Simulation and Prediction of Plant Phenology for Five Crops Based on PhotoperiodxTemperature Interaction

This paper presents a plant phenological model based on genotypextemperaturexphotoperiodinteraction (GPTmodel). In the model, rate of development towardsa specified stage (e.g. flowering) for a given genotype is composedof three components: the genotype's maximum rate of development;any delay due to a non-optimal temperature; and any delay dueto a photoperiod response. It is assumed that development tothe specified stage is an autonomous process established bymost, if not all, genes other than the vernalization genes andthe photoperiod genes; and that this autonomous process is delayedby any activity of the photoperiod genes. Since all physiologicalprocesses are modulated by temperature, any photoperiod responseis inevitably a photoperiodxtemperature interaction. This interactionis simulated by assuming that the photoperiod gene activityoccurs only beyond a critical photoperiod (P_c) and is enlargedby temperature above a base temperature (T_bp) that allows thephotoperiod gene activity. The model is written asR=1/D_b-S_t(T-T_opt)²-S_p(T-T_bp)|P-P_c|, whereRis the expected rate of development to the specifiedstage under any combination of temperature (T) and photoperiod(P). The other model parameters are:S_p, the sensitivity to adelaying photoperiod;T_opt, the optimum temperature for developmentin the absence of the photoperiod response;S_t, the sensitivityto a non-optimum temperature; andD_b, the basic duration to thespecified stage (or intrinsic earliness), the inverse of whichis the maximum rate of development.D_bis observable only ifT=T_optandsimultaneouslyP     

Transpirational Cooling as a Screening Technique for Drought Tolerance in Oil Seed Brassicas

Twenty-two genotypes of five Brassica species (oilseed rapeand mustard), consisting of two different maturity groups anddiffering in plant morphology, were grown on sandy soil withoutpost-sowing irrigation during 1982–83 winter season. Canopytemperature (T_c minus air temperature (T_a, stomatal conductance($) and osmotic adjustment were studied on two different deardays corresponding to the siliqua formation stage in early duration(137–150 d) and late maturing genotypes (151–165d) of oilseed Brassicas. The absolute mid-day values of transpirationalcooling (T_c–T_a) were relatively higher in B.juncea andB. carinata than in B. tomifortii, B. napus and B. campestris.Tc-Tm showed a genetic variability ranging from 0-5 to 4 Cfor early maturing genotypes, and from 0–5 to 5 C forlate maturing genotypes. Mid-day T_c–T_a showed significantpositive correlation with Kh osmotic adjustment and seed yieldin Brassica cultivars. Early genotypes out-yielded the latematuring ones, despite the lower values of AT, and T_c–T_aat siliqua formation in the former rather than later group ofcultivars. It is suggested that average mid-day T_c–T_aas observed with an infrared thermometer, could effectivelybe used as a technique to screen Brassica genotypes for droughttolerance under receding soil moisture conditions.     

In situ Effects of Elevated Atmospheric CO2on Leaf Freezing Resistance and Carbohydrates in a Native Temperate Grassland

The objectives of this study were to quantify changes in leaffreezing resistance and carbohydrate concentrations caused bylong-term (6 years) exposure to elevated CO₂(ambient: 360 µll^-1, elevated: 600 µl l^-1) in five dominant plant speciesgrowing in situ in a native temperate grassland. Across allfive species tested from three functional groups, the mean temperatureat which all leaves were damaged (T₁₀₀) significantly (P = 0.016)increased from -9.6 to -8.5 °C under elevated CO₂ , anda similar marginally significant (P = 0.079) reduction was observedfor the mean temperature that caused 50% leaf damage (T₅₀),from -6.7 to -6.0 °C. The mean temperature at which initialleaf damage was observed (T₀) was not significantly influencedby elevated CO₂ . Although concentrations of soluble sugars(+25%,P = 0.042), starch (+53%, P < 0.001), and total non-structuralcarbohydrates (TNC, +40%, P < 0.001) were significantly higherunder elevated CO₂ , leaf freezing resistance actually decreasedunder elevated CO₂ . Concentrations of soluble sugars were positivelycorrelated with freezing resistance when viewed across all fivecommunity dominants, but within any individual species, no suchrelationships were found. We also found no evidence for ouroriginal hypothesis that increased concentrations of solublesugars increase freezing resistance. Thus, future atmosphericCO₂levels may instead increase the risk of late spring freezingdamage. Furthermore, the strong differences in freezing resistanceobserved among the species, along with decreased freezing resistance,may increase the risk of losing species that have inherentlyweak freezing resistances from the plant community. Copyright2001 Annals of Botany Company CO₂enrichment, frost hardiness, sugar, starch, total non-structural carbohydrates (TNC)     

