bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of nitrate supply on concentrations and translocation of abscisic acid in barley (Hordeum vulgare)
Authors: Brewitz Erica , Larsson Carl‐Magnus , Larsson Marie
Published: May 2006

Spring barley (Hordeum vulgare L. cv. Golf) was grown at different nitrate supply rates, controlled by using the relative addition rate technique, in order to elucidate the relationship between nitrate‐N supply and root and shoot levels of abscisic acid (ABA). The plants were maintained as (1) standard cultures where nitrate was supplied at relative addition rates (RAs) of 0.03, 0.09 and 0.18 day−1, and (2) split‐root cultures at RA 0.09 day−1 but with the nitrate distributed between the two root parts in ratios of 100:0, 80:20 and 60:40. Time‐dependent changes in root and shoot concentrations of ABA (determined by radioimmunoassay using a monoclonal antibody) were observed in both standard and split‐root cultures during 12 days of acclimation to the different nitrate regimes. However, the ABA responses were similar at all nitrate supply rates. Further experiments were performed with split‐root cultures where the distribution of nitrate between the two root parts was reversed from 80:20 to 20:80 so that short‐term effects to local perturbations of nitrate supply could be studied without altering whole‐plant N absorption. Transient increases in ABA concentrations (maximum of 25 to 40% after 3 to 4 h) were observed in both subroot parts, as well as in xylem sap and shoot tissue. By pruning the root system it was demonstrated that the change in ABA had its origin in the subroot part receiving the increased nitrate supply (i.e. switched from 20 to 80% of the total nitrate supply). The data indicate that ABA responses are easily transmitted between different organs, including transmission from one set of seminal roots to another via the shoot. The data do not provide any indication that long‐term nitrate supplies or general nitrogen status of barley plants affect, or are otherwise related to, the average tissue ABA concentrations of roots and shoots.
Autoregulation of soybean nodulation: Delayed inoculation increases nodule number
Authors: Jr Francisco Perigio B. , Harper James E.
Published: May 2006

The influence of seedling age at the time of inoculation on the regulation of nodule number in soybean (Glycine max [L.] Merr.) was examined in cv. Williams 82 and its hypernodulating mutant NOD1‐3. Nodulation was evaluated on plants grown in plastic growth pouches or in vermiculite in 50‐ or 500‐ml glass containers in growth chamber studies. Seeds or seedlings were inoculated once with Bradyrhizobium japonicum strain USDA 110 (10k cells seedling−1) between 0 and 15 days after sowing at 3‐ or 5‐day intervals and were grown for 21 days after inoculation. Nodule number plant−1 was similar across inoculation times in plants grown in growth pouches, but was significantly greater when inoculation was delayed and plants were grown in vermiculite in 500‐ml containers. Plant culture in vermiculite in 50‐ or 500‐ml containers confirmed the suppressive effect of restricted space for root growth on nodulation. Inoculation with 105 or 109 USDA 110 cells revealed that nodulation was inhibited by a high inoculum dose. There was a large increase in nodule number plant−1 when plants were transferred from a restricted rooting environment (growth pouch culture) to a nonrestricted rooting environment (2‐1 hydroponic pots). Autoregulation was also examined in split‐root assemblies of plants in 500‐ml containers of vermiculite. Controls involved concurrent inoculation of both root halves at 0. 4 or 8 days after transplant. Treatments involved time‐separated inoculations of root halves with the primary and secondary inoculations being separated by 4 days. Plants were harvested at 21 days after inoculation. Williams 82 exhibited autoregulation of nodule number on the root half receiving delayed inoculation, regardless of plant age at the time of primary inoculation. Total nodule number plant−1 invariably increased with later inoculation times. In contrast. NOD1 ‐ 3 exhibited little, if any, autoregulation of nodule number. It was concluded that although Williams 82 exhibits autoregulation of nodule number and NODI ‐ 3 does not, there was no finite limit to nodule number in either line since any delay in inoculation resulted in formation of a greater nodule number on both lines if root growth was not restricted. Nodule number in Williams 82 and NODI ‐ 3 appears to be a function of infection sites (root size) at the time of inoculation and of subsequent plant growth.
CO2 uptake and fluorescence responses for a shade‐tolerant cactus Hylocereus undatus under current and doubled CO2 concentrations
Authors: Raveh Eran , Gersani Mordechai , Nobel Park S.
Published: May 2006

Hylocereus undatus (Haworth) Britton and Rose growing in controlled environment chambers at 370 and 740 μmol CO2 mol−1 air showed a Crassulacean acid metabolism (CAM) pattern of CO2 uptake, with 34% more total daily CO2 uptake under the doubled CO2 concentration and most of the increase occurring in the late afternoon. For both CO2 concentrations, 90% of the maximal daily CO2 uptake occurred at a total daily photosynthetic photon flux density (PPFD) of only 10 mol m−2 day−1 and the best day/night air temperatures were 25/15°C. Enhancement of the daily net CO2 uptake by doubling the CO2 concentration was greater under the highest PPFD (30 mol m−2 day−1) and extreme day/night air temperatures (15/5 and 45/35°C). After 24 days of drought, daily CO2 uptake under 370 μmol CO2 mol−1 was 25% of that under 740 μmol CO2 mol−1. The ratio of variable to maximal chlorophyll fluorescence (Fy/Fm) decreased as the PPFD was raised above 5 mol m−2 day−1, at extreme day/night temperatures and during drought, suggesting that stress occurred under these conditions. Fv/Fm was higher under the doubled CO2 concentration, indicating that the current CO2 concentration was apparently limiting for photosynthesis. Thus net CO2 uptake by the shade‐tolerant H. undatus, the photosynthetic efficiency of which was greatest at low PPFDs. showed a positive response to doubling the CO2 concentration, especially under stressful environmental conditions.
Assimilate partitioning in Pachyrhizus erosus tubers under short days
Authors: Vaillant Victor , Desfontaines Lucienne
Published: May 2006

