Salt Tolerance of Cotton: Some New Advances

Referee: Dr. Lin Wu, Department of Environmental Horticulture, University of California, Davis, Davis, CA 95616 Cotton is a dual-purpose crop, widely used for fiber and oil purposes throughout the world. It is placed in the moderately salt-tolerant group of plant species with a salinity threshold level 7.7?dS m^?1, its growth and seed yield being severely reduced at high salinity levels and different salts affect the cotton growth to a variable extent. However, inter- and intraspecific variation for cotton salt tolerance in cotton is considerable and thus can be exploited through specific selection and breeding for enhancing salt tolerance of the crop. There are contrasting reports regarding the crop response to salinity at different plant growth stages, but in most of them it is evident that the crop maintains its degree of salt tolerance consistently throughout its entire developmental phases. In the latter case an effective selection for salt tolerance is possible to be made at any growth stage of the crop. The pattern of uptake and accumulation of toxic ions (Na⁺ and/or Cl^?) in tissues of plants subjected to saline conditions appears to be due mostly to the mechanism of partial ion exclusion (exclusion of Na⁺ and/or Cl^?) in cotton. Maintenance of high tissue K/Na and Ca/Na ratios is suggested to be an important selection criterion for salt tolerance in cotton. While judging the appropriate mechanism of ion transport across the membranes in view of existing literature, it was evident that the PM-ATPase responds to increasing supply of Na⁺ in the growth medium, but the activity of the transport proteins on the plasma membrane alone were insufficient to regulate intracellular Na⁺ levels. Vacuolar-ATPase is also not responsive to increased external Na⁺. The inability of V-ATPase to respond to Na⁺ gave indication of the lack of effective driving force for compartmentalization of Na⁺ in cotton. However, in view of some latest studies concenrning the role of some antioxidants in salt tolerance of cotton it was suggested that high levels of antioxidants and an active ascorbate-glutathione cycle are associated with salt tolerance in cotton. Genetic studies with cotton in relation to salinity tolerance exhibited that most of growth, yield, and fiber characteristics are genetically based and most being QTL controlled and variable. The high additive component of variation can be exploited for breeding to produce further improvement in the salt tolerance of cotton.     

Molecular markers for low-glucosinolate alleles in oilseed rape (Brassica napus L.)

Two recent studies have mapped QTLs associated with the level of seed glucosinolates in oilseed rape (Brassica napus L.). It was likely that the two most significant QTLs identified in each study were the same, as they were linked to RFLP alleles identified by common DNA probes. To investigate the utility of these probes in breeding programmes, they were used to study RFLPs in a range of low- and high-glucosinolate cultivars and breeding lines. It was shown that all low glucosinolate spring and winter cultivars possessed a specific RFLP fragment identified by probe wg3f7 which is linked to theGSL-1 QTL, and all high-glucosinolate cultivars possessed a specific RFLP fragment identified by probe wg7a8, which is linked to theGSL-2 QTL. Cultivar Ariana, which has intermediate levels of glucosinolates possessed the low-glucosinolate fragment atGSL-1 but the high-glucosinolate fragment atGSL-2. A similar result was found with the cvs. Martina and Bronowski which have intermediate and variable levels of glucosinolates. There were no other RFLP fragments identified by other DNA probes which were specific to either the low- or high-glucosinolate phenotypes. The use of probes wg3f7 and wg7a8 in selection of low-glucosinolate lines in breeding programmes is discussed.     

Breeding for Salinity Tolerance in Plants

Accumulation of high levels of salts in the soil is characteristic of arid and semi-arid regions. Although different curative and management measures are being used to render salt-affected soils fit for agriculture, they are extremely expensive and do not provide permanent solutions to overcome the salinity problem. In contrast, a biotic approach for overcoming salinity stress has gained considerable recognition within the past few decades in view of the vast experimental evidence from what has happened in nature concerning the evolution of highly salt-tolerant ecotypes of different plant species, and also from the remarkable achievements that have been made in improveing different agronomic traits through artificial selection.

