bluuebunny/crossref_metadata_2025 huggingface dataset:
Xyloglucan endotransglycosylase activity in pine hypocotyls. Intracellular localization and relationship with endogenous growth
Authors: Barrachina Coral , Lorences Ester P.
Published: March 2003

Since xyloglucan depolymerization has been proposed as one of the biochemical bases for cell wall‐loosening in gymnosperms, we characterized xyloglucan endotransglycosylase (XET) activity during pine hypocotyl growth to establish a possible relationship. XET activity was measured as the incorporation of [3H]XXXGol into partially purified pine hypocotyl xyloglucan. XET specific and total activity was determined in the subapical and basal segments of pine hypocotyls at two different stages of growth in different subcellular fractions. XET activity was found in the apoplastic fluid, the symplastic fluid, and in the fraction of proteins ionically and covalently bound to the cell walls with different distribution profiles. The results showed a relationship between XET activity and hypocotyl growth in all the fractions, suggesting an important role for XET during growth. Consequently, the suggested growth‐promoting effect of XET in angiosperms can also be extended to gymnosperms. Also, the results demonstrate that XET bound to the cell wall is able to act on endogenous wall‐bound xyloglucan as well as soluble polymeric xyloglucan, using them as substrates for the endotransglycosylation reaction.
Latitudinal cline of requirement for far‐red light for the photoperiodic control of budset and extension growth in Picea abies (Norway spruce)
Authors: Clapham David H. , Dormling Ingegerd , Ekberg Lnger , Eriksson Gösta , Qamaruddin Mohammed , Vince‐Prue Daphne
Published: March 2003

To test for the effects of far‐red light on preventing budset in Picea abies, seedlings of six populations originating from latitudes between 67°N and 47°N were grown for 4–8 weeks in continuous incandescent (metal halogen) light at 300 µmol m−2 s−1 and 20°C and then transferred, at the same temperature, to a daily regime of 8 h incandescent light (300 µmol m−2 s−1) followed by 16 h cool white fluorescent light (40 µmol m−2 s−1). (Cool white lamps are deficient in far‐red light, with a R/FR ratio of 7.5 compared with 2.0 for the incandescent lamps.) All the seedlings from 67° and 80% of those from 64° stopped extension growth and set terminal buds within 28 days of the change of regime. The seedlings from 61° and further south continued growing, as did control seedlings from 67° grown as above but with incandescent light at 20 µmol m−2 s−1 replacing cool white illumination. To distinguish between a clinal and ecotypic pattern of variation, the interval between 64° and 59° was investigated by growing populations originating from that area in the same regimes as before. After 28 days in the cool white day‐extension regime, the percentage budset was 86 for the population from 64°, 0 for the population from 59° and 25–50 for the intermediate populations; i.e. the populations showed a clinal variation in requirement for far‐red light according to latitude. Thus northern populations of Picea abies appear to behave as ‘light‐dominant’ plants for the photoperiodic control of extension growth and budset, whereas the more southern populations behave as ‘dark‐dominant’ plants.
Accumulation of γ‐aminobutyric acid in nodulated soybean in response to drought stress
Authors: Serraj Rachid , Shelp Barry J. , Sinclair Thomas R.
Published: March 2003

Nitrogen fixation and nodule permeability to O2 diffusion are decreased by drought stress. Since γ‐aminobutyric acid (GABA) synthesis is rapidly stimulated by a variety of stress conditions including hypoxia, it was hypothesized that decreased O2 availability in nodules stimulates glutamate decarboxylase (GAD) activity (EC 4.1.1.15), thereby resulting in GABA accumulation. First, the amino acid composition of xylem sap was determined in plants subjected to soil water deficits. While the xylem sap concentration of several amino acids increased when the plant was subjected to a water deficit, the greatest increase was in GABA. GABA accumulation was examined in response to stress induced by hypoxia or the addition of polyethylene glycol (PEG) to the nutrient solution. The exposure of soybean nodules to hypoxia for 6 h enhanced the GABA concentration by 6‐fold, but there was no change in GABA concentration in response to the PEG treatment. No major changes in the in vitro GAD activity were measured in nodule cytosol or bacteroids. The present data do not support the hypothesis that decreased nodule O2 permeability and a resulting O2 deprivation inside nodules may stimulate in vitro GAD activity and thus GABA accumulation. However, the data could indicate a possible effect of hypoxia and drought stress on the in vivo activity of GAD.
Peroxidase: Changes in soluble and bound forms during maturation and ripening of apples
Authors: Ingham Lindsay M. , Parker Mary L. , Waldron Keith W.
Published: March 2003

