bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt‐tolerance in plants. II. In vitro translation of m‐RNAs from salt‐tolerant and salt‐sensitive plants on wheat germ ribosomes. Responses to ions and compatible organic solutes
Authors: GIBSON T. S. , SPEIRS J. , BRADY C. J.
Published: April 2006

Abstract Messenger RNA from salt‐sensitive and salt‐tolerant plants Triticum aestivum. Beta vulgaris, Pisum sativum, Chenopodium album and Atriplex nummularia was translated in vitro in a wheatgerm translation system. The optimal monovalent and divalent ion concentrations for translation were independent of the salt tolerance of the plants from which the m‐RNAs were derived. Translation was optimal in 100 120 mol m−3 potassium acetate and 1.5–2.0 mol m−3 Mg2+. Substitution of Na+ for K+, or of Cl− for acetate, was inhibitory. The pattern of polypeptides synthesized from cytoplasmic m‐RNAs of salt‐sensitive and salt‐tolerant plants remained constant in all the conditions examined. The effects of adding the ‘compatible' organic solutes glycine‐betaine and mannitol were examined in the wheat‐germ system primed with RNA from the leaves of Triticum aestivum or Beta vulgaris. The rate of translation, the optimum ionic concentrations and the distribution of polypeptide products were maintained in organic solute concentrations of up to 500 mol m−3. Proline above 300 mol m−3 and surcose above 100 mol m−3 did inhibit translation. The results indicate that translation in plants is unlikely in cytoplasmic K+ concentrations exceeding 180 mol m−3, but would proceed in the presence of up to 500 mol m−3 mannitol or glyinebetaine, or of up to 300 mol m−3 proline.
Environmental and genetic control of crassulacean acid metabolism in two crassulacean species and an F1 hybrid with differing biomass δ13C values
Authors: TEERI J. A. , GUREVITCH J.
Published: April 2006

Abstract The growth, biomass δ13C values, and ability to accumulate titratable acidity at night were compared in eight environmental treatments for Cremnophila linguifolia, Sedum greggii, and their F1 hybrid. In the phytotron, differences in treatment daylength, day/night temperature and water availability were all found to have effects on total plant dry weight, nocturnal accumulation of titratable acidity and biomass δ13C value of at least some of the genotypes. However, there were differences between the genotypes both in the magnitude and direction of response of the phenotypic properties to the treatment variables. The phytotron δ13C values ranged from ‐12.9 to ‐19.2‰ for C. linguifolia, from ‐22.2 to ‐33.4‰ for S. greggii, and from ‐19.2 to ‐24.9‰ for the hybrid. After with‐holding water for 76 h both C. linguifolia and the hybrid had midday Ψleaf values of ‐0.23 MPa; however, S. greggii had a value of ‐1.05 MPa. In contrast to past observations of other species, the daily watered plants of C. linguifolia had less negative δ13C values than did the plants watered only weekly.
Differences between tree species in hydraulic press calibration of leaf water potential are correlated with specific leaf area
Authors: HUNT E. RAYMOND , WEBER JAMES A. , GATES DAVID M.
Published: April 2006

Abstract To determine the usefulness of the J‐14 Hydraulic Press (Campbell Scientific, Inc., Logan, Utah, U.S.A.) in estimating leaf water potential, we calibrated the J‐14 Press against a Scholander‐type pressure chamber for leaves of various tree species. The species tested were: Acer saccharum, Acer negundo, Acer rubrum. Populus tremuloides, Populus grandidentata, Quercus rubra, and Brassaia actinophylla (Schefflera). The regression calibrations were linear with standard errors about the regression less than 0.1 MPa. The regression equations for the four genera were significantly different, with the y‐ intercept increasing and the slope decreasing in order of decreasing specific leaf area (SLA). There were no significant differences between species of the calibration lines within the genera Acer and Populus. These data may indicate that leaves with lower SLA resist mechanical compression by the hydraulic press, causing the J‐14 Press to be less sensitive to differences of leaf water potential. Therefore the J‐14 Press is only a relative measure of leaf water status and does not measure leaf water potential.
Changes in plasmalemma organization in cowpea radicle during imbibition in water and NaCl solutions
Authors: BLISS RICHARD D. , PLATT‐ALOIA K. A. , THOMSON W.W.
Published: April 2006

Abstract Freeze‐fracture electron microscopy of the plasmalemma of dry cowpea radicle cells disclosed a normal‐appearing membrane with a high area density of intramembraneous particles (IMPs). Seeds imbibed in either water or salt solution exhibited decreased area density of IMPs, but water‐imbibed tissue showed the greatest decline. Mean particle size increased with hydration but not enough to suggest aggregation as the cause for this density decrease. Calculations of plasmalemma area expansion during imbibition show that such expansion can account for the decrease in IMPs per unit area in the cytoplasmic side (PF) of the membrane in water‐imbibed, but not in salt‐imbibed, tissue. During imbibition, there is a change in the ratio of IMPs per unit area of the PF versus EF (external) membrane faces, suggesting a relative increase in the number of EF particles. These changes in membrane structure are probably not related to any decrease in membrane permeability during the early phases of imbibition.
Concurrent measurements of stem density, leaf and stem water potential, stomatal conductance and cavitation on a spaling of Thuja occidentalis L.
Authors: DIXON M. A. , GRACE J. , TYREE M. T.
Published: April 2006