The distribution of 14C products in yam bean (Pachyrhizus erosus) plants was measured as a function of time after a 14CO2 pulse‐chase experiment under short‐day conditions. The 14C declined by more than 70% in leaves during the first two hours, indicating that they actively exported carbon. Tubers were strong storage sinks for carbon and accumulated more than 80% of the total incorporated 14C after a 72‐h chase. The data show that, although sucrose represented about 21% of the tuber non‐structural carbohydate, i.e. 15% of the tuber dry weight, 14C did not accumulate in sucrose but in glucose, fructose and starch. The data indicate the existence of a separate sucrose pool which is affected only very slowly by recent assimilates. As a result, recent photosynthates, temporarily stored, may contribute to the reservoir of carbon available for nitrogen fixation. The data also suggest the existence of two distinct pools of amino acids in the tuber, one utilized mostly for protein synthesis and the other probably stored in the vacuole.
Enhanced UV‐B radiation has little effect on growth, δ13C values and pigments of pot‐grown rice (Oryza sativa) in the field
Authors: Kim Hak Yoon , Kobayashi Kazuhiko , Nouchi Isamu , Yoneyama Tadakatsu
Published: May 2006

Predicted increase in ultraviolet‐B (UV‐B: 280–320 mn) radiation may have adverse impacts on growth and yield of rice (Oryza sativa L.), as has been found in studies hitherto. However, most of the studies were conducted in growth chambers or greenhouses where the plants are generally more sensitive to UV‐B than in the field, presumably because of the distorted balance between UV‐B and ultraviolet‐A as well as PAR. This study was conducted to address the effects of enhanced UV‐B on growth and yield of rice under a realistic spectral balance in the field. Three cultivars, “Koshihikari”,‘IR 45’and‘IR 74’were pot‐grown and irradiated with enhanced UV‐B for most of the growing season in the field at Tsukuba, Japan (36°01′N, 140°07′E). The UV‐B enhancement simulated ca 38% depletion of stratospheric ozone at Tsukuba. The results showed no UV‐B effects on plant height, numbers of tillers and panicles, dry weight of the plant parts or the grain yield for any of the 3 cultivars. Natural abundance of 13C in the flag leaves was not altered by the UV‐B enhancement either. While UV‐absorbing compounds showed no response to the UV‐B enhancement, chlorophyll contents decreased with enhanced UV‐B. However, the decrease of chlorophyll was limited to an early growth stage with no effect later. We thus found no extraordinary impact of the nearly doubled UV‐B radiation on rice in the field, and it would appear that a reliable prediction of the effects of UV‐B will require experiments carried out over a number of years under various climatic and solar UV‐B regimes.
Pine genome size diversity and water relations
Authors: Wakamiya Izumi , Price H. James , Messina Michael G. , Newton Ronald J.
Published: May 2006

Important functions of water relations are considered to be related to genome size diversity in gymnosperms. We investigated relationships among genome size, dimensional characteristics of conductive cells, and water relations parameters by using young seedlings of six Pinus species. Xylem hydraulic conductivity was not correlated with genome size and dimensional characteristics of conductive cells, but the water potential at the turgor loss point was. Pinus species with large genome sizes had thick cell walls and small ratios of lumen radii to cell wall thickness in their conductive cells, and those species lost their turgor to tissue dehydration al low water potentials. The characteristics observed in the present study may contribute to pine drought tolerance.
pH and osmotic potential of pine ash as post‐fire germination inhibitors
Authors: Henig‐Sever Nava , Eshel Amrara , Ne'eman Gidi
Published: May 2006

The dominant plant species in native pine forests in Israel (Pinus halepensis. Cistus salviifolius and C. creticus) regenerate from seeds after wildfires. The future structure of the regenerating forest is determined largely by the spatial distribution of the seedlings, which depends on the response of the seeds to conditions in the upper layer of the soil. The pH and osmotic potential (π) of the soil water in this layer is strongly affected by the ash which covers the burned forest floor. The effects of pH and π on the germination of the wild species noted above and the effect of pH on the germination of two crops, radish (Kaphanus sativus radicula) and oat (Avena sativa) were studied in a growth chamber. Bis‐Tris propane and CAPS [3‐(cyclohexylamino)‐l‐propanesulfonic acid] buffer solutions (pH 6–11), as well as mannitol solutions (down to –1.5 MPa) were used. The upper soil layer from a recently burned forest had pH 9 and π–0.08 MPa. Under this pH the germination of P. halepensis and C. creticus was reduced by ca half, and of C. salviifolius by 40%. Germination of radish and oats was reduced by ca 80%. Osmotic potential of –0.1 MPa did not have a significant effect on the germination of any of the species studied. We conclude that the high pH of the soil, caused by ash, is an important environmental factor that controls the regeneration of the forest plant community. Seed adaptation to the high pH may be decisive in determinig the plants' fate the fire‐prone ecosystems.
Identification of some major cytokinins in Phaseolus vulgaris and their distribution
Authors: Hammerton Russell D. , Nicander Ejörn , Tillberg Elisabeth
Published: May 2006

