Chloroplasts utilize photons from solar radiation to synthesize energy-rich molecules of ATPs and NADPHs, which are further used in active cellular processes. Multiprotein complexes (MPCs), including photosystems (PSII and PSI), and the cellular architecture responsible for generation of the proton motive force and the subsequent photophosphorylation, mediate the task of ATP and NADPH synthesis. Both photosystems and other multiprotein assemblies are embedded in thylakoid membranes. Advances in techniques used to study structural biology, biophysics, and comparative genomics and proteomics have enabled us to gain insights of structure, function, and localization of each individual component of the photosynthetic apparatus. An efficient coordination among MPCs is essential for normal functioning of photosynthesis, but there are various stressors that might directly or indirectly interact with photosynthetic components and processes. Cadmium is one of the toxic heavy metals that interact with photosynthetic components and damage photosystems and other MPCs in thylakoids. In plants, iron deficiency shows similar symptoms as those caused by Cd. Our article provides a general overview of chloroplast structure and a critical account of Cd-induced changes in photosystems and other MPCs in thylakoids, and suggests the possible mechanisms involved in mediating these changes. The connection between Cd-induced Fe deficiency and the elevated Cd toxicity under the Fe-deficient condition was also discussed., H. Bashir, M. I. Qureshi, M. M. Ibrahim, M. Iqbal., and Obsahuje seznam literatury
Effect of three Zn2+ concentrations, i.e. 0.075 (cl), 7.50 (c2) and 37.5 (c3) jiM, on rice seedlings was studied at three stages, i.e. 1, 14 and 21 d after transplantation. Typical deficiency symptoms were observed in both solution and sand cultures of cl and c2, but the effects were more pronounced in the solution culture. The c3 concentration was toxic. There was marked reduction in growth, chlorophyll (Chl) contents (particularly Chl b), Hill reaction activity, photophosphorylation rate (particularly non-cyclic photophosphorylation), thylakoid phosphorylation, and i'‘C02-fixation at the cl concentration. However, a similar reduction was also observed in thylakoid phosphorylation at the c3 concentration. Hence the optimum zinc concentration in the nutrient medium lied between c2 and c3 Zn2+. By regression the theoretical optimum Zn concentration was calculated as 19.20 pM (1.28 mg kg'i) Zn2+. Partitioning of ^'^C-photosynthates indicated reduced allocation to sugar and starch fractions and increased fřee amino acids concentration at the cl concentration and vice-versa at c2 and c3.
In leaves of four tomato (Lycopersicon esculentum Mill.) cultivars (Red Cloud, Floradade, Peto 95, and Scorpio) the contents of chlorophyll (Chl) (a+b), Chl a, and β-carotene decreased due to 100 mM NaCl treatment as compared with those of controls. The contents of soluble sugars and total saccharides were significantly increased in leaves of NaCl-treated plants, but the starch content was not significantly affected. Transmission electron microscopy indicated that in leaves of NaCl-treated plants, the chloroplasts were aggregated, the cell membranes were distorted and wrinkled, and there was no sign of grana and thylakoid structures in chloroplasts. and R. A. Khavari-Nejad, Y. Mostofi.
Exposure of two-month-old seedlings of Bruguiera parviflora to NaCl stress (0 to 400 mM) for 45 d under hydroponic culture caused notable disorganisation of the thylakoid structure of chloroplasts in NaCl-treated leaves as revealed from transmission electron microscopy. The absorption spectra of treated and control thylakoid samples were similar having a red peak at 680 nm and Soret peaks at 439 and 471 nm in the blue region of the spectrum. The spectra of treated samples differed from control samples by gradual decrease in absorbance of 100, 200, and 400 mM NaCl treated samples at 471 and 439 nm, which could be due to scattering of radiation in these samples. Thus, absorption characteristics of thylakoid membranes indicated no major alterations in the structural integrity of the photosynthetic membranes during salt stress in B. parviflora. Analysis of pigment protein complexes of thylakoids on non-denaturing gel showed that CP1 complex consisting of photosystem (PS) 1 reaction centre decreased marginally by 19% and the CP47 constituting the core antenna of PS2 declined significantly by 30% in 400 mM NaCl treated samples in respect to control. This decrease in structural core antenna might cause inefficient photon harvesting capacity. However, CP43 content did not alter. An increase in CP2/CP1 ratio from 3.2 in control to 4.0 in 400 mM NaCl treated samples indicated significant structural changes in the thylakoids of salt treated plants. Haem staining of thylakoids revealed significant losses in cytochrome (Cyt)f and Cyt b 6 contents by NaCl stress. However, Cyt b 559 content remained nearly constant in both control and NaCl treated samples. SDS-PAGE of thylakoid proteins showed that the intensity of many of Coomassie stained polypeptide bands ranging from 15-22 and 28-66 kDa regions decreased significantly in NaCl treated samples as compared to control. Electron transport activity of thylakoids, measured in terms of DCPIP photoreduction, was 22% lower in 400 mM NaCl treated plants than in the control ones. Hence, NaCl induces oxidative stress in chloroplasts causing structural alterations in thylakoids. These structural alterations might be responsible for declined efficiency of photosystems and reduced electron transport activity. and A. K. Parida, A. B. Das, B. Mittra.
