木本植物木质部栓塞修复机制:研究进展与问题

维持木本植物体内长距离的水分运输对于植物生存、生长和发育非常重要,但因水分在木质部张力状态下处于亚稳定状态而易发生空穴化和栓塞,导致水力导度降低、生产力下降、甚至植物死亡。面对水分胁迫诱导的空穴化,植物可通过形成抵抗空穴化的解剖结构降低栓塞发生频率,或(和)通过活跃的代谢修复栓塞,其中对木质部栓塞及其修复的发生频率、条件、机制等的认识仍有很大分歧。为此,该文首先综述了木质部栓塞修复过程及时间动态、木质部栓塞形成及修复的发生频率。然后,总结了木质部导管"新的再充水"栓塞修复过程中的4种主要假说:(1)渗透调节假说;(2)反渗透调节假说;(3)韧皮部驱动再充水假说;(4)韧皮部卸载假说。在此基础上,比较了针叶树种和木本被子植物木质部栓塞形成与修复的差异,并分析了木质部栓塞阻力与修复能力之间的权衡关系。最后,提出了木本植物木质部栓塞与修复研究的4个优先研究问题:(1)改进木质部栓塞测定技术;(2)验证"新的再充水"栓塞修复机制假说及引发木质部再充水的信号;(3)阐明木质部栓塞与修复特性的树种间差异及其可能的权衡关系;(4)加强碳代谢和水通道蛋白表达与木质部栓塞及其修复关系的生理生化研究。     

不同品种燕麦种子萌发和幼苗生长的耐盐性

利用NaCl和Na2SO4复盐溶液胁迫处理36个燕麦品种,采用培养皿纸上发芽法,进行种子萌发和幼苗的耐盐能力鉴定,通过分析盐胁迫对不同燕麦种子萌发及幼苗的影响,为燕麦品种耐盐性筛选、盐碱地燕麦栽培和耐盐育种提供理论参考.结果表明:盐分抑制种子的萌发和幼苗生长,低盐浓度(0.4%)适宜各类燕麦生长,对较耐盐的品种有促进萌发、生长的作用,盐浓度1.2%是鉴定燕麦耐盐性的适宜盐浓度;36个品种耐盐性差异较大,可划分为耐盐型、中度耐盐型、不耐盐型3类;燕麦不同品种及不同类型种子萌发的盐浓度范围达极显著差异,各耐盐指标对于燕麦耐盐性的体现存在一定的差异,发芽率、发芽指数、简易活力指数和单株干质量是主要的耐盐指标.     

不同磷效率小麦品种对缺磷胁迫反应的比较

在营养液培养条件下,以根据相对产量为指标筛选出的6个不同磷效率的小麦(Triticum aestivum L.)品种为材料,对其苗期在缺磷条件下生长、根冠磷含量及其分配,以及叶片韧皮部汁液中磷浓度等进行了比较研究.结果表明,缺磷抑制植株地上部生长,但刺激根系生长,导致植株根/冠比增加.无论在供磷或缺磷条件下,磷高效品种的根冠生长速率都低于磷低效品种.缺磷导致植株体内的磷含量下降与根系相比,地上部磷含量的下降速率更快.但在缺磷条件下,不同磷效率的小麦品种根冠间的磷分配变化没有差异.研究发现,在正常供磷条件下,磷高效小麦品种的叶片韧皮部汁液中磷浓度较低,而磷低效品种的叶片韧皮部汁液中磷浓度较高.但开始缺磷后,磷高效品种的叶片韧皮部汁液中的磷浓度下降较慢,使其相对磷浓度较高.缺磷后1 0天,磷低效品种叶片韧皮部汁液中的磷浓度为供磷对照的35.9%,而磷高效品种叶片韧皮部汁液中的磷浓度为供磷对照的59%.     

