bluuebunny/crossref_metadata_2025 huggingface dataset:
Light‐induced pigment degradation in leaves and ripening fruits studied in situ with reflectance spectroscopy
Authors: Merzlyak Mark N. , Gitelson Anatoly A. , Pogosyan Sergei I. , Lekhimena Lucianna , Chivkunova Olga B.
Published: March 2003

Pigment breakdown mediated by activated oxygen species is a consequence and a general symptom of oxidative stress and injury to plants. We have attempted to estimate the patterns of pigment bleaching and follow pigment susceptibility to irradiation as related to the process of senescence/ripening. Light‐induced pigment breakdown was studied in situ in the leaves of a shade‐requiring plant, wax flower (Hoya carnosa R. Br.), as well as in apple (Malus domestica Borlh. cv. Zhigulevskoe) and lemon (Citrus limon Burm. cv. Pavlovsky) fruits, using reflectance spectroscopy. It was found that the sensitivity of plant pigments to photobleaching increases as ripening progresses in lemon fruit. Kinetic analysis showed that in all systems a rapid breakdown of the pigment occurs after a lag‐phase. The signature analysis revealed a common pattern of chlorophyll and carotenoid changes, but degradation of the individual pigments was found to be inhomogeneous. Both in lemon and apple fruits a decrease in reflectance in the band of carotenoid absorption preceded pigment photodestruction. In the fruits, the bulk of chlorophyll b and the long‐wavelength chlorophyll a forms were degraded at early stages of the process whereas the breakdown of both chlorophylls in H. carnosa leaves was more synchronous. Prolonged irradiation induced bleaching of the main chlorophyll a band with maximum at 678 nm in the difference spectra, as well as carotenoids. Some features of reflectance spectra in the bands of chlorophyll and carotenoid absorption were found to be suitable for the differentiation of photo‐induced pigment breakdown from the transformation of the pigments taking place during senescence.
Identification and immunolocalization of superoxide dismutase isoenzymes of olive pollen
Authors: Alché Juan D. , Corpas Francisco J. , Rodríguez‐García Maria I. , Del Río Luis A.
Published: March 2003

Gametophytic tissues of plants are an area largely neglected in the broad literature on free radical processes in plants. In order to study the mechanisms of protection against oxidative stress in pollen, the presence of the key antioxidative enzyme superoxide dismutase (SOD; EC 1.15.1.1) was investigated. Crude extracts of olive tree (Olea europaea L.) pollen were subjected to native PAGE in 10% polyacrylamide gels. The SOD activity staining of gels showed the presence of four isoenzymes. All the SODS were completely inhibited by 2 mM KCN and 5 mM H2O2, and therefore belong to the family of CuZn‐SODS. Isoelectric focusing (pH 3.5‐7) of crude extracts and further detection of SOD activity allowed determination of isoelectric points for the four isoforms, namely 4.60, 4.78, 5.08 and 5.22. The cross‐reactivity of pollen extracts with a polyclonal antibody to cytosolic CuZn‐SOD from spinach leaves was assayed by western blotting. After SDS‐PAGE and immunoblotting, a major polypeptide band of about 16.5 kDa was detected, which is characteristic of the subunit of most CuZn‐SODS. Immunocytochemical studies at TEM level using the same antiserum showed that CuZn‐SOD was localized in the cytoplasm of both vegetative and generative cells, and also in material adhered to the pollen wall. The olive pollen CuZn‐SODS could function in the protection against oxidative stress during pollen development.
Purification and kinetic properties of a castor bean seed acid phosphatase containing sulfhydryl groups
Authors: Afonso Granjeiro Paulo , Veríssima Ferreira Carmen , Mauro Granjeiro José , Mikio Taga Eulázio , Aoyama Hiroshi
Published: March 2003

An acid phosphatase (EC 3.1.3.2) has been identified and purified from castor bean (Ricinus communis L., IAC‐80) seed through sulphopropyl (SP)‐Sephadex, diethylaminoethyl (DEAE)‐Sephadex, Sephacryl S‐200, and Concanavalin A‐Sepharose chromatography. The enzyme was purified 2 000‐fold to homogeneity, with a final specific activity of 3.8 μkat mg−1 protein. The purified enzyme revealed a single diffuse band with phosphatase activity on nondenaturing polyacrylamide gel electrophoresis, at pH 8.3. The relative molecular mass, determined by high‐performance liquid chromatography (HPLC), was found to be 60 kDa. The acid phosphatase had a pH optimum of 5.5 and an akpparent Km value for p‐nitrophenylphosphate of 0.52 mM. The enzyme‐catalyzed reaction was inhibited by inorganic phosphate, fluoride, vanadate, molybdate, p‐chloromercuribenzoate (pCMB), Cu2+ and Zn2+. The strong inhibition by pCMB, Cu2+ and vanadate suggests the presence of sulfhydryl groups essential for catalysis. The castor bean enzyme also recognized tyrosine‐phosphate and inorganic pyrophosphate (KPPi) as substrate. The highest specificity constant (Vmax/Km) was observed with KPPi, making it a potential physiological substrate.
Cultivar variability in the Agrobacterium‐rice cell interaction and plant regeneration
Authors: Lee Sung‐Ho , Shon Young‐Goel , Lee Soo In , Kim Cha Young , Koo Ja Choon , Lim Chae Oh , Choi Young Ju , Han Chang‐deok , Chung Chang Ho , Ryong Choe Zhin , Cho Moo Je
Published: March 2003

