bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen reallocation and photosynthetic acclimation in response to partial shading in soybean plants
Authors: Pons T.L. , Pearcy R. W. 
Published: May 2006

The first trifoliate of soybean was shaded when fully expanded, while the plant remained in high light; a situation representative for plants growing in a closed crop. Leaf mass and respiration rate per unit area declined sharply in the first few days upon shading and remained rather constant during the further 12 days of the shading treatment. Leaf nitrogen per unit area decreased gradually until the leaves were shed. Leaf senescence was enhanced by the shading treatment in contrast to control plants growing in low light. Shaded leaves on plants grown at low nutrient availability senesced earlier than shaded leaves on plants grown at high nutrient availability. The light saturated rate of photosynthesis decreased also gradually during the shading treatment, but somewhat faster than leaf N, whereas chlorophyll contents declined somewhat slower than leaf N.Partitioning of N in the leaf over main photosynthetic functions was estimated from parameters derived from the response of photosynthesis to CO2. It appeared that the N exported from the leaf was more at the expense of compounds that make up photosynthetic capacity than of those involved in photon absorption, resulting in a change in partitioning of N within the photosynthetic apparatus. Photosynthetic nitrogen use efficiency increased during the shading treatment, which was for the largest part due to the decrease in leaf N content, to some extent to the decrease in respiration rate and only for a small part to change in partitioning of N within the photosynthetic apparatus.
Ecotypes of the fungus Bipolaris oryzae with various responses of the mycochrome system
Authors: Kihara J. , Kumagai T. 
Published: May 2006

Two types of fungi based on the light required for induction of conidiophore formation are known as ‘photo‐induced’ and ‘non‐photo‐induced’ sporulators. Conidial development in a ‘photo‐induced’ strain of Bipolaris oryzae (formerly, Helminthosporium oryzae) is controlled by antagonistic action of blue and near‐UV radiation mediated through the ‘mycochrome’ system at two developmental stages: conidiophore induction and conidiophore maturation. Otherwise, conidial development in a ‘non‐photo‐induced’ strain of B. oryzae, unlike that in the ‘photo‐induced’ strain, is controlled by antagonistic action of blue and near‐UV radiation at the conidiophore maturation stage alone. In this study, we collected fungi, B. oryzae, from brown lesion spots on rice leaves cultivated in paddy fields, and investigated the possible existence of a new ecotype different from known ‘photo‐induced’ and ‘non‐photo‐induced’ sporulators. We also investigated the sensitivity of conidial development of each isolate to blue and near‐UV radiation.The isolates were identified as B. oryzae by morphology of hyphae and conidia and the symptomatic brown lesion spots on rice leaves caused by each isolate. There was no distinction between ‘photo‐induced’ and ‘non‐photo‐induced’ strains on rDNA base. Moreover, the existence of a new type of ‘non‐photo‐induced’ sporulator different from the one presently known was confirmed. In this newly identified sporulator, conidial development was not affected by light irradiation. Among 153 isolates, one isolate belonged to a previously known ‘non‐photo‐induced’ sporulator, five isolates belonged to a new ‘non‐photo‐induced’ sporulator ecotype, and over 95% of the isolates were “photo‐induced” sporulators. Among ‘photo‐induced’ strains, there were several subtypes having different sensitivities to near‐UV radiation required for inducing conidiophore formation.
Involvement of putrescine in the inductive rooting phase of poplar shoots raised in vitro
Authors: Hausman Jean‐François , Gevers Claire , Gaspar Thomas 
Published: May 2006

