at intervals of a few minutes in the light and in the dark. The progress curve for uptake in the dark decreased in slope after about 7 min; in the light, by contrast, the slope increased. This effect was more pronounced at pH 7 than at pH 5.5. The pH profile for uptake in the dark rose with increasing pH: in the light the profile flattened, or even fell somewhat, between pH 5.5 and pH 6.5, then rose again. In the dark the proton uncoupler carbonyl cyanide m‐chlorphenylhydrazone (CCCP) had little or no effect, either at pH 5.5 or at pH 7.4; in the light CCCP was strongly inhibitory, particularly at pH 7.4. Increasing concentrations of CCCP produced progressively more and more severe inhibition in the light, but in the dark produced a slight rise in uptake. The ATPase inhibitors quercetin, rutin and diethyl‐stilbestrol, as well as arsenate, all depressed uptake in the light, particularly at higher pH Dark uptake was sensitive only at pH 5.5, not at pH 7.4. In marked contrast to the case of methyl‐3 glucose, where protoplasts which were switched from light to dark took up sugar at the accelerated light rate for the first 7 min in the dark, a switch to darkness produced a Rb+ uptake rate below that for protoplasts held continuously in the dark. It is inferred that the mechanism of Rb+ uptake does not involve proton cotransport.

Information regarding the membrane potential was obtained by following the distribution of tetraphenyl phosphonium (TPP+) between protoplasts and medium. The potential was more negative in the light than in the dark. It was also more negative at pH 7 than at pH 5 both in the light and in the dark. Treatment with CCCP produced no appreciable depolarization within the first 20 min, indicating thet the CCCP inhibition of Rb+ uptake in the light cannot be ascribed to a reduction in potential. An ATP‐fueled K+ porter, or K+‐H+ antiporter, seems the most likely explanation. The maintenance of the rising pH profile in the dark, despite the presence of a CCCP concentration which drastically inhibits light uptake, suggests that the profile does not depend on the operation of the proton pump.
Epidermis effects on spectral properties of leaves of four herbaceous species
Authors: Lin Z. F. , Ehleringer J.
Published: April 2006

The spectral properties of the leaves of the herbaceous species Brassica oleracea L. var. botrytis L., Cerastum tomentosum L., Petunia hybrida Vilm., and Talinum paniculatum (Jacq.) Gaertn. were examined to see what effect the epidermis had on leaf absorptance, reflectance and transmittance. Removal of the epidermis from the side of the leaf surface being illuminated resulted in increases in leaf absorptance and transmittance, and a decrease in reflectance in the 400–800 nm waveband. Removal of the epidermis from the opposite side of an illuminated leaf (effect was similar in both abaxial and adaxial surfaces) resulted in small decreases in both absorptance and reflectance, and corresponding increases in transmittance. Removal of both the upper and lower epidermis resulted in a marked increase in transmittance, while both leaf reflectance and absorptance were decreased. The results suggest that the presence of the epidermis significantly increases leaf absorptance in the photosynthetic wavebands.
Fluorescence induction in Avena sativa investigated by modulated light
Authors: Kjeldstad Berit , Melö Thor B.
Published: April 2006

The structurated slow fluorescence induction of six days old seedlings of Avena sativa L., cv. Seger I (Svalöf, Sweden) has been investigated in its responses to systematic changes in the exciting conditions. The intensity of the exciting light was periodically altered between a high and a low value, and after the third period the resulting fluorescence induction curves became stationary. These stationary responses may all be resolved into four characteristic fluorescence transients, whose forms were rather independent of the exciting conditions. The heights of these transients were examined as a function of the exciting wavelength and the high level intensity. From these data it is concluded that the third transient originates from cyclic electron transport and that the fourth transient monitors the degree of energy transfer from the light harvesting complex to photosystem II. These two last transients of the induction curve are equivalent to the structurated slow fluorescence changes in ordinary induction curves.
Increased activity of aminopeptidase in the cotyledons of red light‐promoted lettuce seeds is controlled by the axis
Authors: Leung David W. M. , Bewley J. Derek
Published: April 2006

The first major reserves to be mobilized following germination of light‐promoted lettuce seeds (Lactuca saliva L. cv. Grand Rapids) are the carbohydrates, largely mannans, located within the cell walls of the endosperm. When these have been depleted, the cotyledonary reserves are hydrolysed; the first of these to decline is protein. Water‐, salt‐ and ethanol‐soluble proteins are mobilized simultaneously, and coincident with their loss from the cotyledons there is an increase in aminopeptidase activity. The level of enzyme activity increases appreciably in irradiated seeds after about 30 h from the start of imbibition. Essential for this increase, at least initially, is the presence of the axis ‐ first to perceive the light stimulus, and then to produce and/or release a chemical promoter which diffuses into the cotyledons and effects the rise in enzyme activity. Protein synthesis in the cotyledons is a prerequisite for both development and maintenance of the increased aminopeptidase activity.
Induction of phenylalanine ammonia‐lyase (PAL) in germinating lettuce seeds (Lactuca sativa)
Authors: Daines Richard J. , Minocha Subhash C. , Kudakasseril G. Jose
Published: April 2006

