bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal transduction in blue light‐induced oxygen uptake in Chlorella cells
Authors: Kamiya Akio
Published: March 2003

In DCMU‐poisoned wild‐type and in non‐photosynthetic pigment mutant cells of Chlorella kessleri, grown heterotrophically with glucose as a carbon source and with nitrate as sole nitrogen source, the known blue light‐enhanced uptake of oxygen and breakdown of starch were reduced by staurosporine and K252a, both potent inhibitors of protein kinase C. This corresponded to sensitivity to these inhibitors of blue light‐induced uptake of nitrate of such organisms. Cells grown with ammonia as sole nitrogen source responded to short wavelength visible irradiation with an increase in oxygen uptake, and this, too, was inhibited by staurosporine and K252a. However, these cells did not show any blue light‐enhanced uptake of nitrate. From these results, enhanced consumption of oxygen under blue light cannot be a consequence of blue light‐induced protein phosphorylation involved in the light‐dependent uptake of nitrate. However, existence of a specific protein phosphorylation within the process of enhancement of oxygen uptake under blue light is not yet proven by the data. There might be a master reaction that induces both processes independently, or there may be influences of other light‐induced processes which lead to enhanced starch breakdown, thereby supplying the glucose for oxidative degradation.
Seasonal pattern of accumulation and effects of low temperatures on storage compounds in Trifolium repens
Authors: Bouchart V. , Macduff J. H. , Ourry A. , Svenning M. M. , Gay A. P. , Simon J. C. , Boucaud J.
Published: March 2003

The seasonal pattern of concentrations of nitrogen, starch and vegetative storage protein (VSP) in stolons of Trifolium repens L. grown in the field were studied. Two different genotypes, cv. Aran and cv. Rivendel, differing in their morphology (stolon thickness and branching rate) but with similar growth rates, were used. Maximum concentrations of starch were found in summer whereas hydrolysis of starch took place throughout winter, suggesting that C storage is more important for winter survival than for promotion of early spring growth. On the other hand, VSP and nitrogen accumulated in autumn and early winter and then decreased when growth was resumed during early spring. For both cultivars, an inverse relationship was found between VSP concentration in stolons and mean air temperature, suggesting that VSP accumulation may be triggered by low temperature. Further experiments with plants grown under different regimes of temperature and daylength, suggested that VSP synthesis is stimulated by low root temperatures, with a slight synergistic effect of short daylength.

The effects of root temperature on growth, N2 fixation, NH4+ uptake and N allocation within Trifolium repens L., were studied under controlled conditions. The shoot growth rate was greatly reduced when root temperatures were lowered from 12 to 6°C, while the rate of stolon growth was less affected. Low root temperatures inhibited N2 fixation more than it did NH4+ uptake, but the relative allocation of N to stolons was increased. Lowering root temperature also increased the accumulation of VSP in stolons. These results are discussed in terms of the mechanism associated with low temperature stimulation of VSP accumulation and its coupling with changes in the source/sink relations for allocation of N, between growth and storage.
A spontaneous point mutation in the Rubisco large subunit gene impairing holoenzyme assembly renders the IVβ plastome mutant of Oenothera extremely light‐ and chilling sensitive
Authors: Dauborn Babette , Brüggemann Wolfgang
Published: March 2003

A spontaneously occurring chloroplast genome (plastome) mutant of Oenothera, IVβ, was identified as a single point mutation in the Rubisco large subunit gene (G337 → C), leading to an V113L exchange, which topologically occurs at the interface of two adjacent large subunits (LSU). The minor sterical hindrance of dimer formation by this amino acid exchange strongly impairs holoenzyme assembly, leading to an accumulation of a processing precursor of the holoenzyme, the B‐complex, consisting of one LSU and 14 units of chaperonine 60 (cpn60). It is associated with very low holoenzyme concentrations in the mutant tissue, but does not affect the kinetic properties of the enzyme once assembled. When grown under moderate or low light, leaf tissue containing the plastome mutant showed decreased Chl contents and Chl a/b ratios, increased relative carotenoid contents and violaxanthin deepoxidation activity, but very low CO2 fixation and O2 evolution rates and was very sensitive to photoinhibition. The light dependence of chlorophyll fluorescence quenching components at low temperature resembled an extremely chilling sensitive Oenothera genotype as compared to the wild‐type. The IVβ mutant thus behaves similarly to the Rubisco SSU antisense plants analysed by Stitt and co‐workers (summarised by Stitt and Schulze 1994) and gives an example of the possible influence of plastome mutations on the sensitivity of the photosynthetic apparatus to excess light by modifying the capacity of the Calvin cycle.
Ethylene negatively regulates local expression of plant defense lectin genes
Authors: Zhu‐Salzman Keyan , Salzman Ron A. , Koiwa Hisashi , Murdock Larry L. , Bressan Ray A. , Hasegawa Paul M.
Published: March 2003

