bluuebunny/crossref_metadata_2025 huggingface dataset:
Stomatal response to environment and a possible interrelation between stomatal effects on transpiration and CO2 assimilation
Authors: HALL A. E. , SCHULZE E.‐D.
Published: April 2006

Abstract It had been hypothesized that if daily CO2 assimilation is to be maximized at a given level of daily transpiration, stomatal apertures should change during the day so that the gain ratio (∂A/∂g)/(∂E/∂g) remains constant. These partial differentials describe the sensitivity of assimilation rate (A) and transpiration rate (E) to changes in stomatal conductance (g). Experiments were conducted to determine whether stomata respond to environment in a manner which results in constant gain ratios.

Gas–exchange measurements were made of the stomatal and photosynthetic responses of Vigna unguiculata L. Walp. in controlled environments. Leaf conductance to water vapour responded to step changes in temperature and humidity so that for different steady‐state conditions the gain ratio remained constant on all but one day. Depletion of water in the root zone resulted in day‐to‐day increases in gain ratio which were correlated with decreases in maximum leaf conductance to water vapour. The significance of the results for plant adaptation and stomatal mechanisms, and methods for measuring the gain ratio, are discussed.
Unidirectional sodium fluxes in red beet storage tissue (Beta vulgaris L. cv. Platronde Egyptische): effects of the phytohormones indol‐3yl‐acetic acid and abscisic acid
Authors: FRANÇOIS G. , BOGEMANS J. , NEIRINCKX L.
Published: April 2006

Abstract. The influence of indol‐3yl‐acetic acid (IAA) and abscisic acid (ABA) on the capacities of the cytoplasm and vacuole and their effects on unidirectional sodium fluxes across the plasmalemma and the tonoplast of aged red beet storage tissue was investigated. After loading the tissue in a labelled NaCl solution the efflux of radio‐activity was measured in unlabelled NaCl. By means of compartmental analysis the capacities and fluxes were determined and compared with those obtained after loading and elution in the presence of IAA or ABA.

It was established that both IAA and ABA affect sodium transport across the principal cell membranes. Both hormones inhibited the efflux across the plasma‐lemma, possibly by affecting a Na+ for H+ exchanging system. Efflux across the tonoplast was stimulated by IAA and influx across the same membrane was enhanced by ABA. It was suggested that IAA stimulated a proton pump at this level while the influence of ABA remained difficult to explain.
Photosynthetic efficiency of Betula pendula acclimated to different quantum flux densities
Authors: ÖQUIST G. , BRUNES L. , HÄLLGREN J‐E.
Published: April 2006

Abstract. Seedlings of Betula pendula were grown in a controlled environment chamber at quantum flux densities of 50, 250 and 600 μmol m−2 s−1. The relationship between the flux densities of absorbed CC2 and quanta was determined for shoots of whole seedlings. Rates of both light‐saturated and in situ (measured under the growing conditions) net photosynthesis were determined and the pholosynthetic quantum yields under light‐limiting conditions were calculated. Anatomical leaf characteristics, chlorophyll contents and sizes and densities of the photosynthetic units (chlorophyll/P700) were determined. Chloroplasts were isolated and their rates of 2,6‐dichlorophenol indophenol photoreduction were measured together with their pool sizes of the electron transport carriers plastoquinone and cylochrome ƒ.

Although acclimated to different quantum flux densities, the three birch populations showed the same quantum yield of net photosynthesis. This was approximately 0.028 in normal air (21.2 kPa oxygen) and about 0.040 when photorespiration was largely inhibited in 2.0 kPa oxygen. In addition, the in situ net photosynthesis rates were limited by the absorbed quantum flux density for low, intermediate and high light grown seedlings. It was concluded that birch acclimated to the three light regimes at different levels of organization (metabolic and anatomical). Thus, the quanta which were absorbed in situ could be transferred into chemical equivalents at an optimal and constant efficiency. The use of different reference bases for expressing rates of net photosynthesis are also discussed.
Photo‐inhibition of internode elongation rate in light‐grown Vigna sinensis L. Control by light quality
Authors: LECHARNY A. , JACQUES R.
Published: April 2006

Abstract. In white light(W) stem elongation of green plants is stimulated when some far‐red light (F) is added to W (Holmes & Smith, 1975, 1977b). The effect of adding F to a background W was quantified using Vigna sinensis L. plants and relatively high fluence rate W. F was given selectively to the 1st internode and the internode elongation rate (E.R) was recorded using linear voltage displacement transducers. Results confirm that adding F to background W stimulates internode E. R. The stimulation is very quickly measurable after switching F on and falls off rapidly after switching F off. The stimulation is not dependent on F fluence rate per per se but is strictly dependent on the quantum flux ratio F/W. These data are strongly in favour of phytochrome as the receptor, whose activity is controlled by the PFR content or the [PFR]/[P] ratio. A common mode of action for phytochrome in W and in darkness is suggested. The results indicate independence and additivity of the E. R.modulation by W light quantity and of the modulation by light quality.
Hypocotyl growth in Sinapis alba L: the roles of light quality and quantity
Authors: HOLMES M. G. , BEGGS C. J. , JABBEN M. , SCHÄFER E.
Published: April 2006

