bluuebunny/crossref_metadata_2025 huggingface dataset:
A new method in growth‐electrophysiology: Pressurized intra‐organ perfusion
Authors: OKAMOTO HISASHI , MIZUNO AKIKO , KATOU KIYOSHI , ONO YOSHINA , MATSUMURA YASUKO , KOJIMA HIROSHI
Published: April 2006

Abstract A new experimental system was devised for the simultaneous measurement of elongation rate and the activity of the spatially separate electrogenic ion pumps of a hypocotyl segment excised from a seedling of Vigna unguiculata L. Walp. under enforced intra‐organ perfusion by artificial solutions. The pathway of the perfusion medium was apoplastic space, including xylem vessels as main routes. The elongation rate of the segment was highly dependent on the perfusion pressure applied. It was possible to increase the growth rate under pressurized perfusion by 10‐30 times as much as that without perfusion. Elongation rate was also dependent on respiration under perfusion, being retarded reversibly by anoxia a few minutes after the activities of the electrogenic ion pumps were stopped. Perfusion pressure had a little influence on the membrane potential (Vpx) below a breakdown level (c. 130 kPa). Perfusion of mannitol or sorbitol solution of appropriate concentration reduced the elongation rate reversibly.
Proton extrusion in seed coats of Phaseolus vulgaris L.
Authors: VAN BEL AART J. E. , PATRICK JOHN W.
Published: April 2006

Abstract. The present investigations were designed to identify proton pumps in seed coats of Phaseolus vulgaris L. Vacated seed‐coat halves were exposed to bathing solutions with indicators for proton pump action and the pH changes in the media were measured. Fusicoccin increased the rate of proton extrusion from the seed coats. Orthovanadate and abscisic acid retarded the proton extrusion evoked by fusicoccin. Abolition of the proton extrusion by parachloromercuriphenylsulphonic acid was partially reversed by diethioerythritol. The extrusion was stimulated by high osmolarities (100 mol m−3 sorbitol), potassium ions (100 mol m−3 KCI) and light. Old seed coats reacted more rapidly to fusicoccin treatments than young ones. Proton pumping in seed coats and cotyledons showed differential responses to fusicoccin, K+ and sucrose. In contrast to seed coats, medium acidification by cotyledons was prohibited by addition of sucrose. The significance of proton pumps for photosynthate transfer in vivo is discussed.
Specific action of blue light on phytochrome‐mediated enzyme syntheses in the shoot of milo (Sorghum vulgare Pers.)
Authors: OELMÜLLER R. , MOHR H.
Published: April 2006

Abstract. This paper describes the effect of prolonged treatments with red or blue light on the capacity of the milo (Sorghum vulgare Pers.) shoot to respond to Pfr in subsequent darkness. Two groups of enzymes were studied. In group I (NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase, NADP‐GPD. EC 1.2.1.13 and ribulose‐bisphosphate carboxylase, carboxylase, EC 4.1.1.39) enzyme formation is strongly enhanced by red light pulses (operating through phytochrome) whereas in group II (NAD‐dependent glyceraldehyde‐3‐phosphate dehydrogenase, NAD‐GPD, EC 1.2.1.12 and NAD‐dependent malate dehydrogenase, MDH. EC 1.1.1.37) enzyme formation hardly responds to red light pulses.

In group 1 a 24‐h treatment with blue light (but not with red light) leads to a strong increase in responsivity to Pfr whereas in group II a 24‐h treatment with blue or red light does not increase responsivity to Pfr in subsequent darkness.

The specific effect of blue light cannot be explained by an effect of light on gross protein synthesis. Rather, the data indicate that amplification of responsivity to Pfr by blue light is a specific process directly related to the mechanism of modulation of gene expression by phytochrome.
The influence of chlorophyll fluorescence on the light gradients and the phytochrome state in a green model leaf under natural conditions
Authors: LORK W. , FUKSHANSKY L.
Published: April 2006

Abstract. The effect of chlorophyll fluoresence on the spectral light gradients within a model green leaf was examined under different light qualities (day‐light, sunset, canopy) and different quantum efficiencies. Light fluxes within the leaf tissue are nearly doubled in the emission domain of fluorescence but the effect on the phytochrome photoequilibrium is very small.
Relationship between the activity of the orotic acid pathway and glucose content of roots of Cucurbita pepo
Authors: LOVATT CAROL J.
Published: April 2006

Abstract. Apical 3‐cm root segments excised from 2‐d‐old squash seedlings (Cucurbita pepo L. cv. Early Prolific Straightneck) that were germinated and grown between sheets of paper towelling moistened with H2O2 incorporated 144±10 nmol (± SE. n= 15) NaH14CO3 into uridine nucleotides (∑UMP) per gram intact roots during the 3‐h incubation period (Lovatt, Albert & Tremblay, 1979). Continued culture of squash seedlings in this manner for an additional 24 or 48 h had no effect or slightly increased (30%) the activity of the orotic acid pathway. However, transfer of 2‐d‐old seedlings to Shive's nutrient solution reduced the activity of the orotic acid pathway within 15 h to 2.3 nmol NaH14CO3 incorporated into ∑UMP per gram apical 3‐cm root segments during the 3‐h incubation period. The observed decrease in capacity to synthesize pyrimidine nuclotides de novo paralleled the reduction in glucose content of the roots and was reversed by supplying glucose during hydroponic culture in Shive's nutrient solution. Root elongation was not affected by the reduced activity of the orotic acid pathway nor by the decreased level of available glucose.
An analysis of resistance to water flow through wheat and tall fescue leaves during pressure chamber efflux experiments
Authors: STROSHINE R. L. , RAND R. H. , COOKE J. R. , CUTLER J. M. , CHABOT JEAN F.
Published: April 2006

