Nucleotide and deduced amino acid sequence of the Rhodobacter sphaeroides gene encoding form II ribulose-1,5-bisphosphate carboxylase/oxygenase and comparison with other deduced form I and II sequences

The nucleotide sequence for the Rhodobacter sphaeroides form II ribulose 1,5-bisphosphate carboxylase/oxygenase was determined. The deduced product is highly homologous with the form II-like enzyme of Rhodospirillum rubrum , but appears to be more distantly related to the large subunit of the L₈S₈ enzyme found in autotrophic bacteria, cyanobacteria and higher plants. Several regions highly conserved among L₈S₈ and L_X enzymes correspond with regions previously implicated in catalytic activity and subunit interactions. An imperfect palindrome and a stem loop structure were identified in the 5' and 3' flanking sequences, respectively, of R. sphaeroides rbpL .     

Iron, sulfur, and chlorophyll deficiencies: A need for an integrative approach in plant physiology

Green plants deficient in nitrogen, sulfur, or iron develop a similar yellow coloration. In each case, the yellow coloration is accompanied by a lowered chlorophyll concentration. This review attempts to collate some of the biochemical information concerning these three seemingly diverse nutritive deficiencies and bares a need for a more integrative approach to plant physiology. The biochemical and biological roles of nitrogen, sulfur and iron in living systems are examined, with emphasis on sulfur and iron. Mechanistically, iron and/or sulfur are highly reactive components of many enzymes. Indeed, iron and sulfur sometimes form Fe₂S₂, Fe₃S₄, or Fe₄S₄ clusters which are very active electron transfer agents. Recently, iron‐sulfur clusters have been reported to serve as sensors of oxidative stress, to couple photosynthesis with several metabolic pathways, to participate in the reduction of sulfite and nitrite, and to participate in regulation of gene expression. Thus, there are several mechanisms by which a deficiency of nitrogen, sulfur, or iron could produce the same low‐chlorophyll, yellow phenotype in plants. Unless the interactions and coordination of the various pathways connected to chlorophyll synthesis are elucidated, it is unlikely that we will select the quickest and most direct path to plant improvement.     

Manganese in biogenic magnetite crystals from magnetotactic bacteria

Magnetotactic bacteria produce either magnetite (Fe₃O₄) or greigite (Fe₃S₄) crystals in cytoplasmic organelles called magnetosomes. Whereas greigite magnetosomes can contain up to 10 atom% copper, magnetite produced by magnetotactic bacteria was considered chemically pure for a long time and this characteristic was used to distinguish between biogenic and abiogenic crystals. Recently, it was shown that magnetosomes containing cobalt could be produced by three strains of Magnetospirillum . Here we show that magnetite crystals produced by uncultured magnetotactic bacteria can incorporate manganese up to 2.8 atom% of the total metal content (Fe+Mn) when manganese chloride is added to microcosms. Thus, chemical purity can no longer be taken as a strict prerequisite to consider magnetite crystals to be of biogenic origin.     

Cellular and ultrastructural features of the regenerating adult eye in the marine gastropod llyanassa obsoleta

Light and electron microscopic techniques were used to study the cellular and ultrastructural components of the regenerating adult eye of the marine prosobranch gastropod Ilyanassa obsoleta. Behavioral tests were used to determine return of vision in animals with generated eyes. As early as 3 days after removal of the adult eye, the regenerating eye primordium appeared as a pigmented mass of cells that invaginated from the surface epithelium in the area of the wound. Twelve days after eye removal, the regenerating eye was very similar to the postmetamorphic juvenile eye and to the adult eye: It contained a retinal layer, as well as an extracellular lens, cornea, connective tissue capsule, and forming optic nerve; vision had returned. Growth of the eye and its components was linear; size ratios established among forming eye components were maintained during growth. The events of eye regeneration appear to recapitulate embryonic eye formation. The sequence of invagination, pigmentation, and lens, optic nerve, and retinal pattern formation are similar.     