Use of the Weibull Function to Calculate Cardinal Temperatures in Faba Bean

The onset of germination of faba bean seeds at constant temperaturewas progressively delayed as that temperature diverged froman optimum of 25.5 ?C. At temperatures below 10 ?C, or above28 ?C, the maximum germination percentage fell to below 90%.There was no germination at 39 ?C. Positive and negative linearrelationships were established between the constant temperaturesand the rates of progress of germination to different percentiles,at sub-optimal and supra-optimal temperatures, respectively.Like germination rates, base temperature (T_b) declined from3.71 to –0.83 ?C as the percentile value increased from10% to 80%. Caution was urged in extrapolating beyond the experimentaldata set. Differences in the ceiling temperature (T_c) with percentilecould not be discerned. Cumulative germination progress curves at each temperature weremodelled by the Weibull, logistic, and cumulative normal distributionfunctions. Cardinal temperatures (T_b and T_c) calculated fromthese data reasonably approximated the actual data. The Weibullfunction demonstrated a good approximation at all percentilelevels, while the logistic and cumulative normal distributionfunctions, as a result of their inherent symmetry, deviatedat the extreme percentiles. It was concluded that the Weibullfunction not only accurately modelled cumulative germinationbut could also be used in the calculation of cardinal temperatures. Key words: Seed germination rate, cardinal temperatures, faba bean, Weibull function, probit and logic scales     

Differential effects of phorbol ester (PMA) on blocker-sensitive ENaCs of frog skin and A6 epithelia

Activation ofprotein kinase C with phorbol 12-myristate 13-acetate (PMA) causedcomplex transient perturbations of amiloride-sensitive short-circuitNa⁺ currents(I_Na) in A6epithelia and frog skins that were tissue and concentration dependent.A noninvasive channel blocker pulse method of noise analysis (18) wasused to investigate how PMA caused time-dependent changes of apicalmembrane epithelial Na⁺ channel(ENaC) single-channel currents, channel open probabilities (P_o), andchannel densities(N_T). In A6epithelia, 5 and 50 nM PMA caused within 7 min concentration-dependentsustained decreases ofP_o (~55% belowcontrol, 50 nM) and rapid compensatory transient increases ofN_T within 7 min(~220% above control, 50 nM), resulting in either small transientincreases of I_Naat 5 nM PMA or small biphasic decreases ofI_Na at 50 nM PMA.In contrast to A6 epithelia, 50 and 500 nM PMA in frog skin causedafter a delay of at least 10 min transient increases ofN_T to~60-70% above control at 30-60 min. Unlike A6 epithelia,P_o was increased~15% above control within 7 min and remained within±10-15% of control for the duration of the 2-h experiments.Despite differences in the time courses of secondary inhibition oftransport in A6 epithelia and frog skin, the delayed downregulation oftransport was due to time-dependent decreases ofN_T from theirpreelevated levels in both tissues. WhereasP_o is decreasedwithin minutes in A6 epithelia as measured by noise analysis or bypatch clamp (8), the discrepancy in regulation ofN_T in A6epithelia as measured by noise analysis and patch clamp is most likelyexplained by the inability of on-cell patches formed before treatmentof tissues with PMA to respond to regulation of their channeldensities.

     

土壤水分胁迫对5个种源油松光合特性的影响

在盆栽条件下,对5个种源油松（山西中条山ZT,山西吕梁山LL,山西太行山TH,陕西洛南LN和陕西黄陵HL）幼苗进行了水分胁迫处理实验,对其净光合速率（P_n）、蒸腾速率（T_r）、气孔导度（G_s）、胞间CO₂浓度（C_i）、水分利用效率（WUE）及P_n与土壤含水量（SWC）的关系进行了研究。结果表明：油松幼苗的P_n、T_r和G_s均随水分胁迫程度的增加呈先上升后下降的趋势,C_i呈先下降后上升的趋势。其中TH种源的P_n、T_r和G_s最高,LN和HL种源的较低。干旱处理的第4天（SWC为15%~25%）,5个种源的P_n、T_r和G_s均达到处理期的最大值;第7天（SWC为7%~9%）,它们的P_n、T_r、G_s和WUE差异均极显著（p<0.01）,且大小顺序均为：ZT>TH>LL>HL>LN;处理的10天后（SWC小于5%）,LL、TH、LN、HL均只表现为呼吸作用。根据P_n与SWC的二次拟合方程（R²=0.980~0.997）中P_n为0时的SWC进行了抗旱性排序,依次为：TH>ZT>LL>HL>LN。     

