Variations in the dorso-ventral organization of leaf structure and Kranz anatomy coordinate the control of photosynthesis and associated signalling at the whole leaf level in monocotyledonous species

Photosynthesis and associated signalling are influenced by the dorso-ventral properties of leaves. The degree of adaxial/abaxial symmetry in stomatal numbers, photosynthetic regulation with respect to light orientation and the total section areas of the bundle sheath (BS) cells and the surrounding mesophyll (M) cells on the adaxial and abaxial sides of the vascular bundles were compared in two C₄[ Zea mays (maize) and Paspalum dilatatum ] and one C₃[ Triticum turgidum (Durum wheat)] monocotyledonous species. The C₃ leaves had a higher degree of dorso-ventral symmetry than the C₄ leaves. Photosynthetic regulation was the same on each side of the wheat leaves, as were stomatal numbers and the section area of the BS relative to that of the M cells (BS/M section area ratio). In contrast, photosynthetic regulation in maize and P. dilatatum leaves showed a marked surface-specific response to light orientation. Compared to the adaxial sides of the C₄ monocotyledonous leaves, the abaxial surfaces had more stomata and the BS/M section area ratio was significantly higher. Differences in dorso-ventral structure, particularly in Kranz anatomy, serve not only to maximize photosynthetic capacity with respect light orientation in C₄ monocotyledonous leaves but also allow adaxial and abaxial-specific signalling from the respective M cells.     

Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene

Changes in carbon metabolism and δ¹³C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phospho enol pyruvate (PEP), the initial acceptor of CO₂ in the C₄ photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4‐fold higher than those of control potato plants (wild‐type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r²= 0.81), and was positively correlated with malate content (r²= 0.88). A significant increase in the δ¹³C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO₂. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C₄‐type carbon metabolism. However, since parameters associated with CO₂ gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.     

The localization of serine hydroxymethyltransferase in leaves of C3 and C4 species

The intracellular distribution of serine hydroxymethyltransferase (EC 2.1.2.1) was studied in young wheat ( Triticum aestivum L. cv. Starke II) leaves by fractionation of protoplasts and further purification of peroxisomes and chloroplasts. Essentially all of the activity in wheat leaves was located in the mitochondria. Within the mitochondria the enzyme was mainly in the matrix as shown by centrifugation of sonicated wheat mitochondria. In the C₄ plants, Zea mays (L. cv. Earliking), Panicum miliaceum and Panicum maximum (cv. Australia) belonging to different C₄ types, serine hydroxymethyltransferase was almost exclusively found in bundle sheath cells. The location of this enzyme in leaves is consistent with its role relative to glycine decarboxylation during photorespiration.     

A survey of photosynthetic carbon metabolism in 4 ecotypes of Phragmites australis in northwest China: Leaf anatomy, ultrastructure, and activities of ribulose 1,5-bisphosphate carboxylase, phosphoenolpyruvate carboxylase and glycollate oxidase

Four ecotypes of Phragmites australis from different habitats in northwest China were examined to compare their photosynthetic characteristics. In a swamp ecotype, the Δ ¹³C value of leaf materials was −34.0‰, and bundle sheath cells contained a small amount of organelles and round-shaped chloroplasts, as being similar to typical C₃ plants. In a dune ecotype, the Δ ¹³C value was −20.9‰ and bundle sheath cells contained oval-shaped chloroplasts with poorly-developed grana. In light and heavy salt meadow ecotypes, Δ ¹³C values were −30.6‰ and −35.6‰, respectively. The shape of bundle sheath chloroplasts in the light salt meadow ecotype was intermediate between those of the swamp and dune ecotypes. Abundance of bundle sheath organelles in the heavy salt meadow ecotype was intermediate. The swamp ecotype had photosynthetic enzyme activities typical of C₃ type plants, whereas the dune ecotype had an increased activity of phosphoenolpyruvate carboxylase (PEPC), a key C₄ enzyme, and a decreased ribulose 1,5-bisphosphate carboxylase (Rubisco) activity. The light salt meadow and heavy salt meadow ecotypes had substantial activities of PEPC, which indicates potential for C₄ photosynthesis. These data suggest that this species evolved the C₃-like ecotype in swamp environments and the C₄-like C₃-C₄ intermediate in dune desert environments, and C₃-like C₃-C₄ intermediates in salt environments.     