Abstract. This is a physical analysis of water movement in wheat (Triticum) and tall fescue (Festuca arundinacea) leaves placed in the Scholander pressure chamber. It takes into account the efflux resistances of water movement through the xylem and water flow across the cell membranes. Xylem resistance was estimated using Poiseuille's law.

Leaves which had been pressurized in the chamber were embedded, sectioned, examined under a light microscope and photographed. Cells were intact but distorted and xylem vessels were intact. Cells in portions of the blade squeezed by the chamber sealing grommet were crushed, but xylem vessels remained intact.

By applying pressure several tenths of a megapascal in excess of the balance pressure, water was forced from each leaf through the severed end which protruded from the chamber. Efflux curves were drawn by plotting the total water expressed as a function of time after the pressure increase. Water efflux from the shortest wheat leaf lasted only 10 min while efflux from the longest continued for up to 40 min. The efflux from a tall fescue leaf which was rehydrated and cut to a shorter length was much more rapid than efflux from the original leaf.

Experiments combined with mathematical analysis suggested that the effect of leaf length on efflux is related to a high resistance to water flow through vascular bundles. Xylem resistance would be sufficient to produce this effect if it were 10 times greater than that predicted by Poiseuille's law. Both the observations of water flow from the cut end of the leaf and the mathematical model suggested very little water flows from bundles with vessels of diameter less than 12 μm. The apparent explanation is high resistance to water flow through these small diameter vessels.
Comparative evaluation of photoionization and flame ionization detectors for ethylene analysis
Authors: BASSI P. K. , SPENCER M. S.
Published: April 2006

Abstract. This paper compares the use of photoionization and flame ionization detectors (PID and FID. respectively) for the analysis of ethylene in plant physiological studies. It is shown that PID has the capability to analyse ethylene levels in the order of 1 mm3 m−3. This represents an increase in sensitivity over FID of several‐fold. Evidence is presented that this enhanced sensitivity allows for measurement of the rate of ethylene production from plants in continuous‐flow systems by taking air samples directly from the air stream, thus eliminating the need for selective collection and concentration of ethylene.
Measurement of free space and sorption of large molecules by cereal roots
Authors: SHONE M. G. T. , AFRC A. V. FLOOD
Published: April 2006

Abstract. Large molecular weight solutes that do not penetrate the root have been used to correct for the surface film in measurements with mannitol of the volume of the Apparent Free Space (FS) in bailey roots. The results are compared with those obtained using other correction techniques for elimination of the surface film. Large molecules seem to be adsorbed on the root surface and the kinetics of adsorption differ between the polyhydric alcohol mannitol or the polysaccharide dextran on the one hand, and the polyether polyethylene glycol (PEG‐4000) on the other. The significance of this difference in kinetics is discussed in relation to the use of PEG as an osmoticum in studies on root water relations and its effect on ion uptake. Although smaller molecular weight PEG's penetrate the FS and diminish sodium uptake from 10 mol m−3 NaCl, more dilute solutions of mannitol and larger PEG polymers are unlikely to affect ion uptake from dilute nutrient solutions. Use of these substances along with labelled nutrients in kinetic studies of the compartmentation of ions in roots can help to distinguish between ions associated with the surface film, those in the FS and those that have crossed the cell membranes into the protoplast.
Carbon dioxide increase: the implications at the ecosystem level*
Authors: SHUGART H. H. , EMANUEL W. R.
Published: April 2006

Abstract Possible effects of increased atmospheric concentrations of CO2 on forest ecosystems are discussed and as an example a simulation case study using a set of mixed‐age and mixed‐species forest stand models is presented. The responses of the models to a simple scenario (uniform growth increase of all trees as a response to CO2 enrichment) include increases in biomass that are considerably less than the increases in growth rate of the trees. These simulations and more general discussion of the possible effects of increased photosynthetic production identify the problem of scaling‐up small time‐scale and space‐scale measurements of plant responses to CO2 enrichment to the ecosystem level.
Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach
Authors: HELDER R. J.
Published: April 2006

Abstract The quantitative approach used here is based on a model comprising a well‐stirred medium, an unstirred layer, and a CO2 absorbing leaf. The unstirred layer is divided up by planes into a number of sub‐layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value.

An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub‐layers, the fluxes across the sub‐layers and the conversions among the carbon components can be estimated.

The CO2 flux decreases, and the HCO−3 flux increases towards the leaf. There are negative fluxes of OH& and CO2–3. H+ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non‐inorganic C buffers with appropriate pKa are present.

The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast.

