Fluctuations in leaf water balance,with a period of 1 to 10 minutes

Summary Water uptake into leaves, and water vapour efflux from leaves, were found to show short-term fluctuations. The fluctuations were observed in a number of parameters of leaf water metabolism. It is suggested that this behaviour is a result of time lags in the transmission of changes in water potential through the leaf.     

植物叶片脯氨酸的变化及其对亚硫酸伤害的防护作用

 在特定污染条件下,植物叶脯氨酸含量与K+渗出量(％)呈负相关变化,并因树种和叶片成熟度而异、脯氨酸含量为成叶>老叶,K+渗出量则是老叶>成叶,外施脯氨酸对植物亚硫酸伤害具有一定的防护作用。     

Effect of magnesium-dependent cell membrane alterations on the transport of K+ in Ehrlich ascites tumour cells

Mg-deficiency or Mg-loading of tumour cells changes the permeability of the cell membrane. The influence of this change on the K+ transport across the membrane was investigated using 86Rb+ and K+ analog. The time course of the influx and efflux rates were estimated by means of a mathematical approach for a two-compartment system with inconstant pool sizes. The comparison of the two states of the cells demonstrates that in Mg-deficient cells the passive K+ efflux is significantly enhanced (40%). This in turn stimulates the active counter transport mediated by the (Na+-K+)-ATPase, raising the ATP consumption by about 30%. However, the enzyme is not able to maintain the cellular K+ content under these conditions. After a short transient increase due to the initially enhanced influx the passive net efflux prevails. Differences in the electrophoretic mobility of the two states of the cells confirm Mg-dependent changes of the cell membrane structure.     

Relationship between Photosynthesis and Respiration: The Effect of Carbohydrate Status on the Rate of CO(2) Production by Respiration in Darkened and Illuminated Wheat Leaves

The rate of dark CO₂ efflux from mature wheat (Triticum aestivum cv Gabo) leaves at the end of the night is less than that found after a period of photosynthesis. After photosynthesis, the dark CO₂ efflux shows complex dependence on time and temperature. For about 30 minutes after darkening, CO₂ efflux includes a large component which can be abolished by transferring illuminated leaves to 3% O₂ and 330 microbar CO₂ before darkening. After 30 minutes of darkness, a relatively steady rate of CO₂ efflux was obtained. The temperature dependence of steady-state dark CO₂ efflux at the end of the night differs from that after a period of photosynthesis. The higher rate of dark CO₂ efflux following photosynthesis is correlated with accumulated net CO₂ assimilation and with an increase in several carbohydrate fractions in the leaf. It is also correlated with an increase in the CO₂ compensation point in 21% O₂, and an increase in the light compensation point. The interactions between CO₂ efflux from carbohydrate oxidation and photorespiration are discussed. It is concluded that the rate of CO₂ efflux by respiration is comparable in darkened and illuminated wheat leaves.     

Effect of Leaf Age on Potassium Efflux and Net Flux in Tomato Leaf Slices

The effects on leaf age on K (⁸⁶Rb) efflux, influx and net fluxinto lamina slices from leaf 7 on a tomato plant (Lycopersiconesculentum Mill.) were determined. The ontogenetic trend inK efflux was dependent on the external K concentration. At externalKCI concentrations between 0.5 and 10.0 mM, K efflux rates increasedduring leaf elongation. Only a small increase in efflux occurredin mature leaves with increasing age. It is suggested that thetonoplast retains its structural integrity through the initialstages of leaf senescence. In fully expanded leaves, a zeronet K flux (a balance between influx and efflux) was achievedat external KCI concentrations between 1.0 and 3.5 mM. The Kcontent of lamina slices from leaves 5 and 13 remained constantwhen bathed in a solution containing 2 to 3 mM K. It is suggestedthat the decline in K concentration in mature tomato leaf tissueis due to a decline in leaf free space K concentrations below1 to 3 mM which would result in a net efflux out of leaf cells. Lycopersicon esculentum Mill., tor ato, free space, ion fluxes, leaf age, leaf ontogeny, potassium     

Pretranstional phenomena in phospholipid/water multilayers.

We have measured the water order in monodomain phospholipid samples using 2H nuclear magnetic resonance (NMR) and analyzed the splittings in terms of critical exponents. Our data and the model developed to interpret them in terms of fluctuations provide an explanation of the puzzling sharp reduction of water order near the chain-ordering phase transition. The temperature range of the fluctuations is approximately the same as that observed for increased 22Na+ efflux from phospholipid vesicles.     

