bluuebunny/crossref_metadata_2025 huggingface dataset:
Freezing of isolated thylakoid membranes in complex media. VIII. Differential cryoprotection by sucrose, proline and glycerol
Authors: Santarius Kurt A.
Published: May 2006

The cryoprotective efficiency of sucrose, proline and glycerol for chloroplast membranes isolated from spinach leaves (Spinacia oleracea L. cv. Monatol) was determined after freeze‐thaw treatment in media containing the predominant inorganic electrolytes of the chloroplast stroma. In most cases, the protective capacity of equimolar concentrations of the cryoprotectants followed the order sucrose > proline > glycerol. The lower the freezing temperature the less cryoprotectant was necessary for comparable preservation of the capacity of photosynthetic electron transport. Likewise, the cryoprotective efficiency of sucrose for cyclic photophosphorylation and light‐induced proton gradient increased with decreasing freezing temperature. In contrast, while proline effectively stabilized these membrane reactions at mild and moderate freezing temperatures, it was much less efficient at more severe freezing stress. Cryoprotection of photophosphorylation and proton gradient formation at given initial concentrations of glycerol was largely independent of the freezing temperature. While dissociation of the peripheral part of chloroplast coupling factor (CF1) during freeze‐thaw treatment cannot be prevented in the presence of lower initial concentrations of proline and glycerol and. at mild freezing temperatures, of sucrose, the latter may stabilize this protein complex at least under more severe freezing conditions. The differences in the cryoprotective efficiency of the solutes are discussed relative to their non‐ideal activity‐concentration profiles, solution properties and penetration behaviour across the thylakoid membrane.
Mechanism of the inhibition of phloem loading by sodium sulfite: Effect of the pollutant on respiration, photosynthesis and energy charge in the leaf tissues
Authors: Maurousset Laurence , Raymond Philippe , Caudillert Monique , Bonnemain Jean‐Louis
Published: May 2006

As in other materials, sodium sulfite (Na2SO3) inhibited both respiration and photosynthesis in leaf tissues of broad‐bean L. cv. Aguadulce). Under our experimental conditions, photosynthesis was more sensitive (significant inhibition at 10 μM) to the pollutant than respiration (significant inhibition only for concentrations higher than 0.1 mM). Sulfite concentrations higher than 0.1 mM also caused the energy charge of leaf tissues to decline sharply. These results suggest that the long, term depolarization of the transmembrane potential difference noticed for concentrations of pollutant higher than 0.1 mM (Maurousset and Bonnemain, Physiol. Plant. 80: 233–237,1990) was mainly due to an indirect inhibition of the plasma membrane H+‐ATPase activity following the decrease of the available level of ATP.
Sugar accumulation in growing subhooks of etiolated Pisum sativum seedlings ‐ Stimulation of sugar exudation and invertase activity in epicotyls by gibberellic acid
Authors: Miyamoto Kensuke , Ueda Junichi , Kamisaka Seiikhiro
Published: May 2006

The epicotyl of 5‐day‐old derooted cuttings of pea (Pisum sativum L. cv. Alaska) with and without cotyledons exuded sucrose and glucose in the presence of EDTA. The amount of sugars exuded was greatly affected by the position at which the epicotyl was cut. The largest amount of sugars was exuded when the epicotyl was cut 2 mm below the hook, leaving the growing subhook. Gibberellic acid (GA) substantially increased the amount of sugars exuded from the epicotyl in the presence of cotyledons but only slightly in their absence. GA stimulated sugar exudation from the cotyledonary node as well as from the epicotyl. In cuttings with cotyledons, GA enhanced invertase activity in the apoplast, and in the intraceUular soluble and bound fractions in the growing subhook. In decotylized cuttings, GA enhanced only soluble invertase activity. GA did not affect invertase activity in the epicotyl below the subhook. These results suggest that GA stimulates sugar accumulation in the growing subhook by stimulating not only phloem loading of sucrose in the cotyledons but also unloading in the subhook.
Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20
Authors: Junttila Olavi , Jensen Einar , Pearce David W. , Pharis Richard P.
Published: May 2006

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A9 (GA9) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA9 could completely substitute for a transfer to a long photoperiod. When [3H]GA9 or [2H2]GA9 was injected into a leaf, no [3H]GA9 was detected in the elongating apex and only traces of [3H]GA9 were found in the shoot above the treated leaf. By the use of gas chromatography‐mass spectrometry (GC‐MS), [2H2]GA20 was identified as the main metabolite of [2H2]GA9 in both the shoot and the treated leaf. In addition, [2H2]GA1 and [2H2]GA29 were also identified as metabolites of [2H2]GA9. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA20 and GA,.
The process of abscisic acid‐induced proline accumulation and the levels of polyamines and quaternary ammonium compounds in hydrated barley leaves
Authors: Pesci Pierantonio , Reggiani Remo
Published: May 2006

