bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the site of synthesis of chIcoroplastic enzymes of nitrogen metabolism by the use of heat‐treated 70S ribosomedeficient rye leaves
Authors: Feierabend Jüurgen
Published: April 2006

The activities of the enzymes nitrate reductase (EC 1.6.6.1), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (GOGAT; EC 1.4.7.1), glutamate‐oxaloacetate aminotransferase (EC 2.6.1.1), and glutamate dehydrogenase (EC 1.4.1.2) were compared in light‐grown green or etiolated leaves of rye seedlings (Secale cereale L. cv. Halo) raised at 22°C, and in the bleached 70S ribosome‐deficient leaves of rye seedlings grown at a non‐permissive high temperature of 32°C. Under normal permissive growth conditions the activities of most of the enzymes were higher in light‐grown, than in dark‐grown, leaves. All enzyme activities assayed were also observed in the heat‐treated 70S ribosome‐deficient leaves. Glutamine synthetase, glutamate synthase, and glutamate‐oxaloacetate aminotransferase occurred in purified ribosome‐deficient plastids separated on sucrose gradients. For glutamate‐oxaloacetate aminotransferase four multiple forms were separated by polyacrylamide gel electrophoresis from leaf extracts. The chloroplastic form of this enzyme was also present in 70S ribosome‐deficient leaves. It is concluded that the chloroplast‐localized enzymes nitrite reductase, glutamine synthetase, glutamate synthase and glutamate‐oxaloacetate aminotransferase, or their chloroplast‐specific isoenzyme forms, are synthesized on cytoplasmic 80S ribosomes.
Isolation and partial characterization of latex lectins from three species of the genus Euphorbia (Euphorbiaceae)
Authors: Nsimba‐Lubaki Makuta , Allen Anthony K. , Peumans Willy J.
Published: April 2006

Three N‐acetylgalactosamine‐specific lectins were isolated from the latices of Euphorbia calcina L., Euphorbia dalberi L. and Euphorbia sp. (an undetermined species) by affinity chromatography on fetuin‐agarose. They are all glycoproteins [about 12.5% (w/w) carbohydrate] of M, around 140 000 and appear to be tetrameric molecules composed of different subunits. All three lectins have similar amino acid (with high contents of asparagine/aspartic acid, giycine and leucine) and carbohydrate (with glucosamine, mannose.) fucose and xylose) compositions. In addition. they are closely related serologically.
Physiological response of cut rose flowers to cold storage
Authors: Faragher J. D. , Mayak S. , Tirosh T.
Published: April 2006

The effects of low temperature storage on the physiology of cut rose flowers (Rosa hybridaL. cv. Mercedes) were studied. Extension of cold storage or increase in temperature (from 3 to 8°C) was accompanied by shortening of vase life and advancement of petal senescence, as reflected in an advance in the timing of the rise in ethylene production and an increase in membrane permeability (ion leakage). Although storage at a relative humidity (RH) of 65% reduced petal water content by 20% in comparison with flowers stored at 95% RH, it did not shorten vase life. The progression of petal senescence was measured during storage at 3°C and during aging at 22°C. Both ethylene production rates and membrane microviscosity measured by fluorescence depolarization increased with time at 3°C and at 22°C, but more slowly at 3°C. At 3°C membrane permeability measured by ion leakage did not increase. Following cold storage the rate of ethylene production in the petals was increased by up to eight times the rate in unstored flowers. Silver thiosulphate extended the vase life of both stored and fresh flowers equally by 2 days, but did not increase the life of stored flowers to that of treated fresh flowers. It is concluded that the primary effect of cold storage on roses is to slow down senescence and that the continued slow senescence leads to shorter vase life. The possible occurrence of sequential processes during senescence and the effects of temperature on these processes is discussed.
Activity and distribution of nitrogen‐metabolism enzymes in the developing maize kernel
Authors: Hadži‐TaškovićŠukalović Vesna
Published: April 2006

The activities of glutamine synthetase (EC 6.3.1.2), glutamate dehydrogenase (EC 1.4.1.2), aspartate aminotransferase (EC 2.6.1.1), alanine aminotransferase (EC 2.6.1.2) and soluble protein content in the developing endosperm and embryo of normal (Oh‐43) and mutant (Oh‐4302) maize were investigated. Maize inbred lines were grown under field conditions and all plants were self‐pollinated. Ears for experiments were harvested over the period of 15 lo 45 days after pollination. After pollination kernel capacity for soluble protein synthesis is located mainly in the endosperm. This progressively decreases and about 40 days after pollination soluble protein synthesis is taken over by the embryo. Comparative data on the activity of the investigated enzymes in the embryo and endosperm indicate that the capacity for synthesis of glutamine and glutamate predominates in the embryo tissue, whereas transamination processes at the initial stages of the embryo development are less intensive than their counterparts in the endosperm. The roles of embryo and endosperm subsequently interchange. Biosynthetic processes of soluble precursors for protein synthesis in the embryo and endosperm of the developing kernel are mutually coordinated.
The increasing desiccation sensitivity of recalcitrant Avicennia marina seeds with storage time
Authors: Farrant Jill M. , Pammenter N. W. , Berjak Patricia
Published: April 2006

To test the hypothesis that desiccation sensitivity increases with storage time, recalcitrant seeds of Avicennia marina (Forssk.) Vierh. were dehydrated by soaking in polyethylene glycol solutions after inreasing periods of storage. Germination characteristics and the ultrastructure of root primorida were assessed before and after dehydration. Short‐term storage enhanced the apparent rate of germination, consistent with the hypothesis that these seeds commence germination in storage. Root primordia of stored seeds initially showed enhanced subcellular activity, including cell division and vacuolation. Increased storage time resulted in the onset and progression of deleterious changes.

