bluuebunny/crossref_metadata_2025 huggingface dataset:
Herbicide multiple‐resistance in a Lolium rigidum biotype is endowed by multiple mechanisms: isolation of a subset with resistant acetyl‐CoA carboxylase
Authors: Tardif François J. , Powles Stephen B.
Published: May 2006

The development of herbicide multiple‐resistance in weed species represents a major threat to current agricultural practices. The mechanistic basis for herbicide multiple‐resistance has been investigated in a population of the annual grass weed Lolium rigidum Gaud. (annual ryegrass) resistant to herbicides affecting 6 target sites. A subset of the resistant population (R2 subset) has been isolated by germination on a medium containing the acetyl‐CoA carboxylase (ACCase, EC 6.4.1.2) inhibiting herbicide, sethoxydim ((2‐[1‐(ethoxyimino)butyl]‐5‐[2‐(ethylthio)propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one)). This 12% R2 subset of the population is 600 times more resistant to sethoxydim and between 30 to 200 times more resistant to other ACCase inhibitors than the bulk of the R population. The subset has a form of ACCase which is 6 to 55 times less sensitive to inhibition by these herbicides than the enzyme present in the bulk of the resistant or in the susceptible population. There was no difference in the uptake and metabolic degradation of [4‐14C]sethoxydim between the R2 subset and the unselected R population. These results show the accumulation of different resistance mechanisms in that single population. Furthermore we propose that this accumulation of multiple resistance mechanisms is the basis for herbicide multiple‐resistance in this biotype.
Growth response of cotton to CO2 enrichment in differing light environments
Authors: Rufty Thomas W. , Thomas Richard B. , Cure Jennifer D. , Cure William W.
Published: May 2006

Experiments were conducted to examine the growth responses of cotton (Gossypium hirsutum L. cv. Coker 315) to CO2 enrichment under different light regimes. Plants were exposed to 350 or 700 μl l−1 CO2 and six light treatments differing in photosynthetic period length (8 or 16 h) and in photosynthetic photon flux density (PPFD) for 32 days of vegetative growth. Higher PPFD (1 100 μmol m−2 s−1) was provided by a combination of high intensity discharge and incandescent lamps (HID), and lower PPFD (550 μmol m−2 s−1) was provided by fluorescent and incandescent lamps (F) or HID and incandescent lamps with shade cloth (HIDs). Growth was generally much slower with the 8‐h photosynthetic periods, but the growth stimulation by CO2 enrichment was larger than with 16‐h photosynthetic periods. After 28 to 32 days of treatment, the growth enhancement with CO2 enrichment was 152 and 78% for 8‐ and 16‐h photosynthetic periods, respectively, under HID; 100 and 77% in F, and 77 and 56% in HIDs. The higher PPFD of HID positively influenced the CO2 effect only at the slower growth rate in the 8‐h light period. The stimulation of leaf area expansion by CO2 enrichment was also greater with the 8‐h photosynthetic period for all light sources. These results, and others on net assimilation rate, shoot to root dry weight ratios and specific leaf weights, suggest that the growth response to CO2 enrichment with the longer photosynthetic period was depressed by limiting factors, perhaps nutritional, in the growth environment. The results also show that extensive variability in CO2 response can occur under light intensities which are often used in growth chamber experiments.
Enhanced K+‐stimulated pyrophosphatase activity in NaCl‐adapted cells of Acer pseudoplatanus
Authors: Zingarelli Luisa , Anzani Paola , Lado Piera
Published: May 2006

Cell suspension cultures of Acer pseudoplatanus L. (Bligny cell line) adapted to growth in the presence of NaCl, are a useful tool for investigating mechanisms for cellular salt tolerance. We compared the activities of vanadate‐sensitive (plasma membrane) and nitrate‐sensitive (tonoplast) ATPases, and tonoplast K+‐stimulated PPase in microsomal fractions (8000–108 000 g) from unadapted and NaCl‐adapted (80 mM) cells of A. pseudoplatanus. Since NaCl reduces the growth rate of the culture, the two cell lines were harvested and compared at both the same cellular density and at the same growth phase (middle exponential phase or beginning of the stationary phase). The ATPase activity of the plasma membrane (expressed both on the basis of protoplast number and in relation to protein content) was not affected by the adaptation to salinity. The two enzyme activities of the tonoplast (mainly as expressed on a protein basis) were higher in adapted than in unadapted cells. However, a preferential increase in PPase activity took place, although the pH dependence, ionic requirements, and apparent Km of the PPase activity were the same in the two cell lines. The three enzyme activities showed different sensitivities to detergents such as Triton X‐100, Brij 58 and lysophosphatidylcholine (LPC). The stimulation of K+‐stimulated PPase activity by detergents was higher in adapted than in unadapted cells. This suggests that the salt‐induced enhancement of the PPase activity might partially depend on a modification of the lipid component of the tonoplast.
Action spectra of phenylalanine ammonia‐lyase and chalcone synthase expression in carrot cells in suspension
Authors: Takeda Junko , Obi Ichiro , Yoshida Kazuichi
Published: May 2006

The fluence‐response relationships and action spectra of light‐induced mRNA accumulation of phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) and chalcone synthase (CHS, EC 2.3.1.74) were investigated in light‐responsive, suspension‐cultured carrot cells after 2,4‐D‐depletion.

