bluuebunny/crossref_metadata_2025 huggingface dataset:
Ethylene and ethane production in response to salinity stress
Authors: CHROMINSKI A. , KHAN M. A. , WEBER D. J. , SMITH B. N.
Published: April 2006

Abstract Ethylene and ethane production in mung bean hypocotyl sections were evaluated as possible indicators of stress due to contact with four salts that are common in natural sites. Ethylene production decreased with increasing concentrations of applied NaCl and KCl. When CaCl2 was applied, the ethylene evolution was greater. However, when MgCl2 was applied, ethylene evolution remained high then decreased and at higher salt concentrations again showed an increase. NaCl (up to 0.1 kmol m−1) and KCl (up to 0.5 kmol m−3) caused a concentration‐dependent increase in ethane production. The ethane production with CaCl2 was the lowest among the salts tested and only a minute increase was noticed with the increase of concentration from 0.01 to 1 kmol m−3. Ethane production showed a distinct maximum at 0.2 kmol m−3 MgCl2. The introduction of 0.01 kmol m−3 CaCl2, as well as anaerobic conditions obtained by purging vials with N2, eliminated that high ethane production. Respiratory activity of the mung bean hypocotyl sections in MgCl2 concentrations from 0 to 0.5 kmol m−3 was correlated with ethane but not with ethylene production. The ethane/ethylene ratio showed three patterns for the four salts tested.
The size and turnover of the glycerol pool in Dunaliella
Authors: GOYAL A. , LILLEY R. McC. , BROWN A. D.
Published: April 2006

Abstract The rate of incorporation of 14C from CO2 into glycerol, and the amount of glycerol in cells of Dunaliella tertiolecta was determined at constant salinity at two representative concentrations of NaCl. From these data, the rate of synthesis and turnover of the glycerol pool was determined. The half‐time for turnover of the glycerol pool was of the order of 1 h in 170 mol m−3 NaCl and almost 6h for 700 mol m−3 NaCl. These results indicate that turnover of the glycerol pool in Dunaliella is relatively slow under steady‐state conditions. Synthesis and dissimilation of glycerol do not apparently constitute a metabolic cycle in the conventional sense. Rather, glycerol metabolism resembles that of the storage polysaccharides which arc commonly produced and degraded by different pathways.
A 13C method of estimation of carbon allocation to roots in a young chestnut coppice
Authors: MORDACQ L. , MOUSSEAU M. , DELEENS E.
Published: April 2006

Abstract A method is described in which 1 year‐old chestnut coppice was fed in situ with air highly enriched in 13CO2 (23%). After 3 days, 13C concentration increases in shoots were measured by mass spectrometry. Respiratory losses between 13C feeding and harvest were estimated using two different methods: (i) a model involving the temperature response of respiration and (ii) direct measurement of 13C content of the CO2 respired by the shoots during the night.

Carbon allocation to roots was deduced by subtracting from the given amount of 13C, the amount remaining in shoots and the 13C respired by the shoots.

The method was tested twice during the growing season. Very little carbon was allocated to roots in late July, but over 80% of assimilated 13C went to roots at the end of September. Despite some approximations in the 13C respiratory losses estimations, the method allowed evaluation of carbon allocation to roots with an error of about 5%.
Environmental influences on the productivity of three desert succulents in the south‐western United States
Authors: NOBEL P. S. , HARTSOCK T. L.
Published: April 2006

Abstract Net CO2 uptake over 24 h periods for shoots of Agave deserti, Ferocactus acanthodes, and Opuntia ficus‐indica was measured under the ranges of water status, air temperature, and photo‐synthetically active radiation (PAR) that occur in the south‐western U.S.A. An environmental productivity index (EPI) was constructed indicating the overall influence of these three factors on net CO2 uptake. Using growth chambers whose conditions were changed monthly to simulate the environmental conditions at a field site, the observed shoot dry weight increases per unit surface area changed in concert with monthly changes in EPI. The observed dry weight gain of the shoot was 17–19% lower than the predicted shoot net CO2 uptake, which could be accounted for by carbon diversion to the roots. Mean monthly EPI was also predicted for 21 sites in the south‐western U.S.A. All three species had low EPIs in the Colorado River basin, which has low annual rainfall and high summer temperatures, and in the north‐central part of the region, which has low temperatures and low PAR during winter when water is available. The two native species, A. deserti and F. acanthodes, had high EPIs beyond their range in coastal southern California, where competition by other vegetation for PAR may limit net CO2 uptake. Such regions as well as south‐central California and south‐central Arizona had high EPIs for all three species, indicating that these areas would be appropriate for the cultivation of O. ficus‐indica.
Influence of stomatal distribution on transpiration in low‐wind environments
Authors: FOSTER J. R. , SMITH W. K.
Published: April 2006