Newly shed seeds and seeds stored up to the stage of cell division were comparatively resistant to desiccation. As storage time increased, subsequent dehydration caused increasing subcellular damange and consequent reduction in the rates of germination relative to non‐dehydrated controls. Ultrastructural results suggest that after the initiation of cell division of seeds in storage, there is a requirement for additional water for the germination process to continue. A model for the behaviour of recalcitrant seeds is proposed.
Effects of switches in nutrient levels during the life cycle of winter wheat
Authors: Erdei László , Jensén Paul , Bérczi Alajos , Bengtsson Bengt , Kylin Anders
Published: April 2006

The effects of switches between high and low nutrient supplies on growth and mineral nutrition of winter wheat (Triticum aestivum L. cv. Martonvásári‐8) were followed in four main developmental phases: tillering, shooting, heading and grain filling. Growth of the shoots was significantly affected by switches. Under low nutrient supply the life cycle was shortened. Root growth was only slightly affected by switches, but an early high nutrient supply followed by low nutrient supply gave an impetus for root development. In general, the growth data indicate that the nutrient status of the plants is determined by the nutrient level supplied during shooting. A high level of nutrients during shooting leads also to high vegetative growth, whereas the best grain yield was obtained by a high dose of nutrients during tillering followed by low nutrient conditions during the shooting stage and later. K+(86Rb) influx in the roots decreased with age. The potential for K+ (86Rb) influx was low in plants of high‐salt status, but it became high in response to switching to low supply at shooting, whereas later switches had no influence on this function in high‐salt plants. The highest K+(86Rb) influx was found in plants starting with high nutrient supply followed by low‐salt conditions; this plant group was outstanding also with respect to its high grain yield.
Enhancing effects of heat shock and gibberellic acid on the thermotolerance in etiolated Vigna radiata. I. Physiological aspects on thermotolerance
Authors: Chen Yih‐Ming , Kamisaka Seiichiro , Masuda Yoshio
Published: April 2006

The effect of heat shock on the thermotolerance of etiolated mung bean seedlings (Vigna radiata L. cv. Wilczek) and the effects of gibberellic acid (GA) were studied. The potentially lethal temperature of etiolated mung bean seedlings was 45°C. But, when seedlings were pretreated with a heat‐shock period at 40°C for 1 h before incubation at 45°C, they become thermotolerant and survived the 45°C treatment. The addition of actinomycin D or cycloheximide during the heat‐shock period decreased the subsequent thermotolerance of the seedlings. Depending upon the time of its application, GA appeared to have multiple effects: (1) when applied during the 40°C heat‐shock period, GA enhanced the heat‐shock effect; (2) when applied during the 45°C potentially lethal temperature period, GA enhanced the subsequent growth of hypocotyls. This suggests that GA makes the seedlings tolerant to the potentially lethal temperature; (3) when GA was applied during a following 25°C growth period to seedlings which had been exposed first to 40°C and then 45°C, it promoted growth, suggesting that GA enhanced the restoration of the seedlings from high temperature damage. The role of GA and heat shock in the acquisition of thermotolerance in etiolated mung bean seedlings are discussed.
Movement of paraquat in resistant and susceptible biotypes of Erigeron philadelphicus and E. canadensis
Authors: Tanaka Yoshiyuki , Chisaka Hideo , Saka Hitoshi
Published: April 2006

Paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium) resistant biotypes of Erigeron philadelphicus and E. canadensis, from fields where paraquat had been used for weed control, showed more than 100 times higher resistance than the susceptible biotype of both plants. Excised leaves of the susceptible biotypes wilted when supplied with more than 5 μM paraquatat at the cut ends, but those from the resistant biotypes did not wilt even at 500 μM. Autoradiographs indicated that (14CH3)‐paraquat taken up through the cut ends was rapidly distributed through the vascular system in leaves of the susceptible biotype, but was barely translocated in leaves of the resistant biotype. The amount of paraquat taken up during 48 h in the resistant biotype was 0.5% of that in the susceptible biotype in light. This difference in paraquat movement may be correlated with paraquat resistance in Erigeron.
Ca2+ effects on ethylene, carbon dioxide and 1‐aminocyclopropane‐1‐carboxylic acid synthase activity
Authors: Burns Jacqueline K. , Evensen Kathleen B.
Published: April 2006

