bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the effect of natural and experimental anoxia on carbohydrate and energy metabolism in Iris pseudacorus rhizomes
Authors: Hanhijärvi Anne M. , Fagerstedt Kurt V.
Published: May 2006

Carbohydrate utilization in Iris pseudacorus rhizomes was investigated under natural conditions in the field for a period of one year. The area of study was under flood from mid‐December to end of May and wet for the rest of the period of study. Rhizome samples were collected in the wild twice monthly. in order to determine glucose content and amount of reducing and non‐reducing sugars in the rhizome core material. For comparison with experimental anoxia, rhizomes were washed and kept under strict anoxia in the dark at +20°C. Carbohydrates were measured in groups as above. The amount of ethanol and the levels, of ATP. ADP and AMP were also measured and adenylate energy charge computed.

Glucose content of the rhizomes was 10 mg g−1 fresh weight in the autumn and decreased during winter to reach ca 5 mg g−1 fresh weight in the spring. Total reducing sugars increased in w inter while the amount of non‐reducing sugars increased during early autumn and decreased during winter and spring. Not all non‐reducing sugar stores had been used up in the spring when growth was resumed. Under experimental anoxia adenylate energy charge remained relatively high for 30 days (near 0.6 or over) and then dropped quickly to bekm 0.3. indicating death of the tissues. After 30 days under anoxia the amount of ethanol still increased and that of total reducing sugars decreased. The level of non‐reducing sugars decreased from 0 to 15 days of anoxia before an increase took place durine the next 20 days.
Analysis of DNA polymerase activity in Petunia protoplasts treated with clastogenic agents
Authors: Benediktsson Indrioi , Spampinato Claudia P. , Andreo Carlos S. , Schieder Otto
Published: May 2006

Clastogenic agents, i.e. agents that can induce chromosome or DNA breakage, have been shown to enhance the rale of direct gene transfer to protoplasts. The effect was analysed at the enzymatic level using protoplast homogenates as well as intact protoplasts. For that purpose existing procedures were modified to enable measurement of DNA polymerase in vivo. In the system used, external DNA was able to enter the cells without the addition of membrane‐permeabilizing compounds. When comparing total DNA polymerase activity of protoplasts irradiated with X‐rays or UV‐light with that of untreated cells we did not observe significant differences. Incubation of protoplasts with high doses of bleomycin affected total DNA polymerase activity negatively. but dideoxythymidine triphosphate‐sensitive activity was not influenced. We conclude that the DNA strand‐breaks induced by low doses of X‐rays. UV‐light or bleomycin do not increase the total or the repair‐DNA polymerase activity and. therefore. that the increase in the transformation rates after DNA strand‐breaking is not preceded by enhanced DNA polymerase activity.
Characteristics of the respiratory peak in batch cultures of Petunia hybrida
Authors: van Emmerik Willie A. M. , van der Plas Linus H. W. , Wagner Anneke M.
Published: May 2006

In batch cultures of Petunia hybrida cv. Rosy Morn Fertile. one respiratory peak is usually observed shortly after subculturing. However, two types of peak respiration could be distinguished, one connected with the dilution process and one with sugar addition at low biomass concentrations. The dilution peak was observed when cells were diluted in medium without sugar, in the presence or absence of mannitol. The sugar peak occurred only after previous dilution of the cells and not when sugar is added at high biomass concentrations Apparently the existence of a dilute suspension is a prerequisite for the induction of the peak. The presence of sugar is not a prerequisite for the increased respiratory activity but it is necessary lor growth: however, growth is possible without the increase in respiration, as was shown by the addition of sugar to a culture with a high biomass concentration. The peak caused by dilution either in the presence or absence of sugar showed no significant differences in height. The height of the peak caused by sugar addition to a previously diluted cell suspension was correlated with the sugar concentration. The respiratory peak disappeared long before the end of the growth period; this decline of the respiratory rates was not connected to sugar or oxygen limitation. In a continuous culture of Petunia hybrida growing at low biomass concentration, the respiration was always at the high level as observed during the peak of batch culture. Growing at lower biomass concentrations might be more expensive for plant cell suspensions.
Identification and quantification of endogenous gibberellins in apical buds and the cambial region of Eucalyptus
Authors: Hasan O. , Ridoutt B.G. , Ross J.J. , Davies N.W. , Reid J.B.
Published: May 2006

Endogenous gibberellins (GAs) were extracted and purified from apical buds of Eucalyptus nitens (Deane and Maid.) Maid. and the cambial region of E. globulus (Labill.). then analysed by capillary gas chromatography‐mass spectrometry. GA1 GA19 GA20 and GA29 were identified by full scan mass spectra. Kovats retention indices and high resolution selected ion monitoring. Using deuterated internal standards. GA1. GA19. GA20 and putative GA29 and GA53 were quantified in the apical buds, while GA4. GA8. GA9 and GA44 were shown to be either absent or present at very low levels. From the cambial region. GA1 and GA20 were quantified at levels of 0.30 ng (g fresh weight)‐1 and 8.8 ng (g fresh weight)‐1 respectively. These data suggest that the early 13‐hydroxylation pathway is the dominant pathway for GA biosynthesis in Eucalyptus.
Monovinyl and divinyl protochlorophyll in different stages of esterification isolated from mutant C‐2A’of the unicellular green alga Scenedesmus obliquus
Authors: Knaust Rosemarie , Senger Horst
Published: May 2006