The determination of the various endogenous cylokinins and their distribution among organs is important in understanding their role in growth and development in the intact plant. Cytokinins in young plants of Phaseolus vulgaris were purified by immunoaffinity chromatography and HPLC, and characterised by UV spectra. Zeatin nucleotide (zeatin riboside‐5′‐monophosphate) and isopentenyladenine nucleotide (isopentenyladenosne‐5′‐monopnosphate) were the most abundant cytokinins in all organs. Their identities were confirmed by GC‐MS. The levels of zeatin, zeatin riboside, isopentenyladenine and isopentenyladenosine never exceeded 5% of the nucleotides, as assessed by a methodology that preserves cytokinin nucleotides. Three extraction methods were compared with qualitatively similar results, though differing in their suppression of nucleotidase activity. Cytokinin nucleotide levels were greater in the stems and petioles than in the roots and leaves on a per gram fresh weight basis, and were greater in the stems than in the other organs on a per plant basis. Levels of the zeatin and isopentenyladenine nucleotides were about equal in the stems and leaves, but in the petioles the zeatin nucleotide levels were about twice the level of isopentenyladenine nucleotide, while in the roots they were about half the isopentenyladenine nucleotide level. The importance of considering the cytokinin form is emphasised.
Changes in the protein composition of cytoplasmic ribsomes during the greening of etiolated barley leaves
Authors: Koyama Kazunari , Wada Akira , Maki Yasushi , Tanaka Ayumi
Published: May 2006

We examined changes in the protein composition of cytoplasmic ribosomes in etiolated barley leaves following illumination. Cytoplasmic ribosomes were isolated from greening barley leaves by sucrose density gradient centrifugation, and were analyzed by radical‐free highly reducing polyacrylamide gel electrophoresis (RFHR‐PAGE). Eighty‐nine proteins were resolved from the ribosomal fraction; among them, 8 proteins changed their copy numbers depending on the stage of greening. We designated these as phase dependent ribosomal proteins (PD1–PD8). Two of the proteins (PD1 and 5) present in the ribosomes of etiolated leaves showed a decrease in level during greening. In contrast, the levels of 6 ribosomal proteins (PD2, 3, 4, 6, 7 and 8) increased as greening proceeded. N‐terminal amino acid sequence of PD8 showed high homology to rat ribosomal protein L34. The ribosomal proteins that appeared after illumination were not found in any fraction of the etiolated leaves, suggesting that they were synthesized after the onset of illumination. Copy numbers of other ribosomal proteins did not change during greening.
Frost resistance and pH of cell effusate in needles of artificially deacclimated Scots pine (Pinus sylvestris)
Authors: Taulavuori Kari , Taulavuori Erja , Niinimaa Ahti , Laine Kari
Published: May 2006

Provenances of seedlings of Scots pine (Pinus sylvestris L.) from northern Finland (65°N) and cuttings from trees of the same species about 30 to 40 years in age were studied in 3 artificial deacclimation experiments during the winter and spring of 1994. The deacclimation conditions varied in terms of temperature rise and photoperiods. Frost resistance and the pH of the cell effusate were studied in order to investigate the possibility of a connection between them. Complete deacclimation was achieved, as shown by a frost resistance of –60°C to –65°C in the seedlings and –8O°C in the cuttings at the beginning of the experiment and decreased to above –10°C by the end. The frost resistance and pH of the cell effusate responded significantly to the increase in temperature that marked the onset of the deacclimation process, whereas the response to different photoperiods was only slight. A highly significant correlation was found between frost resistance and the pH of the cell effusate. These variables were also significantly correlated with the freezing test temperature, indicating the condition of plasmalemma and tonoplast; and with sampling day, indicating the response to deacclimation. In the light of these findings, it is concluded that the pH of the cell effusate with certain reservations, can be used as a time saving, alternative viability test when determining frost resistance.
Chitinase profiles in mature carrot (Daucus carota) roots and purification and characterization of a novel isoform
Authors: Zhang Yeyan , Haunerland Norbert H. , Punja Zamir K.
Published: May 2006

The profile of chaitinases (EC 3.2.1.14) in mature carrot (Daucus carota L. cv. Eagle) roots was studied. Multiple chitinase bands (8–10) were observed in native and sodium dodecylsulfate‐denaturing polyacrylamide gels. The molecular masses of these chitinases were estimated to be from 20 000 to 40 000. One major chitinase was purified and found to be an acidic protein with pI at 4.3 and a molecular mass of 39 500. The optimum pH for enzymatic activity was around 5 and the optimum temperature was 25°C. The enzyme was stable at pHs below 8 and temperatures below 60°C. The protein did not have a chitin‐binding domain, but showed some similarity to the amino acid composition of tobacco class I chitinase. The N‐terminal amino acid sequence did not resemble any of the described classes of chitimases. This chitinase did not possess lysozyme activity and showed antifungal activity when tested against Trichoderma sp.
Far‐red enrichment and photosynthetically active radiation level influence leaf senescence in field‐grown sunflower
Authors: Rousseaux M. C. , Hall A. J. , Sánchez R. A.
Published: May 2006

Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitative changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower (Helianthus annuus L.) canopies. Mean leaf duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly (P < 0.05) reduced from 51 to 19 days as crop population density was increased from 0.47 to 4.76 plants m−2. High compared to low plant population density was associated with earlier reduction in the photosynthetically active radiation (PAR) and red/far‐red ratio (R/FR) reaching the target leaf. However the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR‐reflecting mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR‐ (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly (P < 0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR‐controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both leaf surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR‐ control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decrease in R/FR.
Platanetin and 7‐iodo‐acridone‐4‐carboxylic acid are not specific inhibitors of respiratory NAD(P)H dehydrogenases in potato tuber mitochondria
Authors: Roberts Thomas H. , Rasmusson Allan G. , Møller Ian M.
Published: May 2006

