bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and leaf senescence in spring wheat (Triticum aestivum) grown at different ozone concentrations in open‐top field chambers
Authors: Grandjean Ariane , Fuhrer Jürg
Published: May 2006

Spring wheat (Triticum aestivum L. cv. Albis) was grown during two consecutive seasons (1987, 1988) in open‐top field fumigation chambers at a site in central Switzerland and exposed to different doses of ozone (O3) in order to study O3 effects on growth and leaf senescence. The O3 dose in nonfiltered air (NF) was 42.6 μl I‐1 h in 1987 and 49.2 μ I‐1 h in 1988. The other treatments used were: charcoal‐filtered air (CF) (0.5 × O3 dose in nonfiltered air) and nonfiltered air with one of two levels of O3 added daily (0900–1700 h) (O3‐1 with 1.5 × O3 dose in nonfiltered air and O3‐2 with 1.9 × O3) dose in nonfiltered air). From anthesis through senescence, dry weight of individual ears, and chlorophyll and protein content, glutamate dehydrogenase activity (GDH, EC 1.4.1.3), and the content of free and conjugated 1‐aminocyclopropane‐1‐carboxylic acid (ACC and MACC) in flag leaves were determined. With increasing O3 dose, the decline in chlorophyll and soluble protein contents started earlier, but the rate of decline decreased. Independent of the treatment used, GDH activity was highest during the period of maximal protein loss. With increasing O3 dose, the content of MACC increased, while that of free ACC remained unaffected. In 1988, temporal changes in MACC were related to other senescence processes. It is suggested that with increasing stress from chronic O3 exposure leaf duration is reduced, but that the pattern of senescence processes remains unchanged. Ozone‐induced acceleration of flag leaf senescence could contribute to the observed reduction in ear dry weight accumulation, which may account for yield reduction in spring wheat.
Etiolation as a pretreatment for in vitro establishment and multiplication of mature chestnut
Authors: Ballester A. , Sánchez M. C. , Vieitez A. M.
Published: May 2006

Localized etiolation of branches in the crown of a 30‐year‐old chestnut tree produced plant material that responded much better to establishment and multiplication in vitro than unetiolated material, whose cultures were very difficult to maintain (response being measured in terms of the percentage of cultures established, the mean number of shoots formed per explant, the number of 8‐mm segments per new shoot, the length of longest shoot in each culture, and the coefficient of multiplication). Only 22% of the initial explants from unetiolated material were successfully established, as against 79% for etiolated material, with similar differences between the coefficients of multiplication of the two lines in successive cultures. Accordingly, partial etiolation of branches is proposed as a suitable pretreatment for in vitro propagation of selected mature trees, when physiologically juvenile materials such as stump sprouts, epicormic shoots or root suckers are not available.
Hydrophobicity of protochlorophyllide oxidoreductase, characterized by means of Triton X‐114 partitioning of isolated etioplast membrane fractions
Authors: Selstam Eva , Widell‐Wigge Anna
Published: May 2006

The inner etioplast membrane possesses a pronounced lateral heterogeneity with respect to protein and lipid composition as well as ultrastructural appearance. Little is known about the reason for formation of the regular branched structure shown by the prolamellar body part of the membrane. A specific interaction between the membrane lipids and the dominating protein NADPH‐protochlorophyllide oxidoreductase (PCR, EC 1.6.99.1) might be of major importance. In this study isolated prolamellar bodies and prothylakoids from the leaves of dark‐grown wheat (Triticum aestivum L. cv. Starke II, Weibull) were exposed to Triton X‐114 partitioning in media with 150 mM NaCl and without. By comparing the partitioning of PCR, the ATP synthase (EC 3.6.1.3) polypeptides, and ribulosebisphosphate carboxylaseoxygenase (EC 4.1.1.39) in the different systems, it was concluded that PCR is an integral membrane protein with substantial hydrophilic domains.
Effects of plant water deficit on the daily carbon balance of leaves of cacao seedlings
Authors: Deng Ximin , Joly Robert J. , Hahn Daniel T.
Published: May 2006

The daily carbon balance of individual source leaves of Theobroma cacao L. seedlings was measured at 2‐ to 3‐day intervals during a 19‐day period of increasing plant water deficit and during an 8‐day period of recovery following rewatering. In each case, responses of stressed seedlings were compared to those of irrigated controls. Leaves of irrigated cacao seedlings assimilated approximately 41 mg carbohydrate dm‐2 during 12‐h photoperiods, and exported an average of 34 mg carbohydrate dm‐2 during 24‐h measurement cycles. The rate of carbon export from cacao leaves was sharply reduced as leaf water potential (ψ) declined between ‐0.8 and ‐2.0 MPa. Further, the rate of export was closely associated with the net assimilation rate (A), with export capacity being severely reduced as A fell to near zero. Net accumulation of dry matter occurred as long as A remained greater than approximately 20 mg carbohydrate dm‐2 over the 12‐h photoperiod, but at lower assimilation rates, export exceeded concomitant assimilation. Carbon export continued at the expense of leaf carbon reserves as photoassimilation fell to near zero during periods of severe water stress (ψ < ‐2.0 MPa). Night respiration rate was independent of plant water status.
Changes in polar lipids during ripening and senescence of cherry tomato (Lycopersicon esculentum): Relation to climacteric and ethylene increases
Authors: Güçlü Josette , Paulin André , Soudain Pierre
Published: May 2006

