糙草对水分胁迫的生理适应性研究

用PEG-6000模拟水分胁迫处理糙草(Asperugo procumbensL.)幼苗,测定生理指标,研究其对水分胁迫的生理适应性。结果表明:5%PEG和20%PEG胁迫处理1d后,叶片RWC、CHL含量,MDA和膜相对透性及脯氨酸含量变化不大,抗氧化酶活性升高;5%PEG和20%PEG胁迫处理5d后叶片RWC下降为对照65%、43%,CHL含量下降为对照的53%、46%,MDA和膜相对透性及脯氨酸含量显著升高,抗氧化酶活性显著降低,并低于处理前水平。实验表明糙草幼苗在水分胁迫下叶片持水力较低,在短时间水分胁迫下可通过抗氧化酶之间的相互协调在一定时期能维持活性氧代谢平衡,并阻止或减弱膜脂过氧化的伤害,但随着处理时间的延长,抗氧化酶活性显著降低,膜脂过氧化作用增加,且叶绿素合成遭到破坏。     

盐分和水分胁迫对芦荟幼苗渗透调节和渗调物质积累的影响

用不同浓度NaCl和等渗聚乙二醇(PEG 6000)处理芦荟(Aloe vera L.)幼苗,10 d后测定叶片相对生长速率和厚度、叶片中主要有机溶质、无机离子含量及渗透调节能力.结果表明,-0.44、-0.88 MPa NaCl和PEG处理使芦荟叶片的相对生长速率和叶片厚度明显下降,且盐胁迫对幼苗生长的抑制和叶片含水量降低的效应明显高于等渗的水分胁迫,其叶片渗透调节能力随处理渗透势的降低而增加, -0.88 MPa PEG胁迫的芦荟幼苗的渗透调节能力高于等渗盐分胁迫.在主要渗透调节物质可溶性糖、有机酸、K 、Ca2 和Cl-中,-0.88 MPa PEG处理下含量比相同渗透势的NaCl处理下显著增加的是有机溶质,因此推断有机溶质含量高是PEG胁迫下渗透调节能力较强的主要因素.     

NaCl与干旱胁迫对银沙槐幼苗渗透调节物质含量的影响

以银沙槐幼苗为材料,采用盆栽试验研究不同程度NaCl与干旱胁迫对其叶片渗透调节物质含量的影响,以探讨银沙槐幼苗对NaCl与干旱胁迫的适应性.结果显示,随着单一干旱、盐分及其交叉胁迫程度的增加,幼苗的MDA含量呈上升趋势;幼苗的脯氨酸和可溶性糖含量基本上随NaCl与干旱胁迫程度的加剧呈逐渐上升趋势,在各胁迫水平下均显著高于对照(P<0.05),且在各种重度胁迫处理下均维持在较高水平;幼苗的可溶性蛋白含量在重度干旱与不同盐分交叉胁迫下呈下降趋势.研究表明,银沙槐幼苗中渗透调节物质在其抗旱耐盐性上起到了积极的调节作用;幼苗在盐旱交叉胁迫下表现出交叉适应性.     

干旱胁迫对远志种子萌发及幼苗生长和生理特性的影响

以远志(Polygala tenuifolia Willd.)为研究对象,采用不同浓度(2.5%~25%)聚乙二醇(PEG-6000)模拟不同程度的干旱胁迫,探讨干旱胁迫对远志种子萌发及幼苗生理生化特性的影响。结果表明:(1)随着干旱胁迫强度的增加,远志种子的发芽启动时间推迟,发芽率、发芽势、发芽指数和活力指数降低,但种子发芽率在2.5%~15%PEG胁迫下与对照无显著性差异,而在20%PEG胁迫下均显著低于对照,在25%PEG胁迫下种子不能萌发;在干旱胁迫条件下,远志幼苗生物量降低,胚芽生长受到显著抑制,胚根长度则先伸长后缩短。(2)远志幼苗叶绿素含量在2.5%~10%PEG范围内随胁迫强度的增加和时间的延长而持续上升,在15%和20%PEG胁迫下则表现为先上升后下降,在10%PEG胁迫处理第15天时含量最高,为对照的1.34倍。(3)幼苗叶片的游离脯氨酸、可溶性糖和可溶性蛋白含量随PEG胁迫强度的增加和时间的延长而增加,各指标均在20%PEG胁迫处理第15天时含量最高,分别为对照的1.99倍、1.53倍和1.50倍。(4)随着PEG胁迫时间的延长,远志幼苗叶片超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性先上升后下降,并在10%PEG胁迫处理第10天时活性最强;过氧化物酶(POD)活性随着胁迫时间的延长表现出先上升后下降又上升的特性,并在20%PEG胁迫处理第5天时活性最强;叶片丙二醛(MDA)含量在15%和20%PEG胁迫处理下持续上升,在2.5%~10%PEG胁迫范围内先上升后又有所下降。研究发现,远志种子在轻、中度干旱胁迫下仍可正常萌发,而且幼苗能通过调节自身生长、渗透调节物质含量和抗氧化酶活性主动适应干旱环境,对干旱环境表现出较好的适应能力。     

