Salinity-induced changes in plastoquinone pool redox state in halophytic Mesembryanthemum crystallinum L

We have analyzed the effect of salinity on photosystem II (PSII) photochemistry and plastoquinone (PQ) pool in halophytic Mesembryanthemum crystallinum plants. Under prolonged salinity conditions (7 or 10 days of 0.4 M NaCl treatment) we noted an enlarged pool of open PSII reaction centers and increased energy conservation efficiency, as envisaged by parameters of the fast and slow kinetics of chlorophyll a fluorescence. Measurements of oxygen evolution, using 2,6-dichloro-1,4-benzoquinone as an electron acceptor, showed stimulation of the PSII activity due to salinity. In salt-acclimated plants (10 days of NaCl treatment), the improved PSII performance was associated with an increase in the size of the photochemically active PQ pool and the extent of its reduction. This was accompanied by a rise in the NADP⁺/NADPH ratio. The presented data suggest that a redistribution of PQ molecules between photochemically active and non-active fractions and a change of the redox state of the photochemically active PQ pool indicate and regulate the acclimation of the photosynthetic apparatus to salinity.

Differences in the functioning of photosynthetic electron transport between metallicolous and non-metallicolous populations of the pseudometallophyte Viola tricolor

The objective of this study was to assess the effect of metalliferous conditions on the functioning of photosynthetic electron transport in waste heap populations of a pseudometallophyte, Viola tricolor L. Measurements of chlorophyll a fluorescence and the absorbance changes at 830 nm enabled a non-invasive assessment of photosynthetic apparatus performance. This was complemented by the evaluation of the chlorophyll content. Low temperature chlorophyll fluorescence emission spectra were also recorded. Based on the OJIP test performed in situ, we demonstrated a disturbed condition of photosystem II (PSII) in three metalliferous populations in comparison with a non-metallicolous one. The combined effects of elevated concentrations of zinc, cadmium and lead in soil resulted in the decline of some parameters describing the efficiency and electron flow through PSII. The differences between waste heap populations seemed to be partly correlated with the concentration of heavy metals in the soil. The characteristic of electron transport at photosystem I (PSI) in the light-adapted state revealed increased values of PSI donor-side limitation (Y_ND) and a declined PSI quantum efficiency (Y_I). It was also demonstrated that the waste heap conditions negatively affect the total chlorophyll content in leaves and led to an increased ratio of fluorescence emission at 77 K (F730/F685). The obtained data indicate that, regardless of the high adaptation of metallicolous populations, photosynthetic electron transport is hampered in V. tricolor plants at metal polluted sites.

Changes in content of steroid regulators during cold hardening of winter wheat - Steroid physiological/biochemical activity and impact on frost tolerance

The purpose of experiments was to describe the alterations of content of steroid regulators (brassinosteroids, progesterone) during cold hardening of winter wheat. Further we studied physiological and biochemical changes induced by these steroids in cold hardened winter wheat together with estimation of plant frost tolerance. The endogenous brassinosteroid content was elevated in winter wheat during cold hardening while level of progesterone was lowered. A higher content of brassinosteroids (but not progesterone) was connected to better frost tolerance of winter wheat cultivars. Plant supplementation with brassinosteroid (24-epibrassinolide) and progesterone before cold hardening reduced frost damage. Tests with the inhibitors of the biosynthesis of brassinosteroids and progesterone suggested that these steroids are one of players in regulating the antioxidant system in winter wheat during cold hardening. Their role in regulating the expression of Rubisco or the Rubisco activase gene was less clear. Steroid regulators did not affect the content of the stress hormone ABA. Model studies of the membranes, made on a Langmuir bath, showed an increase in the value of the parameter describing differences in membrane compressibility (resulting from stronger interactions among the molecules in the monolayers). This suggests that 24-epibrassinolide and progesterone enter into the lipid layer and - in a similar way to sterols - stabilise the interaction among lipids. It may be significant step for better frost tolerance. The use of steroid regulators (especially brassinosteroids) as agrochemicals improving frost tolerance of winter cereals will be discussed.

