bluuebunny/crossref_metadata_2025 huggingface dataset:
Site of graviperception in roots: a re‐examination
Authors: Poff Kenneth L. , Martin Hilary V.
Published: May 2006

Two lines of evidence have been cited to support the assertion that the root cap is the sole site of graviperception in the root. The first evidence is based on surgical removal of the cap, which abolishes the response to gravity. This is sufficient to conclude that the cap is involved in gravitropism, but not to conclude that the cap is the site of graviperception. The second is based on the results of centrifugation experiments, in which different parts of the plant are subjected to different centrifugal forces. The data from such experiments have been cited to support the conclusion that the perception of gravity is limited to the rootcap. However, these data actually support the conclusion that gravity is perceived throughout the root tip, and not only in the root cap. We believe that the data support the conclusion that the root cap is involved in root gravitropism, but that there is inadequate evidence to conclude that the cap is the sole site of graviperception.
Apoplastic domains and sub‐domains in the shoots of etiolated corn seedlings
Authors: Epel Bernard L. , Bandurski Robert S.
Published: May 2006

Light Green, an apoplastic probe, was applied to the cut mesocotyl base or to the cut coleoptile apex of etiolated seedlings of Zea mays L. cv. Silver Queen. Probe transport was measured and its tissue distribution determined. In the mesocotyl, there is an apoplastic barrier between cortex and stele. This barrier creates two apoplastic domains which are non‐communicating. A kinetic barrier exists between the apoplast of the mesocotyl stele and that of the coleoptile. This kinetic barrier is not absolute and there is limited communication between the apoplasts of the two regions. This kinetic barrier effectively creates two sub‐domains. In the coleoptile, there is communication between the apoplast of the vascular strands and that of the surrounding cortical tissue. No apoplastic communication was observed between the coleoptile cortex and the mesocotyl cortex. Thus, the apoplastic space of the coleoptile cortex is a sub‐domain of the integrated coleoptile domain and is separate from that of the apoplastic domain of the mesocotyl cortex.
Relation between relative growth rate, endogenous gibberellins, and the response to applied gibberellic acid for Plantago major
Authors: Dijkstra Paul , Ter Reegen Harrie , Kuiper Pieter J. C.
Published: May 2006

Relationships between relative growth rate (RGR), endogenous gibberellin (GA) concentration and the response to application of gibberellic acid (GA3) were studied for two inbred lines of Plantago major L., which differed in RGR. A4, the fast‐growing inbred line, had a higher free GA concentration than the slow‐growing W9, as analyzed by enzyme immunoassay. GA3 application increased total plant weight and RGR3 particularly for the slow‐growing line. Chlorophyll a content and photosynthetic activity per unit leaf area were decreased, while transpiration rate was unaffected by GA3 application. The increase in RGR by GA3 application was associated with an increased leaf weight ratio; specific leaf area and percentage of dry matter in the leaves were only temporarily affected. Root respiration rate per unit dry weight was unaffected.

The correlation between low RGR, low GA concentration and high responsiveness to applied GA3 supports the contention that gibberellins are involved in the regulation of RGR. However, the transient influence of GA3 application on some growth components suggests the involvement of other regulatory factors in addition to GA.
Effect of low growth temperature on coupling between electron transport and proton flux in Vicia faba thylakoids
Authors: Hopkins W. G.
Published: May 2006

Coupling between electron transport and proton flux has been compared in chloroplasts from Vicia faba (cv. Windsor) plants grown at 20 and 5°C. Proton uptake by warm‐grown thylakoids was sensitive to external pH and stimulated by micromolar adenine nucleotide above pH 7.0. Electron transport was modulated by pH, adenine nucleotide and energy transfer inhibitors (triphenyltin and Hg2+). By contrast, proton uptake by cold‐grown thylakoids was generally lower and was insensitive to micromolar ATP. The rate of non‐phosphorylating electron flow in cold‐grown thylakoids was relatively insensitive to pH and Hg2+ and was not modulated by adenine nucleotides or triphenyltin. Stimulation of electron transport by phosphorylating conditions in cold‐grown thylakoids was generally lower and insensitive to pH. It is concluded that the control of proton efflux through CF0‐CF1 differs in thylakoids of V. faba grown at warm and cold temperatures.
Growth and development of Brassica genotypes differing in endogenous gibberellin content. II. Gibberellin content, growth analyses and cell size
Authors: Rood Stewart B. , Zanewich Karen P. , Bray Doug F.
Published: May 2006

Three rapid cycling Brassica rapa genotypes were grown in greenhouse conditions to investigate the possible relationships between endogenous gibberellin (GA) content and shoot growth. Endogenous GA1 GA3 and GA20 were extracted from stem samples harvested at 3 weekly intervals and analyzed by gas chromatography‐mass spectrometry with selected ion monitoring, using [2H2]‐GA1 and [2H2]‐GA20 as quantitative internal standards. During the first 2 weeks, GA levels of the dwarf, rosette (ros), averaged 36% of levels in normal plants (on a per stem basis). Levels in the tall mutant, elongated internode (ein), were consistently higher, averaging 305% of levels in normal plants.