Transformed T0 orchardgrass (Dactylis glomerata L.) plants produced from highly regenerative tissues derived from mature seeds

A highly efficient and reproducible transformation system for orchardgrass (Dactylis glomerata L. cv. Rapido, 2n=42=28) was established using microprojectile bombardment of highly regenerative, green tissues derived from mature seeds. These tissues, induced from embryogenic callus, were bombarded with a mixture of three plasmids containing the hygromycin phosphotransferase (hpt), phosphinothricin acetyltransferase (bar) and #-glucuronidase (uidA; gus) genes. From 147 individual explants bombarded, 11 independent hygromycin-resistant lines (7.5%) were obtained after an 8- to 16-week selection period using 30-50 mg/l hygromycin B. Of the 11 independent lines, ten (91%) were regenerable. The presence and integration of the transgene(s) were assessed using PCR and DNA blot hybridization. Coexpression frequency of the three transgenes (hpt/bar/uidA) in T₀ plants was 20%, and of two transgenes, either hpt/bar or hpt/uidA, 45-60%. Due to greenhouse conditions optimized for the growth of other species, T₁ seed has not been obtained from these plants. While the inability to analyze progeny plants precludes the conclusive demonstration of stable transformation, the results of all molecular and biochemical analyses of T₀ plants are consistent with the production of stably transformed plants. Frequent change in ploidy level was observed in transformed T₀ orchardgrass plants. Plants from only three of the ten independent lines analyzed had the normal tetraploid number of chromosomes (2n=42=28), while plants from seven lines (70%) were octaploid (2n=82=56). The octaploid plants had abnormal morphological features, such as narrower, thicker and more upright leaves.     

Neuromuscular fatigue during a prolonged intermittent exercise: Application to tennis

The time course of alteration in neuromuscular function of the knee extensor muscles was characterized during a prolonged intermittent exercise. Maximal voluntary contraction (MVC) and surface EMG activity of both vastii were measured during brief interruptions before (T₀), during (30, 60, 90, 120, 150 and 180 min: T₃₀, T₆₀, T₉₀, T₁₂₀, T₁₅₀, T₁₈₀) and 30 min after (T₊₃₀) a 3 h tennis match in 12 trained players. M-wave and twitch contractile properties were analyzed following single stimuli. Short tetani at 20 Hz and 80 Hz were also applied to six subjects at T₀ and T₁₈₀. Significant reductions in MVC (P < 0.05; −9%) and electromyographic activity normalized to the M wave for both vastii (P < 0.01) occurred with fatigue at T₁₈₀. No significant changes in M-wave duration and amplitude nor in twitch contractile properties were observed. The ratio between the torques evoked by 20 Hz and 80 Hz stimulation declined significantly (P < 0.001; −12%) after exercise. Central activation failure and alterations in excitation–contraction coupling are probable mechanisms contributing to the moderate impairment of the neuromuscular function during prolonged tennis playing.     

Intracellular pH shifts in cultured kidney (A6) cells: effects on apical Na+ transport

We report, for the epithelialNa⁺ channel (ENaC) in A6 cells,the modulation by cell pH (pH_c)of the transepithelial Na⁺ current(I_Na), thecurrent through the individual Na⁺channel (i), the openNa⁺ channel density(N_o), and thekinetic parameters of the relationship betweenI_Na and theapical Na⁺ concentration. Thei andN_o were evaluatedfrom the Lorentzian I_Na noise inducedby the apical Na⁺ channel blocker6-chloro-3,5-diaminopyrazine-2-carboxamide.pH_c shifts were induced, understrict and volume-controlled experimental conditions, byapical/basolateral NH₄Cl pulses orbasolateral arrest of theNa⁺/H⁺exchanger (Na⁺ removal; block byethylisopropylamiloride) and were measured with the pH-sensitive probe2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Thechanges in pH_c were positivelycorrelated to changes inI_Na and theapically dominated transepithelial conductance. The sole pH_c-sensitive parameter underlyingI_Na wasN_o. Only thesaturation value of theI_Na kinetics wassubject to changes in pH_c.pH_c-dependent changes inN_o may be causedby influencingP_o, the ENaC openprobability, or/and the total channel number,N_T = N_o/P_o.

