Swelling Of Thylakoids Research Articles

Mechanism of growth inhibition mediated by disorder of chlorophyll metabolism in rice (Oryza sativa) under the stress of three polycyclic aromatic hydrocarbons

Photosynthesis mediated by chlorophyll metabolism is the basis for plant growth, and also the important regulatory mechanism of carbon pool in cropland ecosystems. Soil organic pollutants induced growth inhibition in crop plants, herein, we conducted an in-depth investigation on the effects of three representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BaP) on rice (Oryza sativa) growth and photosynthesis. PAHs were absorbed via root uptake and accumulated in leaves, causing the swelling of thylakoids and the increase of osmiophilic granules in chloroplasts. The actual quantum efficiency of PSII was significantly decreased under the stress of PHE, PYR, and BaP by 29.9%, 11.9%, and 24.1% respectively, indicating the inhibition in photon absorption and transfer, which was consistent with the decrease of chlorophyll a (22.3%–32.2% compared to the control) in rice leaves. Twenty-two encoding genes involved in chlorophyll metabolism were determined and the results indicated that the expression of chlorophyll synthetases was downregulated by over 50% whereas the degradation process was promoted. Consequently, the production of carbohydrates and the carbon fixation were inhibited, which revealed by the downregulation of intermediate metabolites in Calvin cycle and the declined carboxylation rate. The disturbed photosynthesis resulted in the decrease of the biomasses of both roots (21.0%–42.7%) and leaves (6.4%–22.1%) under the tested PAH stresses. The findings of this study implied that the photosynthetic inhibition was possibly attributed to the disorder of chlorophyll metabolism, thus providing novel insights into the mechanism of growth inhibition induced by organic pollutants and theoretical basis for the estimation of cropland carbon sequestration potential.

Structural basis for VIPP1 oligomerization and maintenance of thylakoid membrane integrity

Vesicle-inducing protein in plastids 1 (VIPP1) is essential for the biogenesis and maintenance of thylakoid membranes, which transform light into life. However, it is unknown how VIPP1 performs its vital membrane-remodeling functions. Here, we use cryo-electron microscopy to determine structures of cyanobacterial VIPP1 rings, revealing how VIPP1 monomers flex and interweave to form basket-like assemblies of different symmetries. Three VIPP1 monomers together coordinate a non-canonical nucleotide binding pocket on one end of the ring. Inside the ring's lumen, amphipathic helices from each monomer align to form large hydrophobic columns, enabling VIPP1 to bind and curve membranes. Invivo mutations in these hydrophobic surfaces cause extreme thylakoid swelling under high light, indicating an essential role of VIPP1 lipid binding in resisting stress-induced damage. Using cryo-correlative light and electron microscopy (cryo-CLEM), we observe oligomeric VIPP1 coats encapsulating membrane tubules within the Chlamydomonas chloroplast. Our work provides a structural foundation for understanding how VIPP1 directs thylakoid biogenesis and maintenance.

Sodium nitroprusside application improves morphological and physiological attributes of soybean (Glycine max L.) under salinity stress.

Salinity is among the major abiotic stresses negatively affecting the growth and productivity of crop plants. Sodium nitroprusside (SNP) -an external nitric oxide (NO) donor- has been found effective to impart salinity tolerance to plants. Soybean (Glycine max L.) is widely cultivated around the world; however, salinity stress hampers its growth and productivity. Therefore, the current study evaluated the role of SNP in improving morphological, physiological and biochemical attributes of soybean under salinity stress. Data relating to biomass, chlorophyll and malondialdehyde (MDA) contents, activities of various antioxidant enzymes, ion content and ultrastructural analysis were collected. The SNP application ameliorated the negative effects of salinity stress to significant extent by regulating antioxidant mechanism. Root and shoot length, fresh and dry weight, chlorophyll contents, activities of various antioxidant enzymes, i.e., catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) were improved with SNP application under salinity stress compared to control treatment. Similarly, plants treated with SNP observed less damage to cell organelles of roots and leaves under salinity stress. The results revealed pivotal functions of SNP in salinity tolerance of soybean, including cell wall repair, sequestration of sodium ion in the vacuole and maintenance of normal chloroplasts with no swelling of thylakoids. Minor distortions of cell membrane and large number of starch grains indicates an increase in the photosynthetic activity. Therefore, SNP can be used as a regulator to improve the salinity tolerance of soybean in salt affected soils.