It is argued that even better effects are possible if the back‐diffusion of CO2–3 could be prevented by lowering the pH of the unstirred layer.
Chlorophyll a fluorescence: can it shed light on fundamental questions in photosynthetic carbon dioxide fixation?
Authors: SIVAK MIRTA N. , WALKER DAVID A.
Published: April 2006

Abstract A close, immediate and precise relationship between chlorophyll a fluorescence and photosynthetic carbon assimilation in vivo is demonstrated. The examples discussed include kinetics displayed during dark to light transitions plus oscillations and transients observed during changes in the gas phase surrounding the leaf. Remaining uncertainties surrounding the relationship between chlorophyll fluorescence and photosynthesis are attributed to the underlying complexity of the regulatory mechanisms involved. Examples are also given that show how multiple simultaneous measurements of different aspects of the photosynthetic process may contribute to the resolution of these uncertainties. The practical relevance of these matters is also discussed, particularly in relation to the limitations of the photosynthetic process and to the use of chlorophyll fluorescence as a diagnostic probe of chemical and genetic manipulation and stress.
CO2 uptake and transport in leaf mesophyll cells
Authors: COLMAN B. , ESPIE G. S.
Published: April 2006

Abstract The acquisition of inorganic carbon for photosynthetic assimilation by leaf mesophyll cells and chloroplasts is discussed with particular reference to membrane permeation of CO2 and HCO−3. Experimental evidence indicates that at the apoplast pH normally experienced by leaf mesophyll cells (pH 6–7) CO2 is the principal species of inorganic carbon taken up. Uptake of HCO−3 may also occur under certain circumstances (i.e. pH 8.5), but its contribution to the net flux of inorganic carbon is small and HCO−3 uptake does not function as a CO2‐concentrating mechanism. Similarly, CO2 rather than HCO−3 appears to be the species of inorganic carbon which permeates the chloroplast envelope. In contrast to many C3 aquatic plants and C4 plants, C3 terrestrial plants lack specialized mechanisms for the acquisition and transport of inorganic carbon from the intercellular environment to the site of photosynthetic carboxylation, but rely upon the diffusive uptake of CO2.
Sensitivity of stomata and water use efficiency to high CO2
Authors: MORISON JAMES I. L.
Published: April 2006

Abstract The observed responses of stomata to carbon dioxide are reviewed, and the interaction of other known factors on the sensitivity to CO2 are summarized. The role of stomatal response to CO2 is discussed, and it is argued that while the effect of the CO2 response in normal daily stomatal behaviour is presently poorly understood the stomatal response to CO2 will have major impact in improving water use efficiency in future CO2 atmospheres. However, the attenuation of this increase is emphasized so that increases at the crop level will probably be much smaller than those observed at the single leaf assimilation level.
Characteristics of nitrate uptake into seedlings of pea (Pisum sativum L. cv. Feltham First). Changes in net NO−3 uptake following inoculation with Rhizobium and growth in low nitrate concentrations
Authors: DEANE‐DRUMMOND CELIA E. , CHAFFEY N. J.
Published: April 2006

Abstract Nitrate uptake into intact pea seedlings (Pisum sativum L. cv. Feltham First) grown in hydroponic culture has been investigated. Following inoculation with Rhizobium leguminosarum a twofold increase in net nitrate uptake was observed. Changes in morphological characteristics following inoculation were found to decrease the effective area available for absorption.

There was a two‐fold decrease in net nitrate uptake into intact seedlings grown in the presence of N compared with N free media. In the former case net nitrate uptake appeared to stall at regular intervals. In both cases only the initial rates of nitrate uptake were found to be responsive to the external nitrate concentration. The results are discussed in terms of current models for the regulation of NO−3 uptake by higher plants.
The electrogenic proton pumping from parenchyma symplast into xylem—direct demonstration by xylem perfusion
Authors: MIZUNO A. , KOJIMA H. , KATOU K. , OKAMOTO H.
Published: April 2006

Abstract We have devised an experimental system for simultaneous measurement of the activity of the xylem electrogenic ion pump, which is located on the inner cell membrane between the parenchyma symplast (p) and the xylem (x). and pH of the xylem exudate of a hypocotyl segment of Vigna unguiculata under pressurized xylem perfusion. Anoxia caused immediate depolarization of the inner cell membrane followed by alkalization of the xylem exudate several minutes later. Activity of the xylem pump was recovered by reaeration and acidification of the xylem exudate took place. These results indicate that the xylem pump is the respiration‐dependent electrogenic proton‐pump extruding proton from the parenchyma symplast into the xylem.
HCO−3 uptake through the roots and its effect on the productivity of willow cuttings
Authors: VAPAAVUORI E. M. , PELKONEN P.
Published: April 2006

Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and 14C–labelled sodium bicarbonate was fed to the roots. Uptake of 14C‐label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, 14C‐label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid‐labile products, whereas after the 48 h feeding period most of the label was in acid‐stable products.

A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m−3 NaHCO3. After a 4‐week growing period we determined the biomass of leaves, shoots, roots and cuttings.

Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m−3 NaHCO3, but a higher concentration of NaHCO3 (1.470 mol m−3) caused a slight decrease in the dry matter production. At 0.737 mol m−3 NaHCO3 the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.
Differences in seed longevity at the species level
Authors: PRIESTLEY D. A. , CULLINAN V. I. , WOLFE J.
Published: April 2006

Abstract Published seed storage data for 92 species derived from 13 localities were subjected to probit analysis to determine the half‐viability period (P50) for each sample. Estimates of half‐viability period for each species averaged over all 13 localities were calculated using a least square means procedure applied to known values for the half‐viability period for each species at each of its storage stations. The results reported here represent an initial step in the objective organization of seed longevity data.
The role of electrogenic xylem pumps in K+ absorption from the zylem of Vigna unguiculata: the effects of auxin and fusicoccin
Authors: DE BOER A. H. , KATOU K. , MIZUNO A. , KOJIMA H. , OKAMOTO H.
Published: April 2006

Abstract We tested the hypothesis that electrogenic ion pumps, working at the parenchyma symplast/xylem interface of pea hypocotyls, provide the driving force for K+ uptake from the xylem. Solutions of known composition were perfused through a hypocotyl segment. The K+ activity of the solution flowing out of the xylem (K+out) increased (i.e. K+ uptake decreased) when aerobic respiration was inhibited by lack of O2, and this was preceded by a decrease in Vpx (electrical potential difference between parenchyma symplast and xylem). Perfusion with auxin (1AA) and fusicoccin (FC) stimulated the electrogenic activity of the ‘xylem pumps’ (111 and 205% respectively) and stimulated uptake of K + from the xylem (with 71% and 29% respectively). The close correlation between xylem pump activity and K+ uptake corroborated the aforementioned hypothesis. Interestingly, inhibition of pump activity by anoxia was incomplete in the presence of FC. It is thought that FC increases the affinity of the ATP‐requiring xylem pump for ATP, thus ensuring that ATP production during fermentation is sufficient to fuel the pump in the absence of O2.
High‐resolution measurement of growth during first positive phototropism in maize†
Authors: BASKIN T. I. , IINO M. , GREEN P. B. , BRIGGS W. R.
Published: April 2006

Abstract Growth redistribution which occurs as a result of phototropic stimulation was studied in red light‐grown, maize (Zea mays L.) seedlings. The pattern of elongation of small areas (0.1mm2) of coleoptile epidermis on intact plants was analysed from time‐lapse, photomicrographic records. Growth following unilateral, pulse irradiation with blue light was depressed on the illuminated side and was stimulated on the shaded side. The time at which the change in growth rate occurred, on both illuminated and shaded sides, was significantly earlier in apical patches than it was in basal patches. Both kinds of change in the growth rate (stimulation and depression) occurred rapidly such that a new, constant growth rate was often established within five minutes. Micrographic, time‐lapse records were also obtained of growth changes induced by sub‐apical, unilateral application of a spot of an indole‐3‐acetic acid (IAA) and lanolin mixture. Growth on the side of the coleoptile to which IAA had been applied was similar to the growth on shaded sides of phototropically stimulated plants. The distance between apical and basal patches and the elapsed time between their changes in growth rate gave a velocity at which the growth response moved basipetally. Calculation of this velocity for blue light and auxin treatment gave values that were not significantly different. Thus, basipetal movement of a transverse auxin gradient could mediate growth changes that cause curvature of the coleoptile towards first positive fluences of blue light.
Relationship between chloroplast structure and O2evolution rate of leaf discs in plants from different biotopes in South Finland
Authors: ARO E.‐M. , RINTAMÄKI E. , KORHONEN P. , MÄENPÄÄ P.
Published: April 2006

AbstractThe chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O2evolution rate, chlorophyll (Chl) content and Chia/bratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO2‐saturated O2evolution rate (measured at 20°C and 1500 μmol photons m−2s−1) was at a maximum, ranging from 19.2 to 6.9 μmol O2cm−2h−1. Among the species, the Chia/bratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non‐appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O2evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O2evolution rate, the lower was the ratio of the total length of appressed to non‐appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chia/bratio of the leaves was not as clear, a significant negative correlation existed between the Chia/bratio and the ratio of appressed to non‐appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl‐ protein complexes.
Physiological implications of the Münch‐Horwitz theory of phloem transport: effects of loading rates*
Authors: GOESCHL J. D. , MAGNUSON C. E.
Published: April 2006

Abstract Predicted effects of phloem loading rates on the five profiles of unloading rate, osmotic water flux, pressure, transport speed and concentration, in hypothetical sieve tubes with different sink properties, were calculated using the steady‐state mathematical expression of the Münch hypothesis of phloem transport. The prediction that increased loading rates always increases the concentration, and generally increase the speed of translocates through the sieve tube, is emphasized since these parameters are accessible for experimental testing. This particular prediction contrasts with a previous prediction (Tyree, Christy, & Ferrier, 1974), that where concentration was held constant at the loading end, concentration along the rest of the sieve tube would decrease, while speed would increase greatly.