The action spectrum for PAL mRNA accumulation (determined 6 h after a 1‐h light treatment) had a single peak around 290 nm and was similar to that of anthocyanin formation. The action spectrum for CHS mRNA accumulation, determined simultaneously, had two peaks, a sharp peak at 290 nm and a broad peak at 330 to 360 nm. Below 320 nm, the peak wavelength of the spectrum and the shape of the fluence‐response curve for CHS were similar to those of anthocyanin formation. The Bunsen‐Roscoe law of reciprocity in the response to UV‐B light was verified for PAL transcript accumulation, but not for that of CHS, suggesting that the system leading to the expression after UV‐B light perception was different between PAL and CHS.
Abscisic acid: one of the factors affecting male sterility in Brassica napus
Authors: Shukla Amit , Sawhney V.K.
Published: May 2006

The possible involvement of abscisic acid (ABA) in the expression of male sterility in a genic male sterile (GMS) mutant of rapeseed (Brassica napus) was investigated. Three experimental approaches were used, namely, in vitro culture of young wild type (WT) floral buds, semi‐in vivo culture of WT inflorescences, and an analysis of endogenous ABA levels in various tissues of WT and GMS plants. Abscisic acid alone was inhibitory for the growth of WT floral buds in vitro, but low concentrations of ABA (10−8 to 10−6M) in combination with 10−7M benzyladenine, induced near‐mature flower bud development. With an increase in ABA concentration, the percentage of near‐mature floral buds decreased, and petal and stamen development was affected. Abscisic acid (10−6M and higher concentrations) also affected the flower bud length and pollen viability but not ovular viability, of WT inflorescences cultured in semi‐in vivo conditions. The various GMS tissues, including leaves, flowers and stamens had higher endogenous concentration of ABA in comparison to WT tissues. Also, the stamens had the maximum amount of ABA in comparison to other tissues in both genotypes. It is proposed that although ABA is important, it is only one of the plant growth substances involved in the expression of male sterility in the GMS line of B. napus.
Enhancement of ethylene biosynthesis and germination with thidiazuron and some selected auxins in Striga asiatica seeds
Authors: Babiker Abdel Gabbar T. , Cai Tishu , Ejeta Gebisa , Butler Larry G. , Woodson William R.
Published: May 2006

Witchweed [Striga asiatica (L.) Kuntze], an economically important parasitic weed on several poaceous crops, is difficult to control. In nature, germination and subsequent morphogenesis of Striga are cued to specific host‐derived chemical signals. Seeds (approximately 2.4 mg) treated with thidiazuron (TDZ) or the auxins 2,4‐dichlorophenoxy‐acetic acid (2,4‐D), 1‐naphthalene acetic acid (NAA), or 2‐(4‐chloro‐o‐tolyloxy) propionic acid (MCPP) produced little ethylene (66‐138 nl l−1). Combinations of TDZ with the auxins increased ethylene production by 4‐ to 18‐fold. Ethylene production was strongly inhibited (86–92%) by aminoethoxyvinylglycine (AVG), inhibitor of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase. Ethylene evolved from seeds treated with TDZ in combination with 2,4‐D increased after a lag period and was promoted by a pretreatment in 2,4‐D. TDZ or any of the auxins, at the rates tested, effected negligible to low levels of germination (0 to 16%), whereas mixtures of TDZ with the above auxins stimulated 38 to 84% germination. Test solutions containing TDZ and indole‐3‐acetic acid (IAA) were, however, less effective. TDZ/auxin‐induced germination was inhibited by AVG and the ethylene action inhibitor silver thiosulfate (STS). The inhibitory effect of the former was reversed by treatment with ACC. In vitro studies revealed negligible germination (< 1%) on control medium. Seeds germinating on media containing TDZ alone developed into seedlings with distinct shoots and rudimentary roots. Seeds germinating on media containing 2,4‐D, irrespective of TDZ concentration, were induced to form calli. The results are consistent with a model in which both germination and subsequent morphogenesis in Striga are associated with exogenous and endogenous phytohormones.
Herbicide safeners and glutathione metabolism
Authors: Farago Slobodan , Brunold Christian , Kreuz Klaus
Published: May 2006

Herbicide safeners are chemicals which protect crop plants from injury by certain herbicides, without affecting weed control efficacy of the herbicides. The protective mechanism of herbicide safeners has not yet been fully elucidated, but there is increasing evidence that safeners act by selectively enhancing herbicide detoxification in crop plants. To date, two main detoxification pathways have been related to the mode of action of herbicide safeners. The first includes oxidation and subsequent glucose conjugation, mediated by cytochrome P450‐dependent monooxygenases and UDP‐glucosyltransferases, respectively. This pathway appears to be important predominantly in safener protection to aryloxyphenoxypropionate and sulfonylurea herbicides. The second pathway represents the conjugation of thiocarbamate sulfoxides and chloroacetanilide herbicides with glutathione. This mechanism is accomplished by either elevating the levels of reduced glutathione or the activity of glutathione S‐transferase, or both. Since glutathione has been reported to be involved in several stress situations of plants its function associated with safener‐induced herbicide tolerance will be discussed in more detail in this review.
RNA editing in plants
Authors: Araya Alejandro , Bégu Dominique , Litvak Simon
Published: May 2006