Acclimation of the photosynthetic apparatus and alterations in sugar metabolism in response to inoculation with endophytic fungi

The role of an endophytic Zygomycete Mucor sp. in growth promotion and adaptation of the photosynthetic apparatus to increased energy demands of its hosts Arabidopsis arenosa and Arabidopsis thaliana was evaluated. Inoculation with the fungus improved the water use efficiency of the plants and allowed for them to utilize incident light for photochemistry more effectively by upregulating the expression of several photosystem I- and II-related genes and their respective proteins, proteins involved in light harvesting in PSII and PSI and carbon assimilation. This effect was independent of the ability of the plants to acquire nutrients from the soil. We hypothesize that the accelerated growth of the symbiotic plants resulted from an increase in their demand for carbohydrates and carbohydrate turnover (sink strength) that triggered a simultaneous upregulation of carbon assimilation. Arabidopsis plants inoculated with Mucor sp. exhibited upregulated expression in several genes encoding proteins involved in carbohydrate catabolism, sugar transport, and smaller starch grains that indicate a significant upregulation of carbohydrate metabolism.

Lack of tocopherols influences the PSII antenna and the functioning of photosystems under low light

As tocopherols are expected to protect PSII against toxic singlet oxygen it is surprising that the null tocopherol mutant vte1 has been reported to show only a weak enhancement of photosystem II photoinhibition under high irradiance. Based on the view that singlet oxygen is formed also in unstressed conditions, such as low light (LL), we hypothesized that some defense strategies are activated in vte1 in these light conditions. In support for that we noted several symptoms of stress at PSII in the mutant under LL, by means of parameters of fast and slow kinetics of chlorophyll fluorescence and of changes in the relative contribution of PSII antenna in comparison to those of PSI. This was associated with a lower extent of phosphorylation of PSII core proteins (D1 and CP43). PSII RCs do not totally recover from stress in vte1 even after the nocturnal phase. As a clear compensation for the impeded performance of PSII in the vte1 we noted an increased quantum efficiency of PSI. A pronounced changes between WT and the vte1 mutant were also related to conformation of LHCII at the beginning of photoperiod, suggesting the absence of LHCII trimers in the mutant. The thylakoids thickness was similar in WT and vte1 under LL, but a pronounced unstacking of thylakoids was evoked by HL only in vte1. In conclusion, we postulate that action of ¹O₂ on PSII in vte1 leads to some permanent damage at PSII core and at LHCII already under LL.

Changes in lipid peroxidation in stay-green leaves of tobacco with senescence-induced synthesis of cytokinins

The involvement of reactive oxygen species (ROS) in the progress of leaf senescence has long been suggested, but there are contrasting results to either support or deny the positive correlation between the senescence progression and the level of ROS-triggered lipid peroxidation. The inconsistency among reported results can partly be attributed to the poor specificity of the most commonly employed colorimetric assay and changes in the ratio of dry weight/fresh weight during leaf senescence. In this study we determined the end-product of lipid peroxidation malondialdehyde (MDA) by GS-MS, and analyzed its changes during senescence of tobacco leaves as calculated on dry weight basis. In leaves of the wild type plants the MDA level did not change during senescence. In the mutant PSAG12::IPT leaves stayed green because of the elevated synthesis of cytokinins, but the MDA level was much higher in comparison to WT when leaves of the same age were compared. These results clearly show that lipid peroxidation is not associated with leaf senescence, at least in tobacco. This GS-MS method can be used to judge the involvement of lipid peroxidation in senescence in other species.

