嫁接对盐胁迫下西瓜幼苗体内离子和内源激素含量与分布的影响

以小型西瓜‘秀丽’为接穗、耐盐砧木瓠瓜‘超丰抗生王’为砧木,以自根嫁接苗为参照,分析了砧木嫁接对NaCl胁迫下西瓜幼苗根、茎、叶中离子和内源激素含量的影响。结果表明:(1)盐胁迫下,自根嫁接苗Na+主要积累在地上部,K+含量和K+/Na+比下降幅度大;砧木嫁接苗大部分Na+积累在根系中,K+含量和K+/Na+比下降幅度小且在不同部位皆高于自根嫁接苗。(2)盐胁迫下,自根嫁接苗吲哚-3-乙酸(IAA)以及玉米素和玉米核苷的总量(Z+ZR)在根系和接穗茎中显著增加,在叶片中明显下降,赤霉素(GA3)含量在不同部位保持不变或明显增加;而砧木嫁接苗不同部位IAA和(Z+ZR)的含量均显著增加,GA3含量在不同部位保持不变或明显下降。(3)盐胁迫下,两种嫁接组合根系和茎中脱落酸(ABA)含量均明显下降,叶片中ABA含量则显著增加。(4)盐胁迫下,自根嫁接苗和砧木嫁接苗根系和接穗茎中IAA/(Z+ZR)的比值均明显上升,叶片中明显下降,但砧木嫁接苗上升和下降幅度均远大于自根嫁接苗。研究表明,瓠瓜根系对进入根系的Na+具有截留作用;采用瓠瓜砧木嫁接可有效防止Na+在西瓜接穗地上部尤其是在叶片中的大量累积,从而防止离子毒害的发生;瓠瓜砧木嫁接植株体内具有较高的K+含量和K+/Na+比,可有效维持盐胁迫下西瓜嫁接植株体内的离子稳态;瓠瓜砧木嫁接植株体内具有较高的IAA和(Z+ZR)含量,IAA/(Z+ZR)比值较高,对提高西瓜嫁接植株盐胁迫耐性起到了积极的作用。     

盐生植物盐爪爪的耐盐生理特性探讨

当前土壤盐渍化日益严重,是限制植物生长的一个主要环境因子,然而在盐碱自然环境中生长着许多耐盐植物,为更好地了解盐生植物的耐盐机理,该文从无机离子Na+,K+,Ca2+含量、脯氨酸水平、水势变化、丙二醛含量和盐胁迫的表型等生理参数以及半定量RT-PCR检测脯氨酸合成关键酶基因(P5CS)的表达规律等方面探讨盐胁迫下盐爪爪的耐盐特性。结果表明:(1)随着盐浓度的升高,Na+在根和肉质化的叶中显著地富集,且叶中积累的Na+比根中更多;(2)在盐胁迫条件下,随着盐浓度的增加,脯氨酸的含量和脯氨酸合成关键酶基因的表达显著地增强;(3)Na+和脯氨酸是植物有效的渗透调节剂,可使处于低水势的植物细胞仍能从细胞外高浓度的盐溶液中吸收水分;(4)在0和700 mmol·L-1Na Cl处理下,盐爪爪肉质化叶中丙二醛的含量较其它处理高,这表明植物在这两个处理下可能受到了氧化胁迫;(5)从盐胁迫3个月的生长表型来看,低盐环境中生长的盐爪爪植株的生物量更多,肉质化的叶嫩且绿。综上所述,结合对野外生境的调查和实验室长期的盐胁迫表型结果表明盐爪爪的生长是需盐的,相对低的盐浓度环境对盐爪爪的生长是顺境,而无盐或高浓度盐环境对于盐爪爪的生长来说都是逆境。该研究结果为全面深入研究盐爪爪的耐盐特性,以及更好地利用盐爪爪的生物和基因资源改良土壤和提高作物和林木的耐盐性奠定基础。     

