碱胁迫对黑麦草幼苗根系活性氧代谢和渗透溶质积累的影响

为了探讨牧草对碱胁迫的耐受程度,采用营养液砂培方法,研究了不同浓度NaHCO3（0、50、100、150和200 mmol·L^-1）胁迫对黑麦草幼苗根系生长、活性氧代谢和渗透溶质积累的影响。结果表明：NaHCO3胁迫显著抑制黑麦草幼苗根系的生长,其抑制程度随胁迫浓度提高而增强,黑麦草可耐受的最高NaHCO₃浓度约为150 mmol·L^-1。随着NaHCO₃胁迫浓度的增加,黑麦草根中超氧阴离子(O^-·₂)、过氧化氢(H₂O₂)和丙二醛(MDA)含量明显上升,超氧化物歧化酶(SOD)活性和谷胱甘肽(GSH)含量显著下降,过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)活性及抗坏血酸(ASA)含量先升后降。黑麦草根中Na⁺含量随NaHCO₃浓度增大而增加,K⁺含量和K⁺/Na⁺比降低,可溶性糖含量先升后降,脯氨酸含量则先降后升,游离氨基酸含量呈先升后降再升高变化。表明碱胁迫导致的活性氧代谢失调和Na⁺、K⁺失衡及积累有机溶质进行渗透调节时更多能量的消耗可能是黑麦草根系生长受抑的重要因素。     

分布的影响

采用营养液水培,以2个耐盐性不同的黄瓜品种为材料,研究了不同浓度NaCl处理下幼苗植株体内K⁺、Na⁺和Cl^-在器官间的区域化分布及其吸收和运输特性的变化。结果表明：NaCl胁迫下,黄瓜植株体内K⁺含量下降,Na⁺和Cl^-含量升高,变化幅度随NaCl浓度的升高而增大;不同器官间,茎中Na⁺和Cl^-含量最高,上位叶中Na⁺和Cl^-含量最低、K⁺含量下降幅度最小。与耐盐性较弱的“津春2号”相比,耐盐性较强的“长春密刺”根向茎运输的S_K,Na值较高,根系对Na⁺的截留作用较强,茎向上位叶运输的S_{K ,Na}和S_Cl,Na值均较高,叶片中K⁺含量下降幅度较小,K/Na和Cl/Na比值均较高,功能叶中盐分离子尤其是Na+积累较少,植株生物量较高。说明根系对Na⁺的截留能力较强且向上位叶运输Na⁺的选择性较低,是“长春密刺”耐盐性较强的主要原因之一。     

氯化钠胁迫对不同品种南瓜幼苗阳离子含量的影响

选择19个不同类型南瓜品种,研究了300 mmol·L^-1 NaCl胁迫条件下,幼苗地上部和根系Na⁺、K⁺、Ca²⁺含量、Na⁺/K⁺、Na⁺/Ca²⁺、钠-钾和钠-钙运输选择性系数(S_Na⁺,K⁺和S_Na⁺,Ca²⁺值)的变化.结果表明：NaCl胁迫处理8 d后,不同品种南瓜幼苗Na⁺含量均明显增加,而K⁺含量下降,离子平衡被打破.青栗（Q₁）南瓜幼苗根系Na⁺含量、地上部Na⁺/K⁺、Na⁺/Ca²⁺、S_Na⁺,K⁺和S_Na⁺,Ca²⁺值均明显高于黑蜜南瓜（H₂）和黑籽南瓜（H₃）.不同品种南瓜幼苗体内Na⁺含量、地上部Na⁺/K⁺和Na⁺/Ca²⁺、S_Na⁺,K⁺和S_Na⁺,Ca²⁺值变化趋势与NaCI胁迫下不同品种南瓜幼苗盐害指数的结果基本一致,进一步验证了Q₁耐盐性强与NaCl胁迫下地上部Na⁺/K⁺、Na⁺/Ca²⁺、S_Na⁺,K⁺和S_Na⁺,Ca²⁺值较低以及K⁺、Ca²⁺含量较高有关;而H₂和H₃对盐敏感与NaCl胁迫下地上部Na⁺/K⁺、Na⁺/Ca²⁺、S_Na⁺,K⁺和S_Na⁺,Ca²⁺值较高,以及K⁺、Ca²⁺含量较低有关.     

