bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative stress and antioxidant content in Chlorella vulgaris after exposure to ultraviolet‐B radiation
Authors: Malanga Gabriela , Puntarulo Susana
Published: May 2006

Growth of Chlorella vulgaris was measured in cultures irradiated with 0, 0.8, 2.0 and 4.4 kJ m2 UV‐B. Growth expressed as chlorophyll content, declined significantly with increased UV‐B dose. Ultraviolet‐B irradiated cultures in log phase of growth showed a 284% increase in oxygen radical generation and a 145% increase in lipid peroxidation compared with unirradiated cultures, whereas cultures in the stationary growth phase showed no significant changes in these parameters. The activities of superoxide dismutase and catalase increased by 40 and 500%, respectively, after exposure to a UV‐B dose of 4.4 kJ m−2. Contents of the lipophilic antioxidants α‐tocopherol and β‐carotene increased by 180 and 63 amol cell−1 respectively, between log and stationary phases in unirradiated cultures; but in UV‐B‐irradiated cultures these increases were significantly depressed. Photoreducing capacities of chloroplasts were decreased following UV‐B irradiation of both isolated chloroplasts and those isolated from irradiated algae. Cells exposed to UV‐B exhibited increased size and starch accumulation. These results suggest that oxidative stress conditions related to UV‐B exposure trigger an antioxidant response that includes an increase in the activity of the antioxidant enzymes (superoxide dismutase and catalase).
Coordination of photosynthetic and respiratory metabolism in Chlorella vulgaris UAM 101 in the light
Authors: Villarejo Arsenio , Orús María Isabel , Martínez Flor
Published: May 2006

In Chlorella vulgaris UAM 101, the presence of glucose altered the photosynthetic and respiratory metabolism in the light. When glucose was added to the growth medium, an increase in the cellular level of enzymes involved in glucose oxidation, namely glucose‐6‐P dehydrogenase (EC 1.1.1.49) and NAD+‐glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.12), was observed. Glucose also enhanced respiratory O2 consumption. In addition, CO2 released by glucose oxidation was refixed in photosynthesis. The presence of glucose also affected photosynthesis. Phosphoribulokinase (EC 2.7.1.19) and NADP+‐dependent glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.13), two regulatory enzymes of the reductive pentose phosphate cycle, were increased by glucose. However, Rubisco (EC 4.1.1.39) activity of these cells was lower than that of autotrophic cells. Despite these alterations, the photosynthetic O2 evolution was not significantly inhibited by glucose. On the other hand, an increase in the cytosolic NADP+‐glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.9) that is involved in obtaining reducing power for anabolic processes was observed. The CO2 levels in the growth medium did not significantly affect the cellular level of enzymes measured in this work, except those involved in biosynthetic pathways. These data suggest that the effect of glucose on photosynthesis and respiration can be explained by alteration of the cellular level of photosynthetic enzymes and respiratory substrates, respectively.
Gibberellin levels and cold‐induced floral stalk elongation in tulip
Authors: Rebers Mariken , Vermeer Evert , Knegt Erik , Shelton Cathryn J. , van der Plas Linus H. W.
Published: May 2006

To investigate the role of gibberellins (GAs) in the cold requirement of tulip (Tulipa gesneriana L. cv. Apeldoorn), bulbs were dry‐stored at 5°C or at 17°C for 12 weeks prior to planting at 20°C. Only precooled bulbs showed rapid sprout growth and developed a full‐grown flower. Endogenous GA levels were measured in sprouts and basal plates at the time of planting and in the second week after planting, by combined gas chromatography‐mass spectrometry using deuterated internal standards. GA4 was the major gibberellin. while GA1, GA9 and GA34 were present in lower amounts. At the time of planting, sprouts from non‐cooled bulbs contained significantly more GA4 and GA1, per sprout than those from precooled bulbs. Hence, there is no direct correlation between rapid sprout growth after planting and high GA levels at planting. In the second week after planting, floral stalks of precooled bulbs contained 2 to 3 times more GA4 and its metabolite GA34 per floral stalk and per g fresh weight than those of non‐cooled bulbs. The results are discussed with regard to the role of gibberellins in the cold‐induced floral stalk elongation of tulip.
Proteinase inhibitor II is developmentally regulated in Nicotiana flowers
Authors: Ausloos G. R. J. , Proost P. , van Damme J. , Vendrig J. C.
Published: May 2006

Proteinase inhibitors (PI) are expressed in several members of the Solanaceae. According to species, PI can be both developmentally and environmentally regulated. We investigated the presence and developmental regulation of PI in the flowers of Nicotiana plumbaginifolia. By trypsin affinity chromatography a small protein, Np‐PI‐II, was isolated. This protein had an N‐terminus similar to a part of a Nicotiana alata PI‐II, and an inhibitory activity towards trypsin. Inhibitory activity is expressed at very early stages of floral development. No inhibitor is present in the vegetative meristems. The inhibitory activity remains high throughout flower maturation and rapidly declines in the ovary after pollination. In the stigma of mature Nicotiana tabacum flowers trypsin inhibitory activity is detected extracellularly. Proteinase inhibitor activity is not a regular feature of the stigmas of several solanaceous genera.

