bluuebunny/crossref_metadata_2025 huggingface dataset:
dr and spr/sr mutations of Chlamydomonas reinhardtii affecting D1 protein function and synthesis define two independent steps leading to chronic photoinhibition and confer differential fitness
Authors: HEIFETZ P. B. , LERS A. , TURPIN D. H. , GILLHAM N. W. , BOYNTON J. E. , OSMOND C. B.
Published: November 2003

The effects of introduced chloroplast gene mutations affecting D1 synthesis, turnover and function on photosynthesis, growth and competitive ability were examined in autotrophic cultures of Chlamydomonas reinhardtii (Chlorophyta) adapted to low or high irradiance. Few discernible effects were evident when the mutants were grown in low light (LL, 70 μmol m−2 s−1). The herbicide‐resistant psbA mutation Ser264→ Ala (dr) slowed electron transfer and accelerated D1 degradation in cells grown under high light (HL, 600 μmol m−2 s−1). The maximum rate of light‐and CO2‐saturated photosynthesis, cell growth rate and competitive ability in the dr mutant were reduced compared to wild type under HL. However, the wild‐type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. In spr/sr cells grown under HL, D1 synthesis was reduced by 40–60% compared to wild type and D1 degradation was accelerated, leading to a 4‐fold reduction in D1 pool size. The reduced D1 levels were accompanied by an elevation of Fo and a decline in Fv/Fm, quantum yield and maximum rate of CO2‐saturated photosynthesis. Chemostat experiments showed that the growth rate and competitive ability of spr/sr were reduced against both wild type and dr.
Kinetics of nitrate and ammonium absorption and accompanying H+fluxes in roots ofLolium perenneL. and N2‐fixingTrifolium repensL.
Authors: HØGH‐JENSEN H. , WOLLENWEBER B. , SCHJOERRING J. K.
Published: November 2003

Kinetic parameters for NH4+and NO3−uptake were measured in intact roots ofLolium perenneand actively N2‐fixingTrifolium repens.Simultaneously, net H+fluxes between the roots and the root medium were recorded, as were the net photosynthetic rate and transpiration of the leaves. A Michaelis–Menten‐type high‐affinity system operated in the concentration range up to about 500 mmol m−3NO3−or NH4+. InL. perenne, theVmaxof this system was 9–11 and 13–14 μmol g−1root FW h−1for NO3−and NH4+, respectively. The corresponding values inT. repenswere 5–7 and 2 μmol g−1root FW h−1. TheKmfor NH4+uptake was much lower inL. perennethan inT. repens(c.40 compared with 170 mmol m−3), whileKmvalues for NO3−absorption were roughly similar (around 130 mmol m−3) in the two species. There were no indications of a significant efflux component in the net uptake of the two ions. The translocation rate to the shoots of nitrogen derived from absorbed NO3−‐N was higher inT. repensthan inL. perenne, while the opposite was the case for nitrogen absorbed as NH4+.Trifolium repenshad higher rates of transpiration and net photosynthesis thanL. perenne.Measurements of net H+fluxes between roots and nutrient solution showed thatL. perenneabsorbing NO3−had a net uptake of H+, whileL. perennewith access to NH4+andT. repens, with access to NO3−or NH4+, in all cases acidified the nutrient solution. Within the individual combinations of plant species and inorganic N form, the net H+fluxes varied only a little with external N concentration and, hence, with the absorption rate of inorganic N. Based on assessment of the net H+fluxes inT. repens, nitrogen absorption rate via N2fixation was similar to that of inorganic N and was not down‐regulated by exposure to inorganic N for 2 h. It is concluded thatL. perennewill have a competitive advantage overT. repenswith respect to inorganic N acquisition.
Freezing exposure releases bud dormancy in Betula pubescens and B. pendula
Authors: RINNE P. , HÄNNINEN H. , KAIKURANTA P. , JALONEN J. E. , REPO T.
Published: November 2003

Bud dormancy in woody plants is released by long‐term exposure to non‐freezing chilling temperatures, whereas freezing temperatures have been considered to have little or no effect. However, the present results demonstrate that short‐term exposure to freezing can release bud dormancy in Betula pubescens (Ehrh.) and B. pendula (Roth). Short‐term freezing during the dormancy induction phase improved the release of bud dormancy only if an adequate level of dormancy had been reached. In fully dormant or chilled plants both the percentage and the speed of bud‐burst increased, the more so the lower the temperature. Our results rule out the possibility that endogenous abscisic acid could be directly involved in the physiological control of bud dormancy release. The fast, easily applicable method presented here for bud dormancy release could further investigations into the biochemical and biophysical background to the process. The mechanisms of bud dormancy release and its relationship to cold acclimation are discussed in the light of these results, as also are the implications of the findings for modelling of bud dormancy.
Effects of ozone on the plasma membrane proteins in Arabidopsis thaliana (L.) leaves
Authors: TOKARSKA‐SCHLATTNER M. , FINK A. , CASTILLO F. J. , CRESPI P. , CREVECOEUR M. , GREPPIN H. , TACCHINI P.
Published: November 2003