盐胁迫下构树幼苗各器官中K+、Ca2+、Na+和Cl-含量分布及吸收特征

将当年生构树幼苗置于含有不同浓度（04、1、2、3、4 g·kg^-1）NaCl的土壤中,研究其生物量积累、叶片细胞质膜透性和K⁺、Ca²⁺、Na⁺、Cl^-等离子的吸收、分布及运输,并观察盐害症状.结果表明：构树幼苗的叶片质膜透性随着NaCl浓度的增加和胁迫时间的延长而升高,根冠比随NaCl浓度的升高而增加,大于3 g·kg^-1的土壤盐胁迫对构树叶片的质膜透性及植株的生物量积累影响显著.构树幼苗各器官中Na⁺和Cl^-含量随土壤NaCl浓度升高而显著增加,K⁺和Ca²⁺则随之降低,叶片各离子含量均明显高于根和茎.说明盐胁迫影响根系对K⁺和Ca²⁺的吸收,并抑制了它们向地上部分的选择性运输,使叶和茎的K⁺和Ca²⁺含量下降.构树通过吸收积累Na⁺和Cl^-抵御土壤盐分带来的渗透胁迫,但过量的Na⁺和Cl^-积累会造成单盐毒害.作为抗盐性较高的非盐生植物,构树地上部分的拒盐作用不显著.     

外源NO对盐胁迫下黑麦草幼苗根生长抑制和氧化损伤的缓解效应

研究了外源一氧化氮(nitric oxide, NO)对盐胁迫下黑麦草幼苗根生长和氧化损伤的影响。结果表明,5~100 μmol·L^-1的NO供体硝普钠(sodium nitroprusside, SNP)处理显著减轻100mmol·L^-1 NaCl胁迫对黑麦草幼苗根生长的抑制效应,其中50 μmol·L^-1的SNP效果最明显,150 μmol·L^-1以上的SNP处理则抑制根的生长。50 μmol·L^-1 SNP处理提高了100 mmol·L^-1 NaCl胁迫下黑麦草幼苗根组织中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)及液泡膜上H⁺-ATP酶(H⁺-ATPase)和H⁺焦磷酸酶(H⁺-PPase)的活性,使谷胱甘肽(GSH)、抗坏血酸(ASA)和脯氨酸含量及K⁺/Na⁺、(Spd+Spm)/Put比值和根干物质积累量增加,超氧阴离子(O^-₂)、H₂O₂和丙二醛(MDA)含量降低,而1mmol·L^-1NO清除剂PTIO和1 μmol·L^-1 NaNO₂处理(对照)的效果则不明显。由此推断,NO通过提高根组织的抗氧化和渗透调节能力,促进根系对K⁺的选择性吸收及Put向Spd和Spm的转化,降低Na⁺的吸收并加强在液泡中的区隔化缓解盐胁迫对黑麦草幼苗根生长的抑制和膜脂过氧化损伤。     

吸收与分配规律的初步研究

选择苗期耐盐性较强的水稻(Oryza sativa)品种（株系）‘AB52’、‘02402’和‘02435’及敏感品种‘日本晴’, 在网室周转箱内,设置5 000和8 000 mg•L^－1 NaCl两种盐处理,以清水为对照, 研究盐胁迫下苗期水稻植株不同部位Na⁺和K⁺的吸收和分配与品种耐盐性的关系。结果表明,盐胁迫下,株高、绿叶干重和绿叶面积下降,绿叶中的水分含量降低,但茎鞘中的水分含量有所上升。5 000 mg•L^－1 NaCl胁迫处理10 d,耐盐品种所受的生长影响和叶片伤害程度低于敏感品种,但8 000 mg•L^－1 NaCl胁迫处理下品种间差异变小。盐胁迫下,水稻植株吸收 Na⁺和置换出K⁺,但不同器官部位中Na⁺和K⁺的区域化分布特征明显,各部位的Na⁺含量由低到高依次为绿叶、根、茎鞘和枯叶。下部老叶能优先积累较多Na⁺而枯黄;绿叶吸收Na⁺ 相对较少,维持较低的Na⁺水平,同时保持较高且稳定的K⁺含量;植株茎鞘通过选择性吸收大量Na⁺ 和置换出一部分K⁺到叶片中,保持绿叶较稳定的K⁺含量和相对较低的Na⁺含量,维持较高的K⁺ /Na⁺比,从而使植株少受盐害。敏感品种‘日本晴’在盐胁迫下绿叶中的Na⁺含量相对较高,且 5 000 mg●L^－1 NaCl胁迫下绿叶Na⁺含量已接近高值,与在8 000 mg●L^－1 NaCl胁迫下差异不大, 而耐盐品种绿叶吸收较少的Na⁺。另一方面,耐盐品种茎鞘的含K⁺相对较高,在盐胁迫下能吸收容纳较多的Na⁺,而绿叶中K⁺/Na⁺比较高。可以认为,绿叶的K⁺/Na⁺比可作为一个衡量耐盐性的相对指标。     

