bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonium and amino acid metabolism in excised leaves of wheat (Triticum aestivum) senescing in the dark
Authors: Peeters Kurt M. U. , Van Laere André J.
Published: May 2006

Several parameters of amino acid metabolism were studied in detached primary leaves of wheat (Triticum aestivum L. cv. Castell) during a 14 day incubation period in the dark. Protein loss was accompanied by a 5‐fold increase in the total amount of free amino acids during the first 4 days of the incubation period with asparagine being the most important. Beyond this stage a pronounced intracellular accumulation of ammonium occured. A gradual decrease in the levels of free amino acids and ammonium at the later stages of senescence could in part be accounted for by leakage from the leaves. Additionally, some nitrogen was lost due to ammonia volatilization. The rapid decay of the glutamine synthetase (GS; EC 6.3.1.2)‐glutamate synthase (Fd‐GOGAT; EC 1.4.7.1) system and the fast decline of glutamate‐pyruvate transaminase (GPT; EC 2.6.1.2) activity appear to be predominant features of senescence in the dark. Decreasing Fd‐GOGAT activity was slightly compensated by a small and temporary increase in the activity of NADH‐GOGAT (EC 1.4.1.14). Glutamateoxalocetate transaminase (GOT: EC 2.6.1.1) activity, although declining continuously, proved to be much more persistent. Changes in glutamate dehydrogenase (GDH; EC 1.4.1.3) activity closely resembled the profile of ammonium evolution in the leaves and NADP‐isocitrate dehydrogenase (IDH; EC 1.1.1.42) activity revealed a temporary maximum during the period of rapid increase in GDH activity. Increased activity of GDH could also be induced by exogenous ammonium. Ammonium accumulation could, at least partly, be caused by increased asparaginase (EC 3.5.1.1) activity which accompanied the rapid conversion of asparagine to aspartic acid. Asparagine aminotransferase (EC 2.6.1.14) activity declined sharply from the beginning of the senescence period. Although the activity profile of glutaminase (EC 3.5.1.2) was similar to that of asparaginase, glutamine was of little importance quantitatively and an analogous relationship between glutamine and glutamic acid could not be detected.
Cytokinin effects on root growth and possible interactions with ethylene and indole‐3‐acetic acid
Authors: Bertell Gertrud , Eliasson Lennart
Published: May 2006

Etiolated pea seedlings (Pisum sativum L. cv. Weibull's Marma) were used to investigate the effects of exogenous cytokinins on root growth. Benzylaminopurine (BAP) added to the growth solution inhibited the elongation and formation of lateral roots and stimulated swelling of the root tips. Similar effects were obtained with zeatin. The effects were obtained over a wide concentration range down to 0.01 μM. Growth responses appeared only after treatment for several hours, and the duration of treatment had an important influence on the degree of the effects. BAP caused a moderate increase in ethylene production as measured in excised 10‐mm‐long root tips. Lowering ethylene production by treatment with cobalt ions counteracted both the inhibition and swelling caused by BAP. Treatment with silver ions also reversed the effect to some extent, indicating that ethylene is involved in the response of the roots to BAP. To further study the involvement of the increased ethylene production in the elongation and swelling response, the effects were compared with those obtained after application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) in relation to the ethylene produced from this compound. This comparison showed that the increase in ethylene production caused by BAP was too low to explain the response of the roots. However, ACC treatment caused a considerable lowering of the content of indole‐3‐acetic acid (IAA) in the root tips, whereas BAP did not; instead, BAP increased the amount of IAA per root tip. It is concluded that cytokinins influence growth processes in roots via several mechanisms. A synergistic interaction between endogenous IAA, maintained at a high level by the cytokinin treatment, and the increased ethylene levels appears to explain most of the cytokinin effects during the first day of treatment.
Cytokinin biochemistry in relation to leaf senescence. VI. Effect of nitrogenous nutrients on cytokinin levels and senescence of tobacco leaves
Authors: Singh Santokh , Letham D. S. , Zhang Xue‐dong , Palni L. M. S.
Published: May 2006

The effect of nitrogenous nutrients on endogeneous cytokinins and senescence of tobacco leaves was investigated. Ammonium nitrate was the most effective in retarding senescence and its activity was attributed principally to NH4+ ions. Repeated applications or a continuous supply of ammonium nitrate was required for maximal retardation of tobacco leaf senescence. Ammonium nitrate solution supplied via the petioles reduced the senescence retarding effect of dihydrozeatin applied directly to the laminae of detached tobacco leaves. Ammonium nitrate also elevated the endogenous levels of cytokinins (especially zeatin and dihydrozeatin) particularly in growing tobacco leaves excised from near the apex of the plant. Ammonium nitrate induced retardation of leaf senescence may be mediated at least partly by its effect on foliar cytokinin content.
Intraspecific variation in the response of rice (Oryza sativa) to increased CO2– photosynthetic, biomass and reproductive characteristics
Authors: Ziska Lewis H. , Teramura Alan H.
Published: May 2006

Two rice (Oryza sativa L.) cultivars of contrasting morphologies, IR‐36 and Fujiyama‐5, were exposed to ambient (360 μl l−1) and ambient plus 300 μl l−1 CO2 from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO2 resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO2 environment. The photosynthetic response at 5% CO2 and the response of CO2 assimilation (A) to internal CO2 (Ci) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO2 were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO2 environment with a significant increase in harvest index for IR‐36 but not for Fujiyama‐5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO2 environment.
Ornithine cycle in Nostoc PCC 73102. Occurrence and localization of ornithine carbamoyl transferase, and the effects of external carbon and ornithine on nitrogenase activity and citrulline synthesis
Authors: Lindblad Peter
Published: May 2006

