bluuebunny/crossref_metadata_2025 huggingface dataset:
Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent
Authors: SCHULTE P. J. , SMITH J. A. C. , NOBEL P. S.
Published: April 2006

Abstract Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24‐h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one‐third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.
Energy charge during aerobic and anaerobic imbibition of Kalanchoë blossfeldiana seeds
Authors: DEDONDER A. , RETHY R. , FREDERICQ H. , De GREEF J. A.
Published: April 2006

Abstract Adenosine phosphate levels were measured in Kalanchoë blossfeldiana cv. feuerblüte seeds during dark imbibition in aerobic and anaerobic conditions. A correlation between the depth of primary dormancy (light requirement) and the increase of ATP‐content during the first hours of aerobic imbibition was found, but the rise of energy charge from about 0.2 in dry seeds to 0.8 after 18 h is not related to the breaking of dormancy and consequently to germination. In an anaerobic environment, the increase in ATP‐content is dramatically lowered and the energy charge value stabilizes at about 0.4, most probably as the result of fermentation activity.
Salt‐tolerant Triticum×Lophopyrum derivatives limit the accumulation of sodium and chloride ions under saline‐stress
Authors: SCHACHTMAN D. P. , BLOOM A. J. , DVOŘÁK J.
Published: April 2006

Abstract. Cultivars of hexaploid wheat (Triticum aestivum cvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt‐tolerant species (Lophopyrum elongatum or L. ponticum) were compared to determine differences in growth, ion transport and ion accumulation under salt‐stress. Two experiments were conducted in which plants were grown under saline and non‐saline conditions and harvested at various lime intervals throughout ontogeny. Under salt‐stress the growth rate of the cultivars, as compared to the growth rate of the derivatives, decreased more rapidly later in development. Transport rates from root to shoot of Na+ and Cl− reached higher levels in the cultivars. The cultivars accumulated more Na+ and Cl− and relatively less K+ in the shoot. The K+/Na+ ratio was higher in the derivatives than in the cultivars from which they were derived. The addition of chromosomes from Lophopyrum species into wheat altered ion accumulation, growth rates, and ion transport rates from root to shoot.
Discrepancies between water potential isotherm measurements onPinus ponderosaseedling shoots: xylem hysteresis and apoplasmic osmotic potentials *
Authors: HARDEGREE S. P.
Published: April 2006

Abstract.Sap expression, air drying and a combined technique were used to measure the water potential isotherm ofPinus ponderosaLaws, seedling shoots with the pressure chamber. Discrepancies between water relations parameters derived from these techniques can be partially explained by air entry into air drying tissues, hysteresis in the xylem water potential isotherm and dilution of apoplasmic solutes during sap expression.
Diurnal water storage in the stems of Picea sitchensis (Bong.) Carr.
Authors: MILNE R.
Published: April 2006

Abstract. Two models of the relationship between diurnal variation in shoot water potential and transpiration in 14‐year‐old Picea sitchensis (Bong.) Carr. were compared. The first model was a physiologically based resistance‐capacitance (R‐C) analogue with its associated differential equations. The second was a non‐physiological discrete‐difference (D‐D) or stochastic transfer function model. The RC model included only the effect of water storage in the phloem and bark while the D‐D model implicity included all storage mechanisms. The R‐C and D‐D models explained similar fractions (62% and 68% respectively) of the variation in shoot water potential due to diurnal changes in transpiration rate. However, the D‐D model had fewer parameters than the R‐C model. The results from the D‐D model showed that the resistance to flow from soil to shoots along the trunk, (RT), was 5 × 103 MPa kg‐1s and the capacitance of the phloem and bark treated as a single store, (Cs), was 1.6 kg MPa‐1. It is suggested that the resistance to flow into storage (Rs) is much greater than RT and can be disregarded. A non‐linear version of the D‐D model suggested [hat resistance to flow in the trunk increases with increasing transpiration rate.
Leaching of solutes by the action of acidic rain: a comparison of efflux from twigs and single needles of Picea abies (L. Karst.)
Authors: MITTERHUBER E. , PFANZ H. , KAISER W. M.
Published: April 2006

Abstract. Leaching of inorganic cations (K+, Mg2+) and in some cases of inorganic anions and sugars from detached twigs and single needles of spruce Picea abies L. Karst.) in the presence of acid rain (H2SO4, 1 mol m−3) or salt solutions (Na2 SO4, 1 mol m−3) was examined under laboratory conditions. Cation leaching (as percentage of the total water soluble ion content of the tissue per hour) was: K+: 0.01‐0.02%; Mg2+: 0.005‐0.01%; Ca2+: 0.1‐0.2%. Leaching rates of anions were even lower than that and concentrations in the leachate were often below the detection limit of anion chromatography. Spraying with H2SO4 (pH 2.95, 1 mol m−3) increased leaching only transiently. Similar effects were found when Na2SO4 was used instead of H2SO4. The transiently enhanced leaching was apparently due to H+/cation or cation/cation exchange at the twig or leaf surfaces. Feeding of K+ or Al3+ through the stems increased leaching of all cations within a few hours, again demonstrating rapid ion exchange in the apoplast. Leaching of potassium and magnesium from single needles occurred at similar relative rates as from twigs. Loss of Ca2+ ions, however, was even smaller from needles than from twigs. Apparently, a large part of the Ca2+ lost from twigs originated from the bark and not from the needles. Efflux of ions from longitudinal needle sections was about 1000 times taster than the rates obtained with intact needles, indicating that the cuticle was the main barrier Preventing solute loss. In relation to the total amount of mineral nutrients in trees, leaching is considered to be too small to be the primary cause of damage to trees stressed by acid rain, as has been suggested in the literature.
A reduction in the abundance of calium oxalate crystals in Oenothera improves the yield of intact chloroplasts
Authors: WOLFSON R. , SEARS B. B.
Published: April 2006