The contents of polyamines and quaternary ammonium compounds (QAC), substances involved in several kinds of stress phenomena, were tested in abscisk acid (ABA)‐treated barley leaves (Hordeum vulgare L. cv. Georgie) accumulating pro‐line. The characteristic parameters of the accumulation of proline induced by ABA [i.e. kinetics of accumulation, synergistic interaction hormone‐K(Na)Cl, enhancing effect of Cl‐, inhibiting effect of tetraethylammonium chloride (TEA), D‐mannose and glucosamine] were tacking as far as polyamine and QAC content was concerned. Moreover: i) ABA slightly decreased the level of spermine and spermidine, slightly increased that of putrescine but did not influence the level of QAC; ii) the content of polyamines was reduced by KCl; iii) treatment with sorbitol increased the level of polyamines and prevented proline accumulation induced by ABA. These results indicate that there is no relationship between ABA‐induced proline accumulation, polyamine level and QAC level; furthermore, accumulation of proline by ABA treatment is possible without increasing the levels of polyamines and QAC.
Response of sugar beet plants to ultraviolet‐B (280–320 nm) radiation and Cercospom leaf spot disease
Authors: Panagopoulos Ioannis , Bornman Janet F. , Björn Lars Olof
Published: May 2006

Sugar beet (Beta vulgaris L.) plants injected with Cercospora beticota Sace. as well as non‐infected plants were grown under visible light with or without ultraviolet‐B (UV‐B, 280–320 nm) radiation for 40 days. An interaction between UV‐B radiation and Cercospora leaf spot disease was observed, resulting in a large reduction in leaf chlorophyll content, dry weight of leaf laminae, petioles and storage roots. Lipid peraxidation in leaves also increased the most under the combined treatments. This was also true for ultraweak luminescence from both adaxial and abaxial leaf surfaces. However, no correlation between lipid peroxidation and ultraweak luminescence was observed. Ultraviolet‐B radiation given alone appeared to have either a stimulating effect, giving an increase in dry weight of laminae and reducing lipid peroxidation, or no effect. This lack of effect was seen in the absence of change in dry weight of storage roots and chlorophyll content relative to controls. The :study demonstrated a harmful interaction between UV‐B radiation and Cercospom leaf spot disease on sugar beet.
Structural and functional analysis of the reducing side of photosystem I
Authors: Andersen Birgitte , Koch Birgit , Scheller Henrik Vibe
Published: May 2006

Structural analysis of the reducing side of photosystem I (PSI) has been carried out using chemical cross‐linking and monospecific antibodies. Incubation of PSI isolated from barley (Hordeum vulgare L.) with the hydrophilic cross‐linking agent N‐ethyl‐3‐[3‐(dimethylamino) propyl]‐carbodiimide leads to cross‐linking of the PSI‐D subunit with the PSI‐E and PSI‐H subunits. In the presence of ferredoxin, cross‐linking results in the formation of cross‐linked products composed of PSI‐D, PSI‐E and ferredoxin and in a block in steady state NADP+ photoreduction. No cross‐linking of ferredoxin occurs at elevated ionic strength or using heat‐denatured ferredoxin. Cross‐linking of ferredoxin does not inhibit electron transfer from plastocyanin to methyl viologen. Steady state NADP+ photoreduction was analyzed in PSI or thyla‐koids incubated with antibodies against individual PSI subunits. Incubation with antibodies against PSI‐C, ‐H, ‐I, or ‐L had no effect on PSI activity, whereas antibodies against PSI‐D or PSI‐E had similar effects and caused a large decrease in activity. The results provide evidence that the PSI‐D and PSI‐E subunits are localized on the reducing side of PSI, forming a barrier between PSI‐C and the stroma as well as a docking site for ferredoxin. The PSI‐H subunit has an exposed, stromal domain but this does not appear to contribute to the ferredoxin docking.
The effect of exposure to microgravity on the development and structural organisation of plant protoplasts flown on Biokosmos 9
Authors: Rasmussen O. , Klimchuk D. A. , Kordyum E. L. , Danevich L. A. , Tarnavskaya E. B. , Lozovaya V. V. , Tairbekov M.G. , Baggemd C. , Iversen T. ‐H.
Published: May 2006

Preparatory experiments for the IML‐1 (International Microgravity Laboratory) mission to be flown on the Space Shuttle in January, 1992, were performed on a 14 day flight on Biokosmos 9 (Kosmos 2044) in September 1989. The purpose of the experiment was to study the effect of weightlessness on protoplast regeneration. Problems, with late access to the space vehicle meant that the newly isolated protoplasts from hypocotyl cells of rapeseed (Brassica napus L. cv Niklas) and suspension cultures of carrot (Daucus carota L. cv Nobo) had to be stored at 4°C for 36 h prior to the launch of the biosatellite, in order to delay cell wall regeneration until the samples were in orbit. In the flight samples and the ground controls, a portion of the total number of protoplasts regenerated cell walls. The growth of flight rapeseed cells was only 56% compared to the ground control; the respective growth of carrot cells in orbit was 82% of the ground control. Analysis demonstrated that the peroxidase activity and the amount of protein was lower in the flight samples than in the ground controls. The number of different isoenzymes was also decreased in the flight samples. A 54% decrease in the production of cellulose was found in rapeseed, and a 71% decrease in carrot. Hemicellulose production was also decreased in the flight samples compared to the ground controls.