The entire senescence period, including ripening, is characterized in cherry tomato (Lycopersicon esculentum Mill. var. cerasiforme Alef.) by two successive changes in overall polar lipid content. The rise in respiration of the fruit in the climacteric phase is accompanied by a large increase in lipids, notably phospholipids, such as phosphatidylcholine and phosphatidic acid. This suggests the coexistence of anabolic and catabolic processes in this first period. At the degreening stage of the fruit, decreased levels of monogalactosyldiacylglycerol and the disappearance of trigalactosyldiacylglycerol may indicate some degradation of the chloroplast compartment. Following a respiratory upsurge, a sudden breakdown of total lipids occurs concomitantly with maximal ethylene production. This breakdown is essentially caused by a parallel decrease in the amounts of phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid and also phosphatidylglycerol. However, in the cherry tomato, lipid peroxidation, evaluated by alteration of fatty acid distribution, seems insufficient to account for the ethylene peak.
Light‐dependent, chilling effects on phosphorylation of thylakoid proteins and consequences for associated photochemical activities in maize
Authors: Val Jesus , Baker Neil R.
Published: May 2006

When maize (Zea maysL. cv. LG11) leaves are exposed to low temperatures and high light modifications to both photosystem 2 (PS2) and the light‐harvesting chlorophylla/bprotein complex associated with photosystem 2 (LHC2) occur. This study examines the consequences of these modifications for phosphorylation of LHC2 and PS2 polypeptides and the associated changes in electron transport. Maize leaves were chilled at 5°C for 6 h under photon flux densities of 1 500 and 250 μmol m‐2s‐1. Thylakoids were then isolated from the leaves and their abilities to phosphorylate LHC2 and PS2 polypeptides and modify electron transport activities were determined. Measurements of chlorophyll fluorescence induction in the thylakoids were also made. Thylakoids isolated from leaves chilled under high light and from leaves kept in the ambient growth environment had similar phosphoprotein profiles. However, polypeptide phosphorylation in thylakoids from the chilled leaves did not produce a decrease in PS2 electron transport. Chilling leaves under low light produced a decrease in the ability of isolated thylakoids to phosphorylate PS2, but not LHC2, polypeptides, which was not associated with any change in the phosphorylation‐induced decrease in PS2 electron transport. Chilling under high, but not low, light appears to produce changes in membrane organisation that do not affect the ability of the thylakoids to phosphorylate PS2 and LHC2 polypeptides, but which do prevent the phosphorylation‐induced decrease in excitation energy transfer from LHC2 to PS2.
Structure and function of root‐inducing (Ri) plasmids and their relation to tumor‐inducing (Ti) plasmids
Authors: Petersen Steen G. , Stummann Bjarne M. , Olesen Peter , Henningsen Knud W.
Published: May 2006

The abilities of Agrobacterium tumefaciens and A. rhizogenes to transform dicotyle‐dons and cause crown gall and hairy root disease are caused by the presence of tumor inducing (Ti) and root inducing (Ri) plasmids. During transformation plasmid T‐DNA (transferred DNA) is inserted into the plant genome. The T‐region is flanked by 25 bp direct repeats, which are essential for transfer. The T‐regions contain oncogenes that are expressed in the plants. Some of these code for enzymes that synthesize auxin or cytokinin. Another type, present in Ri plasmids only, appears to impose a high hormone sensitivity on the infected tissue. The T‐DNA also contains genes for enzymes synthesizing opines, which the bacteria catabolize. The T‐DNA transfer is initiated by the induction of genes in the virulence (vir) region of the plasmid by phenolic compounds secreted by wounded tissue. The products of the vir‐genes and of chromosomal genes mediate transfer of T‐DNA to the plant cells. Crown gall disease is caused by production of auxin and cytokinin by the transferred T‐DNA. The T‐DNA of Ri plasmids codes for at least three genes that each can induce root formation, and that together cause hairy root formation from plant tissue. Current results indicate that the products of these genes induce a potential for increased auxin sensitivity that is expressed when the transformed cells are subjected to a certain level of auxin. After this stage the transformed roots can be grown in culture without exogenous supply of hormones.
Properties and functions of glutathione reductase in plants
Authors: Smith Ivan K. , Vierheller Thomas L. , Thorne Carol A.
Published: May 2006

The assay and in vitro characterization of glutathione reductase (EC 1.6.4.2) is discussed. In vivo the H2O2‐scavenging system in chloroplasts is the best documented role of reduced glutathione and glutathione reductase in plants. Similarly, redaction of H2O2, outside of the chloroplasts, requires glutathione and glutathione reductase; but the pathway, in terms of intermediates, is controversial. The notion that biological stress frequently causes cellular oxidation has lead to the suggestion that glutathione and glutathione reductase may play a role in stress resistance or tolerance mechanisms. The changes in glutathione reductase levels in response to low temperature, oxidative stress and drought are discussed.
Molecular characterization of corn glutathione S‐transferase isozymes involved in herbicide detoxication
Authors: Timmerman Kurt P.
Published: May 2006