NaCl胁迫对盐芥质膜和液泡膜ATPase活性的影响

以盐生植物盐芥和中生植物拟南芥幼苗为材料,研究了盐胁迫对它们叶片和根质膜、液泡膜H+-ATPase、Ca2+-ATPases和K+-ATPase活性以及H+-ATPase、Na+/H+ 逆向转运蛋白表达的影响.结果显示:在NaCl胁迫下,盐芥叶片和根质膜的H+-ATPase活性分别比对照显著升高41%～212%和35%～53%,液泡膜的H+-ATPase分别显著升高281%～373%和4%～38%,而拟南芥却比相应对照都显著降低;相同盐浓度胁迫下,盐芥叶片的H+-ATPase活性比根部高4～8倍,盐芥根也远高于拟南芥.在NaCl胁迫下,盐芥叶片和根的液泡膜H+-ATPase蛋白质β亚基含量变化与其酶活性变化趋势一致,质膜Na+/H+ 逆向转运蛋白的表达量与Na+含量变化趋势一致.盐胁迫下盐芥根中Ca2+-ATPases和K+-ATPase活性的增加与根中Ca2+和K+含量呈显著正相关.研究发现,在盐胁迫条件下,盐芥能有效增强H+-ATPase蛋白和Na+/H+逆向转运蛋白表达,显著提高其根系与叶片质膜和液泡膜的H+-ATPase、Ca2+-ATPase和K+-ATPase活性,维持细胞质中较高的Ca2+和K+水平,从而缓解盐胁迫的伤害,增强耐盐性.     

盐胁迫下水稻苗期Na+和K+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-1NaCl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-1NaCl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-1NaCl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-1NaCl胁迫下绿叶Na+含量已接近高值,与在8 000 mg·L-1NaCl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.     

NaCl胁迫对滨梅扦插苗生物量和水分积累的影响

以1年生滨梅(Prunus maritima Marshall)扦插苗为实验材料,在盆栽条件下用质量浓度为0.15%、0.29%、0.58%、0.88%、1.17%、1.46%的NaCl溶液进行盐胁迫处理,测定胁迫后根、茎、叶Na+、K+含量以及全叶、一年生茎、二年生茎和根系生物量、含水率、根系活力变化,探讨滨梅的抗盐胁迫机制。结果显示:(1)盐胁迫80d后,随着盐胁迫强度提高,滨梅植株根、茎、叶Na+含量显著提高,而其根、茎K+含量显著降低,根、茎、叶K+/Na+值显著降低;根Na+含量在低于0.58%NaCl胁迫下显著高于茎、叶,而在高于0.58%NaCl胁迫下却表现为叶Na+含量显著高于根、茎。(2)滨梅根、茎、叶生物量均随盐胁迫强度的提高呈先增加后减少的趋势;随着盐胁迫时间的延长,茎、叶生物量在低于0.58%NaCl胁迫下均呈积累趋势,且茎生物量在0.58%NaCl胁迫下显著提高,而根、一年生茎、叶生物量在高于0.58%NaCl胁迫下均显著下降。(3)滨梅茎、叶含水率均随盐胁迫强度的增加呈先增加后减少的趋势,而随着胁迫时间的延长呈逐渐减少趋势;根系活力及根含水率均随盐胁迫强度的提高而增加,但根含水率随着胁迫时间的延长变化不明显。由此可见,滨梅能通过根系稀释并蓄积Na+,保护地上部分正常生长,当进入根系的Na+量超过吸收阈值时,Na+迅速在叶中积累储存,且叶中较高含量的K+对Na+形成了有效的缓冲。     

盐胁迫下白杨无性系苗木体内离子分配及比较

以白杨杂种无性系及其亲本当年生苗木为材料 ,分析了盐胁迫下无性系的离子含量 ,及 Na 、K 、Ca 在植物体内运输和分配特点 ,并对无性系间差异进行了比较。研究表明 ,随盐浓度提高 ,植物体内Na 含量迅速提高 ,K 、Ca 含量降低 ;盐分胁迫下 ,根部 Na 含量较高 ,叶片 Na 中含量最低 ,K 、Ca 含量则相反 ,特别是 Ca ,其分布顺序为叶 >茎 >根。杂种无性系 B430及其亲本新疆杨对 K 和 Ca 运输的选择性比毛白杨高 ,而对 Na 运输的选择性则比毛白杨低 ,从而导致根部存留的 Na 较多 ,叶片分配的 Na 数量较少 ,从而减轻 Na 对叶片的伤害。综合分析表明 B430和新疆杨耐盐能力最强 ,毛新杨其次 ,毛白杨最差。     

