bluuebunny/crossref_metadata_2025 huggingface dataset:
A calcium‐ and phospholipid‐dependent protein kinase from rice (Oryza sativa) leaves
Authors: Karibe H. , Komatsu S. , Hirano H.
Published: May 2006

Protein kinases in plants have not been examined in detail, but protein phosphorylation has been shown to be essential for regulating plant growth via the signal transduction system. A Ca2+‐ and phospholipid‐dependent protein kinase, possibly involved in the intracellular signal transduction system from rice leaves, was partially purified by sequential chromatography on DE52, Phenyl Superose and Superose 12. This protein kinase phosphorylated the substrate, histone III‐S, in the presence of Ca2+ and phosphatidylserine. The apparent molecular mass of the Ca2+‐ and phosphatidylserine‐dependent protein kinase (Ca2+/PS PK), determined by phosphorylation in SDS‐polyacrylamide gel containing histone III‐S, was 50 kDa. The protein kinase differed from Ca2+‐dependent protein kinase (CDPK) in rice leaves in that Ca2+/PS PK showed phospholipid dependency and the molecular mass of Ca2+/PS PK exceeded that of CDPK. Investigations were carried out on changes in Ca2+/PS PK and CDPK activity in the cytosolic and membrane fractions during germination. The maximum activity of Ca2+/PS PK in the cytosolic fraction was observed before imbibition and that of CDPK in the membrane fraction was noted at 6 days following imbibition. Protein kinases are likely to regulate plant growth through protein phosphorylation.
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.
Uptake regions of inorganic nitrogen in roots of carob seedlings
Authors: Cruz C. , Lips S. H. , Martins‐Loução M. A.
Published: May 2006

Three‐week‐old seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO−3 and NH+4 ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH3 species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH+4/NH3 equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent free space.
Effect of laterally applied gibberellin A4/7 on cambial growth and the level of indole‐3‐acetic acid in Pinus sylvestris shoots
Authors: Wang Q. , Little C. H. A. , Odén P. C.
Published: May 2006

Gibberellin A4/7 (GA4/7) was applied in lanolin or ethanol around the circumference at the midpoint of the previous‐year terminal of dormant Pinus sylvestris seedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cambial growth was measured as the radial widths of xylem and phloem, and the level of indole‐3‐acetic acid (IAA) was determined by combined gas chromatography‐mass spectrometry using [136](IAA) as the internal standard. In intact seedlings, both 1 mg GA4/7 g−1 lanolin and 50 mg GA4/7 I−1 ethanol increased phloem production and the cambial region IAA level in the current‐year terminal, without significantly altering its longitudinal growth. In the previous‐year terminal, 1 mg GA4/7 g−1 lanolin promoted phloem production at the application point and increased the cambial region IAA level above this point, whereas 50 mg GA4/7 I−1 ethanol stimulated the production of both xylem and phloem at the treatment site and elevated the cambial region IAA level beneath it. Laterally applied GA4/7 at 50 mg I−1 ethanol stimulated xylem and phloem production in debudded previous‐year terminals treated at the apical cut surface with 1 mg IAA g−1 lanolin, but not in those treated with plain lanolin. However, the promotion of cambial growth in debudded terminals treated apically with 1 mg IAA g−1 lanolin and laterally with 50 mg GA4/7 I−1 ethanol was not associated with an elevated IAA content in the cambial region. The results indicate that exogenous GA4/7 can promote xylem and phloem production provided an IAA source is present, and that it or a metabolic product acts directly, rather than indirectly by stimulating longitudinal growth and/or raising the cambial region IAA level.
Effects of 24‐epibrassinolide on freezing and thermotolerance of bromegrass (Bromus inermis) cell cultures
Authors: Wilen Ronald W. , Sacco Melanie , Gusta Lawrence V. , Krishna Priti
Published: May 2006

The effect of 24‐epibrassinolide (EBS), a brassinosteroid, on the response of smooth bromegrass (Bromus inermis Leyss) cell suspension cultures under low and high temperature stress was evaluated. EBS minimally increased freezing tolerance of bromegrass cells by 3–5°C, but markedly enhanced cell viability following exposure to high temperature stress. The net effect on hardening was, however, less than that obtained with abscisic acid (ABA). Treatment of cells with EBS increased the accumulation of a subset of ABA‐inducible heat‐stable proteins, but unlike ABA, EBS did not induce the expression of dehydrin transcripts which hybridized to a barley dehydrin clone. EBS slightly increased the hsp90 transcript levels, while ABA reduced the level of expression. These results confirm that brassinosteroids confer some stress tolerance to plant cells and further suggest that the mechanisms by which these compounds exert anti‐stress effects may only in part be similar to that of ABA.
Do tomatoes on the plant behave as climacteric fruits?
Authors: Knee Michael
Published: May 2006