Proteinase inhibitors apparently have no function in the development of floral structures and probably act as protective agents against fungal infection of and insect damage to the floral parts and the developing fruit.
An acylcyclohexadione retardant inhibits gibberellin A1 metabolism, thereby nullifying phytochrome‐modulation of cowpea epicotyl explants
Authors: Martínez‐García Jaime F. , García‐Martínez José L.
Published: May 2006

The regulation by phytochrome of stem elongation in light‐grown plants depends on gibberellins (GAs). To investigate whether this is mediated by a change in GA metabolism, the effect of the GA biosynthesis inhibitor LAB 198 999 (an acylcyclohexadione derivative) on the end‐of‐day far‐red (FR) response in cowpea (Vigna sinensis L.) epicotyl explants has been investigated. Growth of epicotyl explants of light‐grown seedlings was enhanced when treated with far‐red light before incubation in the dark (end‐of‐day FR effect). Low doses of LAB 198 999 (0.05 and 0.5 μg explant−1) reduced the effect of FR, whereas 5 to 50 μg explant−1 stimulated elongation of both red light (R)‐ and FR‐treated epicotyl explants while nullifying the differences between R and FR treatments. In paclobutrazol‐treated epicotyl explants, FR enhanced the response to applied GA1 and GA20, whereas LAB 198 999 increased the activity of GA1 and decreased that of GA20, [3H]Gibberellin A1, injected into the basal part of the epicotyl, was transported and metabolized mainly to [3H]GA8 in the apical 20 mm of the epicotyl. The conversion of [3H]GA1 to [3H]GA8 was dramatically reduced by both end‐of‐day FR treatments and LAB 198 999 applications. In addition, both treatments enhanced epicotyl elongation. It is proposed that the regulation of cowpea epicotyl growth by phytocrome is mediated, at least partially, by modifying GA1 degradation.
NaCl‐induced accumulation of tonoplast and plasma membrane H+‐ATPase message in tomato
Authors: Binzel Marla L.
Published: May 2006

NaCl‐induced changes in the accumulation of message for the 70 kDa subunit of the tonoplast H+‐ATPase and plasma membrane H+‐ATPase were studied in hydroponically grown plants of Lycopersicon esculentum Mill. cv. Large Cherry Red. There was increased accumulation of message for the 70 kDa (catalytic) subunit of the tonoplast H+‐ATPase in expanded leaves of tomato plants 24 h after final NaCl concentrations were attained. This was a tissue‐specific response; levels of this message were not elevated in roots or in young, unexpanded leaves. The NaCl‐induced accumulation of this message was transient in the expanded leaves and returned to control levels within 7 days. The temporal and spatial patterns of NaCl‐induced accumulation of message for the plasma membrane H+‐ATPase differed from the patterns associated with the 70 kDa subunit of the tonoplast H+‐ATPase. NaCl‐induced accumulation of the plasma membrane H+‐ATPase message occurred in both roots and expanded leaves. Initially accumulation of the plasma membrane H+‐ATPase message was greater in root tissue than in expanded leaves, but increased to higher levels in expanded leaves after 7 days. These results suggest that increased expression of the tonoplast H+‐ATPase is an early response to salinity stress and may be associated with survival mechanisms, rather than with long‐term adaptive processes.
Temporary suppression of the flash‐induced electrical potential across the thylakoid membrane upon energization
Authors: van Voorthuysen Tijmen , Dassen Hans H. A. , Snel Jan F. H. , Vredenberg Wim J.
Published: May 2006

Energization of the chloroplast thylakoid membrane causes a temporary decrease in the amplitude of the flash‐induced transmembrane electrical potential as monitored by the micro‐electrode technique and by the electrochromic absorbance band shift at 518 nm in chloroplasts of Peperomia metallica. This energization‐dependent decrease of the flash‐induced potential has a relaxation time of recovery in the dark of about 23±4 s. The phenomenon can neither be explained by a decrease of the intrinsic efficiency of photosystem I and II (PSI and PSII) nor by a partial closure of reaction centers of PSI and PSII. This leads us to propose that the energization‐dependent decrease of the amplitude of the flash‐induced electrical potential is caused by either the formation of a fraction of PSI and/or PSII reaction centers with fast charge recombination or by an increase of the membrane capacitance. The dark recovery after energization of the amplitude of the transmembrane electrical potential and that of non‐photochemical fluorescence quenching were found to be comparable, which suggests a common cause for both phenomena.
Peroxidase isoenzymes in the defense response of Capsicum annuum to Phytophthora capsici
Authors: Alcázar M. Dolores , Egea Catalina , Espín Antonio , Candela M. Emilia
Published: May 2006