镧对硝酸盐胁迫下黄瓜幼苗生长及叶片抗氧化酶活性的影响

采用水培方法研究了LaCl₃对硝酸盐胁迫下黄瓜幼苗生长及叶片抗氧化酶活性的影响.结果表明：硝酸盐胁迫显著抑制了黄瓜幼苗的生长,尤其是地上部生长.在处理7 d时,与对照相比,硝酸盐胁迫下的黄瓜单株地上部鲜质量降低了12.77 g,叶片超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性升高,而抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)活性显著降低.外加低浓度（0.05 mmol·L^-1）LaCl₃可以显著提高硝酸盐胁迫下黄瓜幼苗单株鲜质量,比硝酸盐胁迫下提高了35%左右,还提高了叶片热稳定蛋白含量及SOD、POD、CAT、APX、DHAR、GR活性,降低了电解质渗漏率及丙二醛(MDA)含量,在一定程度上缓解了硝酸盐对黄瓜幼苗生长的抑制作用.但外加高浓度LaCl₃（0.5 mmol·L^-1）长期处理对黄瓜硝酸盐胁迫的缓解效果并不明显.因此外加一定浓度的LaCl₃可通过提高黄瓜抗氧化酶活性及热稳定蛋白含量来缓解硝酸盐胁迫.     

外源亚精胺和精胺对NaHCO3胁迫下南蛇藤抗氧化系统的影响

研究了叶面喷施亚精胺和精胺对NaHCO₃胁迫下南蛇藤叶片抗氧化系统的影响.结果表明：外源亚精胺和精胺处理使NaHCO₃胁迫下南蛇藤叶片O₂^-·产生速率、H₂O₂、丙二醛(MDA)含量和电解质外渗率显著降低(P<0.05).亚精胺处理明显提高了盐胁迫下超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)等抗氧化酶的活性,以及还原型谷胱甘肽(GSH)、类胡萝卜素(CAR)和脯氨酸(Pro)等抗氧化剂的含量,但对还原型抗坏血酸(AsA)含量没有作用;精胺处理明显提高NaHCO₃胁迫下POD和APX的活性以及GSH、CAR和Pro的含量,但对SOD和AsA含量影响不显著,甚至引起CAT活性明显降低.亚精胺和精胺处理明显改善了NaHCO₃胁迫下南蛇藤的生长.外源亚精胺和精胺可以改善NaHCO₃胁迫下南蛇藤叶片的膜保护功能,减少叶片中活性氧的积累,从而提高南蛇藤对NaHCO₃胁迫的抗性.     