Blue light-dependent changes in loosely bound calcium in Arabidopsis mesophyll cells: an X-ray microanalysis study

Calcium is involved in the signal transduction pathway from phototropins, the blue light photoreceptor kinases which mediate chloroplast movements. The chloroplast accumulation response in low light is controlled by both phot1 and phot2, while only phot2 is involved in avoidance movement induced by strong light. Phototropins elevate cytosolic Ca(2+) after activation by blue light. In higher plants, both types of chloroplast responses depend on Ca(2+), and internal calcium stores seem to be crucial for these processes. Yet, the calcium signatures generated after the perception of blue light by phototropins are not well understood. To characterize the localization of calcium in Arabidopsis mesophyll cells, loosely bound (exchangeable) Ca(2+) was precipitated with potassium pyroantimonate and analyzed by transmission electron microscopy followed by energy-dispersive X-ray microanalysis. In dark-adapted wild-type Arabidopsis leaves, calcium precipitates were observed at the cell wall, where they formed spherical structures. After strong blue light irradiation, calcium at the apoplast prevailed, and bigger, multilayer precipitates were found. Spherical calcium precipitates were also detected at the tonoplast. After red light treatment as a control, the precipitates at the cell wall were smaller and less numerous. In the phot2 and phot1phot2 mutants, calcium patterns were different from those of wild-type plants. In both mutants, no elevation of calcium after blue light treatment was observed at the cell periphery (including the cell wall and a fragment of cytoplasm). This result confirms the involvement of phototropin2 in the regulation of Ca(2+) homeostasis in mesophyll cells.

High expression of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE coincides with initiation of various developmental pathways in in vitro culture of Trifolium nigrescens

The aim of this study was to identify and examine the expression pattern of the ortholog of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE gene from Trifolium nigrescens (TnSERK) in embryogenic and non-regenerative cultures of immature cotyledonary-stage zygotic embryos (CsZEs). In the presence of 1-naphthaleneacetic acid and N(6)-[2-isopentenyl]-adenine, the CsZE regenerated embryoids directly and in a lengthy culture produced callus which was embryogenic or remained non-regenerative. As revealed by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), the TnSERK was expressed in both embryogenic and non-regenerative cultures, but the expression level was significantly higher in embryogenic ones. An in situ RNA hybridization assay revealed that the expression of TnSERK preceded the induction of cell division in explants, and then, it was maintained exclusively in actively dividing cells from which embryoids, embryo-like structures (ELSs), callus or tracheary elements were produced. However, the cells involved in different morphogenic events differed in intensity of hybridization signal which was the highest in embryogenic cells. The TnSERK was up-regulated during the development of embryoids, but in cotyledonary embryos, it was preferentially expressed in the regions of the apical meristems. The occurrence of morphological and anatomical abnormalities in embryoid development was preceded by a decline in TnSERK expression, and this coincided with the parenchymatization of the ground tissue in developing ELSs. TnSERK was also down-regulated during the maturation of parenchyma and xylem elements in CsZE and callus. Altogether, these data suggest the involvement of TnSERK in the induction of various developmental programs related to differentiation/transdifferentiation and totipotent state of cell(s).

A Different Pattern of Production and Scavenging of Reactive Oxygen Species in Halophytic Eutrema salsugineum (Thellungiella salsuginea) Plants in Comparison to Arabidopsis thaliana and Its Relation to Salt Stress Signaling