Corn (Zea mays L.) glutathione S‐transferases (EC 2.5.1.18) have attracted interest, in part, due to their involvement in the metabolism of several herbicides, including atrazine and alachlor. Three corn, glutathione S‐transferases have been purified, and cDNA clones have been isolated and sequenced for two of these, GST I and GST III. In addition to showing some amino acid sequence similarity to each other, the two sequenced corn glutathione S‐transferases also show some similarity to rat and human enzymes. The corn glutathione S‐transferases responsible for atrazine tolerance have not yet been purified or cloned, but purification attempts indicate that corn has two glutathione S‐transferases with activity towards atrazine. While many glutathione S‐transferases from various organisms have been detected by using 1‐chloro‐2,4‐dinitrobenzene as a substrate, the atrazine‐specific glutathione S‐transferases have very little or no activity with 1‐chloro‐2,4‐dinitrobenzene. This shows the importance of assaying with a variety of substrates when characterizing glutathione S‐transferases.
On the presence of inside‐out plasma membrane vesicles and vanadate‐inhibited K+,Mg2+‐ATPase in microsomal fractions from wheat and maize roots
Authors: Bérczi Alajos , Larsson Christer , Widell Susanne , Møller Ian M.
Published: May 2006

We have estimated the amount of inside‐out plasma membrane (PM) vesicles in microsomal fractions from wheat (Triticum aestivum L. cv. Drabant) and maize (Zea mays L.) roots; non‐latent activities of the PM markers vanadate‐inhibited K+, Mg2+‐ATPase (ΔVO4‐ATPase) and glucan synthase II (GS II, EC 2.4.1.34) were used as markers for inside‐out PM vesicles, latent activities as markers for right‐side‐out PM vesicles, and specific staining with silicotungstic acid (STA) as a general marker for the PM. Separation of presumptive inside‐out PM vesicles from right‐side‐out ones was achieved by counter‐current‐distribution (CCD) in an aqueous polymer two‐phase system. Most of the GS II activity was latent and was found in material partitioning into the upper phase; a distribution which correlated well with that of STA‐stained vesicles. Thus, most of the PM vesicles had a right‐side‐out orientation. ΔVO4‐ATPase, on the other hand, had a dual distribution (particularly pronounced in wheat) and was recovered both in material partitioning into the lower phase and into the upper phase. This indicates that ΔVO4‐ATPase activity was present also in membranes other than the PM. Additional evidence for this interpretation came from sucrose gradient centrifugation of wheat root material. This produced two peaks of ΔVO4‐ATPase activity with the membranes partitioning into the lower phase, none of which coincided with the peak obtained with right‐side‐out PM vesicles. Taken together, these results indicate that only very few inside‐out PM vesicles are present in the microsomal fraction, and that ΔVO4‐ATPase as a marker for the PM, in contrast to GS II, may give quite misleading results with some plant materials. This stresses the need to use well‐defined preparations of scaled, inside‐out PM vesicles in solute uptake studies. The distribution of Ca2+‐inhibited ATPase, on the other hand, agreed well with those of GS II and STA‐stained vesicles both after CCD and sucrose gradient centrifugation, which suggests that Ca2+ inhibition may be a more specific property of the PM H+‐ATPase than vanadate inhibition.
Detection and first characterization of a cell‐wall lytic activity in Chlorella ellipsoidea C‐27
Authors: Satoh Hitoshi , Takeda Hiroshi
Published: May 2006

Cell wall lytic activity was detected in Chlorella ellipsoidea Gernick IAM C‐27 using the [14C]‐labeled cell wall as substrate. The highest activity was obtained at pH 8. and the solubilized product was a polysaccharide of high molecular weight. The lytic activity appeared to be a protease and did not hydrolyse glycosidic bonds of the cell wall polysaccharides. The activity probably solubilizes the cell wall by cleaving the peptide bonds that interconnect the polysaccharides of the cell wall.
Cortical microtubule organization in Vitis protoplasts as affected by concentration of enzyme isolation medium and duration of incubation
Authors: Lee Ni , Wetzstein Hazel Y. , Bornman Chris H.
Published: May 2006

Protoplasts of Vitis rotundifolia Michx. cv. Summit were isolated from mesophyll of axenic shoot cultures under different enzyme concentrations and digestion times. Viability and plating efficiency were assessed and related to the cortical microtubule network, visualized using immunofluorescence. Higher concentrations of enzyme isolation medium significantly decreased protoplast viability and plating efficiency. However, the cortical microtubule network appeared stable, at all concentrations with dense, continuous microtubule strands in both random and parallel arrays. In contrast, longer vs shorter enzyme incubation duration resulted in significantly lower plating efficiency, which was correlated with changes in cortical microtubule organization. With longer incubation, the frequency of parallel microtubule strands decreased; microtubule organization showed increasing disruption, microtubule strands were shortened, fragmented and exhibited only a weak fluorescence labeling. Both high enzyme concentration and prolonged incubation periods negatively affected protoplast regenerability, but in different ways. Microtubule organization was sensitive to duration of incubation, but not to enzyme concentration. It is concluded that the presence of a well‐developed cortical microtubule network does not gurantee regeneration. Other factors related to isolation appear to be involved.
The slender phenotype of pea: stem growth, peroxidase levels and ethylene responses
Authors: Jupe Steven C. , Scott Ian M.
Published: May 2006

Stem elongation growth in a slender line of Pisum sativum L. was much greater than in its two dwarf parental lines due to a greater rate of production of longer internodes. The cellular basis of the greater length of slender internodes was tissue specific. In the epidermis, greater cell length primarily accounted for the longer internodes of the slender plants, but in the outer cortex, greater cell number was the more important factor. The soluble and salt‐extractable peroxidase (EC 1.11.1.7) activities of expanding internodes were much lower in slender plants than in dwarf plants. The proportional effects of ethylene treatment on epicotyl length, diameter and orientation were similar in etiolated slender and dwarf seedlings.
Carbon and nitrogen reserves of leafy spurge (Euphorbia esula) roots as related to overwintering strategy
Authors: Cyr David R. , Bewley J. Derek
Published: May 2006

