bluuebunny/crossref_metadata_2025 huggingface dataset:
Root apical diameter and root elongation rate of rubber seedlings(Hevea brasiliensis)show parallel responses to photoassimilate availability
Authors: Thaler Philippe , Pagès Loïc
Published: March 2003

The hypothesis that root apical diameter may be used to evaluate root growth potential was tested. Temporal variations in the apical diameter of individual roots of rubber seedlings (Hevea brasiliensis) were studied together with their elongation patterns, using root observation boxes under controlled conditions. This study confirmed the overall positive correlation between apical diameter and growth rale. Moreover, the two parameters, varied in the same way during the life of a given root. For roots with short growth duration, there was a parallel quick decrease in both apical diameter and elongation rate, whereas roots that grew for longer periods showed synchronous fluctuations for both parameters. Since the mean values for the secondary roots within a root system exhibited the same trends, variations in apical diameter and elongation rates should depend on factors influencing the whole root system. When related to shoot rhythmic growth, both apical diameter and elongation rates were depressed during the periods of leaf growth. These effects were enhanced and/or prolonged by shading, hence reinforcing the hypothesis that this development depends on assimilate availability. Such results can be interpreted in terms of a source‐sink relationship within the whole plant by considering the apical diameter, representing the size of the meristem related to the number of rneristematic cells, as an indicator of each root's growth potential.
Ozone stimulates apoplastic antioxidant systems in pumpkin leaves
Authors: Ranieri A. , D'Urso G. , Nali C. , Lorenzini G. , Soldatini G. F.
Published: March 2003

The phytotoxiticky of ozone is due to its high oxidant capacity and to its ability to generate toxic molecular species. It is well known that intracellular peroxidases play an important role in eliminating toxic forms of oxygen but little evidence has been reported on the role of peroxidases in the apoplastic compartment. The detoxification systems located in the foliar extracellular matrix and in the intracellular fluid of sensitive pumpkin plants (Cucurbita pepo L. cv. Ambassador) exposed to ozone (150 ppb. 5 days. 5 h day‐1) in a fumigation chamber, were analyzed. The analyses were carried out on both young and mature leaves. Ascorbate peroxidase (EC 1.11.1.11) was found in the extracellular matrix of the pumpkin tissues. Its activity increased in both young and mature leaves as a consequence of the treatment, while at intraeellular levels its effect was most prominent in mature leaves. Analysis of the ascorbie‐dehydroascorbic acid system revealed an enhancement of the pool content in the extracellular matrix of both kinds of leaves as a consequence of fumigation, while at the intracelluiar level small variations were found. Very little variation was observed in the glutathione pool as a consequence of fumigation. The analysis of a lipid peroxidation marker, malondi‐aldehyde. showed the significant effect of ozone on membrane lipids. Following fumigation, the free phenols in the extracellular matrix decreased in both young and mature leaves, while the free and glycoside‐bound phenols of the intracellular fluid showed little increase. The results support the hypothesis that ozone stimulates the an‐tioxidant systems mainly in the apoplast and that ascorbic peroxidase activity, ascorbic acid levels and cell wall stiffening are the most influenced parameters.
Gibberellins are not essential for photoperiodic flower induction of Pharbitis nil
Authors: Takeno Kiyotoshi , Tsuruta Tomohiro , Maeda Takahide
Published: March 2003

The influence on photoperiodic flowering of (2‐chloroethyl)trimethylmmonium chloride (CCC), an inhibitor of gibberellin (GA) biosynthesis, was studied in the short‐day plant Pharbitis nil cv. Violet. The cotyledons contained high levels of endogenous bioactive gibberellins, whereas in the plumules and first leaves the levels were low or undetectable. The first leaf responded to a single‘dark treatment by inducing flowering when it was 10 mm or wider. Similar seedlings, but without cotyledons, were used as the assay plants to study the effect of CCC on photoperiodic flowering. Treatment with CCC had no effect on flowering of seedlings without cotyledons, although stem elongation was inhibited. By contrast. CCC inhibited flowering of the intact seedlings with cotyledons. Gibberellic acid applied to the shoot apex or to the first leaf promoted flowering in the CCC‐treated seedlings without cotyledons. The results indicate thai gibberellins are not essential for the flower induction process in leaves, but that they promote flower initiation and/or later processes in the shoot apices.
Differential regulation of the barley (Hordeum vulgare) transcripts B22E and B12D in mature aleurone layers
Authors: Steinum T. M. , Berner H. S. , Stacy R. A. P. , Salehian Z. , Aalen R. B.
Published: March 2003