Physiological effects of long-term exposure to low and moderate concentrations of atmospheric NH3 on poplar leaves

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

De novo shoot morphogenesis and plant growth of mustard (Brassica juncea) in vitro in relation to ethylene

Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard ( Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO₃. The presence of 20 μ M AgNO₃ or 5 μ M AVG in culture medium containing 5 μ M naphthaleneacetic acid and 10 μ M benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO₃ greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 μ M 2-chloroethylphosphonic acid (CEPA), but AgNO_3-induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC by 70–80%. In contrast, AgNO₃ stimulated all 3 parameters of ethylene synthesis. Both AgNO₃ and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO₃. Leaf discs derived from plants grown with AVG or AgNO₃ were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO₃ in the medium was inhibitory to regeneration of those derived from plants grown with AgNO₃.     

Effects of vitamin D metabolites on axolotl limb regeneration

Vitamin D is essential for normal metabolism of phosphorus and calcium, and differentiation of skeletal elements. 1,25 dihydroxyvitamin-D₃, the biologically active metabolite, acts as an induction/proliferation switch in various cell types and promotes chondrogenesis of chick limb bud mesenchymal cells. The function of vitamin D is mediated through its nuclear receptor, the vitamin D receptor (VDR). The proliferative actions of 1,25(OH)₂-D₃ on limb bud mesenchymal cells are similar to the ones produced by retinoids, such as all- trans retinoic acid (RA) or 9- cis retinoic acid (9- cis ). The retinoids have been shown to be compounds of extreme importance in the field of limb development and regeneration. In order to examine possible roles of vitamin D metabolites on limb regeneration, the effects of 1,25(OH)₂-D₃, 24,25(OH)₂-D₃ and KH1060 (a more potent metabolite) alone or in conjunction with all- trans RA or 9- cis RA on the regenerating axolotl limb. Vitamin D affects limb morphogenesis by generating abnormalities in skeletal elements. Synergism of vitamin D with retinoic acid in affecting pattern formation is suggested by the results.     

老年白内障患者超声乳化联合人工晶状体植入术1210例临床研究

目的：观察老年白内障患者超声乳化联合人工晶体植入术后的治疗效果,探讨白内障超声乳化人工晶状体植入术术中术后并发症及相应处理措施。方法：对1210例1325眼老年白内障超声乳化人工晶状体植入术患者的临床病例资料进行回顾性分析,统计术后疗效并分析术中术后并发症的原因。结果：1325眼术后视力均有不同程度的提高,发生术中晶状体碎核入玻璃体腔1眼,术后并发症主要为一过性高眼压、角膜水肿、晶状体后囊破裂及视网膜脱落,发生率分别为1．36％、7．47％、0．03％和0．02％。结论：超声乳化联合人工晶体植入术对老年白内障患者治疗效果满意。对于术中及术后发生的各种并发症应分析原因并积极的预防。     

Effects of waterborne complexing agents on silver uptake and depuration in rainbow trout

Rainbow trout Oncorhynchus mykiss ( c . 60 g) were exposed for 1 week to 0·1 μM silver as AgNO₃ in ion poor water (Ca c . 150 μM, pH c . 8, water temperature 13° C) with or without waterborne organic matter (27 mg C l⁻¹ as Aldrich humic acid), thiosulphate (5 μM Na₂S₂O₃) or chloride (4 mM KCl). Organic matter decreased Ag accumulation by the gills initially, but did not decrease Ag accumulation by plasma or liver. Thiosulphate decreased the amount of Ag accumulated by the gills for the entire 1 week exposure but had no effect on Ag concentrations in the plasma, liver or bile. Chloride had no effect on Ag uptake in any of the tissues examined. All three complexing agents reduced the decreases in plasma Na and Cl concentrations caused by Ag. To study the effects of waterborne complexing agents on Ag depuration, rainbow trout were exposed to 0·1 μM AgNO₃ for 1 week then placed for 8 days in Ag‐free, ion poor water with or without waterborne organic matter (55 mg C l⁻¹) or thiosulphate (5 μM). These complexing agents did not alter depuration of Ag from the gills, plasma, liver or bile. Thus, once Ag has entered a fish, subsequent elimination of internal Ag is not affected by external complexing agents.     