Peroxidase (POD) enzymes, both soluble and bound, have been implicated in the ripening process of a number of fruits. However, their roles are poorly understood. The aim of this study was to define clearly the classes of POD activity in apple parenchyma tissues on the basis of their solubility in salt solutions, to determine the subcellular localisation of ionically‐bound POD activity, and to determine whether soluble‐ or ionically‐bound POD activities exhibit any relationships with maturation and ripening. The cortical parenchyma of apples (Malus domestica Borkh cv. Cox's orange pippin) was investigated for changes in POD activity during maturation and post‐harvest storage at 0, 4, and 8°C at 100% relative humidity (RH), and controlled atmosphere (CA) storage (4°C in 1.25% O2 and 0.5% CO2). The parenchyma cells contained both soluble and ionically‐bound POD activity. The ionically‐bound POD was located in the cell wall in the middle lamella, plasmodesmata and cell corners, and could be extracted quantitatively with 0.4 M CaCl2 at neutral pH to leave a POD‐free residue. During maturation, both forms of activity increased on a ‘per apple’ basis, but decreased as a function of fresh weight. Under all conditions of storage, soluble POD exhibited a peak of activity at approximately the mid‐point of ripening‐related softening; this event may constitute a biochemical marker. In contrast, ionically‐bound POD generally decreased during ripening, except under CA storage. CA storage inhibited ripening‐related softening after an initial loss of firmness. However, softening resumed after transfer of apples to normal atmosphere storage at 8°C. This may provide a new insight into controlling tissue softening.
Growth, gas exchange, leaf nitrogen and carbohydrate concentrations in NAD‐ME and NADP‐ME C4 grasses grown in elevated CO2
Authors: LeCain Daniel R. , Morgan Jack A.
Published: March 2003

Plants with the C4 photosynthetic pathway have predominantly one of three decarboxylation enzymes in their bundle sheath cells. Within the grass family (Poaceae) bundle sheath leakiness to CO2 is purported to be lowest in the nicotinamide adenine dinucleotide phosphate‐malic enzyme (NADP‐ME, EC 1.1.1.40) group, highest in the NAD‐ME (EC 1.1.1.39) group and intermediate in the phosphoenolpyruvate carboxykinase (PCK, EC 4.1.1.32) group. We investigated the hypothesis that growth and photosynthesis of NAD‐ME C4 grasses would respond more to elevated CO2 treatment than NADP‐ME grasses. Plants were grown in 8‐1 pots in growth chambers with ample water and fertilizer for 39 days at a continuous CO2 concentration of either 350 or 700 µl l−1. NAD‐ME species included Bouteloua gracilis Lag. ex Steud (Blue grama), Buchloe dactyloides (Nutt.) Engelm. (Buffalo grass) and Panicum virgatum L. (Switchgrass) and the NADP‐ME species were Andropogon gerardii Vittman (Big bluestem), Schizachyrium scoparium (Michx.) Nash (Little bluestem), and Sorghastrum nutans (L.) Nash (Indian grass). Contrary to our hypothesis, growth of the NADP‐ME grasses was generally greater under elevated CO2 (significant for A. gerardii and S. nutans), while none of the NAD‐ME grasses had a significant growth response. Increased leaf total non‐structural carbohydrate (TNC) was associated with greater growth responses of NADP‐ME grasses. Decreased leaf nitrogen in NADP‐ME species grown at elevated CO2 was found to be an artifact of TNC dilution. Assimilation (A) vs intercellular CO2 (Ci) curves revealed that leaf photosynthesis was not saturated at 350 µl l−1 CO2 in any of these C4 grasses. Assimilation of elevated CO2‐grown A. gerardii was higher than in plants grown in ambient CO2. In contrast, B. gracilis grown in elevated CO2 displayed lower A, a trait more commonly reported in C3 plants. Photosynthetic acclimation in B. gracilis was not related to leaf TNC or nitrogen concentrations, but A:Ci curves suggest a reduction in activity of both phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39). Some adaptation of stomatal functioning was also seen in B. gracilis and A. gerardii leaves grown in elevated CO2. Our study shows that C4 grasses have the capacity for increased growth and photosynthesis under elevated CO2 even when water and nutrients are non‐limiting. While it was the NADP‐ME species which had significant responses in the present study, we have previously reported significant growth increases in elevated CO2 for B. gracilis.
BiP, HSP70, NDK and PDI in wheat endosperm. I. Accumulation of mRNA and protein during grain development
Authors: DuPont Frances M. , Hurkman William J. , Tanaka Charlene K. , Chan Ronald
Published: March 2003

Biosynthesis and accumulation of seed storage proteins such as the wheat glutens depend on the activity of a variety of other proteins, including chaperones and foldases. cDNA probes and antibodies to two chaperone proteins and a foldase were used to follow mRNA and protein accumulation in developing grains of wheat (Triticum aestivum, cvs Cheyenne and Butte). Endosperm was separated from other grain components and protein accumulation was analyzed on a per mg fresh weight basis. The ER resident chaperone BiP (binding protein) and foldase PDI (protein disulfide isomerase) accumulated to maximal levels in the middle stage of endosperm development, a period of rapid cell expansion and storage protein accumulation, whereas levels of a cytosolic chaperone, HSP70, remained relatively constant throughout grain development. In contrast, nucleoside diphosphate kinase (NDK), a cytosolic enzyme needed for synthesis of nucleoside triphosphates, accumulated early in endosperm development during the period of nuclear division and cell formation. When analyzed as a fraction of total protein the relative abundance of all four proteins peaked early in grain development and then declined. Accumulation of mRNA for the four proteins also peaked early in grain development. Although BiP and PDI formed a declining percentage of total protein as storage protein accumulated, their pattern of accumulation was compatible with a proposed role as catalysts for storage protein folding and accumulation in the ER.
Phosphorus effect on phosphatase activity in endomycorrhizal maize
Authors: Fries Leadir L. M. , Pacovsky Raymond S. , Safir Gene R. , Kaminski Joao
Published: March 2003

