Structural-functional state of thylakoid membranes of wheat genotypes under water stress

Plants were grown in field conditions in the wide area under normal water supply and severe water deficit. Two wheat (Triticum aestivum L.) genotypes contrasting by architectonics and differing in drought-resistance were used: Giymatli-2/17, short stature, with broad and drooping leaves, drought-sensitive, and Azamatli-95, short stature, with vertically oriented small leaves, drought-tolerant). It was found out that Giymatli-2/17 was characterized by relatively low content of Chl a-protein of PS I (CP I) and beta-subunit of ATP-synthase complex, the high content of proteins in the 33-30.5 kDa region and LHC polypeptides (28-24.5 kDa), the intensive fluorescence at 740 nm and more high photochemical activity of PS II under normal irrigation compared with Azamatli-95. However, the content of CP I (M(r) 115 kDa) and apoprotein of P700 with M(r) 63 kDa insignificantly increases in the drought-resistant genotype Azamatli-95 under extreme water supply condition while their content decreases in drought-sensitive cv Giymatli-2/17. Intensity of synthesis alpha- and beta-subunits of CF(1) (55 and 53.5 kDa) also decreases in Giymatli-2/17. The levels of the core antenna polypeptides of FS II with M(r) 46 and 44.5 kDa (CP47 and CP43) remains stable both in normal, and stressful conditions. At the same time the significant reduction is observed in the content of polypeptides in the 33-30.5 kDa region in the more sensitive genotype Giymatli-2/17. There is an increase in the LHC II polypeptides level in tolerant genotype Azamatli-95 in contrast to Giymatli-2/17 (where the content of these subunits is observed decreasing). The intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra (77 K) of chloroplasts from sensitive genotype Giymatli-2/17 under water deficiency and there is a stimulation of the ratio of fluorescence band intensity F687/F740. After exposure to drought, cv Giymatli-2/17 shows a larger reduction in the actual PS II photochemical efficiency of chloroplasts than cv Azamatli-95.     

Decrease of the chlorophyll fluorescence ratio F690/F730 during greening and development of leaves

Summary Using the two-wavelength chlorophyll fluorometer the fluorescence induction kinetics (Kautsky effect) were measured simultaneously in the 690 nm and 730 nm region for ten common tree species during the greening period (April to July). The chlorophyll-fluorescence ratio F690/F730 (i.e. ratio of fluorescence intensity at the two maxima near 690 and 730 nm) was calculated from the laser-induced induction kinetics (He/Ne-laser 632.8 nm) at the fluorescence maximum and the steady state. The ratio F690/F730 decreases with increasing chlorophyll content of developing leaves. Its dependence on the chlorophyll content can be fairly well expressed by a power function which has a general validity for leaves, pigment extracts and chloroplast suspensions. The ratio F690/F730 is somewhat higher at maximum (fm) than at steady-state fluorescence (fs), but there is a very good correlation between both values. The ratio F690/F730 is a good indicator of the chlorophyll content and can be used as a non-destructive measure of the chlorophyll content of leaves. It also appears to be a suitable fluorescence parameter in the future remote sensing of the physiological state of the vegetation by laser-equipped airborne systems.     

Photosynthetic electron transport activity in heat-treated barley leaves: the role of internal alternative electron donors to photosystem II

Electron transport processes were investigated in barley leaves in which the oxygen-evolution was fully inhibited by a heat pulse (48 degrees C, 40 s). Under these circumstances, the K peak (approximately F(400 micros)) appears in the chl a fluorescence (OJIP) transient reflecting partial Q(A) reduction, which is due to a stable charge separation resulting from the donation of one electron by tyrozine Z. Following the K peak additional fluorescence increase (indicating Q(A)(-) accumulation) occurs in the 0.2-2 s time range. Using simultaneous chl a fluorescence and 820 nm transmission measurements it is demonstrated that this Q(A)(-) accumulation is due to naturally occurring alternative electron sources that donate electrons to the donor side of photosystem II. Chl a fluorescence data obtained with 5-ms light pulses (double flashes spaced 2.3-500 ms apart, and trains of several hundred flashes spaced by 100 or 200 ms) show that the electron donation occurs from a large pool with t(1/2) approximately 30 ms. This alternative electron donor is most probably ascorbate.     

