Control of Ion Fluxes in Stomatal Guard Cells

Opening and closing of the stomatal pore is associated with very large changes in K-salt accumulation in stomatal guard cells. This review discusses the ionic relations of guard cells in relation to the general pattern of transport processes in plant cells, in plasmalemma and tonoplast, involving primary active transport of protons, proton-linked secondary active transport, and a number of gated ion channels. The evidence available suggests that the initiation of stomatal opening is regulated through the uptake mechanisms, whereas initiation of stomatal closing is regulated by control of ion efflux at the plasmalemma, and of fluxes to and from the vacuole. In response to a closing signal there are large transient increases in efflux of both Cl^? (or Br^?) and Rb⁺ (K⁺) at the plasmalemma, with also a probable increase in anion flux from vacuole to cytoplasm and decrease in anion flux from cytoplasm to vacuole. A speculative hypothetical sequence of events is discussed, by which the primary response to a closing signal is an increase in Ca²⁺ influx at the plasmalemma, producing depolarisation and increase in cytoplasmic Ca²⁺. The consequent opening of Ca²⁺-sensitive Cl^? channels, and voltage-sensitive K⁺ channels (also Ca²⁺-sensitive?) in the plasmalemma, and of a Ca²⁺-sensitive nonspecific channel in the tonoplast, could produce the flux effects identified by the tracer work; this speculation is also consistent with the Ca²⁺-sensitivity of the response to closing signals and with evidence from patch clamping that such channels exist in at least some plant cells, though not yet all shown in guard cells.     

Effect of Salt Stress on Ion Channel Selective Permeability of Plasmalemma in Sorghum Roots

100 mmol/L, 200 mmol/L and 300 mmol/L NaC1 was used in proper order to treat three-day old seedlings of Sorghum vulgare Pets. The plasma membrane of roots was isolated and purified by aqueous biphasic partition device. The plasmalemma was incorporated into planar bilayer lipid membrane and ion channels were measured by electrical methods. Ion selective permeabilities (PK: PNa) were assayed in asymmetrical solutions containing 100 mmol/L NaC1 in Cis chamber and 100 mmol/L KC1 in Tran with chamber and were calculated from Goldman-Hodgkin-Kaltz equation. PK: PNa was 3.5 in plasmalemma of control roots and 1.5 in plasmalemma of salt stressed roots. It showed that the changes of ion selective permeability was very significant under salt stress. The importance of the change of ion selective permeability is discussed.     

盐胁迫对玉米叶片叶肉细胞生物膜超微结构的影响

研究了NaCl胁迫对玉米叶肉细胞生物膜超微结构的影响. 结果表明：NaCl胁迫破坏了玉米叶片叶肉细胞生物膜的正常结构,50 mmol·L^-1 NaCl处理胁迫下,玉米叶肉细胞核膜,线粒体膜,细胞膜,叶绿体膜,液泡膜都受到不同程度的破坏,叶绿体基粒类囊体膨胀,间质片层空间增大,片层紊乱。100 mmol·L^-1 NaCl处理胁迫下,质膜,液泡膜,线粒体,叶绿体都受到严重的破坏。细胞质膜破坏,破损的叶绿体充斥在细胞间隙中;叶绿体外膜破坏,甚至解体消失,叶肉细胞中充满膜结构,基粒排列方向改变,垛叠层数减少,基粒和基质片层界限模糊不清,有的基粒解体消失,甚至叶绿体完全解体;核膜破坏、解体,核中的染色质高度凝缩;线粒体的数量增多,线粒体膜破坏,脊的数量减少,甚至整个线粒体破损解体;液泡膜破坏;由于各种生物膜的破坏,使细胞内充满许多囊状小泡、多泡体或斑层小体;叶肉细胞发生严重的质壁分离,严重时发生细胞壁断裂;甚至整个细胞溶解。     

高铁血红素对盐胁迫下小麦根部生长受抑的缓解和根尖中离子微域分布的影响

小麦幼苗经不同浓度NaCl处理1 d再转入Hoagland培养液中培养2d后,浓度相对较低(100和200mm01.L-1)的NaCI处理的幼苗根部生长抑制可以恢复,而浓度相对较~i(500 mm01.L-1)的NaCI处理的则不能恢复;预先以高铁血红素(5 pm01.L-1)处理1 d就可以缓解随后200mmol·L-1 NaCI处理引起的小麦根部生长受抑.X射线电子探针检测元素分布的结果表明,高铁血红素还可缓解由NaCI胁迫导致的小麦苗根尖表皮、皮层和中柱细胞中的K 流失,并可提高根系中K /Na 比,从而维持根部的离子稳态.     