Griffonia simplicifolia leaf lectin II (GS‐II) is a N‐acetylglucosamine (GlcNAc) binding protein, consisting of large (rGS‐II) and small (sGS‐II) subunits, that is presumed to function in plant defense because both the holoprotein and the rGS‐II inhibited insect growth and development in feeding bioassays. A cDNA encoding sGS‐II has been isolated and the deduced peptide has sequence similarity to class III chitinases. However, neither the GS‐II holoprotein nor bacterially expressed recombinant sGS‐II proteins had detectable chitinase or lysozyme activities. Both rGS‐II and sGS‐II mRNAs accumulated in response to methyl jasmonate (Me‐JA) treatment but not after wounding in local leaves unless injury was followed by treatment with the ethylene action inhibitor norbornadiene (NBD). Salicylic acid (SA) suppressed wounding/NBD induction of GS‐II transcript accumulation and ethylene inhibited Me‐JA‐induced expression. Apparently, defensive gene expression induced by signal transduction through the octadecanoid pathway in local leaves is suppressed by stress induced ethylene that is produced as a consequence of wounding. However, in leaves systemic to the wound site, rGS‐II mRNA levels increased substantially indicating that physiological levels of ethylene are insufficient to down regulate defensive gene expression away from the site of injury. It seems that G. simplicifolia has evolved a rather specialized response to herbivore attack whereby local activation of defensive gene expression is attenuated in order to mount a more substantial defense distal to the site of invasion.
Abscisic acid and stress regulate the expression of calmodulin in germinating chick‐pea seeds
Authors: Nicolás Carlos , DePrada José María , Lorenzo Oscar , Nicolís Gregorio , Rodriguez Dolores
Published: March 2003

A full‐length cDNA clone for calmodulin has been isolated from a cDNA library constructed from mRNAs of chick‐pea seeds germinated for 48 h in H20, using a calmodulin cDNA clone from Fagus sylvatica as a probe. The amino acid sequence of the clone shows high homology (> 80%) with other plant and animal calmodulins. The corresponding transcripts, analysed by northern blot, are present during embryogenesis, increase along with seed germination and are repressed by abscisic acid and by several stress conditions (water, salt and heat stress) which inhibit chick‐pea seed germination. The results obtained suggest that the expression of calmodulin is related to the ability of these seeds to germinate.
Immediate and steady state extracellular ionic fluxes of growing Arabidopsis thaliana root hairs under hyperosmotic and hypoosmotic conditions
Authors: Lew Roger R.
Published: March 2003

Osmotic‐induced shifts in extracellular ionic fluxes at the apex of growing Arabidopsis thaliana L. root hairs were examined using the extracellular self‐referencing (vibrating) ion‐selective probe technique. With either APW 7 (artificial pond water, pH 7) or APW 7 plus 200 mM mannitol/sorbitol, a steady state was reached in which growth rates were the same (0.75 and 0.82 µm min−1) as were the net fluxes of calcium (inward), potassium (outward), and chloride (inward). The outward flux of protons was about 20‐fold larger in APW 7 plus 200 mM mannitol/sorbitol compared to APW 7 (P= 0.028). Significant changes in ionic fluxes within 5 min of osmotic changes were observed for hyperosmotic treatment: a 7.5‐fold increase in the inward calcium flux (P= 0.041) and a 1.7‐fold increase in the outward potassium flux (P= 0.007). Although the change in the calcium flux was consistent with a process of osmotic adjustment (and not a consequence of binding/release from the cell wall), the magnitude of the flux was considerably less than the potassium efflux. Unlike the situation in other organisms where volume regulation explicitly relies upon modulation of ionic fluxes (especially sodium, potassium and chloride), the root hairs may rely on other mechanisms of osmotic regulation, possibly coupled to differences in proton efflux under steady state growth conditions. The root hairs do exhibit an osmotic‐induced electrical signal (R. R. Lew. 1996. Plant Physiol. 112: 1089–1100) which may be a component of initial signal transduction controlling osmotic regulation.
Membrane lipid composition and restoration of photosynthesis during low temperature acclimation in Synechococcus sp. strain PCC 7942
Authors: Porankiewicz J. , Selstam E. , Campbell D. , Öquist G.
Published: March 2003

We compared temperature acclimation of the cyanobacterium Synechococcus sp. strain PCC 7942 and two psbA inactivation mutants, R2K1 and R2S2C3, following shifts from 37 to 25°C. Wild‐type cultures incubated in the dark at 25°C showed no chill‐induction of lipid desaturation, probably because the lipid acclimation is dependent on photosynthesis. Incubation in the light at 25°C, however, induced considerable increases in membrane lipid desaturation, and within 24 h the monoenoic fatty acids increased from about 46 to about 57%. In parallel with this desaturation the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol (MGDG/DGDG) increased. Both of these lipid changes increase the repulsive forces of the hydrophobic chains of the membrane lipids and thereby alter the physical properties of the membrane. As expected, under irradiation this temperature shift also induced a reversible replacement of the constitutive photosystem II protein, D1:1, with an alternative stress form, D1:2. Photosynthesis decreased to 42% of the control level within the initial 2 h of cold incubation, but later recovered. The D1:2 protein accumulated to high levels between 2 and 4 h after the temperature shift, when desaturation of membrane lipids and MGDG/DGDG ratio had not yet increased significantly. Much of this accumulated D1:2 protein was in a higher molecular mass form, termed D1:2*, which is probably an unprocessed precursor form of the protein. In contrast to the wild‐type cells the psbA inactivation mutants, R2K1 and R2S2C3 did not accumulate any precursor form of D1 protein either at the optimal or low growth temperature.

The R2S2C3 mutant strain expresses only the constitutive D1:1 protein and suffered severe photoinhibition following the temperature shift. Nevertheless, R2S2C3 eventually recovered some photosynthetic activity, induced lipid desaturation and slowly resumed growth at 25°C, thus demonstrating acclimation to the lower growth temperature.

The R2K1 mutant synthesizes only the D1:2 stress form of D1 protein and maintained oxygen evolution at a high level (ca 70% of a control rate) after the low temperature shift. Chill‐induced lipid desaturation and increase in MGDG/DGDG ratio did proceed but, for unknown reasons the strain did not resume growth at the lower temperature. The physical properties of the membrane lipids were not the limiting factor for growth resumption.