Abstract. A comparison is made of the relative effectiveness of light quality and light quantity on the elongation growth of Sinapis alba hypocotyls. The results show that hypocotyl extension rate in plants which have not previously been exposed to light is controlled primarily by the prevailing photon fluence rate when the phytochrome photostationary state lies between ∼0.033 and ∼0.81. Below ∼0.033, changes in photostationary state also have a marked effect on extension rate. Elongation growth in light‐adapted plants is controlled by both photon fluence rate and the spectral quality of the incident radiation at all photoequilibria. Photosynthesis can modify these responses but is not essential as a prior condition for a green plant to respond to changes in light quality and quantity.
Uptake of SO2 in shoots of Scots pine: field measurements of net flux of sulphur in relation to stomatal conductance
Authors: HÄLLGREN J‐E. , LINDER S. , RICHTER A. , TROENG E. , GRANAT L.
Published: April 2006

Abstract. Net fluxes of gaseous sulphur compounds, water vapour and carbon dioxide to current‐ and one‐year‐old shoots of Scots pine were simultaneously measured in the field. The shoots were fumigated in temperature‐controlled assimilation chambers with sulphur dioxide at concentrations ranging from 40 to 250 μg m−3 (15–95 ppb). The hypothesis that stomatal opening regulates the uptake of sulphur dioxide was tested. The following conclusions were reached concerning the dry deposition of sulphur dioxide to a dry coniferous shoot.

There was a marked diurnal variation in the uptake rate of sulphur dioxide. The net deposition velocity of sulphur was about three times higher during the day than during the night during July‐October. Stomatal opening was not the primary factor controlling the dry deposition rate of sulphur dioxide. The net dry deposition rate was significantly smaller than the calculated rate based on stomatal conductances for water vapour.

Part of this deviation could be explained by re‐emission of reduced sulphur compound(s) from the needles. The re‐emission of sulphur was a light‐dependent process and might be of great significance for the sulphur balance calculations.

A variable deposition velocity should be used in atmospheric transport models to account for the diurnal and seasonal variation in the surface resistance of a dry canopy.
Thoughts on the possible role of phytochrome destruction in phytochrome controlled responses
Authors: BLAAUW‐JANSEN G.
Published: April 2006

Abstract. Fluence‐response curves for low‐energy phytochrome responses show two steps at red light exposures c. two orders of magnitude apart. This Feature of the fluence‐response relationship can be interpreted as the consequence of the following processes:

Induction of a photoresponse by a very low level of Pfr.

Activation of a Pfr‐destroying enzyme above a threshold level of [Pfr].

Dependency of the rate of Pfr destruction on [Pfr] once the threshold level is reached.

In this way, adaptation of the phytochrome control system to a broad range of light doses could be realized.
An analysis of photosynthetic response and adaptation to temperature in higher plants: temperature acclimation in the desert evergreen Nerium oleander L*
Authors: BADGER M. R. , BJÖRKMAN O. , ARMOND P. A.
Published: April 2006

Abstract. Factors underlying the process of photosynthetic acclimation to temperature were investigated for the shrub Nerium oleander L. Ramets of a single clone were grown under day/night temperature regimes of 20°C/15°C or 45°C/32°C. Plants grown at the lower temperature regime possessed rates of photosynthesis twice that of the high‐temperature grown plants when CO2 fixation was measured at 20°C. In contrast, the plants grown at the high‐temperature regime had twice the rate of CO2 fixation of the 20°C/l 5°C‐grown plants at a measurement temperature of 45° C. It was determined that the ability to acclimate to changes in temperature regime was present in fully mature leaves. A reciprocal transfer of plants between the two growth regimes resulted in the appearance of the CO2 fixation characteristics appropriate to the new growth temperature after 12–14d. The response of CO2 fixation to light, temperature, and CO2 partial pressure and the temperature responses of soluble and membrane‐bound photosynthetic enzyme systems were analysed to determine which components might be responsible for the superior photosynthetic performance of the 20°C/I5°C‐grown plants at 20°C, and the enhanced high‐temperature stability of the 45°C/32°C plants. The measured photosynthetic capacity of the 20°C/15°C plants could not be attributed to gross morphological, stomatal, or other physical changes, or to a general increase in the concentration of components of the photosynthetic process. Only a single enzyme, Fru‐P2 phosphatase, was affected to an extent similar to that of photosynthesis. The enhanced thermal stability of the 45°C/32°C plants may be attributed primarily to an enhanced stability of the chloroplast membrane‐bound enzymatic activities and the stability of the photosynthetic carbon metabolism enzymes which require lighl for activation.
A precise potentiometric method for determination of algal activity in an open CO2 system
Authors: HOFSLAGARE OLOF , SAMUELSSON GORAN , SJÖBERG STAFFAN , INGRI NILS
Published: April 2006

Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m−3 NaNO3, 20 mol m−3 NH4C1, 20 mol m−3 NH4NO3, and 20 mol m−3 NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m2 s−1, Light‐dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12‐h period. Results obtained in NaNO3, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH4NO3, solution in a similar way to that in NaNO3 solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH4Cl solution showed a decrease in A with time.
Changes in the proportion of endogenous osmotic solutes accumulated by Chlorella emersonii in the light and dark
Authors: SETTER T. L. , GREENWAY H.
Published: April 2006

Abstract. The type of endogenous osmotic solute accumulated by Chlorella emersonii grown at high external osmotic pressure (πext) depended on the light/dark conditions: proline accumulated to high concentrations in cells in the light, while sucrose accumulated to high concentrations in the dark. These findings were made during the alternating light dark cycles used to obtain synchronized cultures, i.e. cultures containing cells at only one stage of development at any one time. Similar decreases in proline and increases in sucrose in the dark were found for cells previously grown in continuous light to obtain non‐synchronized cultures, i.e. cultures containing cells at all stages of development.

In cultures synchronized at 200 mol m −3 NaCl (πext= 1.01 MPa), recently divided ‘daughter cells’ at the beginning of the light periods contained 60 mol m−3 proline and 100mol m−3 sucrose, while mature cells towards the end of light periods contained 130 mol m proline and 20 mol m−3 sucrose. The changes in proline and sucrose which occurred in synchronized cultures were due mainly to light/dark conditions and to a much lesser extent to different stages of cell development. The proportion of proline to sucrose in daughter cells collected from non‐synchronized cultures in continuous light was not different from the proportion in heterogeneous populations of cells.

Results are discussed in relation to the accumulations of two, rather than one, endogenous osmotic solute and to growth reductions of C. emersonii exposed to high external osmotic pressures.
Further examination of the effects of IAA and anoxia on the growth rate and the spatially separate electrogenic ion pumps in bean hypocotyl
Authors: MIZUNO AKIKO , OKAMOTO HISASHI
Published: April 2006

Abstract. Measurements of Vps and Vpx were made on Vigna sesquipedalis hypocotyls in a stream of air or nitrogen during and after the application of IAA in an aerosol added to the gas stream. The lAA‐induced hyperpolarization of Vps and increase in growth rate in air was maintained for at least half an hour after the 50‐min IAA treatment was terminated. Changing from air to O2‐free gas stream in the presence of IAA aerosol depolarized Vps and Vpx, and then reduced growth rate, to the same extent as in hypocotyls in which IAA and O2 supply were terminated simultaneously. Under anoxic conditions, application of an IAA N2‐aerosol had no effect on Vps. Vpx or growth rate.
A method for measuring radial differences in water content of intact tree stems by attenuation of gamma radiation
Authors: EDWARDS W. R. N. , JARVIS P. G.
Published: April 2006

Abstract. A technique is described for the nondestructive measurement of water content variations in the stems of trees.

The density of intact tree stems in the forest was estimated using attenuation of gamma radiation. Water content was calculated after subsequent derivation of the volume fraction of solid matrix.

A radial sequence of such measurements was obtained by measuring a sequence of chords, and assuming homogeneity within concentric tori. Analysis of the source of errors showed that the system was a close approximation of an ideal, rigid‐geometry, mono‐energetic source/detector system, with basic precision dependent on the quantity of gamma radiation measured. Correlation coefficients between the gamma‐attenuation technique and subsequent gravimetric estimates of water content for two field experiments reported here were 0.882 and 0.938.

The technique was shown to be capable of describing the radial and diurnal variation in water content at two heights in the stem of a 20‐year‐old tree of Pinus contorta.
Stomatal response to vapour pressure deficit and the effect of plant water stress
Authors: JOHNSON JON D. , FERRELL WILLIAM K.
Published: April 2006

Abstract The dynamic response of stomata to changes in atmospheric humidity was investigated in Fragaria × ananassa Duch., Picea engelmannii Parry, and Pseudotsuga menziesii (Mirb.) Franco; and the effect of water stress on this response was determined in Pseudotsuga menziesii.

The plants were rotated through three regimes of ambient temperature and vapour pressure deficit: 35°C–3. 5kPa, 35°C–0. 5 kPa, and 20°C–1. 5kPa. Branch and leaflet conductance were measured with a steady‐state porometer, first at ambient vapour pressure deficit and then at one of four treatment conditions achieved by increasing or decreasing vapour pressure within the porometer cuvette. All three species showed similar stomatal response: enhanced conductance at low vapour pressure deficit and depressed conductance at high vapour pressure deficit. Engelmann spruce was more sensitive than Douglas fir and strawberry.

