bluuebunny/crossref_metadata_2025 huggingface dataset:
Chill‐induced wilting and hydraulic recovery in mung bean plants
Authors: BAGNALL DAVID , WOLFE JOE , KING ROD W.
Published: April 2006

The hydraulic conductance of roots of chilling‐sensitive mung bean plants is reduced markedly at low temperatures. When roots are chilled suddenly under high irradiance, or when plants with roots chilled in the dark are exposed to a natural dawn, the stomata remain open for several hours. During this period the plants may wilt severely if the evaporative demand is sufficiently large. Under lower evaporative demand and less severe wilting, the plants may subsequently rehydrate.

Following root chilling there is a rapid (> 30 min) initial change in root conductivity (3. 2‐ fold).

Within hours the hydraulic conductivity of the pathway from stem xylem to leaf tissue decreases dramatically.

Within 1 d, the hydraulic conductivity of the roots decreases further (4. 5‐fold).

Over 5 d these large resistances disappear and conductivity recovers to a value greater than at the start of chilling. This response and stomatal closure allow the plant to rehydrate to a condition similar to that of controls.

There is no simple relation between this hydraulic recovery and the accumulation of abscisic acid in the roots.
Plasmolysis shape in relation to freeze‐hardening of cabbage plants and to the effect of penetrating solutes*
Authors: LEVITT J
Published: April 2006

Abstract In conformity with earlier results, low‐temperature hardening of cabbage seedlings lowered the osmotic potential and increased the permeability to thiourea of the petiole cells. It also decreased the time required for rounding‐up of the protoplasts in cells plasmolysed in 1. 5 × isotonic (or higher) glucose or CaCl2 solutions.

Solutions of dimethylsulphoxide (DMSO), thiourea, urea, and glycerol each accelerated the rate of rounding‐up of protoplasts in plasmolysed cells, compared to the rate in glucose solution of the same hypertonicity. Each also penetrated the cell membranes as indicated by deplasmolysis. Only in the case of DMSO, in which there was very rapid deplasmolysis (5–6 min), was this rounding‐up due to protoplast expansion. In the case of thiourea (deplasmolysis within 30–60 min) rounding‐up occurred almost immediately (less than 2 min), before protoplast expansion was sufficient to induce it. It was concluded that the accelerated rounding‐up was due to a rapid osmotic adjustment in the protoplasm by the penetrating solution, which increased its water content and decreased its viscosity.
Protection of pollen germination from adverse temperatures: a possible role for proline
Authors: HONG‐QI ZHANG , CROES A. F.
Published: April 2006

Abstract After germination, pollen grains of Lilium longiflorum became very sensitive to short periods of heat stress as shown by the greatly reduced germination percentages upon subsequent incubation at the optimal temperature. Addition of proline to the incubation medium made pollen more resistant to heat. It was demonstrated that in a short time a large amount of proline was taken up by the cell. Germination and metabolic functions were completely or partially protected from heat damage by proline treatment. As well, it was shown that proline treatment at least partially protected pollen grains from cold stress. These results suggest that the high proline concentrations found in pollen of many species may confer resistance to germinating pollen grains at unfavourable temperatures thereby enhancing the chances of successful fertilization.
Crystalline arrays of ribosomes in isolated pea chloroplasts
Authors: PRAEKELT UTA M. , ROWE ARTHUR J. , SMITH HARRY
Published: April 2006

Abstract Transmission electron microscopy of chloroplasts isolated by osmotic lysis of pea leaf protoplasts has revealed crystalline arrays of ribosomal particles associated with the thylakoid membranes. Optical diffraction techniques have established the crystallinity of the arrays and an image‐enhancement technique has given an indication of ribosomal macrostructure. A model of crystal‐packing is presented. This apparently artefactual induction of ribosome crystals should provide a valuable approach towards the elucidation of the details of the structure of chloroplast ribosomes.
Abscisic‐acid‐induced turion formation in Spirodela polyrrhiza L. II. Ultrastructure of the turion; a stereological analysis
Authors: SMART CHERYL C. , TREWAVAS ANTHONY J.
Published: April 2006

Abstract The ultrastructural features of the abscisic‐acid‐induced turion of Spirodela polyrrhiza are briefly described and a comparison between turion and vegetative frond tissue was made by stereological analysis. The turion is characterized by its small size, reniform shape, and dark‐brown coloration; the mesophyll is undifferentiated and totally lacking the substantial acrenchyma development found in the vegetative frond. The turion cells have a smaller vacuole and a denser cytoplasm than the cells of the vegetative frond. Stereological analysis showed that the tissues differed quantitatively only in three main respects: air space formation, vacuolation, and starch and cell wall material accumulation. During development, it is suggested that the cells of the turion, while reaching the same final size as the vegetative frond cells, accumulate numerous starch grains, thick cell walls, and large deposits of tannins and anthocyanin pigment at the expense of the vacuolar expansion characteristic of the normal maturity programme. Certain features of the turion ultrastructure indicate a differential cell sensitivity to ABA.
Vacuolated plant cells as ideal osmometer: reversibility and limits of plasmolysis, and estimation of protoplasm volume in control and water‐stress‐tolerant cells
Authors: PALTA JIWAN P. , LEE‐STADELMANN OK YOUNG
Published: April 2006

Abstract. The osmotic behaviour of vacuolated plant cells (adaxial epidermal cells of Allium cepa bulb scales, and epidermal as well as chloroplast containing subepidermal stem base cells of Pisum sativum) was studied over a wide range of CaCl2 concentrations. The following results were obtained.