The protein pattern of leaf plasma membranes from Arabidopsis thaliana (L.) Landsberg erecta was analysed in order to detect changes induced by acute short‐term ozone treatment. Plasma membranes were isolated 0, 3 and 8 h after the end of a 2 h fumigation of the plants with 500 nmol mol−1 of O3. Proteins extracted from plasma membranes were separated by high‐performance two‐dimensional polyacrylamide gel electrophoresis. Eight hours after the end of fumigation, one new protein appeared and the amounts of two other proteins increased significantly. The reported study is a first step towards the identification of plasmalemma proteins altered by ozone and to a more detailed characterization of structural changes occurring in the plasma membrane after ozone exposure.
Water use efficiency of two succulents with contrasting CO2 fixation pathways
Authors: ELLER B. M. , FERRARI S.
Published: November 2003

Two succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C3 pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled‐environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO2 fixation was similar in the two species. This result confirms that the daily CO2 fixation of CAM plants is as high as that of morphologically similar C3 plants adapted to the same habitat. As expected, both species reduced CO2 fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol−1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better ‘water saver’ than a C3 plant does not necessarily hold for CAM and C3 plants with similar growth forms growing under the same environmental conditions.
Influence of ozone on transgenic tobacco plants expressing reduced quantities of Rubisco
Authors: WIESE C. B. , PELL E. J.
Published: November 2003

RbcS‐antisense transformed tobacco plants (Nicotiana tabacum cv. Petit Havana) expressing reduced quantities of Rubisco protein were used to examine the role of Rubisco quantity in determining ozone (O3) sensitivity. Transformed and wild‐type plants were exposed to O3 in the greenhouse and in the field. Stomatal conductance, net photosynthesis and Rubisco protein quantity were measured at various times. Antisense‐transformed genotypes responded to O3 by exhibiting rapid, severe foliar necrosis. The wild‐type plants responded more slowly, exhibiting limited injury. Decreases in stomatal conductance, net photosynthesis or Rubisco quantity in plants exposed to O3 were not observed in asymptomatic leaves. Total biomass was lower for the transformed genotypes and decreased in both genotypes after exposure to O3. Shoot–root ratio and specific leaf area were higher in the transformed genotypes and increased in both genotypes with exposure to O3. Measurements of intercellular airspace demonstrated the presence of larger intercellular spaces in the transformed plants. The indirect effects of the rbcS antisense transformation, including morphological changes in the leaf, probably rendered the transformed plants more sensitive to the oxidant. The decreased quantity of Rubisco is not thought to be directly related to increased O3 sensitivity in the transformed plants.
Control of transpiration from the upper canopy of a tropical forest: the role of stomatal, boundary layer and hydraulic architecture components
Authors: MEINZER F. C. , ANDRADE J. L. , GOLDSTEIN G. , HOLBROOK N. M. , CAVELIER J. , JACKSON P.
Published: November 2003

Concurrent, independent measurements of stomatal conductance (gs), transpiration (E) and microenvironmental variables were used to characterize control of crown transpiration in four tree species growing in a moist, lowland tropical forest. Access to the upper forest canopy was provided by a construction crane equipped with a gondola. Estimates of boundary layer conductance (gb) obtained with two independent methods permitted control of E to be partitioned quantitatively between gs and gb using a dimensionless decoupling coefficient (Ω) ranging from zero to 1. A combination of high gs (c. 300–600 mmol m−2 s−1) and low wind speed, and therefore relatively low gb (c. 100–800 mmol m−2 s−1), strongly decoupled E from control by stomata in all four species (Ω= 0.7–0.9). Photosynthetic water‐use efficiency was predicted to increase rather than decrease with increasing gs because gb was relatively low and internal conductance to CO2 transfer was relatively high. Responses of gs to humidity were apparent only when the leaf surface, and not the bulk air, was used as the reference point for determination of external vapour pressure. However, independent measurements of crown conductance (gc), a total vapour phase conductance that included stomatal and boundary layer components, revealed a clear decline in gc with increasing leaf‐to‐bulk air vapour pressure difference (Va because the external reference points for determination of gc and Va were compatible. The relationships between gc and Vc and between gs and Vs appeared to be distinct for each species. However, when gs and gc were normalized by the branch‐specific ratio of leaf area to sapwood area (LA/SA), a morphological index of potential transpirational demand relative to water transport capacity, a common relationship between conductance and evaporative demand for all four species emerged. Taken together, these results implied that, at a given combination of LA/SA and evaporative demand scaled to the appropriate reference point, the vapour phase conductance and therefore transpiration rates on a leaf area basis were identical in all four contrasting species studied.
The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don
Authors: WALCROFT A. S. , WHITEHEAD D. , SILVESTER W. B. , KELLIHER F. M.
Published: November 2003