Acute exposure to ozone inhibits rapid carbon translocation from source leaves of Pima cotton

Tropospheric ozone (O3 causes significant disruption of growth and yield in upland and Pima cottons. Pima cotton (Gossypium barbadense L.) was exposed to brief pulses (0.75 h) of a range of O3 concentrations (nominally 0.0, 0.2, 0.5, and 0.8 l l^-1) to investigate effects of phloem translocation of ¹⁴C-labelled recent photoassimilate. The initial phase of rapid efflux from source leaves was monitored with a Geiger-Muller Tube as activity remaining in the leaf as a function of time. Visual inspection of unprocessed efflux curves revealed disruption of efflux by O3. Single exponential decay functions were fitted to these efflux curves to extract first order rate constants for phloem leading and longitudinal transport of labelled carbohydrates. A single compartment model was applied, with and without an asymptote of non-transported carbohydrate, to calculate leaf sugar contents. The effect of O3 in retarding efflux of label, decreasing the rate constant, and increasing calculated soluble sugar pools, was consistent regardless of the method of analysis. Following incorporation of the asymptote, calculated rate constants and sugar pools were similar to values from the literature and to preliminary measurements of sugar contents in O3-treated cotton leaves. Total carbohydrate transported from source leaves was reduced both by O3 effects on assimilation (up to 205) and by O3 effects on efflux (up to 70%), but was clearly dominated by the impact on phloem translocation. These rapid efflux kinetics likely reflect oxidant damage at the plasmalemma or plasmodesmata of mesophyll or phloem companion cells. Evaluation of effects of O3 on tonoplast function and consequences for carbohydrate translocation await a more complete compartmental efflux analysis.     

树木气孔浸润级与SO2伤害及ABA的防护作用

以常见绿化树种为材料,通过实地测定和熏烟实验,探讨了气孔浸润级与树木SO2伤害的关系及ABA的防护效应.结果表明,在特定环境下,相同树种的气孔浸润级较为稳定,不同树种的气孔浸润级差异较大;浸润级与叶绿素结合度呈负相关变化,但不明显;与K+渗出量呈正相关(r=0.92,α＜0.01),并按95%的置信度绘制了伤害预测图.不同SO2浓度条件下,对同一树种的气孔浸润级的影响甚小,不超过一个等级,K+渗出量则依大气SO2浓度和树木吸S量的增加而增多.气孔浸润级依ABA溶液处理浓度增大而降低,K+渗出量也相应减少,经2.5mol     

植物叶钾离子（K+）渗出量变化规律及其在大气质量评价中应用

本文以7个阔叶树种为材料,经SO2熏气证实：植物叶K+渗出量与培养液K+浓度和叶片K+含量无关,依光强和植物种类而异,气孔开度大、叶片含硫量高者K+渗出量也多,具有很强的相关性。基于上述规律,提出按刺槐叶K+渗出量的阈值法和统计法(X±S)划分四个污染等级,用来评价沈阳市的污染状况,与理化监测相比基本一致。据大气SO2浓度(ŷ)与K+渗出量(x)之间建立的相关方程：ŷ=0.0111x-0.0259(r=0.879,P<0.01)计算1982和1983年度大气SO2浓度,并按95%置信度绘制预测图,经精度分析,较理化监测更为稳定可靠。     

Mechanism of inducer expulsion in Streptococcus pyogenes: a two-step process activated by ATP.

The mechanism of methyl-beta-D-thiogalactoside-phosphate (TMG-P) expulsion from Streptococcus pyogenes was studied. The expulsion elicited by glucose was not due to exchange vectorial transphosphorylation between the expelled TMG and the incoming glucose since more beta-galactoside was displaced than glucose taken up, and the stoichiometry between TMG and glucose transport was inconstant. Instead, two distinct and sequential reactions, intracellular dephosphorylation of TMG-P followed by efflux of free TMG, mediated the expulsion. This was shown by temporary accumulation of free TMG effected by competitive inhibition of its efflux and by the aid of arsenate, which arrested dephosphorylation of TMG-P but did not affect efflux of free TMG formed intracellularly before arsenate addition. The competitive inhibition of TMG efflux by its structural analogs suggests that a transport protein facilitates the expulsion. Iodoacetate or fluoride prevented TMG-P dephosphorylation and its expulsion. However, provision of ATP via the arginine deiminase pathway restored these activities in the presence of the glycolytic inhibitors and stimulated expulsion in their absence. Other amino acids tested did not promote this restoration, and canavanine or norvaline severely inhibited it. Arginine without glucose neither elicited the dephosphorylation nor evoked the expulsion of TMG-P. Ionophores or ATPase inhibitors did not prevent the expulsion as elicited by glucose or its restoration by arginine. The results suggest that activation of the dephosphorylation-expulsion mechanism occurs independently of a functional glycolytic pathway, requires ATP provision, and is possibly due to protein phosphorylation controlled by a yet unknown metabolite. The in vivo phosphorylation of a protein (approximate molecular weight - 10,000) under the conditions of expulsion was demonstrated.     