Success of a mycorrhizal symbiosis is influenced by the availability of phosphorus (P) in the soil. Maize (Zea mays L. cv. Great Lakes 586) plants were grown under five different levels of soil P, either in the presence or absence of formononetin or the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus intraradices Schenck and Smith. We detected physiological differences in mycorrhizal roots very early in the development of symbiosis, before the onset of nutrient‐dependent responses. Under low P levels, VAM roots accumulated a greater shoot dry weight (13%), root P concentration (15%) and protein concentration (30%) than non‐VAM roots, although root growth was not statistically significantly different. At higher P levels, mycorrhizal roots weighed less than non‐VAM roots (10%) without a concomitant host alteration of growth or root P concentration. Mycorrhizal colonization decreased as soil P increased. Formononetin‐treatment enhanced colonization of the root by G. intraradices and partially overcame inhibition of VAM colonization by high soil P concentrations. This is the first report that formononetin improves root colonization under high levels of soil P. Acid phosphatase (ACP) and alkaline phosphatase (ALP) activities were closely related to the level of fungal colonization in corn roots. ACP activity in corn roots responded more to soil P availability than did ALP activity (38% more). These results suggest that ACP was involved in the increased uptake of P from the soil, while ALP may be linked to active phosphate assimilation or transport in mycorrhizal roots. Thus, soil P directly affected a number of enzymes essential in host‐endophyte interplay, while formononetin enhanced fungal colonization.
Stress‐induced changes in polyamine and tyramine levels can regulate proline accumulation in tomato leaf discs treated with sodium chloride
Authors: Aziz Aziz , Martin‐Tanguy Josette , Larher François
Published: March 2003

The effect of salt stress on proline (Pro) accumulation and its relationship with the changes occurring at the level of polyamine (PA) metabolism and tyramine were investigated in leaf discs of tomato (Lycopersicon esculentum). The rate of accumulation of Pro, PA and tyramine was higher in the salt‐sensitive than in the salt‐tolerant cultivar. In the salt‐sensitive cultivar, Pro started to accumulate 4 h after the onset of the NaCl treatment, its maximum level being reached 27 h later. The lag phase was associated with a rapid decrease in putrescine (Put) and spermidine (Spd) and some increase in 1,3‐diaminopropane (Dap), a product of Spd and/or spermine (Spm) oxidation. This was followed by an increase in agmatine (Agm), cadaverine (Cad), Spm and tyramine. α‐DL‐difluoromethylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC, EC 4.1.1.19), induced a decrease in the Put level in both control and stressed discs, while α‐DL‐difluoromethylomithine (DFMO), an inhibitor of ornithine decarboxylase (ODC, EC 4.1.1.17), caused a decrease in Spd and Spm levels only in salinized discs. These data suggest that ADC is operating under both control and stress conditions, whereas ODC activity is promoted only in response to salt stress. DFMA also depressed the salt‐induced Pro accumulation while DFMO did not inhibit this response. In salt‐stressed leaf discs, the decrease in Spd level in response to methylglyoxal‐bis‐(guanylhydrazone) (MGBG) or cyclohexylammonium (CHA) treatment suggests that salt stress did not block SAM decarboxylase or Spd synthase activities. However, the increased level of Dap reflected a salt stress‐promoted oxidation of PA. CHA and MGBG had no effect on Pro accumulation. Putrescine, Dap and especially tyramine supplied at low concentrations stimulated the Pro response which was, however, suppressed by application of Spm. Treatment with aminoguanidine, an inhibitor of diamine oxidases, also strongly inhibited Pro accumulation. These data suggest that salt‐induced Pro accumulation in tomato leaf discs is closely related to changes in their PA metabolism, either via substrate‐product relationships or regulatory effects at target(s) which remain to be characterized.
Effect of solar radiation (UV and visible) at high altitude on CAM‐cycling and phenolic compound biosynthesis in Sedum album
Authors: Bachereau F. , Marigo G. , Asta J.
Published: March 2003

The field experiment was carried out in order to compare the response of a CAM plant, Sedum album L., to solar radiation at a high altitude (2 100 m) with that at a low altitude location with respect to CAM and phenolic content. Treatment sites included (1) sun‐exposed, low altitude, (2) sun‐exposed, high altitude with different light treatments, including UV‐B and UV‐B + A screening, and (3) shade at high altitude. After a 70‐day treatment period, CAM‐cycling and phenolic compound content were analysed, and high altitude treatments were compared to the low altitude control. The sun‐exposed low altitude control was characterized by CAM‐cycling and a low phenolic compound content during the experiment. In plants transplanted to the high altitude, only the shaded group maintained a CAM‐cycling and a phenolic compound content similar to those of the sun‐exposed low altitude control. Samples under UV‐B and UV‐B + A filters showed similar responses, suggesting the absence of a specific UV‐A radiation effect. The screening of UV‐B or UV‐B + A radiation allowed plants to partially maintain a CAM‐cycling and induced a decrease in phenolic compound content. These responses under UV filters were, however, intermediate between those observed in sun‐exposed and shaded groups. These results demonstrate a specific effect of radiation from both visible (400–800 nm) and UV‐B (280–320 nm) bands on both CAM‐cycling and phenolic biosynthesis in S. album L. plants. These light‐dependent effects are discussed on a physiological basis and a possible interaction between CAM‐cycling and phenolic metabolism is suggested.
Inhibition of maize endosperm cell division and endoreduplication by exogenously applied abscisic acid
Authors: Mambelli Stefania , Setter Tim L.
Published: March 2003

