bluuebunny/crossref_metadata_2025 huggingface dataset:
The photosystem I mutant viridis‐zb63 of barley (Hordeum vulgare) contains low amounts of active but unstable photosystem I
Authors: Nielsen Vibeke Skovgaard , Scheller Henrik Vibe , Møller Birger Lindberg
Published: May 2006

The barley mutant viridis‐zb63 is a nuclear gene mutant that was previously reported to be completely devoid of photosystem (PS) I activity. This investigation was carried out in order to determine the activity level with more sensitive techniques. Flash‐induced absorbance changes and photoreduction of NADP+ showed that the mutant does in fact exhibit about 2% PSI activity compared to the wild‐type, but the mutant has a less stable PSI. A second objective was to determine if the deficiency in PSI was due to the absence of a specific subunit. The mutant contains PSI transcripts in the correct sizes and in similar amounts as in the wild‐type. Isolated chloroplasts of the mutant synthesize the core polypeptides PSI‐A and PSI‐B as well as the iron‐sulfur protein PSI‐C and are capable of import, processing and integration of nuclear‐encoded PSI precursors into the thylakoids. By western blotting, all investigated PSI polypeptides are detected in the mutant thylakoids at a level of 1 to 30% of wild‐type amounts. One polypeptide, PSI‐G, occurs at significantly higher level than the other PSI polypeptides and is possibly associated with the light‐harvesting complex of PSI in the mutant thylakoids. Since the results obtained document that each of the structural components of the PSI complex appears normal in the mutant viridis‐zb63, we conclude that the low level of PSI activity most likely reflects the lack of a factor important for translation of PSI‐A/B or a protein factor that is necessary for assembly of the PSI complex, but is not a component of the functional complex.
Late embryogenesis abundant protein in Arabidopsis thaliana homologous to carrot ECP31
Authors: Yang Heping , Saitou Tsutomu , Komeda Yoshibumi , Harada Hiroshi , Kamada Hiroshi
Published: May 2006

Using carrot ECP31 cDNA as a probe, we isolated AtECP31 cDNA from a seed library of Arabidopsis thaliana. The AtECP31 cDNA contained an open reading frame of 256 amino acids. Its deduced amino acid sequence showed more than 60% identity with those of DCECP31, ZMRAB28 and GHLEA D‐34 which are late embryogenesis abundant (LEA) proteins of carrot, maize and cotton, respectively. Northern blot analysis showed that the transcripts of AtECP31 accumulated specifically in mature seeds. The results suggest that AtECP31 cDNA, which encodes a LEA protein in group 5, might be involved in maturation and desiccation tolerance of seeds. Restriction fragment length polymorphism (RFLP) mapping showed that AtECP31 gene was present on chromosome 3. Cleaved amplified polymorphic sequence (CAPS) mapping allowed us to map more accurately the AtECP31 gene in the region of 28.3–29.6 cM of chromosome 3.
Methods and applications to control the uptake rate of carbon
Authors: Ingestad Torsten , Hellgren Olof , Hesseldahl Hans , Ingestad Ann‐Britt Lund
Published: May 2006

Methods to control carbon and nutrient uptake at different availability of carbon were tested on plants of birch (Betula pendula Roth.) and tomato (Lycopersicon esculentum Mill. cv. Solentos). The present paper accounts for the methods and the possibility to maintain steady‐state, i.e., a long‐term and stable physiological state of acclimated plants. Steady‐state comprises, by definition, equality between constant relative growth rates, and relative uptake rates of carbon and nutrients. Two methods were tested. The first, not previously applied, method (a), was based on a constant relative addition rate of carbon, RAC. In the second method (b), a constant concentration of CO2 in the air, ca, was used to attain non‐limiting conditions. The methods are analogous to those used by us to control plant nutrition, and the generality of fluxes to quantify supply as well as uptake and growth was verified. Thus, different RAC resulted in clear‐cut responses, from strong reduction to non‐limitation of uptake and growth, whereas different ca levels in the range 100 to 700 ppm had comparatively small effects, with an unclear causality. Non‐limiting conditions were achieved at ca≥ 200 ppm. Effects reported in the literature have been based upon the control of ca, similarly to method (b), whereas results comparable to those obtained with method (a) are lacking.

Transpiration rate increased rapidly at ca < 200 ppm CO2, and at low RAC levels, ≤ 0.1 day−1, wilting tendencies were observed. Elevated ca, 500 or 700 ppm, did not increase the relative growth rate (RG) but reduced transpiration and increased both nitrogen productivity (growth rate per unit of nitrogen in the plant) and transpiration productivity (growth rate per unit of water transpired by the plant). Obviously, effects of ca may be due to changed transpiration rate rather than to changed quantitative availability of CO2.

Relative uptake (RUC) and growth (RG) rates were closely equal to the RAC applied (RAC≅ RUC≅ RG); i.e., the purely mathematical conditions defining steady‐state were fulfilled. This unambiguous and straightforward test of reliability confirms that experimental artefacts did not produce uncontrolled or unintended effects, so that the new technique allows an accurate control of CO2 uptake and plant growth. The results add to previous databases and reference systems, where limiting conditions grade and classify plant performance as deviations from maximum growth. Evidently, methodology in experimentation and in evaluation of plant responses, can be based upon unifying concepts and general theories.
Pigments in mesocotyls of corn (Zea mays) and oats (Avena sativa) in darkness, and after irradiation and treatment with 5‐aminolevulinic acid
Authors: Virgin Hemming I.
Published: May 2006