Quantitative and qualitative changes in isoperoxidase patterns from stems of three cultivars of pepper (Capsicum annuum L.). one susceptible, one intermediate and one resistant, were found upon inoculation with Phytophthora capsici using a decapitation method. The peroxidase activity was determined in the intercellular fluid as well as in the cytosolic fraction of the necrotic, healthy and intermediate zones of stems of the three cultivars, 6 days after inoculation. In the intercellular fluid, peroxidase activity of the susceptible cv. Yolo Wonder increased somewhat from 4.7 (healthy zone) to 12.9 (intermediate zone) μmol mg−1 protein min−1, whereas in the intermediate cv. Americano, the peroxidase activity decreased from 123 (healthy zone) to 78 (intermediate zone) μmol mg−1 protein min−1. The most dramatic increase (5.7 to 662 μmol mg−1 protein min−1) in intercellular peroxidase activity was found in the resistant cv. Smith‐5. This, in conjunction with the appearance of an additional acidic isoperoxidase (pI 4.4) specific for the cv. Smith‐5, could be the reason for the resistance of this cultivar against the fungus attack. The release of peroxidase into the intercellular space as a defense reaction was confirmed by histochemical analysis, showing that peroxidase activity occurred in the intercellular spaces of those stems of the resistant cultivar that had not yet been invaded by the fungus, but was detected neither in the other cultivars nor in the intercellular spaces of such stems of the intermediate and susceptible cultivars that contained growing mycelium of P. capsici. The lack of staining in the intercellular spaces of the susceptible cultivars could be attributed to their low content in peroxidase.
Superoxide production by mitochondria isolated from green bell pepper fruit
Authors: Purvis Albert C. , Shewfelt Robert L. , Gegogeine James W.
Published: May 2006

Evidence is increasing to suggest that a wide range of environmentally induced plant disorders, including chilling injury, is mediated by reactive oxygen species produced during stress or upon relief from stress. Mitochondria were isolated from pericarp tissue of chilling‐sensitive bell pepper fruit and their respiratory activity and ability to produce superoxide when supplied with NADH, succinate or malate‐pyruvate were determined. Oxygen uptake rates were greater and less sensitive to cyanide with succinate than with NADH; rates increased and sensitivity to cyanide and respiratory control ratios (RCRs) decreased in fruit stored at 2°C. Disrupting mitochondrial membranes led to increased oxygen consumption with NADH and decreased consumption with succinate. resulting in RCRs of approximately 1 with both substrates. Superoxide production was greater with NADH than with either succinate or malatepyruvate. Superoxide dismutase and cyanide inhibited superoxide production almost completely. Antimycin A did not inhibit superoxide production with NADH, but did partially with succinate, especially in mitochondria sensitive to cyanide. Disrupting mitochondrial membranes enhanced superoxide production with NADH. Superoxide production by mitochondria isolated from fruit stored at 2°C increased with NADH and decreased with succinate. Results provide evidence that mitochondria may be a major source of superoxide in chilling‐sensitive plant tissues exposed to low temperatures.
Effects of sodium chloride on growth, tissue elasticity and solute adjustment in two Acacia nilotica subspecies
Authors: Nabil Mohamed , Coudret Alain
Published: May 2006

The objective of this study was to compare whole plant growth and physiological responses to salt stress of two Acacia nilotica subspecies (ssp. cupressiformis and ssp. tomentosa). Salt stress was induced by adding NaCl at different concentrations to the nutrient solution: 0, 75, 100 and 200 mM. After one month under such stress, plants were still healthy and actively growing in both subspecies up to 100 mM NaCl. Water potential (Ψ) and osmotic potential (π) decreased with salinity and the lower π enabled the plants to maintain turgor. Höfler diagrams confirmed that osmotic adjustment had occurred under all treatments. Furthermore, the point of zero turgor occurred at a higher relative water content. An increase in the elastic modulus (ɛ) was observed under stress (low elasticity of the cell wall). Both osmotic adjustment and a high ɛ modified the capacity of both subspecies to maintain a positive water balance. Accumulation of ions (Na+, K+ and Cl−) and proline could explain such osmotic adjustment. Acacia nilotica ssp. cupressiformis showed a higher absorption of K+ than ssp. tomentosa up to 100 mM NaCl treatment.
Inhibitory effect of S‐carvone on wound healing of potato tuber tissue
Authors: Oosterhaven K. , Hartmans K. J. , Scheffer J. J. C. , van der Plas L. H. W.
Published: May 2006

Wounded tuber tissue of potato (Solanum tuberosum L. cv. Gloria) exposed to the monoterpene S‐carvone did show neither suberization nor cambium layer formation, whereas these processes started after 2–4 days in control tissue. Suberized tissue was clearly visible 24 days after the start of the S‐carvone treatment, when the concentrations of S‐carvone and its bioconversion products in the tissue were almost zero and cambium layer formation had not yet started. The inhibition of wound healing coincided with a lack of induction of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase (HMGR, EC 1.1.1.34). The wounded potato tissue used as control, showed a transient induction of HMGR activity.

In S‐carvone treated tissue, the activities of GR (glutathione reductase, EC 1.6.4.2) and AP (ascorbate peroxidase, EC 1.11.1.11) were induced, and the level of glutathione increased four‐ to five‐fold.
Effect of exogenous auxin on root morphology and secondary metabolism in Tagetes patula hairy root cultures
Authors: Arroo R. R. J. , Develi A. , Meijers H. , Van de Westerlo E. , Kemp A. K. , Croes A. F. , Wullems G. J.
Published: May 2006