Ion Fluxes in 'Isolated' Guard Cells of Commelina communis L.

Ion fluxes have been measured in ‘isolated’ guardcells of Commelina communis L. using ⁸⁶RbCl and K⁸²Br, in epidermalstrips in which all cells other than guard cells have been killedby treatment at low pH. To avoid problems of slow free spaceexchange most fluxes have been measured at pH 3.9, at whichstomata open well in K(Rb) Cl(Br) and are stable for many hours.At pH 3.9 the intracellular ⁸⁶Rb exchanged as a single compartmentwith a half-time of 2–3 h, independent of external concentration(C_o). The influx of ⁸⁶Rb rose with concentration, to a V_maxof about 23 pmol mm^–2 h^–1. The efflux curve of ⁸²Brcould be well fitted by two exponential terms, with half-timesof 38 min (independent of C_o), and 5–35 h (falling withincreasing C_o). Bromide contents of cytoplasm and vacuole (Q_cand Q_v), and fluxes at plasmalemma and tonoplast, were calculatedfrom the efflux kinetics. Over C_o 20–60 mM, as the apertureincreased from 7 µm to 17 µm, the tonoplast flux(0.5–11.5 pmol mm^–2h^–1) was always much lessthan the plasmalemma flux (7–77 pmol mm^–2 h^–1).Q_c and Q_v both increased with aperture. The increase in Q_c of10.3 pmol mm^–2 µm^–1 is adequate to accountfor the osmotic changes required to change the aperture, aspreviously estimated. However, the change in vacuolar contentof only 5.9 pmol mm^–2 µm^–1 is much too smallto account for the osmotic changes required, or to balance thecytoplasmic changes. It appears therefore that increasing KBroutside not only increases the cytoplasmic salt content, andthe Br flux at the tonoplast, but also stimulates the vacuolaraccumulation of some other solute.     

盐与碱胁迫对燕麦离子平衡和有机酸含量的影响

以燕麦品种‘白燕2号’为材料,试验分别设置0、50、100、150、200 mmol/L盐胁迫(NaCl∶Na₂SO₄=5∶1)和碱胁迫(NaHCO₃∶Na₂CO₃=5∶1)处理的温室内盆栽试验,观测燕麦植株生长速率、植株含水率、叶片离子含量及叶片各类有机酸含量,分析不同盐胁迫、碱胁迫对燕麦离子平衡的影响,并比较燕麦对两类胁迫的适应性差异。结果显示：(1)燕麦植株生长速率和植株含水率在低浓度(50和100 mmol/L)盐胁迫下均升高,而高浓度(150和200 mmol/L)盐胁迫下则降低;燕麦植株生长速率和植株含水率均随碱胁迫浓度增加而降低;在相同胁迫浓度下,碱胁迫对植株生长率、植株含水率的影响大于盐胁迫。(2)燕麦叶片K⁺、Ca²⁺、Mg²⁺、H₃PO^-₄、NO^-₃ 含量均随盐、碱浓度升高而降低,而Na⁺、Cl^-、SO^2-₄含量在盐、碱胁迫下均大幅上升;200 mmol/L盐、碱胁迫下,Na⁺ 含量分别较对照增加367.15%和518.41%,Cl^- 含量分别较对照增加785.07%和52.59%,SO^2-₄ 分别较对照增加142.01%和52.86%。(3)200 mmol/L盐、碱胁迫下,有机酸分别较对照增加74.52%和1 232.34%;碱胁迫及高浓度盐胁迫下燕麦叶片的柠檬酸、乌头酸、琥珀酸和苹果酸含量均高于对照,且乌头酸是燕麦响应盐胁迫、碱胁迫的主要有机酸成分,柠檬酸和琥珀酸略有变化,而甲酸、乙酸、乳酸、苹果酸、草酸含量均相对较低。研究表明,碱胁迫对燕麦植株生长速率、植株含水率、叶片离子含量及叶片各类有机酸含量的影响大于盐胁迫;盐胁迫与碱胁迫均引起燕麦叶片阳离子(Na⁺)大量积累,而K⁺、Ca²⁺、Mg²⁺、H₃PO^-₄及NO^-₃吸收受阻;燕麦叶片在盐胁迫下主要通过积累Cl^-调节叶片离子平衡,而碱胁迫下主要通过积累有机酸来调节离子平衡;有机酸是燕麦叶片响应碱胁迫的特异代谢物,其中乌头酸是其有机酸的主要成分。     