大豆种子储藏性磷对幼苗适应低磷胁迫的作用

选用种子大小不同、磷效率不同的两个大豆品种‘巴西10号’(B10)和‘本地2号’(L2),在不同供磷条件下进行营养液浇灌沙培,从大豆萌发至2片三出复叶完全展开期测定植株主要器官总磷、可溶性磷浓度、子叶可溶性蛋白、酸性磷酸酶比活性、植酸酶比活性的变化动态,探讨储藏性磷在大豆幼苗期适应磷胁迫中的作用。结果发现:(1)磷效率不同的两个大豆品种的种子中磷含量差异显著。(2)大豆萌发和幼苗生长过程中子叶的磷逐渐转入根、茎、叶中,并以转入叶中的磷最多,其中磷高效品种B10在发芽过程中子叶磷向各个器官转移的总磷量要高于磷低效品种L2,且持续时间长。(3)大豆萌发和幼苗生长过程中外源供磷水平显著影响子叶磷的转移,在外源供磷充足条件下各器官中总磷均高于低供磷条件,子叶中磷和外源磷存在补偿关系。(4)磷高效品种B10子叶中酸性磷酸酶活性在低磷条件下显著高于高磷条件,但磷低效品种L2在高、低磷间无显著差异。研究表明,大豆种子储藏性磷在幼苗期耐低磷能力建立方面具有重要作用。     

不同磷效率小麦品种对缺磷胁迫反应的比较

在营养液培养条件下,以根据相对产量为指标筛选出的6个不同磷效率的小麦(Triticum aestivum L.)品种为材料,对其苗期在缺磷条件下生长、根冠磷含量及其分配,以及叶片韧皮部汁液中磷浓度等进行了比较研究。结果表明,缺磷抑制植株地上部生长,但刺激根系生长,导致植株根／冠比增加。无论在供磷或缺磷条件下,磷高效品种的根冠生长速率都低于磷低效品种。缺磷导致植株体内的磷含量下降与根系相比,地上部磷含量的下降速率更快。但在缺磷条件下,不同磷效率的小麦品种根冠间的磷分配变化没有差异。研究发现,在正常供磷条件下,磷高效小麦品种的叶片韧皮部汁液中磷浓度较低,而磷低效品种的叶片韧皮部汁液中磷浓度较高。但开始缺磷后,磷高效品种的叶片韧皮部汁液中的磷浓度下降较慢,使其相对磷浓度较高。缺磷后10天,磷低效品种叶片韧皮部汁液中的磷浓度为供磷对照的35．9％,而磷高效品种叶片韧皮部汁液中的磷浓度为供磷对照的59％。     

磷有效性对大豆根冠中碳分配的影响

在水培条件下,研究不同浓度磷影响大豆根冠中碳分配的结果表明：磷有效性对大豆根冠中碳分配的影响依赖于磷浓度与胁迫时间。磷浓度高于0．125mmol．L^-1或低磷胁迫7d以内,大豆根冠中碳分配受到的影响不显著。低磷胁迫14d的大豆的净光合速率和根呼吸速率均显著下降,根冠比显著提高。这显示长期低磷胁迫下大豆碳同化总量和根呼吸消耗的碳量虽然减少,但根系生长的碳消耗则增加,光合碳同化形成的碳水化合物向根部的分配是受到促进的。     

环剥对红松(Pinus koraiensis)韧皮部和木质部碳水化合物的影响

树干环剥可以阻碍韧皮部光合产物的运输并进一步影响光合产物的分配。长时期内,环剥能够导致环痕上部可溶性糖和淀粉的积累,但对于短期内如何影响碳水化合物在木质部和韧皮部内的运输模式所知甚少。以38年生红松(Pinus koraiensis Sieb.etZucc.)为研究材料,分别对环剥上部、下部每隔1~2d采样,区分木质部和韧皮部(树皮)进行可溶性糖和淀粉含量及树干糖呼吸消耗速率测定,确定环剥后的日变化和周变化,并对木质部可溶性糖、淀粉含量与韧皮部中相应指标进行相关关系的回归分析。结果发现:(1)环剥后4周内,在环剥痕上、下部间木质部可溶性糖和淀粉含量,韧皮部中淀粉含量均不存在显著差异(p>0.05),而韧皮部内可溶性糖含量,环剥后第2周出现显著差异,从第4周出现环剥上部显著高于下部的碳水化合物积累现象(p<0.05);(2)环剥阻隔了韧皮部可溶性糖的纵向运输,但是并不影响木质部的纵向运输,而且环剥并没有影响木质部和韧皮部之间的糖和淀粉的相关关系;(3)环剥第1周内环剥上部和下部呼吸消耗速率差异不显著,第2周环剥上部显著高于环剥下部,从第3周开始环剥下部呼吸消耗速率显著下降。推断认为,在环剥处理的4周内,环剥上部冠层新形成的碳水化合物很大一部分均被呼吸消耗掉,导致环剥上部较环剥下部可溶性糖稍有增加;红松胸高直径以下部分所储藏的碳水化合物足以保障2周内红松树干呼吸。     