Leafy spurge (Euphorbia esula L.), a serious perennial weed of temperature range and pasture lands, has continued to colonize despite various control strategies. The persistence of this species can be attributed in part to the presence of an extensive root system containing abundant organic reserves. These components, established towards the end of the growing season, are remobilized to support early spring growth. Carbohydrates comprise the bulk of reserve material with late fall incrents in free sugars being associated with reductions in starch content. Nitrogenous components undergo significant seasonal fluxes, with free amino acids and soluble proteins reaching maxima during late fall. Asparagine, glutamic acid, serine, ornithine, proline, arginine and aspartic acid all contribute significantly to the storage of nitrogen. Changes in nitrate content are associated with the overwintering process. These observations are indicative of the role that nitrogen plays in the overwintering strategy and regenerative capacity of leafy spurge roots.
The effect of sucrose on the levels of abscisic acid, indoleacetic acid and zeatin/zeatin riboside in wheat ears growing in liquid culture
Authors: Lee Bruce , Martin Peter , Bangerth Fritz
Published: May 2006

The influence of a varied sucrose supply on grain size and hormonal contents of detached wheat ears (Triticwn aestivum L. cv. Schirokko) was investigated throughout grain development. In ears led limited amounts, or no sucrose, grain weights in both proximal and distal grain positions of the ear were reduced. Radioimmunoassay for abscisic acid, indoleacetic acid and zeatin/zeatin riboside showed that the changes in the levels of these hormones in grains and bracts were comparable to intact ears when detached ears were well supplied with sucrose. Under conditions of limited sucrose supply, higher abscisic acid levels in the distal and proximal grains of detached ears were found compared to ears supplied with adequate sucrose. Limiting sucrose supply to the ear did not alter the levels of indoleacetic acid or zeatin/zeatin riboside in either the grains or bracts of detached ears.
Regulation of abscisic acid translocation during embryo maturation of Phaseolus vulgaris
Authors: Le Page‐Degivry Marie Thérèse , Barthe Philippe , Prévost Isabelle , Boulon Brigitte
Published: May 2006

When R, S [2‐14C] abscisic acid (ABA) was applied to the leaf of Phaseolus vulgaris, a part of the radioactivity was always found 24 h later in the only pod left on the plant. In early podfill, a large part of the labeled material was found in the maternal tissues while in late podfill, most had migrated to the embryos. During embryogenesis, embryo cells became more and more alkaline with respect to the seed coat cells. These results suggest that the distribution of ABA within the tissue is regulated by the pH differential between the two compartments.

The decrease of endogenous ABA level observed in situ during the second part of the embryo development therefore cannot be explained only in terms of the passive diffusion of the undissociated species (ABA‐H). The empty‐ovules technique revealed that ABA was only partly affected by an inversion of the pH gradient and that metabolic inhibitors influenced the release of ABA. These results indicate that in addition to a diffusive path, an energy‐dependent component was involved.
The C‐S lyases of higher plants. Purification and characterization of homogeneous alliin lyase of leek (Allium porrum)
Authors: Won T. , Mazelis M.
Published: May 2006

The characteristic odors of freshly macerated tissue of Allium species such as garlic and onion are due to the action of the enzyme alliin lyase (EC 4.4.1.4) on endogenous S‐alkyl‐I‐cysteine sulfoxides which are present as secondary amino acids yielding volatile sulfur‐containing products. Purification and characterization of the alliin lyase of leek (Allium porrum L.) has been carried out for comparison with the analogous enzymes previously characterized from garlic and onion. The purification involved homogenization, followed by ammonium sulfate fractionation, elution from an hydroxylapatite column, concentration of the active fractions and passage through a concanavalin A‐Sepharose 4B affinity column. The purified enzyme was found to be a glycoprotein with a pH optimum for activity of 8.0. Sodium dodecylsulfate‐urea polyacrylamide gel electrophoresis gels of the homogeneous leek enzyme showed it consisted of 1 subunit with a molecular weight of 48000. By gel filtration, 2 stable forms of the native enzyme with molecular weights of 386000 and 580000 were found.
Effect of diclofop‐methyl and 2,4‐D on transmembrane proton gradient: a mechanism for their antagonistic interaction
Authors: Shimabukuro Richard H. , Walsh Wendy C. , Wright John P.
Published: May 2006

The site of action of the postemergence graminicide, diclofop‐methyl (DM), in susceptible plants is possibly the plasmalemma. Indole‐acetic acid (IAA)‐ and fusicoccin (FC)‐induced net proton excretion in Avena coleoptiles was inhibited by the free acid, diclofop. However, net proton excretion recovered within 2 h when 2,4‐dichlorophenoxy acid (2,4‐D) was added simultaneously with diclofop. Diclofop depolarized the membrane potential (Em) within 12 min but the Em recovered within 30 min when diclofop was removed and replaced with either IAA or 2,4‐D. The inhibition of IAA‐induced coleoptile growth by DM and the membrane effects of its acid, diclofop, were partially reversed by 2,4‐D if it was added shortly after treatment of the tissue. These results are consistent with the reversal of DM injury in whole plants with 2,4‐D.
Low temperature delays development of photosystem II activity in winter rye leaves
Authors: Griffith Marilyn , McIntyre Heather C. H. , Krol Marianna
Published: May 2006