Differences in shoot height across the genotypes resulted from varying internode length which resulted from epidermal cell length and number being increased in ein and decreased in ros relative to the normal genotype. The exogenous application of GA3 to normal plants increased cell length while the application of paclobutrazol (PP333), a triazole plant growth retardant, reduced cell size. Thus, exogenous GA manipulations mimicked the influence of the mutant genes ros and ein. The dwarf, ros, had reduced shoot dry weights and relative growth rates compared to the other genotypes. Total dry weights were similar in ein and the normal genotype but stem weights were increased in ein, compensating for decreased leaf weights. Thus, the gibberellin‐deficiency of ros resulted in generally reduced shoot growth. The overproduction of endogenous GA by ein did not result in enhanced shoot growth but rather a specific enhancement of internode elongation and stem growth at the expense of leaf size.
Direct isolation of vacuoles from leaf tissue of lettuce (Lactuca sativa) retaining protoplasts within the leaves
Authors: Blom‐Zandstra Margaretha , Koot Hans T. M. , van Hattum Joke
Published: May 2006

A procedure is described in which vacuoles are isolated from leaf tissue of lettuce (Lactuca sativa L.). After incubation in an enzyme solution, the vacuoles are directly extracted from the leaf tissue by osmotic shock using a phosphate buffer. In this method no protoplasts are released from the leaf tissue. This procedure avoids the problems of separating vacuoles from protoplasts with similar density. To evaluate the purity of the vacuoles, the activity of glucan synthetase 11 (EC 2.4.1.34), NAD(P) H‐cytochrome c reductase (EC 1.6.99.3) and malate dehydrogenase (EC 1.1.1.37) was measured. To measure vanadate‐ and nitrate‐sensitive ATPase activity (EC 3.6.1.8) vesicles were prepared from the vacuoles and ATP‐dependent vesicle acidification was measured as acridine orange quenching. Nitrate inhibited the quenching, while addition of vanadate had no effect. It was concluded that the vacuoles were not contaminated with plasma membranes. To evaluate the viability of the vacuoles [14C]‐malate uptake was measured. The vacuoles showed a constant rate of [14C]‐malate uptake during 45 min. This rate was maximal at pH 6.8.
Low external pH replaces 2,4‐D in maintaining and multiplying 2,4‐D‐initiated embryogenic cells of carrot
Authors: Smith David L. , Krikorian A. D.
Published: May 2006

A mixed culture comprised of both embryonic globules and nonembryogenic callus. was derived from seedling hypocotyls of Daucus carota cv. Scarlet Nantes on 2,4‐D‐containing medium using well‐established methods. Then the mixed cultures were transferred to, and serially subcultured on, a hormone‐free medium near pH 4. The medium contained 1 mM NH+ as the sole nitrogen source. When cultured in this way, embryonic globules were able to multiply without development into later embryo stages Nonembryogenic callus did not survive. Continuous culture of embryonic globules on this low pH hormone‐free medium yielded cultures consisting entirely of preglobular stage proembryos (PGSPs). PGSP cultures have been maintained as such with continuous multiplication for nearly 2 years without loss of embryogenic potential. These hormone‐free‐maintained PGSPs continue their development to later embryo stages when cultured on the same hormone‐free medium buffered at pH 5.8. We show that hormone‐free medium near pH 4 can replace 2.4‐D in its ability to sustain multiplication of 2,4‐D‐initiated embryogenic cells of carrot at an acceptable growth rate without their development into later embryo stages. This procedure provides selective conditions that do not permit the growth of nonembryogenic cells while providing an adequate environment for embryogenic cell proliferation and should prove invaluable in studying habituation.
Effect of gibberellic acid on epicotyl growth and carbohydrate distribution in derooted Pisum sativum cuttings with or without cotyledons
Authors: Miyamoto Kensuke , Kamisaka Seiichiro
Published: May 2006

The effect of gibberellic acid (GA) on subhook growth in derooted cuttings of pea (Pisum sativum L. cv. Alaska) grown in the dark was studied in relation to the distribution of sugar‐related compounds in the epicotyl and cotyledons. GA stimulated subhook growth of cuttings with or without cotyledons. In cuttings with cotyledons, the net inflow of sugar‐related compounds (soluble sugars, starch, cell wall polysaccharides and sugars consumed by respiration) to the epicoiyl balanced with the net outflow from the cotyledons. GA stimulated the net inflow of sugar‐related compounds to the epicotyl and the net outflow from cotyledons. Among these compounds, GA substantially increased the amount of soluble sugars, starch and cell wall polysaccharides in the subhook. In cuttings without cotyledons, on the other hand, the net inflow of sugar‐related compounds to the subhook almost balanced with the net outflow from the epicotyl below the subhook. GA stimulated the net inflow of sugar‐related compounds to the subhook and the net outflow from the epicotyl below the subhook. Among these compounds, GA substantially increased the amount of soluble sugars and cell wall polysaccharides in the subhook. These results suggest that GA stimulates an increase in the net inflow of sugar‐related compounds to the subhook, thereby preventing an increase in osmotic potential and stimulating cell wall polysaccharide synthesis, when pea subhook growth is stimulated.
Brassinolide‐induced elongation and auxin
Authors: Sasse Jenneth M.
Published: May 2006

Segments from the hook and subhook zone of the stem of 6‐day‐old etiolated Pisum sativum L. cv. Victory Freezer seedlings were used to study the relationship between brassinolide and auxin in the promotion of elongation. Minor changes in exogenous indole‐3‐acetic acid or4‐chloroindole‐3‐acetic acid concentration affected the kinetics markedly and the ethylene generator ethephon overcame brassinolide‐induced elongation in an antagonistic interaction. Brassinolide‐induced elongation was markedly inhibited by low concentrations of the cellulose biosynthesis inhibitor 2,6‐dichlorobenzonitrile, and diagnostic concentrations of the antiauxin 2‐(p‐chlorophenoxy) isobutyric acid did not affect brassinolide‐induced elongation. As the characteristics of auxin‐induced growth are not displayed in brassinolide‐induced elongation of the upper stem segment, it is proposed that brassinolide does not depend on auxin as a mediator in the promotion of elongation of younger tissues but that it can interact in a very complex manner with auxin. In the elongation of more mature tissues, and in bending responses, brassinolide probably accelerates auxin effects. When split, the upper stem segment was unusual in its lack of specific response to growth regulators, and the slight relief of epidermal tension.
Beneficial interaction between photosynthesis and respiration in mesophyll protoplasts of pea during short light‐dark cycles
Authors: Vani T. , Reddy M. Malla , Raghavendra A. S.
Published: May 2006