I considered the possibility that changes in fruit photosynthesis obscure the occurrence of the climacteric rise in respiration in tomato fruits attached to the plant. Internal CO2 and ethylene concentrations in tomatoes (Lycopersicon esculentum Mill. cv. OH 7814) were analyzed after direct sampling through polyethylene tubes implanted in the external pericarp. Fruits which were shaded with aluminium foil contained up to 60 ml 1−1 CO2, until the internal ethylene concentration exceeded 1 μl l−1, when CO2 concentration declined to below 40 ml l−1; the CO2 concentration in fruits exposed to light only occasionally exceeded 40 ml 1−1. The internal CO2 concentration of detached fruits first declined and then increased along with ethylene concentration, as expected for the climacteric. Detached green fruits under continuous low photosynthetic photon flux density (100 μmol m−2 s−1) contained almost no internal CO2 and produced no CO2. Changes in photosynthesis and an associated CO2‐generating system in green fruits are thought to obscure the climacteric rise in tomato fruits developing on the plant.
Water efflux from the surface of field‐grown grass roots. Observations by cryo‐scanning electron microscopy
Authors: McCully M. E.
Published: May 2006

Field‐grown roots of maize, oats, barley and crabgrass collected at different times of day and night have been examined by cryo‐scanning electron microscopy. Droplets and blobs (their high water content confirmed by X‐ray microanalysis) were observed on the young root surfaces and within interstices of the rhizosheaths of guttating plants, particularly in the early morning. Plants collected at midday and in the afternoon had very few or none of these watery deposits. I propose that water released from the root surface during the night allows the expansion of root‐cap mucilage into the surrounding soil. When transpiration resumes, the mucilage is dried and binds tightly to the surrounding soil particles, thus stabilizing the coherent rhizosheath. This nocturnal water effflux may also facilitate nutrient uptake into the root when transpiration resumes. The water efflux to the rhizosheaths may be driven by root pressure and thus differs from the passive water loss from the root thought to occur during hydraulic lift.
Acclimatization and subsequent gas exchange, water relations, survival and growth of microcultured apple plantlets after transplanting them in soil
Authors: Díaz‐Pérez Juan C. , Sutter Ellen G. , Shackel Kenneth A.
Published: May 2006

Previous findings indicated that leaf conductance and net photosynthesis were positively correlated with water status (relative water content) of tissue‐cultured shoots and plantlets, and that acclimatization was associated with a reduction in leaf conductance and transpiration. In the present study, the effect of acclimatization on plant water status after plants were removed from culture and transplanted in soil, as well as the relation of water status with survival and growth after acclimatization were determined. Tissue‐cultured plantlets (Malus pumila cv. Greensleaves) were acclimatized by exposure to a 4‐day gradual reduction in humidity before they were transplanted. Once plants were transplanted, acclimatized plants maintained a higher relative water content than nonacclimatized plants, probably because of a lower initial stomatal conductance and less transpiration. High plant water status, as indicated by high relative water content, appeared to be an important factor for both plant survival and growth after the plants were transplanted. Higher water status was associated with higher growth rates and net assimilation rates. The differences in gas exchange, water relations and growth characteristics between plantlets in vitro and at 4 weeks after they were transplanted were also studied. Compared to in vitro plants, transplanted plants had a higher water status and higher leaf conductance and net photosynthesis. There was also an increase in the leaf area ratio (leaf area to plant biomass ratio) after they were transplanted which might have contributed to the higher net assimilation rate in transplanted compared to in vitro plants.
Postharvest changes in endogenous ABA levels and ABA metabolism in relation to dormancy in potato tubers
Authors: Suttle Jeffrey C.
Published: May 2006