Abscisic acid (ABA) is thought to play a role in inhibiting or aborting kernel growth during water deficit. To test the responsiveness of early endosperm development to ABA concentrations, cylinders containing (±)ABA in a buffered agar medium were applied to the apical pericarp surface of kernels on intact, well‐watered maize (Zea mays L. cv. Pioneer Brand 3925) plants from 5 to 11 days after pollination (DAP). Endosperm nuclei were analyzed by flow cytometry to assess effects on cell division and endoreduplication. ABA treatments of ≥ 100 µM substantially decreased endosperm cell numbers and fresh weight accumulation, but did not affect average cell size. ABA at ≥ 300 µM decreased the proportion of nuclei in the size classes ≥ 12C, indicating that the rate of transition to endoreduplication status was inhibited, and decreased the progressive advance from 12C to 24C to 48C, indicating that the rate of S‐phase cycling of endoreduplicating cells was inhibited. We conclude that cell division was more responsive to ABA concentrations than were endoreduplication or cell expansion growth.
Physiological and molecular genetic mechanisms regulating hydrolytic enzyme gene expression in cereal grains
Authors: Skadsen Ronald W.
Published: March 2003

In recent years, the analysis of hydrolytic enzyme gene expression in germinating cereals has progressed from a determination of hormone‐responsive promoter elements to the cloning of positive and negative promoter‐binding proteins and the direct in vivo demonstration of their effects on gene expression. Interesting parallels with animal systems have emerged, particularly with regard to the mediation of gibberellin signal transduction through transcriptional regulators encoded by oncogene homologues, calcium signalling pathways, and (possibly) through the phospho‐inositide turnover pathway. New applications of cell microinjection, intracellular fluorescent probes and transient expression with effector/reporter expression plasmids have allowed direct examination of the roles of signal transduction factors and their ultimate targets of their pathways on hormone‐ and sugar‐responsive gene promoter elements. Arabidopsis hormone response mutants have provided cloned candidates for genes encoding trans‐acting regulatory proteins, and these have rapidly led to their counterparts in cereals. The identification of the initial receptor for gibberellin and abscisic acid still proves to be an intractable problem, but candidates have emerged from recent studies. The puzzle of how gibberellin and abscisic acid signal transductions lead to opposing regulatory events at every level proves to be a continuing challenge, but recent studies provide intriguing insights into these complex events. These studies are providing testable models as to how hydrolytic enzyme gene expression in developing and germinating cereal grains is regulated. The following review is constructed to summarize recent physiological, genetic and molecular studies in these areas and, where appropriate, provide correlative information from past studies.
Scavenging of superoxide and hydrogen peroxide in blue‐green algae (cyanobacteria)
Authors: Obinger Christian , Regelsberger Günther , Pircher Andrea , Strasser Georg , Peschek Günter A.
Published: March 2003

Blue‐green algae (cyanobacteria) have evolved as the most primitive, oxygenic, plant‐type photosynthetic organisms. Within a single prokaryotic cell, they have uniquely accommodated both oxygenic photosynthesis and aerobic respiration, which are known to produce superoxide and hydrogen peroxide as inevitable byproducts. Two types of superoxide dismutase have been characterized in both N2‐fixing and non‐N2‐fixing cyanobacteria, namely cytosolic iron‐containing superoxide dismutase and thylakoid‐bound manganese‐containing superoxide dismutase. No qualitative differences between various cell types (vegetative cells, heterocysts) were found. In contrast to chloroplasts, most of the cyanobacterial species show catalatic activity. From two species the corresponding enzymes have been characterized as typical prokaryotic (bifunctional) catalase‐peroxidases with homologies to cytochrome c peroxidases and ascorbate peroxidases. In addition to catalatic activity, some strains exhibit ascorbate peroxidase activity, but to date there are no reports detailing purification and characterization.

Cyanobacteria were found to contain low intracellular ascorbate concentrations (30‐100 µM) and 2‐5 mM glutathione. Both monodehydroascorbate and glutathione reductase activities were detected in most species examined, whereas dehydroascorbate reductase activity was absent. The question as to whether a glutathione‐ascorbate cycle exists in cyanobacteria cannot be answered at present.
Drought tolerance of photosynthetic electron transport under CO2‐enriched and normal air in cereal species
Authors: Flagella Z. , Campanile R. G. , Stoppelli M. C. , De Caro A. , Di Fonzo N.
Published: March 2003

The quantum yield of photosynthetic electron transport (ΦPSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought‐tolerant genotypes, three cereal species were studied; ΦPSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal ΦPSII and both the transient and steady‐state actual ΦPSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O2, 0.035% CO2 in N2) to monitor the whole photosynthetic process under physiological conditions, and CO2 enriched‐low O2 air (1% O2, 5% CO2 in N2) to monitor ΦPSII reduction under stress mainly related to Calvin cycle activity. When ΦPSII related to both assimilatory and non‐assimilatory metabolism was evaluated, the cultivar differences observed under normal Air were more representative of the agronomic performance upon drought stress than under high CO2‐low O2 air. Maximal ΦPSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The ΦPSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chl fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for.
Light and CO2 responses of photosynthesis and chlorophyll fluorescence characteristics in bean plants after simulated acid rain
Authors: Velikova Violeta , Tsonev Tsonko , Yordanov Ivan
Published: March 2003