Allium cepa and Pisum sativum plant cells behave as an ideal osmometer as far as plasmolytic contraction of the protoplast is concerned.

The protoplasts of these cells could be plasmolysed to 15–45% of their original volume without the loss of membrane semi‐permeability.

Cells plasmolysed in 1.0 kmol m−3 CaCl2 could be completely deplasmolysed and upon deplasmolysis the cells resumed protoplasmic streaming.

The above findings (a‐c) indicate that during gradual plasmolysis and deplasmolysis membrane semi‐permeability is maintained.

At very high plasmolysing concentrations vacuoles covered with the tonoplast separated from the rest of the protoplasm in some cells whereas others showed systrophy. Extruded vacuoles were able to respond to osmotic shrinkage.

The non‐solvent space in Allium cells of about 3% also corresponded to the protoplasm volume calculated from the protoplast geometry (mean from results of direct measurement method and subtraction method).

Subepidermal stem base cells of water‐stress‐tolerant Pisum plants had a 75% greater non‐solvent space than the control cells indicating that a water‐stress‐tolerant cell may contain a larger amount of protoplasm and/or a vacuole with a higher content of colloidal material in the vacuole.

Water‐stress‐tolerant cells showed greater tolerance to osmotic dehydration (volume reduction) than control cells.
Changes in the optical properties of cotyledons of Cucurbits pepo during the first seven days of their development
Authors: SEYFRIED MAX , SCHÄFER EBERHARD
Published: April 2006

Abstract. We recently discussed a method for measuring optical properties of light scattering and absorbing plant tissue (Seyfried, Fukshansky & Schafer, 1983). This method has been used to measure the changes in optical properties of cotyledons between 360 and 1000 run during the first 7d of development. The seedlings were either etiolated or grown under continuous white light, the latter either herbicide‐treated (SAN 9789 = Norflurazon) or untreated. Some of the observed changes in seedlings grown under white light are due to chlorophyll accumulation. This accumulation leads to an increase in absorption coefficients at all wavelengths except in the 750 to 850 nm region. Reflectance, transmittance, and the scattering coefficient decreased markedly. Other changes seem to be independent of light conditions since they occur in much the same way under all treatments. These are a generally decreasing reflectance and scattering coefficient and an even stronger decrease of reflectance from the upper face of the cotyledon as compared to the reflectance from the lower face, in particular in the blue region of the spectrum. The observed changes are discussed in terms of light gradients and the resulting problems for in vivo spectroscopy.
Natural convection from leaves at realistic Grashof numbers
Authors: DIXON MICHAEL , GRACE JOHN
Published: April 2006

Abstract.The boundary layer resistance of model leaves was measured in still air, at a range of leaf‐to‐air temperature differences. The results were compared to those calculated from standard formulae for natural convection. The agreement between observed and calculated was only satisfactory when Grashof numbers exceeded about 105. At the lower Grashof numbers, which often prevail in nature, the observed rates of heat transfer considerably exceeded those calculated.
A comparative study of the effects of NaCl salinity on respiration, photosynthesis, and leaf extension growth in Beta vulgaris L. (sugar beet)
Authors: PAPP JEANETTE C. , BALL MARILYN C. , TERRY NORMAN
Published: April 2006

Abstract. Three parameters influencing the capacity for carbon accumulation, i.e. photosynthesis, respiration, and leaf extension growth, were studied in Beta vulgaris L. (sugar beet) cultured in nutrient solution containing 0.5 to 500 mol m−3 NaCl. Leaf extension growth was the parameter most sensitive to salinity: the initial rate of leaf extension and final leaf length each declined linearly with increase in external NaCl concentration. Photosynthetic O2 evolution of thin leaf slices did not decline until salinity levels reached 350 to 500 mol m−3 NaCl, while respiratory O2 consumption was not affected by salinity throughout the range. The results suggest that the influence of salinity on the capacity for carbon accumulation in B. vulgaris occurs primarily through reduction in the area of photosynthetic surface.
Tetraphenylphosphonium (TPP+) is not suitable for the assessment of electrical potentials in Chlorella emersonii
Authors: GIMMLER HARTMUT , GREENWAY HANK
Published: April 2006

Abstract. For Chlorella emersonii, plausible membrane potentials between –80 and –120 mV were calculated from the distribution of the lipophilic cation tetraphenylphosphonium (TPP+) between the cells and the medium. Furthermore, these calculated membrane potentials were influenced in a way expected from the literature, by different metabolic conditions induced by light or dark, anaerobiosis, glucose, and by inhibition or uncoupling of electron transport.

Nevertheless, the experiments presented here indicate that TPP+ is unsuitable as a probe for electrical potentials, at least in Chlorella emersonii. The reasons for this conclusion are as follows:

Much of the incorporated TPP+‐14C could not be exchanged against unlabelled TPP+.

The uptake of TPP+‐14C was very slow and exhibited complex rather than simple saturation kinetics.

A large adsorption of TPP+‐14C took place even after the cells were killed; the adsorption by living cells was only 20–60% higher than with killed cells. Furthermore, the adsorption by killed cells showed kinetics similar to living cells.
Gaseous factors involved in the enhanced elongation of rice coleoptiles under water
Authors: ISHIZAWA KIMIHARU , ESASHI YOHJI
Published: April 2006

Abstract. Elongation responses of intact coleoptiles of rice (Oryza sativa L. ev. Sasanishiki) explants to various gases were examined under submerged conditions in continuously flowing gas‐saturated incubation media. Reduced O2 tension (hypoxia). CO2 and especially C2H4 significantly stimulated coleoptile elongation; the optimal concentrations of O2, CO2 and C2H4 when applied singly were 0.07 m3 m‐3, 0.10 m3 m‐3, and 3 cm3, respectively. However, in addition to these gases other as yet unknown factors were involved in the enhanced elongation of rice coleoptiles under water.

