bluuebunny/crossref_metadata_2025 huggingface dataset:
Phytochrome effects on leaf growth and chlorophyll content in Petunia axilaris
Authors: CASAL J. J. , APHALO P. J. , SÁNCHEZ R. A.
Published: April 2006

Abstract Changes in the phytochrome status at the end of the daily photosynthetic period result in several plant responses. To understand the causal relations among these responses it is useful to investigate species or experimental conditions where the most common correlations among responses are broken. A step in this direction is presented here with Petunia axilaris, where FR‐treated plants showed low chlorophyll content and erect leaves, but‐ contrary to other species‐higher leaf area and plant dry weight. Differences in area expansion were related to the late phase of leaf growth and were due, at least in part, to larger cells in FR‐treated plants. Effects on length/width ratio, specific leaf area, net assimilation rate, shoot/root ratio and leaf number were small or non‐existent. It is suggested that the lower chlorophyll content in FR‐treated plants was not a consequence of scarcity of assimilates.
Lacunar gas discharge: a valid estimate of photosynthetic rates in submerged macrophytes?
Authors: DROMGOOLE F. I. , SORRELL B. K.
Published: April 2006

Abstract Photosynthetic oxygen produced by the submerged aquatic plant Egeria densa Planch, is partitioned into lacunar gas spaces and to the external medium. Despite an apparently linear relationship between volume of lacunar gas discharge and dissolved oxygen release under certain conditions, the partitioning is, as expected from theoretical considerations, not necessarily constant in different conditions. On this basis we believe that lacunar gas discharge is an inconsistent and therefore unreliable method of measuring photosynthesis in submerged macrophytes.
Distribution of alcohol dehydrogenase in roots and shoots of rice (Oryza sativa) and Echinochloa seedlings
Authors: COBB B. G. , KENNEDY R. A.
Published: April 2006

Abstract Aerobically germinated seedlings of rice and Echinochloa were found to survive when placed in an anaerobic environment for 4 d, whereas pea and maize seedlings did not. Although root and shoot growth were inhibited in rice and Echinochloa under anaerobiosis, growth resumed when the seedlings were returned to aerobic conditions. Alcohol dehydrogenase (ADH) activity increased more, and protein synthesis was greater, in the shoots than in the roots under anaerobic conditions. These results suggest that, in anaerobiosis‐tolerant species, ADH activity and protein synthesis in the shoots represents or results from metabolic adaptations to low oxygen. These results are discussed in terms of plant establishment and growth in a low‐oxygen environment.
Solute accumulation, solute potential, germinability and seedling vigour of seeds of finger millet (Eleusine coracana Gaertn.) raised under rain‐fed conditions and under irrigation
Authors: KUMAR S. P. DINESH , SASHIDHAR V. R. , PRASAD T. G. , KUMAR M. UDAYA , SEETHARAM A.
Published: April 2006

Abstract The nature of the solutes accumulated in the grains of ten finger millet genotypes grown under rain‐fed conditions with moisture stress during panicle and grain development were determined. Although grain yield decreased under stress, the solute potential (SP) of seeds from stressed plants was significantly lower (more negative), probably due to the increase in sucrose content. There were no significant changes in the content of total amino acids, free proline, reducing sugars or potassium. The contribution of sucrose to total solute potential was approximately 32% in seeds obtained from stressed plants as compared with only 15% in seeds from irrigated treatment. The germinability and seedling vigour of the seeds from stressed plants was significantly higher under simulated stress with polyethylene glycol (PEG), but was similar to that of seeds of non‐stressed plants under normal conditions.
Oxygen uptake by tobacco leaves after heat shock
Authors: HAVAUX M. , CANAANI O. , MALKIN S.
Published: April 2006

Abstract Small discs punched out from leaves of tobacco (Nicotiana tabacum L.) were exposed for 3 min in the dark to a high temperature of around 48°C. This caused a progressive inhibition of the gas‐exchange (oxygen evolution) type photoacoustic signal, resulting‐ finally in phase inversion (i.e. leading to negative values), which indicates that oxygen uptake replaces the normal oxygen evolution. This effect was also observed in various other plant species. Oxygen uptake was rapidly reversed (within ca. 4–5 min) to a certain low value of oxygen evolution (about 20% of the control) by continuous illumination with relatively strong white light (minimum 55 W m−2). However, a few minutes in darkness following this heat treatment induced reappearence of the uptake signal. This photoacoustically detected oxygen uptake after heat shock may be interpreted as reflecting stimulated oxygen photoreduction (Mehler reaction) caused by (light dependent) inactivation of the Calvin cycle by heat, suggesting that oxygen may act as a major photosynthetic electron acceptor under stress conditions. Leaves suffering from such heat shock effects were completely restored to normal behaviour after a 24‐h incubation at room temperature (25 °C). Analysis of the modulation frequency and wavelength dependence of the photoacoustic signals showed that heat shock‐induced oxygen uptake is a very complex phenomenon, composed of at least two components differing in kinetics and sensitivity to DCMU.
Lead accumulation and its translocation barriers in roots of Allium cepa L.—autoradiographic and ultrastructural studies
Authors: WIERZBICKA M.
Published: April 2006

