bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosynthetic induction in wheat protoplasts and chloroplasts. Autocatalysis and light activation of enzymes
Authors: LEEGOOD R. C. , WALKER D. A.
Published: April 2006

Abstract Unlike wheat chloroplasts, wheat protoplasts showed a pronounced restoration of the induction phase after a short period of darkness. This difference was used to investigate the relative roles of light‐induced reductive activation of enzymes and the auto‐catalytic increase in the level of substrates in the control of the rate of photosynthesis during induction. Light activation and dark inactivation of ribulose 5‐phosphate kinase, fructose 1,6‐biphosphatase and NADP+‐specific glyceraldehydephosphate dehydrogenase were measured. In this respect there was no appreciable difference between protoplasts and chloroplasts. In contrast, the level of photosynthetic intermediates remained constant in darkened isolated chloroplasts, but declined rapidly in chloroplasts isolated from darkened protoplasts. When fructose 1,6‐bisphosphatase was pre‐activated by treating protoplasts with dithiothreitol the lag was only slightly shortened. These results are discussed in terms of control of the rate of the photosynthesis during the lag by substrates rather than limitation imposed by activity of any of the enzymes measured.
Yield components in Hevea brasiliensis– theoretical considerations
Authors: SETHURAJ M. R.
Published: April 2006

Abstract A theoretical analysis of yield components of Hevea brasiliensis is attempted in this paper. The effect of the major yield components, i.e. initial flow rate per unit length of tapping cut, length of the cut, percentage rubber content and plugging index on rubber yield is represented by the formula

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Variation in yield within and between clones can be ascribed to variation to any one of the above components. The importance of high growth rate for maintaining high yield throughout the life cycle of the tree is theoretically elucidated. While the present contention of a theoretical maximum yield of 9.5 t ha−1 with a stand of 350 trees is questioned, the theoretical possibility of attaining that yield by increasing the stand per ha to 600 is analysed.
Genetic variability and heritability of drought‐induced abscisic acid accumulation in spring wheat
Authors: QUARRIE S. A.
Published: April 2006

Abstract. Twenty cultivars of spring wheat were examined for variation in abscisic acid (ABA) accumulation following partial dehydration of excised leaves. A 3‐fold range of ABA concentration was obtained.

A cross between two cultivars which differed in drought‐induced ABA accumulation was used to study the heritability of ABA accumulation and to develop lines differing in their capacity to accumulate ABA. Broad sense heritability was 0–32 between the F2 and F3 generations and 0–70 between the F3 and F4 generations. Apparent homozygosity for ABA accumulation was achieved in several selections at the F4. The possible significance for drought resistance of differences in capacity to accumulate ABA is discussed.
C4 photosynthesis in Cyperus longus L., a species occurring in temperate climates
Authors: JONES M. B. , HANNON G. E. , COFFEY M. D.
Published: April 2006

Abstract. Cyperus longus L., which has a widespread but disjunct distribution throughout Europe and extends northwards into Britain, was found to be a C4 species based upon its Kranz leaf anatomy, low CO2 compensation point and the labelling of malate as an early product of 14CO2 fixation. The photosynthetic characteristics of C. longus are similar to many other C4 species with a high maximum rate of photosynthesis (> 1.5 mg CO2 m −2 s −1) and a relatively high temperature optimum (30–35°C), but unlike many C4 species the rate of photosynthesis does not decline rapidly below the optimum temperature and a substantial rate (0.6 mgCO2 m−2s−1)occursat 15°C. Leaf extension is very slow at 15°C and shows a curvilinear response to temperatures between 15 and 25°C. Leaves extend at a rate of almost 4 cm d−1 at 25°C.
Regularly aligned mitochondria in aleurone and sub‐aleurone layers of developing rice caryopses
Authors: OPARKA K. J. , GATES P. J. , BOULTER D.
Published: April 2006

Abstract. Mitochondria were found to be aligned along the upper periclinal walls of aleurone and endosperm cells in developing rice caryopses. The significance of this distribution is discussed in relation to previous studies of solute transport in rice.
Nutation in georeacting roots
Authors: HEATHCOTE DAVID
Published: April 2006

Abstract. Re‐analysis of published data on the gecocurvature and nutation of the primary root of maize is presented. This analysis demonstrates clear evidence of nutalional oscillations occurring during georesponse. The importance of this evidence in relation to theories of nutation mechanism is discussed.
Interactions between growth, Cl− and Na+ uptake, and water relations of plants in saline environments. I. Slightly vacuolated cells
Authors: GREENWAY H , MUNNS RANA , WOLFE JOE
Published: April 2006

Abstract. Slightly vacuolated cells, i.e. microalgae and meristematic cells of vascular plants, maintain low Cl− and Na+ concentrations even when exposed to a highly saline environment. The factors regulating the internal ion concentration are the relative rate of volume expansion, the membrane permeability to ions, the electrical potential, and the active ion fluxes.

For ion species which are not actively transported, a formula is developed which relates the internal concentration to the rate of expansion of cell volume, the permeability of membranes to that ion, and the electrical potential. For example, when the external concentration of Cl− is high, and Cl− influx is probably mainly passive, the formula predicts that rapid growth keeps the internal Cl− concentration lower than that in a non‐growing cell with the same electrical potential; this effect is substantial if the plasmalemma has a low permeability to Cl−.