Differential effects of chilling on the activity of C4 enzymes in two ecotypes of Echinochloa crus-galli from sites of contrasting climates

Five-week-old plants of Echinochloa crusgalli (L.) Beauv. from Mississippi and from Québec grown under controlled conditions were subjected to dark chilling for 10 h at 5°C or light chilling treatments for 14 h at 7°C under hight light (1 000 μmol m⁻² s⁻¹). The activities of four C₄ enzymes of Québec plants, measured 4 h after the completion of the cold treatment, were not affected by the chilling treatment in the dark. The activities of pyruvate, P_i dikinase (PPDK; EC 2.7.9.1) and NADP⁺-malic enzyme (NADP⁺-ME; EC 1.1.1.40), were significantly reduced in dark-chilled Mississippi plants. Chilling under high light conditions elicited significant levels of reduction in the activities of the four enzymes from both ecotypes but the reductions were significantly less severe for Québec plants. The recovery of activities of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and PPDK for both ecotypes was completed within 36 to 60 hours following the chilling treatment, but NADP⁺-malate dehydro-genase (NADP⁺-MDH; EC 1.1.1.82) and NADP⁺-ME activities of chilled Mississippi plants remained below that of control plants at the end of the 5-day monitoring period. PPDK was inactivated in vitro at 0 and 10°C and the rates of cold inactivation were significantly higher for PPDK extracted from Mississippi plants. The activity of PEPC of Mississippi extracts was slightly, but significantly reduced by a 60 min treatment at 0°C.     

NaCl treatment markedly enhances H2O2-scavenging system in leaves of halophyte Suaeda salsa

The C₃ halophyte Suaeda salsa L. grown under the high concentration of NaCl (200 m M ) was used to investigate the role of the hydrogen peroxide (H₂O₂)-scavenging system [catalase, ascorbate peroxidase, glutathione reductase (GR), ascorbic acid, and glutathione (GSH)] in removal of reactive oxygen species. The activity of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and GR (EC 1.6.4.2) increased significantly after 7 days of NaCl treatment. The isoform patterns of CAT and GR were not affected, but the staining intensities were significantly increased by NaCl treatment. Activities of both the thylakoid-bound APX or GR and stromal APX (S-APX) or GR in the chloroplasts were markedly enhanced under high salinity. Fifty percent of APX in the chloroplasts is thylakoid-bound APX. S-APX and GR activity represented about 74–78 and 64–71% of the total soluble leaf APX and GR activity, respectively. Salt treatment increased the contents of ascorbic acid and GSH. By contrast, a decreased content of H₂O₂ was found in the leaves of NaCl-treated S . salsa . The level of membrane lipid peroxidation decreased slightly after NaCl treatment. The plants grew well with high rate of net photosynthesis under high salinity. These data suggest that upregulation of the H₂O₂-scavenging system in plant cells, especially in the chloroplasts, is at least one component of the tolerance adaptations of halophytes to high salinity.     

Effect of nitrogen nutrition on photosynthesis and growth in C4Panicum species

Abstract. The growth and photosynthetic responses to high and low N nutrition were measured in 2 NADP-malic enzyme and 4 NAD-malic enzyme C₄ subtype Panicum species to evaluate whether differences in C₄ photosynthetic biochemistry result in differences in the N requirement for growth. All species had lower biomass production, photosynthesis rates, and shoot N concentrations at low N, and no consistent differences between the C₄ subtypes were apparent. The assimilation rates (biomass accumulated over the period of growth) for the NADP-malic enzyme species were higher than the NAD-malic enzyme species at high N but not at low N. When assimilation rates were evaluated on a shoot N basis a higher N-use-efficiency was found for the NADP-malic enzyme species at high N. Thus the NADP-malic enzyme Panicum species had a greater amount of growth for a given shoot N concentration, but only above a certain level of shoot N concentrations.     