Abstract Lead migrating through the tissues of Allium cepa L. was found, by electron microscopy, autoradiography and other methods, to encounter at least three barriers to penetration. The layers of protoderm and hypodermic meristematic cells in the root meristematic zone and the layer of endodermis in the mature root zone were barriers to apoplastic transport. The central zone was a barrier to apoplastic and symplastic transport. It comprises the quiescent centre in the root meristem and the central part of the root cap. The cells of the deepest ground meristematic tissue layers seemed to act as a barrier, which keeps lead away from the procambium. Lead accumulated in roots but it was not uniformly distributed between their various tissues. The largest amount of lead accumulated both in ground meristematic and cortex tissues.
Salt tolerance in Aster tripolium L. II. Ionic regulation
Authors: SHENNAN C. , HUNT R. , MACROBBIE E. A. C.
Published: April 2006

Abstract Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m−3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis.

Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.
Field measurement of leaf water potential with a temperature‐corrected in situ thermocouple psychrometer
Authors: WULLSCHLEGER S. D. , DIXON M. A. , OOSTERHUIS D. M.
Published: April 2006

Abstract. The construction and evaluation of a temperature‐corrected in situ thermocouple psychrometer for measurement of leaf water potential (Ψ) is described. The instrument utilized two chromel‐constantan thermocouples which allowed for detection of both the psychrometric zero offset and the temperature differential between the sample and the Peltier measuring junction. The psychrometer was subjected to stable temperature gradients while in contact with reference solutions of sodium chloride, and the effects of thermal gradients were quantified. Regression analysis indicated that temperature differentials were responsible for errors in water potential determinations of approximately –7.73 MPa°C−1. When installed on leaves of field‐grown cotton (Gossypium hirsutum L.), corn (Zea mays L.) and soybean (Glycine max L. Merr) the instrument detected temperature differentials up to 0.1°C (–6.0 μV) which were associated with relatively small shifts in psychrometric zero offsets (–0.05––0.75 μV). Results indicated that substantial errors in apparent Ψ were caused by non‐isothermal conditions between the leaf and the psychrometer measuring junction. The relative magnitude of these errors could be quantified and the corrected results showed good agreement with conventional psychrometric determination of Ψ on excised samples during a diurnal cycle.
A quantitative approach to the inorganic carbon system in aqueous media used in biological research: dilute solutions isolated from the atmosphere
Authors: HELDER R. J.
Published: April 2006

Abstract. The changes in the distribution of dissolved inorganic carbon systems resulting from biological activity are described using the dissociation equations and considering eight variables: the concentrations or activities of H+, OH−, CO2, H2CO3, HCO3−, CO32−, total carbon ∑CO2, carbonate alkalinity A− and base excess B+. Equations for the equilibrium constants K1, K2 and K3, giving their dependence on temperature, are provided. These thermodynamic constants are defined on the infinite dilution scale and their dependence on the pH‐convention adopted is stressed. From the dissociation equations and the eleclroneutrality condition a set of 15 equations were deduced, each representing the relationship between the H+‐activity and one pair of the other variables. The knowledge of two variables will, therefore, enable the calculation of all the other variables, furnishing a complete description of the C‐system. Such a description is needed to permit the calculation of the ionic strength (I) of a solution. Knowing I makes it possible to calculate the activity‐coefficients for bicarbonate and carbonate ions (Debye‐Hueckel equations), which are needed to calculate the working constants K1 and K2 from the thermodynamic ones. Hints for computer programs, some of them including iterative subroutines, are given. Suggestions are made for the experimental determination of K1 and K2. The discussions arc restricted to dilute solutions isolated from a gaseous phase, at 1 atm, external pressure and having an ionic strength of not more than 70 mol m−3. The difficulty of providing causal explanations in studies involving the C‐system is briefly discussed.
Effects of frost hardening, dehardening and freezing stress onin vivochlorophyll fluorescence of seedlings of Scots pine (Pinus sylvestrisL.)
Authors: STRAND M. , ÖQUIST G.
Published: April 2006

Abstract.The kinetics ofin vivochlorophyll fluorescence of photosystem II (PS II) was measured at room temperature and 77 K during frost hardening of seedlings of Scots pine (Pinus sylvestrisL.), and after exposure of frost‐hardened shoots to sub‐freezing temperatures.

A more pronounced decrease in variable fluorescence yield for the upper exposed than for the lower shaded surface of the needles suggested that some photoinhibition occurred during prolonged frost hardening at 50 μmol photons m−2s−1and 4°C.