The effects of postharvest storage duration, and storage and incubation temperatures on the loss of innate tuber dormancy, endogenous levels of free and conjugated abscisic acid (ABA) and the metabolism of (+)‐[3H]ABA were examined over three growing seasons in tubers of potato (Solanum tuberosum L. cv. Russet Burbank). The storage and incubation temperatures used were chosen in order to differentiate between events relating solely to dormancy status vs those relating to the resumption of sprout growth following the termination of dormancy. In tubers stored at 20°C, dormancy was lost and sprout growth began after 35 to 50 days of storage. In contrast, dormancy was lost after 50 to 80 days of storage at 3°C but subsequent sprout growth was initiated only after transfer to 20°C. After 35 days of storage, endogenous levels of free ABA were highest (860 ± 35 pmol g−1 fresh weight) in tubers held at 3°C, intermediate (659 ± 78 pmol g−1 fresh weight) in tubers transferred from 3 to 20°C 7 days prior to analysis and lowest (471°18 pmol g−1 fresh weight) in tubers stored at 20°C. Regardless of temperature, free ABA levels declined with increasing duration of storage. The onset of sprouting was not associated with any threshold level of free ABA. Base‐labile, conjugated ABA was present in lower and more variable amounts than free ABA. The decline in free ABA was not accompanied by a commensurate increase in conjugated ABA. (+)‐[3H]ABA was readily taken up and metabolized by both dormant and nondormant tubers. In short‐term (≤ 7 days) studies, (+)‐[3H]ABA was metabolized to phaseic acid and dihydrophaseic acid. In tubers held at 20°C, dihydrophaseic acid was the major metabolite while in tubers held at 3°C there was a transient accumulation of phaseic acid with dihydrophaseic acid predominating only after 7 days. During postharvest storage, there was no change in the rate of ABA metabolism regardless of the dormancy status and/or growth potential of the tubers. These results demonstrate that ABA is readily metabolized by potato tubers and that the principal route of catabolism consists of the oxidative metabolism of ABA to phaseic and dihydrophaseic acids with minimal esterification to conjugated ABA. These results also suggest that a decline in endogenous ABA below a threshold level is not a prerequisite for the loss of potato tuber dormancy and the onset of sprout growth.
Effect of applied benzyladenine on endogenous cytokinin content during the early stages of bud development of kiwifruit
Authors: Feito I. , Rodríguez A. , Centeno M. L. , Sánchez‐Tamés R. , Fernández B.
Published: May 2006

A short‐term study linked directly to our previous long‐term experiments was conducted to clarify whether or not benzyladenine (BA) acts directly or through endogenous cytokinins in the development of kiwifruit explants. The uptake and metabolism of BA were characterized in kiwifruit explants after 0.5, 1, 2, 8 and 16 h exposure to 8‐[14C]BA on both solidified and liquid Murashige and Skoog media. Endogenous cytokinins were measured by enzyme‐linked immunosorbent assay (ELISA) using polyclonal antibodies. The kinetics of BA uptake by explants cultured under these conditions were different, being higher in explants cultured in liquid medium. The glucosylation rate of BA was faster in explants cultured on solid medium. The levels of active forms of BA (BA and [9R]BA) were higher in explants cultured on liquid medium due to its higher uptake and lower glucosylation. The levels of zeatin‐type cytokinins were influenced by the culture conditions. A direct correlation was observed between morphogenic response and proportion of active forms of BA, but not with zeatin‐type cytokinins.
Occurrence of hemoglobin in the nitrogen‐fixing root nodules of Alnus glutinosa
Authors: Suharjo Usman K. J. , Tjepkema John D.
Published: May 2006

A true hemoglobin (Hb) was shown to be present in the root nodules of Alnus glutinosa L. After purification by gel filtration and ion exchange, the Hb formed a stable complex with oxygen. This oxygen complex could then be converted to carboxyhemoglobin by treatment with CO. Optical absorption spectra typical of Hb were observed. The molecular weight was estimated to be 15 100 by gel filtration, and 18 300 by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. The Hb was largely insoluble when the initial homogenization was done in the absence of a detergent. Under these conditions much of the Hb appears to be associated with clusters of Frankia, the nitrogen‐fixing actinomycete that infects plant cells within the nodules. The exact localization of the Hb in vivo is uncertain. The relatively low average concentration of Hb in Alnus nodules suggests that it is either confined to a relatively small fraction of total nodule volume, or has a function other than facilitation of O2 transport.
Pattern of endoproteolysis following wheat grain germination
Authors: Dominguez Fernando , Cejudo Francisco J.
Published: May 2006

Following cereal grain germination the starch and storage proteins accumulated in the starchy endosperm are mobilized by the concerted action of hydrolytic enzymes, such as amylases and proteases, that are produced and secreted by the scutellum and the aleurone layer. We have studied the pattern of endoproteolytic activities following wheat (Triticum aestivum cv. Chinese Spring) grain germination using SDS‐PAGE containing a gradient of polyacrylamide copolymerized with gelatin, an artificial substrate for plant proteases. Total proteolytic activity increased as seedling growth proceeded and reached a maximum 5–7 days after imbibition. Up to 20 proteolytic bands could be detected in extracts from these grains. The bands were arbitrarily classified into 3 groups; endoproteases of groups I and II showed higher activity at pH 6.5, while those of group III had maximum activity at pH 4.0. Most of group II and III endoproteases were produced by the aleurone layer and scutellum and secreted to the starchy endosperm. The synthesis of most of the proteases of group III, but not of group II, was activated by exogenous GA3 in de‐embryonated wheat grains. Based on activation by thiol‐reagents and inhibition by thiol‐protease inhibitors, it was determined that GA3‐induced proteases were thiol‐proteases.
Effects of moderate drought on ascorbate peroxidase and glutathione reductase activities in mesophyll and bundle sheath cells of maize
Authors: Brown Peter S. , Knievel Daniel P. , Pell Eva J.
Published: May 2006