Abstract Concurrent estimates of stem density, leaf and stem water potential, stomatal conductance and ultrasonic acoustic emissions (cavitations) in an excised sapling of Thuja occidentalis L. were made. As the sapling dehydrated in air, the decline in leaf water potential to about ‐ 2.0 MPa was followed by apparent rehydration of the foliage while the stem showed no sign of rehydration. The rate of acoustic emissions peaked prior to the onset of rehydration which coincided with virtual stomatal closure. There was a significant decline in stem density until maximum foliage rehydration level was reached. From this point, leaf water potential, stem water potential and stem density continued a relatively slow decline while acoustic emission rate and stomatal conductance remained low.

Removal of the bark and majority of foliage from the sapling resulted in increased cavitation and more rapid deelines in leaf and stem water potential and stem density.
The use of light‐induced absorbance changes at 820 nm to monitor the oxidation state of P‐700 in leaves
Authors: HARBINSON J. , WOODWARD F. I.
Published: April 2006

AbstractThe use of the light‐induced absorbance change at 820 nm (ΔA 820) to monitor the oxidation and reduction of P‐700 in irradiated leaves is examined. Results obtained from leaves irradiated with a range of wavelengths of light, poisoned with DCMU, or lacking PS I, are consistent with the proposition that the light‐induced ΔA 820 can be used to monitor P‐700 oxidation in leaves.
An analysis of the accumulation of water and dry matter in tomato fruit
Authors: HO L. C. , GRANGE R. I. , PICKEN A. J.
Published: April 2006

Abstract Previously published data from tomato plants grown in nutrient solutions having one of three electrical conductivities (2, 12 and 17 mS cm−1) were analysed. The rate of water import into the fruit, and the proportion of this conducted by the xylem stream were calculated from the daily rates of transpiration and the net accumulation of water and calcium. The rate of water import decreased as the conductivity of the nutrient solution rose, the maximum daily import rates in the third week after pollination being 3.2, 3.0 and 1.8 g fruit−1 d−1 for fruit grown at 2, 12 and 17 mS cm−1, respectively. During fruit development, the proportion of water imported via the xylem fell from 8–15% to 1–2% at maturity. The principal source of water for tomato fruit growth was phloem sap. Based on the daily rates of net dry matter accumulation, respiration and phloem water import, the calculated dry matter concentration of the phloem sap declined from 7 to 3%, or from 12.5 to 7.8% during fruit development in low or high salinity, respectively. The similar dry matter accumulation of fruit grown at different salinities was due to changes in both volume and concentration of phloem sap. Potassium salts in tomato fruit were calculated lo have contributed –0.29, –0.48 and –0.58 MPa to total fruit osmotic potential in the 2, 12 and 17 mS cm−1 treatments, respectively, which accounted for 38% or 49% of the measured total osmotic potential of the 2 mS cm−1 or 17 mS cm−1 treatments. The contribution of hexoses to total fruit osmotic potential in the young fruit was from about –0.1 to –0.2 MPa at all salinities. The osmotic potential of tomato fruit is regulated more by potassium salts than by hexoses.
Glycerol cycle enzymes and intermediates during adaption of Dunaliella teriolecta cells to hyperosmotic stress
Authors: BELMANS D. , VAN LAERE A.
Published: April 2006

Abstract Dunaliella tertiolecta cells subjected to a hyperosmotic shock of 0.930 osmol kg−1 start almost immediately to synthesize glycerol at a rate of some 100 nmol min−1 mg protein−1. Glycerol synthesis was equally fast in both light and darkness, and was not affected by the nature but only by the concentration of solutes. During the period of rapid glycerol synthesis, which lasted about 1h, the concentration of glycerol‐3‐phosphate transiently increased. During the same period, ATP, fructose 1‐6‐bisphosphate, and triosephosphate content decreased markedly, especially when 0.1 kmol m−3 NaCl‐grown cells were used. The content of hexose‐6‐phosphates, nicotinamide coenzymes, and phosphate underwent no dramatic changes. Since no in vitro activity changes of the glycerol cycle enzymes could be detected during the adaptation period, the activity of glycerol‐3‐phosphate dehydrogenase in vivo is probably increased by a change in concentration of its effectors such as ATP.
Stomatal responses to light and humidity in sugarcane: prediction of daily time courses and identification of potential selection criteria
Authors: GRANTZ D. A. , MOORE P. H. , ZEIGER E.
Published: April 2006