The actions of CO2 and C2H4, unlike that of hypoxia, were accompanied by increases in dry weight of the coleoptiles. The effect of C2H4 occurred independently of O2 concentrations, whereas that of CO2 occurred above 0.08 m3 m‐3O2. Maximum elongation of rice coleoptiles under submerged conditions was obtained when the flowing medium was saturated with a gas mixture containing 0.10 m3 m‐3 O2, 0.10 m3 m‐3 CO2 and 10 cm3 m‐3 C2H4, greatly surpassing elongation in static media. However, elongation in static media was greater than that in a closed atmosphere. The intercellular C2H4 concentration in explants growing in static media was higher than that in a closed atmosphere. These results showed that the coleoptile elongation of rice seedlings under water may be regulated by the accumulation of CO2 and C2H4 in and around the seedlings under hypoxic conditions.
Relationship between salt accumulation and water content of dicotyledonous halophytes
Authors: GLENN EDWARD P. , O'LEARY JAMES W.
Published: April 2006

Abstract. Growth rates and levels of minerals, Na+, K+, Mg++, Ca++, and water were measured in dicotyledonous halophytes grown along a salinity gradient from fresh water to 720 mol m−3 NaCl in a controlled environment greenhouse. Ten test species from the families Chenopodiaceae, Aizoaceae, and Batidaceae exhibited growth stimulation by 180 mol m−3 NaCl and were classified as euhalophytes. Ten others from the families Chenopodiaceae, Aizoaceae, Asteraceae, Brassicaceae, Polygonaceae, Boraginaceae, Malvaceae, and Plumbaginaceae showed their best growth on fresh water and were classified miohalophytes. Salt, and particularly sodium, accumulated in all halophytes but to a significantly greater extent among euhalophytes than miohalophytes. The water content of most species increased when grown on 180 mol m−3 NaCl compared to fresh water; but at higher salinities some of the species underwent dehydration. Dehydration of the succulent S. europaca was not coupled to a proportional decrease in growth. Water content and cation accumulation in euhalophytes appeared to be coordinated to produce a constant osmotic potential gradient within the shoot tissues relative to the external salinity. In contrast, miohalophytes did not appear to regulate osmotic potential as closely as euhalophytes.
Photoperiodic time signals during twilight
Authors: HUGHES J. E. , MORGAN D.C. , LAMBTON P.A. , BLACK C.R. , SMITH H.
Published: April 2006

Abstract. Although daylength has a major effect on flowering and several other aspects of plant development, the actual environmental time signals for the beginning and the end of day are obscure. An intensive spectroradiometric study was carried out in three contrasting environments: namely, unshaded sites, a mature oak woodland and a sugar beet crop. Spectral photon distributions were obtained describing numerous twilight phases and intervening photoperiods throughout the year. From each, absolute photon fluence rates, photon fluence rate ratios and phytochrome photoequilibria were calculated. Although substantial changes in spectral composition occurred during twilight, they were less capable of providing reliable and accurate time signals than the absolute fluence rate; this was especially apparent beneath the canopies. Thus, spectral changes are unlikely to be valuable in photoperiodic perception. The results are discussed in relation to the possible involvement of the known plant photoreceptors in photoperiodism.
Effects of photoperiod and ageing on the carbon isotope composition of Bryophyllum daigremontianum Berger
Authors: DELEENS E. , QUEIROZ O.
Published: April 2006

Abstract. Changes in crassulacean acid metabolism (CAM) in the leaves of Bryophyllum daigremontianum were studied comparatively under closely controlled (phytotron) and semi‐natural (greenhouse) conditions utilizing measurements of natural carbon isotope composition (δ13C) of the total leaf matter. Abrupt transfer of plants from long days to short days resulted in an overall increase of CAM in mature leaves (no. 3 from the apex and older) and thus in a higher CAM level for the whole plant. Study during the course of a year in semi‐natural conditions showed that a progressive increase in length of day and day night temperature differences (February ← June) activated CAM but only a passage to short days (June ← October) produced the maximum CAM. Under the experimental conditions employed, the maximum shift from the C3‐type to the C4‐type of metabolism was observed in plants subjected to semi‐natural progressive variations in the environment, i.e. the δ13C values indicated that for plants in the greenhouse the total carbon flow entering the cells was mediated by phosphoenolpyruvate carboxylase activity.
A field study of photosynthetic temperature acclimation in Carex eleocharis Bailey
Authors: MONSON RUSSELL K.
Published: April 2006