Abstract According to computer energy balance simulations of horizontal thin leaves, the quantitative effects of stomatal distribution patterns (top vs. bottom surfaces) on transpiration (E) were maximal for sunlit leaves with high stomatal conductances (gs) and experiencing low windspeeds (free or mixed convection regimes). E of these leaves decreased at windspeeds > 50 cm s−1, despite increases in the leaf‐to‐air vapour density deficit. At 50 cm s−1 wind‐speed, rapidly transpiring leaves had greater E when one‐half of the stomata were on each leaf surface (amphistomaty; 10.16 mmol H2O m−2 s−1) than when all stomata were on either the top (hyperstomaty; 9.34 mmol m−2s−1) or bottom (hypostomaty; 7.02 mmol m−2s−1) surface because water loss occurred in parallel from both surfaces. Hyperstomatous leaves had larger E than hypostomatous leaves because free convection was greater on the top than on the bottom surface. Transpiration of leaves with large g, was greatest at windspeeds near zero when ∼60–75% of the stomata were on the top surface, while at high windspeeds E was greatest with, 50% of the stomata on top. For leaves with low gs, stomatal distribution exerted little influence on simulated E values. Laboratory measurements of water loss from simulated hypo‐, hyper‐, and amphistomatous leaf models qualitatively supported these predictions.
Cation exchange in isolated xylem cell walls of tomato. II. Direct determination of chemically bound and electrostatically attracted Cd2+ by γ‐γ‐directional correlation measurements
Authors: WOLTERBEEK H. Th. , BODE P. , DE BRUIN M.
Published: April 2006

Abstract Xylem cell walls were isolated from internodes of tomato plants (Lycopersicon esculentum Mill, cv. Tiny Tim). Purification was carried out in Triton X‐100. Experiments were conducted in which the adsorption of Cd2+ (applied as 115CdCl2) in the cell walls was measured. The application of γ‐γ‐directional correlation measurements permitted the direct determination of chemically bound cell wall Cd in experiments where the total adsorption of Cd was also measured. A set of equations is presented by which the adsorption of Cd could be described, thereby considering the presence of co‐ions in the polyelectrolyte phase. In experiments with simultaneous ll5CdCl2 and K82Br applications, measurements were carried out of the presence of 82Br− in the Donnan Free Space (DFS), indicating Cl− action in the process of CdCl2 adsorption.

The cell wall contents of the relevant ions were determined in such a manner that the measurements gave access to the undisturbed equilibrium concentrations. The very small Br− concentrations in the DFS indicated that, at small applied concentrations, internal free Cd may be considered to exist entirely of Cd2+. The results suggest that simultaneous measurement of internal free counter‐ion and co‐ion concentrations may be a relatively easy way to check the reliability of values for apparent formation constants in single cation adsorption experiments. From experiments in which the cell walls were incubated in solutions of varying Cd concentrations, the apparent dissociation constant (KCd2+) for the formation of R2Cd complexes could be calculated as 51±6 mol m−3. The exchange coefficient (KCd2+H+) was shown to vary with the internal free proton concentration and the applied Cd2+ concentration, due to the buffering capacity of the carboxylic acid exchanger.
The relationship between guard cell water potential and the aperture of stomata in Populus
Authors: SCHULTE P. J. , HINCKLEY T. M.
Published: April 2006

Abstract Previous work with clones of Populus trichocarpa demonstrated that the water vapour conductance of leaves from well‐watered cuttings of this species does not decline with loss of turgor from the bulk leaf. In the present study, stomatal responses to water potential in Populus were examined with detached epidermal strips. Stomata in epidermal strips from well‐watered plants of P. trichocarpa did not close at low water potentials which led to plasmolysis of the guard cells. In contrast, stomata of P. deltoides and a P. trichocarpa×deltoides hybrid closed when the guard cells lost turgor. A period of water stress preconditioning resulted in modified stomatal responses in P. trichocarpa such that stomata of stressed and re‐watered plants nearly closed when guard cell turgor was lost.
The relationship between respiration and temperature in leaves of the arctic plant Saxifraga cernua
Authors: McNULTY AMY K. , CUMMINS W. R.
Published: April 2006

Abstract Saxifraga cernua, a perennial herb distributed throughout the arctic and subarctic regions, shows high levels of dark respiration. The amount of respiration exhibited by leaves and whole plants at any temperature is influenced by the pretreatment temperature. Plants grown at 10°C typically show higher dark respiration rates than plants grown at 20°C. The levels of alternative‐pathway respiration (or cyanide‐insensitive respiration) in leaves of S. cernua grown at high and low temperatures were assessed by treating leaf discs with 0.25 mol m−3 salicylhydroxamic acid during measurements of oxygen consumption. Alternative pathway respiration accounted for up to 75% of the total respiration. Tissues from 20°C‐grown plants yielded a Q10 of 3.37 for normal respiration, and of 0.97 for alternative‐pathway respiration. Tissues from 10°C‐grown plants yielded a Q10 of 2.55 for normal respiration, and of 0.79 for alternative‐pathway respiration. The alternative pathway does not appear to be as temperature sensitive as the normal cytochrome pathway.

A simple energy model was used to predict the temperature gain expected from these high rates of alternative‐pathway respiration. The model shows that less than 0.02°C can be gained by leaves experiencing these high respiration rates.
Photosynthesis in frost‐hardened and frost‐stressed leaves of Hedera helix L.
Authors: BAUER H. , KOFLER RENATE
Published: April 2006

Abstract The purpose of this study was to determine the respective extents to which winter reduction of photosynthetic capacity in ivy (Hedera helix L.) is caused by direct frost injury to the photosynthetic apparatus and by preceding protoplasmic changes connected with the acquisition of frost tolerance. Potted juvenile ivy plants were placed in the open under natural weather conditions whilst others were hardened under controlled conditions and subjected to the desired frost stress.