For ion species which are actively transported, the rate of pumping must be considered. For instance Na+ concentrations are kept low mainly by an efficient Na+ extrusion pump which works against the electric field across the membrane. The requirement for Na+ extrusion is related to the external Na+ concentration, the rate of expansion of cell volume, the membrane permeability, and the electrical potential. It is possible that microalgae have a more positive electrical potential than many other plant cells; if so, requirements for high rates of active Na+ extrusion will be lower. The required rates of Na+ extrusion are lower during rapid growth, provided that the permeability of the plasmalemma to Na+ is low.

The energy required for the regulation of Cl− and Na+ concentrations is low, especially in rapidly expanding cells where Na+ extrusion requires only 1–2% of the energy normally produced in respiration. The exclusion of these ions, however, must be accompanied by the synthesis of enough organic compounds to provide adequate osmotic solutes for the increases in volume accompanying growth. This process reduces the substrates available for respiration and synthesis of cell constituents, but the reduction is not prohibitively large—even for cells growing in 750 mol m−3 NaCl, the carbohydrate accumulated as osmotic solute is only 10% of that consumed in respiration.
Sensitivity of tobacco tissue cultures to chloramphenicol and its photodegradation products
Authors: BARG R. , UMIEL N. , NITZAN Y.
Published: April 2006

Abstract. Non‐differentiated tissue cultures (calli) of tobacco were found to be more sensitive to chloramphenicol (CAP) than differentiated tissues (shoots). The difference is especially manifested in darkness and at an irradiation regime lacking u.v. and blue light. Photodegradation of CAP solutions was demonstrated at moderate light fluence rates (6–15 Wm−2). The evidence indicates that the final products of photodegradation may be toxic or non‐toxic according to the irradiation regime. The implication of the present findings in establishing a selection system for resistance to chemicals, and especially CAP, using plant tissue cultures, is discussed.
Enhancement of Pfr‐mediated responses by light pretreatments: persistence of the pretreatment effects
Authors: JOHNSON C. B. , WHITELAM G. C.
Published: April 2006

Abstract. In germinating seedlings of Sinapis alba, nitrate reductase activity is under phytochrome control and becomes accessible to phytochrome at about 15 h from sowing. The induction of the enzyme with pulses of light is strongly affected by pretreatments given prior to 15 h, also acting through phytochrome. It is shown that the effects of these pretreatments can persist undiminished for a considerable time (>40 h) but do not alter the pattern of the subsequent responsiveness to Pfr. The nitrate reductase response is compared with other data pertaining to a similar response.
Direct and indirect effects of light on stomata. I. In Scots pine and Sitka spruce
Authors: MORISON J. I. L. , JARVIS P. G.
Published: April 2006

Abstract.The response of stomatal conductance to broadband blue and red light was measured in whole shoots of Scots pine and Sitka spruce, two species which have low stomatal sensitivity to CO2. In Scots pine, blue light was more than three times more effective than red light (on an incident quantum basis) in opening stomata, particularly at low quantum flux densities (<100μmiol m−2s−1). However, the apparent quantum yield of net CO2assimilation rate in blue light was only half that in red light. The contrasting effects of red and blue light on conductance and assimilation led to higher intercellular CO2concentrations (Ci) in blue light (up to 100 μmol mol−1higher) than in red light. Similar results were obtained with Sitka spruce shoots, though differences in the effectiveness of red and blue light were less marked. In both species, both red and blue light increased conductance in normal and CO2‐free air, indicating that neither red nor blue light exert effects through changes in Cior mesophyll assimilation. However, decreases in Cicaused increases in conductance in both red and blue light, suggesting that these direct effects of light are not wholly independent of CO2.
The dynamics of H+ efflux from the trap lobes of Dionaea muscipula Ellis (Venus's flytrap)
Authors: REA PHILIP A.
Published: April 2006

Abstract. H+ efflux from the trap lobes of Dionaea muscipula Ellis (Venus's flytrap) was measured in vitro. FC, IAA, and 2,4‐D markedly increase the rate of H+ efflux within minutes of their addition to the incubation medium whereas ABA and DES cause the rate to decrease. Consequently, the H+ efflux mechanism of Dionaea is considered to be similar to the H+ extrusion pumps of other higher plants in this respect. However, the H+ extrusion mechanism of Dionaea may be unusual in that long‐term exposure of the trap lobes to known secretion elicitors— bactopeptone, NH4+, Na +, urea, thiourea, glycine or xanthine—also causes a large increase in the steady‐state rate of H+ efflux from the trap lobes. Since the observed H+ effluxes primarily correspond to the adaxial surface of the trap lobes and show similar time‐ and secretion elicitor‐dependencies to the responses seen in situ, it appears that the H+ effluxes measured in vitro bear a direct relationship to those observed in the intact, actively secreting plant.

Three of the secretion elicitors that were tested— K+, NH4+, and urea—have rapid effects on the rate of H+ extrusion in addition to their long‐term effects. K+ and NH4+ cause a rapid acceleration of H+ efflux whereas urea causes a rapid deceleration or, at high external concentrations, reversal of the net flux. The effect of K+ is inferred to result from K+ ‐H+ exchange between the tissue and bathing medium. Studies with structural analogues of NH4+ and urea and inhibitors of the assimilation of reduced nitrogen suggest that the effects of NH4+ and urea result from the pH‐perturbing consequences of their metabolism subsequent to their absorption. These effects are considered to be auxiliary to the elicitation of secretion.