Abstract. Seasonal patterns in photosynthetic temperature acclimation and growth were investigated in the sedge, Carex eleocharis Bailey, a species which has demonstrated a marked capacity for shifts in the photosynthetic temperature optimum in previous growth chamber studies. The seasonal production of new leaves was 90% complete by the earliest study date, June 3. Shifts in the photosynthetic temperature optimum of 10°C (from 15 to 25°C) were observed during the months of June and July. These results indicate that in situ acclimatory adjustments in C. eleocharis occur in existing leaf tissue, rather than new leaves which are produced as the season progresses. Despite the 10°C increase in the temperature optimum, mean mid‐day leaf temperatures were higher than the optimum throughout the summer. A broad temperature response appeared to be more important than the acclimation adjustments in maintaining near‐maximum photosynthesis rates during the mid‐day period. Seasonal shifts in the photosynthetic temperature optimum were not as great as those previously observed in growth chamber studies. This discrepancy arises because of the capacity for growth chamber grown plants to produce new leaves with temperature response characteristics closely tuned to the growth temperature regime. In field‐grown plants the production of 90% of the leaves during the cool portion of the season places limitations on the potential for acclimation to the warmer midsummer temperatures.
Light gradients in shoots subjected to unilateral illumination—implications for phototropism
Authors: PARSONS A. , MACLEOD K. , FIRN R. D. , DIGBY J.
Published: April 2006

Abstract.When an organ is subject to unilateral illumination, light entering the organ is attenuated very efficiently and the irradiance at the ‘shaded’ surface is only a small percentage of that at the illuminated surface. The light gradient across the organ is approximately exponential, being steepest across the first few cell layers. The penetration of light into an organ was found to be similar with red or blue light and was largely independent of the pigmentation of the organ. Studies of light transmission in organs infiltrated with liquids of different refractive index showed that refraction and reflection were the main factors in establishing the light gradient in organs.

The implications of the measured light gradients are discussed briefly in relation to models of phototropism.
Simulated acid rain induces lipid peroxidation and membrane damage in foliage
Authors: CHIA L. S. , MAYFIELD C. I. , THOMPSON J. E.
Published: April 2006

Abstract. Exposure of young bean foliage to acid rain induces free‐radical‐mediated lipid peroxidation and causes the same disruptive changes in the molecular organization of membrane lipid‐bilayers that are observed during natural leaf senescence. Young plants were misted daily for 7d with simulated acid rain for a 2h period. Wide angle X‐ray diffraction revealed the presence of gel‐phase lipid in a fraction containing predominantly chloroplast membranes isolated from treated leaves, and the lipid‐phase transition temperature of these membranes rose from below −30°C to ∼ 36°C over the treatment period. The formation of gel‐phase lipid is known to be associated with lipid peroxidation, and it is therefore significant that production of ethane and levels of malondialdehyde in the leaves, which are both products of lipid peroxidation, rose throughout the treatment period. There was also increased production of ethylene and superoxide radical, which are typical responses of plant tissue to toxicity.
Leaf conductance and transpiration, and water relations of evergreen and deciduous perennials co‐occurring in a moist chaparral site
Authors: CALKIN HOWARD W. , PEARCY ROBERT W.
Published: April 2006

Abstract.Diurnal courses of leaf conductance, water potential and environmental parameters were measured through the year. The seasonal decreases in plant water potentials were greatest in evergreenH. arbutifolia, intermediate in winter deciduousC. occidentalisand least in drought deciduousA. californica.The seasonal patterns of water use were very similar. Estimates of soil root‐stem conductances to liquid water flux indicate that during the spring, conductances are high, that during the early summer there is a daily shift from high morning conductances to lower afternoon conductances, and that late summer conductances are low.
Seasonal progressions of tissue and cell water relations parameters in evergreen and deciduous perennials
Authors: CALKIN HOWARD W. , PEARCY ROBERT W.
Published: April 2006

Abstract.Tissue and cell water relations parameters were followed forHeteromeles arbutifolia, Cercis occidentalisandAesculus californica, in an environment exhibiting seasonally increasing drought. The extensive seasonal osmotic adjustment of evergreenH. arbutifoliaand the moderate adjustment inC. occidentalisclosely matched their respective seasonal decreases in minimum daily water potential. Summer deciduousA. californicaexhibited only small drops in osmotic potential and water potential. Experiments with irrigated plants indicated that drought was not required for the osmotic adjustment ofH. arbutifoliaandC. occidentalis.However, inH. arbutifoliadrought treatment enhanced osmotic adjustment. In irrigatedH. arbutifolia, osmotic adjustment was mainly the result of an accumulation of osmotica. In drought‐stressed plants, the same change in osmotic potential resulted from a combination of accumulation of osmotica and a decrease in symplast volume.
Mathematical description of the seed germination dependency on time and temperature
Authors: WASHITANI IZUMI , TAKENAKA AKIO
Published: April 2006

Abstract. A mathematical model which describes the germination percentage dependency on time and temperature of a seed population was derived from the experimental results with a seed population of Amaranthus patulus Bertol. under sub‐optimal temperature conditions (Washitani & Takenaka, 1984). The equation of the model which is a modified thermal time model is

image

where G is germination percentage at a certain time after the start of imbibition (t) at a certain temperature (T), μT1 and σT1 are the mean and standard deviation of lower limit temperature among the seeds belonging to the seed population, and Tb, m, and A are the parameters characterizing the linear relationship between the rate and temperature, namely, Tb is the base temperature, m, the median of the required thermal time and A, a parameter determining the pattern of the variation of the required thermal time within seed population, respectively. The equation yields time courses for germination which are very similar to those observed by experiment.
Salt‐tolerance in plants. I. Ions, compatible organic solutes and the stability of plant ribosomes
Authors: BRADY C. J. , GIBSON T. S. , BARLOW E. W. R. , SPEIRS J. , WYN JONES R. G.
Published: April 2006