Mesophyll and bundle sheath cells of maize leaves (Zea mays L.) both contain the enzymes ascorbate peroxidase (AP; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) which are involved in hydrogen peroxide detoxification. Since bundle sheath cells of maize are deficient in photosystem II and have high CO2 levels, oxidative stress may be less severe in these cells than in mesophyll cells. The present study was conducted to determine if AP and GR activity levels preferentially increase in mesophyll cells relative to bundle sheath cells when plants are subjected to moderate drought. Although drought inhibited the growth of greenhouse‐grown plants, it did not affect the levels of protein, chlorophyll or AP. GR was unaffected by drought in whole leaf tissue and mesophyll cells, but did increase slightly in bundle sheath cells. This slight increase is of questionable biological importance. AP and GR activity levels were similar in mesophyll cells, bundle sheath cells and in whole leaf tissue. The data suggest that moderate drought has little effect on enzymes of the hydrogen peroxide scavenging system and that mesophyll and bundle sheath cells may be exposed to similar levels of hydrogen peroxide.
Applying the Richards function in freezing tolerance determination with electrolyte and phenolic leakage techniques
Authors: AniśAko Tomasz , Lindstrom Orville M.
Published: May 2006

The purpose of the present study was to apply the Richards function to fit electrolyte and phenolic leakage data for several taxa of woody plants subjected to freezing stress and to determine how the curve inflection point relates to the lethal temperature range. The lowest survival temperature of Fraxinus americana, Lagerstroemia cv. Natchez, Magnolia grandiflora, Rhododendron cv. Red Ruffle and Zelkova serrata was determined based on visual evaluation of oxidative browning facilitated by a modified regrowth test and differential thermal analysis. Lethal injury occurred in all cases within a range of 3°C below lowest survival temperature. Using the Richards function inflection point as an estimate of lethal temperature led to an overestimation of freezing tolerance in most taxa. This overestimation was greater for stems than leaves, and was greater in winter than in summer. The lethal temperature range generally coincided with the initial increase in leakage caused by freezing. The lethal temperature range also was determined by using a point of interception of the lower asymptote of a curve with a line tangential to the inflection point. In most taxa tested estimated lethal temperature based on the point of interception provided an improvement over the estimate based on the point of inflection.
A tonoplast intrinsic protein (TIP) is present in seeds, roots and somatic embryos of Norway spruce (Picea abies)
Authors: Oliviusson Peter , Hakman Inger
Published: May 2006

Many plant species contain a seed‐specific tonoplast intrinsic protein (TIP) in their protein storage vacuoles (PSVs). Although the function of the protein is not known, its structure implies it to act as a transporter protein, possibly during storage nutrient accumulation/breakdown or during desiccation/imbibition of seeds. As mature somatic embryos of Picea abies (L.) Karst. (Norway spruce) contain PSVs, we examined the presence of TIP in them. Both the megagametophyte and seed embryo accumulate storage nutrients, but at different times and we therefore studied the temporal accumulation of TIP during seed development. Antiserum against the seed‐specific a‐TIP of Phaseolus vulgaris recognized an abundant 27 kDa tonoplast protein in mature seeds of P. abies. By immunogold labeling of sectioned mature megagametophytes we localized the protein to the PSV membrane. We also isolated the membranes of the PSVs from mature seeds and purified an integral membrane protein that reacted heavily with the antiserum. A sequence of 11 amino acid residues [AEEATHPDSIR], that was obtained from a polypeptide after in‐gel trypsin digestion of the purified membrane protein, showed high local identity to a‐TIP of Arabidopsis thaliana and to a‐TIP of P. vulgaris. The greatest accumulation of TIP in the megagametophytes occurred at the time of storage protein accumulation. A lower molecular mass band also stained from about the time of fertilization until early embryo development. The staining of this band disappeared as the higher molecular mass (27 kDa) band accumulated in the megagametophyte during seed development. Total protein was also extracted from developing zygotic embryos and from somatic embryos. In zygotic embryos low‐levels of TIP were seen at all stages investigated, but stained most at the time of storage protein accumulation. The protein was also present in mature somatic embryos but not in proliferating embryogenic tissues in culture. In addition to the seed tissue material, the antiserum also reacted with proteins present in extracts from roots and hypocotyls but not cotyledons from 13‐day‐old seedlings.
Wall extensibility during hypocotyl growth: A hypothesis to explain elastic‐induced wall loosening
Authors: Edelmann Hans G.
Published: May 2006

