bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐random leaf orientation in Lactuca serriola L.
Authors: WERK K. S. , EHLERINGER J.
Published: April 2006

Abstract Leaf shapes and leaf orientation of Lactuca serriola serriola and serriola integrifolia were studied. Leaf shapes in L. serriola serriola differed greatly from those of L.serriola integrifolia, but leaf surface areas were similar. In exposed habitats, leaf orientation of cauline leaves of both forms was non‐random, with leaves almost vertical and tending to orient with their lamina normal to the east and west. In the shade, cauline leaves oriented randomly. An experiment demonstrated that the orientation of leaves did not change significantly once they were fully expanded. The leaf orientation in L. serriola affected the diurnal distribution of solar irradiance intercepted by a leaf. Peak solar radiation fluxes are incident on the rosette leaves at midday, but on the cauline leaves the peak solar radiation flux occurs early in the morning and again late in the afternoon. The significance of this unusual leaf orientation is discussed in relation to water loss and carbon gain.
Growth distribution during first positive phototropic curvature of maize coleoptiles*
Authors: LINO MORITOSHI , BRIGGS WINSLOW R.
Published: April 2006

Abastract Measurements of growth increments on the shaded and the irradiated sides of phototropically stimulated maize (Zea mays L.) coleoptiles, obtained over the entire fluence range of the first positive curvature, indicate that the curvature is induced by growth stimulation on the shaded side and compensating inhibition on the irradiated side (length increments on the coleoptile flanks were determined 100 min after 30 s phototropic induction with blue light). At high fluences of blue light, overall stimulation of growth takes place, but this tendency is largely eliminated when only the tip of the coleoptile is irradiated. Time courses for growth increments obtained for the maximum first positive response show that the growth stimulation on the shaded side and the growth inhibition on the irradiated side commence almost simultaneously 20‐30 min after the phototropic induction. The growth on the irradiated side almost ceases, but the growth rate on the shaded side is doubled, relative to the control rate. The onset of differential growth migrates basipetally from the tip at a velocity similar to that for polar auxin transport. The first positive phototropic response of the coleoptile is concluded to be the consequence of lateral redistribution of growth, which is not necessarily accompanied by changes in the net growth. The results are consonant with the Cholodny‐Went theory of tropisms, in which lateral redistribution of auxin is considered to be the cause of tropic responses.
Dynamic changes of protoplasmic volume and of fine structure during osmotic adaptation in the intertidal red alga Porphyra umbilicalis
Authors: KNOTH AXEL , WIENCKE CHRISTIAN
Published: April 2006

Abstract Cells of Porphyra umbilicalis show a biphasic osmotic regulatory response. After transfer from 1 × into 3.5 × artificial seawater medium (osmotic upshock) the protoplasts shrink rapidly, then recover their original size within 3 h and continue to increase over the next 14 d. After retransfer from 3.5 × into 1 × medium (osmotic downshock) the protoplasts swell immediately and then adjust to the normal size in 1 x medium. Parallel to the shrinkage of the protoplasts after osmotic upshocks the plasmalemma at first gets a wavy surface which becomes smooth again during the following adaptation process. Immediately after osmotic upshock the vacuolar volume increases and it decreases drastically after osmotic downshock. After osmotic upshocks only small vacuoles are present at first. In adapted plants, however, the vacuolar system is mainly composed of large vacuoles. The volume of the protoplasm without the vacuoles is regulated osmotically. Parallel to the increase in the vacuolar volume after osmotic upshocks there is an increase in the number of intramembraneous particles on the PF‐face of the tonoplast. This high value is reduced rapidly to the original number after osmotic downshock. The findings are discussed in relation to the function of the vacuoles as compartments of inorganic ion accumulation during osmotic adaptation.
Isolation and activity of the photodynamic pigment hypericin
Authors: KNOX J. P. , DODGE A. D.
Published: April 2006

Abstract. Hypericin, a photodynamic pigment, occurring in members of the Hypericaceae, can induce photosensitivity in grazing animals. The pigment has been isolated from the glandular trichomes located on the calyx of Hypericum hirsulum. Hypericin is shown to be capable of sensitizing the photo‐oxidation of methyl linolenate. This activity is reduced in the presence of crocin, a carotenoid. Evidence for the generation of singlet molecular oxygen by hypericin is provided by the monitoring of oxygen consumption during the photosensitized oxidation of imidazole. Rates of oxygen consumption were modified by deuterium oxide and sodium azide. The photodynamic action of hypericin on pea leaf discs results in the promotion of photo‐oxidative damage, measured by pigment loss and ethane production. These results are discussed in relation to the possible function of hypericin within the plant and the role of photo‐dynamic reactions in nature.
Comparison of chlorophyll fluorescence emission characteristics of wheat leaf tissue and isolated thylakoids as a function of excitation wavelength
Authors: PERCIVAL M.P. , BAKER N.R.
Published: April 2006

