bluuebunny/crossref_metadata_2025 huggingface dataset:
Unusual composition of thylakoid membranes of the resurrection plant Boea hygroscopica: Changes in lipids upon dehydration and rehydration
Authors: Navari‐Izzo Flavia , Ricci Federico , Vazzana Concetta , Quartacci Mike F.
Published: May 2006

Boea hygroscopica is a resurrection plant that is able to pass from biosis to anabiosis and vice versa following slow dehydration, but loses this ability following a rapid water loss. Fresh leaves were detached from plants grown in well‐watered conditions and subjected to either rapid or slow dehydration and rehydration. Upon rehydration only slowly dried leaves revived. Analysis of thylakoid membranes revealed a rather small amount of total lipids (1,4–2 μmol g−1 dry weight) in comparison with other flowering plants. The main glycolipid was digalactosyldiacylglycerol (DGDG) rather than monogalactosyldiacylglycerol (MGDG) as is common in higher plants.

Linoleic acid was the main fatty acid (30–40 mol% of total fatty acids), while linolenic acid was present from 14 to 26 mol%. In both the fresh and rehydrated leaves nearly all lipid components were present in similar amounts. Following dehydration the DGDG/MGDG molar ratio, which was 1.1 in control and rehydrated leaves, doubled by the end of the rapid drying period and was three times as high in slowly dried leaves. The total polar lipid/free sterol molar ratio as well as the free fatty acid level assumed the highest values in the rapidly dehydrated leaves. A shift towards the more unsaturated fatty acids was observed in all lipid classes upon dehydration irrespective of whether it was slow or rapid. Our data show only small differences between rapidly and slowly dehydrated leaves which can be correlated to the capacity of slowly dehydrated leaves to revive.
Mobilization of sulphur in soybean cotyledons during germination
Authors: Sunarpi  , Anderson J. W.
Published: May 2006

Soybean seeds (Glycine max L. cv, Stephens) contain a large amount of sulphur (ca 40 μ mol seed−1), mostly in the insoluble fraction in the cotyledons. During germination in nutrient solution lacking sulphur the amount of insoluble sulphur decreases to very low levels. This is accompanied by a transitory increase in the pool of soluble sulphur which then declines. All of the sulphur lost from the cotyledons is quantitatively recovered in the seedling. In the short term, the root and the stem are the most important sinks for sulphur from the cotyledons but as growth proceeds the shoot becomes the dominant sink for remobilized sulphur. Within the shoot most of the sulphur is recovered in leaves L1 and L2. The growth of L3 and, to a lesser extent, L2, was retarded due to sulphur insufficiency. The cotyledons of plants treated with 20 μM sulphate also exhibited mobilization of sulphur from the insoluble fraction except that the maximum rate of loss of sulphur occurred somewhat later. Plants grown with sulphate exhibited a net gain of sulphur and did not exhibit sulphur insufficiency. In these plants, endogenous sulphur from the cotyledons was directed into L1–L3 and this sulphur remained within these leaves for the duration of the experiment. The delivery of exogenous sulphur (supplied as [35S]sulphate via the roots) to the leaves increased with leaf number. In leaves L1–L3, the level of exogenous sulphur in any one leaf declined with time, indicating that this sulphur was remobilized and did not mix with the sulphur derived from the cotyledons. It was concluded that the cotyledons are an important source of sulphur to support early plant growth and development of soybean.
Matric potential evaluations and measurements for gelled substrates
Authors: Beruto Dario , Beruto Margherita , Ciccarelli Carlo , Debergh Pierre
Published: May 2006

A new method for evaluating the matric potential of gelled media has been developed. The method allows the derivation of the matric potential as a limit of a series of measurements of water potential values from gelled media prepared without added components, from agar powders progressively cleaned of mineral impurities. Three commercial agar brands were tested, and for these the matric potential was found to contribute only between 1 and 2% of their total water potential. Thermodynamic features relating matric and osmotic potentials are described. New hypotheses for understanding the water flux mechanism from gel to tissue cultured explants are discussed. Movement of water along polymeric chains is postulated to be a facilitated step in comparison with bulk movement.
Citrus rootstock responses to herbivory by larvae of the sugarcane rootstock borer weevil (Diaprepes abbreviatus)
Authors: Mayer Richard T. , Shapiro J. P. , Berdis E. , Hearn C. J. , McCollum T. G. , McDonald R. E. , Doostdar H.
Published: May 2006