The mutant C‐2A’of the unicellular green alga Scenedesmus obliquus accumulates the chlorophyll‐precursors protocbloropbyllide and the already eslerified protochlorophyll when grown heterotrophically in the dark. Two derivatives of protochlorophyll. monovinyl protochlorophyll (MV‐PChl) and divinyl protochlorophyll (DV‐PChl), were isolated from dark‐grown cells of mutani C‐2A’and characterized by absorption and fluorescence spectroscopy. Their molecular masses were determined by plasma desorption mass spectrometry. Both MV‐ and DV‐PChl were mainly esterified with geranylgeraniol. However, some esterification with the more saturated alcohols dihydrogeranylgeraniol. tetrahydrogeranylgeraniol and phytol could also be detected.
Cysteine proteinase forms in sprouting potato tuber
Authors: Michaud Dominique , Nguyen‐Quoc Binh , Bernier‐Vadnais Nathalie , Faye Loïc , Yelle Serge
Published: May 2006

Transformation of plants with exogenous proteinase inhibitor genes represents an attractive strategy for the biological control of insect pests. However, such a strategy necessitates a thorough characterization of endogenous proteinases. which represent potential target enzymes for the exogenous inhibitors produced. In the present study. changes in general endoproteolytic activity were monitored during sprouting of potato (Solanum tuberosum L. cv. Kennebec) tuber. Quantitative data obtained using standard procedures showed that an increase in cysteine proteinase (EC 3.4.22) activity occurs during sprouting. This increased activity results from the gradual appearance of new cysteine proteinase forms, as demonstrated by the use of class‐specific proteinase activity gels. While only one cysteine proteinase form was present during early sprouting, at least six new active forms of the same class were shown to appear gradually after the mature tuber was sown, suggesting the involvement of a complex cysteine proteolytic system in the last stages of tuber protein breakdown. Interestingly, oryzacystatins I and II. two cysteine proleinase inhibitors potentially useful for insect control, had no effect on any tuber proteinase delected. Similar results were obtained with leaf, stem and stolon proteinases. This apparent absence of direct interference supports the potential of oryzacystatin genes for production of insect‐tolerant transgenie potato plants.
Variation in total and specific RNA during inwintering of two contrasting populations of Picea abies
Authors: Clapham D. H. , von Arnold S. , Dormling I. , Ekberg I. , Eriksson G. , Larsson C.‐T. , Norell L. , Qamaruddin M.
Published: May 2006

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies (L.) Karst. were cultivated in a phytotron under continuous lighl and 20°C for 10 weeks. Subsequently they were exposed to a regime of long nights (16 h). initially at 20°C but with stepwise lowering to 10°C over 12 weeks. Samples of needles were taken for total RNA extraction and studies of gene expression at intervals from just before the change of regime and onwards. At the same time samples were taken for abseisic acid (ABA) determination. Extension growth, degree of budrest and frosl tolerance were also recorded. The main results were as follows. (1) Extractable total RNA per g fresh weight of needles increased by 150–250% through the period of long nights. (2) The capacity of the total RNA to direct protein synthesis in a cell‐free system declined in response to long nights to a minimum value of 5% (northern population) and 23% (southern population) of the reference values under continuous light. (3) In vitro translatability was highly correlated with the size of the polyadenylated fraction of the total RNA, which declined also when normalized to needle fresh weight rather than total RNA. (4) A peak of abscisic acid content in the southern population at 3 days into the long night treatment coincided with a trough in the in vitro translatability of the total RNA. (5) The steady state levels of rbcS‐mRNA as a fraction of total RNA declined rapidly to a final value of about 15% of the reference value in both populations, the decline being more rapid for the northern population. (6) In contrast. ubiquitin‐mRNA showed an initial increase, particularly in the northern population, and at the end of the long night treatment was only 40% under the reference value. (7) Rapid changes in the molecular characters occurred during the first 3–4 weeks when the morphological and physiological changes were most rapid.
Induction of a wheat Em promoter by ABA and optically pure ABA analogs in white spruce (Picea glauca) protoplasts
Authors: Dong Jin‐Zhuo , Pilate Gilles , Brams Suzanne R. A , Dunstan David I.
Published: May 2006

In white spruce (Picea glauca) protoplasts, abscisic acid (ABA) and optically pure ABA analogs induced expression of a reporter gene under regulation of a wheat ABA‐responsive promoter. A fusion of a 650 bp promoter fragment from the wheat Em gene promoter and the Escherichia coli uidA sequence encoding β‐glucuronidase (GUS) was linked in the plasmid pBM 113Kp. Expression of the Em‐uidA fusion varied among 6 white spruce genotypes. Protoplasts from 4‐day‐old embryogenic suspension cultures gave the highest GUS activity relative 10 other stages in the 7‐day growth cycle of suspension cultures. Racemic ABA [R.S‐(±)‐ABA] induced a significant increase of protoplast GUS activity over background at a concentration of 1 × 10−5M, but maximum GUS activity was found at 1 × 10−3M, ABA stereochemistry had a significant effect on gene expression. The natural isomer of ABA [S‐(+)‐ABA] was an effective inducer at a concentration as low as 1 × 10−7M, but a concentration of greater than 1 × 10−4M was required for induction by [R‐(—)‐ABA]. Moreover, analogs with the same configuration at C‐l1 as that of natural ABA were more effective for induction of expression from the Em‐uidA. insert at 1 × 10−4M than were their enamiomers. Plasnud pBI511. carrying the chloramphenicol acety] transferase (CAT) gene driven by the constitutively expressed, tandemly duplicated cauliflower mosaic virus 35S promoter, was co‐electroporated with pBM113Kp for monitoring Ihe influence of addition of exogenous ABA or ABA analogs on heterologous gene expression in protoplasts. CAT activity was not significantly affected by the presence or absence of ABA or the analogs used.
Cytokinins in phloem and xylem saps of Sinapis alba during floral induction
Authors: Lejeune P. , Bernier G. , Requier M.‐C. , Kinet J.‐M.
Published: May 2006