Responses of photosynthesis (A) to intercellular CO2 concentration (ci) in 2‐year‐old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4‐fold increase in Vcmax, the maximum rate of carboxylation (10.7–43.3 μol m−2 s−1 and a 3‐fold increase in Jmax, the maximum electron transport rate (20.5–60.2 μmol m −2 s−1). The temperature optimum for Jmax was lower than that for Vcmax, causing a decline in the ratio Jmax:Vcmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg−1, and there were linear relationships between N concentration and both Vcmax and Jmax. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg−1 near the base to 1.54 mol kg−1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.
Heat shock temperature acclimation of normal secretory protein synthesis in barley aleurone cells
Authors: CAMPBELL J. D. , FIELDING L. A. , BRODL M. R.
Published: November 2003

Exposure of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers to 40°C for a period of 3 h results in the selective suppression of the synthesis and secretion of hydrolytic enzymes; other normal cellular protein synthesis continues during heat shock. This suppression is correlated with secretory protein mRNA destabilization and the dissociation of stacked ER lamellae during heat shock (Belanger et al. 1986, Proceedings of the National Academy of Sciences USA 83, pp. 1354–1358). In this report we examined the effect of exposure to extended periods of heat shock. If exposure to 40°C was continued for a period of 18 h, the synthesis of α‐amylase, the predominant secreted hydrolase, resumed. This was accompanied by increased α‐amylase mRNA levels and the reformation of ER lamellae. Though initial exposure (3 h) to 40°C reduced protein secretion to ∼10% of that observed in aleurone cells maintained at 25°C, exposure for prolonged periods (16–20 h) permitted the resumption of protein secretion to ∼66% of non‐heat‐shocked control levels. The resumption of normal secretory protein synthesis during prolonged exposure to 40°C was correlated with an increase in the incorporation of [14C]glycerol into phosphatidylcholine and an increase in the ratio of saturated to unsaturated fatty acids in lipids isolated from ER membrane preparations. Increased fatty acid saturation has been demonstrated to enhance thermostability in biological membranes, and such changes in membrane composition may be important to the recovery of secretory protein synthesis at the ER.
Root respiration in citrus acclimates to temperature and slows during drought
Authors: BRYLA D. R. , BOUMA T. J. , EISSENSTAT D. M.
Published: November 2003

Citrus seedlings were grown in soil columns in which the root system was hydraulically separated into two equal layers; this enabled us to maintain roots in the upper layer without water for 110 d. The columns were placed into waterbaths modified so that soil temperatures in the top layer could be maintained at 25°C or at 35°C, while temperature in the bottom layer was maintained at 25°C. We hypothesized that, if citrus plants were grown in dry soil for an extended period, root mortality would increase if the cost of maintaining the roots was increased by elevating the soil temperature. However, during the drought period we did not observe any root mortality, even at the higher soil temperature. Moreover, we did not find that root respiration was increased by prolonged exposure to drought and higher soil temperature. We did find that root respiration rates slowed in dry soil. Furthermore, when the soil columns were switched from one temperature treatment to another, root respiration rates in wet soil rapidly increased when moved to a higher temperature or rapidly decreased when moved to a lower temperature. But after only 4 d, respiration rates returned to their original level; root respiration in dry soil was not affected by either short‐or long‐term shifts in soil temperature. Root respiration in citrus appears to acclimate rapidly to changes in soil temperature.
The reflectance properties of plant internodes modify elongation responses to lateral far‐red radiation
Authors: SEAVERS G. P. , SMITH H.
Published: November 2003

The quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied. Reflectance of incident light, which was either normal or longitudinal to the internode axis, was investigated. Increasing the angle of incidence caused a greater proportion of incident light to be reflected. Light striking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the reflected light quality. At larger angles, interactions with the internode were reduced. As a parallel investigation, the extension growth rate of light‐grown Sinapis alba L. seedlings was monitored continuously using sensitive linear displacement transducers. When the angle of illumination by fibre‐optic probes, presenting far‐red light to the growing internode, was changed from 0° to 45°, an increase was observed in stem extension rate. There is a possibility that this rate increase was the result of a fall in the red:far‐red ratio (R:FR) present inside the plant internode as the angle of incidence was altered. However, it is more likely that it was due to the larger surface area of stem being illuminated. The consequences of these observations are discussed in relation to the potential influence of such modified reflections on canopy light environments and resultant shade responses which may occur when light of known R:FR impinges on plant internodes at angles other than 0°. The possibility is discussed that plants may perceive the quality of reflected radiation from neighbouring plants to be substantially different dependent upon the angle at which it is reflected.
The responses of wild‐type and ABA mutant Arabidopsis thaliana plants to phosphorus starvation
Authors: TRULL M. C. , GUILTINAN M. J. , LYNCH J. P. , DEIKMAN J.
Published: November 2003