Considerable improvements in salt tolerance of important crop species have been achieved in the past 2 decades using barley, rice, pearl millet, maize, sorghum, alfalfa, and many grass species. Such achievements relied solely on assessment of the phenotypic expression of the features involved. Knowledge of the underlying physiological mechanisms producing those salt-tolerant individuals was not clearly known. The present review highlights the relationships between different physiological/biochemical variables being recommended as selection criteria, and salt tolerance of different plant species. This paper also lists different sources of genetic variation for salt tolerance since it is evident that for successful improvement in a character there must be a great amount of genetic variation present in the gene pool of a species.     

Salinity Tolerance in Some Selected Aquatic Oligochaetes

Salt tolerance of the freshwater tubificid Limnodrilus hoffmeisteri varied from an LD 50 of 10 ppt to 10.5 ppt for mature and immature worms without sediment, 9.4 to 10.5 in sand, and 14.3 for immatures acclimated to 5 ppt. Ilyodrilus templetoni was similarly intolerant to higher salinities. The estuarine Tubificoides gabriellae tolerated salt water, but was susceptible to freshwater, with LD 50's of 2 and 3.5 when acclimated to 5 and 10 ppt sea water. It survived immersion in freshwater for 3 hours. The estuarine naidids Paranais litoralis and frici experienced mortalities at both high and low salinities but showed a wide tolerance range. The coastal tubificid Monopylephorus irroratus showed almost complete tolerance to the salinity range employed. The findings reflected field distributions especially when interstitial salinities were measured, but worms did not occupy the full range of habitats possible in terms of salinity alone.     

Variation in the glucosinolate content of vegetative tissues of Chinese lines of Brassica napus L

The glucosinolate content of leaves, stems and roots of a range of Chinese oilseed rape (Brassica napus L.) breeding lines was analysed. Total content and spectrum of individual glucosinolates varied widely, and there was no correlation between seed and vegetative tissue glucosinolate content. Lines with low seed glucosinolates (00) did not necessarily have low glucosinolate content in vegetative tissues; nor did high seed glucosinolate lines always have high vegetative tissue content. There was no correlation between the glucosinolate content of leaf, stem, and root in any given line. It appears that glucosinolate synthesis and accumulation is under tissue-specific control, and the mutation which blocks accumulation of glucosinolates in seeds does not influence other tissues. The responses of these lines to elicitors was also examined. Methyl jasmonate and salicylic acid treatments produced increases in leaf indolyl and aromatic glucosinolates respectively. However, the extent of such increases differed widely between the lines, and there were other, less consistent, effects on other classes of glucosinolate. There seems to be greater variation in glucosinolate accumulation in rape than has previously been reported, and the lines described here have considerable potential for evaluating the effects of manipulating glucosinolate profiles on pest and disease interactions.     

Oxidative Stress Tolerance Mechanism in Rice under Salinity

The research was conducted to investigate comparative oxidative damage including probable protective roles of antioxidant and glyoxalase systems in rice (Oryza sativa L.) seedlings under salinity stress. Seedlings of two rice genotypes: Pokkali (tolerant) and BRRI dhan28 (sensitive) were subjected to 8 dSm⁻¹ salinity stress for seven days in a hydroponic system. We observed significant variation between Pokkali and BRRI dhan28 in phenotypic, biochemical and molecular level under salinity stress. Carotenoid content, ion homeostasis, antioxidant enzymes, ascorbate and glutathione redox system and proline accumulation may help Pokkali to develop defense system during salinity stress. However, the activity antioxidant enzymes particularly superoxide dismutase (SOD), catalase (CAT) and non-chloroplastic peroxidase (POD) were observed significantly higher in Pokkali compared to salt-sensitive BRRI dhan28. Higher glyoxalase (Gly-I) and glyoxalase (Gly-II) activity might have also accompanied Pokkali genotype to reduce potential cytotoxic MG through non-toxic hydroxy acids conversion. However, the efficient antioxidants and glyoxalase system together increased adaptability in Pokkali during salinity stress.     