Plant water status significantly altered stomatal response to vapour pressure deficit. The relationship of conductance of xylem water potential was linear under ambient conditions but became curvilinear when conductance was measured above and below ambient vapour pressure deficit. Between −0. 5 MPa and −2. 0 MPa xylem water potential, the stomata were sensitive to vapour pressure deficit, but below − 2. 0 MPa, the sensitivity decreased.
Transition from primary dormancy to secondary dormancy in cocklebur seeds
Authors: ESASHI YOHJI , KURAISHI RITSU , TANAKA NATSUO , SATOH SHIGERU
Published: April 2006

Abstract The transition from primary dormancy to secondary dormancy was examined using upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds. The non‐after‐ripened seeds with primary dormancy responded to chilling, anoxia, KCN, and NaN3 with an increase in germination. However, their maximal responses to these treatments only occurred after a period of water imbibition, probably a reflection of the increasing growth potential of the axial tissue which was accompanied by the increase in the capacities of respiration and ethylene production. On the other hand, the establishment of secondary dormancy was accompanied by a decrease in respiration and ethylene production of seeds, and in the growth potential of both axial and cotyledonary tissues. The decrease in growth potential of these tissues occurred regardless of whether they were excised from after‐ripened seeds or non‐after‐ripened seeds. It is inferred that the primary dormancy of cocklebur seeds is a state maintained in un‐germinated seeds for a long time through a spontaneous transition to secondary dormancy.
Salt activation and inhibition of membrane ATPase from roots of the halophyte Atriplex nummularia
Authors: LERNER H. R. , REINHOLD LEONORA , GUY RACHEL , BRAUN YAEL , HASIDIM MIRIAM , POLJAKOFF‐MAYBER ALEXANDRA
Published: April 2006

Abstract Salt‐stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep‐tible to inhibition by KC1 or NaCl up to 450 mol m‐3 but showed a broad peak of activity between 150 and 300 mol m−3. At pH 8 stimulation occurred at 50 mol m−3 but concentrations above 100 mol m−3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m−3 of NaCl or KC1; concentrations higher than 150 mol m−3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m−3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m−3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt‐activated ATPase activity but simultaneously inhibited MgATPase activity.
Abscisic‐acid‐induced turion formation inSpirodela polyrrhizaL. I. Production and development of the turion
Authors: SMART CHERYL C. , TREWAVAS ANTHONY J.
Published: April 2006

AbstractThe production, growth, and development of the abscisic‐acid‐induced turion (a small dormant bud) ofSpirodela polyrrhizawere investigated. Addition ofABAto a culture ofS. polyrrhizaresulted in growth inhibition at concentrations as low as 10−6molm−3, growth being completely arrested at 10−2mol m. Over a single order of magnitude range around I0−4molm−3,ABAalso induced the production of turions. The range of turion‐producing concentrations ofABAwas found to be much narrower than previously reported, turion production having a clearly defined threshold, optimum, and upper limit. The possibility that growth inhibition and turion formation are integrally linked aspects of a single response is discussed. Only primordia ≤0.7 mm long at the time ofABAaddition could be induced to develop into turions and the events leading to turion formation were found to be reversible up to 72 h inABA. It is concluded thatin terms of turion formationthere is a sensitivity window to abscisic acid lasting some 4–20h in the normal developmental life of frond cells. Providing cells experience the appropriate signal in this sensitivity window they initiate a new programme which eventually leads to turion formation. Microscopical analysis showed that the cells within this sensitivity window were still actively dividing. It is suggested that the developmental switch‐over to rapid cell expansion and separation marks the end of thisABAsensitivity window.
Light and dark assimilation of nitrate in plants
Authors: ABROL Y. P. , SAWHNEY S. K. , NAIK M. S.
Published: April 2006

Abstract. Heterotrophic assimilation of nitrate in roots and leaves in darkness is closely linked with the oxidative pentose phosphate pathway. The supply of glucose‐6‐phosphate to roots and chloroplasts in leaves in darkness is essential for assimilation of nitrite into amino acids. When green leaves are exposed to light, the key enzyme, glucoses‐phosphate dehydrogenase, is inhibited by reduction with thioredoxin. Hence the dark nitrate assimilatory pathway is inhibited under photoautotrophic conditions and replaced by regulatory reactions functioning in light. On account of direct photo‐synthetic reduction of nitrite in chloroplasts and availability of excess NADH for nitrate reduclase, the rate of nitrate assimilation is extremely rapid in light. Under dark anaerobic conditions also nitrate is equally rapidly reduced to nitrite on account of abolition of competition for NADH between nitrate reductase and mitochondrial oxidation.
Leaf area index, canopy structure and photosynthesis of red clover (Trifolium pratense L.)
Authors: JOGGI D. , HOFER U. , NÖSBERGER J.
Published: April 2006

Abstract. The influence of leaf age, total leaf area and its dispersion in space on canopy photosynthesis were studied using microswards of red clover (Trifolium pratense L.) which were established in the greenhouse. Two varieties, Renova (flowering) and Molstad (non‐flowering), were sown in separate plastic boxes at densities of 225, 400 and 625 plants per m2.

Vertical distribution of photosynthetically active radiation (PAR), leaf area, leaf age and 14CO2‐fixation were determined periodically. Net photosynthesis and dark respiration of canopies were measured. Maximum photosynthetic capacity of individual leaves was measured on plants taken from the intact canopy or from plants where shading of the growing leaves had been prevented.