Effects of light quality on chlorophyll-forms Ca 684, Ca 690 and Ca 699 of the diatom Phaeodactylum tricornutum

Colored light modifies the relative concentration of chlorophyll-forms of the diatom Phaeodactylum tricornutum compared to white-light control. No change in the ratio carotenoids/chlorophylls was observed after 4 days exposure to green light (max: 530 nm), blue light (max: 470 nm) or red light ( > 650 nm) of same intensity.However, the absorption spectra were modified, the content in Ca 684, Ca 690, Ca 699 forms increased in red and green light cultures and photosynthetic unit size of PS II decreased by 30% in green and blue light cultures.Fluorescence emission and fluorescence excitation spectra according to the Butler and Kitajima method (1975) were carried out for each culture. Ca 669 form was predominant in the two photosystems. The newly appeared far red forms fluoresce at 715 nm like PS I forms.We conclude that these new forms originated in a rearrangement of PS II forms. They do not transmit excitation energy to reaction center of PS I and are disconnected from the other chlorophyll-forms of the photosynthetic antennae.Abbreviations ABS absorption - Ca chlorophyll-complex - chla chlorophyll a - chl c chlorophyll c - chl t total chlorophylls - D.C.M.U. 3-(3, 4 dichlorophenyl) 1-diméthyl-urea - d^v division - F fluorescence - PS I and PS II photosystem I and photosystem II     

Chlorophyll limitation in plants remodels and balances the photosynthetic apparatus by changing the accumulation of photosystems I and II through two different approaches

Arabidopsis plants with a reduced expression of CHL27 ( chl27 ), an enzyme (EC 1.14.13.81) required for the synthesis of Pchlide, are chlorotic and have a Chl a / b ratio two times higher than wild-type (WT). Knockdown plants transformed with a construct constitutively expressing CHL27 recovered regarding Chl level, a / b ratio and 77K fluorescence. A negative correlation was found between total Chl and Chl a / b ratio in the examined plants. The chl27 plants fail to assemble WT amounts of complete PSI and PSII, leading to an elevated PSII/PSI ratio. The PSI remaining in chl27 is fully functional with a quantum yield higher than for WT. Despite a severe reduction of photosystem II antennae protein (LHCII) and an increased proportion of stroma lammella, the chl27 plants are able to perform state transitions. No major differences were found regarding PSII quantum yield, qN and 1 − qp whereas non-photochemical quenching was decreased by a factor two in chl27 plants. The PSII quantum yield for dark-adapted plants and plants given 10 min recovery after high light treatment were similar for both WT and chl27 showing that chl27 plants are not more susceptible to photoinhibition than WT. Taken together the plant manage to acclimate and to balance the two photosystems well even when it is severely limited in Chl. The way to achieve this differs for the two photosystems: regarding PSI a general reduction of core and antenna subunits occurs with no apparent change in the antenna composition; whereas for PSII there is a preferential loss of antenna proteins.     

Subunit stoichiometry of the chloroplast photosystem II antenna system and aggregation state of the component chlorophyll a/b binding proteins

Photosystem (PS) II membranes, obtained by the method of Berthold et al. (Berthold, D. A., Babcock, G. T., and Yocum, C. F. (1981) FEBS Lett. 134, 231-234), have been fractionated by a sucrose gradient ultracentrifugation method which allows the quantitative separation of the three major chlorophyll binding complexes in these membranes: the chlorophyll (chl) a binding PSII reaction center core, the major light-harvesting complex II, and the minor chl a/b proteins called CP26, CP29, and CP24. Each fraction has been analyzed for its subunit stoichiometry by quantitative sodium dodecyl sulfate-polyacrylamide gel electrophoresis methods. The results show that 12 mol of light-harvesting complex II and 1.5 mol of each of the minor chl a/b proteins are present per mol of the PSII reaction center complex in PSII membranes. These data suggest a dimeric organization of PSII, in agreement with a recent crystallographic study (Bassi, R., Ghiretti Magaldi, A., Tognon, G., Giacometti, G. M., and Miller, K. (1989) Eur. J. Cell Biol. 50, 84-93) and imply that such a dimeric complex is served by antenna chl a/b proteins whose minimal aggregation state includes three polypeptides. This was confirmed by covalent cross-linking of purified antenna complexes.     