The responses of roots to feeding by larvae of a citrus root weevil (Diaprepes abbreviatus) were investigated in Citrus grandis (L.) Osb. x Poncirus trifoliata (2N) (L.) Raf.; C. grandis x P. trifoliata (4N); P. trifoliata x C. grandis (Flying Dragon x Nakon); C. paradisi Macf. x P. trifoliata (Swingle citrumelo); C. aurantifolia (Christm.) Swingle (Citrus macrophylla); C. reticulata Blanco (Cleopatra mandarin); C. sinensis (L.) Osb. x P. trifoliata (Carrizo citrange); C. aurantium (L.) (sour orange). Chitinase, chitosanase. β‐1,3‐glucanase, peroxidase and lysozyme activities were measured and significant differences were observed for some of the cultivars between infested and uninfested rootstocks. Generally, increased activities were observed for chitinases and decreased activities were observed for the other enzymes measured. Numerous significant differences in hydrolase and peroxidase activities were observed between cultivars. Immunological detection revealed that new protein bands occurred in root protein extracts for six of the eight cultivars infested with larvae when an antibody to a class I potato leaf chitinase was used. Antibodies generated against two citrus chitinases of Mr 24 000 (basic chitinase cv. Valencia (C. sinensis) callus, BCVC) and Mr 28 000 (basic chitinase/lysozyme cv. Valencia callus, BCLVC) indicated that chitinases in Carrizo were induced in infested roots when the BCVC antibody was employed. These findings justify calling these proteins pathogenesis‐related proteins. The chitinase that BCLVC was prepared from exhibited high lysozyme activities, and the results of western blots showed the presence of proteins at Mr 24 000 and 27 000 which are presumed to be lysozymes. Similar tests using antibodies against β‐1, 3‐glucanases and peroxidases indicated a diminution of protein bands that cross‐reacted with infested root protein extracts compared with what occurred in controls. All of the root extracts were tested against chitosans with various percentages of acetylation; activities were linearly dependent on the amount of chitosan acetylation; i.e. the larger the amount of acetylation, the greater the activity. Significant differences in hydrolase activities were observed between infested and uninfested roots for the rootstocks using the variously acetylated substrates. All of the root protein extracts were capable of degrading peritrophic membranes removed from larvae of D. abbreviatus. This suggests that citrus chitinases may play a role in disrupting the peritrophic membrane such that ingested substances that pose a hazard to the insect may penetrate the membrane more easily.
Short‐term effects of boron, germanium and high light intensity on membrane permeability in boron deficient leaves of sunflower
Authors: Cakmak Ismail , Kurz Hannes , Marschner Horst
Published: May 2006

The effects of varied boron (B) supply (0.01–50 μM and light intensity (100–580 μpmol m−2 s−1) on plant growth, leaf symptoms and membrane permeability of leaves were studied in sunflower plants over a 10‐day‐period of growth in nutrient solution. Membrane permeability was measured by incubating isolated young leaves in aerated distilled water. Additional experiments showed the effect of short‐term supply (20 min to 2 h) of B and germanium (Ge) on membrane permeability of B‐deficient leaves incubated in distilled water. Low supply of B decreased shoot and root growth and caused brown‐purple pigmentation of young leaves, particularly under high light intensities. Leakage of K‐ from leaves increased with severity of B deficiency whereas, in B‐sufficient leaves, leakage of solutes was low. Also leakage of phenolics, amino acids and sucrose was enhanced by B deficiency. Compared to B‐sufficient leaves, the leakage from B‐deficient leaves was 35‐fold higher for K+, 45‐fold higher for sucrose and 7‐fold higher for phenolics and amino acids. Increases in solute leakage were marked in leaf areas with brown‐purple pigmentation and particularly pronounced by increasing light intensity or by exposure of leaves to continuous light. In severely B‐deficient leaves grown under high light intensity, treatment with B and Ge up to 1 000 μMM for 20 min resulted in an immediate decrease in K+ efflux to about the same levels as in B‐sufficient leaves. Similar rapid decreases in K+ efflux were also found in B‐deficient leaves when exposed to darkness for 16 h or 30 h before the leakage measurement.

The results demonstrate a particular role for B in maintaining the integrity of plasma membranes. Boron presumably stabilizes the structure of the plasma membrane by complexing membrane constituents. It also has a protective effect on membrane constituents by complexing phenolics, so that oxidation of phenolics to highly toxic quinones and oxygen free radicals is prevented or limited. In these functions, boron seems to be to a large extent replaceable by germanium.
Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?
Authors: Johnsson Anders , Brown Allan H. , Chapman David K. , Heathcote David , Karlsson Christina
Published: May 2006

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time.

Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g‐stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided Plants at two stages of coleoptile development were tested. Plant responses were obtained using time‐lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g‐doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g‐doses, chiefly because the data were more variable.

It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm× 1), with m‐values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well‐defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.
Effect of a constant supply of different nitrogen sources on protein and carbohydrate content and enzyme activities of Anabaena variabilis cells
Authors: Sanz Andrés P. , Moreno‐Vivián Conrado , Maldonado José M. , González‐Fontes Agustín
Published: May 2006

The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied in Anabaena variabilis ATCC 29413 cells grown under a constant supply of either N, NO−3 or NH+4 at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO−3 or NH+4 concentrations in the medium. In cultures containing 0.1 mM NO−3 or 0.1 mM NH+4 nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2‐grown cells. This activity was still present with 1 mM NO−3 or 1 mM NH+4 in the medium and even with 10 mM NO−3, but it was completely inhibited by 5 mM NH+4. Ferredoxin‐nitrate reductase (EC 1.7.7.2) activity was detected only in NO−3 grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+4, promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+‐isocitrate dehydrogenase (EC 1.1.1.42), and NAD+‐malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon‐nitrogen metabolism in cyanobacteria.
Desiccation‐sensitive Hopea odorata seeds: Sensitivity to abscisic acid, water potential and inhibitors of gibberellin biosynthesis
Authors: Garello Ginette , Le Page‐Degivry Marie‐Thérèse
Published: May 2006