模拟干旱胁迫对枣树幼苗的抗氧化系统和渗透调节的影响

用不同浓度的PEG-6000对抗旱性不同的1年生枣树(Zizyphus jujuba)幼苗进行渗透胁迫处理后,研究了不同抗旱性品种枣树幼苗的抗氧化酶活性和渗透调节物质含量的变化.结果显示,干旱胁迫下3种枣苗叶片的相对含水量(RWC)均降低,丙二醛(MDA)含量和细胞质膜相对透性均增加.在30%PEG胁迫下除骏枣1号的SOD活性降低外,3个品种枣苗在干旱胁迫下SOD和POD活性都增加;狗头枣2号的过氧化氢酶(CAT)活性在胁迫下明显增加,而木枣1号和骏枣1号的CAT活性均随着胁迫程度的增加而逐渐下降;木枣1号和骏枣1号的APX活性随着胁迫程度的增加先增加后降低,而狗头枣2号明显增加.干旱胁迫下,除骏枣1号的脯氨酸(Pro)含量和木枣1号的可溶性糖含量在30%的胁迫水平下降低(P>0.05)外,3种干旱胁迫水平下3个品种枣苗的Pro和可溶性糖含量均增加.总之,干旱胁迫下,枣苗叶片相对含水量、抗氧化酶(SOD、POD、CAT和APX)活性、渗透调节物质Pro和可溶性糖含量均为:狗头枣2号>木枣1号>骏枣1号,而MDA含量和膜透性均为骏枣1号>木枣1号>狗头枣2号,表明3个品种的抗旱性为:狗头枣2号>木枣1号>骏枣1号,研究结果与其品种的实际抗旱性一致.     

土壤水分胁迫对燕麦叶片渗透调节物质含量的影响

以旱棚内盆栽的'内农大莜一号'燕麦品种为材料,测定了其不同水分胁迫下各生育期叶片的脯氨酸、可溶性糖含量和细胞膜相对透性,分析土壤含水量对燕麦叶片渗透调节物质的影响,以明确燕麦不同生育时期的抗旱特性.结果表明:(1)随着土壤相对含水率的下降,燕麦各生育期叶片脯氨酸含量、可溶性糖含量、细胞膜相对透性均呈上升趋势.(2)随着生育期的推进,燕麦叶片脯氨酸含量在30%和45%土壤含水量下呈持续上升趋势,而在含水量 60%、75%、90%处理下则于生育前期上升,灌浆期略有下降;随着生育期的延续,可溶性糖的含量呈先升后降的抛物线型变化,且其最大值随水分胁迫强度增加而提前,含水量 30%和45%处理的最大值均出现在拔节期,含水量60%和75%处理则分别出现在孕穗期和开花期;随着生育期的延续,各处理燕麦叶片的细胞膜相对透性均呈持续上升趋势.可见,水分胁迫能诱导燕麦叶片渗透调节物质的积累,且增幅随着胁迫强度的增加而上升,从而使燕麦表现出较强的抗旱性.     