Abstract Polysomes and ribosomes recovered from a number of plant species were tested for stability when incubated at 25°C in salt solutions in the absence of ATP and initiation factors. Stability was assessed by sucrose density gradient analysis. The stability was inversely proportional to salt concentrations above 125 mol m−3 KCl. Polysomes were less stable in the presence of Na+ than K+ salts, and were much less stable in Cl− than in acetate salts. Polysomes from Triticum aestivum. Hordeum vulgare, Capsicum annuum, Helianthus annuus. Pisum sativum, Atriplex nummularia, Beta vulgaris, Cladophora sp., Enteromorpha sp. and Corallina cuvieri were similarly sensitive to KCl. Polysomes from Ulva lactuca were more sensitive than the other species. Cytoplasmic and plastid polysomes from T. aestivum were similarly unstable in 500 mol m−3 KCl. Unprogrammed ribosomal subunit couples from T. aestivum, B. vulgaris and U. lactuca showed Mg2+‐dependent conformational instability and dissociation in KCl. Slight differences in ribosomal stability were observed between species, but these were unrelated to the salt tolerances of the plants. The ‘compatible’ organic solutes, glycinebetaine and proline, failed to reduce ion‐induced instability. Ribosome yield and polysome profiles were similar in leaves of B. vulgaris containing significantly different levels of both Na+ and Cl− after growth in media containing 50 or 200 mol m−3 NaCl. The results are consistent with the hypothesis that plants maintain a cytoplasmic solute environment that is compatible with ribosomal stability.
Spontaneous and induced blocking and unblocking of phloem transport
Authors: GOESCHL J. D. , MAGNUSON C. E. , FARES Y. , JAEGER C. H. , NELSON C. E. , STRAIN B. R.
Published: April 2006

Abstract Steady‐state labelling with 11CO2 was used to observe the blocking of phloem transport, induced by chilling short regions of stems or petioles of velvetleaf (Abutilon theophrasti Medic.) or cotton (Gossipium hirsutum L.). The abruptness of these blockages was evidenced by sharp decreases in 11C activity below, and increases above a 2 to 3 cm region cooled from 28°C to 18 or 13°C for periods as short as 2 min. Abrupt unblocking of transport in velvetleaf occurred a few minutes after rewarming, as evidenced by a sharp rise and and overshoot in 11C activity. Recovery of transport in cotton was more prolonged and was marked by occasional spontaneous blocking and unblocking of transport at various points along the petiole or stem, not necessarily in the cooled region. Similar spontaneous events were often observed in undisturbed cotton plants, but only rarely in velvetleaf.
The effect of temperature and oxygen on the CO2 compensation point of the marine alga Ulva lactuca
Authors: COLMAN BRIAN
Published: April 2006

Abstract The CO2 compensation point of Ulva lactuca frond sections has been measured in artificial seawater using a sensitive gas‐chromatographic method. Under nitrogen the compensation point remained relatively constant at 3–6 cm3 m−3 at temperatures from 10 to 30°C while in air‐saturated medium (0.3 kg m−3 O2) the compensation point rose from 5 cm3 m−3 at 10°C to 11 cm3 m−3 at 30°C. These responses of the compensation point to temperature and oxygen concentration indicate that there is little photorespiratory CO2 loss in this marine macroalga, and the low values of these compensation points indicate that inorganic carbon is actively accumulated by the plant.
Dye‐flow apparatus to measure the variation in axial xylem permeability over a stem cross‐section
Authors: BOOKER R. E.
Published: April 2006

Abstract Equipment and methodology are described that allows the radial variation in axial xylem permeability (hydraulic conductivity) over a tree cross‐section to be measured and the flow paths to be identified by the strictly controlled flow of dye through a specimen. The apparatus can be calibrated so that the point‐to‐point variation of absolute permeability over a xylem cross‐section can be calculated from the dye‐flow patterns, which otherwise show only relative variations in permeability. The effect of using different dyes and dye concentrations on the penetration time and the shape of the dye patterns was investigated. The penetration time through the wood of identical end‐matched specimens is appreciably longer for fixing dyes than for non‐fixing dyes, and for the fixing dyes it depends strongly on the dye concentration. However, the dye patterns of the end‐matched specimens were indistinguishable with fixing and non‐fixing dyes, and independent of dye concentration. The fixing dye toluidine blue at 0.25% to 0.5% (w/w) was found most suitable as it yields a clear permanent pattern.
Phytochrome behaves as a dimer in vivo
Authors: BROCKMANN J. , RIEBLE S. , KAZARINOVA‐FUKSHANSKY N. , SEYFRIED M. , SCHÄFER E.
Published: April 2006

Abstract It is well established that phytochrome exists as a dimer in vitro. A comparison of the relative photoequilibrium concentrations of PrPr, PrPfr and PfrPfr, with the relative sizes of the Pfr‐pools which undergo dark reversion in the intact plant, leads to the hypothesis that phytochrome also exists as a dimer in vivo, This hypothesis is in accordance with kinetic properties of the phytochrome system under continuous irradiation. Additional support for this view is provided by the observation that Pfr‐destruction after a red light flash, which should favour the formation of PrPfr dimers, is paralleled by a decay of Pr, even if the presence of Pr cycled through Pfr can be excluded. Preliminary observations could indicate an interaction of the subunits of a phytochrome dimer during the process of phototransformation.
Regulation of the transcription of heat shock genes in nuclei from soybean (Glycine max) seedlings
Authors: SCHÖFFL F. , ROSSOL I. , ANGERMÜLLER S.
Published: April 2006