Where the unloading mechanism was assigned saturable (enzyme‐like) kinetics, increased loading rates (in the range well below the Vmax of the sink) caused both transport speed and concentration to increase. However, as loading rates approached the Vmax of the sinks, speed reached a maximum and then declined, and concentration increased substantially. This was particularly true at very high values of Km, e.g. > 0.1 mol cm−3.
Experimental tests of the Münch–Horwitz theory of phloem transport: effects of loading rates*
Authors: MAGNUSON C. E. , GOESCHL J. D. , FARES Y.
Published: April 2006

Abstract Extended square‐wave tracer kinetics using 11CO2 were used to measure the speed of transport and activity level (proportional to concentration) in the phloem at high and low loading rates in six species of plants. In all cases, increased loading rates resulted in increased concentration. In most cases speed also increased, however, in two cases speed was lower and tracer activity was much higher at the higher loading rate. All the responses are consistent with the Münch Horwitz theory of phloem transport, depending upon the equation used to represent the unloading mechanism as described in a previous paper (Goeschl & Magnuson, 1986). For example, the latter two cases are consistent with the assumption that the unloading rate was limited by a process with saturable kinetics (enzyme‐like).
Sealed lysimeters for the direct estimation of dinitrogen fixation by grain legume crops
Authors: SIMS A. P. , BARBER D. J. , FOLKES B. F. , WALLS D.
Published: April 2006

Abstract A new technique has been devised for the direct estimation of the contribution of N2‐fixation to the total nitrogen of a legume crop. Sealed lysimeters and ancillary equipment are described by which it is possible to enclose in a gas‐tight system the roots of some of the plants within the crop, together with their associated core of soil. The normal soil atmosphere can then be replaced by one containing 15N2, thus allowing, from the 15N content of the resulting plants direct calculation of the N2‐fixation. Regular monitoring is necessary to ensure that soil O2, CO2 and moisture contents are maintained at normal field levels.

The results indicate that the technique is capable of achieving its objectives and, provided the seedlings establish well initially, the resultant plants fully match the field average at final harvest. It has been possible to maintain the labelling of the soil atmosphere sufficiently constant to ensure that reliable and highly reproducible estimates of N2‐fixation are obtained. Using Pisum sativum cv. Meteor at densities of 160 plants m−2, fixation accounted for about 90% of the total nitrogen uptake. The limitations and merits of the method are compared with those of the 15N‐fertilizer dilution method.
Metabolic response of Medicago sativa L. and Lotus corniculatus L roots to anoxia
Authors: BARTA A. L.
Published: April 2006

Abstract Differential rates of fermentation and energy production have been implicated in the response of plant species to extended root anoxia. This study describes the metabolic response to anaerobiosis of waterlogging‐tolerant birdsfoot trefoil (Lotus corniculatus L.) and waterlogging‐sensitive alfalfa (Medicago sativa L.). Studies were carried out on glasshouse‐grown plants subjected to root anaerobiosis in nutrient solution. Rate of fermentation, as estimated by CO2 evolution, declined significantly upon anaerobiosis in both species but was proportionally less, relative to the aerobic control, in trefoil. Another indicator of carbon flux through glycolysis, the concentration of glucose‐6‐phosphate, was also significantly lower in trefoil roots relative to aerobic controls. Both species showed significantly increased root exudation of K+, sugars and andno‐N, especially during the first 2 d of root anaerobiosis, indicating changes in membrane selective permeability.

The energy status of roots subjected to anaerobiosis declined sharply in both species but trefoil roots maintained higher ATP/ADP ratios for up to 4 d of anaerobiosis. The results are consistent with the hypothesis that increased fermentation activity maintains a more favourable root energy status. This higher energy status may facilitate survival by maintaining crucial root activities, such as maintenance of membrane stability.
Models of carbon metabolism in C3‐C4 intermediate plants as applied to the evolution of C4 photosynthesis
Authors: PEISKER M.
Published: April 2006

Abstract Models developed to explain the biphasic response of CO2 compensation concentration to O2 concentration and the C3‐like carbon isotope discrimination in C3‐C4 intermediate species are used to characterize quantitatively the steps necessary in the evolution of C4 photosynthesis. The evolutionary stages are indicated by model outputs, CO2 compensation concentration and δ13C value. The transition from intermediate plants to C4 plants requires the complete formation of C4 cycle capacity, expressed by the models as transition from C4 cycle limitation by phosphoenolpyruvate (PEP) regeneration rate to limitation by PEP carboxylase activity. Other steps refer to CO2 leakage from bundle sheath cells, to further augmentations of C4 cycle components, to the repression of ribulose‐1,5‐bisphos‐phate carboxylase in the mesophyll cells, and to a decrease in the CO2 affinity of the enzyme. Possibilities of extending the suggested approach to other physiological characteristics, and the adaptive significance of the steps envisaged, are discussed.
Comparative ecophysiology of CAM and C3 bromeliads. I. The ecology of the Bromeliaceae in Trinidad
Authors: SMITH J. A. C. , GRIFFITHS H. , LÜTTGE U.
Published: April 2006

Abstract This article deals with the physiological ecology of the Bromeliaceae, a large neotropical family containing both terrestrial and epiphytic forms, as well as many species with crassulacean acid metabolism (CAM).

The article is in two parts. In the first, we review what is known of the occurrence of CAM and C3 species in the Bromeliaceae. The photosynthetic pathways are discussed in the context of the major taxonomic divisions within the family and the great diversity of bromeliad life‐forms. Of the three subfamilies, the Pitcairnioideae contain both C3 and CAM species and are essentially all terrestrial. In contrast, the Tillandsioideae are entirely epiphytic or saxicolous, with CAM species being restricted to the genus Tillandsia, And in the Bromelioideae all species show CAM, but terrestrial and epiphytic forms are found in about equal numbers. The evidence suggests that both CAM and the epiphytic habit arose more than once in the family's evolutionary history.