Abstract.Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited with 550 nm rather than 450 nm radiation. Such excitation wavelength dependent changes in the emission spectrum occurred over an excitation spectral range of 440–660 nm and appeared to be directly related to the total quantity of radiation absorbed at a given excitation wavelength. Experiments with isolated thylakoid preparations demonstrated that changes in the fluorescence emission spectrum of the leaf were attributable to the optical properties of the leaf and were not due to the intrinsic characteristies of the thylakoid photochemical apparatus. This was not the case for the observed excitation wavelength dependent changes in the 685 nm fluorescence induction curve obtained from leaf tissue infiltrated with DCMU. Excitation wavelength dependent changes in the ratio of the variable to maximal fluorescence emission and the shape of the variable fluorescence induction were observed for leaf tissue. Isolated thylakoid studies showed that such changes in the leaf fluorescence kinetics were representative of the way in which the photochemical apparatusin vivowas processing the absorbed radiation at the different excitation wavelengths. The results are considered in the context of the use of fluorescence emission characteristics of leaves as non‐destructive probes of the photochemical apparatusin vivo.
Comparison between two methods of generating pressure—volume curves
Authors: RITCHIE G. A. , RODEN J. R.
Published: April 2006

Abstract. Pressure—volume (P—V) curves were generated on roots and shoots of coastal Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings using two procedures. In the first (Method A), samples were dehydrated inside a pressure chamber. Exuded stem sap was collected and weighed at successive pressure increases to derive the P—V curve. In the second method (Method B). excised samples were allowed to dry outside the pressure chamber by evapotranspiration. They were weighed periodically to determine sap loss and their corresponding balance pressures were determined in a pressure chamber in order to derive the P—V curve.

Estimates of volume averaged osmotic potential at full turgor and water potential at zero turgor which were derived graphically from the P—V curves, were different for each method. In general, estimates were more negative in Method A, by as much as 1.5 MPa in one case. Also, Method B did not record an osmotic adjustment in seedlings which were subjected to severe water stress while Method A did.
Effect of boundary layer conductance on the response of stomata to humidity
Authors: BUNCE J. A.
Published: April 2006

Abstract. Leaf conductance responses to leaf to air water vapour partial pressure difference (VPD) have been measured at air speeds of 0.5 and 3.0 ms−1 in single attached leaves of three species in order to test the hypothesis that leaf conductance response to VPD is controlled by evaporation from the outer surface of the epidermis, rather than by evaporation through stomata. Total conductance decreased linearly with increassing VPD at both air speeds, but was decreased 1.6 3.0 times as much as by a given incrase in VPD at high than at low air speed. depending on species. In all species the relationship between leaf conductance and the gradient for evaporation from the epidermis was the same at both values of boundary layer conductance, supporting the hypothesis that direct epidermal evaporation controls stomatal guard cell behaviour in responses of stomata to VPD in these species.
Ultrastructure of wheat coleoptile mitochondria at short‐term anoxia and post‐anoxia
Authors: VARTAPETIAN B. B. , ZAKHMYLOVA N. A. , GENEROZOVA I. P.
Published: April 2006

Abstract. Mitochondrial ultrastructure in the cells of coleoptiles of 4 d seedlings was investigated under conditions of a 1.5, 3, and 36 h anoxia and with subsequent transfer of the seedlings, after a 1.5 h anoxia, from the anaerobic into an aerobic medium. Even with short‐term anoxia (1.5 h) destructive changes take place in the ultrastructure of mitochondria, which are reversible not only following the transfer of these seedlings from the anaerobic into aerobic conditions, but also with their continued maintenance under strict anoxia. Irreversible changes in the ultrastructure of mitochondria were seen only with a more prologed (36 h and longer) anoxia. The observed phenomena are discussed from the viewpoint of energy provision of the seedling cells in anoxia and post‐anoxia.
Enzyme patterns in energy metabolism during flower induction in spinach leaves
Authors: BONZON M. , AGOSTI R. DEGLI , WAGNER E. , GREPPIN H.
Published: April 2006

Abstract. Time series measurements of six enzymes linked to different pathways in energy metabolism [NAD‐ and NADP‐dependent glyceraldchyde‐3‐phosphate dehydrogenase (NAD‐ and NADP‐GPDs), adenylate kinase (AK), malate dehydrogenase (MDH), glucose‐6‐phosphate dehydrogenase (G‐6PDH) and 6‐phosphogluconate dehydrogenase (6‐PGDH)] have been performed in spinach leaves subjected to different photoperiodic treatments, inductive or not of the flowering process. It is shown that the vegetative and the floral states are characterized by specific enzyme patterns, respectively. Among the six enzymes measured, only three of them present a particular behaviour during the early period of flower induction and probably might be specific markers of this physiological change in the leaves. It is concluded that in a C3 plant such as spinach, floral induction in the leaves mostly involves a reorganization of the ‘vegetative’ metabolic network possibly through a change in phase relationships in the different pathways in energy metabolism.
The effect of temperature and ageing on root apical meristems during seedling growth of Triticum aestivum L.: a specific effect on nucleoli
Authors: JORDAN E. G. , COOPER P. J. , MARTINI G. , BENNETT M. D. , FLAVELL R. B.
Published: April 2006