Higher plant mitochondrial RNAs undergo predetermined modifications which involve differences of splicing and trimming of the primary transcripts. These post‐transcriptional modifications are specific C‐to‐U changes occurring mostly in the coding regions of mRNAs without changing the reading frame. Editing of mRNAs can lead to the formation or initiation of stop codons. Plant mitochondrial proteins issued from edited mRNAs are more similar to non‐plant homologous proteins suggesting that this process is involved in the production of functional polypeptides. RNA editing in non‐coding regions are also observed and may represent a new mechanism for modulating gene expression. Three possible biochemical mechanisms can account for RNA editing in plant mitochondria: nucleotide replacement, base exchange and deamination. Although some evidence shows that RNA editing proceeds by a deamination mechanism, several questions remain to be solved: What are the signals recognised by the biochemical machinery for such a specific process? What are the reasons that make an additional process acquired by land plant mitochondria for faithful gene expression?
Changes in in vivo fluorescence quenching in rye and barley as a function of reduced PSII light harvesting antenna size
Authors: Falk Stefan , Krol Marianna , Maxwell Denis P. , Rezansoff David A. , Gray Gordon R. , Huner Norman P. A.
Published: May 2006

The relationship between the size of the light harvesting antenna to photosystem II (LHCII) and quenching of non‐photochemical and dark level fluorescence was studied in wild‐type rye (Secale cereale L. cv. Musketeer) and barley (Hordeum vulgare L. cv. Gunilla) as well as in the barley chlorophyll b‐less chlorina F2 mutant (H. vulgare L. cv. Dornaria, chlorina‐F2). Exposure for 10 min to an irradiance of 500 μmol m−2 s−1 resulted in a strong (0.71–0.73) non‐photochemical (qs) quenching of the fluorescence yield in wild‐type (WT) material, while the barley chlorina F2‐mutant was quenched to 75% of this level. Relaxation of qs in darkness revealed a fast initial decay, related to relaxation of the high‐energy‐state dependent (qE) part of qs. Etiolated seedlings of rye and barley exposed to intermittent light (IML) for 36 cycles of 2 min light and 118 min darkness had suppressed Chl b and LHCII‐production in both WT rye and barley, while the barley chlorina F2‐mutant became totally devoid of all LHCII‐polypeptides. It was found that the levels of qs and qs were similar in control grown barley chlorina F2 and IML‐grown WT rye and barley, but qs was reduced by 30 to 35% and qs by 50 to 65%, respectively, as compared to control‐grown. WT plants. No significant qs could be detected in IML‐grown barley chlorina F2. It is clear, from these changes in in vivo fluorescence quenching in rye and barley that a significant level of qs is detectable even in the absence of LHCII. Only when the proximal antennae are totally absent, does qE completely disappear. We conclude that the presence of LHCII is not an absolute requirement for qE‐quenching and suggest that distal as well as proximal antenna may contribute to qE in vivo.
High light fluence impairs light‐harvesting Chl a/b complex apoprotein syntheses and/or membrane uptake in the CD3 mutant of wheat
Authors: Duysen Murray , Otto Paul , Williams Norm
Published: May 2006

The CD3 mutant of wheat is a chlorophyll(Chlo‐deficient mutant the phenotype of which depends upon the accumulation of the light‐harvesting Chl a/b protein complex in leaves in response to the intensity of illumination. In the present studies, the rates of synthesis and/or uptake, and degradation of the light‐harvesting Chl apoprotein in chloroplasts of wild‐type wheat (Triticum aestivum L. selection ND 496) and CD3 wheat leaf segments were examined in response to two different intensities of illumination. We were interested particularly in the 21. 23 kDa proteins of the light‐harvesting Chl a/b complex of photosystem I (LHCI) and the 25. 27. 29 kDa proteins of the light‐harvesting Chl a/b complex of photosystem II (LHCII). The accumulation of [35S]‐Met into the light‐harvesting Chl protein of CD3 wheat chloroplasts was impaired by a high but not by a low light fluence. The levels of radiolabel in the supernatant fractions of leaf tissue homogenates from the wild‐type and CD3 wheats were not significantly different over time, suggesting that the cellular uptake of [35S]‐Met was not limiting in the mutant. The high fluence did not enhance the degradation of light‐harvesting Chl protein from CD3 wheat thylakoids. Our data indicate an impairment in the light‐harvesting Chl protein synthesis/membrane uptake system in CD3 wheat leaves under high fluence. A recovery in levels of the inner LHCPII, but not of LHCPI, was observed in the Chl‐deficient wheat mutant after a prolonged (4 days) exposure to high fluence. Under low fluence, LHCP was added to both photosystem II (PSH) and photosystem I (PSI) but only that added to PSI remained in thylakoids after seedlings were switched to high fluence.
Xylanase treatment of plant cells induces glycosylation and fatty acylation of phytosterols
Authors: Moreau Robert A. , Powell Michael. J. , Whitaker Bruce D. , Bailey Bryan A. , Anderson James D.
Published: May 2006

Treatment of tobacco suspension cells (Nicotiana tabacum cv. KY 14) with a purified β‐1,4‐endoxylanase from Trichoderma viride [1 μg enzyme (ml cells)−1] caused a 13‐fold increase in the levels of acylated sterol glycosides and elicited the synthesis of phytoalexins. A commercial preparation of xylanase from Trichoderma viride caused an identical shift in sterols. In contrast, a commerical xylanase from Aureobasidium pullaulans had no effect on the levels of acylated sterol glycosides, but did elevate the levels of sterol esters. Treatment of the cells with Cu2+ or Ag+ also evoked a severalfold increase in the levels of acylated sterol glycosides. Analysis of the various sterol lipid classes revealed that the large xylanase‐induced increase in acylated sterol glycosides occurred at the expense of sterol esters, free sterols and sterol glycosides. Further analyses revealed that the most abundant phytosterol in each of the four classes of sterol lipids was β‐sitosterol. Linoleic acid was the most abundant fatty acid in the sterol esters, and palmitic and linoleic acids were the most abundant fatty acids in the acylated sterol glycosides. Glucose was the only sugar moiety in the sterol glycoside and acvlated sterol glycosides. Glucose was the only sugar moiety in the sterol glycoside and acylated sterol glycoside fractions. The results of the present study demonstrate that xylanase from Trichoderma viride induces a dramatic shift in the level of acylated sterol glycosides, indicating that endoxylanase was probably the active component in the cellulase enzyme preparations used in our previous study.
Purification and differential expression of enolase from maize
Authors: Lal Shailesh K. , Kelley Philip M. , Elthon Thomas F.
Published: May 2006