Regulation of elongase activity by abscisic acid and temperature in microspore‐derived embryos of oilseed rape (Brassica napus)

Growth temperature and ABA both affect the level of erucic acid (22:1) in microspore‐derived embryos (MDEs) of oilseed rape. We have previously shown that these stimuli act independently. In the present study we investigated the effects of growth temperature (15 vs 25°C) and ABA (0 vs 5 µ M ) on the characteristics and activity of the elongase complex, the enzymes synthesising 22:1. Due to inhibition by the substrate oleoyl‐CoA at low concentrations (< 10 µ M ) it was not possible to determine values for K_m and V_max. Elongase activities from preparations extracted from MDEs grown under different conditions showed an optimum temperature higher than 30°C, with a Q₁₀ value of about 3. We found considerable effects of temperature and exogenous ABA on total elongase activity in MDEs. Our results suggest that the accumulation of 22:1 is regulated by the amount of elongase enzyme and not by changes in the intrinsic characteristics of the enzyme. Elongase activity correlated closely with the absolute amount of 22:1 (µmol), whereas the correlation between elongase activity and the fraction of 22:1 (% of fatty acids) in oil was poorer. Including the total activity of acyltransferases did not improve the correlation. Acyltransferase activity itself correlated poorly with the total amount of oil formed.     

Analysis of QTLs for erucic acid and oil content in seeds on A8 chromosome and the linkage drag between the alleles for the two traits in Brassica napus

The history of canola breeding began with the discovery of germplasm with low erucic acid content in seeds of spring forage cultivar in tbe 1950's.FAEI,mutations led to a dramatic decrease of the seed erucic acid content in Arabidopsis thaliana.The products of the two FAEI loci.BnA8.FAEI and BnC3.FAEI,showed additive effects to the level of erucic acid content in oilseed rape.Previous research believed that the pleiotropy of FAEI was responsible for the decrease in seed oil content along with the reduction of seed erucic acid content in the modern cultivars.TN DH population was developed from a canola cultivar Tapidor and a Chinese traditional cultivar Ningyou7.The population had been tested in 10 and 11 environments to map QTLs for the erucic acid content and oil content in seeds.As the map resolution increased,a novel QTL for seed erucic acid content was revealed,after Meta-analysis,7 cM away from the most significant seed erucic acid content QTL where BnA8.FAEI is located.Seven independent QTLs for seed oil content(qOC) were detected around the two seed erucic acid content QTLs(qEA)across 39.20 cM on linkage group A8.Two of the qOCs co-localized with the two qEAs,respectively,and were detected in a single environment.The otherfive qOCs were detected in 10 of ll environments independent of qEAs.Alleles from Tapidor in all the QTLs at the 0-39.20 cM region contributed negative effects to either erucic acid content or oil content in seeds.Parallel,genocontent source.Through rounds of crossbreeding with oil-cropped cultivars and intensive selection for multi generations,Tapidor still had the controlled by the five qEA-independent qOCs,with low seed erucic acid content.Ninety cultivars of B.napus from 8 countries were used to analyze the genetic drag with 9 molecular markers located in the QTL confidence intervals (24.04cM) on linkage group A8.It was noticed that more than 46% of the cultivars with low seed erucic acid content trait remained the genotype of low seed oil content at least in one locus.Backcross and marker-assisted selection could break the genetic drag between the low oil content and erucic acid in seeds in the process for breeding modern high seed oil content canola cultivars.     

Analysis of QTLs for erucic acid and oil content in seeds on A8 chromosome and the linkage drag between the alleles for the two traits in Brassica napus

The history of canola breeding began with the discovery of germplasm with low erucic acid content in seeds of spring forage cultivar in the 1950's.FAE1 mutations led to a dramatic decrease of the seed erucic acid content in Arabidopsis thaliana.The products of the two FAE1 loci,BnA8.FAE1 and BnC3.FAE1,showed additive effects to the level of erucic acid content in oilseed rape.Previous research believed that the pleiotropy of FAE1 was responsible for the decrease in seed oil content along with the reduction ...     