Previously, B12D and B22E have been characterized as Barley aleurone and embryo (Balem) transcripts, expressed during seed maturation and embryo germination. The open reading frame of B12D cDNAs encodes a protein of unknown function highly conserved in mono‐ and dicotyledonous species, while B22E encodes a metallothionein‐like protein. Several slightly different B22E transcripts have earlier been identified. Our objective was to investigate the number of B12D genes, and B12D and B22E expression patterns in mature aleurone. Genomic Southern hybridization and primer extension experiments suggest the presence of a B12D gene family in barley with at least 8 or 9 members. B12D transcripts can also be identified in the starchy endosperm, and a primer extension analysis indicates that some of these genes are expressed in the starchy endosperm only. A number of genes appear to be transcribed in all tissues investigated; starchy endosperm, pericarp, immature and mature embryos and aleurone, and mature aleurone incubated with GA3. One B12D gene, HvB12Dg1, was isolated and shown by particle bombardment with a promoter‐GUS construct to be transcriptionally active. The HvB12Dg1 promoter contains elements similar to those of the gibberellic acid response complex (GARC). B12D transcripts are found in the aleurone of imbibed embryoless grains, while B22E transcripts are barely detectable. However, both transcripts are up‐regulated by the presence of the germinating embryo. For B22E this effect is not mimicked by applying GA3 exogenously to imbibed embryoless grains, while the B12D transcript level increases 2‐ to 3‐fold, at most. On the other hand, ABA can suppress B12D expression. Our investigations indicate that gibberellic acid may not be directly involved in the up‐regulation of all transcripts induced in the aleurone during germination.
Photosynthesis, leaf conductance and water relations of in vitro cultured grapevine rootstock in relation to acclimatisation
Authors: Fila Gianni , Ghashghaie Jaleh , Hoarau Jackson , Cornic Gabriel
Published: March 2003

Leaf net CO2 uptake and leaf photosynthetic capacity were investigated in micropropagated 41B grapevine rootstock (Vitis vinifera‘Chasselas’×Vitis berlandieri, Mill. De Gr.) plants grown in the presence of four sucrose concentrations (6.25, 12.5, 25.0 or 37.5 g l−1). Sucrose concentration in the medium during growth in vitro did not affect the leaf photosynthetic performance of plants neither before nor after transplantation. The maximum photosynthetic rate, measured as CO2‐dependent O2 evolution, was 7.3 µmol m−2 s−1 before transplanting and 15.4 µmol m−2 s−1 one month after transplantation. The maximum quantum yield of O2 evolution (on the basis of incident light) was about 0.07 for all sucrose treatments both before and after transplantation. Dry biomass before transplanting was highest in plants grown with 25.0 or 37.5 g l−1 sucrose in the medium. One month after transplantation the highest dry biomass was also observed for the same treatments. Survival of plants was 100% for all treatments. Leaf conductance to water vapour was always higher in plants before than after transplantation. Both before and after transplanting it increased with increasing light intensity and decreased slightly with increasing CO2 molar ratio in in vitro plants. Stomata of plants before transplantation were unresponsive to vapour pressure deficit. In vitro plants experience an acute water stress when they are maintained with the whole root system in water and exposed to ambient controlled conditions in a growth chamber. However, there was no wilting of the leaves when similar plants with roots cut off were left in the same conditions. Hydraulic conductivity was low at both root and shoot‐root connection levels. It is likely that water supply could be limiting during transplantation because of the low root and root‐stem connection conductivity. Water uptake by roots rather than water loss from the shoots would be of primary importance for the maintenance of water balance during acclimatisation.
The role of ABA in freezing tolerance and cold acclimation in barley
Authors: Bravo León A. , Zúñiga Gustavo E. , Alberdi Miren , Corcuera Luis J.
Published: March 2003

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley (Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT50, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT50 of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.
Induction of an ACC synthase cDNA by ozone in light‐grown Arabidopsis thaliana leaves
Authors: Vahala Jorma , Schlagnhaufer Carl D. , Pell Eva J.
Published: March 2003

The rate‐limiting enzyme in the ethylene biosynthesis pathway is 1‐aminocyclo‐propane‐1‐carboxylate (ACC) synthase. We have investigated an ozone (O3)‐induced ACC synthase gene in Arabidopsis thaliana. Four previously reported ACC synthase genes from A. thaliana (ACS1, ACS2, ACS4 and ACS5) were not induced in response to O3 stress. An O3‐induced 1 098‐bp cDNA encoding ACC synthase was isolated from foliage of A. thaliana; this sequence was identical to that of ACS6 which could be induced by multiple stimuli including touch. When plants were treated with 350 nl l−1 of O3 for 2 or 6 h. the evolution of ethylene became maximal after 1.5 h and gradually decreased thereafter. Similarly, the mRNA transcript of O3‐induced ACC synthase was detected after 30 min of exposure, attained a maximum level after 1 h, and then declined. Visible damage in O3‐treated plants was observed at the end of the 2‐h exposure. This ACC synthase gene in A. thaliana provides a useful tool for studying O3‐induced responses related to ethylene production at the molecular and genetic levels.
Leaf anatomical changes in Populus trichocarpa, Quercus rubra, Pseudotsuga menziesii and Pinus ponderosa exposed to enhanced ultraviolet‐B radiation
Authors: Nagel Linda M. , Bassman John H. , Edwards Gerald E. , Robberecht Ronald , Franceshi Vincent R.
Published: March 2003