Abstract. Growth and cytology of root apical meristems of Chinese Spring wheat were studied in relation to temperature. The maximum rate of growth increased with temperature, a marked rise occurring between 10°C and 12°C. At all temperatures studied nucleolar volume increased to a maximum and then declined. The maximum nucleolar size achieved showed particular temperature sensitivity, higher volumes being attained at lower temperatures. The peak at 5°C was 70% higher than at 20°C. However, in comparison, cell and nuclear volumes were only 38% and 47% larger, respectively. Ultrastructural analysis of the nucleoli revealed a temperature‐dependent relationship between the proportion of granular component and dense fibrillar component. The results are discussed in relation to the regulation of ribosome synthesis and function during growth and development at different temperatures.
Extraorgan freezing in wintering flower buds of Cornus officinalis Sieb. et Zucc.
Authors: ISHIKAWA MASAYA , SAKAI AKIRA
Published: April 2006

Abstract. Extraorgan freezing as a mechanism for increasing cold hardiness was shown using flower buds of Cornus officinalis Sieb. et Zucc. Differential thermal analysis (DTA) revealed that florets in flower buds of C. officinalis owed their cold hardiness to deep supercooling and also that slower cooling rates increased the supercooling ability of florets. During slow stepwise cooling (5°C h−1), the water content of florets decreased and that of scales (involucral bracts) increased, which resulted in accumulation of ice within the scales. This was more extensive in early winter and early spring buds than mid‐winter ones. Flower buds with silicone oil in the space between florets and scales also showed a similar decrease in water content of florets and an increase in that of scales. This indicated that water migration from the florets to the scales probably took place by way of the peduncles and the receptacle, possibly through their vascular traces, and not directly from the surface of the florets to the ice sink in the form of vapour. Possible mechanisms of extraorgan freezing are postulated along with this finding.
Nutrients‐mediated shift in temporal expression of phytochrome controlled β‐amylase synthesis in mustard (Sinapis alba L.) cotyledons
Authors: MANGA V. A. , SHARMA R.
Published: April 2006

Abstract. In cotyledons of mustard (Sinapis alba L.) seedlings grown with distilled water (DW) phytochrome controlled increase in β‐amylase (E.C. 3.2.1.2) level takes place at about 42 h after sowing (starting point), while the photoresponse escapes from photoreversibility at 30 h after sowing. The temporal onset of starting point is presumed to be determined by innate process of developmental homeostasis, which is not amenable to influence of environmental factors such as light and nutrients. However, the temporal appearance of onset of phytochrome controlled increase in β‐amylase level (starting point) in seedlings grown with Hoagland's nutrient solution (HS) is delayed by 9 h as compared to DW‐grown seedlings. Concomitantly, the temporal appearance of the loss of photoreversibility of phytochrome mediated increase in β‐amylase level (coupling point) is also delayed by 9 h in HS‐grown seedlings. HS does not influence the primary action of phytochrome, the lifetime of components involved in signal chain of above photoresponse and the turnover of β‐amylase enzyme. These results indicate that HS‐induced temporal shift in onset of starting point of above photoresponse is caused by interaction of nutrients with the process of developmental homeostasis.
Photosynthetic characteristics of Lactuca serriola L.
Authors: WERK K. S. , EHLERINGER J.
Published: April 2006

Abstract. Gas exchange responses of intact leaves of Lactuca serriola serriola and L. serriola integrifolia were examined. The light, temperature and intercellular CO2 dependence of photosynthesis of these two forms of L. serriola were indistinguishable. Dependence of photosynthesis on leaf temperature differed only slightly between plants grown at approximately 10/3°C and those grown at 33/25°C with the thermal optimum shifting 4°C. Transpiration was shown to increase exponentially with leaf temperature. The gas exchange characteristics of L. serriola are discussed in relation to water relations, carbon gain and compass leaf orientation under field conditions.
Auxin action: the search for the receptor
Authors: CROSS J. W.
Published: April 2006

Abstract. The molecular specificity of the substances which have auxin activity implies the existence of specific receptors. There have been many efforts to identify and isolate these receptors on the assumption that they should bind auxins with affinities coordinate to their activities in bioassays. However, the known complexity of auxin uptake and metabolism make this assumption seriously deficient. Although several such binding sites have, in fact, been identified, proof of a connection between these sites and auxin action has been lacking. Definite proof would include a requirement that the site be reconstituted, together with the appropriate macro‐molecular machinery, to construct a model of an auxin response. At the moment, our ignorance of the biochemistry and molecular biology of auxin growth responses makes such a proof difficult. However, two avenues of research promise to accelerate the rate of progress. The increasingly potent tools of molecular biology should soon allow the dissection of auxin‐regulated gene expression, while improved knowledge of plasma membrane proton pumps and the mechanism of cell wall biosynthesis should produce, in parallel, an understanding of the auxin regulation of acid growth.
The influence of temperature during seed development on the germination characteristics of millet seeds
Authors: MOHAMED H. A. , CLARK J. A. , ONG C. K.
Published: April 2006

Abstract. The cardinal temperatures, rate of germination and final percentage germination of pearl millet seeds were measured for seeds raised in greenhouses maintained at mean air temperatures of 19, 22, 25, 28 and 31°C. The results showed that cardinal temperatures for germination are unaffected by the temperature during seed development and growth. However, the conditions during seed growth did affect seed size and, subsequently, germination rate and seed viability.
Leaf hygrometer v. pressure chamber: a comparison of pressure–volume curve data obtained on single leaves by alternating measurements
Authors: KIKUTA S. B. , KYRIAKOPOULOUS E. , RICHTER H.
Published: April 2006