The response of pericarp disks from ripening tomato (Lycopersicon esculentum Mill. cv. Traveler‘76) to CaCl2, additions was studied to determine the effect of Ca2+ on ethylene and CO2 production. Application of 5 mM CaCl2 resulted in a 2, 20, 33, 39, and 50% increase in ethylene production in disks obtained from preclimacteric minimum, climacteric rise, climacteric peak, one, and two days postclimacteric fruit, respectively. CaCl2 concentrations of 10 and 50 mM gave no additional stimulation of ethylene production; CO2 production at 5 mM CaCl2 was not different from controls, but is increased at 10 and 50mM CaCl2. CaCl2 also increased ethylene production in disks treated with 1‐aminocyclopropane‐1‐carboxylic acid (ACC) or aminoethoxy‐vinylglycine. Chloride salts of K+, Na+, Mg2+, Sr2+ and La3+ did not stimulate ethylene production. SrCl2 stimulated ethylene production to a lesser degree than CaCl2. Disks from potato (Solanum tuberosum L. cv. Katahdin) tubers produced greater quantities of ethylene and ACC when 5 mM CaCl2 was included in the incubation medium (K. B. Evensen, 1983. Physiol. Plant. 60:125–128). Ca2+‐treated disks had more than three times as much ACC synthase activity as control disks after 18 to 24 h incubation, when ethylene and ACC were maximal. The apparent Km for S‐adenosylmethionine was 13 μM at 29°C, pH 8.0 in extracts from both Ca2+‐treated and control disks. Inclusion of 1 to 50 mM CaCl2 in the assay medium did not significantly affect enzyme activity. ACC synthase extracted from control and Ca2+‐treated disks had a pH optimum of 8.5 and an apparent molecular weight of 72 kdalton, estimated by gel filtration. It is likely that the presence of Ca2+ in the buffer allows greater synthesis of ACC synthase as part of the wound‐healing response in potato, while in tomato the predominant effect is on membrane stabilization.
Localization of NADPH‐protochlorophyllide oxidoreductase in dark‐grown wheat (Triticum aestivum) by immuno‐electron microscopy before and after transformation of the prolamellar bodies
Authors: Ryberg Margareta , Dehesh Katayoon
Published: April 2006

The localization of NADPH‐protochlorophyllide oxidoreductase (PChlide reductase, EC 1.6.99.–) in dark‐grown and in irradiated dark‐grown leaves of wheat (Triticum aestivum L. cv. Walde) was investigated by subjecting thin sections of Lowicryl K4M‐embedded leaf pieces to a monospecific antiserum raised against PChlide reductase followed by protein A‐gold. A well‐preserved antigenicity of the tissue was achieved by polymerizing the resin under UV‐light at low temperature. In dark‐grown leaves PChlide reductase was found in prolamellar bodies only. In leaves irradiated for 30 min with white light PChlide reductase was found not only in the transformed prolamellar bodies but also to a large extent in connection with the prothylakoids. The localization of PChlide reductase is discussed in relation to fluorescence emission spectra of the dark‐grown and greening leaves. We conclude that the light‐dependent transformation of protochlorophyllide to chlorophyllide initiates a translocation of PChlide reductase from the prolamellar bodies to the prothylakoids.
Water pathways in wheat leaves. III. The passage of the mestome sheath and the function of the suberised lamellae
Authors: Canny M. J.
Published: April 2006

The fluorochrome sulphorhodamine G, when present in the transpiration stream in wheat leaves, passes rapidly out of the veins and produces fluorescence in the mesophyll and epidermal cell walls. The path of movement of the dye out of the tracherary elements and across the mestome sheath to the parenchyma sheath cells was followed by rapid freezing, freeze‐subsitution, dry embedding in resin, sectioning and epifluorescence microscopy. The sulphorhodamine solution was visible in tracheary elements, and, where it had passed out of the tracheary elements, strongly fluorescent in some of the cell walls. The patterns of wall fluorescence are used to chart the movements of water from the xylem through some of the radial walls of mestome sheath cells near the xylem to the free space of the mesophyll. The suberised lamellae of the mestome sheath cells must form an incomplete barrier near the xylem to permit passage of the dye. A hypothesis is formulated that the function of the suberised lamellae is to keep separate the oppositely directed fluxes of water and assimilates through the sheath. It is further proposed that the function of pits in living cells is a similar insulation of the symplastic traffic from the wayward waters of the apoplast.
Patterns of mitochondrial development in reserve tissues of germinated seeds: A survey
Authors: Morohashi Yukio
Published: April 2006

Patterns of mitochondrial development in reserve tissues of several species of seeds were examined during 3 to 4 days after the start of imbibition. In starch‐storing seeds (cowpea, kidney bean, Egyptian kidney bean, mung bean, black gram and soybean), mitochondrial activities (state 3 respiration rate, respiratory control ratio) increased during the first 1 to 2 days after imbibition and leveled off thereafter. The initial increase in the activities was little affected by cycloheximide and chloramphenicol. Activities of mitochondrial enzymes (succinate dehydrogenase, EC 1.3.99.1; NAD+‐malate dehydrogenase, EC 1.1.1.37; cytochrome oxidase, EC 1.9.3.1) did not change much during the experimental period. This suggests that mitochondrial development in starch‐storing seeds is primarily due to improvement of pre‐existing mitochondria. On the other hand, in the lipid‐storing seeds examined (pumpkin, cucumber, okra and castor bean), the rate of mitochondrial respiration and activities of mitochondrial enzymes continued to increase markedly during the experimental period. These increases were strongly inhibited by cycloheximide and chloramphenicol. This indicates that active de novo synthesis of mitochondrial proteins is primarily responsible for the development of organelle activities. The possibility was suggested that the patterns of mitochondrial development in reserve tissues of imbibed seeds might be determined by the kinds of reserve substances.
The effect of abscisic acid on epidermal cells: protoplast swelling and ATPase activity
Authors: Itai Chanan , Roth‐Bejerano Nurit
Published: April 2006

Isolated epidermal protoplasts of Commelina communis L. increase in volume in the presence of KCl. Since this swelling is an osmotic phenomenon it reflects K+ influx. ATP slightly decreased the volume of the protoplasts, pointing towards the possibility that K+ uptake is passive. On the other hand abscisic acid (ABA) and sodium orthovanadate increased the swelling, and their effect was reversed by ATP. This may support the suggestion that ABA inhibits the active and ATPase‐mediated relase of K+ from epidermal cells. Mg2+‐dependent, K+‐stimulated ATPase activity was found in the microsomal fraction from epidermal cells. This activity was vandadate sensitive. ABA increased the basal activity in the presence of Mg2+ but inhibited the K+ stimulation.
Photocontrol of in vitro bud differentiation in Saintpaulia ionantha leaves and Lycopersicon esculentum cotyledons
Authors: Lercari Bartolomeo , Tognoni Franco , Anselmo Gianni , Chapel Daniele
Published: April 2006