In this paper the effects of indole‐3‐acetic acid (IAA) on growth of Tagetes patula hairy root cultures and secondary product formation are presented. The biosynthesis of thiophenes, sulfurous compounds with nematicidal activity, was inhibited by IAA application, as was evident from a decrease of [35S] sulfur incorporation. The inhibition only occurred after the roots had developed numerous laterals as a result of auxin action. However, in roots cultured in the absence of IAA, there was no significant correlation between branching and thiophene accumulation. Therefore, development of lateral roots is not a sufficient condition for a low capacity to synthesize thiophenes. The highest rate of thiophene accumulation in the roots culture is at its maximum. Hence, growth and the production of thiophenes appear to be compatible in T. Patula hair roots.
Purification and properties of a neutral invertase from the roots of Cichorium intybus
Authors: Van den Ende Wim , Van Laere André
Published: May 2006

Multiple activity peaks of neutral invertase (EC 3.2.1.26) were found in chicory roots (Cichorium intybus L. var. foliosum cv. Flash). The main activity peak was purified by a combination of anion‐exchange chromatography, hydrophobic interaction chromatography, chromatofocusing and gel filtration. This protocol produced a 77‐fold purification and a specific activity of 1.6 μmol (mg protein)−1 min−1. The mass of the enzyme was 260 kDa as estimated by gel filtration and 65 kDa on SDS‐PAGE. Optimal activity was found between pH 7 and 7.5. The purified enzyme exhibited hyperbolic saturation kinetics with a Km between 10 and 20 mM for sucrose. No other products than glucose and fructose could be detected. Raffinose was hydrolyzed at a rate of 2.4% relative to sucrose whereas the enzyme did not hydrolyze maltose, cellobiose, trehalose, 1‐kestose, 1.1‐nystose or inulin. Neutral invertase activity was completely inhibited by HgCl2 and AgNO3 and partially inhibited by CoCl2, and ZnSO4 (1 mM). Pyridoxal phosphate (Ki≅ 500 μM), Tris (Ki≅ 1.2 mM), glucose and fructose (Ki≅ 16 mM) were strong inhibitors of the enzyme. Fructose and Tris behaved as competitive inhibitors. A possible role for the enzyme's activity in vivo is discussed.
Guard cell responses to potassium ferricyanide
Authors: Vavasseur Alain , Lascève Gérard , Cousson Alain
Published: May 2006

Micromolar concentrations of potassium ferricyanide inhibit light‐induced stomatal opening. The extent of the inhibition is dependent on the presence of carbon dioxide and the concentration of potassium ferricyanide needed to obtain 50% inhibition of stomatal opening is 40‐fold higher in CO2‐free air than in normal air. The fungal toxin, fusicoccin (1 μM), overcame the ferricyanide inhibition of stomatal opening indicating that the electron acceptor may interact more or less directly with the activity of the plasma membrane H+‐ATPase. Although potassium ferricyanide strongly inhibited stomatal opening, it had only minor effects on stomatal maintaining or stomatal closure due to darkness or ABA.
Salt stress increases ferredoxin‐dependent glutamate synthase activity and protein level in the leaves of tomato
Authors: Berteli Francisco , Corrales Elena , Guerrero Consuelo , Ariza María J. , Pliego Fernando , Valpuesta Victoriano
Published: May 2006

Ferredoxin‐dependent glutamate synthase (EC 1.4.7.1) catalyzes an essential step in the pathway of glutamate biosynthesis. Exposing detached tomato (Lycopersicon esculentum) leaves for 6 h to 12 g l−1 NaCl resulted in a significant two‐fold increase in the activity of ferredoxin‐dependent glutamate synthase extracted from the leaves. Western blot studies demonstrated that salt treatment also increased the ferredoxin‐dependent glutamate synthase content of the leaves. A similar effect of salt on the concentration of this enzyme was found in the leaves of hydroponically‐grown tomato plants. The induction of ferredoxin‐dependent glutamate synthase under salt stress may provide the glutamate required for the proline synthesis which is a common response to salt stress.
Monitoring of aluminium‐induced inhibition of root elongation in four maize cultivars differing in tolerance to aluminium and proton toxicity
Authors: Llugany Mercé , Poschenrieder Charlotte , Barceló Juan
Published: May 2006

Four maize cultivars, which differ in tolerance to acid soils under field conditions (Zea mays L., acid soil‐tolerant C 525 M, BR 201 F and Adour 250, and acid soil‐sensitive HS 7777) were used to study the influence of pH (4.3 and 6.0) and Al (0, 20 and 50 μM) on the elongation of seminal roots in nutrient solution. Root elongation was inhibited by high H+ concentrations (pH 4.3) in cultivars C 525 M, Adour 250 and HS 7777 but not in BR 201 F. After 20 h exposure to Al, root elongation rates were more inhibited in cultivars BR 201 F and HS 7777 than in C 525 M and Adour 250. The use of a computerized linear displacement transducer system with high resolution (1 μm) allowed the monitoring of short‐term responses of root elongation to Al. In the three cultivars affected by H+ toxicity, but not in the acid‐tolerant BR 201 F, Al supply caused an immediate, but transient increase of relative root elongation rates. This result supports the hypothesis that Al‐induced growth stimulation is caused by amelioration of proton toxicity. The time required for 20 μM Al to induce a 5% decrease of root elongation rates was shorter in the Al‐sensitive BR 201 F (33 min) and HS 7777 (86 min) than in the Al‐tolerant C 525 M (112 min) and Adour 250 (146 min) cultivars. However, the response‐time to Al may be overestimated in the proton‐sensitive cultivars, due to the transient stimulation of root elongation rates induced by Al. According to our results, experiments intended to investigate primary mechanisms of Al toxicity should be started after less than 30 min exposure to toxic Al concentrations, using pH conditions which avoid Al‐induced growth stimulation due to amelioration of proton toxicity.
Regulation of transcript level and nitrite reductase activity by phytochrome and nitrate in turions of Spirodela polyrhiza
Authors: Appenroth Klaus‐J. , Oelmüller Ralf
Published: May 2006