Abstract. Data for the construction of pressure‐volume curves were obtained by measuring water potentials of detached leaves repeatedly and alternately, with a pressure chamber and a leaf hygrometer. Good agreement between the parameters of the two resulting curves was observed. Regression lines on values after the loss of turgor were always more negative for the thermocouple data, with a maximum difference for the osmotic potential at full saturation of 0.25 MPa in Triticum and a minimum of 0.01 MPa in Populus. Neither the slopes of the regression lines nor the intercepts with the axes were statistically different. We see no reason for using one of these two unrelated methods as a standard against which the other is calibrated. Implications for the theory of pressure‐volume curves are discussed.
Dynamic model of the response of a vegetative grass crop to light, temperature and nitrogen
Authors: JOHNSON I. R. , THORNLEY J. H. M.
Published: April 2006

Abstract A previously described growth model of the vegetative grass crop is extended to include a simple representation of the root system, uptake of nitrogen from a soil nitrogen pool, and response to fertilizer application. The model simulates the processes of light interception, photosynthesis, partitioning of new growth, leaf area expansion, growth and maintenance respiration, ageing of plant tissues, senescence, recycling of substrates from senescing tissues, nitrogen uptake by the plant, leaching, mineralization, and fertilizer application. A principal component of the model, nitrogen uptake, is assumed to depend positively on plant carbon substrate concentration and soil nitrogen concentration, and to be inhibited by plant nitrogen substrate concentration. The dynamic responses to different levels of soil nitrogen, of shoot and root growth, nitrogen uptake and root activity, carbon and nitrogen plant substrate concentrations, and the fraction of substrate carbon used by the shoots, are examined; realistic behaviour is observed. The model predicts nitrogen fertilizer responses of yield and plant nitrogen content, which are compared directly with experimental data; good agreement is obtained.
Freezing avoidance in Andean giant rosette plants
Authors: RADA F. , GOLDSTEIN G. , AZOCAR A. , MEINZER F.
Published: April 2006

Abstract Frost avoidance mechanisms were studied in Espeletia spicata and Espeletia timotensis, two Andean giant rosette species. The daily courses of soil, air and tissue temperatures were measured at a site at circa 4000 m. Only the leaves were exposed to subzero temperatures; the apical bud and stem pith tissues were insulated by surrounding tissues. The leaf tissues avoided freezing by supercooling rather than by undergoing active osmotic changes. The temperatures at which ice formed in the tissues (the supercooling points) coincided with injury temperatures indicating that Espeletia tissue does not tolerate any kind of ice formation. For insulated tissue (apical bud, stem pith, roots) the supercooling point was around ‐ 5°C coinciding with the injury temperature. Supercooling points of about –13 to ‐ 16°C were observed for leaves. These results contrast with those reported for Afroalpine giant rosettes which tolerate extracellular freezing. The significance of different adaptive responses of giant rosettes to similar cold tropical environments is discussed.
Transmission properties of an oak canopy in relation to photoperception
Authors: HUGHES J. E. , MORGAN D. C. , BLACK C. R.
Published: April 2006

Abstract The spectra of incoming daylight and shadelight in a mature oak woodland were measured at intervals during the canopy cycle, and mean transmittance spectra were derived. Transmittance was spectrally neutral at ca. 0.55 during the light phase but, following leaf emergence, transmittance of PAR (400–700 nm) fell to ca. 0.1. Simultaneously, the red : far‐red transmittance ratio fell to circa 0.6. Both showed little change during the summer and autumn until senescence, indicating that the optical properties of the canopy were surprisingly stable. There was no evidence that cloud cover influenced mean canopy transmittance, although transient sunflecks introduced great variability which, in combination with sampling bias, might explain previous contradictory reports. The red : far‐red fluence rate ratio in the woodland showed a temporary increase in late summer, a result of a small increase in the red : far‐red ratio of incoming daylight during this period. Reflectance and transmittance spectra and pigment content of sun and shade leaves were measured. Leaf transmittance spectra showed changes correlated with those of the canopy, and were related to changes in pigment content.
Evaluation of a technique for the measurement of chlorophyll fluorescence from leaves exposed to continuous white light
Authors: ÖGREN E. , BAKER N. R.
Published: April 2006

AbstractAn instrument for the generation and measurement of modulated chlorophyll fluorescence signals from leaves exposed to continuous, highintensity white light is described. Modulated fluorescence is generated in the leaf by pulsed diodes emitting low‐intensity yellow radiation and is detected with a photodiode whose output is fed to an amplifier locked in to the frequency of the lightemitting diodes. Comparisons are made between the modulated fluorescence signals measured with this instrument and the continuous fluorescence signals emitted from dark‐adapted leaf tissue and isolated thylakoids when photosynthetic activity is induced by exposure to a range of intensities of continuous broad‐band, blue‐green light. The modulated fluorescence signals were similar to the continuous fluorescence signals, but they were not always identical. The small differences between the two signals are mainly attributable to differences in the populations of chloroplasts being monitored in the two measurements as a result of differential penetration of the modulated and actinic light sources into the sample.
Cell wall elasticity: I. A critique of the bulk elastic modulus approach and an analysis using polymer elastic principles
Authors: WU HSIN‐I , SPENCE RICHARD D. , SHARPE PETER J. H. , GOESCHL JOHN D.
Published: April 2006