The aim of the study was to clarify the pigment content and light‐induced pigment formation in the grass mesocotyl (oats, Avena sativa L. cv. Seger I, and corn, Zea mays L. cv. Seneca). This organ, localized between root and coleoptile, only develops in darkness. To date, there are no data on its pigment content in the literature. The data found indicate a close relationship with conditions in roots, particularly with respect to the importance of yellow pigments as bleaching‐preventing agents and response to red and blue light. The mesocotyl contained small amounts of both Pchl628–632 and Pchl636–642 with a dominance of the former. Occasionally minute amounts of Pchl650–652 were present, particularly in corn. The highest pigment concentration was found in the zone around the primordia of the pair of roots, which after several days in darkness protruded from the upper part of the mesocotyl close to the attachment to the coleoptile. Carotenoids were not detectable with absorption spectrophotometry. All pigments present in darkness were rapidly bleached in daylight and in strong red and blue light, and no more were synthesized under continuous irradiation. In continuous weak red and blue light small amounts of chlorophyll were formed at the same time as the protochlorophylls disappeared. Red light seemed to be somewhat more effective than blue, at least in corn. This chlorophyll biosynthesis stopped at very low values. The mesocotyls never became visibly green. Normal chloroplasts with grana did not develop. Mesocotyls, which had been irradiated for a short time, with no additional pigment formed, synthesized small amounts of Pchl when placed in darkness. ALA treatment of dark‐grown mesocotyls yielded Pchl628–632 to a higher degree than did irradiation.
Pravastatin: A tool for investigating the availability of mevalonate metabolites for primary and secondary metabolism in Catharanthus roseus cell suspensions
Authors: Imbault Nadine , Thiersault Martine , Dupéron Paulette , Benabdelmouna Abdellah , Doireau Pierre
Published: May 2006

In the C20 strain of Catharanthus roseus, 2,4‐dichlorophenoxyacetic acid (2,4‐D) reduces alkaloid accumulation by inhibiting the synthesis of precursors of alkaloid terpenoids. However, the presence of this growth regulator is necessary to promote growth, as measured in terms of dry weight and sterol content. The terpenoid metabolism implicated in the accumulation of alkaloids would therefore be the target of 2,4‐D inhibition and not the metabolism leading to sterol biosynthesis. The specific inhibition by pravastatin of 3‐hydroxy‐3‐methylglutaryl CoA reductase (EC 1.1.1.34), the enzyme that catalyses mevalonate synthesis, enables the limitation of mevalonate on sterol content and on alkaloid accumulation to be studied. In presence of pravastatin cells are supplied with labelled mevalonate. Under these conditions the mevalonate is incorporated into sterols but not into alkaloids accumulated in the absence of 2,4‐D. The inhibition of sterol biosynthesis induced by pravastatin is not overcome by zeatin or a cytokinin‐like compound, whereas the inhibition of alkaloid accumulation can be partially overcome. The use of pravastatin shows that the availability of mevalonate for primary and secondary metabolism is differently regulated in Catharanthus roseus cells.
Flotation of lipid‐protein particles containing triacylglycerol and phospholipid from the cytosol of carnation petals
Authors: Hudak Katalin A. , Thompson John E.
Published: May 2006

Lipid‐protein particles ranging from 20 to 250 nm in diameter have been isolated from the cytosol of carnation petals by flotation centrifugation and also by ultrafiltration. The cytosolic lipid‐protein particles resemble oil bodies, lipid‐protein particles found in oil‐bearing seeds, in that they contain triacylglycerol, are circumscribed by phospholipid that is not organized in a bilayer, appear to be derived from membranes and can be isolated by flotation. However, the cytosolic particles are distinguishable from oil bodies in that triacylglycerol is not the dominant lipid. Indeed, they contain a spectrum of lipids in addition to phospholipids and triacylglycerol including free fatty acids, sterol and wax esters, phosphatidic acid and diacylglycerol. These same lipids are present in corresponding microsomal membranes as well, but in much smaller proportions relative to phospholipid. The lipid‐protein particles from carnation petals contain a 17‐kDa protein that is of similar size to oil body oleosin, but does not cross‐react with anti‐oleosin antibodies. The data indicate that these cytosolic particles are structurally and chemically similar to oil bodies and are consistent with the notion that their genesis may be a means of removing destabilizing lipids from membrane bilayers.
Protease inhibitors of pigeonpea (Cajanus cajan) and its wild relatives
Authors: Pichare M. M. , Kachole M. S.
Published: May 2006

Plant protease inhibitors have been implicated in defense against insect pests. Podborer and pod fly are major pests of developing seeds of pigeonpea (Cajanus cajan L. Millsp.). Therefore, we studied the presence of protease inhibitors in seeds of pigeonpea and its wild relatives. Seed extracts were analyzed for protease inhibitor activities by caseinolytic assay, and the number of protease inhibitors determined by polyacrylamide gel electrophoresis. Besides trypsin and chymotrypsin inhibitors, seed extracts contained weak papain inhibitor(s) but no bromelain inhibitor. Treatment of seed extract with bromelain generated new active forms of trypsin inhibitors. The relative amounts of different trypsin inhibitors and the total trypsin inhibitor activity varied with different extraction media. Trypsin inhibitors were not detectable in pigeonpea leaves. The profiles of trypsin and chymotrypsin inhibitors in almost all the cultivars of pigeonpea analyzed were similar; however, those in wild relatives were quite variable.
Responses to ultraviolet‐B radiation (280–315 nm) of pea (Pisum sativum) lines differing in leaf surface wax
Authors: Gonzalez R. , Paul N. D. , Percy K. , Ambrose M. , McLaughlin C. K. , Barnes J. D. , Areses M. , Wellburn A. R.
Published: May 2006

