Search

The aim of the present study was to investigate the photosynthetic properties and transcriptomic profiles of wildtype and chlorophyll (Chl) b-lacking rice (Oryza sativa L.). The plastid ultrastructure of the Chl b-lacking rice (i.e., loss of starch granules, abundant vesicles, and abundant plastoglobuli) indicated abnormal plastid development, whereas the analysis of transcriptome profiles and differentially expressed genes revealed that gene encoding PsbR (PSII core protein) was downregulated in the mutant, thereby reducing the Chl accumulation of the mutant. Meanwhile, in regards to Chl biosynthesis and degradation pathways, GluTR gene was downregulated, whereas UROD, CPOX, and MgCH genes were upregulated. The qPCR results were generally consistent with those of the transcription analysis, except for the finding that NOL genes, which regulate Chl b degradation, were upregulated. These results suggest that both the reduction in Chl accumulation and increase in conversion rate of Chl b to Chl a caused Chl a/b ratio amplification in mutant. The present study also provides evidence for Chl b degradation via pheophorbide b.

The aim of the present study was to investigate the photosynthetic properties and transcriptomic profiles of wildtype and chlorophyll (Chl) b-lacking rice (Oryza sativa L.). The plastid ultrastructure of the Chl b-lacking rice (i.e., loss of starch granules, abundant vesicles, and abundant plastoglobuli) indicated abnormal plastid development, whereas the analysis of transcriptome profiles and differentially expressed genes revealed that gene encoding PsbR (PSII core protein) was downregulated in the mutant, thereby reducing the Chl accumulation of the mutant. Meanwhile, in regards to Chl biosynthesis and degradation pathways, GluTR gene was downregulated, whereas UROD, CPOX, and MgCH genes were upregulated. The qPCR results were generally consistent with those of the transcription analysis, except for the finding that NOL genes, which regulate Chl b degradation, were upregulated. These results suggest that both the reduction in Chl accumulation and increase in conversion rate of Chl b to Chl a caused Chl a/b ratio amplification in mutant. The present study also provides evidence for Chl b degradation via pheophorbide b. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the significance of blue light (B) in the growth and photosynthetic capacity of cucumber. Gas exchange, chlorophyll (Chl) fluorescence kinetics, chloroplast ultrastructure, and leaf growth were investigated to explore the influence of three different light qualities of light emitting diodes (LEDs) on plant morphogenesis and the development of photosynthetic apparatus in cucumber ( Cucumis sativus) leaves from emergence to full expansion under weak light [50 μmol(photon) m s]. We found that B could significantly increase the leaf area (LA), shoot elongation, Chl a/ b, net photosynthetic rate, and stomatal conductance ( g). In addition, the comparisons of maximal quantum yield of PSII photochemistry and the photosynthetic performance index between B-, W (white light)-, and R (red light)-grown leaves suggested that B was essential for the development of photosynthetic apparatus under weak light. B-grown leaves had the lowest Chl content under weak light, however, they had well-developed chloroplasts with the highest degree of stacked lamellae and the lowest starch accumulation. This could explain to a considerable extent the highest net photosynthetic rate per Chl unit. The results demonstrated that B optimized photosynthetic performance by improving the photosynthetic rate, increasing LA, and prolonging active photosynthesis duration under low irradiance. Therefore B is necessary to ensure healthy development of chloroplasts and highly efficient photosynthetic functions in cucumbers under a weak light environment. More importantly, our study also provided theoretical and technical support for the development of light environmental control technology. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The progressive decline in cotton leaf photosynthesis with season could be accounted for by gaining an insight into ontogenic changes in chloroplast integrity and epicuticular wax ultrastructure. Therefore, the sequence of ultrastructural changes in chloroplast and epicuticular wax morphology were probed in 10-, 20-, 40-, and 60-d-old cotton ( Gossypium hirsutum L.) leaves using electron microscopy. Scanning electron microscopy illustrated that the epicuticular wax on the periclinal walls of the convex epidermal cells occurred as striations and persisted as such during the course of leaf aging. The degree of wax spread, however, increased as the leaf progressed towards senescence. Transmission electron microscopy revealed that a 20-d-old photosynthetically active leaf possessed healthy chloroplasts (6.8 μm long and an area of 9.7 μm2) with absolute membrane integrity depicted by large appressed grana stacks of thylakoids interconnected by non-appressed stroma lamellae. The thylakoid membrane network was oriented parallel to the long axis of the chloroplast and a few small plastoglobuli (1.85 μm2) scattered in the stroma. Conversely, membrane integrity was lost with leaf age after 20 d as evidenced by disruption of the grana and stroma lamellae. Concurrent with the membrane damage, extensive occlusion of chloroplast by several large spherical plastoglobuli (5.68 μm2) occurred, the rate of occlusion increased with leafage distending the chloroplast as evidenced by proliferation of its cross-sectional area (12.8 μm2). Of particular interest was the finding that the plastoglobuli ensued through the chloroplast envelope into the cytoplasm. The progressive loss of chloroplast membrane integrity coupled with increased leaf waxiness may have limited photosynthetic activities of cotton leaves during senescence. [ABSTRACT FROM AUTHOR]