Our results demonstrate that in the wild‐type the chill‐induced desaturation of membrane lipids follows after the exchange of the two forms of the D1 proteins, but the D1 exchange results in accumulation of unprocessed D1:2* polypeptides until the lipid composition later acclimates. We also show that the lipid desaturation process in Synechococcus sp. strain PCC 7942 is dependent upon photosynthetic activity.
Characterization of pedicel β‐glucuronidase activity in developing maize (Zea mays) kernels
Authors: Muhitch Michael J.
Published: March 2003

A conspicuous endogenous maize (Zea mays L.) β‐glucuronidase (GUS) activity was observed in histochemical assays of non‐transformed maize kernels, confounding the use of Escherichia coli gusA as a reporter gene. Appearance of the endogenous activity was developmentally dependent and highly tissue‐specific, being localized to the upper pedicel (basal maternal kernel) tissues where the black layer forms in the latter stages of kernel development. Pedicel homogenates exhibited GUS activity using either p‐nitrophenyl‐β‐D‐glucuronide or 4‐methylumbelliferyl‐β‐D‐glucuronide (MUG) as substrates. Pedicel GUS was apparently not the result of endophyte contamination of enzyme isolates since no endophytes could be cultured. The MUG‐based activity had a pH optimum of 4 to 5 and was separable into two isoforms by anion exchange chromatography with Km values for MUG of 2.2 and 2.7 µM for the early‐ and late‐eluting forms, respectively. The pedicel GUS isoforms had very similar characteristics: native Mr of approximately 32000, stimulation by assay at 60°C, inhibition at high ionic strength or in the presence of EDTA and relative insensitivity to the E. coli GUS inhibitor saccharic acid‐1,4‐lactone. Only the early‐eluting form, however, was capable of hydrolyzing the histocbemical GUS substrate 5‐bromo‐4‐chloro‐3‐indoyl‐β‐D‐glucuronide. Neither isoform exhibited antifungal activity against Fusarium moniliforme. In contrast to the in vitro activity, pedicel endogenous GUS measured histochemically was completely inhibited by saccharic acid‐1,4‐lactone, unaffected by EDTA and greatly decreased by incubation at elevated assay temperature. A modification of the standard histochemical GUS assay allowed complete suppression of endogenous GUS activity while enhancing E. coli‐derived GUS activity in kernels transiently expressing the gusA gene. Possible roles of these endogenous GUS activities within the black layer region of the kernel pedicel are proposed.
Light dependent activation of CO2 assimilation and the ratio of Rubisco activase to Rubisco during leaf aging of rice (Oryza sativa)
Authors: Fukayama Hiroshi , Uchida Naotsugu , Azuma Tetsushi , Yasuda Takeshi
Published: March 2003

The effects of the ratio of Rubisco activase to Rubisco (activase/Rubisco ratio) on light dependent activation of CO2 assimilation were investigated during leaf aging of rice. Changes of photosynthetic CO2 gas exchange rates in relation to step increases of light intensity from two photon flux densities of 60 µmol m−2 s−1 (low initial PFD) and 500 µmol m−2 s−1 (high initial PFD) to saturated PFD of 1 800 µmol m−2 s−1 were measured. These photosynthetic activation processes were considered to be limited by the Rubisco activation rate when analyzed by the relaxation method. The relaxation time of low initial PFD gradually declined from 3 to 33 days after leaf emergence and showed high and negative correlation to the activase/Rubisco ratio. The initial rate of Rubisco activation under low initial PFD linearly correlated to the amounts of Rubisco activase, whereas these were almost constant from 3 to 23 days after leaf emergence. But these correlations could not be recognized in the case of high initial PFD. Moreover, the relaxation times were more sensitive to intercellular CO2 concentration (Ci) under high initial PFD than under low initial PFD, especially, at Ci below 300 µl l−1. These results suggest the involvement of the activase/Rubisco ratio in the photosynthetic activation under relatively low initial PFD, and the limitation of photosynthetic activation under relatively high initial PFD by Rubisco carbamylation during leaf aging of rice.
A transient increase in apoplastic peroxidase activity precedes decrease in elongation rate of B73 maize (Zea mays) leaf blades
Authors: De Souza Isabel R. P. , MacAdam Jennifer W.
Published: March 2003

Peroxidase (EC 1.11.1.7) activity from homogenized tissue or in apoplastic fluid was analyzed along the developmental gradient of expanding B73 maize (Zea mays L.) leaf blades. Soluble plus ionically bound peroxidase activity from homogenized tissue was present in high levels at the leaf base, which includes the region of cell division, and decreased as tissue was displaced away from the base by growth. A different pattern of change in peroxidase activity was seen in apoplastic fluid extracted from segments of intact tissue, where an increase in peroxidase activity preceded a rapid decrease in leaf elongation rate. Similar patterns in peroxidase activity from homogenized and intact tissue have been found in leaf blades of tall fescue (Festuca arundinacea Schreb.), suggesting a common phenomenon. At the location within the elongation zone where the increase in apoplastic peroxidase activity occurred, the activities of neutral and acidic (pl 4.6) peroxidase isoforms were also elevated in both the homogenate and in apoplastic fluid. The coincidence of these isoforms with the decline in leaf elongation rate suggests they may contribute to cessation of growth. At the distal end of the elongation zone, the activities of other acidic peroxidases (pI 5.6 and 5.7) increased in the homogenate and in apoplastic fluid, and remained elevated as tissue was displaced into the maturation region. The location of their appearance and their relatively high activity in the maturation region suggest the involvement of these isoforms in lignification.
Ripening‐induced acceleration of volatile aldehyde generation following tissue disruption in tomato fruit
Authors: Riley John C. M. , Thompson John E.
Published: March 2003