The growth patterns of plants subjected to phosphorus starvation resemble those caused by treatment with ABA, suggesting that ABA could mediate the response of the plant to phosphorus starvation. We examined the role of ABA in phosphorus stress by comparing growth and biochemical responses of Arabidopsis thaliana ABA mutants aba‐1 and abi2‐1 to those of wild‐type plants. We first characterized acid phosphatase production of wild‐type Arabidopsis in response to phosphorus starvation. We found that several acid phosphatase isozymes are present in roots and shoots, but only a subset of these isozymes are induced by phosphorus stress, and they are induced in both organs. Production of acid phosphatase in response to phosphorus stress was not affected by the aba‐1 or abi2‐1 mutations. Low phosphorus also resulted in decreased growth of both wild‐type and ABA mutant plants, and the root‐to‐shoot ratio was increased in both wild type and mutants. Anthocyanins accumulated in response to phosphorus stress in both wild‐type and mutant plants, but the increase was reduced in the aba‐1 mutant. Thus, two different ABA mutants responded normally in most respects to phosphorus stress. Our data do not support a major role for ABA in coordinating the phosphorus‐stress response.
Rates of stomatal opening in conifer seedlings in relation to air temperature and daily carbon gain
Authors: PEPIN S. , LIVINGSTON N. J.
Published: November 2003

Experiments were conducted on well watered 1‐year‐old Douglas fir [Pseudotsuga menziesii(Mirb.) Franco], western hemlock [Tsuga heterophylla(Raf.) Sarg.] and western redcedar (Thuja plicataDonn) seedlings to determine the effects of temperature on whole‐plant photosynthetic and stomatal responses to short‐term fluctuations in irradiance (Q). Following a step change inQ, time constants (τ, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar τAdecreased from 30 ± 4 min at 5 °C to 10 ± 1 min at 25 °C. In all cases, τAwas within 10–15% of τgs. There was considerable variation in τ among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for τ accounted for 99% of the diurnal variability inAandgsfor seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of dailyAwere within 2% of those measured. Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3–4 episodes (≥1 h) of shade (200 or 500 μmol m−2s−1) or complete darkness during the day. In such cases, dailyAwas overestimated by up to 4 and 21%, respectively, if a function for τ was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in τ could lead to increases in daily carbon gains of almost 5% depending on the frequency and degree of shading. If these daily gains were translated into increased dry matter production and compounded, seasonal gains would be even larger.
Oxygen sensitivity of C4 photosynthesis: evidence from gas exchange and chlorophyll fluorescence analyses with different C4 subtypes
Authors: MAROCO J. P. , KU M. S. B. , EDWARDS G. E.
Published: November 2003

Because photosynthetic rates in C4 plants are the same at normal levels of O2 (c, 20 kPa) and at c, 2 kPa O2 (a conventional test for evaluating photorespiration in C3 plants) it has been thought that C4 photosynthesis is O2 insensitive. However, we have found a dual effect of O2 on the net rate of CO2 assimilation among species representing all three C4 subtypes from both monocots and dicots. The optimum O2 partial pressure for C4 photosynthesis at 30 °C, atmospheric CO2 level, and half full sunlight (1000 μmol quanta m−2 s−1) was about 5–10 kPa. Photosynthesis was inhibited by O2 below or above the optimum partial pressure. Decreasing CO2 levels from ambient levels (32.6 Pa) to 9.3 Pa caused a substantial increase in the degree of inhibition of photosynthesis by supra‐optimum levels of O2 and a large decrease in the ratio of quantum yield of CO2 fixation/quantum yield of photosystem II (PSII) measured by chlorophyll a fluorescence. Photosystem II activity, measured from chlorophyll a fluorescence analysis, was not inhibited at levels of O2 that were above the optimum for CO2 assimilation, which is consistent with a compensating, alternative electron How as net CO2 assimilation is inhibited. At suboptimum levels of O2, however, the inhibition of photosynthesis was paralleled by an inhibition of PSII quantum yield, increased state of reduction of quinone A, and decreased efficiency of open PSII centres. These results with different C4 types suggest that inhibition of net CO2 assimilation with increasing O2 partial pressure above the optimum is associated with photorespiration, and that inhibition below the optimum O2 may be caused by a reduced supply of ATP to the C4 cycle as a result of inhibition of its production photochemically.
Heat stress affects the organization of microtubules and cell division in Nicotiana tabacum cells
Authors: SMERTENKO A. , DRÁBER P. , VIKLICKÝ V. , OPATRNÝ Z.
Published: November 2003