The regeneration of buds from leaves of Saintpaulia ionantha Wendl cv. Sona and from cotyledons of Lycopersicon esculentum Mill. cv. UC 105 was studied in response to continuous light and daily light pulses. The regeneration of buds from cotyledons of Lycopersicon esculentum is high under continuous red and white light. Trie effect of light may be related to phytochrome. In Saintpaulia ionantha blue light appears to be very effective. The experimental results suggest that the blue light effects involve both a blue light absorbing photoreceptor and phytochrome
Characterization of prolamellar bodies, from dark‐grown seedlings of Scots pine, containing light‐ and NADPH‐dependent protochlorophyllide oxidoreductase
Authors: Selstam Eva , Widell Anna
Published: April 2006

Cotyledons of conifers have a light‐independent pathway for chlorophyll biosynthesis. To investigate whether the prolamellar body of Scots pine (Pinus sylveslris L.) is similar to the better known prolamellar body of wheat, etioplast membrane fractions were isolated from cotyledons of dark‐grown Scots pine. Dark‐grown cotyledons contained both chlorophyll and protochlorophyllide, 158 and 10 nmol (g fresh weight)’respectively, and had a chlorophyll a to b ratio of 4.2. The content of glyco‐ and phospholipids was 7.1 μmol (g fresh weight)1. About 40 mol % of these lipids were the specific plastid lipids – monogalactosyl diacylglycerol. digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol in the relative amounts 50, 35 and 7 mol %. The mol ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol was 1.7. Low temperature fluorescence emission spectra of intact cotyledons and homogenate showed maxima at 633, 657, 686, 696 nm and a broad peak at 725–735 nm. The maxima at 633 and 657 nm represented different forms of protochlorophyllide and the other emission maxima represented chlorophyll protein complexes. The 657 nm form of protochlorophyllide was phototransformable both in vivo and in the isolated membranes. The phototransformable protochlorophyllide was substantially enriched in the prolamellar body fraction.

The specific activity of light dependent protochlorophyllide oxidoreductase in the prolamellar body fraction was found to be 2 nmol chlorophyllide formed [(mg protein)−1 min−1]. The molecular weight of the enzyme polypeptide was determined as 38 000 dalton with sodium dodecylsulphate‐polyacrylamide gel electrophoresis.
Protection of bean seedlings against heat and chilling injury by triadimefon
Authors: Asare‐Boamah N. K. , Fletcher R. A.
Published: April 2006

Triadimefon [1‐(4‐chlorophenoxy)‐3,3‐dimethyl‐l‐(l,2,4‐triazol‐l‐yl)‐2‐butanone] is a triazoie fungicide which protects bean (Phaseolus vulgaris L. cv. Spring Green) plants from heat and chilling injury. When the plants were exposed to heat shock by dipping the shoots in hot (50°C) distilled water for 2 min or exposing the plants to cold (1°C) for 8 h the primary leaves showed visual symptoms of injury 2 days after treatment and thereafter there was a progressive decline in chlorophyll and an increase in electrolyte leakage indicative of a loss of membrane integrity. There was a loss of metabolic (respiratory) activity in the root meristems when the roots were dipped in hot (48°C) water. All these symptoms of heat and chilling injury in the controls were either delayed or prevented by root application of triadimefon.
Localization and partial characterization of the extracellular proteins centrifuged from pea internodes
Authors: Morrow David L. , Jones Russell L.
Published: April 2006

The proteins removed from the extracellular space of dark‐grown pea (Pisum sativum L. cv. Alaska) internode sections by centrifugation were studied. A large number of proteins were resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis. These proteins ranged in size from 10 to 150 kdalton and their removal from the cell wall was greatly facilitated by the presence of salts of divalent and trivalent cations in the infiltration medium. Pulse‐labelling experiments with [35S)‐methionine showed that many of the proteins extracted from the cell wall incorporated radioactivity and that treatment with indoleacetic acid (IAA) altered the pattern of radiolabel incorporation. One of the proteins centrifuged from pea internode sections possessed per‐oxidase (EC 1.11.1.7) activity. The activity of this peroxidase increased less in auxin‐treated internode segments than in untreated controls. Antibodies were raised to the total protein fraction extracted by centrifugation and used to localize antigens on protein blots. Most of the proteins centrifuged from pea internode sections were stained by a dye coupled to the cell wall antiserum. Light microscopic immunohistochemical studies showed that the proteins centrifuged from dark‐grown pea internodes were localized almost exclusively in the cell wall and intercellular spaces of pea internode tissue. Light microscopic immunohistochemistry also showed that antibodies to extracted proteins penetrate into the apoplast of abraded pea internode segments and split pea stems. These antibodies did not influence growth of IAA‐treated or control tissue.
Potassium utilization and fluxes in wild salt‐tolerant relatives of the cultivated tomato
Authors: Taleisnik‐Gertel Edit , Tal Moshe
Published: April 2006