Low non‐freezing temperatures induced frost tolerance in ivy leaves down to about – 12°C (50% injury = TL50) without impairing net photosynthetic rate as measured under standard conditions (20°C, light saturation, natural CO2 level; = Standard‐Fn. Only if the leaves froze (below − 3°C to −4°C) was a reversible inhibition of Standard‐Fn observed. As long as the temperatures did not fall below approximately −8°C the inhibition was small and Standard‐Fn reached about 80–90% of the control. In this case the stomatal opening narrowed, giving a poorer supply of CO2 to the mesophyll cells. Maximal frost tolerance (TL5O−20°C to −24°C) developed only with severe frosts below about − 10°C. After such frosts, Standard‐Fn was reduced to less than 20% of the control. The dependence of the rate of net photosynthesis on the internal CO2 concentration showed a lower initial slope, thus indicating disturbances of chloroplast functions. However, neither in outdoor plants nor in those artificially frosted at – 20°C could there be found an appreciable inhibition of the electron transport capacity from H2O to dichlorophenol indophenol or of ribulose bisphosphate carboxylase.

If intact, severely frosted ivy plants were then held at higher temperatures (20/15°C), Standard‐Fn recovered completely in approximately 10 d. Furthermore, following a frost period with temperatures down to −12°C, mild weather caused a distinct improvement in Standard‐Fn in outdoor plants, and there was no loss of maximum frost tolerance. Thus it can be concluded that the inhibition of Standard‐Fn after severe frosts is not due to the development of maximal frost tolerance, but rather may be attributed to frost damage to the photosynthetic apparatus.
Factors affecting the decomposition of 2‐chloroethylphosphonic acid in soils
Authors: GOUDEY J. S. , SAINI H. S. , SPENCER MARY S.
Published: April 2006

Abstract The ethylene‐releasing compound 2‐chloroethylphosphonic acid (ethephon) stimulates germination of dormant seeds under laboratory conditions and it may prove to be an effective means of administering ethylene to promote germination of seeds in the field. We examined the decomposition of ethephon in different soils to determine which properties of soils influence the activity (ethylene release) of ethephon. The release of ethylene from ethephon was not affected by the type of soil, the texture, the presence of organic matter, or levels of extractable SO2−4, PO3−4 NO−3, K+ or Na+. The rate of decomposition was, however, dependent on soil pH and was influenced by the soil moisture content. Very little ethylene was released from ethephon in soils with a pH <7.7 and with a moisture content < 10%.
Water flow and water storage in Agave deserti: osmotic implications of crassulacean acid metabolism
Authors: SMITH J. A. C. , SCHULTE P. J. , NOBEL P. S.
Published: April 2006

Abstract Water flow and water storage were investigated for Agave deserti, a desert succulent showing crassulacean acid metabolism (CAM). The anatomy and water relations of the peripheral chlorenchyma, where CAM occurs, and the central water‐storage parenchyma were investigated for its massive leaves so that these tissues could be incorporated as discrete elements into an electrical‐circuit analogue of the whole plant. The daily cycling of osmotic pressure was represented by voltage sources in series with the storage capacitors. With soil water potential and leaf transpiration rate as input variables, axial water flow through the vascular bundles and radial flows into and out of storage during the day/night cycle were determined.

The predominantly nocturnal transpiration was coincident with increases in cell osmotic pressure and in titratable acid of the leaf chlorenchyma. In the outer layers of the chlorenchyma, water potential was most negative at the beginning of the night when transpiration was maximum, while the water‐storage parenchyma reached its minimal water potential 9 h later. The roots plus stem contributed 7% and the leaves contributed 50% to the total water flow during maximal transpiration; peak water flow from the soil to the roots occurred at dawn and was only 58% of the maximal transpiration rate. Over each 24‐h period, 39% of the water lost from the plant was derived from storage, with flow into storage occurring mainly during the daytime. Simulations showed that the acid accumulation rhythm of CAM had little impact on water uptake from the soil under the conditions employed. In the outer chlorenchyma, water potential and water flows were more sensitive to the day/night changes in transpiration than in osmotic pressure. Nevertheless, cell osmotic pressure had a large influence on turgor pressure in this tissue and determined the extent to which storage was recharged during the latter part of the night.
Wavelength dependence of suppression of potato sprout growth by light
Authors: McGEE E. , JARVIS M. C. , DUNCAN H. J.
Published: April 2006

Abstract Light is used commercially to prevent the sprouts on seed potatoes from growing so long that they are knocked off at planting. We investigated the relationship between wavelength and growth inhibition, using a very long irradiation time of 23 d with a 12‐h photoperiod. The inhibition showed a narrow peak of far‐red activity centered on 707 nm, with a shoulder in the red whose size depended on the degree of inhibition chosen as standard, because the log photon‐fluence rate/response lines were not parallel. There was also inhibitory activity in the blue (< 500 nm). In many respects the wavelength relationship resembled the action spectra for growth inhibition in dark‐grown seedlings, but in the latter the red peak is, or quickly becomes, more pronounced than the far‐red peak: this did not happen with potato sprouts. Blue light caused a positive phototropic response at similar or lower fluence rates. Greening became visible only at the highest fluence rates, between the two spectral regions inhibitory to growth. Broadband sources had much less inhibitory activity in the 650–750‐nm region.
Acclimatization of K+ uptake to changes in root temperature: experiments with oilseed rape and barley in flowing solution culture
Authors: MACDUFF J. H. , HOPPER M. J. , WILD A.
Published: April 2006