The effects of simulated acid rain on some chlorophyll fluorescence characteristics and photosynthetic gas exchange at different light intensities and CO2 concentrations of bean plants were investigated. Measurements were carried out 3, 5 and 24 h after spraying. The results showed that a single acid rain (pH 1.8) treatment of bean plants reduced gas exchange, the maximal carboxylating efficiency and photochemical quenching. This treatment led also to increased CO2 compensation point and non‐photochemical quenching and changed the shape of CO2 and light curves of photosynthesis. Both stomatal and non‐stomatal factors contributed to the decreased photosynthetic rate, but their proportion changed with time of recovery of the photosynthetic ampparatus. Three hours after the treatment, the stomatal factors predominated in photosynthesis reduction, while during the next experimental period (5–24 h), mainly non‐stomatal factors determined the decreased photosynthetic rate. It is suggested that the effects observed in consequence of acid rain treatment could be due to an increased intracellular accumulation of H+ and harmful ions contained in the cocktail. This probably led to impaired membrane permeability, enhancement of stroma acidity, uncoupled electron transport and insufficient accumulation of ATP and NADPH, which affected carbon metabolism.
Neutral invertase is a novel type of sucrose‐cleaving enzyme
Authors: Sturm Arnd , Hess Daniel , Lee Hoi‐Seon , Lienhard Susanne
Published: March 2003

Metabolism of sucrose, a mobile source of energy and carbon, is an absolute requirement for the survival of heterotrophic plant organs. In these organs, different isoforms of invertase with discrete subcellular locations hydrolyze the disaccharide into hexoses and, thereby, feed sucrose into various biochemical pathways. In contrast to the invertases with acidic pH optima and a vacuolar or extracellular location, knowledge about the molecular nature of the cytoplasmic invertases (neutral and alkaline invertases) is still in its infancy. Here we report the cDNA cloning of a neutral invertase from carrot based on a partial peptide sequence from the purified enzyme. The function of the encoded polypeptide was confirmed by expression of the cDNA in Escherichia coli. The recombinant protein cleaved sucrose into glucose and fructose with the highest activity between pH 6.5 and 7.0. Unlike acid invertase, neutral invertase does not have the characteristics of a typical plant β‐fructofuranosidase and sucrose akppears to be its sole substrate. The deduced amino acid sequence shares no similarity with sequences of acid invertases. The polypeptide is cysteine‐rich and homologous sequences were only detected in the genomes of plants and photosynthetic bacteria. Hence, this protein must have evolved independently of other sucrose‐cleaving enzymes. Transcripts for neutral invertase were found in all organs at different stages of development with slightly higher levels in developing organs, suggesting a more general and possibly a growth‐related function of the enzyme in carrot sucrose metabolism.
Calcium regulation of senescence in rose petals
Authors: Torre Sissel , Borochov Amihud , Halevy Abraham H.
Published: March 2003

Rose plants grown at high relative humidity (RH) produce flowers with a shorter vase life than those grown at low RH. The calcium content of the former is lower than that of the latter. The present study was conducted to examine the possible involvement of calcium in the regulation of rose flower senescence. In whole cut flowers and in detached petals of cvs Mercedes and Baroness, CaCl2 treatment promoted bud‐opening and delayed senescence. The treated flowers stayed turgid and continued their initial postharvest growth for longer periods of time. The membrane protein content in detached petals decreased with time, in parallel to the decline in membrane phospholipids (PLs). Calcium treatment delayed the decrease in both membrane proteins and PL and increased ATPase activity in the aging petals. Electrolyte leakage, which is a reliable indicator of petal‐membrane senescence, was postponed in calcium‐treated flowers. Calcium treatments also sukppressed ethylene production with age. We suggest that the calcium‐induced delay in rose petal senescence involves the protection of membrane proteins and PLs from degradation, thus preserving the integrity of the membranes, reducing ethylene production, and hence maintaining solute transport and tissue vitality.
Indole‐3‐acetic acid metabolism in hormone‐autotrophic, embryogenic callus of Inmil® cherry rootstock (Prunus incisa×serrula‘GM 9’) and in hormone‐dependent, nonembryogenic calli of Prunus incisa×serrula and Prunus domestica
Authors: Michalczuk Lech , Druart Philippe
Published: March 2003

Callus derived from the roots of Inmil® cherry rootstock (Prunus incisa×serrula) proliferates in a hormone‐free solid medium. When transferred to a hormone‐free liquid medium, such callus forms somatic embryos. On the other hand, leaf‐derived callus of P. incisa×serrula and leaf‐ and root‐derived calli of P. domestica require exogenous auxin for sustained growth and never form embryos. Levels of free and esterified indole‐3‐acetic acid (IAA) were similar in both types of calli grown on a solid medium, whereas the amide‐conjugated IAA was higher in the root‐derived embryogenic one. Transfer to a liquid medium did not affect the level of both free and conjugated IAA in the nonembryogenic callus, but in the embryogenic callus it decreased the level of amide‐conjugated IAA. Isotopic dilution of