Abstract Run‐off transcription in nuclei isolated from soybean seedlings was used to test the hypothesis that the expression of heat shock genes is controlled at the level of transcription. Only nuclei p retreated by a heat shock at 41°C prior to their isolation synthesized RNA from heat shock genes. The specificity of transcripts was determined by Southern blot hybridization of [32P]‐labelled run‐off RNA with DNA fragments from several heat shock and non‐heat shock genes. The strand selectivity of heat shock gene transcription was exemplified by single stranded DNA probes. Low concentrations of α‐amanitin completely inhibited the synthesis of heat shock specific RNA, but only partially inhibited the synthesis of ribosomal RNA. The overall transcription of nuclei isolated from heat shock tissue was reduced by more than 20% compared to that in nuclei from control tissue. This decline is consistent with a decrease in the transcriptional activity of non‐heat shock genes transcribed by RNA polymerases I and II. Our results suggest that temperature stress induces the transcriptional activation of heat shock genes and has a negative effect on the transcription of other genes.
Early stomatal closure in waterlogged pea plants is mediated by abscisic acid in the absence of foliar water deficits
Authors: JACKSON M. B. , HALL K. C.
Published: April 2006

Abstract Soil waterlogging decreased leaf conductance (interpreted as stomatal closure) of vegetative pea plants (Pisuin sativum L. cv. ‘Sprite’) approximately 24 h after the start of flooding, i.e. from the beginning of the second 16 h‐long photo‐period. Both adaxial and abaxial surfaces of leaves of various ages and the stipules were affected. Stomatal closure was sustained for at least 3 d with no decrease in foliar hydration measured as water content per unit area, leaf water potential or leaf water saturation deficit. Instead, leaves became increasingly hydrated in association with slower transpiration. These changes in the waterlogged plants over 3 d were accompanied by up to 10‐fold increases in the concentration of endogenous abscisic acid (ABA). Waterlogging also increased foliar hydration and ABA concentrations in the dark.

Leaves detached from non‐waterlogged plants and maintained in vials of water for up to 3 d behaved in a similar way to leaves on flooded plants, i.e. stomata closed in the absence of a water deficit but in association with increased ABA content. Applying ABA through the transpiration stream to freshly detached leaflets partially closed stomata within 15 min. The extractable concentrations of ABA associated with this closure were similar to those found in flooded plants. When an ABA‐deficient ‘wilty’ mutant of pea was waterlogged, the extent of stomatal closure was less pronounced than that in ordinary non‐mutant plants, and the associated increase in foliar ABA was correspondingly smaller. Similarly, waterlogging closed stomata of tomato plants within 24 h, but no such closure was seen in ‘flacca’, a corresponding ABA‐deficient mutant.

The results provide an example of stomatal closure brought about by stress in the root environment in the absence of water deficiency. The correlative factor operating between the roots and shoots appeared to be an inhibition of ABA transport out of the shoots of flooded plants, causing the hormone to accumulate in the leaves.
Photon requirement for growth of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)
Authors: OSBORNE B. A. , GEIDER R. J.
Published: April 2006

Abstract Photon requirements for growth (φg−1) of the diatom Phaeodactylum tricornutum were determined under nutrient‐sufficient conditions at two photon flux densities corresponding to light limited and near‐saturating conditions for growth. The value of φg−1 based on assimilated carbon was light‐dependent and varied from 8.8 to 14.0 mol photon mol C−1 with the minimum value at the lowest photon flux density. These results are lower than might be predicted for microalgal growth based on the Z scheme of photosynthesis. Conversion of these values for carbon fixation to estimates based on oxygen evolution is problematical due to uncertainty over the appropriate assimilatory quotient (Qa= mol O2 mol C−1). Minimum values based on oxygen evolution rates ranged from 6.2 to 7.6 mol photon mol O2−1 using a Qa of 1.41 mol O2 mol C−1 obtained by Myers (1980). These estimates are similar to our previous measurements for photosynthesis and indicate a high efficiency for light energy transforming reactions during growth. The values of (φg−1 obtained in this work indicate a number of inadequacies in our understanding of the energetics of microalgal growth and are inconsistent with our present knowledge of photosynthetic energy coupling in plant cells.
Supply and partitioning of assimilates to roots of Medicago sativa L. and Lotus corniculatus L. under anoxia
Authors: BARTA A. L.
Published: April 2006

Abstract A current explanation of the mechanism of flooding injury to roots suggests that oxygen deficiency depresses the supply of respirable carbohydrates sufficiently to inhibit fermentation. However, even though it has been shown that phloem transport of assimilate is sharply reduced to anaerobic roots, inhibition of assimilate metabolism has also been suggested to be an important factor. This study examines these hypotheses by relating assimilate supply and metabolic activity in anoxic roots of alfalfa (Medicago sativa L.), a flood‐intolerant species, and birdsfoot trefoil (Lotus corniculatus L.), a flood‐tolerant plant. Roots were made anoxic (severe O2 deficiency) for 2, 4 or 6 d and shoots were labelled with 14CO2. Assimilate transport to the roots and metabolism to structural components were significantly decreased in both species in response to anoxia. Trefoil exhibited significantly greater 14C incorporation into the residue fraction at 4 d anoxia than did alfalfa, and this was consistent with the greater flooding tolerance of trefoil. When assimilate supply to O2‐deficient roots was decreased by shoot shading, shoot fresh weight was reduced by both anoxia and light treatments. Root‐soluble sugars were significantly decreased by shading but were greatly increased in response to anoxia. Root starch concentration also increased under anoxia. Root K+ concentration was reduced by anoxia only. The energy status (ATP/ADP) of roots was significantly decreased by shading; however, anoxia reduced the energy status only in unshaded plants. The data indicate that carbohydrate supply to anaerobic roots does not appear to be a limiting factor in the metabolic response of alfalfa roots. Alternatively, metabolism of assimilate in anoxic roots may be an important determinant of survival.
Membrane alterations in winter rye and Brassica napus cells during lethal freezing and plasmolysis
Authors: SINGH J. , IU B. , JOHNSON‐FLANAGAN A. M.
Published: April 2006