The respiratory uptake or photosynthetic evolution of oxygen by mesophyll protoplasts of pea (Pisum sativum L. cv. Arkel) were monitored during successive short. (3–5 min) cycles of darkness and illumination. The rate of respiration was nearly doubled after 3–4 short periods of illumination while there was a 15–20% enhancement in photosynthesis with cycles of illumination and darkness preceding illumination. Such interaction between photosynthesis and respiration was statistically significant when bicarbonate was present in the reaction medium. The inhibitors of photosynthesis [3(3,4–dichlorophenyl)‐l,l‐dimethylurea (DCMU), glyceraldehyde] decreased respiration after periods of illumination, whereas inhibitors of respiratory electron transport (Rotenone, antimycin A, NaN3) suppressed photosynthesis, as well. We suggest that a rapid beneficial interaction exists between photosynthesis and respiration in protoplasts, even during short cycles of light and darkness.
Indole‐3‐acetaldehyde reductase in Phycomyces blakesleeanus. Characterization of the enzyme
Authors: Ludwig‐Müller Jutta , Schramm Peter , Hilgenberg Winy
Published: May 2006

lndole‐3‐acetaldehyde reductase (lAAld reductase EC 1.2.3.1) from Phycomyces blakesleeanus Bgff., a 38 kDa polypeptide as determined by gel filtration, is probably localized in the cytoplasm. The formation of indole‐3‐ethanol (lEt) is dependent on the presence of NAD(P)H. The enzymatic reduction of IAAId shows a pH optimum between 6 and 8 and a temperature optimum at 30°C. Enzyme activity follows Michaelis Menten kinetic (Km= 200 μM for IAAId; Km= 24 μM for NADPH). The isoelectric point of the IAAId reductase is at pH 5.4. Phenylacetaldehyde and benzaldehyde are competitive substrates. Hydroxymeihylindole promotes the reductive IEt formation, whereas NADP+ is a non‐competitive inhibitor. Changes in lAAJd reductase activity correlate with certain developmental stages of the fungus.
Measurements of redox activity at the plasmalemma
Authors: Rubinstein Bernard , Stern A. I. , Chalmers J. D. C.
Published: May 2006

Studies of the components and role of redox activity at the plasmalemma are dependent on the use of sensitive assay procedures. Many methods have been developed to measure redox activity, but special problems arise when the plasmalemma is the focus of the investigation. In this review, the methods and probes for analyzing electron transport at the plasmalemma are critically evaluated. Determinations of hydrogen peroxide are also included, although no firm evidence exists that the appearance of this substance is dependent on transplasmalemma electron transport. Procedures include those based on light absorption (spectrophatometric) and electrical changes (polarographic, potentiometric, amperometric/coulometric), as well as those dependent on radioactive, fluorescent, light emitting and electron spin resonance probes. The estimation of proton fluxes in the presence of redox probes is also considered. It is concluded that measurements of redox activity at the plasmalemma can be performed on tissues, cells, membrane vesicles and solubilized preparations, but no one procedure is ideal; furthermore, care must be taken to insure that the probes themselves are not altering the system being studied.
Glycine metabolism by plant mitochondria
Authors: Oliver David J. , Neuburger Michel , Bourguignon Jacques , Douce Roland
Published: May 2006

The predominant substrate oxidized by plant leaf mitochondria in the light is glycine. These mitochondria have evolved specific mechanisms to support this metabolic function including a glycine/serine transporter, high concentrations of the glycine decarboxylase multienzyme complex (EC 2.1.2.10) and the enzyme serine hydroxymethyltransferase (EC 2.1.2.1), and a high‐capacity, high‐specificity oxaloacetate transporter that shuttles out NADH produced by glycine oxidation. Transcription of the genes for the glycine decarboxylase complex is under both temporal and spatial control and they are expressed predominantly in green leaf tissue. This is an example of an unusual light‐induced mitochondrial protein that responds like the chloroplast enzymes involved in photosynthesis.
Are‐examination of NaCI effects on phosphoenolpyruvate carboxylase at high (physiological) enzyme concentrations
Authors: Manetas Yiannis
Published: May 2006

Inhibition of phosphoenolpyruvate carboxylase (EC 4.1.1 31) from the C4‐halophyte Salsola soda L. by NaCI is compeutive to phosphoenolpyruvate (PEP). Physiological (betaine, glycerol) and synthetic (polyethylene glycol) osmotica and the allosteric activator glucose‐6‐phosphate (G6P) increase the apparent affinity of the enzyme for PEP and also alleviate the inhibition by NaCl. Physiological osmotica that either increase the Km(PEP) (proline) or are neutral (sorbitol), do not protect the enzyme against NaCI attack. In the absence of cosolutes and, G6P, the enzyme is self‐protected when its concentration in the assay medium is increased to more physiological values. In addition, the amount of betaine needed for complete protection is inversely related to native protein concentration in the assay. Exogenous protein (bovine serum albumin or bovine skin gelatin) have no effect on either Km(PEP), or extent of NaCl inhibition. These results can be better explained with the exclusion volume theory and the inferred assumption that both cosolutes and high protein concentration strengthen intrinsic aggregation properties of enzymes. It is suggested that the extremely high phosphoenolpyruvate carboxylase concentration in the cytoplasm and the accumulation of compatible solutes in response to water stress fully protect the enzyme in vivo against the chaotropic effects of NaCI.
Characterization of the 12S storage protein of Brassica napus (cruciferin): Disulfide bonding between subunits
Authors: Rödin Joakim , Rask Lars
Published: May 2006