Photosynthetic performance of quinoa (Chenopodium quinoa Willd.) after exposure to a gradual drought stress followed by a recovery period

Drought is an abiotic scourge, one of the major environmental stress factors that adversely affect plant growth and photosynthesis machinery through a disruption of cell organelles, arrangement thylakoid membranes and the electron transport chain. Herein, we probed the effect of drought stress on photosynthetic performance of Chenopodium quinoa Willd. Beforehand, plants were subjected to water deficit (as 15% Field Capacity, FC) for one (D-1W) or two weeks (D-2W), and were then re-watered at 95% FC for 2 weeks. Light and electron microscopy analysis of leaves showed no apparent changes in mesophyll cell organization and chloroplast ultrastructure after one week of drought stress, while a swelling of thylakoids and starch accumulation were observed after the prolonged drought (D-2W). The latter induced a decrease in both PSI and PSII quantum yields which was accompanied by an increase in F0 (minimum fluorescence) and a decline in Fm (maximum fluorescence). Drought stress influenced the fluorescence transients, where the major changes at the OJIP prompt FI level were detected in the OJ and IP phases. Prolonged drought induced a decrease in chl a fluorescence at IP phase which was readjusted and established back after re-watering and even more an increase was observed after 2 weeks of recovery. The maximum quantum yield of primary photochemistry (φPo) was unaffected by the different drought stress regimes. Drought induced an increase in the ABS/RC and DI0/RC ratios which was concurrent to a stable φPo (maximum quantum yield of PSII primary photochemistry). A substantial decrease in PI(ABS) was detected especially, during severe drought stress (D-2W) suggesting a drop in the PSII efficiency and the level of electron transport through the plastoquinone pool (PQ pool) towards oxidized PSI RCs (P700+). The immunoblot analysis of the main PSII proteins revealed considerable changes in the D1, D2, CP47, OEC, PsbQ and LHCII proteins under drought. These changes depend on the stress duration and recovery period. The main message of this investigation is the elevated recovery capacities of PSII and PSI photochemical activities after re-watering.

Structural Basis for VIPP1 Oligomerization and Maintenance of Thylakoid Membrane Integrity

Vesicle-inducing protein in plastids (VIPP1) is essential for the biogenesis and maintenance of thylakoid membranes, which transform light into life. However, it is unknown how VIPP1 performs its vital membrane-shaping function. Here, we use cryo-electron microscopy to determine structures of cyanobacterial VIPP1 rings, revealing how VIPP1 monomers flex and interweave to form basket-like assemblies of different symmetries. Three VIPP1 monomers together coordinate a non-canonical nucleotide binding pocket that is required for VIPP1 oligomerization. Inside the ring’s lumen, amphipathic helices from each monomer align to form large hydrophobic columns, enabling VIPP1 to bind and curve membranes. In vivo point mutations in these hydrophobic surfaces cause extreme thylakoid swelling under high light, indicating an essential role of VIPP1 lipid binding in resisting stress-induced damage. Our study provides a structural basis for understanding how the oligomerization of VIPP1 drives the biogenesis of thylakoid membranes and protects these life-giving membranes from environmental stress.

Salinity tolerance of quinoa (Chenopodium quinoa Willd) as assessed by chloroplast ultrastructure and photosynthetic performance

Quinoa has been widely used as a model crop for understanding salt-tolerance in halophyte plants. However, a salt tolerance mechanism regarding the photosynthetic activity is poorly evaluated. Here we report the effects of salt stress on photosynthesis of the halophyte Chenopodium quinoa cultivated under different NaCl concentrations (0, 100, and 300 mM). Our results revealed no apparent effect of moderate salinity (100 mM NaCl) on plant growth while, a reduction of plant biomass production was detected under 300 mM NaCl without any symptom of toxicity. No significant effect on the chloroplasts ultrastructure was observed under moderate salinity. Some morphological deformations of chloroplasts such as swelling of thylakoids, disruption of envelope, accumulation of starch grains and plastoglobuli were observed following prolonged exposure to severe stress. Under moderate salinity, no considerable change was detected on the rate of primary photochemistry (fluorescence O-J phase) and the reduction of the PQ pool (J-I phase), no apparent effects on the minimal (F0), the maximal fluorescence (Fm) and the maximal photochemical efficiency (Fv/Fm) showing a high stability of PSII. The high PSII efficiency was also confirmed by the donor side intactness (constant Fk/Fj ratio) and stable antenna size. The high stability of PSII efficiency was also demonstrated by enhanced communication between antenna complex and PSII reaction centre and the stability of OEC complex (PsbQ and PsbO proteins). However, high salinity (300 mM NaCl) results in a swelling of thylakoids and disappearance of grana and in a decrease of Fm and (Fv/Fm) leading to the down-regulation of PSII activity. In addition, a significant increase in F0 occurred and could be associated to the presence of some QA− in darkness in equilibrium with a partially reduced PQ pool. High salt treatment could be responsible for the thermal phase which induced an increase in chl a fluorescence (JIP rise with oxidized PQ pool).