Control by light and nitrate of the appearance of nitrite reductase (NIR; EC 1.7.7.1) activity was investigated in turions of Spirodela polyrhiza during the pre‐germination period to establish the nature of the coaction between these factors. A cDNA clone coding for tobacco NIR was available as a probe. In the period immediately after transfer from after‐ripening conditions (5°C. darkness) to germination conditions (25°C; phase 1, from 0 to 72 h after start of the experiments) a nitrate‐dependent increase in NIR activity was observed, presumably because of the temperature shift. During this phase light had no effect on the nitrate‐dependent increase in NIR activity. In contrast, after a pre‐treatment of 72 h in darkness at 25°C following cold afterripening responsiveness to phytochrome appeared, with light inducing a nitrate‐dependent increase in NIR activity (phase II, from 72 to 120 h after start of the experiments). Application of nitrate (10 mM) in phase II also resulted in an increase of NIR activity in light or darkness although highest NIR activities were observed in the presence of light. Ammonium did not affect the appearance of NIR activity. In all experiments, a single isoform of NIR was detectable in both phases. It was concluded that the mode of coaction between light (via phytochrome) and nitrate is different in phase I and phase II and depends on the developmental state of the plant organs. Furthermore, the response patterns of nitrate reductase and NIR activities to both factors is so similar in turions that co‐regulation of both enzymes can be assumed, as found previously in tobacco seedlings. Northern blot analyses revealed a low NIR transcript level in the absence of nitrate in darkness during phase II. Both light and nitrate alone were sufficient to stimulate the NIR mRNA steady state level and the highest transcript level was detectable in the presence of both stimulators. This demonstrates a synergistic effect of both factors on steady state NIR transcript level.
Aminoethoxyvinylglycine, cobalt and ascorbic acid all reduce ozone toxicity in mung beans by inhibition of ethylene biosynthesis
Authors: Wenzel A. A. , Schlautmann H. , Jones C. A. , Küppers K. , Mehlhorn H.
Published: May 2006

Evidence is presented in support of the hypothesis that stress ethylene formation determines ozone toxicity in plants. In studies with mung beans (Vigna radiata) ozone toxicity was reduced not only when plants had been pretreated with aminoethoxyvinylglycine (AVG) but also after pretreatment of plants with CoCl2 and ascorbic acid. While AVG prevents the enzymatic conversion of S‐adenosylmethionine (SAM) to I‐aminocyclopropane‐I‐carboxylic acid (ACC), cobalt and free radical scavengers such as ascorbic acid inhibit the subsequent conversion of ACC to ethylene. Stomatal opening was not affected by pretreatment of plants with inhibitors of ethylene biosynthesis.
Characteristics of action potentials generated spontaneously in Helianthus annuus
Authors: Zawadzki Tadeusz , Dziubiśka Halina , Davies Eric
Published: May 2006

A novel experimental set‐up and method of recording of electrical potential differences in plants have been developed which enable continuous, 8‐channel monitoring of electrical activity over extended periods of time using inserted, extracellular electrodes. The investigations were carried out on 21‐ to 23‐day‐old Helianthus annuus plants, and spontaneously‐generated action potentials were recorded during monitoring sessions lasting for 3 days and nights. Characteristics of these spontaneous action potentials were elaborated, adopting as parameters their typical form, amplitude, duration, velocity, direction, and distance of propagation and frequency of occurrence in morphologically different parts of the plant, Variability, similarities, and interdependence of the above parameters in individual plants and in a group of 15 plants were determined. A hypothesis concerning propagation of action potentials in plants along specific impulse‐propagating ‘columns’ is discussed. The frequency of generated impulses is highest at night and lowest in the day and also displays an apparent 24‐h rhythm. Presumably this mechanism is under both endogenous and exogenous control and may be partly dependent on a biological clock.
Effects of silver nitrate and polyethylene glycol on white spruce (Picea glauca) somatic embryo development: enhancing cotyledonary embryo formation and endogenous ABA content
Authors: Kong Lisheng , Yeung Edward C.
Published: May 2006

In vitro cultures and endogenous abscisic acid (ABA) analyses with gas chromatography‐selected ion monitoring‐mass spectrometry (GC‐SIM‐MS) were used to study the effects of AgNO3 and polyethylene glycol (PEG) on white spruce (Picea glauca) somatic embryo maturation and endogenous ABA contents, Normally, in the absence of ABA, white spruce somatic embryos cannot mature. However, AgNO3 and PEG stimulated somatic embryo maturation by increasing the number of cotyledonary embryos. A combination of 100 μM AgNO3 and 40 g l−1 PEG was the treatment that was most effective in enhancing cotyledonary embryo formation without exogenous ABA. Either AgNO3 or PEG was able to increase endogenous ABA levels of the embryogenic culture but a combination of AgNO3 and PEG was the most effective treatment. Stimulation of cotyledonary embryo formation by AgNO3 occurred only at low ABA levels, while PEG promoted embryo formation at all exogenous ABA concentrations. Germination tests indicated that AgNO3 had no negative effects on embryo germination and conversion while the PEG‐treated embryos failed to germinate.
Seasonal variation in the nuclear genome size of ray cells in the vascular cambium of Fraxinus americana
Authors: Zhong Y. , Mellerowicz E. J. , Lloyd A. D. , Leinhos V. , Riding R. T. , Little C. H. A.
Published: May 2006