It is proposed that H+ efflux from the trap lobes is mediated by a K+‐H+ exchange mechanism, the activity of which is modified by long‐term exposure to secretion elicitors and/or short‐term exposure to factors which alter the availability of endogenous H+ ions.
Quantum yields for CO2 uptake in some diploid and tetraploid plant species
Authors: OSBORNE B. A. , GARRETT M. K.
Published: April 2006

Abstract. Quantum (photon) yields for CO2 uptake on an absorbed photon fluence rate (PFR) basis (φa) were determined for a number of diploid and tetraploid species under a range of experimental conditions. Little variation in φa was found either between species or across ploidy levels, which suggests that there are no intrinsic differences in the kinetics of CO2 fixation. Variations in photosynthetic rate or quantum yield expressed on an incident PFR basis (φj) were found to be largely due to differences in leaf absorptance. On this basis these results do not support the biochemical evidence showing ploidy‐related differences in the Km (CO2) of ribulose ‐1,5‐bisphosphate carboxylase/oxygenase. However, there are obvious difficulties in relating in vitro enzyme kinetic data to in vivo studies and these problems are discussed.
Kinetic changes with temperature of phosphoenolpyruvate carboxylase from a CAM plant
Authors: BUCHANAN‐BOLLIG IRENE C. , KLUGE MANFRED , MÜLLER DETLEF
Published: April 2006

Abstract.Purified and crude phosphoenolpyruvate carboxylase from the CAM plantKalanchoë daigremontianaHamet et Perrier (Bryophyllum diagremontianum) was assayed at temperatures between 10 and 45° C. The optimum temperature of the enzyme activity changed with substrate availability and effector concentration in the assay.l‐malate inhibited the enzyme activity and lowered the optimum temperature. Glucose‐6‐phosphate raised the optimum temperature to 43°C.Kmvalues for phosphoenolpyruvate increased with assay temperature from 0.12 mol m‐3at 15° C to 0.36 molm−3at 35° C. Inhibition by malate increased with temperature and acidity of the assay. In the crude enzyme 50% of control activity was inhibited by 1.65 mol m‐3malate at 15° C and by 0.5 mol m‐3at 35° C (at pH 7.0). With purification malate sensitivity was lost (Kivalues for malate at least 10 times higher). The shift in optimum temperatures for PEP‐carboxylase activity thus results from changes in the kinetic parameters with temperature and allosteric effectors. The often low optimum temperatures for CO2fixation observed in nature may thus be the result of substrate and effector concentrations in the cytoplasm and the antagonistic effect of temperature on substrate affinity and effector efficiency on phosphoenolpyruvate carboxylase.
Regulation of phenylalanine ammonia‐lyase activity and growth in lettuce by light and gibberellic acid
Authors: BARNES LOIS , JONES RUSSELL L.
Published: April 2006

Abstract The effects of light and gibberellic acid (GA3) on growth and phenylalanine ammonia‐lyase (PAL) activity were studied in seedlings of lettuce (Lactuca sativa L.). Using an in vivo assay for PAL it was shown that wounding caused by excising hypocotyls results in an increase in PAL activity with time that can mask the effect of light on the activity of this enzyme. When hypocotyl sections were excised from light‐treated seedlings immediately prior to the in vivo assay of PAL, light was shown to cause a marked increase in PAL activity. Experiments with an inhibitor of PAL activity, α‐aminooxy‐β‐phenylpropionic acid (AOPP), confirmed that the volatile radioactive products measured in the in vivo assay resulted from the activity of PAL. Gibberellic acid suppresses the light‐induced increase in PAL activity and there is an inverse relationship between GA3‐induced growth and the activity of PAL. Over a wide range of GA3 concentrations, the activity of PAL is also inversely correlated with growth rate along the length of the hypocotyl section; the upper halves of sections elongate more rapidly and have lower levels of PAL than the lower halves. Despite the strong correlation between growth and PAL activity, experiments with AOPP and t‐cinnamic acid show that it is unlikely that elongation is regulated directly by products of PAL activity.
CAM activity and day/night changes in the ultrastructure of stem chlorenchyma of Cissus quadrangularis L. as influenced by drought
Authors: DE SANTO A. VIRZO , LIGRONE R. , ALFANI A. , FIORETTO A. , RUSSO G.
Published: April 2006

Abstract Stem chlorenchymatous cells from well‐watered and water‐stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52‐58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress.
Abscisic‐acid‐induced turion formation in Spirodela polyrrhiza L III. Specific changes in protein synthesis and translatable RNA during turion development
Authors: SMART CHERYL C. , TREWAVAS ANTHONY J.
Published: April 2006

Abstract The developmental process leading to the formation of the abscisic acid (ABA) induced turion of Spirodela polyrrhiza was accompanied by a repression of nucleic acid and protein synthesis. DNA synthesis in the developing lurion (induced by 10−4mol m−3 ABA) was inhibited within 3h of ABA addition, followed by a repression of protein synthesis after 24 h, while RNA synthesis was not inhibited until 3 d. The inhibitory effect of ABA on protein synthesis was found to be selective and the synthesis of several novel proteins appeared to be induced. These effects were specific to ABA‐sensitive tissue.