The ability of leaves to acclimate photosynthetically to low temperature was examined during leaf development in winter rye plants (Secale cereale L. cv. Puma) grown at 20°C or at 6°C. All leaves grown at 6°C exhibit increased chlorophyll (Chl) levels per leaf area, higher rates of uncoupled, light‐saturated photosystem I (PSI) electron transport, and slower increases in photosystem II (PSII) electron transport capacity, when compared with 20°C leaves. The stoiehiometry of PSI and PSII was estimated for each leaf age class by quantifying Chl in elcctrophorctic separations of Chl‐protein complexes. The ratio of PSII/PSI electron transport in 20°C leaves is highly correlated with the ratio of core Chl a‐proteins associated with PSII (CPa) to those associated with PSI (CP1). In contrast, PSII/PSI electron transport in 6°C leaves is not as well correlated with CPa/CP1 and is related, in part, to the amount and organization of light‐harvesting Chl a/b‐proteins associated with PSII. CPa/CP1 increases slowly in 6°C leaves, although the ratio of CPa/CP1 in mature 20°C and 6°C leaves is not different. The results suggest that increased PSI activity at low temperature is not related to an increase in the relative proportion of PSI and may reflect, instead, a regulatory change. Photosynthetic acclimation to low environmental temperature involves increased PSI activity in mature leaves shifted to 6°C. In leaves grown entirely at 6°C, however, acclimation includes both increased PSI activity and modifications in the rate of accumlation of PSII and in the organization of LHCII.
Identification of free mannose and partial characterization of a mannose‐6‐phosphate isomerase from Lilium longiflorum bulbs
Authors: Miller William B.
Published: May 2006

The existence of free mannose in storage bulbs of Lilium longiflorum Thunb, was established using preparative high performance liquid chromatography, gas chromatography and gas chromatography‐mass spectroscopy. Free mannose was not detected in developing (importing) bulb tissues. Mannose, a relatively rare hexose in plant tissue, probably arises from the hydrolysis of glucomannan, a hemicellulosic carbohydrate polymer known to be present in Lilium storage tissues. A calculation of total mannose residues per bulb (prior to versus after reserve hydrolysis and export) indicated that mannose is metabolized, probably in sucrose biosynthesis. A mannose‐6‐phosphate isomerase (EC 5.3.1.8) was isolated from Lilium bulbs and purified 155‐fold with 29% yield. The molecular weight of the enzyme was estimated by gel filtration to be 64 kDa, and the Km for mannose‐6‐phosphate was 0.42 mM. It is concluded that glucomannan is functioning as a reserve carbohydrate in Lilium storage tissues and that the mannose‐6‐phosphate isomerase is responsible for the entry of mannose into the sucrose biosynthetic pathway.
Ecological implications of correlative inhibition between plant shoots
Authors: Novoplansky Ariel , Cohen Dan , Sachs Tsvi
Published: May 2006

Plants of Pisum sativum var. arvense Poir. cv. Dun were grown with two equal shoots kept in different light conditions. In these plants a darkened shoot was inhibited and it eventually withered and died; it elongated and became etiolated only when the shoot in the stronger light was removed. A similar result was obtained in simulated ecological conditions, when the shoot in the inferior light was merely shaded: this shoot was severely inhibited, though it did survive. The inhibition of the shaded shoot was more pronounced when the plants were stressed by the removal of large parts of their cotyledonary reserves. These results demonstrate an integration of responses to the light environment with the correlative inhibition between shoots of the same plant. This integration enables the plant to use its developmental resources optimally in heterogeneous environments, rather than merely growing where conditions are ‘appropriate’.
Strategies for acclimation to seasonal drought inCeratonia siliqualeaves
Authors: Nunes Maria Antonieta , Catarino Fernando , Pinto Eugénio
Published: May 2006

Plants ofCeratonia siliquaL. (carob tree) were subjected to a slow cycle of soil water depletion in summer and in winter. Recently mature and fully turgid leaves were squeezed in a pressure chamber in order to analyse changes in the components of water potential related to the acclimation to drought. Mathematical expressions were fitted to the primary data in order to calculate the elasticity modulus and the dependence of turgor pressure on relative osmotic water content. Osmotic and water potentials decreased significantly in leaves acclimated during the summer (about 0.7 and 0.9 MPa decrease, respectively) whereas in winter the elastic properties of the wall had changed: modulus of the non‐stressed leaves was 26 MPa compared to 7.5 MPa in leaves subjected to drought stress. The results indicate thatCeratonialeaves can, to some extent, maintain turgor under situations of soil drought, using different strategies according to the season.
Tissue stresses in growing plant organs
Authors: Kutschera U.
Published: May 2006

Rapidly growing plant organs (e.g. coleopties, hypocotyls, or internodes) are composed of tissues that differ with respect to the thickness, structure, and extensibility of their cell walls. The thick, relatively inextensible outer wall of the epidermal cells contains both transverse and longitudinally oriented cellulose‐microfibrils. The orientation of microfibrils of the thin, extensible walls of the parenchyma cells seems to be predominantly transverse. In many growing organs (i.e. leafstalks), the outer epidermal wall is supported by a thickened inner epidermal wall and by thick‐walled subepidermal collenchyma tissue. Owing to the turgor pressure of the cells the peripheral walls are under tension, while the extensible inner tissue is under compression. As a corollary, the longitudinal tensile stress of the rigid peripheral wall is high whereas that of the internal walls is lowered. The physical stress between the tissues has been described by Sachs in 1865 as ‘tissue tension’. The term ‘tissue stress’. however, seems to be more appropriate since it comprises both tension and compression. Hitherto no method has been developed to measure tissue stresses directly as force per unit cross‐sectional area. One can demonstrate the existence of tissue stresses by separation of the tissues (splitting, peeling) and determining the resulting strain of the isolated organ fragments. Based on such experiments it has been shown that rapid growth is always accompanied by the existence of longitudinal tissue stresses.
Glycolate metabolism in cyanobacteria
Authors: Renström Eva , Bergman Birgitta
Published: May 2006