NaCl胁迫对菊芋幼苗生长及其离子吸收运输的影响

在温室采用砂培试验,比较研究了NaCl胁迫对2个菊芋(Helianthus tuberosusL.)品种‘南芋8号’(Ht 1,耐盐性较强)和‘南芋1号’(Ht 2,耐盐性较弱)幼苗生长及其离子吸收运输的影响。结果表明:(1)与对照相比,低浓度NaCl处理(255、0 mmol.L-1)促进了Ht 1根干物质积累和根冠比增加,有利于其养分吸收;较高浓度NaCl处理(1002、00 mmol.L-1)均显著降低2个品种的总干物质重以及叶片、茎、根干物质重,且Ht 2降幅较Ht 1大;(2)NaCl处理对菊芋幼苗根部相对含水量(RWC)没有显著影响,但对叶片和茎部RWC的影响较大,而且高浓度盐胁迫(200 mmol.L-1)下,耐盐品种Ht 1较Ht 2叶片能够保持较高的RWC;(3)NaCl处理下,Ht 1比Ht 2根部对K 的选择性较强,且由根部吸收的大量Na 和Cl-在运输过程中被区域化在茎部,因而向代谢活性较高的叶片运输量相对较少,这是Ht 1耐盐能力较强的一个重要原因。     

盐胁迫对苹果器官中钙镁铁锌含量的影响

以盆栽2年生富士苹果树(砧木为平邑甜茶M.hupehensisReld)为试材,研究了盐胁迫对苹果矿质营养平衡的影响.结果表明,在盐胁迫下,苹果各器官不同时期的单位干样中Ca、Mg、Fe和Zn含量的平均值没有明显变化,但各元素与Na的比值明显下降,特别是在高盐(3‰NaCl)胁迫下下降更为明显,从而破坏了树体内元素平衡.在无盐和盐胁迫下,苹果各器官中Ca含量的顺序为主干韧皮部＞叶片、新梢＞根＞主干木质部;Mg含量为新梢、根＞主干木质部、主干韧皮部、叶片;Fe含量为根＞叶片＞主干韧皮部、新梢＞主干木质部;Zn含量为新梢＞叶片＞根、主干韧皮部＞主干木质部.与对照相比,器官中各元素含量在胁迫期间表现出不同程度的波动性.     

外源一氧化氮对NaCl胁迫下番茄幼苗生长和光合作用的影响

以2个耐盐性不同的番茄品种为材料,研究了外源NO供体硝普钠(SNP)处理对100mmol·L-1NaCl胁迫下番茄幼苗生长和光合作用的影响。结果表明:外源NO能使盐胁迫下的番茄幼苗叶片叶绿素含量、净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)升高,胞间CO2浓度(Ci)下降,叶绿素荧光参数Fv/Fm、Fv/Fo和T1/2增高,脯氨酸和可溶性糖含量升高。可见,外源NO有利于番茄幼苗对光能的捕获和转换,促进番茄的生长,降低盐胁迫对番茄的抑制作用。     

Transport, synthesis and catabolism of abscisic acid (ABA) in intact plants of castor bean (Ricinus communis L.) under phosphate deficiency and moderate salinity