Cells of free‐living nitrogen‐fixing Nostoc PCC 73102, a filamentous heterocystous cyanobacterium originally isolated from coralloid roots of the cycad Macrozamia. were examined for the presence of ornithine carbamoyl transferase (OCT) by native‐PAGE/in situ activity stain, and SDS‐PAGE/Western immunoblots. Transmission electron microscopy and immunocytological labeling were used to study the cellular and subcellular distribution of OCT in the Nostoc cells. Moreover, the effects of photoautotrophic and dark heterotrophic growth metabolism on growth, nitrogenase activity and in vivo citrulline synthesis were investigated. PAGE in combination with in situ activity staining demonstrated an in vitro active OCT with a molecular weight of approximately 80 kDa. SDS‐PAGE/Western immunoblots revealed that a polypeptide with a molecular weight of approximately 38 kDa was immunologically related to OCT purified from pea (Pisum sativum L. cv. Alaska). Immunolocalization demonstrated that the OCT protein was located both in vegetative cells and heterocysts. Using the particle analysis of an image processor, the labeling associated with the photosynthetic vegetative cells was calculated to be 75.6 (± 5.5) gold particles μm−2 compared with 62.0 (± 7.5) in the nitrogen‐fixing heterocysts. Glucose and fructose stimulated both cyanobacterial growth and nitrogenase activity in light and darkness. Addition of exogenous ornithine decreased nitrogenase activity. In light grown cells, additions of glucose and fructose in combination with ornithine not only stimulated growth and nitrogenase activity but also in vivo citrulline synthesis, measured as 14CO2‐fixation into [14C]‐citrulline. In darkness no stimulation was observed on in vivo citrulline synthesis. The substantial stimulation of nitrogenase activity by additions of external glucose and fructose, both in the light and in darkness, was not followed by a simultaneous stimulation of in vivo citrulline synthesis.
A reappraisal of nitrate inhibition of nitrogenase in A317, a nitrate reductase‐deficient mutant of pea (Pisum sativum)
Authors: Walsh K. B. , Carroll B. J.
Published: May 2006

Symbiotic plants of Pisum sativum L. cv. Juneau and its nitrate reductase‐(EC 1. 6. 6. 1)‐deficient mutant, A317, were exposed to nitrate for up to 8 days and assessed for nitrate assimilation, nitrogenase activity and nodule carbohydrate status. The mutant, A317, was not impaired in its ability to absorb nitrate over up to 8 days, but was leakier with respect to nitrate reduction ability than previously realized, as 63% of the nitrate absorbed by the plant over 8 days was assimilated (in contrast to 93% in the wild type). After 2 days exposure to 5 mM nitrate, nitrogenase (EC 1.18.2.1) activity was less affected in A317 (84% of initial) than in Juneau (46% of initial): nodule starch reserves were less depleted in A317 (70% of initial) than in Juneau (26% of initial). It was concluded that nitrate reduction is a major cause of nitrate inhibition of nodule activity, and that its effect may be mediated through a decrease in the availability of carbohydrate to the nodules. Longer term (> 4 day) exposure of A317 plants to nitrate resulted in accumulation of nitrate in plant tissues, an associated necrosis of shoot tissue, a marked decrease in nodule starch content and a severe inhibition of nodule activity. This consideration of the effect of the duration of exposure to nitrate is used to resolve a discrepancy between previous reports on the sensitivity to nitrate of nitrogenase activity in nitrate reductase‐deficient mutants of pea.
Researching the controls of adventitious rooting
Authors: Haissig Bruce E. , Davis Tim D. , Riemenschneider Don E.
Published: May 2006

Cloning is crucial in horticulture and forestry for commercial production of plants and in genetic improvement programs. However, inability to induce adventitious root formation (rooting) often limits cloning of woody plants by cuttage or tissue culture. To improve cloning, past physiological and biochemical studies of rooting have largely been aimed at understanding controls by researching post‐translational processes. Still, the sought‐for controls of rooting remain obscure. However, those controls may be discovered by searching for and studying direct genetic effects, using current molecular genetic technologies and new plant materials (e.g., non‐rooting mutants, normally rootless plants). In particular, applying molecular genetic technologies in studies at the transcriptional and translational levels may soon reveal the controls of rooting. We review strategies for achieving that goal.
Amino acids are general growth inhibitors of Nicotiana silvestris in tissue culture
Authors: Bonner Carol A. , Rodrigues Astride M. , Miller Jacqueline A. , Jensen Roy A.
Published: May 2006