CaCl_2对UV-B辐射下菠菜叶片光合特性的影响

以"丹麦旺盛菠菜"为材料,通过UV-B和CaCl2复合处理,测定光合色素含量、Hill反应活力、叶绿素荧光、MDA含量和抗氧化酶活性等参数,探讨了CaCl2对UV-B辐射下菠菜叶片电子传递链和光合膜酶保护系统的影响。结果表明,UV-B处理下,光合色素含量、chl/car、类囊体膜上PSII潜在活性(Fv/Fo)、光化学淬灭系数(qP)、非光化学淬灭系数(qN)、PSII光量子产量(ΦPSⅡ)、原初光能转化效率(Fv/Fm),以及Hill反应活力等降低,chla/chlb和MDA含量升高;喷洒CaCl2可不同程度缓解UV-B的伤害。不同处理下,POD、SOD和CAT活性的变化呈现补偿效应。UV-B强度与菠菜叶片PSII功能受损程度呈正相关,CaCl2则主要通过提高chlb含量、类囊体膜上的光量子产量和POD活性,以缓解伤害。重度UV-B辐射下,CaCl2使chlb含量显著提高可能是导致PSII捕光效率提高的重要因素。     

Investigations of the Blue-green Fluorescence Emission of Plant Leaves

The UV light (337 nm) induced blue-green fluorescence emission of green leaves is characterized at room temperature (298 K) by a maximum near 450 nm (blue region) and a shoulder near 525 nm (green region) and was here also studied at 77 K. At liquid nitrogen temperature (77 K) the blue (F450) and green fluorescence (F525) are much enhanced as is the red chlorophyll fluorescence near 735 nm. During development of green tobacco leaves the blue fluorescence F450 (77 K) is shifted towards longer wavelengths from about 410 nm to 450 nm. The isolated leaf epidermis of tobacco showed only slight fluorescence emission with a maximum near 410 nm. The green fluorescence F525 was found to mainly originate from the mesophyll of the leaf, its intensity increased when the epidermis was removed. The red chlorophyll fluorescence emission was also enhanced when the epidermis was stripped off; this considerably changed the blue/red fluorescence ratios F450/F690 and F450/F735. The epidermis, with its cell wall and UV-light-absorbing substances in its vacuole, plays the role of a barrier for the exciting UV-light. In contrast to intact and homogenized leaves, isolated intact chloroplasts and thylakoid membranes did not exhibit a blue-green fluorescence emission.     

Contrasting effect of dark-chilling on chloroplast structure and arrangement of chlorophyll-protein complexes in pea and tomato: plants with a different susceptibility to non-freezing temperature

The effect of dark-chilling and subsequent photoactivation on chloroplast structure and arrangements of chlorophyll–protein complexes in thylakoid membranes was studied in chilling-tolerant (CT) pea and in chilling-sensitive (CS) tomato. Dark-chilling did not influence chlorophyll content and Chl a/b ratio in thylakoids of both species. A decline of Chl a fluorescence intensity and an increase of the ratio of fluorescence intensities of PSI and PSII at 120 K was observed after dark-chilling in thylakoids isolated from tomato, but not from pea leaves. Chilling of pea leaves induced an increase of the relative contribution of LHCII and PSII fluorescence. A substantial decrease of the LHCII/PSII fluorescence accompanied by an increase of that from LHCI/PSI was observed in thylakoids from chilled tomato leaves; both were attenuated by photoactivation. Chlorophyll fluorescence of bright grana discs in chloroplasts from dark-chilled leaves, detected by confocal laser scanning microscopy, was more condensed in pea but significantly dispersed in tomato, compared with control samples. The chloroplast images from transmission-electron microscopy revealed that dark-chilling induced an increase of the degree of grana stacking only in pea chloroplasts. Analyses of O-J-D-I-P fluorescence induction curves in leaves of CS tomato before and after recovery from chilling indicate changes in electron transport rates at acceptor- and donor side of PS II and an increase in antenna size. In CT pea leaves these effects were absent, except for a small but irreversible effect on PSII activity and antenna size. Thus, the differences in chloroplast structure between CS and CT plants, induced by dark-chilling are a consequence of different thylakoid supercomplexes rearrangements. Dedicated to Prof. Zbigniew Kaniuga on the 25th anniversary of his initiation of studies on chilling-induced stress in plants.     