The relationship between the changes in the protein and mRNA profiles during the development of the turion was investigated. The rapid general inhibition of protein synthesis at early stages of lurion formation could not be accounted for by the level of translatable mRNA, indicating an effect of ABA at the translational level. The specific alteration to the pattern of in vivo labelled proteins could have resulted, however, from control of the level of specific mRNAs for those particular proteins. Only after 3 d in ABA, when the developing primordium is committed to the turion developmental pathway, is there a total inhibition in the production of mRNA leading to the shutdown of all primary processes and the onset of the irreversible events leading to the dormant state.
Water velocity, growth‐form and diffusion resistances to photosynthetic CO2 uptake in aquatic bryophytes
Authors: JENKINS JANET T. , PROCTOR M. C. F.
Published: April 2006

Abstract. Boundary‐layer resistances of aquatic bryophytes for CO2 diffusion in water were estimated from wind tunnel measurements of evaporation of aniline in air, using the principle of dynamic similarity. The results indicated resistances at water velocities between 0.02 and 0.2 m s −1 ranging from about 35 to 5 s mm−1 and 70 to 9 s mm−1, respectively, for the mat‐forming liverworts Nardia compressa and Scapania undulata, measured on a projected area (canopy) basis. Over a range of velocities from 0.01 to 0.2 m s−1 the estimated CO2 boundary‐layer resistance of the streamer‐like shoots of the moss Fontinalis antipyretica is between about 180 and 15 s mm−1. Comparison with experiments on photosynthetic 14CO2‐uptake at a range of water velocities suggests that boundary‐layer resistance limits photosynthesis at velocities below about 0.01 m s−l in Fontinalis and below about 0.1 m s−1 in the mat‐forming species. It is suggested that high leaf‐area index allows the mat growth form more effectively to exploit the low boundary‐layer resistance at high velocities while remaining relatively invulnerable to drag. By contrast, the streamer form allows Fontinalis to maximize surface area under conditions where boundary‐layer resistance is limiting.
Penetration of light into soil and its role in the control of seed germination
Authors: BLISS D. , SMITH H.
Published: April 2006

Abstract Light transmitted through soil, and the leaf litter of two tree species, was measured using a spectroradiometer. In general, a greater penetration by longer wavelengths, especially far‐red, was noted. This was most marked in a dry sand sample. The effect was less in the case of clay‐loam aggregates. Moisture in the samples had an opposite effect in these two cases, causing an increase in transmission through sand but a decrease through clay loam aggregates. Reduction in particle size was found to reduce both the total light transmitted and the red/far‐red ratio (R : FR). Red wavelengths were also more attenuated by a layer of freshly fallen oak (Quercus rotrur) leaves than were far‐red wavelengths. A layer of Corsican pine (Pinus nigramaritima) needles however, was found to act as a neutral density filter over the 400 800 nm range.

Prolonged exposure to soil‐filtered light was found to affect the germination of seven species tested. Plantago major demonstrated an approximately linear decrease in germination with increasing depth. Rumex obtusifotius showed an apparent threshold response at 4 6 mm depth, as did Cecropia obtusifolia but at a slightly greater depth. Digitalis purpurea germinated very poorly in darkness, yet was extremely photosensitive with very high germination even at 10 mm depth. Galiutn aparine and Chenopodium album showed a two‐phase response with germination reaching a peak at 2 mm depth.

The implications for the function of the photoreceptor phytochrome in the control of germination are discussed in relation to soil‐transmitted light and with regard to the results of the germination tests.
A method for controlling the within‐root CO2 concentration
Authors: GOOD B. J.
Published: April 2006

Abstract A method is presented for the control of carbon dioxide concentrations within the roots of Fraxinus pennsylvanica Marsh. The results indicated a linear fit of the root CO2 concentrations to the CO2 levels of the treatment gases: y= l.l. x+105 (r= 0.98, 18 d.f.). The method presented for controlling CO2 can be easily modified for other gas mixtures and plant species.
The effect of genotype and environment on the fatty acid content of barley (Hordeum vulgare L.) grains
Authors: DE MAN WALTER
Published: April 2006

Abstract A comparison was made of the content of total and some individual fatty acids in grains of nine barley varieties grown at six sites in Belgium. The varieties represented six‐ and two‐rowed winter types and two‐rowed spring types. The results showed that the winter types contain more linolenic acid (C18 : 3) than spring types and that six‐rowed barleys have less total fatty acids than two‐rowed barleys, due mainly to a low concentration of palmitic (C16:0), oleic (CI8 : 1) and linoleic (C18 : 2) acids. Analysis of variance showed that fatty acid content is affected by both the genotype and the environment and multiple regression analysis suggested that weather conditions before and after flowering affected lipid composition.
Biphasic fluence‐response curves for light induced germination of Arabidopsis thaliana seeds
Authors: CONE J. W. , JASPERS P. A. P. M. , KENDRICK R. E.
Published: April 2006