Photosynthetic Capacity, Stomatal Behavior and Chloroplast Ultrastructure in Leaves of the Endangered Plant Carpinus putoensis W.C.Cheng during Gaseous NO2 Exposure and after Recovery

Foliar uptake of gaseous NO2 mainly occurs through the stomata and disrupts normal plant growth, but no detailed reports about the physiological responses of plants exposed to NO2 are available. In this study, to study leaf physicochemical responses, stomatal characteristics and chloroplast structure, we observed the leaves of Carpinus putoensis W.C.Cheng after exposure to NO2 (6 μL/L) for five time periods (0, 1, 6, 24, and 72 h) and after 30 days of recovery following NO2 exposure. Our results showed that short-duration exposure to a high concentration of NO2 had significant negative impacts (p < 0.05) on the chlorophyll content, photosynthesis and chloroplast-related physicochemical processes of C. putoensis leaves; with the exception of one hour of NO2 exposure, which was helpful for plant physiological responses. Moreover, NO2 exposure significantly increased the thickness of the palisade/spongy tissue and caused swelling of the thylakoids within the chloroplasts; this thylakoid swelling could be reversed by removing the pollutant from the air flow. Restoration of unpolluted air alleviated the toxic effects of NO2, as indicated by an increased chlorophyll content, net photosynthesis, and PSII maximum quantum yield. These results could support the development of a treatment for roadside trees that are exposed to NO2 as a major road pollutant.

Comparative analysis of salt stress, duration and intensity, on the chloroplast ultrastructure and photosynthetic apparatus in Thellungiella salsuginea

Salinity is one of the most important abiotic stress affecting plant growth and productivity worldwide. Photosynthesis, together with cell growth, is among the primary process affected by salinity. Here, we report the effects of salt stress on photosynthesis in the model halophyte Thellungiella salsuginea. Plants were grown in hydroponic system and then treated for 2 weeks with different NaCl concentrations (0, 100, 200 and 400 mM). Leaf analysis using both photonic and transmission electron microscopes showed some changes in mesophyll cell organization, including shape and dimension. Under high NaCl concentration (400 mM) a swelling of thylakoids and starch accumulation was also observed. The obtained results also showed a change in the photosynthetic efficiency of both photosystems (PSI and PSII), depending on both NaCl concentrations and duration of the stress treatment. Under moderate salinity (100 and 200 mM NaCl) no significant variation was observed in PSI and PSII yield parameters. Chlorophyll a fluorescence transient showed some variations in OJ, JI and IP phases under salt stress depending also on NaCl levels and the duration of stress. Under high salinity PSII donor side was affected as well as quantum yield of PSI which also showed a donor side limitation. A significant decrease on quantum yields Y(I) and Y(II) under high salt treatment (400 mM NaCl) for prolonged period of time (15 days) was observed. The decrease of these parameters was quantitatively compensated by a corresponding increase of energy thermal dissipation Y(NPQ) in photosystem II and a increase in the Y(ND) in PSI. Analysis of derived parameters from the OJIP transient curve revealed that ABS/RC decreased under NaCl treatment by reason of the increase in size of antenna of active reaction centers. An increase in the performance index PI(ABS), a slight decrease in the rate of DIO/RC, TRO/RC and the level of electron transport per PSII RC (ETO/RC) were observed during the first days of salt stress treatment reflecting a high PSII efficiency.

Overexpression of plastidic maize NADP-malate dehydrogenase (ZmNADP-MDH) in Arabidopsis thaliana confers tolerance to salt stress.