不同浓度NaCl和Na2CO3处理对菊芋幼苗光合及叶绿素荧光的影响

 以砂培菊芋(Helianthus tuberosus)幼苗作为试验材料,分别进行不同浓度NaCl (50、 100、150、200、250 mmol&;#8226;L^－1)和Na₂CO₃ (25、50、 75、100、125 mmol&;#8226;L^－1)胁迫处理,以1/2全营养液作为对照,处理7 d后研究NaCl和Na₂CO₃胁迫处理对菊芋幼苗叶片光合作用及叶绿素动力学 参数的影响。结果表明：1)在NaCl处理下,当浓度小于150 mmol&;#8226;L^－1时,增加了菊芋的叶绿素含量、净光合速率(Net photosynthetic rate, P_n)和气孔导度(Stomatal conductivity, G_s),对荧光参数PSⅡ的电子传递情况( F_m/F_o)、PSⅡ原初光能转换效率(F_v/F_m)、PSⅡ量子效率 (Actual quantum yield of PSⅡ under actinic irradiation,φPSⅡ)和光化学猝灭系数(Photochemical quenching coefficient, qP)和非 光化学猝灭系 数(Non-photochemical quenching coefficient, NPQ)没有显著影响,随着浓度的增加,各项生理指标与对照相比除了NPQ显著 增加,其余均显著降低;2)在Na₂CO₃胁迫处理下,随着Na₂CO₃浓度的增加,与对照相比菊芋幼苗叶绿素含量、P_n、G_s以及叶绿素a荧光诱导动力 学参数F_m/F_o、F_v/F_m、φPSⅡ和qP均显著降低,NPQ显著增加;3)就NaCl和Na₂CO₃相比而言,在相同Na⁺浓度情况下,处于Na₂CO₃胁迫下的菊芋 幼苗的叶绿素含量、P_n、G_s以及叶绿素a荧光诱导动力学参数F_m/F_o、F_v/F_m、φPSⅡ和qP下降幅度和NPQ的增加幅度均显著大于NaCl,这说明 NaCl和Na₂CO₃胁迫均对菊芋幼苗造成不同程度的伤害,但在相同Na⁺浓度情况下,Na₂CO₃的伤害程度大于NaCl。由此说明菊芋对盐的忍耐程度高 于碱。     

等渗盐分、干旱胁迫下冬小麦叶片部分渗透调节物质的动态变化

分别以PEG-6000、NaCl模拟干旱胁迫及盐胁迫,采用水培方法研究了抗旱耐盐冬小麦沧-6001在干旱胁迫、盐胁迫条件下叶片可溶性糖、脯氨酸和可溶性蛋白质含量的动态变化以及Na⁺、K⁺在地上部和根系的分布。结果表明可溶性糖和可溶性蛋白变化趋势相似,其含量随干旱胁迫或盐胁迫时间延长而增加,但在胁迫处理后期下降,并且随胁迫强度增加,二者出现下降时间提前;脯氨酸在干旱胁迫条件下快速积累达到峰值后下降但在胁迫处理后期再次增加,在盐胁迫条件下,随胁迫强度的增加和胁迫时间的延长而增加;Na⁺在干旱胁迫下随胁迫程度增加而下降,盐胁迫条件下随胁迫程度的增加而增加,K⁺在干旱胁迫或盐胁迫下均随胁迫程度的增加而下降,且在根系中下降的速度大于地上部。     

燕麦对松嫩草地三种主要盐分胁迫的生理适应策略

为明确燕麦幼苗对松嫩盐碱草地3种主要盐分Na Cl、Na HCO_3和Na_2CO_3的适应机制,设定不同浓度梯度(48—144 mmol/L)的胁迫处理液,测定燕麦幼苗的生长与生理指标变化。结果表明,尽管试验设定的Na Cl浓度并不影响幼苗的存活率,但在各组胁迫处理下,随着浓度的增加,燕麦幼苗的分蘖数、植株高度、茎叶与根系的生物量均呈下降趋势,下降幅度为Na_2CO_3Na HCO_3Na Cl。另外,与Na Cl胁迫相比,Na_2CO_3与Na HCO_3胁迫下茎叶与根中积累了更多的有毒Na~+,同时K~+下降幅度也更大,并且根系中含有更高的Na~+与更低的K~+以及更高的Na~+/K~+。在Na Cl胁迫下,燕麦幼苗积累大量的无机Cl~-和脯氨酸来维持细胞内的渗透与离子平衡,而Na HCO_3与Na_2CO_3胁迫造成了燕麦幼苗体内阴离子的亏缺,此时幼苗主要通过积累大量的有机酸和更多的脯氨酸来维持渗透与离子平衡。上述结果表明,碱性盐Na_2CO_3与Na HCO_3对植物的胁迫伤害程度大于中性盐Na Cl,并且Na_2CO_3的毒害效应最强,而燕麦幼苗对不同的盐分胁迫伤害也有会产生不同的生理适应策略。     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