Progress in understanding the role of NAD(P)H oxidation in plant respiration is restricted by the lack of access to specific inhibitors of each of the unknown number of NAD(P)H dehydrogenases in the inner mitochondrial membrane. Platanetin (3,5,7,8‐tetrahydroxy‐6‐isoprenyl flavone) is known to be an inhibitor of extermal NADH oxidation by plant mitochondria, while 7‐iodo‐acridone‐4‐carboxylic acid (IACA) is an inhibitor of an internal, rotenone‐insensitive NAD(P)H dehydrogenase isolated from yeast mitochondria.

Here we show that platanetin inhibits external NAD(P)H oxidation by intact potato (Solanum tuberosum L. cv. Bintje) tuber mitochondria, deamino‐NADH oxidation by Complex I assayed using inside‐out submitochondrial particles from these mitochondria, and rotenone‐insensitive NAD(P)H oxidation by these submitochondrial particles. IACA was found to inhibit the oxidation of external NADH and succinate by intact mitochondria with similar efficiency. However, IACA also inhibited NADPH and duroquinol oxidation by intact mitochondria as well as deamino‐NADH and NAD(P)H oxidation by inside‐out submitochondrial particles. This indicates that IACA has several sites of inhibition in the electron transport chain. The lack of specificity of both platanetin and IACA prevents these inhibitors from being used to shed more light on the identity of the NAD(P)H dehydrogenases in plant mitochondria.
Impact of sugar concentration in vitro on photosynthesis and carbon metabolism during ex vitro acclimatization of Spathiphyllum plantlets
Authors: Van Huylenbroeck Johan M. , Debergh Pierre C.
Published: May 2006

Photosynthesis and carbon metabolism were followed during the acclimatization of micropropagated Spathiphyllum cv. Petite shootlets cultured with two different sucrose concentrations (3 and 6%). Increased sugar supply resulted in inhibition of photosynthesis, nonfunctional photosynthetic reaction centers, a more mixotrophic metabolism and higher starch and sucrose reserves at the end of the in vitro period. During the first days of acclimatization, net photosynthesis and adenosine diphosphoglucose (ADPG) pyrophosphorylase (EC 2.7.7.27) activity decreased for both treatments. In this period, sucrose was mainly used as nutrient reserve by plants cultured on 6% sucrose, as evidenced by a strong increase in sucrose synthase (EC 2.4.1.13) activity together with a severe decline in sucrose content. In the same period, sucrose breakdown and synthesis were in balance for plants cultured on 3% sucrose and the starch content increased slightly. After one week plants started to recover and full photosynthetic capacity developed. Two weeks after ex vitro transplantation, no differences between plants micropropagated with 3 or 6% sucrose could be found for photosynthesis, carbohydrate pools or enzyme activities. At the end of acclimatization the starch content increased again.
Drought stress in seedlings: Lipid metabolism and Lipid peroxidation during recovery from drought in Lotus comiculatrus and Cerastium fontanum
Authors: Olsson Marie , Nilsson Katrina , Liljenberg Conny , Hendry George A. F.
Published: May 2006

Seedling survival of drought during the first days following germination can be one of the most critical factors in successful establishment of the species. Seventy‐two hour old seedlings of Cerastium fontanum Baumg. and Lotus corniculatus L. were exposed to severe desiccation for 36 h and the recovery of the whole plants monitored over the subsequent 17 days. The analysis exposed the very different responses to water stress in the two species. The effects of water stress on the less drought tolerant L. corniculatus within the first 5 to 10 days after drought treatment included a 2‐fold larger loss in dry weight than in C. fontanum and a 2‐fold rise in lipid peroxidation (thiobarbituric acid‐reactive substances), in triacylglycerols and in free fatty acids. The ratio of mo‐nogalactosyl diacylglycerols/digalactosyl diacylglycerols (MGDG/DGDG) declined 3‐fold, while the proportion of MGDG was some 12‐fold lower. In contrast, in the relatively drought‐tolerant seedlings of C. fontanum no changes of this order were recorded in the days immediately following rehydration. The relationship between these changes in lipid metabolism, lipid peroxidation and drought‐induced damage in terms of growth is discussed in the context of seedling recovery and survival in the two species.
Short‐term responses of Brassica rapa plants to low root temperature: Effects on nitrate uptake and its translocation to the shoot
Authors: Bigot Jacques , Boucaud Jean
Published: May 2006

Brassica rapa L. plants were grown hydroponically for 5 or 6 weeks at 20°C and then half batches of plants were transferred to tanks in which the root temperature was lowered decrementally over 1 h to 7°C. Changes in nitrate uptake rate (NUR) and nitrate transfer from roots were studied in relation to transpiration and root pressure xylem exudation flow rates over a 48‐ or 72‐h period. The response of plants following the root temperature decrease was biphasic. During phase 1, NUR and water and solute flow rates through the root decreased sharply. Coping mechanisms came into operation during phase 2, and tended to offset the effects of low temperature. The 3‐h cold‐treated roots exhibited a very low NUR but 48‐h cold‐treated roots partly recovered their ability to absorb nitrate. Transpiration rate decreased more slowly (during 24 h) than both root xylem exudation and parameters of root conductivity (during 6 h). Beyond these respective times, transpiration rate was balanced while root xylem exudation clearly increased, but without returning to the level of control plants. Nitrate transfer to the root xylem was strongly and rapidly affected by low root temperature, but the subsequent readjustment was such that no or little difference compared with the control was apparent after 48 h. Water and solute flows were strongly decreased when nitrate was replaced by chloride in the culture solution during exudation sampling. The major role of nitrate in root hydraulic conductivity and root xylem exudation is discussed.
Mycorrhiza formation on Norway spruce (Picea abies) roots affects the pathway of anaplerotic CO2 fixation
Authors: Wingler Astrid , Wallenda Thomas , Hampp Rüdiger
Published: May 2006