Thirteen cultivars of rice (Oryza sativa) were tested for plant regeneration from calli initiated from the scutella of mature seeds by water stress treatment using a high concentration of agarose, and examined for their response to Agrobacterium tumefaciens LBA4404, carrying a plasmid pTOK233, harboring genes for kanamycin resistance (nptII), hygromycin resistance (hpt) and β‐glucuronidase (gus). Plant regeneration frequency was considerably increased in most of the cultivars when the calli were treated with water stress, as compared with untreated controls. In particular, the cultivars Dongjinbyeo, IR43, Nagdongbyeo and Sinseonchalbyeo showed an increased frequency of shoot regeneration. Expression of GUS was detected in all of the co‐cultivated cultivars. Based on GUS expression at 3 days after co‐cultivation with A. tumefaciens, three rice cultivars (Dongjinbyeo, Hwayoungbyeo and Nagdongbyeo) were judged highly susceptible to A. tumefaciens, while Milyang 23, Nonganbyeo and Samgangbyeo cultivars were weakly susceptible. Plantlets were readily regenerated when the hygromycin‐resistant calli were transferred to a regeneration medium containing hygromycin. Intense blue staining was observed in GUS assays of leaf segments, roots and flower organs from regenerated plants. Stable integration and expression of the introduced hpt and gus genes were confirmed by Southern blot analysis of the transformants. Therefore, Dongjinbyeo and Nagdongbyeo cultivars proved to be both highly susceptible to A. tumefaciens and highly responsive to plant regeneration.
bushy, a dominant pea mutant characterised by short, thin stems, tiny leaves and a major reduction in apical dominance
Authors: Symons Gregory M. , Murfet Ian C. , Ross John J. , Sherriff Leanne J. , Warkentin Thomas D.
Published: March 2003

The spontaneous, single‐gene dominant, pea (Pisum sativum L.) mutant bushy is characterised by short, thin stems, tiny leaves and a proliferation of basal lateral branches. We symbolised the dominant mutant allele bsh and the recessive wild‐type allele BSH. Some effects were very large, e.g. the reduction in internode length was around 10‐fold in pure mutant plants. The effect on branching was qualitative under our conditions as the wild‐type did not branch and the mutant branched extensively. Analysis of epidermal cells indicated the reduction in internode length arose principally from a reduction in cell length. The bushy mutation also altered root morphology with a reduction in the number and length of lateral roots. Time to first open flower was increased but node of flower initiation was not affected. In a few cases, bushy plants died before producing an open flower even though tiny abortive flower buds were produced in the upper leaf axils. In pure mutant plants, individual seed weight was reduced by 30%, number of seeds per pod was reduced 3‐fold, and seed number per plant was reduced 4‐fold. However, pod size was essentially normal for a given seed content, and the flowers were fertile and of normal structure. Grafting studies showed the primary action of the bushy mutation occurred in the shoot. In summary, the reduced cell and shoot elongation, loss of apical dominance and a primary action in the shoot, all point toward auxin deficiency (or perceived deficiency) as a possible cause of the bushy phenotype. The overall characteristics of bushy make it a useful mutant for research on plant development.
A nuclear mutant of Arabidopsis thaliana selected for enhanced sensitivity to light‐chill stress is altered in PSII electron transport activity
Authors: Tarantino Delia , Vianelli Alberto , Carraro Luisa , Soave Carlo
Published: March 2003

Chilling in the light imposes a considerable level of stress on the photosynthetic apparatus, resulting in a decrease of photosystem II activity and the quenching of maximum and variable fluorescence. We selected in a fah‐1 mutagenized population of Arabidopsis thaliana, which permits a direct visible evaluation of the intensity of chlorophyll (Chl) fluorescence, a monogenic recessive nuclear mutant hypersensitive to photoinhibition induced by light and cold. The major phenotypic trait of the mutant is the appearance of chlorotic areas on developed leaves. Photochemical analyses indicate that the mutant is hypersensitive to photoinhibition in excess light in the cold but also at room temperature. The susceptibility to photoinhibition is a consequence of perturbations in photochemistry already present in unstressed plants. Such perturbations result in a greater fraction of the primary acceptor QA remaining in the reduced state even at low light fluxes. From estimates of the number of total and functional PSII units and measurements of PSII quantum yield and QA− reoxidation kinetics, the basic lesion of the mutant seems restricted to PSII photochemistry likely affecting the rate of electron transport from QA− to QB.
Effect of nitrogen concentration on fructan and fructan metabolizing enzymes in young chicory plants (Cichorium intybus)
Authors: Van den Ende Wim , De Roover Joke , Van Laere André
Published: March 2003