Hexanal and cis‐3‐hexenal are principal flavor volatiles in ripe tomato fruit, but whether they accumulate during ripening or are formed upon maceration of the tissue has not been clarified. This has been addressed by measuring levels of these aldehydes in green and ripe fruit with discrimination between intrinsic aldehyde content and aldehyde generation following tissue disruption. Volatile sampling of tomato fruit homogenates was accomplished by purge/trapping, followed by thermal desorption on a gas chromatograph equipped with a mass selective detector. Incubation of some samples with alcohol dehydrogenase to convert the aldehydes to their respective alcohols permitted positive identification of the isomeric form of hexenal as cis‐3‐hexenal. Red and green tomato fruit homogenized in buffer with saturated CaCl2 contained low (0.1‐0.8 µg g−1 fresh weight) levels of hexanal and cis‐3‐hexenal; thus there is minimal endogenous volatile content in intact fruit. Volatile levels increased rapidly, up to 10‐fold, following homogenization of ripe tomato fruit in the absence of CaCl2, and more modestly in corresponding green tomato fruit homogenates. Incubation with the appropriate lipoxygenase/hydroperoxide lyase substrate (linoleic acid for hexanal, linolenic acid for cis‐3‐hexenal) doubled the amount of volatile compound produced. Hexanal generation was suppressed in the presence of linolenic acid, suggesting that the enzyme complex has greater affinity for this substrate. As well, levels of cis‐3‐hexenal, but not hexanal, tended to decline within 30 min of homogenization, possibly reflecting a specific degradative process. The results collectively indicate that the contribution of six‐carbon aldehydes to tomato fruit flavor is attributable to metabolism invoked following tissue disruption rather than within the intact fruit.
Phytochrome A does not mediate reduced stem extension from cool day‐temperature treatments
Authors: Runkle Erik S. , Pearson Simon
Published: March 2003

Stem elongation can be suppressed by a temperature drop at the onset of the photoperiod (DROP) or with a cooler day than night temperature (DT and NT, respectively), commonly described as DIF (DT ‐ NT). To test our hypothesis that phytochrome A (phyA) mediated the reduction of stem elongation caused by −DIF and DROP, we conducted experiments with photomorphogenic mutants of tomato (Solarium lycopersicon L.) and transgenic potato (Solarium tuberosum L.). The plants studied were tomato mutants fri1 (deficient in phyA) and tri3 (deficient in phytochrome B1 [phyBl]) and their isogenic wild‐type (WT) cv. Moneymaker, nontransformed potato, and two lines each of antisense phyA (15‐9 and 15‐11) and overexpressed phyA (PS‐2 and PS‐4). Plants were placed in three temperature regimens with a daily mean of 20°C: a constant 20°C (0 DIF), an 8°C DROP for 3 h, and a ‐ 8°C DIF. For all tomato genotypes, −DIF and DROP reduced intemode length by ≥ 21% and stem elongation by 30% compared to that of plants at 0 DIF. Interactions between temperature treatment and genotype were nonsignificant. For potato, −DIF, but not DROP, significantly reduced intemode length of WT (by 39%) and both antisense lines (by 36 or 48%) but only one of the two lines of overexpressed phyA plants (by 18%). The −DIF significantly reduced stem length for only antisense phyA (by 36 or 48%) and WT (by 35%) plants. Thus, at least for tomato and potato, it appears that phyA does not control stem extension in relation to cool‐temperature treatments.
Role of ethylene in acceleration of flower senescence by filament wounding in Portulaca hybrid
Authors: Ichimura Kazuo , Suto Kenichi
Published: March 2003

Factors accelerating flower senescence of Portulaca hybrid were investigated. Self‐and cross‐pollination, emasculation and removing of pistil significantly accelerated senescence. However, wounding of filaments was much more effective in accelerating flower senescence. Senescence was further accelerated by an increase in the number of wounded filaments, and ethylene production was also accelerated by wounding of filaments. Treatment with 0.1 µl 1−1 ethylene for 1 h significantly accelerated flower senescence, and the senescence of both the intact and filament‐wounded flowers was markedly delayed by exposure to norbornadiene (NBD), an inhibitor of ethylene action. The sensitivity to ethylene increased significantly within 1 h after wounding of filaments, but ethylene production did not. These results suggest that acceleration of flower senescence by wounding of filaments is caused by an increase in the sensitivity to ethylene and the subsequent production of ethylene.
Foliar antioxidant status of plants from naturally high‐CO2 sites
Authors: Badiani Maurizio , Paolacci Anna Rita , Fusari Angelo , Bettarini Isabella , Brugnoli Enrico , Lauteri Marco , Miglietta Franco , Raschi Antonio
Published: March 2003

We compared the foliar antioxidant status of native Agrostis stolonifera L. communities growing at two distinct CO2‐enriched sites of geothermal origin (E) and at a control field location with normal CO2. Compared to the control, plants from both E‐sites showed an increased size of the GSH pool, essentially due to enhanced GSSG levels, and a consequent decrease in the ratio between reduced and oxidised glutathione forms. Such differences were maintained and even enhanced in the vegetatively‐propagated progenies of control and E‐plants, grown under both greenhouse conditions and normal CO2 levels. The above results confirmed previous observations on native and crop plants exposed to elevated CO2. It is therefore suggested that changes in the glutathione redox balance might be of adaptive significance under conditions of permanent exposure to high CO2.
Effect of CO2 enrichment on non‐structural carbohydrates in leaves, stems and ears of spring wheat
Authors: Sild E. , Younis S. , Pleijel H. , Selldén G.
Published: March 2003