Activities of carboxylation enzymes were analyzed in the mycelium of the mycorrhizal fungus Amanita muscaria (L. ex Fr.) Hooker, in non‐mycorrhizal short roots of Norway spruce (Picea abies [L.] Karst.) and in myconhizas of these two partners. While pyruvale carboxylase (PC, EC 6.4.1.1) and phosphoenolpyruvate carboxykinase activities (PEPCK.EC 4.1.1.49) could be detected in the mycelium of A. muscaria, phosphoenolpyruvate carboxyknase (PEPC, EC 4.1.1.31) was only active in root tissue. In A. muscaria, PC activity was generally low (around 10 nmol mg−tprotein min−) but PEPCK activity was above 250 nmol mg−1 protein min−1. Mycorrhizal development on short roots decreased PEPC activity by more than 75%, although dilution by the fungal biomass in mycorrhizas was only 35%. This reduction in activity was paralleled by a decreased content of PEPC protein. By means of micro‐analytical methods it was shown that PEPC activity was lowest in the central zones of the mycorrhizas, Whereas PEPC activity was highest in the corresponding central sections in non‐mycorrhizal short roots. 14CO2 labelling, on the other hand, revealed that in vivo CO2 fixation was higher in mycorrhizas compared to non‐mycorrhizal short roots. It is concluded that fungal carboxylases (probably PEPCK) are important for anaplerotic CO2 fixation during nitrogen assimilation in mycorrhizas of Norway spruce.
Protochlorophyllide transformations and chlorophyll accumulation in epicotyls of pea (Pisum sativum)
Authors: Böddi Béla , Evertsson Ivar , Ryberg Margareta , Sundqvist Christer
Published: May 2006

Low‐temperature fluorescence emission spectra of epicotyls of 6.5‐day‐old dark‐grown seedlings of pea (Pisum sativumL.) showed the dominance of short‐wavelength protoch lorophyllide forms with emission maxima at 629 and 636 nm, respectively. The presence of long‐wavelength protochlorophyllide with emission maxima around 650 nm was just detectable. Accordingly, irradiation with millisecond flashes gave a minute formation of chlorophyllide. The chlorophyll(ide) formation varied along the epicotyl. Irradiation with continuous light for 1.5 h resulted in an evident accumulation of chlorophyll(ide) in the upper part of the epicotyl. Only small amounts accumulated in the middle section. The conversion of protochlorophyllide to chlorophyllide was temperature dependent and almost arrested at 0°C. The chlorophyll(ide) formed had one dominating fluorescence peak at 681 nm. Irradiation for 24 h gave almost 100 times more chlorophyll in the upper part of the epicotyl than in the lower part. Electron micrographs from the upper part of the epicotyl irradiated for 6 h showed plastids with several developing thylakoids, while the plastids in the lower part of the epicotyl had only a few thylakoids. The dominance of short‐wavelength protochlorophyllide forms indicated the presence of protochlorophyllide not bound to the active site of NADPH‐protochlorophyllide oxidoreductase (EC 1.3.1.33). The inability of the short‐wavelength form to transform into chlorophyllide with flash light denotes a dislocation from the active site. The time and temperature dependence of the chlorophyll(ide) formation in continuous light indicates that a relocation is required of the short‐wavelength protochlorophyllide before chlorophyllide formation can occur.
Exploring the signaling pathway of circadian bioluminescence
Authors: Mittag Maria , Hastings J. Woodland
Published: May 2006

Bioluminescence in the unicellular dinoflagellate Gonyaulax polyedra represents an excellent model for studying a circadian controlled process at the biochemical and molecular levels. There are three key components involved in the bioluminescence reaction: the enzyme, luciferase, its substrate, luciferin, and a luciferin‐binding protein (LBP), which sequesters the substrate at pH 7.5 and thus prevents it from reacting with the enzyme. All components are tightly packed together in organdies, designated scintillons. The entire bioluminescent system is under circadian control with maximum amounts in the night. For both proteins circadian control is exerted at the translational level. In case of Ibp mRNA a small interval in its 3’untranslated region serves as a cis‐acting element to which a trans‐factor binds in a circadian manner. The binding activity of this factor decreases at the beginning of the night phase, when synthesis of LBP starts, and it increases al the end of the night, when synthesis of LBP stops indicating that it functions as a clock‐controlled represser.
In vivo evidence for the involvement of phospholipase A and protein kinase in the signal transduction pathway for auxin‐induced corn coleoptile elongation
Authors: Yi Hanju , Park Doonam , Lee Youngsook
Published: May 2006

