bluuebunny/crossref_metadata_2025 huggingface dataset:
The composition of lipids and fatty acids determined at various stages of haploid and diploid generations in the fern Adiantum capillus‐veneris
Authors: Sato Naoki , Furuya Masaki
Published: April 2006

The composition of lipids and fatty acids was determined at various developmental stages of gametophytes and sporophytes in the fern Adiantum capillus‐veneris L. When the lipid content was expressed per g fresh weight, triacylglycerol was a major reserve lipid in spores and remained the dominant lipid in the gametophytes up to the 15th day after germination, but it was a minor one in the pinnae of sporophytes. In contrast, triterpenoids were abundant in sporophytes but not detected in gametophytes. When the content of fatty acids was expressed in percentage of the total fatty acids, the content of arachidonic acid in phosphatidylcholine and linolenic acid in diacyglyceryltrimethylhomoserine and phosphatidylcholine was significantly higher in both pinnae and petioles of sporophtes than in gametophytes. Significant differences in fatty acid composition of phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and triacylglycerol were also noted between gametophytes and pinnae of sporophytes. All these differences were attributed to the difference of generation rather than tissue differences or age.

The content of monogalactosyldiacylglycerol, hexadecatrienoic acid in monogalactosyldiacylglycerol, and 3‐trans hexadecenoic acid in phosphatidylglycerol was higher in the pinnae of sporophytes than in gametophytes or in young leaves of sporophytes. Electron microscopy of the ultrastructure of chloroplasts indicated that the high content of these components was consistent with the development of chloroplasts in pinnae.
Imipramine affects circadian leaf movements in Oxalis regnellii
Authors: Rinnan T. , Johnsson A. , Götestam K. G.
Published: April 2006

The sensitivity of the circadian leaf movement of Oxalis regnellii Mig. to imipramine (a tricyclic dibenzazepine) was investigated. Imipramine, like Li+, is used as a therapeutic agent against depressive disorders in man. The therapeutic effects of the two substances might be mediated via effects on basic circadian rhythms and the cellular level. It was indeed possible to influence the circadian movement of Oxalis by imipramine; pulses (10−3M, 4h) phase shifted the rhythms and caused advances. A phase response curve is presented. No period change of the movements was caused by permanent presence of imipramine (5 ‐ 10−5 or 10−5M). The nature of the imipramine‐induced phase shift is discussed and compared with Li−1 effects on the same circadian system.
The relation between nitrogen deficiency and leaf senescence
Authors: Mei Hui‐Sheng , Thimann Kenneth V.
Published: April 2006

Because the “mobilization” of nitrogen resulting from nutritional nitrogen deficiency is also prominent during leaf senescence, the characteristics of these two syndromes were compared. Oat plants (Avena sativa L. cv. Victory) were raised on a nutrient solution, complete except for nitrogen supply (i.e., with only the seed protein as nitrogen source), and the senescence of their leaves was compared with that of controls grown on a full nutrient solution. The N‐deficient plants flowered after forming only 4 leaves and each set a single seed. The nitrogen lack affected the content of chlorophyll somewhat more than the content of the amino acids or protein nitrogen. However, spraying the plants with kinetin solution was able to retain 20–30% of the chlorophyll and protein. During senescence, the chlorophyll appears to be less stable in the N‐deficient leaves than in the controls, while the protein is somewhat more stable than in the controls. Also, when the detached leaves from N‐deficient plants senesced in white light or in darkness, kinetin delayed their senescence almost as effectively as that of control leaves. Most strikingly, the stomata of N‐deficient leaves after detachment and floating on water were largely closed in light, just as in senescence, but could be partially induced to open by kinetin treatment. Since stomatal closure has earlier been shown to cause senescence, the characteristic syndrome of foliar nitrogen deficiency is concluded to be partly that of senescence.
Cold acclimation in Pinus sylvestris: Phospholipids in purified plasma membranes from needles of pine
Authors: Hellergren J. , Lundborg T. , Widell S.
Published: April 2006

Effects of cold acclimation on needles of Scots pine (Pinus sylvestris L., Provenance Södra Ydre) were studied at the membrane level. Before and after a period of cold acclimation the plasma membranes were isolated from the needles by a aqueous polymer two‐phase partition technique. Fatty acid composition of total lipids or of individual phospholipids from the plasma membrane showed that the plasma membrane fraction was different from the other microsomal fractions analyzed, especially the 18:2 levels of the individual phospholipids. Furthermore, the cold acclimation period did not result in a decreased saturation level in the plasma membranes. Different steps in cold acclimation reactions at the membrane level are discussed.
Hormonal regulation of tuber induction in radish (Raphanus sativus). Role of ethylene
Authors: Vreugdenhil D. , Oerlemans A. P. C. , Steeghs M. H. G.
Published: April 2006

When young radish (Raphanus sativus L. cv, Novired RS) plants were exposed to low levels of ethylene, the fresh weight and dry weight of the tubers significantly increased. This was mainly because ethylene reduced the percentage of plants that hardly or not at all formed a tuber. Decaptated seedling cultured in vitro, were supplied with several plant growth regulators in order to determine a possible correlation between the induction of radial growth and the biosynthesis of ethylene in the hypocotyl. Indole‐3‐acetic acid, or in combination with 6‐benzylaminopurine, induced growth of the hypocotyl and markedly enhanced ethylene biosynthesis. However, the application of a precursor and an inhibitor of ethylene biosynthesis revealed that there is no direct causal relationship between radial growth and ethylene evolution. It is suggested that ethylene favoured tuber growth in intact plants by changing the partitioning of assimilates in the plant, rather than by the induction of cambial activity.
Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. II. Photosynthetic electron transport
Authors: Ögren Erling , Öquist Gunnar
Published: April 2006