Abstract The traditional bulk elastic modulus approach to plant cell pressure‐volume relations is inconsistent with its definition. The relationship between the bulk modulus and Young's modulus that forms the basis of their usual application to cell pressure volume properties is demonstrated to be physically meaningless. The bulk modulus describes stress/strain relations of solid, homogeneous bodies undergoing small deformations, whereas the plant cell is best described as a thin‐shelled, fluid‐filled structure with a polymer base. Because cell walls possess a polymer structure, an alternative method of mechanical analysis is presented using polymer elasticity principles. This initial study presents the groundwork of polymer mechanics as would be applied to cell walls and discusses how the matrix and microfibrillar network induce nonlinear stress/ strain relationships in the cell wall in response to turgor pressure. In subsequent studies, these concepts will be expanded to include anisotropic expansion as regulated by the microfibrillar network.
Xylem perfusion of tap root segments of Plantago maritima: the physiological significance of electrogenic xylem pumps
Authors: DE BOER A. H. , PRINS H. B. A.
Published: April 2006

Abstract A method is described for perfusing xylem vessels in tap root segments of the halophyte P. maritima. Use of excised segments allowed recording of the trans‐root potential (TRP) at both ends of a segment. It was shown that there can be a spatial variation of electrogenic ion pump activity along the xylem in one root segment. The pH of perfusion solutions, differing in buffering capacity, was adjusted by the root segment to pH 5.1–5.6 during How through the xylem. This pH range was similar to that of sap produced by root pressure. The K+ activity in the outflow solution (K+out) was rather constant at 12–13 mol m−l3 despite input K+ activities ranging from 8 to 20 mol m−l3. Addition of fusicoccin (10−l2 mol m−l3) to the perfusion solution induced a strong acidification of the xylem sap, a decrease in K+out and an increase in Na+out. Inhibition of aerobic respiration through anoxia inhibited electrogenic proton pumping into the xylem and led to an increase in K+out and a decrease in Na+out. It is suggested that transport of K+ and Na+ to the shoot of the halophyte P. maritima is regulated in the tap root by means of ion exchange between xylem vessels and xylem parenchyma and that this exchange is energized by proton translocating ATPases.
Reversal of ethylene action on cocklebur seed germination in relation to duration of pre‐treatment soaking and temperature
Authors: ESASHI YOHJI , SAIJOH YUKIO , ISHIDA SATOKO , OOTA HIROSHI , ISIZAWA KIMIHARU
Published: April 2006

AbstractAt 23°C, both C2H4and CO2stimulated the germination of freshly imbibed upper cocklebur (Xanthium pennsylvanicumWallr.) seeds, but C2H4, unlike CO2, changed to an inhibitor of germination under some soaking conditions. However, when seeds were pre‐soaked for more than several hours at 23 °C prior to treatment, C2H4strongly inhibited their germination at 33 °C, the degree of inhibition increasing with the duration of pre‐soaking. Maximum inhibition occurred at 1–3 cm3m−3C2H4when seeds were pre‐soaked for 1 week; further increases of C2H4concentration and pre‐soaking period decreased the inhibitory effect. C2H4was synergistic with CO2when C2H4promoted germination, whereas it was antagonistic when inhibitory. Such a transition of the C2H4action occurred at ca. 27 °C. Also 1‐andnocyclopropane‐1‐carboxylic acid, a C2H4precursor, inhibited the germination of pre‐soaked seeds at 33 °C, although it promoted the germination at 23 °C. When pre‐soaked seeds were prepared for germination by chilling at 8 °C for 3 d, the inhibitory effect of C2H4on the subsequent germination was manifested even at 23 °C. The reversal of the C2H4action from promotion to inhibition in cocklebur seed germination is discussed in relation to the engagement of two respiratory pathways in the imbibed seeds.
Turgor‐sensitive transport in developing seeds of legumes: the role of the stage of development and the use of excised vs. attached seed coats
Authors: WOLSWINKEL P. , AMMERLAAN A.
Published: April 2006

Abstract After removal of the embryo from developing seeds of Vicia faba L. and Pisum sativum L., the ‘empty’ ovules were filled with a substitute medium (pH 5.5) and the effect of the osmolality of this solution on assimilate transport was exandned. In pulse‐labelling experiments with a mixture of [3H]sucrose and [14C]α‐andnoisobutyric acid (AIB), a solute concentration of 400 mol m−3 (100 mol m3− sucrose + 300 mol m−3 mannitol) was too low to maintain sugar and andno acid transport into empty ovules of V. faba in a very early stage of development (embryo dry weight < 100 mg) on the same level as transport into intact ovules within the same fruit. A 550‐mol m−3 solution could maintain the normal rate of transport. In experiments with seeds in a more advanced stage of development (embryo dry weight > 250 mg), transport of labelled sucrose and AIB into empty ovules filled with a 400‐mol m−3 solution was practically equal to transport into intact ovules within the same fruit. Experiments without isotopes, on sugar and andno acid release from the seed coat, confirmed the important role of the osmotic environment. A very low osmolality of the solution (e.g. 50 mol m−3 mannitol) enhanced net efflux of assimilates from excised seed coats and cotyledons, by inhibiting resorption from the apoplast.
Compatible solutes and their effects on phosphoenolpyruvate carboxylase of C4‐halophytes
Authors: MANETAS Y. , PETROPOULOU Y. , KARABOURNIOTIS G.
Published: April 2006