Ultrastructural analysis of the cell aggregates from the protoplasts cultured in orbit, demonstrated that hydrolysis and disappearance of reserve starcb occurred in the flight cell plastids. The mitochondria were more varied in appearance in the flight samples than in the ground control cells. An increased frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds was also observed. Fluorescence analysis showed a decrease of the calcium content in cell cultures under space flight compared to the ground controls.

One general effect of the stay onboard the space vehicle was a retardation of the regeneration processes. Callus cultures obtained from the flight samples grew very slowly compared to callus regenerated from the ground controls, and two years after the Biokosmos 9 flight there appears to be no further growth in the samples exposed to microgravity. Callus cultures from the ground controls, however, continue to grow well. A simulation experiment for IML‐1 performed in January 1990 at ESTEC (European Space Technology Center), The Netherlands, has resulted in regenerated plants. These observations are discussed and compared to the results obtained on Biokosmos 9.
Theories and methods on plant nutrition and growth
Authors: Ingestad Torsten , I. Ågren Gõran
Published: May 2006

A theory comprising two basic concepts relating nutrition and growth is presented. The first concept is a nutrient flux model and is based upon studies of plants at constant internal nutrient concentrations, where a formal mathematical derivation shows that the relative uptake rate (RU) and the relative growth rate (RG) are equal. Deviations from equality are results of experimental insufficiencies and errors. The second concept is based on the observation that RG is linearly related to the internal nutrient concentration. The slope represents nutrient productivity (Pn), an important parameter expressing growth rate per unit of nutrient. Light and the plant genome, for example, influence the value of the proportionality factor, Pn, but not the formal relationship between the internal nutrient concentration and RG

Not only the theory itself but many results and conclusions are very different from those obtained with traditional methods. In experiments where RU was controlled during the exponential period of growth, the relationships between treatment (the relative addition rate, RA), nutrient uptake (RU) and growth (RG) were reproduced with extremely low variability. In agreement with theory, internal nutrient concentration and RG remained stable over time (steady‐state).

An extension of the theory is based upon the empirical assumption that after exponential growth, self‐shading and ageing reduce Pn in proportion to biomass. This assumption has been successfully applied in predicting growth of forest stands, but the nature of the growth reduction is little understood. The generalized model has few parameters and can easily be rewritten to suit different experimental aims, for example to establish reference values and to model changes in soil fertility. Further extension and understanding of the model and different interpretations of the parameters are discussed.
Influence of UV‐B radiation on developmental changes, ethylene, CO2 flux and polyamines in cv. Doyenne d'Hiver pear shoots grown in vitro
Authors: Predieri Stefano , Krizek Donald T. , Wang Chien Y. , Mirecki Roman M. , Zimmerman Richard H.
Published: May 2006

In vitro shoots of cv. Doyenne ?Hiver pear (Pyrus communis L.) were irradiated under controlled environments for 6 h per day at 5 different levels of biologically effective UV‐B radiation (UV‐BBE). UV‐B exposure caused a progressive increase in apical necrosis above background levels and stimulated leaf abscission. Shoots grown for 2 weeks at 7. 8 mol m−2 day −1 of photosynthetic photon flux (PPF) and treated with 8. 4 or 12. 0 kJ m−2 day −1 UV‐BBE produced up to 4 times more ethylene than those given 2. 2 or 5. 1 kJ m−2 day−1 UV‐BBE or untreated controls. Exposure of shoots to 12 kJ m−2 day −1 of UV‐BBE caused an increase in free putreseine content after 4 to 14 days of irradiation. Shoots showed a decrease in CO2 uptake after 3 days of UV‐B: thereafter, they appeared to recover their photosynthetic capacity. Under typical PPF conditions used in micropropagation (90 μmol m−2 S−1). 8. 4 kJ m−2 day −1 of UV‐B radiation was injurious to realatively tender tissues of in vitro pear shoots: increasing the level of UV‐BBE to 12 kJ m−2 day−1 produced even more adverse effects.
Effect of temperature on plasma membrane and tonoplast ion channels in Arabidopsis thaliana
Authors: Colombo Roberta , Cerana Raffaella
Published: May 2006

The temperature dependence of the activity of ion channels was investigated, by means of the patch‐clamp technique in the ‘whole‐cell’ configuration, using protoplasts and vacuoles isolated form Arabidopsis thaliana L. cultured cells. The effect of temperature changes in the range 11–22°C was tested on the hyperpolarization and depolarization‐activated K+ currents in the plasma membrane and on the hyperpolarization‐activated K− currents in the tonoplast (vacuolar membrane). All 3 kinds of currents were unaffected by increasing temperature up to 15°C and were activated between 15 and 20°C.
32P uptake and transport to shoots in Pinuus serotina seedlings under aerobic and hypoxic growth conditions
Authors: Topa Mary A. , Cheeseman John M.
Published: May 2006