In Sinapis alba, a long‐day plant (LDP) which can be induced by a single long day (LD), it has been suggested that cytokinins may be part of a multicomponent floral stimulus. In order to determine cytokinin fluxes during floral transition, we developed a technique to collect phloem sap reaching the apical part of the shoot, close to the target bud. Exudates collected from roots, leaves, and the apical part of the shoot were analysed by radioimmunoassay for cytokinins. Such analyses confirm previous observations, obtained using the Amaranthus bioassay. indicating thai cytokinin export from the roots and mature leaves is enhanced 2–5 fold during floral transition. The flux of cytokinins directed to the upper part of the shoot through the phloem is also rapidly increased (ca 1.5–2 fold) by the inductive treatment, between 9 and 25 h after start of the LD. We suggested that the shoot apical merislem of 2‐month‐old Sinapis plants probably has a low cytokinin level. Induced leaves rapidly produce a signal which is transported to the roots where it alters cytokinin production and/or export. In addition, or as a consequence, leaf‐cytokinins are exported via the phloem to the apical meristem where they induce a mitotic peak and some other events normally associated with the floral transition.
Measurement of CO2 and HCO3− fluxes in cyanobacteria and microalgae during steady‐state photosynthesis
Authors: Badger Murray R. , Palmqvist Kristin , Yu Jian‐Wei
Published: May 2006

A mass spectrometric procedure is described which allows the simultaneous estimation of both CO2 and HCO−3 fluxes associated with cyanobacteria and green algae during steady‐stale photosynthesis. This technique utilizes the chemical disequilibrium which exists between CO2 and HCO−3 during photosynthesis in cell suspensions which lack carbonic anhydrase activity. The kinetic equations which are derived for flux determinations are based on models of photosynthesis in both cyanobacteria and green algae which seem most reasonable given our present level of understanding, together with direct measurement of [CO2] estimation of [HCO−3] and application of the kinetic rate constants for the interconversion of CO2 and HCO−3 From measurements made in the light, net uptake of both CO2 and HCO−3 can be readily determined. In addition, analysis of the dark phase immediately following light‐off provides the possibility of also determining the CO2 evolution whích ís occurring during photosynthesis, and thus also the gross CO2 uptake rates in the light. Results are presented for the response of dissolved inorganic carbon (C1) flux rates to external C, in low‐C1 grown cells of both Synechococcus PCC7942 and Chlamydomonas reinhardtii and these are consistent with previous studies showing that such cells possess capacities to utilize both CO2 and HCO−3 for photosynthesis. The advantages and potential errors which are inherent in this technique are discussed together with its potential for future studies on C1 transport under various experimental conditions.
Carbonic anhydrase activity and inorganic carbon fluxes in low‐ and high‐C1 cells of Chlamydomonas reinhardtü and Scenedesmus obliquus
Authors: Palmqvist Kristin , Yu Jian‐Wei , Badger Murray R.
Published: May 2006

Carbonic anhydrase (CA) activity associated with high‐ and low‐dissolved inorganic carbon (C1) grown cells was examined in whole cells by measuring 18O exchange from doubly labeled CO2 (13C18O18O). Both algal species showed the presence of extracellular (periplasmic) as well as intracellular CA activity, which were both greatly increased in low‐C1 cells. The periplasmic CA activity was at least 40‐fold higher in lowcompared to high‐C1 cells in both C. reinhardtii and S. obliquus. while low‐C1 cells of S. obliquus showed the highest activity of internal CA. The CA inhibitor ethoxyzolamide showed a strong inhibition of the C1 uptake process in both C. reinhardtii and S. obliquus as in cyanobacteria. which may indicate that the nature of the primary uptake process is similar in both green algae and cyanobacteria. By using a mass spectrometnc disequilibrium technique it was possible to separate the C1 fluxes of net HCO−3‐uptake and net CO2‐uptake during steady‐state photosynthesis in high‐ and Sow‐C1 grown cells of Chlamydomonas reinhardtii (WT. 2137+) and Scenedesmus obliquus (WT. D3). It was found that both high‐ and low‐C1 cells of the two algae can utilize both CO2 and HCO−3 for photosynthesis, although low‐C1 cells have a higher affinity for the uptake of both C1 species. Induction at low‐C1 causes an increase in the affinity of both species for HCO−3 and CO2; changes in net CO2‐uptake were, however, significantly greater.
Presence and role of jasmonate in apple embryos
Authors: Ranjan Rajiv , Miersch Otto , Sembdner Giinther , Lewak Stanistaw
Published: May 2006

(‐)Jasmonic acid (JA) was identified in extracts front embryos of apple (Mulus domestica) by combined gas chromatography‐mass spectromelry. Quantification of JA in embryos isolated from seeds at different perexts of stratification by gas chromalography combined with mass spectrometry/selective ion monitoring indicated a sharp peak at day 30. At the same time the maximal ratio of conjugated to free JA was found by enzyme‐linked imrnunosorbent assay (ELISA). Germination of embryo.s was stimulated by added JA and inhibited by salieylhydroxamic acid (SHAM, an inhibitor of lipoKygenase). Both stimulation and inhibition disappeared in embryos stratified for more than 30 days. Methyl jasmonate was more effective in stimulation of embryo germination than free JA. while JA‐isoleucine inhibited germination. The possible mechanism responsible for changes in JA level as wel! as the role of JA and its conjugates in removal of dormancy in apple seeds are discussed.
Role of ethylene in senescence of watercress leaves
Authors: Philosoph‐Hadas Sonia , Meir Shimon , Aharoni Nehemia
Published: May 2006