Auxin‐induced elongation of com coleoptiles is accompanied by cell wall acidification, which depends upon H+‐pump activity. We tested the hypothesis that phospholipase A and a protein kinase are involved in the pathway of auxin signal transduction leading to H+ secretion, and elongation of corn coleoptiles. Initially, the pH of the bath solution at 50–100 μm from the surface of a coleoptile segment (pHo) ranged between 4.8 and 6.6 when measured with an H+‐sensitive microelectrode. Twenty or 50 μM lysophosphatidylcholine, 50 μM linolenic acid or 50 μM arachidonic acid induced a decline in pHo by 0.3 to 2.1 units. The effect was blocked by 1 mM vanadate, suggesting that lysophosphatidylcholine or linolenic acid induced acidification of the apoplast by activating the H+‐pump. Lysophosphatidylcholine and linolenic acid also accelerated the elongation rate of the coleoptiles. While linolenic acid and arachidonic acid, highly unsaturated fatty acids, promoted pHo decrease and coleoptile elongation, linoleic acid, oleic acid, and stearic acid, fatty acids with a lesser extent of unsaturation, had no such effects. The effects of lysophosphatidylcholine, linolenic acid, and arachidonic acid on H+ secretion were not additive to that of indoleacetic acid (IAA), suggesting that lysophospholipids, fatty acids and auxin use similar pathways for the activation of the H+‐pump. The phospholipase A2 inhibitors, aristolochic acid and manoalide, inhibited the IAA‐induced pHo decrease and coleoptile elongation. The general protein kinase inhibitors, H‐7 or staurosporine, blocked the IAA‐ or lysophosphatidylcholine‐induced decrease in pHo. H‐7 also inhibited the coleoptile elongation induced by IAA or lysophosphatidylcholine. These results support the hypothesis that phospholipase A is activated by auxin, and that the products of the enzyme, lysophospholipids and fatty acids, induce acidification of the apoplast by activating the H+‐pump through a mechanism involving a protein kinase, which in turn promotes com coleoptile elongation.
Differential chilling sensitivity in cucumber (Cucumis sativus) seedlings
Authors: Rab Abdur , Saltveit Mikal E.
Published: May 2006

Cucumber (Cucumis sativus L. cv. Poinsett 76) seeds were chilled at 2.5°C in a study of the chilling sensitivity and recovery of radicle tissue. The effect of chilling on radicle growth and the production of carbon dioxide and ethylene was measured. Chilling sensitivity of radicles increased as they grew from 1 to 7 mm in length. The length, not the age of the radicles, determined the level of chilling sensitivity. Apical tissue was most sensitive to chilling and slowest to recover from chilling, followed by subapical and basal tissue. Our data demonstrate that the chilling sensitivity of young seedling radicles differs along their length and that the rapid chilling‐induced inhibition of elongation is probably due to an inability of meristematic cells to remain viable and active when chilled.
Physiological adaptation during cell dehydration and rewetting of a newly‐isolated Chlorella species
Authors: Chen Pei‐Chung , Lai Ching‐Long
Published: May 2006

A new terrestrial species of green alga (Chlorella sp. strain DT) that survives under extremely dry conditions was isolated from an arid mountainous area of Taiwan. The water content of the cells dropped to less than 3% after 3 h dehydration at 42°C. The dried cells could regrow if they were rewetted. The photosynthetic activity of the cells ceased following 2 h of dehydration, but respiratory activity was still detectable after 3 h desiccation. During the rewetting process, respiration increased immediately and then decreased to a steady level after 5 days of rewetting, matching the net photosynthetic oxygen evolution. The cells had 38% neoxanthin (1520 nmol g−1 dry weight), 39% lutein (1580 nmol g−1 dry weight), and 14% violaxanthin (570 nmol g−1 dry weight) of total carotenoids, but only 5.1%β‐carotene (210 nmol g−1 dry weight), 3.8%α‐carotene (150 nmol−1 g dry weight) and a trace of antheraxanthin and zeaxanthin. Upon dehydration, zeaxanthin and carotene contents increased and recovered to normal levels after 8 days of rewetting. The photoprotective xanthophyll cycle was found in these cells. It appears that the energy dissipation process for preventing photodamage is perhaps one of the tolerance mechanisms in this Chlorella strain.
The contrasting role of auxin in submergence‐induced petiole elongation in two species from frequently flooded wetlands
Authors: Rijnders Jan G. H. M. , Barendse Gerard W. M. , Blom Cornelis W. P. M. , Voesenek Laurens A. C. J.
Published: May 2006

The involvement of auxin in the submergence‐induced petiole elongation has been investigated in Rumex palustris and Ranunculus sceleratus. Both wetland species are capable of enhanced petiole elongation upon submergence or treatment with exogenous ethylene (5μl l−1). Treatment of intact Rumex palustris plants with 1‐naphthalene acetic acid (NAA) at 10−4M enhanced petiole elongation, while treatment with N‐1‐naphthylphthalamic acid (NPA) had no effect on petiole elongation. The elongation response after NAA or NPA treatment was comparable for plants in both submerged and drained conditions. Pre‐ageing of detached petioles of Rumex palustris for 3 h in light or in dark conditions had no effect on the submergence‐induced elongation. In comparison to intact plants, detached petioles of Rumex palustris, with or without lamina, did not show significant differences in responsiveness to IAA between drained or submerged conditions. This was in contrast to Ranunculus sceleratus where submergence caused a clear increase in responsiveness towards IAA. Removal of the lamina, the putative source of auxin, or treatment with NPA did not hinder the submergence‐induced elongation of detached Rumex palustris petioles, but severely inhibited elongation of detached Ranunculus sceleratus petioles. This inhibition could be restored by application of NAA, suggesting the specific involvement of auxin in the submergence response of Ranunculus sceleratus. It is concluded that, in contrast to Ranunculus sceleratus, auxin is probably not involved in the submergence‐induced petiole elongation of Rumex palustris.
Demonstration of in vitro starch branching enzyme activity for a 51/50‐kDa polypeptide isolated from developing barley (Hordeum vulgare) caryopses
Authors: Sun Chuanxin , Sathish P. , Ek Bo , Deiber Anna , Jansson Christer
Published: May 2006