We examined the effects o long‐term hypoxic growth conditions on net uptake and transport of P to shoots of pond Pine (Pinus serotina Michx.), a moderately flood‐tolerant southern pine. Seedlings were grown under aerobic orhypoxic solution conditions for 4–5 weeks in continuously flowing solution culture containing 100 μM P. Short – and long‐term 32P. experiments were then concluded with intact seedlings to determine rates of 32P influx, efflux and net transport to the shoot. Shoot fresh weight/root fresh weight ratios were significantly higher under hypoxic gorwth conditions, reflecting the larger reduction in root growth than shoot growth, despite extensive aerechyma formation in roots. Estimates for the unidirectional influx of 32P in aerobic and hypoxic seedlings were 1.43 and 3.20 μmol P (gFW root)−1 h−1, respectively. However, 32P accumulation between the two treatments became similar within 8 h, suggesting that efflux was also higer in seedlings from the hypoxic treatment. Indeed in a separate experiment, hypoxic growth conditions increased efflux by over 60%. Transport of 32P to shoots was significantly reduced under hypoxic growth conditions, despite higher root P concentrations and lower shoot P concentrations. After 48 h, 32P accumulation in roots was similar between the two treatments. Yet total accumulation of seedling 32P decrcased by 31% under the hypoxic treatment, largely because of reduced transport of 32p to the shoot. The lower accumulation of 32 by shoots of seedlings in the hypoxic treatment may be the result of a direct inhibition on the transport process in O2‐defident tissues, but could also reflect a slower turnover or labeling of the ool available for transport. Indeed, the percentage of total 32P in. roots present in the soluble P. (or transportable form of P) was about 33% lower in seedlings from the hypoxic treatment, probably reflecting increased assimilation into organic compounds as well as chelation with iron. Our results suggest that P transport to the shoots of acclimated seedlings may be more sensitive to hypoxic solution conditions than influx at the root Plasmalemma.
Induction and activation of the alternative oxidase of potato tuber mitochondria
Authors: Lidén Annika C. , Åkerlund Hans‐Erik
Published: May 2006

Potato tubers (Solanum tubersum L. cv. Grata) were stored for atleast 1 week at room temperature and then incubated with an equal amount of apples (Malus domestica L.) for 2 days. After this treatment, intact tuber mitochondria isolated by Percoll gradient centrifugation showed a high degree of induction of the alternative oxidase, measured as cyanide‐resistant, salicylhydroxamic acid‐sensitive respiration. With succinate as substrate an activity of more than 130 nmol O2(mg protein) 1 min t was obtained. An assay of the alternative oxidase using duroquinol as an electron donor was developed. To become reliable the assay required the presence of defatted bovine serum albumin (BSA) and catalase (EC 1. 11. 1. 6). Furthermore, a lowering of the assay temperature to 15°C improved the stability of the duroquinol‐based activity. One remarkable finding was that with duroquinol (or external NADH) as substrate the alternative oxidase was synergistically activated by succinate (as well as by malate) even in the presence of the succinate dehydrogenase inhibitor malonate. Our interpretation is that succinate and malate (indirectly) activate the alternative oxidase and that this activation is part of a physiological mechanism for regulation of the alternative oxidase.
Embryology in Norway spruce (Picea abies). An analysis of the composition of seed storage proteins and deposition of storage reserves during seed development and somatic embryogenesis
Authors: Hakman Inger
Published: May 2006

Seed cones were collected from open‐pollinated trees of Norway spruce (Picea abies) in a seed orchard from pollination until maturation of the seeds. Immature embryos were isolated for embryogenic tissue cultures that were maintained either on solidified medium or as liquid cultures. By transferring young somatic embryos to medium containing 90 mM sucrose and 7. 6 μM ABA growth continued to mature embryos that accumulated storage reserves in both the hypocotyl‐shoot axis and the cotyledons. Both zygotic and somatic embryos at different developmental stages were processed for microscopy as were the megagametophytes. Total protein was extracted from the seed material at intervals during development and analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. These analyses revealed that storage protein started to accumulate in the megagametophytes at the time when embryos were growing into the gametophytic tissue, while it occurred a few weeks later in the embryos at rapid embryo growth and organ differentiation. Lipid bodies also became abundant in the mature plant material. Although plastids with prominent starch grains were very frequent in both megagametophytes and embryos during development they were not observed in the desiccated tissues. Zygotic and somatic embryos displayed a similar developmental pattern.