盐胁迫下水稻叶绿体中Na~ 、Cl~-积累导致叶片净光合速率下降

研究了 0～ 2 0 0mmol/L的NaCl胁迫下耐盐性不同的水稻品种Pokkali(耐盐 )和Peta(盐敏感 )根系、叶片和叶绿体中Na 、K 和Cl-含量的变化及其与叶片光合作用的关系。结果表明 :随着NaCl胁迫时间和浓度的增加 ,供试 2个品种在根、叶片和叶绿体中Na 、Cl-含量增加 ,K 含量下降。耐盐品种体内Na 、Cl-含量增加或K 含量减少的幅度小于盐敏感品种。在 2 0 0mmol/L的NaCl胁迫下盐敏感品种根、叶片和叶绿体中的Na /K 分别是耐盐品种的 2 0 8%、30 8%和 2 97%。与Na 相比 ,耐盐品种根系对K 的吸收和向叶片运输的选择性 (SK ,Na)较强。但在经过0、10 0和 2 0 0mmol/L的NaCl处理后 2个品种叶绿体中的Na /K 均高于叶片 (SK ,Na均小于 1)。盐胁迫下水稻叶绿体中Na 、Cl-含量和Na /K 与叶片净光合速率呈极显著负相关。     

盐胁迫对3种华南园林植物元素特性的影响

为筛选耐盐园林植物,研究了盐胁迫下狗牙花(Ervatamia divaricate)、红背桂(Excoecaria cochinchinensis)和花叶假连翘(Duranta erecta)的养分积累和分配规律。结果表明,盐胁迫增加了所有植物器官的Na和叶片K含量、狗牙花和红背桂各器官的Cl和N含量,但降低了所有植物枝干、红背桂和花叶假连翘根的K含量;各植物的P含量变化各异。盐胁迫增加了所有植物Na和Cl的积累量,并富集于枝干和叶片;狗牙花和花叶假连翘各器官的N、P和K积累量及红背桂各器官的P和K积累量随着Na Cl的浓度增加而下降。总之,盐胁迫使植物Na和Cl含量和积累量升高,而各器官生物量以及N、P和K积累量下降。3种植物中,狗牙花和花叶假连翘能更好地适应华南地区盐胁迫环境。     

NaCl胁迫对4种豆科树种幼苗生长和K~+、Na~+含量的影响

以合欢、刺槐、国槐和皂荚4种豆科树种盆栽实生幼苗为试验材料,研究了NaCl胁迫下4个树种幼苗的生长、耐盐临界浓度和Na+、K+含量的变化,并对其耐盐性进行了比较.结果表明:NaCl胁迫抑制了4个树种幼苗的生长,苗木的干物质积累量减小、根冠比增大,尤其对合欢和皂荚的影响较大;以相对干质量降至对照组50%时的NaCl浓度作为生长临界NaCl浓度(C50)指标,4个树种的耐盐强弱顺序为:刺槐(5.0‰)>国槐(4.5‰)>皂荚(3.9‰)>合欢(3.0‰);随NaCl浓度的增加,各树种幼苗根、茎、叶中Na+含量逐渐增加,K+含量先增加后减小(合欢根除外),而K+/Na+差异较大.相同浓度NaCl胁迫下,幼苗器官的Na+分布为根>茎>叶,K+因树种和NaCl浓度不同而各异,以叶片中较多,K+/Na+为叶>茎>根.NaCl胁迫下,刺槐的K+含量和K+/Na+较高,地上部分Na+含量较低,幼苗干物质量大,耐盐性较强;而合欢的K+/Na+较小,高浓度NaCl胁迫下地上部分的Na+含量较高,幼苗干物质量小,耐盐性较差.苗木地上部分对K+的积累和根部对Na+的滞留是影响豆科树种耐盐性能的主要因素.     