To test the hypothesis that leaf surface wax influences plant responses to UV‐B, 6 lines of cultivated pea (Pisum sativum L.), selected as having more or less wax, were grown at 0 or 6.5 kJ m‐2 day‐1 plant‐weighted UV‐B against a background of 850–950 μmol m‐2 s‐1 photosynthetically active radiation. In the 4 lines with least leaf surface wax the amount of wax on adaxial and abaxial leaf surfaces was increased following exposure to 6.5 kJ m‐2 day‐1 UV‐B, but UV‐B decreased surface wax in Scout, which had the greatest wax deposits. On the adaxial leaf surface, UV‐B radiation caused a shift in wax composition from alcohols to esters and hydrocarbons and the ratio of short to long chain length alkyl ester homologues was increased. There was no evidence of a shortening in carbon chain length of hydrocarbons, primary alcohols or fatty acids due to UV‐B and no significant correlation between wax amount and UV reflectance from leaves.

UV‐B induced significant increases in UV‐absorbing compounds in the expanded leaves and buds of most lines. UV‐B reduced the growth of all lines. Foliage area (leaves plus stipules) declined by 5–30%, plant dry weight by 12–30%, and plant height by 24–38%. Reductions in growth occurred in the absence of any changes in chlorophyll fluorescence or photosynthetic rate. UV‐B also had no major effect on carbon allocation patterns. The effects of UV‐B on growth appeared to be due to changes in tissue extension and expansion. Indeed, many of the responses to UV‐B observed in this study of pea appear more consistent with indirect effects being expressed in developing tissues rather than through the direct action of UV‐B on mature tissues.

There was no evidence that wax amount or biochemistry was associated with the sensitivity of the lines to UV‐B radiation. Furthermore, induction of pigments was not correlated with changes in growth. However, lines with the greatest constitutive amounts of pigments in unexpanded bud tissues were most tolerant of elevated UV‐B.
The effect of CO2 on ethylene evolution and elongation rate in roots of sunflower (Helianthus annuus) seedlings
Authors: Finlayson Scott A. , Reid David M.
Published: May 2006

Both carbon dioxide and ethylene can affect the rate of root elongation. Carbon dioxide can also promote ethylene biosynthesis by enhancing the activity of 1‐aminocylopropane‐1‐carboxylic acid (ACC) oxidase. Since the amount of CO2 in the soil air, and in the atmosphere surrounding roots held in enclosed containers, is known to vary widely, we investigated the effects of varying CO2 concentrations on ethylene production by excised and intact sunflower roots (Helianthus annuus L. cv. Dahlgren 131). Seedlings were germinated in an aeroponic system in which the roots hung freely in a chamber and were misted with nutrient solution. This allowed for treatment, manipulation and harvest of undamaged and minimally disturbed roots. While exposure of excised roots to 0.5% CO2 could produce a small increase in ethylene production (compared to roots in ambient CO2), CO2 concentrations of 2% and above always inhibited ethylene evolution. This inhibition of ethylene production by CO2 was attributed to a reduction in the availability of ACC: however, elevated CO2 had no effect on ACC oxidase activity. ACC levels in excised roots were depressed by CO2 at a concentration of 2% (as compared to ambient CO2), but n‐malonyl‐ACC (MACC) levels were not affected. Treating intact roots with 2% CO2 inhibited elongation by over 50%. Maximum inhibition of elongation occurred 1 h after the CO2 treatment began, but elongation rates returned to untreated values by 6 h. Supplying these same intact roots with 2% CO2 did not alter ethylene evolution. Thus, in excised sunflower roots 2% CO2 treatment reduces ethylene evolution by lowering the availability of ACC. Intact seedlings respond differently in that 2% CO2 does not affect ethylene production in roots. These intact roots also temporarily exhibit a significantly reduced rate of elongation in response to 2% CO2.
Space stress and genome shock in developing plant cells
Authors: Krikorian A. D.
Published: May 2006

In the present paper I review symptoms of stress at the level of nucleus in cells of plants grown in space under nonoptimized conditions. It remains to be disclosed to what extent gravity “unloading” in the space environment directly contributes to the low mitotic index and the chromosomal anomalies and damage that's is frequently, but not invariably, demonstrable in space‐grown plant. Evaluation of the available facts indicates that indirect effects play a major role and that there is a significant biological component to the susceptibility to stress damage equation as well. Much remains to be learned on how to provide strictly controlled, optimal environments for plant growth in space. Only after optimized controls become possible will one be able to attribute any observed space effects to lowered gravity or to other significant but more indirect effects of the space environment.
With chlorophyll pigments from prolamellar bodies to light‐harvesting complexes
Authors: Sundqvist Christer , Dahlin Clas
Published: May 2006

The biosynthetic chain leading from 5‐aminolevulinic acid to chlorophyll is localised to the plastid. Many of the enzymes are nuclear‐encoded. NADPH‐protochlorophyllide oxidoreductase (EC 1.3.1.33) is one such enzyme which is encoded by two different genes and can exist in an A and a B form. Its import into the plastid seems to be facilitated when protochlorophyllide is present in the chloroplast envelope. Within the plastid the reductase is assembled to thylakoids or prolamellar bodies. The specific properties of the reductase together with the specific properties of the lipids present in the etioplast inner membranes promote the formation of the three‐dimensional regular network of the prolamellar bodies. The reductase forms a ternary complex with protochlorophyllide and NADPH that gives rise to different spectral forms of protochlorophyllide. Light transforms protochlorophyllide into chlorophyllide and this photoreaction induces a conformational change in the reductase protein which leads to a process of disaggregation of enzyme, pigment aggregates and membranes, which can be followed spectroscopically and with electron microscopy. The newly formed chlorophyllide is esterified by a membrane‐bound nuclear‐encoded chlorophyll synthase and the chlorophyll molecule is then associated with proteins into active pigment protein complexes in the photosynthetic machinery.
Phenotypic characterization of sym 21, a gene conditioning shoot‐controlled inhibition of nodulation in Pisum sativum cv. Sparkle
Authors: Markwei Carol M. , LaRue Thomas A.
Published: May 2006