The nuclear DNA content in ray cells from the 1‐year‐old vascular cambium of white ash (Fraxinus americana L.) trees was determined at intervals during the annual cycle of cambial activity and dormancy by using Feulgen microspectrophotometry. By 10 September, these cells had entered dormancy in G1 with a normal DNA distribution and a minimal average DNA content of 2.65 pg. The average amount of DNA increased to 3.51 pg by 30 November, remained at this elevated value until at least 30 March, when the cambium was still dormant, then declined to the minimum level on 1 May and 10 June, when the cells were mitotically active. The springtime decline appeared to occur both before and during cell division. Between 1 May and 10 June, the prophase (4C) and telophase (2C) DNA contents decreased significantly. The amount of nuclear DNA measured by microspectrophotometry was verified by using flow cytometry and image analysis. The results support the view that there is an annual oscillation in the nuclear genome size of shoot meristematic cells in tree species native to the northern temperate zone.
Differential localization of two acid proteinases in germinating barley (Hordeum vulgare) seed
Authors: Marttila Salla , Jones Berne L. , Mikkonen Anita
Published: May 2006

A cathepsin D‐like aspartic proteinase (EC 3.4.23) is abundant in ungerminated barley (Hordeum vulgare) seed while a 30 kDa cysteine endoproteinase (EC 3.4.22) is one of the proteinases synthesized de novo in the germinating seed. In this work, the localization of these two acid proteinases was studied at both the tissue and subcellular levels by immunomicroscopy. The results confirm that they have completely different functions. The aspartic proteinase was present in the ungerminated seed and, during germination, it appeared in all the living tissues of the grain, including the shoot and root. Contrary to previous suggestions, it was not observed in the starchy endosperm. By immunoblotting, the high molecular mass form of the enzyme (32 + 16 kDa) was found in all the living tissues, whereas the low molecular mass form (29 + 11 kDa) was not present in the shoot or root, indicating that the two enzyme forms have different physiological roles. The aspartic proteinase was localized first in the scutellar protein bodies of germinating seed, and later in the vacuoles which are formed by fusion of the protein bodies. In contrast to the aspartic proteinase, the expression of the 30 kDa cysteine proteinase began during the first germination day, and it was secreted into the starchy endosperm; first from the scutellum and later from the aleurone layer. It was not found in either shoots or roots. The 30 kDa cysteine proteinase was detected in the Golgi apparatus and in the putative secretory vesicles of the scutellar epithelium. These results suggest that the aspartic proteinase functions only in the living tissues of the grain, as opposed to the 30 kDa cysteine proteinase which is apparently one of the proteases initiating the hydrolysis of storage proteins in the starchy endosperm.
Importance of arabinogalactan proteins for the development of somatic embryos of Norway spruce (Picea abies)
Authors: Egertsdotter Ulrika , von Arnold Sara
Published: May 2006

The morphology of somatic embryos of Norway spruce (Picea abies) varies among different cell lines, from less developed somatic embryos with small embryonic regions (group B) to well developed embryos with large embryonic regions (group A). Only well developed somatic embryos will undergo a maturation process after a treatment with ABA and develop into mature somatic embryos, which is required for plant regeneration. We have previously shown that the presence of specific extracellular proteins can be correlated with the morphology of the somatic embryos. In the present study we show that extracellular proteins concentrated from group A cell lines can stimulate group B embryos to develop further and that seed extract can stably convert B embryos into A embryos. The arabinogalactan protein (AGP) fraction of the extracellular proteins and of the seed extract was shown to be an active component for stimulating B embryos to develop further. Furthermore, the amount and type of extracellular AGPs, as detected with β‐glucosyl Yariv reagent and monoclonal antibodies, varied among different types of tissues and cell lines. The data show that development of somatic embryos in Norway spruce is associated with particular extracellular AGPs, which have a regulatory function.
Automorphosis of maize shoots under simulated microgravity on a three‐dimensional clinostat
Authors: Hoson Takayuki , Kamisaka Seiichiro , Yamamoto Ryoichi , Yamashita Masamichi , Masuda Yoshio
Published: May 2006