Flows of abscisic acid (ABA) were investigated in whole plantsof castor bean (Ricinus communis) grown in sand culture undereither phosphate deficiency or moderate salinity. Xylem transportof ABA in P-deficient plants was stimulated by a factor of 6whereas phloem transport was affected only very slightly. ABAdeposition into leaves of P-deficient plants was not appreciablydifferent from the controls because of strong net degradationin leaves. Since conjugation of ABA was strongly reduced inall organs of P-deficient plants ABA was presumably metabolizedmainly to phaseic acid and dihydrophaseic acid. The increasedimport of ABA occurred predominantly into fully differentiatedbut not senescent leaves and showed a good correlation withthe inhibition of leaf conductance under P deficiency. As with low-P-plants salt stress increased ABA synthesis inroots and associated transport in the xylem. However, salinitycaused a distinctly greater accumulation of ABA in the leaves,stem segments and the apex than in P-deficient plants. As opposedto P deficiency, ABA export in the phloem from the leaves wasstimulated by salinity. Modelling of ABA flows within an individualleaf over its life cycle showed that young growing leaves importedABA from both phloem and xylem, whereas the adult non-senescentleaves were a source of ABA and thus provided a potential shoot-to-rootstress signal as well as an acceptor for reciprocal signalsfrom root to shoot. In senescing leaves ABA flows and accumulationwere somewhat retarded and ABA was lost in net terms by exportfrom the leaf. Key words: Abscisic acid, phosphorus deficiency, salt stress, phloem and xylem transport     

Overexpression of GmAAP6a enhances tolerance to low nitrogen and improves seed nitrogen status by optimizing amino acid partitioning in soybean

Amino acid transport via phloem is one of the major source‐to‐sink nitrogen translocation pathways in most plant species. Amino acid permeases (AAPs) play essential roles in amino acid transport between plant cells and subsequent phloem or seed loading. In this study, a soybean AAP gene, annotated as GmAAP6a, was cloned and demonstrated to be significantly induced by nitrogen starvation. Histochemical staining of GmAAP6a:GmAAP6a‐GUS transgenic soybean revealed that GmAAP6a is predominantly expressed in phloem and xylem parenchyma cells. Growth and transport studies using toxic amino acid analogs or single amino acids as a sole nitrogen source suggest that GmAAP6a can selectively absorb and transport neutral and acidic amino acids. Overexpression of GmAAP6a in Arabidopsis and soybean resulted in elevated tolerance to nitrogen limitation. Furthermore, the source‐to‐sink transfer of amino acids in the transgenic soybean was markedly improved under low nitrogen conditions. At the vegetative stage, GmAAP6a‐overexpressing soybean showed significantly increased nitrogen export from source cotyledons and simultaneously enhanced nitrogen import into sink primary leaves. At the reproductive stage, nitrogen import into seeds was greatly enhanced under both sufficient and limited nitrogen conditions. Collectively, our results imply that overexpression of GmAAP6a enhances nitrogen stress tolerance and source‐to‐sink transport and improves seed quality in soybean. Co‐expression of GmAAP6a with genes specialized in source nitrogen recycling and seed loading may represent an interesting application potential in breeding.     

Root-shoot interactions in mineral nutrition

In this paper four classes of co-operative root-shoot interations are addressed. (I) Nitrogen concentrations in the xylem sap originating from the root and in the phloem sap as exported from source leaves are much lower than those required for growth by apices and developing organs. Enrichment of xylem sap N is achieved by xylem to xylem (X-X) transfer, by which reduced N, but not nitrate, is abstracted from the xylem of leaf traces and loaded into xylem vessels serving the shoot apex. Nitrogen enrichment of phloem sap from source leaves is enacted by transfer of reduced N from xylem to phloem (X-P transfer). Quantitative data for the extent of the contribution of X-X and X-P transfer to the nutrition of young organs of Ricinus communis L. and for their change with time are presented. (II) Shoot and root cooperate in nitrate reduction and assimilation. The partitioning of this process between shoot and root is shifted towards the root under conditions of nitrate- and K-deficiency and under salt stress, while P deficiency shifts nitrate reduction almost totally to the shoot. All four changes in partitioning can be attributed to the need for cation-anion balance during xylem transport and the change in electrical charge occurring with nitrate reduction. (III) Even maintenance of the specificity of ion uptake by the root may – in addition to its need for energy – require a shoot-root interaction. This is shown to be needed in the case of the maintenance of K/Na selectivity under the highly adverse condition of salt stress and absence of K supply from the soil. (IV) Hormonal root to shoot interactions are required in the whole plant for sensing mineral imbalances in the soil. This is shown and addressed for conditions of salt stress and of P deficiency, both of which lead to a strong ABA signalling from root to shoot but result in different patterns of response in the shoot.     