The physico‐chemical nature of wall loosening of plants is still a matter of speculation. For a better understanding of the mechanistic principles in which polymer interactions may be affected during wall loosening, the rheological properties of sunflower (Helianthus annuus L.) were investigated during white light (WL)‐ and auxin (IAA)induced growth changes. As rheological parameter, the capacity for elastic shrinkage of standard hypocotyl segments after release of turgor‐mediated wall stress by freezing/thawing was studied (relative reversible length). Segment length remaining after shrinkage relative to turgid length has been designated as relative irreversible length. The following results were obtained: Temporary growth inhibition of in planta growing hypocotyls by WL is characterized by a temporary increase in relative irreversible length and a complementary decrease of relative reversible length. Analogously, but with opposite effect, IAA‐induced growth of hypocotyl segments is characterized by a decrease in relative irreversible length and an increase in relative reversible length; i.e., an increased capacity to shrink elastically per standard length. The changes of the two wall‐rheological parameters follow similar principles in hypocotyls grown in planta and ex planta and independent of whether the growth rate was changed by either WL conditions or IAA concentration. As suggested earlier (Edelmann 1994) the results indicate that growth may be regulated by wall loosening mechanisms which initially result in elastic (reversible) wall extension. To render this extension irreversible, it must be fixed subsequently. The finding that loosened walls also become shorter in irreversible length per standard length once tensional stress is released is new. It represents pivotal evidence for an initially elastic‐induced wall loosening.
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.
FITC‐dextran for measuring apoplast pH and apoplastic pH gradients between various cell types in sunflower leaves
Authors: Hoffmann Bernd , Kosegarten Harald
Published: May 2006

The liquid in the free space of leaf cell walls, the apoplast, is in direct contact with the plasma membrane and its nutrient uptake systems. Therefore, the pH of the apoplast is of utmost interest. We have elaborated a non‐destructive method by which excised sunflower leaves (Helianthus annuuscv. Erika) were perfused with fluorescein isothiocyanate‐dextran (FITC‐dextran) (4 000 Da) via the transpiration stream. We showed that leaf apoplast pH can be measured by using the fluorescence ratio technique together in conjunction with this dye. Evidence is provided that FITC‐dextran does not penetrate the plasma membrane over a period of ca 17 h from the beginning of dye perfusion. Dye enrichment in the leaf apoplast did not cause an ‘inner filter effect’ and thus the fluorescence ratio was only dependent on pH. In vivo calibration yielded a pKa of 5.92, which was virtually identical to the pKa of 5.93 calculated for dye solutions. Hence, FITC‐dextran can be detected in complex environments and covers a pH range prevailing in the leaf apoplast.

Based on this method we developed a microscope image technique visualizing pH gradients between various cell types. The pH in the lumen of the xylem vessel was ca 0.3–0.5 units lower than that of the apoplast of surrounding cells. Nitrate present in the leaf apoplast caused an increase in pH, especially in the dark. Under these conditions, in the intercostal area, the apoplast pH around the stomata was ca 0.5–1.0 units higher than that of the surrounding epidermal cells.
Variability of photosynthetic gas exchange parameters, dark respiration, and stomatal numbers in species of Polygonum
Authors: Apel Peter , Peisker Martin
Published: May 2006

Within the genus Polygonum a large variation was found between species with regard to stomatal number, gas phase resistance, intracellular resistance and dark respiration. Interspecific variation in CO2 compensation concentration and intercellular CO2 concentration at constant external concentration were comparatively small. Correlations were found between stomatal number and gas phase resistance, stomatal number and Γ, and Γ and the product of dark respiration rate and intracellular resistance. The influence of dark respiration and stomatal number on photosynthetic gas exchange is discussed. It was concluded that dark respiration in light was enhanced by 22% as a mean value in 9 Polygonum species and by 62% in Polygonum lapathifolium.
Effect of abscisic acid on stomatal opening in isolated epidermal strips of abi mutants of Arabidopsis thaliana
Authors: Roelfsema M. Rob G. , Prins Hidde B. A.
Published: May 2006

Abscisic acid‐insensitive mutants of Arabidopsis thaliana L. var. Landsberg erecta were selected for their decreased sensitivity to ABA during germination. Two of these mutants, abi‐1 and abi‐2, display a wilty phenotype as adult plants, indicating disturbed water relations. Experiments were undertaken to find out if this results from insensitivity of mutant stomates to ABA.

