bluuebunny/crossref_metadata_2025_split huggingface dataset:
Embryology in Norway spruce (Picea abies). An analysis of the composition of seed storage proteins and deposition of storage reserves during seed development and somatic embryogenesis
Authors: Hakman Inger 
Published: May 2006

Seed cones were collected from open‐pollinated trees of Norway spruce (Picea abies) in a seed orchard from pollination until maturation of the seeds. Immature embryos were isolated for embryogenic tissue cultures that were maintained either on solidified medium or as liquid cultures. By transferring young somatic embryos to medium containing 90 mM sucrose and 7. 6 μM ABA growth continued to mature embryos that accumulated storage reserves in both the hypocotyl‐shoot axis and the cotyledons. Both zygotic and somatic embryos at different developmental stages were processed for microscopy as were the megagametophytes. Total protein was extracted from the seed material at intervals during development and analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. These analyses revealed that storage protein started to accumulate in the megagametophytes at the time when embryos were growing into the gametophytic tissue, while it occurred a few weeks later in the embryos at rapid embryo growth and organ differentiation. Lipid bodies also became abundant in the mature plant material. Although plastids with prominent starch grains were very frequent in both megagametophytes and embryos during development they were not observed in the desiccated tissues. Zygotic and somatic embryos displayed a similar developmental pattern.By sequential salt‐extraction and dilution two fractions highly enriched in storage protein were obtained. One fraction (G‐1), requiring higher salt concentration for protein solubilization, was dominated by a protein migrating to around M, 55000–60000 when separated under non‐reduced condition. After exposure to reducing agent this protein was replaced by two new ones with M, 33000 and 22000 giving evidence of disulfide bonded polypeptides. The other fraction (G‐2), was dominated by polypeptides around M, 42000 and low molecular mass polypeptides (<14000).
Garlic (Allium sativum) chitinases: characterization and molecular cloning
Authors: Van Damme Els J. M. , Willems Pieter , Torrekens Sophie , Van Leuven Fred , Peumans Willy J. 
Published: May 2006

Leaves and bulbs of garlic (Allium sativum L.) contain a chitinase which can be separated into three different isoforms with similar molecular structure and N‐ terminal amino acid sequence. SDS‐PAGE of the alkylated chitinase revealed two distinct polypeptides of 32 and 33 kDa. Induction studies of the chitinase in leaves of garlic plants indicated that not only treatment with ethephon or salicylate and wounding but also a temperature shock strongly increased the enzyme level.cDNA libraries constructed from poly(A)‐rich RNA isolated from young garlic shoots and bulbs were screened for chitinase clones using the cDNA clone CCH4 encoding a basic potato chitinase as a probe. Two different cDNA clones (designated CHITAS 1 and CHITAS 2)of ca 1 000 bp were isolated and their sequences analyzed. The amino acid sequences deduced from both cDNA clones were homologous though not identical to the N‐terminal sequences of the mature chitinases. Although both clones encode highly homologous chitinases their sequences definitely differ in that they have different signal peptides and one of them contains a glycine‐rich domain. The garlic chitinases are apparently translated from an mRNA of 1200 nucleotides which encodes a proprotein of approximately 32 or 33 kDa for CHITAS 1 and CHITAS 2, respectively. Co‐translational removal of the signal peptide will result in a 30 (for CHITAS 1) or 31 kDa (for CHITAS 2) protein with an isoelectric point of 4. 94 (for CHITAS 1) or 6. 12 (for CHITAS 2). Garlic chitinases are encoded by a small gene family as shown by Southern blot analysis of genomic DNA isolated from garlic.The garlic chitinases show a high degree of sequence homology to the previously isolated chitinases from dicotyledonous as well as monocotyledonous species, indicating that these proteins have been conserved from an evolutionary point of view.
Kinetic resolution of different recovery phases of photoinhibited photosystem II in cold‐acclimated and non‐acclimated spinach leaves
Authors: van Wijk Klaas J. , van Hasselt Philip R. 
Published: May 2006