AbstractStomatal sensitivities to light and VPD have potential as quantitative selection criteria in programs designed to enhance water‐use efficiency of sugarcane and other crops. These responses were characterized using gas exchange techniques and then simulated by a mathematical relationship describing conductance as a function of photon fluence rates and VPD values. The same form of relationship simulated stomatal responses of well‐watered greenhouse‐ and field‐grown plants. A comparison between simulated and measured conductance values showed a close correlation, indicating that light and VPD responses of stomata are dominant input signals modulating stomatal conductance in sugarcane. Observed conductance of Hawaiian sugarcane in a commerical production area appeared larger than required to support prevailing rates of carbon assimilation, since predicted intercellular CO2was greater than required to saturate its C4photosynthesis. Manipulation of the relationship describing stomatal conductance allowed us to simulate the responses of plants with hypothetically altered stomatal sensitivities to VPD or to light, using micrometeorological data collected in the field. Further simulation indicated that selection for clones with altered stomatal sensitivity to either light or VPD could improve the water‐use efficiency of sugarcane without inhibiting current high levels of productivity.
Direct response of peroxidase isozyme relative mobility to short‐term environmental temperature changes in flax (Linum usitatissimum)
Authors: FIELDES MARY ANN , TYSON H. , GAUDREAULT P.‐R.
Published: April 2006

Abstract Flax plants were transferred from 30°C to 15°C temperatures, and then back to 30°C during their vegetative growth phase. Reciprocal transfers were also made from 15°C to 30°C, and then back to 15°C for an identical period at the same time. Plants were also retained in a constant 30°C or 15°C in growth chambers with identical lighting conditions. The reciprocal transfer period lasted 6 d. The relative mobility (Rm) of an anionic leaf peroxidase isozyme, reflecting its molecular weight/conformation and/or net charge, was monitored over a period starting before the reciprocal transfers and finishing after the return to original temperatures. Two of the four flax types which were studied showed isozyme relative mobility responses related either to the different constant temperatures, or to the transfer from 15°C to 30°C. The responses were not reversible on return to the original lower temperature. Thus, exposure to 30°C, even for a transient 6 d period, produced a one way Rm shift. This suggests a developmental switch‐over in the particular form of peroxidase glycoprotein being synthesized, rather than an adaptive response triggered by external environmental changes.
Light‐dependent damage to photosynthesis in olive leaves during chilling and high temperature stress
Authors: BONGI G. , LONG S. P.
Published: April 2006

AbstractThe leaves of olive are long lived and likely to experience both chilling and high temperature stress during their life. Changes in photosynthetic CO2assimilation resulting from chilling and high temperature stress, in both dim and high light, are investigated. The quantum yield (φ) of photosynthesis at limiting light levels was reduced following chilling (at 5°C for 12 h), in dim light by approximately 10%, and in high light by 75%; the difference being attributed to photoinhibition. Similar reductions were observed in the light‐saturated rate of CO2uptake (Amax). Decrease inAmaxcorrelated with a halving of the leaf internal CO2concentration (ci), suggesting an increased limitation by stomata following photoinhibition. Leaves were apparently more susceptible to photoinhibitory damage if the whole plant, rather than the leaf alone, was chilled. On return to 26 °C, I he photosynthetic capacity recovered to pre‐stress levels within a few hours if leaves had been chilled in high light for 8 h or less, but did not fully recover from longer periods of chilling when loss of chlorophyll occurred. Leaves which were recovering from chilling in high light showed far more damage on being chilled a second time in high light. Three hours in high light at 38 °C reduced φ by 80%, but φ recovered within 4h of return to 26 °C. Although leaves of Olive are apparently less susceptible to photoinhibitory damage during chilling stress than the short‐lived leaves of chilling‐sensitive annual? crops, the results nevertheless show that photoinhibition during temperature stress is potentially a major factor influencing the photosynthetic productivity of Olive in the field.
Interaction between CO2enrichment and salinity stress in the C4non‐halophyteAndropogon glomeratus(Walter) BSP
Authors: BOWMAN W. D. , STRAIN B. R.
Published: April 2006

AbstractIncreasing atmospheric CO2may result in alleviation of salinity stress in salt‐sensitive plants. In order to assess the effect of enriched CO2on salinity stress inAndropogon glomeratus, a C4non‐halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm3m−3CO2with 0 or 100 mol m−3NaCl watering treatments. Increases in leaf area and biomass with increasing CO2were measured in salt‐stressed plants, while decreases in these same parameters were measured in non‐salt‐stressed plants. Tillering increased substantially with increasing CO2in salt‐stressed plants, resulting in the increased biomass. Six weeks following initiation of treatments, there was no difference in photosynthesis on a leaf area basis with increasing CO2in salt‐stressed plants, although short‐term increases probably occurred. Stomatal conductance decreased with increasing CO2in salt‐stressed plants, resulting in higher water‐use efficiency, and may have improved the diurnal water status of the plants. Concentrations of Na+and Cl−were higher in salt stressed‐plants while the converse was found for K+. There were no differences in leaf ion content between CO2treatments in the salt‐stressed plants. Decreases in photosynthesis in salt‐stressed plants occurred primarily as a result of decreased internal (non‐stomatal) conductance.
Locating active proton extrusion pumps in leaves
Authors: CANNY M. J.
Published: April 2006