Evaluation of three techniques used to determine surfactant phytotoxicity

Three techniques were used to measure and compare the phytotoxicities of Triton X-45 and Agral 90 (two organic surfactants) with two organosilicone surfactants (Silwet L-77 and L-7607), and to compare these four non-ionic compounds with a cationic tallow amine surfactant (Hyspray). Total ion efflux and ethylene response methods were used in vivo and in vitro, while a betacyanin efflux method was an in vitro system only. The first two methods, using intact leaves, were considered to be more closely related to normal spraying conditions than the betacyanin efflux test which used explant material. However, the use of intact leaves was thought to bias the results in favour of the leaf penetration properties of the surfactants rather than their phytotoxicities. The in vitro pigment efflux method provided a simple way of ranking the surfactants in order of their potential phytotoxicities, especially with regard to effects on membrane permeability. This ranking, in increasing order of toxicity, was: Silwet L-7607, Silwet L-77, Agral 90, Triton X-45 and Hyspray.     

树木气孔浸润级与SO2伤害及ABA的防护作用

以常见绿化树种为材料,通过实地测定和熏烟实验,探讨了气孔浸润级与树木SO₂伤害的关系及ABA的防护效应.结果表明,在特定环境下,相同树种的气孔浸润级较为稳定,不同树种的气孔浸润级差异较大;浸润级与叶绿素结合度呈负相关变化,但不明显;与K⁺渗出量呈正相关(r=0.92,α＜0.01),并按95%的置信度绘制了伤害预测图.不同SO₂浓度条件下,对同一树种的气孔浸润级的影响甚小,不超过一个等级,K⁺渗出量则依大气SO₂浓度和树木吸S量的增加而增多.气孔浸润级依ABA溶液处理浓度增大而降低,K⁺渗出量也相应减少,经2.5mol·L^-1×4h剂量的SO₂熏烟,预涂30mol·L^-1ABA者,降低了1.5～3个浸润级,K⁺渗出量减少36.5%～54.8%,其测定值与自然对照值相近,防护作用显著.     

Characteristics of a Diurnal Rhythm of Assimilate Translocation in Grapevine Plants

Characteristics of photoassimilate efflux from the leaves of grapevine (Vitis vinifera L., var. Rkatsiteli) plants under natural conditions and upon darkening, defoliation, and ABA treatment at short exposures (2, 6, and 24 h) as well as diurnal pattern of starch content in the leaves were investigated. Translocation of assimilates from the leaves of grapevine usually occurred at night and started after 20:00 or 21:00. However, such pattern of translocation was not strictly determinated and could be changed upon the action of some factors. Darkening, defoliation, and treatment with ABA initiated the translocation of photoassimilates from the leaves in the daytime. Darkening and ABA treatment turned out to be more efficient than defoliation. Darkening and defoliation significantly changed the character of partitioning of photoassimilates in the stem. We corroborated the opinion that in grapevine, the efflux of assimilates from source leaves is also governed by the feedback mechanism and probably much depends on the level of carbohydrates.     

Over-expression of PHO1 in Arabidopsis leaves reveals its role in mediating phosphate efflux

Inorganic phosphate (Pi) homeostasis in multi-cellular eukaryotes depends not only on Pi influx into cells, but also on Pi efflux. Examples in plants for which Pi efflux is crucial are transfer of Pi into the xylem of roots and release of Pi at the peri-arbuscular interface of mycorrhizal roots. Despite its importance, no protein has been identified that specifically mediates phosphate efflux either in animals or plants. The Arabidopsis thaliana PHO1 gene is expressed in roots, and was previously shown to be involved in long-distance transfer of Pi from the root to the shoot. Here we show that PHO1 over-expression in the shoot of A. thaliana led to a two- to threefold increase in shoot Pi content and a severe reduction in shoot growth. (31) P-NMR in vivo showed a normal initial distribution of intracellular Pi between the cytoplasm and the vacuole in leaves over-expressing PHO1, followed by a large efflux of Pi into the infiltration medium, leading to a rapid reduction of the vacuolar Pi pool. Furthermore, the Pi concentration in leaf xylem exudates from intact plants was more than 100-fold higher in PHO1 over-expressing plants compared to wild-type. Together, these results show that PHO1 over-expression in leaves leads to a dramatic efflux of Pi out of cells and into the xylem vessel, revealing a crucial role for PHO1 in Pi efflux.     