To investigate the effects of heat stress on the plant cytoskeleton, the structure of microtubule arrays in N. tabacum suspension cells incubated at 38 or 42°C was analysed. Whilst incubation at 42 °C resulted in the disruption of the majority of cellular microtubules after 30 min, in cells exposed to 38 °C all the microtubule arrays were preserved even after 12 h of incubation, although their organization was altered. The most susceptible were the microtubules of the mitotic spindle and the phragmoplast. Several abnormalities were observed: (i) splitting of the spindle into several parts; (ii) elongation of the spindles; (iii) formation of microtubule asters in mitotic cells, and (iv) elongation of phragmoplast microtubules. Exposure of cells to 38 °C caused a decrease in the mitotic index but an accumulation of telophase cells. The recovery of normal microtubule organization occurred after 12 h. Treatment of the cells subjected to heat stress conditions with an inhibitor of protein synthesis, cycloheximide, did not prevent either the alterations of microtubule organization or accumulation of cells containing phragmoplasts. Therefore, heat shock proteins do not seem to be directly responsible for the microtubule disorganization induced by heat stress.
Active oxygen species production in tobacco cells elicited by cryptogein*
Authors: SIMON‐PLAS F. , RUSTÉRUCCI C. , MILAT M.‐L. , HUMBERT C. , MONTILLET J.‐L. , BLEIN J.‐P.
Published: November 2003

We analyse the relationship between active oxygen species (AOS) production and pH changes induced in tobacco cells by cryptogein, a fungal proteinaceous elicitor of defence mechanisms in plants. When tobacco cells were treated with cryptogein, an intracellular acidification, an alkalinization of the extracellular medium and a transient burst of AOS (H2O2) were observed. Treatment of elicited cells with either diphenyleneiodonium (DPI), an inhibitor of the neutrophil NADPH oxidase, or Tiron, which scavenges O2˙− abolished AOS production. These data suggest the involvement of a NADPH oxidase‐like enzyme leading to H2O2 production through O2˙− dismutation. Although H2O2 production could be, per se, the origin of the pH changes observed, we showed that it was not the main cause, since DPI and Tiron did not inhibit extracellular alkalinization. On the other hand, cryptogein‐induced changes in pH could be abolished using fusicoccin (FC), which is known to stimulate the plasmalemma H+ ATPase. Consequently, the observed changes in pH induced by cryptogein could be mainly due to the inhibition of the plasmalemma H+‐ATPase activity. Furthermore, changes in extracellular pH were shown to modulate the intensity of AOS production by elicited cells. The possible regulation of the NAD(P)H oxidase activity of plant cells by changes in pH is further discussed.
Two isoforms of the GBSSI class of granule‐bound starch synthase are differentially expressed in the pea plant (Pisum sativum L.)
Authors: DENYER K. , BARBER L. M. , EDWARDS E. A. , SMITH A. M. , WANG T. L.
Published: November 2003

In addition to the GBSSI isoform of starch synthase described previously, the pea plant contains a second, granule‐bound isoform, GBSSIb. GBSSI is abundant in pea embryos and Rhizobium root nodules, is present at low levels in pods and is absent from leaves. Mutations at the lam locus eliminate GBSSI from all of these organs. GBSSIb is present in pods, leaves and nodules and is unaffected by mutations at the lam locus. GBSSI and GBSSIb are very similar in molecular mass, primary sequence, activity and antigenic properties. GBSSIb, like GBSSI, can synthesize amylose in the presence of malto‐oligosaccharides in isolated starch granules. However, its role in vivo is unclear. The lam mutation eliminates amylose from the starch of embryos but does not affect the relatively small amounts of amylose‐like material in the starch of pods, leaves and nodules. The significance of these results for understanding of the regulation of amylose synthesis is discussed.
Carbon isotope discrimination in irrigated and droughted potato (Solanum tuberosum L.)
Authors: JEFFERIES R. A. , MACKERRON D. K. L.
Published: November 2003

Carbon isotope discrimination (Δ) was measured in irrigated and droughted potato. Under irrigation, Δ in leaflets at given nodes increased (P < 0.001) between 21 and 63 d after emergence (DAE), which was attributed to increasing stomatal conductance (gs) during leaf expansion. The effect of leaf position on Δ was non‐significant in mature leaves. Under drought, Δ decreased (P < 0.001) in successive leaves up the stem, reflecting changes in gs and water stress. At each node Δ remained constant or decreased, suggesting that effects of water stress were greater than changes with leaf expansion. There were significant differences in Δ between cultivars in both treatments, and in the progressive decrease in Δ up the stem under drought. Differences in Δ between cultivars were consistent with differences in stomatal control of leaf water status following water stress. Values for Δ in tubers were consistently lower than in stem and leaf, and decreased more rapidly.

Differences in Δ between cultivars did not reflect dry matter production in either treatment, and differences in water use were non‐significant between cultivars under drought. So, plants can achieve similar dry matter production through different growth strategies when irrigated or droughted, and Δ does not provide a simple, indirect method of selecting for dry matter production under water stress.
Evidence that the induction of crassulacean acid metabolism by water stress in Mesembryanthemum crystallinum (L.) involves root signalling
Authors: EASTMOND P. J. , ROSS J. D.
Published: November 2003

