bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential changes in the electron transport properties of thylakoid membranes during aging of attached and detached leaves, and of isolated chloroplasts
Authors: MISRA A. N. , BISWAL U. C. 
Published: April 2006

Abstract. Aging of chloroplasts both in vivo and in vitro causes a considerable loss in the 2,6‐dichlorophenol indophenol (DCPIP)‐Hill reaction with water as electron donor. The loss can be reduced by exogenous electron donors like diphenyl carbazide (DPC). suggestive of aging‐induced damage of the oxygen evolving system. Aging also brings about a considerable loss in methylviologen (MV) reduction mediated by Photosystem I (PS I) of chloroplasts with an ascorbate‐DCPIP couple as the electron donating system.The loss in the electron transport ability of the plastids is faster during in vitro compared to in vivo aging of the chloroplasts.Light protects the photo‐electron transport ability of chloroplasts during aging of intact leaves in contrast to its action during aging of the isolated organelles.
Changes in tissue protein pattern in relation to auxin induction of DNA synthesis
Authors: MELANSON D. , TREWAVAS A. J. 
Published: April 2006

Abstract. When artichoke tuber tissue was cultured in mineral salts, the induction of DNA synthesis and subsequent cell division was dependent upon the presence of auxin in the incubation medium. Evidence is provided that an obligatory set of metabolic events precedes auxin‐induced DNA synthesis, and previous work has associated these with protein synthesis. As a consequence the auxin‐induced changes in nuclear and cytoplasmic proteins have been investigated. Using 2D gel electrophoresis, qualitative alterations in nuclear non‐histone proteins have been detected from the earliest treatment times with auxin. These changes were progressive, starting with four novel proteins after 3 h auxin treatment and ending with about forty when DNA synthesis commences some 18–21 h later. Qualitative alterations in phosphorylated nuclear proteins due to auxin treatment were only detectable when DNA synthesis commenced. In contrast, few qualitative alterations in cytoplasmic proteins were detectable, with the major change being in phosphorylated proteins at the onset of DNA synthesis.A possible model of auxin action is outlined which involves sequential and progressive changes in the synthesis of nuclear proteins and the control of gene expression eventually leading to DNA synthesis.
Stomatal responses of pearl millet (Pennisetum americanum [L.] Leeke) to leaf water status and environmental factors in the field
Authors: HENSON I. E. , ALAGARSWAMY G. , BIDINGER F. R. , MAHALAKSHMI V. 
Published: April 2006

Abstract. Factors affecting stomatal conductance (g1) of pearl millet (Pennisetum americanum [L.] Leeke), cultivar BJ 104, were examined in the field in India during the dry season.Diurnal changes in g1 were evaluated for upper expanded leaves at flowering on two occasions using plants subjected to varying degrees of water stress. Except for the most severely stressed treatment, diurnal changes in g1 closely matched changes in irradiance (I), the promotive effect of which largely overcame opposing influences on g1 of increasing atmospheric vapour pressure deficit, and decreasing leaf water and turgor potentials (Ψ, Ψp).Two main effects of water stress on g1 were evident: (i) a decrease in the amplitude of the mid‐day peak in g1, and (ii) a decrease in the time over which high g1 was maintained, resulting in early (mid‐day) closure and hysteresis in the relationship between g1 and I.Leaf conductance was greatest for upper leaves and decreased down the canopy. At equivalent depths in the canopy g1 was higher in flowering than in photoperiodically‐retarded plants of the same age. The magnitude of water stress‐induced stomatal closure increased down the plant, and was more marked in retarded than in flowering plants.Within individual stress treatments Ψ of upper leaves decreased linearly as transpiration flux increased. It is concluded that stomatal behaviour of upper leaves of pearl millet at flowering largely operates to maximize assimilation rather than to minimize water loss.
Transport of gases into leaves
Authors: CSIRO R. LEUNING 
Published: April 2006

Abstract. Transport of gases between the intercellular spaces of plant leaves and the surrounding air is analysed in terms of multicomponent collision processes through an isothermal, porous septum. Interaction of diffusing species with each other and with the pore walls is described using a modified Stefan–Maxwell equation and an equation relating the pressure gradient to the sum of the diffusive fluxes, weighted by their appropriate Knudsen diffusivities. Viscous How arising from an excess pressure within the leaf is also considered.Equations are derived which describe the flux densities of water vapour and CO2 through the stomata. The analysis is general and is applicable to trace gases other than CO2. A simple conductance is defined for water vapour to relate the flux and mol fraction difference across the stomata, viz. Nw=−gw, δxw/xa. A simple conductance cannot be defined for CO2 because the flux of water vapour has a significant influence on the CO2 gradient. The equation derived for the intercellular mol fraction of CO2 is in terms of the fluxes of CO2and water vapour and represents a ‘large‐pore’ (d > μm) approximation which requires no information about stomalal geometry. Analogous equations are developed for transfer of gases through the leaf boundary layer. Sample calculations are presented to illustrate the effect of neglecting the interaction of water vapour and CO2 on the calculated intercellular and surface concentrations of CO2. Equations for computing water vapour and CO2 flux densities from leaf chamber measurements are also presented.
Associations between plant production and some physiological components of drought resistance in wheat
Authors: BLUM A. , MAYER J. , GOZLAN G. 
Published: April 2006