Isolated thylakoids from halophytic Eutrema salsugineum (Thellungiella salsuginea) produces more H2O2 in comparison to glycophytic Arabidopsis thaliana. The first objective of this study was to verify whether this feature is relevant also to the intact chloroplasts and leaves. Enhanced H2O2 levels in chloroplasts and leaves of E. salsugineum were positively verified with several methods (electron microscopy, staining with Amplex Red and with diaminobenzidine). This effect was associated with a decreased ratio of [Formula: see text]/H2O2 in E. salsugineum in comparison to A. thaliana as detected by electron paramagnetic resonance method. As a next step, we tested how this specific ROS signature of halophytic species affects the antioxidant status and down-stream components of ROS signaling. Comparison of enzymatic antioxidants revealed a decreased activity of ascorbate peroxidase (APX), enhanced activity of glutathione peroxidase, and the presence of thylakoid-bound forms of iron superoxide dismutase (FeSOD) and APX in E. salsugineum. These cues were, however, independent from application of salt stress. The typical H2O2-dependent cellular responses, namely the levels of glucosinolates and stress-related hormones were determined. The total glucosinolate content in E. salsugineum water-treated leaves was higher than in A. thaliana and increased after salinity treatment. Treatment with salinity up-regulated all of tested stress hormones, their precursors and catabolites [abscisic acid (ABA), dihydrophaseic acid, phaseic acid, 1-aminocyclopropane-1-carboxylic acid, salicylic acid, jasmonic acid, cis-(+)-12-oxo-phytodienoic acid and jasmonoyl-L-isoleucine] in A. thaliana, whereas in E. salsugineum only a stimulation in ethylene synthesis and ABA catabolism was noted. Obtained results suggest that constitutively enhanced H2O2 generation in chloroplasts of E. salsugineum might be a crucial component of stress-prepardeness of this halophytic species. It shapes a very efficient antioxidant protection (in which glucosinolates might play a specific role) and a fine tuning of hormonal signaling to suppress the cell death program directed by jasmonate pathway.

[Cytokinins and photosynthesis]

Almost six decades of studies explained many aspects of cytokinin complex metabolism, such as, biogenesis, degradation, signal perception and interaction with other phytohormones (mainly with auxins). A dual character of cytokinins' action on the nuclear genes (activation and repression) has been explained by recognition of the two types on nuclear receptors, which ensure a precise mechanism of self-control. Cytokinins promote the process of photosynthesis at different levels of plant- and cellular organization (development of leaves and plastids, influence on the photosynthetic proteins, activation of photosynthetic genes, etc.). An anti-senescing action of these hormones has been recently attributed to the activation of intra-cellular invertase, which suppress floem loading and change the sink-source pattern of the leaf.

A risk of essential thrombocythemia in carriers of constitutional CHEK2 gene mutations

Germline mutations of the CHEK2 gene have been reported in some myeloid and lymphoid malignancies, but their impact on development of essential thrombocythemia has not been studied. In 16 out of 106 (15.1%) consecutive patients, newly diagnosed with essential thrombocythemia, we found one of four analyzed CHEK2 mutations: I157T, 1100delC, IVS2+1G>A or del5395. They were associated with the increased risk of disease (OR=3.8; P=0.002). The median age at ET diagnosis among CHEK2+/JAK2V617F+ patients was seven years lower than that among CHEK2-/JAK2V617F+ (52 vs. 59 years; P=0.04), whereas there was no difference in the medians of hematologic parameters between these groups. The results obtained suggest that CHEK2 mutations could potentially contribute to the susceptibility to essential thrombocythemia. The germline inactivation of CHEK2, as it seems, has no direct impact on the development of disease, but it could cause disruption of cell cycle checkpoints and initiate or support the cancerogenic process of essential thrombocythemia at a younger age.

Thyroid hormones control lipid composition and membrane fluidity of skeletal muscle sarcolemma

Sarcolemma membrane lipid phase of skeletal muscles of hyperthyroid animals was compared to that of control (euthyroid) ones. Hyperthyroidism caused 15% decrease in cholesterol and 70% increase in the phospholipid content of the membrane. This was accompanied by the alterations in proportions between individual phospholipid classes, and was followed by changes in the composition of phospholipid fatty acids. The calculated fatty acid unsaturation index was higher for membrane lipid phase of hyperthyroid animals than of euthyroid ones. Thyroxine-induced alterations in the lipid composition of sarcolemma caused changes in the membrane fluidity and the activity of calmodulin-stimulated (Ca(2+)-Mg(2+)-ATPase. Measurements of the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the lipid phase transition of membrane vesicles occurred at 25.9 degrees C and at 28.9 degrees C for preparations isolated from hyperthyroid and euthyroid rabbits, respectively. Arrhenius plot break-point temperature for CaM-stimulated (Ca(2+)-Mg(2+)-ATPase activity was lower in membrane preparations isolated from hyperthyroid (26.9 degrees C) than from euthyroid ones (30.0 degrees C). Thus, the increase of the membrane fluidity presumably caused that the enzyme was characterized by the lower activation energy value. This phenomenon may be viewed as a supplementary mechanism for activation of the enzyme by thyroid hormones to previously reported elevation of the amount of (Ca(2+)-Mg(2+)-ATPase protein exerted by hyperthyroidism (Famulski et al. (1988) Eur. J. Biochem., 171, 363-368; Famulski and Wrzosek (1988) in The Ion Pumps-Structure, Function and Regulation (Stein, W.D., ed.), pp. 355-360, Alan R. Liss, New York).