When fruits of Hopea odorata are shed, seed water content is high. These seeds are not tolerant to desiccation and germination usually occurs within the first week after abscission. To determine the factors involved in the control of germination, isolated embryos were cultured in vitro and their sensitivity to abscisic acid (ABA), water potential and inhibitors of gibberellin biosynthesis was determined. Moreover, free ABA content was quantified by radioimmunoassay and ABA metabolism was studied by feeding [3H]‐ABA to embryos. Reproductive units of the desiccation‐sensitive seeds of Hopea odorata contain several embryos, all of which are germinable and may give, according to their developmental stages, plantlets that range from those that are prematurely developed as a result of precocious germination to those that are normal. Whatever the developmental stage, the free abscisic acid (ABA) content of the embryo was low. This low endogenous ABA and the inability of high levels of exogenously applied ABA to inhibit germination could be explained by an active ABA metabolism as demonstrated by both a rapid [3H]‐ABA turnover and the existence of high levels of endogenous conjugates. Moreover, both a decrease in the water potential of the culture medium, alone or in addition with ABA, and an inhibition of gibberellin biosynthesis, could induce a reversible inhibition of germination. Such an interaction between ABA, GA and water potential is discussed in the light of results recently reported in hormone‐deficient or hormone‐insensitive mutants.
Heat stress effects on sink activity of developing maize kernels grown in vitro
Authors: Cheikh Nordine , Jones Robert J.
Published: May 2006

The objective of this study was to determine the effect of short‐term (4 days) and long‐term (8 days) heat stress (35°C) on sink activity of maize (Zea mays L.) kernels. Beginning at 3 days after pollination (DAP) kernels were grown in vitro at 25°C and 24 h later were transferred to 35°C for either 4 or 8 days. Each treatment had a control that was maintained continously at 25°C. Two experiments were designed to examine the uptake and distribution of 14C among hexoses, sucrose and starch in the pedicel placento‐chalazal (pedicel/p‐c). endosperm, and pericarp tissues of kernels exposed to heat stress for 4 or 8 days. Kernels cultured in vitro were placed in 14C‐sucrose medium either during the period of heat stress (experiment 1; 5 to 13 DAP) or immediately following heat‐stress treatments (experiment 2; 10 to 22 DAP). In both experiments no significant effect of heat stress was observed on the total radioactivity accumulated in the kernels until about 17 DAP, after which heat‐stressed kernels accumulated less 14C than the control. During the linear fill period, the endosperm of kernels exposed to heat stress accumulated more radioactivity associated with hexoses and sucrose and less radioactivity incorporated into starch, as compared to the control. Kernels heat stressed for 4 days showed a partial recovery in starch synthesis by 21 DAP, but to levels of only 65% of that of the control. Kernels heat stressed for 8 days did not recover. When 14C‐sucrose was supplied during the heat stress period (5–13 DAP). kernels from all treatments accumulated more hexoses that sucrose in the pedicel/p‐c. However, during the period following heat stress (10–22 DAP), pedicel/p‐c accumulated sucrose, but only in kernels exposed to long‐term heat stress. Soluble invertase activity was inhibited by both short‐term and long‐term heat stress, whereas the activity of insoluble invertase was affected only by long‐term heat stress. These results support the hypothesis that the disruption of kernel growth and more particularly endosperm starch biosynthesis, in response to heat stress, is mainly associated with changes in carbon utilization and partitioning between the different nonstructural carbohydrates within the endosperm rather than with a limitation in carbon supply to the kernel. Therefore, the effect on sink activity does not seem to be attributable to a thermal disruption of kernel uptake of sugars, but rather it is a consequence of heat perturbation of other physiological processes such as endosperm sugar metabolism and starch biosynthesis.
Development of antioxidative defense system of wheat seedlings in response to high light
Authors: Mishra Neelara P. , Fatma Tasneem , Singhal Gauri S.
Published: May 2006

Changes in the activities of enzymes involved in the detoxification of reactive oxygen species in wheat seedlings (Triticum aestivum L.) in response to variations in the light environment were studied. Activities of ascorbate peroxidase, superoxide dismutase, monodehydroascorbate reductase, dehydroascorbate reductase, glutalhione reductase and catalase were much lower in seedlings grown under low‐light conditions than in those grown under high‐light conditions. Activities of all these enzymes significantly increased within 24 h of transfer of the low‐light‐grown seedlings to the high‐light regime. The results suggest that the increase in enzyme activities was an adaptive response of the plants to higher amounts of active oxygen species generated at higher light intensities. An accumulation of glutathione was also observed, which could also be a part of the defense strategy to meet the increased generation of active oxygen species upon transfer of low‐light‐grown plants to high‐light conditions.
A procedure for quantification of cytokinins as free bases involving scintillation proximity immunoassay
Authors: Wang J. , Letham D. S. , Taverner E. , Badenoch‐Jones J. , Hocart C. H.
Published: May 2006

Cytokinins occur in a diversity of forms and determination of their individual levels requires extensive purification. However, determination of the total level of each major base in free, riboside and nucleotide forms would often be adequate. Hence, a methanolysis procedure which releases cytokinin bases from 9‐ribosyl derivatives was developed and applied to plant extracts. A simple procedure, involving low pressure column chromatography, for purification of the cytokinin bases in treated extracts, and a scintillation proximity immunoassay for their quantification, were developed. The total level of each cytokinin base [N6‐(2‐isopentenyl)adenine, zeatin and dihydrozeatin] in free and ribosylated forms determined by these methods is reported for several plant tissues and the results are compared with those obtained after additional purification by HPLC. Values for zeatin were not changed by HPLC but isopentenyl‐adenine and dihydrozeatin levels were usually reduced indicating the presence of unknown compounds which cross‐react in the immunoassay. Modifications to the above purification method to quantify O‐glucosyl cytokinins are also described.