Abstract. Drought resistance in terms of plant production under conditions of drought stress was previously defined for several spring wheat (Triticum aestivum L.) varieties. Four varieties, differing in their drought resistance by this definition, were compared in their physiological responses to water stress, as induced by polyethylene glycol 6000 in the growth medium.Drought resistance was associated with osmotic adjustment, total root mass production under stress, maintenance of some stomatal permeability under stress, and maintenance of turgor at a given level of drought stress, by either osmotic adjustment or elevated plant water potential.Drought resistance was not associated, in this experiment, with plant top growth under stress or non‐stress conditions, maximum leaf area per plant, plant transpiration, and total root mass production under non‐stress conditions.
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.
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.
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.
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.
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.
A systematic approach to the simulation of short‐term processes in the plant‐environment complex
Authors: CHRISTIAN K. R. , MILTHORPE F. L. 
Published: April 2006

Abstract. A conceptual framework is presented for modelling short‐term processes in the plant and its environment as an integrated system. Flows of water, water vapour, heat, momentum, CO2, soluble carbohydrate and phosphorus are all described by equations of the same general type, i.e. in terms of diffusivity‐type parameters, capacities and potential gradients. A representative volume of the crop is divided horizontally into layers and vertically between crop and environment for treatment by a finite‐difference method. Vertical flow occurs in the atmosphere, soil, stems and larger roots, andilateral flow between leaves and air, and between finer roots and soil. The interception of direct sunlight and the flux densities of downward and upward diffuse radiation within layers are calculated by a step‐wise procedure.The conversions of materials within the plant are treated as functions of appropriate state variables. Schemes for carbon and phosphorus provide for flow to and from the translocation system, and for photosynthesis, respiration and growth.A model of a fully‐established lucerne crop is described and the sensitivity of model performance to changes in a number of parameter values explored. Simulation runs under varying conditions indicate realistic prediction of diurnal trends.
A study of the impaired growth of roots of Zea mays seedlings at low oxygen concentrations
Authors: ATWELL B. J. , THOMSON C. J. , GREENWAY H. , WARD G. , WATERS I. 
Published: April 2006

Abstract. Seedlings of Zea mays L. were grown in the dark at 27°C. Four‐day‐old seedlings were then exposed for 3 days to solutions equilibrated with gas mixtures to give O2 concentrations between 0.02 and 0.25 mol m−3. Root growth was impaired just as severely at 0.06 as 0.02 mol O2 m−3 while growth at 0.16 mol O2 m−3 was about the same as in solutions in equilibrium with air (0.25 mol O2 m−3).Growth of young seedlings at low O2 concentrations was inhibited to the same extent in nutrient solution and 0.5 ml m−3 CaCl2, showing that the adverse effect of O2 deficits on growth was not due to less uptake of inorganic nutrients. Furthermore, at low O2 concentrations neither exposure of the shoots to a relative humidity of 100% (26.0 g H2O m−3) nor excision of the entire shoot enhanced root growth relative to that in plants with shoots at a relative humidity of 50% (13.0 g H2O m−3). Therefore, for these seedlings growing in the dark, impairment of root growth at low O2 concentrations was not a consequence of water deficits in the shoot or of other shoot‐root interactions.Total soluble sugars and amino acid concentrations were generally greater at low (0.02–0.06 mol O2m−3) than at high O2 concentrations (0.16–0.25 mol O2 m −3). This applied specifically to the root apices (0–2 mm) and expanding (2–15 mm) tissue except in some experiments where sugar concentrations in expanding tissue were slightly greater at high than at low O2 concentrations.Critical O2 pressures for respiration of excised root segments were approximately 0.117 and 0.065 mol O2 m−3 in the expanding and expanded zones of the roots, respectively. In contrast, the critical O2 pressure exceeded 0.20 mol O2 m−3 in the apex, suggesting that O2 supply for metabolic processes is most likely to be sub‐optimal in this zone. Our results show clearly that the adverse effects of low O2 concentrations are unlikely to be a consequence of substrate shortage for either respiration or synthesis of macromolecules; low rates of ATP regeneration in growing root tissues are the logical cause for impaired growth in young seedlings while they are being sustained by seed reserves.
A simple method for determining the boundary layer resistance in leaf cuvettes
Authors: PARKINSON K. J. 
Published: April 2006

Abstract. A new method is described for determining the boundary layer resistance over wet filter paper exposed within a leaf cuvette, based on the energy balance of the filler paper. The boundary layer resistance is calculated by an iterative procedure from measurements of the relative humidity and temperature of the air in the cuvette. Comparisons between the new and the conventional method, involving measurement of the filter paper temperature, show close agreement.To simplify the method further, a graph has been constructed for the relationship between boundary layer resistance and cuvette relative humidity at temperatures from 15 to 35°C, determined at one value of the ratio of the flow rate through the cuvette to the filter paper area.An analysis of errors suggests that the new method is less sensitive than the conventional to errors in temperature and humidity.
Physiological effects of sulphur dioxide. 1. The effect of SO2 on photosynthesis and stomatal regulation of Vicia faba L.
Authors: KROPFF M. J. 
Published: April 2006

Abstract. The effect of short‐term SO2 fumigation on photosynthesis and transpiration of Vicia faba L. was measured at different irradiances and SO2 concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO2 and the magnitude of the reduction was linearly related to the rate of SO2 uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.The effect of SO2 on photosynthesis was measured at different CO2 concentrations to analyse the contribution of stomatal and non‐stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO2 diffusion increased as a result of SO2 exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO2 fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO2 concentration.Analysis of gas‐exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO2 exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO2 than for O2.