Field‐grown spring wheat (Triticum aestivum L. cv. Dragon) was exposed to ambient and elevated CO2 concentrations (1.5 and 2 times ambient) in open‐top chambers. Contents of non‐structural carbohydrates were analysed enzymatically in leaves, stems and ears six times during the growing season. The impact of elevated CO2 on wheat carbohydrates was non‐significant in most harvests. However, differences in the carbohydrate contents due to elevated CO2 were found in all plant compartments. Before anthesis, at growth stage (GS) 30 (the stem is 1 cm to the shoot apex), the plants grown in elevated CO2 contained significantly more water soluble carbohydrates (WSC), fructans, starch and total non‐structural carbohydrates (TNC) in the leaves in comparison with the plants grown in ambient CO2. It is hypothesised that the plants from the treatments with elevated CO2 were sink‐limited at GS30. After anthesis, the leaf WSC and TNC contents of the plants from elevated CO2 started to decline earlier than those of the plants from ambient CO2. This may indicate that the leaves of plants grown in the chambers with elevated CO2 senesced earlier. Elevated CO2 accelerated grain development: 2 weeks after anthesis, the plants grown in elevated CO2 contained significantly more starch and significantly less fructans in the ears compared to the plants grown in ambient CO2. Elevated CO2 had no effect on ear starch and TNC contents at the final harvest. Increasing the CO2 concentration from 360 to 520 μmol mol−1 had a larger effect on wheat non‐structural carbohydrates than the further increase from 520 to 680 μmol mol−1. The results are discussed in relation to the effects of elevated CO2 on yield and yield components.
Pyrophosphate: d‐fructose‐6‐phosphate 1‐phosphotransferase activity patterns in relation to sucrose storage across sugarcane varieties
Authors: Whittaker Anne , Botha Frederik C.
Published: March 2003

Pyrophosphate: d‐fructose‐6‐phosphate 1‐phosphotransferase (PFP; EC 2.7.1.90) and ATP:
d‐fructose‐6‐phosphate 1‐phosphotransferase (PFK; EC 2.7.1.11) activities were determined in sugarcane varieties differing in sucrose content. For this purpose, activities were measured in those internodes where the maximum rate of sucrose accumulation occurs. The specific activity of internodal PFP varied significantly between the sugarcane varieties and was inversely correlated with the sucrose content. There was also a highly significant inverse correlation between PFP and sucrose content in a segregating F1 population. PFK activity was comparable to, or lower than, PFP activity and no relationship was evident between PFK activity and sucrose content. In all tissues investigated, the fructose 2,6‐bisphosphate levels were probably sufficient to ensure full activation of PFP. The levels of PFP activity appear to be controlled by the expression of the β‐subunit of the protein. The molecular mass of the PFP subunit polypeptide(s) was approximately 63 kDa. There was an inverse correlation between sucrose content and the partitioning of radiolabel into respiration in internodal tissue slices labelled with [U‐14C]glucose across 3 sugarcane lines. The estimated flux of carbon into respiration correlated directly with PFP activity.
Differential expression and regulation of translation initiation factors ‐4E and ‐iso4E during maize germination
Authors: Dinkova Tzvetanka D. , Sánchez de Jiménez Estela
Published: March 2003

Messenger RNA translation is a tightly regulated event in maize axes during germination. To obtain a deeper understanding of this process, the present research was centered on the expression regulation of the translation initiation factor eIF‐4E within this period. Two maize eIF‐4E isoforms were isolated by mGTP‐Sepharose affinity chromatography. The eIF‐iso4E protein content remained at a constant level in the axes during the first 24 h of maize germination, whereas the eIF‐4E level increased after 12 h of germination as indicated by western blot analysis. Fast in vivo eIF‐iso4E, but not eIF‐4E, de novo synthesis was found within 6–12 h of germination. Northern blot analysis of total RNA from ungerminated axes with cDNAs encoding either ‐iso4E or ‐4E indicated that both transcripts were present in the stored mRNA pool of maize axes. Transcription for any of these mRNAs was not detected before 12 h of germination. Northern blots of polysomal RNAs indicated that the eIF‐iso4E stored transcript is selectively recruited into polysomes for translation as early as 6 h of germination, whereas this does not occur for the eIF‐4E transcript. The above data demonstrate differential 4E isoform expression regulation during maize germination. Expression of the eIF‐iso4E protein appears to be translationally controlled, whereas the expression of the eIF‐4E protein might be regulated at the transcriptional level.
The ascorbate system in recalcitrant and orthodox seeds
Authors: Tommasi Franca , Paciolla C. , Arrigoni O.
Published: March 2003

Recalcitrant seeds of Ginkgo biloba L., Quercus cerris L., Aesculus hippocastanum L. and Cycasrevoluta Thunb. are shed by the plant at a high moisture content, contain a large amount of ascorbic acid (ASA) and maintain high ascorbate (ASC) peroxidase (EC 1.11.1.11) activity. Three proteins showing ASC peroxidase activity are present in G. biloba seeds. Conversely, dry orthodox seeds (Vicia faba L., Avena sativa L., Pinus pinea L.) are completely devoid of ASA and ASC peroxidase. Experimentally induced rapid variations of the water level in both recalcitrant and orthodox seeds do not affect the ASC peroxidase; slow dehydration affects the ASC peroxidase activity moderately in recalcitrant seeds, but provokes a complete loss of germinability. Another peculiar difference between orthodox and recalcitrant seeds concerns the ascorbate recycling enzymes, ascorbate free radical (AFR) reductase (EC 1.6.5.4) and dehydroascorbate (DHA) reductase (EC 1.8.5.1). The DHA reduction capability is low in recalcitrant seeds, but is high in the orthodox ones. In contrast, AFR reductase activity is high in recalcitrant seeds and low in the orthodox ones. Data reported here concerning the ASC system appear to contribute to better understanding the recalcitrance. The presence of three different proteins showing ASC peroxidase activity in the archaic seed‐bearing plant G. biloba and its involvement in the spermatophyte evolution is discussed.
How doesLobaria pulmonariaregulate photosystem II during progressive desiccation and osmotic water stress?
Authors: Chakir Samira , Jensen Manfred
Published: March 2003