Leaf discs from spinach were exposed to a photon flux density of 1250 μmol m−2s−1 at 5°C for 2 or 3 h in ambient air. Photoinhibition of photosystem II (PS II) was measured by means of chlorophyll fluorescence. Recovery of photosystem II was followed at 6°C and 20°C in low light or darkness for periods up to 12 h.The experimental setup allowed kinetic resolution of different phases of recovery. The experiments revealed a temperature dependent dark recovery phase and two distinct light‐ and temperature dependent phases: (1) A relatively fast, light dependent recovery phase occurred in parallel with partial recovery of basic fluorescence at 6°C and 20°C. A population of PS II centers with very slow fluorescence induction kinetics, which had accumulated during photoinhibition treatment, disappeared during this phase. This fast recovery phase is proposed to represent reactivation of photoinhibited PS II, without dissassembly or incorporation of new D1‐protein. (2) A relatively slow light‐dependent recovery phase took place at 20°C, but not at 6°C. In the presence of the chloroplast translation inhibitor streptomycin, part of the 2nd phase was inhibited. This phase is proposed to involve assembly of new Photosystem II centers, which is partly dependent on de novo synthesis of D1‐reaction center protein, but presumably is also using a preexisting pool of D1‐protein. Cold acclimation of the leaves resulted in a decreased sensitivity for photoinhibition of photosystem II. Recovery of photoinhibited photosystem II at 6°C of the cold‐acclimated leaves was faster than in non‐acclimated leaves, but this effect can be ascribed to diminished photoinhibitory damage.
The rate of protein synthesis in needles of Norway spruce (Picea abies): Light stimulation, regulation through photophosphorylation, stress enhancement
Authors: Schmitz H. , Löffel U. , Weidner M. 
Published: May 2006

The incorporation of 14C‐leucine into the total‐protein fraction of needles of Norway spruce (Picea abies [L.] Karst.) during short time incubation was used as a measure of protein synthesis in the light and in the dark. Light saturation curves, obtained for needles of different ages (new flush and 1 and 2 years old) or at different seasons (summer‐winter) followed the Michaelis‐Menten algorithm, exhibiting marked differences with regard to light saturation (Vmax) and the half‐saturation constant (K5. 2). The light saturation curves of ATP level (mg g−1 fresh weight) and of leucine incorporation into protein (nmol mg−1 h−1) matched each other, suggesting that photophosphorylation may be decisive for the rate of protein synthesis in the light. This is confirmed by the action spectrum of leucine incorporation. which resembled an action spectrum of leaf photosynthesis, and also by partial inhibition of protein synthesis by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), an inhibitor of non‐cyclic photophosphorylation. Light stimulated protein synthesis showed pronounced seasonal fluctuations with a summer maximum.Furmigation of 5 years old spruce trees for 3 months with SO2 in combination with O3 and/or NO2 caused a distinct enhancement of the protein synthesis rate in the light and, at a reduced absolute level, also in the dark. A similar result was obtained for 40 to 70 years old spruce stands when healthy and sick trees were compared: the latter being afflicted by the novel type of forest decline, which is characterized by yellowish bronze discolouration of sun‐exposed older needles and partial loss of older needle generations (3 to 4 years old). The 1 year old needles of the unhealthy trees showed a markedly increased 14C‐leucine incorporation rate which, in the dark, was even more pronounced than in the light. Stress‐physiological mechanisms, which could possibly explain this stimulation, are discussed.
Influence of magnesium deficiency on rates of leaf expansion, starch and sucrose accumulation, and net assimilation in Phaseolus vulgaris
Authors: Fischer Erika Sigrid , Bremer Elke 
Published: May 2006

Twenty one‐day‐old Phaseolus vulgaris‘Saxa’plants were cultured in a growth chamber and the plants supplied with either a complete or a Mg‐free nutrient solution. From 6 days after transfer to the Mg‐free solution, the rate of increase of the area of the second trifoliate leaf was considerably reduced; by day 11 the sucrose concentration in the first trifoliate leaf had increased 6. 2‐fold at the end of the dark period and 4. 6‐fold after the light period as compared with the control plants. Corresponding starch concentrations increased 6. 6‐fold and 2. 9‐fold respectively. After days 5 to 6 the assimilation rates declined in the first trifoliate leaf of the plants showing deficiency, in comparison with the plants fully supplied with nutrients; respiration increased during darkness. The reduction in net assimilation rate was to a great extent reversible after resupply of magnesium.The reduction of magnesium concentration in the deficient plants was much more marked in the expanding leaves than in the mature primary leaves and roots. Sucrose and starch accumulation did not occur when the first trifoliate leaf was partially shaded, although magnesium concentration, as in the unshaded leaves, was reduced to 13% of that of the control plants. The consequences of magnesium deficiency in the expanding first trifoliate leaf are discussed in terms of the possibility of sink limitation.
Effects of ethephon and norbornadiene on sterol and glycoalkaloid biosynthesis in potato tuber discs
Authors: Bergenstråhle Annika , Tillberg Elisabeth , Jonsson Lisbeth 
Published: May 2006