In the second part we consider the photosynthetic ecology of the various bromeliad life‐forms in more detail using the specific example of Trinidad (West Indies). CAM bromeliads tend to be centred on the drier regions of the island and C3 forms on the wetter areas. However, at any one site there is a marked vertical stratification of species within the forest profile. Based on the known habitat preferences of the bromeliads, six contrasting sites were selected for field studies in Trinidad. These ranged from arid coastal scrub to montane rain forest, the vegetational and climatic characteristics of which are described here. The constancy of δ13C values (carbon‐isotope ratios) for individual CAM species in these markedly different habitats emphasized the need for ecophysiological studies to characterize environmental effects on CO2 assimilation and transpiration. The following papers in this series present the results of a comparative investigation of gas exchange and leaf water relations of CAM and C3 bromeliads in situ at the various sites.
Comparative ecophysiology of CAM and C3 bromeliads. III. Environmental influences on CO2 assimilation and transpiration
Authors: GRIFFITHS H. , LÜTTGE U. , STIMMEL K.‐H. , CROOK C. E. , GRIFFITHS N. M. , SMITH J. A. C.
Published: April 2006

Abstract Field measurements of the gas exchange of epiphytic bromeliads were made during the dry season in Trinidad in order to compare carbon assimilation with water use in CAM and C3 photosynthesis.

The expression of CAM was found to be directly influenced by habitat and microclimate. The timing of nocturnal CO2 uptake was restricted to the end of the dark period in plants found at drier habitats, and stomatal conductance in two CAM species was found to respond directly to humidity or temperature. Total night‐time CO2 uptake, when compared with malic‐acid formation (measured as the dawn‐dusk difference in acidity, ΔH+), could only account for 10–40% of the total ΔH+ accumulated. The remaining malic acid must have been derived from the refixation of respired CO2 (recycling). Within the genus Aechmea (12 samples from four species), recycling was significantly correlated with night temperature at the six sample sites. Recycling was lowest in A. fendleri (54% of ΔH+ derived from respired CO2), a CAM bromeliad with little water‐storage parenchyma that is restricted to wetter, cooler regions of Trinidad.

Gas‐exchange rates of C3 bromeliads were found to be similar to those of the CAM bromeliads, with CO2 uptake from 1 to 3 μmol m−2 s−1 and stomatal conductances generally up to 100 mmol m−2 s−1. The midday depression of photosynthesis occurred in exposed habitats, although photosynthetically active radiation (PAR) limited photosynthesis in shaded habitats. CO2 uptake of the C3 bromeliad Guzmania lingulata was saturated at around 500 μmol m−2 s−1 PAR, suggesting that epiphytic plants found in the shaded forest understorey are shade‐tolerant rather than shade‐demanding.

Transpiration ratios (TR) during CO2 fixation in CAM (Phase I and IV) and C3 bromeliads were compared at different sites in order to assess the efficiency of water utilization. For the epiphytes displaying marked uptake of CO2, TR were found to be lower than many previously published values. In addition, the average TR values were very similar for dark CO2 uptake in CAM (42 ± 41, n= 12), Phase IV of CAM (69 ± 36, n= 3) and for C3 photosynthesis (99 ± 73, n= 4) in these plants. It appears that recycling of respired CO2 by CAM bromeliads and efficient use of water in all phases of CO2 uptake are physiological adaptations of bromeliads to arid microclimates in the humid tropics.
Gravity can induce epinastic bending of isolated leaves
Authors: HENSEL W. , KRUFT M.
Published: April 2006

Abstract Isolated leaves of Plectranthus fruticosus were grown in cubic plastic cuvettes, and were supplied via their cut petioles with nutrient solution and indole‐3‐acetic acid (10−6m). Holes bored in the cuvette walls allowed the petioles to be oriented at approximately 60°, 90° or 120° to the vertical. Growth of the leaves initially oriented at angles of 60° and 90°, which simulated the situation in the intact plant, did not result in epinastic bending of the petiole. Inversion of the leaves (adaxial surface of the petiole downwards) and orientation of the adaxial/abaxial surfaces of the horizontal petiole parallel to the gravity vector, however, yielded strong epinastic bending of the petioles. In the latter case, this bending was not in the direction of the gravity vector (evidence for point (iii), below). Furthermore, epinastic bending occurred, when the isolated leaves were rotated on a clinostat (petioles parallel to the rotation axis or inclined to the rotation axis at an angle of 30°; 3 r.p.m.). Since a possible influence of the shoot was excluded, it is concluded that (i) perception and response are restricted to the leaf, (ii) gravity alone is sufficient to induce epinasty, (iii) a gravitropic component of the response can probably be excluded. The clinostat induced epinasty may not have been caused by nullifying the effect of gravity but due to continuous gravistimulation of the leaf.
Survival of Cornus sericea L. stem cortical cells following immersion in liquid helium
Authors: GUY C. L. , NIEMI K. J. , FENNELL A. , CARTER J. V.
Published: April 2006