Abstract With appropriate pretreatment of the seeds fluence‐response curves for the induction of germination of Arabidopsis thaliana show two phases. A proportion of the population responds to very low fluence (VLFR), 104–10−2μmolm−2 establishing 10−4–10−2% of the total phytochrome in the far‐red absorbing form (Pfr) and a proportion of the population respond to low fluence (LFR), 1–1000 μmolm−2, establishing 1–75% Pfr. The VLFR is nol normally seen because the pre‐existing Pfr level satisfies the Pfr requirement or use of green safelight establishes more Pfr than necessary to saturate the VLFR. Endogenous Pfr was depicted by a 24 h 35°C treatment, presumably as a result of dark destruction and/or dark reversion to the red absorbing form of phytochrome (Pr), making it possible to visualize the VLFR. A short pulse of 35°C treatment in combination with an appropriate temperature regime is also able to sensitize a proportion of the seed population. The proportion of the population showing the VLFR is determined by the duration of the cold imbibition pretreatment as well as the duration of the 35°C treatment. Complex fluence‐response curves were observed in which a proportion of the seeds being promoted in the VLFR range, were inhibited at higher fluences before being further promoted in the LFR range. This was particularly clear for seed batches being sensitized by a short 35°C treatment. The VLFR may be of significance in the natural environment, enabling seeds buried in the upper layer of the soil to germinate, where the fluence rate falls off sharply and the LFR is not satisfied. A model is presented to explain the two phases in the fluence‐response curves.
Phase and amplitude relations between transpiration, water potential and stem shrinkage
Authors: WRONSKI E. B. , HOLMES J. W. , TURNER N. C.
Published: April 2006

Abstract An electrical analogue describing the phase and amplitude relations between transpiration, water potential and stem shrinkage for trees was developed. Observations of shrinking and swelling at various heights up a Pinus radiata tree were obtained over several weeks in summer and autumn.

The relative amplitude in shrinkage increased by a factor of two up the stem, but phase lags were small. The data obtained were used in conjunction with the electrical analogue of the How pathway to obtain an estimate of the relative magnitude of the capacitance of the living bark and the sapwood, and to predict phase lags between transpiration and leaf water potential, and lags in transpirational flux up the stem.

The results suggest that if water potentials recover by dawn, phase lags in water potential down tree stems arc small and that the exchange between water stored in the sapwood and the transpiration stream is irreversible over the diurnal time scale.
The effect of high levels of carbon dioxide on dark respiration and growth of plants
Authors: REUVENI J. , GALE J.
Published: April 2006

Abstract Raising ambient levels of CO2 during the night, between 350 and 950cm3m−3, reduced the dark respiration rate of Medicago sativum seedlings. The percentage effect was greater for maintenance respiration than for dark respiration as a whole, and when the plants were in a low photosynthate status. Twenty‐four h carbon balance studies confirmed a reduction in night time respiration and an increase of net carbon gain when night time [CO2] was high. Growth experiments showed a small but significant increase of dry weight in Medicago sativum seedlings exposed to high [CO2] (∼ 1200 cm3m−3) at night. This effect was greater for plants grown with Rhizobium nodules than for plants grown with nitrate in the absence of Rhizobium. A similar, but smaller and statistically non‐significant effect of high night time [CO2] on growth was found for Xanthium strumarium seedlings. The significance of these findings is discussed in relation to the rising CO2 content of the atmosphere.
Thioproline‐induced accumulation of proline in barley leaf sections
Authors: BEFFAGNA N. , PESCI P. , RADICE M.
Published: April 2006

Abstract Treatment of barley leaf sections with 0.1 mol m−3 thioproline (L‐thiazolidine‐4‐carboxylic acid) was found to induce a marked increase in proline together with some decrease in glutamate, whereas the levels of other andno acids were not influenced. This result is discussed in relation to the significance of the increase in proline in tissues treated with abscisic acid or subjected to water stress.
Comparative ecophysiology of CAM and C3 bromeliads. IV. Plant water relations
Authors: SMITH J. A. C. , GRIFFITHS H. , LÜTTGE U. , CROOK C. E. , GRIFFITHS N. M. , STIMMEL K.‐H.
Published: April 2006

Abstract An investigation was carried out into the water relations of CAM and C3 bromeliads in their natural habitat during the dry season in Trinidad. Measurements were made of xylem tension with the pressure chamber and of cell‐sap osmotic pressure and titratable acidity on crushed leaf samples. A steady‐state CO2 and H2O‐vapour porometer was also used so that changes in leaf water relations during individual day‐night cycles could be directly related to gas‐exchange patterns in situ.

Xylem tension changed in parallel with transpiration rate and in general reached its maximum value in CAM bromeliads at night and in C3 bromeliads during the day. In addition, large nocturnal increases in cell‐sap osmotic pressure and titratable acidity (ΔH+) typically occurred in the CAM bromeliads. The C3‐CAM intermediate Guzmania monostachia showed slight nocturnal acidification, but had higher values of xylem tension during the day. Very high values of AH+ were observed in the CAM species when the tanks of the epiphytic bromeliads contained water: Aechmea nudicaulis showed a mean maximum ΔH+ of 474 mol m−3, the highest value so far observed for CAM plants. On some nights dew formed on the leaf surfaces of the epiphytes, partially curtailing gas exchange and leading to a marked decrease in xylem tension in both C3 and CAM species.

