bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation of aluminum‐tolerant cell lines of tobacco in a simple calcium medium and their responses to aluminum
Authors: Rama Devi S. , Yamamoto Yoko , Matsumoto Hideaki
Published: March 2003

Aluminum (Al)‐tolerant cell lines (ALT301 and ALT401) of tobacco were isolated in a simple calcium (Ca) solution from ethyl methane sulfonate (EMS)‐treated suspension cultured tobacco cells (Nicotiana tabacum L. cv. Samsun, a cell line SL) at the logarithmic phase of growth. A highly tolerant cell line ALT301 exhibited the accumulation of Al and the deposition of callose to the same extent as the parental SL cells during the exposure to Al. However, the Al‐treated ALT301 cells grew much better than the Al‐treated SL cells after transfer to Al‐free growth medium. Compared to SL cells, ALT301 cells were more tolerant to toxicity of copper and iron, but not to that of lanthanum. These results suggest that ALT301 cells have an internal tolerance mechanism, which makes cells grow normally in spite of Al accumulation and Al‐induced lesion represented by the deposition of callose. This tolerance mechanism seems also to be effective against copper and iron toxicity. A slightly tolerant cell line ALT401 also accumulated Al to the same degree as SL cells, but deposited significantly less callose than did SL cells (43% of SL). The growth of ALT401 cells after Al treatment was only slightly better than that of SL cells. Thus, it seems that ALT401 cells have a mechanism to protect cells only from the Al‐induced deposition of callose, which is not enough to overcome the Al‐induced inhibition of growth. The different phenotypes exhibited by these Al‐tolerant cell lines suggest that the deposition of callose is not directly related to the inhibition of growth in Al‐treated cells.
Two forms of phycobilisomes in the Antarctic red macroalga Palmaria decipiens (Palmariales, Florideophyceae)
Authors: Lüder Ulrike H. , Knoetzel Jürgen , Wiencke Christian
Published: March 2003

The phycobilisomes (PBS), the light‐harvesting antennae, from the endemic Antarctic red macroalga Palmaria decipiens were isolated on discontinuous sucrose gradients in two discrete bands and not in one as expected. To exclude methodical faults, we also isolated PBS from the temperate Palmaria palmata and the unicellular red algae Porphyridium cruentum and Rhodella violacea. In P. palmata the PBS were separated in two discrete bands, whereas the PBS from Porphyridium and Rhodella were found in one band. The double‐banded PBS (PBSup and PBSlow) from P. decipiens were further characterized by absorption and fluorescence spectroscopy, native and SDS‐PAGE as well as by negative staining. The phycobiliproteins RIII‐phycoerythrin, RI‐phycocyanin and allophycocyanin were identified and 3 γ‐subunits were described. The PBSup and PBSlow showed no significant differences in their absorption spectra and phycobiliprotein ratios although the negative stained PBSlow were smaller. Differences were found in their low molecular mass subunit complexes, which are assumed to be r‐phycoerythrin. The polypeptide pattern of the PBSup and PBSlow showed no differences in the molecular masses of their subunits and linker polypeptides, but in their percentage distribution. The results suggest that the PBSlow is a closer packed and PBSup a little more loosely aggregated hemiellipsiodal PBS form. We discuss the ecophysiological function of two PBS forms in P. decipiens and suggest advantages in the rapid acclimation to changes in environmental light conditions.
The impact of different phytosterols on the molecular dynamics in the hydrophobic/hydrophilic interface phosphatidylcholine–liposomes
Authors: Hellgren Lars I. , Sandelius Anna Stina
Published: March 2003

Plant sterols differ from cholesterol in having an alkyl group at Δ‐24, and, in the case of stigmasterol, also a Δ‐22 double bond. The effects of 10 mol% of three plant sterols (campesterol, β‐sitosterol, stigmasterol) and cholesterol on the molecular dynamics and phase behavior in multilamellar liposomes made from different phosphatidylcholine (PC) molecular species have been compared, utilizing the fluorescent probe Laurdan (2‐dimethyl‐amino‐6‐laurylnaphthalene). Laurdan reports the molecular mobility in the hydrophilic/hydrophobic interface of the membrane by determining the rate of dipolar relaxation of water molecules close to the glycerol backbone of PC. Our results showed that the Δ‐24 alkyl group of plant sterols did not affect their ability to reduce molecular mobility in this region of the PC membranes. However, the plant sterols had a decreased capacity compared to cholesterol to inhibit formation of co‐existing domains of gel and liquid‐crystalline phases in membranes composed of equimolar dilauroyl‐PC and dipalmitoyl‐PC. The Δ‐22 double bond present in stigmasterol decreased the ability of this sterol, compared to the other phytosterols, to reduce the molecular mobility at the hydrophobic/hydrophilic interface in membranes made of a saturated PC molecular species. However, in membranes made from 16:0/18:2‐PC, a lipid species common in plant plasma membranes, stigmasterol was as efficient as other sterols in affecting the polarity and molecular mobility at the hydrophilic/hydrophobic interface of the membrane at 25°C, but was, in contrast to the other sterols, without effect at 0°C. Our results thus confirm as well as contradict the results of previous studies of the interactions between saturated PC and sterols, where other membrane regions were probed. The physiological relevance of the findings is discussed.
Isolation and expression of two pectate lyase genes during fruit ripening of banana (Musa acuminata)
Authors: Pua Eng‐Chong , Ong Choon‐Kiat , Liu Pei , Liu Jian‐Zhong
Published: March 2003