氮离子束注入对小麦苗期耐盐性的影响

采用能量为25keV的不同剂量的N 注入新疆春小麦种胚后,研究盐胁迫对小麦幼苗体内生理生化指标的影响。结果表明,在6×1016N /cm2剂量注入新春11号时,盐胁迫后小麦幼苗的SOD活性、脯氨酸含量、可溶性糖含量、可溶性蛋白含量均增加,幼苗生长良好,说明该剂量处理新春11号有利盐胁迫下小麦幼苗的生长。     

Rapid Effects of IAA on Cell Surface Proteins from Intact Carrot Suspension Culture Cells

Suspension cultures of carrot (Daucus carrota L.) which had an absolute requirement for exogenously supplied auxin were grown in medium containing indoleacetic acid (IAA) as the sole auxin source. Putative cell surface proteins were extracted from the intact cells. Resupply of IAA to cultures partially depleted of auxin resulted in rapidly increased activities of three enzyme activities subsequently extracted. Two of the enzyme activities which increased, peroxidase and pectinesterase, have been implicated in the literature as important to cell wall development, structure, and growth. The other enzyme activity which was increased, IAA oxidase, may be involved in the degradation of IAA In vivo. Polypeptides in the extracts were found to increase equally as rapidly as the enzymes in response to IAA as determined with sodium dodecyl sulfate-polyacrylamide electrophoretic gels stained with silver. It is not known whether the changes in enzyme and polypeptide levels in the protein extracts were due to auxin effects on protein synthesis, transport, or extractability.     

小麦耐盐细胞系对盐胁迫的伤害性反应

通过逐级提高ＮａＣｌ浓度的筛选方法,得到了能在１．５％ＮａＣｌ下生长良好的小麦（ＴｒｉｔｉｃｕｍａｅｓｔｉｖｕｍＬ．）耐盐细胞系。在盐分胁迫下,耐盐细胞系含水量的降低幅度小于不耐盐细胞系（对照）,Ｈ２Ｏ２含量和Ｏ－２产生速率的增加幅度也明显小于对照细胞系。同时,膜的相对透性、膜脂过氧化和脱酯化程度的提高幅度也明显低于对照细胞系。表明盐分对小麦细胞系膜的伤害与活性氧介导的膜脂过氧化和脱酯化有关,而耐盐细胞系比对照细胞系表现出较强的抗活性氧伤害的能力。     

小麦耐盐突变体盐胁迫下的蛋白质组分析

首次采用双向电泳的方法分析1％NaCl胁迫72h的一对小麦耐盐(RH8706-49)及敏盐突变体(H8706-34)的蛋白质组。经过MALDI-TOF分析和数据库检索发现两者在H^ -ATP酶β亚基、谷氨酰胺合成酶前体、OEC33和RuBP羧化酶小亚基等5个候选蛋白存在质或量的差异。这5种蛋白均为叶绿体蛋白,它们很可能在盐胁迫下对维持叶绿体及整个细胞的功能起到重要作用。     

Effect of Viral Double-Stranded RNA on Protein Synthesis in Intact Cells

The addition of purified, noninfectious, double-stranded RNA of bovine enterovirus, a picornavirus, to intact cells in culture results in a rapid cessation of cellular polypeptide synthesis. This inhibition is specific for host cell protein synthesis since the translation of picornavirus-specific proteins is not affected by the double-stranded viral RNA.     

Concentrations of Vacuolar Inorganic Ions in Individual Cells of Intact Wheat Leaf Epidermis

A method is described for quantitative determination of themajor inorganic constituents of individual cells of higher plants.The approach utilizes a modified pressure probe to extract samplesof undiluted vacuolar sap from single cells. Subsamples of constantvolume are taken from these sap samples and are freeze-driedon to thin films along with similarly-sized droplets of standards.The films are placed in a scanning electron microscope and elementalcontent of the freeze-dried material is determined by X-raymicroanalysis. The method has been used to compare levels ofa range of ions in two distinct types of epidermal cell froma young wheat leaf and, in association with nanolitre osmometry,was used to assess the relative importance of the inorganicions in the generation of turgor pressure in these cells. Itwas found that the concentrations of the major inorganic ionswithin the vacuole was constant both within and between twoanatomically distinct groups of epidermal cells on a leaf. Key words: Pressure probe, vacuolar ion levels, single cell sampling, wheat     

Ion Fluxes and Short-Circuit Current in Internally Perfused Cells of Valonia ventricosa

Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I _sc) was 97 pEq/cm² sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm² sec) and large net influxes of K (80 pEq/cm² sec) and Cl (50 pEq/cm² sec). Unidirectional K influx was proportional to I _sc, but more than one-half of the I _sc remained unaccounted for. Both the I _sc and PD were partly light-dependent, declining rapidly during the first 1–2 min of darkness. Ouabain (5 x 10^-4 M) had little effect on the influx of Na or K and had no effect on I _inf or PD. Fluid was absorbed at a rate of about 93 pliter/cm² sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared.     