Starch branching enzyme (SBE, EC 2.4.1.18) activity was followed in developing barley (Hordeum vulgare L. cv. Golf) caryopses during a period of one month after anthesis. Caryopses with the highest specific activity, and corresponding to a fresh weight of around 60 mg per caryopsis, were homogenized and the soluble extract used for branching enzyme purification by FPLC chromatography. Four branching enzyme activity fractions were resolved. From one of these fractions, which exhibited high activity in both the phosphorylation stimulation and amylose branching assays, a branching enzyme preparation containing two related polypeptides of 51 and 50 kDa was obtained. Native polyacrylamide gel electrophoresis and gel filtration showed that the 51/50‐kDa polypeptide is monomeric. A combination of phosphorylation stimulation and amylose branching gel assays, SDS‐PAGE, and TLC was used to demonstrate the branching activity of the 51/50‐kDa polypeptide. The activity was further confirmed by spectroscopic analyses of iodine‐glucan complexes. SBEs from four different plant species were compared using the phosphorylation stimulation gel assay.
Nuclear and genomic changes in floating and submerged buds and leaves of heterophyllous waterchestnut (Trapa natans)
Authors: Bitonti M. B. , Cozza R. , Wang G. , Ruffini‐Castiglione M. , Mazzuca S. , Castiglione S. , Sala F. , Innocenti A. M.
Published: May 2006

The heterophyllous macrophyte waterchestnut (Trapa natans L.) produces floating and submerged leaves which are strikingly different in morphology. In the present work, we compared, through cytological, cytochemical and immunocytochemical analyses, the nuclear features of the shoot meristem in floating and submerged buds that produce the different leaves. The occurrence of DNA polymorphism in the two types of leaves was studied by using the random amplified polymorphic DNA (RAPD) approach. The light microscope study of chromatin organization revealed an articulate structure of the nuclei, with prominent chromocentres in both floating and submerged buds. However, the meristematic nuclei of floating buds, as compared to those of submerged buds, displayed peculiar features which seem to be related to a higher proportion of A‐T‐ricn sequences and a higher level of DNA methylation of the nuclear genome. Moreover, RAPD analysis showed polymorphism between the genomic DNAs of floating and submerged leaves. These results show that organs of an individual plant living in different environmental conditions undergo changes in genome organization which may predispose those organs to function more effectively in different environments.
The influence of enriched rhizosphere CO2 on N uptake and metabolism in wild‐type and NR‐deficient barley plants
Authors: Cramer M. D. , Savidov N. A. , Lips S. H.
Published: May 2006

Positive influences of high concentrations of dissolved inorganic carbon (DIC) in the growth medium of salinity‐stressed plants are associated with carbon assimilation through phosphoenolpyruvate carboxylase (PEPc) activity in roots; and also in salinity‐stressed tomato plants, enriched CO2 in the rhizosphere increases NO−3uptake. In the present study, wild‐type and nitrate reductase‐deficient plants of barley (Hordeum vulgare L. cv. Steptoe) were used to determine whether the influence of enriched CO2 on NO−3 uptake and metabolism is dependent on the activity of nitrate reductase (NR) in the plant. Plants grown in NH4+and aerated with ambient air, were transferred to either NO3− or NH4+ solutions and aerated with air containing between 0 and 6 500 μmol mol−1 CO2. Nitrogen uptake and tissue concentrations of NO3− and NH4+ were measured as well as activities of NR and PEPc.

The uptake of NO−3 by the wild‐type was increased by increasing CO2. This was associated with increased in vitro NR activity, but increased uptake of NO3− was found also in the NR‐deficient genotype when exposed to high CO2 concentrations; so that the influence of CO2 on NO3− uptake was independent of the reduction of NO3− and assimilation into amino acids. The increase in uptake of NO3− in wild‐type plants with enriched CO2 was the same at pH 7 as at pH 5, indicating that the relative abundance of HCO3− or CO2 in the medium did not influence NO3− uptake. Uptake of NH4+ was decreased by enriched CO2 in a pH (5 or 7) independent fashion. Thus NO3− and NH+4 uptakes are influenced by the CO2 component of DIC independently of anaplerotic carbon provision for amino acid synthesis, and CO2 may directly affect the uptake of NO3− and NH4+ in ways unrelated to the NR activity in the tissue.
Changes in nitrogen source modify distribution of excitation energy in the cyanobacterium Phormidium laminosum
Authors: Ochoa de Alda Jesús A. G. , Tapia María I. , Franck Fabrice , Llama María J. , Serra Juan L.
Published: May 2006