An open-top chamber for measuring soil respiration and the influence of pressure difference on CO2 efflux measurement

1. A new open-top chamber for measuring CO₂ efflux from the soil is reported here. The new design enables measurement of the equilibrium CO₂ efflux, when there is no detectable pressure difference between the chamber and outside nor leakage of CO₂ into or out of the chamber.
2. In previous dynamic-chamber techniques, the measured CO₂ efflux is dependent on the pressure difference between the inside and outside of the chamber, and a negative pressure difference of –1Pa may cause an order of magnitude increase in measured CO₂ efflux. Although the measured CO₂ efflux is less sensitive to a positive pressure difference than to a negative one, a positive pressure difference of even a few tenths of a Pa will lead to a considerable underestimation in soil CO₂ evolution.
3. The influence of pressure difference on measured CO₂ efflux is negligible in the new design and the estimated CO₂ efflux is close to the undisturbed soil respiration rate. Flow rates up to 8lmin^–1, or air movement over the soil surface up to 55cmmin^–1, will not affect CO₂ evolution from the soil. The influence of pressure difference is related to the type of soil being measured and this has also been reported here for the new design.     

Effect of gibberellic acid on growth and carbohydrate metabolism of developing tubers of potato (Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Ostara) were grown in aerated water culture in a controlled environment. When the tubers had reached a diameter of 1–3 cm. ¹⁴C-labelled or unlabelled gibberellic acid (GA₃) was applied to the surface of the stolons at points approximately 1 crn from the developing tubers, and treatment continued for 10 days. - Significant quantities of GA₃ moved into tuber tissue within 2–4 days of hormone application. This influx of GA₃ was accompanied by a marked reduction in both the activity of ADPG-pyrophospharylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase and an increase in the activity of UDPG-pyrophosphorylase. Starch phosphorylase activity initially increased slightly but then fell, whereas the activity of starch synthase remained constant throughout the experiment. The soluble sugar composition of the tubers changed qualitatively towards a pattern characteristic of growing stolon tips prior to tuber initiation, but there was no clear evidence of net starch degradation. Changes in the activities of the enzymes were observed prior to noticeable effects of the hormone on tuber growth rate or the development of new stolons at the tuber eyes. - GA₃- treated tubers imported more ¹⁴C from labelled photosynthate than expected on the basis of growth rate. However, the capacity to convert solub#e-¹⁴C to ethaTiol-insoluble-¹⁴C (predominantly starch) was reduced in comparison with non-treated tubers. - The observed changes in carbohydrate composition and enzyme activities indicate that GA₃ induces a drastic change in potato tuber metabolism towards a pattern characteristic for the termination of the storage process.     

Biomass, reproductive output, and physiological responses of rapid-cycling Brassica (Brassica rapa) to ozone and modified root temperature

Brassica rapa L. (rapid-cycling Brassica), was grown in environmentally controlled chambers to determine the interactive effects of ozone (O₃) and increased root temperature (RT) on biomass, reproductive output, and photosynthesis. Plants were grown with or without an average treatment of 63 ppb O₃. RT treatments were 13°C (LRT) and 18°C (HRT). Air temperatures were 25°C/15°C day/night for all RT treatments.
Ozone affected plant biomass more than did root temperature. Plants in O₃ had significantly smaller total plant d. wt, shoot weight, leaf weight, leaf area and leaf number than plants grown without O₃. LRT plants tended to have slightly smaller total plant d. wt, shoot weight, root weight, leaf weight, leaf area, and leaf number than HRT plants. For all variables, LRT plants grown in O₃ had the smallest biomass, and plants grown in HRT without O₃ had the largest biomass.
Ozone reduced both fruit weight and fruit number; LRT also reduced fruit weight but had no effect on fruit number. Ozone reduced photosynthesis but RT had no effect. Conductance and internal CO₂ were unaffected by O₃ or RT.
These studies indicate that plant growth with LRT might be more reduced in the presence of O₃ than growth in plants with HRT, which might be able to compensate for O₃-caused reductions in photosynthesis to avoid decreased biomass and reproductive output.     