Developmental changes of enzymes of malate metabolism in relation to respiration, photosynthesis and nitrate assimilation in peach leaves

The developmental profile of the activities of some enzymes involved in malate metabolism, namely phosphoenolpyruvate carboxylase (PEPC; EC 4. 1. 1. 31), NAD⁺-linked (EC 1. 1. 1. 37) and NADP⁺-linked (EC 1. 1. 1. 82) malate dehydrosenase (MDH), NAD⁺linked (EC 1. 1. 1. 39) and NADP⁺-linked (EC 1. 1. 1. 40) malic enzyme (ME), has been determined in leaves of peach [ Prunus persica (L.) Batsch cv. Maycrest], a woody C₃ species. In order to study the role of these enzymes, their activities were related to developmental changes of photosynthesis, respiration, and capacity for N assimilation. Activities of PEPC, NAD(P)⁺-MDH and NADP⁺-ME were high in young expanding leaves and decreased 2- to 3-fold in mature ones, suggesting that such enzymes play some role during the early stages of leaf expansion. In leaves of peach, such a role did not seem to be linked to C₃ photosynthesis or nitrate assimilation, in that photosynthetic O₂ evolution and activities of nitrate reductase (EC 1. 6. 6. 1) and glutamine synthetase (EC 6. 3. 1. 2) increased during leaf development. In contrast, leaf respiration strongly decreased with increasing leaf age. We suggest that in expanding leaves of this woody species the enzymes associated with malate metabolism have anaplerotic functions, and that PEPC may also contribute to the recapture of respiratory CO₂.     

CO2-concentrating mechanisms in Egeria densa,a submersed aquatic plant

Egeria densa is an aquatic higher plant which has developed different mechanisms to deal with photosynthesis under conditions of low CO₂ availability. On the one hand it shows leaf pH-polarity, which has been proposed to be used for bicarbonate utilization. In this way, at high light intensities and low dissolved carbon concentration, this species generates a low pH at the adaxial leaf surface. This acidification shifts the equilibrium HCO₃^–/CO₂ towards CO₂, which enters the cell by passive diffusion. By this means, E. densa increases the concentration of CO₂ available for photosynthesis inside the cells, when this gas is limiting. On the other hand, under stress conditions resulting from high temperature and high light intensities, it shows a biochemical adaptation with the induction of a C₄-like mechanism but without Kranz anatomy. Transfer from low to high temperature and light conditions induces increased levels of phospho enol pyruvate carboxylase (PEPC, EC 4.1.1.31) and NADP-malic enzyme (NADP-ME, EC 1.1.1.40), both key enzymes participating in the Hatch-Slack cycle in plants with C₄ metabolism. Moreover, one PEPC isoform, whose synthesis is induced by high temperature and light, is phosphorylated in the light, and changes in kinetic and regulatory properties are correlated with changes in the phosphorylation state of this enzyme. In the present review, we describe these two processes in this submersed angiosperm that appear to help it perform photosynthesis under conditions of extreme temperatures and high light intensities.     

Zeaxanthin and non‐photochemical quenching in sun and shade leaves of C3 and C4 plants