The accumulation of glycoalkaloids that normally takes place in aerobically incubated potato (Solanum tuberosum L.) tuber discs has been found to be inhibited by the ethylene‐releasing substance ethephon. Using ethephon and the ethylene action inhibitor norborna‐2,5‐diene, the effect of ethylene on the synthesis of sterols and glycoalkaloids, which partly share their biosynthetic pathway, was investigated.Control discs showed incorporation of (2‐14C)mevalonic acid into free sterols, steryl esters, steryl glycosides and acylated steryl glycosides at 24 h, thereafter the radioactivity decreased in free sterols and steryl esters concomitant with the appearance of radioactivity in glycoalkaloids. Discs with ethephon additions contained more radioactivity in all sterol classes at all time‐points, but no glycoalkaloids were formed.The enzyme S‐adenosyl‐l‐methionine:sterol C24 methyltransferase (SMT, EC 2. 1. 1. 41), located at one presumed branching point in the sterol and glycoalkaloid pathway, was characterized and found to exhibit similar characteristics as in other plants, but a lower specific activity. The activity of SMT increased in ageing tuber discs and this increase was further stimulated by ethephon, but inhibited by norborna‐2,5‐diene. The activity of the glycoalkaloid‐specific enzyme UDP‐glucose:solanidine glucosyltransferase (EC 2. 4. 1) also increased after slicing, but here ethephon additions counteracted the induction. The activity of the sterol‐specific UDP‐glucose:sterol glucosyltransferase (EC 2. 4. 1) was unaffected by either tuber slicing or ethephon additions.The results indicate that ethylene stimulates sterol synthesis in wounded potato discs, and that the wound‐induction of SMT is regulated by ethylene.
Modulation of the blue light response of stomata of Commelina communis by CO2
Authors: Lascève Gérard , Gautier Hélène , Jappé Jocelyne , Vavasseur Alain 
Published: May 2006

Effects of CO2 on stomatal movements of Commelina communis L. were studied with plants, epidermal strips and guard cell protoplasts. With plants, the stomatal response induced by a blue light pulse was studied for different ambient CO2 concentration ranging from CO2‐deprived air to 100 Pa in darkness or under red light. It was observed that the blue light response could be obtained not only under a red light background but also in darkness and CO2‐free air, the two responses being quite similar.With epidermal strips, the effect of CO2 on ferricyanide reductase activity at the guard cell plasmalemma was studied by transmission electron microscopy. In the presence of ferric ions, reduced ferricyanide gives an electron dense precipitate of Prussian Blue. In darkness and air, no precipitate was observed. In darkness and CO2‐free air as well as under light and normal air, a precipitate was found along the plasmalemma of the guard cells, indicating a ferricyanide reductase activity. With guard cell protoplasts suspended in a medium either in equilibrium with air or in a CO2‐free medium the H+ extrusion induced by a blue light pulse added to a red light background was measured. A low CO2 content was obtained by adding photosynthetic algae to the suspension of guard cell protoplasts. In a CO2‐free medium the rate of H+ extrusion was enhanced.The results are discussed on the basis of a possible competition for reducing power between CO2 fixation and a putative blue light dependent redox chain located on the plasma membrane.
Transient changes in length and growth of wheat coleoptile segments following treatments with osmotica and auxin
Authors: Bleiss W. , Ehwald R. 
Published: May 2006