     

Ionic Currents across the Plasmalemma of Chara inflata Cells: III. WATER-RELATIONS PARAMETERS AND THEIR CORRELATION WITH MEMBRANE ELECTRICAL PROPERTIES

The water-relations parameters of Chara inflata cells were determineddirectly using the micro pressure probe technique. The turgorpressure of cells in artificial pond water (₀ = 0.06 MPa) wasabout 0.65 MPa and the half-time (T_1/2) for water exchange wasabout 6.5 s. The calculated values of the hydraulic conductivity(L_P) were in the range 1–2 ? 10^–6m s^–1 (MPa)^–1.The volumetric elastic modulus () was 32.8 MPa for turgor rangingfrom 0.77 to 0.82 MPa. Large changes in the water-relations parameters and the electricalproperties of the membrane occurred when the turgor was decreasedto low values. These changes included: (i) a decrease in theT_1/2 for water exchange, (ii) an increase in L_P and (iii) depolarizationof the membrane potential difference (V_m). The micro pressure probe, which enabled the turgor pressureof the cell to be altered, was used in combination with thevoltage-clamp technique to determine the relationship betweenK⁺ and Cl^– conductances of the plasmalemma and the cellturgor. The K⁺ conductance increased reversibly as the turgorwas reduced in the range 0 to 0.6 MPa and the Cl^– -conductanceincreased as the turgor was reduced in the range 0.1 to 0.5MPa. It is suggested that these pressure-dependent K⁺ and Cl^–conductances may have a dual role in electrical events and thenon-electrical responses such as changes in the cell volume. Key words: Chara inflata, membrane conductances, ion channels, water-relations parameters     

4种杂交杨对土壤水分变化的生态学响应

以田间持水量的100% (T1, 对照)、70% (T2)、50% (T3)和30% (T4)为4个水分处理梯度, 比较研究了4种不同品系的杂交杨(Populus)——15-29 (P. trichocarpa × P. deltoids)、DN-2 (P. deltoids × P. nigra)、DN-14274 (P. deltoids × P. nigra)和R-270 (P. deltoids × P. nigra)在不同水分处理和不同处理阶段对水分亏缺的反应。结果表明, 4种杂交杨品系对水分亏缺较敏感, 都通过关闭气孔、降低叶面积以有效地调节水分的散失, 降低光合速率、蒸腾、水势, 增加水分利用效率, 改变生物量的分配等一系列生理适应机制以及形态策略, 来应对不同程度的水分亏缺, 只是不同品系的适应程度不同。在生物量分配上, R-270主要降低叶干重, 而其它3个品系的叶、茎和根干重全部降低; 随着水分亏缺的加重, 15-29和R-270的根冠比增加, 根部获得更多的同化物分配, 从而有利于水分的吸收, 增加其抗旱性。DN-2的碳同位素组成δ¹³与水分利用效率呈显著正相关(r= 0.631, p<0.01)。而R-270的δ¹³与水分利用效率呈负相关, 但不显著, 只有在处理T4下呈显著负相关(r= -0.732, p<0.01), 表明土壤水分影响了碳同位素的分馏, 不同品系相反的结果表明同位素分馏的遗传变异。与T3和T4相比, T1和T2处理的苗木具有较高的生物量、叶面积、光合速率、蒸腾、水势以及气孔导度, 说明4个杂交杨品系在充足或适当的灌溉条件下具有较高的生产力。在T3和T4处理下, 4个品系表现出不同的生存策略, 但生产力均较低, 因此在干旱胁迫下很难形成高生产力。与DN-2和DN-14274相比, 15-29和R-270对水分胁迫表现出更强的适应性反应, 具有较强的抗旱性, 可用作防护林品种。     

Distinctive G protein-dependent signaling in smooth muscle by sphingosine 1-phosphate receptors S1P1 and S1P2