Leaf anatomical characteristics are important in determining the degree of injury sustained when plants are exposed to natural and enhanced levels of ultraviolet‐B (UV‐B) radiation (280–320 nm). The degree to which leaf anatomy can adapt to the increasing levels of UV‐B radiation reaching the earth's surface is poorly understood in most tree species. We examined four tree species, representing a wide range of leaf anatomical characteristics, to determine responses of leaf area, specific leaf weight, and leaf tissue parameters after exposure to ambient and enhanced levels of UV‐B radiation. Seedlings were grown in a greenhouse with photosynthetically active radiation of 39 mol m−2 day−1 and under one of three daily irradiances of biologically effective UV‐B radiation (UV‐BBE) supplied for 10 h per day: (1) approximate ambient level received at Pullman, Washington on June 21 (1 x ); two times ambient (2 x ), or three times ambient (3 x ). We hypothesized the response of each species to UV‐B radiation would be related to inherent anatomical differences. We found that the conifers responded anatomically to nearly an equal degree as the broad‐leaved trees, but that different tissues were involved. Populus trichocarpa, an indeterminate broadleaf species, showed significantly thicker palisade parenchyma in recently mature leaves at the 3 x level and in older leaves under the 2 x level. In addition, individual leaf area was generally greater with increased UV‐B irradiance. Quercus rubra, a semi‐determinate broadleaf species, exhibited significantly thicker palisade parenchyma at the 2 x and 3 x levels as compared to controls. Psuedotsuga menziesii, an evergreen coniferous species with bifacially flattened needles, and Pinus ponderosa, an evergreen coniferous species with a complete hypodermis, showed no significant change in leaf area or specific leaf weight under enhanced UV‐B radiation. Epidermal thickness was unchanged in P. menziesii. However, P. ponderosa increased the thickness and number of hypodermal layers produced, presumably decreasing penetration of UV‐B radiation into the leaf. We concluded that differences in inherent leaf anatomy of the four species examined are important in the responses to enhanced levels of UV‐B radiation.
Ozone sensitivity in Triticum durum and T. aestivum with respect to leaf injury, photosynthetic activity and free radical content
Authors: Reichenauer T. G. , Goodman B. A. , Kostecki P. , Soja G.
Published: March 2003

Sensitivity to ozone is highly variable in cultivars of different wheat species, leading to differences in leaf injury and yield. Not much is known about the physiological background of these differences. The objective of this study was to compare the effects of ozone on photosynthetic parameters in Triticum aestivum L. (spring wheat cv. Nandu, winter wheat cv. Perlo) and Triticum durum Desf. (cv. Extradur). Plants cultivated in pots were exposed to 80 nmol mol−1 ozone, or were used as control plants in a greenhouse. Stages of growth and senescence of single leaves were recorded. Light‐saturated net photosynthesis, leaf conductance for water vapour, and chlorophyll fluorescence were measured. Stomatal limitation was calculated from CO2 response curves, and the free radical content of whole leaves measured by EPR spectroscopy. Senescence of single leaves was enhanced by the ozone‐treatment in all three cultivars, in the order Nandu > Perlo > Extradur. Development of whole plants was slightly delayed in Perlo and Nandu, but was accelerated significantly in Extradur. The rate of net photosynthesis under light saturation (Asat) decreased significantly in older, ozone‐fumigated leaves of Perlo and Nandu but not of Extradur. Leaf conductance (g1) showed a similar behaviour, but stomatal limitation (l) was similar between ozone‐treated and control plants. Thus, an ozone‐induced closure of stomata was not the reason for the observed difference in Asat. Perlo and Nandu showed a significant, only partly reversible decrease in Fv/Fm in ozone‐fumigated leaves, whereas in Extradur the decrease was fully reversible only in older leaves. Whole leaves of Extradur, in contrast to Perlo and Nandu, showed no increase in EPR free radical signals. The higher ozone tolerance of Extradur was thus not caused by decreased ozone uptake via the stomata, but by a better ability of photosynthetically active mesophyll cells to cope with photooxidative stress.
Mitochondrial and peroxisomal ascorbate peroxidase of pea leaves
Authors: Jiménez A. , Hernández J. A. , Barceló A. Ros , Sandalio L. M. , Del Río L. A. , Sevilla F.
Published: March 2003

The isoenzyme pattern and the substrate specificity of the membrane‐bound mitochondrial and peroxisomal ascorbate peroxidases (APX; EC 1.11.1.11) from pea leaves are studied. The substrate specificity of both APXs was assayed using the electron donors ascorbate and pyrogallol, whereas o‐dianisidine, hydroquinone, tetramethylbenzidine and 4‐methoxy‐α‐naphthol were also assayed with mitochondrial APX (mitAPX). In leaf mitochondria, the specific activity of APX was similar with pyrogallol and ascorbate, the activity being inhibited by p‐CMS. mitAPX showed low activity with the guaiacol peroxidase (GPX)‐type substrates, tetramethylbenzidine and 4‐methoxy‐α‐naphthol. Activity of mitAPX with hydroquinone suggest a potential role of mitAPX in the drainage of electrons from the mitochondrial electron chain at the level of ubiquinone. In peroxisomes, the APX (perAPX) specific activity was much higher with pyrogallol than with ascorbate. This perAPX was more sensitive to incubation with Triton X‐100 than the mitAPX. By native PAGE the mitAPX was resolved in 6 isoenzyme bands, and the activity of the 3 main bands (mitAPX III, III′ and IV) was inhibited by p‐CMS. These 3 major isozymes were also present in mitochondrial membrane fractions. Staining for GPX activity with 4‐methoxy‐α‐naphthol revealed that the APX detected in mitochondria did not have the capacity to oxidize 4‐MN, and therefore cannot be considered as true GPX. When intact peroxisomes and peroxisomal membranes were subjected to native PAGE, no APX activity could be detected and this was probably due to the inactivation of perAPX. Results obtained suggest that pea mitochondrial APX (mitAPX) represent a distinct and novel isozyme different from those APXs of chloroplast and cytosolic origin previously reported. The peroxisomal APX (perAPX), however, appears to ressemble the chloroplast APXs as regards its sensitivity to Triton X‐100.
Flavonoids in seed and root exudates of Lotus pedunculatus and their biotransformation by Mesorhizobium loti
Authors: Steele Helen L. , Werner D. , Cooper J. E.
Published: March 2003