Photoinhibition of photosynthesis in Lemna gibba L. was induced by exposing intact plants to a high photosynthetic photon flux density of 1 750 μmol m−2 s−1 at a low temperature of 3°C. Subsequently isolated chloroplasts showed pronounced reductions in the capacity of whole chain electron transport, measured as Hill activity, and in the efficiency of electron transport to the primary electron acceptor Q of photosystem II, measured as variable chlorophyll fluorescence at 20°C. These changes proceeded with similar kinetics (probably of the first‐order reaction), suggesting that the site of photoinhibition is in the electron transfer to Q. A partial uncoupling of the whole chain electron transport also occured. The capacity of electron transport mediated by photosystem I was unaffected. The extent of photoinhibition of photosynthetic electron transport, as produced by a 2 h exposure of L. gibba to three different combinations of photon flux density and temperature was studied. It was shown that intrinsically similar states of photoinhibition, on the evidence of their time courses of recovery, were induced by either a high photon flux density and 25°C or by a moderate photon flux density and 3°C.
Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. III. Chlorophyll fluorescence at 77 K
Authors: Ögren Erling , Öquist Gunnar
Published: April 2006

Photoinhibition in Lemna gibba L. was studied by interpreting chlorophyll fluorescence characteristics at 77 K on the basis of the bipartite model of Butler and co‐workers (Butler 1978). Application of this analysis to chloroplasts (isolated from plants before and after exposure to a photosynthetic photon flux density of 1 750 μmol m−2 s−1 at 3°C for 2 h) revealed that photoinhibition had the following effect on primary events in photosynthesis. Firstly, the fluorescence of PS II increased (44%) in the state of open traps (Fo) and decreased (32%) in the state of closed traps (Fm). It is suggested, that the Fo‐decrease reflects increased quenching by radiationless decay, both effects occurring at PS II reaction centers. Secondly, the rate constant for transfer of excitation energy from PS II to PS I (kT(μ→J)) increased by 34%. However, in the state of closed traps, the flux of excitation energy via this transfer process decreased, most likely because of increased quenching by radiationless decay at PS II reaction centers. Thirdly, the probability for fluorescence from PS I decreased (19%). This indicates increased quenching by radiationless decay.
Effect of root anaerobiosis on the water relations of several Pyrus species
Authors: Andersen P. C. , Lombard P. B. , Westwood M. N.
Published: April 2006

Solution culture experiments were designed to investigate the plant water relations of 3 Pyrus species subjected to root anaerobiosis. Root anaerobiosis induced partial stomatal closure prior to alterations in leaf water potential (ΨLW) or root osmotic potential (ΨRπ). In contrast, stomatal closure was accompanied by a decline in root hydraulic conductivity (Lp). Anoxia markedly reduced ΨLW for Pyrus communis L. and eventually led to wilting and defoliation. Pyrus betulaefolia Bunge and Pyrus calleryana Decne, however, were less affected by root anaerobiosis. To delineate if the increased root resistance was in the radial or longitudinal direction, 10−4M cistrans abscisic acid (ABA) was added to detopped root systems of P. communis in solution culture after steady‐state rates of Lp were established. A consistent 25 to 30% promotion of Lp was observed 1.5 h after the addition of ABA for aerobically treated plants. ABA did not influence Lp when applied to roots previously deprived of O2 for 4 days. Additional evidence against the limiting resistance being in the radial direction was obtained when water fluxes were compared through intact P. communis roots, roots with all feeder roots detached, and stems without root systems. Severing feeder roots from anaerobically treated plants did not increase water flux to rates observed for aerobically treated plants. Resistance progressed basipetally to eventually encompass the stem itself. These results can only be explained by occlusion of the xylem vessels.
Preparation and polypeptide composition of chlorophyll‐free plasma membranes from leaves of light‐grown spinach and barley
Authors: Kjellbom Per , Larsson Christer
Published: April 2006

Chlorophyf l‐free preparations of plasma membranes from leaves of barley (Hordeum vulgare L. cv. Kristina) and spinach (Spinada oleracea L. cv. Viking II) were obtained by partition in an aqueous dextran‐polyethylene glycol two‐phase system. CJlu‐can synthetase II (EC 2.4,1.34), a marker for the plasma membrane, was highly enriched in both preparations. Silicotungstic acid, a specific stain for the plasma membrane, indicated a purity close to 100% for the barley preparation. Both plasma membrane preparations contained a light‐reducible b‐cytochrome, as shown by low temperature spectroscopy. The plasma membranes had a tow protein content compared to the bulk of intracellular membranes. The polypeptide composition of the barley and spinach plasma membranes showed striking similarities, with.the most prominent polypeptides in the 49‐58 kdalton region, and some further prominent bands in the 30 kcialton region. Some high molecular weight polypeptides in the 73‐110 kdalton region were also typical for the plasma membranes compared to the microsomal fractions.
Ultrastructural alterations to chloroplasts in triazine‐resistant weed biotypes
Authors: Vaughn Kevin C. , Duke Stephen O.
Published: April 2006