Ionic Interactions of Petiole and Lamina During the Life of a Leaf of Castor Bean (Ricinus communis L.) Under Moderately Saline Conditions

Ion (K⁺, Na⁺, Mg²⁺, Ca²⁺ and Cl) flows and partitioning in thepetiole and lamina of leaf 6 of castor bean {Ricinus communisL.) plants growing in the presence of a mean of 71 mol m^–3NaCl were described by an empirical modelling technique. Thiscombined data on changes in ion contents of petiole and lamina,ion: carbon molar ratios of phloem bleeding sap and pressure-inducedxylem exudates of the leaf with previously described informationon the economies of C and N in identical leaf material. Datawere expressed as daily exchanges of ions in xylem and phloem,or depicted as models of ion balance and transport activityof petiole and lamina during four consecutive phases of leaflife. The early import phase was characterized by high intakeof K and Mg through phloem, and of Ca mainly through xylem,but only limited intake of Na and Cl. The next phase up to fullleaf expansion showed similar relative differences in xylemintake between ions and the onset of rapid phloem export fromthe lamina of K and Mg, some export of Na and Cl but scarcelyany of Ca. The next mature phase, marked by maximal photosynthesisand transpiration by the leaf, showed high xylem intake of allions in xylem. This was more than matched by phloem export ofMg and K, but by only fractional re-export of Na and Cl andagain very limited cycling through the leaf of Ca. The finalpre-senescence phase exhibited similar behaviour, but with generallygreater contribution to phloem transport from mobilization ofion reserves of the lamina. The petiole retained particularlylarge amounts of Na and Cl in its early growth, thereby protectingthe lamina from excessive entry of salt, but these petiolarpools, together with those or other nutrient ions, were laterpartially mobilized to the lamina via the xylem stream. Datawere discussed in relation to the relatively high salt toleranceexhibited by the species. Key words: Ricinus communis, xylem and phloem transport, ion balance, K+ economy, Na+ exclusion, NaCl-stress, salt tolerance, leaf development     

Change in uptake, transport and accumulation of ions in Nerium oleander (rosebay) as affected by different nitrogen sources and salinity

Background and Aims

The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants.

Methods

Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined.

Key Results

Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na⁺ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1·8, 1·9 and 2·7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na⁺ accumulated in roots in nitrate-fed plants was about 1·5 times higher than that in ammonium-fed plants. Similarly, Cl⁻ transport via the xylem to the shoot and its retranslocation via the phloem (Cl⁻ cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K⁺ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K⁺ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants.

Conclusions

The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na⁺ and Cl⁻ in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na⁺ and Cl⁻ in shoots probably caused harmful effects and reduced growth of plants.Key words: Mineral cycling, Nerium oleander, nitrogen source, salinity, xylem and phloem transport     

Coordination between Bradyrhizobium and Pseudomonas alleviates salt stress in soybean through altering root system architecture

It is a well accepted strategy to improve plant salt tolerance through inoculation with beneficial microorganisms. However, its underlying mechanisms still remain unclear. In the present study, hydroponic experiments were conducted to evaluate the effects of Bradyrhizobium japonicum USDA 110 with salt-tolerant Pseudomonas putida TSAU1 on growth, protein content, nitrogen, and phosphorus uptake as well as root system architecture of soybean (Glycine max L.) under salt stress. The results indicated that the combined inoculation with USDA 110 and TSAU1 significantly improved plant growth, nitrogen and phosphorus contents, and contents of soluble leaf proteins under salt stress compared to the inoculation with the symbiont alone or compared to un-inoculated ones. The root architectural traits, like root length, surface area, project area, and root volume; as well as nodulation traits were also significantly increased by co-inoculation with USDA 110 and TSAU1. The plant-growth promoting rhizobacteria (PGPR) P. putida strain TSAU1 could improve the symbiotic interaction between the salt-stressed soybean and B. japonicum USDA 110. In conclusion, inoculation with B. japonicum and salt-tolerant P. putida synergistically improved soybean salt tolerance through altering root system architecture facilitating nitrogen and phosphorus acquisition, and nodule formation.     

Identification of three wheat globulin genes by screening a Triticum aestivum BAC genomic library with cDNA from a diabetes-associated globulin

Background

Plant systemic signaling characterized by the long distance transport of molecules across plant organs involves the xylem and phloem conduits. Root-microbe interactions generate systemic signals that are transported to aerial organs via the xylem sap. We analyzed the xylem sap proteome of soybean seedlings in response to pathogenic and symbiotic interactions to identify systemic signaling proteins and other differentially expressed proteins.