Cruciferin (12S globulin) is a large, neutral, oligomeric protein synthesized in rapeseed (Brassica napus) during the seed development. It is composed of six subunit pairs. Each pair consists of one heavy α chain (30 kDa) and one light β chain (20 kDa). Four different subunit pairs exist. In contrast to earlier studies, our investigations using two‐dimensional electrophoresis showed, that the majority of α and β chains of each subunit are disulfide‐linked. Analysis of subunit composition of cruciferin hexamers by ion‐exchange chromatography suggested that a large array of hexamers exist, composed of mixed combinations of the four subunits.
Variation in organic and mineral components in young Eucalyptus seedlings under saline stress
Authors: Prat Daniel , Fathi‐Ettai Riyad Abdullah
Published: May 2006

Salt (NaCl) tolerance of 3 eucalypt species (Eucalyptus alba Reinw. ex Bl., E. camaldulensis Dehnh and E. microtheca f.v. Muell.) was studied: three‐month‐old seedlings grown in a greenhouse were watered by a saline solution (up to 700 mM) for 1 month. Mineral, water and sugar contents were highly affected by the saline stress. Sodium, K and Ca were accumulated in the leaves. No significant differences were found between E. camaldulensis and E. microtheca, the tolerant species, in water and mineral contents. Sugar contents were greater in E. microtheca. In E. microtheca Na was highly accumulated in roots [up to 910 μmol (g fresh weight)−1], less in stems [up to 580 μmol (g fresh weight)‐1] and leaves [up to 410 μmol (g fresh weight)−r]. Chloride was also accumulated, its content was greater than the total content of Na and K, especially in the salt‐tolerant provenance. Potassium and Ca contents were variously affected by the saline stress whereas soluble protein, amino acid and sugar contents were increased. Just after the saline stress, plants showed a large increase in the Na content of the leaf while the decrease in the K content of the stem and leaf continued. Plants were killed by the stress, probably because of too high accumulation of Na in leaves or roots according to the provenance. Osmoregulation and especially the participation of Na are discussed.
The involvement of a G‐protein in phytochrome‐regulated, Ca2+‐dependent swelling of etiolated wheat protoplasts
Authors: Bossen Margreet E. , Kendrick Richard E. , Vredenberg Willem J.
Published: May 2006

The red light (R)‐induced swelling of mesophyll protoplasts, isolated from dark‐grown wheat (Triticum aestivum L. cv. Arminda) leaves, was inhibited by guanosine‐5′‐0‐(2‐thiodiphosphate) (GDP‐β‐S). In darkness or after control irradiation with far‐red light (FR), guanosine‐5′‐O‐(3‐thiotriphosphate) (GTP‐γ‐S) induced swelling to the same extent as after R. Both GDP‐β‐S and GTP‐γ‐S were introduced into the cytoplasm by means of electroporation. The possibility of R‐induced activation of the phosphatidylinositol pathway of transmembrane signalling was investigated. Neomycin, Li+ and l‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine (H7) inhibited the R‐induced swelling. Phorbol 12‐myristate 13‐acetate (PMA) induced swelling after control irradiation with FR. Neomycin and Li+ also inhibited GTP‐γ‐S‐induced swelling. These results suggest that a GTP‐binding protein is involved in the phytochrome‐regulated swelling response. Addition of N6, 2′‐0‐dibutyryladenosine 3′:5′‐cyclic monophosphate (DB‐cAMP) induced swelling to the same extent as R‐irradiation. The calmodulin antagonist N‐(6‐aminohexyl)5‐chloro‐l‐naphthalenesulfonamide (W7) induced swelling after FR, while R‐induced swelling was not affected. The less active analogue N‐(6‐aminohexyl)‐l‐naphthalenesulfonamide (W5) induced no swelling after FR. It is speculated that the protoplast volume is correlated with the cytoplasmic concentration of free Ca2+.
Effect of broad‐band ultraviolet and visible radiation on hydrogen peroxide formation by cultured rose cells
Authors: Murphy Terence M.
Published: May 2006

Broad‐band radiation from a high‐pressure Hg‐vapor lamp, including ultraviolet wavelengths from 290 to 400 nm, blue, green and red wavelengths, did not induce the synthesis of H2O2 in cultured rose cells. This was in contrast to the effects of shortwave (254 nm) ultraviolet radiation, even though, like shortwave ultraviolet radiation, the UV‐B component of the broadband radiation induced a striking K+ efflux from the cells, and this efflux has been associated with H2O2 synthesis in a previous report. The UV‐A and visible wavelengths were shown to inhibit the synthesis of H2O2. This effect was associated with inhibition of peroxidase, an enzyme reported to be involved in the synthesis of H2O2 in cell walls. UV‐B radiation inhibited the alternate pathway for mitochondrial electron transport, but there was no evidence that this effect contributed to the inhibition of H2O2 synthesis in cells treated with broad‐band radiation.
Influence of temperature on root development and phosphate influx in winter wheat grown at different P levels
Authors: Aðalsteinsson Sveinn , Jensén Paul
Published: May 2006