A comparative analysis of glycolate excretion in 11 cyanobacteria showed that 8 strains, although grown and assayed in air, excreted glycolate. The largest quantities were excreted by the filamentous strains Plectonema boryanum 73110 and Anabaena cylindrica (Lemm). The carbon lost by excretion was at most 9% of the net fixed carbon in air for heterocystous cyanobacteria but increased (up to 60%) in some strains under a high pO2 (0.03 kPa CO2 in pure O2). A. cylindrica excreted glycolate at a maximum level of 2 and 10 μmol (mg chl a)−1 h−1 in air and at high pO2, respectively. The excretion continued for several hours. Increases in light intensity and pO2 and a shift in pH from 7 to 9 increased the amount of glycolate excreted. A. cylindrica also showed the most O2‐sensitive fixation of CO2. In vitro activity of phosphoglycolate phosphatase (EC 3.1.3.18) was found in all strains tested, with the highest activities noted for Gloeobacter violaceus 7.82 and Gloeothece 6909 and for young cultures of A. cylindrica. The lowest activities were found in Anabaena 7120 and Anacystis nidulans 625, strains excreting no or only minor quantities of glycolate.
Role of the outer tissue in abscisic acid‐mediated growth suppression of etiolated squash hypocotyl segments
Authors: Wakabayashi Kazuyuki , Sakurai Naoki , Kuraishi Susumu
Published: May 2006

Exogenously applied abscisic acid (ABA) substantially suppressed the elongation of hypocotyl segments of etiolated squash (Cucurbita maxima Duch. cv. Houkou‐Aokawaamaguri) after a 3 h lag period, without changes in the osmolalities of the apoplastic and symplastic solutions in the segment.

Segments with the outer tissues removed elongated more rapidly than unpeeled segments (whole segments). ABA did not suppress the elongation of peeled segments. When the segments were incubated in [14C]‐glucose, radioactivity was more effectively incorporated into the cell wall fractions of the outer than into those of the inner tissue. ABA significantly inhibited the incorporation of radioactivity into hermicellulose and cellulose of the outer tissue prior to the suppression of segment elongation, but it did not inhibit the incorporation into the pectic traction of the outer tissue or into any of the cell wall fractions of the inner tissue. These results indicate that ABA primarily affected the outer tissue, in which it specifically reduced the synthesis of hemicellulose and cellulose prior to the ABA‐mediated suppression of growth.
Photosynthetic reinvigoration of leaves following shoot decapitation and accelerated growth of coppice shoots
Authors: Tschaplinski Timothy J. , Blake Terence J.
Published: May 2006

Changes in photosynthesis and water relations of remaining leaves and regrowth over the first 50 days following shoot decapitation were studied in Populus deltoides Bartr. ×nigra L. I‐262 (DN22) and Populus maximowiczii×nigra L. MN9 to determine if these changes were correlated with the reinvigoration of growth that occurs after shoot decapitation. There was a 7‐fold increase in net photosynthesis of the remaining leaves 5 days after shoot removal, indicating a rapid, substantial reinvigoration. Diurnal photosynthetic patterns of retained stump leaves and new coppice leaves showed that decapitation increased the photosynthetic potential of tissue by increasing net photosynthetic rates in the early afternoon, thereby eliminating the post‐midday reduction typical of intact plants. The retained stump leaves exhibited lower midday xylem pressure potentials than comparable leaves on intact plants due to higher stomatal conductance, suggesting that an alleviation of plant moisture stress was not the cause of enhanced net photosynthesis of retained leaves. The results suggest that leaves of intact plants typically photosynthesize well below their capacity and that growth of new stump sprouts coincides with higher photosynthetic rates of coppice foliage.
The role of sink demand in carbon partitioning and photosynthetic reinvigoration following shoot decapitation
Authors: Tschaplinski Timothy J. , Blake Terence J.
Published: May 2006

Photosynthesis, growth, and carbon partitioning of vigorous coppice shoots were compared with the slower growing intact shoots of Populus maximowiczii×nigra L. MN9 to determine the relationship between carbon partitioning and photosynthetic rate. Relative height growth rate of coppice shoots was 2.2 times that of intact shoots with net photosynthetic rate 1.9 times that of intact shoots. Coppice leaves exported a larger proportion of newly‐fixed assimilate (11% compared with 6%) after a 4‐h chase. The greater export from coppice leaves was correlated with a greater proportion of [14C]‐labelled photosynthate deposited as starch in stems 4 cm below the point of label application. Coppice leaf assimilate levels were reduced to 15% that of leaves on intact plants, but coppice leaves had twice the concentration of labelled sucrose. Carbohydrates constituted 55% of the water‐soluble [14C]‐labelled photosynthate in leaves of coppice shoots compared with 40% in intact shoots. The results suggest that carbon allocation and partitioning in coppice shoots were altered towards production and export of new assimilate, and support the hypothesis that photosynthetic rate is responsive to sink demand for assimilates.
Stomatal response of hybrid poplar to incident light, sudden darkening and leaf excision
Authors: Ceulemans Reinhart , Hinckley T. M. , Impens I.
Published: May 2006