Distribution of UV-shielding of the epidermis of sun and shade leaves of the beech (Fagus sylvatica L.) as monitored by multi-colour fluorescence imaging

Plants can protect against damaging ultraviolet (UV) radiation by accumulating UV-absorbing substances in the epidermis of the leaves. Sun and shade leaves of a free standing beech tree (Fagus sylvatica L.) were studied for the differences in UV-shielding of the epidermis by means of multi-colour fluorescence images taken with UV and blue excitation. The distribution of the fluorescence intensity was detected over intact leaves in the emission maxima in the blue at 440 nm (F440), in the green at 520 nm (F520), in the red at 690 nm (F690) and in the far red at 740 nm (F740). Images of the logarithmic ratio between F690 excited in the blue and the UV (log (^BF690/^UVF690)) were calculated representing the relative absorption of UV in the epidermis and thus the degree of UV-shielding. It was found that UV-shielding is stronger for sun leaves than for shade leaves and better for the upper (adaxial) leaf side than for the lower (abaxial) leaf side of both leaf types. Within one leaf the highest value for the ratio log (^BF690/^UVF690) and thus the highest UV-shielding was found at the leaf rim which in broad leaves contains young tissue.     

水分和光照对厚皮甜瓜苗期植株生理生态特性的影响

以厚皮甜瓜‘西博洛托’为试材,研究了温室内育苗基质含水量和光照强度对厚皮甜瓜苗期植株生长发育和生理生态特性的影响.结果表明:不同基质含水量和光照强度对厚皮甜瓜苗期植株生长发育影响显著,随基质含水量的降低,苗期植株叶绿素a、叶绿素b和总叶绿素含量升高,叶片相对含水量和比叶面积下降,基质含水量为60%～80%时,幼苗净光合速率最高;随着光照强度的减弱,幼苗的叶绿素a、叶绿素b、总叶绿素含量以及叶片相对含水量、比叶面积和胞间CO2浓度升高,叶绿素a/b和净光合速率下降.在不同处理中,以80%基质含水量 100%温室光照处理的幼苗生长最健壮,壮苗指数、净光合速率等指标最高.     

Effects of copper on the growth,photosynthesis and nutrient concentrations of Phaseolus plants

Bean plants (Phaseolus vulgaris L. var. Zargana Kavala) were grown under conditions of increasing Cu concentrations in the growth medium (0.5-160.5 µM). Generally, the Cu concentrations between 0.5-1.5 µM were deficient, 1.5-10.5 µM were optimal, and 10.5-160.5 µM were toxic to plant growth. The Cu toxicity was associated with marked increases in plant tissue Cu concentrations. Under the Cu-deficient and optimal growth conditions, Cu was located primarily in the leaves. Under Cu toxicity, it was primarily sequestered in the roots. With increasing Cu in the growth medium, there was a positive correlation between Cu concentrations in the roots, stems and leaves, Ca in the roots, and K and Mg in the leaves. In contrast, Ca concentrations in the leaves and stems showed a negative correlation. The chlorophyll (Chl) concentration increased with increasing leaf Cu concentration, however, the Chl a/b ratio decreased. Since with an increasing leaf Cu concentration the leaf area decreased more markedly than the leaf dry mass, the net photosynthetic rate (PN) per leaf area increased and per dry mass decreased. The increase in PN per leaf area was almost entirely accounted for by the increase in Chl concentration. The initial Chl fluorescence (F0) increased with increasing leaf Cu concentration. The ratio of variable to maximum fluorescence (Fv/Fm) under Cu toxicity decreased. The half-time for the rise from F0 to Fm (t1/2) remained relatively unchanged with increasing leaf Cu concentration. Therefore the Cu-stress caused a small decrease in the efficiency of photosystem 2 photochemistry, but its primary effect was on growth.     

Increase of the chlorophyll fluorescence ratio F690/F735 during the autumnal chlorophyll breakdown

Summary The chlorophyll content and the fluorescence induction kinetics at two wavelengths (690 nm and 735 nm) have been measured in leaves of nine common broadleaf tree species during the autumnal chlorophyll breakdown. The ratio of the chlorophyll fluorescence maxima F690/F735 was determined at fluorescence maximum (fm) and at steady-state conditions (fs) by the laser-induced fluorescence emission using the two-wavelength fluorometer. The ratio F690/F735 increases with the leaf discolouring during the autumnal chlorophyll breakdown. The relationship between the chlorophyll content and the ratio F690/F735 can be expressed by a power function (curvilinear relationship) which is valid for all the species examined. In most cases the ratio F690/F735 measured in the upper leaf side is lower than that in the lower leaf side, but the trend is the same along the decreasing chlorophyll content. The ratio F690/F735 is always higher at maximum fluorescence than at steady-state fluorescence in the upper as well as lower leaf side and these values are well fitted in a linear correlation. This study confirms the usefulness of the ratio F690/F735 as a suitable non-destructive indicator of the in-vivo chlorophyll content, especially at medium and low chlorophyll content.     