The growth of the wild tomato species Lycopersicon peruvianum (L.) Mill, and L. pennellii (Correll) D'Arcy, was compared with that of the cultivated tomato, L. esculentum Mill. cv. VE 234, under conditions of reduced K+ supply. Growth was impaired less in the wild than in the cultivated species. The higher efficiency of K+ utilization in the wild species was not associated with more efficient JC uptake from the medium. The rate of K+ uptake by whole plants was similar in the three species, but the rate of uptake by detached root tips was lower in the wild species. The permeability of the plasma membrane to K+ was apparently similar in root tips of the three species, but the tonoplast permeability was much lower in the wild than in the cultivated species.
Localization of ornithine decarboxylase and changes in polyamine content in root meristems of Zea mays
Authors: Schwartz M. , Altman A. , Cohen Y. , Arzee T.
Published: April 2006

Polyamine content and the activity of arginine decarboxylase (EC 4.1.1.19) and ornithine decarboxylase (EC 4.1.1.17) were studied with respect to meristematic activity in primary roots and in developing lateral roots of Zea mays L.(cv. Neve Ya'ar 170) seedlings. Comparative localization of active ornithine decarboxylase and of meristematic activity were determined by labelling roots either with α‐[5‐14C]‐difluoromethyl ornithine or with [3H]‐thymidine, respectively.

Lateral roots were formed during the 72 h post‐decapitation period, accompanied by an initial decline in putrescine content and by a significant increase in spennidine con‐tent at 48–72 h. High levels of spermidine and lower levels of putrescine were found in the primary root apex as well. A marked increase in ornithine and arginine decarboxylase activity, as measured by 14CO2 release, was found during the 72 h post‐decapitation period of lateral root development. This increase in ornithine decarboxylase activity was confirmed also by a parallel rise in the incorporation of α‐[5‐14C]‐difluoromethyl ornithine into trichloroacetic acid‐insoluble fractions. Microautoradiographs of longitudinal and cross sections of roots, labelled with α‐[5‐14C]‐difluoromethyl ornithine, showed that ornithine decarboxylase is localized mainly in the meristematic zones, as evidenced by [3H]‐thymidine incorporation. A close correlation between meristematic activity and polyamines was demonstrated in situ, suggesting that polyamine content and biosynthesis may have a role in meristematic activity in corn roots.
Electromanipulation of plant protoplasts
Authors: Zachrisson Anders , Bornman Chris H.
Published: April 2006

The current status of electromanipulation, that is, electrofusion and electroporation, of plant protoplasts is reviewed. Parameters for electromanipulation as well as their practical implications are discussed. Some comparisons with the use of polyethylene glycol are made and the advantages of electromanipulation are considered.
Stomatal closure by ultraviolet radiation
Authors: Negash Legesse , Björn Lars Olof
Published: April 2006

The effect of ultraviolet radiation (UV) (255–325 nm) on stomatal closure was investigated on tef [Eragrostis tef (Zucc) Trotter] in the presence of white light (ca 50 ·mol m−2 s−1). The action spectrum showed that UV (ca 2 ·mol m−2 s−1, half band width about 10 nm) of 285 nm or shorter wavelengths was very efficient in causing stomatal closure. The effectiveness decreased sharply towards longer wavelengths. Radiation of 313 nm or longer wavelengths was practically without effect. Increasing UV intensity increased stomatal resistance. When stronger white light (5 to 9 times stronger than the one used during irradiation) was administered, stomates re‐opened rapidly irrespective of whether the UV was on or off, although a subsequent gradual closing tendency was observed when the UV was on.
Inhibition of IAA‐induced cell elongation in Avena coleoptile segments by galactose: Its effect on UDP‐glucose formation
Authors: Inouhe Masahiro , Yamamoto Ryoichi , Masuda Yoshio
Published: April 2006

The effect of exogenously applied galactose on the cell wall polysaccharide synthesis and UDP‐sugar levels in oat (Avena sativa L. cv. Victory I) coleoptile segments was studied to clarify the mechanism of inhibition of IAA‐induced cell elongation by galactose, and the following results were obtained: (1) The inhibition of IAA‐induced cell elongation by galactose became apparent after a 2 h‐lag, while the lag was shortened to 1 h when galactose was added to the segments after more than 1 h of IAA application. (2) Galactose inhibited the [14C]‐glucose incorporation into cellulosic and non‐cellulosic fractions of the cell wall and the increase in net polysaccharide content in the fractions during long‐term incubation. (3) The dominant sugar nucleotide in oat coleoptiles was UDP‐glucose (2.1 nmol segment−1). Galactose application caused a remarkable decrease in the UDP‐glucose level, accompanying a strong accumulation of galactose‐1‐phosphate and UDP‐galactose. (4) Galactose‐1‐phosphate competitively inhibited the UTP: a‐d‐glucose‐1‐phosphate uridylyltransferase (EC 2.7.7.9) activity of the crude enzyme preparation from oat coleoptiles. From these results we conclude that galactose inhibits the IAA‐induced cell elongation by inhibiting the formation of UDP‐glucose, which is a key intermediate of cell wall polysaccharide synthesis.
Adaptation of the tetrazolium method for testing the seed viability, and scanning electron microscopy study of some Western European orchids
Authors: Van Waes J. M. , Debergh P. C.
Published: April 2006

A modified tetrazolium method was formulated for use with seeds of Western European orchids. The sequence of treatments which gave the highest percentage of coloured (i.e. viable) embryos was: (1) pretreatment in a solution of 5% (w/v) Ca(OCl)2+ 1% (v/v) Tween‐80, (2) soaking for 1 day in sterile water, (3) the classical tetrazolium test. The optimal duration of the pretreatment in Ca(OCl)2+ Tween‐80 depends upon the species, and to investigate the effect a scanning electron microscopy study was performed on the testa of 3 species. For a given species, the optimal pretreatment period was not affected by the year of harvest or the source of the seed lots.
Changes in auxin protectors and IAA oxidases during the rooting of chestnut shoots in vitro
Authors: Mato M. C. , Vieitez A. M.
Published: April 2006