The plastidic C4 Zea mays NADP-malate dehydrogenase (ZmNADP-MDH), responsible for catalysis of oxaloacetate to malate, was overexpressed in Arabidopsis thaliana to assess its impact on photosynthesis and tolerance to salinity stress. Different transgenic lines were produced having ~3-6-fold higher MDH protein abundance and NADP-MDH enzyme activity than vector control. The overexpressors had similar chlorophyll, carotenoid, and protein content as that of vector control. Their photosynthetic electron transport rates, carbon assimilation rate, and consequently fresh weight and dry weight were almost similar. However, these overexpressors were tolerant to salt stress (150mM NaCl). In saline environment, the Fv/Fm ratio, yield of photosystem II, chlorophyll, and protein content were higher in ZmNADP-MDH overexpressor than vector control. Under identical conditions, the generation of reactive oxygen species (H2O2) and production of malondialdehyde, a membrane lipid peroxidation product, were lower in overexpressors. In stress environment, the structural distortion of granal organization and swelling of thylakoids were less pronounced in ZmNADP-MDH overexpressing plants as compared to the vector control. Chloroplastic NADP-MDH in consort with cytosolic and mitochondrial NAD-MDH plays an important role in exporting reducing power (NADPH) and exchange of metabolites between different cellular compartments that maintain the redox homeostasis of the cell via malate valve present in chloroplast envelope membrane. The tolerance of NADP-MDH overexpressors to salt stress could be due to operation of an efficient malate valve that plays a major role in maintaining the cellular redox environment.

Electrons and proton transfer in chloroplasts in silico: 1. The effect of topological factors on energy coupling in chloroplasts with a nonuniform distribution of protein complexes

This paper presents a theoretical study of the effects of topological factors (density of thylakoid packing in grana) on the efficiency of energy coupling in chloroplasts. The study is based on a mathematical model of electron and proton transport processes coupled to ATP synthesis in chloroplasts. The model was developed by the authors earlier, and the nonuniform distribution of electron transport and ATP synthase complexes in the membranes of granal and intergranal thylakoids was taken into account in the model. The results of numerical experiments enabled the analysis of the distribution of lateral profiles of the transmembrane pH difference and the concentrations of mobile plastoquinone and plastocyanin electron transporters in granal and intergranal thylakoids and the dependence of this distribution on the metabolic state of class B chloroplasts (photosynthetic control state or the conditions of intensive ATP synthesis). Moreover, the influence of topological factors (the density of thylakoid packing in grana and the degree of thylakoid swelling) that affect the rate of diffusion of protons and mobile electron carriers in the intrathylakoid space and in the interthylakoidal gap was investigated. The results of numerical experiments that involved the variation of geometric parameters of the system revealed the influence of thylakoid thickness and the distance between the granal thylakoids on the lateral pH profiles inside the thylakoids (pHi) and in the interthylakoidal gap (pHo). Acidification of the intrathylakoid space characterized by the pHi value increased concomitantly to the increase of the width of the interthylakoidal gap l o and decreased concomitantly to the increase of the width of the intrathylakoidal space l i.

The sphingolipid biosynthetic enzyme Sphingolipid delta8 desaturase is important for chilling resistance of tomato.

The physiological functions of sphingolipids in animals have been intensively studied, while less attention has been paid to their roles in plants. Here, we reveal the involvement of sphingolipid delta8 desaturase (SlSLD) in the chilling resistance of tomato (Solanum lycopersicum cv. Micro-Tom). We used the virus-induced gene silencing (VIGS) approach to knock-down SlSLD expression in tomato leaves, and then evaluated chilling resistance. Changes in leaf cell structure under a chilling treatment were observed by transmission electron microscopy. In control plants, SlSLD was highly expressed in the fruit and leaves in response to a chilling treatment. The degree of chilling damage was greater in SlSLD-silenced plants than in control plants, indicating that SlSLD knock-down significantly reduced the chilling resistance of tomato. Compared with control plants, SlSLD-silenced plants showed higher relative electrolytic leakage and malondialdehyde content, and lower superoxide dismutase and peroxidase activities after a chilling treatment. Chilling severely damaged the chloroplasts in SlSLD-silenced plants, resulting in the disruption of chloroplast membranes, swelling of thylakoids, and reduced granal stacking. Together, these results show that SlSLD is crucial for chilling resistance in tomato.