The methods described facilitate the quantification of the total amount of each cytokinin base in forms closely associated with cytokinin action, and the detection of cytokinin biosynthesis by labelled precursor incorporation.
Expression of an mRNA with sequence similarity to pea dehydrin (Psdhn 1) in guard cells of Vicia faba in response to exogenous abscisic acid
Authors: Shen Liming , Outlaw William H. , Epstein Lloyd M.
Published: May 2006

The function and location of guard cells uniquely subject them to stress. First, stomatal movements require large fluctuations in the concentration of potassium salts. Second, guard cell inner walls are the first surfaces exposed to evaporation and apoplastic solutes may accumulate there as a result. We have therefore investigated whether guard cells exhibit atypical expression of dehydrin genes because dehydrins accumulate in vegetative tissues in response to water stress. We have also assayed for osmotin mRNA, which is up‐regulated in leaves in response to various stresses. mRNA probes for several representative genes were used with RNA extracts from control and water‐stressed Vicia faba leaflets. Correlatively, these probes were used with RNA extracts from “isolated’ guard cells that had been incubated with combinations of abscisic acid, mannitol and Ca2+. (Isolated guard cells are epidermal strips sonicated to destroy cells other than guard cells.) Hybridization with the probe prepared for a dehydrin from Pisum sativum (Psdhn 1) was detected in leaf extracts only if the leaf had been stressed. Similarly, after 1‐ and 6‐h incubations with abscisic acid, isolated guard cells contained an mRNA that hybridized with the probe for Psdhn 1. Appearance of this abscisic acid‐dependent mRNA required neither mannitol nor exogenous Ca2+. Regardless of the conditions or tissue, no hybridization was detected with the probe against osmotin, but our interpretation of this result is qualified. The simplest conclusion is that atypical expression of dehydrin is not the mechanism by which guard cells cope with their peculiar function and location.
Increased N‐acylphosphatidylethanolamine biosynthesis in elicitor‐treated tobacco cells
Authors: Chapman Kent D. , Conyers‐Jackson Allison , Moreau Robert A. , Tripathy Swati
Published: May 2006

Previous studies with tobacco (Nicotiana tabacum L.) cell suspensions indicated that elicitation of defense response (production of phytoalexins) with xylanase (1,4‐β‐D‐xylanxylanohydrolase: EC 3.2.1.8) resulted in a dramatic acylation of phytosterols (Moreau et al. 1994). N‐acylphosphatidylethanolamine (NAPE), an acylated derivative of phosphatidylethanolamine (PE), was recently demonstrated to be synthesized in vivo in plant tissues (Chapman and Moore 1993a). Here we report that acylation of PE was increased in elicitor‐treated cells. NAPE levels increased 3‐fold (from 1.6 to 4.8 mol% of total phospholipids) after a 2‐h treatment of cell suspensions with xylanase (1 δg ml−1). Specific activity of NAPE synthase increased in parallel with NAPE levels. Levels of NAPE and NAPE synthase activity declined during the period of 2–4 h after elicitation while levels of acylated sterolglycosides (ASG) continued to increase. Radiolabeling studies with [2−14C]‐ethanolamine confirmed that three times as much NAPE was synthesized in elicitor‐treated cells compared to that in unelicited cells. Patterns of incorporation of [1‐14C]‐palmitic acid into membrane phospholipids in elicitor‐treated cells suggested that increased acylation of lipids may be a result of changes in the acyl‐coenzyme A pool. Treatment of cells with purified ethylene biosynthesis‐inducing xylanase (EIX; 1 δg ml−1 cells) resulted in increased levels of NAPE synthase activity comparable to those observed with the commercial preparations of xylanase. Boiled xylanase did not elicit an increase in the specific activity of NAPE synthase. Collectively our results demonstrate that the accumulation of NAPE in tobacco cells is attributable to increased activity of NAPE synthase. This suggests that NAPE may be specifically synthesized to play a protective role in membranes of plant cells as has been suggested for membranes of damaged animal cells.
Photoreduction of monovinyl‐ and divinyl‐protochlorophyllide in vitro and in vivo in the light‐dependent greening mutant C‐2A' of Scenedesmus obliquus
Authors: Knaust Rosemarie , Urbig Thomas , Senger Horst
Published: May 2006

Dark‐grown cells of mutant C‐2A' of Scenedesmus obliquus accumulate monovinyl‐and mainly divinyl‐protochlorophyllide (PChlide). Both PChlide‐forms are equally well photoconverted in vitro by the NADPH‐protochlorophyllide oxidoreductase of the light‐dependent greening mutant C‐2A’of Scenedesmus obliquus. The chlorophyllide (Chlide) resulting from this photoconversion in vivo has a predominantly monovinyl character. Only small traces of a transient Chlide‐form with divinyl fluorescence could be detected.
Solubilization and hydrophobicity test by Triton X‐114‐partitioning of NADPH‐protochlorophyllide oxidoreductase from the unicellular algaScenedesmus obliquus, mutant C‐2A'
Authors: Urbig Thomas , Schiller Hilmar , Senger Horst
Published: May 2006