Abstract Changes in the net uptake rate of K+ and in the average tissue concentration of K+ were measured over 14 d in response to changes in root temperature with oilseed rape (Brassica napus L. cv. Bien venu) and barley (Hordeum vulgare L. cv. Atem). Plants were grown in flowing nutrient solutions containing 2.5 mmol m−3 K+ and were acclimatized over 49 d (rape) or 28 d (barley) to low root temperature (5°C) prior to steady–state treatments at root temperatures between 3 °C and 25 °C, with common air temperature. Uptake of K+ was monitored continuously over 14 d and nitrogen was supplied as NH4++ NO−3 or NH+4 or NO−3. Unit absorption rates of K+ increased with time and with root temperature up to Day 4 or 5 following the change in root temperature. Thereafter they usually approached steady‐state, with Q10≃ 2.0 between 7 °C and 17°C, although rates became similar between 7 °C and 13°C. Uptake of K+ by rape plants was invariably greater under NO−3 nutrition compared with NH+4. The percentage K+ in the plant dry matter increased with temperature from 2% at 3 °C to 4% at 25 °C in rape, but there was less effect of temperature on the average concentrations of K+ in the plant fresh weight or plant water content. Concentrations of K+ in the leaf water fraction of rape plants decreased with increasing root temperature, but in barley they increased with increasing root temperature. Concentrations of K+ in the root water fraction were relatively stable with respect to root temperature. The results are discussed in terms of compensatory changes in K+ uptake following a change in root temperature and the relationships between growth, shoot: root ratio and K+ composition of the plant.
The magnitude of the temperature‐driven contribution to within‐plant transport
Authors: THORNLEY J. H. M.
Published: April 2006

Abstract The contribution from temperature gradients within a plant to convective transport is calculated. Its magnitude depends primarily on the temperature differences in the plant and the radius of the conducting elements; the other quantities affecting it are well‐established physical constants. Assuming a temperature difference in the plant of 1 K and a conductive element radius of 10−4 m, the speed of convective flow is 0.5 cm h−1 and this is independent of distance.
The role of nodal and internodal responses in gravitropism and autotropism in Galium aparine L
Authors: HEATHCOTE D. G.
Published: April 2006

Abstract This time course and location of gravitropically induced curvatures in stems of goosegrass (Galium aparine L.), a member of the Rubiaceae, have been investigated. In the early stages of the response (0–5 h), curvature develops throughout the growing region, and is followed by an autotropic straightening which affects the internodes only, leading to the production of essentially straight internodes some 15 h after the onset of gravistimulation. Curvatures developing in the nodal regions, however, continue to increase over this period, and are not subject to reversal by autotropism. The nodal curvatures are not entirely dependent on the presence of any other part of the plant, since marked curvatures can be induced in isolated nodal segments. This pattern of response leads ultimately to correction of the growth direction of the plant by means of curvature responses confined exclusively to the nodes, despite the initial participation of both nodes and internodes in the gravitropic reaction.
Towards a quantitative definition of plant hormone sensitivity
Authors: WEYERS J. D. B. , PATERSON N. W. , A'BROOK R.
Published: April 2006

Abstract A definition of plant hormone sensitivity is proposed which is based on the initial rates of responses at different hormone concentrations. By analogy with enzyme kinetics, it is concluded that simple concentration‐response curves can be described by a function containing three ‘sensitivity parameters’. Objective methods for determining the values of these parameters and for comparing curves are described. These methods are used to describe the responses of Commelina communis L. stomata to abscisic acid. If certain assumptions are valid, the sensitivity parameters can be assigned physicochemical meanings. To validate the assumptions, certain experimental criteria must be fulfilled and these are discussed.
Cation exchange in isolated xylem cell walls of tomato. I. Cd2+ and Rb+ exchange in adsorption experiments
Authors: WOLTERBEEK H. Th.
Published: April 2006

Abstract Purified xylem cell walls were prepared from isolated xylem bundles of tomato (an inbred line of Lycopersicon esculentum Mill, cv. Tiny Tim). Adsorption and exchange experiments were carried out with 115Cd2+, 82Rb+ and 82Br−. The application of γ‐ray spectroscopy permitted the simultaneous measurement of several ions applied together. The cell‐wall water volume was shown to be independent of the external pH and solution ionic strength, possibly due to the presence of lignin. The Donnan Free Space (DFS) volume could be determined as a constant 0.15 dm3 per kg cell‐wall dry weight. Consequently, the total cell‐wall cation exchange capacity (CEC) could be estimated based on the DFS volume, and amounted to approximately 1000 mol m−3 negative charges. The results of Cd2+ ‐Rb+ exchange experiments indicated an apparent CEC value of about 350–450 mol m−3 DFS, at external pH ∼ 4. These data are in agreement with earlier reports on xylem wall CEC, and indicate the weak acid characteristics of the charge groups. The rational selectivity coefficient RCdRb, of the cell wall was shown to depend on external ion fractions and ionic strength, with a maximum RCdRb of 450 at ionic Cd2+ fraction near 0.3, based at the smallest experimental ionic strength of the external solution. The adsorption of Cd2+, applied at relatively high concentrations, was shown to be stimulated by simultaneous application of high Rb+ concentrations.
Photosynthetic responses to salinity in two clones of Agrostis stolonifera
Authors: ROBERTSON* K. P. , WAINWRIGHT S. J.
Published: April 2006