Detached watercress leaves showed a rapid senescence rate as compared with other herbs. It was therefore of interest to investigate the role of ethylene in the rapid senescence of watercress leaves, and So estimate the efficacy of various inhibitors of elhylene synthesis (aminoethoxyvinylglycine, AVG) and action (CO2, Ag+) in retarding senescence processes. The progress of senescence in watercress bunches (leaves attached to cut stems) and in detached leaves was estimated by measuring the rate of chlorophyll (Chl) loss, proteolysis and lipid oxidation. Evidence is presented showing that application of 11% CO2 to watercress bunches in a flow‐through system had a long‐lasting effect on senescence, exhibited by highly efficient retardation of all the senescence processes tested. On the other hand, application of AVG (O.1 mM) or Ag‐(30 μM) to detached leaves affected Chl loss much more than prciteolysis. These results suggest that the senescence‐retarding activity of CO2 cannot be attributed solely to its action as an anli‐ethylene agent and that not all senescence‐associated processes are regulated by ethylene.
A comparison of low temperature growth vs low temperature shifts to induce resistance to photoinhibition in spinach (Spinacia oleracea)
Authors: Gray G. R. , Boese S. R. , Huner N. P. A.
Published: May 2006

Plants of Spinacia oleracea L. cv. Savoy grown under cold‐hardening (5°C) and nonhardening (16°C) conditions were exposed to a photoinhibitory irradiance of 1300 μmol rrr: m‐2 S‐1 5°C for 12 h. Plants grown at 5°C exhibited a greater resistance to photoinhibition at low temperature in comparison to plants grown at 16°C as measured by the photochemical efficiency of photosyslem II. In contrast, tuily expanded leaves of plants grown at 16°C and then shifted to 5°C for 10 days did not exhibit increased resistance to photoinhibition. This was observed irrespective of the phoioperiod experienced during the shift to a lower temperature. Furthermore, spinach grown at 16°C and subsequently exposed to a stepped, daily decrease in temperature from 16 to 1°C over 10 days w ith a concomitant reduction in photoperiod. also did not exhibit any change in susceptibility to photoinhibition. Thus, a decrease in photoperiod accompanied by either an abrupt or stepped low temperature shift cannot induce increased resistance to photoinhibition. This confirms the hypothesis that growth and development at cold‐hardening temperature are absolute requirements for the acquisition of resistance to photoinhibition at low temperature.
Possible involvement of volatile compounds in the after‐ripening of cocklebur seeds
Authors: Esashi Yohji , Zhang Ming , Segawa Kazuya , Furihata Taiei , Nakaya Minoru , Maeda Yutaka
Published: May 2006

The mechanism of emergence from primary dormancy, the process of after‐ripening, in cocklebur (Xanthium pennsylvanicum) seeds was examined in relation to the involvement of volatile compounds and to the relative humidity (RH) in which the seeds were stored. The after‐ripening of these seeds proceeds only at water contents between 7 and 14% which are conditioned under RHs of 33% to 53% and are identified with water‐binding region II. After‐ripening of cocklebur seeds occurred even in water‐binding region I. imposed by 12% RH. when exposed to HCN gas during the storage period. Exposure of dormant seeds to acetaldehyde (ethanal) retarded after‐ripening. even in water‐binding region II. thus decreasing germinability. This decrease of germinability by ethanal was found also in the after‐ripened seeds, suggesting that ethanal accelerates seed deterioration rather than retarding the after‐ripening. The contents of ethanal. ethanal and HCN were high only in the dormant seeds held at 12% RH. Regardless of RH. a possible conversion of ethanal to ethanol. perhaps via alcohol dehydrogenase. was far larger in dormant than in non‐dormant seeds. In contrast, the reverse conversion of ethanol to ethanal was more profound in non‐dormant seeds. Pre‐exposure of both types of seeds to HCN reduced the contents of both ethanal and ethanol at 12% RH. The contents of various adenylales including ATP in seed tissues were higher in dormant seeds stored at 12% RH than in non‐dormant seeds after‐ripened at 44% RH. It is suggested that emergence of cocklebur seeds from primary dormancy by HCN treatment at 12% RH may result from the reduction in the contents of ethanal via an unknown mechanism incurring the consumption of ATP. This implies involvement of volatile compound metabolism at the water‐binding region II in the after‐ripening process of cocklebur seeds.
Effects of fungal infection and wounding on the expression of chitinases and β‐1,3 glucanases in near‐isogenic lines of barley
Authors: Ignatius Sheba M. J. , Chopra Renu K. , Muthukrishnan S.
Published: May 2006

Chitinases (EC 3.2.1.14) and β‐1.3 glucanases (EC 3.2.1.39) have been known to play a vital role in the defense of plants against fungal pathogens. The pattern of induction of these two enzymes subsequent to infection by powdery mildew was studied in 10 pairs of near‐isogenic lines of barley (Hordeum vulgare L.) which possess powdery mildew resistance genes. These isogenic lines have been grotiped according to their reaction to the fungus. The induction patterns varied between the resistant and the susceptible cultivars within each group and between different groups. More tsozymcs were induced in susceptible varieties of highly resistant groups and the overall levels and the number of isozymes of chitinases and β‐1.3 glucanases were lower in groups with low resistance. The effect of powdery mildew infection and mechanical wounding on the cellular localization of chitinases and β‐1.3 glucanases in barley leaves has also been studied. The 31 kDa leaf chitinase, L‐CH2, and trace amounts of a 25 kDa chitinase. L‐CH3. were present in healthy leaves. Wounding increased the levels of L‐CH3 within I ft h. Powdery mildew infection increased the levels of L‐CH3 both in intercellular fluid and in intracellular extract of leaves. A /3‐I.3 glucanase. GH, also increased after infection and wounding. In infected barley leaves, GL‐1 was present both in intercellular space and intracellular extract. It is concluded that powdery mildew resistance genes exhibit qualitative and quantitative differences in the expression of chitinases and β‐1.3 glucanases. Further, chitinases and β‐1.3 glucanases appear to be a response to active infection rather than the factors responsible for disease resistance.
Photoinactivation of catalase in needles of Norway spruce
Authors: Schittenhelm Jürgen , Toder Susanne , Fath Simone , Westphal Stefan , Wagner Edgar
Published: May 2006