Abstract Cold‐acclimated stems of red‐osier dogwood (Cornus sericea L.) were sampled in midwinter and early spring and subjected to the following low temperature treatments: (a)0 →−40 → 0°C; (b) 0 →−40 →− 196 → 0°C; (c) 0 →−40 →−196 →−269 →−196 → 0°C; (d) 0 →−40 →−269 →−196 → 0°C; (e) 0 →−196 → 0°C; (f) 0 →−269 →−196 →0°C. The cortical parenchyma cells of the outer stem layers survived exposure to −269°C when pre‐frozen to −40°C and either transferred directly to −269°C or to −196°C and then to −269°C (treatments c and d). Acclimated stems transferred to a greenhouse (22°C) 2 weeks prior to the low temperature treatments deacclimated and were not able to survive freezing to −10°C. Cortical cells of stem samples taken in March, near the time when dogwood naturally deacclimates, survived −196°C (treatment b), but not −269°C (treatment cord). Thus, the freezing tolerance of dogwood varies seasonally from near −10°C to below −269°C.
Adaptation to chilling: photosynthetic characteristics of the cultivated tomato and a high altitude wild species
Authors: YAKIR D. , RUDICH J. , BRAVDO B.‐A.
Published: April 2006

Abstract When tomato plants of the high‐altitude species Lycopersicon hirsutum and of the cultivated Lycopersicon esculentum were grown at 24/18°C (day/night), the effects of temperature, photon flux density, and intercellular CO2 concentration up to about 600 μl l−1 on net CO2 uptake were similar in the two species. Acclimation of these plants at 12/6°C (day/night) resulted, after 4 d or longer, in a similar downward shift of about 5°C in the optimum temperature for CO2 uptake. However, in comparison with the cultivated species, the high‐altitude plants achieved a higher rate of CO2 uptake at saturating concentrations of intercellular CO2, maintained a higher level of saturating‐light CO2 uptake rate at 10°C after exposure to chilling stress (10°C and photon flux density of 400 μmol m−2s−1 d and 5°C night) for 7–18 d, and displayed a better capacity for rapid recovery after prolonged stress. The greater capacity for CO2 uptake observed in the high‐altitude species during and after exposure to chilling stress was also reflected in its higher growth rate under those conditions compared with plants of L. esculentum. These advantages of the high‐altitude species may partly explain its ability to survive and complete its life cycle under the environmental conditions prevailing in its natural habitat.
The soluble carbohydrates of Euglena gracilis—their identity and response to increased external solute concentration
Authors: DWYER M. R.
Published: April 2006

Abstract Mannitol and trehalose were the predominant soluble carbohydrates in Euglena gracilis strain z growing heterotrophically in complete darkness or in light. The ratio of trehalose to mannitol was correlated with the water activity of the medium. That is, extracts of Euglena gracilis adapted to grow in media supplemented with either sodium chloride or glucose, thereby reducing the water activity, yielded molar ratios of trehalose to mannitol 10 times greater than extracts of cultures grown under conditions in common usage.
Effect of calcium ion on cytoplasmic streaming during turgor regulation in a brackish water charophyte Lamprothamnium
Authors: OKAZAKI Y. , TAZAWA M.
Published: April 2006

Abstract The brackish water charophyte Lamprothamnium succinctum regulates its turgor pressure against changes in the external osmotic pressure. Upon hypotonic treatment, the rate of cytoplasmic streaming in the internodal cells fell to almost zero, and then recovered to the original value within 20 min. The decrease could be inhibited by lowering the external Ca2+ concentration in the hypotonic medium. Also, cytoplasmic streaming in tonoplast‐free cells of L. succintum was sensitive to Ca2+ like freshwater charophyte. Thus, the concentration of free Ca2+ in the cytoplasm seems to increase transiently upon hypotonic treatment.
Differential effects of gabaculin and laevulinic acid on protochlorophyllide regeneration
Authors: CAIGER D. P. , PEARSON S. A. , SMITH A. J. , ROGERS L. J.
Published: April 2006

Abstract The effects of gabaculin (3‐amino 2,3‐dihydrobenzoic acid) and laevulinic acid on the regeneration of protochlorophyllide from exogenous δ‐aminolaevulinic acid in leaves of dark‐grown barley (Hordeum vulgare) after a brief light treatment were compared. Gabaculin, a potent inhibitor of chlorophyll biosynthesis, did not inhibit this process showing that it affects the formation of δ‐aminolaevulinic acid rather than its further metabolism. Laevulinic acid, which is an inhibitor of δ‐aminolaevulinic acid dehydratase, prevented regeneration of protochlorophyllide provided pools of intermediates in the biosynthetic sequence were depleted. Formation of relatively large amounts of protochlorophyllide in some experiments suggests a lack of control in the utilization of δ‐aminolaevulinic acid for protochlorophyllide synthesis.
Quantitative short‐term uptake of inorganic phosphate by the Chara hispida rhizoid
Authors: BOX R. J.
Published: April 2006

Abstract The rhizoid of Chara hispida L. made a small contribution to the uptake of inorganic phosphate under laboratory conditions. At 1 mmol m−3 phosphate the rhizoid contributed about 4% to the uptake of the whole plant over 4 h. Under these conditions about half of the phosphate taken up by the rhizoid was translocated into the shoot. The rates of uptake and translocation increased with increasing external phosphate concentrations.