E132 (sym 21) is a stable pleiotropic mutant of Pisum sativum cv. Sparkle obtained by mutagenesis with ethyl methane sulfonic acid. The line forms few nodules and short, highly branched roots. Microscopy studies revealed that infection by rhizobia is normal, and low nodulation is mainly due to a low rate of emergence of the nodule meristems. E132 shoots depressed nodulation on Sparkle stocks, whereas in reciprocal grafts more nodules formed on E132 stocks than on control roots or self‐grafted Sparkle plants. Nodule number on the mutant was slightly increased by exogenous ethylene inhibitors, which, however, did not alter the root phenotype.
Impact of elevated atmospheric CO2 on nitrate reductase transcription and activity in leaves and roots of Plantago major
Authors: Fonseca Filomena , Bowsher Caroline G. , Stulen Ineke
Published: May 2006

Vegetative plants of an inbred line, A4, of Plantago major ssp. pleiosperma (L.) Pilger were grown at 350 μl I−1 or at elevated (700 μl I−1) CO2 in non‐limiting nutrient solution with nitrate. Both the relative growth rate (RGR) and the root to total plant weight ratio (RWR) were increased by elevated CO2. However, the stimulation of both RGR and RWR was transient and did not last longer than 8 days. To investigate the physiological mechanisms involved in this stimulation, related changes in C/N metabolism were examined. In the roots soluble sugar concentration increased during the transient period of RGR stimulation (up to 23%), as did the root respiration rate. Changes in nitrogen metabolism were also restricted to this period and consisted of an increase in (1) in vivo and in vitro root nitrate reductase (EC 1.6.6.1) activity. (2) in vitro leaf nitrate reductase activity, (3) leaf and root nitrate reductase mRNA and (4) reduced nitrogen concentration in the roots. The elevated CO2‐related signal for the increase in nitrate reductase transcript levels in the roots is discussed in terms of the increased availability of soluble sugars. The results suggest that the short‐term enhancement of root carbon and nitrogen metabolism may be responsible for the transient effect of elevated CO2 on whole plant RGR.
Influence of photosynthetic photon flux densities before and during long‐term chilling on xanthophyll cycle and chlorophyll fluorescence quenching in leaves of tomato (Lycopersicon hirsutum)
Authors: Jung Sunyo , Steffen Kenneth L.
Published: May 2006

A high‐altitude ecotype of tomato (Lycopersicon hirsutum f. typicum Humb. and Bonpl.) has previously been shown to resist further loss of photosynthetic function after three to four days of chilling stress. This study examined the influence of PPFD prior to, and during chilling on the development of protective zeaxanthin and energy‐dependent quenching mechanisms in this ecotype. Five‐week‐old tomato plants were acclimated to either low PPFD (60 μmol m−2 s−1) or high PPFD (550 μmol m−2 S−1) at 25/20°C (day/night) for three days, and then exposed to a temperature of 5/5°C and a PPFD of either 60 or 550 μmol m−2 s−1 for three days. The plants acclimated to low PPFD had lower Chl a/b ratio, and lower level of total Chl per leaf area, total xanthophyll cycle pool and β‐carotene. The capacity of their photosynthetic system to resist photoinhibition and to recover photosynthetic function was also lower compared to that of the plants acclimated at high PPFD but exposed to the same chilling stress. In the plants chilled at low PPFD, energy‐dependent quenching preceded the formation of zeaxanthin on the first day of chilling and there was an overall reduction in the conversion of violaxanthin to zeaxanthin as compared to the plants chilled at high PPFD. During the last day of chilling‐induced photoinhibition, energy‐dependent quenching in any of the treatments did not increase, but zeaxanthin levels increased continuously throughout the three days of chilling. Our results suggest that light‐acclimation before chilling affects the capacity of the plants to resist chilling‐induced photoinhibition. In addition, photoinhibitory quenching appears to be a major component for quenching excessive energy at the latter stage of long‐term chilling.
Antioxidant role of glutathione associated with accelerated aging and hydration of triploid watermelon seeds
Authors: Hsu J. L. , Sung J. M.
Published: May 2006

Hydration offers an effective means for raising seed performance in many crop species. The objective of the present study was to evaluate the effect of hydration in vermiculite on germinability and antioxidant capacity of glutathione in artificially aged triploid seeds of two watermelon cultivars. Aging was achieved by incubating the seeds at 45°C and 79% relative humidity for 6 days and then air‐drying them to their original moisture level (4%). Hydration was achieved by mixing untreated and aged seeds with moist vermiculite No. 3 at 25°C for 24 h. The partially hydrated seeds were air‐dried at 25°C for 36 h to 4.7% moisture level. Aged seeds germinated more slowly and poorly than unaged seeds. Aging also decreased the level of glutathione and reduced the activity of several enzymes involved in glutathione antiperoxidation. The germinability of aged triploid seeds was restored partially by hydration in vermiculite. The glutathione content and the activity of antiperoxidative enzymes using glutathione as substrate were also increased by hydration. The changes in germination and glutathione level in relation to aging and hydration were similar for the two cultivars, despite differences in their germination performance and related physiological traits.
Effect of different nitrogen nutrients on the viability, protein synthesis and tannin production of Scots pine callus
Authors: Laukkanen Hanna , Julkunen‐Tiitto Riitta , Hohtola Anja
Published: May 2006