Responses of abaxial and adaxial stomata ofPopulus trichocarpaTorr. & Gray. × P.deltoidesBartr. (ex Marsh.) cv. Unal to incident light, sudden darkening and leaf excision in the light and in the dark were studied on 5‐year‐old trees in the field using diffusion porometry. Stomatal closure in the dark was found to be incomplete in most cases studies. Stomata closed after leaf excision in the dark within 90 min. Stomatal closure after darkening of an entire tree or an entire branch (white the rest of the tree was in the light) was slower, and complete stomatal closure was noticed only for adaxial stomata after 3 h. Adaxial stomata were more reactive and sensitive than abaxial stomata to sudden darkening and leaf excision in the light and the dark. In all treatments, stomatal response was more responsive in mature leaves than in young, still expanding leaves.
Changes in ethanol, lactate and malate content in Acer pseudoplatanus cells: effects of fusicoccin and O2 availability
Authors: Cerana Raffaella , Patti Vittoria , Lado Piera
Published: May 2006

Changes in the contents of ethanol, lactate and malate were determined at different activities of the plasma membrane H+ pump [in the presence and absence of fusicoccin (FC)] and at different O2 availability in cultured cells of Acer pseudoplatanus L. FC induced acidification of the medium under all tested conditions of O2 availability. At low O2 concentrations both ethanolic and lactic fermentations occurred, and FC markedly stimulated lactate production but had no effect on ethanol production. There was also a small, stimulating effect of FC on malate production. At high O2 concentrations no ethanol production was observed and lactate production was reduced. Under these conditions the stimulating effect of FC on lactate production decreased, while that on malate production increased. FC‐induced synthesis of lactate and malate is interpreted as depending on the activation of lactate dehydrogenase (EC 1.1.1.27) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (alkaline pH optima), respectively, due to the alkalinization of the cytoplasmic pH resulting from the stimulation of the H+ pump by FC. These results suggest that the balance between the two pH stat systems depends on the availability of O2.
Effect of acidic fog on needle surface and water relations of Picea abies
Authors: Mengel Konrad , Hogrebe Andreas M. R. , Esch Andreas
Published: May 2006

Young spruce trees [Picea abies (L.) Karst.) exposed to acidic fog (pH 3) showed a disintegration of the epicuticular waxes of the current year's needles as compared with trees treated with a fog of pH 5. The fog treatment was followed by a period in which the trees received different water supply. Under water stress conditions, trees that had been exposed to the acidic fog showed significantly higher transpiration rates than control trees that were treated with a fog of pH 5. The water loss of the controls was 0 at the middle of the photoperiod, while the trees pretreated with acidic fog still showed a substantial transpiration rate at this time. Water loss of excised twigs measured in the dry atmosphere of a desiccator also provided evidence that the water holding capacity of needles pretreated with acidic fog was affected. There is evidence that particularly the cuticular transpiration was increased by pretreatment with acidic fog. The xylem water potential of twigs pretreated with acidic fog was significantly lower than that of twigs pretreated with a fog of pH 5, while the osmotic potential was not affected by the different fog treatments. It is suggested that in draught years trees with a damaged cuticle caused by acidic fog will be affected in their resistance against water stress. In this way acidic fog could be involved in forest decline now widely spread in Central Europe.
The formation and translational activity of polysomes from developing lupin seeds
Authors: Gwóźdź Edward A. , Deckert Joanna E.
Published: May 2006

The formation and in vitro translational activity of total, free and membrane‐bound polysomes from various stages of developing cotyledons of yellow lupin seeds (Lupinus luteus L. cv. Iryd) has been investigated. The early stages of seed formation were characterized by a low level of polysomes that progressively increased. The main features of the cotyledons at the middle phase of development were full expansion growth and the highest amount of polysomes observed in all three poly so me fractions. In The final stages of emhryogenesis. the seed dehydration was accompanied by‐gradual loss of all types of polysomes, at which the membrane‐attached formations were degraded earlier than the free ones. By means of a wheat germ‐derived cell‐free system for protein synthesis, a correlation was demonstrated between cotyledon growth, polysome formation and their capacity for protein synthesis in vitro. As compared to the free polysomes, both the total and membrane‐bound formations were more active in protein synthesis in vitro. Analysis of the translational products by means of immunoprecipitation and gel electrophoresis followed by fluorography showed that only membrane‐bound polysomes produced polypeptides of higher molecular weight, including subunits of a legumin‐like protein.
Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response
Authors: Baumgartner Nicole , Fondeville Jean‐Claude
Published: May 2006

Baumgartner, N. and Fondeville, J. C. 1989. Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response.