Two cDNAs, designated MWPL1 and MWPL2, encoding putative pectate lyases (Pel; EC 4.2.2.2), which catalyze the cleavage by β‐elimination of α‐1→4‐linked galacturonosyl residues of pectins found mostly in middle lamella and primary cell wall in plants, were isolated from ripening fruit of banana (Musa acuminata) and their expressions in fruit during ripening and in response to ethylene were investigated. MWPL1 and MWPL2 encode a single polypeptide of 407 and 454 amino acid residues, respectively. The two cDNAs shared an overall identity of 75% in both nucleotide and deduced amino acid sequences. Sequence comparison of MWPL1 and other plant Pels revealed the homology ranging from 76% with zinnia to 48% with ragweed. Southern analysis indicated that MWPL1 might be present as a single copy gene, and there might be up to two copies of MWPL2 in the banana genome. The two cDNAs were expressed differentially and/or spatially in various banana organs, with female flower and fruit tissues showing accumulation of the MWPL2 transcript, which was not detected in root, pseudostem, leaf, male flower and ovary, whereas the MWPL1 transcript was not detectable in all organs tested. In fruit tissue during ripening, although transcripts of both members were not detectable in unripe preclimacteric fruits, they began to accumulate as ripening progressed and the level remained high thereafter in overripe fruits. However, the magnitude of transcript accumulation differed between the two Pel members, with substantially more abundant MWPL2 than MWPL1 in ripening fruit. Similar differential transcript accumulation was also observed between peel and pulp, where the former was markedly higher than the latter. Expression of both Pel members was also affected by exogenous ethylene, whose presence at 5–100 ppm stimulated accumulation of MWPL1 and MWPL2 transcripts in preclimacteric fruit, suggesting that ethylene may play an important regulatory role in regulating Pel expression during fruit ripening of the banana.
The use of ethylene‐suppressed lines to assess differential sensitivity to ethylene of the various ripening pathways in Cantaloupe melons
Authors: Flores F. , Ben Amor M. , Jones B. , Pech J. C. , Bouzayen M. , Latché A. , Romojaro F.
Published: March 2003

Physiological characterization of ethylene‐suppressed Cantaloupe Charentais melons (Cucumis melo var. cantalupensis Naud cv. Védrantais) revealed that some ripening‐associated events, like degreening of the rind and cell separation in the peduncular abscission zone, are totally dependent on ethylene. By contrast, some other ripening events, like softening and membrane deterioration, depend only partially on ethylene and display some ethylene‐independent components. Application of increasing levels of exogenous ethylene on these antisense 1‐aminocyclopropane‐1‐carboxylic acid oxidase fruits enabled the determination of the gradual sensitivity of various ripening pathways to the hormone. The threshold level of ethylene capable of physiological activity varied from 1 ppm for degreening of the rind to 2.5 ppm for softening, membrane deterioration and cell separation in the peduncular abscission zone. Up to a saturating dose of 5 ppm, the extent of rind degreening was proportionally related to the level of applied ethylene. The saturating levels of ethylene for flesh softening (2.5 ppm) and for membrane deterioration and cell separation in the peduncular abscission zone (5 ppm) were much lower than the internal ethylene found at the climacteric peak of wild‐type fruit (over 100 ppm). The cessation of ethylene treatment resulted in a complete arrest of the rind degreening and peduncular cell separation indicating that both ripening pathways are completely dependent on ethylene. On the contrary, softening and membrane deterioration, though significantly slowed upon removal of ethylene treatment, continued to proceed in the absence of the hormone, thereby unmasking the ethylene‐independent component of softening and membrane deterioration. The presence of ethylene‐independent components in the regulation of individual pathways indicates that the ripening of climacteric fruit involves a substantial portion of non‐climacteric regulation.
The inhibition of ammonium uptake in excised birch (Betula pendula) roots by batatasin‐III
Authors: Wallstedt Anna , Sommarin Marianne , Nilsson Marie‐Charlotte , Munson Alison D. , Margolis Hank A.
Published: March 2003