Abstract Stabilized microscopic preparations of an apoplastic fluorescent tracer, sulphorhodamine G (SR), have previously shown it confined to leaf cell walls. SR has a pK of 3.2, is dissociated at normal wall pH, and therefore does not enter cells. In transpiring soybean leaves, the SR showed a major internal water pathway in the walls of the paraveinal mesophyll (PVM), which has been implicated in the temporary storage of protein. Also the SR penetrated the PVM and bundle sheath cells, staining organelles and vacuoles, but not other leaf cells. This implies that sufficient SR is undissociated in these walls to allow penetration, and that the pH of the PVM walls is lower than that of most other cells. It is proposed that proton extrusion pumps are revealed by the low wall pH, and that these pumps are probably involved in collecting ammo acids from the transpiration stream.
Tomato pollen development: stages sensitive to chilling and a natural environment for the selection of resistant genotypes
Authors: PATTERSON B. D. , MUTTON L. , PAULL R. E. , NGUYEN V. Q.
Published: April 2006

Abstract The time during which pollen development is most sensitive to chilling was investigated. Five cultivars of tomato (Lycopersicon esculentum Mill.) bearing flower buds at different stages of development were kept at 7°C for 1 week under 12‐h light periods, during which time growth stopped. After returning the plants to minimum temperatures of 18°C, the presence of chromatin in the pollen was assessed daily as the flowers reached anthesis. The results suggested that there are two stages of acute sensitivity to cold during pollen development, each of which results in cold‐stressed plants having pollen empty of chromatin. The first and most sensitive stage is about 11.2 d (SE = 0.3 d) before anthesis, and this is followed by a second stage of sensitivity about 5.6±0.2 d before anthesis. Flowers that had wholly developed under simulated natural temperatures that decreased diurnally from a maximum of 18°C to a minimum of 7°C also had defective pollen, but pollen of normal appearance was regained within 14°d on return to higher temperatures. Plants of L. esculentum, and a form (LA 1363) of the wild species L. hirsutum from high altitudes in the Andes, as well as F1 and F3 generations of their hybrid, were grown to the flowering stage at an altitude of 600 m in Hawaii and then grown for a further 30°d at 2000 m, where night temperature was below 10°C. The high altitude environment severely affected the quality of pollen produced and its release from the stamen in L. esculentum, but not in L. hirsutum LA 1363. The results with the hybrids suggested that such tropical mountain environments can be used as a natural phytotron in the selection of chilling resistance that is only expressed in the mature plant.
The temperature acclimation of photosynthetic responses to CO2 in Zea mays and its relationship to the activities of photosynthetic enzymes and the CO2‐concentrating mechanism of C4 photosynthesis
Authors: WARD D. A.
Published: April 2006

Abstract Associations between photosynthetic responses to CO2 at rate‐saturating light and photosynthetic enzyme activities were compared for leaves of maize grown under constant air temperatures of 19, 25 and 31°C. Key photosynthetic enzymes analysed were ribulose bisphosphatc (RuBP) carboxylase, phosphoenolpyruvate (PEP) carboxylase, NADP‐malic enzyme and pyruvate, Pi dikinasc. Rates of CO2‐saturated photosynthesis were similar in leaves developed at 19°C and 25°C but were decreased significantly by growth at 31°C. In contrast, carboxylation efficiency differed significantly between all three temperature regimes. Carboxylation efficiency was greatest in leaves developed at 19°C and decreased with increasing temperature during growth. The changes of carboxylation efficiency were highly correlated with changes in the activity of pyruvate, Pi dikinase (r= 0.95), but not with other photosynthetic enzyme activities. The activities of these latter enzymes, including that of RuBP carboxylase, were relatively insensitive to temperature during growth. The sensitivity of quantum yield to O2 concentration was lower in leaves grown at 19°C than in leaves grown at 31°C. These observations support the novel hypothesis that variation in the capacity for CO2 delivery to the bundle sheath by the C4 cycle, relative to the capacity for net assimilation by the C2 cycle, can be a principal determinant of C4 photosynthetic responses to CO2.
Rapid cellular responses to auxin and the regulation of growth
Authors: BRUMMELL D. A. , HALL J. L.
Published: April 2006

Abstract The cellular responses rapidly evoked by auxin are reviewed, and related to a consideration of how growth rate is regulated in excised segments and in whole dicotyledonous plants. Two processes, synthesis of proteins and of cell wall components, are both promoted by auxin and essential for auxin‐stimulated growth, whereas other processes show little promotion by auxin or do not appear essential for growth. Current models for the cellular regulation of growth by auxin are briefly discussed, and a new model presented. Auxin is suggested to act by bringing about a transient increase in cytosolic Ca2+ levels, which through the stimulation of protein kinases converts a cytoplasmic protein factor to an active state capable of binding auxin. The protein‐auxin complex induces mRNA synthesis, which effects the increased synthesis of cell wall components and their incorporation into the wall, resulting in wall loosening and growth. It is proposed that the factor limiting growth in floating excised segments may initially be cell wall pH, but that this is not the case in whole plants and growth is instead mediated by increased protein and matrix cell wall synthesis. Differences are noted between monocotyledonous coleoptiles and dicotyledonous stems in some metabolic processes possibly involved in auxin growth responses, and it is cautioned that observations made on one tissue may not necessarily be applicable to the other. Care should also be taken in applying conclusions drawn from studies on excised tissue to the interpretation of growth regulation in the whole plant.
A computer‐controlled multi‐titration system to study transpiration, OH− efflux and nitrate uptake by intact lettuce plants (Lactuca sativa L.) under different environmental conditions
Authors: BLOM‐ZANDSTRA MARGARETHA , JUPIJN G. L.
Published: April 2006