Effects of high-temperature stress (HTS) and PEG-induced water stress (WS), applied separately or in combination, on the functional activity and ultrastructure of the photosynthetic apparatus (PSA) of maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were investigated. In maize plant tissues WS provoked the decrease in RWC by 10.9 %, HTS by 7.0 %, and after simultaneous application of the both treatments the decrease was 32.7 % in comparison with control plants. Similar but more expressed changes were observed in sunflower plants. Sunflower was more sensitive to these stresses. Net photosynthetic rate decreased significantly after all treatments, more in sunflower. In mesophyll chloroplasts after separately applied WS and HTS the number of grana and thylakoids was reduced and electron-transparent spaces appeared. At combined stress (WS+HTS) granal and stromal thylakoids were considerably affected and chloroplast envelope in many of them was partially disrupted. and I. Dekov, T. Tsonev, I. Yordanov.
Cations such as Mg2+ regulate spillover of absorbed excitation energy mainly in favour of photosystem (PS) 2. Effect of low concentration (<10 mM) of the monovalent cation Na+ on chlorophyll (Chl) a fluorescence was completely overridden by divalent cation Mg2+ (5 mM). Based on Chl a fluorescence yield and 77 K emission measurements, we revealed the role and effectiveness of anions (Cl-, SO42-, PO43-) in lowering the Mg2+-induced PS2 fluorescence. The higher the valency of the anion, the lesser was the expression of Mg2+ effect. Anions may thus overcome Mg2+ effects up to certain extent in a valency dependent manner, thereby diverting more energy to PS1 even in the presence of MgCl2. They may do so by reversing Mg2+-induced changes. and Anjana Jajoo, Sudhakar Bharti.
In Amaranthus tricolor the leaf structure included three layers of chlorenchyma on the vascular bundle periphery, namely, mesophyll cells (MSCs) with few chloroplasts, outer larger round bundle sheath cells (BSCs) with many chloroplasts in a centripetal position, and inner smaller BSCs with few chloroplasts around the vascular bundle cells. The ultra-thin sections showed that BSCs had abundant organelles, namely many large and round mitochondria with well-developed cristae in the cytoplasm. The chloroplasts in the BSCs were lens-like bodies, which seemed to be oval on cross sections. Granal and intergranal thylakoids were usually distinguished. Grana were stacked in parallel with prevailing plane of thylakoid lamellae. The chloroplasts in the MSCs appeared smaller than those in the BSCs and contained less stacked thylakoids but abundant peripheral reticulum. The ultra-thin sections of immunogold-labelled anti-ribulose-1,5-bisphosphate carboxylase/oxygenase (anti-RuBPCO) exhibited high density of RuBPCO labelling in the stroma region of chloroplasts of the BSCs. Some anti-RuBPCO immunogold particles were observed in the stromal region of MSCs chloroplasts. The anti-activase (A) immunogold-labelling indicated that RuBPCOA was mainly distributed in the stroma region of both BSCs and MSCs chloroplasts. From the chloroplast ultrastructure and localisation of RuBPCO and RuBPCOA we deduced that the photosynthetic carbon reduction cycle and the formation of assimilatory power function in both MSC and BSC chloroplasts of A. tricolor. and J. Hong ... [et al.].
The last step for biosynthesis of c type cytochromes, indispensable for photosynthesis in cyanobacteria and plants, involves heme transport across the membrane and its covalent attachment to the apoprotein. In cyanobacteria, heme attachment occurs in the thylakoid lumen and probably also in the periplasm and requires at least four proteins, believed to be organized in intrinsic membrane protein complex. To allow isolation and identification of such complex, CcsB protein was tagged with 6xHis tag on its N terminus and expressed under the strong psbAII promoter in the cyanobacterium Synechocystis sp. PCC 6803. Similarly, CcsA protein was tagged with FLAG tag under the control of the same promoter. Although expression of both proteins under strong cyanobacterial promoter did not increase steady state contents of the CcsB protein, the fusion tags did not influence properties of the CcsB and CcsA proteins and the resulting mutants had the same phenotype as the wild type. Protein fraction containing CcsBHis protein was partially isolated from the solubilised membranes under native conditions.
Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts. and J. Kutík ... [et al.].
Differences in ultrastructural parameters of mesophyll cell (MC) chloroplasts, contents of photosynthetic pigments, and photochemical activities of isolated MC chloroplasts were studied in the basal, middle, and apical part of mature or senescing leaf blade of two maize genotypes. A distinct heterogeneity of leaf blade was observed both for structural and functional characteristics of chloroplasts. In both mature and senescing leaves the shape of MC chloroplasts changed from flat one in basal part of leaf to nearly spherical one in leaf apex. The volume density of granal thylakoids decreased from leaf base to apex in both types of leaves examined, while the amount of intergranal thylakoids increased in mature leaves but decreased in senescing leaves. The most striking heterogeneity was found for the quantity of plastoglobuli, which strongly increased with the increasing distance from leaf base. The differences in chloroplast ultrastructure were accompanied by differences in other photosynthetic characteristics. The Hill reaction activity and activity of photosystem 1 of isolated MC chloroplasts decreased from leaf base to apex in mature leaves. Apical part of senescing leaf blade was characterised by low contents of chlorophyll (Chl) a and Chl b, whereas in mature leaves, the content of Chls as well as the content of total carotenoids (Car) slightly increased from basal to apical leaf part. This was reflected also in the ratio Chl (a+b)/total Car; the ratio of Chl a/b did not significantly differ between individual parts of leaf blade. Both genotypes examined differed in the character of developmental gradient observed along whole length of leaf blade. and J. Kutík ... [et al.].