Enolase was purified from maze (Zea mays L. inbred B73)seeds to a 55 and 56 kDa protein doublet based upon sodium dodecyl sulfate – polyacrylamide gel electrophoresis. Purification included ammonium sulfate‐precipitation, gel filtration, Mono Q, and Phenyl Superose chromatography. Two‐dimensional gels further resolved the 56 kDa protein into three isoselectric forms. Polyclonal antibodies raised against the purified proteins, were found to bind specifically to both the 55 and 56 kDa proteins during purification. Theses antibodies did not recognized a 56 kDa protein when the strain was complemented with maize enolase (pZM245). Maize enolase antibodies recognized a extracts indicated that the 55 kDa form of enolase was more abundant in roots. Enolase protein levels remained unchanged in maize roots after 24 h of anaerobiosis, even though the specific activity of enolase increased to twice its initial levels. A plastid form of enolase in maize could not be found as either enolase activity or protein (with immunoblots).
Effects of paclobutrazol and chilling temperatures on lipids, antioxidants and ATPase activity of plasma membrane isolated from green bell pepper fruits
Authors: Lurie S. , Ronen R. , Lipsker Z. , Aloni B.
Published: May 2006

The effects of paclobutrazol treatment on plasma membrane lipid composition and ATPase activity of bell pepper fruit (Capsicum annuum) subjected to chilling temperatures were assessed. Application of the growth regulator paclobutrazol affected plant growth and fruit morphology. The plants were more compact and the fruits were less elongated than control fruits. There was about 60% more plasma membrane on a fresh weight basis from treated fruits. At harvest there was no difference in sterol to phospholipid ratio, or in phospholipid fatty acid composition of control compared with paclobutrazol treated fruit. However, plasma membrane ATPase acitivity of treated fruit was two times higher than that of control fruit. After storage at chilling temperature (2°C), the control fruit developed more chilling iniury, and had greater weight loss and a higher rate of K+ leakage than paclobulrazol treated fruit. Plasma membrane phospholipid content decreased and saturation of phospholipid fatty acids was higher than in control fruit. These two changes were largely absent in plasma membrane from treated fruit. At harvest antioxidant levels in the plasma membrane of paclobutrazol treated peppers were higher than in those of controls and changed little during storage, whereas levels in control fruit plasma membrane decreased 66%. ATPase activity increased and then decreased in control fruit held at low temperature, whereas in treated fruit activity was constant. The protective effect of paclobutrazol against chilling injury of pepper fruit may result from a combination of its effect on fruit morphology, and protection of the lipids against oxidative stress.
Characterization of asparaginyl endopeptidase activity in endosperm of developing and germinating castor oil seeds
Authors: Cornel Fiona A. , Plaxton William C.
Published: May 2006

A spectrophotometric assay was devised to characterize the asparaginyl (Asn) endopeptidase activity from the endosperm of castor oil seeds. (Ricinus communis L. var. Baker 296). The assay measures the release of p‐nitroaniline from the hydrolysis of benzoyl‐l‐Asn‐p‐nitroanilide. Assay sensitivity was improved through diazotization of the reaction product with N(]‐napthy])‐ethylenediamine dihydrochloride: diazotized p‐nitroaniline was determined spectrophotometrically at 548 nm (ɛ548= 1.64 × 10−1M−1 cm−2). By using this assay. Asn endopeptidase activity was detected in endosperm extracts of developing, mature and germinating castor seeds. Comparison of the Asn endopeptidase activities of developing and germinating castor endosperms revealed that they: 1) have identical pH‐activity profiles with optimal activity occuring at pH 5.4: 2) are heat‐labile proteins displaying comparable thermal stability profiles, and 3) are activated and inhibited by dithiothreitol and thiol modifying reagents, respectively. Thus, the Asn endopeptidases of developing and germinating castor seeds are very similar, if not identical, cysteine proteases. The most significant increase in the activity of endosperm Asn endopeptidase occurs during the full coryledon to maturation stage of seed development, this period coincides with the most active phase of reserve protein accumulation by ripening castor oil seeds. Asn endopeptidase activity of fully mature (dry) castor seeds was about 2‐fold lower than that of muturation stage ripening castor oil seed. Asn endopeptidase activity showed a slight reduction over the inicial 2‐day period following seed imbibition, and then rapidly decreased over the next several days of germination. The results are compatible with the proposal that Asn endopeptidase functions both to process storage preproteins following their import into protein bodies of developing seeds, as well as to participate in the mobilization of storage proteins during the early phase of seed germination.
Acquisition of desiccation tolerance by isolated maize embryos exposed to different conditions: the questionable role of endogenous abscisic acid
Authors: Bochicchio Adriana , Vernieri Paolo , Puliga Serenella , Balducci Francesca , Vazzana Cuncetta
Published: May 2006