In northern Sweden, plants growing in association with the clonal dwarf shrubEmpetrum hermaphroditumusually exhibit limited growth and are N‐depleted. Previous studies suggest that this negative effect byE. hermaphroditummay be explained, at least in part, by the release of phenolic compounds, particularly the dihydrostilbene, batatasin‐III from foliage to soil. In the present work, we investigated whether batatasin‐III has the potential to interfere with NH4+uptake in birch (Betula pendula) roots. Excised birch roots were exposed to batatasin‐III during brief periods in15NH4+solutions, and then analyzed for labeled N. Batatasin‐III inhibited N‐NH4+uptake by 28, 89 and 95% compared with the control, when roots were treated with 0.1, 1.0 and 2.8 mMof batatasin‐III, respectively. The effect of 1.0‐mMbatatasin‐III was greater at pH 4.2 than at pH 6.8. In addition, the inhibition of N‐NH4+uptake by batatasin‐III was not reversed after rinsing the roots in water and transferring them to a batatasin‐III free solution. Furthermore, birch seedlings immersed in a 1.0‐mMbatatasin‐III solution for 2 h, and then replanted in pots with soil, had decreased growth, such that 10 weeks after treatment, the dry mass of both shoots and roots was reduced by 74 and 73%, respectively, compared with control seedlings. This suggests that a brief exposure to batatasin‐III may have a long‐term inhibitory effect on whole plant growth. Using plasma membrane vesicles isolated from easily extractable spinach (Spinacia oleracea)leaves, it was found that batatasin‐III strongly inhibited proton pumping in isolated plasma membrane vesicles, while it only slightly inhibited ATP hydrolytic activity. The uncoupling of proton pumping from ATP hydrolytic activity suggests that batatasin‐III disturbs membrane integrity. This hypothesis was further supported by a greater efflux of ions from birch roots immersed in a batatasin‐III solution than from roots in a control solution.
Free radical generation and antioxidant content in chloroplasts from soybean leaves exposed to ultraviolet‐B
Authors: Galatro Andrea , Simontacchi Marcela , Puntarulo Susana
Published: March 2003

The aim of this work was to study the effect of ultraviolet‐B (UV‐B) exposure on oxidative status in chloroplasts isolated from soybean (Glycine max cv. Hood). Chloroplasts were isolated from soybean leaves excised from either control seedlings or those exposed to 30 and 60 kJ m−2 day−1 of UV‐B radiation for 4 days. Chloroplastic oxidative conditions were assessed as carbon‐centered radical, carbonyl groups and ascorbyl radical content. Treatment with UV‐B increased the carbon‐centered radical‐dependent EPR signal significantly by 55 and 100% in chloroplasts from leaves exposed to 30 and 60 kJ m−2 day−1 UV‐B, respectively, compared to radical content in chloroplasts from control leaves. The content of carbonyl groups increased by 37 and 62% in chloroplasts isolated from soybean leaves irradiated for 4 days with 30 and 60 kJ m−2 day−1 UV‐B, respectively. The content of soluble metabolites in isolated chloroplasts should not be taken as absolute in vivo values; however, these data are valuable for comparative studies. UV‐B exposure did not significantly affect ascorbyl radical content compared to controls. The content of ascorbic acid and thiols in chloroplasts isolated from leaves exposed to 60 kJ m−2 day−1 UV‐B was increased by 117 and 20.8%, respectively, compared to controls. Neither the content of total carotene nor that of β‐carotene or α‐tocopherol was affected by the irradiation. The results presented here suggest that the increased content of lipid radicals and oxidized proteins in the chloroplasts isolated from leaves exposed to UV‐B could be ascribed to both the lack of antioxidant response in the lipid soluble fraction and the modest increase in the soluble antioxidant content.
Changes in the activities of antioxidant enzymes in response to virus infection and hormone treatment
Authors: Clarke Sean F. , Guy Paul L. , Burritt David J. , Jameson Paula E.
Published: March 2003

Activities of enzymes involved in the detoxification of reactive oxygen species (catalase, glutathione reductase, peroxidase and superoxide dismutase (SOD)) were examined in the leaves of Phaseolus vulgaris L. var. Top Crop treated with plant hormones and infected with a non‐lesion‐forming isolate of white clover mosaic potexvirus (WClMV). The activities of catalase, glutathione reductase and SOD rapidly declined after infection while peroxidase activity was enhanced. These changes occurred before the rapid increase (5 days) in WClMV replication. A mild chlorosis appeared 7–10 days after inoculation but necrosis was never observed on inoculated leaves. Plants treated with dihydrozeatin, salicylic acid and jasmonic acid prior to WClMV inoculation showed elevated catalase, glutathione reductase, and peroxidase activity, while SOD activities remained the same as in water‐treated controls. These treatments all inhibited virus replication with enzyme activities remaining near control levels. We propose that a decline in free radical scavenging capacity may be required before a rapid increase in virus replication can take place. Treatments increasing the ability of the plant to scavenge reactive oxygen species may hinder virus replication. A possible role for reactive oxygen species as a requirement for virus replication is discussed.
Seasonal pattern of monoterpene synthase activities in leaves of the evergreen tree Quercus ilex
Authors: Fischbach Robert Josef , Staudt Michael , Zimmer Ina , Rambal Serge , Schnitzler Jörg‐Peter
Published: March 2003

Monoterpene synthase activities were measured in current year and 1‐year‐old leaves of holm oak (Quercus ilex L.). The monoterpene synthase activities of the leaves strongly changed with leaf development and leaf age. Enzyme activities increased rapidly in spring after leaf emergence, reaching maximum values in summer, which declined during the following winter period. In the next spring monoterpene synthase activities recovered in the old leaves to about one‐third of values in the previous years and showed a similar seasonal variation as in young leaves. In both leaf age classes the pattern of enzymatic monoterpene formation was stable with α‐pinene (33%), β‐pinene (28%), and myrcene (26%) as prominent compounds followed by minor fractions of sabinene (10%) and limonene (3%). Monoterpene emission correlated with the activity of the synthetizing enzymes, indicating that monoterpene synthase activities in Q. ilex reflect the seasonal monoterpene emission potential of the leaves.
Expression of Oryza sativa MAP kinase gene is developmentally regulated and stress‐responsive
Authors: Huang Hao‐Jen , Fu Shin‐Feng , Tai Ying‐Hsia , Chou Wan‐Chi , Huang Dinq‐Ding
Published: March 2003