By sequential salt‐extraction and dilution two fractions highly enriched in storage protein were obtained. One fraction (G‐1), requiring higher salt concentration for protein solubilization, was dominated by a protein migrating to around M, 55000–60000 when separated under non‐reduced condition. After exposure to reducing agent this protein was replaced by two new ones with M, 33000 and 22000 giving evidence of disulfide bonded polypeptides. The other fraction (G‐2), was dominated by polypeptides around M, 42000 and low molecular mass polypeptides (<14000).
Cytokinins in photoperiodic induction of flowering in Chenopodium species
Authors: Macháčková Ivana , Krekule Jan , Eder Josef , Seidlová Frideta , Strnad Miroslav
Published: May 2006

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non‐inductive for flowering in leaves, stems, roots and apical parts of short‐day Chenopodium rubrum and long‐day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum, has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far‐red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.
Garlic (Allium sativum) chitinases: characterization and molecular cloning
Authors: Van Damme Els J. M. , Willems Pieter , Torrekens Sophie , Van Leuven Fred , Peumans Willy J.
Published: May 2006

Leaves and bulbs of garlic (Allium sativum L.) contain a chitinase which can be separated into three different isoforms with similar molecular structure and N‐ terminal amino acid sequence. SDS‐PAGE of the alkylated chitinase revealed two distinct polypeptides of 32 and 33 kDa. Induction studies of the chitinase in leaves of garlic plants indicated that not only treatment with ethephon or salicylate and wounding but also a temperature shock strongly increased the enzyme level.

cDNA libraries constructed from poly(A)‐rich RNA isolated from young garlic shoots and bulbs were screened for chitinase clones using the cDNA clone CCH4 encoding a basic potato chitinase as a probe. Two different cDNA clones (designated CHITAS 1 and CHITAS 2)of ca 1 000 bp were isolated and their sequences analyzed. The amino acid sequences deduced from both cDNA clones were homologous though not identical to the N‐terminal sequences of the mature chitinases. Although both clones encode highly homologous chitinases their sequences definitely differ in that they have different signal peptides and one of them contains a glycine‐rich domain. The garlic chitinases are apparently translated from an mRNA of 1200 nucleotides which encodes a proprotein of approximately 32 or 33 kDa for CHITAS 1 and CHITAS 2, respectively. Co‐translational removal of the signal peptide will result in a 30 (for CHITAS 1) or 31 kDa (for CHITAS 2) protein with an isoelectric point of 4. 94 (for CHITAS 1) or 6. 12 (for CHITAS 2). Garlic chitinases are encoded by a small gene family as shown by Southern blot analysis of genomic DNA isolated from garlic.

The garlic chitinases show a high degree of sequence homology to the previously isolated chitinases from dicotyledonous as well as monocotyledonous species, indicating that these proteins have been conserved from an evolutionary point of view.
Kinetic resolution of different recovery phases of photoinhibited photosystem II in cold‐acclimated and non‐acclimated spinach leaves
Authors: van Wijk Klaas J. , van Hasselt Philip R.
Published: May 2006

Leaf discs from spinach were exposed to a photon flux density of 1250 μmol m−2s−1 at 5°C for 2 or 3 h in ambient air. Photoinhibition of photosystem II (PS II) was measured by means of chlorophyll fluorescence. Recovery of photosystem II was followed at 6°C and 20°C in low light or darkness for periods up to 12 h.

The experimental setup allowed kinetic resolution of different phases of recovery. The experiments revealed a temperature dependent dark recovery phase and two distinct light‐ and temperature dependent phases: (1) A relatively fast, light dependent recovery phase occurred in parallel with partial recovery of basic fluorescence at 6°C and 20°C. A population of PS II centers with very slow fluorescence induction kinetics, which had accumulated during photoinhibition treatment, disappeared during this phase. This fast recovery phase is proposed to represent reactivation of photoinhibited PS II, without dissassembly or incorporation of new D1‐protein. (2) A relatively slow light‐dependent recovery phase took place at 20°C, but not at 6°C. In the presence of the chloroplast translation inhibitor streptomycin, part of the 2nd phase was inhibited. This phase is proposed to involve assembly of new Photosystem II centers, which is partly dependent on de novo synthesis of D1‐reaction center protein, but presumably is also using a preexisting pool of D1‐protein. Cold acclimation of the leaves resulted in a decreased sensitivity for photoinhibition of photosystem II. Recovery of photoinhibited photosystem II at 6°C of the cold‐acclimated leaves was faster than in non‐acclimated leaves, but this effect can be ascribed to diminished photoinhibitory damage.
Inhibition of electron flow around photosystem I in chloroplasts of Cd‐treated maize plants is due to Cd‐induced iron deficiency
Authors: Siedlecka Anna , BaszyńAski Tadeusz
Published: May 2006

Photosystem I activity of chloroplasts isolated from 21 days old maize seedlings (Zea mays L. cv. Hidosil) cultivated in a nutrient solution containing different concentrations of Cd (10,20,30μM) was investigated. Cd markedly decreased ferredoxin(Fd)‐dependent NADP+ photoreduction, while it had no effect on electron transport from 2. 6‐dichlorophenolindophenol to methyl viologen, indicating that the metal interferred with electron transport on the reducing side of photosystem I. The decrease in electron transport correlated with a low Fd content, which in turn was correlated with a low Fe concentration, suggesting Cd‐induced Fe deficiency. In in vitro experiments direct Cd inhibition of Fd‐dependent NADP+ photoreduction required much higher Cd concentrations than those observed in Cd‐treated plants.
Abscisic acid content at defined levels of bud dormancy and frost tolerance in two contrasting populations of Picea abies grown in a phytotron
Authors: Qamaruddin Mohammed , Dormling Ingegerd , Ekberg Inger , Erikason Gösta , Tillberg Elisabeth
Published: May 2006