Auxin protectors and IAA oxidase activity were comparatively analyzed in the upper and the lower parts of shoots of chestnut (Castanea sativa Mill.) cultivated in vitro with indolebutyric acid (IBA) pretreatment. Rhizogenesis of the shoots is accompanied by an increase in auxin protectors in the lower parts and by a decrease of these protectors in the upper parts. Besides, the IAA oxidase activity declines in the basal parts during the rooting process while it increases in the upper ones. These biochemical events would enhance the IAA level in the rooting region of the shoots. In untreated, non‐rooted cuttings, the IAA oxidase activity remains low in the upper parts and high in the basal parts of the shoots. The results thus indicate that the IBA treatment may control the endogenous auxin level of the cuttings, either through a direct regulation of the IAA oxidase system or more indirectly through the transport of auxin protectors.
Kinetic and proteolytic identification of heat‐induced conformational changes in the urea herbicide binding site of isolated Phaseolus vulgaris chloroplast thylakoids
Authors: Wiest Steven C.
Published: April 2006

Kinetic parameters of 3‐(3, 4‐dichlorophenyl)‐1, 1‐dimethyl urea (DCMU)‐induced inhibition of electron transport in chloroplast thylakoids isolated from Phaseolus vulgaris L. cv. Oregon 1604 were determined from analysis of a convergent, parallel electrical circuit. Through this analogue, the apparent affinity of the purported binding site for DCMU (K1) and the relative amount of DCMU‐insensitive electron transport (vmax1/vo) were obtained using a reiterative non‐linear least squares curve‐fitting procedure. Exposure of thylakoids to heat caused a gradual increase in K1 (or decrease in the affinity of the thylakoid for DCMU) with an apparent activation energy of 134 kJ mol−1. Tryptic susceptibility of a protein region regulating K1 also decreased gradually with exposure to 45°C, suggesting that the heat‐induced increase in K1 might be due to a protein conformational change. On the other hand, thylakoid exposure to 45°C resulted in a rapid (<5 min) irreversible increase in vmaxI/vo, which was also the apparent result of a conformational change in a region of the protein which regulates this function. These results are suggestive of the existence of differential thermal sensitivities of proteins within the thylakoids and, perhaps, of different regions within a single membrane protein.
Daily changes in uptake, reduction and storage of nitrate in spinach grown at low light intensity
Authors: Steingröver Eveliene , Ratering Pieter , Siesling Johan
Published: April 2006

Under poor light conditions, as normally used during winter production of greenhouse vegetables, the nitrate concentration in the shoot of spinach (Spinacia oleraceaL. cv. Vroeg Reuzenblad) showed a diurnal rhythm. This rhythm was mainly caused by a decrease during the day, followed by an increase during the night in the leaf blade nitrate concentration. Nitrate was mainly located in the vacuoles of the leaf blades. A strong correlation was found between net uptake of nitrate by the roots and the nitrate concentration in the leaf blade vacuoles. The nitrate concentration in the leaf blades increased during the initial hours of the night. This increase was caused by a marked increase in the net uptake rate of nitrate by the roots during the first hours of the dark period. During the second part of the night both net uptake rate of nitrate by the roots and the vacuolar nitrate concentration in the leaf blades remained constant.

We conclude that nitrate is taken up for osmotic purposes when light conditions are poor because of a lack of organic solutes. During the night, nitrate influx into the vacuole is needed for replacement of organic solutes, which are metabolized during the night, and possibly also for leaf elongation growth. During the day, vacuolar nitrate may be exchanged for newly synthesized organic solutes and be metabolized in the cytoplasm. A strong diurnal rhythm in nitrate reductase (NR; EC 1.6.6.1.) activity was absent, due to the poor light conditions, and in vitro NR activity was not correlated with nitrate flux from the roots. In vivo NR activity also lacked a strong diurnal rhythm, but it was calculated that in situ nitrate reduction was much lower during the night, so that the major nitrate assimilation took place during the day.
Compartmental analysis of Rb+ efflux from roots of intact high‐salt barley plants
Authors: Klemedtsson Åsa Kasimir , Pettersson Sune
Published: April 2006

The validity of compartmental analysis of Rb+ efflux from roots of intact high‐salt barley plants (Hordeum vulgare L. cv. Salve) was examined. 86Rb+ was used as a tracer. Rb+ (1 mM) was included together with 3 mM K+ in the growth medium, and steady‐state conditions were assumed to prevail during the experiment. Three phases of efflux were revealed with half‐times of 23 min, 109 min and 12 h, respectively; and the time span of the experiment had to be at least 20 h to make determination of the slow phase possible. We cannot state what compartments in the root the 3 different slopes represent. A comparison of slopes was made between the plots of In efflux vs time and In content vs time. In spite of correction for tracer transport from the roots to the shoot, the slopes for the slow phase did not agree unless up to 85% of the root content of Rb+ is assumed not to participate in efflux.
Xylem cavitation caused by drought and freezing stress in four co‐occurring Juniperus species
Authors: Willson Cynthia J. , Jackson Robert B.
Published: April 2006