Root development was studied in winter wheat (Triticum aestivum L. cv Starke II) grown at 5,10, 15 and 20°C in nutrient solutions with phosphate concentrations of 10, 100 or 1000 μM. The plants were grown for 38 days (5 and 10°C), 19 days (15°C) or 14 days (20°C). At the end of the cultivation period the phosphate influx in the roots was determined with 32P‐phosphate. Root development (lateral and seminal roof length and number) was monitored throughout the cultivation period on the same individuals by repeated (approximately every second day) photocopying of the roots for measurements with digitizer and appropriate software. The 5°C treatment yielded no laterals, and the seminals were only slightly affected by the different phosphate treatments. The 10 μM phosphate treatment gave high root:shoot dry weight ratio, high average lateral root length and high specific root length [m root (g root fresh weight)‐1]. The 1000 μM phosphate treatment yielded the highest number of laterals per m seminal root, and usually also the highest absolute numbers. Phosphate influx decreased with increased P status of the roots. It is argued that phosphate influx is dependent on factors such as P status, root geometry and relative root extension rate.
Lipid biosynthesis in seeds of mustard (Brassica juncea) influenced by zinc and sulphur deficiency
Authors: Munshi S. K. , Vats Seema , Dhillon K. S. , Sukhija P. S.
Published: May 2006

In developing seeds of mustard (Brassica juncea L. cv. RLM 198) the period between 20 and 30 days after fertilization (DAF) was identified as the period of active lipid biosynthesis, although dry matter continued to accumulate until maturity. The period of lipid synthesis was associated with a decrease in starch, soluble sugars and protein, thus, giving rise to precursors for the biosynthesis of lipids. Besides decreasing the dry matter content (on both % and seed basis), Zn and S deficiency caused a significant (P > 0.05) reduction in oil content. As compared to control, the decrease in oil content was 11, 12 and 18% at 30 DAF and 4, 9 and 16% at maturity in Zn, S and (Zn+S) deficient treatments, respectively. Throughout the period of seed development, a significant decrease in starch and protein with a slight accumulation of soluble sugars was observed due to deficiency of Zn or S. The rate of [l‐14C]‐acetate incorporation into total lipids, which was maximal at 30 DAF, also displayed a significant decrease due to the abovementioned mineral deficiencies. Addition of Zn or S in vitro, enhanced the lipid synthesis at all stages of seed development. Under Zn and S deficiency, the phospholipids increased from 10 to 30 DAF and then declined until maturity. However, the proportion of glycolipids and free fatty acids increased, with a corresponding decrease in total glycerides. Further, in deficiency treatments, there was an increase in 22:1 with a corresponding decrease in 18:1, 18:2 and 18:3 in developing and mature mustard seeds.
Boron is required for the stimulation of the ferricyanide‐induced proton release by auxins in suspension‐cultured cells of Daucus carota and Lycopersicon esculentum
Authors: Goldbach Hciner E. , Hartmann Dorothea , Rötzer Thomas
Published: May 2006

Boron deficiency reduces the ferricyanide‐induced net proton release of suspension‐cultured carrot (Daucus carota L.) and tomato (Lycopersicon esculentum Mill.) cells by more than 50%. This effect is reversed within 60 to 90 min by the addition of B. Vanadate (400 μM) completely suppresses the proton release, indicating an ATPasedriven process. The differences between B treatments do not appear when auxins are omitted from the experimental solution, but can be observed within less than 30 min after the addition of auxin to auxin‐deficient cell cultures. This suggests, that an adequate supply of B is required for the auxin action to take place. The results are discussed with respect to the primary functions of B in membranes and transport processes, and its possible influence on auxin‐induced metabolic events.
The light‐induced unrolling of the grass leaf — A study of polarity, light‐piping and stimulus transmission
Authors: Virgin Hemming I.
Published: May 2006

Primary leaves of dark‐grown barley (Hordeum vulgare L. cv. Weibull's Ida) unroll in darkness when cut into sections shorter than about 2 cm; the shorter the more unrolling. The unrolling pattern of irradiated leaf sections longer than about 2 cm indicates a polarity in the leaves: the top end of the basal section of a divided leaf unrolls more than the base end of the distal section. Earlier reported findings of a stimulus transmission from irradiated to non‐irradiated areas can be fully explained by light‐piping and by mechanical, mutual influence between irradiated and non‐irradiated areas.
Effect of low nitrate supply to nodulated lucerne on time course of activites of enzymes involved in inorganic nitrogen metabolism
Authors: Arrese‐Igor C. , García‐Plazaola J. I. , Hernández A. , Aparicio‐Tejo P. M.
Published: May 2006

Plants of lucerne (Medicago sativa L. cv. Aragón) inoculated with several strains of Rhizobium meliloti were supplied with a low level of nitrate (5 mM). After 1 week, normalised nodule mass, obtained by dividing nodule weight by shoot weight, was decreased by one‐fourth. This result closely paralleled the bacteroid protein content of nodules, whereas the cytosolic content remained constant. Nitrate reductase activity (NRA, EC 1.7.99.4) of bacteroids increased rapidly after nitrate supply, with actual rates being highly dependent on the Rhizobium strain. The expression of cytosolic NR (EC 1.6.6.1) also varied depending on the bacterial strain but was largely insensitive to nitrate feeding. Nitrite reductase activity (NiRA, EC 1.7.2.2) of either bacteroid or plant origin was independent of the R. meliloti strain. Activation occurred after 3 and 7 days, respectively, of nitrate feeding. Significant amounts of nitrite were obtained throughout the experimental period from buffered extracts of both bacteroids and cytosol of nodules. However, when these nodules were ground in the presence of inhibitors of enzyme activity, nitrite was only found in nodules containing strain 102‐F‐51 after 1 week of treatment. These results agree with the recent hypothesis that nitrite plays a role in a secondary stage of nodule damage by nitrate. We propose that NiRA rather than NRA can be used as an internal probe of nitrate access to the infected region of nodules.
Expression of chloroplast photosynthesis genes during leaf senescence
Authors: Bate Nicholas J. , Straus N. A. , Thompson J. E.
Published: May 2006