Witloof chicory seeds (Cichorium intybus L. var. foliosum cv. Flash) were sown in acid‐washed vermiculite in a controlled environment growth chamber. Plants received a nitrogen poor (“N‐poor”: 0.2 mM NH4NO3) but otherwise complete medium, or a nitrogen rich (“N‐rich”: 2 mM NH4NO3) medium. After 1 month of growth the fructan concentration in the “N‐poor” plants was about five times higher and also the activity of sucrose:sucrose 1‐fructosyl transferase (1‐SST; EC 2.4.1.99) was twice as high as in “N‐rich” plants. The activities of the catabolic enzymes fructan 1‐exohydrolase (1‐FEH; EC 3.2.1.80) and acid invertase (EC 3.2.1.26) were higher in the “N‐rich” plants where significant energy was invested in root and leaf growth. After one month of growth, part of the “N‐poor” plants were switched to the “N‐rich” medium. One day after this switch, a sharp decrease in sucrose and glucose concentration was observed in the roots. During the following days, both the activities of 1‐SST and fructan:fructan 1‐fructosyl transferase (1‐FFT; EC 2.4.1.100) decreased and the 1‐FEH and invertase activities increased. These changes were correlated with a decrease in fructan concentration. Ten days after the switch, glucose and sucrose concentrations increased again and fructan synthesis resumed. During this period 1‐SST activity increased and 1‐FEH activity decreased. Apparently 1‐SST, 1‐FFT and 1‐FEH simultaneously control fructan in young chicory roots. The rather unexpected finding that 1‐FEH activity, which was believed to occur only in older material, can be induced in very young roots indicates that this enzyme can be induced at any physiological stage.
Purification and characterization of a neutral peroxidase induced by rubbing tomato internodes
Authors: Loukili Az‐eddine , Limam Ferid , Ayadi Abdelkader , Boyer Nicole , Ouelhazi Lazhar
Published: March 2003

Rubbing applied to a young tomato internode inhibited the elongation of this internode and increased soluble peroxidase activity. These morphological and biochemical changes were observed both at the site of rubbing (local response) and in the neighbouring internode (systemic response). The cellular, biochemical, and molecular mechanisms leading to inhibition of internode elongation are not fully understood. It was proposed that mechanical stimuli increased the oxidation of IAA, via the induction of specific peroxidases and stimulated the lignification processes. In order to gain more information about the role of these enzymes, analysis of changes in peroxidase activities were performed. Qualitative analysis of isoperoxidases, by means of native cathodic PAGE, showed four induced isoforms termed C1, C2, C3, and C4. The major isoform (C2) was purified to homogeneity and partially characterized. This isoform is probably unglycosylated, with a molecular mass of 36 kDa and a neutral pI of 7.1. The effects of pH and temperature on the activity were determined with guaiacol as electron donor. Optima were obtained at pH 5 and at a temperature of 55°C. The activity of the purified enzyme was not affected by Ca2+, Mg2+ and Mn2+ as was reported for some basic peroxidases. Analysis of substrate specificity revealed that this isoperoxidase acted on ABTS, o‐dianisidine, pyrogallol, guaiacol, coniferyl alcohol (monolignol) and IAA but not on syringaldazine. Activitiy of C2 isoperoxidase on coniferyl alcohol and IAA suggests a possible role of peroxidase C2 in inhibition of internode elongation, observed in rubbed plants, probably via an increase in lignification processes and regulation of IAA levels in internode tissues.
The effect of ultraviolet radiation on photosynthesis and ultraviolet‐absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)
Authors: Karsten Ulf , Bischof Kai , Hanelt Dieter , Tüg Helmut , Wiencke Christian
Published: March 2003

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]‐A+UV‐B, solar without UV‐B, solar) on photosynthesis and the metabolism of UV‐absorbing mycosporine‐like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV‐A+UV‐B did not affect photosynthesis during the course of a day, solar without UV‐B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV‐A, and PAR+UV‐A+UV‐B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow‐water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV‐absorbing MAAs were detected in this alga, namely mycosporine‐glycine, shinorine, porphyra‐334, palythine, asterina‐330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV‐A and UV‐B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5‐fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5‐fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV‐A+B or with solar without UV‐B showed unchanged MAA contents, indicating a strong UV‐B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.
Physiological function of water channels as affected by salinity in roots of paprika pepper
Authors: Carvajal Micaela , Martínez Vicente , Alcaraz Carlos Francisco
Published: March 2003

The sap flow (Jv) and the osmotic pressure‐dependent hydraulic conductance (L0) of detached exuding root systems from paprika pepper plants (cv. Albar) were measured. Plants stressed with NaCl (30 mM) and with six times the macronutrients of the Hoagland nutrient solution (6×HNS) were compared with controls grown in complete Hoagland nutrient solution. Jv of +NaCl and +6×HNS plants decreased markedly, but recovered to values similar to those of controls after removal of the treatments. Hydraulic conductance L0 was always less in NaCl plants than in controls and 6×HNS. A total increase in the ion concentration of the xylem (except Na+ and Cl−) was observed with both treatments. In control and 6×HNS plants, HgCl2 treatment (50 μM) caused a sharp decline in L0 to values similar to those of NaCl‐stressed roots, but were restored by treating with 5 mM dithiothreitol (DTT). However, in NaCl roots only a slight effect of Hg2+ and DTT was observed. In each treatment, there was no difference in the flux of K+ into the xylem after HgCl2 and DTT application. The results suggest that NaCl decreased L0 of the roots by reducing either the activity or abundance of Hg‐sensitive water channels. The putative reduction in water‐channel function of NaCl‐treated plants did not seem to be due to the osmotic effect.
Abscisic acid levels in seeds of the gibberellin‐deficient mutant lh‐2 of pea (Pisum sativum)
Authors: Batge Shona L. , Ross John J. , Reid James B.
Published: March 2003