Reversible inhibition of photosynthesis after exposure to sub‐freezing temperatures was initially manifested as an increase of steady‐state energy‐dependent fluorescence quenching (qE) and a reduction in the rate of O2evolution. Further inhibition after treatment at still lower temperatures caused a progressive decline of steady‐state photochemical quenching (qQ) and the rate of O2evolution, whereas qEremained high. This implies an inactivation of enzymes in the photosynthetic carbon reduction cycle decreasing the consumption of ATP and NADPH, which is likely to cause an increase of membrane energization and a reduction of the primary electron acceptor (QA) of PS II. Alternatively, the changes in qQand qEmight be attributed to an inhibition of photophosphorylation. Severe, irreversible damage to photosynthesis resulted in a suppression of qEand of variable fluorescence yield, probably because the photochemical efficiency of PS II was impaired.

Changes in the fast fluorescence kinetics at room temperature after severe freezing damage were interpreted as an inhibition of the electron flow from QAto the plastoquinone pool. It is suggested that irreversible freezing injury to needles of frost‐hardenedP. sylvestriscauses damage to the QB,‐protein.
Stomatal limitation of photosynthesis and reduced growth of the halophyte, Plantago maritima L., at high salinity
Authors: FLANAGAN L. B. , JEFFERIES R. L.
Published: April 2006

Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m−3 NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m−3 NaCl was only 20% of that in plants at low salinity. Both the Na+ and K+ content of leaves and roots increased with external salinity. There was no change in the Na+/K+ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na+ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO2 and by ribulose‐1,5‐bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO2 concentration. The increased stomatal limitation of photosynthesis resulted in higher water‐use efficiency of plants grown at high salinity.
Persistent xylem cross‐walls reduce the axial hydraulic conductivity in the apical 20 cm of barley seminal root axes: implications for the driving force for water movement
Authors: SANDERSON J. , WHITBREAD FIONA C. , CLARKSON D. T.
Published: April 2006

Abstract. Xylem vessels in the apical 25 cm of barley seminal axes were examined by scanning electron microscopy of fractured freeze dried or critical point dried specimens. In the apical 11 cm, there were three cross walls cm−1 root in the central xylem vessel. The frequency then declined with distance but did not become less than 1.0 cm−1 root until the 22–25‐cm zone.

Suction was applied to the proximal end of segments of seminal axes whose surfaces had been sealed with wax to prevent radial entry of water. Perfusion of the xylem with solutions of Tinopal CBS‐X revealed the conductive xylem vessels by fluorescent staining of their walls. In the apical 20 cm of the axis, only a variable number of smaller xylem vessels conduct water. Beyond this zone, the much larger central vessel becomes functional.

The flow of water (Jv) in the apical zone was very much less for a given presure (△P) than in the proximal zone > 25 cm from the tip, and could be predicted by the Poiseuille equation provided the correct number of functional vessels are known. This information, together with earlier results on water uptake along the root length are used to predict the attenuation of the hydrostatic driving force for water uptake along the root length.

Estimates of K+ concentrations in stelar parenchyma and xylem vessels were made by electron microproble X‐ray analysis. These results show that [K+] in the xylem vessels may be two to three times greater in the zone 1–2 cm from the root tip than in the basal zone. Such a gradient of solute potential may, to some extent, offset the decreasing influence of the leaf water potential in apical zones where xylem is not fully conductive.
Light and electron microscope studies on pollen development in barley (Hordeum vulgare L.) grown under copper‐sufficient and deficient conditions
Authors: JEWELL A. W. , MURRAY B. G. , ALLOWAY B. J.
Published: April 2006

Abstract. Pollen development in copper‐deficient barley plants is highly irregular resulting in low and variable pollen fertility. The main cause of this sterility was found to be the abnormal development of the tapetum which becomes expansionary and invasive as the pollen develops. The ultrastructure of both tapetum and microspores is different from that of control material with irregularities of exine deposition, endopolyploidy of tapetal nuclei and an alteration of organelle composition being correlated with low fertility.
Plant coated vesicles
Authors: COLEMAN J. , EVANS D. , HAWES C.
Published: April 2006

Abstract. Coated vesicles are organelles frequently encountered in many plant cell types often in association with the plasma membrane, Golgi apparatus, partially coated reticulum and multivesicular bodies. They are readily identified by a characteristic cage or basket composed of interlocking triskelions of the protein clathrin which are bound to the surface of the vesicle membrane. Although their transport function has been well studied and characterized in mammalian systems, the possible importance of coated vesicles as transport organelles in plant cells is only just beginning to be explored. In this review, the authors describe the structure of higher plant coated vesicles and discuss their possible involvement in the endocytosis of marcromolecules, in exocytosis and in the intracellular transport of material between cytoplasmic compartments. Their possible role in maintaining the macromolecular composition of the plasma membrane whilst allowing recycling of excess lipid bilayer and their potential application as vehicles for the introduction of foreign macromolecules into plant cells are discussed.
Effects of temperature and oxygen depletion on metabolic rates of tomato and carrot cell cultures and cuttings measured by calorimetry
Authors: CRIDDLE R.S. , BREIDENBACH R.W. , LEWIS E.A. , EATOUGH D.J. , HANSEN L.D.
Published: April 2006