Growth conditions and methods to isolate epidermal strips were optimized to study stomatal movement. Wild type stomates required external ionic conditions comparable to those found for other species such as Commelina communis. The largest light‐induced opening of A. thaliana stomates was found at an external KCl concentration of 50 mM. Stomatal apertures were increased by lowering external Ca2+ to 0.05 mM. The apertures of stomates incubated with 10 μM ABA were not altered by changes in Ca2+ from 0.05 to 1.0 mM.

Stomates of all abi mutants showed a light‐stimulated stomatal opening. The opening of wild type and abi‐3 stomates was inhibited by ABA, while stomates of abi‐1 and abi‐2 did not respond to ABA. The insensitivity of abi‐1 and abi‐2 stomates to ABA may thus explain the observed disturbed water relations.
Long‐distance transport of 35S‐sulphur in 3‐year‐old beech trees (Fagus sylvatica)
Authors: Herschbach Cornelia , Rennenberg Heinz
Published: May 2006

35S‐L‐cysteine was fed to a mature leaf of 3‐year‐old beech trees via a flap. After 1 to 4 h the distribution of 35S‐radioactivity was analysed in the leaves as well as the bark and wood of the trunk and the main root. Transport of 35S out of the fed leaf amounted to 0.3–1.2% of the total 35S taken up. The branches of the trees did not act as sink organs for the exported radioactivity. The main portion of the 35S‐radioactivity transported out of the fed leaf was found in basipetal parts of the trunk. Only a small portion of 35S‐radioactivity was transported in acropetal direction. The distribution of the 35S‐radioactivity within the trunk showed a higher portion of 35S in the bark than in the wood. In both tissues, bark (70 to 80%) and wood (60 to 70%), the 35S was predominantly found in the HCl soluble fraction. However, 35S‐cysteine, the compound fed to the leaves was not exported out of the fed leaf. Along the trunk 35S‐cysteine was neither determined in bark nor in wood sections. The only low molecular mass S‐compounds found was 35S‐glutathione (GSH). The 35S‐sulphate detected in bark and wood origined from cysteine oxidation in the leaf tissue and from contamination of the 35S‐cysteine feeding solution. The ratio of GSH to sulphate decreased with increasing distance from the fed leaf. Apparently, 35S‐radioactivity was transported as sulphate and GSH in the phloem in basipetal direction, but GSH was removed preferentially out of the phloem along the transport path. 35S‐radioactivity exported out of the phloem and transported into the wood of the trunk was not retranslocated in the xylem. It may therefore be assumed that part of the 35S translocated was stored in ray cells, medullary sheath cells and/or pith parenchyma cells. Girdling experiments in which the bark of the trunk was peeled off basipetal to the branch containing the fed leaf support these assumptions.
Wounding regulates polysomal incorporation of hsp70 and tch1 transcripts during signal storage and retrieval
Authors: Henry‐Vian Chantal , Vian Alain , Davies Eric , Ledoigt Gérard , Desbiez Marie‐Odile
Published: May 2006

In Bidens pilosa L. (var. radiatus), wounding of both cotyledons induces the inhibition of hypocotyl growth. This morphogenic response occurs only if plantlets have been tranferred 24 h before from a non‐permissive (ion‐rich) to a permissive (deionized water) incubation medium. We have defined three kinds of experimental conditions where the wound‐response depends on the ionic content of the incubation medium: (1) permissive, allowing inhibition of hypocotyl growth; (2) non‐permissive, leading to storage of the wound signal; and (3) conditions required to recall the stored wound signal. Under these three experimental conditions, the accumulation of two stress‐related genes, tch1 (calmodulin) and hsp70, was investigated using northern blots of poly(A)+ and polysomal RNA. Under permissive conditions the wound response was characterized by a marked increase in tch1 and hsp70‐like poly(A)+RNA and by a slight association of these mRNAs with polysomes, 30 to 60 min after mechanical perturbation. In contrast, under non‐permissive conditions, we only observed a decrease in the accumulation of the two transcripts incorporated into polysomes. Under conditions that allow expression of the previously‐stored wound signal, we showed an increase in transcript accumulation (hsp70‐like gene) or an increase in the level of mRNA associated with polysomes (tch1‐like gene). These results suggest that transcriptional and post‐transcriptional regulation may occur at least at the level of transcript incorporation into the polysomes. This mechanism would be involved both after the immediate wound response and during the storage of the wound information.
Involvement of signal transduction pathway components in photoperiodic flower induction in Pharbitis nil
Authors: Borochov Amihud , Spiegelstein Hanna , Halevy Abraham H.
Published: May 2006