Seedlings of maize (Zea mays L. cv. Golden Cross Bantam T‐51) were grown under microgravity conditions simulated by a three‐dimensional clinostat. On the clinostat, maize shoots exhibited curvatures in three different portions: (1) the basal transition zone connecting roots and mesocotyls, (2) the coleoptile node located between mesocotyls and coleoptiles, and (3) the elongating region of the coleoptiles. Even non‐clinostatted control shoots showed some degree of curvature away from the caryopsis in the transition zone and bending toward the caryopsis in the coleoptile node. Clinostat rotation greatly stimulated these curvatures. Control coleoptiles elongated almost straightly, whereas coleoptiles on the clinostat bent either away from or toward the caryopsis depending on the timing of rotation. The curvature in all three portions became larger with time, both in control and clinostatted seedlings. There was no difference in the osmotic concentration of the cell sap between the convex and the concave halves of any portion. However, in coleoptile nodes and coleoptiles, the faster‐expanding convex side exhibited a higher extensibility of the cell wall than the opposite side, and this appears to be a cause of the curvature. Thus, changes in the cell wall metabolism may be involved in automorphosis, which governs the life cycle of plants under a microgravity environment.
Effects of hypergravity on the elongation and morphology of protonemata of Adiantum capillus‐veneris
Authors: Kasahara Hirokazu , Yanagiya Kazumi , Takeuchi Yuichi , Yamashita Masamichi , Yamada Mitsuhiro
Published: May 2006

Elongation growth of protonemata of Adiantum capillus‐veneris, which can be controlled by light irradiation, was examined under acropetal and basipetal hypergravity conditions (from ‐13 to +20 g) using a newly developed centrifugation equipment. Elongation of the protonemata under red light was inhibited by basipetal hypergravity at more than +15 g but was promoted by acropetal hypergravity from ‐5 to ‐8 g. Division of the protonemal cells that was induced by white light was inhibited under basipetal hypergravity at +20 g but was unaffected under acropetal hypergravity at ‐15 g. Upon exposure to continuous red light for 7 to 8 days, most of the protonemata grew as filamentous cells in the absence of a change in the normal gravitational force (control), but more than half of the protonemal cells were abnormal in terms of shape when maintained under hypergravity at +20 g.
Characterization of somatic hybrids of potato by use of RAPD markers and isozyme analysis
Authors: Rasmussen J. O. , Rasmussen O. S.
Published: May 2006

Electrofusion of mesophyll protoplasts from two male sterile dihaploid Solanum tuberosum genotypes. DHAK‐11 and DHAK‐33, was performed. Selection of putative fusion products was based on vigorous callus growth. Regeneration of rooted putative hybrid plants was scored 14 weeks after fusion. Characterization of hybrids was performed by use of morphological assessment, random amplified polymorphic DNA (RAPD), and cytological and isozyme analysis. The rate of regenerated hybrids from callus was ca 6%. Of the putative hybrids, 45% were confirmed as true hybrids. Morphological assessment of the putative hybrids revealed that tetraploid and neartetraploid hybrids were vigorous plants with intermediate characteristics between the two parental phenotypes in respect to internode length, leaf size and shape, and purple pigmentation on the abaxial side of the leaves. Near‐hexaploid hybrids were slender plants with small leaves and short petioles. Selected RAPD primers showed unique marker bands for the two parental genotypes. Hybrid plants revealed the unique marker bands from both parents. A total of 53 randomly chosen decamer primers were tested and 26 primers (49%) detected polymorphism between the two dihaploid parentals. Two primers revealed that one parental marker band was missing in two aneuploid hybrids. However, of 51 putative hybrids, a double test with two independently chosen primers showed unequivocally the hybrid character of 23 plants. The ploidy level of the hybrids was analysed by chromosome numbers in root tip cells and by number of guard cell chloroplasts. A strong correlation between the chromosome number and the number of chloroplasts was obtained. The hybrid nature of all RAPD‐verified hybrids was confirmed by isozyme analysis with malate dehydrogenase.
Diagnosis of damage to Norway spruce (Picea abies) through biochemical criteria
Authors: Wild Aloysius , Schmitt Volker
Published: May 2006

Bioindication can be carried out at different hierarchical levels, eg. cell, organism, and ecosystem. While the monitoring of damage by visible criteria (e.g. loss of needles) is connected with the organism as a whole, the monitoring of damage by biochemical indicators is above all connected with cell metabolism.

The degree of vitality of a tree can be ascertained through the integration of a number of biochemical parameters. Furthermore, a differential diagnosis of a particular stress pattern can be carried out because of the feedback pattern of several biochemical indicators. In order to describe and interpret biochemical or physiological changes that have been caused by a number of factors, multivariate statistical methods are being used more frequently. Apart from cluster and discriminant analysis, it is especially factor analysis which provides a helpful tool when dealing with problems in the field of environmental analysis. Factor analysis can be used for an integrating as well as a differentiating assessment.

Within the framework of forest damage research, numerous changes at the level of cell metabolism have been detected to which a bioindicative character can be attached. A number of physiological and biochemical parameters with bioindicative character concerning Norway spruce are presented.
The isoflavonoid phytoalexin pathway: From enzymes to genes to transcription factors
Authors: Dixon Richard A. , Harrison Maria J. , Paiva Nancy L.
Published: May 2006