Abstract Cells fixed during freezing or plasmolysis were used to study membrane alterations in hardened and non‐hardened Brassica napus suspension‐cultured cells and rye leaf mesophyll cells. The plasmalemma in non‐hardened rye mesophyll cells formed multilamellar vesicles during lethal freezing at high subzero temperatures (–5°C). These vesicles became highly condensed at lower subzero temperatures (–10°C). Conversely, cold‐hardened rye mesophyll cells did not undergo membrane alterations at these temperatures. The results from plasmolysis of B. napus and rye mesophyll cells hardened by ABA at 25 °C and low temperature (2°C), respectively, verify the cell response to lethal freezing. Again there was a continuum of responses with 1 kmol m−3 balanced salt causing multilamellar protrusions. Appression of the plasmalemma against the tonoplast to form multilamellar vesicles and the invagination of these vesicles into the tonoplast were also observed in rye cells undergoing lethal plasmolysis. Increasing the plasmolysing solution to 3 kmol m−3 occasionally caused the formation of multilamellar vesicles on the cell surface of hardened rye mesophyll cells.
The uptake of nitrate and ammonium nitrogen in Chara hispida L.: the contribution of the rhizoid
Authors: BOX R. J.
Published: April 2006

Abstract The uptake of ammonium and nitrate nitrogen by cultured plants of the green freshwater alga Chara hispida L. has been compared quantitatively with the contribution of its rhizoidal tissue. In the short‐term, the rhizoid takes up 7–20% of the ammonium nitrogen, and about 15% of the nitrate that is taken up by whole plants under similar conditions. The uptake was studied over a range of both temperatures and external concentrations. The apparent activation energy for the uptake of NH4+ and NO3− by the whole plant was found to be 50 kJ mol−1 and 30 kJ mol−1, respectively. For the rhizoid, the values were similar for both nitrogenous ions, 106 kJ mol−1 and 70–100 kJ mol−1. The rhizoidal uptake mechanism for ammonium nitrogen operates more efficiently compared to that in the whole plant. Nitrate is taken up by the rhizoid by a mechanism with a substrate affinity higher than in the plant taken as a whole. The possible ecological significance of the results is discussed.
Ethylene stimulates the accumulation of ripening‐related mRNAs in tomatoes
Authors: MAUNDERS M. J. , HOLDSWORTH M. J. , SLATER A. , KNAPP J. E. , BIRD C. R. , SCHUCH W. , GRIERSON D.
Published: April 2006

Abstract Seven cDNA clones for ripening‐related mRNAs were used as hybridization probes to study the regulation of gene expression during tomato (Lycopersicon esculentum Mill) ripening. The mRNAs corresponding to each clone were detected by Northern blotting and the sizes of the transcripts compared with the molecular weights of polypeptides identified previously by hybrid‐release translation. Dot hybridization to poly(A)+ mRNA from leaves, roots, unripe and ripe tomatoes established that five of the clones encoded mRNAs that were ripening specific and two encoded mRNAs also expressed in other organs. Appearance of these ripening‐specific mRNAs was correlated with ethylene production as ripening commenced and occurred before lycopene synthesis began. Thereafter, the mRNAs increased to maximum levels at the orange stage and then declined slowly as fruit turned red. When mature green fruit were picked before any increase in ethylene synthesis occurred and placed in air plus 10 cm3 m−3 ethylene, substantial changes in translatable mRNA were noted within 30 h. Five mRNAs that increased in amount directed the synthesis in vitro of polypeptides similar in size to those encoded by the five ripening‐specific clones. Several different patterns of mRNA accumulation were observed, with increases in concentration of the order of 300‐fold.
Photosynthesis, transpiration and salt fluxes through leaves of Leptochloa fusca L. Kunth
Authors: GORHAM J.
Published: April 2006

Abstract Salt excretion by glands on the leaves of Leptochloa fusca was studied. The rate of excretion was strongly dependent on temperature up to 39°C, which is near the optimum for photosynthesis in this thermophilic C4 grass. The concentration of salt in the xylem required to sustain the observed rate of excretion was low (about two orders of magnitude less than the external concentration). Salt excretion is concluded to be a secondary mechanism of salt tolerance, with exclusion at the roots being the major mechanism. The rate of salt excretion was strongly dependent on temperature.
Relationship between cation accumulation and water content of salt‐tolerant grasses and a sedge
Authors: GLENN E. P.
Published: April 2006