Previous studies indicate that conifers are vulnerable to cavitation induced by drought but in many cases, not by freezing. Rarely have vulnerability to drought and freezing stress been studied together, even though both influence plant physiology and the abundance and distribution of plants in many regions of the world. We studied vulnerability to drought‐ and freezing‐induced cavitation, along with wood density, conduit reinforcement, tracheid diameter, and hydraulic conductivity, in four Juniperus species that typically occupy different habitats, but uniquely co‐occur at the same site in Arizona, AZ. We combined drought with a freeze‐thaw cycle to create freezing‐induced vulnerability curves. All four species demonstrated greater vulnerability to drought + freezing‐ than to drought‐induced cavitation alone (P < 0.0001). Mean tracheid diameter was correlated with vulnerability to drought + freezing‐induced cavitation (r = 0.512, P = 0.01). The vulnerability to cavitation of each species followed expected rankings based on relative moisture within each species' natural distribution. Species with naturally drier distributions showed greater resistance to both drought‐ and drought + freezing‐induced cavitation. Even conifer species with relatively small tracheid diameters can experience xylem embolism after a single freeze‐thaw cycle when under drought stress.
Comparison of four methods for measuring osmotic potential of tree leaves
Authors: Callister Andrew N. , Arndt Stefan K. , Adams Mark A.
Published: April 2006

Osmotic potential (π) of tree leaves is usually determined by pressure‐volume (PV) analysis, which is too time consuming for large‐scale assessments such as ecological surveys and genetic screening. We investigated methods for rapid measurement of π in sclerophyllous species. The osmotic potential of expressed sap (ES), freeze‐thaw leaf discs and hot water extracts – measured using a variety of techniques – were compared with PV analysis using sclerophyllous species; Eucalyptus globulus Labill., E. camaldulensis Dehnh., E. cladocalyx F. Muell. and non‐sclerophyllous species; Populus nigra L and Alnus jorullensis H.B.K. All methods were sensitive to changes in π and produced results that were unequal but well correlated (r2 0.82–0.90). The proportion of leaf water extracted in ES was reduced by low water content and sclerophylly without affecting method accuracy. PV analysis provided a poor correction for apoplastic dilution of ES. Results of ES osmometry and PV analysis were comparable, and osmometry of ES is proposed as a suitable method for large‐scale investigations of leaf π.
Ethylene and carbon dioxide production by developing strawberries show a correlative pattern that is indicative of ripening climacteric fruit
Authors: Iannetta Pietro P. M. , Laarhoven Luc‐Jan , Medina‐Escobar Nieves , James Euan K. , McManus Michael T. , Davies Howard V. , Harren Frans J. M.
Published: April 2006

Laser photoacoustic spectroscopy continuously quantified the ethylene (C2H4) produced by strawberry flowers and fruits developing in planta. C2H4 was first detected as flower buds opened and exhibited diurnal oscillations (to approximately 200 pl flower−1 h−1) before petal abscission. Exogenous application of silver thiosulphate (STS) to detached flowers inhibited petal abscission and flower senescence. In fruit, C2H4 production was maintained at a ‘low level’ (10–60 pl fruit−1 h−1) until fruit expanded when levels increased in a diurnal pattern (to 200 pl fruit−1 h−1). After expansion, C2H4 production declined to a low level until fruit attained the red‐ripe stage for at least 24 h. After this time, C2H4 levels increased linearly (no diurnal fluctuation) to approximately 1 nL fruit−1 h−1. Twenty‐four hours after the re‐initiation of C2H4 production by red fruit, CO2 levels increased approximately three‐fold, indicative of a respiratory climacteric. STS applied to fruits developing in planta and dissected fruit parts ex situ established that C2H4 production is regulated by negative feedback until fruits had expanded. The C2H4 produced by red‐ripe fruit was regulated by positive feedback. Anti‐1‐amino‐cyclopropane‐1‐carboxylic acid oxidase IgG localization identified immunoreactive antigens of 40 and 30 kDa (Mr) within the fruit achenes of expanding and red‐ripe fruit. Analysis of dissected fruit showed that seed C2H4 accounts for 50% the C2H4 that is detectable from ripe fruit.
Water relations of phyllodinous and non‐phyllodinous Acacias, with particular reference to osmotic adjustment
Authors: Warwick Nigel W. M. , Thukten
Published: April 2006

An investigation was made into the effects of long‐ and short‐term water stress on the growth and water relations of species of Acacia belonging to four major sections of the subgenus Phyllodineae; the bipinnate‐leaved Botrycephalae and the phyllodinous Juliflorae, Phyllodineae and Plurinerves. The germplasm was collected from sites within a narrow rainfall band [700–800 mm mean annual rainfall (m.a.r.)]. Shoot and root mass were significantly decreased in three of the four sections by water stress. The exception was the Juliflorae that showed a conservative growth strategy. A high root/shoot ratio is associated with tolerance to arid or semiarid environments, however, the highest root/shoot ratio was found for the temperate Botrycephalae. Measurements were made of the capacity for active and partial osmoregulation. All sections showed a biphasic response to drought stress for natural logarithm plots of relative water content (RWC) vs. osmotic potential in one or both experiments. This pattern of response has previously only been reported in a few plant species. Osmotic adjustment (OA) ranged from 1.6 MPa for the Botrycephalae to 3.4 MPa for Juliflorae at RWC of 60%. Active osmoregulation in the second phase was lower for the Botrycephalae and Phyllodineae than for the Juliflorae and Plurinerves. Although the germplasm was collected within a narrow and relatively high m.a.r. band, the sections with arid and semiarid relatives (Juliflorae and Plurinerves) still retained a higher degree of xeromorphic character and drought tolerance as determined by the growth responses and the higher capacity for OA.
Oxidative stress, phospholipid loss and lipid hydrolysis during drying and storage of intermediate seeds
Authors: Dussert Stéphane , Davey Mark. W. , Laffargue Andréina , Doulbeau Sylvie , Swennen Rony , Etienne Hervé
Published: April 2006