Ultrastructural, morphometric and physiological techniques were used to determine the consistent chloroplast differences between triazine‐resistant (R) and triazine‐susceptible (S) biotypes of Amaranthus hybridus L., Chenopodium album L., and Brassica campestris L. All R biotypes had a larger proportion of the chloroplast volume as grana lamellae and a lower proportion of starch and stroma lamellae than S biotypes. In the R biotypes, a greater percentage of grana contain larger numbers of thylakoids per granum. A greater proportion of chlorophyll associated with the light‐harvesting chlorophyll alb protein and a lower chlorophyll alb ratio, traits associated with an increase in grana lamellae, were noted in R biotypes. Chloroplasts of S biotypes could be modified to ultrastructural phenocopies of those in R biotypes by treatment with sublethal levels of the PSII inhibiting herbicides, bentazon, diuron, atrazine and prometon. Despite the structural similarities to R biotypes, the modified S biotypes were not resistant to atrazine as determined by fluorescence measurements. Thus, the structural alterations observed are apparently secondary effects of impaired photosynthetic electron transport in R biotypes, and are not the cause of triazine resistance.
Influences of PAR, temperature and water vapor concentration on gas exchange by ferns
Authors: Nobel Park S. , Calkin Howard W. , Gibson Arthur C.
Published: April 2006

The effects of photosynthetically active radiation (PAR), leaf temperature and the leaf‐to‐air water vapor concentration drop on net CO2 uptake and water vapor conductance were surveyed for 14 species of ferns. Most previous studies indicated that ferns have extremely low maximal rates of net CO2 uptake, below 2 umol m−2 s−1, whereas the average maximal rate observed here at 250 C was 7 umol m−2 s−1. Net CO2 uptake reached 90% of saturation at an average PAR (400 to 700 nm) of only 240 umol m−2 s−1, consistent with the typically shaded habitats of most ferns. Maximal CO2 uptake rates were positively correlated with the PAR for 90% saturation (r2=0.59), the chlorophyII per unit leaf area (r2=0.30), the water vapor conductance (r2=0.65), and the CO2 residual conductance (r2=0.69). A higher water vapor conductance (gwv) was correlated with a greater fractional change in gwv as the leaf‐to‐air water vapor concentration drop (Δcwv) was raised from 5to20 g m−3 (r2=0.90). Specifically, for species with low gwv of about I mm s−1 the ratio of gwv at Δcwv= 5 g m−3 to that at Δcwv= 20 g m−3 was near 1, but it was near 2 for species with gwv of about 4 mm s−1. Such a relationship, which can prevent excessive transpiration, has apparently not previously been pointed out in surveys of other plant groups.
Are two photoreceptors involved in the flowering of a long‐day plant?
Authors: Tanada Takuma
Published: April 2006

The effect of daylength extension with narrow spectral bands on the flowering of a long‐day plant, Brassica campestris L. cv. Ceres, was investigated to obtain clues to the identity of the photoreceptor involved. Extension of a 9 h photoperiod with 5 h of light pulses at various wavelengths resulted in maximal flowering occurring after irradiation at 710 nm, less at 730 nm, and none at 550, 660 and 750 nm. Flowering at 710 and 730 nm was negated by simultaneous exposures at 550 nm, but not at 660 nm. A short preirradiation at 660 nm enabled a following irradiation at 750 nm to induce flowering. This latter induction was prevented by 550 nm irradiation.

Short flashes of light at 710 nm induced flowering that was negated by a following flash at 550 nm but not at 660 nm. The negation by 550 nm radiation was prevented by subsequent flashes at 710 nm, indicating photoreversibility. A flash at 660 nm enabled subsequent light flashes at 750 nm to initiate flowering that was reversed by a following 550 nm flash.

From the results showing the necessity of red and far‐red lights, it is proposed that flowering in this long‐day plant is due to two photoreceptors ‐ one is phytochrome and the other an unknown pigment with far‐red, green photoreversible properties. By using fluence response data, it is deduced that the unidentified photoreceptor has weak absorption bands in the far‐red, but has a strong absorption band in the green. Flowering is induced when effects of red light absorbed by phytochrome interact with effects of far‐red light absorbed by the unidentified photoreceptor.
Ethylene production and toxigenicity of methionine and its derivatives with riboflavin in cultures of Verticillium, Fusarium and Colletotrichum species exposed to light
Authors: Tzeng Dean D. , DeVay James E.
Published: April 2006