Mitogen‐activated protein kinase (MAPK) pathways are modules involved in the transduction of extracellular signals to intracellular targets in all eukaryotes. In plants, there is evidence for MAPKs playing a role in the signalling of abiotic stresses, pathogens, plant hormones, and cell cycle cues. The large number and divergence of plant MAPKs indicates that this ancient mechanism of signal transduction is extensively used in plants. However, there have been no reports of classical MAPK module in rice. In this report, we have isolated a MAPK from rice (Oryza sativa) termed OsMAPK2. The cloned cDNA is 1457 nucleotides long and the deduced amino acid sequence comprised 369 amino acid residues. Sequence analysis revealed that the predicted amino acid sequence is 72% identical to tobacco wound‐induced protein kinase (WIPK). Southern analysis suggested a single OsMAPK2 gene in rice. Analysis at the mRNA level has shown that OsMAPK2 is expressed in all plant organs and high relative amounts of OsMAPK2 were detected in the mature panicles in comparison with in the immature panicles. In suspension‐cultured cells, the OsMAPK2 mRNA transcript increased markedly upon temperature downshift from 26°C to 4°C and sucrose starvation. In contrast, the OsMAPK2 mRNA level rapidly declined in rice cell challenged by high temperature. A similarly rapid response of OsMAPK2 was observed in stress‐treated seedlings, demonstrating that response of the MAPK pathway occurs also in intact plants. These results suggest that this OsMAPK2 may function in the stress‐signalling pathway as well as panicle development in rice.
Characterization of the developmental stages of cypress zygotic embryos by two‐dimensional electrophoresis and by cytochemistry
Authors: Sallandrouze Anne , Faurobert Mireille , El Maâtaoui Mohamed
Published: March 2003

Biochemical changes that characterize megagametophyte and zygotic embryo development in the conifer Cupressus sempervirens L. (Cupressaceae) were studied by complementary methods of cytochemistry and two‐dimensional electrophoresis (2‐DE). These analyses revealed that early in their development megagametophytes and embryos were characterized by the predominant elaboration of starch in association with a low protein content. As their development proceeded, starch content gradually decreased while protein body synthesis progressively intensified, both in the megagametophyte and the embryo. In parallel, an increase in protein level as well as an accumulation of specific polypeptides could be observed in the two tissues. During maturation, protein bodies accumulated to high levels both in megagametophyte and embryo cells, whereas starch could no longer be detected. Protein levels were high in mature seeds and reached 12% and 8% of the megagametophyte and embryo DW, respectively. Some sets of polypeptides accumulated more specifically at this time in both megagametophyte and embryo. Some of these began to first accumulate in the megagametophyte during embryo development before their concentration rose in the embryo at cotyledonary stage. Others displayed a more specific‐embryo accumulation pattern.
Phosphate sensing in higher plants
Authors: Abel Steffen , Ticconi Carla A. , Delatorre Carla A.
Published: March 2003

Phosphate (Pi) plays a central role as reactant and effector molecule in plant cell metabolism. However, Pi is the least accessible macronutrient in many ecosystems and its low availability often limits plant growth. Plants have evolved an array of molecular and morphological adaptations to cope with Pi limitation, which include dramatic changes in gene expression and root development to facilitate Pi acquisition and recycling. Although physiological responses to Pi starvation have been increasingly studied and understood, the initial molecular events that monitor and transmit information on external and internal Pi status remain to be elucidated in plants. This review summarizes molecular and developmental Pi starvation responses of higher plants and the evidence for coordinated regulation of gene expression, followed by a discussion of the potential involvement of plant hormones in Pi sensing and of molecular genetic approaches to elucidate plant signalling of low Pi availability. Complementary genetic strategies in Arabidopsis thaliana have been developed that are expected to identify components of plant signal transduction pathways involved in Pi sensing. Innovative screening methods utilize reporter gene constructs, conditional growth on organophosphates and the inhibitory properties of the Pi analogue phosphite, which hold the promise for significant advances in our understanding of the complex mechanisms by which plants regulate Pi‐starvation responses.
Short‐term effects of salt stress on antioxidant systems and leaf water relations of pea leaves
Authors: Hernández José A. , Almansa Maria S.
Published: March 2003