Micropropagated poplar shoots rooted 100% on a rooting medium (A) containing NAA, but they did not root in the absence of auxin (NA). Putrescine, but not spermidine and spermine, promoted rooting up to 42% when added to the NA medium. Cyclohexylamine (CHA), an inhibitor of spermine synthase, also promoted (up to 36%) rooting in the absence of auxin. The inhibitors of polyamine biosynthesis DFMA (α‐difluoromethylarginine) and DFMO (α‐difluoromethylomithine), aminoguanidine (AG) and methylglyoxal‐bis‐guanylhydrazone (MGBG), inhibited rooting when applied in the presence of auxin and had no effect in its absence.The rooting inductive phase (in the presence of auxin) was determined by periodical transfer of shoots from A to NA medium, and by changes in peroxidase activity, to be 7 h. Putrescine (not spermidine and spermine) accumulated to a maximum during the inductive phase. Both putrescine and CHA promoted rooting on NA medium when applied during the first 7 h. In contrast DFMA and AG inhibited rooting during this period. The results point to the involvement of putrescine and its Δ1‐pyrroline pathway, in the inductive phase of rooting in poplar shoots.
The effect of light quality on the induction of efficient photosynthesis under low CO2 conditions in Chlamydomonas reinhardtii and Chlorella pyrenoidosa
Authors: Borodin Valery , Gardeström Per , Samuelsson Göran 
Published: May 2006

The effect of blue and red light on the adaptation to low CO2 conditions was studied in high‐CO2 grown cultures of Chlorella Pyrenoidosa (82T) and Chlamydomonas reinhardtii(137+) by measuring O2 exchange under various inorganic carbon (Ci) concentrations. At equal photosynthetic photon flux density (PPFD), blue light was more favourable for adaptation in both species, compared to red light. The difference in photosynthetic oxygen evolution between cells adapted to low Ciunder blue and red light was more pronounced when oxygen evolution was measured under low Ci compared to high Ci conditions. The effect of light quality on adaptation remained for several hours. The different effects caused by blue and red light was observed in C. pyrenoidosa over a wide range of PPFD with increasing differences at increasing PPFD. The maximal difference was obtained at a PPFD above 1 500 μmol m−2s−1. We found no difference in the extracellular carbonic anhydrase activity between blue‐ and red light adapted cells. The light quality effect recorded under Ci‐limiting conditions in C. reinhardtii cells adapted to air, was only 37% less when instead of pure blue light red light containing 12.5% of blue light (similar PPFD as blue light) was used during adaptation to low carbon. This indicates that in addition to affecting photosynthesis, blue light affected a sensory system involved in algal adaptation to low Ci conditions. Since the affinity for Ci of C. Pyrenoidosa and C. reinhardtii cells adapted to air under blue light was higher than that of cells adapted under red light, we suggest that induction of some component(s) of the Ci accumulating mechanism is regulated by the light quality.
Physiological effects of five months exposure to low concentrations of O3 and NH3 on Douglas fir (Pseudotsuga menziesii)
Authors: van Hove L. W. A. , Bossen M. E. 
Published: May 2006

Three years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed lo filtered air, O3 (day and night concentrations of 78 and 30 μgm−3: respectively). NH3 (54 μg m−3) and to a mixture of NH3+O3 (day and night concentrations of 49 + 83 and 49 + 44 μg m−3 respectively), for 5 months in fumigation chambers. Both gas exchange and chlorophyll fluorescence were measured on shoots which had sprouted at the beginning of the exposure period. After 4. 8, 10 and 20 weeks of exposure, light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. Net CO2 assimiialion was measured at maximum light intensity of 560) μmol m−2 S−1 (Pn.560). After 8 and 10 weeks of exposure also light response curves of CO2 assimilation were assessed.Shoots exposed to O3 showed a reduction in net CO2 assimilation as compared to the control shoots during the entire exposure period. The reduction was related lo a lower chlorophyll content and a lower electron transport rate, whereas no effect on quantum yield efficiency (qy) was observed. In contrast, shoots exposed to NH3 showed a positive effect on photosynthesis. Shoots exposed to NH3. + O3 showed a rapid increase in Pn.560, in the period between 4 and 8 weeks to a level equal of that of the NH3‐treatment. After this period a decline in Pn.560 was observed.After 10 weeks of exposure shoots exposed to O3 showed an increased transpiration rate in the dark as compared to the control shoots. In addition, water use efficiency (WUE) declined as a result of an increase in leaf conductance. Both observations indicate that the stomatal apparatus was affected by O3. A high transpiration rate in the dark was also found for shoots esposed to NHX. However, shoots exposed to NH3+ O3 showed neither an effect on WUE, nor an effect on transpiration rate in the dark. The possibility that NH3 delayed the O3 induced effects on photosynthesis and stomatal conductance is discussed.
Involvement of protein phosphorylation in the sensitivity of photosystem II to strong illumination
Authors: Giardi Maria T. , Komenda Josef , Masojidek Jiri 
Published: May 2006