Abstract Phosphoenolpyruvate carboxylase (PEPCase), extracted from two Poaceae (Cynodon dactylon and Sporobolus pungens) grown on saline soil, was affected physiologically by betaine and proline. Its affinity for phosphoenolpyruvate (PEP) was increased and full protection against NaCl inhibition was observed; enzymic activity was also stabilized when assayed at low PEP levels. Betaine has the same effects on PEPCase extracted from a Chenopodiaceae (Salsola soda), whereas proline behaves as a competitive inhibitor, i.e. it does not protect the enzyme against NaCl and it accelerates inactivation at low PEP levels. Betaine was only compatible with PEPCase extracted from Saisola kali, without any effect on activity, protection or stabilization, but proline was again inhibitory.

The levels of free proline in the two salt‐stressed Poaceae were high, whereas in the Chenopodiaceae the free proline was low, as in non‐stressed plants. The above data indicate that osmoregulators could not only be compatible with cytoplasmic enzymes, but they could either promote or inhibit enzyme activity, depending on the source of enzyme. Coevolution of PEPCase with the osmolyte selected for, could also be inferred.
Inheritance of cyanide‐resistant respiration in two cultivars of pea (Pisum sativum L.)
Authors: MUSGRAVE M. E. , MURFET I. C. , SIEDOW J. N.
Published: April 2006

Abstract Two pea cultivars (Pisum sativum L., cvs. Alaska and Progress No. 9) shown previously to differ with regard to the appearance of the cyanide‐resistant (alternative) pathway of respiration in axis tissue, were found to show this same difference in mature leaf tissue and in epicotyl mitochondria. The possible relationship between dwarf growth form and lack of alternative respiration in cv. Progress No. 9 was tested in two ways. When dwarfism was alleviated in Progress No. 9 by application of exogenous gibberellin A1, no appearance of the alternative pathway was observed. In a survey of eight other dwarf pea cultivars, five were found to have an alternative pathway comparable to that shown by the tall cv. Alaska, while three lacked the pathway (cf. Progress No. 9). In reciprocal crosses between Alaska and Progress No. 9, the alternative pathway capacity of F1 progeny resembled that of the maternal parent. This pattern was maintained in all the F2 generation, indicating maternal inheritance of the trait. These data suggest that alternative respiration in pea is, to some extent, under the control of an organellar genome.
Problems with the application of quin‐2‐AM to measuring cytoplasmic free calcium in plant cells
Authors: CORK R. J.
Published: April 2006

Abstract Attempts have been made to use the fluorescent calcium quin‐2 to measure cytoplasmic free calcium in a variety of plant cells. Failure to measure intracellular fluorescence can be attributed to extracellular hydrolysis of the membrane‐permeable ester quin‐2‐AM used to load the cells. Attempts to overcome this problem by long incubation times showed that the by‐product of ester hydrolysis, formaldehyde, is inhibitory to cell growth. Thus, it seems that the applicability of the acetoxymethyl ester of quin‐2 for cytoplasmic calcium measurements in plant cells is limited, though quin‐2 could still be very useful in some cells, especially if more suitable esters or micro‐injection are used.
Book Review
Authors: RUSSELL G.
Published: April 2006

Book Reviewed are in this Article:

THE PHYSIOLOGICAL ECOLOGY OF SEAWEEDS. By C. S. Lobban, P. J. Harrison & M. J. Duncan
Comparative ecophysiology of CAM and C3 bromeliads. II. Field measurements of gas exchange of CAM bromeliads in the humid tropics
Authors: LÜTTGE U. , STIMMEL K.‐H. , SMITH J. A. C. , GRIFFITHS H.
Published: April 2006

Abstract The results described represent the first detailed measurements of gas exchange of epiphytic plants with crassulacean acid metabolism (CAM) in the humid tropics. A portable steady‐state CO2 and H2O porometer was used to measure net exchange rates of CO2 and H2O vapour (JCO2, JH2O), leaf temperature (T1), air temperature (TA), air relative humidity (RH) and photosynthetically active radiation (PAR) for bromeliads in the field during the dry season in February and March 1983 on the tropical island of Trinidad. Different lengths of tubing (up to 25 m) were used so that the gas exchange could be measured of bromeliads in situ in their epiphytic habitats. Derived parameters such as leaf‐air water‐vapour‐concentration difference (Δw), water‐vapour conductance of leaves (g) and internal CO2 partial pressure (piCO2) could be calculated.

The particular problems of making such measurements in the humid tropics due to high relative humidities and high dew‐point temperatures are discussed. The long and often broad, strap‐like leaves of bromeliads are well suited for measurements with the steady‐state porometer. It is shown that CAM activity varies along the length of individual leaves, and variability between different leaves is also demonstrated.