The effect of exogenous ABA on acquisition of desiccation tolerance has been well documented for the embryos of several species. including maize (Zea mays L.). It has also been suggested that endogenous ABA plays a role in regulating the same phenomena. To test this hypothesis, endogenous ABA was quantified by radioimmunoassay. Our results show that: (1) during embryogenesis in maize, endogenous ABA increase‐concomitantly with the acquisition of desiccation tolerance: (2) ABA deficient embryos of the vp5 mutant are desiccation intolerant, but tolerance can he induced by exogenous ABA: and (3) desiccation tolerance is acquired if desiccation sensitive embryos undergo a slow drying treatment, during which ABA increases. However, when embryos were preincubated in fluridone to prevent ABA accumulation during slow drying, desiccation tolerance was induced in spite of the low level of endogenous ABA in the embryo. Our results cast doubts on an exclusive role of ABA in the acquisition of desiccation tolerance in maize embryo.
Characterization of a glutamine/proton cotransporter from Ricinus comnmnis roots using isolated plasma membrane vesicles
Authors: Weston Kim , Hall J.L. , Williams Lorraine E.
Published: May 2006

The mechanism of glutamine transport at the plasma membrane of sink tissue cells was investigated using isolated plasma membrane vesicles from roots of Ricinus communis L. var. sanguineous. Glutamine transport was found to be driven by both the pH gradient (ΔpH) and a membrane potential (ΔΨ) (alkaline and negative internal), which were created artificially across the plasma membrane. Glutamine wus accumulated 15–20‐fold in the presence of both a ΔpH and ΔΨ. There appeared to be a direct pH effect on ΔPS‐driven transport, as a higher rate of transport was observed at pH 5.5 than at pH 7.5. The ΔpH +ΔΨ ‐driven transport showed saturation kinetics with a Km of 287 μM. Altering the membrane potential changed the Vmax but had no effect on the Km of glutamine transport. These results are consistent with the presence of a proton‐coupled, carrier‐mediated system for glutamine uptake in Ricinus roots. A range of protein modifiers and transport inhibitors had limited effects on glutamine transport: highest inhibition uas observed with cytochalasin D. When glutamine transport was compared in plasma membrane vesicles isolated from the root lips of Ricinus and from the remainder of the root tissue a lower level of transport was observed in the root tips. A method for the solubilization and reconstitution of glutamine transport activity using the detergent CHAPS is also described.
The effect of handling on photosynthesis, transpiration, respiration, and nitrogen and carbohydrate content of populations of Lolium perenne
Authors: Kraus Edwin , Kollöffel Chris , Lambers Hans
Published: May 2006

Two populations of perennial ryegrass (Lolium perenne L.) S23, selected for contrasting rates of yield and mature leal dark respiration, were used in this study. Since previous work showed that yield decreased severely in population GL66 due to mechanical perturbation, possible effects on respiration rates were examined. Apart from a transient increase in population GL72, there was no effect on the respiration rate but mechanical perturbation did affect other processes. Handling caused transpiration ratesinthe light to increas for GL72, and in the dark to decrease for GL66. In the logger term, the nitrogen content decreased in handled plants grown at high density. These results emphasize that handling plants should be reduced to a minimum since it might have major effect on several processes. It is concluded that the original selection for the Lolium population was indeed on contrasting rates in yield and respiration. Furthermore it is argued that the existence of low‐ and high‐yielding genotypes can be attributed to the dissimilar responses of different genotypes to mechanical influence.
ABA content and sensitivity during the development of dormancy in lily bulblets regenerated in vitro
Authors: Djilianov Dimitar , Gerrits Merel M. , Ivanova Aneta , van Onckelen Harry A. , de Klerk Geerl‐Jan M.
Published: May 2006

We measured ABA content and sensitivity in bulblels of Lilium speciosum Thunb, regenerating from scale explants in vitro at temperatures (15, 20 or 25°C) that allowed the development of various levels of dormancy (very low, intermediate or high, respectively). The one‐step purification and the accuracy of the immunoassay were confirmed by HPLC and by liquid chromatography/mass spectrometry. ABA content was not correlated with dormancy development. Sensitivity to ABA was determined as the difference in sprouting performance of excised bulblets on medium with and without ABA. In bulblets regenerating at 20 or 25°C. ABA sensitivity was high during the period of dormancy establishment and decreased thereafter. Dormant hulblets were almost completely insensitive to ABA. The changes in sensitivity to ABA were confirmed by measuring the level of ABA in bulblets at the time of sprouting. This level was, as expected, highest in bulhlels with low ABA‐sensitivity. Briefly cold‐treated bulblets, in which dormancy may he re‐established by culture at 20°C, again became sensitive to ABA. ABA sensitivity decreased with increasing temperature bulblets that regenerated at I5°C and hardly developed any dormancy, were very sensitive to ABA. It was concluded that in addition to ABA sensitivity another, still unknown, factor played a key role in dormancy development.
Purification and characterization of ferredoxin‐NADP+ reductase from the green alga Chlorella fusca
Authors: Cartagena Elisa , Bes María Teresa , Gómez‐Moreno Carlos , Peleato María Luisa
Published: May 2006