The pterocarpan phytoalexins of the Leguminosae are synthesized from L‐phenyl‐alanine via a minimum of 11 enzymatic steps involving the central phenylpropanoid pathway, three reactions of flavonoid biosynthesis, and the isoflavonoid branch pathway. The extractable activities of all these enyzmes, and of enzymes supplying precursors from primary metabolism, increase in response to fungal infection or exposure of plant cells to elicitor macromolecules isolated from the cell walls of yeast or plant pathogenic fungi. The involvement of reductases and cytochrome P450 hydroxylases places a high demand for NADPH on elicited cells. The NADPH is most likely supplied by activation of the pentose phosphate pathway. Genes or cDNAs encoding 7 of the enzymes involved in the synthesis of the phytoalexin medicarpin have been cloned from alfalfa and/or other species. Induction of enzyme activity results from transcriptional activation of the corresponding genes, leading to increased steady state levels of translatable mRNAs. This transcriptional activation is programmed through the interaction of sets of elicitor/infection‐modulated transcription factors with their cognate cis elements in the promoters of the phytoalexin biosynthetic genes. Gene activation occurs through generation of intracellular signals which lead to modulation of transcription factor activity, through either increased synthesis of the factor(s), activation via reversible post‐translational modification (e.g. phosphorylation/dephos‐phorylation), translocation of factors from cytoplasm to nucleus, or combinations of these. Coordinated induction of the enzymes of phytoalexin synthesis may involve multiple signals and factors for transcriptional activation, as well as feedback and feed‐forward fine controls at both transcriptional and post‐transcriptional levels. In beneficial mycorrhizal interactions, induction of early pathway genes is uncoupled from that of later, phytoalexin‐specific genes.
HMG‐GoA reductase and terpenoid phytoalexins: Molecular specialization within a complex pathway
Authors: Weissenborn Deborah L. , Denbow Cynthia J. , Laine Marko , Lång Saara S. , Yang Zhenbiao , Yu Xueshu , Cramer Carole L.
Published: May 2006

Terpenoid phytoalexins and other defense compounds play an important role in disease resistance in a variety of plant families but have been most widely studied in solanaceous species. The rate‐limiting step in terpenoid phytoalexin production is mediated by 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase (HMGR), which catalyzes mevalonic acid synthesis. HMGRs are involved in the biosynthesis of a broad array of terpenoid compounds, and distinct isoforms of HMGR may be critical in directing the flux of pathway intermediates into specific end products. Plant HMGRs are encoded by a small gene family, and genomic or cDNA sequences encoding HMGR have been isolated from several plant species. In tomato, four genes encode HMGR; these genes are differentially activated during development and stress responses. One gene, hmg 2, is activated in response to wounding and a variety of pathogenic agents suggesting a role in sesquiterpene phytoalexin biosynthesis. In contrast, expression patterns of tomato hmg l suggest a role in sterol biosynthesis and cell growth. Other plant species show an analogous separation of specific HMGR isoforms involved in growth and/or housekeeping function and inducible isoforms associated with biosynthesis of phytoalexins or other specialized “natural products”. We are applying a variety of cell and molecular techniques to address whether subcellular localization and/or differential expression of these isoforms are key factors in determining end product accumulation during development and defense.
Inhibition of hypocotyl elongation by ultraviolet‐B radiation in de‐etiolating tomato seedlings. I. The photoreceptor
Authors: Ballaré Carlos L. , Barnes Paul W. , Flint Stephan D.
Published: May 2006

Broad‐band UV‐B radiation inhibited hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 μmol m−2 s−1 of UV‐B radiation provided against a background of white light (> 620 μmol m−2 s−1 between 320 and 800 nm), and was similar in wild‐type and phytochrome‐1‐deficient aurea mutant seedlings. These observations suggest that the effect of UV‐B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m−2 s−1 of monochromatic UV radiation against a while light background (63 μmol m−2 s−1 showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV‐B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad‐hand UV‐B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10−4M, which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV‐A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV‐B. Kl applied after UV‐B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV‐B perception by tomato seedlings during de‐etiolation may be a flavin.
Inhibition of hypocotyl elongation by ultraviolet‐B radiation in de‐etiolating tomato seedlings. II. Time‐course, comparison with flavonoid responses and adaptive significance
Authors: Ballaré Carlos L. , Barnes Paul W. , Flint Stephan D. , Price Steven
Published: May 2006

UV‐B radiation inhibits hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order lo further characterize the response and gain insight into its potential ecological significance, the time‐course of inhibition was measured and compared with the time‐course of flavonoid accumulation in the same seedlings. When a background of strong (> 620 μmol m−2 s−1) white light (WL) was supplemented with low irradiance UV‐B (∼ 3 μmol m−2 s−1). substantial (∼ 50%) inhibition of elongation occurred within 3 h of the light treatment. The magnitude of UV‐B‐induced elongation inhibition was similar in wild type (WT) and au‐mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV‐B on elongation, induction of flavonoid accumulation in WT and au seedlings undergoing de‐etiolation was a much slower response. Several UV‐absorbing compounds appeared to be specifically induced by light, and some of them accumulated faster under the WL + UV‐B treatment than under WL alone. However, there was little or no delectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific UV‐B effect was measurable only after 6 h of continuous treatment. Indeed. UV‐B‐screening properties of crude alcoholic extracts were not different between WL and WL + UV‐B treatments until after 9 or 24 h. When the light treatments were applied to seedlings that were just breaking through the soil surface. UV‐B was found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de‐etiolating seedlings is an evolved response lo UV‐B, which may serve to minimize seedling exposure to sunlight until protective pigmentation responses (triggered by WL and UV‐B) have taken place in the seedlings epidermis.