Abstract. Oenothera plants grown as shoot meristem cultures on media having a low calcium concentration had a reduced abundance of raphides when compared to greenhouse‐grown plants or shoot meristem cultures grown on higher concentrations of calcium. Plants from the low‐calcium media also yielded a higher proportion of intact chloroplasts during subcellular fractionation.
Frequency as a property of physiological signals in plants
Authors: DUE G.
Published: April 2006

Abstract. The ‘hormone’ idea is based on a peculiarly chemical notion of substance and time. Although the chemical view of substance is advanced, its view of time is primitive compared to that of physics. This leads to considerable difficulties when applied to oscillatory systems, such as the nutating hypocotyl. There is evidence of involvement of a wide range of oscillatory systems in plants. In considering the properties of such systems, the possibility of physiological signals based on frequency becomes apparent. Some implications of this possibility for both theory and experimental programmes are discussed.
The effect of sodium fluoride on cereal seed germination and seedling growth
Authors: KAUR J. , DUFFUS C.
Published: April 2006

Abstract. Fluoride has been shown to inhibit germination and seedling establishment in barley cv. Natasha, wheat cv. Axona and rice cv. Ishikari. The concentrations of fluoride were selected so as to give a satisfactory dose‐response relationship and also to relate to levels of fluoride present under natural conditions. Concentrations used were zero, 0.5, 1.0, 10 and 40 mol m−3 sodium fluoride. In germination studies, barley was found to be least tolerant and rice most tolerant of fluoride. The inhibition was found to be a response to fluoride itself and the observed effects were not due to pH, sodium or an unspecific effect of halide ion. Phosphate, applied at two concentration levels, was unable to overcome the inhibition. Fluoride was also shown to inhibit seedling growth. The inhibitory effects of fluoride may be accounted for by a wide range of metabolic effects including inhibition of gibberellic acid–triggered alpha amylase activity during germination, and later on to inhibition of chlorophyll synthesis in the developing leaves.
Microsome protein phosphorylation in Acer pseudoplatanus cells as influenced by intracellular alkalinization
Authors: BASSO B. , ROSA P. , TOGNOLI L.
Published: April 2006

Abstract. The authors have previously shown that cell treatments causing intra‐cellular alkalinization stimulate the in vivo phosphorylation of a 33‐K Dalton polypeptide (33 KP) (Tognoli & Basso, 1987). Here, the authors report that this polypeptide belongs to a protein associated with the microsomal membranes. They show that treatment of cells which induce intracellular alkalinization stimulate 33‐KP phosphorylation, whether the phosphorylation is performed in vivo (cells loaded with 32Pi before treatments) or in vitro (microsomes from control and treated cells, incubated with γ32P ATP). In both cases, 33 KP is phosphorylated on a serine residue. Microsomes do not show any phosphatase activity towards this phosphorylated protein, indicating involvement of a protein kinase reaction as an effector of changes induced by intracellular alkalinization. The number of phosphorylated sites or molecules of this protein increases as a result of intracellular alkalinization, suggesting that intracellular alkalinization causes topological or conformational modifications to a protein kinase or its substrate protein. The in vitro phosphorylation is not specifically influenced by the pH of the in vitro phosphorylation medium, suggesting that protein phosphorylation is not directly controlled by cytoplasmic pH.
Drought adaptability of Agrobacterium rhizogenes‐induced roots in oilseed rape (Brassica napus var. oleifera)
Authors: VARTANIAN N. , BERKALOFF A.
Published: April 2006

Abstract. Soil grown oilseed rape (Brassica napus L. var. oleifera M., cv. Darmor) seedlings at the cotyledon stage (one week old), were inoculated in vivo at the base of the hypocotyl with Agrobacterium rhizogenes harbouring the pRi 15834 plasmid. Resulting adventitious root formation was observable about 2 or 3 weeks after infection. Differential Ri‐induced root emergence and subsequent development occurred depending on water conditions and closeness of the wounding site to the soil surface: either thin, hairy roots growing rapidly and plagiotropically at the soil level under humid atmosphere, or hairless and fleshy, slowly growing aerial roots developed. The hairy roots were highly drought susceptible, whereas aerial roots revealed some potential for drought tolerance. Unlike normal roots, none of these Ri‐induced roots appeared able to give rise to drought rhizogenesis in plants subjected to progressive drought stress. However, under hardening, achieved through successive and moderate drought stress‐rehydration cycles, both types of Ri‐induced roots improved drought tolerance and could express the morphogenetic differentiation programme leading to the formation of short, tuberized, drought‐adapted, roots. These results, discussed in terms of hormonal imbalance and drought tolerance regulation, suggest that the Ri T‐DNA gene expression, responsible for adventitious root induction and growth behaviour, is further regulated through the host plant.
The occurrence of amoeboid plastids in the actinorhizal root nodules of Alnus glutinosa (L.) Gaertn.
Authors: GARDNER I. C. , ABBAS H. , SCOTT A.
Published: April 2006