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies were cultivated under continuous light and 20°C for 10 weeks. To arrest growth, induce terminal bud dormancy and promote frost tolerance the seedlings were then exposed to 16 h nights for 12 weeks, with gradually lower temperature during the last 6 weeks. Samples for estimating the abscisic acid content of the needles were taken just before the onset of the night treatment, at day 3 of the treatment, and then with one, and later 2 week, intervals. From the second week onwards (third week for frost tolerance) bud dormancy and frost tolerance were assessed at the same time as abscisic acid (ABA) determinations. Phosphate‐buffered saline extracts were purified on mini‐columns (in some cases immunoaffinity colums) and quantified by HPLC. The degree of dormancy was estimated by transferring the seedlings to growth conditions and determining the number of days until growth was resumed. The frost tolerance of the needles exposed to –10°C and –20°C was classified in 6 classes. The frost tolerance of the terminal buds was estimated as the number of seedlings that showed some growth after 6 weeks in growth conditions. The night treatment rapidly induced terminal bud dormancy in both populations, but the release of dormancy occurred earlier in the northern population. The needles and the terminal buds became highly frost tolerant more rapidly in the northern than in the southern population and before the temperature decrease. The degree of dormancy began to decline before full frost tolerance was obtained in the southern population and this decline continued in both populations, while frost tolerance remained at a high level. The southern population showed a transient peak in ABA content at day 3. Although the ABA content of the northern population was lower than in the southern before the 16‐h night treatment, it increased in the northern population during the treatment period, in particular after the temperature decrease.
The unusual sugar composition in leaves of the resurrection plant Myrothamnus flabellifolia
Authors: Bianchi Giorgio , Gamba Anna , Limiroli Rita , Pozzi Nicoletta , Elster Ralph , Salamini Francesco , Bartels Dorothea
Published: May 2006

To understand mechanisms of osmoprotection, the composition of sugars and related compounds were analyzed in extracts of fully hydrated and desiccated leaves of the desiccation‐tolerant resurrection plant Myrothamnus flabellifolia. During the dehydration process the concentrations of fructose and glucose decrease, whereas sucrose, arbutin and glucopyranosyl‐β‐glycerol increase. The substances were identified by GC‐MS and NMR‐analyses. This is the first report of large amounts of glucopyranosyl‐β‐glycerol in higher plants which may act as an osmoprotectant. Significant levels of the nonreducing sugar trehalose were present in all samples tested.
Accumulation of canthaxanthin in Chlorella emersonii
Authors: Malis S. Arad , Cohen E. , Ben Amotz A.
Published: May 2006

A strain of Chlorella emersonii grown under high light intensity and low nitrogen degrades its chlorophyll and synthesizes canthaxanthin as the major carotenoid. Nitrogen starvation or high light alone does not induce canthaxanthin production. Norflurazon, a carotene inhibitor at the level of phytoene desaturase, inhibits production of canthaxanthin in C. emersonii with no accumulation of phytoene. Chlorella vulgaris and C. sp. 993 exposed to similar conditions do not respond in the same way as C. emersonii.
The rate of protein synthesis in needles of Norway spruce (Picea abies): Light stimulation, regulation through photophosphorylation, stress enhancement
Authors: Schmitz H. , Löffel U. , Weidner M.
Published: May 2006

The incorporation of 14C‐leucine into the total‐protein fraction of needles of Norway spruce (Picea abies [L.] Karst.) during short time incubation was used as a measure of protein synthesis in the light and in the dark. Light saturation curves, obtained for needles of different ages (new flush and 1 and 2 years old) or at different seasons (summer‐winter) followed the Michaelis‐Menten algorithm, exhibiting marked differences with regard to light saturation (Vmax) and the half‐saturation constant (K5. 2). The light saturation curves of ATP level (mg g−1 fresh weight) and of leucine incorporation into protein (nmol mg−1 h−1) matched each other, suggesting that photophosphorylation may be decisive for the rate of protein synthesis in the light. This is confirmed by the action spectrum of leucine incorporation. which resembled an action spectrum of leaf photosynthesis, and also by partial inhibition of protein synthesis by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), an inhibitor of non‐cyclic photophosphorylation. Light stimulated protein synthesis showed pronounced seasonal fluctuations with a summer maximum.