The effect of thyroxine on the calmodulin-dependent (Ca2+-Mg2+)ATPase activity and protein phosphorylation in rabbit fast skeletal muscle sarcolemma

Enzymatic properties and the protein pattern of sarcolemma fractions isolated from three groups of rabbits: euthyroid, hyperthyroid and hypothyroid, were studied. The amount of phosphorylated intermediate formed by the calmodulin-dependent (Ca2+-Mg2+)ATPase and the activity of this enzyme as well as that of (Na+-K+)ATPase were the highest in membranes isolated at the hyperthyroid state. On the other hand, sarcolemma obtained from the hypothyroid animals exhibited a decreased activity of (Na+-K+)ATPase, while the activity of calmodulin-dependent (Ca2+-Mg2+)ATPase was the same as in the preparations obtained from euthyroid animals. Thyroid hormones also changed the protein pattern of muscle sarcolemma. Membranes isolated from hyperthyroid animals lacked peptides of apparent molecular masses of 41 kDa and 53 kDa, while a peptide of the apparent molecular mass of 63 kDa was enriched in the preparation from hypothyroid animals. Thyroid hormones affected endogenous cAMP-dependent protein phosphorylation. The sarcolemma fraction obtained from hyperthyroid animals exhibited a decreased phosphorylation of peptides of apparent molecular masses of 30 kDa and 47 kDa, while the cAMP-independent phosphorylation of several other peptides was augmented. Moreover, sarcolemma preparations isolated from hyperthyroid animals showed higher activity of cAMP-independent protein kinase(s) and lower activity of cAMP-dependent protein kinase when compared to the euthyroid preparations. It is proposed that thyroxine increases the content of calmodulin-dependent (Ca2+-Mg2+)ATPase protein and affects the activity of cAMP-independent and cAMP-dependent protein kinases bound to sarcolemma.

Properties and topology of enzymes methylating phosphatidylethanolamine to phosphatidylcholine in sarcoplasmic reticulum

1. The synthesis of phosphatidylcholine (PC) by stepwise methylation of phosphatidylethanolamine (PE) is carried out by two enzymes in sarcoplasmic reticulum (SR) membrane of rabbit fast-twitch skeletal muscles. 2. Two methyltransferases (Met I and Met II) have a different pH optimum and affinity for methyl donor--S-adenosyl-L-methionine (SAM). 3. Met I is an integral SR membrane protein which active site faces the cytoplasmic surface of the membrane. 4. Met II is a peripheral, loosely bound protein, localized mainly on the extracytoplasmic (luminal) part of the SR membrane.

Phospholipase C and diacylglycerol lipase activities associated with plasma membranes of chromaffin cells isolated from bovine adrenal medulla