Analysis of the flavonoid content of seed and root exudates of Lotus pedunculatus was undertaken using multiple coupled analytical techniques: capillary zone electrophoresis coupled to a UV spectral array detector (CZE‐UV), high performance thin‐layer chromatography with densitometry (HPTLC‐UV) and gas chromatography with mass spectrometry (GC‐MS). These procedures provided separation, identification and structural confirmation of the previously unidentified flavonoids in this plant's seed and root exudates and were particularly applicable to samples from a small seeded legume. Catechin, naringenin, kaempferol, quercetin aglycone and 3 different glycosides of quercetin were detected in seed exudate. Sterile root exudates contained catechin, naringenin and quercetin in addition to apigenin, kaempferol and other flavones and flavanones for which partial identifications were obtained. When sterile root exudate was incubated with Mesorhizobiumloti, changes in its flavonoid content were detected. Analysis of bacterial cells after incubation revealed the presence of quercetin, kaempferol and one other flavone. The monocyclic aromatics protocatechuic acid and phloroglucinol were detected in both the incubated root exudate and its bacterial cells.
Endogenous cytokinin accumulation and cytokinin oxidase activity during shoot organogenesis of Petunia hybrida
Authors: Auer Carol A. , Motyka Václav , Březinová Alena , Kamínek Miroslav
Published: March 2003

Changes in endogenous cytokinin content and cytokinin oxidase activity were characterized in leaf explants from two Petunia hybrida Vilm. genetic lines which differed in their shoot organogenic response to exogenous N6‐benzyladenine (BA). Endogenous cytokinin content in leaf explants of the highly shoot organogenic line, St40, increased 1.7‐fold during the shoot induction phase (days 6–10) and had an additional 2.6‐fold cytokinin increase correlated with the shift from induction to the shoot development phase. The cytokinins isopentenyl adenine (iP) and isopentenyl adenosine (iPAR) increased, while the cytokinins zeatin, zeatin riboside and dihydrozeatin remained at consistently low levels. In contrast, isoprenoid cytokinins did not accumulate in petunia TLV1 leaf explants which were incapable of shoot induction during 12 days of culture with BA. Cytokinin oxidase activity continuously increased in leaf explants of both petunia genotypes in response to BA, with a larger increase in St40. These results suggest that the differences in organogenic response in the two petunia genotypes may be the result of differences in BA uptake and metabolism which subsequently affects the accumulation of isoprenoid cytokinins and the activity of cytokinin oxidase in the early stages of shoot development.
Role of plant growth substances in MS33‐controlled stamen filament growth in Arabidopsis
Authors: Fei Houman , Sawhney Vipen K
Published: March 2003

The rapid growth of stamen filaments just before flower anthesis in Arabidopsis thaliana does not occur in the male sterile33 (ms33, formerly known as msZ) mutant. ms33 filaments were approximately 40% shorter than the wild type (WT), and there was corresponding reduction in the epidermal cell length of filaments. This suggests that MS33 controls the final cell‐elongation phase of filament growth. Both low temperatures and gibberellic acid (GA3) restored filament and cell growth in intact ms33 flowers, but these treatments only had a small promotive effect on WT filaments. Decapitation experiments involving the removal of the anther had the opposite effect on WT and ms33 filaments; growth was inhibited in WT, but was increased in ms33 filaments. In young stamen primordia cultured in vitro, filament growth was less in WT, but more in ms33, than in respective in vivo produced filaments. Plant growth substances (PGSs), GA3 and indole‐3‐acetic acid (IAA) were promotive, zeatin had no effect, and abscisic acid (ABA) and ethrel inhibited filament growth in both intact and decapitated WT and ms33 filaments. Together these observations suggest that MS33 is activated immediately before anthesis and that the MS33 product either regulates temporal biosynthesis of gibberellins (GAs) and/or IAA or makes the filament tissue sensitive to these PGSs, which in turn trigger cell elongation and filament growth. The data also suggest that ms33 mutant anthers contain a relatively high ratio of growth inhibitors to promoters, which inhibits epidermal cell elongation and filament growth.
Purification, immunolocalization, cryoprotective, and antifreeze activity of PCA60: A dehydrin from peach (Prunus persica)
Authors: Wisniewski Michael , Webb Robert , Balsamo Ron , Close Timothy J , Yu Xiao‐Ming , Griffith Marilyn
Published: March 2003