In pea (Pisum sativum L.) plants the effect of short‐term salt stress and recovery on growth, water relations and the activity of some antioxidant enzymes was studied. Leaf growth was interrupted by salt addition. However, during recovery, growth was restored, although there was a delay in returning to control levels. Salt stress brought about a decrease in osmotic potential and in stomatal conductance, but at 48 h and 24 h post‐stress, respectively, both parameters recovered control values. In pea leaves, a linear increase in the Na+ concentration was observed in salt treated plants. In the recovered plants, a slight reduction in the Na+ concentration was observed, probably due to a dilution effect since the plant growth was restored and the total Na+ content was maintined in leaves after the stress period. A significant increase of SOD activity occurred after 48 h of stress and after 8 h of the recovery period (53% and 42%, respectively), and it reached control values at 24 h post‐stress. APX activity did not change during the stress period, and after only 8 h post‐stress it was increased by 48% with respect to control leaves. GR showed a 71% increase after 24 h of salt stress and also a significant increase was observed in the recovered plants. A strong increase of TBARS was observed after 8 h of stress (180% increase), but then a rapid decrease was observed during the stress period. Surprisingly, TBARS again increased at 8 h post‐stress (78% increase), suggesting that plants could perceive the elimination of NaCl from the hydroponic cultures as another stress during the first hours of recovery. These results suggest that short‐term NaCl stress produces reversible effects on growth, leaf water relations and on SOD and APX activities. This work also suggests that both during the first hours of imposition of stress and during the first hours of recovery an oxidative stress was produced.
Chilling tolerance of maize, cucumber and rice seedling leaves and roots are differentially affected by salicylic acid
Authors: Kang Ho‐Min , Saltveit Mikal E.
Published: March 2003

Salicylic acid (SA) is one component of a complex signalling pathway that is induced by a number of biotic and abiotic stresses. Exposing seedling radicles to aqueous solutions of 0.5 mM salicylic acid for 24 h before chilling at 2.5°C for 1–4 days reduced the chilling‐induced increase in electrolyte leakage from maize and rice leaves, and cucumber hypocotyls, but not from their radicles. The SA treatments that induced chilling tolerance in the aerial portion of the seedlings did not induce chilling tolerance in the radicles, even though the SA treatments were applied to the radicles. A comparison of activity among five antioxidant enzymes showed that SA did not alter enzyme activities in the radicles, but that chilling tolerance induced by SA in the aerial portions of maize and cucumber plants was associated with an increase in the activity of glutathione reductase and guaiacol peroxidase.
Iron stress responses in the cyanobacterium Synechococcus sp. PCC7942
Authors: Sandström Stefan , Ivanov Alexander G , Park Youn‐Il , Öquist Gunnar , Gustafsson Petter
Published: March 2003

In the present study, we describe the sequential events by which the cyanobacterium Synechococcus sp. PCC 7942 adapts to iron deficiency. In doing so, we have tried to elucidate both short and long‐term acclimation to low iron stress in order to understand how the photosynthetic apparatus adjusts to low iron conditions. Our results show that after an initial step, where CP43′ is induced and where ferredoxin is partly replaced by flavodoxin, the photosynthetic unit starts to undergo major rearrangements. All measured components of Photosystem I (PSI), PSII and cytochrome (Cyt) ƒ decrease relative to chlorophyll (Chl) a. The photochemical efficiencies of the two photosystems also decline during this phase of acclimation. The well‐known drop in phycobilisome content measured as phycocyanin (PC)/Chl was not due to an increased degradation, but rather to a decreased rate of synthesis. The largest effects of iron deficiency were observed on PSI, the most iron‐rich structure of the photosynthetic apparatus. In the light of the recent discovery of an iron deficiency induced CP43′ ring around PSI a possible dual function of this protein as both an antenna and a quencher is discussed. We also describe the time course of a blue shift in the low temperature Chl emission peak around 715 nm, which originates in PSI. The shift might reflect the disassembly and/or degradation of PSI during iron deficiency and, as a consequence, PSI might under these conditions be found predominantly in a monomeric form. We suggest that the observed functional and compositional alterations represent cellular acclimation enabling growth and development under iron deficiency, and that growth ceases when the acclimation capacity is exhausted. However, the cells remain viable even after growth has ceased, since they resumed growth once iron was added back to the culture.
Pb and Cd uptake in rice roots
Authors: Kim Yu‐Young , Yang Young‐Yell , Lee Youngsook
Published: March 2003

Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb2+ and Cd2+ are affected by the presence of K+, Ca2+ or Mg2+. K+ had a little effect on uptake or toxicity of Pb2+ and Cd2+. Ca2+ or Mg2+ blocked both Cd2+ transport into rice roots and Cd2+ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca2+ blocked both Pb2+ transport into the root and Pb2+ toxicity on root growth. The protective effect of Ca2+ on Pb2+ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb2+ toxicity. Mg2+ did not ameliorate the Pb2+ toxicity on root growth as much as Ca2+ did, although it decreased Pb2+ uptake into roots similarly as Ca2+ did. These results suggest that the protective effect of Ca2+ on Pb2+ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb2+ and Cd2+ may compete with divalent cations for transport into roots of rice plants.
The bushy pea mutant is IAA‐deficient
Authors: Symons Gregory M. , Ross John J. , Murfet Ian C.
Published: March 2003