Catalase IEC 1.11.1.6) activity in Norway spruce (Picea abies [L.] Karst.) needles was examined under different environmental conditions. When shade‐adapted spruce trees were exposed to full sunlight or to high light intensities in growth chambers, the catalase activity decreased. Under continuous light the activity was reduced in comparison to the control grown in light/dark cycles. The reduction of the activity was not temperature dependent. Under field conditions the activity was higher in hranches oriented north than in those oriented south. A diurnal rhythm with a maximum in the night was delected. The reduction in catalase activity also occurred in young white needles of Picea ahies vur. argenteospica. which are free of chlorophyll. It is concluded that in Norway spruce needles there is a ligh:‐dependent photoinactivation of catalase. which is not temperature‐dependent.
Light regulation of nitrate reductase in green leaves of higher plants
Authors: Lillo Cathrine
Published: May 2006

Light stimulates de nova synthesis, as well as activation of higher plant nitrate reductase at the protein level. In green leaves, the light effects are mediated through photosynthetically active light by products of the Calvin cycle. A daily, light‐induced increase in nitrate reduclase (NR) mRNA. protein, and activity is observed in various higher plants. Glucose or sucrose can replace light in eliciting the increase in nitrate reductase mRNA accumulation, and sonic metabolite from nitrate assimilation exerts a negative feedback on transcription of the nitrate reductase genes. The positive feedforward induced by sugars, and the negative feedback from nitrogen compound(s) apparently result in the circadian rhythms of NR mRNA observed in various plants. Nitrate reductase shows hysteretic behaviour, converting between a low and a high activity form in response to NAD(P)H. The low activity form is inhibited by calcium/ magnesium, as opposed to the high activity form that is not inhibited. Examination of nitrate reductase activity in crude extracts made from plants before and after a light‐dark transition suggests the existence of two different forms of nitrate reductase: a‘light form’with a pH optimum of 7.8 in potassium phosphate buffer that is not inhibited by calcium or magnesium, and a “dark form’with li pH optimum of 7.5 that is strongly inhibited by calcium or magnesium. It is postulated that a transient lack of NADH as a result of decreased illumination can convert nitrate reductase into the less active form in situ.
Graviresponding sites in shoots of normal and‘lazy’rice seedlings
Authors: Abe Kiyomi , TakAhashi Hideyuki , Suge Hiroshi
Published: May 2006

We have examined the graviresponding sites in the shoots of seedlings of rice (Oryzasativa L.) and their relation to the agravitropic growth of a‘lazy’line. The graviresponding sites of the seedling shoots of a japonica type of rice. cv. Kamenoo. shifted from the mesocotyl/coleoplile region to the leaf‐shealh base when the shoots grew in the dark. A lazy line ot rice. lazy‐Kamenoo. showed gravicurvature in the mesocotyl/ coleoptile region at the early stage of growth, hut eventually lost its graviresponse as the seedlings grew. The loss of graviresponsiveness of lazy‐Kamenoo was attributed to a reduced response of the coleoptile and a diminished response of the leal‐sheath base to gravity. Later. the leaf‐sheath base of lazy‐Kamenoo became gravitropically incompetent. causing agravitropic growth of the shoots. Thus, shoots of lazy‐Kamenoo lose graviresponsiveness in an organ‐dependent fashion.
The nitrogen‐sink is involved in the regulation of nitrogenase activity in white clover after defoliation
Authors: Hartwig Ueli A. , Heim Ignaz , Lüscher Andreas , Nösberger Josef
Published: May 2006

In an attempt to manipulate plant nitrogen‐sink strength, various defoliation treatments were applied to white clover (Trifolium repent L. cv. Ladino) grown in a controlled environment. Nitrogenase activity and its oxygen limitation were measured as H; evolution in Ar:O2 using a flow‐through gas exchange system. An experiment to monitor the response of nitrogenase activity to various degrees of defoliation showed that the removal of up to 50% of the leaf are a had no effect on nitrogenase activity within 6 h. If more than 50% of the leaf area was removed. the nitrogenase activity decreased in relation to the loss of leaf area. This was accompanied by a corresponding increase in the O2 limitation of nitrogenase activity. In the experiment to determine the N‐sink strength after defoliation, the dry weight increase w as initially unaffected by the removal of 4% of the leaf area, whereas removal of 85% or 100% of the leaf area resulted in a dry weight loss for several days. The time course of nitrogen assimilation was similar to that of dry weight increase. This study provides substantial evidence that after a severe defoliation the nitrogen demand is temporarily restricted due to the lack of dry weight increase. Since the plant's ability to store organic nitrogen is very limited. it seems plausible that nitrogen assimilation in the still fully intact symbiotic system had to be down‐regulated. Consequently, to avoid ammonia toxicity. nitrogenase activity had to be reduced. Such an interpretation is supported by the fact that complete defoliation of nitrogen‐Starved plants caused a much milder decrease in nitrogenase activity compared to the decrease in plants well supplied with nitrogen. The present data are consistent with the hypothesis that after defoliation nitrogenase activity is adjusted in response to the reduced demand for symbiotically fixed nitrogen (nitrogen‐sink strength), It is proposed that such an adjustment could he made by a nitrogen feedback mechanism that regulates a variable oxygen‐diffusion barrier in the nodules.
Responses of Nicotiana tabacum to CO2 enrichment at low‐photon flux density
Authors: Sicher Richard C. , Kremer Diane F.
Published: May 2006