Transcripts for thylakoid proteins encoded in the chloroplast genome that show decreased synthesis in senescing primary leaves of bean (Phaseolus vulgaris) have been examined by Northern and dot blot analyses. In young, 7‐day‐old leaves pulse‐labelled with 35S‐methionine, all of the major chloroplast DNA‐encoded thylakoid proteins become radiolabelled, including the 68 kDa protein of PSI encoded by psaAl and psbA2, the D‐1, D‐2, CP47 and CP43 proteins of PSII encoded by psbA, psbD, psbB, and psbC, respectively, and cytochrome f and cytochrome b6 encoded by petA and petB, respectively. By contrast, in pulse‐labelled, senescent 28‐day‐old leaves, the only chloroplast‐encoded thylakoid protein showing active synthesis is the D‐1 protein of PSII. Total RNA levels decline by ≅ 9 fold between 7 and 28 days on a fresh weight basis. Dot blot analyses using gene‐specific hybridization probes indicate that steady state transcript levels for all of the chloroplast DNA‐encoded proteins examined maintain the same proportion of total RNA over this period. This means that these transcripts also decline by =9 fold between 7 and 28 days. Thus, reduced synthesis of the 68 kDa protein of PSI, the CP47 and CP43 proteins of PSII, cytochrome f and cytochrome b6 can presumably be attributed, at least in part, to a decline in steady state levels of corresponding message. It is apparent from Northern blot hybridizations that there are also qualitative changes in transcript pattern for petA, psbC and psbD between 7 and 28 days that perhaps reflect alterations in post‐transcriptional processing. These alterations may also contribute to the decreased synthesis of the CP43 protein and cytochrome f. The continued active synthesis of the D‐1 protein of PSII in the senescent 28‐day‐old leaves, despite the =9 fold decrease in the steady state level of its transcript, suggests that the psbA transcript is preferentially translated relative to transcripts for other chloroplastencoded thylakoid proteins.
Mechanism of the inhibition of phloem loading by sodium sulfite: Effect of the pollutant on the transmembrane potential difference
Authors: Maurousset Laurence , Bonnemain Lean‐Louis
Published: May 2006

Sodium sulfite (Na2SO3) decreased uptake from 1 mM sucrose by the parenchyma and by the veins of leaves of broadbean (Vicia faba L. cv. Aguadulce). The decrease depended on the concentration of the pollutant and the duration of pretreatment. The inhibition was non‐competitive. Sulfite affected the transmembrane potential difference (PD) of the leaf tissues. The short‐term response obeyed an ‘all or nothing’ law. At 0.1 mM and above, sulfite led to a quick depolarization of one‐third of the initial potential after a lag phase of about 5 min; for concentrations lower than 0.1 mM, sulfite did not affect the potential. By contrast, the long‐term effect of Na2SO3 on the transmembrane PD strongly depended on its concentration. After 2–12 h of pretreatmemt there was no effect at 10 μM, a weak effect at 0.1 mM, and then increasing depolarization as the pollutant concentration increased. The inhibitory effect of Na2SO3 on sucrose uptake is thus, at least partly, due to its effect on a component of the proton‐motive force. ΔΨ. However, the lack of correlation noticed with 0.1 mM Na2SO3 between the effect on sucrose uptake and the long‐term effect on transmembrane PD suggests numerous sites of sulfite action.
Short‐term effects of manipulating the source:sink ratio of white clover (Trifolium repens) plants on export of carbon from, and morphology of, developing leaves
Authors: Chapman D. F. , Robson M. J. , Snaydon R. W.
Published: May 2006

The source:sink ratio of clonal white clover (Trifolium repens L.) plants was manipulated by shading or removing leaves, and the consequences for carbon export from, and for the weight, area and net photosynthesis of, developing leaves were determined. When treatments were imposed just before young leaves usually change from C sinks to C sources, no effect on the point at which the sink‐to‐source transition occurred was observed, Leaves exported a similar proportion of the C they fixed, irrespective of stresses imposed upon the rest of the plant. However, differences in the destination of exported C were observed. More C moved to the stolon apex, and less to the stolon tissue itself, from leaves at Carlson stage 0.8 (leaflets about 60% unfolded) when mature leaves were removed or shaded. When 2 out of 3 mature leaves were removed from a stolon, short‐term responses such as a 10% increase in net photosynthesis of the residual mature leaf, and greater export of C from this leaf to the apex, partially compensated very young leaves for loss of C supply. The result was that, when these young leaves were fully unfolded, they had similar surface area to those which had developed on undefoliated plants, but weighed nearly 20% less. Thus the immediate response to defoliation was an increase in the speeific leaf area [cm2 (g of dry weight)−1] of new leaves, and the assimilation rate (net photosynthesis×area) of these leaves remained unchanged.
EDU and ozone protection: Foliar glycerolipids and steryl lipids in snapbean exposed to O3
Authors: Whitaker Bruce D. , Lee Edward H. , Rowland Randy A.
Published: May 2006