Metabolic Effects on Ion Fluxes in Tolypella intricata

The uptake of C1 ions by cells of Tolypella intricata is greatlyincreased by light, and must be an active process. K ions inthe cells (at 90–110 mM concentration) are in approximateelectrochemical equilibrium with the external solution, butthe K influx is affected (directly or indirectly) by cellularmetabolism. The K influx is increased by light, and the increaseis greater in the presence of C1 than when C1 is removed fromthe solution. K uptake is inhibited by chemicals which alsoinhibit the C1 pump.It is suggested that light increases thepermeability of the plasmalemma to K, but there must also belinks between K and C1 uptake. The possible nature of theselinks is discussed.The internal Na concentration (3–10mM) is considerably below the expected equilibrium concentration,but the Na influx is also very low (and is not increased bylight). The permeability of the plasmalemma to Na is thus verylow, and there can be little active extrusion of Na under normalconditions.     

盐胁迫对不同抗盐性小麦叶片荧光诱导动力学的影响

以不同抗盐性小麦为材料,研究了NaCl胁迫对叶片叶绿素。荧光诱导动力学的影响。指出150 mmol/L NaCl使小麦幼苗生长降低,叶绿素含量下降,同时使光系统Ⅱ的潜在光化学活性和原初光能转化率降低,使光反应受到抑制。     

An Enhancing Effect of Exogenous Mannitol on the Antioxidant Enzyme Activities in Roots of Wheat Under Salt Stress

The role of mannitol as an osmoprotectant, a radical scavenger, a stabilizer of protein and membrane structure, and protector of photosynthesis under abiotic stress has already been well described. In this article we show that mannitol applied exogenously to salt-stressed wheat, which normally cannot synthesize mannitol, improved their salt tolerance by enhancing activities of antioxidant enzymes. Wheat seedlings (3 days old) grown in 100 mM mannitol (corresponding to −0.224 MPa) for 24 h were subjected to 100 mM NaCl treatment for 5 days. The effect of exogenously applied mannitol on the salt tolerance of plants in view of growth, lipid peroxidation levels, and activities of antioxidant enzymes in the roots of salt-sensitive wheat (Triticum aestivum L. cv. Kızıltan-91) plants with or without mannitol was studied. Although root growth decreased under salt stress, this effect could be alleviated by mannitol pretreatment. Peroxidase (POX) and ascorbate peroxidase (APX) activities increased, whereas superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) activities decreased in Kızıltan-91 under salt stress. However, activities of antioxidant enzymes such as SOD, POX, CAT, APX, and GR increased with mannitol pretreatment under salt stress. Although root tissue extracts of salt-stressed wheat plants exhibited only nine different SOD isozyme bands of which two were identified as Cu/Zn-SOD and Mn-SOD, mannitol treatment caused the appearance of 11 different SOD activity bands. On the other hand, five different POX isozyme bands were determined in all treatments. Enhanced peroxidation of lipid membranes under salt stress conditions was reduced by pretreatment with mannitol. We suggest that exogenous application of mannitol could alleviate salt-induced oxidative damage by enhancing antioxidant enzyme activities in the roots of salt-sensitive Kızıltan-91.     

Growth Behaviour of Suspension Cultures of Rice and Transient Expression of Electroporated Gene in Intact Cells

Suspension cultures of Indics (Basmati 370 and Improved Sabarmati) and Japonica (Taipei 309) rice were established from scutellum-derived callus obtained by culture of the mature seeds. The suspension cultures contain groups of small and cytoplasmically rich cells with a Qubling time of 3.6–5.1 days, as measured by Increase In packed cell volume. The suspension cells of Indica rice var Improved Sabarmati were employed to optimize electroporation-mediated delivery of the plasmid pBl 221 having β-glucuronidase gene under the control of eukaryotic expression signals. GUS activity was determined both fluorometrically and hisotchemlcally. Maximum expression was obtained when cells were electroporated at 600 V cm^-1 with capacitance selected at 400 μF.