In an attempt to clarify the interactions between the available nitrogen source and the photosystems in cyanobacteria, O2 exchange and fluorescence emission were monitored in spheroplasts and intact cells of the non N2‐fixing cyanobacterium Phormidium laminosum (strain OH‐1‐p.Cl1) growing on different nitrogen sources or in the absence of nitrogen. Short‐term (time scale of seconds to minutes), NH+4 addition to NO−3‐growing or N‐starved cells and, to a minor extent, NO−3addition to N‐starved cells, induced state 2 transitions both in light and dark. Long term (time scale of days), the fluorescence yield of PSII relative to that of PSII at 77 K was higher in NO−3‐ than in NH+4 growing cells, and even higher in N‐starved cells. In the dark, the plastoquinone pool was more reduced in NH+4‐ than in NO−3‐growing cells. Both PSII and PSI activities and the degree of linking between both photosystems were affected in the long term, so that non‐cyclic electron transport decreased in parallel to the ferredoxin requirement to assimilate each nitrogen source. Results indicate that nitrogen metabolism exerts short‐ and long‐term control over the photosynthetic apparatus, which acclimates to the energy requirement of the available nitrogen source.
Effects of low temperature, high salinity and exogenous ABA on the synthesis of two chloroplastic drought‐induced proteins in Solanum tuberosum
Authors: Pruvot Ghislaine , Massimino Jacqueline , Peltier Gilles , Rey Pascal
Published: May 2006

Two chloroplastic proteins of 32 and 34 kDa were previously shown to be substantially synthesized in response to a progressive water deficit in whole Solanum tuberosum plants (G. Pruvot, S. Cuiné, N. Gault, G. Peltier and P. Rey, unpublished data; G. Pruvot, S. Cuiné, G. Peltier and P. Rey. 1996. Planta 198: 471–479). These chloroplastic drought‐induced stress proteins, named CDSP 32 and CDSP 34, accumulated in the stroma and in the thylakoids, respectively. In this study, we investigated the effects of low temperature and high salinity on the synthesis of the CDSP proteins. Whereas the CDSP 32 synthesis was not modified in response to a cold treatment, an increased synthesis of CDSP 32 was observed in salt‐stressed plants, resulting in accumulation of the protein. The thylakoid CDSP 34 protein exhibited enhanced synthesis and substantial accumulation in response to cold and high salinity. A significant increase in the leaf abscisic acid content (at least 2.5‐fold) was measured in plants subjected to water deficit, high salinity or low temperature. The contribution of ABA to the synthesis of the two proteins was investigated by spraying well‐watered plants with a 100 μM/ ABA solution for 15 days. This treatment resulted in a 15‐fold increase in the leaf ABA content. Whereas synthesis of the CDSP 32 protein was not affected by exogenous ABA, synthesis of the CDSP 34 protein was substantially enhanced. Based on these results, we conclude that ABA likely mediates the increased synthesis of CDSP 34 upon drought, low temperature and high salinity and suggest that another signal, likely related to high osmolarity, is involved in the induction of CDSP 32 synthesis.
The myrosinase‐glucosinolate system, its organisation and biochemistry
Authors: Bones Atle M. , Rossiter John T.
Published: May 2006

The myrosinase‐glucosinolate system is involved in a range of biological activities affecting herbivorous insects, plants and fungi. The system characteristic of the order Capparales includes sulphur‐containing substrates, the degradative enzymes myrosinases, and cofactors. The enzyme‐catalyzed hydrolysis of glucosinolates initially involves cleavage of the thioglucoside linkage, yielding D‐glucose and an unstable thiohydroximate‐O‐sulphonate that spontaneously rearranges, resulting in the production of sulphate and one of a wide range of possible reaction products. The products are generally a thiocyanate, isothiocyanate or nitrile, depending on factors such as substrate, pH or availability of ferrous ions. Glucosinolates in crucifers exemplify components that are often present in food and feed plants and are a major problem in the utilization of products from the plants. Toxic degradation products restrict the use of cultivated plants, e.g. those belonging to the Brassicaceae. The myrosinase‐glucosinolate system may, however, have several functions in the plant. The glucosinolate degradation products are involved in defence against insects and phytopathogens. and potentially in sulphur and nitrogen metabolism and growth regulation. The compartmentalization of the components of the myrosinase‐glucosinolate system and the cell‐specific expression of the myrosinase represents a unique plant defence system. In this review, we summarize earlier results and discuss the organisation and biochemistry of the myrosinase‐glucosinolate system.
Maturation‐related loss in rooting competence by loblolly pine stem cuttings: The role of auxin transport, metabolism and tissue sensitivity
Authors: Diaz‐Sala Carmen , Hutchison Keith W. , Goldfarb Barry , Greenwood Michael S.
Published: May 2006

A comparison of rooting ability of stem cuttings made from hypocotyls and epicotyls from 50‐day‐old seedlings of loblolly pine (Pinus taeda L.) reveals a dramatic decline by epicotyl cuttings, which do not root at all in 20–30 days in the presence or absence of auxin. In contrast, almost all the hypocotyls root during this time, but only in the presence of exogenously applied auxin. The failure of epicotyls to root does not appear to be due to differences in [14C]‐labeled auxin uptake, transport, metabolism, or tissue distribution in the two types of cuttings. At the cellular level, initial responses to auxin, such as differentiation of the cambium into parenchyma, occur in both types of cuttings, but localized rapid cell division and root meristem organization are not observed in epicotyls. Autoradiography revealed that radioactivity from a‐naphthalene acetic acid is bound in the cortex but not concentrated at sites of root meristem organization prior to the organization of the meristem in hypocotys. During the development of the epicotyl. cellular competence to form roots appears to be lost. Although this loss in competence is not associated with a concurrent loss in ability to transport auxin polarly, the latter process appears to play a key role in rooting other than to move auxin to the site of root formation. The phytotropin N‐(1‐naphthyl)phthalamic acid inhibits rooting if applied during the first 3 days after the cutting is made, but does not affect auxin concentration or metabolism at the rooting site.