The aim of this study was to investigate whether the root system of Mesembryanthemum crystallinum (L.) plays a role in triggering the induction of crassulacean acid metabolism (CAM) during water stress. Depriving well‐irrigated plants of water, by allowing the soil surrounding the roots to dry, caused increased daily losses in leaf relative water content (RVVC) and mesophyll cell turgor pressure. The RWC of the roots also declined. Subsequently plants exhibited physiological characteristics of CAM photosynthesis (i.e. diurnal fluctuations in leaf titratable acidity and nocturnal net CO2 fixation). When the root system of plants was divided equally between two soil compartments and one half deprived of water, plants exhibited physiological characteristics of CAM without prior changes in leaf RWC content or mesophyll cell turgor pressure. Only the RWC of the water‐stressed portion of the roots was reduced. These data suggest that in water‐stressed plants daily changes in leaf water relations greater than those observed in well‐irrigated plants, are not essential to trigger CAM expression. It is probable that a reduction in soil water availability can be perceived by the roots of M. crystallinum and that this information is conveyed to the leaves triggering the transition from C3 to CAM photosynthesis.
Soil CO2 concentration does not affect growth or root respiration in bean or citrus
Authors: BOUMA T. J. , NIELSEN K. L. , EISSENSTAT D. M. , LYNCH J. P.
Published: November 2003

Contrasting effects of soil CO2 concentration on root respiration rates during short‐term CO2 exposure, and on plant growth during long‐term CO2 exposure, have been reported. Here we examine the effects of both short‐ and long‐term exposure to soil CO2 on the root respiration of intact plants and on plant growth for bean (Phaseolus vulgaris L.) and citrus (Citrus volkameriana Tan. & Pasq.). For rapidly growing bean plants, the growth and maintenance components of root respiration were separated to determine whether they differ in sensitivity to soil CO2. Respiration rates of citrus roots were unaffected by the CO2 concentration used during the respiration measurements (200 and 2000 μmol mol−1), regardless of the soil CO2, concentration during the previous month (600 and 20 000 μmol mol−1). Bean plants were grown with their roots exposed to either a natural CO2 diffusion gradient, or to an artificially maintained CO2 concentration of 600 or 20 000 μmol mol−1. These treatments had no effect on shoot and root growth. Growth respiration and maintenance respiration of bean roots were also unaffected by CO2 pretreatment and the CO2 concentration used during the respiration measurements (200–2000 μmol mol−1). We conclude that soil CO2 concentrations in the range likely to be encountered in natural soils do not affect root respiration in citrus or bean.
Microclimate above grass adversely affects spring growth of seedling snow gum (Eucalyptus pauciflora)
Authors: BALL M. C. , EGERTON J. J. G. , LEUNING R. , CUNNINGHAM R. B. , DUNNE P.
Published: November 2003

Growth of snow gum seedlings (Eucalyptus pauciflora Sieb. ex Spreng.) was studied in response to differences in microclimate caused by differential heat exchange between seedlings, grass and bare, moist soil during winter and spring. Seedlings were planted in a pasture either directly into grassy groundcover or in circular patches of bare soil of 30, 60 or 120 cm in diameter. There were no differences in maximum air temperatures at seedling leaf height between treatments. However, minimum air temperature increased by 2 °C with increase in patch diameter from 0 to 120 cm such that seedlings surrounded by grass experienced lower minimum temperatures with more frequent and more severe frosts than seedlings growing in large patches of bare soil. These small‐scale differences in minimum temperature affected both photosynthetic and growth processes. Over winter, seedlings were photoinhibited, with depression in midday Fv/Fm linearly related to minimum temperatures. In spring, repeated frosts and lower minimum temperatures led to a delay in the recovery of Fv/Fm, a delay in bud‐break, damage to elongating stems and developing leaves, lower rates of stem elongation, and ultimately a shorter growing season for seedlings in grass compared to those in bare soil patches. Thus, microclimate above grass adversely affects spring growth of juvenile Eucalyptus pauciflora and may account for much of the competitive inhibition of tree seedling growth by grass during spring.
Virus‐induced differences in the response of oat plants to elevated carbon dioxide
Authors: MALMSTRÖM C. M. , FIELD C. B.
Published: November 2003

Disease is an integral element of agricultural and natural systems, but the roles pathogens play in determining ecosystem response to elevated CO2 have rarely been examined. To investigate whether disease can alter the response of plants to CO2, we examined the effects of doubled CO2 (∼700 μmol mol−1) on Avena sativa infected with barley yellow dwarf virus (BYDV), a common pathogen of cereals and grasses. Oats infected with BYDV showed a significantly greater biomass response to CO2 enrichment than did healthy plants. Root mass of diseased plants increased by 37–60% with CO2 enrichment, but was largely unaffected in healthy plants. CO2 enrichment increased midday leaf‐level photosynthesis and instantaneous water use efficiency by 34 and 93% in healthy plants and by 48 and 174% in infected plants. Foliar carbohydrates increased with both CO2 enrichment and BYDV infection, but the two factors affected individual pools dissimilarly. CO2 enrichment may alter the epidemiology of BYDV by increasing the persistence of infected plants.
The combined effects of CO2 concentration and solar UV‐B radiation on faba bean grown in open‐top chambers
Authors: VISSER A. J. , TOSSERAMS M. , GROEN M. W. , MAGENDANS G. W. H. , ROZEMA J.
Published: November 2003