Abstract. The invasion of the actinomycete Frankia into the root cells of Alnus glutinosa with subsequent nodule formation effects a number of ultrastructural changes in the host cell cytoplasm. Among other changes the amyloplasts rapidly lose their starch and acquire an amoeboid or pleomorphic form. Such plastids occur predominantly in the mature vesicle‐containing, nitrogen‐fixing cells of the nodule. They lack starch, have an electron dense stroma and a complex lamellar system. This last would appear to be associated with a distinct membranous reticulum which can be extensive. The flexible form of these plastids is mirrored in their ability to enclose portions of host cytoplasm together with organelles and even other plastids. Their close association with cristate mitochondria suggests an active metabolic role in the nodule symbiosis.
Water potential and plant metabolism: comments on Dr P. J. Kramer's article ‘Changing concepts regarding plant water relations’, Volume 11, Number 7, pp. 565–568, and Dr J. B. Passioura's Response, pp. 569–571
Authors: BOYER J. S.
Published: April 2006

Abstract. Kramer (1988) and Passioura (1988) highlight an important principle in plant physiology, namely that roots affect the activity of shoots. It is safe to say that anyone who has observed plants could cite many examples. What is in contention, however, is the interpretation of the water potential (Ψw) after some investigators (Bates & Hall, 1981; Blackman & Da vies, 1985; Eavis & Taylor, 1979; Gollan, Passioura & Munns, 1986; Termaat, Passioura & Munns, 1985; Turner, Schulze & Gollan, 1985) observed that roots in water deficient media can affect shoot physiology in ways not involving the Ψw of the shoot. As a result, some investigators (Sinclair & Ludlow, 1985; Passioura, 1988) question the Ψw concept on the grounds indicated by Passioura (1988): if roots affect shoot activity by means other than by changing shoot Ψw, the Ψw concept must be wrong. This is unfortunate. It has been known for years that metabolic reactions generally do not respond directly to the Ψw or its components. Nevertheless, the shoot Ψw, and its components play important roles in the physiology and metabolism of plants. Often these roles are interactive with roots. In what follows, I will review some of the evidence for these principles.
Histochemistry, ultrastructure and possible significance of dead parenchyma cells with specialized walls in the leaf and rhizome of Sansevieria
Authors: ALFANI A. , LIGRONE R. , FIORETTO A. , DE SANTO A. VIRZO
Published: April 2006

Abstract. The internal parenchyma of the leaf and rhizome in 36 species of Sansevieria is made of dead cells and living cells arranged in a regular pattern. Intercellular spaces are lacking. The walls of dead cells consist of an inner amorphous layer positive to the fluorescence test for callose, a middle suberin‐like layer and an outer fibrillar layer. In about half of the species examined, the inner layer forms distinctive thickenings. Detached leaves of Sansevieria lose water very slowly, and are able to recover it quickly. The pattern of leaf dehydration appears to be related to leaf morphology, whereas no relation is evident between the pattern of leaf rehydration and leaf morphology. Neither leaf dehydration nor leaf rehydration pattern is affected by the presence of wall thickenings in the dead parenchyma cells. The fresh weight per unit volume of both turgid and droughted leaves is nearly 1, denoting that the dead cells are filled with water and do not undergo substantial cavitation during drought. The data indicate that the dead parenchyma cells of Sansevieria are a specialized water‐storing system.
Cartesian‐diver microrespirometry: a technique for the accurate measurement of respiratory flux in plant cells
Authors: OWEN J. H. , LAYBOURN‐PARRY J.
Published: April 2006

Abstract. A Cartesian‐diver microrespirometer system is described which can be used to measure respiratory fluxes of oxygen accurately for cells of higher plants in a liquid phase. This microrespirometry technique has been adapted from protozoological and microfaunal studies to plant physiology. The Cartesian‐diver has considerable scope for investigation of oxygen flux in plant cells and has several advantages compared to the oxygen electrode in terms of sensitivity to changing oxygen levels in respiring material. Because the volumes of liquid are small in the Cartesian‐divers, diffusional distances arc measured in micrometres and there is no need for stirring to overcome diffusional problems, thus minimizing the risk of mechanical damage to the experimental material. In addition, only very small quantities of experimental material are required for the Cartesian‐diver which is invaluable where only limited amounts of tissue or numbers of cells can be obtained. Examples of respiratory oxygen consumption by protoplasts from intercalary meristematic regions of light‐grown barley (Hordeum vulgare L.c.v. Patty) seedlings, in response to abscisic and gibberellic acids, are presented. The advantages and disadvantages of Cartesian‐diver microrespirometry compared to oxygen electrodes are also discussed.
Crassulacean acid metabolism (CAM) in high elevation tropical cactus
Authors: KEELEY J. E. , KEELEY S. C.
Published: April 2006