Net photosynthetic rate of canopies increased linearly with leaf area index (LAI) up to an LAI of 3.5 and then declined at higher LAI, independent of variety and sowing density. Below the optimum LAI, net photosynthesis depended mainly on interception of PAR. Decrease in canopy photosynthesis above the optimum LAI was due to a higher proportion of old leaves with decreased photosynthetic capacity, and not to an increase in respiring plant parts. It is concluded that LAI and position of leaf age categories in the canopy are more important than vertical distribution of leaf area in determining canopy photosynthesis of red clover.
Transmembrane hyperpolarization and increase of K+ uptake in maize roots treated with permeant weak acids
Authors: MARRÈ M. T. , ROMANI G. , MARRÈ E.
Published: April 2006

Abstract. Treatment with weak acids (butyrate, isobutyrate, trimethylacetate, DMO) at a concentration of I mol m−3 in apical maize root segments induced a rapid, marked hyperpolarization (ca. 30 mV) of the transmembrane electrical potential, stable for at least 30 min. With butyrate, this effect increased with the increase of butyrate concentration in the medium, reaching a value of ca. 75 mV at a concentration of 5 mol m−3.

Both the butyrate uptake and the hyperpolarization were roughly proportional to the pH‐regulated, undissociated/dissociated acid ratio in the medium. The butyrate‐induced hyperpolarization was reduced progressively, but was still present when K+ concentration in the medium was raised from 1 to 10 mol m−3.

The hyperpolarization was accompanied by a significant increase of K+ uptake, and was almost completely suppressed by the presence of the protonophore carbonylcyanid‐p‐trichlorometoxy‐phenylhydrazone (CCCP) and strongly reduced by erytrosin B, an inhibitor of some animal ATPases and of a K+‐activated, DCCD‐ and vanadate‐sensitive Mg2+‐ATPase from plant microsomes. The hyperpolarization effect of butyrate was additive to that of fusicoccin at low, but not at high (5 mol m−3), concentrations of the weak acid. These results suggest that the intracellular pH regulates the activity of the electrogenic proton pump at the plasmalemma.
Relationships between root morphology and nitrogen availability in a recent theoretical model describing nitrogen uptake from soil
Authors: ROBINSON DAVID , RORISON I. H.
Published: April 2006

Abstract. The effect upon potential maximum nitrogen uptake rate of root morphology and nitrogen availability in soil was investigated using a simple nutrient transport model. Parameter values appropriate to an ecological or an agricultural context were introduced from the literature. The model predicted that the maximum uptake rate of nitrate was morphology‐dependent only at extremely low concentrations. For ammonium, this was so for all realistic concentrations, assuming a high potential maximum uptake rate. The important concentration range for ammonium was two orders of magnitude greater than that for nitrate. With a lower potential maximum uptake rate of ammonium, root morphology was important below 15/igNg′ soil, the concentration range in this case being a single order of magnitude greater than that for nitrate. The effects of root hairs were to decrease the threshold concentration for morphology‐dependence, and to minimize root dry weight per unit volume of soil needed to maintain maximum nitrogen uptake rate. The effects of simultaneous mass flow of solution were negligible. The possible significance of these effects upon plant growth are discussed in relation to nitrogen availability.
Influence of insulating dead leaves and low temperatures on water balance in an Andean giant rosette plant
Authors: GOLDSTEIN GUTLLERMO , MEINZER FREDERICK
Published: April 2006

Abstract.The influence of insulating dead leaves on water balance inEspeletia timotensisCuatr., an Andean caulescent giant rosette plant, was studied under field and laboratory conditions. Removal of the dead leaf layer surrounding the stem changed the pattern of diurnal stem temperature variation and produced transient and permanent effects on water balance. The pattern of liquid water flow resistance increase at low stem temperatures suggested that much of the water flow in the stem was through living membranes, probably those of the pith cells. The pith was determined to be an important source of stored water for daily transpirational needs. The lethal effects of dead leaf removal were attributed to one or more of the following causes: (1) inhibition of pith recharge by subfreezing stem temperatures; (2) embolisms in stem xylem; (3) freezing injury to pith tissue. The results suggested that an insulating layer of marcescent leaves and the presence of an internal water reservoir closer to the rosette than the soil water are important adaptations for maintenance of a favourable water balance in tropical alpine habitats where freezing temperatures occur regularly but last only a few hours.
Estimation of an effective soil water potential at the root surface of transpiring plants
Authors: JONES HAMLYN G.
Published: April 2006

Abstract. A simple method is described for estimating an average of ‘effective’ soil water potential at the root surface for transpiring plants. The method is based on measurements of leaf water potential and leaf conductance to water vapour in stressed plants and in well‐watered controls, and uses the simple Ohm's law analogue for water flow in the soil‐plant system. The technique is applied to data for field‐grown apple trees and to previously published data for wheat and cowpea.
Turgor‐regulated translocation
Authors: LANG ALEXANDER
Published: April 2006

Abstract.The role played by potassium in plants is examined, in particular its connection with phloem translocation. The possibility emerges that trans‐location may be a turgor‐regulated process in which potassium plays a central role.