Results

We observed the increase of a serine protease and peroxidase in the xylem sap in response to Phytophthora sojae elicitor treatment. The high molecular weight fraction of soybean xylem sap was found to promote the growth of Neurospora crassa in vitro at lower concentrations and inhibit growth at higher concentrations. Sap from soybean plants treated with a P. sojae elicitor had a significantly higher inhibitory effect than sap from control soybean plants. When soybean seedlings were inoculated with the symbiont Bradyrhizobium japonicum, the abundance of a xyloglucan transendoglycosyl transferase protein increased in the xylem sap. However, RNAi-mediated silencing of the corresponding gene did not significantly affect nodulation in soybean hairy root composite plants.

Conclusion

Our study identified a number of sap proteins from soybean that are differentially induced in response to B. japonicum and P. sojae elicitor treatments and a majority of them were secreted proteins.     

The uptake and flow of C, N and ions between roots and shoots in Ricinus communis L. III. Long-distance transport of abscisic acid depending on nitrogen nutrition and salt stress

Seedlings of Ricinus communis L. were cultivated in quartz sandand supplied with media which contained either different concentrationsof nitrate or ammonium nitrogen and were treated with a lowsalt stress. The concentration of ABA was determined in tissuesand in xylem and phloem saps. Between 41 and 51 day after sowing,abscisic acid (ABA) flows between roots and shoots were modelled.Long-distance transport of ABA was not stimulated under conditionsof nitrate deficiency (0.2 mol m^–3). However, when ammoniumwas given as the only N source (1.0 mol m^–3), ABA transportin both xylem and phloem was increased significantly. Mild saltstress (40 mol m^–3 NaCl) increased ABA transport in nitrate-fedplants, but not in ammonium-fed plants. The leaf conductancewas lowered by salt treatment with both nitrogen sources, butit was always lower in ammonium-fed compared to nitrate-fedplants. A negative correlation of leaf conductance to ABA levelsin leaves or flow in xylem was found only in comparison of ammonium-fedto nitrate-fed plants. Key words: Abscisic acid, ammonium, Ricinus communis, phloem, xylem, transport, nitrate, nitrogen nutrition     

Comparing symbiotic performance and physiological responses of two soybean cultivars to arbuscular mycorrhizal fungi under salt stress

The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.     

Epistatic Association Mapping for Alkaline and Salinity Tolerance Traits in the Soybean Germination Stage

Soil salinity and alkalinity are important abiotic components that frequently have critical effects on crop growth, productivity and quality. Developing soybean cultivars with high salt tolerance is recognized as an efficient way to maintain sustainable soybean production in a salt stress environment. However, the genetic mechanism of the tolerance must first be elucidated. In this study, 257 soybean cultivars with 135 SSR markers were used to perform epistatic association mapping for salt tolerance. Tolerance was evaluated by assessing the main root length (RL), the fresh and dry weights of roots (FWR and DWR), the biomass of seedlings (BS) and the length of hypocotyls (LH) of healthy seedlings after treatments with control, 100 mM NaCl or 10 mM Na₂CO₃ solutions for approximately one week under greenhouse conditions. A total of 83 QTL-by-environment (QE) interactions for salt tolerance index were detected: 24 for LR, 12 for FWR, 11 for DWR, 15 for LH and 21 for BS, as well as one epistatic QTL for FWR. Furthermore, 86 QE interactions for alkaline tolerance index were found: 17 for LR, 16 for FWR, 17 for DWR, 18 for LH and 18 for BS. A total of 77 QE interactions for the original trait indicator were detected: 17 for LR, 14 for FWR, 4 for DWR, 21 for LH and 21 for BS, as well as 3 epistatic QTL for BS. Small-effect QTL were frequently observed. Several soybean genes with homology to Arabidopsis thaliana and soybean salt tolerance genes were found in close proximity to the above QTL. Using the novel alleles of the QTL detected above, some elite parental combinations were designed, although these QTL need to be further confirmed. The above results provide a valuable foundation for fine mapping, cloning and molecular breeding by design for soybean alkaline and salt tolerance.