Ethylene was produced by Verticillium dahliae Kleb. grown in liquid Czapek's medium. The rate of ethylene production was enhanced by light but was not affected by shaking or the growth rate of the cultures. L‐, D‐ and DL‐methionine, DL‐ethionine and a‐keto‐y‐methylthiobutyric acid (KMBA) were good substrates for ethylene production. KMBA may be an intermediate in ethylene production and it appears to be degraded to ethylene either enzymatically by peroxidase or photochemically in the presence of riboflavin. Addition of riboflavin or briefly heating the cultures to 100°C enhanced ethylene production greatly, while the addition of sodium azide, potassium cyanide and catalase were very inhibitory. The SS4 (non‐defoliating) pathotype of V. dahliae produced significantly more ethylene (up to 108.4 nl ethylene h1 from 20 ml‐10‐day‐old cultures) than did the T9 (defoliating) pathotype with all substrates tested. The results suggest that the in vitro rate of ethylene production is not related to the relative virulence of pathotypes of V. dahliae on cotton. A number of Verticillium species, Fusarium oxysporum f. sp. vasinfectum and Colletotrichum dematium var. truncatum were able to produce ethylene in liquid Czapek's medium containing 1 mM L‐methionine under continuous light. Riboflavin, although highly stimulatory to ethylene production, caused a fungicidal reaction to all the fungi tested in Czapek's medium containing L‐methionine under continuous light. The fungicidal effect of the riboflavin‐methionine‐light combination occurred at concentrations of riboflavin and methionine less than 1.33 μM and 0.5 mM, respectively. No fungicidal activity was detected when the cultures were grown in total darkness or when either methionine or riboflavin was omitted from the culture medium.
Characteristics of the reverse reaction of NADP+‐isocitrate dehydrogenase from castor bean seeds
Authors: Satoh Yasohachi , Nakamura Yasunori
Published: April 2006

The reductive carboxylation of α‐ketoglutarate by purified NADP+‐isocitrate dehydrogenase (EC 1.1.1.42) from maturing castor bean seeds (Ricinus communis L.) has been characterized. The optimum pH for the reaction was 6.5, whereas pH 8.5 was optimum for oxidation of isocitrate (forward reaction). The enzyme utilized NADH as well as NADPH as the reducing agent in the reverse reaction, but only NADP+ in the forward reaction. The Km values for NADPH and NADH were 0.044 and 2.8 mM respectively, and for α‐ketoglutarate and HCO3 4.1 and 3.7 mM. The enzyme was activated by various cations including Mg2+, Mn2+, Co2+, Zn2+, Ni2+ and Co2+. Km values for Mg2+ Mn2+, Co2+ and Zn2+ were 12, 34, 37 and 49μM respectively.
Shoot RNA, cambrial activity and indolebutyric acid effectivity in seasonal rooting of juvenile and mature Ficus pumila cuttings
Authors: Davies F. T.
Published: April 2006

The seasonal influence on adventitious root formation was studied in woody leaf bud cuttings of Ficus pumila L., creeping fig. Juvenile cuttings rooted easily, whereas only mature cuttings treated with indolebutyric acid (IBA) exceeded 30% rooting. Greater rooting occurred in IBA‐treated juvenile and mature cuttings than controls, regardless of the month each experiment was initiated. Seasonal changes influenced rooting in all treatments except IBA treated juvenile cuttings where percentage rooting was not affected. Higher vascular cambial activity and shoot RNA levels occurred in juvenile and mature forms during peak rooting periods. Highest RNA was recorded with juvenile materials during maximum rooting periods, while lowest RNA was observed in mature shoots during low rooting intervals.
Defoliation effects on mycorrhizal colonization, nitrogen fixation and photosynthesis in the Glycine‐Glomus‐Rhizobium symbiosis
Authors: Bayne Henry G. , Brown Milford S. , Bethlenfalvay Gabor J.
Published: April 2006

Soybean [Glycine max (L.) Merr. cv. Wells] plants grown in a greenhouse were inoculated with Rhizobium japonicum strain 61A118 and the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. & Trappe. Plants were defoliated (26, 48 and 66%) throughout the growth period and evaluated for VAM colonization, N2, fixation and photosynthesis at harvest (six weeks). Photosynthate stress as a result of defoliation affected nodulation and nodule activity most severely. Colonization of the roots by the VAM fungus was little affected in comparison, and the intensity of colonization increased with increasing stress. The CO2‐exchange rate decreased less with defoliation than did leaf mass, and photosynthetic efficiency increased with the severity of defoliation. The increase in photosynthetic efficiency was significantly correlated with increases in leaf P (r = 0.91) and N (r = 0.97) concentrations. The results suggest that the VAM fungus should not be regarded as a simple P source and C sink in the tripartite legume association. Threeway source/sink relationships (VAM‐P, Rhizobium‐N, and host leaf‐C) are discussed.
A minimal model of light‐induced circadian rhythms of nitrate reductase activity in leaves of barley
Authors: Lillo Cathrine , Ruoff Peter
Published: April 2006

Observed circadian rhythms of nitrate reductase (NR) (EC 1.6.6.1) activity in leaves of barley (Hordeum vulgare L. cv. Herta) under continuous light conditions are described by a simple kinetic model. The oscillatory mechanism has been decomposed into the negative and positive feedback loops which are necessary according to present theories of chemical oscillating systems. Our results indicate that the decrease of NR activity in darkness can be considered as a reversible unimolecular conversion of the active form of NR into an inactive form, forming a negative stabilizing feedback loop. The light‐induced increase of NR activity is related to a positive destabilizing feedback loop. In our treatment this process is represented as an autocatalytical reaction.
The occurrence of inorganic pyrophosphate: d‐fructose‐6‐phosphate 1‐phosphotransferase in higher plants. I. Initial characterization of partially purified enzyme from Sanseviera trifasciata leaves
Authors: Kowalczyk S. , Januszewska B. , Cymerska E. , Maslowski P.
Published: April 2006