The plasma membranes of bovine adrenal chromaffin cells were isolated and the activities of enzymes involved in arachidonic acid liberation were investigated. Only a minute activity of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) could be detected using externally added phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as substrate. When membranes were treated with exogenous phospholipase C (orthophosphoric acid diester phosphohydrolase, EC 3.1.4.1) there was a liberation of free fatty acids from the sn-2 position of PC. The enzyme responsible for this effect could be demonstrated to be a diacylglycerol lipase (glycerol ester hydrolase, EC 3.1.1.3) localized in the plasma membrane. Using phosphatidylinositol (PI) as a substrate, it was found that an endogenous phospholipase C exists which co-purifies with the membrane preparation. The produced diacylglycerol is subsequently hydrolyzed by diacylglycerol lipase liberating arachidonic acid. The two enzymes, phospholipase C and diacylglycerol lipase were characterized. Phospholipase C was found to be calcium dependent and PI specific, showing an activity of 60 pmol/micrograms protein per h (1.2 mM Ca2+), whereas the diacylglycerol lipase was calcium independent hydrolyzing diacylglycerol at a rate of 7.2 pmol/micrograms protein per h. The lipase but not the phospholipase C was inhibited 50% by 1.7 mM para-bromophenacylbromide.

Phospholipid biosynthesis in sarcoplasmic reticulum membrane during development

Biosynthesis of phosphatidic acid, phosphatidylcholine and phosphatidylethanolamine in the sarcoplasmic reticulum membrane has been investigated. The results show that sarcoplasmic reticulum, in addition to its main function, i.e. transport and accumulation of Ca2+, is able to synthetize phospholipids by the same pathways as endoplasmic reticulum of other tissues. The changes of activity of enzymes involved in phospholipid biosynthesis during muscle development have been analysed. The extent of sn-glycero-3-phosphate and lysophosphatidylcholine acylation by acyl-CoA or free fatty acids in the presence of ATP and CoA is the same at every stage of development. The specific activity of glycerolphosphate acyltransferase(s) increases progressively during development up to about the 10th day of postnatal life and then decreases to the adult level. Linoleate esterifies sn-glycero-3-phosphate to a higher extent than palmitate, especially during postnatal period. The main product of sn-glycero-3-phosphate acylation is phosphatidic acid. The specific activity of lysolecithin acyltransferase increases from the embryonic period to a maximum between the 4th and the 9th day of postnatal life followed by a decrease to the adult value. the low embryonic value to a maximum at about the 3rd day of postnatal life, followed by a decrease to the adult value. The activity of cholinephosphotransferase decreases from a high value observed during the earliest embryonic period studied until the 3rd day before birth, and then begins to increase again from about the 5th day of postnatal life. The activity of ethanolaminephosphotransferase decreases continuously with age. The main product of phosphatidylethanolamine methylation is phosphatidylmonomethylethanolamine. The specific activity of phosphatidylethanolamine methyltransferase increases from

Changes in the structure, composition and function of sarcoplasmic-reticulum membrane during development

The structure, chemical composition and function of the microsomal fraction, isolated by differential centrifugation and purified on sucrose gradients, from muscle of fetal, newborn and young rabbits were characterized and compared with those of sarcoplasmic reticulum vesicles from adult muscle. Negative staining shows that the microsomal vesicles isolated from muscles of embryos and newborn animals are smooth, in contrast to vesicles obtained from adult muscle which contain 4-nm particles on their surface. The particles appear first in the microsomal vesicles from muscles of 5--8-day-old rabbits. Their number increases with the age of the animals. Ca2+-pump protein, with molecular weight about 100000, accounts for 10% of the total protein content in sarcoplasmic reticulum membrane, isolated at the earliest stages of development analysed. Its amount increases continuously with the rabbit's age to the adult value of about 70% of total sarcoplasmic reticulum protein. The low amount of 100000-dalton protein and lack of 4-nm surface particles in sarcoplasmic reticulum vesicles obtained from fetal and newborn rabbits are strictly correlated with the low activity of Ca2+-dependent ATPase and the ability to take up Ca2+. These activities rise in parallel with the age of the rabbits. On the other hand, Mg2+-dependent ATPase activity is very high at the early stages of development and declines continuously to a low value in sarcoplasmic reticulum from adult muscle. The sarcoplasmic reticulum membrane from fetal and newborn rabbits contains a higher amount of lipids as compared with the membrane present in the muscle of adult animals. The ratio of both phospholipid to protein and neutral lipid to protein decreases with the age of the rabbits. The composition of sarcoplasmic reticulum phospholipids also changes during development.