Cellular markers indicative of ozone stress on bioindicator plants growing in a tropical environment

Ozone (O3) is an oxidative pollutant that causes visible foliar symptoms in sensitive plants. Importantly, cellular markers induced by physiological alterations, including oxidative burst (OB), hypersensitive response-like (HR-like) reactions, and accelerated cell senescence (ACS), precede these symptoms. Because little is known about the effects of ozone in tropical environments, we aimed to identify these cellular markers in Nicotiana tabacum, Ipomoea nil and Psidium guajava growing in an urban area of tropical Sao Paulo, Brazil, and describe the specific physiological alterations that trigger the development of visible symptoms. Cell wall wart-like protrusions, an OB cellular marker, and swelling of thylakoids and mitochondrial membranes, as well as accumulation of plastoglobuli, all markers of ACS, were cell markers common to all species studied. Cellular markers indicating HR-like reaction, as observed in the asymptomatic leaves of N. tabacum and I. nil, are precursors of future development of necrotic areas, featuring the visible symptoms. On the other hand, the main cause of visible symptoms in P. guajava appeared to be the accumulation of phenolic compounds in the mesophyll tissue, an ACS marker. Based on this line of evidence, these bioindicator plants growing in a tropical environment show the damaging effects of O3 pollution, even before visible symptoms develop. Moreover, this damage can be detected through a distinct group of cellular markers.

Changes in chloroplast lipid contents and chloroplast ultrastructure in Sulla carnosa and Sulla coronaria leaves under salt stress

The possible involvement of chloroplast lipids in the mechanisms of NaCl tolerance was studied in leaves of two varieties of Fabaceae: Sulla carnosa and Sulla coronaria, which were subjected to 200mM NaCl over 20days. Changes in membrane lipid peroxidation, chloroplast lipids content, fatty acids (FA) composition and the ultrastructure of chloroplasts under salt stress were investigated. Chloroplast lipids were separated and quantified by high performance liquid chromatography coupled to evaporative light scattering detection (HPLC/ELSD). The results showed that salinity induced a significant decrease in digalactosyldiacylglycerol (DGDG), phosphatidylglycerol (PG) and sulfoquinovosylglycerol (SQDG) content in both S. carnosa and S. coronaria leaves, whereas monogalactosyldiacylglycerol (MGDG) content did not change significantly in S. carnosa leaves. The MGDG/DGDG ratio remained stable in S. coronaria leaves but increased in those of S. carnosa. In addition, the unsaturated-to-saturated fatty acids ratio (UFAs:SFAs) did not change under salt stress in S. coronaria leaves, while it decreased significantly in S. carnosa leaves. Moreover, salinity did not induce significant changes in MGDG and DGDG unsaturation level in S. carnosa leaves, in contrast to S. coronaria, in which salinity seems to enhance the unsaturation level in MGDG, DGDG and PG. Furthermore, the level of membrane lipid peroxidation, as expressed by malondialdehyde (MDA) levels, increased at 200mM in S. carnosa leaves, while it did not change significantly in those of S. coronaria. With respect to the ultrastructure of chloroplasts at 200mM NaCl, investigated by transmission electron microscopy (TEM), salt-stress caused the swelling of thylakoids in S. carnosa mesophyll. These ultrastructural changes were observed especially in the spongy tissue in S. coronaria. Taken together, these findings suggest that the stability of MGDG/DGDG ratio, the unchanged unsaturation level, and increasing unsaturation level in MGDG, DGDG and PG may be effective to some degree in suppressing the ultrastructural damage caused by salinity effects and may contribute to protect the chloroplast membrane integrity against salt stress.

Coordinated rearrangements of assimilatory and storage cell compartments in a nitrogen-starving symbiotic chlorophyte cultivated under high light

A quantitative micromorphometric study of the cell compartment rearrangements was performed in a symbiotic chlorophyte Desmodesmus sp. 3Dp86E-1 grown on nitrogen (N) replete or N-free medium under 480 μmol PAR quanta m(-2) s(-1). The changes in the chloroplast, intraplastidial, and cytoplasmic inclusions induced by high light (HL) and N starvation were similar to those characteristic of free-living chlorophytes. The N-sufficient culture responded to HL by a transient swelling of the thylakoid lumen and a decline in photosynthetic efficiency followed by its recovery. In the N-starving cells, a more rapid expansion and thylakoid swelling occurred along with the irreversible decline in the photosynthetic efficiency. Differential induction of starch grains, oil bodies, and cell wall polysaccharides depending on the stress exposure and type was recorded. Tight relationships between the changes in the assimilatory and storage compartments in the stressed Desmodesmus sp. cells were revealed.