Dehydrins are glycine‐rich, hydrophilic, heat‐stable proteins and are generally induced in response to a wide array of environmental stresses. In previous research (Artlip et al. 1997, Plant Molecular Biology 33: 61–70), a full‐length dehydrin gene, ppdhn1, was isolated from peach, and its expression was associated with qualitative and quantitative differences in cold hardiness in sibling genotypes of evergreen and deciduous peach. Similar results were obtained for levels of the corresponding 60 kDa peach dehydrin protein (PCA60). The objective of the present study was to purify the PCA60, test the purified protein for cryoprotective and/or antifreeze activity, and to determine the cellular localization of PCA60 using immunomicroscopy. PCA60 was extracted from winter bark tissues of peach (Prunus persica [L.] Batsch) and purified in a two‐step process. Separation was based on free‐solution isoelectric focusing followed by size exclusion. Purified PCA60, as well as crude protein extract, preserved the in vitro enzymatic activity of lactate dehydrogenase after several freeze‐thaw cycles in liquid nitrogen. PCA also exhibited distinct antifreeze activity as evidenced by ice crystal morphology and thermal hysteresis. This is the first time antifreeze activity has been demonstrated for dehydrins. Immunomicroscopy, utilizing an affinity‐purified, polyclonal antibody developed against a synthetic peptide of the lysine‐rich consensus portion of dehydrins, indicated that PCA60 was freely distributed in the cytoplasm, plastids, and nucleus of bark cells and xylem parenchyma cells. Although the functional role of dehydrins remains speculative, the data support the hypothesis that it plays a role in preventing denaturation of proteins exposed to dehydrative stresses.
Response of phenolic metabolism to the application of carbendazim plus boron in tobacco
Authors: Ruiz Juan M. , Garcia Pablo C. , Rivero Rosa M. , Romero Luis
Published: March 2003

In view of the essential role of phenolic compounds in the development of pathogen resistance in plants, and given the influence that fungicides and boron (B) exert over phenolic metabolism, the aim of the present study was to determine the individual effect of the application of a fungicide, as well as to determine the joint effect of the fungicide and B on the metabolism of phenolic compounds in tobacco plants (Nicotiana tabacum L. cv. Tennessee 86). The fungicide applied was carbendazim (carb), a preventative fungicide, with a purity of 100% at a concentration of 2.6 mM. Boron was applied in the form of H3BO3 at: 1.6 mM (B1), 4 mM (B2), 8 mM (B3), 16 mM (B4), 32 mM (B5), or 64 mM (B6). In all, there were eight treatments: one without carb and without B (control), one with only carb, and six combinations of carb with each concentration of B. The results indicated that the foliar application with carb alone led to increases in phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5) activity and a foliar accumulation of phenols. This effect of the carb alone could signify an additional tolerance mechanism to pathogenic infection, given the participation of phenolic compounds in the lignification of plant cell walls. The joint application of carb and B increased both the biosynthesis and the oxidation of the phenolic compounds, especially in carb plus B3, while the application of carb plus B5 or carb plus B6 reduced these processes as well as the foliar biomass.
Protochlorophyllide, NADPH‐protochlorophyllide oxidoreductase, and chlorophyll formation in the lip1 mutant of pea
Authors: Seyyedi Mehdi , P. Timko Michael , Sundqvist Christer
Published: March 2003

The early steps in chloroplast development were characterized in wild‐type pea (Pisum sativum L. cv. Alaska) and the lip1 mutant with light‐independent photomorphogenesis. When grown in darkness, the wild type had a long slender epicotyl and undeveloped leaves while the lip1 mutant had seedlings with short epicotyls and well‐developed leaves. The leaves of the wild‐type Alaska pea had two fluorescence emission maxima of protochlorophyllide (Pchlide) at 630 and 655 nm. Leaves from the lip1 mutant had a fluorescence emission maximum at 632 nm with only a small shoulder at 655 nm. Flash irradiation of wild‐type leaves gave chlorophyllide (Chlide) with a fluorescence peak at 692 nm exhibiting a Shibata shift to 682 nm. The Chlide formed in lip1 leaves was diminutive with a maximum at 677 nm. Continuous irradiation led to the formation of a significant amount of Chlide, the esterification of which was considerably delayed in the lip1 plants. The transcript level of NADPH‐protochlorophyllide oxidoreductase (POR) was the same in dark‐grown lip1 and wild‐type leaves. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and immunoblots indicated the presence of POR (EC 1.3.1.33) in leaves of both wild‐type and lip1 dark‐grown seedlings. Just one band at 36 kDa was detectable. The level of the protein both in wild type and the lip1 mutant was stable during 6 h of irradiation. Large regular prolamellar bodies (PLBs) were common in dark‐grown wild‐type etioplasts, whereas lip1 etioplast inner membranes consisted mostly of prothylakoids (PTs). When present in lip1, the PLBs were rudimentary, but often a number of plastoglobuli were assembled in the etioplasts. The high content of POR was unexpected considering the observed lack of PLBs and Pchlide fluorescing at 655 nm. Immunogold labeling showed a distribution of POR among the PTs. It can be concluded that the formation and accumulation of POR in pea is, in itself, insufficient to induce PLB formation or the formation of long‐wavelength Pchlide forms. It appears that there also must be other factor(s) of importance, which are significant for the formation of the PLBs.
Mitochondrial β‐oxidation of fatty acids in higher plants
Authors: Masterson Christine , Wood Clifford
Published: March 2003