The Role of the Stem in the Partitioning of Na+ and K+ in Salt-Treated Barley

Hordeum vulgare cv. California Mariout was grown for 50 d insand culture at 100 mol m^–3 NaCl. Xylem sap was collectedthrough incisions at the base of individual leaves along thestem axis by applying pressure to the root system. K⁺ concentrationsin the xylem sap reaching individual leaves increased towardsthe apex, while concentrations of Na⁺, NO₃^–, and Cl^–declined. Phloem exudate was obtained by collecting into Li₂EDTAfrom the base of excised leaves. K/Na ratios of phloem exudatesincreased from older to younger leaves. K/Na ratios in xylem sap and phloem exudate were combined withchanges in ion content between two harvests (38 and 45 d aftergermination) and the direction of phloem export from individualleaves, to construct an empirical model of K⁺ and Na⁺ net flowswithin the xylem and phloem of the whole plant. This model indicatesthat in old leaves, phloem export of K⁺ greatly exceeded xylemimport. In contrast, Na⁺ export was small compared to importand Na⁺ once imported was retained within the leaf. The direction of export strongly depended on leaf age. Old,basal leaves preferentially supplied the root, and most of theK⁺ retranslocated to the roots was transferred to the xylemand subsequently became available to the shoot. Upper leavesexported to the apex. Young organs were supplied by xylem andphloem, with the xylem preferentially delivering Na⁺ , and thephloem most of the K⁺ . For the young ear, which was still coveredby the sheath of the flag leaf, our calculation predicts phloemimport of ions to such an extent that the surplus must havebeen removed by an outward flow in the xylem. Within the culm,indications for specific transfers of K⁺ and Na⁺ between xylemand phloem and release or absorption of these ions by the tissuewere obtained. The sum of these processes in stem internodes and leaves ledto a non-uniform distribution of Na⁺ and K⁺ within the shoot,Na⁺ being retained in old leaves and basal stem internodes,and K⁺ being available for growth and expansion of young tissues. Key words: Hordeum vulgare L., K⁺, Na⁺, stem, salt stress     

Na+, K+ and Cl- in Xylem Sap Flowing to Shoots of NaCl-Treated Barley

Munns, R. 1985. Na⁺, K⁺ and Cl^– in xylem sap flowing toshoots of NaCl-treated barley.—J. exp. Bot. 36: 1032–1042. Na⁺, Cl^– and K⁺ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m^–3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 5–10 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na⁺]_x, was only 4.0 mol m^–3 at external [NaCl] of25–150 mol m^–3, and increased to 7.0 mol m^–3at 200 mol m^–3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25–150 mol m^–3 externalNaCl and indicates little change even at 200 mol m^-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na⁺ or Cl^–. The fluxes of Na⁺, Cl^– and K^– increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K⁺ increased even when [K⁺]_x wasgreater than external [K⁺], indicating that membrane transportprocesses modify the K⁺ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na⁺, K⁺, Cl^– fluxes, salinity, barley     

盐胁迫对杂交酸模叶片光合活性的抑制作用

以杂交酸模(Rumex K-1)为试材,研究了不同浓度(100～300 mmol·L^-1) KCl和NaCl胁迫对杂交酸模幼苗叶片光合活性及渗透调节的影响.结果表明：200 mmol·L^-1浓度的NaCl对杂交酸模幼苗叶片光合活性的抑制作用大于KCl;当浓度增大到300 mmol·L^-1时,KCl对杂交酸模叶片光合活性的抑制作用显著大于NaCl.300 mmol·L^-1 KCl和NaCl处理植株的叶片水势分别为-0.93 MPa和-1.05 MPa,渗透势分别为-1.43 MPa和-1.10 MPa,说明KCl对杂交酸模植株过多的伤害不是渗透胁迫造成的;经过300 mmol·L^-1KCl胁迫后,杂交酸模叶片中Na⁺含量急剧降到对照植株的11.4％,而补充25 mmol·L^-1 NaCl可以明显缓解KCl对杂交酸模光合活性的伤害,说明Na⁺的亏缺和高浓度K⁺的积聚可能是导致高浓度KCl对杂交酸模光合活性的伤害比NaCl更严重的主要原因.     

