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.     

Interplay of Troponin- and Myosin-Based Pathways of Calcium Activation in Skeletal and Cardiac Muscle: The Use of W7 as an Inhibitor of Thin Filament Activation

To investigate the interplay between the thin and thick filaments during calcium activation in striated muscle, we employed n-(6-aminohexyl) 5-chloro-1-napthalenesulfonamide (W7) as an inhibitor of troponin C and compared its effects with that of the myosin-specific inhibitor, 2,3-butanedione 2-monoxime (BDM). In both skeletal and cardiac fibers, W7 reversibly inhibited ATPase and tension over the full range of calcium activation between pCa 8.0 and 4.5, resulting in reduced calcium sensitivity and cooperativity of ATPase and tension activations. At maximal activation in skeletal fibers, the W7 concentrations for half-maximal inhibition (K_I) were 70–80 μM for ATPase and 20–30 μM for tension, nearly >200-fold lower than BDM (20 mM and 5–8 mM, respectively). When W7 (50 μM) and BDM (20 mM) were combined in skeletal fibers, the ATPase and tension-pCa curves exhibited lower apparent cooperativity and maxima and higher calcium sensitivity than expected from two independent activation pathways, suggesting that the interplay between the thin and thick filaments varies with the level of activation. Significantly, the inhibition of W7 increased the ATPase/tension ratio during activation in both muscle types. W7 holds much promise as a potent and reversible inhibitor of thin filament-mediated calcium activation of skeletal and cardiac muscle contraction.     

Effects of Irradiance-Sulphur Interactions on Enzymes of Carbon,Nitrogen, and Sulphur Metabolism in Maize Plants

The effect of sulphur deprivation and irradiance (180 and 750 µmol m^–2 s^–1) on plant growth and enzyme activities of carbon, nitrogen, and sulphur metabolism were studied in maize (Zea mays L. Pioneer cv. Latina) plants over a 15-d-period of growth. Increase in irradiance resulted in an enhancement of several enzyme activities and generally accelerated the development of S deficiency. ATP sulphurylase (ATPs; EC 2.7.7.4) and o-acetylserine sulphydrylase (OASs; EC 4.2.99.8) showed a particular and different pattern as both enzymes exhibited maximum activity after 10 d from the beginning of deprivation period. Hence in maize leaves the enzymes of C, N, and S metabolism were differently regulated during the leaf development by irradiance and sulphur starvation.     

Ionic control of renal gluconeogenesis IV. Effect of extracellular phosphate concentration

Isolated rat renal tubules from glucose from pyruvate, malate, glycerol and α-ketoglutarate. The rate of glucose formation from all but glycerol is enhanced by an increase in Ca²⁺ concentration. Because changes in inorganic phosphate concentrations influence the uptake and retention of calcium by isolated cells, the effect of changes in phosphate concentration upon renal gluconeogenesis was examined. It was found that changing phosphate concentration altered the metabolism of isolated rat renal tubules in three ways which dependend upon the Ca²⁺ concentration. In the absence of Ca²⁺, increasing phosphate concentration from 0.07 to 1.2 mM led to a stimulation of the decarboxylation of [U-¹⁴C]malate, [1-14C]pyruvate, [2-¹⁴C]-pyruvate, α-keto[5-¹⁴C]glutarate and [1,3-¹⁴C₂]glycerol, and to an increase in ATP concentration but had no effect upon the rate of glucose formation from malate, pyruvate, α-ketoglutarate but a slight stimulation of glucose production from glycerol. A further increase in phosphate above 1.2 mM had no effect on any of these parameters. In the presence of either low (0.2 mM) or high (2.0 mM) Ca²⁺, changing phosphate concentration had no effect upon the decarboxylation of any of these substrates except glycerol whose decarboxylation was stimulated by increasing medium phosphate concentration. In the presence of calcium, increasing phosphate concentration led to an inhibition of glucose formation from malate, pyruvate and α-ketoglutarate but not from glycerol. Also in the presence of calcium both parathyroid hormone and cyclic AMP stimulated glucose formation, and under these conditions increasing phosphate concentration led to an inhibition of glucose formation. In tubules treated with parathyroid hormone an increase in phosphate concentration from 0.07 to 6.0 mM led to a significant increase in cyclic AMP concentration even though the rate of glucose formation decreased.Analysis of metabolite concentrations and rates of substrates decarboxylations, under a variety of conditions, revealed that P_i altered renal gluconeogenesis at a site different from those controlled by changes in Ca²⁺ concentration. The P_i-control site was tentatively identified as the glyceraldehyde phosphate dehydrogenase-glycerate kinase reaction sequence. However, the effect of changing P_i concentration upon parathyroid hormone-induced alterations in cyclic AMP concentration could not be explained by this action of P_i, and was probably due to an effect of P_i upon cellular calcium distribution. Thus, changes in P_i concentration appear to have two cellular effects, only one of which is related to a change in cellular calcium metabolism.     