A simple mechanistic hypothesis is proposed and the evidence for it is discussed. The hypothesis is strongly supported by both the direct and the circumstantial evidence.

An important conclusion is the need to reassess the importance of the translocation process in the control of assimilate partitioning. Hitherto, as implied by Münch's hypothesis, control has been assumed to be exerted by source and/or sink activity with the translocation pathway playing a more passive secondary role. If the present proposal is correct the translocation process emerges instead as a dominant factor in the control of assimilate partitioning.
Growth and development of Pinus radiata D. Don: the effect of light quality
Authors: MORGAN D. C. , ROOK D. A. , WARRINGTON I. J. , TURNBULL H. L.
Published: April 2006

Abstract. Plants of Pinus radiata of two physiological ages, juvenile (seedlings and micropropagated plantlets) and adult (rooted cuttings from mature trees), were grown under lighting fromthree combinations of metal halide (MH) and tungsten halogen (TH) lamps for up to 10 months in controlled environment rooms. The three lamp combinations, MH alone, 50: 50 MH: TH and 25:75 MH: TH by wattage, produced red: farred ratios of 4.59, 1.51, and 1.15, respectively. Photosynthetic photon flux density was 700 μmol m−2 s−1. An increase in proportion of TH lamps markedly increased shoot elongation and internode length, decreased numbers of fascicles per unit stem length and increased the proportion of stem weight in both juvenile and adult material. In addition, in adult material, it increased the number of fascicle initials and expanded fascicles per growth flush, reduced the duration of the ‘rest’ phase between growth flushes, accelerated the rate of elongation growth during each flush, and increased apical dominance. Tracheid length, but not diameter or wall thickness, was significantly affected by light quality and found to be associated with longer internodes. Any treatment effects on needle weight or length, stem diameter or root weight were non‐significant or very small. Different clones from either the juvenile micro‐propagated material or the mature rooted cuttings each showed similar patterns of response, although they often differed in the degree of response to light quality. The main response could be related solely to the red: far‐red ratio and the calculated phytochrome photoequilibrium. This is the first report of phytochrome‐controlled photomorphogenesis in older specimens of a woody perennial. Recommendations for artificial light sources for growing P. radiata and some ecological implications of the results are presented.
The relationship between stomatal conductance, transpiration rate and tracheid structure in Pinus radiata clones grown at different water vapour saturation deficits
Authors: WHITEHEAD D. , SHERIFF D. W. , GREER D. H.
Published: April 2006

Abstract. Stomatal conductance and needle water potential of P. radiata clones were measured after 2, 5 and 8 months on plants grown in controlled environment rooms with markedly different water vapour saturation deficits (D). Conductance was significantly lower at high D, but water potential differences between treatments were not significant. When trees were moved between treatments most of the changes in conductances occurred within 2 h, with residual changes after 24 h. Water potentials were not different 24 h after the trees were moved. The effects were completely reversible.

Transpiration rates of individual trees were highest in the high D treatment and lowest in the low D treatment. They were not linearly related to D because of decreasing conductance with increasing D.

Height growth, diameter growth and foliage areas were not significantly different between treatments. Tracheid lumen diameters tended to be larger in trees grown at higher D although treatment differences were not significant.

There were significant clonal differences in shoot conductance and tracheid dimensions.
High and low temperature tolerances and their relationships to distribution of agaves
Authors: NOBEL PARK S. , SMITH STANLEY D.
Published: April 2006

Abstract. The potential influence of tissue tolerances to extreme temperatures on distributional limits was investigated for 15 taxa (14 species) of leaf‐succulent agaves from the south‐western United States and northern Mexico. As a group, the agaves exhibited a moderate low temperature tolerance of – 11°C (based on a 50% inhibition in the number of mesophyll cells taking up a stain, neutral red). However, nearly all of the species were able to tolerate extremely high tissue temperatures of over 60°C. Nocturnal acid accumulation by these crassulacean acid metabolism plants was about 6°C more sensitive to temperature extremes than was cellular membrane integrity.

High and low temperature acclimation in response to changing day/night air temperatures was observed in all 15 taxa, with high temperature acclimation averaging two‐fold greater than low temperature acclimation (3.8°C versus 2.0°C per 10°C change in ambient temperature). Species occupying the coldest habitats exhibited the greatest low temperature tolerances and acclimation; several such species, such as Agave utahensis and A. schottii, had small rosette sizes which resulted in higher minimum leaf temperatures. Species from the hottest habitats had among the greatest high temperature tolerances and acclimation; the two species from open desert scrub habitats, A. deserti and A. lecheguilla, had the lowest leaf shortwave absorptances observed, which would result in lower maximum leaf temperatures. Thus morphology and tissue tolerances to stressful temperatures reflect the temperature extremes of a plant's native habitat, although low temperature tolerance appears to limit the distribution of agaves more than high temperature tolerance.
Contribution of osmotic adjustment to the dehydration tolerance of water‐stressed pigeon pea (Cajanus cajan (L.) millsp.) leaves
Authors: FLOWER D. J. , LUDLOW M. M.
Published: April 2006

Abstract Water‐stressed pigeonpea leaves have high levels of osmotic adjustment at low leaf water potentials. The possible contribution of this adjustment of dehydration tolerance of leaves was examined in plants grown in a controlled environment. Osmotic adjustment was varied by withholding water from plants growing in differing amounts of soil, which resulted in different rates of decline of leaf water potential.