Among 30 plant species examined, the PPi‐phosphofructokinase (EC 2.7.1.90) was found in leaves of 21 plants. Some of the plants exhibit no activity of ATP‐dependent phosphofructokinase but display only activity of PPi‐phosphofructokinase. A partly purified preparation of PPi‐phosphofructokinase with specific activity of 8.4 Hmol (mg protein)−1 min−1 was obtained from Sanseviera trifasciata leaves. The enzyme is restricted to the cytoplasm, it exhibits pronounced substrate specifity, requires Mg2+ ions, is inhibited by AMP, PEP, methylenediphosphonate and stabilized by mercaptoethanol. At pH 7.8 with 1.5 mM MgCl2 the following KM values were observed: pyrophosphate, 0.58 mM; fructose 6‐phosphate, 0.8 mM. The KM values for substrates of reverse reaction (pH 7.3; 2 mM MgCl2) are of the same order of magnitude: 0.83 mM for fructose 1,6‐diphosphate, and 0.14 mM for orthophosphate. The molecular weight of the studied enzyme is about 125 000 dalton as estimated by gel filtration.
Flow sorting and culture of plant protoplasts
Authors: Harkins Kristi R. , Galbraith David W.
Published: April 2006

Conditions have been established for the rapid flow analysis of leaf protoplasts of Nicotiana tabacum L. cv. Xanthi using a flow cytometer‐cell sorter. A procedure based upon chlorophyll autofluorescence was devised to permit the systematic evaluation of flow conditions in order to identify those under which protoplast damage was minimized. These conditions were employed for the flow sorting of protoplasts, following which it was possible to regenerate the sorted protoplasts into complete plants. The application of flow sorting is discussed for the rapid identification and selection of somatic hybrids produced by protoplast fusion.
Effect of glucose on glutamate dehydrogenase and acid phosphatase and its reversal by cyclic adenosine 3′:5′‐monophosphate in single cell cultures of Asparagus officinalis
Authors: Tassi Francesca , Restivo F. M. , Puglisi P. P. , Cacco G.
Published: April 2006

Cell cultures of Asparagus officinalis L. ev. “Argenteuil” were used to study the effect of glucose on the synthesis of glutamate dehydrogenase and acid phosphatase. Both the enzymes are progressively repressed by increasing the glucose concentration in the culture medium. Furthermore, synthesis of glutamatc dehydrogenase and acid phosphatase in cells grown in the presence of high glucose concentrations is derepressed by the addition of the cyclic adenosine 3′:5′‐monophosphate to the culture medium. These data support the hypothesis that also in cells from higher plants a regulatory mechanism exists with some similarities to the “catabolite repression” mechanism operating in several prokaryotes and lower eukaryotes.
Phases in potassium transport and their regulation under near‐equilibrium conditions in wheat seedlings
Authors: Erdei Lásló , Oláh Zoltán , Bérezi Alajos
Published: April 2006

Potassium uptake and release in roots and translocation to the shoots were studied in 14‐day‐old winter wheat (Tritictum aestivum L. cv. Martonvásári 8) of different K status. Transport processes were measured in the growth solutions for 5 h ensuring near‐equilibrium conditions. The uptake showed three phases: (1) at low external K+ concentrations it increased with increasing concentrations and culminated at 0.1 mM: (2) between 0.1 and 1 mM it decreased, and (3) it increased again above 1 mM: The release of K+ showed a constant low level below 1 mM while paralleling the uptake above that. The uncoupler 2,4‐dinitrophenol inhibited uptake phases (1) and (2), whereas it did not affect either phase (3) or K+ release. Translocation showed similar patterns. It is concluded that phases (1) and (2) depend on metabolic energy while phase (3) is mostly passive. It is emphasized that different types of regulation seem to operate in the transport mechanism: i.e. limitation by transport sites, control by negative feedback and by K+/K+ exchange, respectively.
Free radical and free radical scavenger effects on indole‐3‐acetic acid levels and ethylene production
Authors: Parups E. V.
Published: April 2006

Stable free radicals, together with horseradish peroxidase, promoted degradation of indole‐3‐acetic acid (IAA). These reactions were retarded by the free radical scavengers Bromoxynil, Na‐benzoate and kinetin. Certain free radicals promoted, but the free radical scavenger Bromoxynil retarded ethylene production in apple slices and mung bean stem tissues. The interdependency of free radicals and free radical scavengers in systems controlling IAA levels and ethylene production is discussed.
Induction of phenylalanine ammonia‐lyase in hypocotyls of sunflower seedlings by light, excision and sucrose
Authors: Tena Manuel , López‐Valbuena Rafael , Jorriń Jesús
Published: April 2006

Light, excision and sucrose increased extractable phenylalanine ammonia‐lyase (PAL) activity from hypocotyl tissue of sunflower (Helianthus annuus L. cv. Peredovik) to 2–6 times the basal level. Intact sunflower seedlings or whole hypocotyls incubated in water or 0.1 M sucrose exhibited, in continuous light, a pattern in which PAL peaked 4 and 28 h after the beginning of the illumination. When 0.5 cm long hypocotyl segments were incubated in water or 0.1 M sucrose, they exhibited, both in continuous light and in the dark, a pattern in which PAL rose during an initial period of 10 h (assay in sucrose and light) to 48 h (assay in water and dark) and then remained nearly constant at a high value for at least the next 10 h. When whole hypocotyls were incubated in 0.1 M sucrose, a third pattern in PAL activity was found in which PAL peaked after 28 h and subsequently declined. In all the above systems the increase in PAL activity was significantly reduced by cycloheximide. Furthermore, the subsequent decay of PAL activity following illumination was prevented by delayed transfer to cycloheximide. It is suggested that the results can be explained on the basis of a turnover mechanism involving continued de novo enzyme synthesis and subsequent synthesis of a PAL‐inactivating system.
Effects of water stress on the water relations of Phaseolus vulgaris and the drought resistant Phaseolus acutifolius
Authors: Parsons Lawrence R. , Howe Teresa K.
Published: April 2006