NADPH‐protochlorophyllide oxidoreductase (PChilde reductase, EC 1.3.1.33), a key enzyme in light‐dependent greening and the conversion of etioplasts into chloroplasts was investigated in the the greening mutant C‐2A' of the unicellular green algaScenedesmus obliquus.In the absence of detergent, the solubilization of the enzyme increased with high glycerol concentrations in the buffer. Solubilization capacities of 4 non‐ionic or zwitterionic detergents, Triton X‐100, CHAPS, octylglucoside and decyl‐maltopyranoside, were compared. Due to the addition of these detergents, the enzyme activity in the soluble fraction was increased severalfold. Hydrophobicity of the enzyme was analyzed by Triton X‐114 phase partitioning. The protein had a preference for the aqueous phase, but its distribution was strongly influenced by the glycerol concentration of the buffer. These results indicate that the PChlide reductase of the green algaScenedesmus obliquusis a hydrophobic, membrane‐associated enzyme, but not an integral membrane protein.
Effect of ABA and slow drying on DNA replication in carrot (Daucus carota) embryoids
Authors: Tetteroo Frans A. A. , Bino Raoul J. , Bergervoet Jan H. W. , Hasenack Birgit
Published: May 2006

Addition of abscisic acid (ABA) at the torpedo‐shaped stage of development and slow dehydration are two parameters necessary to produce completely desiccation‐tolerant carrot (Daucus carota L.) embryoids. The mode of action of these parameters is still largely unidentified. Employing flow cytometry we investigated their effect on DNA replication and cell cycle activity of the developing embryoids. DNA replication was determined as percentage of 4C nuclei. Addition of ABA did not alter DNA replication and cell cycle during embryoid development in vitro, in spite of the putative quiescent state of the torpedo‐shaped embryoids. In contrast, during slow drying the nuclei were preferentially arrested in the presynthesis G0/G1‐phase and the amount of G2 nuclei decreased. Dry zygotic carrot embryos do not contain any G2 nuclei and are completely desiccation tolerant. The decline of G2 nuclei in dry somatic embryoids seems to coincide with the increase in desiccation tolerance, which is incomplete compared to zygotic embryos. Our results suggest that in order to withstand anhydrobiosis, DNA replication may be controlled during the embryoid developmental program and slow dehydration, but not by the plant growth regulator ABA.
The effect of daylength on the transition to flowering in phytochrome‐deficient, late‐flowering and double mutants of Arabidopsis thaliana
Authors: Koornneef Maarten , Hanhart Corrie , van Loenen‐Martinet Patty , Blankestijn de Vries Hetty
Published: May 2006

The effect of daylength on flowering was investigated in the following mutants of Arabidopsis thaliana: phytochrome B deficient (hy3=phyB); phytochrome chromophore deficient (hy2); late‐flowering (co, gi. fca and fwa); the hy2 and hy3, late‐flowering double mutants and the hy2, hy3, late‐flowering triple mutants. The hy mutants flower with fewer rosette leaves than the Landsberg erecta wild type under both long day and short day conditions and express this effect to a different degree in all late‐flowering mutant backgrounds and under both daylengths, with the exception of fca under short days. The number of cauline leaves and days to flowering is less affected by the hy genotype. The hy2, hy3 double mutants flower with even fewer rosette leaves than the hy2 and hy3 monogenic mutants, suggesting an inhibitory role for phytochrome B and other stable phytochromes on flowering. The complex interaction between phytochrome, daylength and the effect of the late‐flowering genes on the various parameters that describe the transition to flowering in Arabidopsis is discussed.
Effects of clinorotation and microgravity on sweet clover columella cells treated with cytochalasin D
Authors: Hilaire Emmanuel , Paulsen Avelina Q. , Brown Christopher S. , Guikema James A.
Published: May 2006

The cytoskeleton of columella cells is believed to be involved in maintaining the developmental polarity of cells observed as a reproducible positioning of cellular organelles. It is also implicated in the transduction of gravitropic signals. Roots of sweet clover (Melilotus alba L.) seedlings were treated with a microfilament disrupter, cytochalasin D, on a slowly rotating horizontal clinostat (2 rpm). Electron micrographs of treated columella cells revealed several ultrastructural effects including repositioning of the nucleus and the amyloplasts and the formation of endoplasmic reticulum (ER) whorls. However, experiments performed during fast clinorotation (55 rpm) showed an accumulation (but no whorling) of a disorganized ER network at the proximal and distal pole and a random distribution of the amyloplasts. Therefore, formation of whorls depends upon the speed of clinorotation, and the overall impact of cytochalasin D suggests the necessity of microfilaments in organelle positioning. Interestingly, a similar drug treatment performed in microgravity aboard the US Space Shuttle Endeavour (STS‐54, January 1993) caused a displacement of ER membranes and amyloplasts away from the distal plasma membrane. In the present study, we discuss the role of microfilaments in maintaining columella cell polarity and the utility of clinostats to simulate microgravity.
Application of trifluralin to embryogenic microspore cultures to generate doubled haploid plants in Brassica napus
Authors: Zhao Jiping , Simmonds Daina H.
Published: May 2006