Effects of polyaromatic hydrocarbons on photosystem II activity in pea leaves

The acute effects of three typical polyaromatic hydrocarbons (PAHs): naphthalene (Naph), phenanthrene (Phen) and fluoranthene (Flu) on photochemical activity of photosystem II (PSII) in detached leaves of 3-week-old pea plants were studied. The leaves were exposed in water with PAHs under white light for 0.5–72 h. The activity of PSII was examined by prompt and delayed chlorophyll a (Chl a) fluorescence. The effects of PAHs depended on their concentration and exposure time. This dependency was more significant in the presence of chemical stressors (Triton X-100 or acetone) or under high intensity irradiance. Increased content of PAHs and long-term exposure (24–72 h) led to significant reduction of the maximum photochemical quantum efficiency (Fv/Fm) of PS II, changes in the polyphasic fluorescence induction (OJIP), and to decreasing amplitudes of fast and slow components of delayed Chl a fluorescence. The damage of PSII depended on water solubility of a given type of PAHs, their concentration and exposure time. During short-time exposure the compound with highest water-solubility – naphthalene – revealed the strongest effect. During long-time exposure the compounds with low water-solubility –Phen, Flu-revealed the strongest effect as the corresponding PAH accumulates in the thylakoids especially when the solution is oversaturated containing a solid phase. The reduction of PSII activity at the presence of naphthalene (30 mg L−1) was accompanied by transient generation of H2O2 as well as swelling of thylakoids and distortion of cell plasma membranes, which was indicated by electron microscopy images. Distortion of thylakoid membranes due to accumulation of PAHs as well as the development of oxidative stress seems to be the main pathways of PAHs influencing the photochemical activity of PS II.

Ultrastructural response of cabbage outer leaf mesophyll cells (Brassica oleracea L.) to excess of nickel

Changes in the structure and in the ultrastructure of cabbage outer leaf mesophyll cells [<em>Brassica oleracea</em> L.] cv. Sława from Enkhouizen were examined by means of light and electron microscopy. The examined plants were grown on the basic Murashige and Skoog medium with addition of excesive concentrations of nickel (added as NiSO<sub>4</sub> x 7H<sub>2</sub>O),i.e. Ni 5, Ni 10 and Ni 20 mg/dm<sup>3</sup>. In Ni 5 mg samples mainly adaptation changes to the conditions of stress were observed. These changes were manifested by the increase of cytoplasm content and by cytoplasm vacuolization, by the increase of nucleus and nucleous volume, nucleolus vacuolization, the increase of plasmalemma invaginations and of the amount of rough ER, by the central arrangement of smooth ER and of the thylakoids of chloroplasts; it was also shown by the growth of the number of mitochondria and of peroxisomes in the cell. In Ni 10 mg samples, apart from adaptation changes, such as the increase of the nucleus volume, increase of plasmalemma invaginations, cytoplasm and nucleolus vacuolization, degeneration changes were also observed. They concerned mainly the nucleus (the increasing amount of condensed chromatin), ER (swelling and fragmentation of rER and sER), mitochondrium (swelling and reduction of cristae), Golgi apparatus (disintegration and decay) and chloroplasts (changes of shape, swelling and reduction of thylakoids, disappearance of starch and presence of big plastoglobuli). In Ni 20 mg samples cell protoplasts were in different stages of degeneration and the cell organelles that were identifiable, were usually damaged.

Salinity-induced subcellular accumulation of H2O2 in leaves of rice

The localization of salt-induced H(2)O(2) accumulation in the leaves of rice was examined using 3,3-diaminobenzidine and CeCl(3) staining at ultrastructure level. When the 3-week-old rice plants were affected by 100mM NaCl for 14days, the swelling of thylakoids and the destruction of thylakoid membranes were observed. H(2)O(2) accumulation was also observed in the chloroplast of the leaf treated with NaCl. The electron dense products of 3,3-diaminobenzidine and CeCl(3) were mainly observed especially around the swelling of thylakoids. H(2)O(2) accumulation and any ultrastructural changes were not observed in the chloroplasts under dark condition. Furthermore, treatment with ascorbic acid suppressed both H(2)O(2) accumulation and the changes in chloroplast ultrastructure. These results suggest that light-induced production of excess H(2)O(2) under salinity is responsible for the changes in chloroplast ultrastructure. H(2)O(2) accumulation was also observed in the mitochondria, peroxisomes, plasma membrane, and cell walls under light but not dark, suggesting that these organelles are also the source of H(2)O(2) and the production is light dependent under salinity.