Abstract. Isothermal heat‐conductance calorimetry was used to monitor responses of tomato and carrot metabolism to changes in temperature and oxygen concentrations. Calorimetric measurements of metabolic heat evolution from tissue segments and cultured cells was found to be a sensitive, nondestructive estimate of metabolic rates. Short‐term measurements of metabolic rates of cells in culture correlate well with calorimetric measurements made on tissue sections. The results accurately predict the growth properties of intact plants based on the generally recognized characteristics of these two species. The calorimetric method provides another means for rapid evaluation of plant responses to physical and chemical stresses and is of value for screening and selection.
The isolation of leaf protoplasts from the submerged aquatic angiosperm Potamogeton lucens L.
Authors: STAAL M. , PRINS H. B. A. , VAN HARMELEN M. , HELDER R. J.
Published: April 2006

Abstract. A method for isolating protoplasts from leaves of the submerged aquatic angiosperm Potamogeton lucens L. is described. The protoplasts are produced enzymatically from leaf strips using 1.5% (w/v) Cellulysin, 0.3% (w/v) Macerozyme R10, and 2.5% (v/v) β‐glucuronidase at 27°C in the dark. Subsequently the protoplasts are purified on a discontinuous Ficoll gradient. The yield obtained is approximately 20% of the starting material on a chlorophyll basis. The viability is high, namely more than 90% as estimated with Evans Blue. Cells of the intact leaves of P. lucens can use HCO3− for photosynthesis. 14CO2 fixation experiments at pH 6.0 and 8.5 suggest that these isolated protoplasts can also use bicarbonate as a carbon source.
Molecular biology of metal tolerances of plants
Authors: TOMSETT A. B. , THURMAN D. A.
Published: April 2006

Abstract. The review discusses some of the important aspects of the molecular biology of metal tolerances in animals, fungi and plants. First, results of classical ecological and genetical studies are briefly outlined. The evidence for the occurrence and properties of metal‐binding proteins (metallothioneins) and peptides (phytochelatins) in fungi and plants is described. It is concluded that at present there is no firm evidence to suggest that a protein homologous with the metallothioneins of animals and fungi occurs in plants. The discovery of phytochelatins, γ‐glutarnyl peptides, containing only glutamic acid, cysteine and glycine, in plants is described and evidence for their role in heavy metal tolerance is assessed. The difference between sulphur metabolism in animals and plants and its relationship to heavy metal tolerances is discussed in terms of the occurrences of metallothioneins in animals and phytochelalins in plants. Future prospects for research in this area are outlined in terms of identification of plant genes coding for metallothioneins and for the enzymes involved in the synthesis of phytochelatins.
Nodulation of legumes by rhizobium
Authors: DOWNIE J. A. , JOHNSTON A. W. B.
Published: April 2006

Abstract. The formation of nitrogen‐fixing nodules on leguminous plants is the culmination of an integrated development involving many plant and bacterial genes. This review focuses on the structure, function and regulation of the bacterial genes involved in the nodulation process. We attempt to interpret recent observations on these genes in the context of signal exchanges which occur between the macro‐and micro‐symbionts.
Ion currents associated with root tips, emerging laterals and induced wound sites in Nicotians tabacum: spatial relationship proposed between resulting electrical fields and phytophthoran zoospore infection
Authors: MILLER A. L. , SHAND E. , GOW N. A. R.
Published: April 2006

Abstract Growing roots of Nicotiana tabacum var. Havana generate transcellular ion currents which traverse developing and wounded tissues. Positive current of around 10 mA m−2 enters meristematic and elongating cells at the tip of primary roots. The growing tips of first order laterals are also traversed by a similar positive current with a density of around 2.0 mA m−2, as are immature laterals emerging at the primary root surface. These self‐generated ion currents flow basipetally through developing tissues and leave from mature non‐elongating tissue. A large positive current of around 70 mA m−2 also enters induced wound sites on the primary root surface. Motile zoospores of the fungal pathogen Phytophthora parasitica var. nicotianae have been reported to associate preferentially with these regions of the root. This might suggest that electrotaxis may be part of the mechanism by which zoospores locate root regions susceptable to fungal infection.
A method for measuring hydraulic conductivity and embolism in xylem
Authors: SPERRY J. S. , DONNELLY J. R. , TYREE M. T.
Published: April 2006

Abstract Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time‐dependent reductions in flow rate, and because of variable degrees of embolism. Using Acer saccharum Marsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m−3 oxalic) prevent long‐term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow‐impeding air emboli have been removed by repeated high‐pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long‐term (> 4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short‐term (< 4h) measurements may be caused by movements of air emboli in vessels and/or participate matter.
Mechanical freeze‐thaw damage and frost hardening in leaves and isolated thylakoids from spinach. II. Frost hardening reduces solute permeability and increases extensibility of thylakoid membranes
Authors: HINCHA D. K. , SCHMITT J. M.
Published: April 2006