Shoot-Dependent Regulation of Sodium and Potassium Fluxes in Roots of Whole Barley Seedlings

Unidirectional fluxes and the cytoplasmic and vacuolar contentsof potassium and sodium in root cells of intact barley seedlings(Hordeum vulgare L., cv. Villa) were determined by use of compartmentalanalysis. In addition, the net vacuolar accumulation J_cv andthe xylem transport ø_cx of K⁺ and Na⁺ were measured.Both of these data were needed for the evaluation of the effluxdata. Fluxes and compartmental contents of K⁺ and Na⁺ were comparableto data obtained with excised roots. The effect of the shoot-to-rootratio—as varied by partial excision of the seedlings seminalroots—on the fluxes and contents was investigated. Highershoot-to-root ratios induced an increase in xylem transport,in plasmalemma influx, and also in the cytoplasmic content ofK⁺ and Na⁺. With potassium the plasmalemma efflux was almostunaltered while the tonoplast fluxes and vacuolar content weredecreased (in presence of Na⁺). With sodium, on the other hand,the plasmalemma efflux and the tonoplast fluxes were also increasedin the plants having one root and a high shoot-to-root ratio.These changes occurred even under conditions of low humidity,when transpiration was low and guttation occurred. The latterwas also increased at the high shoot-to-root ratio. The observedchanges could be due to a relieved feedback control of ion fluxesby the shoot and mediated in part by a relatively higher supplyof photosynthates in the plants having one root In addition,hormonal signals were suggested to participate. In particulara possibly decreased level of cytokinins in the plants havingonly one root could contribute to the signal. The observed changesappear to be responses of the plant to an alteration that canoccur under natural conditions when the root system is damaged.     

The intercellular distribution of vacuolar solutes in the epidermis and mesophyll of barley leaves changes in response to NaCl

Concentrations of inorganic and organic solutes were measuredin sap extracted from individual mesophyll and epidermal cellsof the third leaf of barley. During the development of the thirdleaf plants were grown in various salt solutions (NaCl; 2, 50,100, and 150 mM, KCI; 100 mM or KNO₃; 100 mM). Leaves were analysed2–4 d after full expansion. Cell-sap was extracted usinga modified pressure probe and analysed for its osmolality, concentrationsof P, Na⁺ K⁺ Ca²⁺, and Cl^– and, in some cases, of nitrate,hexoses and total amino acids. Salt treatment caused differentialchanges in the concentrations of solutes in mesophyll and epidermalcells, but did not affect the basic pattern of solute compartmentationbetween these tissues. Calcium was found at osmotically significantconcentrations only in the epidermis, whereas P and organicsolutes were almost exclusively found in the mesophyll. Chlorideand Na⁺ accumulated preferentially in the epidermis, althoughmesophyll concentrations also increased considerably. At 150mM external NaCl, mesophyll cells contained 302 mM Na and 167mM Cl^–, compared to 29 mM Na⁺ and 16 mM Cl^– in thecontrol. Mesophyll Cl^– levels were even higher in the100 mM KCl treatment (216 mM) where mesophyll and epidermalK⁺ accumulated to 424 and 491 mM, respectively. These huge increasesin mesophyll Na⁺ Cl^– and K⁺ were not associated with abreakdown in leaf performance since net rates of photosynthesisdecreased only by less than 20%. Under control (2 mM NaCl) conditions,solutes followed patterned gradients between the various epidermalcell types. The extent of these gradients changed with leafage. During 50 mM NaCl treatment, gradients in Cl^–, nitrateand malate concentrations progressively disappeared, with malateconcentrations approaching zero. Potassium and Na⁺ exhibitedaltered distribution profiles, whereas Ca²⁺ distribution wasunaffected. NaCl-dependent increases in osmolalities differedbetween cells. Exposure of plants to 150 mM NaCl caused qualitativelysimilar changes in both epidermal solute and osmolality profiles,although absolute values differed from those at 50 mM NaCl.In particular, epidermal Cl^– and Na⁺ increased to about500 mM and K⁺ disappeared (<<5 mM) from the vacuole ofcertain epidermal cell types completely. Key words: Barley leaf epidermis, mesophyll, salt stress, single-cell analysis, vacuolar solutes