The growth of Nicotiana silvestris in suspension culture is inhibited by all of the common protein amino acids at the millimolar level, except for L‐glutamine. A defined experimental system for growth/inhibition studies has been established, and growth studies were carried out with cells that had been maintained in the exponential growth phase for at least 10 generations (EE cells). The following results were obtained after particularly detailed studies with aromatic amino acids. The onset of inhibition was preceded by a duration of normal growth rate which varied within a range of 12 to 48 h. The degree of inhibition was directly proportional to amino acid concentration and inversely related to the initial cell density of the inoculum. A slowed, but still exponential rate of growth persisted during an early phase of inhibition. Under sufficiently severe conditions, this was followed by progressive diminution of growth rate and eventual lysis. The most drastic inhibitory effects caused by aromatic amino acids were in the order: phenylalanine, tryptophan and tyrosine. When EE cells cultivated under conditions of growth inhibition were diluted into fresh medium, immediate resumption of growth at the uninhibited rate occurred and persisted. On the other hand, when growth‐inhibited EE cells were diluted into medium containing the same concentration of amino acid used in the first round of growth, an initial burst of uninhibited growth lasting about 24 h was followed by a drastic, progressively declining growth rate which deteriorated to cell death and lysis. When cells in stationary phase were used as an inoculum, as is done in typical growth characterizations with suspension cultures, the sensitivity to inhibition during the subsequent exponential growth phase was several‐fold greater than was the case with EE cells. Hypotheses that growth inhibition might be caused by ammonia toxicity, keto‐acid toxicity, or by inhibition of nitrate utilization were ruled out. Observations that provide new insight are: (i)growth‐inhibited cells undergo drastic plasmolysis, (ii) L‐glutamine is an effective antagonist of amino‐acid inhibitors, and (iii) growth‐inhibited cells exhibit a transient restoration of normal growth rate upon dilution into fresh growth medium. These results implicate a linkage of amino acids with osmotic regulation and nitrogen metabolism.
Multiple forms of ADPglucose pyrophosphorylase of rice endosperm
Authors: Nakamura Yasunori , Kawaguchi Kentaro
Published: May 2006

ADPglucose pyrophosphorylase from developing rice (Oryza sativa) endosperm was purified. The final preparation yielded 6 major protein spots as separated by two‐dimensional polyacrylamide electrophoresis. All 6 polypeptides had similar molecular weights of ca 50 kDa and cross‐reacted with polyclonal antibodies raised against two main protein bands among them. The results suggest that the rice endosperm ADPglucose pyrophorsphorylase is tetrameric and composed of multiple subunits with similar amino acid structure.
Lignin release and photomixotrophism in suspension cultures of Picea abies
Authors: Simola Liisa Kaarina , Lemmetyinen Juha , Santanen Arja
Published: May 2006

The effect of different concentrations of sucrose (0‐4%) and of two growth regulators (0–50 μM 2,4‐D and 0–25 μM kinetin) was tested on growth and chlorophyll content of suspension cultures of Picea abies (L.) Karst. originating from chlorophyllous embryo callus in an elevated CO2 (2%) atmosphere. A continuous chlorophyllous suspension culture was achieved on a medium containing 2% sucrose and a low level of organic nitrogen (0.25 mM arginine and 0.5 mM glutamine) supplemented with 2,4‐D (0.5 μM) and kinetin (2.5 μM). The same medium with 4% sucrose gave the best growth response, but a negative correlation between chlorophyll level and growth was observed. The chlorophyllous cultures grew slowly in a medium with low (0.5%) sucrose or without any carbohydrate source, suggesting photomixotrophism. A high concentration of kinetin inhibited both growth and chlorophyll synthesis. Release of lignin into the nutrient medium was observed in several experiments, especially in slow‐growing cultures supplemented with sucrose. Only a few successive passages of suspensions that produced lignin could be cultured before cell death. The cultures releasing lignin may be unique for studies on synthesis and biodegradation of this very complex compound.
Inhibition of Pisum sativum epicotyl elongation by white light – Different effects of light on the mechanical properties of cell walls in the epidermal and inner tissues
Authors: Miyamoto Kensuke , Ueda Junichi , Hoson Takayuki , Kamisaka Seiichiro , Masuda Yoshio
Published: May 2006

White fluorescent light (5 W m−2) inhibited subhook growth in derooted Alaska pea cuttings. In the inner tissue of the subhook, it inhibited the increase in osmotic potential during 18 h incubation. In the epidermis, on the other hand, light did not affect the osmotic potential. Light increased the minimum‐stress relaxation time (T0) of the inner tissue cell walls, but did not change T0 of the epidermal cell wall. Light decreased tissue stress determined by the split test and the ability of the inner tissue to extend by water absorption. The short‐term light effect on subhook growth. T0, and the tissue stress almost disappeared when pea cuttings were transferred to darkness. These facts suggest that light changes the mechanical properties of the cell wall in the inner tissue of shoots, and decreases tissue stress, which is considered to be the driving force of shoot growth.
Purification and characterization of leucine aminopeptidase from kidney bean cotyledons
Authors: Mikkonen Anita
Published: May 2006

A leucine aminopeptidase (EC 3,4,11.1) was purified from cotyledons of resting kidney beans (Phaseolus vulgaris L. cv. Processor) by acidic extraction, ammonium sulfate fractionation and chromatography on DEAE‐Sephacel, Sephacryl S‐300, Mono Q HPLC and Superose HPLC columns. The yield of the 317‐fold purified enzyme was 9%. On gel filtrations on Sephacryl S‐300 and Superose HPLC the elution volumes of the enzyme corresponded to an M, of 360 000. The enzyme gave one band on native gel electrophoresis and an electrophoretic titration in an immobilized pH gradient gave a single curve with a pI of 4.8. Two bands were observed in an SDS‐gel electrophoresis with Mr values of 58 000 and 60 000 both with and without reduction by 2‐mercaptoethanol, indicating that subunits of the enzyme are not linked by disulphide bridges. The purified enzyme most rapidly liberated Leu and Ala of the N‐termini of di‐and oligopeptides, optimally at pH 9.0 ± 0.5. The enzyme was stable in the presence of glycerol, dithiothreitol and Mg2+, while the latter also had an activating effect. Bestatin inhibited the enzyme competitively with Leu‐Gly‐Gly with a Ki‐value of 1.5nM. These observations indicate that the purified aminopeptidase from the cotyledons of resting kidney beans corresponds to the cytosolic leucine aminopeptidase of mammalian tissues (EC 3.4, 11.1). The high enzyme activity observed suggests that this aminopeptidase has an important role in the production of free amino acids during germination.
Changes in the level of MACC during cold hardening and dehardening in winter wheat
Authors: Macháčková Ivana , Hanišová Alena , Krekule Jan
Published: May 2006