Abstract Thylakoids isolated from cold‐acclimated spinach (Spinacia oleracea L.) leaves were more resistant against mechanical freeze‐thaw injury measured as plastocyanin release, than thylakoids from non‐acclimated leaves. They were more resistant against solute influx during freezing and they were able to re‐expand to a larger volume in comparison to non‐hardy controls. Likewise, plastocyanin was released from thylakoids of non‐acclimated but not of frost‐hardy leaves under conditions of mild in situ freezing stress for several days.
Ecophysiological investigations of Chara vulgaris L. grown in a brackish water lake: ionic changes and accumulation of sucrose in the vacuolar sap during sexual reproduction
Authors: KIRST G. O. , JANSSEN M. I. B. , WINTER U.
Published: April 2006

Abstract Chara vulgaris L. growing in a brackish water lake was investigated in a field study during the main growth season (May to October 1985). Sucrose content and the ionic concentrations of the cations Na+, K+, Mg2+ and Ca2+ and the anions Cl− and SO42‐ of the vacuolar sap were estimated. Sucrose concentration in the vacuolar sap of vegetative growing plants was negligible, but with the beginning of the sexual reproduction period (fructification) the sucrose content increased from about 2 mol m−3 to 110 mol m−3. This level remained constant until the end of the fructification period. In spite of the increase of the sucrose concentration the osmotic potential of the vacuolar sap was constant. This was achieved by changing the ionic concentrations accordingly; in old or vegetative growing plants the ionic content accounted for about 80% of the vacuolar osmotic potential, but was about 63% during fructification. Sucrose is considered as a major photosynthate to supply the developing antheridia and oogonia and to serve as a precursor for the starch stored in the eggs.
Some thoughts about the use of predicted values of the state of phytochrome in plant photomorphogenesis research
Authors: MANCINELLI A. L.
Published: April 2006

AbstractPredicted values of photoequilibrium ratios and rates of photoconversion and cycling, calculated from known optical parameters of purified phytochrome and the spectral photon flux distribution of the light sources used, arc often applied in the evaluation of the relationships between the state of phytochrome and the expression of phytochrome‐mediated responses. This is commonly done when the state of phytochromein vivocannot be determined experimentally. The ‘predicted’ states of phytochrome may be quite different from the actual onesin vivofor several reasons: the particular set of optical parameters of purified phytochrome used in the calculations and the difficulties encountered in correcting the predicted values for the contribution of the non‐photochemical reactions (dark reversion, destruction, synthesis), the effects of the optical properties of the tissue (light attenuation, scattering, trapping) on the rate of phytochrome photo‐conversion, and the geometrical relationships between irradiated sample and the light source. At present, in many studies, it is not possible to avoid using predicted values of the state of phytochrome. The limitations imposed by the use of ‘predicted’ values in the interpretation of results obtained in plant photomorphogenesis research should be always clearly stated.
Regulation of protein synthesis in root, shoot and embryonic tissues of germinating barley during salinity stress
Authors: RAMAGOPAL S.
Published: April 2006

AbstractProtein synthesis during seed germination, a stage vulnerable to salinity stress, was investigated. The responses of barley genotypes, CM72 (California Mariout 72) and Prato, toward salinity were different during seed germination. Germination of CM72 was unaffected up to 0.34 kmol m−3(2%) NaCl, but that of Prato was reduced 30% by 0.17 kmol m3NaCl and 75% by 0.34 kmol m−3NaCl. Therefore, the former genotype is relatively more salt‐tolerant than the latter. Protein synthesis in roots, shoots, and embryos was investigated in these two genotypes before and after salinity stress. The uptake of S‐methionine and its incorporation into protein were significantly reduced by salinity in both genotypes. The inhibition of global protein synthesis was significant in roots and shoots. Proteins from different tissues were resolved by single and two dimensional gels. The steady‐state protein levels were maintained remarkably well during salinity stress in roots and shoots. Likewise, proteins in germinating embryos were stable except for a 42‐kilodalton protein unique to the salt tolerant genotype which was apparently degraded during salinity stress. Salinity, around 0.34 kmol m−3NaCl, induced both quantitative and qualitative changes in the expression of some proteins labelledin vivo.The quantitative changes included repression or enhancement of synthesis of selected groups of proteins. Around 8% of the nearly 400 resolved proteins in a tissue was affected this way. Some of the proteins in this category were specific to each genotype. About 1 % of the total showed qualitative changes; these proteins were expressed only during salinity stress. In roots, two proteins (28, 41.7 kilodaltons) were detected in CM72 and five (28, 45, 60.5, 76.5, 82.5 kilodaltons) in Prato; only the 28‐kilodalton protein was common to both genotypes. In shoots, four proteins (45, 60.5, 76.5, 82.5 kilodaltons) were found only in Prato and these were similar to those induced in roots. The four new proteins (32, 37.5, 89, 92 kilodaltons) in germinating embryos were apparently induced only in CM72; these were distinctly different from those detected in developed roots and shoots. The unique protein changes induced by salinity stress during germination (this study) and seedling growth studies reported earlier (Ramagopal, 1987b) are apparently different. The findings demonstrate that ontogeny plays an important role in the expression of tissue‐specific proteins during salinity stress in the salt tolerant and sensitive barley genotypes.
Photosynthetic responses of two heliotropic legumes from contrasting habitats
Authors: PRICHARD J. M. , FORSETH I. N.
Published: April 2006