We examined expression of sphingosine 1-phosphate (S1P) receptors and sphingosine kinase (SPK) in gastric smooth muscle cells and characterized signaling pathways mediating S1P-induced 20-kDa myosin light chain (MLC₂₀) phosphorylation and contraction. RT-PCR demonstrated expression of SPK1 and SPK2 and S1P₁ and S1P₂ receptors. S1P activated G_q, G₁₃, and all G_i isoforms and stimulated PLC-1, PLC-3, and Rho kinase activities. PLC- activity was partially inhibited by pertussis toxin (PTX), G or G_q antibody, PLC-1 or PLC-3 antibody, and by expression of G_q or G_i minigene, and was abolished by a combination of antibodies or minigenes. S1P-stimulated Rho kinase activity was partially inhibited by expression of G₁₃ or G_q minigene and abolished by expression of both. S1P stimulated Ca²⁺ release that was inhibited by U-73122 and heparin and induced concentration-dependent contraction of smooth muscle cells (EC₅₀ 1 nM). Initial contraction and MLC₂₀ phosphorylation were abolished by U-73122 and MLC kinase (MLCK) inhibitor ML-9. Initial contraction was also partially inhibited by PTX and G_q or G antibody and abolished by a combination of both antibodies. In contrast, sustained contraction and MLC₂₀ phosphorylation were partially inhibited by a PKC or Rho kinase inhibitor (bisindolylmaleimide and Y-27632) and abolished by a combination of both inhibitors but not affected by U-73122 or ML-9. These results indicate that S1P induces 1) initial contraction mediated by S1P₂ and S1P₁ involving concurrent activation of PLC-1 and PLC-3 via G_q and G_i, respectively, resulting in inositol 1,4,5-trisphosphate-dependent Ca²⁺ release and MLCK-mediated MLC₂₀ phosphorylation, and 2) sustained contraction exclusively mediated by S1P₂ involving activation of RhoA via G_q and G₁₃, resulting in Rho kinase- and PKC-dependent MLC₂₀ phosphorylation. muscle contraction; signal transduction     

The Effect of Calcium on the Fluidity and Phase Properties of Microsomal Membranes Isolated from Postclimacteric Golden Delicious Apples

Calcium and magnesium have been found to stabilize and preservethe ethylene-synthesizing capacity of postclimacteric GoldenDelicious apple slices. In order to assess if this reflectsan effect at the membrane level, we have used three spin labelsto assay changes in the physical properties of isolated microsomalmembranes treated with calcium. A surface spin label, 18NP (an18 carbon alkane with a terminal quaternary amine attached toa nitroxyl-containing pyrollidine ring), reported a 20.8% increasein rotational correlation time (_c) at 25?C and a 25.3% increasein activation energy (E_a) calculated from linear Arrhenius plotsof _c for microsomal membranes treated with 50 mM CaCl₂. Regionsdeeper within the bilayer were probed using two fatty acid spinlabels—I(l2,3), stearic acid bearing a paramagnetic nitroxidegroup on carbon 5, and I(1,14), stearic acid bearing a paramagneticnitroxide group on carbon 16. The calcium effect was less pronounceddeeper within the lipid bilayer, there being only a 10.6% increasein _c and a 6% increase in the value of an order parameter (S)calculated from spectra recorded at 25?C for microsomes treatedwith 50 mM CaCl₂ and labelled with I(1,14) and I(12,3) respectively.There was no significant change in E_a for I(1,14)-labelled membranestreated with 50 mM CaCl₂. Similar trends were observed for membranestreated with 5 mM CaCl₂, although the degree of change was lessand differences were not always significant. Wide-angle X-raydiffraction revealed that untreated microsomal membranes frompostclimacteric apples were exclusively liquid-crystalline at25?C, as were microsomes treated with 50 mM CaCl₂. The transitiontemperature, defined as the highest temperature at which gelphase lipid could be detected, was below –25?C for bothtreated and untreated membranes. It is apparent, therefore, that Ca^2$ rigidifies and stabilizesmembranes, particularly at their surfaces. Inasmuch as partsof the ethylene biosynthetic pathway appear to be membrane-associated,this rigidification may, in part, act to preserve ethylene production. (Received August 3, 1981; Accepted November 4, 1981)     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