Between‐site comparisons were also made for a wide range of habitats from arid coastal scrub to montane rain forest. Compared with values characteristic of other life‐forms, xylem tension and cell‐sap osmotic pressure were low for all bromeliads, and did not differ significantly in co‐occurring CAM and C3 bromeliads. Mean maximum xylem tension (10 species in total) ranged from 0.29 M Pa at the montane sites to 0.67 MPa at the most arid site, and mean minimum osmotic pressure (17 species) from 0.51 to 0.97 MPa. At the arid sites the bromeliads were exclusively CAM species, two of which (Aechmea aquilega and Bromelia plumieri) grew terrestrially in the undergrowth of the coastal scrub. Xylem tension in these species was low enough to indicate that they must be functionally independent of the substratum during the dry season. In the wetter part of Trinidad, no between‐site differences in leaf water relations were found along an altitudinal gradient in the Northern Mountain Range; seasonal differences in this area were also small. Overall, leaf water relations and gas exchange in the bromeliads were strongly affected both by short‐term changes in water availability and by longer‐term climatic differences in the various regions of the island.
Cell age‐related differences in the interaction of a potential‐sensitive fluorescent dye with nuclear envelopes of Acetabularia mediterranea
Authors: MATZKE M. A. , MATZKE A. J. M. , NEUHAUS G.
Published: April 2006

Abstract. To study whether an electrical potential difference exists across the nuclear envelope or inner nuclear membrane of plant cells, the authors have used an optical probe of membrane potential, the cationic fluorescent dye, DiOC6(3) (MW = 572.5). This dye was microinjected into the nucleoplasm of isolated Acetabularia nuclei (which are still surrounded by a thin layer of cytoplasm) and its subnuclear localization visualized by fluorescence microscopy. Striking differences, which seemed to be correlated with the developmental stage of the isolated nucleus, were observed. In nuclei isolated from cells at the stage of early cap stage formation, the dye was restricted to the nuclear envelope. In nuclei isolated from cells with intermediate or fully developed caps, there was increased nucleoplasmic staining, and the staining of the envelope was frequently diminished or abolished. In all nuclei, the dye remained within the nucleus after injection. Cytoplasmic staining was only observed when nuclei isolated from cells at the stage of early cap formation were incubated in a hyper‐ or hypo‐tonic medium. Various ionophores, injected before the dye into the nucleoplasm, had no effect on the subsequent nuclear localization of DiOC6(3), although they did rapidly induce nucleolar condensation in nuclei isolated from cells at the stage of early cap formation. The results suggested that the electrical properties of Acetabularia nuclear envelopes or inner nuclear membranes change during cell maturation. Furthermore, the retention of the dye in the nucleoplasm under isotonic conditions indicated that the nuclear pores were not open channels for molecules of this size.
Characterization of the effects of metabolic inhibitors, ATPase inhibitors and a potassium‐channel blocker on stomatal opening and closing in isolated epidermis of Commelina communis L.
Authors: KARLSSON P. E. , SCHWARTZ A.
Published: April 2006

Abstract. The specific effects of hypoxia and various inhibitors on stomatal opening in the light and closing in the dark were characterized in isolated epidermis from Commelina communis L. Reducing the guard cell metabolism with hypoxia and the uncoupler carbonyl cyanide‐m‐chloro‐phenyl‐hydrazone, CCCP, respectively, inhibited both stomatal opening and closing. Stomatal closing was very efficiently blocked by CCCP and this effect could be readily reversed by washing out the inhibitor. The authors were unable to inhibit stomatal opening with ATPase‐inhibitors, without also affecting closing. Orthovanadate, up to 2 mol m−3, affected neither opening nor closing. Dicyclohexylcarbodiimide, DCCD, and diethylstilbestrol, DES, inhibited opening as well as closing to about 50%. The K+ ‐channel blocker tetraethylammonium chloride, TEA‐Cl, inhibited both stomatal opening and closing, as did phenyl acetic acid, PAA, a compound considered to interfere with blue light induced stomatal opening. The results are discussed in the view that the uncontrolled K+ leakage from the guard cells is low, that K+ efflux during stomatal closing, as well as K+ influx during opening, occurs through specific K+‐channels and that ATP and/or a membrane potential seems to be needed to keep these channels open.
Curve fitting of germination data using the Richards function
Authors: BERRY G. J. , CAWOOD R. J. , FLOOD R. G.
Published: April 2006

Abstract. The fitting of the generalized Richards function to germination data by using two nested iterative and least squares regression procedures to estimate the four parameters (all of which can be associated with features of biological growth) is demonstrated. The program also involves a procedure of parallel curve analysis which makes comparisons between two curves by examining the whole process represented by the curve and not just a point or portion thereof. Excellent agreement between observed and expected values was obtained by analyzing data which defined patterns of germination exhibiting a range of rates and final percentages. The program also calculates a number of derived quantities including maximum daily rate of germination and time to 50% of final germination.
Inhibition of expression of tomato‐ripening genes at high temperature
Authors: PICTON S. , GRIERSON D.
Published: April 2006

Abstract. Ripening tomato fruits incubated at 35°C fail to achieve normal pigmentation, soften little and show a marked decline in ethylene evolution. Labelling studies in vivo indicate that protein synthesis continues throughout incubation at 35°C although the spectrum of labelled proteins is different to that observed at 25°C. Translation of mRNAs in vitro shows traces of several ‘heat‐shock’ mRNAs at 35°C and the loss of several others normally found in fruit ripened at 25°C. Using ripening‐related cDNA clones as hybridization probes the expression of 12 ripening‐related genes was followed during incubation at 25°C and 35°C. In general, there was a marked decline in the amounts of these mRNAs following incubation of ripening fruit at 35°C. In particular, mRNA homologous to pTOM 6, a cDNA clone coding for polygalacturonase, a major cell wall degrading enzyme, showed a rapid decline following incubation at 35°C and after 72‐h at elevated temperature was undetectable. There was no recovery of expression during 120 h at 35°C and the application of exogenous ethylene did not overcome the inhibition of ripening or lead to the renewed accumulation of polygalacturonase mRNA. It is proposed that the failure to soften normally at elevated temperature is due, in part, to the suppression of polygalacturonase mRNA and that the inhibition of other facets of ripening at 35°C is due to the inhibition or reduced expression of other, as yet unidentified, ripening‐related genes.
Effect of high external NaCl concentration on ion transport within the shoot of Lupinus albus. II. Ions in phloem sap
Authors: MUNNS RANA , LORRAINE TONNET M. , SHENNAN CAROL , ANNE GARDNER P.
Published: April 2006