NaC1胁迫对4种豆科树种幼苗生长和K+、Na+含量的影响

以合欢、刺槐、国槐和皂英4种豆科树种盆栽实生幼苗为试验材料,研究了NaC1胁迫下4个树种幼苗的生长、耐盐临界浓度和Na+、K+含量的变化,并对其耐盐性进行了比较.结果表明:NaC1胁迫抑制了4个树种幼苗的生长,苗木的干物质积累量减小、根冠比增大,尤其对合欢和皂荚的影响较大;以相对干质量降至对照组50%时的NaC1浓度作为生长临界NaC1浓度(C50)指标,4个树种的耐盐强弱顺序为:刺槐(5.0‰)＞国槐(4.5‰)＞皂荚(3.9‰)＞合欢(3.0‰);随NaC1浓度的增加,各树种幼苗根、茎、叶中Na+含量逐渐增加,K+含量先增加后减小(合欢根除外),而K+/Na+差异较大.相同浓度NaC1胁迫下,幼苗器官的Na+分布为根＞茎＞叶,K+因树种和NaC1浓度不同而各异,以叶片中较多,K+/Na+为叶＞茎＞根.NaC1胁迫下,刺槐的K+含量和K+/Na+较高,地上部分Na+含量较低,幼苗干物质量大,耐盐性较强;而合欢的K+/Na+较小,高浓度NaC1胁迫下地上部分的Na+含量较高,幼苗干物质量小,耐盐性较差.苗木地上部分对K+的积累和根部对Na+的滞留是影响豆科树种耐盐性能的主要因素.     

Temperature and water stress affect plant–pollinator interactions in Borago officinalis (Boraginaceae)

Climate change alters the abiotic constraints faced by plants, including increasing temperature and water stress. These changes may affect flower development and production of flower rewards, thus altering plant–pollinator interactions. Here, we investigated the consequences of increased temperature and water stress on plant growth, floral biology, flower‐reward production, and insect visitation of a widespread bee‐visited species, Borago officinalis. Plants were grown for 5 weeks under three temperature regimes (21, 24, and 27°C) and two watering regimes (well‐watered and water‐stressed). Plant growth was more affected by temperature rise than water stress, and the reproductive growth was affected by both stresses. Vegetative traits were stimulated at 24°C, but impaired at 27°C. Flower development was mainly affected by water stress, which decreased flower number (15 ± 2 flowers/plant in well‐watered plants vs. 8 ± 1 flowers/plant under water stress). Flowers had a reduced corolla surface under temperature rise and water stress (3.8 ± 0.5 cm² in well‐watered plants at 21°C vs. 2.2 ± 0.1 cm² in water‐stressed plants at 27°C). Both constraints reduced flower‐reward production. Nectar sugar content decreased from 3.9 ± 0.3 mg/flower in the well‐watered plants at 21°C to 1.3 ± 0.4 mg/flower in the water‐stressed plants at 27°C. Total pollen quantity was not affected, but pollen viability decreased from 79 ± 4% in the well‐watered plants at 21°C to 25 ± 9% in the water‐stressed plants at 27°C. Flowers in the well‐watered plants at 21°C received at least twice as many bumblebee visits compared with the other treatments. In conclusion, floral modifications induced by abiotic stresses related to climate change affect insect behavior and alter plant–pollinator interactions.     

Effect of uniconazole and limited water on growth,water relations,and mineral nutrition of “Lalandei” Pyracantha