The divinyl-chlorophyll a/b-protein complexes of two strains of the oxyphototrophic marine prokaryote Prochlorococcus – characterization and response to changes in growth irradiance

Apoproteins of the antenna complexes of Prochlorococcus marinus clone SS120 (= CCMP 1375) and Prochlorococcus sp. clone MED4 (= CCMP 1378) cross-reacted with an antibody against the 30 kDa CP 5 complex of Prochlorothrix hollandica antenna. For the MED4 strain, which has a high divinyl-chlorophyll a to divinyl-chlorophyll b (DV-Chl a/b) ratio ranging from 11.4 to 15.0 (w/w), the major antenna proteins had an apparent molecular mass of 32.5 kDa. In contrast for the SS120 strain, which has a low DV-Chl a/b ratio ranging from 1.1 to 2.2, antenna apoproteins were observed in the range 34–38 kDa. For both strains, these apoproteins decreased at high growth irradiance but more markedly in the latter. Partially purified antenna fractions had a DV-Chl a/b ratio ca. 7-fold lower for SS120 than for MED4 at 30 mol photons m-2 s-1. For both strains, the 77 K fluorescence emission spectra of whole thylakoids displayed a major peak at 685 nm and a broad but very low shoulder above 700 nm. Energetic coupling of the antenna to both PS II and PSI reaction centers was demonstrated for SS120 by the strong contribution of DV-Chl b in both the 77 K excitation fluorescence spectra and the oxidized minus reduced absorption difference spectra of P700. The PS I to PS II ratio of Prochlorococcus SS120 was determined as being 0.7 ± 0.1 at low light.     

The photochemical trapping rate from red spectral states in PSI-LHCI is determined by thermal activation of energy transfer to bulk chlorophylls

The average fluorescence decay lifetimes, due to reaction centre photochemical trapping, were calculated for wavelengths in the 690- to 770-nm interval from the published fluorescence decay-associated emission spectra for Photosystem I (PSI)-light-harvesting complex of Photosystem I (LHCI) [Biochemistry 39 (2000) 6341] at 280 and 170 K. For 280 K, the overall trapping time at 690 nm is 81 ps and increases with wavelength to reach 103 ps at 770 nm. For 170 K, the 690-nm value is 115 ps, increasing to 458 ps at 770 nm. This underlines the presence of kinetically limiting processes in the PSI antenna (diffusion limited). The explanation of these nonconstant values for the overall trapping time band is sought in terms of thermally activated transfer from the red absorbing states to the "bulk" acceptor chlorophyll (chl) states in the framework of the Arrhenius-Eyring theory. It is shown that the wavelength-dependent "activation energies" come out in the range between 1.35 and 2.7 kcal mol(-1), increasing with the emission wavelength within the interval 710-770 nm. These values are in good agreement with the Arrhenius activation energy determined for the steady-state fluorescence yield over the range 130-280 K for PSI-LHCI. We conclude that the variable trapping time in PSI-LHCI can be accounted for entirely by thermally activated transfer from the low-energy chl states to the bulk acceptor states and therefore that the position of the various red states in the PSI antenna seems not to be of significant importance. The analysis shows that the bulk antenna acceptor states are on the low-energy side of the bulk antenna absorption band.     

CO2和O3浓度倍增及其复合作用对大豆叶绿素含量的影响

利用开顶箱(OTC)法研究了在CO2和O3浓度倍增及其复合作用下,大豆叶片叶绿素含量及叶绿素a／b值的变化规律。结果表明,不同生育时期大豆叶片中叶绿素含量不同,Chla、Chlb和ChlT都表现出低．高一低的趋势,而且不同处理间变化不同步。不同处理间比较,O3处理的植株叶绿素含量下降最为明显,其次是复合处理的影响,而CO2浓度倍增对提高叶片叶绿素含量有一定的作用。Chla/b呈下降趋势,受CO2倍增影响最明显,有利于提高作物的光合性能。     

Studies on the Localization and Spectral Characteristics of the Fluorescence Emission of Differently Pigmented Wheat Leaves