Changes in the level of 1‐(malonylamino)‐cyclopropane‐1‐carboxylic acid (MACC) were determined in 6 winter wheat cultivars during cold hardening at 4°C. The cultivars differed by one degree of frost resistance within the range of degree II to VII of the COMECON scale. The time‐course of changes in MACC level showed a similar pattern in all 6 cultivars; i.e. increase till day 6, no changes for the next 10 days, and then a steady decrease till the end of the hardening period. There was little difference between the final and the initial levels. The increase of MACC level, expressed as per cent of the original level, was not directly correlated with either the degree of frost resistance of the actual percentage of survival. In some cultivars. mean errors exceeded the difference in MACC accumulation between cultivars closest on the resistance scale.

The fate of MACC during the second half of hardening and after transfer of plants to 25°C was studied in cultivars Bezostaya and San Pastore. During the second half of the hardening period the level of MACC decreased in the leaves of both cultivars, but increased significantly in the roots. Within two days of transfer of the hardened plants to 25°C, the MACC level in leaves increased again, while that in the roots decreased. This finding, together with the preliminary evidence of very low MACC metabolism, strongly suggest that MACC accumulates in roots during the hardening period and when transferred to 25°C, it moves from roots to leaves.
Characterization of early events leading to the formation of chlorophyll‐proteins of PSII in Euglena gracilis
Authors: Yamamoto Yasusi , Mizobuchi Akihiro , Hiramatsu Hiroyuki , Shioi Yuzo
Published: May 2006

Development of chlorophyll‐proteins in photosystem II was studied with Euglena gracilis Z. during dark‐light transition. Upon illumination of the dark‐grown cells, protochlorophyllide was photoconverted to chlorophyll(ide) a with a low efficiency (14%). After a lag time of 1‐2 h, chlorophylls, apoproteins of antenna chlorophyll‐protein complex CP 43/47 and of light‐harvesting chlorophyll‐protein complex (LHCII) accumulated in the thylakoid membrane in a coordinated fashion. There was, however, a significant difference in the stability between the newly formed LHCII and CP 43/47 judging from non‐denaturing lithium dodecyl sulfate‐polyacrylamide gel electrophoresis. The possibility that efficiencies of incorporation and stabilization of chlorophylls in the apoproteins differ among the chlorophyll‐proteins in the early stage of greening of Euglena is discussed.
Photosynthetic competence of plantlets grown in vitro. An automated system for measurement of photosynthesis in vitro
Authors: Dubé Sylvain L. , Vidaver William
Published: May 2006

An aseptic gas exchange and hydroponic system (AGEHS) has been developed in an attempt for characterization of physiological requirements for photoautotrophic growth in vitro and alleviation of the needs for ex vitro acclimatization. The AGEHS monitors and controls several parameters relevant to plant growth. Shootlets of Chrysanthemum × morifolium Ramat. cv. Envy were treated with flow of air or CO2‐enriched air under controlled relative humidity, elevated photosynthetic photon flux density (PPFD) and hydroponic irrigation. After 15 days of treatment, plantlets gained more than 3 times as much dry weight as those from a conventional culture tube treatment. This study shows that it is possible to favour photoautotrophic growth when elevated PPFD, enhanced air‐exchange and hydroponic medium flow are provided concurrently. This enhancement is achievable through careful increments of light quanta, balanced with increments of humidified air flow and/or CO2 content in air which seem to be necessary to avoid potential photoinhibition and premature water exhaustion from gelled media.
Determination of developmental stage to obtain high frequencies of embryogenic microspores in Brassica napus
Authors: Telmer Cheryl A. , Simmonds Daina H. , Newcomb William
Published: May 2006

Individual buds of Brassica napus cv. Topas, near the first pollen mitosis, were used for microspore culture. Bud and petal lengths were recorded. Microspores isolated from the individual buds were plated and small samples were fixed for cytology. Following embryo induction and three weeks of culturing, numbers of embryos were scored. Bud and petal lengths did not accurately indicate which buds would supply microspores that would form embryos at high frequencies. Fluorescence microscopy was used to examine nuclei stained with Hoechst 33258 and vacuolar morphology of microspores was revealed by the weaker fluorescence due to glutaraldehyde fixation. Following isolation, nuclear and vacuolar characteristics were used to stage the microspores as miduninucleate, late uninucleate vacuolate, late uninucleate, mitotic, or binucleate. The relationship of developmental stage to the frequency of microspore‐derived embryos was evaluated. A classification scheme was developed which uses the relative proportions of microspores at each of the stages to identify microspore isolations that would form embryos at high frequencies. It was found that when 1 to 87% of the isolated microspores were binucleate, 21.4 ± 3.0% of the viable microspores developed into embryos. This was a significant (P < 0.001) increase over the other 3 classes. The ability to select highly embryogenic microspore isolations is of great advantage for developmental cell biology studies.
The Nostoc‐Gunnera magellanica symbiosis: Phycobiliproteins, carboxysomes and Rubisco in the cyanobiont
Authors: Söderbäck Erik , Bergman Birgitta
Published: May 2006