The lh‐2 mutation in garden pea (Pisum sativum L.) blocks an early step in the gibberellin (GA) biosynthesis pathway, the three‐step oxidation of ent‐kaurene to ent‐kaurenoic acid. As a result, only low levels of GAs, including the bioactive GA1, are found in shoots and seeds of lh‐2 plants. Mutant plants are dwarf in stature, and show increased seed abortion and decreased seed weight, compared with seeds of the tall wild‐type (WT) progenitor (cv. Torsdag). The aberrant seed development of lh‐2 plants is associated with reduced levels of GA1 and GA3, and with an accumulation of abscisic acid (ABA) in young seeds (pre‐contact point). This ABA accumulation is typically 3‐ to 4‐fold, and can be up to 6‐fold, compared with control plants. To investigate whether the accumulation of ABA is partly responsible for causing the observed seed abortion in lh‐2 plants, we constructed a double mutant between the lh‐2 allele and wil. The wil mutation blocks ABA biosynthesis, and reduces ABA levels in young seeds by 10‐fold. Introduction of the wil mutation reduces the endogenous ABA levels in young lh‐2 seeds, but fails to rescue the seeds from abortion. This indicates that the effects of lh‐2 on seed development are not mediated through increased ABA levels, and is consistent with previous evidence that GAs are the controlling factor underlying the lh‐2 seed phenotype in pea.
Oxygen‐dependent electron flow influences photosystem II function and psbA gene expression in the cyanobacterium Synechococcus sp. PCC 7942
Authors: Campbell Douglas , Clarke Adrian K. , Gustafsson Petter , Öquist Gunnar
Published: March 2003

During acclimated growth in Synechococcus sp. PCC 7942 a substantial proportion of the electrons extracted from water by photosystem II ultimately flow back to oxygen. This flow increases rapidly under high light, which allows Synechococcus to maintain photosystem II centers largely open, even under excessive excitation. The electron flow to oxygen with increasing light accounts for the progressive discrepancy between the light response curve of measured oxygen evolution, and the light response curve of photosystem II activity estimated from fluorescence measures. In cells under anoxia this flexible electron sink is lost and photosystem II centers suffer partial closure at the growth light intensity, with closure becoming more severe under excess light. As predicted from earlier work this PSII closure results in rapid loss of psbAI message, encoding the D1:1 protein of PSII, and induction of psbAII/AIII encoding the alternate D1:2 protein. The changes in the mRNA pool are not, however, reflected at the protein level, and D1:1 remains in the thylakoid membranes. There is no accumulation of D1:2, despite some continued synthesis of other proteins. PSII closure, therefore, results in repression of psbAI and induction psbAII/AIII expression, but D1:1/D1:2 exchange is blocked by anoxia, downstream from transcription. D1:1 protein and PSII activity are quite stable under anoxia and moderate illumination. Nevertheless, upon recovery under oxygenic conditions, the existing D1:1 is lost from the membranes, resulting in a transient drop in PSII activity. This suggests that under normal conditions the cells use oxygen to facilitate preemptive turnover of D1 proteins.
Quantitative trait loci for polyamine content in an RFLP‐mapped potato population and their relationship to tuberization
Authors: Davies Peter J. , Šimko Ivan , Mueller Suzanne M. , Yencho G. Craig , Lewis Candice , McMurry Susan , Taylor Mark A. , Ewing Elmer E.
Published: March 2003

DNA‐based genetic markers are now widely used by geneticists to locate genes for quantitative traits, and may also serve as a valuable tool for dissecting complex physiological phenomena. Van den Berg et al. (1996a QTL analysis of potato tuberization. Theor Appl Gen 93: 307–316), using restriction fragment length polymorphism (RFLP)‐mapped populations of potato, detected eleven quantitative trait loci (QTLs) for tuberization. Taylor et al. (1992 Expression and sequence analysis of cDNAs induced during the early stages of tuberisation in different organs of the potato plant [Solanum tuberosum L.]. Plant Mol Biol 20: 641–651) have identified one of the genes associated with tuberization as that for the enzyme S‐adenosylmethionine decarboxylase (SAMdc), an enzyme of the polyamine biosynthetic pathway. Chromosomal loci for SAMdc and arginine decarboxylase were established on the potato and tomato chromosomal maps, respectively, by hybridizing cDNA probes for these genes to RFLP digests. The polyamine content of leaves from an RFLP‐mapped potato population was analyzed by fluorescence detection following HPLC, with quantitation using an internal standard. The data were analyzed by the ‘qGene’ statistical program, and QTLs for polyamines were detected on seven chromosomes. At least six QTLs were found for spermine, two for spermidine, and two for putrescine. A spermidine QTL was on chromosome 5 linked to marker TG441, very close to the place where SAMdc mapped. There was some congruence between QTLs for spermine and those previously detected for tuberization and dormancy, but relationships were not consistent.
Expression of photosynthesis‐ and senescence‐related genes during leaf development and senescence in silver birch (Betula pendula) seedlings
Authors: Valjakka Maarit , Luomala Eeva‐Maria , Kangasjärvi Jaakko , Vapaavuori Elina
Published: March 2003

Leaf development and senescence were studied in greenhouse‐grown silver birch (Betula pendula Roth) seedlings over a period of 7 weeks. Prior to the experiment, leaves from 100 seedlings were marked for five sampling dates. Timing of the developmental phases was studied with biochemical analyses of total soluble protein, Rubisco protein, chlorophyll concentration and at the level of gene expression related to photosynthesis, energy metabolism, ethylene synthesis and protein degradation. During the sampling period, an initial increase in photosynthetic capacity could be seen, when expression of the Rubisco small subunit gene (RbcS) and Rubisco protein (EC 4.1.1.39) were examined. Down‐regulation of photosynthesis, visible as a decrease in Rubisco protein and RbcS mRNA, started soon after full expansion of the leaves and processes related to senescence followed. mRNA accumulation for the ethylene‐forming enzyme 1‐aminocyclopropane‐1‐carboxylic acid oxidase increased first during the onset of senescence. Protein degradation was observed as a loss of soluble proteins, with a simultaneous increase in the leucine aminopeptidase (EC 3.4.11.1) mRNA levels. The mRNA levels of ribonuclease‐like pathogenesis‐related protein 10 also increased clearly during senescence, but the mitochondrial phosphate translocator mRNA showed only a slight increase. Chlorophyll concentration of the leaves decreased after the mRNA levels of these senescence‐related genes had become more abundant.
8‐Epixanthatin, a light‐induced growth inhibitor, mediates the phototropic curvature in sunflower (Helianthus annuus) hypocotyls
Authors: Yokotani‐Tomita Kaori , Kato Jun , Yamada Kosumi , Kosemura Seiji , Yamamura Shosuke , Bruinsma Johan , Hasegawa Koji
Published: March 2003