Ferredoxin‐NADP+ reductase (FNR, EC I.18.1.2) from the green algae Chlorella fusca Shihira et Kraus 211–15, was purified to homogeneity. The molecular mass was 36.8 kDa as determined by SDS‐polyacrylamide gel electrophoresis. The enzyme exhibits the typical spectrum of a flavoprotein with an absorption maximum at 459 nm and an A273/459 ratio of 7.2. It contains one mol of FAD per mol of protein and the calculated extinction coefficient is 9.8 mM cm−1. Four different forms of the purified enzyme were detected by isoelectric focusing (pI between 5.4 and 5.9), even when protease inhibitors were used during the first steps of the purification. Kinetic parameters were determined for several FNR‐catalyzed reactions. NADP+ photoreduction gave comparable rates when either ferredoxin or flavodoxin was used.
Epidermal focussing and effects on light utilization in Oxalis acetosella
Authors: Myers David A. , Vogelmann Thomas C. , Bornman Janet F.
Published: May 2006

lmage analysis was used to quantify the lateral heterogeneity of the radiation field within the palisade of Oxialis acetosella L. leaves. Oxalis acetosella epidermal cells focus light up to four times incident irradiance, resulting in regions of high and low internal fluenec rate within the palisade. Chlorophyll fluorescence from leaves irradiated with directional light was found to originate primarily from palisade cell chloroplasts located within focal zones. When the internal radiation field was made more homogeneous by using diffuse light or by coating the leaf with a layer of mineral oil to eliminate epidermal focussing, the characteristics of the chlorophyll fluorescence signal were altered: non‐photochemical quenching (qN) increased, while relaxation of qN was slowed. This indicates that upper palisade chloroplasts may fine‐tune their light utilization to the intra leaf light microenvironment.
Actin in mating structures of Chlamydomonas eugametos gametes
Authors: Kalshoven H.W. , Brederoo J. , Emons A.M.C. , Musgrave A. , Schuring F. , Wells B. , van den Ende H.
Published: May 2006

The presence of actin in Chlamydomonas eugametos mating structures was studied using monoclonal anti‐actin antibodies. Immunofluorescent labelling of mating gametes clearly stained their mating structures and this was confirmed at the electron microscope level by immunogold labelling of sections. Anti‐actin labelling also strongly stained the flagella at the flagellar collar regions and weakly stained the rest of the flagella. Treatment of gametes with 6–8% ethanol induced mating structures which protruded as large ‘balloons’. Balloons stained brilliantly with anti‐actin antibodies and weakly with FITC‐phalloidin, a fluorescent reagent that stains F‐actin. Isolated mating structure balloons and flagella were analyzed using western blotting. A prominent 43 kDa band, co‐migrating with actin in erythrocyte ghosts, reacted with anti‐actin antibodies. The results indicate that actin is present in mating structures and flagella of both mating types of C, eugametos.
Respiration of mitochondria isolated from tulip bulbs stored at 5 and 17°C
Authors: Kanneworff Wouter A. , van der Plas Linus H. W.
Published: May 2006

For the production of good quality flowers, tulip (Tulipus gesneriana L.) bulbs need a period of low temperature. In cultivar Apeldoom a treatment of 12 weeks at 5 C can be used. In the bulb scales the respiratory metabolism has to adjust to this low temperature. Mitochondria isolated from the bulb scales are able to use succinate. NADH and pyruvate as respiratory substrates. Respiratory characteristics of these mitochondria changed after transfer of the bulbs to 5°C and the adaptation was complete within 2 weeks. Both state 3 respiration and respiratory control increased. Alternative pathway capacity was constitutively present at both 5°C and 17°C: it was low and substrate dependent at both temperatures. During the following weeks of the treatment no significant changes took place. However, when bulbs were transferred to 17°C after storage at 5°C. various responses could be demonstrated. In bulbs only cooled for a short period no readjustment to this higher temperature occurred. In bulbs stored for longer periods the change depended on the duration of the 5°C treatment. The nature of the re‐adaptation is discussed
Ripening‐related changes in the cell walls of Spanish pear (Pyrus communis)
Authors: Martin‐Cabrejas Maria A. , Waldron Keith W. , Selvendran Robert R. , Parker Mary L. , Moates Graham K.
Published: May 2006

Unripe Spanish pears (Pyras commanis L. ev. Blanquilla) were ripened at 18°C for 5 and 10 days. Softening of the cortical tissues was associated with swelling of parenchyma cell walls from 1 to more than 5 μm in 10 day ripe pears, by which time the pears were over ripe. However, there was little indication of cell separation and the middle lamella could be detected between most cell walls. Furthermore, cell separation was constrained by regions rich in plasmodesmata where wall swelling was prevented. Parenchyma cells in the 500 μm of tissue underlying the epidermis did not undergo ripening‐related changes to the same extent as those of the cortex. These cells, in combination with a sub‐epidermal layer of lignified sclereid clusters, constituted a relatively tough and protective skin. Ripening of the cortical tissues was associated with a depletion of alcohol‐insoluble pectic polysaccharides, as indicated by the decrease in arabinose and uronic acid. Analysis of alcohol‐insoluble cell wall preparations enriched in either parenchyma or sclereid cell walls indicated that this change was predominantly associated with the parenchyma walls. Such changes were less prominent in the peel. The decrease in pectic polysaccharides was accompanied by an increase in their solubility. During ripening, the sclereid clusters of the cortex continued in develop, as indicated by an increase in their size and yield of cell wall xylose and glucose. Cortical parenchyma cells radiating from the sclereids were firmly attached to the lignified cells. This was due to lignification extending from the sclereids into the primary walls of the parenchyma cells. We conclude that dissolution of pectic polysaccharides is one of several factors which determine softening during ripening of Spanish pears.
Microtubular organization in protoplasts and cells of somatic embryo‐regenerating and non‐regenerating cultures of Larix
Authors: Staxén Irina , Klimaszewska Krystyna , Bornman Chris H.
Published: May 2006