5个油松种源光合特性的比较研究

为了揭示自然条件下不同种源油松光合特性的差异,为优良种源选择提供依据,在黄土高原种源实验地,对5个油松种源（陕西洛南LN,陕西黄陵HL,山西吕梁山LL,山西灵空山LK,辽宁千山QM）幼苗的光合生理特征及其与环境因子的关系进行了研究。结果表明：5个油松种源的净光合速率（P_n）呈双峰型,蒸腾速率（T_r）、气孔导度（G_s）亦基本呈双峰型,第1峰值均出现在上午8:00,有明显的光合午休现象。种源QM的水分利用效率（WUE）日变化呈单峰性,峰值出现在10:00,而种源LN、LL、LK和HL呈双峰型,第一峰值出现在8:00,第二峰值出现在12:00~16:00。种源LN、LL、LK和QM午间净光合速率的下降主要由气孔因素引起的,而种源HL则主要由叶肉细胞同化能力的降低引起的。种源LK的日均P_n、T_r和WUE均高于其他种源,是高光合、高蒸腾和高水分利用效率的种源,而种源HL属于低光合、低蒸腾和低水分利用效率的种源。T_a是影响各种源的P_n的首要因子,其次是VPD;RH是影响种源LN、LL和LK的T_r的首要因子;而T_a和VPD是影响种源HL和QM的T_r的主要因子。     

LY-294002-inhibitable PI 3-kinase and regulation of baseline rates of Na(+) transport in A6 epithelia

Blocker-inducednoise analysis of epithelial Na⁺ channels (ENaCs) was usedto investigate how inhibition of an LY-294002-sensitive phosphatidylinositol 3-kinase (PI 3-kinase) alters Na⁺transport in unstimulated and aldosterone-prestimulated A6 epithelia. From baseline Na⁺ transport rates(I_Na) of 4.0 ± 0.1 (unstimulated) and9.1 ± 0.9 µA/cm² (aldosterone), 10 µM LY-294002caused, following a relatively small initial increase of transport, acompletely reversible inhibition of transport within 90 min to 33 ± 6% and 38 ± 2% of respective baseline values. Initialincreases of transport could be attributed to increases of channel openprobability (P_o) within 5 min to 143 ± 17% (unstimulated) and 142 ± 10% of control (aldosterone) frombaseline P_o averaging near 0.5. Inhibition oftransport was due to much slower decreases of functional channeldensities (N_T) to 28 ± 4% (unstimulated)and 35 ± 3% (aldosterone) of control at 90 min. LY-294002 (50 µM) caused larger but completely reversible increases ofP_o (215 ± 38% of control at 5 min) andmore rapid but only slightly larger decreases ofN_T. Basolateral exposure to LY-294002 induced nodetectable effect on transport, P_o or N_T. We conclude that an LY-294002-sensitive PI3-kinase plays an important role in regulation of transport bymodulating N_T and P_o ofENaCs, but only when presented to apical surfaces of the cells.

     

Decreased affinity for oxygen of cytochrome-c oxidase in Leigh syndrome caused by SURF1 mutations

Mutations in the gene SURF1 prevent synthesis of cytochrome-c oxidase (COX)-specific assembly protein and result in a fatal neurological disorder, Leigh syndrome. Because this severe COX deficiency presents with barely detectable changes of cellular respiratory rates under normoxic conditions, we analyzed the respiratory response to low oxygen in cultured fibroblasts harboring SURF1 mutations with high-resolution respirometry. The oxygen kinetics was quantified by the partial pressure of oxygen (PO₂) at half-maximal respiration rate (P₅₀) in intact coupled cells and in digitonin-permeabilized uncoupled cells. In both cases, the P₅₀ in patients was elevated 2.1- and 3.3-fold, respectively, indicating decreased affinity of COX for oxygen. These results suggest that at physiologically low intracellular PO₂, the depressed oxygen affinity may lead in vivo to limitations of respiration, resulting in impaired energy provision in Leigh syndrome patients. oxygen kinetics; mitochondrial disease     

Proton Transport and pH Control in Sinapis alba Root Hairs: A Study carried out with Double-Barrelled pH Micro-electrodes