The bushy mutant of pea (Pisum sativum L.) is characterized by short, thin stems, very small leaves and profuse branching. The bushy phenotype is conferred by a dominant allele, termed bsh. Here we show that bushy plants contain lower levels of free indole‐3‐acetic acid (IAA) than wild‐type (WT) plants. On emergence from the growth medium, bushy seedlings do not immediately display the mutant phenotype, and the effect of bsh on IAA content is small. After 10–14 days, the bushy phenotype begins to develop, and while the IAA content rises in WT plants, it falls in the mutant. The resulting difference in IAA level between WT and mutant can be up to 12‐fold. Although there is a deficiency of free IAA in bushy plants, the total IAA content (including free and conjugated forms) was not reduced in comparison with the WT. Furthermore, in bushy plants, the level of the main IAA conjugate in pea, IAAsp, was not reduced to the same extent as that of IAA, and metabolism studies indicated that faster IAA deactivation might contribute to IAA deficiency in the mutant. Application of IAA to bushy plants did not result in a WT phenocopy. However, the short internodes and profuse branching of bushy plants is consistent with classical views on how IAA affects plant development.
Fructosyl transferase and hydrolase activities in rhizophores and tuberous roots upon growth of Polymnia sonchifolia (Asteraceae)
Authors: Itaya Nair Massumi , Machado de Carvalho Maria Angela , De Cássia Leone Figueiredo‐Ribeiro Rita
Published: March 2003

The underground reserve organs of yacon (Polymnia sonchifolia Poep. Endl.), similarly to other economically important Asteraceae, accumulate more than 60%, on a DW basis, of inulin type β(2‐1) fructans, mainly oligomers (GF2–GF16). Although sucrose:sucrose 1‐fructosyl transferase (1‐SST), fructan:fructan 1‐fructosyl transferase (1‐FFT) and fructan 1‐exohydrolase (1‐FEH) were properly described and characterized from a number of plant species, detailed information about their activities in different organs during development are rather scarce in the literature. In the present work 1‐SST, 1‐FFT and 1‐FEH activities were measured monthly in rhizophores and tuberous roots of yacon plants during their complete growth cycle under field conditions. Results showed that 1‐SST activity in rhizophores was always higher than 1‐FFT activity and increased up to 8 months of cultivation, decreasing to initial values at the end of the growth period. In the tuberous roots 1‐SST activity was also higher than 1‐FFT but varied differently. The higher values were found at the beginning of tuberization (3‐month‐old plants) and at the flowering phase (7‐month‐old plants). Results also showed that synthesizing activities in yacon plants were always higher in rhizophores than in the tuberous roots, while hydrolysing activity predominated in the latter, mainly when 1‐kestose and nystose were used as substrates. 1‐FEH from yacon plants showed low efficiency when commercial inulin from Helianthus tuberosus was utilized as substrate. The analysis of the enzymatic activities performed during growth of yacon clearly indicated the most appropriate source organ and phase of development to obtain the highest enzymatic activities for purification purposes and for the production of fructo‐oligosaccharides (FOS). Furthermore, the results suggested that the relative levels of activities of 1‐SST, 1‐FFT and 1‐FEH could be involved in the chain length distribution of the fructan molecules found in rhizophores and in tuberous roots of this species.
Cold acclimation in silver birch (Betula pendula). Development of freezing tolerance in different tissues and climatic ecotypes
Authors: Li Chunyang , Puhakainen Tuula , Welling Annikki , Viherä‐Aarnio Anneli , Ernstsen Arild , Junttila Olavi , Heino Pekka , Palva E. Tapio
Published: March 2003

A number of environmental cues including short day photoperiod (SD) and low temperature (LT) are known to interact in triggering growth cessation, cold acclimation and other adaptive responses in temperate‐zone tree species. Proper timing of these responses is particularly important for survival of trees in the boreal and subarctic regions. Therefore, we used a northern tree species, silver birch (Betula pendula Roth) as an experimental model to investigate the effect of SD and LT on development of freezing tolerance and on levels of endogenous abscisic acid (ABA) in short‐term experiments under controlled conditions. We characterized differences in SD and LT‐induced cold acclimation between three different climatic ecotypes from southern, central and northern habitats. The results demonstrated that cold acclimation was rapidly triggered by exposing the plants to SD or LT, and that a combination of the different treatments had an additive effect on freezing tolerance. Freezing tolerance induction was not uniform in the different tissues, the buds and leaves developed freezing tolerance more rapidly than the stem, and the young leaves had a higher freezing tolerance than the old leaves. The ability of the leaves to respond to SD and LT and similarity of the bud and leaf responses indicate that birch leaves provide a rapid and convenient system for studies on molecular mechanisms of cold acclimation. Development of freezing tolerance was dependent on the climatic ecotype, the northern ecotype was clearly more responsive to both SD and LT than the two more southern ecotypes. Development of freezing tolerance induced by SD and LT was accompanied by transient changes in ABA levels. These alterations in ABA levels were ecotype‐dependent, the northern ecotype reacting more strongly to the environmental cues.
Photoregulation of phenylalanine ammonia‐lyase (PAL) and chalcone synthase (CHS) in the accumulation of anthocyanin in alpine and prairie ecotypes of Stellaria longipes under varied R/FR
Authors: Alokam Suneetha , Li Yujing , Li Wenze , Chinnappa C. C. , Reid David M.
Published: March 2003