CAM-related changes in chloroplastic metabolism of Mesembryanthemum crystallinum L.

Crassulacean acid metabolism (CAM) is an intriguing metabolic strategy to maintain photosynthesis under conditions of closed stomata. A shift from C3 photosynthesis to CAM in Mesembryanthemum crystallinum plants was induced by high salinity (0.4 M NaCl). In CAM-performing plants, the quantum efficiencies of photosystem II and I were observed to undergo distinct diurnal fluctuations that were characterized by a strong decline at the onset of the day, midday recovery, and an evening drop. The temporal recovery of both photosystems’ efficiency at midday was associated with a more rapid induction of the electron transport rate at PSII. This recovery of the photosynthetic apparatus at midday was observed to be accompanied by extreme swelling of thylakoids. Despite these fluctuations, a persistent effect of CAM was the acceptor side limitation of PSI during the day, which was accompanied by a strongly decreased level of Rubisco protein. Diurnal changes in the efficiency of photosystems were parallel to corresponding changes in the levels of mRNAs for proteins of PSII and PSI reaction centers and for rbcL, reaching a maximum in CAM plants at midday. This might reflect a high demand for new protein synthesis at this time of the day. Hybridization of run-on transcripts with specific probes for plastid genes of M. crystallinum revealed that the changes in plastidic mRNA levels were regulated at the level of transcription.

Sex-specific responses and tolerances of Populus cathayana to salinity

Responses of males and females to salinity were studied in order to reveal sex-specific adaptation and evolution in Populus cathayana Rehd cuttings. This dioecious tree species plays an important role in maintaining ecological stability and providing commercial raw material in southwest China. Female and male cuttings of P. cathayana were treated for about 1 month with 0, 75 and 150 mM NaCl. Plant growth traits, gas exchange parameters, chlorophyll pigments, intrinsic water use efficiency (WUEi), membrane system injuries, ion transport and ultrastructural morphology were assessed and compared between sexes. Salt stress caused less negative effects on the dry matter accumulation, growth rate of height, growth rate of stem base diameter, total number of leaves and photosynthetic abilities in males than in females. Relative electrolyte leakage increased more in females than in males under salinity stress. Soil salinity reduced the amounts of leaf chlorophyll a, chlorophyll b and total chlorophyll, and the chlorophyll a/b ratio more in females than in males. WUEi decreased in both sexes under salinity. Regarding the ultrastructural morphology, thylakoid swelling in chloroplasts and degrading structures in mitochondria were more frequent in females than in males. Moreover, females exhibited significantly higher Na(+) and Cl(-) concentrations in leaves and stems, but lower concentrations in roots than did males under salinity. In all, female cuttings of P. cathayana are more sensitive to salinity stress than males, which could be partially due to males having a better ability to restrain Na(+) transport from roots to shoots than do females.

Two types of ammonium uncoupling in pea chloroplasts.

The effect of ammonium on ATP synthesis, electron transfer, and light-induced uptake of hydrogen ions in pea chloroplasts was studied. It is shown that the dependence of these reactions on ammonium concentration could be due to effects of two different uncoupling processes. The first process is induced by low ammonium concentrations (<0.2 mM); the second one is observed in the NH(4)Cl concentration interval of 0.5-5.0 mM. The first type of uncoupling is stimulated by palmitic acid or by N,N'-dicyclohexylcarbodiimide, while the second is stimulated by chloroplast thylakoid swelling caused by energy-dependent osmotic gradients. In the presence of the fluorescent dye sulforhodamine B, which does not penetrate through the cell membrane, this swelling causes the dye to enter the lumens. It is supposed that ammonium activates two different routes of cation leakage from the lumen. The first route involves channel proteins, while the second is a mechanosensitive pore that opens in response to osmotic gradients.