The major phases of CAM, i.e. nocturnal stomalal opening, CO2 uptake and dark fixation as malic acid (Phase I), daytime stomatal closure and light‐dependent assimilation of CO2 derived from decarboxylation of the malic acid (Phase III), and late‐afternoon stomatal opening with direct light‐dependent assimilation of atmospheric CO2 (Phase IV) were all clearly shown by CAM bromeliads in situ. Their expression and magnitude depended on the environmental conditions. An early‐morning peak of CO2 uptake as is characteristic of Phase II of CAM was not detected during the night‐day transition. A bromeliad intermediate between C3 and CAM, Guzmania monostachia, showed substantial net CO2 uptake in the early morning but no net uptake integrated over the whole of the night.
Comparative ecophysiology of CAM and C3 bromeliads. V. Gas exchange and leaf structure of the C3 bromeliad Pitcairnia integrifolia
Authors: LÜTTGE U. , KLAUKE B. , GRIFFITHS H. , SMITH J. A. C. , STIMMEL K.‐H.
Published: April 2006

Abstract Pitcairnia integrifolia is endemic to northern Trinidad and the Paria peninsula of Venezuela and is the only member of the bromeliad‐subfamily Pitcairnioideae in Trinidad. It is terrestrial with roots fully functional in water and solute uptake, grows on exposed steep rocky cliffs and can occur just above the spill zone of sea waves under continuous sea spray. Thus, it can be subject both to water stress, particularly during the dry season, and to salt stress.

Gas exchange of P. integrifolia leaves was measured on a clear day in Trinidad. Uptake of CO2 and leaf conductance to diffusion of water vapour had two peaks during the light period, a larger one in the early morning and a smaller one in the late afternoon, which were separated by an extended midday depression of gas exchange. CO2 partial pressure in the leaf air‐spaces increased during the midday depression. Leaf temperatures reached a maximum of 51.6°C and leaf‐air water‐vapour‐concentration differences were also very high during the midday depression, when quantum fluxes were up to 2 mmol m−2 s−1 and higher. The midday depression is considered as a functional adaptation to temporary water stress.

Although P. integrifolia is subject to sea‐spray, an internal osmotic pressure of only 0.91 MPa indicated that NaCl is not accumulated. Leaf epidermis cells are thick‐walled and have a prominent cuticle. The abaxial leaf surface with the trichomes is not wettable, and the trichomes apparently do not function in water and solute uptake. They cover the stomata densely and may create a favourable microenvironment around them. They also have a high reflectance. This does not prevent overheating of the leaves, but does reduce the photosynthetically active radiation penetrating to the mesophyll. The trichomes may thus contribute to the prevention of photoinhibition at high incident quantum flux.
CAM induction by photoperiodism in green callus cultures from a CAM plant
Authors: BRULFERT J. , MRICHA A. , SOSSOUNTZOV L. , QUEIROZ O.
Published: April 2006

Abstract Green calli obtained from leaves of the CAM‐inducible plant Kalanchoe blossfeldiana cv. Montezuma were grown either under long‐day or short‐day regimes in the Phytotron of Gif‐sur‐Yvette. Callus cells were found to be CAM inducible by the short‐day treatment, according to levels and diurnal oscillations of malate pools and phosphor‐enolpyruvate (PEP) carboxylase (EC.4.1.1.31) capacity. De novo synthesis of PEP carboxylase was shown to occur under the short‐day regime. In spite of continuous net CO2 output, CAM‐like patterns of CO2 exchange by calli were obtained under the short‐day treatment. After 2 months under both photoperiodic conditions, spontaneous organogenesis in callus tissues gave rise to numerous shootlets which were determined as photoperiod dependent for CAM; the same was so for plants originating from these shootlets.
Structural and metabolic properties of green tissue cultures from a CAM plant, Kalanchoë blossfeldiana hybr. Montezuma
Authors: KLUGE M. , HELL R. , PFEFFER A. , KRAMER D.
Published: April 2006

Abstract Crassulacean acid metabolism (CAM) was studied in mixotrophic callus tissue cultures of Kalanchoë blossfeldiana hybr. Montezuma and compared with plants propagated from the calli.

The ultrastructural properties of the green callus cells are similar to mesophyll cells of CAM plants except that occasionally abnormal mitochondria were observed. There was permanent net CO2 output by the calli in light and darkness, which was lower in darkness than in light. The calli exhibited a diurnal rhythm of malic acid, with accumulation during the night and depletion during the day. 14C previously incorporated by dark CO2 fixation into malate was transferred upon subsequent illumination into end products of photosynthesis. All these data indicate that CAM operates in the calli tissue. The results revealed that the capacity for CAM is obviously lower in the calli compared with plantlets developing from the calli, or with ‘adult’ plants. The data suggest also that CAM in the calli was not limited by the activities of CAM enzymes.
Multiple or multiphasic uptake mechanisms in plants?
Authors: NISSEN P.
Published: April 2006