We studied mRNA accumulation and enzyme activity of phenylalanine ammonia‐lyase (PAL) and chalcone synthase (CHS) in alpine and prairie ecotypes of Stellaria longipes. The results show that light is required for the induction of PAL and CHS and accumulation of anthocyanins. Although both the ecotypes showed higher levels of anthocyanins under high R/FR (1.9) than under low R/FR (0.7), neither of the ecotypes showed any significant difference in the transcript abundance of PAL or CHS between low R/FR and high R/FR. However, both ecotypes showed significantly higher levels of CHS activity under high R/FR than under low R/FR corresponding to their anthocyanin accumulation. These results indicate that in S. longipes regulation of CHS activity is more specific to anthocyanin synthesis than PAL under varied R/FR, with a time lag between the enzyme activity and the accumulation of anthocyanins.
Oxygen‐independent temperature regulation of the microsomal oleate desaturase (FAD2) activity in developing sunflower (Helianthus annuus) seeds
Authors: Martínez‐Rivas José M. , Sánchez‐García Alicia , Sicardo M. Dolores , García‐Díaz M. Teresa , Mancha Manuel
Published: March 2003

The temperature and oxygen regulation of the microsomal oleate desaturase (FAD2, EC 1.3.1.35) activity has been studied in developing sunflower (Helianthus annuus L.) seeds. In plants cultivated in growth chambers, the linoleic acid content in the seed lipids increased along the 25/15°C (day/night) cycle, except during the first hours of the warm period, where it decreased significantly. In contrast, FAD2 activity decreased notably at the beginning of the warm period, showing a small and continuous increase during the rest of the cycle. The temperature effect on the linoleic acid content and the FAD2 activity was also investigated using peeled seeds and detached achenes subjected to temperature changes. In peeled seeds, a change of temperature from 10 to 30°C brought about a significant decrease of FAD2 activity. On the contrary, when the temperature shifted from 30 to 10°C, FAD2 activity only increased slightly. Unlike peeled seeds, detached achenes showed a fast and dramatic increase or decrease in the level of FAD2 activity in response to a temperature change from 30 to 10°C, or from 10 to 30°C, respectively. The in vivo and in vitro thermal properties of the FAD2 enzyme were also studied. Optimal temperature and heat‐resistance profile showed similar patterns in both conditions. All these data support the hypothesis that temperature regulates FAD2 activity by two different and independent mechanisms: a direct effect, and an indirect effect affecting oxygen availability. Furthermore, these results suggest that the low thermal stability of the enzyme is the main factor responsible for the direct temperature effect on FAD2 activity.
Tuberculosis in renal transplant recipients
Authors: Lattes R. , Radisic M. , Rial M. , Argento J. , Casadei D.
Published: March 2003

Tuberculosis (TB) has been described in kidney transplant recipients as an infection with predominantly pulmonary involvement. We report the impact of TB in kidney transplantation. Clinical records of adult kidney recipients, transplanted between 1 January 1986 and 31 December 1995 were analyzed for sex, age, graft origin, immunosuppressive therapy, TB sites, diagnostic methods and concomitant infections. Annual incidence, mean time of onset, relation to rejection treatment, tuberculin skin test (PPD) and outcome were analyzed. Patients with a history of TB or graft loss in the first month were excluded. TB was diagnosed in 14 of 384 (3.64%). Mean age at transplantation was 35 years. Twelve of these received the graft from a living donor. All had triple immunosuppression with cyclosporine. Ten had pulmonary TB, three extrapulmonary infection and one disseminated disease. In 13 cases an invasive diagnostic procedure was performed.Mycobacterium tuberculosiscultures were positive in all cases; microscopy revealed acid‐fast bacilli (AFB) in 6, and adenosine deaminase was elevated in CSF and pleural effusion in 2. Annual incidence varied from 0% to 3.1%. At the time of TB presentation 8 patients had other concomitant infections (cytomegalovirus, nocardia,Pneumocystis carinii, disseminated herpes simplex virus). Median time of onset was 13 months. Diagnostic results became available post‐mortem in 2 cases, and one had TB in a failing allograft. TB was treated with 4 drugs including rifampin in 10 patients. Cyclosporine was discontinued in one, lowered in one and increased in 8. During treatment 5 patients had rejection episodes. At 1 year, graft survival was 72.7% and patient survival 90.9%. TB was more prevalent when recipient and donor were both PPD positive. In summary: although TB is a growing threat in the transplant setting, early and aggressive diagnosis with meticulous monitoring of immunosuppression allows a successful outcome for both patient and graft. Optimal prophylaxis guidelines have yet to be completely defined.
Opportunistic infections after blood and marrow transplantation
Authors: Wingard J.R.
Published: March 2003