Four types of differently phosphorylated hylakoids isolated from field grown spinach (Spinacia oleracea L.) were tested for the sensitivity of photosystem II (PSII) to photoinactivation. Phosphorylation of light‐harvesting II complexes (LHCII) protected PSII electron transfer from photoinhibitory damage, while the phosphorylation of the PSII core polypeptides slightly accelerated the decline of electron transfer during high irradiance treatment. Dephosphorylation of the CP43 apoprotein and PsbH protein by an alkaline phosphatase resulted in an extreme sensitivity of the thylakoids to strong illumination. The PSII photoinactivation of thylakoids with the impaired oxygen‐evolving complex was found to be independent of phosphorylation.The thylakoids of the thermophilic cyanobacterium Synechococcus elongates were used in order to compare the plants with an organism where LHCII complexes are missing and the PSII core proteins are not phosphorylated.
Comparison of the effect of natural and experimental anoxia on carbohydrate and energy metabolism in Iris pseudacorus rhizomes
Authors: Hanhijärvi Anne M. , Fagerstedt Kurt V. 
Published: May 2006

Carbohydrate utilization in Iris pseudacorus rhizomes was investigated under natural conditions in the field for a period of one year. The area of study was under flood from mid‐December to end of May and wet for the rest of the period of study. Rhizome samples were collected in the wild twice monthly. in order to determine glucose content and amount of reducing and non‐reducing sugars in the rhizome core material. For comparison with experimental anoxia, rhizomes were washed and kept under strict anoxia in the dark at +20°C. Carbohydrates were measured in groups as above. The amount of ethanol and the levels, of ATP. ADP and AMP were also measured and adenylate energy charge computed.Glucose content of the rhizomes was 10 mg g−1 fresh weight in the autumn and decreased during winter to reach ca 5 mg g−1 fresh weight in the spring. Total reducing sugars increased in w inter while the amount of non‐reducing sugars increased during early autumn and decreased during winter and spring. Not all non‐reducing sugar stores had been used up in the spring when growth was resumed. Under experimental anoxia adenylate energy charge remained relatively high for 30 days (near 0.6 or over) and then dropped quickly to bekm 0.3. indicating death of the tissues. After 30 days under anoxia the amount of ethanol still increased and that of total reducing sugars decreased. The level of non‐reducing sugars decreased from 0 to 15 days of anoxia before an increase took place durine the next 20 days.
Ultrasonic acoustic emissions from excised stems of two Thryptomene species
Authors: van Doom Wouter G. , Jones Rodney B. 
Published: May 2006

Stems of Thryptomene vaxicola (A. Cunn.) Shau. cut in air and immediately placed in water at 20°C showed ultrasonic acoustic emissions after 8 to 12 h. whereas no emissions were found in Thryptomene catycina Lindl.) Stapf, within 100 h. Stem water potential declined in a similar manner in both species: a high frequency of acoustic emissions stalrted at approximately –1 000 kPa in T.saxicola., but had not commenced at –5300 kPa in T. calycina. The rates of water uptake were similar in both species. Acoustic emissions in T.saxicola placed in water were prevented h recutting 15 cm of the stems under water.For comparison, cut stems which were air‐dehydrated at 20°C exhibited a primary peak in the frequency of emission after 3–5 h in T. saxicola and 15 h in T. catycina, corresponding to a water potential of –1000 kPa and less than –5000 kPa. respectively. After 6. 16. and 24 h of dehydration in air and subsequent placement in water for 24 h. the rates of water uptake of T. calycina were not lower than in controls not held dry, How ever. in T. saxicola water uptake rates had decreased after 16 h of dehydration and were very low after 24 h.The results show that ultrasonic acoustic emissions may occur in freshly cut stems placed in water, and that they occur at a water potential similar to that in stems allowed to dehydrate in air. The number ol emissions in T.saxicola stems placed in water was apparently too low to inhibit water uptake. When held dry. the cavitated xylem elements may be a cause of reduced water uptake in T. saxicola.
Metabolic changes associated with cold‐acclimation in contrasting cultivars of barley
Authors: Murelli Carla , Rizza Fulvia , Albini Franca Marinone , Dulio Andrea , Terzi Valeria , Cattivelli Luigi 
Published: May 2006