Intensity, spectral characteristics and localization of the UV-laser (337 nm) induced blue-green and red fluorescence emission of green, etiolated and white primary leaves of wheat seedlings were studied in a combined fluorospectral and fluoromicroscopic investigation. The blue-green fluorescence of the green leaf was characterized by a maximum near 450 nm (blue region) and a shoulder near 530 nm (green region), whereas the red chlorophyll fluorescence exhibited maxima in the near-red (F690) and far-red (F735). The etiolated leaf with some carotenoids and traces of chlorophyll a, in turn, showed a higher intensity of the blue-green fluorescence with a shoulder in the green region and a strong red fluorescence peak near 684 to 690 nm, the far-red chlorophyll fluorescence maximum (F735) was, however, absent. The norfluorazone-treated white leaf, free of chlorophylls and carotenoids, only exhibited blue-green fluorescence of a very high intensity. In green and etiolated leaves the blue-green fluorescence primarily derived from the cell walls of the epidermis and the red fluorescence from the chlorophyll a of the mesophyll cells. In white leaves the blue-green fluorescence emanated from all cell walls of epidermis, mesophyll and leaf vein bundles. The shape and intensity of the blue-green and red fluorescence emission is determined by the reabsorption properties of chlorophylls and carotenoids in the mesophyll, thus giving rise to quite different values of the various fluorescence ratios F450/F690, F450/F530, F450/F735 and F690/F735 in green and etiolated leaves.     

Green synthesis of fluorescent carbon dots using chloroplast dispersions as precursors and application for Fe3+ ion sensing

Water‐soluble carbon dots (CDs) were synthesized using a one‐step hydrothermal treatment of chloroplast dispersions extracted from fresh leaves as a green carbon source. The CD solution showed an emission peak centred at 445 nm when excited at 300 nm. The synthesized CDs were uniform and monodispersed with an average size of 5.6 nm. When adding ferric(III) ions (Fe³⁺) to the solution of the original CDs, the fluorescence intensity decreased significantly. Based on the linear relationship between fluorescence intensity and concentration of Fe³⁺ ions, an effective method for rapid, sensitive and selective Fe³⁺ sensing in aqueous solution could be established. Under optimum conditions, the extent of the fluorescence quenching of prepared CDs strongly depended on the Fe³⁺ ions over a wide concentration range 1.0–100.0 μM with a detection limit (3σ/k) of 0.3 μM. Furthermore, the quantitative determination of Fe³⁺ ions in environmental water samples was realized.     

The chlorophyll fluorescence ratio F690/F730 in leaves of different chlorophyll content

The red laser-induced chlorophyll-fluorescence induction kinetics of predarkened leaf samples were registered simultaneously in the 690 and 730 nm regions i.e., in the region of the two chlorophyll fluorescence emission maxima. From the induction kinetics the chlorophyll fluorescence ratio F690/F730 was calculated. The ratio F690/F730 shows to be dependent on the chlorophyll content of leaves. It is significantly higher in needles of damaged spruces (values of 0.45–0.9) than in normal green needles of healthy trees (values of 0.35–0.5). During development and greening of maple leaves the ratio F690/F730 decreases with increasing chlorophyll content. Determination of the ratio F690/F730 can be a suitable method of monitoring changes in chlorophyll content in a non-destructive way in the same leaves during development or the yellowish-green discolouration of needles of damaged spruces in the Black Forest with the typical tree decline symptoms.Abbreviations F690/F730 ratio of the fluorescence yield at the two fluorescence-emission maxima in the 690 and 730 nm regions - F_m maximum fluorescence - F_s steady-state fluorescence     

The effects of elevated CO2 (0.5%) on chloroplasts in the tetraploid black locust (Robinia pseudoacacia L.)

Some ploidy plants demonstrate environmental stress tolerance. Tetraploid (4×) black locust (Robinia pseudoacacia L.) exhibits less chlorosis in response to high CO₂ than do the corresponding diploid (2×) plants of this species. We investigated the plant growth, anatomy, photosynthetic ability, chlorophyll (chl) fluorescence, and antioxidase activities in 2× and 4× black locusts cultivated under high CO₂ (0.5%). Elevated CO₂ (0.5%) induced a global decrease in the contents of total chl, chl a, and chl b in 2× leaves, while few changes were found in the chl content of 4× leaves. Analyses of the chl fluorescence intensity, maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), K‐step (V_k), and J‐step (V_J) revealed that 0.5% CO₂ had a negative effect on the photosynthetic capacity and growth of the 2× plants, especially the performance of PSII. In contrast, there was no significant effect of high CO₂ on the growth of the 4× plants. These analyses indicate that the decreased inhibition of the growth of 4× plants by high CO₂ (0.5%) may be attributed to an improved photosynthetic capacity, pigment content, and ultrastructure of the chloroplast compared to 2× plants.