The effect of two different media on the growth, metabolism and viability of Scots pine (Pinus sylvestris) callus cultures was studied. Inorganic nitrogen in the culture media (modified MS) was in the form of either KNO3 or NH4NO3. The cultures were started from buds of mature Scots pine. Growth was poor on the medium with KNO3, but this compound had a noticeable effect on the metabolism of the callus, which was reflected in alterations in protein and polyphenol synthesis and the pH of the culture medium. Although the fresh mass, water content and viability of the callus decreased when KNO3 was the exclusive inorganic nitrogen nutrient, protein synthesis was more abundant. Electrophoretic analyses indicated alterations in the patterns of soluble proteins and purified glycoproteins. Phenylalanine ammonia‐lyase (EC 4.3.1.5) activities were high in all the calluses, and concentrations of condensed tannins and their precursors, catechins, were higher than in intact buds. The role of inorganic nitrogen nutrition in the deterioration of tissues is discussed on the basis of the effect of ammonium on the metabolism of pine callus.
Seasonal changes in the physical state of crown water associated with freezing tolerance in winter wheat
Authors: Yoshida Midori , Abe Jiro , Moriyama Masahisa , Shimokawa Shigezou , Nakamura Yoshio
Published: May 2006

The relationship between freezing tolerance (expressed as LT50, the lethal freezing temperature for 50% of plants) and the amount and physical state (as determined by spin‐lattice [T1] and spin‐spin [T2] relaxation times of protons) of water in crown tissue was examined in contrasting winter wheat (Triticum aestivum L.) varieties grown under field conditions from 1992 to 1994. During acclimation, the LT50 values decreased from around ‐7 to ‐17, ‐20 and ‐27°C in PI 173438, Chihokukomugi and Valuevskaya, respectively. Tissue water content decreased continuously through autumn to reach a plateau around 3 g H2O (g dry weight)‐1 in early winter when LT50 was still decteasing, and then gradually increased under snow cover. A significant negative correlation was found between mean minimum air temperatures and freezing tolerance prior to the establishment of continuous snow cover. In contrast, a positive association between mean minimum temperatures and crown tissue water content was significant only when air temperatures were above 0°C, as water content did not decrease further at sub‐zero temperatures. Seasonal changes in T1 were closely related to changes in freezing tolerance. T1 decreased until January even though water content stopped decreasing. Further tests on 15 field‐grown varieties confirmed a strong negative association between freezing tolerance and T1. The results suggest that cold hardening is comprised of two stages, with the transition occurring at ca 0°C. Development of hardiness was related to (1) a reduction in water content in the first stage (at minimum temperatures > 0°C), and (2) a change in physical state of water without much reduction in water content in the second stage. Varietal differences in hardiness thus arise due to changes in both water content and physical state of water.
Carotenogenic and abscisic acid biosynthesizing activity in a cell‐free system
Authors: Cowan A. K. , Richardson G. R.
Published: May 2006

Abscisic acid is considered an apocarotenoid formed by cleavage of a C‐40 precursor and subsequent oxidation of xanthoxin and abscisic aldehyde. Confirmation of this reaction sequence is still awaited, and might best be achieved using a cell‐free system capable of both carotenoid and abscisic acid biosynthesis. An abscisic acid biosynthesizing cell‐free system, prepared from flavedo of mature orange fruits, was used to demonstrate conversion of farnesyl pyrophosphate, geranylgeranyl pyrophosphate and all‐trans‐β‐carotene into a range of β,β‐xanthophylls, xanthoxin, xanthoxin acid, 1′,4′‐trans‐abscisic acid diol and abscisic acid. Identification of product carotenoids was achieved by high‐performance liquid chromatography and on‐line spectral analysis of individual components together with co‐chromatography. Putative C‐15 intermediates and product abscisic acid were identified by combined capillary gas chroma‐tography‐mass spectrometry. Kinetic studies revealed that β‐carotene, formed from either famesyl pyrophosphate or geranylgeranyl pyrophosphate, reached a maximum within 30 min of initiation of the reaction. Thereafter, β‐carotene levels declined exponentially. Catabolism of substrate β‐carotene into xanthophylls, putative abscisic acid precursors and product abscisic acid was restricted to the all‐trans‐isomer. However, when a combination of all‐trans‐ and 9‐cis‐β‐carotene in the ratio 1:1 was used as substrate, formation of abscisic acid and related metabolites was enhanced. Biosyn‐thetically prepared [14C]‐all‐trans‐violaxanthin, [14C]‐all‐trans‐neoxanthin and [14C]‐9′‐cis‐neoxanthin were used as substrates to confirm the metabolic interrelationship between carotenoids and abscisic acid. The results are consistent with 9′‐cis‐neoxan‐thin being the immediate carotenoid precursor to ABA, which is oxidatively cleaved to produce xanthoxin. Formation of abscisic aldehyde was not observed. Rather, xanthoxin appeared to be converted to abscisic acid via xanthoxin acid and 1′,4′‐trans‐abscisic acid diol. An alternative pathway for abscisic acid biosynthesis is therefore proposed.
Monitoring copper‐induced changes in fine root geometry of birch (Betula pendula) using nutrient film technique (NFT)
Authors: Aöalsteinsson Sveinn , Gussarsson Monika , Asp Håkan , Jensén Paul
Published: May 2006