外源-5氨基乙酰丙酸对干旱胁迫下紫花苜蓿生理特性及次生代谢物含量的影响

为验证喷施不同浓度5-氨基乙酰丙酸(ALA)对紫花苜蓿的响应,该研究以紫花苜蓿品种‘农牧806’为实验材料,用不同浓度(0、5、10、15、20、25 mg·L~(-1))的ALA喷施处理15%聚乙二醇(PEG-6000)模拟干旱胁迫下的紫花苜蓿幼苗,并测定其相关的生理生化指标以及次生代谢物质积累量。结果表明:(1)与对照相比,15%PEG干旱胁迫使得紫花苜蓿叶片中光合色素含量降低,渗透调节物质含量以及抗氧化酶活性增高。(2)与15%PEG处理相比,ALA+15%PEG复配处理下紫花苜蓿幼苗叶片叶绿素a、b和类胡萝卜素以及叶绿素总量分别增加,抗氧化酶(CAT, POD, SOD)活性升高,可溶性蛋白和脯氨酸以及黄酮和皂苷含量上升,丙二醛、H_2O_2和·OH的含量降低,各浓度ALA对15%PEG不同时长胁迫的恢复效果不同。研究发现,叶面喷施适量浓度ALA能够有效提高干旱胁迫下紫花苜蓿叶片抗氧化酶活性以及渗透调节物质、次生代谢物(黄酮、皂苷)含量和光合色素含量,从而增强紫花苜蓿对干旱胁迫的耐受性,并以10 mg·L~(-1)ALA的缓解效果较显著。     

外源茉莉酸甲酯对盐胁迫下小桐子幼苗渗透调节和脯氨酸代谢的影响

以小桐子幼苗为材料,采用人工气候箱内水培试验,设置不同浓度(0、20、40、60、80、100μmol·L^(-1))茉莉酸甲酯(MeJA)和150 mmol·L^(-1)NaCl胁迫处理,分析不同处理条件下小桐子幼苗叶片的组织活力、MDA含量、水势、含水量和叶片渗透调节物质脯氨酸、甜菜碱和可溶性糖的含量,以及脯氨酸代谢关键酶P5CS、OAT和甜菜碱合成关键酶BADH活性和相关基因表达水平,探讨外源茉莉酸甲酯对盐胁迫下小桐子幼苗渗透调节能力的影响及其机制。结果表明:(1)外源MeJA处理可提高盐胁迫下小桐子幼苗叶片的组织活力和叶片含水量,降低小桐子幼苗叶片的MDA含量和水势,且60μmol·L^(-1)浓度处理效果最佳。(2)外源MeJA处理可提高盐胁迫下小桐子幼苗叶片的脯氨酸、甜菜碱和可溶性糖的含量,且60μmol·L^(-1)MeJA处理显著提高了盐胁迫下小桐子幼苗内源茉莉酸、脯氨酸和甜菜碱的含量。(3)60μmol·L^(-1)MeJA也提高了盐胁迫下小桐子BADH、P5CS和OAT的活性,并上调了JcBADH、JcP5CS、JcOAT基因的表达水平,但MeJA降低了脯氨酸降解酶ProDH的活性,下调了JcProDH基因的表达。研究发现,在盐胁迫条件下,外源MeJA通过活化脯氨酸生物合成的谷氨酸和鸟氨酸途径,尤其是鸟氨酸途径,以及抑制脯氨酸降解途径来促进小桐子幼苗脯氨酸的积累,同时MeJA也激活了幼苗体内甜菜碱的生物合成过程,从而强化了盐胁迫下幼苗的渗透调节作用和耐盐性,表明MeJA诱导的渗透调节在小桐子耐盐性形成过程中发挥着重要作用。     

干旱胁迫对不同玉米自交系苗期渗透调节的影响

以5个抗旱性不同的玉米骨干自交系黄早四、掖478、郑58、旱21、齐319为试验材料,对持续水分胁迫下玉米幼苗的叶片相对含水量、渗透调节能力(OA)、脯氨酸含量和可溶性糖含量的变化规律进行了研究。结果表明:随着干旱胁迫的加重,叶片相对含水量呈现下降的趋势,渗透调节能力和可溶性糖含量呈现先上升后又下降的趋势,脯氨酸含量呈现持续上升的趋势;在持续干旱条件下,不同自交系各个指标的变化幅度不同,说明不同种质资源对干旱胁迫的响应方式不同,渗透调节能力也有差异。在水分胁迫的前7d中,渗透调节能力逐渐增加,第7天时达到最大值,OA从大到小的排列顺序为齐319郑58掖478旱21黄早四;但此后,除旱21外,其余4个自交系的OA都随之下降。旱21和齐319以可溶性糖和脯氨酸为主要的渗透调节因子,黄早四则以脯氨酸为主要的渗透调节物质。     