Effects of the antiozonant EDU, N‐[2‐(2‐oxo‐1‐imidazolidinyl) ethyl]‐N'‐phenylurea, on the content and composition of foliar lipids in snapbean (Phaseolus vulgaris L. cv. Bush Blue Lake 290) before and after a single, acute ozone (O3) exposure were assessed. Pretreatment with EDU conferred protection against O3‐induced necrosis and losses of glycerolipids and chlorophyll. Systemic treatment of snapbean plants with EDU did not significantly alter membrane lipids in the first trifoliate leaf. Leaves of untreated controls had lost ca 50% of both galacto‐ (GL) and phospholipids (PL) by the end of a 3 h exposure to 0.4 μl l−1 O3. A decline in the ratio of mono‐ to di‐galactosyldiacylglycerol (MGDG/DGDG) was associated with the loss of GL, and a decline in the ratio of linoleic to linolenic acid (18:2/18:3) was associated with the loss of PL in untreated controls. EDU‐treated plants showed no significant loss of foliar GL and PL. The MGDG/DGDG ratio declined only slightly, and the 18:2/18:3 ratio in PL increased during O3 exposure of EDU‐treated seedlings. The level of total membrane sterols, including free sterols (FS), acylated steryl glycosides (ASG) and steryl glycosides (SG), did not change during O3 exposure of either treated or untreated plants. However, in the controls the proportions of ASG and SG increased at the expense of FS, and the ratio of stigmasterol/sitolsterol increased in FS and SG. In EDU‐treated plants, a relatively small increase in SG was offset by a decrease in FS, and there was no change in the stigmasterol/sitosterol ratio in ASG, SG or FS. The results indicate that EDU may confer tolerance to O3 through induction of enzyme systems involved in the elimination of activated oxygen species and free radicals.
Leaf thionins, a novel class of putative defence factors
Authors: Apel Klaus , Bohlmann Holger , Reimann‐Philipp Ulrich
Published: May 2006

Leaf thionins of barley have been identified as a novel class of highly abundant polypeptides with antifungal activity, which are present in walls and vacuoles of barley leaf cells. Similar thionins occur not only in monocotyledonous but also in various dicotyledonous plants. The leaf thionins of barley are encoded by a complex multigene family, which consists of at least 50–100 members per haploid genome. The toxicity of these thionins for plant pathogenic fungi and the fact that their synthesis can also be triggered by pathogens strongly suggest that leaf thionins are involved in the mechanism of plant defence against microbiol infection.
Changes in the polypeptide profiles during photoinduction of Xanthium strumarium
Authors: Kannangara T. , Durkin J. P. , ApSimon J. , Wightman F.
Published: May 2006

The polypeptides in the leaf blades, petioles and apices from photoinduced and noninduced Xanthium strumarium L. were compared by two dimensional gel‐electrophoresis. A 15 kDa and a 16 kDa polypeptide were detected in gels of the leaf blade from noninduced, but not from induced, plants. Similarly, an acidic 9 kDa polypeptide was detected in the apices from noninduced plants, but not in apices from induced plants. Both the apices and petioles from noninduced plants showed a 34 kDa polypeptide which was absent in tissues from induced plants. Thus, the disappearence of identifiable polypeptides from photoinduced tissues may be associated with the photoinductive short‐day treatment that leads to flowering.
Distribution of enzyme activities within the developing maize (Zea mays) kernel in relation to starch, oil and protein accumulation
Authors: Dochlert Douglas C.
Published: May 2006

The association of enzyme activities in developing kernels with specific storage product accumulation at maturity was analyzed in different parts of Zea mays inbred OH43 kernels. Maize kernels were harvested at 20 and 55 days post‐pollination and dissected into basal region, pericarp, embryo, lower endosperm, middle endosperm and upper endosperm. Mature (55 days pos(‐pollination) kernel parts were analyzed for starch, total protein, zein and oil content. Immature (20 days post‐pollination) kernel parts were assayed for activities of 15 enzymes of sugar and amino acid metabolism. Statistical analyses of the data suggested that glucokinase (EC 2.7.1.2) fructokinase (EC 2.7.1.4) and phosphofructokinase (EC 2.7.1.1 11) activities were primarily associated with oil accumulation, whereas ADP′‐glueose pyrophosphorylasc (EC 2.7.7.27) and sucrose synthase (EC 2.4.1.13) activities were associated with starch accumulation. The results suggest that oil biosynthesis utilizes inveitase‐mediated sucrose degradation in a pathway not requiring pyrophosphatc. whereas starch biosynthesis utilizes a sucrose synthase‐mediated pathway of sucrose degradation in a pathway requiring pyrophosphatc. Additional groups of enzyme activities were associated with each oilier but not with any specific storage product and appeared to be associated with general metabolic activity.
Histone variants from pea (Pisum sativum): Their differential presence in fractions obtained by DNase I digestion of nuclei
Authors: Rodrigo M. Isabel , Franco Luis
Published: May 2006