Effects of copper on fine root geometry (number, length) and K and Cu content in birch (Betula pendula Roth) were studied. After pre‐cultivation, the plants were grown in a nutrient film technique (NFT) system and exposed to additional 0–5 μM for a period of 8 days. The NFT system permitted undisturbed growth of the roots during monitoring. Copper experiments were carried out in a split‐root setup both with a uniform and differentiated Cu supply to investigate growth responses of roots grown in a homogeneous and heterogeneous root environment, respectively. At uniform external Cu supply, average root length was affected by increased Cu concentration during the first four days while the next four days only the overall root length (product of root length and root number) was significantly reduced. During the first four days in the split‐root experiments with differentiated Cu supply, additional Cu primarily reduced root number on the Cu‐treated parts of the root system but at stronger Cu concentration the overall root length was also significantly reduced. In contrast, number and average root length of the part of the root system not exposed to Cu increased when 1, 2 and 5 μM Cu was added to the other side. Growth parameters were affected differently in the beginning of the heavy metal exposure compared to later stages of exposure, which may indicate acclimatisation to Cu stress.
Polyamines inhibit lipid peroxidation in senescing oat leaves
Authors: Borrell A. , Carbonell L. , Farràs R. , Puig‐Parellada P. , Tiburcio A. F.
Published: May 2006

Exogenous diaminopropane, spermidine, spermine and guazatine, an inhibitor of polyamine oxidase (EC 1.5.3.3) activity, were able to inhibit loss of chlorophyll and reduce the level of malondialdehyde in dark‐incubated Avena sativa L. cv. Victory leaves, as well as in leaves subjected to osmotica used for protoplast isolation. Both lipoxygenase (EC 1.13.11.12) activity and enzyme‐protein levels were reduced by incubation with spermine. The results provide support for the contention that the inhibition of lipid peroxidation by polyamines may be one of the mechanisms responsible for their anti‐senescence effects.
Flooding resistance of Rumex species strongly depends on their response to ethylene: Rapid shoot elongation or foliar senescence
Authors: Banga Minke , Bögemann Gerard M. , Cornelis W. P. M. Blom , Laurentius A. C. J. Voesenek
Published: May 2006

Rumex palustris is a flooding‐resistant amphibious species from frequently flooded riversides, whereas Rumex acetosella is flooding‐sensitive and grows on dry sandy soils. Upon complete submergence, both species accumulate ethylene to similar levels. After more than four days, however, the ethylene concentration in R. acetosella plants strongly rises to an extremely high level, whereas it remains much lower in R. palustris plants. This latter species responds to ethylene with enhanced leaf elongation, whereas elongation in R. acetosella is insensitive to ethylene. Elongation rates of leaves were measured continuously during the first 8 h of submergence. A comparison of the elongation rates of R. palustris, R. acetosella and silver‐treated R. palustris plants demonstrated that R. palustris plants responded to ethylene within 1 h of submergence. In R. acetosella, clear symptoms of senescence and decay were observed within two weeks of submergence. In R. palustris plants, only the oldest leaf was senescent. To investigate the role of ethylene in the senescence process, the effects of silver ions on submerged plants, and the effects of prolonged exposure to an extremely high ethylene level on drained plants were studied in both Rumex species. The results demonstrated that although ethylene accelerated senescence of submerged R. acetosella plants, the process may have been caused by other factors. The slower senescence of R. palustris plants could not be explained by their lower ethylene concentration. Rather, it was caused by a much lower sensitivity of the senescence process to ethylene. Moreover, other factors may be less unfavourable in R. palustris than in R. acetosella plants under submerged conditions.
The effect of ABA analogs on callus viability and gene expression in Craterostigma plantagineum
Authors: Chandler John W. , Abrams Suzanne R. , Bartels Dorothea
Published: May 2006

We have used callus tissue of the desiccation‐tolerant plant, Craterostigma plantagineum Hochst to probe the stereochemical requirements of ABA in the desiccation tolerance response, using ABA analogs. Callus was treated with (S)‐(+)‐ABA and (R)‐(‐)‐ABA and two pure isomer derivatives of each, and viability after a drying treatment and the expression of four desiccation‐induced late embryogenesis abundant (LEA)‐type transcripts and sucrose synthase from Craterostigma were measured. Both stereoisomers alone caused transcript expression and highest viability. The two derivatives of (R)‐(‐)‐ABA gave poor or no transcript expression and no viability, suggesting that alteration of a ring double bond to a single bond in this series of compounds is significant in ABA perception for both responses. One (S)‐(+)‐ABA derivative was effective in inducing all transcripts and causing callus viability. The other analog derivative induced all protein transcripts without concomitant tissue viability after drying. This suggests that some other ABA‐inducible factor(s) are vital for desiccation tolerance of callus.
Leaf malformation during early development in Sorghum. Evidence for an embryonic developmental window
Authors: Amzallag G. Nissim , Seligmann Hervé , Lerner Henri R.
Published: May 2006