Continuous measurements of cytoplasmic pH (pH_c) in Sinapis roothairs have been carried out with double-barrelled pH-micro-electrodesin order to gain information on translocation of protons acrossthe plasmalemma and cytoplasmic pH control. (i) The cytoplasmicpH of Sinapis (7–33 ? 0–12, standard conditions)changes no more than 0.1 pH_c, per pH_o-unit, regardless of whethercyanide is present or not. (ii) Weak acids rapidly acidify pH_cand hyperpolarize, while weak bases alkalize pH_c and depolarizethe cells, (iii) 1.0 mol M,³ NaCN acidifies the cytoplasm by0.4 to 0.7 pH-units, but alkalizes the vacuole. (iv) 20 mmolm^–3 CCCP has no significant effect on pH_c, if added atpH 9.6 or 7.2, but acidifies pH_c by 1.3 units at pH 4.3. Inthe presence of CCCP, cyanide acidifies the cytoplasm, (v) Chloridetransiently acidifies pH_c, while K⁺, Na⁺, and have no significant effects, (vi) Cytoplasmic buffer capacityforms a bell-shaped curve versus pH_c with an optimum of about50 mol m^–3 H⁺pH_c-unit. The modes of proton re-entry and the effects of active and passiveproton transport on cellular pH control are critically discussed.It is suggested that the proton leak, consisting of H⁺-cotransport(e.g. H⁺/Cl^–) rather than H⁺-uniport, is no threat topH_c. The proton export pump, although itself reacting to changesin pH_c, influences pH_c only to a minor extent. It is concludedthat buffer capacity and membrane transport play moderate rolesin pH_c control in Sinapis, while the interlocked H⁺-producingand -consuming reactions of cellular metabolism are the mainregulating factors. This makes pH control in Sinapis quite differentfrom bacterial and animal cells. Key words: Cytoplasmic pH, double-barrelled pH micro-electrode, pH control, proton transport, Sinapis     

硅对生姜叶片水、二氧化碳交换特性的影响

为探讨硅对生姜植株的生理效应,以莱芜大姜为试材,研究了水培营养液中不同硅素水平对生姜植株生长、硅含量及叶片光合作用和蒸腾作用的影响.结果表明：植株各器官硅含量及生物量均随营养液硅素水平的升高而显著增加,1.0 (T₁)、1.5 (T₂)、2.0 (T₃) mmol·L^-1硅(Si)处理植株叶片硅 (SiO₂) 含量分别比CK增加604.4%、834.8%和1130.4%,单株生物量分别比CK增加9.4%、19.4%和22.8%.随着硅素水平的升高,叶片Mg²⁺ TPase、Ca²⁺ ATPase活性及光合速率(P_n)和水分利用效率(WUE)提高,蒸腾速率(T_r)降低.一天中在11:00时,T₁、T₂、T₃处理的生姜叶片P_n和WUE分别比CK提高11.2%、21.8%、28.2%和23.1%、55.9%、54.8%,T_r分别比CK降低6.3%、17.1%和19.2%.此外,硅素还显著提高了生姜叶片光合作用饱和光强、CO2羧化效率及类胡萝卜素含量,但对叶绿素含量无显著影响.本试验条件下,以15～20 mmol·L-1硅素(Si)处理效果最好.     

Photoinhibition and the diurnal variation of phytoplankton photosynthesis--I. Development of a photosynthesis--irradiance model from studies of in situ responses

Diurnal series of fluorescence and photosynthesis assays wereconducted in high altitude (3803 m), tropical (16°), LakeTiticaca (Peru/Bolivia). Near-surface diurnal thermoclines formedon typical days of high photon flux density (PFD, {small tilde}2000 µE m^–2 s^–1). In the depth range of diurnalstratification profiles of in vivo fluorescence, both without(F_a and with (F_b DCMU, exhibited a mean decrease of 64% frommorning to mid-day, but little change (mean increase of 1.5%)through the afternoon. Three times during the day surface, mid-depth(3–5 m) and deep (15–20 m) phytoplankton sampleswere incubated with H¹⁴CO₃^– under short (<2 h) exposuresto a range of in situ PFDs. Comparison of phytoplankton in differentsamples (ANOVA) showed identical photosynthetic response insunrise (isothermal) samples but a significant drop in surfaceand mid-depth photosynthesis at all PFDs during times of diurnalstratification. Similarly, both low-light () and light-saturated(P² _max photosynthetic parameters were lower in mid-day surfacesamples compared to deep samples. In addition, previously photoinhibitedsamples had a higher threshold intensity for photoinhibition,I_T. These results, together with diurnal time series of fluorescencefrom in situ incubations, demonstrate that recovery from extendedepisodes of photoinhibition during diurnal stratification isslower than suggested by previous observations in vitro. Photosynthesisby near-surface phytoplankton is different in light increasingup to I_T than light decreasing from I_T. This effect can be modeledby reducing and P_max as a function of the maximum photoinhibitingPFD in the diurnal light history. ¹Present address: Division of Molecular Plant Biology, Universityof California, Berkeley, Berkeley, CA 94720, USA