Abstract The response of photosynthesis, Fe, to salinity was examined in two clones of Agrostis stolonifera, one derived from a salt marsh (SM) and the other from an inland site (IL). The response of young and old leaves was examined over one week of salt treatment and changes in leaf water relations and concentrations of Na+, Cl− and K+ ions were also monitored. Sodium+ and chloride− concentrations rose much more sharply in the older leaves of both clones and Fe declined to ca. zero by Day 4. Fe in the young leaves of the SM clone was unaffected by salt whilst the young leaves of the IL clone showed a 20% reduction in Fe within 24 h of salt application. This decline was due to a decline in stomatal conductance and a reduction in the photosynthetic capacity of the mesophyll and was associated with a greater accumulation of Na+ and Cl− ions and loss of K+ ions than in the SM clone. The significance of the salt exclusion from the young leaves of the SM clone to its growth on the salt marsh is discussed.
Salt tolerance in Aster tripolium L. I. The effect of salinity on growth
Authors: SHENNAN C. , HUNT R. , MACROBBIE E. A. C.
Published: April 2006

Abstract A study of the growth of the maritime halophyte Aster tripolium L. has been carried out over a range of salinity treatments. The regression approach to growth analysis using frequent small harvests has been used to allow ‘continuous’ measurement of growth over a period of 36 d. Salinity was applied with the major ions present in ratios typical of those found in seawater. Growth was inhibited in terms of both dry weight production and leaf expansion at salinity levels equivalent to 0.625 strength sea water (full culture solution 300) and above, with the greatest effect being seen in terms of leaf area. Aster tripolium did not show increased succulence at high salinity, leaf fresh weight to dry weight ratio in fact declined, whilst leaf fresh weight per unit area remained constant. It should be noted that the plants exhibit low growth rates due to the low light intensity used.
Salt tolerance in Aster tripolium L. III. Na and K fluxes in intact seedlings
Authors: SHENNAN C.
Published: April 2006

Abstract Uptake and transport of Na and K was studied using the radioactive tracers 22Na and 42K in intact Aster tripolium L. seedlings grown at two salinities CS 10 and CS 100, (containing 10mol m−1 and 100 mol m−3 Na, respectively, together with other major ions in the proportions found in sea water). At both salinities a much greater proportion of the Na than K taken up by the plant was subsequently transported to the shoot. Most 42K fluxes were reduced by about 40% in CS 100 plants relative to CS 10 except root accumulation which increased. Experiments involving changing the salinity from CS 10 to CS 100 showed that 42K fluxes remained constant for at least 40 h, indicating that competition with Na for uptake sites was not the cause of the reduced flux in CS 100 plants. 22Na fluxes responded immediately to a change in salinity with all fluxes increasing six‐fold when the salinity was raised. When the salinity was lowered, however, root accumulation returned to the level in CS 10 control plants whereas transport to the shoot was inhibited by the previous high salinity treatment, being reduced to only 35% of the rate in CS 10 plants. The time courses of osmotic adjustment and Na accumulation following an increase in salinity were found to be very similar, with sufficient Na being accumulated to account for the observed increase in sap osmotic pressure.
Suberin lamellae in the hypodermis of maize (Zea mays) roots; development and factors affecting the permeability of hypodermal layers
Authors: CLARKSON D. T. , ROBARDS A. W. , STEPHENS J. E. , STARK M.
Published: April 2006

Abstract The development of suberin lamellae in the hypodermis of Zea mays cv. LG 11 was observed by electron microscopy and the presence of suberin inferred from autoliuorescence and by Sudan black B staining in nodal (adventitious) and primary (seminal) root axes. Suberin lamellae were evident at a distance of 30–50 mm from the tip of roots growing at 20°C and became more prominent with distance from the tip. Both oxygen deficiency and growth at 13°C produced shorter roots in which the hypodermis was suberized closer to the root tip. There were no suberin lamellae in epidermal cells or cortical collenchyma adjacent to the hypodermis. Plasmodesmata were not occluded by the suberin lamellae: there were twice as many of them in the inner tangential hypodermal wall (1,14 μn−2) as in the junction between the epidermis and hypodermis (0.54 μm−2).

Water uptake by seminal axes (measured by micropotometry) was greater at distances more than 100 mm from the root lip than in the apical zone where the hypodermis was unsuberized. In the more mature zones of roots grown at 13°C rates of water uptake were greater than in roots grown at 20°C even though hypodermal suberization was more marked.