The effects of decreasing water potential (Ψ) on O2evolution and fluorescence yield at room temperature and at 77 K were investigated using the lichenLobaria pulmonaria. Changes in Ψ were created either by atmospheric desiccation or by osmotic dehydration, with either sucrose, sorbitol or NaCl as osmoticum. Independent of the method used to establish Ψ, similar inactivation patterns were obtained and were reversible after reincubation in pure water for 10 min. Our data indicate that exposure to increasing water stress acts at two levels. In the first phase, at ‘mild’ stress, i.e. at Ψ greater than −13, −16 and −20 MPa for drying, NaCl and sucrose treatments, respectively, a progressive decline in O2production and the fluorescence yield (ΔF/Fm′ and Fv/Fm) was correlated with increases in non‐photochemical quenching (qN). At the same time the photochemical quenching (qp) changed only sligthly, indicating the absence of overreduction. The Folevel remained relatively constant in this first stage of water loss. A ΔpH mediated down regulation and a donor side limitation of photosystem (PS) II are discussed. When the water stress was severe, a further decrease in the fluorescence yield was observed and correlated with a considerable decrease in Fo(second phase). Kinetic analysis of the 77 K emission showed that osmotic stress and atmospheric desiccation possibly lead to an increased spillover from PS II to PS I. In addition, a strong negative effect of NaF on the recovery from dehydration was found. This may indicate a state transition mediated by the displacement/recoupling of light harvesting complex (LHC) II from/to PS II. The photoprotective role of spatial rearrangements of antenna complexes during desiccation is discussed.
Molecular cloning and expression of a cDNA encoding 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase from apricot fruit (Prunus armeniaca)
Authors: Mbéguié‐A‐Mbéguié Didier , Chahine Hala , Gomez Rose‐Marie , Gouble Barbara , Reich Maryse , Audergon Jean Marc , Souty Michel , Albagnac Guy , Fils‐Lycaon Bernard
Published: March 2003

Little is known on gene expression during ripening of apricot fruit (Prunus armeniaca cv. Bergeron), in particular for the enzymes involved in ethylene biosynthesis. ACC oxidase (EC 1.4.3) catalyses the last step of the ethylene biosynthesis pathway in higher plants. Based on sequence conservation of ACC oxidases, a reverse transcriptase‐polymerase chain reaction (RT‐PCR) experiment was carried out to synthesize a homologous ACC oxidase probe from apricot fruit. This probe was further used to isolate a full length ACC oxidase cDNA, Pa‐ACO, from a ripe fruit cDNA library. Pa‐ACO is 1 236 bp long and contains a single open reading frame encoding a mature peptide of 319 amino acids with a calculated molecular mass of 36.17 kDa and a pI of 5.07. Immunoblot analysis allowed us to associate a 40 kDa protein to apricot fruit ACC oxidase. Pa‐ACO belongs to a multi‐gene family, is fruit specific and is transcriptionally regulated during ripening of apricot fruit.
Totipotency, somatic embryogenesis, and Harry Waris (1893–1973)
Authors: Krikorian Abraham D. , Kaarina Simola Liisa
Published: March 2003

F. C. Steward and Jakob Reinert in the late 1950s, independently and with different degrees of scientific exactness, demonstrated that somatic cells of cultivated carrot can produce embryo‐like structures in aseptic culture. Growth substances in the nutrient medium were viewed as central to the process. The now classic papers of Steward and Reinert have found a special and enduring place in the literature of plant development. But Harry Waris also deserves credit for his observation that vegetative cells sloughed off from aseptically germinated seedlings reared in liquid nutrient medium can produce ‘embryos’. In his studies, seedlings of Oenanthe aquatica (Umbelliferae) were maintained in culture for protracted periods under nutrient conditions designed to foster imbalance in protein metabolism, but without exogenous growth hormones. Seedlings placed in media with high concentrations of glycine grew normally for 3–4 months; after this a “period of morbidity” occurred, followed by production of new plants from the root tips. These new plants, later called “neomorphs”, in turn reproduced by colorless outgrowths of leaf epidermis. Such outgrowths, and “nodules” formed in a callus produced by the original seedlings, passed through stages described as “nodule”, “fusiform”, and a stage with two or more “lobes”. Transfer of the neomorphs to a medium lacking glycine resulted in the development of normal plants. We show that Waris was among the first, if not the first, to observe and recognize somatic embryo production in aseptic culture, and indeed to call them “embryos”. We also discuss his investigations in the context of understanding development at the cellular level, then and now.
Free‐air CO2 enrichment of wheat: leaf flavonoid concentration throughout the growth cycle
Authors: Estiarte Marc , Peñuelas Josep , Kimball Bruce A. , Hendrix Donald L. , Pinter Jr Paul J. , Wall Gerard W. , LaMorte Robert L. , Hunsaker Douglas J.
Published: March 2003