In the nitrogen fixing symbiosis between Nostoc and the angiosperm Gunnera, the cyanobiont is found in stem glands and is thought to have a heterotrophic mode of nutrition. To investigate whether the photosynthetic machinery in the cyanobiont is down‐regulated in the symbiosis, the presence of the phycobiliproteins, phycoerythrin and phycocyanin, and ribulose‐1,5‐bisphosphate carboxylase oxygenase (Rubisco, EC 4.1.1.39) in cyanobionts of Gunnera magellanica Lam. and in a free‐living (cultured) isolate of the cyanobacterium was studied by immunoelectron microscopy. Carboxysomes were numerous in all vegetative cells (ca 3.5 per cell section), and on an area basis they showed a high Rubisco label compared to the cytoplasm; but recalculation on a volume basis demonstrated that the carboxysomal fraction of Rubisco decreased in the cyanobiont along the plant stem. Along the whole Gunnera stem both types of phycobiliproteins were present in the symbiotic Nostoc and in amounts equivalent to or above those detected in the free‐living isolate. As the symbiotic Nostoc is located intracellularly, out of reach of light in the plant stem, the findings indicate a lack of regulation of the photosynthetic protein synthesis in the symbiotic state.
Measurements of intra‐and extracellular pH in the liverwort Conocephalum conicum during action potentials
Authors: Trębacz K.
Published: May 2006

During action potentials triggered by electricity and light, measurements of intra‐ and extracellular pH in the liverwort Conocephalum conicum L. were carried out by the use of antimony‐filled H+‐sensitive microelectrodes. Intracellular pH increased transiently by about 0.05 unit in the course of an action potential, while extracellular pH, measured at the surface of the thallus, remained unchanged. Switching the light off caused a transient increase in intracellular pH by less than 0.1 unit. Turning the light on produced a fast pH decrease by about 0.15 unit followed by a slow increase. When the light was intensive enough, the action potential thus triggered caused a slight increase in intracellular pH superimposed on the phase of a slow pH increment.

The magnitude and time course of the intracellular pH changes seem insufficient for a role as messenger between action potential and the up to 100% increase in the rate of respiration that has been registered in Conocephalum conicum as a consequence of excitation.
Monoterpene content in Origanum syriacum as affected by environmental conditions and flowering
Authors: Dudai Nativ , Putievsky Eli , Ravid Uzi , Palevitch Dan , Halevy Abraham H.
Published: May 2006

A high content of essential oil in the foliage of two chemotypes of field‐grown Origanum syriacum L. was found between August and October. The content of phenolic monoterpenes in the essential oil was low from November to January, while the content of p‐cymene was high. The effect of environmental conditions and flowering on the two chemotypes was similar. Controlled experiments revealed that under long photoperiods the content of essential oils in the foliage and of phenolic monoterpenes in the oil increased, while that of p‐cymene decreased. A similar effect was observed when an 8 h natural light day was extended by 8 h low‐intensity incandescent light. When the 16 h day was composed of 12 h natural light, the effect on oil content and composition was intensified. Under short‐day photoperiods, increasing temperature or light intensity enhanced the relative content of p‐cymene, while that of phenolic monoterpenes and the γ‐terpinene generally decreased. Flowering decreased the essential oil content in the leaves and the relative content of the phenolic monoterpenes in the essential oil. Since environmental conditions influence flowering, they had both direct and indirect effects on the essential oil content and composition.
Influence of 9‐β‐l(+)‐adenosine on malate dehydrogenase activity in rice
Authors: Savithiry Srinivasan , Wert Violet , Ries Stanley
Published: May 2006

The activity of malate dehydrogenase (MDH, EC 1.1.1.37) in rice (Oryza sativa L. cv. California M‐201) roots was increased within 25 min by a foliar application of 37 nM of 9‐β‐l(+)‐adenosine [l(+)‐adenosine]. A similar concentration of 9‐β‐d(‐)‐adenosine [d(‐)‐adenosine] did not affect MDH. Triacontanol (2.7 nM) which elicits l(+)‐adenosine in plants also increased MDH activity in roots of rice seedlings. whereas neither octacosanol nor a mixture of equimolar concentrations of triacontanol and octacosanol had any effect on MDH activity. l(+)‐Adenosine increased MDH activity of rice seedlings grown at 10.20 and 40°C. The effect was measurable 24 h after application at 10 and 20°C, but not 6 h after treatment at 40°C. Ninety minutes after l(+)‐adenosine was applied to the foliage of plants grown at 10, 20 and 40°C, MDH activity in the roots was 40, 30 and 9% more, respectively, than in the untreated controls. The concentration of water soluble protein was also increased by l(+)‐adenosine and was positively correlated with MDH activity. When measured 90 min after application of l(+)‐adenosine at different times of day, MDH activity and dry weight were increased most when l(+)‐adenosine was applied 9 and 12 h after the lights came on in a 16‐h photoperiod. The optimum light intensity for the response of rice to l(+)‐adenosine, as measured by MDH activity, was 450 μmol m−2 s−1.
Quantification of ethylene losses in different container‐seal systems and comparison of biotic and abiotic contributions to ethylene accumulation in cultured tissues
Authors: Mensuali‐Sodi A. , Panizza M. , Tognoni F.
Published: May 2006