C‐IAA taken up from a medium was faster in the embryoegenic than in the nonembryogenic calli, which shows that the rate of IAA metabolism was higher in embryogenic callus. Besides IAA, indole‐3‐ethanol and indole‐3‐acetyl‐N‐aspartate were detected in nonembryogenic calli and in in vitro‐grown shoots of P. domestica, whereas in embryogenic callus and in in vitro‐grown shoots of P. incisa×serrula indole‐3‐acetamide was detected.
Influence of in vitro culture conditions on glucosinolate composition of microspore‐derived embryos of Brassica napus
Authors: Möllers C. , Nehlin L. , Glimelius K. , Iqbal M. C. M.
Published: March 2003

Microspore‐derived embryos (MDEs) of Brassica napus were used to study the influence of sucrose, jasmonic acid (JA), and abscisic acid (ABA) on dry weight and total glucosinolate (GSL) content as well as on specific GSLs. An improved procedure was developed to enable the detection of alkenyl and indole GSLs in single MDEs although they were cultured in medium containing 13% sucrose, where the accumulation of GSL is very low. A sucrose content of 2% and below in the culture medium of the embryos was necessary to significantly increase the total GSL content in embryos of three different rapeseed cultivars. The increase in total GSL content was caused predominantly by higher contents of the indole GSL glucobrassicin (GBC). Contents of 4‐hydroxy‐3‐indolyl glucosinolate (4OH), neoglucobrassicin (NEO), and 4‐methoxyglucobrassicin (4ME) were also increased. Alkenyl GSL content remained largely unaffected and increased significantly only in embryos cultured at the lowest tested sucrose concentration of 1%. Growing the embryos in the presence of JA did not change the alkenyl GSL content but led to a 7‐fold increase in the indole GSL content. Significant increases were found for GBC, 4OH and NEO, whereas 4ME content was not affected. The JA treatment did not affect the morphology or dry weight of the MDEs. In contrast, a treatment with ABA significantly reduced the dry weight and the indole GSL content of the embryos. In the combined JA and ABA treatment, the stimulative effect of JA on indole GSL biosynthesis could not override the inhibitory effect of ABA on growth and indole GSL biosynthesis of the embryos.
Preferential accumulation of d‐pinitol in Acrostichum aureum gametophytes in response to salt stress
Authors: Sun Wendell Q. , Li Xiao‐Ping , Ong Bee‐Lian
Published: March 2003

Growth and metabolic responses to salt stress were studied in gametophytes of Acrostichum aureum L. (a mangrove fern). Gametophytes were cultured in 0–170 mM NaCl solutions. The growth of gametophytes was best in low NaCl concentrations (35 and 85 mM), and was retarded at higher NaCl concentrations. Photosynthetic rate of gametophytes was also significantly reduced when grown in high NaCl concentrations. Severe salt stress (>120 mM NaCl) led to a preferential accumulation of
d‐pinitol in gametophytes, whereas the sporophyte accumulated
d‐1‐O‐methyl‐muco‐inositol. The content of
d‐pinitol reached up to 50% of the soluble carbohydrate pool of gametophytes under 155 and 170 mM NaCl. The accumulation of
d‐pinitol and other cyclitols in gametophytes was correlated with the retention of photochemical efficiency of photosystem II and the survival of gametophytes after transfer to solutions containing 340 and 600 mM NaCl, respectively.
Inducible expression of plasma membrane H+‐ATPase in the roots of figleaf gourd plants under chilling root temperature
Authors: Ahn Sung Ju , Im Yang Ju , Chung Gap Chae , Cho Baik Ho
Published: March 2003

Figleaf gourd plants were grown under different root temperatures and the acclimation process of the roots was investigated. Conditioning of the roots by a gradual decrease (2°C h−1) in root temperature to 6°C considerably lowered the electrolyte leakage of the plant leaves compared to non‐conditioned roots. A root temperature of 6°C was critical for the increase in H+‐ATPase (EC 3.6.1.35) activity in the plasma membranes of the roots and this increase was abolished by the addition of cycloheximide in the root medium. The H+‐transport rate of the plasma membranes was also increased by low root temperature. Increases in the amount of the plasma membrane H+‐ATPase gene transcription and translation in the plant roots under chilling root temperature were demonstrated by Northern and Western blot analysis, respectively. A correlation between the leaf temperature, measured by an infra‐red thermometer, and the H+‐ATPase activity suggests the involvement of H+‐ATPase in the root acclimation process.
Estimation of the bioenergetic costs of fruit and other organ synthesis in apple
Authors: Walton Eric F. , Wünsche Jens N. , Palmer John W.
Published: March 2003

The specific bioenergetic cost of apple fruit (Malus domestica Borkh. cv. Braeburn) growth was calculated from seasonal elemental analysis (for carbon, hydrogen, nitrogen, and sulphur) and ash data. Specific cost changed during fruit development and at harvest was 1.16 g glucose g−1 dry weight of which 0.142 g glucose g−1 dry weight was consumed in growth respiration. Comparisons of those end‐of‐season values with those from a range of other apple cultivars (early through late maturing, and with a range of sugar/acid ratios) showed little difference, despite variations in elemental composition. Specific costs ranged between 1.15 and 1.16 g glucose g−1 dry weight, and growth respiration between 0.136 and 0.148 g glucose g−1 dry weight. Specific costs were also calculated for leaves (extension and spur), wood (1 and 2 year), and trunk and roots (fine and coarse). Leaves had the greatest cost (mean 1.44 g glucose g−1 dry weight), then wood and trunk (mean 1.38 g glucose g−1 dry weight), and fruit had the smallest. Specific growth costs were also calculated from heats of combustion data. Little difference was observed between the two methods, but the values calculated from the elemental analysis data tended to be higher than those calculated from the heats of combustion data.
Tissue browning of in vitro cultures of Scots pine: Role of peroxidase and polyphenol oxidase
Authors: Laukkanen Hanna , Häggman Hely , Kontunen‐Soppela Sari , Hohtola Anja
Published: March 2003