The relationships between non‐radiative energy dissipation and the carotenoid content, especially the xanthophyll cycle components, were studied in sun and shade leaves of several plants possessing C₃ ( Hedera helix and Laurus nobilis ) or C₄ ( Zea mays and Sorghum bicolor ) photosynthetic pathways. Sun‐shade acclimation caused marked changes in the organisation and function of photosynthetic apparatus, including significant variation in carotenoid content and composition. The contents of zanthophyll cycle pigments were higher in sun than in shade leaves in all species, but this difference was considerably greater in C₃ than in C₄ plants. The proportion of photoconvertible violaxanthin, that is the amount of violaxanthin (V) which can actually be de‐epoxidised to zeaxanthin, was much greater in sun than in shade leaves. The amount of photoconvertible V was always linearly dependent on the chlorophyll a/b ratio, although the slope of the relationship varied especially between C₃ and C₄ species. The leaf zeaxanthin and antheraxanthin contents were correlated with non‐radiative energy dissipation in all species under different light environments. These relationships were curvilinear and variable between sun and shade leaves and between C₃ and C₄ species. Hence, the dissipation of excess energy does not appear to be univocally dependent on zeaxanthin content and other photoprotective mechanisms may be involved under high irradiance stress. Such mechanisms appear largely variable between C₃ and C₄ species according to their photosynthetic characteristics.     

Coordinated accumulation of the chloroplastic and cytosolic pyruvate,Pi dikinases with enhanced expression of CAM in Kalanchoë blossfeldiana

Recent studies reveal that the intracellular localization of pyruvate,Pi dikinase (PPDK, EC 2.7.9.1) in mesophyll cells of malic enzyme (ME)-dependent Crassulacean acid metabolism (CAM) plants varies among species, occurring not only in the chloroplasts but also in the cytosol in some species. The facultative CAM plant Kalanchoë blossfeldiana accumulates PPDK in both compartments of the mesophyll cells. In this study, the patterns of accumulation of the chloroplastic and cytosolic PPDKs were investigated for K. blossfeldiana plants with different CAM activities by immunogold labeling and electron microscopy. Greater CAM activity was found in plants grown under drought conditions with short days than under well-watered conditions with long days, and in lower leaves than in higher leaves. There was a trend that plants and leaves with greater CAM activity show denser labeling for PPDK in both the cytosol and chloroplasts. However, the ratio of the density of PPDK labeling in the cytosol to that in the chloroplasts was almost constant (2.4–3.0). Higher labeling for phosphoenolpyruvate carboxylase (EC 4.1.1.31) in the cytosol was also correlated with higher CAM activity but there was almost no difference in the density of labeling for ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) in the chloroplasts. These results indicate that the increase in accumulation of cytosolic PPDK is closely associated with the increase of chloroplastic PPDK during enhanced CAM expression. This suggests that both PPDKs are involved in CAM function.     

Effects of cyanide and cold treatment on sugar catabolism in apple seeds during dormancy removal

The ratio of glycolysis to the pentose phosphate pathway (PPP, C₆/C₁ ratio), and the activities of glucose 6-phosphate dehydrogenase (EC 1.1.1.49) and pyruvate kinase (PK, EC 2.7,1.40) were determined in apple seeds ( Malus domestica Borb, cv. Antonówka) submitted to cold and warm stratifications. Our results indicated that the elimination of embryonal dormancy in apple seeds was connected with a change from domination of PPP to domination of glycolysis in sugar catabolism during cold stratification. Cyanide pretreatment affected the C₆/C₁ ratio and the activities of the enzymes under study in such a manner that the maxima of PPP and glycolysis appeared earlier during stratification. We suggest a regulatory role of cyanide in removal of dormancy.     

Relationship between photosystem II activity and CO2 fixation in leaves

There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO₂ fixed. A measure of the quantum yield of photosystem II, Φ_II (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals Φ_II times incident light intensity times the fraction of incident light absorbed by PSII. In C₄ plants, there is a linear relationship between PSII activity and CO₂ fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C₄ species. In C₃ plants, both CO₂ fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO₂, or per O₂ reacting with RuBP). The rates of PSII activity associated with photosynthesis in C₃ plants, based on estimates of the rates of carboxylation (v_o) and oxygenation (v_o) at various levels of CO₂ and O₂, largely account for the PSII activity determined from fluorescence measurements. Thus, in C₃ plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO₂ fixation.     