Cereal plants become more resistant to freezing when first exposed to a period of cold‐acclimation. Many physiological and molecular changes have been shown to occur at low temperatures, but the role and the contribution of each to frost resistance is still poorly understood. Two cultivars of barley (Hordeum vulgare L.), the winter barley Onice and the spring barley Gitane, were acclimated under controlled conditions under an 8‐h photoperiod at 4°C (light) and 2°C (dark) for 21 days. Changes in free proline, ABA, water‐soluble carbohydrates and free fatty acids were measured to assess their involvement in cold‐acclimation and to explain the different frost‐resistant capacities of the two cultivars. Exposure of barley plants to low temperature resulted in an equal increase in proline in both cultivars. During the first days of cold acclimation, ABA levels showed a peak in the frost‐resistant cultivar, lasting about 24 h, followed by a decrease. The water soluble carbohydrates reached their highest content after 3 days of hardening, although after 14 to 21 days of acclimation the carbohydrate content was similar to that of unhardened plants. The frost‐resistant Onice had a much higher free fatty acid content than the frost‐sensitive Gitane. Furthermore in Onice 86% of free farty acids was represented by unsaturated molecular species. Inolenic acid alone being 71%. In contrast, in the frost‐sensitive cultivar only 31% of free fatty acids was unsaturated and a large amount of 9‐oxo‐nonanoic acid, a product present in the linolenic acid cascade, was also detected.The ABA content after 2 days of hardening and the free fatty acid composition were clearly different between the two cultivars and may explain, at least in part, the different frost‐resistant capacities of Onice and Gitane.
Copper and photosystem II: A controversial relationship
Authors: Barón Matilde , Arellano Juan B. , Gorgé Julio López 
Published: May 2006

Copper is an essential micronutrient for higher plants and algae and has a direct impact on photosynthesis. It is a constituent of the primary electron donor in photosystem I, the Cu‐protein plastocyanin. Many authors have also described Cu as a constituent of photosystem II (PSII). However, high Cu concentrations inhibit the photosynthetic electron transport, especially in PSII. In addition, both Cu deficiency and Cu toxicity interfere with pigment and lipid biosynthesis and, consequently, with chloroplast ultrastructure thus negatively influencing the photosynthetic efficiency.In this review, the different functions proposed for the metal in PSII are reviewed. With reference to the effect of toxic Cu on PSII, the polemic results concerning its mechanism of action and Cu‐binding sites are discussed. Other effects of Cu toxicity and Cu deprivation on the thylakoid membrane are also briefly described.
Gravitropic responses of the Avena coleoptile in space and on clinostats. I. Gravitropic response thresholds
Authors: Brown Allan H. , Chapman David K. , Johnsson Anders , Heathcote David 
Published: May 2006

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g‐force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow‐speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.1 and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostal experiments on earth using the same apparatus.Characteristic gravitropistic response patterns of Avena were not substantially different from those observed in ground‐based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than 0.1 g.
Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings
Authors: Schmidke Ilka , Stephan Udo W. 
Published: May 2006