Abstract Salt‐tolerant grasses and a sedge were grown at three salinities in a controlled‐environment greenhouse. They were measured for growth rate, ash content, water content and cations. Fourteen species from the genera Sporobolus, Aeluropus, Leptochloa, Paspalum, Puccinellia, Hordeum, Elymus, Distichlis and Spartina survived up to the highest salt treatment (540 mol m−3 NaCl). These were designated halophytes. Eleven species from the genera Triticum, Phragmites, Dactylotenium, Cynodon, Polypogon, Panicum, Jovea and Heleocharis only survived up to 180 mol m−3 NaCl and were designated salt‐tolerant glycophytes. All species except Distichlis palmeri grew fastest on the non‐saline control treatment. All species tended to have higher Na+ contents and lower K+ and water contents on saline treatments compared to control plants. Halophytes differed from glycophytes in having statistically significant lower water contents on the non‐saline treatment, and lower ash contents and Na:K ratios on 180 mol m−3. However, the range of values among species was greater than the differences between halophytes and glycophytes. All species appeared to use Na+ accumulation and loss of water as the main means of osmotic adjustment. Three halophytic species were grown for a longer period of time to check the above results. The osmolality of the cell sap was measured directly by the vapour pressure method and compared to calculated values based on Na+, K+ and water contents (and assuming a balancing anion such as Cl−). Na+ and K+ alone could account for greater than 75% of the osmotic potential at all salinities. Hence, the accumulation of organic solutes did not appear to be an important factor in the osmotic adjustment of these species. The results support the conclusion that grasses coordinate Na+ uptake and water loss to maintain a constant osmotic potential gradient between the shoot tissues and the external solution. The results were compared to a previous study with dicotyledonous halophytes at the same location.
A novel technique for identification of sites of anion transport in intact cells and tissues using a fluorescent probe
Authors: DEANE‐DRUMMOND CELIA E. , GATES P.
Published: April 2006

Abstract The purported blocker of anion transport 4, 4′ di‐isothiocyano‐2‐2′ stilbene disulfonate (DIDS) has been shown to partially inhibit 36Cl− influx, 36CIO−3 influx and 35SO2−4 influx into Pisum salivum L. cv. Feltham First seedlings. This inhibitory effect could be prevented by pretreatment with the respective unlabelled medium. There was no effect of DIDS on 14C methylamine influx. The results are consistent with the hypothesis that the binding of DIDS to the site of anion‐carrier interaction is responsible for its observed inhibitory effects on anion fluxes. The fluorescent properties of DIDS upon binding to membrane proteins was exploited in an attempt to examine the major sites of anion pumping in whole roots. The results show clearly that in the presence of DIDS the epidermal layers became brightly fluorescent, while cortical layers did not fiuoresce. Lycopersicum esculentum cells taken from locular fluid were plasmolysed using sucrose solution, and the patterns of fluorescence in the presence of DIDS showed in an unambiguous way that the fluorescence is associated with cell membranes. The potential usefulness of this technique to probe sites of anion transport in whole plants and tissues is discussed.
Inhibition of fusicoccin‐stimulated K+/H+ transport in root tips from maize seedlings pretreated with Chlorsulfuron
Authors: DE AGAZIO MARINA , GIARDINA MARIA CARMELA
Published: April 2006

Abstract Fusicoccin (FC)‐stimulated K+ (86Rb) uptake and proton extrusion of maize (Zea mays) root apical segments were inhibited by pretreatment of 4‐day‐old seedlings with the herbicide Chlorsulfuron. In the range of Chlorsulfuron concentrations 0.01‐10 mmol m−3, the percentage of inhibition was 15% at 0.01 mmol m−3 and progressively increased with Chlorsulfuron concentration up to 60% at 10 mmol m−3. At the maximum concentration tested (10 mmol m−3), the inhibition was evident after 1.5 h of pre‐treatment. The binding of FC to microsomal fractions of root segments from Chlorsulfuron‐pretreated seedlings was inhibited by 30%. It is suggested that Chlorsulfuron causes an alteration at the plasmalemma level involving the FC binding sites. The ineffectiveness of Chlorsulfuron in inhibiting FC‐stimulaled K+ uptake when administered to excised segments, while inhibiting the enzyme acetolactate synthase, pointed out by Ray (1984) as the site of action of Chlorsulfuron in pea plants, suggests that the observed inhibition of K+ uptake and H+ extrusion is not induced by Chlorsulfuron inhibition of this enzyme. An alternative site of action of Chlorsulfuron is hypothesized in maize plants.
Proline overproduction in cells of the green alga Nannochloris bacillaris resistant to azetidine‐2‐carboxylic acid
Authors: VANLERBERGHE G. C. , BROWN L. M.
Published: April 2006

Abstract Cells of N. bacillaris have been selected that are resistant to the toxic proline analogue azetidine‐2‐carboxylic acid (A2C) in 7% artificial seawater (ASW). This phenotype is stable in the absence of selection pressure. A2C resistance at low salinity was demonstrated to be due to an overproduction of proline in these cells, while levels of other amino acids were unaffected. Both wild‐type and A2C‐resistant cells respond to growth in high salinity media (100% ASW, 200% ASW) by accumulation of proline, but proline levels at all salinities are higher in the A2C‐resistant cells than in the wild‐type. Proline overproduction in the A2C‐resislant cells did not affect fluctuations in the levels of other salinity‐dependent solutes, such as homarine. A mutant with this level of specificity over a wide range of water potentials has not been reported for other plants and algae. Both the wild‐type and A2C‐resistant cells were able to grow over the entire salinity range tested (7%‐300% ASW). However, the A2C‐resistant cells showed a lower division rate than the wild‐type in 300% ASW, and yield of A2C‐resislant cells was lower than yield of wild‐type cells at the salinity extremes (7% ASW, 300% ASW). The response or wild‐type and A2C‐resistant cells to rapid increases in salinity were similar for both growth and photosynthesis. The presence of a constitutive high level of proline in the A2C‐resistant cell line did not confer any obvious increased tolerance to salinity shocks, indicating that there are other important factors in the biochemical adaptation to salinity in these cells.