The response of faba bean seedlings to the combined effects of increased atmospheric CO2 concentrations ([CO2]) and solar UV‐B irradiance was studied using open‐top chambers transparent to UV‐B radiation. The purpose of the study was to determine whether effects of increased [CO2] on growth and physiology are modified by the present solar UV‐B fluence rate in the Netherlands. Seedlings were exposed to 350 or 700 μmol mol−1 CO2. At both [CO2], solar UV‐B irradiance was either present or reduced using polyester foil opaque to UV‐B radiation. To obtain information on the time dependence of increased [CO2] and UV‐B radiation effects, three harvests were performed during the experiment. CO2 enrichment resulted in increased biomass production at all harvests. At the final harvest, UV‐B radiation did not affect biomass production but a significant decrease was observed after 14 d of treatment. A reduction of the UV‐B fluence increased shoot length at both [CO2] throughout the experiment. UV‐B radiation slightly altered biomass allocation. Plants grown at reduced levels of UV‐B radiation invested less biomass in flowers and more in stem material compared to plants grown at ambient UV‐B levels. CO2 enrichment resulted in a stimulation of net photosynthesis after 26 and 38 d of treatment. UV‐B reduction did not alter this response. After 26 d of treatment, photosynthetic acclimation to CO2 enrichment was observed, which was probably the result of accumulation of carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV‐B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV‐B radiation was limited to UV‐A transmittance of leaves. Under prevalent experimental conditions, UV‐B radiation did not affect the measured physiological parameters. Most open‐top chambers used for climate change research are constructed of materials which do not transmit UV‐B radiation. Our results indicate that part of the ‘chamber effects’ on plant height often described in the literature might be explained by the absence of solar UV‐B radiation in these chambers.
CO2‐concentrating mechanisms: a direct role for thylakoid lumen acidification?
Authors: RAVEN J. A.
Published: November 2003

A testable mechanism of CO2 accumulation in photolithotrophs, originally suggested by Pronina & Semenenko, is quantitatively analysed. The mechanism involves (as does the most widely accepted hypothesis) the delivery of HCO3− to the compartment containing Rubisco. It differs in proposing subsequent HCO3− entry (by passive uniport) to the thylakoid lumen, followed by carbonic anhydrase activity in the lumen; uncatalysed conversion of HCO3− to CO2, even at the low pH of the lumen, is at least 300 times too slow to account for the rate of inorganic C acquisition. Carbonic anhydrase converts the HCO3− to CO2 at the lower pH maintained in the illuminated thylakoid lumen by the light‐driven H+ pump, generating CO2 at 10 times or more the thylakoid HCO3− concentration. Efflux of this CO2 can suppress Rubisco oxygenase activity and stimulate carboxylase activity in the stroma. This mechanism differs from the widely accepted hypotheses in the required location of carbonic anhydrase, i.e. in the thylakoid lumen rather than the stroma or pyrenoid, and in the need for HCO3− influx to thylakoids. The capacity for anion (assayed as Cl−) entry by passive uniport reported for thylakoid membranes is adequate for the proposed mechanism; if the Cl− channel does not transport HCO3−, HCO3− entry could be by combination of the Cl− channel with a Cl− HCO3− antiporter. This mechanism is particularly appropriate for organisms which lack overt accumulation of total inorganic C in cells, but which nevertheless have the gas exchange characteristics of an organism with a CO2‐concentrating mechanism.
Combined effects of elevated CO2 and air temperature on carbon assimilation of Pinus taeda trees
Authors: TESKEY R. O.
Published: November 2003

Branches of 22‐year‐old loblolly pine (Pinus taeda, L.) trees growing in a plantation were exposed to ambient CO2, ambient + 165 μmol mol−1 CO2 or ambient + 330 μmol mol−1 CO2 concentrations in combination with ambient or ambient + 2°C air temperatures for 3 years. Field measurements in the third year indicated that net carbon assimilation was enhanced in the elevated CO2 treatments in all seasons. On the basis of A/Ci, curves, there was no indication of photosynthetic down‐regulation. Branch growth and leaf area also increased significantly in the elevated CO2 treatments. The imposed 2°C increase in air temperature only had slight effects on net assimilation and growth. Compared with the ambient CO2 treatment, rates of net assimilation were ∼1·6 times greater in the ambient + 165 μmol mol−1 CO2 treatment and 2·2 times greater in the ambient + 330 μmol mol−1 CO2 treatment. These ratios did not change appreciably in measurements made in all four seasons even though mean ambient air temperatures during the measurement periods ranged from 12·6 to 28·2°C. This indicated that the effect of elevated CO2 concentrations on net assimilation under field conditions was primarily additive. The results also indicated that the effect of elevated CO2 (+ 165 or + 330 μmol mol−1) was much greater than the effect of a 2°C increase in air temperature on net assimilation and growth in this species.
Inhibition of photosynthesis by solar radiation in Dunaliella salina: relative efficiencies of UV‐B, UV‐A and PAR
Authors: HERRMANN H. , HÄDER D.‐P. , GHETTI F.
Published: November 2003