Microspore or anther culture has been used to produce desirable meiotic recombinants in numerous species. However, the utilization of these recombinants relies on inefficient genome doubling procedures to obtain fertile doubled haploid plants. This study presents a simple and rapid procedure to generate fertile doubled haploids in Brassica napus cv. Topas using trifluralin (α,α,α‐trifluoro‐2,6‐dinitro‐N,N‐dipropyl‐p‐toluidine), a plant specific microtubule inhibitor. The effects of trifluralin on microtubule depolymerization and chromosome doubling in embryogenic microspore cultures of B. napus were examined and compared with those of colchicine. Indirect immunofluorescence labeling of isolated microspores indicated that microtubules were depolymerized within 30 min of trifluralin treatment and after 3–8 h of colchicine treatment. The direct application of these microtubule inhibitors to microspore cultures resulted in the recovery of fertile doubled haploid plants. Continuous culture in the presence of colchicine, was more effective than 18‐h treatments for fertile plant production but resulted in abnormal embryo formation and recalcitrant plant regeneration. The application of 1 or 10 μM trifluralin during the first 18 h of microspore culture was found to be the superior method for doubled haploid production. The embryos generated after trifluralin treatment developed normally, germinated readily and of the plants produced, close to 60% were fertile. The use of trifluralin to double chromosomes very early in microspore cultures is a simple process requiring minimal manipulation and should be very useful for genetic studies and breeding programs of B. napus and possibly other species.
Reduction, assimilation and transport of N in normal and gibberellin‐deficient tomato plants
Authors: Cramer M. D. , Nagel O. W. , Lips S. H. , Lambers H.
Published: May 2006

A fast‐growing normal and a slow‐growing gibberellin‐deficient mutant of Lycopersicon esculentum (L.) Mill. cv. Moneymaker were used to test the hypothesis that slow‐growing plants reduce NO3− in the root to a greater extent than do fast‐growing plants. Plants that reduce NO3− in the root may grow more slowly due to the higher energetic and carbon costs associated with root‐based NO3− reduction compared to photosynthetically driven shoot NO3− reduction. The plants were grown hydroponically with a complete nutrient solution containing 10 mM NO3− and the biomass production, gas exchange characteristics, root respiratory O2 consumption, nitrate reductase activity and translocation of N in the xylem were measured. The gibberellin‐deficient mutants accumulated more total N unit−1 dry weight than did the faster‐growing normal plants. There were no significant differences between the genotypes in the rates of photosynthesis expressed on a leaf dry weight basis. The plants differed in the proportion of photosynthetic carbon available to growth due to a greater proportion of daily photo‐synthate production being consumed by respiration in the slow‐growing genotype. This difference in allocation of carbon was associated with differences in the specific leaf area and specific root length. In addition, a greater leaf weight ratio in the fast‐growing than in the slow‐growing plants indicates a greater investment of carbon into biomass supporting photosynthetic production in the former. We did not find differences in the activity or distribution of nitrate reductase or in the N composition of the xylem sap between the genotypes. We thus conclude that the growth rate was determined by the efficiency of carbon partitioning and that the site of NO3− reduction and assimilation was not related to the growth rate of these plants.
Respiratory energy demand for protein turnover and ion transport in wheat leaves upon water deficit
Authors: Zagdańska Barbara
Published: May 2006

The effect of water stress on the respiratory energy demand for the main biosynthetic and transport processes was estimated in the leaves of spring wheat (Triticum aestivum L. cv. San Pastore) acclimated and non‐acclimated to drought. ATP‐consuming processes were assessed from the effects of selective inhibitors of RNA synthesis, protein synthesis and proteolysis, Ca2+‐ATPase and P‐type ATPases on respiration. The proportions of energy consumed by these processes were compared with the theoretical ATP production calculated from the rate of oxygen consumption measured manometrically. Respiratory energy production increased significantly in both acclimated leaves and in leaves stressed by drought. In the fully grown wheat leaves, Ca2+‐dependent reactions and protein turnover consumed about 37% and 34% of the total respiratory energy, respectively. The costs of ion transport constituted another 15% of the total ATP production. Both acclimation and drought stress in non‐acclimated leaves resulted in a decrease of leaf sensitivity towards inhibitors of RNA and protein syntheses as well as a decrease in Ca2+‐mediated processes; but also in an increase of leaf sensitivity towards inhibitors of proteolysis and ouabain‐sensitive ATPase in non‐acclimated plants. This indicates a shift in ATP input into the energy‐requiring processes towards greater expenses for ion transport upon water deficit. However, in acclimated leaves under drought stress, distribution of respiratory energy became almost the same as in control plants.
Transport of zinc and manganese to developing wheat grains
Authors: Pearson J. N. , Rengel Z. , Jenner C. F. , Graham R. D.
Published: May 2006

An understanding of the transport pathway used by Zn and Mn to enter developing grains may allow measures to increase the Zn and Mn content of wheat grain grown on Zn/Mn deficient soils. For this reason, transport of Zn and Mn into developing grains of wheat (Triticum aestivum L. cv. Aroona) was investigated. Detached ears (18–22 days post‐anthesis) were cultured for 48 h in a solution containing 185 kBq of 65Zn and 185 kBq of 54Mn. Transport of 65Zn to the grain was unaffected by removal of glumes but was slightly reduced after the lemma was removed. Heat girdling the peduncle slightly reduced the amount of 65Zn transported to the grain, whilst heat girdling the rachilla reduced transport of 65Zn to the grain to a greater degree, suggesting phloem transport to the rachilla. The transport inhibitor CCCP (carbonyl cyanide m‐chlorophenyl hydrazone) blocked 65Zn transport to grain but not to lemma and glumes. Removing glumes and lemma and heat girdling the peduncle did not affect transport of 54Mn, but transport was slightly affected by heat girdling the rachilla, indicating xylem transport. CCCP blocked transport of 54Mn into the grain but not to lemma and glumes. It was concluded that xylem‐to‐phloem transfer of Zn occurs in the rachis and to a lesser extent in peduncle and lemma. The results suggest that the lemma may be an important site for phloem loading when the concentration of Zn within the xylem is high. The data also suggest that Mn was predominantly translocated to the spikelets in the xylem, but that transport to the grain was dependent upon membrane transport before entering the grain. Phloem loading of Mn into the grain vascular system may have occurred at the site of xylem discontinuity in the floral axis.
Effect of the rol genes from Agrobacterium rhizogenes on polyamine metabolism in tobacco roots
Authors: Altabella T. , Angel E. , Biondi S. , Palazón J. , Bagni N. , Piñol M. T.
Published: May 2006