Abstract An apparatus is described in which water and nutrient uptake (NO−3) and pH were measured and controlled by a microcomputer. Measurements were made twice hourly using appropriate electrodes, both in the nutrient solutions in which the plants were grown and in standard reference solutions. The signals from the electrodes were amplified to a range of 0–10 V and were fed to an A/D converter activated by the computer. The needs for water, NO−3, H+ and OH− were then calculated and the necessary adjustments were made to the solutions by automatic injection of the correct amounts to each container in turn. These amounts were records of water and nitrate uptake and pH shift and were saved on disc. The plants were arranged on a turntable which gave additional benefit by smoothing out variations in light intensity. The system allowed a different solution to be maintained for each plant if required.
Early detection of neighbour plants by phytochrome perception of spectral changes in reflected sunlight
Authors: BALLARÉ C. L. , SÁNCHEZ R. A. , SCOPEL ANA L. , CASAL J. J. , GHERSA C. M.
Published: April 2006

Abstract We have tested the hypothesis that a plant may detect the presence of a neighboug42r, before being shaded by it, through the perception of the spectral composition of reflected sunlight. Within seedling canopies the red: far‐red ratio (R: FR) of the light received by a sensor with a geometry approximating that of a stem was significantly reduced by selective reflection. This effect was observed before any reduction in the amount of photosynthetic light energy received by an individual seedling could be detected. Small green fences of grass, east‐west orientated, altered the spectral distribution of the light on the north (sunlit) side of them. Fully illuminated seedlings of Sinapis alba grown on the north side of these green fences produced longer internodes and had a lower leaf: stem dry weight ratio than those grown in front of fences of bleached grasses. A similar redistribution of growth was elicited in seedlings of Chenopodium album, Datura ferox and S. alba growing in full sunlight by exposing plants to additional small quantities of far‐red reflected by selective mirrors. These results suggest that the change in the R: FR ratio serves as an early warning signal of oncoming competition.
Sodium‐induced calcium deficiency in salt‐stressed corn
Authors: MAAS E. V. , GRIEVE C. M.
Published: April 2006

Abstract The effect of the Na+/Ca2+ ratio in the root media on salt‐stressed corn (Zea mays L. cvs DeKalb XL‐75 and Pioneer 3906) was determined in greenhouse experiments. Plants grown in a complete nutrient solution salinized with 86.5 mol m−3 NaCl exhibited severe Ca2+ deficiency symptoms at the four‐leaf stage. The symptoms disappeared when part of the NaCl was replaced with 10 mol m−3 CaCl2 (Na+/Ca2+ molar ratio = 5.7). Salt stress at an iso‐osmotic potential of −0.4 MPa substantially decreased shoot growth at all solution Na+/Ca2+ ratios from 34.6 to 0.26. However, the dry weights of blades at 26 d of age were much less when plants were salinized with NaCl alone, particularly that of DeKalb XL‐75 which was more susceptible to Na‐induced Ca2+ deficiency than was Pioneer 3906. The growth of sheaths was similarity reduced by sail stress at all Na+/Ca2+ ratios. The symptoms of Ca2+ deficiency were correlated with low Ca2+ concentrations in the leaf tissue. Ca2+ concentrations in the developing blades of NaCl‐stressed plants were much lower than in control plants. As the Na+/Ca2+ ratio in the solution was decreased, Ca2+ levels increased in both the blades and sheaths while Na+ concentrations greatly decreased. DeKalb XL‐75 was much less effective than Pioneer 3906 in restricting the uptake of Na+. The results clearly indicate that NaCl stress may cause lesions and unique plant responses that are not manifested on agronomic plants grown on saline soils.
Root: shoot ratio as a balance between nitrogen productivity and photosynthesis
Authors: ÅGREN G. I. , INGESTAD T.
Published: April 2006

Abstract It is shown how root : shoot ratios can be derived from two plant characteristics, (i) the nitrogen productivity (amount of biomass produced per unit of nitrogen in the biomass and per unit of time) and (ii) the relationship between photo‐synthetic rate and internal nitrogen concentration. Derived root: shoot ratios are compared with experimental data for seedlings of seven tree species grown with stable internal nitrogen concentrations. Agreement is good but more exact knowledge of the relationship between nutrient status and photosynthesis is needed. It is shown that a formula derived for the root: shoot ratio can also be applied under non‐steady‐state conditions.
A convenient screening test system and a model for thermal germination responses of wild plant seeds: behaviour of model and real seeds in the system
Authors: WASHITANI I.
Published: April 2006