When the shoot was in darkness, 32P‐translocation from the rhizoid was less than half of that found when the shoot was illuminated. When the rhizoid medium was anaerobic the translocation rate was lower than the rate in aerobic conditions and illumination of the shoot had no effect on the uptake or translocation of phosphate.

Translocated 32P accumulated in the apical growing regions of the plant. This was first noted in the secondary apices nearest to the rhizoids.
Quantum yields of photosynthesis at temperatures between −;2°C and 35°C in a cold‐tolerant C3 plant (Pinus sylvestris) during the course of one year
Authors: LEVERENZ J. W. , ÖQUIST G.
Published: April 2006

Abstract Quantum yields of photosynthetic CO2 uptake by Pinus sylvestris (L.) shoots were measured at temperatures between −; 2°C and 35°C from September 1984 to September 1985. The ratio of variable to peak fluorescence of photosystem II (Fv/Fp) was also measured. Quantum yield measured at 25°C varied with time from a low winter value of 0.017 to a high summer value of 0.057. This variation was strongly correlated to variation in FvFp(r2= 0.91).

The response of quantum yield to temperature changed with season. During winter, quantum yield was essentially constant between 0°C and 35°C. The constancy above 5°C was associated with a strong increase in intercellular space CO2 (Ci) with temperature. In June, the quantum yield peaked at 5°C, decreased sharply below 5°C, and was rather constant between 25°C and 35°C. This insensitivity to increased temperature above 25°C was attributed to a large increase in Ci In contrast, by September, the quantum yield was less sensitive to temperature below 5°C and more sensitive above 25°C, despite an unchanged Ci response with increasing temperatures as compared with June. In August, quantum yields were lowered at 0, 5 and 15°C, apparently as a result of high carbohydrate levels in the leaves. Overall, the results suggest that there are sites other than in photosystem II or at ribulose bisphosphate carboxylase/oxygenase at which the quantum yield of photosynthetic CO2 uptake is affected. Possible causes for the changes in efficiency are discussed.
Analysis of growth rates during phototropism: modifications by separate light‐growth responses
Authors: RICH T. C. G. , WHITELAM G. C. , SMITH H.
Published: April 2006

Abstract The changes in growth rate during phototropism in light‐grown mustard (Sinapis alba L.) seedlings have been investigated to clarify the pattern of differential growth which causes curvature. It is shown that deliberately induced phytochrome‐mediated straight‐growth responses can modify the pattern of differential phototropic growth. A comparison of techniques used to analyse phototropic responses in mustard shows that separate light‐growth responses can explain the contradictory published data. When white light is moved from above to one side, straight‐growth responses not mediated directly by the blue photo‐receptor are induced by an increase in the amount of light within the hypocotyl, and these modify the pattern of differential growth. In the absence of such separate light‐growth responses, phototropism is caused by a redistribution of growth within the plant axis.
Multiphasic uptake of phosphate by corn roots
Authors: NANDI S. K. , PANT R. C. , NISSEN P.
Published: April 2006

Abstract The concentration dependence of phosphate uptake was studied using root sections of corn (Zea mays L. cv. Ganga 5). Detailed and wide‐range (57 concentrations in the range 1 μmol m−3‐75 mol m−3), precise (average SEM < 2.5%, n= 6) and reproducible (similar patterns in three independent experiments and for 5, 10, 15, 20, 25 and 30°C) data revealed six (or seven) concentration‐dependent phases separated by ‘jumps’ or sharp breaks. These transitions were independent of temperature and occurred over relatively narrow concentration ranges (0.0001–0.0004, 0.08–0.31, 1.0–3.5, (7.5–10), 18–20 and 57–59 mol m−3). The intermediate phases obeyed Michaelis‐Menten kinetics, whereas sigmoidal kinetics were observed at lower concentrations. Uptake within each of the two highest phases increased more rapidly with increasing external phosphate concentration than predicted from Michaelis‐Menten kinetics but also saturated more rapidly. The latter finding is not consistent with free diffusion across the plasmalemma at high external phosphate concentrations. Kinetic models yielding continuous isotherms, e.g. the sum of one or two Michaelis‐Menten terms and a diffusion term, cannot account for the data.
Effects of desiccation and controlled rehydration on germination in vitro of pollen of walnut (Juglans spp.)
Authors: LUZA J. G. , POLITO V. S.
Published: April 2006

Abstract Moisture content and germination percentages on agar‐solidified medium were determined for pollen of Juglans regia and J. nigra at the time of release from anther and at 24‐h intervals until germination fell to zero. Moisture content of fresh J. regia pollen ranged from 4.6 to 12.1%, and from 3.9 to 4.0% for J. nigra pollen; in vitro germination percentages were uniformly high throughout these ranges. Germination declined as pollen moisture fell below 5% in J. regia with regression analyses predicting 50% germination at 3.9–4.4% moisture. After 4 d at ambient laboratory conditions, all pollen had lost the ability to germinate when incubated directly on medium. This pollen was incubated in chambers where humidity was maintained at saturation and 33% saturation, and retested. Pollen up to 22 d old and having moisture contents as low as 2.6% regained the ability to germinate in vitro when it was incubated in a water‐saturated environment before being placed on the agar‐solidified medium.