An Endogenous Aminoenkephalinase Inhibitor: Purification and Characterization of Arg0-Met5-Enkephalin from Bovine Striatum

Abstract: Arg⁰-Met⁵-enkephalin (Arg⁰-MEK) was isolated from bovine striatum and purified to homogeneity. The peptide was extracted with trichloroacetic acid, followed by column chromatography successively on Bio-Sil C₈, semipreparative HPLC Radial-Pak C₁₈, fast protein liquid chromatography (FPLC) Mono S, HPLC Ultrasphere-ODS, Supelco C₁₈, Lichromsorb C₁₈, and μBondapak C₁₈. The peptide content was followed by radioimmunoassay with an antibody against synthetic Met-enkephalin. For each of the six HPLC and FPLC systems, the elution time of the immunoreactive fractions coincided exactly with that of synthetic Arg⁰-MEK. The purified peptide showed a highly homogeneous profile in three different analytical HPLC systems. Its retention time and three-dimensional UV spectrum were identical to those of the synthetic Arg⁰-MEK. The structure of the purified material was identified by microsequencing as the hexapeptide Arg-Tyr-Gly-Gly-Phe-Met. Ninety percent of the purified peptide was in oxidized form containing equimolar amounts of Met-( R )- and Met-( S )-sulfoxide. The reduced Arg⁰-MEK inhibited aminoenkephalinase with a K _i of 2.2 µ M , and its sulfoxide analogue inhibited it with a K _i of 8.9 µ M . The reduced or oxidized peptide suppressed the electrically induced contraction of rat vas deferens with an ED₅₀ of 5 µ M , and the effect could be reversed by equimolar naloxone. Our data indicate that Arg⁰-MEK is an immediate Met-enkephalin precursor and an endogenous inhibitor.     

Chromosome numbers of C3 and C4 variants within the species Alloteropsis sernialata (R.Br.) Hitchc. (Poaceae)

FREAN, M. L. & MARKS, E., 1988. Chromosome numbers of C₃ and C₄ variants within the species Alloteropais semialata (R.Br.) Hitch. (Poaceae). In a study of mid-lamina leaf sections, different variants of A. semialata were found to have C₃ or C₄ anatomy. The C₄ leaf showed a specialized photosynthetic vascular bundle sheath not present in the C₃ form. Chromosome counts made from pollen mother cell squashes showed that the C₃ form of A. semialata is a fertile diploid 2n = 2x = 18 and the C₄ form, a fertile allohexaploid 2n = 6x = 54. The cytological evidence suggests that the two forms should be considered as separate species.     

Stimulation of respiration by Pb2+ in detached leaves and mitochondria of C3 and C4 plants

The exposure of detached leaves of C₃ plants (pea, barley) and C₄ plant (maize) to 5 m M Pb (NO₃)₂ for 24 h caused a reduction of their photosynthetic activity by 40–60%, whereas the respiratory rate was stimulated by 20–50%. Mitochondria isolated from Pb²⁺-treated pea leaves oxidized substrates (glycine, succinate, malate) at higher rates than mitochondria from control leaves. The respiratory control (RCR) and the ADP/O ratio were not affected. Pb²⁺ caused an increase in ATP content and the ATP/ADP ratio in pea and maize leaves. Rapid fractionation of barley protoplasts incubated at low and high CO₂ conditions, indicated that the increased ATP/ADP ratio in Pb²⁺-treated leaves resulted mainly from the production of mitochondrial ATP. The measurements of membrane potential of mitochondria with a TPP⁺-sensitive electrode further showed that mitochondria isolated from Pb²⁺-treated leaves had at least as high membrane potential as mitochondria from control leaves. The activity of NAD-malate dehydrogenase in the protoplasts from barley leaves treated with Pb²⁺ was 3-fold higher than in protoplasts from control leaves. The activities of photorespiratory enzymes NADH-hydroxypyruvate reductase and glycolate oxidase as well as of NAD-malic enzyme were not affected. The presented data indicate that stimulation of respiration in leaves treated by lead is in a close relationship with activation of malate dehydrogenase and stimulation of the mitochondrial ATP production. Thus, respiration might fulfil a protective role during heavy metal exposure.     