Furmigation of 5 years old spruce trees for 3 months with SO2 in combination with O3 and/or NO2 caused a distinct enhancement of the protein synthesis rate in the light and, at a reduced absolute level, also in the dark. A similar result was obtained for 40 to 70 years old spruce stands when healthy and sick trees were compared: the latter being afflicted by the novel type of forest decline, which is characterized by yellowish bronze discolouration of sun‐exposed older needles and partial loss of older needle generations (3 to 4 years old). The 1 year old needles of the unhealthy trees showed a markedly increased 14C‐leucine incorporation rate which, in the dark, was even more pronounced than in the light. Stress‐physiological mechanisms, which could possibly explain this stimulation, are discussed.
Refixation of xylem sap CO2 in Populus deltoides
Authors: Stringer Jeffrey W. , Kimmerer Thomas W.
Published: May 2006

Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO2 in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO2 to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO2 in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of three Populus deltoides trees had mean dissolved inorganic carbon concentrations (CO2+H2CO3+HCO−3) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[14C]NaHCO3, 99. 6% of the label was fixed in the light. Seventy‐seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue in P. deltoides leaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO2 delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO2 uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[14C]CO2. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5‐s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO2 delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C‐3 photosynthesis.
Age of potato seed‐tubers influences protein synthesis during sprouting
Authors: Kumar G. N. Mohan , Knowles N. Richard
Published: May 2006

The effect of seed‐tuber age on the ability of tuber tissue to synthesize protein during sprouting was examined. As seed‐tuber age advanced from 4 to 32 months (at 4°C, 95% relative humidity), soluble protein concentration of tubers decreased linearly, with a concomitant increase in free amino acid concentration. The age‐induced loss of tuber protein may thus be due to increased proteolysis, decreased protein synthesis, or both. Five‐ and 17‐month‐old seed‐tubers were compared for their ability to incorporate radiolabeled amino acids into soluble protein at equivalent stages of sprout development. Tuber respiration was profiled through each sprouting stage to characterize the physiological status of the seed‐tubers prior to incorporation studies. Five‐month‐old seed‐tubers maintained a constant rate of respiration during sprouting. In contrast, respiration of 17‐month‐old tubers increased as sprout dry matter increased, resulting in a 2‐ to 3‐fold greater respiratory rate from the older tubers, relative to the younger tubers, at similar stages of sprout development. Prior to sprouting, the rate of incorporation of amino acids into trichloroacetic acid‐precipitable protein of tissue from 5‐month‐old tubers was 2. 9‐fold higher than that from 17‐month‐old tubers. More importantly, protein‐synthetic capacity of tissue from younger tubers increased about 1. 7‐fold during sprout development. Despite the higher respiratory activity and faster total sprout dry matter accumulation from older seed‐tubers, protein synthesis remained at a low and constant level through all stages of sprouting. Protein‐synthetic capacity thus declines with advancing tuber age, and this may contribute to reduced growth potential during the latter stages of establishment by affecting the ability of seed‐tubers to synthesize enzymes involved in mobilization and translocation of tuber reserves to developing plants.
Influence of magnesium deficiency on rates of leaf expansion, starch and sucrose accumulation, and net assimilation in Phaseolus vulgaris
Authors: Fischer Erika Sigrid , Bremer Elke
Published: May 2006

Twenty one‐day‐old Phaseolus vulgaris‘Saxa’plants were cultured in a growth chamber and the plants supplied with either a complete or a Mg‐free nutrient solution. From 6 days after transfer to the Mg‐free solution, the rate of increase of the area of the second trifoliate leaf was considerably reduced; by day 11 the sucrose concentration in the first trifoliate leaf had increased 6. 2‐fold at the end of the dark period and 4. 6‐fold after the light period as compared with the control plants. Corresponding starch concentrations increased 6. 6‐fold and 2. 9‐fold respectively. After days 5 to 6 the assimilation rates declined in the first trifoliate leaf of the plants showing deficiency, in comparison with the plants fully supplied with nutrients; respiration increased during darkness. The reduction in net assimilation rate was to a great extent reversible after resupply of magnesium.

The reduction of magnesium concentration in the deficient plants was much more marked in the expanding leaves than in the mature primary leaves and roots. Sucrose and starch accumulation did not occur when the first trifoliate leaf was partially shaded, although magnesium concentration, as in the unshaded leaves, was reduced to 13% of that of the control plants. The consequences of magnesium deficiency in the expanding first trifoliate leaf are discussed in terms of the possibility of sink limitation.
Short period leaf movements in Oxalis regnellii
Authors: Pedersen Marit , Johnsson Anders , Mæhle Jørgen , Dalløkken Runar
Published: May 2006

Oxalis regnellii Mig. is a trifoliate plant, and the three leaflets usually show synchronized up and down movements with a circadian period of 26–27 h. The three leaflets can also perform desynchronized ultradian oscillations, and we report on such rhythms under different conditions. A study of the occurrence of ultradian leaf movement rhythms as a function of irradiance is presented. At an irradiance of approximately 1 μW cm−2, the occurrence was maximal and ca 30%. The periods varied from 5 to 15 h. Four other cases of ultradian rhythms in different conditions are also presented. In one case spontaneous ultradian rhythms occurred, and in another, two of the leaflets showed ultradian rhythms when the third leaflet had received a light pulse. In two more cases, the three leaflets on a leaf were separated by physical cuts along the petiole between the pulvini; in both cases the period was approximately 5 h. Possible mechanisms to explain the ultradian rhythms in Oxalis regnelli are discussed.
Composition and positional distribution of fatty acids in polar lipids from Chlorella ellipsoidea differing in chilling susceptibility and frost hardiness
Authors: Joh Toshio , Yoshida Tsuguhiko , Yoshimoto Makoto , Miyamoto Takahisa , Hatano Shoji
Published: May 2006