The possible participation of several major components of the signal transduction pathway in photoperiodic flower induction was examined in Pharbitis cotyledons. Exogenous applications of GTP‐γ‐S (1–10 μM) or of the phorbol ester, phorbol 12‐myristate‐13‐acetate (PMA, 0.1–5.0 μM) to Pharbitis plants held under a marginal inductive period (11.5 h dark) significantly increased their flowering response. Membrane lipid fluidity, GTP‐binding and protein kinase activity were increased following a single flowering‐inducing dark period of 16 h; however, a light‐break of 10 min that abolished flower induction failed to reverse the dark‐induced increase in these processes. Photo‐inductive dark conditions significantly increased the content of diacylglycerol (DAG) and phosphoinositides in the cotyledon membranes, together with the activities of their kinases, and a light break decreased them to control levels and below. In addition, a single spraying with GTP‐γ‐S or PMA at 1 μM significantly increased both the lipid content and the kinase activities. These compounds also enhanced the kinase activities in vitro. It is concluded that DAG and phosphoinositide metabolism play a role in the linking of the photoperiodic induction of the phytochrome with the flowering response in Pharbitis nil.
Purification of plasma membranes from leaves of conifer and deciduous tree species by phase partitioning and free‐flow electrophoresis
Authors: Toll Elena , Castillo Federico J. , Crespi Pierre , Crèvecoeur Michèle , Greppin Hubert
Published: May 2006

Purified plasma membrane fractions were obtained from leaves of Picea abies L., Pinus sylvestris L., Fagus sylvatica L. and Quercus robur L., whereas plasma membranes from Pinus halepensis Mill, proved to be more difficult to obtain, perhaps due to the higher content of volatile substances in this plant species. Plasma membranes were purified by both phase partitioning and free‐flow electrophoresis from microsomal fractions and identified on the basis of biochemical and in some cases morphological and cytochemical markers. Electron micrographs revealed that membrane vesicles from Pinus sylvestris exhibited a very clear dark‐light‐dark pattern and measurements of membrane thickness showed that it ranged from 6 to 10 nm. Most membranes were 8 nm thick and stained with phosphotungstic acid at low pH, both typical characteristics of the plasma membrane. Enzymatic identification of plasma membranes consisted in the determination of the vanadate‐sensitive ATPase (EC 3.6.1.3) activity. The specific activity in the upper phase (U2) fraction was 10–25 times higher than those in the lower phase and microsomal fractions, depending on plant species. 1,3‐β‐glucan synthase II (EC 2.4.1.3), another putative plasma membrane marker, was not detected in the plasma membrane‐enriched fractions of conifer needles and showed a very low specific activity in membranes of deciduous trees. Contamination by membranes of other origin was determined by analysis of membrane markers: cytochrome c oxidase (EC 1.9.3.1) for mitochondria, inosine diphosphatase (EC 3.6.1.6) for Golgi apparatus, cytochrome c reductase (EC 1.6.2.4) for endoplasmic reticulum, and pyrophosphatase (EC 3.6.1.1) for tonoplasts. The main, but relatively low contamination, was due to tonoplasts, as determined by the activity of pyrophosphatase. Plasma membrane characteristics were quite different depending on the season during which needles were taken. Membrane preparations of better quality were more easily obtained from samples taken during winter.
Carotenoid composition in Zea mays developed at sub‐optimal temperature and different light intensities
Authors: Haldimann Pierre , Fracheboud Yvan , Stamp Peter
Published: May 2006

The content and composition of pigments were examined in the third leaf of Zea mays L. plants grown under controlled environment at near‐optimal temperature (24°C) or sub‐optimal temperature (14°C) at a light intensity of either 200 or 600 μmol m−2 s−1. Compared to leaves grown at 24°C, leaves grown at 14°C showed a large reduction in the chlorophyll (Chl) content, a marked decrease in the Chl a/b ratio, and a large increase in the ratio of total carotenoids/Chl a+b. Leaves grown at 14°C showed a much lower content of β‐carotene than leaves grown at 24°C, while the content of the carotenoids of the xanthophyll cycle (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was markedly higher in the former leaves as compared to the latter leaves; neoxanthin and lutein were affected by the growth temperature to a much lesser extent. The xanthophylls/β‐carotene ratio was about three times higher in leaves grown at 14°C as compared to leaves grown at 24°C. On a chlorophyll basis, the two types of leaves hardly differed in their level of β‐carotene, while the levels of the xanthophylls (including lutein and neoxanthin) were higher in 14°C‐grown leaves as compared to 24°C‐grown leaves. In leaves grown at 14°C, 40 and 56% of the V+A+Z pool was in the form of zeaxanthin at low light intensity and high light intensity, respectively. Only trace amounts of zeaxanthin, if any, were present in leaves grown at 24°C. The changes in the pigment composition induced by growth at sub‐optimal temperature were more pronounced at a light intensity of 600 as compared to 200 μmol m−2 s−1. In the given range, the light intensity slightly affected the composition of pigments in leaves grown at 24°C. The physiological significance of the modifications to the pigment composition induced by growth at sub‐optimal temperature is discussed.
Ammonium uptake in carrot cell structures is influenced by pH‐dependent cell aggregation
Authors: Steiner Henry‐York , Dougall Donald K.
Published: May 2006