Sleeves of epidermal/hypodermal cells (plus some accessory collenchyma) were isolated from the basal 60 mm of nodal axes by enzymatic digestion (drisclase). The roots were either kept totally immersed in culture solution or had the basal 50 mm exposed to moist air above the solution surface. In both treatments the permeabilities to tritiated water and 86Rb were low (circa 10−5mms−1) in sleeves isolated from the extreme base. In roots grown totally immersed, however, the permeability of sleeves increased 10 to 50‐fold over a distance of 40 mm. In roots exposed to moist air the permeability remained at a low level until the point where the root entered the culture solution and then increased rapidly (> 50‐fold in a distance of 8 mm). Growth of roots in oxygen depleted (5% O2) solutions promoted the development of extensive cortical aerenchymas. These developments were not associated with any reduction in permeability of sleeves isolated from the basal 40 mm of the axis.

It was concluded that the presence of suberin lamellae in hypodermal walls does not necessarily indicate low permeability of cells or tissues to water or solutes. The properties of the walls (lamellae?) can be greatly changed by exposure to moist air, perhaps due to increased oxygen availability.
Electron microscopic structure and oxygen evolution activity of thylakoids fromAvicennia marinaprepared under different osmotic and ionic conditions
Authors: PRESTON C. , MACKIE N. D. , WHITECROSS M. I. , CRITCHLEY C.
Published: April 2006

AbstractStacking of thylakoid membranesin vitrowas assessed using electron microscopy. Grana stacks of spinach thylakoids formed when 5 mol m−3MgCl2was present, but no stacking of thylakoids from the mangroveAvicennia marinaoccurred in the presence of 10 mol m−3? MgCl2. Isolation of mangrove thylakoids with a high osmotic strength medium did not induce grana formation if the medium consisted only of sorbitol or glycinebetaine. Addition of cations to the high osmotic strength medium did induce some loose‐grana formation, with divalent cations being more effective than monovalent cations. Glycinebetaine was a better osmoticum than sorbitol for grana formation provided divalent cations had been added. Oxygen evolution activity of the preparations was influenced by the amount of membrane stacking, with the preparations with the greatest amount of stacked membrane having the highest activity. Isolation with sorbitol or glycinebetaine based media did not alter this pattern, nor did assay in sorbitol or glycinebetaine. Mangrove thylakoids have a requirement for both a high osmotic strength and divalent cations for grana formationin vitrowhich may be related to the low water potential of the plant environmentin vivo.
Recovery of photosynthesis from water stress in Eucalyptus pauciflora—a process in two stages
Authors: KIRSCHBAUM M. U. F.
Published: April 2006

Abstract. Seedlings of Eucalyptus pauciflora Sieb. ex. Spreng. were stressed by withholding water. They were then rewatered, and the time course of recovery of photosynthesis was followed. Recovery always followed a distinct bi‐phasic pattern. A first, rapid, stage of recovery commenced between 5 and 60 min after rewatering and was completed by between 30 min and four h after rewatering. Recovery in this stage always involved concurrent increases in stomatal conductance and the leaf's capacity to assimilate CO2 at any intercellular partial pressure of CO2 [A(pi) relationship]. This stage of rapid recovery was followed either by a constant or gradually declining rate of photosynthesis for the remainder of the light period. In plants kept to a normal diurnal cycle, a second stage of recovery occurred and was completed during the night following rewatering. In this second stage of recovery, the A(Pi) relationship recovered to 90–100% of prestress values. In contrast, the recovery of stomatal conductance was not complete by the first day after rewatering. In darkness, complete recovery of the A(pi) relationship required as little as five h. If plants were kept in continuous high light, then between six and 16 h elapsed after rewatering before the second stage of recovery commenced. After this lag, almost complete recovery of the A(pi) relationship was possible. These results indicate that water stress has two independent and parallel effects on the mesophyll capacity for photosynthesis. The first may be simply reversible when the plant is rewatered, while the second may involve damage to the photosynthetic machinery that requires protein synthesis for its reversal.
Ice formation and tissue response in apple twigs
Authors: ASHWORTH E. N. , ECHLIN P. , PEARCE R. S. , HAYES T. L.
Published: April 2006

Abstract. The response of apple twig tissue to a freezing stress was examined using a combination of low temperature scanning electron microscopy and freeze substitution techniques. Bark and wood tissues responded differently. In the bark, large extracellular ice crystals were observed in the cortex. The adjacent cortical cells collapsed and a large reduction in cell volume was observed. The extent of cell collapse throughout the bark was not uniform. Cells in the periderm, phloem and cambium exhibited little change in cell volume compared to cortical cells. Large extracellular ice crystals were not observed in the xylem or pith tissues. The xylem ray parenchyma and pith cells did not collapse in response to a freezing stress, but retained their original shape. The pattern of ice formation and cell response was not observed to change with season or the level of cold acclimation. This study supported the concept that bark and xylem tissues exhibit contrasting freezing behaviour. The observations were consistent with the idea that water in bark freezes extracellularly while water in xylem ray parenchyma and pith cells may supercool to temperatures approaching –40 °C prior to freezing intracellularly.
Heat shock and the protection against metal toxicity in wheat leaves1
Authors: ORZECH K. A. , BURKE J. J.
Published: April 2006