Abstract. Phloem sap was collected from petioles of growing and fully expanded leaves of lupins exposed to 0–150 mol m−3 [NaCl]ext, for various periods of time. Sap bled from growing leaves only after the turgor of the shoot was raised by applying pneumatic pressure to the root. Increased pressure was also needed to obtain sap from fully expanded leaves of plants at high [NaCl]ext. Exposure to NaCl caused a rapid rise in the Na+ concentration in phloem sap to high levels. The Na+ concentration reached 20 mol m−3 within a day of exposure and reached a plateau of about 60 mol m−3 in plants at 50–150 mol m−3 [NaCl]ext, after a week. There was a slower, smaller increase in the Cl− concentration. K+ concentrations in phloem sap were not affected by [NaCl]ext. Cl− concentrations in phloem sap collected from growing leaves were similar to those from old leaves while Na+ concentrations were somewhat increased, suggesting that there was no reduction in the salt content of the phloem sap while it flowed within the shoot to the apex. Calculations of ion fluxes in xylem and phloem sap indicated that Na+ and Cl− fluxes in the phloem from leaves of plants at high NaCl could be equal to those in the xylem. This prediction was borne out by observations that Na+ and Cl− concentrations in recently expanded leaves remained constant.
The use of positron emission tomography for studies of long‐distance transport in plants: uptake and transport of 18F
Authors: McKAY R. M. L. , PALMER G. R. , MA X. P. , LAYZELL D. B. , McKEE B. T. A.
Published: April 2006

Abstract. Positron emission tomography (PET) has been utilized to obtain dynamic images of long distance nutrient translocation in plants. Positron emitting 18F, produced by a Van de Graaff accelerator using the reaction 18O(p,n)18F, was fed in solution to excised stems of Glycine max positioned vertically in a large‐aperture PET detector system. Images of tracer activity were recorded with a time resolution of 0.5 min and a spatial resolution of 4 mm. Maximum tracer activities at stem sites were obtained within 3 min of the pulse feed. A model is presented enabling evaluation of regional values for tracer flow, tracer binding, flow speed and flow volume. Analysis of data for one stem position yielded a flow volume of 2.1mm3 min−1 and a flow speed of 36cm min−1. Comparison with the distribution of 14C‐inulin, which was simultaneously fed to the cut stems, indicates the 18F is suitable for use as an apoplastic tracer; 92% of the tracer activity accumulated in the leaves. The fraction of 18F that remained bound was most concentrated at stem nodal regions, an observation consistent with the existence of transfer cells at these sites. Advantages and limitations of PET applied to plant physiological investigations are discussed.
Homologies to the tomato endopolygalacturonase gene in the peach genome
Authors: LEE E. , SPEIRS J. , GRAY J. , BRADY C. J.
Published: April 2006

Abstract. Peach endopolygalacturonase was isolated from the mesocarp tissue of soft ripe, freestone peach fruit, but was not detectable in mature pre‐ripening fruit. It is a basic protein with a Mr of approximately 45000 Da, and cross‐reacts with antibody to tomato endopolygalacturonase. Using a cDNA to the tomato enzyme as a probe, a fragment of peach genomic DNA was isolated which encoded about 50% of the peach enzyme. The nucleotide sequence of the fragment was determined and the amino acid sequence of part of the peach endopolygalacturonase peptide derived. Coding regions of the peach gene show extensive homology with related regions of the tomato gene. Introns are dissimilar. Endopolygalacturonase activity occurs in ripe ‘freestone’peaches but not in the firmer ‘clingstone’varieties. Hybridization studies identified a similar gene fragment in freestone, semi‐freestone and clingstone peach varieties.
Changes in starch and soluble sugars in relation to the acquisition of desiccation tolerance during maturation of Brassica campestris seed
Authors: LEPRINCE O. , BRONCHART R. , DELTOUR R.
Published: April 2006

Abstract. We investigated the onset of desiccation tolerance in developing embryos of Brassica campestris seeds and possible correlated ultrastructural modifications in the radiele cells. Since the acquisition of desiccation tolerance is a long asynchronous process which took 9 d to be achieved, we determined criteria allowing us to separate freshly intact harvested seeds into desiccation intolerant and desication tolerant batches that differed in age by only 2 d. No particular structural modifications were found except a strong depletion of intraplastidial starch (‐90%) coincident with the appearance of stachyose and an increase of sucrose (+30%) on the acquisition of desiccation tolerance. As we did not observe an increase of lipid reserves as a consequence, we suggest that these metabolic events can be a key factor towards the acquisition of desiccation tolerance.
An automated greenhouse sand culture system suitable for studies of P nutrition
Authors: LYNCH J. , EPSTEIN E. , LÄUCHLI A. , WEIGHT G. I.
Published: April 2006