Inhibition of photosynthesis after exposure to solar radiation was investigated in the marine green alga Dunaliella salina by monitoring photosynthetic optimal quantum yield Fv/Fm and efficiency of oxygen production. Samples were exposed to solar radiation in Ancient Korinth, Greece (37°58′ N, 23°0′ E) in August 1994. Within 30 min, Fv/Fm and efficiency of oxygen production decreased with similar kinetics with increasing exposure time. The inhibition, however, diminished when ultraviolet radiation was progressively excluded by means of colour filter glasses. Samples exposed for 3 h showed complete or partial recovery of photosynthesis, with almost the same rate under all irradition conditions. The fit of the experimental data with an analytical model describing inhibition of photosynthesis as a function of a linear combination of the photon fluence in the UV‐B, UV‐A and PAR allows one to estimate the relative mean effectiveness for inhibition by the three spectral ranges [about 2 × 10−4, 4 × 10−6 and 2 × 10−7 (μmol photons m−2)−1 for UV‐B, UV‐A and PAR, respectively].
A sensitive computer‐controlled pH‐stat system allows the study of net H+ fluxes related to nitrogen uptake of intact plants in situ
Authors: WOLLENWEBER B.
Published: November 2003

Proton fluxes related to the acid–base balance of intact plants were investigated in detail. A multi‐channel titration system was developed in order to regulate the pH in two different sets of nutrient solutions. This system also allowed computation of the dynamics of proton fluxes associated with nutrient uptake in situ.

The pH‐stat system presented here has proved to be very reliable and sensitive. By additions of acid or base to the nutrient solutions, the set pH could typically be maintained within 0·01 pH units. Experiments investigating net proton fluxes correlated with nitrogen uptake are described. The results show a rapid response of proton fluxes to changes in the form of nitrogen supplied, indicating that alterations in net proton fluxes are directly induced by the nature of the nitrogen source. The stoichiometry of proton fluxes connected to nitrogen uptake could be followed online, and the results are discussed in relation to the charge and acid–base balances of the whole plant.
UV‐B component of sunlight causes measurable damage in field‐grown maize (Zea mays L.): developmental and cellular heterogeneity of damage and repair
Authors: STAPLETON A. E. , THORNBER C. S. , WALBOT V.
Published: November 2003

Ultraviolet radiation has diverse morphogenetic and damaging effects on plants. The end point of damage is reduced plant growth, but in the short term UV radiation damages specific cellular components. We measured cyclobutane pyrimidine dimers in maize DNA from plants grown in natural solar radiation. Green maize tissues had detectable DNA damage, roots had less damage, and anthers had much more damage than green leaves. This heterogeneity in damage levels may reflect differences in dose received or in damage repair. The architecture of green tissues had no measurable effects on DNA damage levels, as leaf sheath and leaf blade were equivalent. We observed a slight increase in damage levels in plants sampled at the end of the day, but there was no accumulation of damage over the growing season. We measured photoreactivation, and found substantial levels of this light‐dependent repair in both the epidermis and inner cell layers of leaves, and in all organelles that contain DNA – the nucleus, chloroplasts and mitochondria. We conclude that maize has efficient mechanisms for photorepair of daily UV‐induced DNA damage that prevent accumulation.
The effect of elevated CO2 on the chemical composition and construction costs of leaves of 27 C3 species
Authors: POORTER H. , VAN BERKEL Y. , BAXTER R. , DEN HERTOG J. , DIJKSTRA P. , GIFFORD R. M. , GRIFFIN K. L. , ROUMET C. , ROY J. , WONG S. C.
Published: November 2003

We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice‐ambient partial pressure of atmospheric CO2. These species comprised wild and agricultural herbaceous plants as well as tree seedlings. Both average responses across species and the range in response were considered. Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non‐structural carbohydrates (TNC). To a lesser extent, decreases were found for organic N compounds and minerals. Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids. When expressed on a TNC‐free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics.

In terms of glucose required for biosynthesis, the increase in costs for one chemical compound – TNC – was balanced by a decrease in the costs for organic N compounds. Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found. This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for N AD(P)H and ATP] in the process of constructing 1 g of biomass. The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.
Aluminium speciation in the presence of wheat root cell walls: a wet chemical study
Authors: MASION A. , BERTSCH P. M.
Published: November 2003

Hydrolysis of Al3+ was performed in the presence of isolated root cell walls from a series of wheat cultivars (Triticum aestivum L.) known to have differential tolerance to Al contamination. Aluminium speciation was dependent on the cell wall concentration. At low cell wall concentrations, significant amounts of the very toxic Al13 species were formed. At higher cell wall concentrations, formation of the tridecamer was hindered or completely inhibited. The sensitive wheat cultivars displayed a higher affinity for aluminium than the tolerant cultivars. A possible Al tolerance mechanism based on cell wall permeability is discussed.