To test the predictions that plants will have a larger flavonoid concentration in a future world with a CO2‐enriched atmosphere, wheat (Triticum aestivum L. cv. Yecora Rojo) was grown in a field experiment using FACE (free‐air CO2 enrichment) technology under two levels of atmospheric CO2 concentration: ambient (370 μmol mol−1) and enriched (550 μmol mol−1), and under two levels of irrigation: well‐watered (100% replacement of potential evapotranspiration) and half‐watered. We also studied the effects of CO2 on the concentration of total non‐structural carbohydrates (TNC) and nitrogen (N), two parameters hypothesized to be linked to flavonoid metabolism. Throughout the growth cycle the concentration of isoorientin, the most abundant flavonoid, decreased by 62% (from an average of 12.5 mg g−1 on day of year (DOY) 41 to an average of 4.8 mg g−1 on DOY 123), whereas the concentration of tricin, another characteristic flavone, increased by two orders of magnitude (from an average of 0.007 mg g−1 of isoorientin equivalents on DOY 41 to an average of 0.6 mg g−1 of isoorientin equivalents on DOY 123). Although flavonoid concentration was dependent on growth stage, the effects of treatments on phenology did not invalidate the comparisons between treatments. CO2‐enriched plants had higher flavonoid concentrations (14% more isoorientin, an average of 7.0 mg g−1 for ambient CO2 vs an average of 8.0 mg g−1 for enriched CO2), higher TNC concentrations and lower N concentrations in ukpper canopy leaves throughout the growth cycle. Well‐irrigated plants had higher flavonoid concentrations (11% more isoorientin, an average of 7.1 mg g−1 for half watered vs an average of 7.9 mg g−1 for well‐watered) throughout the growth cycle, whereas the effect of irrigation treatments on TNC and N was more variable. These results are in accordance with the hypotheses that higher carbon availability promoted by CO2‐enrichment provides carbon that can be invested in carbon‐based secondary compounds such as flavonoids. The rise in atmospheric CO2 may thus indirectly affect wheat‐pest relations, alter the pathogen predisposition and improve the UV‐B protection by changing flavonoid concentrations.
Lipid and fatty acid composition in non‐embryogenic calli and embryogenic tissues in wild cherry (Prunus avium)
Authors: Reidiboym‐Talleux Lydia , Grenier‐De March Ghislaine
Published: March 2003

In Prunus avium, the lipid and fatty acid composition of non‐embryogenic calli and embryogenic tissues was studied. The embryogenic tissues were characterised by a higher content of triglycerides and total phospholipids than non‐embryogenic calli. Neutral lipids (NL) from embryogenic tissues akppeared less saturated than NL from non‐embryogenic calli. Somatic embryogenesis was associated with considerable proportions of linoleic acid in both NL and phosphatidylcholine (PC) (23% in NL and 60% in PC), together with high proportions of palmitic acid in phosphatidylethanolamine (PE) and phosphatidylinositol (PI) (92% in PE and 62% in PI). Conversely, non‐embryogenic calli were characterised by a considerable proportion of palmitic acid in NL (74%) and high proportions of oleic acid in PE (100%) and PC (84%). These results suggest differences between the lipid biosynthetic pathway of embryogenic tissues when compared with that of non‐embryogenic calli.
Presence of guanine nucleotide‐binding proteins in Catharanthus roseus transformed roots
Authors: Suárez‐Solis Victor Manuel , Carrillo‐Pech Mildred R , Muñoz‐Sánchez J Armando , Coria‐Ortega Roberto , Hernández‐Sotomayor Sm Teresa
Published: March 2003

Biochemical analysis revealed the presence of GTP‐binding proteins (G‐proteins) in Catharanthus roseus hairy root cultures. In a microsomal fraction, several proteins, with molecular masses of 17, 21, 38, 42, 65, and 79 kDa were substrates for ADP‐ribosylation by cholera toxin. Antisera raised against a conserved amino‐acid sequence (GTSNSGKSTIVKQMK) of mammalian Gα subunits recognized three proteins of 42, 50, and 79 kDa. Incubation of nitrocellulose blots with [α‐32P]‐GTP also indicated the presence of several proteins (17, 21, 50, and 79 kDa) that could bind GTP. In this system, we previously identified a phosphatidylinositol 4,5‐bisphosphate‐phospholipase C (PLC, EC 3.1.4.11) activity. As the activation of PLC by G‐proteins was described, we decided to see whether, in our system, G‐protein activators, such as guanosine 5‐o‐(3‐thiotriphosphate) (GTPΓS) and sodium fluoride ions, were able to regulate PLC activity in C.roseus transformed roots. Our results show that these agents regulated PLC activity in an inhibitory fashion and that this effect is dose‐dependent. GTP was ineffective in producing either stimulation or inhibition of PLC activity. Our results demonstrate that non‐hydrolyzable guanine nucleotides and fluoride ions exert an inhibitory effect on membrane PLC activity. In summary, a set of proteins of 17, 21, 38, 42, 50, and 79 kDa present in C.roseus transformed roots possessed at least two of the three main characteristics of a GTP‐binding protein, and one of these proteins may be involved in the regulation of PLC activity in C.roseus transformed roots.
Seasonal emission of monoterpenes by the Mediterranean tree Quercus ilex in field conditions: Relations with photosynthetic rates, temperature and volatility
Authors: Peñuelas Josep , Llusià Joan
Published: March 2003