Ethylene losses and release were compared in four container‐ seal systems for in vitro cultures: Erlenmeyer flasks sealed with silicone, caoutchouc or styrene butadiene stoppers and glass bottles with screw caps supplied with caoutchouc septa. The last systems Proved to be the most suitable (i. e. minimum ethylene loss and release) to determine ethylene accumulation during axillary budding of lavandin (Lavandula officinalis Chaix × Lavandula latifolia Villars cv. Grosso). Gelling agents (agar and Gelrite) also discharges ethylene and agar was identified as the main abiotic source. Mathematical elaboration of experimental data was then performed to estimate biological ethylene production.
Photosynthetic activity and chloroplast structural characteristics in triazine‐resistant biotypes of three weed species
Authors: De Prado Rafael , Domínguez Carmen , Rodríguez Isabel , Tena Manuel
Published: May 2006

Triazine‐resistant (R) and susceptible (S) biotypes of Chenopodium album, Conyza bonaeriensis and Setaria glauca were compared in terms of photosynthetic activity, chloroplast ultrastructure, and polar‐lipid composition of thylakoid membranes. Concerning photosynthetic activity, R relative to S biotypes showed lower rates in photosystem II electron transport (R/S ratios in the 0.3‐0.5 range), which were correlated with increases in the ratio of I to P levels of the fluorescence emission curve, but similar rates in both whole‐chain electron transport by thylakoids and photosynthetic oxygen evolution at different light intensities and at temperatures of 20 and 30°C by leaf discs. Concerning chloroplast structural characteristics, R and S biotypes did not show differences in degree of thylakoid appression and chlorophyll a/b ratio. However, thylakoid polar‐lipids of R biotypes exhibited a higher degree of unsaturation, specially, in its monogalactosyl diglyceride fraction; they were richer in trans‐hexadecenoic acid in its phospholipid fraction and they had higher contents in monoglactosyl diglyceride. The above results are discussed in relation to possible differences in photosynthetic performance between R and S plants.
Do microtubules orient plant cell wall microfibrils?
Authors: Emons A. M. C. , Derksen J. , Sassen M. M. A.
Published: May 2006

Cortical microtubules (MTs) allegedly orient nascent cellulose microfibrils (CMFs) in plant cells. The frequently observed parallelism between them, and the effect of MT‐depolymerizing agents, are the bases for this hypothesis. Data have, however, accumulated about cells in which MTs and CMFs are not in parallel alignment. These data will be reviewed. MT orientation cannot be the only factor determining CMF orientation, but MTs could overrule other factors in cells where, for instance, they are more tightly attached to the plasma membrane than in other cells. MT and CMF orientations could, however, both be controlled by a third factor, and CMFs may even impose orientation on MTs.
Low external pH prevents cell elongation but not multiplication of embryogenic carrot cells
Authors: Smith David L. , Krikorian Abraham D.
Published: May 2006

Embryogenic cultures of cultivated carrot (Daucus crota cv. Scarlet Nantes) were initiated from seedling hypocotyls on hormone‐containing nutrient medium and from wounded zygotic embryos on hormone‐free medium. Both of these cultures were maintained with continuous multiplication as unorganized, embryogenic cell masses on hormone‐free medium at pH 4.0, containing NH+4 as the sole nitrogen source. When grown on hormone‐free medium at pH 4.0, neither culture contained any elongated cells. Virtually all cells were densely cytoplasmic and nearly spherical. Some cells were enlarged, not densely cytoplasmic, but always spherical. When either culture was transferred to an auxin‐containing medium at pH 5.8, numerous elongated cells were produced. Elongated cells were observed when either naphthaleneacetic acid or 2,4‐dichlorophenoxyacetic acid was used, and whether the nitrogen source was NH+4 alone or a combination of NH+4 and NO−3. Elongated cells were more abundant when a combined nitrogen source was used. When cultures containing elongated cells were transferred to and multiplied on hormone‐free or hormone‐containing medium buffered at pH 4.0, all elongated cells disappeared after 2 weeks. No elongated cells were observed in any of the lines tested at pH 4.0. These results clearly show that it was the pH of the culture medium and not the presence or absence of an auxin or the nitrogen source(s) that permitted or prevented cell elongation in the embryogenic cultures tested.
Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in Chlamydomonas reinhardtii
Authors: Ramazanov Z. , Cárdenas J.
Published: May 2006

Interaction between induction of carbonic anhydrase (CA) activity, induction of inorganic carbon (Ci) concentrating mechanisms and the photorespiratory glycolate pathway has been studied in wild type 6145c and photorespiratory mutant 18–7F (low in phosphoglycolate phosphatase activity) cells of C. reinhardtii. Cell transfer from high CO2 (5%, v/v) to low CO2 (0.03%) provoked an increase of extracellular and total (extracellular plus intracellular) CA in both wild type and mutant cells. During adaptation to low CO2 conditions, both strains excreted ammonium to the medium at a similar rate in the presence of l‐methionine‐d‐l‐sulfoximine (MSX), an inhibitor of glutamine synthetase (GS). MSX also provoked ammonium excretion by air adapted wild type and mutant cells, even though both strains had high levels of CA activity and of Ci concentrating activities.