Callus cultures from shoot tips of mature Scots pine (Pinus sylvestris L.) were characterized by rapid browning and an inability to regenerate. The peroxidase (POD) and polyphenol oxidase (PPO) activities and relationship to browning in such cultures were compared with embryogenic and non‐embryogenic cultures of Scots pine, started from immature embryos of three different pine clones. The browning in callus cultures derived from pine buds was visible approximately after 2 weeks of culture, and continued thereafter until the callus was dark brown and poorly growing. The non‐embryogenic cultures induced from immature embryos showed either light yellow coloring or browning, whereas the embryogenic cultures showed browning. POD activity increased during the first 4 weeks in callus tissue initiated from pine buds, and was significantly higher than in pine buds or cultures derived from immature embryos. The ability of cultures initiated from pine buds to oxidize catechol was notably high compared with cultures initiated from immature embryos, regardless of the time of measurement. Addition of catalase revealed that both POD and PPO were able to use catechol as substrate. An antibody raised against broad bean (Vicia faba) chloroplast PPO was used to recognize PPO. One polypeptide with a molecular mass of 50 kDa was detected in all pine samples on SDS‐PAGE and non‐denaturing PAGE. Another polypeptide with a molecular mass of 70 kDa was shown exclusively in the light‐yellow non‐embryogenic cultures. The results suggest that especially the high POD activities in callus tissues started from mature trees cause rapid and early browning and possibly subsequent cell death.
Ascorbate‐dependent hydrogen peroxide detoxification and ascorbate regeneration during germination of a highly productive maize hybrid: Evidence of an improved detoxification mechanism against reactive oxygen species
Authors: De Gara Laura , Paciolla Costantino , De Tullio Mario C. , Motto Mario , Arrigoni Oreste
Published: March 2003

Ascorbate content and the activities of some key enzymes involved in the detoxification from reactive oxygen species were investigated in germinated embryos of two Zea mays L. inbred lines (B73 and Mo17) and of their heterotic F1 hybrid (B73×Mo17). The F1 hybrid showed a higher ascorbate biosynthetic capability owing to a higher activity of
l‐galactono‐Γ‐lactone dehydrogenase (EC 1.6.5.4), the last enzyme in ascorbate biosynthesis. Ascorbate peroxidase (EC 1.11.1.11), ascorbate free radical reductase (EC 1.6.5.4) and dehydroascorbate reductase (EC 1.8.5.1) activities were much higher in the F1 hybrid than in either inbred line, whereas catalase (EC 1.11.1.6) activity was similar in the three genotypes. Native polyacrylamide gel electrophoresis (PAGE) analysis showed three forms of cytosolic ascorbate peroxidase, both in parental lines and in the F1 hybrid. On the other hand, a complex pattern of proteins with dehydroascorbate reductase activity was observed, with the hybrid combining the different dehydroascorbate‐reducing proteins expressed by the inbred lines. The possible involvement of the enzymes of the ascorbate system in the phenomenon of hybrid vigour is discussed.
Silverleaf whitefly stress impairs sugar export from cotton source leaves
Authors: Lin Tong‐Bao , Wolf Shmuel , Schwartz Amnon , Saranga Yehoshua
Published: March 2003

Silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring, is one of the most noxious pests of numerous field and vegetable crops, causing billions of dollars worth of damage throughout the world. SLW is a phloem feeder whose feeding is likely to interfere with phloem transport. The aim of this study was to test the hypothesis that SLW infestation impairs carbohydrate export from source leaves, and consequently increases their carbohydrate content. The youngest fully expanded leaves of cotton (Gossypium hirsutum L., cv. Siv'on), grown under SLW‐infested and noninfested conditions, were characterized for their diurnal changes in carbohydrate content and photoassimilate export. SLW infestation induced a considerable reduction in net photosynthetic rate (Pn), coupled with increased sucrose, glucose and fructose and decreased starch concentrations. Export rate was determined after

CO2 pulse‐labeling both by in situ monitoring of leaf radioactivity and by analyzing the content and radioactivity of the major carbon metabolites. Radioactive counting indicated a lower rate of

C efflux for the infested plants. A similar trend was found for the specific activities of sucrose and the three soluble sugars combined (sucrose, glucose and fructose). A single exponential decay function with asymptote was fitted to the above efflux curves. All the calculated exponential coefficients demonstrated lower export rates after SLW injury. These results indicate that SLW impairs photoassimilate export, suggesting possible down‐regulation of Pn due to increased foliar soluble sugar contents.
ACC oxidase is found in seedlings of two (Coniferales, Gnetales) of the four gymnosperm orders
Authors: Reynolds Elizabeth A. , John Philip
Published: March 2003