The tepary bean (Phaseolus acutifolius Gray var. latifolius), a drought resistant species, was compared under water stress conditions with the more drought susceptible P. vulgaris L. cvs Pinto and White Half Runner (WHR). In order to better understand the basis for the superior drought resistance of tepary, this study was designed to determine the relationships among leaf water potential, osmotic potential, turgor potential, and relative water content (RWC).

Plants were prestressed by withholding irrigation water. These stress pretreatments changed the relation between leaf water potential and relative water content of both species so that prestressed plants had lower water potentials than controls at the same leaf RWC. Tepary had lower water potentials at given RWC levels than Pinto or WHR; this can account for part of the superior resistance of tepary. In all genotypes, prestressed plants maintained osmotic potentials approximately 0.2 MPa lower than controls. Tepary reached osmotic potentials that were significantly lower (0.15 to 0.25 MPa) than Pinto or WHR. Both control and prestressed tepary plants had 0.05 to 0.25 MPa more turgor than Pinto or WHR at RWC values between 65 and 80%. Both prestressed and control tepary plants had greater elasticity (a lower elastic modulus) than Pinto or WHR. This greater turgor of tepary at low RWC values could be caused by several factors including greater tissue elasticity, active accumulation of solutes, or greater solute concentration.

Tepary had significantly lower osmotic potentials than the P. vulgaris cultivars, but there was little difference in osmotic potential between Pinto and WHR. Knowledge of differences in osmotic and turgor potentials among and within species could be useful in breeding for drought resistance in Phaseolus.
The physiological basis of seed dormancy in Avena fatua IV. Alternative respiration and nitrogenous compounds
Authors: Adkins Stephen W. , Simpson Graham M. , Naylor James M.
Published: April 2006

Sodium nitrate and nitrite induced germination in a partly after‐ripened dormant line of Avena fatua L. The dose‐response curves for their stimulation of germination and oxygen uptake were similar, indicating that these compounds may stimulate germination by promoting oxygen uptake. Time‐sequence studies showed that nitrate and nitrite stimulated oxygen uptake as much as 70% prior to the first signs of germination. A similar ammonium chloride treatment failed to induce germination or elevate the rate of oxygen uptake, indicating that nitrate and nitrite may promote these events by acting as electron acceptors. The stimulation of germination and oxygen uptake by nitrate and nitrite were not significantly inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and oxygen uptake by nitrate and nitrite do not require the operation of the alternative pathway of respiration. The stimulation of germination and oxygen uptake by nitrate and nitrite were not inhibited by sodium azide, an inhibitor of cytochrome‐mediated respiration; however both germination and oxygen uptake were prevented when salicylhydroxamic acid and sodium azide were applied together. Thus, stimulation of germination and oxygen uptake by nitrate and nitrite require the operation of only one or other of the pathways of respiration; however a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of these compounds as promotors of respiration is discussed with reference to dormancy and the involvement of the Krebs cycle.
Thigmomorphogenesis: Ethylene evolution and its role in the changes observed in mechanically perturbed bean plants
Authors: Biro R. L. , Jaffe M. J.
Published: April 2006

Mechanical perturbations, in the form of either rubbing or wounding, cause ethylene evolution from bean internodes (Phaseolus vulgaris L. cv. Cherokee Wax). This evolution begins 45 to 60 min after perturbation or wounding and peaks about 2 h later. Maximal thigmomorphogenesis occurs if internodes are perturbed when they are 10 mm or less in length. Maximal ethylene evolution, however, occurs in longer internodes. When one internode is perturbed, ethylene evolution is not observed from other internodes even though they respond thigmomorphogenetically by exhibiting decreased elongation. Ethylene evolution is apparently a result of increased 1‐amino‐cyclopropane‐1‐carboxylic acid (ACC) production after perturbation. Inhibitors of ACC and ethylene synthesis block increased radial growth but not reduced elongation. Ethylene may therefore be only one of several factors causing thigmomorphogenesis.
Competition and fruit set in the Washington navel orange
Authors: Guardiola J. L. , García‐Marí F. , Agustí M.
Published: April 2006

In the Washington navel orange [Citrus sinensis (L.) Osbeck] an increase in the number of flowers results in a reduction of flower weight at anthesis and the initial fruit growth rate, and the number of developing fruitlets increases. Most of these fruitlets are shed during post‐anthesis, and the final set of fruit is unrelated to the number of flowers and to the total amount of metabolites and mineral elements used up in fructification but appears to be controlled by the capacity of the tree to supply metabolites to the developing fruitlets during post‐anthesis. When the number of flowers is too large, there is a reduction both in the number of initially developing fruitlets and in their growth rate. The final set of fruit is reduced through a different mechanism acting at anthesis and involving differences in mineral composition, which impairs the capacity of the fruit to act as a sink.
Effects of cold on CO2 exchange in winter rape leaves
Authors: Maciejewska Urszula , Tomczyk Jerzy , Kacperska Alina
Published: April 2006