Pyracantha (Pyracantha coccinea M. J. Roem. Lalandei) plants were treated with uniconazole at 0.5 mg ai container^–1 as a medium drench, 150 mg ai L^–1 as a foliar spray, or left untreated. Plants from all treatments were placed under three water regimes: drought acclimated, nonacclimated and later exposed to drought, or nonstressed. Acclimated plants were conditioned by seven 4-day stress cycles (water withheld), while nonacclimated were well watered prior to a single 4-day stress cycle at the same time as the seventh drought cycle of acclimated plants. Nonstressed plants were well watered throughout the study. Nonstressed plants had higher leaf water potentials and leaf conductances than acclimated and nonacclimated plants, and transpiration rates were higher in nonacclimated than acclimated plants. Uniconazole did not affect leaf water potential, leaf conductance, or transpiration rate. Acclimated plants had smaller leaf areas and leaf, stem, and root dry weights than nonacclimated or nonstressed plants. Plants drenched with uniconazole had the lowest stem and root dry weights. Acclimated plants also contained higher N concentrations than nonacclimated or nonstressed plants, and higher P concentrations than nonacclimated plants. Uniconazole medium drench treatments increased levels of Mn and P. Calcium concentration was increased in plants receiving either medium drench or foliar applications.     

Home range geometry of the desert scorpion Paruroctonus mesaensis

Summary The selection pressures experienced by clonal plants in heterogeneous environments may be significantly affected by physiological integration among ramets via rhizome connections. We experimentally examined how connections affected the response to saline soil conditions in Ambrosia psilostachya clones from natural saline basins in eastern Nebraska. Paired stems connected by uniform lengths of rhizome were grown in partitioned pots in 3 watering regimes: (1) both stems watered with tapwater, (2) both stems watered with salt water (1% NaCl), and (3) one stem watered with salt water and one with tapwater. All plants survived and grew in salt water, yet dry weight gain of salt-salt plants was only 34% of that for plants in uniform tapwater. Salt plants connected to tapwater plants had 2-fold higher dry weight gain than salt-salt plants. Their tapwater neighbors had significantly smaller biomass than pairs with both stems growing in tapwater. Measurements of leaf stomatal conductance, transpiration rate and water potential, together with root-shoot allocation patterns, suggest that rhizomes transported both water and photosynthate from tapwater plants to their neighbors in saline soil. These results indicate that ramets in a locally inferior environment can be helped by their neighbors, but at some cost to the contributing ramet. We discuss the consequences of this phenomenon for the evolution of local adaptation in populations of rhizomatous plants.     

A Proline-, Threonine-, and Glycine-Rich Protein Down-Regulated by Drought Is Localized in the Cell Wall of Xylem Elements

A cDNA clone encoding a proline-, threonine-, and glycine-rich protein (PTGRP) was isolated from a wild tomato species (Lycopersicon chilense) (L.X. Yu, H. Chamberland, J.G. Lafontain, Z. Tabaeizadeh [1996] Genome 39: 1185-1193). Northern-blot analysis and in situ hybridization studies revealed that PTGRP is down-regulated by drought stress. The level of the mRNA in leaves and stems of 8-d drought-stressed plants decreased 5- to 10-fold compared with that in regularly watered plants. The mRNA re-accumulated when drought-stressed plants were rewatered. Antibodies raised against a glutathione S-transferase/PTGRP fusion protein were used to elucidate the subcellular localization of the protein by immunogold labeling. In regularly watered L. chilense plants, PTGRP protein was found to be localized in xylem pit membranes and disintegrated primary walls. Examination of sections from drought-stressed plants revealed a significant decrease in the levels of labeling. In these samples, only a few scattered gold particles were detected in the same areas. In the leaf tissues of plants that had been rewatered for 3 d following an 8-d drought stress, the labeling pattern was similar to that of the regularly watered plants. To our knowledge, PTGRP is the first drought-regulated protein that has been precisely localized in the cell wall.     

The Effect of Elevated [CO2] on Growth and Photosynthesis of Two Eucalyptus Species Exposed to High Temperatures and Water Deficits