Abstract A convenient test system for screening the thermal germination behaviour of seeds was developed for both basic and applied research in seed germination ecophysiology. Only two temperature‐controlled facilities, a test period of about a month and a relatively small number of sample seeds arc needed to obtain information on the thermal‐germination parameters of individual seed populations, such as lower or higher limit temperatures, and thermal times required for germination. In the test system, the germination performances of sample seed populations were compared under two temperature regimes: a gradually increasing temperature regime and a gradually decreasing temperature regime, in which the seeds were subjected to gradually changing temperatures in the range of 4 36°C. In order to assess the effects of various values for thermal‐germination parameters on the patterns of germination performance in the system, the behaviour of model seeds characterized by a definite set of thermal germination parameters were investigated. Referring to the results of the simulations, the actual germination patterns of some wild‐seed populations in the test system were interpreted in terms of thermal‐germination parameters.
Biosynthesis of ethylene in higher plants: the metabolic site of inhibition by phosphate*
Authors: FUCHS YORAM , MATTOO AUTAR K. , CHALUTZ EDO , ROT ILANA
Published: April 2006

Abstract. Phosphate inhibited endogenous as well as 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐stimulated ethylene synthesis in slices of tomato fruit, segments of carrot root and pea hypocotyls. ACC concentrations of up to 10 mol m−3 did not overcome this inhibition. Phosphate inhibited the conversion of 14C ACC to ethylene in tomato fruit and vegetative tissue. Enzymatic conversion of ACC to ethylene by pea seedling homogenate was also inhibited by phosphate with a linear concentration dependency. The formation of ACC from S‐adenosylmethionine (SAM) by extracts of pink tomatd fruit was slightly, but not significantly, affected by phosphate. However, the SAM to ACC conversion was greater when extracts from tomato fruit were made in phosphate rather than in HEPES‐KOH buffer. Non‐enzymatic ethylene synthesis from ACC in a model system was stimulated by phosphate. We suggest that phosphate is an inhibitor of ethylene biosynthesis in higher plants and that one site of its control is the conversion of ACC to ethylene.
Nutrient inflows into apple roots. I. 32P‐orthophosphate uptake from solution by M.9 rootstocks and Worcester Pearmain seedlings
Authors: BHAT K. K. S.
Published: April 2006

Abstract. The rates of uptake of 32P‐labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the 32P‐phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of 32P‐phosphate concentration in solution at the root surface over the range 0.25–10 mmol m−3. The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.

The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m−3. Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm−3. Except perhaps in the case of the low‐P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.

At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low‐P plants than for high‐P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P.
Cell wall architecture: normal development and environmental modification of guard cells of the Cyperaceae and related species*
Authors: MISHKIND M. , PALEVITZ B. A. , RAIKHEL N. V.
Published: April 2006

Abstract. The development and cell wall architecture of guard cells in the Cyperaceae were studied with light and electron microscopy. Development occurs along parallel files and results in a stomatal complex that consists of two guard cells each flanked by a subsidiary cell. The developmental pattern and general morphology are thus similar to that in the Gramineae. Several key differences, however, were observed. Wall synthesis in the Cyperaceae, as observed in the polarization and fluorescence microscope, occurs suddenly, within three to four complexes along a file, but is more gradual in the Gramineae. Mature cell walls in the Cyperaceae predominantly contain microfibrils oriented radially relative to the pore, while those in the Gramineae contain axial microfibrils. This difference was demonstrated in numerous species using freshly‐collected as well as preserved material. In Cyperus esculentus, however, the alignment of microfibrils appears to be subject to environmental modification. Plants grown in the greenhouse contain guard cells with axial microfibrils, compared to the radial arrangement found in those grown in the field. In the former, wall is deposited gradually, as in the Gramineae. On return to more stressful conditions, radially micellated guard cells again develop. In each case, the cortical cytoplasm adjacent to areas where the wall is to thicken contains microtubules oriented parallel to the microfibril alignment characteristic of that treatment. These results are discussed in terms of the role of varied wall architecture in stomatal mechanics, the regulation of cell wall biosynthesis, and the evolutionary relationship of the Cyperaceae, Gramineae, and other taxa.
Effect of water stress on the enzymes of nitrogen metabolism in mung bean (Vigna radiata Wilczeck) nodules
Authors: KAUR AMARJIT , SHEORAN I. S. , SINGH RANDHIR
Published: April 2006

Abstract. Water stress created by withholding irrigation in mung bean resulted in decreased leaf water potential and nodule moisture content. Decreased leaf water potential was associated with decreased activity of nitrogenase, glutamine synthetase (GS), asparagine synthetase (AS), aspartate amino transferase (AAT), xanthine dehydrogenase (XDH) and uricase. However, the activity of glutamate dehydrogenase increased three‐fold under severe stress. The activity of allantoinase and allantoicase was not affected by moderate stress but decreased under severe stress. The in vitro production of allantoic acid from allantoin and uric acid in the cytosol fraction decreased more than its production from xanthine and hypoxanthine. The production of NADH also decreased under stress.