Regulation of sucrose efflux from soybean leaf discs

Net sucrose efflux from discs of fully expanded leaves of soybean (Glycine max [L.] Merr.) plants was studied to characterize sucrose efflux into the apoplast. Net sucrose efflux had a Q₁₀ of 2.3, was linear for at least 3.5 hours, and was selective for sucrose over glucose. Sulfhydryl group inhibitors reduced sucrose efflux by up to 80%. There was a biphasic promotion of sucrose efflux by KCl with an apparent saturable component up to about 20 millimolar, above which the effect was linear. Sucrose efflux was promoted by NaCl as a linear function of concentration. Monovalent cation ionophores did not affect sucrose efflux, regardless of external KCl concentration. Light in the absence of added HCO₃-increased sucrose efflux by about 20%. Sucrose efflux was promoted by increasing pH from 4 to about 8, above which no additional effect was observed. When leaf discs were bathed at pH 6.0, the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) increased sucrose efflux by about 25%. CCCP in the presence of valinomycin had the same effect as CCCP alone. Inhibition of plasmalemma ATPase activity with N,N′-dicyclohexylcarbodiimide, diethylstilbestrol, or orthovanadate increased sucrose efflux. These data indicate that sucrose efflux from soybean leaf discs is not a result of simple leakage but is a regulated process.     

Diurnal Changes in the Sugar and Organic Anion Concentrations in Red Beet Leaves

Marked diurnal fluctuations in the concentrations of ethanolsoluble sugars and organic anions occurred in red beet leaves.These fluctuations were related to solar radiation and air temperature.Leaves from four plots which had received different manurialtreatments contained significantly different mean sugar andanion concentrations, but the patterns of the diurnal fluctuationswere not affected by the manurial treatments. The results indicated a daily production of photosynthate equalto about 19 per cent per day (leaf-weight basis), compared tothe net assimilation rate of 17 per cent per day as estimatedfor similar plants from dry-weight increase. From the results no evidence can be adduced to support the hypothesisthat sugar accumulated in the leaves to an extent which inhibitedphotosynthesis.     

渗透胁迫对烤烟体内钾素累积的影响

以烤烟K326为材料,研究了PEG渗透胁迫对烤烟体内钾素累积的影响。结果表明：旺长期内短时间低渗透胁迫强度刺激了烟株中K^ 的累积,胁迫时间延长或胁迫强度增加时,K^ 累积速率逐渐降低,甚至导致体内钾的损失。钾累积量的这种变化与渗透胁迫导致的根细胞膜结构的破坏及质膜选择透过性功能的降低有关。胁迫程度较高或时间较长时,细胞膜的相对透性增加,导致根中的K^ 大量外流。这说明短时间的低渗透胁迫不会明显降低烟叶的含钾量,但烤烟对干旱的御胁迫性及胁变修复性较小,烤烟生育期内特别是对水分变化最敏感的旺长期应有合适的水分供应,以提高烟根的吸钾速率、降低钾的外流损失。     

Membrane homoeostasis and multidrug resistance in yeast

The development of MDR (multidrug resistance) in yeast is due to a number of mechanisms. The most documented mechanism is enhanced extrusion of drugs mediated by efflux pump proteins belonging to either the ABC (ATP-binding cassette) superfamily or MFS (major facilitator superfamily). These drug-efflux pump proteins are localized on the plasma membrane, and the milieu therein affects their proper functioning. Several recent studies demonstrate that fluctuations in membrane lipid composition affect the localization and proper functioning of the MDR efflux pump proteins. Interestingly, the efflux pumps of the ABC superfamily are particularly susceptible to imbalances in membrane-raft lipid constituents. This review focuses on the importance of the membrane environment in functioning of the drug-efflux pumps and explores a correlation between MDR and membrane lipid homoeostasis.     

Effects of Age on Sodium Fluxes in Primary Bean Leaves

The effects of age on sodium fluxes in primary-leaf sections from control and decapitated bean plants were determined. It was assumed that at high external salt concentrations the measurements represent mainly fluxes through the tonoplast, and that in brief efflux experiment subsequent to free-space exchange efflux from the cytoplasma is essentially measured. Net- and influxes to the vacuoles increase during the period of leaf expansion and net chlorophyll synthesis. Both fluxes and amount of chlorophyll decrease rapidly in senescing leaves. The exchangeability of previously absorbed sodium also increased in senescing leaves. Decapitation delayed senescence and very much reduced the decreases in net flux and influx, and the exchangeability of sodium. The results are discussed in relation to solutes redistribution in the plant.