The distribution of the endogenous auxin‐inhibiting substance, 8‐epixanthatin, was determined in the lighted and shaded sides of phototropically‐stimulated, de‐etiolated sunflower (Helianthus annuus L. cv. Taiyo) hypocotyls. From 40 min after the onset of phototropic stimulation, the growth rate at the lighted side was inhibited, whereas that at the shaded side showed no change. In the lighted side, 8‐epixanthatin increased by 20 min after the onset of unilateral illumination and, after 40 min, reached a 3‐fold larger concentration than that in the shaded side. Unilateral application of 8‐epixanthatin suppressed the growth of etiolated hypocotyls at the applied side only, causing the hypocotyls to bend at the site of application. It is concluded that phototropic curvature in sunflower hypocotyls is caused by a lateral gradient of the auxin‐inhibiting substance 8‐epixanthatin.
Cloning of Arabidopsis and barley cDNAs encoding HAK potassium transporters in root and shoot cells
Authors: Rubio Francisco , Santa‐María Guillermo E. , Rodríguez‐Navarro Alonso
Published: March 2003

Systematic reverse transcription‐polymerase chain reaction (RT‐PCR) isolations of cDNA fragments using specific primers for HAK mRNAs have revealed that plant HAK K+ transporters are extensively expressed in shoots and roots. At least 13 genes encoding this type of transporter have been identified in Arabidopsis. Apparently, most plant HAK transporters do not show functional expression in trk1 trk2 yeast mutants. In one of them, however, a point mutation increased the Vmax of transport approximately 10‐fold without affecting the Km or cation selectivity, suggesting that regulatory problems or targeting to the plasma membrane are the cause of failure for functional expression of this clone in yeast. The K+:Rb+:Cs+ selectivity of bacterial and eukaryotic Kup‐HAK transporters are coincident with the selectivity data given in the literature about alkali cation transport in different plant tissues, indicating that HAK transporters may be the most representative plant K+ transporters. Phylogenetic analysis of the 19 plant translated sequences that belong to this type of transporter shows that there are 4 different groups. In group I and II there are members in which high‐affinity K+ or Rb+ transport activity has been demonstrated. In other groups this has not been proved. However, present information suggests that all HAK transporters may be K+ transporters.
Conditioning period, CO2 and GR24 influence ethylene biosynthesis and germination of Striga hermonthica
Authors: Babiker Abdel Gabbar T. , Ma Yongqing , Sugimoto Yukihiro , Inanaga Shinobu
Published: March 2003

Germination of witchweed (Striga hermonthica [Del.] Benth), an important root parasite on poaceous crops, requires pretreatment ‘conditioning’ in a warm moist environment and a subsequent exposure to a stimulant. The roles of conditioning period, CO2 and a strigol analogue (GR24) in ethylene biosynthesis and germination of the parasite were investigated. Conditioning increased the seeds’ capacity to oxidize exogenous 1‐aminocyclopropane‐1‐carboxylic acid (ACC). Exogenous CO2 increased the seeds capacity to oxidize ACC by 3‐ to 9‐fold. A combination of GR24 and ACC increased ethylene production by more than 3‐fold in comparison with the rates obtained using these compounds separately. Aminoethoxyvinylglycine (AVG) completely inhibited ethylene induction by GR24, but not by ACC. A GR24 treatment, made subsequent to conditioning in GR24, did not induce ethylene. However, seeds conditioned in GR24 and then given 1 mM ACC produced 293 nl l−1 ethylene. ACC oxidase (ACCO) activity in crude extracts was increased by conditioning and CO2. The enzyme displayed an absolute requirement for ascorbate. Absence of exogenous Fe2+ reduced enzyme activity only by 14%. GR24 applied during conditioning reduced germination in response to a subsequent GR24 treatment. ACC was, invariably, less effective in inducing S. hermonthica germination than GR24 even at concentrations which induce more ethylene than concurrent GR24 treatments. The results are consistent with a model in which conditioning removes a restriction on the ethylene biosynthetic pathway in S. hermonthica seeds. GR24 modulates the key enzymes in ethylene biosynthesis. The stimulant suppresses ethylene biosynthesis in unconditioned seeds and promotes it in conditioned ones. Germination of S. hermonthica results from the joint action of GR24 and the ethylene it induces.
Beech trees exposed to high CO2 and to simulated summer ozone levels: Effects on photosynthesis, chloroplast components and leaf enzyme activity
Authors: Lütz Cornelius , Anegg Sabine , Gerant Dominique , Alaoui‐Sossé Badr , Gérard Joëlle , Dizengremel Pierre
Published: March 2003