The influence of temperature on the CO2 exchange rates was investigated in winter rape plants (Brassica napus L. var. oleifera cv. Górczański) subjected to cold (2°C) pretreatment. After one or two days of cold pretreatment both photosynthesis and dark respiration still readily responded to changes in the temperature of measurement. Prolongation of plant exposure to cold caused not only a marked depression of photosynthesis but also photosynthesis became less temperature and light dependent. In contrast, prolonged cold pretreatment only slightly affected the sensitivity of dark respiration to temperature. In the cold‐pretreated plants the rate of dark respiration was higher that that in the untreated ones at comparable temperatures of measurement. To obtain a full reversion of the cold‐induced changes in photosynthesis and dark respiration rates the plants had to be exposed to higher (25°C) temperature for 3–7 days.

It seems that low temperature brings about two types of effects in plants with regard to photosynthesis and respiration: a direct response consisting in the rapid and readily reversible reduction of both photosynthesis and respiration; and an indirect one which consists in long lasting modifications of photosynthesis and dark respiration rates and may be related to the cold‐induced changes in biochemical properties in photosynthetic and respiratory systems.
Effects of water stress on internal water relations of apple leaves
Authors: Fanjul Luis , Rosher Philip H.
Published: April 2006

The capacity of apple (Malus pumila Mill. cv. James Grieve and Golden Delicious) pot‐ and orchard‐grown trees to adjust osmotically in response to drought was investigated. Stressed leaves exhibited alterations in the moisture release curves when compared to well hydrated control leaves. Results suggest that osmotic adjustment occurred in both field‐ and pot‐grown trees. Water potential for zero turgor was lowered by 0.5 MPa in leaves of potted trees and by 1.1 MPa in leaves of field‐grown trees as a result of stress treatments. A decrease in the osmotic potential was responsible for that adjustment allowing the leaf to maintain turgor at lower water potentials and relative water contents. The extent of adjustment was similar for both potted and orchard trees despite the difference in the rate of stress imposition and its intensity. Changes in the concentration of sugars apparently contributed to this adjustment.
Flavonol content of guard cell and mesophyll cell protoplasts isolated from Vicia faba leaves
Authors: Weissenböck G. , Schnabl H. , Sachs G. , Elbert Chr. , Heller F.‐O.
Published: April 2006

Guard cells of the lower epidermis of leaflets of Vicia faba L. cv. Weißkernige Hangdown contain several kaempferol 3,7‐O‐glycosides. This was demonstrated for the first time by the use of isolated, highly purified guard cell protoplasts for flavonol estimation and quantitation. From a total of ca 12 kaempferol glycosides, three were identified by comparative thin layer chromatography and high performance liquid chromatography as kaempferol 3‐O‐glucoside 7‐O‐rhamnoside (major component), 3‐O‐rhamnogalactoside 7‐O‐rhamnoside and 3,7‐O‐bisglucoside (minor components). On average, the total flavonol content was estimated to be 85 fmol protoplast−1. From comparative investigations including alkaline‐induced (green) fluorescence characteristics of flavonols and UV‐microscopical studies we suggest that kaempferol glycosides are present in guard cells and epidermal cells in similar quantities, and that these compounds are in the vacuole.

By contrast, mesophyll protoplasts have a low flavonol content (one sixth that of guard cells). In spite of the different total flavonol contents, individual components of each cell‐type are the same. However, they show differences in their quantitative distribution.
Changes in the content and distribution, in different organs, of the flavour precursors, the S‐alk(en)yl‐L‐cysteine sulphoxides, during seedling development of onions (Allium cepa) grown under light and dark regimes
Authors: McCallion Barbara J. , Lancaster Jane E.
Published: April 2006

Flavour precursors accumulated rapidly in onion seedlings (Allium cepa L. cv. Pukekohe Longkeeper, May and Ryan) after emergence of the cotyledon. (±)‐S‐1‐Propyl‐L‐cysteine sulphoxide, found mainly in the shoots, was the predominant flavour precursor. (±) Trans‐S‐1‐propenyl‐L‐cysteine sulphoxide was important during very early seedling growth when very high concentrations were reported in the root and hypocotyl. (±)‐S‐1‐Methyl‐L‐cysteine sulphoxide, a minor component in seedlings grown under a normal light regime, was significant during early cotyledon development in seedlings grown in the dark. It is concluded that onion seedlings would be a suitable tissue in which to investigate the biosynthetic pathways of the S‐alk(en)yl‐L‐cysteine sulphoxides.
Influence of osmotic stress on the respiration of potato tuber callus
Authors: van der Plas Linus H. W. , Wagner Marijke J.
Published: April 2006

Potato tuber (Solanum tuberosum L. cv. Bintje) callus shows a decrease in fresh weight and an increase in dry weight upon transfer to nutrient medium supplemented with 0.3 or 0.5 M mannitol. The osmolarity of the intracellular fluid increases simultaneously. Probably mannitol is taken up from the medium till the osmolarity of the tissue is in equilibrium with that of the medium. After osmotic adaptation, on a medium with 0.5 M mannitol, growth is negligible, although the tissue retains its viability.