Dry lettuce seeds (achenes of Lactuca sativa L. cv. Grand Rapids) contain no detectable phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) activity. Enzyme activity could be detected in these seeds within 4 h of imbibition under white light. The specific activity of PAL increased rapidly during the next 12–16 h of imbibition. Far‐red light completely suppressed germination as well as the development of PAL. Gibberellic acid (GA3, 0.1 mM), although effective in causing almost 100% germination in dark, did not induce proportionate increases in PAL. Seed germination as well as PAL activity were substantially inhibited by cis‐4‐cyclohexene‐l, 2‐dicarboximide (CHDC, 1.0 mM) both in light and dark. Both GA3 and benzyladenine (BA, 0.1 mM) retarded radicle elongation in light. Concomitantly, a decrease in PAL activity was observed. Benzyladenine was able to reverse the effects of CHDC on germination but PAL activity was still highly reduced, probably due to the inhibitory effects of BA on elongation of the radicle. More than 95% of the extractable PAL was found to be present in the radicle. When seeds incubated in white light for 10 h were transferred to FR, further increases in PAL activity as well as the growth of the radicle were severely inhibited. It is suggested that the induction of PAL in light‐sensitive lettuce seeds is coincidental with the germination of seeds, and the amount of PAL per germinated seed is related to the extent of elongation of the embryonic axes.
Critical evaluation of the in vivo nitrate reductase assay for detection of two nitrate pools in wheat leaves
Authors: Høg Kirsten , Hartvigsen Marianne B. , Rasmussen Ole S.
Published: April 2006

The usefulness of the nitrate‐free in vivo nitrate reductase assay for the study of nitrate pools in wheat leaves was investigated. Leaf sections from 7‐day‐old wheat seedlings, exposed 24 h before harvest to 1.5, 3.0 or 5.0 mM KNO3 were used. After 2 to 4 h of incubation nitrite production ceased, reaching a plateau. The time required to reach the plateau and the level of the plateau increased with increasing endogenous nitrate content. At nitrite plateau the amount of nitrate left in the tissue was independent of the original nitrate content in the tissue. Addition of nitrate at plateau caused resumed nitrite production. It is concluded that nitrate was the limiting factor in nitrite production.

Oxygen inhibited nitrate reduction and stimulated further assimilation of nitrite. A considerable initial leakage of nitrate from tissue to the assay medium, followed by a slower continuous leakage, was observed throughout the incubation. N2‐flushing or inclusion of Triton X‐100 in the assay medium increased nitrite production by making more nitrate available for reduction. These treatments also increased the leakage of nitrate. At plateau levels the amount of nitrate left in the tissue was dependent on the oxygen tension in the assay medium. Under low oxygen tension nearly all nitrate in the tissue was available for reduction. Nitrite production at plateau is not a useful index for a metabolic nitrate pool and nitrate left in the tissue is not a useful index for a nitrate storage pool because both parameters are highly dependent on the oxygen tension in the assay medium. Further, in view of the considerable leakage, the nitrate‐free in vivo nitrate reductase assay cannot be used to detect two separate nitrate pools in wheat leaves.
Nutrient requirements and stress response of Populus simonii and Paulownia tomentosa
Authors: Hui‐jun Jia , Ingestad Torsten
Published: April 2006

The aim of this investigation was to estimate the optimum nutrient requirements and responses to low relative nutrient addition rates of seedlings of two important broadleaf tree species in China, Populus simonii Carr. and Paulownia tomentosa (Thunb.) Steud. In preliminary experiments the optimum nutrient proportions were estimated under high concentration conditions. The nutrients consumed were replaced by means of daily additions determined by pH and conductivity titrations without changing the nutrient solutions. A relatively high K level was needed in relation to nitrogen; higher than in birch or grey alder seedlings. To obtain a high relative growth rate, suitable proportions by weight were 100 N:70 K:14 P:7 Ca:7 Mg for the Populus seedlings and 100 N:75 K:20 P:8 Ca:9 Mg for the Paulownia seedlings.

In studies of nutrient stress responses the relative nutrient addition rate was used as the treatment variable under low conductivity conditions. The responses and relationships were similar to those described for birch, grey alder and Salix. The relative addition rate, and there was also a strong linear regression between relative growth rate and nitrogen status. Relative growth rates were high and the maximum weight increase was about 19% day−1 in Populus and over 25% day−1 in Paulownia. The nitrogen productivity of Paulownia was very high, 0.26 g dry weight (g N)−1 h−1, and for Populus it was 0.16 g dry weight (g N)−1 h−1.