Young trees of European beech (Fagus sylvatica L.) were exposed in a phytotron to different levels of ozone and CO2 under the climatic simulation of one vegetation period. High ozone levels were simulated similar to high ozone concentration in the field (up to 110 ppb), while CO2 was added as 300 ppm to the present level of ca 380 ppm. Our study describes different aspects of photosynthesis from the leaf level to the reactions of selected thylakoid components at different harvest times during growth of the beech trees under the different fumigation regimes. Ozone effects appeared in the first weeks of the treatment as a stimulation of chlorophyll fluorescence (Fv/Fm), in oxygen production and in ribulose‐1,5‐bisphosphate carboxylase/oxygenase activity, while the summer and early autumn harvests showed strong reductions in these parameters. Only phosphoenolpyruvate carboxylase (PEPcase) activity remained higher under high ozone. The effects of high CO2 appeared in general as a small stimulation in enzyme activity like PEPcase in spring. However, with increasing time of fumigation, reductions of all parameters were observed. Especially chlorophylls showed strong reductions under high CO2. The combined treatment with high ozone plus high CO2 resulted mostly in an amelioration of the negative ozone effects, although control levels were not reached.
Effect of light quality and 5‐azacytidine on genomic methylation and stem elongation in two ecotypes of Stellaria longipes
Authors: Tatra Gurminder S. , Miranda Jacintha , Chinnappa Chendanda C. , Reid David M.
Published: March 2003

Changes in cytosine methylation are known to occur in response to various environmental stimuli, therefore, we looked at methylation changes in relation to stem elongation. More specifically, we investigated the response of genomic cytosine methylation to irradiance‐mediated plasticity of stem elongation in two ecotypes of Stellaria longipes. Ramets of S. longipes were grown under high and low ratios of red/far‐red light (F/FR; 3.7 and 0.7, respectively). Stem elongation and methylated cytosine content were measured over a period of 7 days. Ramets of S. longipes demonstrated the highest level of demethylation after 4 days of long‐day warm (LDW) treatment, which coincides with the first day of rapid stem elongation initiation. The extent of demethylation associated with day 4 depended upon the relative ratio of R/FR light. In particular, those plants treated with low R/FR light ratios showed a lower level of methylation, and were taller than the high R/FR light grown counterparts. In addition, prairie ecotype plants demonstrated lower day 4 methylation levels, as well as longer day 7 stem lengths, than the alpine ecotype plants within the same R/FR light treatments. To investigate if the degree of methylation was a crucial factor in controlling the stem elongation response, ramets of both alpine and prairie plants were grown in MS media supplemented with 5‐azacytidine (5‐AzaC), and grown for 14 days under a R/FR ratio of 3.7 and two different PAR values. 5‐AzaC treatments demonstrated that the prairie ecotype plants required greater doses of 5‐AzaC, and thus lower methylation levels, than the alpine ecotype plants in order to promote maximal stem elongation. These observations suggest that DNA demethylation is involved in the shade‐avoidance response.
Regulation of flower pigmentation and growth: Multiple signaling pathways control anthocyanin synthesis in expanding petals
Authors: Weiss David
Published: March 2003

Anthocyanins are the major flower pigments in higher plants. In most cases, anthocyanin accumulation is an integral part of flower development and the processes of petal pigmentation and cell expansion are tightly linked. Activation of the anthocyanin pathway during petal development requires a complex interaction between environmental and developmental signals. Using Petunia hybrida flowers as a model, some of these signals were identified and characterized. Gibberellins (GAs), sugars and light were shown to be required for the induction of anthocyanin gene transcription and for accumulation of the pigment in the developing corolla. It was also shown that the effect of these signals is not specific for the pigment's biosynthesis, they also control petal cell expansion and induce the expression of genes from various pathways. These results support a model in which GAs, light and sugars promote the activity of master transcription regulators that control various pathways to complete the entire process of flower development.
Stamen abscission and water balance in Metrosideros flowers
Authors: Sun Jian , Jameson Paula E. , Clemens John
Published: March 2003

Cymules (3‐flowered units borne on single pedicels) were cut from inflorescences of Metrosideros collina J.R. & G. Forst. cv. Tahiti and used to test the effects of ethephon and ethylene on stamen abscission in the presence of silver thiosulphate (STS) and 1‐methylcyclopropene (1‐MCP), and to test the effects of holding solutions on cymule water balance and the progression of floral development. Flower bud and stamen abscission occurred in response to 0.5–5.0 and 0.1 μl l−1 ethylene, respectively. Ethylene effects were partially negated by scrubbing exogenous ethylene, and more completely negated by STS (2.0 mM). 1‐MCP caused greater ethylene production and inhibited stamen abscission for only 1–2 days after treatment. Ethephon (10‐10 000 mg l−1) induced stamen wilting rather than abscission, an effect that was not negated by STS. Stamen wilting was negatively correlated with stamen relative water content, and the increase in stamen wilting was generally reduced by treatments that enhanced cymule mass. Stamen wilting was least using a 100 g l−1 sucrose pulse or holding solutions containing 30–40 g l−1 sucrose, with hydroxyquinoline citrate (200 mg l−1) maintained at pH 5. Our results indicate that 1‐MCP may be relatively ineffective in blocking the effects of ethylene on the abscission of organs, such as the stamens of M. collina, which are highly sensitive to this hormone.
Ascorbic acid metabolism during white spruce somatic embryo maturation and germination
Authors: Stasolla Claudio , Yeung Edward C.
Published: March 2003