Semicontinuously grown wild carrot (Daucus carota L.) cells were used in an investigation of the effect of culture medium pH on ammonium uptake in suspension cultures as a first step in exploring the relationship between pH and anthocyanin biosynthesis. In contrast to published data showing decreasing uptake rates with decreasing culture medium pH, ammonium‐limited, semicontinuous carrot cell cultures showed a 25% greater ammonium uptake rate at pH 4.5 than at pH 5.5. When cells that had been grown semicontinuously in medium with a pH of 4.5 or 5.5 were grown in batch cultures at pH 4.5, 5.5 or 6.5 the ammonium uptake rates were those of the semicontinuous cultures, indicating that the pH of the batch culture medium had no effect on ammonium uptake rates over 7 days. The cell culture was composed of very small aggregates when it was grown semicontinuously in medium at pH 4.5, but was composed of large aggregates when it was grown semicontinuously in medium at pH 5.5. The aggregation/disaggregation of the cells was pH dependent, as changing the pH of the semicontinuous culture medium altered the extent of the aggregation. We conclude that the change in culture medium pH caused the cells to aggregate or disaggregate which in turn decreased or increased the rate of ammonium uptake from the medium.
Quantifying sink and source limitations on dry matter partitioning to fruit growth in peach trees
Authors: DeJong Theodore M. , Grossman Yaffa L.
Published: May 2006

We describe an approach for determining the degree of sink and source limitations on peach (Prunus persica L. Batsch) fruit growth during several growth periods. Source limitations on fruit growth may be due to either a shortfall in assimilate supply within the tree (supply limitation) or to a deficiency in the capacity of the translocation system to deliver assimilates in sufficient quantity to support the maximum fruit growth rate (transport/competition limitation). To ascertain the potential maximum rate of fruit growth, fruit thinning treatments were used. One month after bloom, the number of fruits per tree was adjusted to between 50 and 700 on an early and a late maturing peach cultivar (cvs Spring Lady and Cal Red, respectively). Rates of potential sink demand, potential source supply and actual fruit growth were estimated from sequential harvests of all fruits on 42 trees on two (Spring Lady) and three (Cal Red) dates. These values were used to estimate the proportion of potential growth achieved, and the supply and transport/competition limitations on fruit growth. The results indicated that source limitations were significant on trees with moderate to high fruit numbers. These source limitations were due to supply limitations during all harvest intervals and to transport/competition limitations during the early harvest intervals. Sink limitations occurred to the greatest extent during the mid‐period of fruit growth on the later maturing cultivar.
Dormancy and germination of olive embryos as affected by temperature
Authors: Voyiatzis Demetrios G.
Published: May 2006

Olive seeds do not germinate promptly when placed under favourable conditions, which is a problem in raising young plants for breeding or experimental purposes. In a series of experiments an investigation of the role of temperature in the germination of olive embryos was conducted. Naked, unchilled olive embryos (Olea europaea L. cv. Chalkidikis), cultured in vitro at 20°C, had a germination capacity of 73%, whereas that of embryos which had previously been chilled at 10°C for 2 or more weeks reached 96%. Intact seeds did not germinate at 20°C unless they had previously been subjected to 10°C for 3 or 4 weeks. Embryos chilled while in the intact seed and excised just before transfer to 20°C, reacted in a similar way to naked embryos, but reached their maximum germination capacity after 4 weeks at 10°C. Under constant temperature conditions the highest germination percentage of embryos was observed at 10 and 15°C and the highest germination rate at 15°C, while a moderate capacity and rate of germination occurred at 20°C, and a very low percentage and rate at 25 and 30°C. Prechilling at 10°C did not affect germination at 15°C, but improved the percentage and the rate of germination at 20, 25 and 30°C. The germination percentages of embryos chilled for 1 or 2 weeks at 10°C and then transferred to 25°C were lower than those of similarly chilled embryos transferred to 20°C. The chilling effect could not be reversed at 25°C when the embryos had been chilled for 3 or more weeks. The results show that olive seeds exhibit a state of dormancy that is caused by factors residing partly in the endosperm and partly within the embryo.