Abstract. Several taxa of cacti are distributed in high elevation tropical alpine habitats between 4000–4700 m in central Peru. This region has a marked dry season with soil water potentials as low as – 25 MPa. The barrel type cactus Oroya peruviana and the low ceaspitose Tephrocactus floccosus (both the typical hairy form and a hairless form) all exhibited diurnal fluctuations of malic acid (10–100 μmol/g FW), indicative of CAM photosynthesis. δ3C carbon isotope ratios were – 13 to – 14 suggesting that for these CAM plants the bulk of the net carbon gain is through night‐time carbon uptake. This occurs in spite of overnight temperatures below 0°C. CAM activity was observed on nights when air temperature dropped to – 8°C and subepidermal temperatures reached as low as –3°C. In central Peru, the typical form of T. floccosus has a dense covering of long silvery white hairs. Comparisons with an adjacent ‘hairless’ form showed that the hairy morph maintained a subepidermal temperature several degrees higher during the night. At a site where the ‘hairless’ morph was rare, the hairy T. floccosus had substantially higher overnight acid accumulation. At another site where the ‘hairless’ morph was abundant, the hairy T. floccosus had substantially lower acid accumulation relative to the ‘hairless’ form.
The influence of simulated shadelight and daylight on growth, development and photosynthesis of Pinus radiata, Agathis australis and Dacrydium cupressinum
Authors: WARRINGTON I. J. , ROOK D. A. , MORGAN D. C. , TURNBULL H. L.
Published: April 2006

Abstract. Juvenile seedlings, micropropagated plantlets, and adult rooted cuttings of Pinus radiata, together with seedlings of Agathis australis and Dacrydium cupressinum, were grown under either high (670/μmol m−2 s−1) or low (200 μmol m−2 s−1) photosynthetic photon flux density (PPFD) and, at low PPFD, under three red:far‐red (R/FR) conditions, approximately simulating canopy shadelight, daylight and one intermediate value. In all types of P. radiata, a shade‐intolerant species, stem height and diameter, stem and needle dry weight, and apical dominance were markedly increased by a reduction in R:FR ratio while fascicle density was decreased. In contrast, these increases were considerably less for the shade‐tolerant D. cupressinum and moderately tolerant A. australis. With the exception of the P. radiata seedlings, height growth was greatest in all species under high compared to low PPFD for daylight R:FR ratio conditions. Total shoot (or plant) dry weight was increased approximately two‐fold in all species and types by the higher PPFD. Shoot extension rates were negatively correlated with calculated phytochrome photoequilibrium with P. radiata, the most shade‐intolerant species, having the highest change in rate per unit change in photoequilibrium (i.e. very responsive), and D. cupressinum, the most shade tolerant species evaluated, having the smallest change (i.e. largely unresponsive). Within the spectral quality treatments at low PPFD, it is suggested that higher rates of dry matter accumulation under the low R:FR ratio were the result of reduced mutual shading of adjacent leaves as a consequence of photomorphogenically‐controlled internode lengths rather than of enhanced photosynthesis per se. The significance of the results is discussed in relation to planting stock management in nurseries, the management of forest canopies for understorey seedling growth, and to the construction of representative growth simulation models. Consequences for controlled environment lighting are also considered.
Characterization and propagation of acoustic emission signals in woody plants: towards an improved acoustic emission counter
Authors: TYREE M. T. , SPERRY J. S.
Published: April 2006

Abstract. The physics of ultrasonic acoustic emissions (AEs) was investigated for AE transmission through wood and transducers. The physical properties measured were velocity, attenuation and frequency composition of AEs produced by two sources: cavitation events in xylem and pencil lead breaks. The authors also measured the relative sensitivity of various combinations of ultrasound transducers and amplifiers to aid in the selection of a measuring system optimized for cavitation detection in woody plants. Some of the authors' conclusions are: (1) Softwoods (Thuja, Pinus) attenuate AEs more rapidly than hardwoods (maple, birch). (2) The velocity of AEs in wood exceeds that measured by others in water so the main medium of AE transmission must be the cellulose. (3) The strongest frequencies of AEs are in the range of 100–300 kHz. (4) Cavitation‐induced AEs tend to shift to higher frequency as wood dehydration progresses. (5) One cannot determine the locus of origin of AEs from its frequency composition. (6) The frequency composition of the acoustic emissions probably cannot be determined at all with the sensors used because of their tendency to ‘ring’. The data collected in this paper were used to aid in the design of an improved AE counter having a seven‐fold increase in signal to noise ratio compared to counters previously used in our laboratory. The improved counter, model 4615 Drought Stress Monitor, is now commercially available from Physical Acoustics Corp., Princeton, NJ, U.S.A.
Wall extensibility, wall pH and tissue osmolality: significance for auxin and ethylene‐enhanced petiole growth in semi‐aquatic plants
Authors: RIDGE I. , OSBORNE D. J.
Published: April 2006