Effects of CO2 enrichment on photosynthesis and on dry matter allocation were examined in two tobacco (Nicotiana tabaum L.) genotypes. Samsun and W38. Plants were grown from seed in controlled environment chambers at a photosynthetic photon flux density of 450 μmol m−2 s−1. Averaged over the 9 day study, net photosynthesis rates were 14.2±0.5 and 13.0±0.4 μmol m−2 s−1 in elevated (70 Pa) and in ambient (35 Pal CO2 air. respectively, when measured at the irradiance and CO2 partial pressure employed for plant growth. However. photosynthesis rates of plants grown in elevated CO2 were 50% less than those of the ambient controls on the last day of treatment, when measured al 70 Pa CO2 air and an irradiance of 900 μmol m−2 s−1 Total plant dry weight and specific leaf weight were greater (P < 0.051 in enriched‐CO2‐grown than in ambient‐CO2‐grown plants. Leaf starch, measured during the first hour of the photoperiod. increased over 7 days of treatment in elevaled‐CO2‐grown but not in ambient‐CO2‐grown plants. Ribulose 1.5‐bisphosphate carboxylase/oxygenase (Rubisco) activities of tobacco plants grown at 35 and 70 Pa CO2 air were 58.5±4.5 and 48.5±3.7 umol m−2 s−1. respectively, between days 0 and 9 of the study. Rubisco activation state. Rubisco protein concentration. soluble protein and total chlorophyll were unaffected by CO2 enrichment. The above findings demonstrated that photosynthesis was down regulated in tobacco plants after 7 to 9 days of CO2 enrichment at low photosynthetic photon flxu density, but less than at moderate irradiances.
Rapid purification of the plasma membrane H+‐ATPase in its non‐activated form using FPLC
Authors: Johansson Fredrik , Sommarin Marianne , Larsson Christer
Published: May 2006

The plasma membrane H‐ATPase (EC 3.1.6.35) was solubilized from isolated spinach (Spinacia oleracea) leaf plasma membranes using the detergent dodecyl‐β‐d‐maltoside and subsequently purified to near homogeneity by ion exchange chromatography (FPLC). The enzyme purified in the presence of glycerol and ATP showed no loss in activity during 8 h on ice nor upon freezing at ‐80°C and thawing, and the recovery was up to 75%. Addition of a phospholipid mixture only marginally increased the activity, whereas addition of lysophosphalidylcholine (lyso‐PC) resulted in a 2‐fold increase in activity and a decrease in Km lor ATP from ca 300 μM to 100 μM. The membrane‐bound and the purified H‐ATPases showed very similar properties, also in their responses to lyso‐PC. which is believed to activate the enzyme by displacement of its C‐terminal inhibitory domain. Taken together, the data indicate that the H‐ATPase is purified in a non‐activated form suitable for regulatory studies.
Stimulation of somatic embryogenesis in carrot by ethylene: Effects of modulators of ethylene biosynthesis and action
Authors: Nissen Per
Published: May 2006

Endogenous levels of ethylene appeared to he suhoptimal for somatic embryogenesis in a suspension culture of carrot. Low concentrations of 1‐aminocyclopropane‐1‐carboxylic acid (ACC). 2‐chloroethylphosphonic acid (ethephon) and elhylene stimulated embryogenesis whereas higher concentrations were inhibitory. The stimulation by ACC was through its conversion to ethylene. whereas the inhibition by ACC was not. Low concentrations of AgNO3. an inhibitor of ethylene action, inhibited embryo‐genesis but stimulated ethylene production. Aminoethoxyvinylglycine (AVG) and aminooxyacetic acid (AOA). commonly used inhibitors of ACC synthase. inhibited both embryogenesis and ethylene production. However, the inhibition of embryogenesis was not related to the inhibition ote ethylene production. Very low concentrations of AVG stimulated embryo production in a way unrelated to its effect on ethylene production. Salicylic acid and CoCl2. inhibitors of ACC oxidase in other systems, inhibited embryogenesis but. again, in way(s) unrelated to their inhibition of ethylene production. In fact, low concentrations of salicylic acid stimulated rather than inhibited ethylene production. The results show that in suspension‐cultured cells, caution is warranted in the interpretation of results obtained with agents presumed to inhibit ethylene biosynthesis. The stimulation of somatic embryogenesis by ethylene unequivocally shows that the inhibition of embryo development by 2.4‐dichlorophenoxyacetic acid (2.4‐D) and other auxins cannot be through their stimulatory effect on ethylene production.
The effect of 8 days of microgravity on regeneration of intact plants from protoplasts
Authors: Rasmussen Ole , Baggerud Carolyn A. , Larssen Hilde C. , Evjen Kjetl , Iversen Tor‐Heiming , Kylin A.
Published: May 2006