Using tobacco root cultures, we explored the possibility of a correlation between the expression of the rol genes from the TL‐DNA (rolA, rolB, rolC) of Agrobacterium rhizogenes and changes in polyamine content and metabolism. Transgenic roots were induced by inoculation of Nicotiana tabacum cv. Xanthi leaf discs with a disarmed strain of A. tumefaciens harbouring the rolA, rolB and rolC genes either singly or in combination; the presence of these genes on the plant genome was confirmed by Southern blot analysis. Transgenic roots, especially those transformed either by a combination of the three rol genes (A+B+C) or the rolC alone, grew faster than the untransformed roots. Putrescine, spermidine and traces of spermine were present in all samples, both in free and bound forms. While rolA roots showed increased levels of free and bound polyamines as compared with controls, accumulation of polyamines in rolB and rolC roots was inhibited or mantained, with the exception of a 66 and 48% increase, respectively, in the PCA‐soluble conjugated fraction. In roots transgenic for all three rol genes (A+B+C), the polyamine content remained almost unaltered compared with controls, suggesting that rolB and rolC genes could nullify or compensate the rolA effects. The higher polyamine contents found in roots transformed by rolA paralleled with higher ornithine (EC 4.1.1.17) and arginine (EC 4.1.1.19) decarboxylase activities as well as higher nicotine production. It is suggested that polyamine metabolism in root cultures is altered by expression of rol genes.
A device to estimate the light gradients relevant to phototropism in the laboratory and the field
Authors: Firn Richard D. , Digby John
Published: May 2006

An apparatus has been devised to measure the irradiance falling on a central point from each of 48 points of the compass. The apparatus has been used to estimate the magnitude and spatial distribution of light gradients in a variety of situations which are known to cause phototropism.

Measurements show that the typical laboratory treatments used to induce phototropism produce extreme light gradients which are not typical of the light gradients likely to be experienced by seedlings growing in the natural environment. Diffuse light which is always present in the natural environment, ensures that all flanks of seedlings will be subject to potentially physiologically significant light stimulation. Such findings need to be taken into account when devising and testing models of phototropic detection in plants.
Ultrastructural changes in aging leaves of a light‐grown achlorophyllous mutant of barley
Authors: Cowan A. K. , Botha C. E. J. , Hartley B. J. , Cross R. H. M.
Published: May 2006

The pattern and sequence of cellular degradation during the course of leaf senescence remains obscure and the nature of the trigger that induces cell senescence is unknown. In order to probe the pre‐mortem phase of senescence temporal changes in cell ultrastucture were studied in aging leaves of light‐grown achlorophyllous Hordeum vulgare L. cv. Dyan mutant seedlings. Electron microscope examination of the ultrastructure of mesophyll cell plastids revealed the absence of ribosomes and a highly disorganized prolamellar body. Both the number and size of plastoglobuli increased with aging and this change coincided with depletion of starch grains and dilation of lamellar membranes. Aging of mesophyll cells occurred coincident with a decline in ribosome content of the cytoplasm and loss of matrix granularity. Loss of ribosomes associated with the outer nuclear envelope membrane and a reduction in chromatin were also apparent. Only after 10 days was there evidence of loss of internal membrane integrity and swelling of mitochondrial cristae. Compartmentation was thus maintained during the aging process with membrane dissolution occurring late in senescence. These results suggest that an inability to produce chlorophyll and carotenoids and form thylakoid stacks due to the absence of plastid ribosomes, contributes to the rapid onset of senescence in light‐grown achlorophyllous seedlings. Furthermore, disruption of chloroplast ribosome synthesis/assembly may constitute part of the plastid signal involved in triggering cell senescence.
DNA uptake by imbibition and expression of a foreign gene in rice
Authors: Yoo Junhi , Jung Guhung
Published: May 2006

Uptake of DNA by imbibition of dry and viable rice (Oryza sativa L.) embryos from a DNA solution and expression of a foreign gene were detected using two different vectors contaíning gusA (β‐glucuronidase) and hpt (hygromycin phosphotransferase) as reporter genes. The frequency of transient expression of gusA and hpt genes using the CaMV35S promoter was about 30 to 50%. The main sites of gusA gene expression were meristems of roots and vascular bundles of leaves. Also, DNA uptake, integration and expression of the hpt gene in selected rice were investigated by various PCR methods and Southern blot analysis of genomic DNA. It was shown that the hygromycin phosphotransferase (HPT) DNA was present in the rice genome in an integrated form and not as a plasmid form.
The possible role of fructose 2,6‐bisphosphate in the cyanide‐mediated removal of embryonic dormancy in apple
Authors: Bogatek Renata
Published: May 2006