Salt adaptation was induced in two successive generations of Sorghum bicolor, and the germination of their seeds was compared. When germinated in the absence of NaCl, the progeny of adapted plants displayed a specific malformation at the first two leaves, which was never observed in progeny of control plants. The frequency of leaf malformation was enhanced in progeny of the second generation of adapted plants, indicating a cumulative influence of salt adaptation. When germinated in the presence of 75 mM NaCl, seedlings from seeds of salt‐adapted plants never displayed the leaf malformation, whereas it was observed on seedlings from seeds of control plants germinated in the presence of 75 mM NaCl. The occurrence of leaf malformation was analyzed for progeny of 20 salt‐adapted plants germinated in the absence of NaCl. The link with the reproductive characters of the parents indicates a strong parental control on the expression of the leaf malformation. A comparison with previous data relative to the leaf malformation in Sorghum suggests the existence of a developmental window which ‘opens’during embryo morphogenesis. This enables the imprinting of the embryo by the parent's physiological environment. This conclusion is related to other data describing a long‐term maternal influence in plants.
Effects of manganese toxicity on photosynthesis of white birch (Betula platyphylla var. japonica) seedlings
Authors: Kitao Mitsutoshi , Lei Thomas T. , Koike Takayoshi
Published: May 2006

The effects of manganese (Mn) toxicity on photosynthesis in white birch (Betula platyphylla var. japonica) leaves were examined by the measurement of gas exchange and chlorophyll fluorescence in hydroponically cultured plants. The net photosynthetic rate at saturating light and ambient CO2 (Ca) of 35 Pa decreased with increasing leaf Mn concentrations. The carboxylation efficiency, derived from the difference in CO2 assimilation rate at intercellular CO2 pressures attained at Ca of 13 Pa and O Pa, decreased with greater leaf Mn accumulation. Net photosynthetic rate at saturating light and saturating CO2 (5%) also declined with leaf Mn accumulation while the maximum quantum yield of O2 evolution at saturating CO2 was not affected. The maximum efficiency of PSII photochemistry (Fv/Fm) was little affected by Mn accumulation in white birch leaves over a wide range of leaf Mn concentrations (2–17 mg g−1 dry weight). When measured in the steady state of photosynthesis under ambient air at 430 μmol quanta m−2 s−1, the levels of photochemical quenching (qP) and the excitation capture efficiency of open PSII (F′v/F′m) declined with Mn accumulation in leaves. The present results suggest that excess Mn in leaves affects the activities of the CO2 reduction cycle rather than the potential efficiency of photochemistry, leading to increases in QA reduction state and thermal energy dissipation, and a decrease in quantum yield of PSII in the steady state.
Response of oxidative stress defense systems in rice (Oryza sativa) leaves with supplemental UV‐B radiation
Authors: Dai Qiujie , Yan Bin , Huang Shaobai , Liu Xiaozhong , Peng Shaobing , Miranda M. Lourdes L. , Chavez Arlene Q. , Vergara Benito S. , Olszyk David M.
Published: May 2006

The impact of elevated ultraviolet‐B radiation (UV‐B, 280–320 nm) on membrane systems and lipid peroxidation, and possible involvement of active oxygen radicals was investigated in leaves of two UV‐B susceptible rice cultivars (Oryza sativa L. cvs IR74 and Dular). Rice seedlings were grown in a greenhouse for 10 days and then treated with biologically effective UV‐B (UV‐BBE) radiation for 28 days. Oxidative stress effects were evaluated by measuring superoxide anion (O2) generation rate, hydrogen peroxide (H2O2) content, malondialdehyde (MDA) concentration and relative electrolyte conductivity (EC) for IR74 and Dular at 0 (control), 6 or 13 kJ m−2 day−1 UV‐BBE. Significant increases in these parameters were found in rice plants grown at 13 vs 0 kJ m−2 day−1 UV‐BBE after 28 days; indicating that disruption of membrane systems may be an eventual reason for UV‐B‐induced injury in rice plants. There was a positive correlation between O2− generation and increases in EC or MDA in leaves. Activities of enzymatic and nonenzymatic free radical scavengers were measured for IR74 after 7, 14, 21 and 28 days of exposure to 13 or 0 UV‐BBE to evaluate dynamics of these responses over time. Activities of catalase and superoxide dismutase (but not ascorbate peroxidase) and concentrations of ascorbic acid and glutathione were enhanced by 13 vs 0 UV‐BBE after 14 days of UV‐B exposure. Further exposure to 28 days of UV‐B was associated with a decline in enzyme activities and ascorbic acid, but not glutathione. It is suggested that UV‐B‐induced injury may be associated with disturbance of active oxygen metabolism through the destruction and alteration of both enzymatic and nonenzymatic defense systems in rice.
Daminozide and prohexadione have similar modes of action as inhibitors of the late stages of gibberellin metabolism
Authors: Brown Robert G. S. , Kawaide Hiroshi , Yang Young‐Yell , Rademacher Wilhelm , Kamiya Yuji
Published: May 2006

One of the effects of daminozide is to retard shoot growth in certain plant species, but its mode of action is unclear. Prohexadione, an acylcyclohexanedione, also causes retardation of shoot growth, but it is active in all plant systems tested so far. This inhibition has been shown to be a result of competition with the natural co‐substrate, 2‐oxoglutarate, at the active site of hydroxylases involved in the later stages of the gibberellin (GA) biosynthesis pathway. In order to determine the mode of action of daminozide in relation to prohexadione, the potencies of the two retardants as inhibitors of 3β‐hydroxylation of GAs in cell‐free systems from pumpkin (Cucurbita maxima) endosperm and French bean (Phaseolus coccineus) cotyledons were studied. Several compounds, related to or representing structural links between daminozide and prohexadione, were also included in this investigation. Daminozide was found to inhibit only the bean 3β‐hydroxylase to a significant degree, whereas prohexadione inhibited both the bean and pumpkin enzymes.