Direct and indirect effects of Cd2+ on photosynthesis in sugar beet (Beta vulgaris)

Sugar-beet plants ( Beta vulgaris L. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μ M CdCl₂ to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μ M CdCl₂ to the assay media. The photosynthetic properties were characterized by measurement of CO₂ fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO₂-dependent O₂ evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd²⁺ impeded CO₂ fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd²⁺ was applied through the culture medium the capacity for, and the maximal quantum yield of CO₂ assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd²⁺-cultivated plants showed an increased rate of dark respiration.     

Promotive Effect of Low Concentrations of NaHSO3 on Photophosphorylation and Photosynthesis in Phosphoenolpyruvate Carboxylase Transgenic Rice Leaves

Spraying a 1-2 mmol/L solution of NaHSO3 on the leaves of wild-type rice (Oryza sativa L.)Kitaake (WT), phosphoenolpyruvate carboxylase (PEPC) transgenic (PC) rice and PEPC phosphate dikinase(PPDK) transgenic rice (PC PK), in which the germplasm was transformed with wild-type Kitaake as the gene receptor, resulted in an enhancement of the net photosynthetic rate by 23.0%, 28.8%, and 34.4%,respectively, for more than 3 d. It was also observed that NaHSO3 application caused an increase in the ATP content in leaves. Spraying PMS (a cofactor catalysing the photophosphorylation cycle) and NaHSO3 separately or together on leaves resulted in an increase in photosynthesis with all treatments. There was no additional effect on photosynthetic rate when the mixture was applied, suggesting that the mechanism by which NaHSO3 promotes photosynthesis is similar to the mechanism by which PMS acts and that both of compounds enhanced the supply of ATE After spraying a solution of NaHSO3 on leaves, compared with the WT Kitaake rice, a greater enhancement of net photosynthetic rate was observed in PEPC transgenic(PC) and PEPC PPDK transgenic (PC PK) rice, with the greatest increase being observed in the latter group. Therefore ATP supply may become the limiting factor that concentrates CO2 in rice leaves transformed with an exogenous PEPC gene and exogenous PEPC PPDK genes.     

Immunogold localization of photosynthetic enzymes in leaves of various C4 plants, with particular reference to pyruvate orthophosphate dikinase

Cellular localization of photosynthetic enzymes was investigated by immunogold electron microscopy for leaves of nine C4 grasses (three NADP-malic enzyme (NADP-ME)subtype species, three NAD-malic enzyme (NAD-ME) subtype species, and three phosphoenolpyruvate carboxykinase (PCK) subtype species), two C4 sedges (NADP-ME subtype species) and two C4 dicots (an NADP-ME and an NADP/NAD-ME subtype species). In leaves of all species, immunogold labelling was present for phosphoenolpyruvate carboxylase in the cytosol of the mesophyll cells (MC) and for ribulose-1,5-bisphosphate carboxylase/oxygenase in the chloroplasts of the bundle sheath cells (BSC). However, considerable specific variation was found in the intercellular patterns of labelling for pyruvate orthophosphate dikinase (PPDK). In the NADP-ME grasses, two NAD-ME grasses, and the dicots, significant labelling for PPDK was present in the both the BSC and the MC chloroplasts. In the other NAD-ME grass, the PCK grasses, and the sedges, labelling for PPDK was present almost exclusively in the chloroplasts of the MC. These patterns were observed in the leaves of both young seedlings and mature plants. These results indicate that the accumulation of PPDK in leaves of C4 plants is not necessarily restricted to the MC, although the chloroplasts of the MC accumulate more than those of the BSC.Key words: C4 plants, immunolocalization, phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, ribulose-1,5-bisphosphate carboxylase/oxygenase.