Abstract Borstlap (1983) has alleged that (a) there are no abrupt changes in curves for the concentration dependence of solute uptake in plants, and (b) many such uptake isotherms may be described by the sum of two Michaelis‐Menten terms and a linear term. These claims are considered in detail in connection with the recent finding (Nandi, Pant & Nissen, 1987) that phosphate uptake by corn roots increased more rapidly within the higher phases, i.e. at high external phosphate concentrations, but also levelled off faster than predicted from Michaelis‐Menten kinetics. Similar deviations are, in retrospect, also found for uptake of other solutes and result in fewer phases at high external solute concentrations. The simplified and strikingly similar multiphasic patterns in the present paper show that (a) the abrupt changes in published isotherms are not due to error in the data, and (b) uptake isotherms cannot be adequately represented by the sum of two Michaelis‐Menten terms and a linear term, or by similar continuous functions, if sufficiently detailed and precise data are used. These findings are not consistent with the existence of multiple uptake mechanisms, including free diffusion, in the plasmalemma. Uptake occurs instead by a single, multiphasic mechanism for each solute or group of related solutes. The similarities in the multiphasic patterns indicate, furthermore, that influx of the various solutes may be coupled.
Amino acid uptake by Ricinus communis roots: characterization and physiological significance
Authors: SCHOBERT C. , KOMOR E.
Published: April 2006

Abstract Roots of sterile‐grown, intact 6‐day‐old seedlings of Ricinus communis possess at least two independent active amino acid uptake systems, one for neutral and one for basic amino acids. The kinetics of uptake of L‐proline and L‐arginine, which were taken as representative substrates for the two systems, are biphasic. At low concentrations (0.01–0.5 mol m−3) Michaelis ‐Menten kinetics prevail, changing to a linear concentration dependence at higher substrate concentrations (1–50 mol m−3). L‐glutamate uptake velocity is linear over the whole substrate concentration range.

For comparison the uptake kinetics of nitrate and ammonium were determined as well as interactions among the different nitrogen sources. The Km value for nitrate uptake was 0.4 mol m−3, and for ammonium 0.1 mol m−3. The uptake capacity for nitrate or ammonium was approximately the same as for amino acids. The interaction between the uptake systems for organic and inorganic nitrogen is small.

Two hypotheses for the physiological significance of amino acid uptake by roots were considered:

(i) Uptake of amino acids from the soil‐determination of amino acids in soil and in soil water indicates that they might contribute 15–25% to the nitrogen nutrition of the plant.

(ii) Amino acid uptake systems of root cells serve primarily as retrieval of amino acids delivered from the phloem‐ it was found that 14C L‐glutamine, which was delivered to the cotyledon and transported to the root via the phloem, was not lost by the roots, whereas it appeared in the bathing medium if L‐glutamine was applied externally to the root to compete for the uptake sites; this suggests that an apoplastic pool of amino acids in the root exists due to their efflux from the phloem.
Germination and emergence of Sorghum bicolor. genotypic and environmentally induced variation in the response to temperature and depth of sowing
Authors: HARRIS D. , HAMDI Q. A. , TERRY A. C.
Published: April 2006

Abstract The germination of Sorghum bicolor seeds of 9 genotypes was tested at temperatures between 8°C and 48°C on a thermal gradient plate. Samples were tested from three regions of the panicle expected to differ in temperature during grain filling. Seeds of a tenth genotype, SPV 354, produced in controlled‐environment glasshouses at different panicle temperatures, were tested similarly. In addition, the emergence of SPV 354 was measured from planting depths of 2 and 5 cm at mean soil temperatures of 15, 20 and 25°C. Four methods of calculating mean germination rate for the nine genotypes were compared. Germination characters like base, optimum and maximum temperature (Tb, To, Tm), thermal time (θ)and the germination rate at To(Rmax showed only small differences between methods. There was a range of genotypic variation in all characters: Tb 8.5–11.9°C; To, 33.2–37.5°C; Tm, 46.8–49.2°C; θ, 23.4–38.0°Cd; Rmax, 0.69–1.14‐d‐1. In contrast, mean germinability (G) was between 90% and 100% over the temperature range 13–40°C. Panicle temperature had no effect on any germination character in SPV 354. However, deeper burial increased θ for emergence and decreased G, irrespective of soil temperature except at 5 cm. Increasing panicle temperature, by reducing seed size, reduced G and increased θ by about 10% only at 15°C and 5 cm depth.
Response of wheat seedlings to short‐term drought stress with particular respect to nitrate utilization
Authors: TALOUIZITE A. , CHAMPIGNY M. L.
Published: April 2006

Abstract. The effect of short‐term changes in the water potential (from 0 to – 2.5 MPa) by addition of PEG 4000 to the nutrient solution was investigated with respect to nitrate uptake and reduction in 3‐week‐old wheat plants (Triticum aestivum, cv Fidel). Plants were harvested at the end of 12‐h treatments in the dark. The water potential of the mature leaves was similar to that of the medium down to – 0.8 MPa and was maintained at this level even though the external water potential was much lower. The medium water potential of 0.8 was a threshold level below which elongation of the youngest leaf was inhibited. Increase of the PEG concentration in the medium brought about a decrease of evapotranspiration and enhancement of nitrate uptake. No difference in the rate of nitrate reduction was observed, although the in vitro nitrate reductase activity was lowered. Nitrate accumulation in the shoot was ascribed both to the stimulation of net uptake from the medium, and to the mobilization and translocation of nitrate from the root. It is suggested that increase in the storage pool of nitrate in shoots was related to the role of NO3− as an osmoticum.