The biochemical and physiological basis of intermediate seed storage behaviour was examined by investigating the effects of equilibrium drying under relative humidities (RHs) of 9–81% and of storage at 20 or 5°C on coffee seed viability and antioxidant, lipid and sugar status. Slow drying induced a significant decrease in the concentrations of the pools of two major antioxidants, glutathione and ascorbate, and an increase in the free fatty acid (FFA) content of seeds, independent of the RH employed. Seeds stored at 81% RH and 20°C lost their viability very rapidly and showed an extensive loss and oxidation of antioxidants, an accumulation of FFA and a selective loss of phospholipids, in particular phosphatidylethanolamine (PE). Interestingly, the changes in PE content were not due to fatty acid de‐esterification and the increase in FFA levels resulted from neutral lipid hydrolysis. Decreasing the storage temperature to 5°C considerably slowed both the loss of seed viability and the level of oxidative stress as well as the rates of lipid hydrolysis. No decline in seed viability was observed under storage conditions of 45% RH/20°C. After 1 year under 45% RH/5°C, the loss of seed viability was found to be due to imbibitional damage and could be circumvented by pre‐humidifying or pre‐heating seeds before sowing.
Indole‐3‐acetic acid attenuates the fungal lesions in infected potato tubers
Authors: Terrile María C. , Olivieri Florencia P. , Bottini Rubén , Casalongué Claudia A.
Published: April 2006

In this report, we demonstrated that potato tubers pre‐treated with 100 µM of indole‐3‐acetic acid (IAA) and then inoculated with Fusarium solani f. sp. eumartii (F. eumartii) showed a decrease in the fungal lesion compared with non‐IAA pre‐treated and inoculated tubers. Consequently, we tested the addition of different concentrations of IAA on the fungal growth and on the proteolytic activity when the fungus was grown in liquid culture medium. Fungal growth did not change under different phytohormone concentrations, but the activity of Fusarium extracellular serine protease (FESP) clearly decreased. The inhibition of FESP activity by IAA was dose dependent. Moreover, FESP as well as others extracellular pectinolytic activities detected in IAA pre‐treated and inoculated tubers decreased compared with controls. In addition, the ability of IAA production by F. eumartii was tested, and the role of IAA on potato–F. eumartii interaction is discussed.
cDNA array analysis of stress‐induced gene expression in barley androgenesis
Authors: Maraschin Simone de F. , Caspers Martien , Potokina Elena , Wülfert Florian , Graner Andreas , Spaink Herman P. , Wang Mei
Published: April 2006

Different aspects of androgenesis induction have been studied in detail, but little is known about the molecular mechanisms associated with this developmental switch. We have employed macroarrays containing 1421 expressed sequence tags covering the early stages of barley zygotic embryogenesis to compare the gene expression profiles of stress‐induced androgenic microspores with those of uninucleate microspores as they progressed into binucleate stage during pollen development. Principal component analysis defined distinct sets of gene expression profiles that were associated with androgenesis induction and pollen development. During pollen development, uninucleate microspores were characterized by the expression of cell division‐related genes and transcripts involved in lipid biosynthesis. Progress into binucleate stage resulted in the significant increase in the level of transcripts associated with starch biosynthesis and energy production. These transcripts were downregulated in androgenic microspores. These results indicate that stress blocks the expression of pollen‐related genes. The induction of androgenesis by stress was marked by the upregulation of transcripts involved in sugar and starch hydrolysis, proteolysis, stress response, inhibition of programmed cell death, and signaling. Further expression analysis revealed that the induction of genes encoding alcohol dehydrogenase 3, metalloprotease FtsH, cysteine protease 1 precursor, phytepsin precursor (aspartic protease), and a 26S proteasome regulatory subunit was associated with the androgenic potential of microspores, whereas the induction of transcripts involved in signaling and cytoprotection was associated with stress responses. Taken together, these expression profiles represent ‘bio‐markers’ associated with the androgenic switch in microspores, providing a substantial contribution toward understanding the molecular events underlying stress‐induced androgenesis.
Screening a Wheat Collection for Leaf Position at Different Stages of Growth
Authors: Borojević S. , Denćić S.
Published: April 2006

A collection of hexaploid ‐wheat consisting of 1400 entries from 36 countries was screened for leaf position at four stages of growth over two years. At the shooting stage, more than 80 % of the entries showed the curved position of the flag and the second leaf, about 15 % the erect position, while the horizontal position did not occur. At the heading stage more than 10 % of the genotypes with curved and some with erect position assumed horizontal position. At the milk stage, half of the genotypes with the erect position in earlier stages of growth assumed horizontal and even pendulous position; the majority of genotypes had curved position of leaves. At the dough stage, only about 2 % of the genotypes maintained erect flag leaf position, while 45 % had curved and about 45 % pendulous position of leaves.

When an erect leaf assumes horizontal position, the lamina is completely straight without any curving, which is different from genotypes classified as having horizontal position at heading and milk stage. The position of the second leaf, in general, followed the pattern of the flag leaf. Through the stages of growth the curved position was more stable than either erect or horizontal positions. Leaves were more erect and stable in position under conditions with lower rainfall and higher temperatures (1983) than in the rainy year with lower temperatures (1984). Most of the high‐yielding cultivars with short straw had a curved position, which is probably the consequence of unintended selection to fit a dense canopy.