Abstract. Auxin and ethylene both enhance cell elongation in intact petioles of the semi‐aquatic plants Regnellidium diphyllum and Nymphoides peltata. The authors now show that auxin but not ethylene increases the in vitro extensibility of cell walls. No response to ethylene occurs in auxin‐depleted tissue. Neither hormone regulates cell expansion by direct control of internal osmolality (OS). During growth of segments, OS (and hence turgor) declines rapidly over the first 5–6 h with a net loss of osmotic solutes. Thereafter, an apparent threshold OS is maintained with net gains in osmostic solutes (Nymphoides) or further net losses (Regnellidium). Although wall extensibility determines initial rates of hormone‐induced cell expansion, the primary control of wall loosening appears to differ in the two species. Nymphoides shows typical ‘acid growth’, and fusicoccin, auxin and ethylene (with auxin) all enhance proton secretion. In Regnellidium, neither low pH nor fusicoccin (FC) alters the rate of cell expansion, although proton secretion is stimulated by FC. Stress relaxation studies using low pH treatment of living or frozen‐thawed segments show increases in the extensibility of walls in vitro for Nymphoides but not for Regnellidium. The authors propose that extensibility may be controlled by wall pH in Nymphoides but the availability of effective wall‐loosening sites determines extensibility in Regnellidium.
Nitrate availability and shoot area development in small willow (Salix viminalis)
Authors: JAMES A. , McDONALD S.
Published: April 2006

Abstract. The effect of nitrate supply upon leaf area development in willow (Salix viminalis) was investigated. Rooted cuttings were grown in culture solution at two different rates of exponentially‐increasing nitrate supply and with free access to other nutrients. During the lag‐phase in attaining stable nutrition, the rate of production of unfolded leaves, in the treatment with poorer N‐supply, decreased. After acclimation to the different N‐availabilities, the rate of dry matter increase per plant nitrogen was constant and the same in both treatments. The ratio of total leaf area to total amount of nitrogen in the plant was slightly higher in the treatment with poorer nitrogen supply. During the exponential (stable) phases of growth, nearly all the increase in total leaf area was attributable to main‐stem leaves; large numbers of leaves on axillary shoots in the treatment with better N‐supply contributed little to the total area. During the stable growth phase, the rate of production of unfolded leaves was the same in both treatments. Higher maximum values of relative rate of increase in area of single leaves were found with a better N‐supply and at higher leaf positions on the main stem. The duration of leaf expansion was not much affected by N‐supply. Final leaf size was greater at higher positions on the main‐stem. Within a treatment (investigated for poorer N‐supply), differences in final leaf size were proportional to differences in numbers of epidermal cells. Final leaf size was greater, at the same node, in the treatment with better N‐supply. Better N‐availability had increased the final size but not the number of epidermal cells. It was concluded that the higher exponential rate of total area increase with a better N‐supply was largely associated with higher rates of expansion in epidermal cells.
Epidermal conductance, stomatal density and stomatal size among genotypes of Sorghum bicolor (L.) Moench
Authors: MUCHOW R. C. , SINCLAIR T. R.
Published: April 2006

Abstract. The ability of a plant to survive severe water deficits depends on its ability to restrict water loss through the leaf epidermis after stomata attain minimum aperture. At this stage, the rate of water loss is regulated by the epidermal conductance (gc). Low gc would be a useful selection criterion to identify genotypes with enhanced survival capability. Consequently, variation in gc among Sorghum bicolor (L.) Moench genotypes was evaluated. Since there is little conclusive evidence linking gc with leaf waxiness, alternative hypotheses relating gc to stomatal trails were also examined. Epidermal conductance varied from 6.3 to 17.6mmol m−2 s−1 among sorghum genotypes. It was unrelated to stomatal pore length which varied with genotype and to pore depth which was similar for all genotypes measured. However, gc, increased with increasing stomatal density. This indicates that stomatal density plays a direct role in water loss even at very low conductances. The association of low stomatal density with low gc is consistent with the hypothesis that at the smallest stomata aperture, water loss from the epidermis above guard cell teichodes becomes a significant source of leaf water loss. Since low gc is directly related to crop survival under severe water deficits, it is recommended that genotypes with low gc. be selected using the selection criterion of stomatal density.
Leaf wall yield threshold of field‐grown soybean measured by vapour pressure psychrometry
Authors: RANDALL H. C. , SINCLAIR T. R.
Published: April 2006

Abstract. Wall‐yield threshold pressures of growing leaves obtained from field‐grown soybean (Glycine max [L.] Merr.) plants were measured in vapour pressure psychrometers. The plants were grown either under well‐watered or water deficit conditions. Wall‐yield threshold pressures were measured at night when turgor pressure was expected to exceed the wall‐yield threshold pressure both in drought‐stressed and well‐watered growing leaves. Wall‐yield threshold pressure increased as the area of the growing leaves increased in both treatments. After an 8‐d drought, wall‐yield threshold pressure in leaves which had recently emerged from the meristem was 0.50 MPa, while in well‐watered leaves these values ranged from 0.03 to 0.23 MPa. Upon release from drought, wall‐yield threshold pressure rapidly returned to unstressed values.
Kinetics of thigmocurvature in two tendril‐bearing climbers
Authors: CARRINGTON C. M. S. , ESNARD J.
Published: April 2006