Changes in ascorbic acid (AA) metabolism were investigated in 3 different cell lines of white spruce; a non‐embryogenic line (NE)WS and two embryogenic lines with low (E)WS1 and high (E)WS2 percentage of embryo germination. During embryo maturation, a high AA/dehydroascorbate (DHA) ratio was observed in the two embryogenic cultures. The increment of this ratio was mainly ascribed to the high ability of the (E)WS1 and (E)WS2 lines to generate AA from its last precursor, l‐galactono‐γ‐lactone, since no increase in the activities of the AA‐recycling enzymes, i.e., AA free‐radical reductase (AFRR) and DHA reductase (DHAR), was observed as the embryos developed. During the partial drying treatment needed for successful embryo germination, the ability to de novo generate AA continued to increase in the embryos of the two embryogenic lines, although the total ascorbate pool (AA+DHA) sharply decreased. A reactivation of the overall AA metabolism was observed at the inception of germination, especially in the (E)WS2 embryos. These results suggest that (1) the ability to metabolically alter the AA/DHA ratio may be a fundamental requirement for somatic embryo maturation and (2) the restoration of the AA metabolism during the first days of germination may be necessary for successful embryo germination.
Characterization and expression of two members of the peach 1‐aminocyclopropane‐1‐carboxylate oxidase gene family
Authors: Ruperti Benedetto , Bonghi Claudio , Rasori Angela , Ramina Angelo , Tonutti Pietro
Published: March 2003

The characterization and expression of PP‐ACO1 and PP‐ACO2, two members of the peach 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase (ACO) gene family, are reported. PP‐ACO1 is organized in 4 exons interrupted by 3 introns, whereas PP‐ACO2 has only 2 of the 3 introns present in PP‐ACO1. Comparison of the deduced amino acid sequences of PP‐ACO1 and PP‐ACO2 reveals a 77.7% identity. PP‐ACO1 and PP‐ACO2 show highest degree of similarity with petunia (PH‐ACO3; 84.1%) and apple (85.4%) ACO genes, respectively. PP‐ACO1 is expressed in flowers, fruitlet abscission zones, mesocarp and in young fully expanded leaves. PP‐ACO1 transcript accumulation strongly increases during fruitlet abscission, in ripe mesocarp and senescing leaves, and is enhanced by propylene. PP‐ACO2 mRNA accumulation is detected in fruits only during early development and is unaffected by propylene treatment. Both ACO genes are expressed in epicotyl and roots of growing seedlings, although a stronger accumulation of PP‐ACO2 mRNA is observed.
Effect of ripening on texture, microstructure and cell wall polysaccharide composition of olive fruit (Olea europaea)
Authors: Mafra Isabel , Lanza Barbara , Reis Ana , Marsilio Vincenzo , Campestre Cristina , De Angelis Mario , Coimbra Manuel A.
Published: March 2003

Olive fruits at the green, cherry and black stages were used to investigate the structural and microstructural changes in tissues during ripening. Scanning electron microscopy (SEM) tissue fracture of green olives resulted in cell wall breakage of epicarp and mesocarp cells. Tissue fracture resulted in fewer broken cells in cherry than in green olives and even less in black olive tissues. Cell separation occurred in the middle lamella region in some of the cells of the cherry fruit and in most of the black olive cells. Solubilization and loss of pectic polysaccharides, mainly the arabinan moiety, and glucuronoxylans occurred in the green to cherry stages. The pulp cell wall constituent polysaccharides, pectic polysaccharides, cellulose, glucuronoxylans and xyloglucans, were degraded and/or solubilized at the cherry to black ripening stages. The resultant depolymerization of the pectic polymers, especially those of the middle lamella region, was consistent with the progressive cell separation at the different ripening stages by SEM. This showed that partial solubilization of pectic, hemicellulosic and cellulosic polysaccharides within the cell wall matrix weakened the cell wall structures, preventing the breaking of cells when the tissues were fractured.
Auxin modification of the incompatibility response in Theobroma cacao
Authors: Hasenstein K. H. , Zavada M. S.
Published: March 2003

The time course and control of floral abscission and fruit set in Theobroma cacao were studied after spray application of growth regulators. 1‐Naphthaleneacetic acid (NAA) prevented flower abscission in a concentration dependent manner and induced the early stages of fruit development. The cytokinin benzylaminopurine (BAP) counteracted NAA but resulted in longer fruit retention. Measurements of endogenous levels of indole‐3‐acetic acid showed an inverse correlation between the number of flowers per plant and auxin content. The results suggest that the genetic control of self‐incompatibility in T. cacao may be modulated by the hormonal content of the flower.
Involvement of multiple cis‐elements in the regulation of GA responsive promoters: Definition of a new cis‐element in the Amy32b gene promoter of barley (Hordeum vulgare)
Authors: Gómez‐Cadenas Aurelio , Zentella Rodolfo , Sutliff Thomas D. , Ho Tuan‐Hua David
Published: March 2003