Protoplasts were isolated from both somatic embryo‐regenerating and non‐regenerating cultures of hybrid larch (Larix x eurolepis Henry) and fractionated on a discontinuous Percoll density gradient, whereby a highly embryogenic protoplast fraction could be enriched. This fraction was cultured for 14 days, and the differentiating protoplasts, cells, proetmbryos and embryo‐like cell clusters sampled at days 3, 5 and 14. Immunofluorescence studies showed that the microtubules became organized into parallel and helical arrays in protoplast‐derived cells of the embryogenic tissue as early as day 3 in culture, at which time the protoplast‐derived cells started to elongate. In most of the protoplasts from non‐regenerating tissue the microtubules retained a random orientation for a longer period. Preprophase bands were observed in both lines. Mitotic spindles consisted mainly of kinetochore‐associated microtubules and displayed broad polar regions at metaphase. The spindle poles contracted at anaphase, giving the spindles a pointed appearance. A difference between the two tissue lines was observed at telophase, when the phragmoplast in the non‐regenerating tissue had a normal appearance, while a proportion of the phragmoplasts from the embryo‐regenerating line were branched or Y‐shaped. Y‐shaped phragmoplasts resulted in two nucleated cells and one enucleated cell after fusion of the cell plate with the plasma membrane. The early rearrangement of cortical microtubules is an indication that organized growth is occurring but, as this phenomenon has been observed also in regenerating non‐emhryogenic cells, it appears to be a doubtful indicator of the distinction between emhryogenic and non‐embryogenic development.
The relationship between nodule adenylates and the regulation of nitrogenase activity by O2 in soybean
Authors: de Lima Maria L. , Oresnik Ivan J. , Fernando S. Milanthi , Hunt Stephen , Smith Ron , Turpin David H. , Layzell David B.
Published: May 2006

Nodulated soybeans (Glycine max L. Merr, cv. Maple Arrow) were exposed to various physiological and environmental treatments to determine the relationship between nodule adenylate pools and the degree of O2 limitation of nitrogenase. Adenylate energy charge (AEC = [ATP + 0.5 ADP]/[ATP + ADP + AMP]) and ATP/ADP ratios declined under conditions of decreased (10%) external pO2 but increased in nodules exposed to elevated (30%) external pO2. Nitrogenase activity was inhibited by both pO2 treatments, but recovered towards initial levels within 45 min. AEC also returned to initial levels during this period. To account for these and related data in the literature, it was hypothesized that 1) legume nodules regulate infected cell O2 concentration (Oi) to maintain adenylate pools at levels which limit respiratory metabolism: 2) treatments which decrease Oi alter the adenylate pools and further limit nodule metabolism; 3) treatments which increase Oi to levels in excess of a narrow range alter the adenylate pools and activate biochemical pathways which are not conducive to nitrogenase activity. In a preliminary test of these hypotheses, changes in AEC and ATP/ADP ratio were studied in nodules in which nitrogenase activity was inhibited by stem girdling, nitrate fertilization and exposure to an Ar:O2 atmosphere. All three treatments caused an increased O2 limitation of nodule respiration and nitrogenase activity. However, decreases in AEC were observed only in the stem girdling and nitrate fertilization treatment: Ar:O2 exposure had no effect on whole nodule AEC. While this result challenged the hypotheses suggesting a central role for adenylates in the regulation of O2‐limited metabolism, it was noted that the Ar:O2 treatment would differ from the other treatments in that it would have a specific effect on the ATP demands for NH3 assimilation in the plant fraction. Since AEC and ATP/ADP ratio would be affected by both the rate of ATP synthesis (potentially an O2‐limited process) and the demand for ATP, changes in these parameters in the whole nodule may not be a reliable indicator of adenylate‐mediated O2 limitation. Futher studies are needed to examine in vivo changes in adenylate pools in the plant and bacteroid fractions in nodules which vary in their degree of O2‐limited metabolism.
Influence of UV‐B radiation on photosynthetic light‐response curves, absorption spectra and motility of four phytoplankton species
Authors: Ekelund Nils G. A.
Published: May 2006

Several unicellular algae were exposed to artificial UV‐B (280–320 nm) radiation after adaptation to high (43 W m−2) and low (19 W m−2) visible light. UV‐B radiation had different effects on rates of photosynthesis, motility and absorption spectra for these species. Photosynthesis of Euglena gracilis and the diatom Phaeodactylum tricomution was more sensitive to UV‐B inhibition than that of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum. Not only UV‐B radiation but also high visible light had a photoinhibitory effect on photosynthesis in all four organisms. The effect on photosynthesis was observed both on the quantum yield and on the light saturation rate of photosynthesis. The dinoflagellates, in contrast to E. gracilis and P. tricorntum, absorbed strongly in the UV region (334 nm) and their absorption peaks increased after growth under high visible light or with or without UV‐B radiation for one week. The swimming speed of H. triquetra decreased more after low visible light and UV‐B radiation compared to high visible light and UV‐B radiation. The negative effects of UV‐B radiation on P. minimum and E. gracilis were most pronounced after high visible light.
Temperature and chemical shocks induce chilling tolerance in germinating Cucumis sativus (cv. Poinsett 76) seeds
Authors: Jennings Paul , Saltveit Mikal E.
Published: May 2006