Two species of eucalyptus (Eucalyptus macrorhyncha and Eucalyptus rossii) were grown for 8 weeks in either ambient (350 [mu]L L-1) or elevated (700 [mu]L L-1) CO2 concentrations, either well watered or without water additions, and subjected to a daily, 3-h high-temperature (45[deg]C, maximum) and high-light (1250 [mu]mol photons m-2 s-1, maximum) stress period. Water-stressed seedlings of E. macrorhyncha had higher leaf water potentials when grown in elevated [CO2]. Growth analysis indicated that increased [CO2] may allow eucalyptus species to perform better during conditions of low soil moisture. A down-regulation of photosynthetic capacity was observed for seedlings grown in elevated [CO2] when well watered but not when water stressed. Well-watered seedlings grown in elevated [CO2] had lower quantum efficiencies as measured by chlorophyll fluorescence (the ratio of variable to maximal chlorophyll fluorescence [Fv/Fm]) than seedlings grown in ambient [CO2] during the high-temperature stress period. However, no significant differences in Fv/Fm were observed between CO2 treatments when water was withheld. The reductions in dark-adapted Fv/Fm for plants grown in elevated [CO2] were not well correlated with increased xanthophyll cycle photoprotection. However, reductions in the Fv/Fm were correlated with increased levels of nonstructural carbohydrates. The reduction in quantum efficiencies for plants grown in elevated [CO2] is discussed in the context of feedback inhibition of electron transport associated with starch accumulation and variation in sink strength.     

Root-to-shoot signalling when soil moisture is heterogeneous: increasing the proportion of root biomass in drying soil inhibits leaf growth and increases leaf abscisic acid concentration

To determine whether root-to-shoot signalling of soil moisture heterogeneity depended on root distribution, wild-type (WT) and abscisic acid (ABA)-deficient (Az34) barley (Hordeum vulgare) plants were grown in split pots into which different numbers of seminal roots were inserted. After establishment, all plants received the same irrigation volumes, with one pot watered (w) and the other allowed to dry the soil (d), imposing three treatments (1 d: 3 w, 2 d: 2 w, 3 d: 1 w) that differed in the number of seminal roots exposed to drying soil. Root distribution did not affect leaf water relations and had no sustained effect on plant evapotranspiration (ET). In both genotypes, leaf elongation was less and leaf ABA concentrations were higher in plants with more roots in drying soil, with leaf ABA concentrations and water potentials 30% and 0.2 MPa higher, respectively, in WT plants. Whole-pot soil drying increased xylem ABA concentrations, but maximum values obtained when leaf growth had virtually ceased (100 nm in Az34, 330 nm in WT) had minimal effects (<40% leaf growth inhibition) when xylem supplied to detached shoots. Although ABA may not regulate leaf growth in vivo, genetic variation in foliar ABA concentration in the field may indicate different root distributions between upper (drier) and lower (wetter) soil layers.     

Changes in respiration,dry-matter production and its partition in rice (Oryza sativa L.) in response to water deficits during the grain-filling period

A simple, physiologically based model was devised and used for estimating the respiration rate and the overall conversion efficiency of photosynthate into the grain dry-matter in dehydrated plants relative to well watered controls. The model described mathematically the partitioning of assimilate produced by current photosynthesis and of assimilate stored previously between the grain and those plants parts other than grain (the “straw”). Using data obtained from the dry-matter analysis and CO₂ gas exchange measurements, the model gave us two independent estimates of the respiration rate and the overall conversion efficiency; one for the plants given a prolonged dark period and the other for those grown in a normal light and dark cycle. The rate of dark respiration increased with mild water stress: 4.3 mg g⁻¹ day⁻¹ in control plants with leaf water potential of around −0.4 MPa and 11.3 mg g⁻¹ day⁻¹ in dehydrated plants with leaf water potential of around −1 MPa, when both the control and dehydrated plants were left in the dark for ten days. Similar values were obtained for plants in a normal light and dark cycle: 5.6 in well watered and 8.1 mg g⁻¹ day⁻¹ in the stressed plants. Accordingly, the overall conversion efficiency (the ratio of grain dry-matter against the gross carbohydrate input to the construction and maintenance processes) was 0.7 to 0.8 for the well hydrated control and 0.4 to 0.5 for moderately dehydrated plants. With increasing water deficits, however, the respiration rate decreased: 4.8 mg g⁻¹ day⁻¹ when plants were severely stressed (below −3 MPa in midday leaf water potential). The decrease in straw dry weight alone overestimates dry-matter partition of the stored assimilate in the straw into grain by 20 to 30% in well watered plants and the error increases to 50 to 60% in more dehydrated plants.     