The Amy32b gene is a member of the low‐pI α‐amylase gene family of barley, whose expression is tightly regulated by hormones in the aleurone layer. Four cis‐elements are known to be important for the GA induction of this gene: GARE, amylase box, pyrimidine box, and O2S. These sequences are located between −101 and −149 relative to the transcription start site. In the present work, we have created a series of Amy32b promoter‐GUS reporter constructs introducing mutations in the −79 to −93 region. Using a transient expression system, we have functionally defined an additional region (−81 to −89) essential for the GA activation of the Amy32b promoter. This region is highly conserved among barley, wheat, and wild oat low‐pI α‐amylase promoters. Interestingly, in contrast with the variability in the relative distances among other cis‐elements, this region maintains a nearly constant distance to GARE, which suggests that the function of these elements might be coupled. The involvement of this and other sequences in the transactivation of Amy32b by a transcription factor, GAMyb, has also been studied. Our results indicate that the only indispensable element for the GAMyb transactivation of the α‐amylase promoter is GARE. The present work brings new evidence to the proposed model that considers the GAMyb‐GARE interaction as a critical point for the GA induction of α‐amylase genes, but also strengthens the notion that multiple sequences are required for full regulation of α‐amylase promoters.
Developmental expression and perturbation of arabinogalactan‐proteins during seed germination and seedling growth in tomato
Authors: Lu Hua , Chen Ming , Showalter Allan M.
Published: March 2003

Arabinogalactan‐proteins (AGPs) are a family of highly glycosylated hydroxyproline‐rich glycoproteins present throughout the plant kingdom. A synthetic chemical reagent, (β‐d‐Gal)3 Yariv reagent, specifically binds AGPs and can be used for histochemical staining, isolating and probing the function of AGPs. Here, the role of AGPs in tomato (Lycopersicon esculentum Mill. cv. UC82B) seed germination and seedling growth was examined by following expression of AGPs during these events and by treatment with (β‐d‐Gal)3 Yariv to perturb AGP function. AGP expression changed during germination and seedling development both quantitatively and qualitatively as revealed by analysis of total AGP content, crossed electrophoresis patterns, RNA blots using LeAGP‐1 probe, and western blots with LeAGP‐1, JIM13, and MAC207 antibodies. (β‐d‐Gal)3 Yariv treatment of seeds and developing seedlings did not affect percent seed germination, but markedly inhibited seedling growth in roots and to a lesser degree in shoots. Root growth inhibition encompassed reductions in overall root length, epidermal root cell elongation, root cell numbers and root hair formation. This growth inhibition was reversible following removal of (β‐d‐Gal)3 Yariv. In a related experiment, water uptake by tomato seedlings was greatly inhibited by (β‐d‐Gal)3 Yariv treatment. Based on these experiments, AGPs are clearly associated with tomato seedling development and likely to function in root growth, more specifically in cell elongation, cell proliferation, root hair formation and water uptake.
Continuous CO2 enrichment leads to increased nodule biomass, carbon availability to nodules and activity of carbon‐metabolising enzymes but does not enhance specific nitrogen fixation in pea
Authors: Cabrerizo Pablo M. , González Esther M. , Aparicio‐Tejo Pedro M. , Arrese‐Igor Cesar
Published: March 2003

Recent research has shown that nodule nitrogen fixation is limited under a wide range of environmental constraints by lowered carbon flux within the nodule due to down‐regulation of sucrose synthase activity. The aim of this work was to elucidate whether an increase in both carbon flux and activity of enzymes of carbon metabolism in nodules may lead to an increased nitrogen fixation. We report the effects caused by a continuous exposure to atmospheric CO2 enrichment in nodulated pea plants. CO2 enrichment led to an enhanced whole‐plant growth and increased nodule biomass. Moreover, nodules of plants grown at increased CO2 showed a higher sugar content as well as enhancement of some activities related to nodule carbon metabolism, such as sucrose synthase, UDP glucose pyrophosphorylase and phosphoenolpyruvate carboxylase. Indeed, acetylene reduction activity, measured by the classical technique, was increased more than four times. However, when specific nitrogen fixation was determined as hydrogen evolution, no significant differences were detected, consistent with the lack of changes of enzymes involved in nitrogen metabolism such as glutamate synthase and aspartate aminotransferase. These results are discussed in the context of the regulation of nitrogen fixation and nodule metabolism.
Effect of 1‐methylcyclopropene on ethylene‐induced abscission in citrus
Authors: Zhong GuangYan , Huberman Moshe , Feng Xu Qiao , Sisler Edward C. , Holland Doron , Goren Raphael
Published: March 2003

Pre‐treatment of citrus leaves and leaf explants (Citrus sinensis [L.] Osbeck cv. Shamouti), with 1‐methylcyclopropene (1‐MCP), induced endogenous ethylene production when leaves were further incubated in air. The induction of ethylene production was 1‐MCP concentration‐dependent. Abscission was concomitantly delayed. In leaves pre‐treated with 1‐MCP followed by exposure to ethylene, abscission was significantly delayed in comparison with those without 1‐MCP pre‐treatment. When leaf explants were co‐treated for 24 h with ethylene and 1‐MCP, abscission was delayed quite efficiently. The Lineweaver‐Burke plot yielded a half‐maximal value of 0.234 μl l−1 for the effect of ethylene on abscission. 1‐MCP−1 competed kinetically with ethylene with a Ki value of approximately 1.4−5.5 nl l−1 1‐MCP. Under these experimental conditions there was some competition between 1‐MCP and ethylene. However, ethylene was not able to completely counteract the inhibitory effect of 1‐MCP. Pre‐treatment with 1‐MCP, followed by exogenous ethylene treatment, suppressed the induction of endo‐β‐glucanase (EG) activity at the laminar abscission zone. The ethylene‐dependent accumulation of the hydrolyse gene was demonstrated by blocking the accumulation of CsCel a1 mRNA by 1‐MCP. Six hours of exposure of leaves to 1‐MCP at various times during a total of 24 h ethylene treatment efficiently reversed ethylene induction of CsCel a1 gene at mRNA level up to 18 h. The results demonstrate that the induction of abscission by ethylene is controlled at mRNA level at the abscission zone.