The effects of pretreatment with HCN on the level of fructose 2.6‐bisphosphate (F‐2,6‐P2). on activity of fructose 6‐phosphate 2‐kinase (EC 2.7.1.150; F‐6‐P. 2K. enzyme synthesizing F‐2,6‐P2), as well as on activities of PP1‐dependent and ATP‐dependent phosphofructokinases (EC 2.7.1.90. PP1‐PFK and EC 2.7.1.11, ATP‐PFK) were studied in cultured, dormant embryos of apple (Malus domestica Borb. cv. Antonówka). HCN increased the F‐2.6‐P2 level and F‐6‐P, 2K activity in embryonal axes (3‐fold), but had no effect in cotyledons. HCN pretreatment of embryos or the addition of F‐2.6‐P2 to enzyme extract stimulated PP1, ‐PFK activity, whereas the activity of ATP‐PFK was slightly inhibited by HCN in axes and in cotyledons. Glycolysis is one of the first processes in the germination of apple embryos, and the stimulation of glycolysis by HCN may be the result of F‐6‐P, 2K activation in the axes. This will lead to accumulation of F‐2,6‐P2, which, in turn, enhances glycolysis by activation of PP1PKF.
The cryptic‐growth response of maize coleoptiles and its relationship to H2O2‐dependent cell wall stiffening
Authors: Hohl Michael , Greiner Heribert , Schopfer Peter
Published: May 2006

Auxin‐mediated elongation growth of maize (Zea mays L.) coleoptile segments can be nullified by lowering the turgor pressure by 0.45 MPa. Under these conditions irreversible segment length (lin) measured after freezing/thawing increases steadily over a period of 8 h although the in vivo length (ltot) remains constant. This phenomenon, designated as ‘cryptic growth’, is an indication of a wall‐stiffening process which appears to be an intrinsic component of irreversible cell wall extension. Using a range of metabolic inhibitors it is demonstrated that cryptic growth is caused by a temperature‐sensitive biochemical process in the cell wall which depends on the presence of O2 and active peroxidase, but not on ATP and protein synthesis. Inhibition of cryptic growth by anaerobic conditions can be alleviated by extermal H2O2. Moreover, cryptic growth can be partially inhibited by the antioxidant ascorbate. It is concluded that cryptic growth represents a wall‐stiffening reaction mediated by peroxidase‐catalyzed, H2O2‐dependent cross‐linking of phenolic residues of wall polymers. The experimental demonstration of a wall‐stiffening reaction in a rapidly growing organ supports the concept that irreversible cell elongation (growth) is caused by an interplay of two chemorheological reactions, a turgor‐dependent wall‐loosening reaction and a separate wall‐stiffening reaction which fixes the viscoelastically extended wall structure through oxidative cross‐linking and thus conferring irreversibility to wall extension.
Characterisation of a Ca2+‐dependent ATP hydrolysis associated with the vacuolar membrane of wheat roots
Authors: Allen Gethyn J. , Morais Francisco , Muir Shelagh , Wyn Jones R. Gareth , Leigh Roger A.
Published: May 2006

Microsomal fractions from wheat tissues exhibit a higher level of ATP hydrolytic activity in the presence of Ca2+ than Mg2+. Here we characterise the Ca2+‐dependent activity from roots of Triticum aestivum lev. Troy) and investigate its possible function. Ca2+‐dependent ATP hydrolysis in the microsomal fraction occurs over a wide pH range with two slight optima at pH 5.5 and 7.5. At these pHs the activity co‐migrates with the major peak of nitrate‐inhibited Mg2+. Cl‐ATPase on continuous sucrose gradients indicating that it is associated with the vacuolar membrane. Ca2+‐dependent ATP hydrolysis can be distinguished from an inhibitory effect of Ca2+ on the plasma membrane K+, Mg2+‐ATPase following microsomal membrane separation using aqueous polymer two phase partitioning. The Ca2+‐dependent activity is stimulated by free Ca2+ with a Km of 8.1 μM in the absence of Mg2+ ([CaATP] = 0.8 mM). Vacuoiar membrane vacuolar preparations contain a higher Ca2+‐dependent than Mg2+‐dependent ATP hydrolysis, although the two activities are not directly additive. The nucleotide specificity of the divalent ion‐dependent activities in vacuolar membrane‐enriched fractions was low. hydrolysis of CTP and UTP being greater than ATP hydrolysis with both Ca2+ and Mg2+ The Ca2+‐dependent activity did discriminate against dinucleotides, and mononucleotides. and failed to hydrolyse phosphatase substrates. Despite low nucleotide specificity the Mg2+‐dependent activity functioned as a bafilomycin sensitive H+‐pump in vacuolar membrane vesicles.

Ca2+‐dependent ATP hydrolysis was not inhibited by the V‐, P‐, or F‐type ATPase inhibitors bafilomycin. vanadate and azide, respectively. nor by the phosphatase inhibitor molybdate, but was inhibited 20% at pH 7.5 by K+. Possible functions of Ca2+‐dependent hydrolysis as a H+‐pump or a Ca2+‐pump was investigated using vacuolar membrane vesicles. No H+ or Ca2+ translocating activity was observed under conditions when the Ca2+‐dependent ATP hydrolysis was active.