Response of carbonic anhydrase to polyethylene glycol-mediated water stress in wheat

Carbonic anhydrase (CA) activity in wheat leaves changed upon leaf dehydration: it decreased at mild stress (relative water content, RWC, 81 %), but increased at severe water stress (RWC 74 %). Phosphoenopyruvate carboxylase activity was not significantly affected by these stresses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Natural products as modulators of the nuclear receptors and metabolic sensors LXR,FXR and RXR

Nuclear receptors (NRs) represent attractive targets for the treatment of metabolic syndrome-related diseases. In addition, natural products are an interesting pool of potential ligands since they have been refined under evolutionary pressure to interact with proteins or other biological targets.This review aims to briefly summarize current basic knowledge regarding the liver X (LXR) and farnesoid X receptors (FXR) that form permissive heterodimers with retinoid X receptors (RXR). Natural product-based ligands for these receptors are summarized and the potential of LXR, FXR and RXR as targets in precision medicine is discussed.     

The photosynthetic characteristics of differently shaped leaves in Populus euphratica Olivier

There is a distinct leaf shape polymorphism within a single plant of P. euphratica Olivier. The anatomical structure, carbon isotope discrimination (Δ¹³C), and stomatal and photosynthetic behaviour were investigated in broad-ovate (BOL) and lanceolate (LL) leaves, located at the top and bottom in crown, respectively, of a mature Euphrates poplar growing in its native habitat. Both types of leaves had a non-Kranz anatomy and low Δ¹³C values. However, Δ¹³C of a LL was in average 3.2‰ larger than that of a BOL. In comparison with the LL, the BOL had a smaller stomatal conductance, causing subsequent decreases in transpiration rate and ratio of CO₂ concentrations in intercellular spaces to air. Carbon assimilation rate and water use efficiency were higher in the BOLs than in the LLs. The BOL exhibited C₄-like enzymological features, the activity of glycollate oxidase, and the ratio of activities of ribulose-1,5-bisphosphate carboxylase (RuBPC) to phosphoenolpyruvate carboxylase (PEPC) was lower in BOL than in LL throughout the whole growing season. The lowered ratio of RuBPC/PEPC in BOL was mainly associated with a marked decline in the activity of RuBPC, and only a slight increase in the activity of PEPC. These differences might contribute to microclimate adaptation in both types of leaves. This revised version was published online in June 2006 with corrections to the Cover Date.     

Estimation of pyruvate,phosphate dikinase activity in maize leaf tissue by (phosphoenolpyruvate plus pyrophosphate)-dependent phosphorylation of AMP

Crude extracts of maize leaf tissue catalysed the phosphorylation of AMP by ³²PPi in the presence of phosphoenolpyruvate (PEP). The reaction was enhanced by F^? and NH₄⁺. The optimum concentrations of AMP, PEP and PPi were 0.3, 10 and 1 mM, respectively. Under these conditions, ca75% of the AMP phosphorylated by ³²PPi was present as ATP and ca25 % as ADP. The activity was reversibly cold labile. The specific activity of crude extracts in the presence of F^? was proportional to enzyme concentration only at protein concentrations < 25,μg/ml. Partially purified pyruvate, phosphate dikinase (PPD) from maize leaf quantitatively phosphorylated AMP to ATP in a (PEP plus PPi)-dependent reaction with the concomitant production of 0.9 mol of pyruvate per mol of AMP phosphorylated. It was concluded that (PEP plus PPi)-dependent phosphorylation of AMP provides a reliable method for estimating PPD activity in crude extracts of maize. Crude maize extracts also catalysed ³²Pi-ATP and ³²PPi-ATP exchange but these activities were not specific for PPD.