Abstract Photosynthetic responses to light, temperature and leaf‐to‐air water vapour concentration deficit for Strophostyles helvola (L.) Ell. in an open beach site, and Amphicarpa bracteata (L.) Ell. in two deciduous forest sites were quantified. Photosaturated rates of net CO2 assimilation were 52.1 ± 4.6, 11.0 ± 1.6 and 4.1 ± 0.3 μmol m−2s−2 for plants in beach, roadside and closed canopy sites, respectively. In terms of photosynthesis, plants in the beach site were more tolerant of higher leaf temperatures and water vapour concentration deficits than were plants in forested sites. Heliotropic leaf movements in the beach site reduced calculated total daily transpiration by 2%, increased total daily carbon gain by 8% and reduced the transpiration ratio by 9% relative to an horizontal leaf. During long‐term sunflecks in forested sites, heliotropism reduced transpiration by 15%, increased carbon gain by 71% and reduced the transpiration ratio by 50% relative to an horizontal leaf. We hypothesize that heliotropic leaf movements in mesic, high‐light, low‐nitrogen habitats may increase carbon return on nitrogen investment in photosynthesis, while heliotropism in canopy gaps may represent a morphological mechanism to reduce damage to low‐light acclimated photosynthetic systems during long‐term sunflecks.
A mechanistic model for photosynthesis based on the multisubstrate ordered reaction of ribulose 1,5 bisphosphate carboxylase
Authors: FARAZDAGHI H. , EDWARDS G. E.
Published: April 2006

Abstract. A mechanistic model of photosynthesis is developed based on the characteristics of ribulose 1,5‐bisphosphate (RuBP) carboxylase and the assimilation of CO2 as an ordered reaction with RuBP binding before CO2. An equation is derived which considers the effects of light (for regeneration of RuBP) and CO2. Taking values for the maximum turnover of RuBP carboxylase at substrate saturation, the maximum carboxylation efficiency (maximum increase in rate per increase in CO2 concentration) and the minimum quantum requirement for the C3 pathway, photosynthesis in the absence of photorespiration is simulated. In the model, at varying concentrations of CO2, the efficiency of light utilization approaches a maximum value as photon flux density decreases. Similarly, with a given maximum carboxyation capacity, at varying photon flux densities the carboxylation efficiency approaches a constant maximum value (equal to Vmax/KmCO2) as CO2 is decreased. However, a decrease in the state of activation of RuBP carboxylase under low light results in a lower carboxylation efficiency. Limits on the rate of photosynthesis, as the maximum capacity for regeneration of RuBP is reduced relative to carboxylation potential, or as the maximum capacity of the carboxylase varies, are considered.
Isolation of nuclear shells from plant cells
Authors: GALCHEVA‐GARGOVA Z. I. , MARINOVA E. I. , KOLEVA S. T.
Published: April 2006

Abstract. Nuclei from Zea mays and Phaseolus vulgaris root meristematic and differentiated cells were treated according to a recently developed simple procedure for isolation of nuclear lamina of Ehrlich Ascite Tumor (EAT) cells. As revealed by electron microscopy, the residual structures obtained represented empty nuclear shells, resembling those previously isolated from animal cells. Moreover, the composition of the residual nuclear structures from plant cells was found to be very similar to that described previously for the nuclear lamina purified by the adopted procedure. As demonstrated by SDS‐polyacrylamide gel electrophoresis, the plant nuclear shells contained a small number of proteins in the 65‐45 kD range. Two proteins — 62 and 50 kD—were most characteristic for beans, while a 55‐kD protein was abundant in maize. When blotted on nitrocellulose paper, some of the proteins of plant nuclear shells were immunoreactive with sera containing antibodies against the proteins of EAT nuclear envelopes. The degree of phosphorylation of the proteins of plant nuclear shells was found to be higher in meristematic than in differentiated maize root cells, correlating with the mitotic activity of the starting material.
Modelling of the responses to nitrogen availability of two Plantago species grown at a range of exponential nutrient addition rates
Authors: HIROSE T. , FREIJSEN A. H. J. , LAMBERS H.
Published: April 2006

Abstract. Plantago major ssp. major and P. lanceolata were grown in solution culture with exponential nutrient addition rates. Compared with P. lanceolata, P. major major showed a higher shoot weight ratio (SWR, fraction of plant dry weight in the shoot) and a higher net assimilation rate (NAR, expressed on a leaf dry weight basis) at equal plant (PNC) and shoot (SNC) nitrogen concentration, respectively. No difference was observed in shoot nitrogen ratio (SNR, fraction of plant nitrogen in the shoot) against PNC between the two species. The effect of these differences in matter partitioning and NAR on plant growth was examined by using a growth model. The model assumed (1) that the SWR and SNR are a linear function of PNC and (2) that the NAR is a rectangular hyperbolic function of SNC. Curvilinear relationships were observed between relative growth rate (RGR) and PNC. P. major major had a higher RGR at equal PNC and, thus, a higher nitrogen productivity (NP) than P. lanceolata. Steady‐stale exponential growth was simulated for different nitrogen availability in the environment. P. major major had a higher RGR over the whole range of nitrogen availability but the difference attenuated with decreasing availability of nitrogen. The simulation also showed P. lanccolata having higher plasticity in the shoot/root ratio, which resulted from its higher variability in PNC.
Ecophysiology of fire‐stimulated seed germination in Cistus incanus ssp. creticus (L.) Hey wood and C. salvifolius L.
Authors: THANOS C. A. , GEORGHIOU K.
Published: April 2006