Roots of 24‐h‐old germinated cucumber (Cucumis sativus cv. Poinsett 76) seeds were subjected to thermal and chemical stresses, equilibrated at 25°C for 2 h and chilled at 2.5°C for 96 h. The germinated seeds were then held at 25°C for 72 h after they were chilled and the elongation of the primary root was used as a measure of chilling tolerance. Control roots elongated from an initial length of 0.2 cm to a final length of 6.3 cm at the end of 72 h. while chilled roots elongated to a final length of only 0.4 to 0.6 cm. Exposure to 0.4 M ethanol for 4 h or to 40°C for 1 h induced substantial chilling tolerance and the roots had a final length of 4.1 and 3.1 cm. respectively. Exposure to 7.5°C for 3 h conferred less chilling tolerance (elongation to 1.4 cm). while exposure to other chemicals (i.e. aqueous solutions of Ca(NO3)2, mannitol. methanol and NaCl) produced less, though still significant increases in chilling tolerance. A more severe chilling treatment of 144 h at 2.5°C was required to consistently induce elevated rates of ion leakage. Only the heat and the ethanol shock treatments significantly reduced chilling‐induced ion leakage. Inclusion of the protein synthesis inhibitor cycloheximide negated the protective effects of these shock treatments. It appears that de novo protein synthesis is required for induction of chilling tolerance by a variety of chemical and thermal shock treatments.
Growth and CO2 uptake for cladodes and fruit of the Crassulacean acid metabolism species Opuntia ficus‐indica during fruit development
Authors: Inglese Paolo , Israel Alvaro A. , Nobel Park S.
Published: May 2006

Growth and daily net CO2 uptake were measured for fruit of Opuntia ficus‐indica and for its cladodes with 0. 5, 10 and 15 fruit and for cladodes after fruit removal. Growth of individual fruit decreased but fruit dry weight per cladode increased as the number of fruit per cladode increased. Removal of fruit decreased the total daily net CO2 uptake of the bearing cladode by about 10%. From 15 to 45 days after flowering, nocturnal CO2 uptake per unit area of the fruit averaged 19% of that of cladodes and then declined, as did the chlorophyll content and the activity of the CO2‐fixing enzymes. Fruit growth for O. ficus‐indica was supported by the bearing cladode as well as other cladodes, especially for cladodes with more than 5 fruit.
Effect of excess Cu on the photosynthetic apparatus of runner bean leaves treated at two different growth stages
Authors: Maksymiec Waldemar , Russa Ryszard , Urbanik‐Sypniewska Teresa , Baszyński Tadeusz
Published: May 2006

Runner bean plants (Phaseolus coccineus L., cv Piekny Jas) were treated with excess Cu (20 mg l−1 in the form of CuSO4.5H2O) at different stages of growth to investigate, 10 days after the element treatment, the effect of Cu on acyl lipid and polypeptide composition of the thylakoid membranes and their PSII photochemistry. The plants treated with Cu in the initial stage of leaf growth showed a strong reduction in the area and fresh weight of the primary leaves. The concentration of chlorophyll and acyl lipids slightly increased when calculated on leaf area or fresh weight basis. The decrease in individual acyl lipid classes expressed on chlorophyll basis was accompanied by lower accumulation of some extrinsic polypeptides of the oxygen evolving complex and decrease in PSll activity (80% of control). Chlorophyll a fluorescence measurements suggest an inhibitory effect of Cu on the acceptor side of PSII due to induced inhibition of the Calvin cycle and down‐regulation of electron transport. However, plants treated with Cu by the end of the intensive growth stage of the primary leaves showed chlorosis and almost unchanged leaf area. Moreover, significant changes in acyl lipid content as well as a distinct loss of core antenna PSII polypeptides and oxygen evolving complex subunits were observed. Changes in chlorophyll a fluorescence parameters of the thylakoid membranes suggest that low PSII activity (50% of control) may result from an alteration both in the acceptor and donor sides of PSII and its reaction centre. The growth stage of plants in which Cu was applied to plants and the duration of Cu action appears to be of great importance for the interpretation of experimental data.
Effect of acetate on growth and ammonium uptake in the microalga Scenedesmus obliquus
Authors: Combres C. , Laliberté G. , Reyssac J. Sevrin , de la Noüe J.
Published: May 2006

The effect of acetate on growth and rate of ammonium uptake in Scenedesmus obliquus (UTEX 78) was investigated under light‐limiting conditions. Addition of acetate to autotrophic cells with a growth constant of 0.71 day−1 resulted in an increase in the growth rate (mixotrophy, k = 1.3 day−1), and in the presence of acetate, growth occurred in the dark (heterophy, k = 0.44 day−1). The rate of ammonium uptake in autotrophy (17.8 amol cell−1 min−1) was similar to that in heterotrophy (17.4 amol cell−1 min−1) but was 3.7 times lower than that in mixotrophy (65.9 amol cell−1 min−1). In general, mixotrophic cells showed optimum ammonium uptake at the acetate concentration at which they were grown. In autotrophy, uptake of ammonium leveled off at about 12.5 μM while no saturation was observed in mixotrophic cells. An increase in the rate of uptake of ammonium was observed in autotrophic cells within 1 h after the addition of acetate. The activity of isocitrate lyase (EC 4.1.3.1), a key enzyme for the regulation of the glyoxylate cycle responsible for acetate catabolism, showed a 3.9‐fold increase in activity after 24 h in the dark in the presence of acetate. The level of isocitrate lyase activity in cells grown for 24 h in the dark in the presence of 0–20 mM acetate also increased as a function of acetate concentration.