PEG-6000模拟干旱协迫对大蓟叶片生理特性的影响

以大蓟幼苗为试验材料,采用梯度浓度的聚乙二醇(PEG-6000,浓度为5%、10%、15%、20%、25%、30%)模拟干旱胁迫24h、48h和72h,测定大蓟叶片相对含水量(RWC)、丙二醛(MDA)含量、渗透调节物质含量及保护酶活性随胁迫时间的变化,探讨大蓟的耐旱性和抗旱生理机制。结果表明:(1)随干旱胁迫时间的延长和PEG-6000浓度增加,叶片RWC均呈降低趋势,最大降幅为55.86%,MDA含量均大幅度增加,最大增幅为186.21%。(2)随干旱胁迫时间延长,叶片可溶性糖与游离脯氨酸含量在PEG-6000浓度≤10%时逐渐升高,在大于10%时呈先升高后降低的变化趋势;而随PEG浓度增加,可溶性糖与游离脯氨酸含量在各时间点均呈先上升后下降趋势,可溶性糖峰值在处理24h、48h和72h依次出现在PEG浓度为20%、20%和10%时,游离脯氨酸峰值则依次出现在PEG浓度为20%、15%和15%条件下,两指标的最大增幅均出现在胁迫处理48h时PEG浓度分别为20%和15%,且分别为CK的4.7和10.7倍。(3)随PEG浓度增加,叶片保护性酶(SOD、POD和CAT)活性除SOD在24h时呈逐渐升高趋势外,其余时间点下均呈先升高后下降趋势,3种酶最大增幅依次为370.14%、248.91%和118.78%,前二者均出现在胁迫72h、15%PEG浓度下,后者出现在胁迫48h、10%PEG浓度下。研究认为,长时间(72h)、15%PEG-6000浓度胁迫下,大蓟具有较强的渗透调节能力和较高的酶活性,表现出较强的耐旱能力;若超过此胁迫浓度,大蓟渗透调节能力降低,酶活性减弱,含水量持续降低,MDA持续增加,生理代谢受到明显抑制。     

Osmotic Adjustment and Osmotic Constituents in Roots of Mung Bean Seedlings

Osmotic adjustment in roots of mung bean seedlings (Vigna mungo(L.) Hepper) and the effect of cotyledon excision on the osmoticadjustment were investigated. The major osmotic constituentsin roots of intact seedlings were K⁺, Cl^–, free aminoacids and sugars (glucose, fructose and sucrose). All theseintracellular concentrations distinctly increased under osmoticstress and contributed to about 80% of the intracellular osmoticpressure of the root cell sap. Cotyledon excision remarkablysuppressed both the osmotic adjustment and the elongation inroots. However, the effect of cotyledon excision on intracellularK⁺ and Cl^– concentrations in roots was quite small. Twodifferent mechanisms are likely for the osmotic adjustment inroots. One is the K⁺ and Cl^–-dependent osmotic adjustmentwhich is cotyledon-independent, and the other is the osmoticadjustment dependent on the supply of free amino acids and sugarsfrom cotyledons. (Received September 20, 1986; Accepted January 14, 1987)     

Osmotic Properties of Mitochondria

The osmotic behavior of rat liver mitochondria has been studied in a sucrose medium. The mitochondria behave like a two compartment system. One compartment is permeable to sucrose and has a volume of 1.22 µl/(mg mitochondrial dry weight) in a 272 milliosmol sucrose medium; the second, inaccessible to sucrose, has a volume of 0.555 µl/mg dry weight) under the same conditions. Part of the water in the sucrose inaccessible space is apparently not free to participate in osmotic phenomena. This volume is 0.272 µl/(mg dry weight) under the same conditions. It is suggested that the osmotically inactive water corresponds to the water of hydration of the mitochondrial macromolecules. The volume of the remainder of the water in the sucrose inaccessible space depends inversely on the osmolality of the medium, as is to be expected. The volume of water in the sucrose accessible space is constant, independent of the osmolality of the medium, as is the volume of the mitochondrial framework plus the nonvolatile solutes.     