Abstract. Seed germination characteristics were investigated in the most common Cistus species in Greece, namely C. incanus ssp. creticus and C. salvifolius. In addition to the soft seed subpopulation, both species produce a large fraction of hardcoated, water‐impermeable seeds which can be softened and, thus, promoted to germinate by mechanical scarification and thermal pretreatment. Temperature and light control of seed germination are unimportant. In the ecological context of the Mediterranean ecosystems, the eventually advantageous, opportunistic strategy of germination is based on: (a) seed heterospermy (which allows the smaller, softcoated fraction to germinate promptly each year while the majority of the seeds, the hard ones, accumulate in the soil); (b) the seed population heterogeneity in relation to coat hardness (so that any heat conditions produced by fire induce the softening and germination of a certain seed fraction); (c) the notably low germination rate (which suppresses premature germination); (d) the wide, Mediterranean‐type (relatively cool), temperature range of germination (while higher temperatures simply inhibit but do not induce any dormancy); and (c) the apparent lack of photo‐sensitivity (enabling germination under every light regime). In non‐fire years, the temporal distribution of field germination and seedling appearance might be partly determined by the seed dispersal strategy of the individual Cistus species. Nevertheless, the post‐fire regeneration response is manifested in the form of a huge wave of germination (of practically all seeds softened by the fire heat), shortly after the onset of the rainy season.
Continuous flow rhizostat for the study of aluminum toxicity
Authors: BRASSARD P. , KRAMER J. R. , NOSKO P. , KERSHAW A.
Published: April 2006

Abstract. Wide variations in total aluminum (AL) concentration reported to have a toxic effect on plants arc attributed to imprecise definition of the chemical environment at the root interface. Because AL can complex with natural ligands and form time‐dependent metastable species in water, the requirements of a fixed AL speciation in the nutrient medium can only be met by simultaneously holding constant the pH, the AL/OH ratio and the renewal time of the solution. It is also important that the root be constantly perfused by a fresh solution so that the root interface is as chemically close to the bulk solution as possible. The rhizostat presented here uses a process controller to constantly replenish four tanks containing different combinations of nutrients and AL. The solution is pumped from each tank to a tray where it is continuously delivered to seedlings growing on artificial medium. This rhizostat provides an accurate control for AL speciation. Preliminary experiments on white spruce seedlings show that levels of 10 micromolal or less total AL are sufficient to cause toxic effects at pH of 4.5 and without the formation of AL complexes.
The molecular anatomy and function of thylakoid proteins
Authors: MARDER J. B. , BARBER J.
Published: April 2006

Abstract. The structure of chloroplast membrane proteins and their organization into photosynthetically‐active multimeric complexes is described. Extensive use has been made of information derived from gene sequencing and other biochemical studies to predict likely protein conformations. These predictions have been assimilated into structural models of the various thylakoid complexes. The enzymatic activities of the complexes have also been described and where possible related to individual polypeptides.
Photoinactivation of catalase at low temperature and its relevance to photosynthetic and peroxide metabolism in leaves
Authors: VOLK S. , FEIERABEND J.
Published: April 2006

Abstract In green as well as in etiolated leaves of rye (Secale cereale L. ev. ‘Halo’), exposed to strong light at low temperature (0.4°C) catalase was inactivated. Other heme‐containing enzymes (peroxidases) and various enzymes of photosynthetic, photorespiratory or peroxide metabolism were not photoinactivated. After returning plants from a low to a physiological temperature (22°C), catalase activity recovered within 12 h through new synthesis. The leaf contents of H2O2 and organic peroxides were not affected by the photoinactivation of catalse. The content of malondialdehyde generally increased after exposure to a higher light intensity. High‐light‐induced increases of ascorbate, and particularly of glutathione, were more marked in catalase‐deficient than in normal leaves. Photoinactivation of catalase was accompanied by severe inhibition of photosynthesis. Photoinhibition of photosynthesis was not related to the lack of catalase because photosynthesis was not impaired when catalase activity was kept low by growing the plants under non‐photorespiratory conditions. Photoinhibition appeared to result from photodamage in primary photochemistry of photosystem II, as indicated by a decrease of the maximal variable fluorescence. Photoinhibition of photosynthesis and of catalase have in common that in both instances proteins are involved that are continuously inactivated in light and, therefore, particularly sensitive to stress conditions that prevent their replacement by repair synthesis.
Vascular transport and soybean nodule function: II. A role for phloem supply in product export*
Authors: WALSH K. B. , CANNY M. J. , LAYZELL D. B.
Published: April 2006