Photosynthesis and wood structure in Pinus radiata D. Don during dehydration and immediately after rewatering

Abstract. Experiments were carried out on Pinus radiata (D. Don) trees grown as cuttings from clonal parent stock. Some of these trees were about 0.4 m high while others were about 5 m high; all were grown in containers. The stem diameters at the tops and at the bottoms of the large trees, rates of photosynthesis, and needle water potentials were measured both when the trees were well watered and as they dehydrated after water was withheld. The water potentials of well-watered plants was highest in the small trees and lowest at the top of the large trees. When water was withheld, photosynthesis was in most cases unaffected by a small reduction in water potential, but the rate of photosynthesis fell as water potentials declined further. The stems of the large trees expanded at a constant rate when the trees were well watered and for part of the dehydration period, while subsequent stem shrinkage and the fall in photosynthesis both occurred at approximately the same time.
Water potentials increased little in the 24 h after rewatering, and significant rates of photosynthesis were not measured until 2 or 3 d later while renewed stem expansion was not measured until 2 d after rewatering.
Water deficits reduced the lumen diameter of newly matured stem tracheids, but increased the thickness of their walls. After 1 month of water potentials of about −2.4 MPa, tracheid lumen diameter and wall thickness were both much reduced, and this reduction continued in tracheids maturing shortly after rewatering.     

咸水浇灌后持续干旱条件下棉花生长及光合作用的变化

用咸水(不同浓度的NaCl溶液)浇灌盆栽棉花植株,随后进行持续干旱处理.测定干旱处理期间棉花的生长情况、光合速率、叶绿素荧光等参数的变化,并对植株的相对含水量、水势、渗透势等水分状况和Na⁺、K⁺含量进行分析,探索环境Na⁺在棉花适应干旱胁迫中的作用.结果表明: 干旱可以明显抑制植株的生长,降低叶片的净光合速率;用25～100 mmol·L^-1NaCl溶液浇灌后进行持续干旱处理的棉花植株,其株高、生物量、净光合速率和F_v/F_m值均明显高于用水浇灌后进行持续干旱处理的植株.同时,前者的土壤和叶片相对含水量、细胞膨压、Na⁺含量也明显高于后者,但植株水势和组织渗透势则显著低于后者,且组织渗透势的降低与Na⁺含量具有显著相关性.上述结果说明,土壤适量Na⁺的存在能够提高土壤和植株的保水力、增加棉花对Na⁺的吸收和积累、降低组织渗透势,从而增强植株吸水力、保持较高的细胞膨压,维持相对较高的光合速率和生长速度.土壤中存在一定浓度的NaCl可以有效缓解干旱对棉花的不利影响.     

Surface disinfection of Atlantic halibut Hippoglossus hippoglossus eggs with ozonated sea-water inactivates nodavirus and increases survival of the larvae

Disinfection by ozonation of sea-water may reduce the risk of transmission of nodavirus, a major fish pathogen, via Atlantic halibut Hippoglossus hippoglossus eggs. In the present study, eggs at 4 d prior to hatching were exposed to nodavirus and then to ozonated sea-water using different concentrations (0.3 to 10 mg l-1) and exposure times (0.5 to 10 min). None of the larvae from virus-exposed eggs washed with ozonated sea-water developed viral encephalopathy and retinopathy (VER), which was detected in all dead larvae from eggs exposed to nodavirus but not washed with ozonated sea-water. In the non-treated control group about 20% of the dead larvae developed the disease. This suggests that the halibut eggs taken from a large-scale production facility were already contaminated with nodavirus. The egg groups which had been treated with 4 mg O3 l-1 for 0.5 min or with lower total ozone exposures had a higher survival and no adverse effects on the development of the larvae after hatching were observed. Although a slight delay in hatching was found, after 2 d the cumulative hatching had normalised. In the egg groups with high total exposure (4 mg O3 l-1 for 1 min or higher total ozone exposures) a pronounced negative effect on hatching was observed. Our results indicate that the egg surface may be important in the transfer of nodavirus and that nodavirus associated with the surface of the egg may be inactivated by ozonated sea-water.