A statistical evaluation of the hypocotyl hook opening (hook opening index) was used for measurement of the hook angle in lots of etiolated Sinapis alba L. cv. Albatros seedlings. Studies of the kinetics for hook opening were carried out in continuous fluorescent white, blue and red light (6, 15 and 40 μmol m‐2s‐1) with 2‐day‐old dark‐grown seedlings. At the beginning of the irradiation period the photoresponse in red light was the opposite to that in blue (low photon fluences). Blue rapidly induced the hook opening (in less than 20 min), while red produced hook tightening (photon fluences up to 70 mmol m‐2), which precedes the normal progressive hook opening. For low fluences, the data were consistent with the involvement of phytochrome and a specific blue light photoreceptor. A phytochrome effect was observed in the hook opening, dependent upon a high irradiance response (HIR). This HIR (like that for the inhibition of the hypocotyl elongation) was characterized by a wavelength response curve with maxima in the blue and far‐red regions of the spectrum.
Occurrence of protochlorophyll and its phototransformation to chlorophyll in mutant C‐2A’ of Scenedesmus obliquus
Authors: Kotzabasis Kiriakos , Schüring Max‐Peter , Senger Horst
Published: May 2006

The pigment mutant C‐2A’ of the unicellular green alga Scenedesmus obliquus accumulates protochlorophyllide and small amounts of protochlorophyll in darkness. Protochlororphyll was isolated and characterized by thin layer chromatography and absorption and fluorescence spectroscopy. The protochlorophyll was photoreduced by light to chlorophyll both in vitro and in vivo.
Effect of chlorocholine chloride and gibberellic acid on the anthocyanin synthesis in radish seedlings
Authors: Jain V. K. , Guruprasad K. N.
Published: May 2006

Anthocyanin synthesis in radish (Raphanus sativus L. cv. Scarlet Globe) seedlings after treatment with chlorocholine chloride (CCC) and gibberellic acid (GA) has been investigated. CCC promotes and GA3 inhibits the synthesis. When both substances are given together, CCC reverses the inhibition caused by GA3. Simultaneous external feeding of anthocyanin precursors (sucrose and phenylalanine) reverses the GA3 inhibition. A higher amount of total free amino acids, in particular phenylalanine, was present in CCC‐treated seedlings compared to controls grown on distilled water. The amount of phenylalanine was lower in seedlings treated with both CCC and GA3 as compared to seedlings treated with CCC alone, and total free sugars (reducing plus non‐reducing) was lower in CCC treated seedlings than in controls grown on distilled water. We conclude that CCC and GA3 control the anthocyanin synthesis at the level of precursors.
Plant growth analysis: towards a synthesis of the classical and the functional approach
Authors: Poorter Hendrik
Published: May 2006

A method of calculating relative growth rates (RGR) and net assimilation rates is presented. The method is based on the fitting of a polynomial through the relative growth rate values calculated by the ‘classical’ approach rather than through the In‐transformed plant weights as in the ‘functional’ method. Additional ways of reducing the harvest‐to‐harvest variation characteristic of the classical approach are discussed. The main advantages of the present approach over the functional one are: (1) The degree of the polynomial can be increased (within certain limits) without inducing spurious fluctuations in RGR. Thus, quite complex trends in RGR can be described. (2) There is little interference between RGR values in different parts of the experiment. The main advantages over the classical approach are: (1) The erratic fluctuations in RGR are dampened. (2) As frequent small harvests are allowed, the workload at each harvest can be diminished and a more reliable impression of ontogenetic drift in RGR can be obtained. (3) RGR is described by a continuous function, thus facilitating further calculations and compilations.
Effect of the auxin, 2‐(2‐methyl‐4‐chloro‐phenoxy)propionic acid, on cell cycle regulation in maize embryonic tissues
Authors: Baíza Ana María , Sànchez‐de‐Jiménez Estela
Published: May 2006

During seed maturation, cells from embryonic tissues stop division at different phases of the cell cycle. In maize, neither these phases nor the effect of exogenous auxin on them are known. Disinfected whole maize (Zea mays L. Mexican commercial hybrid H30) seeds or sectioned embryonic axes were incubated in Murashige and Skoog medium, with or without 2‐(2‐methyl‐4‐chlorophenoxy)propionic acid (MCPP), a synthetic auxin. For some in vitro experiments, radioactive [3H]‐thymidine was also added. After the stated incubation period, meristems of mesocotyl, primary and seminal roots from embryonic axes were dissected, fixed, and analyzed under a microscope. The percentage of mitotic indices was recorded. In the labeling experiments, labeled and non‐labeled percentage of mitotic figures (MI %) were determined. It was found that cell division is a programmed event in the meristematic tissues of maize embryonic axes. Populations of cells entering cell division were obseved during the germination process. The mesocotyl was the first tissue to divide, followed by seminal and primary roots.

Meristematic cells from dry embryos are arrested during the G2 and G1 phases of the cell cycle. MCPP has a differential effect, stimulating G2 cells to enter cell division. It is concluded that MCPP might regulate the cell cycle at specific points.
Relation of cell wall peroxidase activity with growth in epicotyls of Cicer arietinum. Effects of calmodulin inhibitors
Authors: Sanchez Oskar J. , Pan Alberto , Nicolás Gregorio , Labrador Emilia
Published: May 2006

Sánchez, O.J., Pan, A., Nicolás, G. and Labrador, E. 1989. Relation of cell wall peroxidase activity with growth in epicotyls of Cicer arietinum. Effects of calmodulin inhibitors.

Peroxidases are bound ionically to cell walls in epicotyls of Cicer arietinum L. cv. Castellana. The cell wall peroxidase activity increases during the growth of epicotyls, being the lowest in 3‐day‐old epicotyls with high growth capacity. The cell wall phenolic compounds, postulated natural substrates of cell wall peroxidases, also increase during growth.

The calmodulin inhibitors chlorpromazine and trifluoperazine decrease the elongation rate of epicotyls of Cicer arietinum. These inhibitors also cause an increase in the cell wall peroxidase activity and in the level of phenolic compounds. A possible regulatory effect of calmodulin on peroxidase activity is postulated.