Abstract. Growth of marked zones of watermelon and passion fruit tendrils was measured following brief thigmostimulation. In each case, curvature involved growth promotion on the non‐contact side of the tendril. Substantial shrinkage also occurred on the contact side of the passion fruit tendril but very little shrinkage took place in the watermelon tendril. Curvature was detected 10s and 1 min after the completion of stimulation in watermelon and passion fruit, respectively. The rapidity of this curvature argues against the mediation of the response by plant growth substances.
Ascorbate free radical enhances vacuolization in onion root meristems
Authors: HIDALGO A. , GONZALEZ‐REYES J. A. , NAVAS P.
Published: April 2006

Abstract. Ascorbate free radical (AFR) induced cell elongation in merislems of Allium cepa roots by promoting a high vacuolization as shown by the increased vacuole volume, vacuole volume density, tonoplast surface and tonoplast surface density. Accordingly, both plasma membrane‐ and tonoplast‐associated ATPases and vacuole soluble acid phosphatase of meristematic cells were also increased. Neither the other subcellular organelles nor cell proliferation appeared to be significantly affected. It is suggested that AFR may be involved in some plasma membrane events related to the initiation of plant cell elongation.
A model of nitrogen flows in grassland
Authors: THORNLEY J. H. M. , VERBERNE E.L.J.
Published: April 2006

Abstract. The model comprises three submodels, which together give an integrated picture of nitrogen pools and fluxes in grassland under grazing or cutting. The first submodel represents the interaction of the grazing animal with the sward through intake and the production of excreta: the second is concerned with the growth of the vegetative grass crop and its response to light, temperature and nitrogen; these two submodels are interfaced with a submodel of soil carbon and nitrogen pools and processes, including dead shoot and root material, dead and live soil organic matter, and three pools representing mineral nitrogen. No account is taken of water, which is assumed to be non‐limiting, or the possible effects of soil pH and soil aeration. The model is used to simulate a range of management strategies as applied to stocking density and fertilizer application, examining both steady‐state and non‐steady‐state conditions. The model highlights the long time scales associated with grassland systems, the role of the grazing animal in modifying carbon and nitrogen flows, and the importance of soil conditions to grassland productivity and fertilizer response. The productivity of grazed swards may be greater or less than that of cut swards depending on stocking density and fertilizer application, although nitrogen recovery (as calculated here) is always lower in grazed swards. The model is able to stimulate mineralization and immobilization, and place these in the context of plant processes and the grazing animal.
Variation in stomatal aperture in leaves of Avena fatua L. observed by low‐temperature scanning electron microscopy
Authors: VAN GARDINGEN P. R. , JEFFREE C. E. , GRACE J.
Published: April 2006

Abstract.A novel technique to record the variability of stomatal aperture over the leaf surface is described. This combines observations of leaf surfaces using low‐temperature scanning electron microscopy (LTSEM), with digital image analysis to produce the most accurate aperture measurements obtained to date. Leaf samples are rapidly immobilized by cryo‐fixation in liquid nitrogen and stored in a purpose‐built cryo‐storage system. Specimens can be collected in the field, remote from the cryopreparation system, and stored for up to several weeks before being examined on the LTSEM. The advantages of this method are that the time frame of the measurements is accurately known, and is identical for all stomatal apertures in a sample, and the precision of the measurements is not limited by the resolving power of the microscope. Measurements of stomatal aperture were obtained from leaves of field grownAvena fatuausing the above procedure. Leaf surface conductance (gsur) was determined by porometry immediately before cryo‐fixation of the same region of the leaf. Measurements of aperture size showed a high degree of variability within each specimen, with coefficients of variation similar to those found in previous studies. Stomatal conductance (gs) was calculated from stomatal dimensions using formulae derived elsewhere. A linear regression between the computed values of gsand porometric estimates of gsurshowed good agreement with the regression line passing through the origin with a slope of 1.0 (R2=0.96). Applications of the experimental system are discussed.
Physiological effects of long‐term exposure to low and moderate concentrations of atmospheric NH3 on poplar leaves
Authors: VAN HOVE L. W. A. , VAN KOOTEN O. , ADEMA E. H. , VREDENBERG W. J. , PIETERS G. A.
Published: April 2006

Abstract. Poplar shoots (Populus euramericana L.) obtained from cuttings were exposed for 6 or 8 weeks to NH3 concentrations of 50 and 100 μgm−3 or filtered air in fumigation chambers. After this exposure the rates of NH3 uptake, transpiration, CO2 assimilation and respiration of leaves were measured using a leaf chamber. During the long‐term exposure also modulated chlorophyll fluorescence measurements were carried out to obtain information about the photosynthetic performance of individual leaves. Both fluorescence and leaf chamber measurements showed a higher photosynthetic activity of leaves exposed to 100 μg NH3 m−3. These leaves showed also a larger leaf conductance and a larger uptake rate of NH3 than leaves exposed to 50 μg m−3 NH3 or filtered air. The long‐term NH3 exposure did not induce an internal resistance against NH3 transport in the leaf, nor did it affect the leaf cuticle. So, not only at a short time exposure, but also at a long‐term exposure NH3 uptake into leaves can be calculated from data on the boundary layer and stomatal resistance for H2O and ambient NH3‐concentration. Furthermore, the NH3 exposure had no effect on the relation between CO2‐assimilation and stomatal conductance, indicating that NH3 in concentrations up to 100 μg m−3 has no direct effect on stomatal behaviour; for example, by affecting the guard or contiguous cells of the stomata.
Carbon dioxide enrichment reduces shoot growth in sweet chestnut seedlings (Castanea sativa Mill.)*
Authors: MOUSSEAU M. , ENOCH H. Z.
Published: April 2006