The subcellular localization of β‐oxidation of fatty acids in plants has been the subject of controversy for many years. Peroxisomes have been accepted as the sole site of fatty acid β‐oxidation for the past 15 years, whilst a proposed dual location, in both mitochondria and peroxisomes, has been disputed. Accumulated evidence demonstrating mitochondrial β‐oxidation now demands that a dual location for plant β‐oxidation must be considered.
Circadian rhythms in plants: a millennial view
Authors: Robertson McClung C.
Published: March 2003

Circadian rhythms are endogenous rhythms with periods of approximately 24 h. These rhythms are widespread both within any given organism and among diverse taxa. As genetic and molecular biological studies, primarily in a subset of model organisms, have begun to identify the components of circadian systems, there is optimism that we will soon achieve a detailed molecular understanding of circadian timing mechanisms. Although plants have provided many examples of rhythmic outputs, and our understanding of photoreceptors of circadian input pathways is well‐advanced, plants have lagged behind other groups of organisms in the identification of components of the central circadian oscillator. However, there are now a number of promising candidates for components of plant circadian clocks, and it seems probable that we will soon know the details of a plant central oscillator. Moreover, there is also accumulating evidence that plants and other organisms house multiple circadian clocks, both in different tissues and, quite probably, within individual cells. This provides an unanticipated level of complexity with the potential for interaction among these multiple oscillators.
Antioxidant status of anoxia‐tolerant and ‐intolerant plant species under anoxia and reaeration
Authors: Blokhina Olga B. , Virolainen Eija , Fagerstedt Kurt V. , Hoikkala Antti , Wähälä Kristiina , Chirkova Tamara V.
Published: March 2003

The redox potential of the cell, as well as the antioxidant status of the tissue, are considered to be important regulatory constituents in an adaptive response in plants. Here the involvement of active antioxidants ascorbic acid (AA), reduced glutathione (GSH) and α‐ and β‐tocopherols in reactive oxygen species scavenging, and the effect of anoxic stress on their reduction state were studied in 4 anoxia‐tolerant and ‐intolerant plant species: Iris germanica L., Iris pseudacorus L., wheat (Triticum aestivum L. cv. Leningradka) and rice (Oryza sativa L. cv. VNIIR). The initial antioxidant content (both AA and GSH) was higher in the rhizomes of the more anoxia‐tolerant Iris spp., as compared with that of the roots of the cereals. The predominant form of ascorbate was dehydroascorbic acid (DHA) in the cereals and AA in the Iris spp. Imposition of anoxia with subsequent reoxygenation resulted in an overall depletion of the reduced forms of antioxidants. No concurrent increase in oxidised forms (DHA and conjugated glutathione) was observed in anoxic samples. α‐tocopherol content in Iris spp. was in the range 1–2 μg g−1 fresh weight, while β‐tocopherol content was higher in the anoxia‐intolerant I. germanica (7.2 μg g−1 fresh weight) as compared with the tolerant I. pseudacorus (1.5 μg g−1 fresh weight). In I. pseudacorus, a significant decrease in α‐ and β‐tocopherol levels was observed only after long‐term (45 days) anoxia. The results suggested exclusion of AA and GSH from the redox cycling under prolonged anoxia, and a concomitant decrease in the redox state, as well as an anoxia‐induced depletion of α‐ and β‐tocopherols.
Polyamine, ethylene and other physico‐chemical parameters in tomato (Lycopersicon esculentum) fruits as affected by salinity
Authors: Botella M. Ángeles , Del Amor Francisco , Amorós Asunción , Serrano María , Martínez Vicente , Cerdá Antonio
Published: March 2003

Tomato plants (Lycopersicon esculentum Mill. cv. Daniela) were grown in perlite bags under greenhouse conditions to study the effect of different salinity levels (20, 40 and 60 mM NaCl) on fruit fresh weight, firmness, color, ethylene production, total 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and polyamine levels. Saline treatments were applied at different times: at the beginning of the plant growth period, and at the developmental stages of flowering of the first cluster and fruit growth of first cluster. Salinity, in general, increased fruit firmness, the intensity of red color, total ACC and ethylene production, while decreasing the final fruit weight. Polyamine levels (spermidine and putrescine) were also increased with salinity, especially when it was applied at the fruit growth of first cluster stage. The relationship between fruit firmness and elevated polyamine content as a result of saline stress is discussed.
Gibberellins in the control of photoperiodic flower transition in Pharbitis nil
Authors: Kulikowska‐Gulewska Halina , Majewska Magdalena , Kopcewicz Jan
Published: March 2003

The role of gibberellins in the photoperiodic flower induction of short‐day plant Pharbitis nil has been investigated. It has been found that the endogenous content of gibberellins in the cotyledons of P. nil is low before and after a 16‐h‐long inductive dark period. During the inductive night the content of gibberellins is high at the beginning of darkness and about the middle of the dark period. Exogenous GA3 when applied to the cotyledons of non‐induced plants does not replace the effect of the inductive night but it can stimulate the intensity of flowering in plants cultivated on suboptimal photoperiods. GA3 could also reverse the inhibitory effect of end‐of‐day far‐red light irradiation on P. nil flowering. 2‐Chloroethyltri‐methylammonium chloride (CCC) applied to the cotyledons during the inductive night also inhibited flowering. GA3 could reverse the inhibitory effect of CCC. The obtained results strongly suggest that gibberellins are involved in the phytochrome controlled transition of P. nil to flowering. Their effect could be additive to that of photoperiodic induction.
The mechanism of cobalt toxicity in mung beans
Authors: Liu J. , Reid R. J. , Smith F. A.
Published: March 2003