During recovery from severe stress, the activity of XDH and uricase further decreased, whilst that of allantoinase and allantoicase increased compared to the control. This corresponded with the higher content of ureides during recovery. The recovery in other enzymes was not complete although leaf water potential and nodule moisture content recovered fully within 24 h.
Diurnal cycles of leaf extension in unsalinized and salinized Beta vulgaris
Authors: WALDRON L. J. , TERRY N. , NEMSON J. A.
Published: April 2006

Abstract. Continuous high resolution measurement of sugar beet leaf extension over 5 d in growth chambers showed average leaf extension rates (LER) in darkness to be from three to six times those in light for plants growing in non‐salinized media. The changes in LER in light‐dark transitions occurred within seconds, a response which was more rapid than stomatal opening or closing. When the growth medium was salinized to 100 mol m−3 NaCl, LER's were reduced by about 50% in darkness and 90% in light, markedly increasing the ratio of dark to light LER.

A 2‐d episode of root‐zone salinity imposed midway through a 5‐d period of measurement decreased LER and produced higher leaf temperatures. LER and diurnal leaf temperature patterns reverted to their pre‐salinized levels when root‐zone salinity was removed. Thus, the effects of short episodes of high sodium chloride in the growth medium appear to be reversible, suggesting a water stress mechanism of growth reduction rather than toxicity effects of salt.
Morphological and physiological changes in black alder induced by water stress
Authors: SEILER J. R.
Published: April 2006

Abstract. Black alder seedlings were exposed to 12 weeks of sublethal water stress by watering only when visibly wilted. Control seedlings were watered regularly throughout the treatment period. Stressed seedlings exhibited significant osmotic adjustment of over 0.4 MPa. The water stress treatment also significantly reduced leaf size, increased epicuticular wax content, and increased the root shoot ratio. The response of leaf conductance to decreasing leaf water potential was influenced by the previous water stress treatment Stressed seedlings had a much lower initial leaf conductance, but showed a gradual drop in leaf conductance as leaf water potential decreased; whereas, control seedling leaf conductance fell rapidly. These morphological and physiological modifications in response to moisture stress have the potential for significantly improving black alder drought tolerance.
Lignin degradeation by white rot fungi
Authors: HARVEY P. J. , SCHOEMAKER H. E. , PALMER J. M.
Published: April 2006

Abstract. The wood‐degrading white‐rot fungus Phanerochaete chrysosporium, has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood‐degrading fungi in general, attack lignin.
Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content
Authors: WILLIAMS K. , PERCIVAL F. , MERINO J. , MOONEY H. A.
Published: April 2006

Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency (EB). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.

Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.
Leaf Diffusive Conductance and Tap Root Cell Turgor Pressure of Sugarbeet
Authors: PALTA J. A. , WYN‐JONES R. G. , TOMOS A. DERI
Published: April 2006

Abstract. The interrelationships of leaf diffusive conductance, tap root cell turgor pressure and the diameter of the tap root of sugarbeet were studied. The study was conducted on well‐watered plants growing in pots under artificial light in the glasshouse. In a typical experiment, on illumination (400 μmol m−2 s−1) leaf conductance increased from 0.6 to 7.4 mm s−1. Cell turgor pressure in the tap root decreased from 0.8 MPa to 0.45 MPa and the root diameter (9.0 cm) contracted by 145μm. Removal of light resulted in the reversal of each of the above parameters to their previous values. Quantitively similar results were obtained when sugar beet plants were uprooted and the response of each of the parameters was measured. The sequence of events however was different. On stimulation by light, changes in leaf diffusive conductance preceded the turgor and root diameter changes (which were simultaneous) by some 15–20min. In contrast, on uprooting the simultaneous changes in root turgor pressure and diameter preceded the changes in leaf conductance. The lag times between changes in diffusive conductance and turgor pressure in the root were between 20 and 30 min.

Tap root turgor pressure and diameter correlated strongly and permitted the calculation of an apparent whole root volumetric elastic modules (55–63 MPa). The small changes in tissue volume relative to the transpiration rate suggest that the tap root is not a significant source of transpirational water during the day.
Identification of chitinase mRNA in abscission zones from bean (Phaseolus vulgaris Red Kidney) during ethylene‐induced abscission
Authors: GOMEZ LIM M. A. , KELLY P. , SEXTON R. , TREWAVAS A. J.
Published: April 2006

Abstract. Total RNA was extracted from bean leaf abscission zones at different times after the induction of abscission by ethylene. The RNA was translated in the wheat germ system and the products analysed by SDS‐PAGE. Products of molecular weight (raw) 42, 32 and 17 kD were seen to accumulate substantially during the induction. An attempt was made to establish that the mRNA species which produced the 32 kD product, which was coded for the ethylene‐regulated enzyme chitinase. Mature chitinase (30 kD) was purifed from ethylene‐treated abscission zones and used to raise monospecific antibodies in rabbits. These antibodies recognized the 32 kD product and mature chitinase. The 2 kD difference in molecular weight was due to the presence of the signal sequence which could be removed by microsomal membranes. Chitinase was also detected by enzymatic assay and immunoblotting of crude homogenates from ethylene‐treated abscission zones. Chitinase appears to be ubiquitous in bean plants and probably does not have a direct role in abscission.
Water translocation inKalanchoë daigremontianaduring periods of drought
Authors: SCHÄFER C. , LÜTTGE U.
Published: April 2006

Abstract.Kalanchoë daigremontianastrongly reduced daily water loss within 6 d of drought using CAM to restrict transpiration and net CO2uptake to the dark period.