Abstract. Two‐year‐old potted sweet chestnut seedlings were grown at 350 ppm CO2 and 700 ppm, day and night in constantly ventilated tunnels during two full growing seasons, near Paris, France (48° N, 2° E). Enrichment with CO2 caused an unusual shoot growth response. After the end of July, stem elongation ceased in 62% of the CO2 enriched plants as compared with 37% in the control. The leaves of CO2‐enriched seedlings showed early senescence, indicated by premature yellowing and a decrease in chlorophyll content. This was associated with nutrient dilution brought about by the rapid growth of these trees. The increase in total dry weight of the CO2‐enriched seedlings was essentially the result of increase in the root dry weight (69%). Shoot weight decreased by 22% relative to the control. Total leaf area per enriched plant was 25% smaller than the control. This unusual pattern of growth and carbon allocation of the CO2 treated Chestnut trees emphasizes the concept of a response specificity within trees to an increase of atmospheric CO2.
The effect of soil drought on water‐use efficiency in a contrasting Great Basin desert and Sierran montane species
Authors: DeLUCIA E. H. , HECKATHORN S. A.
Published: April 2006

Abstract. The effect of soil drought on water‐use efficiency (WUE) and water relations was examined for potted Artemisia tridentata Nutt. and Pinus ponderosa Laws., a dominant Great Basin desert shrub and a Sierran montane tree, respectively. Before the onset of drought, A. tridentata had slightly higher photosynthetic rates than P. ponderosa and A. tridentata maintained positive photosynthetic rates at substantially lower water potentials (Ψ). Complete stomatal closure and cessation of photosynthesis occurred at a Ψ of ca. −2.5 MPa for P. ponderosa and less than −5.0 MPa for A. tridentata. Repeated drought cycles caused a small increase in bulk modulus of elasticity for A. tridentata and neither species exhibited significant osmotic adjustment. WUE was similar at Ψ≥−1.0 MPa but as Ψ decreased P. ponderosa consistently maintained higher WUE than A. tridentata. The primary factor contributing to higher WUE for P. ponderosa was the rapid decrease in stomatal conductance with decreasing Ψ. Comparatively low WUE for A. tridentata, a drought tolerant species, suggests that efficient use of water is a conservative ecophysiological ‘strategy’ that can be detrimental in a competitive water‐limited environment. The combination of profligate use of water and a high degree of drought tolerance may be a more successful combination of physiological characteristics in certain dry habitats.
Comparison of photosynthesis and productivity of Gunnera tinctoria Molina (Mirbel) with and without the phycobiont Nostoc punctiforme L.
Authors: OSBORNE B. A.
Published: April 2006

Abstract. Marked increases in growth and nitrogen content were found with Gunnera tinctoria Molina (Mirbel) plants infected (+Nostoc) with the cyanobacterium Nostoc punctiforme L., in comparison to uninfected (—Nostoc) plants and this was attributed to N2‐fixation by the phycobiont. Whilst host and symbiont can be grown separately, preliminary data indicates that the host plant is reliant on the cyanobacterium to meet its nitrogen requirements because it has little capacity to assimilate nitrate. Although the maximum light‐saturated rate of photosynthesis was higher in the +Nostoc plants, there was no reduction in photosynthetic efficiency under lightlimiting conditions, despite marked differences in plant nitrogen status. Differences in photosynthetic rate were implicated as the major reason for the differences in plant productivity. Stomatal conductance was insensitive to changes in plant nitrogen status and did not parallel the variation in photosynthetic rates. The ecological significance of the largely invariant stomatal response and the consequences of differences in water and nitrogen‐use efficiencies between + and —Nostoc plants is discussed.
Heat shock proteins in Sorghum bicolor and Pennisetum americanum I. genotypic and developmental variation during seed germination
Authors: HOWARTH C.
Published: April 2006

Abstract The capacity to synthesize heat shock proteins (HSPs) during seed germination of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum) has been examined. HSP synthesis is detectable in a thermotolerant genotype of sorghum during the first hour of imbibition of the seed under high temperature stress. A non‐coordinate control of HSP synthesis during germination was revealed. Genotypic differences were manifest in the stage of germination at which the ability to synthesize HSPs was first apparent and this related to the thermosensitivity of that genotype.
Assessing the phytotoxicity of mononuclear hydroxy‐aluminum
Authors: KINRAIDE T. B. , PARKER D. R.
Published: April 2006