Respiration increases upon transfer to medium with extra mannitol, especially when expressed on a fresh weight basis. On this basis cytochrome and alternative pathway capacities do not change appreciably. The respiratory increase is exclusively caused by an increased engagement of the alternative pathway. The participation of this pathway in uninhibited respiration increases from about 10 to 90% upon transfer to medium with extra mannitol. The increase in respiration is partly correlated with the decrease in fresh weight upon transfer. Per disc, the capacities of the cytochrome and alternative pathway decline. Yet, total respiration per disc significantly increases due to the increased participation of the alternative pathway. This results in an almost equal ATP‐production per disc before and after transfer. We suggest, that the alternative pathway functions as a reserve capacity in potato callus, which is switched on when ATP‐production coupled to the cytochrome pathway is impaired.
Long distance transport of potassium in cereals during grain filling in detached ears
Authors: Haeder Hans‐Eckhard , Beringer Helmut
Published: April 2006

Ears of wheat plants (Triticum aestivum L. cv. Kolibri), which were given different and uniform K+‐nutrition in two experiments, were cut at 2, 4 and 6 weeks after anthesis at 15 cm below the ear. These detached ears were fed 30 mM (experiment 1) or 15, 30, 60 or 90 mM86Rb‐K2 malate (experiment 2) and 146 mM [14C]‐sucrose. After a pulse period of 6 and 4 h, respectively, the ears were transferred to identical non‐labeled solutions for additional 0, 4, 8 or 20 h.

About 50% of the K+ and sucrose supplied was absorbed by detached ears. This rate declined with plant age and decreasing transpiration. Within the 6 and 4 h uptake period less than 7% of the absorbed K+, but 20% of the sucrose taken up were incorporated into the grain. During the chase period labeled K+ in the grain increased to 15% and 14C even to 50% of total tracer uptake. Incorporation of labeled K+ into the grain was not affected by the previous K+ nutrition of the plant and was proportional to the K+ concentration in the uptake solution. Transition of K+ from xylem into phloem during its acropetal transport is assumed. No evidence was found that the grain itself could control its uptake of K+.
Long distance transport of potassium in cereals during grain filling in intact plants
Authors: Haeder Hans‐Eckhard , Beringer Helmut
Published: April 2006

Translocation of labeled potassium (K+) from the root to the ear and its distribution within the culm during 4, 8 and 12 h of uptake was studied in intact wheat plants (Triticum aestivum L. cv. Kolibri) 3 and 5 weeks after anthesis at 0.5 and 5.0 mM K+ concentration in the uptake solution. Uptake of labeled K+ into the shoot was proportional to the K+ concentration applied. After 4 h of uptake about 2% and after 12 h about 7% of labeled K+ applied to the roots were taken up into the shoot at both K+ concentrations. After 12 h of uptake only 6% of the total label in the culm had reached the ear, while about 40% of the label was found in the upper three internodes. In spite of an increasing concentration of labeled K+ during 12 h in the uppermost internode (peduncle), translocation of K+ into the rachis was low. The low and uniform K+ content found generally in grain dry weight seems therefore to be due to a controlled K+ supply to the ear.
Urate oxidase of Chlamydomonas reinhardii
Authors: Pineda Manuel , Fernández Emilio , Cárdenas Jacobo
Published: April 2006

Urate oxidase (EC 1.7.3.3) of Chlamydomonas reinhardii cells grown on purines and purine derivatives has been partially characterized. Crude enzyme preparations have a pH optimum of 9.0, require O2 for activity, have an apparent Km of 12 μM for urate, and are inhibited by high concentrations of this substrate. Enzyme activity was particularly sensitive to metal ion chelating agents like cyanide, cupferron, diethyldithiocarbamate and o‐phenanthroline, and to structural analogues of urate like hypoxanthine and xanthine. Chlamydomonas cells grow phototrophically on adenine, guanine, hypoxanthine, xanthine, urate, allantoin or allantoate as sole nitrogen source, indicating that in this alga the standard pathway of aerobic degradation of purines of higher plants, animals and many microorganisms operates. As deduced from experiments in vivo, urate oxidase from Chlamydomonas is repressed in the presence of ammonia or nitrate.
Changes in growth and water‐soluble solute concentrations in Sorghum bicolor stressed with sodium and potassium salts
Authors: Weimberg Ralph , Lerner H. R. , Poljakoff‐Mayber A.
Published: April 2006

Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na2SO4, K2SO4 or with variable mixtures of either NaCl/KCl or Na2SO4/K2SO4 at osmotic potentials ranging from 0 to ‐0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14‐day‐old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na2SO4 < KCl = K2SO4. Inhibition of growth by mixtures of Na+ and K+ salts was the same as by K+ salts alone. Roots responded differently. Root growth was not affected by Na+ salts in the range of 0 to ‐0.2 MPa while it was stimulated by K+ salts. The major cation of leaves was K+ because S. bicolor is a Na+‐excluder, while Na+ was the major cation in roots except at low Na+/K+ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride‐plants (plants growing in media in which the only anion of the salinizing salts was Cl−) and 50 fold in Sulphate‐plants (the only anion of the salinizing salts was SO42‐). Proline increased 60 and 18 fold in Chloride‐ and Sulphate‐plants, respectively, as growth media potentials decreased from 0 to ‐0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)−1 (the monovalent cation level in non‐stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)−1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.