The metal micronutrients (MN) copper, iron, manganese, and zinc are transported via the phloem in the course of remobilization and circulation. The extent of these processes and transport species are still largely unknown. The Ricinus seedling was used to study the transport of these metal micronutrients as well as their interactions with the plant‐endogenous chelator nicotianamine (NA) by daily measurements of the concentrations in the seedling parts and in the sieve tube sap obtained from a cut at the hypocotyl hook.The concentrations of these micronutrients in the phloem exudate decreased slightly from day 4 to day 8 of seedling development. Maximum values at day 4 were 65 μM for Zn, 63 μM for Fe, 27 μM for Cu, and 12 μM for Mn. The phloem transport rates reached maxima of 0.12 nmol cm−2h−1 for Zn and Fe at days 6 and 7, corresponding to the maximum exudation rates. The magnitude of these transport rates were in agreement with the net translocation rates estimated by analyses of the concentrations in the individual seedling parts.The NA content of the seedlings increased from day 0 (seed before sowing) until day 8, from 16 nmol to 474 nmol, which corresponds to an average net synthesis rate of about 100 nmol day−1 between the days 4 and 8. The NA:MN ratio was constant at 0.5 in the seedlings within this period. The NA concentrations and the sum of the concentrations of all four micronutrients in the sieve tube sap showed a constant ratio of 1.25 over the entire experimental period. Thus, both complex partners were subject to a cotransport in the phloem.Removal of the supplying endosperm led to a decrease in MN and NA concentrations in the sieve tube sap to about 80% while an average excess of NA of 1.1 was maintained. Since the concentrations of other amino acids, also possible chelators of metal micronutrients, fall to about 10% after removal of the endosperm, their role seems to be negligible as vehicles of MN transport in the phloem. Thus it is suggested that the divalent micronutrients considered in this study are loaded and maybe transported as NA complexes.
Gibberellin‐regulated plant genes
Authors: Huttly Alison K. , Phillips Andrew L. 
Published: May 2006

Gibberellins (GAs) are involved in the control of a number of key developmental processes in plants, including endosperm mobilisation stem elongation and flowering. In many of these systems, GA modulates the transcription of specific genes. The aim of this paper is to review current progress in identifying and characterising GA‐regulated genes; both the control of gene expression and the function of the gene products are discussed. The most well‐characterised system in which GA is active in controlling transcription is the aleurone layer of cereal grains, where it induces the synthesis of a range of hydrolytic enzymes, including a‐amylase. Analysis of the promoters of a‐Amy1 and a‐Amy2 genes by transient expression in aleurone cells and protoplasts together with DNase 1 footprinting and gel‐retardation assays, has identified a number of cis‐acting elements important for high‐level, GA‐regulated expression. In particular a GA‐response element (GARE) including the sequence TAACRRA has been characterised. Recent reports describe cDNA clones encoding trans‐acting factors that bind to elements in the a‐amylase promoters. Expression of the factor capable of binding to the TAACRRA element is itself induced by GA.In elongating tissues, GA has been shown to control the expression of a number of genes, including the tonoplast intrinsic protein, a water channel which may regulate water flux into the vacuole during cell expansion. In flower development, expression of flavonoid biosynthetic genes, such as chalcone synthase in Petunia corollas, is regulated by GA at the level of transcription.Analysis of GA‐response mutants led to the suggestion that one consequence of GA action is to regulate its own biosynthesis. Genes encoding GA 20‐oxidase and 3β‐hydroxylase have recently been shown to be down‐regulated by applied GA, providing a possible mechanism for feedback regulation of the GA biosynthetic pathway.There is evidence that cells perceive GA at the cell surface, implying the existence of a signal transduction system between plasma membrane and nucleus. This signal transduction system has barely begun to be elucidated but is likely to become a major focus of gibberellin research.
The alternative respiration pathway in plants: Role and regulation
Authors: Wagner Anneke M. , Krab Klaas 
Published: May 2006

In the past few years, knowledge of the nature and regulation of the alternative oxidase in plant mitochondria has increased greatly. The protein has been characterized and mechanisms that regulate its activity have been described. The consequences of these regulatory mechanisms are that in vivo the cytochrome pathway and the alternative pathway may compete for electrons. The implications for the interpretation of the ‘Bahr and Bonner’ inhibitor titrations, formerly used to estimate the partitioning of electrons over the two pathways, are discussed.It is proposed that activation and engagement of the alternative oxidase may keep Q reduction levels low in order to prevent harmful high levels of free radical production. A model is presented for the regulation of alternative oxidase protein induction, involving a signalling function of active oxygen species.