Abstract. Wheat (Triticum aestivum L. var. TAM‐W101) leaf segments exhibited an acquired protection against metal toxicity following exposure of the seedlings to heat shock temperatures in the dark. The acquired protection of the leaf segments to cadmium was 400‐fold greater than leaf segments from seedlings kept at 25°C and exhibited the greatest change in protection of the five metals tested. Increased protection against aluminium and iron toxicity was also detected in the leaf segments from heat shocked seedlings. The concentration of aluminium at which a 50% loss of 2,3,5‐triphenyltetrazolium chloride reduction occurred was 5.5 mol m−3 in control leaf segments and 20 mol m−3 in the leaf segments from heat shocked seedlings. The 50% loss of 2,3,5‐triphenyltetrazolium chloride reduction in the leaf segments from heal shocked seedlings was four‐fold higher for iron. A small, yet reproducible change in the 2,3,5‐triphenyltetrazolium chloride reduction was observed for copper and no change in reduction was observed for zinc treatments in the leaf segments from heat shocked seedlings. These data indicate that exposure of wheat seedlings to heat shock temperatures results in the acquisition of protection against metal toxicity to otherwise lethal concentrations of aluminium, cadmium, and iron.
The nitrogen balance of Raphanus sativus x raphanistrum plants. II. Growth, nitrogen redistribution and photosynthesis under NO3− deprivation
Authors: KOCH G. W. , SCHULZE E.‐D. , PERCIVAL F. , MOONEY H. A. , CHU C.
Published: April 2006

Abstract. Wild radish plants deprived of, and continuously supplied with solution NO−3 for 7 d following 3 weeks growth at high NO−3 supply were compared in terms of changes in dry weight, leaf area, photosynthesis and the partitioning of carbon and nitrogen (NH2‐N and NO−3‐N) among individual organs. Initial levels of NO−3‐N accounted for 25% of total plant N. Following termination of NO−3 supply, whole plant dry weight growth was not significantly reduced for 3 d, during which time plant NH2‐N concentration declined by about 25% relative to NO−3‐supplied plants, and endogenous NO−3‐N content was reduced to nearly zero. Older leaves lost NO−3 and NH2‐N, and roots and young leaves gained NH2‐N in response to N stress. Relative growth rate declined due both to decreased net assimilation rate and a decrease in leaf area ratio. A rapid increase in specific leaf weight was indicative of a greater sensitivity to N stress of leaf expansion compared to carbon gain. In response to N stress, photosynthesis per unit leaf area was more severely inhibited in older leaves, whereas weight‐based rates were equally inhibited among all leaf ages. Net photosynthesis was strongly correlated with leaf NH2‐N concentration, and the relationship was not significantly different for leaves of NO3−‐supplied compared to NO−3‐deprived plants. Simulations of the time course of NO−3 depletion for plants of various NH2‐N and NO−3 compositions and relative growth rates indicated that environmental conditions may influence the importance of NO−3 accumulation as a buffer against fluctuations in the N supply to demand ratio.
Enhancement of ABA responsiveness in wheat embryos by high temperature*†
Authors: WALKER‐SIMMONS M.
Published: April 2006

Abstract. Mature wheat (Triticum aestivum L.) grain often possesses high‐temperature dormancy which restricts the grain from germinating at warm temperatures (25–30°C). Isolated embryos from such grain exhibited little high‐temperature dormancy when germinated in water. Dormancy was restored by the application of abscisic acid (ABA) to the embryos. The ability of ABA to block germination in isolated embryos was enhanced significantly by elevating the germination temperature. ABA was 100 times more effective in reducing embryonic germination at 30°C than at 15°C. These temperature effects on embryonic response to ABA are a useful system for studying the mechanism of ABA action in seed dormancy.
Variation in response of five identical steady‐state porometers1
Authors: REICH P. B. , WALTERS M. B. , TABONE T. J.
Published: April 2006

Abstract. Variation in response was measured for live identical steady‐state porometers manufactured and calibrated by Li‐Cor, Lincoln, NE, U.S.A. Mean values for relative humidity, air and leaf temperature, transpiration and leaf conductance were compared in two experiments, one with random measurements among a population of leaves and the other using paired observations on the lateral sides of individual leaves. Comparisons were made using young newly expanded leaves of potato (Solarium tuberosum, cv. Norland) plants grown under controlled environmental conditions in the Biotron at the University of Wisconsin‐Madison. Average mean differences among porometers were 5, 11 and 12% for relative humidity, leaf conductance and transpiration, respectively.
Photoregulation: diverse gene responses in greening seedlings
Authors: THOMPSON W. F.
Published: April 2006

Abstract. Light effects on the expression of nuclear genes for plastid proteins and for the 18S, 5.8S and 25S ribosomal RNAs are discussed, together with some recent information concerning the expression of chloroplast genes in developing plastids. Emphasis is given to the diversity of different responses observed with different genes and evidence for light effects at both transcriptional and post‐transcriptional levels.
Genetic engineering strategies for manipulation of the heat shock response
Authors: SCHÖFFL F.
Published: April 2006

Abstract. The heat shock response in plants is well characterized at the levels of RNA and protein synthesis. Increasing information is becoming available about the DNA sequences of heat shock protein genes and their mechanism of transcriptional regulation. Relatively little is known about their biochemical functions and physiological importance. The heat shock response is highly conserved in nature and the heat shock proteins appear to confer thermotolerance on cells that express them.