Inner structure of isolated intact chloroplasts was observed for the first time by a method of laser scanning microscopy at the temperature of liquid nitrogen at 77 K. The microscope, based on gradient index optics, has a maximum resolution of 440 nm at the wavelength of 650 nm. Chloroplasts were excited into the Q-band of chlorophyll b by a krypton laser line at 647.6 nm and fluorescence was detected using two different interference filters. The 680 nm interference filter detects the regions where photosystem (PS) 2 mainly occurs, the 730 nm interference filter detects domains with predominant location of PS1. Since PS1 occurs mainly in stroma lamellae, whereas PS2 occurs mainly in grana regions we were able to view the structure of thylakoid membrane in isolated intact chloroplast that is the closest to in vivo state. [ABSTRACT FROM AUTHOR]

Field studies were conducted to investigate ontogenic changes in leaf photosynthesis and chloroplast ultrastructure of a single cotton (Gossypium hirsutum L.) leaf subtending the fruit. A 20-d old leaf was the most physiologically active with net photosynthetic rate (PN) of 16.5 μmol m-2 s-1 and nitrogen (N) concentration of 168 mmol m-2. These values declined with leaf age and a close relationship existed between them. Concurrent with declines in PN, ultrastructural alterations occurred in the chloroplast: the 20-d old leaf had increased grana number and thylakoids per granum and a few plastoglobuli. Afterwards, the grana number and thylakoids per granum declined with leaf age indicating disintegrated grana and stroma lamellae. Concomitant with disintegrated membrane system was the presence of numerous large plastoglobuli. The PN was closely related to grana number and thylakoids per granum suggesting that the decline in PN with leaf age was associated with ultrastructural changes in the chloroplast. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Morphological, anatomical and ultrastructural changes, the quantity and quality of stomata, and the chlorophyll (Chl) content in primary outer leaves of cabbage plants cv. Sława from Enkhouizen were examined. The plants were grown in agar with basic MS medium containing added nickel (as NiSO4×7 H2O) in concentrations of 0, 5, 10, and 20 g m-3 (Ni0, Ni5, Ni10, Ni20). Reduction of leaf blade area, of succulence and of leaf density, and growth of specific leaf area were noticed in plants treated with all concentrations of Ni. In Ni-treated plants the total number of stomata and open stomata decreased, and the number of defective stomata in both adaxial and abaxial side of leaves was higher. In all Ni-treated samples the volume of spongy and palisade mesophyll cells was smaller in comparison to control, and it was decreasing when the Ni concentration was increasing; at the same time, the number of mesophyll cells on the same area of cross sections of leaves was increasing. In comparison to control, the intercellular spaces of mesophyll tissue decreased in Ni10 and Ni20 plants and increased in Ni5 plants. In Ni5 plants the number of chloroplasts in mesophyll cells was higher than in the Ni0 control. Reduction of grana size and increase of number of non-appressed lamellae, which often had central arrangement, were observed. In the Ni10 and Ni20 plants, the number and size of chloroplasts decreased, and their internal membranes (especially grana) were reduced and swollen. In Ni5 plants the concentration of Chl in leaves was slightly higher than in the control; in Ni10 and Ni20 plants it was lower than in the control. [ABSTRACT FROM AUTHOR]