The effects of cobalt on the growth and nutrient balance of mung beans were investigated. Inhibition of seedling growth occurred at 5 μM Co and was associated with chlorosis of the younger leaves. Analysis of nutrient concentrations in root and leaf tissue of mung beans treated with 5 μM Co showed that none of the macronutrients and only two of the micronutrients, Mn and Fe, were significantly affected. The Mn concentration in roots was reduced by 55% and the Fe concentration in the leaves by 80%. Uptake of Fe into roots was not inhibited by Co but transport of Fe to the shoot was greatly reduced. It was shown that the effect of Co on growth was additive to that of Fe deficiency, which argues against Co‐induced Fe deficiency as the primary cause of growth inhibition by Co. Rather, it was considered that the high concentrations of Co in the roots and leaves compared with essential micronutrient cations can disrupt a range of metabolic processes due to competitive interactions. Comparison of the toxic effects of Co with those of other toxic trace metals Cd, Cu, Ni and Hg showed that at an applied concentration of 5 μM, there were obvious differences in both the visual symptoms and in nutrient concentrations. The main difference between Co and the other metals was that only Co stimulated the uptake of S into the plant and its transport to the shoots, where the S concentration in the leaves was increased 2‐fold. The common feature of all the trace metals examined was the strong inhibition of Fe transport to the shoot. A possible mechanism for the interaction of other trace metals with Fe transport is discussed.
Two γ‐tubulin isoforms are differentially expressed during development in Helianthus annuus
Authors: Petitprez Michel , Caumont Catherine , Barthou Henri , Wright Michel , Alibert Gilbert
Published: March 2003

The cytoskeleton is involved in major developmental events in plant cell growth and differentiation. Nucleation events play a key role in the dynamic and organization of the microtubule (Mt) cytoskeleton. Among many proteins involved in Mt nucleation, γ‐tubulin has been identified as an essential component of the Mt organizing centers (MTOC). In protoplasts, somatic embryogenesis induction has been correlated with remodeling of Mt cytoskeleton. We have investigated the specific developmental expression of γ‐tubulin in Helianthus annuus. Two γ‐tubulin isoforms have been detected by immunoblotting, with bands at 52 and 58 kDa. The larger γ‐tubulin (58 kDa) is present in all the sunflower tissues tested and is associated with the nucleus. The smaller γ‐tubulin (52 kDa), differing from the former at the carboxy‐terminal end, is only present in meristematic and dedifferentiated cells and is not bound to the nucleus. This first demonstration of the presence of two γ‐tubulins in plant cells is discussed in terms of distinct roles in the nucleation and organization of Mts.
Effects of nutrient supply on photosynthetic acclimation and photoinhibition of one‐year‐old foliage of Picea abies
Authors: Grassi Giacomo , Colom Manuel Rodolfo , Minotta Gianfranco
Published: March 2003

The present study examined the effect of nutrient supply on acclimation potential and photoinhibitory susceptibility in one‐year‐old foliage of shade‐grown Norway spruce (Picea abies Karst.) seedlings transferred to high‐light, as compared to seedlings grown in shade or in high‐light. After the transfer, the photosynthetic response to intercellular CO2 and chlorophyll fluorescence parameters were measured, and the allocation of leaf N within the photosynthetic apparatus was estimated. The effects of light and nutrient supply markedly differed. Light availability positively affected both photosynthetic capacity on an area basis (but not on a mass basis) and leaf N allocation to ribulose‐1,5‐biphosphate carboxylase/oxygenase (Rubisco), thereby increasing photosynthetic capacity per unit nitrogen. By contrast, nutrient supply in high‐light affected photosynthetic capacity both on an area and a mass basis, but did not affect the allocation of N within the photosynthetic apparatus. Fluorescence parameters indicated that shade‐grown seedlings transferred to high‐light with low‐nutrient supply, underwent prolonged photoinhibition. By contrast, transferred seedlings with high‐nutrient supply were able to avoid photoinhibition, increasing their photosynthetic capacity on an area basis. On the whole, nutrient shortage was found to prevent the acclimation response and to increase the photoinhibitory susceptibility to changing light conditions in P. abies mature needles.
Regulation of alcohol dehydrogenase gene expression in barley aleurone by gibberellin and abscisic acid
Authors: Macnicol Peter K. , Jacobsen John V.
Published: March 2003