Osmotic relations of nerve fiber

Summary The volumetric elastic modulus of the sheath and the osmotic swelling pressure of the axoplasmic polymer network of the giant axon ofLoligo vulgaris were measured. Evidence was obtained that (1) the elastic modulus of the sheath, (2) the swelling pressure of axoplasm, and (3) theeffective osmotic pressure difference due to mobile solutes determine axonal volume. The contributions of the sheath and the axoplasm were significant because theeffective osmotic pressure due to mobile solutes was a small fraction of thetheoretical bulk osmotic pressure due to these solutes. The giant axon was converted from an imperfect to a near perfect osmometer by minimizing the contribution of the sheath and the axoplasmic gel.The early experiments were undertaken in the Stazione Zoologica, Naples, and the Democritus Nuclear Research Center, Athens, Greece; the more recent experiments were undertaken in facilities provided by Prof. N. Nikolaou, Aegina, Greece.     

Osmotic sensitivity of canine spermatozoa

The objective of this study was to determine osmotic tolerance of canine spermatozoa. The study comprised three experiments: (1) spermatozoa suspended either in an egg yolk-citrate (EYC) extender or in Kenney skim milk extender were exposed to NaCl solutions ranging from 290 to 1500 mOsm; (2) spermatozoa suspended in EYC were exposed to 550 to 1500 mOsm solutions of glucose, galactose, or fructose; and (3) spermatozoa suspended in EYC or glucose-bovine serum albumin (G-BSA) were exposed to 0.6 M (approximately 900 mOsm) or 1.2 M (approximately 1600 mOsm) solutions of glycerol, ethylene glycol (EG), or dimethyl sulfoxide (Me(2)SO). In all experiments, motility and membrane integrity of spermatozoa were assessed after they were diluted into isotonic medium at 37 degrees C. Exposure of canine spermatozoa to solutions of either NaCl or monosaccharides at osmolalities >500 mOsm caused a significant reduction of motility (P<0.01). Motility of spermatozoa was more affected by osmotic stress than their membrane integrity. Osmotic sensitivity of canine spermatozoa was dependent on the type of extender; spermatozoa suspended in the Kenney extender were more resistant to osmotic stress than those suspended in the EYC extender. Despite their sensitivity to exposure to high concentrations of nonpermeating agents, canine spermatozoa were rather resistant to exposure to glycerol and EG. However, Me(2)SO was toxic to canine spermatozoa; motility was substantially reduced after spermatozoa were exposed to 0.6 M Me(2)SO. The type of extender also affected the sensitivity of canine spermatozoa to Me(2)SO; spermatozoa suspended in the EYC extender were more resistant than those suspended in G-BSA. It was concluded that canine spermatozoa are sensitive to osmotic stress, but are tolerant to shrinking and swelling caused by exposure to permeating cryoprotectants.     

Osmotic responses of maize roots

Water and solute relations of excised seminal roots of young maize (Zea mays L) plants, have been measured using the root pressure probe. Upon addition of osmotic solutes to the root medium, biphasic root pressure relaxations were obtained as theoretically expected. The relaxations yielded the hydraulic conductivity Lp _r) the permeability coefficient (P _sr), and the reflection coefficient (σ _sr) of the root. Values of Lp _r in these experiments were by nearly an order of magnitude smaller than Lp _r values obtained from experiments where hydrostatic pressure gradients were used to induce water flows. The value of P _sr was determined for nine different osmotica (electrolytes and nonelectrolytes) which resulted in rather variable values (0.1·10^-8–1.7·10^-8m·s^-1). The reflection coefficient σ _sr of the same solutes ranged between 0.3 and 0.6, i.e. σ _sr was low even for solutes for which cell membranes exhibit a σ _s≈1. Deviations from the theoretically expected biphasic responses occured which may have reflected changes of either P _sr or of active pumping induced by the osmotic change. The absolute values of Lp _r, P _sr, and σ _sr have been critically examined for an underestimation by unstirred layer effecs. The data indicate a considerable apoplasmic component for radial movement of water in the presence of hydrostatic gradients and also some solute flow byppassing root protoplasts. In the presence of osmotic gradients, however, there was a substantial cell-to-cell transport of water. Cutting experiments demonstrated that the hydraulic resistance for the longitudinal movement of water was much smaller than for radial transport except for the apical ends of the segments (length=5 to 20 mm). The differences in Lp _r as well as the low σ _sr values suggest that the simple osmometer model of the root with a single osmotic barrier exhibiting nearly semipermeable properties should be extended for a composite membrane model with hydraulic and osmotic barriers arranged in series and in parallel.