The variants of the core histones of Pisum sativum L. cv. Lincoln have been resolved by two dimensional polyacrylamide gel electrophoresis. Acetic acid, 8 M urea, 7.2 mM Triton X‐100 was used in the first dimension. The second dimension was run in the presence of either anionic (sodium dodecylsulphate) or cationic (cetyltrimethyl‐aminonium bromide) detergents. Four putative variants were found for the H2B histone class, 4 for H3 and 3 for H2A. Peptide mapping with (Staphylococcus aureus V8 protease was used, together with other criteria, to characterize the variants. The pattern of histone variants is not organ specific and, in an attempt to determine whether the diversity of histone variants plays some functional role, the kinetics of release of core histones by extensive DNase I digestion of nuclei was studied. H2A and H2B were released under our conditions of digestion, but the lime course of release of the different H2A variants showed a certain specificity.
Changes in parameters of the plasmalemma ATPase during cold acclimation of apple (Mains domestica) tree bark tissues
Authors: Mattheis J. P. , Kctchie D. O.
Published: May 2006

A plasmalemma fraction was isolated from homogenized apple tree (Mains domestica Borkh ‘Golden Delicious’) hark tissues using aqueous phase partitioning and ultra‐centrifugation. Results of marker enzyme assays indicated that a membrane preparation highly enriched in plasma membranes was obtained. ATPase activity in this preparation possessed a high specificity for ATP as substrate, was inhibited by vanadate, diethylstilbcsterol and dicyclohexylcarbocHimide, and was insensitive to inhibitors of mitochondria! and tonoplasl ATPases. Specific activity of the plasma‐lemma ATPase increased during cold acclimation prior to the attainment of vegetative maturity. Kinetic parameters (Km, Vln) determined from assays performed at different temperatures (10, 30°C) indicated a differential effect of cold acclimation on enzyme activity. Vm increased during cold acclimation, whereas Km increased when determined at 30°C but declined at 10°C. Acclimation treatments during April and May resulted in alteration of ATPase kinetics in the absence of any increase in bark frost hardiness. Changes in ATPase kinetics may be related more to enhanced low temperature metabolism than to frost hardiness per se.
Modulation of endogenous protein phosphorylation in plant mitochondria by respiratory substrates
Authors: Petit Patrice X. , Sommarin Marianne , Pical Christophe , Møller Ian M.
Published: May 2006

Purified mitochondria from potato (Solanum tuberosum L. cv. Bintje) tubers were incubated with [γ32P]‐ATP, respiratory substrates and various effectors. The total incorporation of 32P into proteins was measured and the phosphoprotein pattern investigated by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis and autoradiography. Total incorporation was strongly reduced (by 70–80%) by the respiratory substrates, succinate, pyruvate and NADH. The half‐maximal inhibition was at 0.03, 0.3, and 0.3 mM, respectively. The labelling of the major phosphoproteins of 40 and 42 kDa (probably both the α‐subunit of the pyruvate dehydrogenase, EC 1.2.4.1) as well as of minor polypeptides of 26–33 kDa was reduced. A concomittant increase in the labelling of the 14 and 16 kDa bands occurred in the presence of succinate in fall but this increase could not be detected in late winter. The reduction in total labelling caused by NADH and succinate was unaffected by changes in the membrane potential (e.g. addition of uncouplers) or by inhibition of electron transport (e.g. by KCN). Malonate inhibition of succinate oxidation reversed the effects of succinate on labelling‐ The mechanism(s) by which respiratory substrates might affect protein kinase activity is discussed.
Stimulation of ethylene production by a cell wall component from mature green tomato fruit
Authors: Tong Cindy B. S. , Gross Kenneth C.
Published: May 2006

Pectic (carbonate‐soluble, covalently‐bound pectin, CBP) material stimulated increased ethylene production when vacuum‐infiltrated into whole, mature green tomato (Lycopersicon esculentum Mill. cv. Rutgers) fruit. Activity was greatest if CBP was extracted from mature green tomatoes with jellied locules. CBP extracted from mature green tomatoes with immature seeds had no elicitor activity, while CBP from turning or red ripe tomatoes was only moderately active. Infiltration of CBP from normal mature green fruit into ripening inhibitor (rin) mutant tomato fruit stimulated ethylene production and attenuated red pigmentation in these fruits. Partial purification of the active material was accomplished using DEAE‐Sephadex and BioGel P‐100 chromatography. The most highly purified fraction is comprised of neutral carbohydrate (95%) with a relatively low content of amino acids (1%) and a uronic acid content of less than 5%. This material may be an endogenous trigger of ethylene production and ripening.
Distribution of diamine oxidase activity and polyamine pattern in bean and soybean seedlings at different stages of germination
Authors: Scoccianti Valeria , Torrigiani Patrizia , Bagni Nello
Published: May 2006

Diamine oxidase (DAO, EC 1.4.3.6.) activity and polyamine content were measured in the shoot apex, leaves, epicotyl, cotyledons, hypocotyl and roots of light‐grown bean (Phaseolus vulgaris L. cv. Lingot) and soybean (Glycine max L. cv. Sakai) seedlings at 3 different stages of germination (5, 8 and 14 days) as well as in embryos and cotyledons from soaked seeds. No DAO activity was detected in embryos and cotyledons of either plants. In bean seedlings DAO activity was only detectable in the shoot apex, primary leaves and cotyledons, while in soybean the activity was only detectable in the hypocotyl and roots. During seedling growth, in both plants, a different pattern of DAO activity was observed. In both species spermidine and spermine were the most abundant polyamines in embryos and cotyledons. Cadaverine, absent in bean, was only detected in soybean embryos. In the seedlings of both plants, increasing gradients of putrescine, spermidine and spermine from base to shoot apex were found. A high concentration of cadaverine was present in soybean hypocotyls and roots. A possible correlation between DAO activity and the endogenous content of the preferential substrate is discussed in relation to the possible involvement of the enzyme in regulating the cellular level of polyamines.