Modern genetic engineering and gene transfer techniques offer new possibilities to alter the expression of heat shock genes in transgenic plants by interference with the processes of transcription and translation. New strategies are discussed for selection of regulatory mutants of the heat shock response (trans‐active factors), genetic engineering of cis‐active promoter elements, the use of antisense RNA, and the overexpression of heat shock proteins.
A role for haemoglobin in all plant roots?
Authors: APPLEBY C. A. , BOGUSZ D. , DENNIS E. S. , PEACOCK W. J.
Published: April 2006

Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation.
Molecular approaches to the analysis of nitrate assimilation
Authors: WRAY J. L.
Published: April 2006

Abstract. The application of molecular approaches such as mutant analysis and recombinant DNA technology, in conjunction with immunology, are set to revolutionize our understanding of the nitrate assimilation pathway. Mutant analysis has already led to the identification of genetic loci encoding a functional nitrate reduction step and is expected to lead ultimately to the identification of genes encoding nitrate uptake and nitrite reduction. Of particular significance would be identification of genes whose products contribute to regulatory networks controlling nitrogen metabolism. Recombinant DNA techniques are particularly powerful and have already allowed the molecular cloning of the genes encoding the apoprotein of nitrate reductase and nitrite reductase. These successes allow for the first lime the possibility to study directly the role of environmental factors such as type of nitrogen source (NO3− or NH4+) available to the plant, light, temperature water potential and CO2 and O2 tensions on nitrate assimilation gene expression and its regulation at the molecular level. This is an important advance since our current understanding of the regulation of nitrate assimilation is based largely on changes of activity of the component steps. The availability of mutants, cloned genes, and gene transfer systems will permit attempts to manipulate the nitrate assimilation pathway.
Elicitors and defence gene activation
Authors: TEMPLETON M. D. , LAMB C. J.
Published: April 2006

Abstract. Plants respond actively to infection and other environmental stresses by synthesizing phytoalexins and defence‐related proteins. This response can be induced in plant cell suspension cultures with compounds known as elicitors. These are often carbohydrates of fungal origin. In bean, transcriptional activation of the defence genes commences less than five minutes after elicitor addition, thus it is clearly a very rapid response implying few biochemical steps exist between elicitor interaction and the initiation of defence gene transcription. The induction of phytoalexin biosynthesis during incompatible interactions of bean with Colletotrichum lindemuthianum occurs rapidly during the initial contact between the host and pathogen. This appears to be a direct response to molecular recognition of the pathogen. In compatible interactions however, the pathogen grows biotrophically and phytoalexin biosynthesis is not triggered until lesions begin to form. Thus this may be a response to tissue damage rather than direct molecular recognition. Many bean defence genes, including those regulating key points in the phytoalexin biosynthetic pathway, exist in the genome as small multigene families. In some cases there is differential regulation within a family in response to developmental and environmental signals. The analysis of the cis‐acting sequences involved in the regulation of chalcone synthase has been facilitated by the use of electroporated protoplasts as a transient assay system. This work and the use of DNA footprinting and gel‐retardation assays will help identify the corresponding trans‐acting factors involved in the regulation of these genes. While progress is being made in understanding the mechanisms of transcriptional activation of defence genes little is known of how plants recognize pathogens and elicitors or how this signal is transduced to the nucleus.
Plant regulated aspects of nodulation and N2 fixation
Authors: VANCE C. P. , EGLI M. A. , GRIFFITH S. M. , MILLER S. S.
Published: April 2006

Abstract. Root nodule organogenesis is described. Plant regulated aspects of nodulation and N2 fixation are reviewed and discussed. Since the effective N2 fixing symbiosis requires the interaction of the host plant and bacterium in an appropriate environment (the rhizosphere and the root nodule) it is essential that research aimed at improving N2 fixation involve a knowledge and understanding of the plant genes that affect nodule development, growth, and function. Current knowledge of host plant genes involved in N2 fixation is summarized. Various experimental approaches to the study of the host plant's contribution to nodulation are noted. The functions of nodule specific proteins (nodulins) in symbiosis are delineated. Future areas of research are suggested.
The influence of water deficits on needle conductance, assimilation rate and abscisic acid concentration of seedlings of Pinus radiata D. Don
Authors: SQUIRE R. O. , NEALES T. F. , LOVEYS B. R. , ATTIWILL P. M.
Published: April 2006

Abstract Seedlings of Pinus radiata, 10–20 weeks old and hitherto fully watered, responded rapidly when water was withheld. Wilting occurred 9d later, at which time soil matric water potential at dawn (Ψm) was –1.06MPa and shoot water potential (Ψ) was –1.9 MPa. Small reductions in Ψm elicited large responses in assimilation rate (A) and leaf conductance to water vapour (g). Seedlings appear to be more sensitive to small water deficits than are older Plants of P. radiata. After rewatering, significant increases of A and g occurred within one day, but neither regained the values measured prior to the imposition of a single drying cycle. This residual effect of drought on A, after one or six drying cycles, was partially caused by a decrease in photosynthetic capacity.

In plants wilted for the first time, the concentration of abscisic acid (ABA) in the bulk foliage increased 3.4 times as Ψ decreased to –1.77 MPa. In comparison, pretreatment with six drying cycles significantly reduced Ψ to –2.13 MPa (indicating some osmotic adjustment) and induced only a doubling of ABA concentration. However, these differences in Ψ and ABA concentration did not Persist after the plants of all pretreatments had been watered for 7 d, although g of drought‐pretreatment Plants remained approximately half that of continuously‐watered plants.