Leaf material and seedlings of species representing all gymnosperm orders were tested for 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase activity. Seedlings of Pinus nigra, Pinus radiata, Pseudotsuga menziesii, Cupressocyparis leylandii, Ephedra major and E. nevadensis showed high level in vitro ACC oxidase activity. The enzyme from seedlings of Pinus nigra var. nigra (Arnold) was shown to resemble the angiosperm enzyme in a requirement for ascorbate, carbon dioxide and Fe(II). In contrast, seedlings of Ginkgo biloba, Dioon edule, Zamia furfuraceae and Cycas revoluta showed no detectable ACC oxidase activity. Leaf material from species representing all orders of gymnosperms was also tested for ACC oxidase activity in vitro, but none could be demonstrated. The results presented here support an origin of ACC oxidase in a common ancestor of the angiosperms, Gnetales and Coniferales.
Changes in cell‐wall properties of wheat (Triticum aestivum) roots during aluminum‐induced growth inhibition
Authors: Tabuchi Akira , Matsumoto Hideaki
Published: March 2003

The effects of aluminum (Al) on root elongation, the mechanical extensibility of the cell wall, and the amount of cell‐wall polysaccharides in the roots of Al‐resistant (Atlas 66) and Al‐sensitive (Scout 66) cultivars of wheat (Triticumaestivum L.) were examined. Exposure to 10 μM AlCl3 for 6 h inhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wall in the roots of both cultivars, but prominently only in the roots of Scout 66. The amount of hemicellulose in the 10‐mm region of root apex of Scout 66 was increased by the exposure to Al, especially in the apical regions. Al did not influence the neutral sugar composition of either pectin or hemicellulose in Scout 66 roots. However, Al increased the weight‐average molecular mass of hemicellulosic polysaccharides and the amounts of wall‐bound ferulic and diferulic acids in Scout 66 roots. These findings suggest that Al modifies the metabolism of cell‐wall components and thus makes the cell wall thick and rigid, thereby inhibiting the growth of wheat roots.
PSII‐S gene expression, photosynthetic activity and abundance of plastid thioredoxin‐related and lipid‐associated proteins during chilling stress in Solanum species differing in freezing resistance
Authors: Rorat Tadeusz , Havaux Michel , Irzykowski Witold , Cuiné Stéphan , Becuwe Noëlle , Rey Pascal
Published: March 2003

We investigated the role of non‐photochemical energy quenching (NPQ) in cold acclimation in potato. We first analyzed the expression of the PsbS gene, which encodes a PSII subunit involved in NPQ, during chilling treatment in two potato species, a cold‐tolerant Solanum sogarandinum and a cold‐sensitive Solanum tuberosum (cv. Cisa). In in vitro plantlets, a transient transcript accumulation was observed after 1 h in the light at room temperature in both species, and this light‐induced PsbS transcript accumulation was strongly amplified at 4°C. Nuclear run‐off transcription experiments indicated that this increase likely originates from a higher transcriptional activity of PsbS gene. In phytotron‐grown plants, chilling treatment was shown also to result in a substantial increase in PsbS mRNA level. However, no change in protein abundance was noticed in either Solanum species. PSII photochemistry and photosynthetic electron transport were severely decreased in S. tuberosum plants at low temperature, while both activities were only slightly affected in S. sogarandinum. NPQ was substantially reduced in both species during chilling stress. These results indicate that neither PsbS nor NPQ are involved in acclimation of S. sogarandinum to low temperature. In contrast, the level of two other plastid proteins, one related to thioredoxins, CDSP32, and the other homologous to plastid lipid‐associated proteins, CDSP34 (for chloroplastic drought‐induced stress proteins of 32 and 34 kDa, respectively), was higher at low temperature in the cold‐tolerant species. This result is discussed in relation to the potential roles of CDSPs in the protection of photosynthetic structures.
Impact of four years exposure to different levels of ozone, phosphorus and drought on chlorophyll, mineral nutrients, and stem volume of Norway spruce, Picea abies
Authors: Wallin Göran , Karlsson Per Erik , Selldén Gun , Ottosson Susanne , Medin Eva‐Lena , Pleijel Håkan , Skärby Lena
Published: March 2003

Saplings of one clone of Norway spruce, Picea abies (L.) Karst, were planted in 120 l pots in 1991 and exposed to three levels of ozone, two levels of phosphorus and two levels of water supply in 42 open‐top chambers (OTCs), during 1992–1996. The effects of pots and OTCs were also tested. Nutrient concentrations of the needles were not affected by ozone, while the low phosphorus supply (LP) and drought stress (D) treatments had significant effects on several mineral nutrients, e.g. phosphorus, calcium, magnesium, manganese, sulphur and boron. Ozone reduced the chlorophyll concentration in the 2‐ and 3‐year‐old needles in 1994 and 1995. The highest ozone concentration reduced the stem volumes (− 8%), as well as the stem lengths (− 5%), of the saplings in 1993 and 1994, after two and three years of exposure. After the fourth growing season this ozone‐induced reduction in stem volume disappeared which might be caused by pot limitation. LP supply and D both caused large decreases in the stem volume and length. The needles from LP treatment had as high P concentration as 1.2–1.5 mg g−1, implying a need for increasing the critical value for phosphorus. The OTC enclosure stimulated the stem volume growth significantly compared to saplings growing in ambient plots. This was suggested to be attributed to the slightly higher temperature in the OTCs. The overall result is that ozone in southern Sweden is likely to have negative effects on Norway spruce trees, although much less than other environmental factors, e.g. water and phosphorus.