The dependence of elongation on the osmotic potential of the medium was investigated, using coleoptile segments (CS) of Triticim aestivum L. (cv. Hartri) and an optoelectronic device. The study aimed at separating the osmoelastic response from the irreversible growth response when an osmoticum (mannitol) was added, and to compare both processes in order to consider the possibility of growth‐induced reduction in turgor pressure.The prompt inhibition of elongation registered just after addition of 50 mM mannitol as well as the subsequent resumption of the original elongation rate could be quantitatively explained by the extent and the kinetics of the osmoelastic relaxation. An initial reduction in the irreversible elongation component by mild osmotic stress could not be demonstrated.Above a critical value, the irrevesible growth was insensitive to a further increase in water potential. The minimum turgor pressure required to drive steady growth was not far from zero in both the presence and absence of auxin.The rate (r) of osmotically caused shortening per unit change of water potential
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was determined from the kinetics of CS shortening induced by addition of mannitol at nearly isotonic concentration (300 mM). This parameter relates a fractional change in length to the difference in water potential between inside and outside, and was assumed to depend largely on the hydraulic resistance of the tissue and cuticle. It was found to be independent of IAA. The relatively low value of Γ suggests significant reduction of turgor at high growth rates. In accordance with this conclusion, the extent of osmoelastic shortening after a transfer to 300 mM mannitol (dependent on wall strain) was significantly decreased in the presence of IAA.Addition of 100 μM IAA to CS growing at a constant rate induced pronounced oscillations in the rate of elongation, which may be connected with the change in elastic cell wall strain. Whereas the steady state growth rate before the addition of IAA was the same in the presence and in the absence of 50 mM mannitol, the maximum growth rate found after addition of IAA was substantially reduced in the mannitol variant.
Foliar uptake of Cd by pea (Pisum sativum) and sugar beet (Beta vulgaris)
Authors: Greger Maria , Johansson Monica , Stihl Alvar , Hamza Karim 
Published: May 2006

Pea (Pisum sativum L. cv. Fenomen) and sugar beet (Beta vulgaris L. cv. Monohill) were cultivated in nutrient media without or with 10 μM CdCl2. Leaves of the same size and stage of development, detached or still attached to the intact plants, were submerged into redistilled water containing 1 to 250 μM CdCl2. The uptake experiments were run for 1 to 8 h at pH 3.6 and 5.1. Cuticular transpiration rate, density of leaf and density of stomata were also measured. Percentage of open stomata was studied at different pH.Foliar uptake of Cd into the leaf is evident since Cd is transported from the exposed part of the pea leaves, through the petioles and into the stipules, and since the Cd concentration of the leaves increases with time and external Cd concentration. The foliar uptake depends on the permeability of the cuticular membrane, which is increased by a high intrinsic Cd level, which in turn enhances the foliar uptake of Cd in sugar beet. Higher cuticular permeability in pea than in sugar beet is shown by a 2.5 times higher cuticular transpiration rate and a 4 times lower density of leaf for pea, which causes a 7 times higher foliar uptake in pea than in sugar beet. Low pH decreases the net uptake of Cd, probably by an exchange reaction in the cutin and pectin of the cuticular membrane. Stomata are not directly involved in the Cd uptake, and the differences in the sum total of stomatal aperture area per unit leaf area is not related to differences in foliar uptake of Cd. Percentage of open stomata, calculated as average of both sides of the leaves, was not affected by changes in pH: but especially at high pH. proportionally more stomata were open on the adaxial than on the abaxial side.
ABA promotion of ethylene production in anther culture of Brussels sprouts (Brassica oleracea var. gemmifera) and its relevance to embryogenesis
Authors: Biddington Norman L. , Robinson Helen T. , Lynn James R. 
Published: May 2006

Abscisic acid (ABA) inhibited embryogenesis in anther culture of Brussels sprouts. This was accompanied by enhanced ethylene production during the first half of the anther culture period followed by a reduction in ethylene during the latter half, when compared to anthers not treated with ABA. The enhancement of ethylene production by ABA 6 h and 48 h after the start of the culture period was counteracted by the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). Both AVG and the ethylene antagonist AgNO3 removed much of the ABA inhibition of embryogenesis, suggesting that at least part of the ABA effect on embryo production is mediated through increased ethylene biosynthesis.ABA promotion of ethylene production was reduced by high temperature: less ethylene evolved from ABA‐treated anthers following a 24 h treatment at 35°C than from ABA‐treated anthers incubated continuously at 25°C. A high temperature treatment such as this is invariably necessary for embryogenesis in Brussels sprouts anther culture.
Occurrence of hydroxylated jasmonic acids in leaflets of Solanum demissum plants grown under long‐ and short‐day conditions
Authors: Helder Hans , Miersch Otto , Vreugdenhil Dick , Sembdner Günther 
Published: May 2006