Characterization, Localization, and Biosynthesis of an Interstitial Retinol-Binding Glycoprotein in the Human Eye

Abstract: Human eyes contain an M_r 135K retinol-binding protein that is analogous to interstitial retinol-binding protein (IRBP) in the subretinal space of bovine eyes. It is a glycoprotein, because it binds ¹²⁵I-concanavalin A, ¹²⁵I-wheat germ agglutinin and ¹²⁵I- Lens culinaris hemagglutinin. It does not bind Ricinus communis agglutinin I. After desialation, it binds Ricinus communis agglutinin I, but loses its capacity to bind wheat germ agglutinin. These observations, coupled with the known specificities of these lectins, suggest that at least one of the oligosaccharide chains is a sialated, biantennary complex type containing fucose. Both by direct analysis of dissected ocular tissues and by immunocytochemistry it was shown that human interstitial retinol binding protein is an extracellular protein that is confined predominantly to the subretinal space. Monkey retinas incubated in vitro in medium containing [³H]leucine were shown to synthesize and secrete this protein into the medium, a conclusion that was confirmed by immunoprecipitation with an immunoglobulin fraction prepared from rabbit antibovine IRBP serum. Virtually no other labeled proteins were detectable in the medium. It is concluded that interstitial retinol-binding protein meets many of the requirements for a putative transport protein implicated in the transfer of retinol between the pigment epithelium and retina during the visual cycle, and that the neural retina may play an important role in regulating its amount in the subretinal space.     

INDIVIDUAL VARIATION IN THE DISTRIBUTION OF LENS POTENCY IN WOLFFIAN LENS REGENERATION

After lentectomy in newts, lens regeneration originates from the iris. The regenerant was externally observed with a stereomicroscope as a depigmented area (DA) of the iris, and the extent of DA up to 15 days after lentectomy was measured. The extent of DA was found to differ among individuals, whereas it was the same in both eyes of each animal. In a number of animals one eye was used for lentectomy. After measuring the DA, two groups of animals were selected; a "W-group" with an extremely wide DA that deviated from the standard value, and "N-group", with an extremely narrow DA. Six iris sectors obtained from the animals of the W-group or N-group were implanted into lentectomized eyes of other animals to investigate the difference in the distribution of lens potency in these two groups. Animals of the W-group possessed a wider distribution of lens potency than animals of the N-group. Pulse-labelling with ³H-thymidine on lentectomized eyes of both groups was done 0, 3, 5, 7 and 12 days after lentectomy. DNA-synthesis began earlier and continued longer in the dorsal part of the iris of the W-group than in that of the N-group. The distribution of lens potency in the iris is discussed on the basis of these findings.     

Optic nerve regeneration after intravitreal peripheral nerve implants: trajectories of axons regrowing through the optic chiasm into the optic tracts

We have studied axon regeneration through the optic chiasm of adult rats 30 days after prechiasmatic intracranial optic nerve crush and serial intravitreal sciatic nerve grafting on day 0 and 14 post-lesion. The experiments comprised three groups of treated rats and three groups of controls. All treated animals received intravitreal grafts either into the left eye after both left sided (unilateral) and bilateral optic nerve transection, or into both eyes after bilateral optic nerve transection. Control eyes were all sham grafted on day 0 and 14 post-lesion, and the optic nerves either unlesioned, or crushed unilaterally or bilaterally. No regeneration through the chiasm was seen in any of the lesioned control optic nerves. In all experimental groups, large numbers of axons regenerated across the optic nerve lesions ipsilateral to the grafted eyes, traversed the short distal segment of the optic nerve and invaded the chiasm without deflection. Regeneration was correlated with the absence of the mesodermal components in the scar. In all cases, axon regrowth through the chiasm appeared to establish a major crossed and a minor uncrossed projection into both optic tracts, with some aberrant growth into the contralateral optic nerve. Axons preferentially regenerated within the degenerating trajectories from their own eye, through fragmented myelin and axonal debris, and reactive astrocytes, oligodendrocytes, microglia and macrophages. In bilaterally lesioned animals, no regeneration was detected in the optic nerve of the unimplanted eye. Although astrocytes became reactive and their processes proliferated, the architecture of their intrafascicular processes was little perturbed after optic nerve transection within either the distal optic nerve segment or the chiasm. The re-establishment of a comparatively normal pattern of passage through the chiasm by regenerating axons in the adult might therefore be organised by this relatively immutable scaffold of astrocyte processes. Binocular interactions between regenerating axons from both nerves (after bilateral optic nerve transection and intravitreal grafting), and between regenerating axons and the intact transchiasmatic projections from the unlesioned eye (after unilateral optic nerve lesions and after ipsilateral grafting) may not be important in establishing the divergent trajectories, since regenerating axons behave similarly in the presence and absence of an intact projection from the other eye.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Difference between dorsal and ventral iris in lens producing potency in normal lens regeneration is maintained after dissociation and reaggregation of cells from the adult newt, Cynops pyrrhogaster