The growth and development of protoplasts of rapeseed (Brassica napus L. cv Line) and carrot (Daucus carota L. cv. Navona) were studied onboard the Space Shuttle‘Discovery’during an 8‐day International Microgravity Laboratory [IML‐l) mission in January 1992. The Flight experiments were carried out in‘Biorack'. a fully controlled cell biological experimental facility. under microgravity conditions and in a l‐g centrifuge. Parallel experiments were performed in a‘Biorack’module on the ground. After retrieval, some samples were subcultured on appropriate media and analysed for callus growth and regeneration to intact plants. The remainder were used for biochemical analysis. Samples fixed on board the Space Shuttle were kept in l% glutaraldehyde fixative at 4°C for 3–7 days for microscopy analysis after retrieval. Protoplasts exposed to microgravity conditions showed a delay in cell wall synthesis. Cells were swollen in appearance and formed cell aggregates with only few cells. Callus were obtained from protoplasts cultured under microgravity (Fogl). on the l‐g centrifuge on board the shuttle (Flg), under normal l‐g conditions on the ground (G1g) and on a centrifuge on the ground giving 1.4 g (Gl.4g). Regeneration of intact rapeseed plants was obtained from Flg. Glg and G1.4g. However, no plants were regenerated from protoplasts exposed to microgravity (Fog). Biochemical analysis indicated that the microgravity samples (Fog displayed a reduced packed cell volume, an increased concentration of soluble proteins per cell, and a reduced specific activity of peroxidase in the cytoplasm. Morphometric analysis of fixed samples demonstrated that 3‐day old protoplasts under microgravity conditions were significantly larger than protoplasts kept on the l‐g centrifuge in space. UItrastructural analysis by transmission electron microscopy showed that protoplasts exposed to microgravity conditions for 3 days had larger vacuoles and a slightly reduced starch content compared to Flg cells. Cell aggregates formed under microgravity conditions (Fog) had an average of 2–I cells per aggregate while aggregates formed under Flg had 8–12 cells.
Optimization of transient gene expression in pollen of Norway spruce (Picea abies) by particle acceleration
Authors: Martinussen Inger , Junttila Olavi , Twell David
Published: May 2006

In order to optimize transient gene expression in Norway spruce pollen after DNA delivery with particle bombardment, effects of different conditions during homhardmenl were analysed using β‐glucuroniduse (GUS) driven by the rice Act I promoter and Inciferase (LUS) driven by the tomato !at52 promoter as reporter genes. Transient gene expression was significantly increased hy using two bombardments. Also the distance from the stopping plate to the sample was critical to gam maximum gene expression. There was no significant difference between gold and tungsten particles, and the number of positively stained pollen increased with increasing DNA concentration, from 5 to 40 pg DNA added in the DNA/tungsten solution The DNA delivery to Norway spruce pollen was most efficient at a chamber pressure above 70 kPa.
A stress‐induced oxidative burst in Eucheuma platycladum (Rhodophyta)
Authors: Collén Jonas , Pedersén Marianne , Bornman C. H.
Published: May 2006

A hurst of hydrogen peroxide has been found in the red macroalga Eucheuma platycladwn Schmitz as a response to mechanical stress. After exposure of pieces of thalli (2 cm) broken from the plant and stirred with a magnetic bar an oxidative burst was registered, as measured by luminol dependent chemiluminescence (LDC). The burst was totally inhibited by cataluse (EC 1.11.1.6). showing the generation of H2:O2; Ten g of seaweed in 300 ml sea water caused a maximal medium concentration of LDC corresponding to 7 u.M H2O2; The burst decayed after about 30 min. The decay is probably caused by increased catalase aciivity of the sea water. due to leakage of catalasc from the seaweed. Addition of NaN3 caused a dramatic increase in LDC. probably due to inhibition of catalase. Similar bursts of active oxygen, involving active oxygen species such as O2, H2O2 and OH. have been reported as pan of the hypcrsensitive reaction in some higher plants, e.g. tobacco. potato and soybean. Exposure of plants or cell suspension cultures to some pathogenic bacteria, fungi, inorganic elicitors or physical damage causes an oxidalive burst that is often followed by necrosis. The production ot active oxygen is thought to he a first defence against invading pathogens. We assume that the oxidative burst from E. platycladum is of a defensive nature, providing a protection against grazers and pathogenic organisms. To our knowledge this is the first repoil of an oxidalive burst from seaweeds.
Water deficit, leaf rolling and susceptibility to photoinhibition in field grown sorghum
Authors: Corlett J. E. , Jones H. G. , Massacci A. , Masojidek J.
Published: May 2006

Chlorophyll fluorescence and gas‐exchange techniques were used to investigate changes in photosynthelic performance in response to high light and mild water deficit, in two cultivars of the C., plant sorghum (Sorghurn bicofor [L.] Moench). grown under field conditions. For all leaves fully exposed to the sun, the efficiency of phcttosystem 11 (PSII) showed a mid‐day decline, hut with substantial over‐night recovery: the magnitude of the mid‐day decline was enhanced by water deficit. There was no corresponding decline in leaves not exposed to full sunlight, either because they were shaded by other leaves or else because of leaf‐roiling. Net assimilation rates appeared more sensitive to water‐deficit than was PSI1 efficiency. Shade‐adapted leaves had lower rates of photosynthesis in full sun (and lower stomatal conductances) than well‐exposed leaves. When these shade‐adapted leaves were suddenly exposed to full sunlight, fluorescence quenching was slow. especially when plants were well‐watered. For the latter, photochemical quenching (qp)was small even after several minutes. indicating a continuing imbalance between energy funnelled to PSI1 and subsequent electron transport. Shade‐adapted leaves that were water stressed were better able to withstand a sudden increase in irradiance than those that were well watered. It is suggested that the shade‐adapted eaves from unirrigated plants. having a lower s'tomatal conductance than the irrigated leaves, had been acclimated by receiving energy in excess of that required to fix CO2, thus leading to the operation of dissipative mechanisms. A shortened protocol for quenching analysis is proposed that enables non‐photochemical quenching to be partitioned into rapidly and slowly relaxing components (the latter including photoinhibition) by relating results to a theoretical maximum yield of variable fluorescence. This is particularly suitable for screening field material.
Ultrasonic acoustic emissions from excised stems of two Thryptomene species
Authors: van Doom Wouter G. , Jones Rodney B.
Published: May 2006