The composition and positional distribution of fatty acids in the polar lipids from 4 strains of Chlorella differing in chilling susceptibility and frost hardiness were analyzed by enzymatic hydrolysis and gas‐liquid chromatography. Analysis of the polar lipids from chilling‐sensitive, chilling‐resistant and chilling‐sensitive revertant strains of Chlorella ellipsoidea IAM C‐102 showed that the sum of palmitic and trans‐3‐hexadecenoic acid in phosphatidylglycerol (PG) is about 60% for the sensitive strains and 53% for the resistant strain. The sum of dipalmitoyl and 1‐palmitoyl‐2‐(trans‐3‐hexadecenoyl) PG as estimated from the positional distribution of their fatty acids, is about 10% in the case of each of the three strains. The contents of unsaturated fatty acids in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were higher in the resistant than in the sensitive strain. This suggests that unsaturation of fatty acids in not only PG but also PC and PE is involved in chilling sensitivity of Chlorella. On the other hand, lipid changes during the development of frost hardiness of C. ellipsoidea IAM C‐27, a frost hardy strain, were examined. The results showed that fatty acids in most lipid classes are unsaturated in the hardening process but their degree of unsaturation is not greatly different from that of the chilling‐resistant strain, suggesting that not only unsaturation of fatty acids in lipids but also other factors are necessary for the development of frost hardiness.
Phytochrome‐mediated control of respiratory activities of mitochondria in cotyledons of dark‐grown cucumber seedlings
Authors: Morohashi Yukio , Sasanuma Shin‐ichirou , Seto Tadahito
Published: May 2006

Mitochondria isolated from cotyledons of dark‐grown cucumber (Cucumber sativus L., cv. Shimotsuki‐Aonaga) seedlings after illumination with continuous far‐red light showed an increased capacity for oxidation of malate or α‐ketoglutarate, as compared with those from cotyledons of non‐illuminated seedlings. This increase is supposed to be caused by phytochrome action (high irradiance response). Exogenous NAD+ had no effect on the rate of the oxidation of α‐ketoglutarate or malate by mitochondria isolated from far‐red light‐treated cotyledons, but it enhanced the oxidation rate of mitochondria from control cotyledons to the level of mitochondria from light‐treated ones. The NAD (NAD++ NADH) content was higher in mitochondria isolated from continuously far‐red light‐treated cotyledons than in mitochondria from controls. The NAD content was also increased by the treatment with a red light pulse and this response was reversed by a subsequent far‐red light pulse. It is proposed that phytochrome controls respiratory activities of cucumber mitochondria by changing the size of the NAD pool in the mitochondria.
Effects of ethephon and norbornadiene on sterol and glycoalkaloid biosynthesis in potato tuber discs
Authors: Bergenstråhle Annika , Tillberg Elisabeth , Jonsson Lisbeth
Published: May 2006

The accumulation of glycoalkaloids that normally takes place in aerobically incubated potato (Solanum tuberosum L.) tuber discs has been found to be inhibited by the ethylene‐releasing substance ethephon. Using ethephon and the ethylene action inhibitor norborna‐2,5‐diene, the effect of ethylene on the synthesis of sterols and glycoalkaloids, which partly share their biosynthetic pathway, was investigated.

Control discs showed incorporation of (2‐14C)mevalonic acid into free sterols, steryl esters, steryl glycosides and acylated steryl glycosides at 24 h, thereafter the radioactivity decreased in free sterols and steryl esters concomitant with the appearance of radioactivity in glycoalkaloids. Discs with ethephon additions contained more radioactivity in all sterol classes at all time‐points, but no glycoalkaloids were formed.

The enzyme S‐adenosyl‐l‐methionine:sterol C24 methyltransferase (SMT, EC 2. 1. 1. 41), located at one presumed branching point in the sterol and glycoalkaloid pathway, was characterized and found to exhibit similar characteristics as in other plants, but a lower specific activity. The activity of SMT increased in ageing tuber discs and this increase was further stimulated by ethephon, but inhibited by norborna‐2,5‐diene. The activity of the glycoalkaloid‐specific enzyme UDP‐glucose:solanidine glucosyltransferase (EC 2. 4. 1) also increased after slicing, but here ethephon additions counteracted the induction. The activity of the sterol‐specific UDP‐glucose:sterol glucosyltransferase (EC 2. 4. 1) was unaffected by either tuber slicing or ethephon additions.

The results indicate that ethylene stimulates sterol synthesis in wounded potato discs, and that the wound‐induction of SMT is regulated by ethylene.