Water translocation from old to young leaves of the plant was an additional mechanism which reduced the negative effects of drought on the water relations of young leaves. Excision of old leaves after 7–9 d of drought resulted in a decrease in the water content of young leaves. This was observed despite a decrease in transpirational water loss from young leaves. Water content in young leaves increased slightly in plants with all their leaves in place.

The dry weight of young leaves clearly increased during the experimental period when old leaves were present, but it remained relatively constant in plants without old leaves. Obviously, in addition to water, solutes were transported from old to young leaves of the plant via the phloem. Xylem tension was higher in young compared to old leaves; thus, water translocation could have occurred via xylem elements.

Since transport of organic matter in the phloem is also linked to water flow, phloem transport additionally may contribute effectively to the balance of the water budget in young leaves.
Concentrations of CO2 and O2 in floodwater and in internodal lacunae of floating rice growing at 1–2 metre water depths
Authors: SETTER T. L. , KUPKANCHANAKUL T. , KUPKANCHANAKUL K. , BHEKASUT P. , WIENGWEERA A. , GREENWAY H.
Published: April 2006

Abstract. Environment and plant measurements were made to determine what factors may limit growth of deepwater and floating rice plants during partial or complete submergence. Field surveys included measurements of temperature, pH, light, O2 and CO2 in floodwater in Thailand. In addition, measurements were made of O2 and CO2 concentrations inside internodal lacunae of deepwater and floating rice growing at 0.5–2.0 m water depths.

The bulk of measurements were taken during periods when the changes in water level were less than 50 mm d−1. In the 0–0.02 m surface layer of floodwater at any location there were large changes in oxygen concentrations over diurnal cycles: there were decreases during the night down to 0.02–0.18 mol m−3 O2 at 0600 h and increases during the day to 0.13–0.28 mol m−3 O2 at 1500 h (0.28 mol m−3 being 120% of the O2 concentration of air saturated water at 30°C). During the day oxygen concentrations decreased with increasing water depth; concentrations just above the soil surface were occasionally zero. Most of this gradient disappeared during the night, and at dawn the 0.6 m surface layer of water had uniform low O2 concentrations.

O2 concentrations were also measured during flash floods in Thailand. In contrast to the conditions with only small increases in water level, the O2 concentrations in the water during flash floods were more uniform with depth and changed little over a diurnal cycle, the O2 ranging between 0.14–0.19 mol m−3.

In most locations floodwater contained 0.2–1.9 mol m−3 CO2 and 0.7–1.6 mol m−3 bicarbonate; however, in a location with acid sulphate soil CO2 was only 0.05–0.2 mol m−3, and bicarbonate concentrations were several fold lower. Concentrations of CO2 in floodwater increased with increasing water depth.

O2 and CO2 concentrations inside internodal lacunae of rice were determined in the field when water depth were 1–2 m. Concentrations of O2 in internodes at the water surface were 16–20%, and decreased to 10% and 5% at 0.8 and 1.8 m water depth respectively. There was no diurnal cycle in O2 concentrations inside internodes. In contrast, CO2 concentrations in the lacunae increased with water depth and ranged from 1–3% in internodes at the water surface to 5–10% in internodes at 1.8 m water depth. There was evidence for a diurnal cycle in CO2 concentrations in the basal internode near the soil surface, CO2 increased during the day and decreased during the night.

The above data are used to show that there is little or no relationship between gas concentrations in floodwater and internodal lacunae of rice plants. Results are discussed in relation to O2 supply to submerged portions of rice and metabolism of these tissues at low O2 concentrations.
The effects of continuous illumination on the function and structure of Micrasterias torreyi Bail. (Conjugatophyceae)
Authors: LEHTONEN J. , VUORIO P. , MÄKI J.
Published: April 2006

Abstract. The division rate of Micrasterias torreyi cells grown under continuous illumination first accelerated but soon slowed down, and the cells lost their ability to divide after about 1 month. During the treatment the cells became pale green, the pyrenoids became fewer in number and defects appeared in the chloroplasts. After 1 month, the cells also soon died, even when subjected to intermittent illumination. The most striking structural alterations were found in the chloroplasts: the starch granules lost their typical structure, the lamellae were damaged and numerous electron dense precipitates appeared in the chloroplasts. The precipitates were similar to those formed in cells treated with supraoptimal external calcium concentrations and X‐ray microanalysis showed that the precipitates were rich in calcium in both cases. The results suggest that light controls and activates the Ca2+ uptake in the plasma membrane as well as in the chloroplast envelope, that the large sized chloroplasts of Micrasterias are effective in regulation of cytoplasmic Ca2+ concentration, and that the injuries caused by continuous illumination may be largely due to the accumulation of Ca2+ in the chloroplasts.