GS increased in both strains after transfer from high to low CO2 conditions. However, this increase was abolished by aminooxyacetate, an inhibitor of the glyoxylate‐serine aminotransferase, and by glycolaldehyde, an inhibitor of triose phosphate to ribulose 1,5‐bisphosphate conversion. CA synthesis did not occur in the presence of either aminooxyacetate or glycolaldehyde. Algae grown in high CO2 in the presence of aminooxyacetate did not induce Ci concentrating mechanisms. Integration of these three processes, i.e., CA synthesis, Ci‐concentration, and photorespiratory glycolate pathway is proposed in the framework of carbon metabolism of the alga.
A method to record circadian plant movements, with application to Oxalis leaf rhythms
Authors: Pedersen Marit , Eidesmo Terje , Johnsson Anders
Published: May 2006

A transducer was developed to record the circadian movement of the individual leaflets in Oxalis regnellii Mig. The method can easily be adapted to measure other kinds of plant movements as well. It is based on the detection of the shadow each leaflet casts on the small side of a specially formed Perspex plate. The light is guided through the Perspex and collected by a phototransistor, which provides an electrical signal that is proportional to the light intensity falling onto it. The output signal can be made a linear function of the leaf angle. This equipment was used in experiments to study the coupling between the 3 leaflets in Oxalis. Pulses of 4 h of red light were given to one of the leaflets, the two others were shielded from the light. A phase response curve was determined for each leaflet, but there was no significant difference in the phase response between the 3 leaflets. Experiments were also made in which the 3 leaflets were separated physically by cuts along the petiole between the pulvini. In this case ultradian oscillations were observed.
Hormonal requirement and tissue competency for shoot organogenesis in two cultivars of Brassica napus
Authors: Julliard Jacques , Sossountzov Lucienne , Habricot Yvette , Pelletier Georges
Published: May 2006

An investigation of the regeneration ability of explants taken from the floral stem of Brassica napus var. oleifera was performed in the winter cultivars Darmor and Bienvenu. Our purpose was to compare the regeneration ability of the two genotypes, to compare the competence of the different tissues of the stem and then to study histologically the regeneration of shoots. A strong genotypic effect was observed between the two cvs; Bienvenu had a poorer ability to produce shoots when cultured in the presence of benzyladenine: regeneration commenced later; the percentage of explants producing shoots and the number of shoots per regenerating explant were much lower. The comparison between the regeneration ability of different explants, i.e stem segments, internal stem segments, thin cell layer and peels, showed that the superficial tissues were able to regenerate roots but not shoots. Contrariwise, internal stem segments regenerated only shoots. The origin of shoots was investigated in stem segments of cv. Darmor. A kinetic histological analysis showed the basic role played by phloem and phloem‐associated cells in shoot formation.
Changes in water relations and in some physiological functions of bean under very light osmotic shock induced by polyethylene glycol
Authors: Raggi Vittorio
Published: May 2006

Bean plantlets (Phaseolus vulgaris L. cv. Topcrop) were stressed at the age of 16–18 days by gradual (2–8%) or abrupt addition of 6% (w/v) polyethylene glycol Mw 6000 (PEG 6000) to Hoagland solution. Leaf conductance, photosynthesis, internal CO2 partial pressure (Ci), relative water content (RWC), water content/dry weight (H2O/DW), apoplastic PEG concentrations and weight of leaves, stems and roots were determined. Leaf conductance, photosynthesis and Ci were determined on non‐detached primary leaves, and leaf potentials (water, osmotic and turgor potentials) were investigated in freshly detached (non‐rehydrated) primary leaves, both in treated and control plants; RWC and osmotic potential were also assessed at the null turgor point. Low PEG 6000 concentrations induced early and evident decrease in leaf conductance and photosynthesis, whereas Ci decreased only moderately and tended to recover during advanced stress. There were moderate though significant decreases in RWC and H2O/DW, no change or increases in water potential, no significant changes in osmotic potential and a moderate but significant increase in turgor potential. Even when referred to null turgor point, RWC significantly decreased and osmotic potential was unchanged. It was concluded that apoplastic PEG 6000 accumulation at evaporating sites would account for the early decrease in conductance which would also justify the unchanged or the prevalent increase in water potential and turgor potential. The subsequent PEG diffusion and concentration in the leaf apoplastic water would have induced the RWC and H2O/DW decrease and the final turgor flexion documented.
Immunocytochemical localization of NAD‐dependent glyceraldehyde‐3‐phosphate dehydrogenase in soybean nodules
Authors: Zammit Adrian , Copeland Les , Miller Celia , Craig Stuart
Published: May 2006

Polyclonal antibodies raised against NAD‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (D‐glyceraldehyde‐3‐phosphate:NAD+ oxidoreductase [phosphorylating], EC 1.2.1.12) from the plant cytosolic fraction of soybean [Glycine max (L.) Merr. cv. Williams] nodules were used to study the subcellular location of the enzyme and its relative distribution between infected, interstitial and cortical cells of soybean (cv. Lincoln) nodules. Post‐embedding immunogold labelling was carried out on nodules harvested 5, 12, 19 and 25 days after the first sign of nodulation. Labelling for glyceraldehyde‐3‐phosphate dehydrogenase was observed over the cytoplasm and nuclei of infected and uninfected cells, as well as over the nucleoid regions of bacteroids. In 5‐day‐old nodules, label also bound adjacent to the peribacteroid membranes. Statistical analysis of the number of gold particles per cell area indicated that in 5‐day‐old nodules, glyceraldehyde‐3‐phosphate dehydrogenase was distributed equally between infected, interstitial and cortical cells, but in older nodules the enzyme was more prominent in the interstitial and cortical cells than in infected cells.
The role of hormones on morphogenesis of thin layer explants from normal and transgenic tobacco plants
Authors: Altamura Maria Maddalena , Capitani Francesca
Published: May 2006