Abstract. Maintenance of realistically low solution P concentrations under controlled conditions is a major difficulty in studies of P nutrition. In this report, we describe a relatively simple and economical sand culture system capable of sustaining plant growth to maturity under controlled yet realistic P regimes. The system uses Al2O3 as a solid‐phase P buffer, and modern process control technology to control irrigation and addition of other mineral nutrients. Aspects of the design, use and potential applications of automated solid‐phase systems are discussed. The system was used to grow Phaseolus vulgaris to matarity at 0.4 mmol m3, 1.0 mmol m3 and 27 mmol m3 P with and without mycorrhizal inoculation. At flowering, low solution P concentrations were associated with reduced leaf concentrations of P in nonmycorrhizal plants, and reduced leaf concentrations of Ca in both mycorrhizal and nonmycorrhizal plants. Mycorrhizal inoculation increased leaf P, K, Mg and Mn concentrations, but reduced leaf N concentration. Low P regimes reduced final seed yield by diminishing both the number of pods per plant and the number of seeds per pod. Mycorrhizal inoculation significantly enhanced seed yield under low P regimes by increasing seed weight, the number of pods per plant, and the number of seeds per pod.
Two mutants of Arabidopsis thaliana that become chlorotic in atmospheres enriched with CO2
Authors: MSU‐DOE N. N. ARTUS
Published: April 2006

Abstract. Two nonallelic, nuclear recessive mutants of Arabidopsis thaliana (L.) Heynh. which become chlorotic when grown in an atmosphere enriched to 20000 cm3 CO2 m‐3 have been isolated. For one of the mutants, chlorosis begins at the veins and gradually spreads to the interveinal regions. A minimum photon flux density of ca 50 μmol m‐2 s‐1 is required for this response. For the other mutant, the yellowing is independent of the light intensity and begins at the basal regions of the leaves and spreads to the tips. The injurious effects of CO2 seem to be restricted to photosynthetic tissues, since root elongation and callus growth were not inhibited by a high atmospheric CO2 concentration for either mutant. Neither mutant became chlorotic in a low O2 atmosphere that suppressed photorespiration as effectively as the elevated CO2 does. Thus, the mutations do not impose a requirement for photorespiration. The possibilities that the high CO2‐sensitive phenotypes are caused by an effect of CO2 in stomata, on ethylene synthesis, or on mineral uptake are discussed but are considered unlikely.
Stimulation of chlororespiration by heat and high light intensity in oat plants
Authors: QUILES MARÍA JOSÉ
Published: April 2006

High irradiance and moderate heat inhibit the activity of the photosynthetic apparatus of oat (Avena sativaL.) leaves. The incubation of oat leaves under high light intensity in conjunction with high temperatures strongly decreased the maximal quantum yield of photosystem (PS) II, indicating the close synergistic effect of both stress factors on PS II inhibition and the subsequent irreversible damage to the photosynthetic apparatus. The PS I A/B protein levels remained similar to control values in leaves incubated under high light intensity or moderate heat, and decreased only when both stress factors were simultaneously applied. Immunoblot analysis of thylakoid membranes using specific antibodies raised against the NDH‐K subunit of the thylakoidal NADH dehydrogenase complex (NADH DH) and against plastid terminal oxidase (PTOX) revealed an increase in the amount of both proteins in response to high light intensity and/or heat treatments. In addition, these stress treatments were seen to stimulate the activity of electron donation by NADPH and ferredoxin to plastoquinone, the PTOX activity in plastoquinone oxidation and the NADH DH activity in thylakoid membranes. Incubation withn‐propyl gallate (an inhibitor of PTOX) inhibited the increase of NDH‐K and PTOX levels under high light intensity and heat, and slightly stimulated the activity of electron donation by NADPH and ferredoxin to plastoquinone. Antimycin A (an inhibitor of cyclic electron flow) increased the NADH DH activity and preserved the levels of NDH‐K and PTOX in thylakoid membranes from leaves incubated under high light intensity and heat. The up‐regulation of the PTOX and the thylakoidal NADH DH complex under these stress conditions supports a role for chlororespiration in the protection against high irradiance and moderate heat.
Functionality of resistance gene Hero, which controls plant root‐infecting potato cyst nematodes, in leaves of tomato
Authors: CABRERA POCH H. L. , MANZANILLA LÓPEZ R. H. , KANYUKA K.
Published: April 2006

The expression of host genomes is modified locally by root endoparasitic nematode secretions to induce the development of complex cellular structures referred as feeding sites. In compatible interactions, the feeding sites provide the environment and nutrients for the completion of the nematode’s life cycle, whereas in an incompatible (resistant) interaction, the host immune system triggers a plant cell death programme, often in the form of a hypersensitive reaction, which restricts nematode reproduction. These processes have been studied in great detail in organ tissues normally infected by these nematodes: the roots. Here we show that host leaves can support a similar set of programmed developmental events in the potato cyst nematode Globodera rostochiensis life cycle that are typical of the root‐invading nematodes. We also show that a gene‐for‐gene type specific disease resistance that is effective against potato cyst nematodes (PCN) in roots also operates in leaves: the expression of the resistance (R) gene Hero and members of its gene family in leaves correlates with the elicitation of a hypersensitive response only during the incompatible interaction. These findings, and the ability to isolate RNA from relevant parasitic stages of the nematode, may have significant implications for the identification of nematode factors involved in incompatible interactions.