Abstract Al3+ is an important rhizotoxic ion in acid soils around the world. Al3+ is in equilibrium with mononuclear hydroxy‐Al species, such as AlOH2+ and AL(OH)2+, but the toxicity of these species has not been determined. Polynuclear Al may also coexist with Al3+, and one of these species, AlO4Al12(OH)24(H2O)1274, is very toxic. In order to determine the toxicity of mononuclear hydroxy‐Al we have reanalysed the results of previously published, solution‐culture experiments and have performed new experiments. Several problems are inherent in these studies. At pH values less than 5.0, the activities of the mononuclear hydroxy‐Al species are low relative to Al3+, but attempts to change the ratio by raising the pH generally initiate the formation of polynuclear Al. (We discovered that mononuclear solutions are stable for many days when {Al3+}/{H+}3≤ 108.8, where braces denote activities.) We avoided, or accounted for, polynuclear Al in our studies. In addition, we used up‐to‐date equilibrium constants to compute Al species, very simple culture media (generally containing CaCl2, AlCl3 and HCl as the only inputs), short‐term (2d) growth, and an Al‐sensitive wheat variety (Triticum aestivum L. cv. Tyler) that permitted low Al levels and, consequently, higher pH values without Al polymerization. Experiments were designed in which the solutions were constant in {Al3+} and variable in mononuclear hydroxy‐Al or were orthonal (factorial) in {Al3+} and {AlOH2+}. Linear and nonlinear, simple and multiple, regression analyses of these and previous experiments failed to reveal any toxicity for mononuclear hydroxy‐Al to Tyler wheat.
The fate of vitamin D3 and indolylbutyric acid applied to cuttings of Populus tremula L. during adventitious root formation
Authors: PYTHOUD F. , BUCHALA A. J.
Published: April 2006

Abstract Treatment of green cuttings of Populus tremula L. with vitamin D3 enhances adventitious rooting and synergy is observed on simultaneous application with indolylbutyric acid. Translocation experiments with labelled vitamin D3 and IBA, fed to the base of the cuttings, showed that such synergy was not due to an effect of one substance on the translocation of the other. When indolylbutyric acid was fed to the base of the cuttings, a high proportion was rapidly converted into conjugates which, on saponifaction, released inter alia indolylbutyric acid, but no indolylacetic acid. On the other hand, vitamin D3 was metabolized to give products similar to those produced in non‐sterile aqueous solutions of vitamin D3 stored under the conditions of culture of the cuttings. Such a mixture is as effective as vitamin D3 itself in promoting adventitious rooting. A preliminary examination of the products showed that extensive oxidation of vitamin D3 had occurred and some of the individual components were synthesized and tested for their effect on rhizogenesis in P. tremula.
Cold tolerance in sporobolus virginicus (L.) Kunth robust form, tissue cultures and whole plants
Authors: STRAUB P. F. , GALLAGHER J. L.
Published: April 2006

Abstract Sporobolus virginicus (L.) Kunth robust form, is a coastal C4 grass species in tropical and subtropical regions. An artificial freeze test was used to determine the response of tissue exposed to low temperature. The response was monitored by three methods: measuring respiration rates as carbon dioxide flux before and after freezing, conducting a triphenyl tetrazolium chloride (TTC) viability assay, and observing growth of tissue cultures and the regrowth of shoots and roots from rhizome buds. The TTC assay overpredicted the survival temperature in rhizomes, when based on a 50% of control as lethal value, but was a good indicator of survival in callus and suspension cultures. Respiration rates of callus tissue declined with low temperature exposure and paralleled the TTC results. Rhizome tissue however had a more complex respiratory response. High, post‐freeze, respiration rates during thawing of rhizomes at + 5.0°C were correlated with injury, detected both by a TTC assay and by the measurement of carbon dioxide flux. High respiration rates, measured after the thawing period, due to disabled rhizomes that were ultimately inviable, provide an explanation for the overprediction of the TTC assay. S. virginicus was found to be freeze‐sensitive, LT50= ‐ 2.5°C, with no hardening ability and it was concluded that cellular resistance defines the limits of freezing tolerance. However, avoidance of freezing strain through an underground perenniating organ probably allows S. virginicus to survive on the polar end of its range where episodic frosts may decrease temperatures to the lower limits of the cellular tolerance of a species.
The formation and distribution of ice within dormant and deacclimated peach flower buds
Authors: ASHWORTH E. N. , DAVIS G. A. , WISNIEWSKI M. E.
Published: April 2006

Abstract A freeze‐fixation technique was used to examine the distribution of ice crystals and the pattern of freezing in peach flower buds. In dormant buds, ice crystals formed at localized sites within the bud axis and scales. Ice crystal formation disrupted tissues and mechanical injury from repetitive freezethaw cycles was apparent. There was evidence of ice formation in the floral organs of dormant buds exposed to −25°C but none observed in buds exposed to either −5 or −10°C. The distribution of ice crystals was different in deacclimated buds. In addition to large ice crystals within the subtending bud axis and scales, evidence of large crystals within the developing floral organs was noted. These crystals were most prominent in the lower portions of the developing flower and peduncle, and caused a separation of the epidermal layer from adjacent cells. The distribution of ice crystals within both dormant and deacclimated peach flower buds corroborated the results of previous thermal analysis experiments.