Abstract The ureide content of soybean (Glycine max (L.) Merr.) nodules was unaffected by variations in the transpirational rate, while whole plant manipulations designed to decrease phloem supply to nodules resulted in lower rates of nitrogenase activity and an increase in the ureide content of the nodules. The rate of ureide export from the nodule was estimated from the exponential rate of decrease in the pool size of ureides in nodules, following exposure to an N2‐free atmosphere (Ar:O2). Export was greatly reduced under treatments which reduced phloem supply to the nodule. A water budget for nodules suggested that the delivery of water to the nodule via mass flow in the phloem was comparable to that required for export of ureides from the nodule in the xylem from the nodule. Therefore, we suggest that xylem export from nodules is related to the phloem supply to the nodule rather than to the transpirational flux in the parent root. This suggestion is related to the reported decreases in nodule permeability to gases under conditions of phloem deprivation.
Control of intracellular glutathione and its effect on ultraviolet radiation‐induced K+ efflux in cultured rose cells
Authors: HUERTA A. J. , MURPHY T. M.
Published: April 2006

Abstract Modification of the ‘intracellular concentration of reduced glutathione’ (IC‐GSH) affected the response of cultured rose cells (Rosa damascena) to ultraviolet radiation (UV)‐induced leakage of K+. High IC‐GSH induced by incubation of cells in 10 mol m−3 GSH (IC‐GSH increased linearly with time from 20 to about 600 μmol g−1 in 61.2 ks) caused cells to become significantly less sensitive to UV. Low IC‐GSH induced by treatment with 1 mol m−3 buthionine sulphoximine (BSO) plus 1 mol m−3 diethylmaleate (DEM) (IC‐GSH decreased from 20 to about 3 μg g−1 in 61.2 ks) reduced, rather than increased, the UV‐sensitivity of the cells. However, treatment with DEM also induced a large transient K+ leakage; and treatment with BSO induced a slight leakage. The K+ leaked was recovered by 3.24 ks. Following K+ recovery, the DEM‐treated cells showed almost complete insensitivity to UV, and BSO‐treated cells showed a slightly reduced sensitivity to UV. These results are in agreement with our previous findings that other treatments (heat, cycloheximide, UV), which also cause a transient leakage of K+, also reduce the induction of K+ leakage by a subsequent UV treatment. We conclude that high IC‐GSH may play a role in protecting plant cells from UV‐induced K+ leakage. Increased UV‐sensitivity with low ICGSH was not observed, we believe, because of the transient K+ leakage, though the mechanism of reduced sensitivity to UV induced by transient leakage of K+ is not known at this time. Treatment with UV did not reduce the IC‐GSH, showing that this is not the mechanism by which UV induces K+ leakage.
Does turgor prevent endocytosis in plant cells?
Authors: GRADMANN D , ROBINSON D. G.
Published: April 2006

Abstract. The energetics of coated vesicle‐mediated endocytosis in turgid plant cells are discussed in terms of the known ATP requirement for clathrin cage dissociation and on the basis of the elementary expression for the energy w = P · v, where P corresponds to the turgor and v to the vesicle volume. The authors' calculations indicate that the possibility for formation of coated vesicles by endocytosis is limited to a rather low turgor range (P below about 0.1 MPa). This view is consistent with reports of well‐developed clathrin coats on the plasma membranes in those cells having very low turgor such as root hairs and naked flagellates.
Changes in glutamate dehydrogenase activity of Chlamydomonas reinhardtii under different trophic and stress conditions
Authors: MUÑOZ‐BLANCO J , CARDENAS J.
Published: April 2006

Abstract. Under stress conditions (darkness, nitrogen starvation, high ammonium concentrations, glutamine synthetase and glutamate synthase inhibition) glutamate dehydrogenase animating activity levels of Chlamydomonas cells varied inversely to those of glutamine synthetase. Nitrogen and carbon sources also influenced glutamate dehydrogenase levels in Chlamydomonas, the highest values being found in cells cultured mixotrophically with ammonium, under which conditions glutamate dehydrogenase and glutamine synthetase levels were likewise inversely related. These facts, together with the analysis of internal fluctuations of ammonium, 2‐oxoglutarate, and the amino acid pool as well as the variations of certain enzymes involved in carbon metabolism indicate that glutamate dehydrogenase animating activity is adaptative, being involved in the maintenance of intracellular levels of L‐glutamate when they cannot be maintained by the GS‐GOGAT cycle, and probably more connected with carbon than nitrogen metabolism.
Citric acid excretion and precipitation of calcium citrate in the rhizosphere of white lupin (Lupinus albus L.)
Authors: DINKELAKER B. , RÖMHELD V. , MARSCHNER H.
Published: April 2006

Abstract. White lupin (Lupinus albus L.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO3, pH(H2O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X‐ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13‐week‐old plants was about 1 g plant−1, representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO3 and precipitation of calcium citrate in the zone of proteoid roots.