The level of osmotic adjustment was inversely related to leaf water potential in all treatments. In addition, at any particular water potential, plants that had experienced a rapid development of stress exhibited less osmotic adjustment than plants that experienced a slower development of stress. Leaves with different levels of osmotic adjustment died at water potentials between –3.4 and –6.3 MPa, but all leaves died at a similar relative water content (32%). Consequently, leaves died when relative water content reached a lethal value, rather than when a lethal leaf water potential was reached. Osmotic adjustment delayed the time and lowered the leaf water potential when the lethal relative water content occurred, because it helped maintain higher relative water contents at low leaf water potentials. The consequences of osmotic adjustment for leaf survival in water‐stressed pigeonpea are discussed.
Factors affecting the induction and release of secondary dormancy in Kalanchoë seeds
Authors: RETHY R. , DEDONDER A. , FREDERICQ H. , DE GREEF J.
Published: April 2006

Abstract. Several short daily R irradiations are required from the first day of incubation on water to induce germination of Kalanchoë seeds. When the same light treatment is given after a prolonged dark incubation period at 20°C, secondary dormancy prevents germination. Factors controlling the induction and breaking of secondary dormancy have been investigated. The induction of secondary dormancy is very temperature dependent. Locally puncturing the seed coat strongly delays it. Secondary dormancy is not induced in the presence of GA3 during the first 10 d of dark incubation, although this growth substance cannot induce dark germination. Prolonged or cyclic daily R irradiations can relieve secondary dormancy of seeds kept on water, even after a dark period of 20 d. A 24 h treatment at 4°C restores responsiveness to short R exposures of slightly secondarily dormant seeds. The synergism between GA3 and Pfr in non‐dormant Kalanchoë seeds, leading to high effectiveness of even one short FR irradiation, still occurs in seeds made secondarily dormant before transfer to GA3, but more R or FR irradiations, in combination with GA3, are required for the release of secondary dormancy. A combination of red light and 6‐benzyl‐aminopurine is ineffective in removing dormancy.
Electrical sizing of cells of the halophilic alga Dunaliella parva
Authors: ZMIRI A. , WAX Y. , GINZBURG B‐Z.
Published: April 2006

Abstract. The cell volume of two strains of the halophilic alga Dunaliella parva was measured by two direct methods and by electrical sizing. The results from the direct methods agreed with each other and were consistently larger than those obtained from electrical sizing. Statistical analysis showed that the cell volume populations obtained by electrical size of D. Parva cells is due to the cell membrane having an unusually low electrical resistance relative to other cell membranes.
Light interception by grain legume row crops
Authors: CHARLES‐EDWARDS D. A. , LAWN R. J.
Published: April 2006

Abstract. Four contrasting grain legume species (Glycine max, Vigna radiata. Vigna mungo and Vigna angularis) were grown as row crops with both 0.5 m and 1.0 m spacings between row centres. Light transmission profiles, at ground level, across rows of plants, were obtained for each crop on a number of occasions during growth. The proportion of the incident downward light flux density intercepted by each crop at solar noon was found to be simply and directly related to the product of the proportion of the ground area covered by the crop's leaf canopy and the proportion of the downward light flux density incident at the row centre that was intercepted by the crop. The average proportion of the incident light energy intercepted over the whole day could be related to the proportion intercepted at solar noon.
Possible significance of changes in the light requirement of Cirsium palustre seeds after dispersal in ash coppice
Authors: PONS T. L.
Published: April 2006

Abstract. It is demonstrated that after the feelling of ash coppice Cirsium palustre becomes established from seed that was produced during the previous coppice cycle and has lain underground for several years. These seeds are light‐requiring and it is probable that their germination is triggered by exposure to light during coppicing in winter.

It is assumed that the seeds become light‐requiring because phytochrome in the far‐red absorbing form high. This facilitates their incorporation in the seed bank in summer. However, the disappearance of Pfr is inhibited at low temperatures; this means that the seeds can store the light stimulus in winter and will not germinate until they experience higher temperatures in spring. The significance of the inhibition of seed germination under a leaf canopy is that it enhances the seeds chance of being incorporated in the soil seed bank.
Carbon dioxide blocks the stigma callose response following incompatible pollinations in Brassica
Authors: O'NEILL PATRICIA , SINGH M. B. , NEALES T. F. , KNOX R. B. , WILLIAMS E. G.
Published: April 2006