Under short‐day (SD) conditions both 11‐OH‐jasmonic acid (11‐OH‐JA) and a smaller quantity of 12‐OH‐JA occurred in leaflets of Solanum demissum Lindl. Plants which had formed tubers. This is the first time that 11‐OH‐JA has been detected as a native substance in higher plants. Under long‐day (LD) conditions no tubers were formed and none of these compounds were detectable. A positive correlation was found between the occurrence of 11‐OH‐JA and 12‐OH‐JA in leaflets of S. demissum and tuber formation, but a causal relation has yet to be proved. The (‐)‐JA content in leaflets was not significantly different under short and long days. Mild stress applied to detached SD and LD leaflets caused a rapid accumulation of JA in these leaflets. Upon this treatment an increase in the levels of hydroxylated JAs was detected in SD leaflets only.JA was a potent promotor of tuber formation in vitro in S. demissum explants. Lipoxygenase (LOX: EC 1.13.11.12) is involved in the biosynthesis of JA. Under SD conditions, application of salicylhydroxamic acid (SHAM), an inhibitor of LOX activity, to the roots did not prevent tuber formation in vivo. It is suggested that daylength controls the hydroxylation of JA. The enzyme(s), responsible for the hydroxylation of JA, would only be effective under SD conditions.
Expression and occurrence of uracil‐DNA glycosylase in higher plants
Authors: Bones Atle M. 
Published: May 2006

Uracil‐DNA glycosylase (UDG) is the first enzyme in the base excision repair pathway for removal of uracil in DNA. DNA repair capacity is likely to be a critical factor in mutagenesis and thereby in the capacity to prevent genetic damage and unwanted variation. We have studied expression of UDG in 9 higher plant species. The highest expression of UDG was measured in Solanum tuberosum. A comparison of 6 Solanum tuberosum cultivars showed that the specific activity ranged from 30 pmol mg1 protein min−1 in the cultivar Laila to 80 pmol mg−1 protein min−1 in the cultivar Ostara. Measurement of UDG in Begonia X cheimantha gave no indications of enzyme activity. The possible effects of no or low UDG activity is discussed.In vitro cultures of Solanum tuberosum and Thymus vulgaris were used to examine the effect of auxin and cytokinin on the UDG activity. Axillary shoots of Solanum tuberosum were cultured on medium including 20 variations in hormone concentration. Auxin (1‐naphtaleneacetic acid) increased the expression of UDG. Plants cultured on medium supplemented with 3 mg 1−1 1‐naphtaleneacetic acid showed a specific UDG activity which was approximately 3‐fold higher than the activity in controls. The cytokinin benzyladenine reduced the specific UDG activity at concentrations in the range 0.25–10 mg 1−1.In vitro cultured Saintpaulia ionantha was used to examine UDG activity during initiation, conditioning and multiplication cycles. In general, highest expression of UDG was measured in the conditioning cycle on hormone free medium. Measurement of UDG expression during single subculture periods, clearly showed that UDG expression may vary over one culture period. Expression of UDG was in general highest three weeks after transfer to fresh medium.Of different seedling organs from 0‐ to 15‐day‐old Brassica napus L., roots and hypocotyls showed the highest UDG activities. In cotyledons a very low and nearly constant specific activity was observed. In 12‐day‐old seedlings the activity in roots was approximately 20 times higher than the activity in cotyledons.
Carbohydrate content and glycosidase activities following cold hardening in two grass species
Authors: Tronsmo A. M. , Kobro G. , Morgenlie S. , Flengsrud R. 
Published: May 2006

The freezing resistance of the grass species Phleum pratense L. (timothy) and Phalaris arundinaces L. increases significantly after cold hardening. The content and composition of soluble carbohydrates were determined in the plants after short day treatment, cold hardening and dehardening. The amounts of mono‐, di‐ and trisaccharides were reduced during the short day treatment, increased during cold hardening and decreased again during dehardening. The total amounts of soluble carbohydrates (mono‐, di‐, tri‐ and polysaccharides) were the same in hardened and dehardened plants, indicating that during hardening soluble polysaccharides (fructose polymers, fructans) were converted to mono‐ and oligosaccharides. Sucrose increased most after hardening conditions and, in P. arundinacea, a significant increase in 1‐F‐fructosylsucrose (isokestose) was also observed.Invertase (β‐fructofuranosidase. EC 3.2.1.26) activity increased following cold hardening and decreased following dehardening, while the α‐galactosidase (EC 3.2.1.22) activity seemed to increase after dehardening. The glycosidases are probably involved in the mobilisation of polysaccharides during cold hardening.