Stems of Thryptomene vaxicola (A. Cunn.) Shau. cut in air and immediately placed in water at 20°C showed ultrasonic acoustic emissions after 8 to 12 h. whereas no emissions were found in Thryptomene catycina Lindl.) Stapf, within 100 h. Stem water potential declined in a similar manner in both species: a high frequency of acoustic emissions stalrted at approximately –1 000 kPa in T.saxicola., but had not commenced at –5300 kPa in T. calycina. The rates of water uptake were similar in both species. Acoustic emissions in T.saxicola placed in water were prevented h recutting 15 cm of the stems under water.

For comparison, cut stems which were air‐dehydrated at 20°C exhibited a primary peak in the frequency of emission after 3–5 h in T. saxicola and 15 h in T. catycina, corresponding to a water potential of –1000 kPa and less than –5000 kPa. respectively. After 6. 16. and 24 h of dehydration in air and subsequent placement in water for 24 h. the rates of water uptake of T. calycina were not lower than in controls not held dry, How ever. in T. saxicola water uptake rates had decreased after 16 h of dehydration and were very low after 24 h.

The results show that ultrasonic acoustic emissions may occur in freshly cut stems placed in water, and that they occur at a water potential similar to that in stems allowed to dehydrate in air. The number ol emissions in T.saxicola stems placed in water was apparently too low to inhibit water uptake. When held dry. the cavitated xylem elements may be a cause of reduced water uptake in T. saxicola.
Four cytosolic‐type CuZn‐superoxide dismutases in germinating seeds of Pinus sylvestris
Authors: Strcller Steffen , Karpinski Stanislaw , Hällgren Jan‐Erik , Wingsle Gunnar
Published: May 2006

A differential analysis of CuZn‐superoxide dismutase (SOD. EC 1.15.1.1) isozymes after native‐polyacry lamide gel elecrrophoresis (PAGE) and isoelectric focusing (IEF) indicated that germinating seeds of Scots pine (Pinus sylvestris L.) 3 days after the start of imbibition (3 DAI) contain five CuZn‐SOD isozymes. Two isozymes co‐migrated on native–PAGE but were separated after IEF. CuZn‐SODs of Scots pine were purified from germinating seeds (3 DAI) by anion‐exchange chromatography, hydrophobic interaction chromatography and chromatofocusing. The final separation of CuZn‐SOD isozymes was accomplished by native‐PAGE. CuZn‐SOD isozymes were electroblotted and their NH2‐terminal amino acid sequence was determined. Comparisons of the amino acid sequences with sequences of CuZn‐SOD isozymes from other plant sources indicated that one CuZn‐SOD isozyme was of the chloroplastic type whereas the other four isozymes belonged to the cytosolic‐type CuZn‐SODs, The NH2‐terminal amino acid sequence of the chloroplastic CuZn‐SOD and of one cytosolic‐type CuZn‐SOD were identical to those of two previously isolated, sequenced and localized CuZn‐SOD isozymes from Scots pine needles. Two cytosolic‐type CuZn‐SOD isozymes showed a homology at 20 out of 21 NH2‐terminal amino acids. Mitochondria and glyoxysomes were isolated by differential and Percoll density‐gradient centrifugation from germinating seeds (3 DAI). The cell fractionation experiments did not suggest that a major part of the CuZn‐SOD activity in germinating seeds was derived from glyoxysomes or mitochondria.
Carotenoid composition and down regulation of photosystem II in three conifer species during the winter
Authors: Adams William W. , Demmig‐Adams Barbara
Published: May 2006

The carotenoid composition of the needles of three conifer species. Ponderosa pine (Pinus ponderosa). Douglas fir (Pseudotsuga menziesü) and blue spruce (Picea pun—gens). growing in full sunlight was found to differ between the summer and the winter, with higher levels of lutein and the carotenoids of the xanthophyll cycle and lower levels of α‐carotene being present during the winter. In addition, the extent of the de‐epoxidation of violaxunthin to antheraxanthin and zeaxanthin at midday was greater during the winter than during the summer. The latter two carotenoids were also found to be retained at high levels overnight on cold days during the winter. Associated with the retention of antheraxanlhin and zeaxanthin were sustained depressions of photosystem II (PSII) efficiency. These decreases in photo system II efficiency were accompanied by changes in chlorophyll fluorescence characteristics that are indicative of increased levels of energy dissipation in the chlorophyll pigment bed. Sustained depressions in PSII efficiency are commonly interpreted as “photoinhibitton”. We therefore suggest that low temperature‐induced photo inhibition in these conifers during the winter was due to a down regulation of photosystem II that involved sustained xanthophyll cycle‐associated energy dissipation. Furthermore, the predawn conversion state of the xanthophyll cycle responded rapidly to day to day variation in temperature. Being less epoxidized on colder days and more epoxidized on both previous and subsequent warmer days. Such flexibility in the response of the santhophyll cycle to changes in temperature may be important in the regulation and protection of the photosynthetic apparatus of such evergreen plants in a climate that experiences relatively rapid changes in temperature.