Abstract. Carbon dioxide is known to overcome sporophytic self‐incompatibility in Brassica. Elevated CO2 (30 mmol CO2 mol‐1 air), supplied via a flowthrough gas system, was shown to block the formation of rejection callose in the surface stigmatic papillae of Brassica campestris var. T15 following self‐pollination. Possible mechanisms by which CO2 may affect callose formation are discussed.
Carbon, water and nutrient relations of two mistletoes and their hosts: A hypothesis*
Authors: SCHULZE E.‐D. , TURNER N. C. , GLATZEL G.
Published: April 2006

Abstract. The carbon, water and nutrient relations of the xylem parasites Loranthus europaeus and Viscum laxum and their respective hosts. Quercus robur and Pinus sylvestris, were followed throughout clear days in July in order to study water and nutrient interactions in a simple system in which the plant growth depends on the host for its water and nutrients. At similar quantum flux densities, temperatures and vapour pressure deficits, the mistletoes had higher rates of transpiration and lower leaf water potentials than their hosts, but similar rates of CO2 assimilation. Based on measurements of the nutrient content of the xylem and on seasonal measurements of the biomass and the tissue nutrient content, the present study suggests that the high rates of transpiration may be necessary for the parasites to take up sufficient nitrogen from the xylem of the host for production of biomass (leaves, fruits and stems).
Mechanism of nitrate uptake intoChara corallinacells: lack of evidence for obligatory coupling to proton pump and a new NO3−/NO3−exchange model
Authors: DEANE‐DRUMMOND CELIA E.
Published: April 2006

Abstract.Nitrate uptake intoChara corallinacells at different external pH (pHo) after different NO3−pretreatment conditions has been investigated. Following NO3−pretreatment (0.2 mol m−3NO3−) there was little effect of pHoon subsequent net NO3−uptake intoCharacells. After N deprivation (2 mmol m−3NO3−) there was a pronounced effect of pHoon nitrate uptake, the maximum rate occurring at pHo4.7. There was no consistent relationship between OH−efflux and NO3−uptake in short term experiments (< 1 h). NO3−efflux was also sensitive to pHo, the maximum rate occurring at ∼ pHo5.0. An inhibitor of the proton pump, DES, immediately stimulated NO3−uptake into cells pretreated with NO3−and prevented the time‐dependent decrease in NO3−, uptake intoCharacells that had been previously treated with low N (2 mmol m−3NO3−). NO3−efflux was found to be very sensitive to DES withKi= 0.7 mmol m−3. At the optimum pHofor NO3−uptake the effect of DES on membrane potential (ψm) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO3−uptake and H+pump activity. A new model for NO3−uptake is proposed which involves NO3−/NO3−exchange at steady state.
Germination responses of a non‐dormant seed population of Amaranthus patulus Bertol. to constant temperatures in the sub‐optimal range
Authors: WASHITANI ISUMI , TAKENAKA AKIO
Published: April 2006

Abstract. The germination responses of a nondormant seed population of Amaranthus patulus Bertol, at constant sub‐optimal temperatures in the range of 10–34°C were analysed through a detailed time‐course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage, v. temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required ‘thermal times’ (θ), the distribution of which could be approximated for the seed population by the following distribution function:

image

where m is the median of the distribution and A is a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol−1 with all 20–80% subpopulations.
Evidence for the H+‐co‐transport of d‐alanine by the digestive glands of Dionaea muscipula Ellis
Authors: REA PHILIP A.
Published: April 2006

Abstract. The net uptake of 14C‐D‐alanine by the adaxial surfaces of the trap lobes of Dionaea muscipula Ellis (Venus's flytrap) is positively correlated with the rate of H+ efflux from the trap lobes. Effectors that stimulate H+ efflux (secretion elicitor, fusicoccin and auxin) enhance D‐alanine uptake whereas effectors that inhibit H+ efflux (diethylstilbestrol) retard uptake. It is proposed that amino acid uptake by the digestive glands of the trap lobes proceeds via a mechanism which mediates the co‐transport of H+ ions and amino acids. A model is presented in which a positively charged ternary complex of carrier plus amino acid plus H+ is transported down an inwardly directed H+ electrochemical potential difference generated by the secretion‐elicitor‐provoked discharge of HCl into the trap cavity.
The role of maintenance respiration in plant growth
Authors: AMTHOR JEFFREY S.
Published: April 2006

Abstract Plant growth is the balance of photosynthetic gains and respiratory losses, and it is therefore essential to consider respiration in analyses of plant productivity. The partitioning of dark respiratory losses into two functional components, a growth component and a maintenance component, has proved useful. The growth loss is that associated with synthesis of new biomass while the maintenance loss is that associated with maintenance of existing biomass.

Experimental evidence indicates that the respiratory cost of maintenance in herbaceous plants is about equal to the cost of growth over a growing season, with daily maintenace expenditures less important in the small, rapidly growing plant but increasing in significance as plant size increases and the relative growth rate decreases. Because it is such a large fraction of the total carbon budget of a plant, any variations in maintenance requirements may result in significant alterations in productivity. In the present work the theoretical and empirical bases of maintenance respiration are described: magnitudes of maintenance expenditures are summarized; and applications to models of plant growth and productivity are discussed. It is concluded that the costs of maintenance should be included in analyses of plant growth.