The expression of the Adh1 gene (alcohol dehydrogenase, EC 1.1.1.1) was studied in the aleurone layer of barley (Hordeum vulgare cv. Himalaya). Expression increased markedly during grain development at the levels of activity, enzyme protein and mRNA. mRNA content, but not enzyme activity, could be increased further by exogenous abscisic acid (ABA) when isolated, de‐embryonated developing grains were pre‐treated with gibberellic acid (GA3) or fluridone. In isolated mature aleurone layers incubated with exogenous hormones, ADH mRNA was strongly up‐regulated by ABA and down‐regulated by GA3 within 6 h. With ABA, this increase in mRNA was followed by an increase in ADH protein and activity, peaking at 18 h. With GA3, the decrease in mRNA was accompanied by simultaneous decreases in protein and activity. In general, GA3 counteracted the effect of ABA and vice versa. In the aleurone of germinating grain, ADH activity decayed in a distal direction from the embryo, consistent with down‐regulation by gibberellin(s) diffusing from it. It was concluded that ADH gene expression in the aleurone of the intact grain is regulated by an ABA/gibberellin interaction.
Role of the Arabidopsis CBF transcriptional activators in cold acclimation
Authors: Thomashow Michael F. , Gilmour Sarah J. , Stockinger Eric J. , Jaglo‐Ottosen Kirsten R. , Zarka Daniel G.
Published: March 2003

Many plants increase in freezing tolerance upon exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. A fundamental goal of cold acclimation research is to identify genes with key roles in this response. Here we review results from our laboratory regarding the discovery of a family of transcriptional activators in Arabidopsis (Arabidopsis thaliana) that regulates the expression of freezing tolerance genes. Specifically, we have identified 3 genes that encode nearly identical transcriptional activators that bind to the CRT (C‐repeat)/DRE (dehydration responsive element) DNA regulatory element present in the promoters of many cold‐ and drought‐inducible genes, including those designated COR (cold‐regulated). These regulatory genes, CBF1, CBF2 and CBF3 (CRT/DRE binding factor), are located in tandem array on chromosome 4. Overexpression of the CBF genes in Arabidopsis induces expression of the entire battery of known COR genes and increases freezing tolerance without a low temperature stimulus. We have, therefore, proposed that the CBF genes are ‘master switches’ that activate a regulon of genes involved in cold acclimation. Significantly, the CBF genes themselves are responsive to low temperature; the levels of CBF transcripts begin increasing within 15 min of transferring plants to low temperature followed by accumulation of COR gene transcripts at 2–4 h. The CBF genes do not appear to be subject to autoregulation as the promoter regions have no evident CRT/DRE elements and overexpression of CBF1 does not induce expression of CBF3. Thus, we have suggested that COR gene induction involves a two‐step cascade of transcriptional activators: the first step, CBF induction, involving an unknown activator present at normal growth temperature and the second step, COR gene induction, involving the action of the CBF activators.
Regulation of 7S globulin gene expression in zygotic and somatic embryos of oil palm
Authors: Morcillo Fabienne , Hartmann Caroline , Duval Yves , Tregear James W.
Published: March 2003

We describe here the characterization and expression analysis of the oil palm GLO7A gene encoding a 7S globulin protein. Previous work carried out in our laboratory showed that 7S globulins accumulate in the oil palm zygotic embryo mostly between the 14 and 17 weeks after pollination. To investigate further the regulation of 7S globulin gene expression in both zygotic and somatic embryos of oil palm, we isolated a cDNA clone, GLO7A, for use as a probe in northern hybridization studies. The nucleotide sequence of the GLO7A cDNA reveals that it encodes a polypeptide of 572 amino acids (66 kDa) sharing significant sequence similarities with various vicilin‐like proteins of both dicotyledonous and monocotyledonous plants. Northern hybridization analysis shows that 7S globulin mRNA accumulation in zygotic embryos is temporally regulated with a profile essentially the same as that observed at the protein level. In somatic embryos, 7S globulin proteins were found to occur in amounts approximately 80 times lower than those in zygotic embryos. This lack of 7S globulin protein accumulation in somatic embryos is mirrored by a low accumulation of the GLO7A mRNA. The in vitro production of 7S globulins (and more generally salt‐soluble proteins) is improved by the addition to the culture medium of arginine, sucrose and ABA, the effects of these 3 components being additive. To investigate further the action of the 3 molecules of interest, we performed parallel studies on mRNA and protein abundance. Our studies of transcript accumulation suggest that ABA and sucrose act directly on mRNA synthesis or stability; however, it appears that there are also translational or post‐translational regulatory factors which act to limit protein accumulation in somatic embryos. The GLO7A gene promoter was cloned and sequenced to assess whether GLO7A gene expression might be modulated by cis‐acting promoter elements related to those found in other plants. Two motifs resembling ABREs (ABA‐responsive elements) and one motif resembling a seed‐specific promoter element were identified within the 5′ flanking sequence.
Oil bodies and their associated proteins, oleosin and caleosin
Authors: Frandsen Gitte I. , Mundy John , Tzen Jason T. C.
Published: March 2003

Oil bodies are lipid storage organelles which have been analyzed biochemically due to the economic importance of oil seeds. Although oil bodies are structurally simple, the mechanisms involved in their formation and degradation remain controversial. At present, only two proteins associated with oil bodies have been described, oleosin and caleosin. Oleosin is thought to be important for oil body stabilization in the cytosol, although neither the structure nor the function of oleosin has been fully elucidated. Even less is known about caleosin, which has only recently been described [Chen et al. (1999) Plant Cell Physiol 40: 1079–1086; Næsted et al. (2000) Plant Mol Biol 44: 463–476]. Caleosin and caleosin‐like proteins are not unique to oil bodies and are associated with an endoplasmatic reticulum subdomain in some cell types. Here we review the synthesis and degradation of oil bodies as they relate to structural and functional aspects of oleosin and caleosin.