Opportunistic infections are major causes of morbidity and mortality following bone marrow transplantation. Technological advances in stem cell procurement, the introduction of hematologic growth factors to speed engraftment, the development of new immunosuppressive regimens to control graft‐versus‐host disease (GVHD), the development of technology to perform graft engineering with removal of T lymphocytes in toto or subpopulations of T lymphocytes, the use of molecular techniques to optimize donor and recipient matching, advances in blood banking, and development of international donor registries, are among the various factors that have led to tremendous changes in transplant practices. Because of such changes in transplant practices, along with the advent of new antimicrobial agents, and development of infection control measures affecting pathogen exposure, alterations in the interplay between host and potential pathogens have occurred. Shifts in the incidence and types of opportunistic pathogens are taking place. Several historically important infectious syndromes are today well controlled; others have diminished in importance early after transplant but are more problematic at a later time; new emerging pathogens are being recognized due to selection pressures from antimicrobial usage and new hosts, such as recipients of alternate donor allogeneic transplant procedures, with even more profound and prolonged immune suppression. Such shifts and new syndromes pose continuing new challenges to the transplant clinician (
Note).
The therapeutic prescription for the organ transplant recipient: the linkage of immunosuppression and antimicrobial strategies
Authors: Rubin R.H. , Ikonen T. , Gummert J.F. , Morris R.E.
Published: March 2003

Infection and rejection, the two major barriers to successful organ transplantation, are closely linked, with immunosuppressive therapy being central to the pathogenesis of both. After almost two decades when azathioprine and prednisone, supplemented by antilymphocyte antibody therapy, were the cornerstones of post‐transplant immunosuppressive programs, there has been a major increase in the therapeutic armamentarium available to treat rejection: cyclosporine, tacrolimus, mycophenolate mofetil, rapamycin, and antibodies directed against the interleukin‐2 receptor. These agents are potent inhibitors of microbial specific T cell function, thus potentiating opportunistic infection with herpes group viruses, fungal and mycobacterial species,Strongyloides stercoralis, and a variety of intracellular pathogens. The mechanisms by which each of these drugs exerts its effects are an important determinant of the antimicrobial strategies that will be necessary to combat infection. Indeed, strategies to limit these infections are being linked to the nature of the immunosuppressive therapy required in a particular patient. Thus, the therapeutic prescription for the transplant patient is said to have two components: an immunosuppressive component to prevent and treat rejection, and an antimicrobial one to make it safe. In addition to using antimicrobial agents therapeutically, in the transplant patient prevention is stressed in which antibiotics are deployed prophylactically or preemptively (Note).
Infections of the central nervous system in transplant recipients
Authors: Singh N. , Husain S.
Published: March 2003

Central nervous system (CNS) infections, accounting for 4–29% of CNS lesions in transplant recipients, are a significant post‐transplant complication. Focal CNS infectious lesions or brain abscesses have been documented in 0.36–1% of the transplant recipients. Mycelial fungi, particularlyAspergillus, are by far the most frequent etiologies of post‐transplant brain abscesses. Bacteria, with the exception ofNocardia, are rarely associated with brain abscesses in transplant recipients. Time of onset and concurrent extraneural lesions have implications relevant towards invasive diagnostic procedures in transplant recipients with brain abscesses. Meningoencephalitis in transplant recipients is predominantly due to viruses, e.g., herpesviruses, and less frequently due toListeria monocytogenes,Toxoplasma gondii, andCryptococcus. Despite a wide, and at times perplexing array of opportunistic pathogens that can cause CNS infections, the temporal association of the infection with the time elapsed since transplantation, risk factors, clinical manifestations, and neuroimaging characteristics of the lesion can allow a reasoned and rational approach towards the recognition, diagnosis, and appropriate management of CNS infections in transplant recipients.
Hepatitis B in transplantation
Authors: Bain V.G.
Published: March 2003

Hepatitis B has been a major challenge within the field of transplantation over the past few decades. Due to aggressive recurrence post‐transplant, patients with hepatitis B have been excluded from the benefits of both solid organ and bone marrow transplants. Progress has been made, however, through an improved understanding of the biology of hepatitis B and the development of new antiviral strategies that can reliably suppress the virus. Patients with hepatitis B are now candidates for transplantation in an increasing number of circumstances. Careful pre‐transplant evaluation is mandatory, together with a tailored antiviral regimen depending on the replicative status of the virus and the organ being transplanted. Minimizing steroid dose following transplantation is an important part of the strategy to reduce the risk of viral reactivation. Lamivudine has been an important development and it has assumed an increasing role in the management of these patients. As additional antivirals are developed, increasingly effective drug combinations will prevent viral recurrence as well as the emergence of drug‐resistant mutants, which plagues the use of single agents. It is a rapidly evolving field and there is every reason for continued optimism.
Interferon and cytotoxic chemotherapy for the treatment of post‐transplant lymphoproliferative disorder
Authors: Davis Connie L.
Published: March 2003

Abstract:Interferon‐α and cytotoxic chemotherapy may be effective treatment modalities for the post‐transplant lymphoproliferative disorder. Interferon‐α may result in a complete response in up to 40% of patients, while chemotherapy may be effective in 75% of those failing local surgical excision, a reduction in immunosuppression, and an antiviral agent. Interferon may be used early after diagnosis in patients with relatively slowly growing tumors. Chemotherapy should be selected for patients with bulky, rapidly growing malignancies. The toxicity of chemotherapy may be minimized by discontinuing maintenance immunosuppression during chemotherapy, administering GCSF, and providing antimicrobial prophylaxis. Rejection is minimized by the reintroduction of maintenance immunosuppression when the patient is no longer neutropenic.