The organogenic potential of thin layer stem explants of non‐reproductive tobacco plants was tested on a hormone‐free medium and under various hormonal conditions. A comparison was made between thin layers excised from normal and transgenic plants at the same developmental stage. The transgenic plants were transformed by insertion of TR‐ and TL‐DNA from Agrobacterium rhizogenes 1855 root‐inducing plasmid. The aim was to identify hormonal conditions capable of stimulating the expression of the flowering competence present in the differentiated stem tissues at the induced stage before any visible sign of transition to reproductive development. Flower neoformation, observed at the end of the culture period (day 25), occurred on untransformed thin layers only with kinetin treatment. Explants from transgenic plants showed flower bud regeneration on hormone‐free medium, indoleacetic acid alone (1 μM), kinetin alone (1 μM), and most abundantly on indoleacetic acid plus kinetin (1 μM each). No flower formation was observed on indolebutyric acid plus kinetin (10 μM and 0.1 μM, respectively) in both normal and transgenic explants. The latter treatment enhanced rooting instead, above all in the transgenic explants. On hormone‐free medium vegetative bud formation was well expressed both by untransformed and transgenic explants, and enhanced by the combined, equimolar concentrations of indoleacetic acid and kinetin.

The results show that cytokinin allows flowering in florally determined stem explants from normal plants. In the transgenic explants, the flowering response increases when indoleacetic acid is added to cytokinin, thus suggesting a role for auxin in enhancing the expression of the florally determined state in thin cell layers of non‐reproductive plants.
Assimilation of nitrate and ammonium by the Scots pine (Pinus sylvestris) seedling under conditions of high nitrogen supply
Authors: Flaig Holger , Mohr Hans
Published: May 2006

Seedlings of Scots pine (Pinus sylvestris L.) were grown on perlite for 21 days under controlled conditions. Apart from the water control, KNO3 (15 mM), (NH4)2SO4 (7.5 mM), and NH4NO3 (15 mM) were offered to study the effects of a high nitrogen supply on nitrogen assimilation. In some experiments 1.3 mM potassium was added to the basic ammonium solutions. In labelling studies nitrate and ammonium were 2.3 atom%15N‐enriched. It was found that over the 21‐day period approximately three times more ammonium‐N was taken up than nitrate‐N. However, nitrate and ammonium, applied simultaneously, were taken up to the same extent as if they were applied separately (additivity). The presence of K+ in the medium did not affect N‐uptake. Among the soluble N‐containing compounds nitrate, ammonium and 8 amino acids were quantified. It was found that assimilation of nitrate can cope with the uptake of NO−3 under all circumstances. Neither free nitrate nor ammonium or amino acids accumulated to an extent exceeding the values of water‐grown seedlings. On the other hand, in case of high ammonium supply considerably more nitrogen was taken up than could be incorporated into nonsoluble N‐containing substance (‘protein’). The remaining nitrogen was found to accumulate in intermediary storage pools (free NH4+, glutamine, asparagine, arginine). Part of this accumulated N could be incorporated into protein when potassium was offered in the nutrient solution. It is concluded that potassium is a requirement for a high rate of protein synthesis not only in crop plants but also in conifers.
Differences in fructose‐2,6‐bisphosphate metabolism between sections of developing barley leaves
Authors: Nielsen Tom H.
Published: May 2006

In order to study the regulation of carbohydrate metabolism in leaf tissue the activity of fructose‐6‐phosphate,2‐kinase was determined in individual sections of developing primary leaves of barley. Activity was about 25‐fold higher in the leaf tip than in the leaf sheath when measured on a fresh weight basis. There was a gradual increase in enzyme activity from the leaf base to the leaf tip. The higher activity of fructose‐6‐phosphate,2‐kinase in the apical parts of the leaf was associated with higher levels of fructose‐2,6‐bisphosphate. This was especially pronounced when isolated leaf segments were treated with vanadate and kept in darkness. As compared to the kinase, little difference was observed in the fructose‐2,6‐bisphospatase activity among leaf sections. The significance of these patterns for regulation of carbohydrate metabolism in different tissues is discussed.
Analysis of apoplastic solutes in the cortex of soybean nodules
Authors: Streeter John G.
Published: May 2006

Various techniques were used to extract solutes from the free space of intact soybean [Glycine max (L.) Merr.] nodules. A variety of solutes (carbohydrates, amino acids, organic acids, ions) was found, but the major solute obtained with all methods was allantoic acid. Most work was done with a technique involving vacuum infiltration of intact detached nodules with water. This approach provided rapid sampling of the apoplastic solutes, and the results indicated that solutes were not derived from the xylem and phloem of ruptured vascular bundles. Infiltration of intact nodules with Fast Green showed dye penetration only to the barrier in the inner cortex, indicating that infected tissues did not contribute to solute composition. Although allantoic acid was the only ureide which could be detected in solute samples, no evidence was obtained for the presence of allantoinase in the cortical apoplast. The results suggest the transport of allantoic acid by an apoplastic route in nodules or the release of allantoic acid to the cortical apoplast in response to treatments which disrupt ureide export. Calculated values for solute concentrations in the cortical apoplast were in the hundred millimolar range, suggesting that apoplastic solutes may represent a significant osmotic component in the nodule cortex.