Further information was obtained from the GC‐MS analysis of GAs found in the newly formed parts of the shoots of peanut seedlings treated with the two compounds. Both growth retardants inhibited the formation of GA1, whereas its immediate precursor, GA20, accumulated. Furthermore, levels of GA8 (2β‐hydroxy GA1) were also reduced, but by a smaller relative amount.

These results clearly indicate for the first time that daminozide has the same mode of action as prohexadione in distinct plant species, namely to inhibit the 3β‐hydroxylase and, to a lesser extent, the 2β‐hydroxylase. This is probably due to the structural similarity of the two inhibitors with 2‐oxoglutarate.
Cell wall metabolism in ripening fruit. VIII. Cell wall composition and synthetic capacity of two regions of the outer pericarp of mature green and red ripe cv. Jackpot tomatoes
Authors: Huysamer Marius , Greve L. Carl , Labavitch John M.
Published: May 2006

Pericarp discs were excised from mature green and red ripe tomato (Lycopersicon esculentum Mill. cv. Jackpot) fruit and kept in sterile tissue culture plates for 4 days, including 2 days of incubation with D‐[U‐13C]‐glucose. Cell walls were prepared and differentially extracted with dimethylsulfoxide (DMSO), trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetic acid (CDTA). Na2CO3, 4 M KOH and 8 M KOH. Cell wall noncellulosic neutral sugar (NS) composition and cell wall synthetic capacity (i.e. incorporation of density label into cell wall sugars) were determined by using a gas chromatograph coupled to a flame ionization detector and a mass spectrometer, respectively. In the crude cell wall, there was significantly less galactose (Gal) and glucose (Glc) in the “outer”2‐mm pericarp region, including the cuticle, compared to the “inner”2‐mm region immediately below it (closer to the locules). In the CDTA‐soluble pectin, rhamnose (Rha), arabinose (Ara) and Gal accounted for approximately 90% of the total NS. The ratios of these sugars were very similar in the total (12C plus 13C) sugars, and also in the newly synthesized ([13C]‐labeled) sugars, suggesting that newly synthesized NS associated with the chelator‐extractable pectic fraction has a composition very similar to that of preexisting NS. In the 4 M KOH‐soluble material, xylose (Xyl) and Glc accounted for approximately 70% of the total NS. The ratio of these sugars was very similar in the total sugars, but much lower in the newly synthesized portion. This suggests that the hemicellulosic polymers synthesized during the ripening process are different in type and/or proportion from those present in the developing fruit. Because the outer pericarp of tomatoes contains at least two distinct tissue types and these have a distinct cell wall composition, analysis of tomato cell wall polysaccharide composition by homogenization of the entire outer pericarp will obscure subtle changes associated with ripening/softening within specific tissue types.
Cell wall composition and elasticity of dormant and growing white spruce (Picea glauca) seedlings
Authors: Renault Sylvie , Zwiazek Janusz J.
Published: May 2006

White spruce [Picea glauca (Moench) Voss.] seedlings were used to study the changes in cell wall composition and elasticity in mature needles before and after the resumption of growth following winter dormancy. Dormant seedlings showed high cell wall elasticity that decreased after the resumption of shoot growth. Cell wall hemicellulose content increased 3 days after planting and decreased after the buds flushed. Non‐cellulosic glucose and arabinose were the sugars showing the most pronounced changes related to shoot growth. Arabinose was the most abundant sugar residue in the pectin and hemicellulose fractions and it decreased until day 10 after planting. At the same time, the levels of glucose in pectin and hemicellulose increased. The results provide evidence for cell wall carbohydrate turnover in dormant and active seedlings before and after bud flushing.
Paraquat toxicity is reduced by metal chelators in rice leaves
Authors: Chang Chin Jung , Kao Ching Huei
Published: May 2006

The possible mediatory role of transition metals in paraquat (PQ) toxicity in rice leaves was investigated. Metal chelators (2,2′‐bipyridine, 8‐hydroxylquinoline and 1,10‐phenanthroline) reduced PQ toxicity in rice leaves. The reduction of PQ toxicity by 1,10‐phenanthroline (PA) is closely associated with the decrease in lipid peroxidation and increase in activities of enzymes detoxifying active oxygen species. Our results support the notion that iron or copper plays a major role in PQ toxicity in detached rice leaves. Reduction of PQ toxicity by PA in detached rice leaves is most likely mediated through chelation of iron or copper and an increase in superoxide dismutase and glutathione reductase activities.
The anionic protease inhibitor BWI‐1 from buckwheat seeds. Kinetic properties and possible biological role
Authors: Dunaevsky Yakov E. , Gladysheva Inna P. , Pavlukova Ekaterina B. , Beliakova Galina A. , Gladyshev Dmitry P. , Papisova Alla I. , Larionova Natalja I. , Belozersky Mikhail A.
Published: May 2006

Kinetic characteristics and effects on the growth of filamentous fungi of one of the main anionic protease inhibitors, BWI‐1, isolated from buckwheat seeds, have been studied. The inhibition constants of bovine trypsin, chymotrypsin and cathepsin G from human granulocytes with BWI‐1 were found to be 1.1, 67 and 200 nM, respectively. Analysis of the amino acid sequence of BWI‐1 in the vicinity of the reactive site revealed its homology to the potato proteinase inhibitor I family. It is suggested that the inability of BWI‐1 to bind elastase of human granulocytes is due to the basic nature of the amino acid residue (Arg) at the Pj position in its reactive site. It was demonstrated that BWI‐1 was able to suppress the germination of the spores and the growth of the mycelium of two filamentous fungi.