In Wolffian lens regeneration, lentectomized newt eye can produce a new lens from the dorsal marginal iris, but the ventral iris has never shown such capabilities. To investigate the difference of lens regenerating potency between dorsal and ventral iris epithelium at the cellular level, a transplantation system using cell reaggregates was developed. Two methods were devised for preparing the reaggregates from pigmented iris epithelial cells. One was rotating cells in an agar-coated multiplate on a gyratory shaker and the other was incubating cells in a microcentrifuge tube after slight centrifugation. Reaggregates made of dorsal iris cells that had been completely dissociated into single cells were phenotypically transformed into a lens when placed in the pupillary region of the lentectomized host eye. None of the ventral reaggregates produced a lens. Even dorsal reaggregates could not transdifferentiate into lens when they were placed away from the pupil. The produced lenses from the reaggregates were morphologically and immunohistochemically identified. To obtain evidence whether produced lenses really originated from singly dissociated cells, we labeled dissociated cells with a fluorescent dye (PKH26) before reaggregate formation and then traced it in the produced lens.     

Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers

An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO₂] on architectural as well as on physiological characteristics of two poplar clones ( Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO₂ ] (ambient + 350 μmol mol^–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO₂] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO₂] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO₂] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO₂] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO₂] enrichment had little effect on daily canopy light interception and photosynthesis.     

Effects of alkaloids on feeding by Phormia reginaconfirm the critical role of sensory inhibition

Abstract. Inhibition of peripheral chemoreceptors by micromolar concentrations of alkaloids may account for feeding deterrence. Earlier work showed a reduction in both the proboscis extension response and sensory activity recorded from sugar-sensitive cells in tarsal D and labellar 'largest' hairs when the stimulating solution was sucrose mixed with alkaloids. In the present work a similar behavioural effect was also seen when alkaloids were mixed with pyranose and furanose sugars as well as with water and deuterium oxide. Behavioural deterrence continued after the stimulus was removed. Complete recovery occurred after 120 s. To check against the possibility of a central inhibitory state (CIS) having been established two sets of experiments were run in which quinine was applied to a single tarsus followed by a sucrose post-test to the contralateral tarsus. In one half of the tests sugar was applied first (S₁Q₂), and in the other half quinine first (Q₁S₂). Comparable tests were run with contralateral labellar hairs. No CIS was set up by Q₁; however, a central excitatory state (CES) was set up by S₁. In order to test (a) whether quinine had different effects on other known or unknown receptors and (b) post-ingestive effects, volumes imbibed in single drinks of sucrose with and without quinine were compared. Volumes of the mixture imbibed were not significantly different from what was predicted based on the known reduction in sensory acitivty.     

Interaction of elevated CO2 and O3 on growth, photosynthesis and respiration of three perennial species grown in low and high nitrogen

Seedlings of three species native to central North America, a C₃ tree, Populus tremuloides Michx., a C₃ grass, Agropyron smithii Rybd., and a C₄ grass, Bouteloua curtipendula Michx., were grown in all eight combinations of two levels each of CO₂, O₃ and nitrogen (N) for 58 days in a controlled environment. Treatment levels consisted of 360 or 674 μmol mol^-1 CO₂, 3 or 92 nmol mol^-1 O₃, and 0.5 or 6.0 m M N. In situ photosynthesis and relative growth rate (RGR) and its determinants were obtained at each of three sequential harvests, and leaf dark respiration was measured at the second and third harvests. In all three species, plants grown in high N had significantly greater whole-plant mass, RGR and photosynthesis than plants grown in low N. Within a N treatment, elevated CO₂ did not significantly enhance any of these parameters nor did it affect leaf respiration. However, plants of all three species grown in elevated CO₂ had lower stomatal conductance compared to ambient CO₂-exposed plants. Seedlings of P. tremuloides (in both N treatments) and B. curtipendula (in high N) had significant ozone-induced reductions in whole-plant mass and RGR in ambient but not under elevated CO_2. This negative O₃ impact on RGR in ambient CO₂ was related to increased leaf dark respiration, decreased photosynthesis and/or decreased leaf area ratio, none of which were noted in high O₃ treatments in the elevated CO₂ environment. In contrast, A. smithii was marginally negatively affected by high O_3.