The relationships of monoterpene emission with temperature, light, photosynthesis and stomatal conductance (gs) were studied in Quercus ilex L. trees throughout the four annual seasons under field conditions. The highest monoterpene emission was measured in spring and summer (midday average of 11 μg [g DW]−1 h−1), whereas the lowest rates were found in autumn and winter (midday averages of 0.51 and 0.23 μg [g DW]−1 h−1, respectively). In spring and summer, limonene was the monoterpene emitted at highest rate (midday averages of 5.27–6.69 μg [g DW]−1 h−1), whereas α‐pinene was emitted the most in autumn and winter (midday averages of 0.31 μg [g DW]−1 h−1). The monoterpenes limonene, α‐pinene and β‐pinene represented about 75–95% of total detected monoterpenes. The total monoterpene emission rates represented about 0.04% of carbon fixed in autumn, 0.17% in winter, 0.84–2.51% in spring and 1.22–5.13% in summer. Significant correlations of total monoterpene emission with temperature were found when considering either summer emission or the emission over the entire year, whereas significant correlations with net photosynthetic rates were only found when considering summer season. Among individual terpenes, the most volatile, α‐pinene and β‐pinene, were more correlated with temperature than with net photosynthetic rates whereas the less volatile limonene was more correlated with net photosynthetic rate. Thus, under field conditions it seems that dependency of monoterpene emission on photosynthetic rate or temperature is partly related with volatility of the compounds. Influences of seasonality, temperature, photosynthetic rates and volatility should be considered in inventories and models of emission rates in Mediterranean ecosystems.
Effects of SO2 fumigations on photosynthetic CO2 gas exchange, chlorophyll a fluorescence emission and antioxidant enzymes in the lichens Evernia prunastri and Ramalina farinacea
Authors: Deltoro V. I. , Gimeno C. , Calatayud A. , Barreno E.
Published: March 2003

The effects of elevated gaseous SO2 concentrations in the lichens Evernia prunastri (L.) Ach. and Ramalina farinacea (L.) Ach. were investigated by means of gas exchange, modulated chlorophyll fluorescence analysis and antioxidant enzyme assays. The response to SO2 of the studied species differed markedly. Net photosynthetic rates were more adversely affected in E. prunastri than in R. farinacea. In addition, processes dependent on thylakoid membrane integrity such as PSII‐mediated electron flow and nonphotochemical quenching were reduced to a greater extent by exposure to SO2 in E. prunastri. Moreover, the ability to reoxidize the quinone pool was lower in this species. Finally, the activity of chloroplastidic and cytoplasmic antioxidant enzymes was decreased in E. prunastri in response to fumigations but increased in R. farinacea. The results suggest that the ability to process and deal with the SO2 once it has been absorbed must play a role in determining the sensitivity of these lichen species to this air pollutant.
Changes in hormonal balance and meristematic activity in primary root tips on the slowly rotating clinostat and their effect on the development of the rapeseed root system
Authors: Aarrouf J. , Schoëvaërt D. , Maldiney R. , Perbal G.
Published: March 2003

The morphometry of the root system, the meristematic activity and the level of indole‐3‐acetic acid (IAA), abscisic acid (ABA) and zeatin in the primary root tips of rapeseed seedlings were analyzed as functions of time on a slowly rotating clinostat (1 rpm) or in the vertical controls (1 rpm). The fresh weight of the root system was 30% higher throughout the growth period (25 days) in clinorotated seedlings. Morphometric analysis showed that the increase in biomass on the clinostat was due to greater primary root growth, earlier initiation and greater elongation of the secondary roots, which could be observed even in 5‐day‐old seedlings. However, after 15 days, the growth of the primary root slowed on the clinostat, whereas secondary roots still grew faster in clinorotated plants than in the controls. At this time, the secondary roots began to be initiated closer to the root tip on the clinostat than in the control. Analysis of the meristematic activity and determination of the levels in IAA, ABA and zeatin in the primary root tips demonstrated that after 5 days on the clinostat, the increased length of the primary root could be the consequence of higher meristematic activity and coincided with an increase in both IAA and ABA concentrations. After 15 days on the clinostat, a marked increase in IAA, ABA and zeatin, which probably reached supraoptimal levels, seems to cause a progressive disturbance of the meristematic cells, inducing a decrease of primary root growth between 15 and 25 days. These modifications in the hormonal balance and the perturbation of the meristematic activity on the clinostat were followed by a loss of apical dominance, which was responsible for the early initiation of secondary roots, the greater elongation of the root system and the emergence of the lateral roots near the tip of the primary root.
Effect of Al on the phytosiderophore‐mediated solubilization of Fe and uptake of Fe‐phytosiderophore complex in wheat (Triticum aestivum)
Authors: Chang Yi‐Chieh , Ma Jian Feng , Iwashita Takashi , Matsumoto Hideaki
Published: March 2003

The effect of Aluminum (Al) on phytosiderophore‐mediated solubilization of insoluble Fe and the uptake of phytosiderophore‐Fe3+ complex was examined in wheat (Triticum aestivum L. cv. Atlas 66). Al addition did not affect the Fe solubilization by 2′‐deoxymugineic acid (DMA), although Cu addition significantly inhibited the solubilization capacity. Addition of ten times more Al than Fe to the solution of DMA‐Fe3+ complex did not decrease the absorption of the DMA‐Fe3+ complex at 375 nm. Furthermore, NMR study indicated that Al did not shift the proton chemical shifts of DMA. All these results suggest that Al could not form a complex with the phytosiderophore, and is thereby unlikely to affect the process of phytosiderophore‐mediated solubilization of Fe. Exposure of root to Al up to 100 μM for 3 h did not inhibit the DMA‐Fe3+ uptake by the roots, but longer pretreatment (>6 h) inhibited the uptake of the DMA‐Fe3+ by more than 50%. Neither the uptake of DMA‐Fe3+ nor root elongation was inhibited by 24 h pretreatment with 10 μM Al, but both uptake and root elongation were inhibited by higher Al (>20 μM) pretreatment. These results suggest that Al did not directly block the transport of the phytosiderophore‐Fe3+ complex, and that the decreased uptake of the phytosiderophore‐Fe3+ complex resulted from the roots being damaged by Al.