西藏白菜型油菜遗传多样性的RAPD分析

通过利用22个10bp随机引物对来自西藏高原地区107份白菜型油菜种质资源材料的PAPD分析,探讨了西藏白菜型油菜品种之间的遗传分化关系,结果表明：（1）供试的107份材料共产生236条谱带,其中210条谱带有多态性,占88．98％,说明白菜型油菜在西藏高原地区具有较丰富的遗传多样性;（2）根据引物扩增出的DNA指纹图谱,运用UPGMA分析法,在遗传距离为0．078处,可将供试的107份白菜型油菜划分为11个类群,发现来自于同一地区或气候相似区的品种往往聚在一起,表明西藏高原白菜型油菜品种的相似性与其原产地的地理,气候背景密切相关,并在此基础上,结合西藏高原农业发展历史,气候背景以及地形地貌特点和植物地理学,植物区系学,植物进化论等方面的综合分析,提出西藏高原是世界白菜型油菜起源地的观点。     

圆柏属常绿木本植物叶片水分、渗透调节物质的季节变化与抗冷冻性的关系

以祁连圆柏（Sabina przewalskii）和圆柏（Sabina chinensis）为材料,研究了圆柏属植物的抗冷冻性与叶片水分和渗透调节物质季节变化的关系。结果表明,随秋季气温下降,叶片组织相对含水量（RWC）和自由水含量（FWC）下降,束缚水含量（BWC）、脯氨酸（Pro）、游离氨基酸（FAA）、可溶性蛋白质（SP）和可溶性糖（SS）含量增加,翌年春季气温回升,相对含水量和自由水含量增加,束缚水含量下降,有机渗透调节物再次增加。有机渗透调节物在秋末冬初及初春的增加正好与圆柏属植物抗冻锻炼及脱冻恢复生长的时间相吻合,因而是植物抗冻及脱冻适应的重要生理响应,在降低细胞冰点、防止细胞结冰引起的膜机械伤害、抑制膜脂过氧化、保护膜稳定性方面具有重要作用。祁连圆柏的相对含水量和自由水含量均低于圆柏,3种有机渗透调节物含量均高于圆柏,表明祁连圆柏在抗冷冻性诱导中具有更广泛的适应性策略。     

Time of day of leaf wounding determines plant biomass and affects the interplay between growth and defence in Brassica crops

• Recent discoveries pointed out the importance of the mutual correlation between timing of environmental stress and plant fitness. However, the internal reshaping of plant growth under daily stress sensing, and their metabolic coordination remain to be investigated. Thus, we studied the connection between time of day, growth and defence to understand how plant fitness is affected by diurnal stress inputs.
• We examined if simulated herbivory (leaf wounding) in the morning, at midday or the evening differentially influence plant defence state vs growth in three crop species of Brassica: broccoli (Brassica oleraceae), turnip greens (B. rapa) and rapeseed (B. napus).
• The data revealed that plant's tolerance of wounding stress is diurnally regulated in Brassica crops. Trade-offs between biomass and investment in glucosinolates (GSL) and phenolics were affected by timing of leaf stress. Negative correlations between biomass and induction of defence compounds were found for plants treeated in the morning and evening. However, the correlations were positive for midday treatment. Interestingly, we revealed a new connection between plant growth and changes in aliphatic GSLs and flavonoids in response to wounding.
• These data suggest that metabolic stress-dependent circadian oscillations in leaf defences could be one mechanism conferring a competitive advantage to plants to anticipate daily environmental variations by synchronizing them with growth. Moreover, this work provides first insights into how secondary metabolites are linked to growth response in a timing-related manner.

     

芥菜(Brassica juncea)花粉胚状体与离体种胚脂肪酸的变化

在油菜改良品质育种中,利用单个花粉胚状体筛选低或无芥酸株系,需要了解花粉胚状体在发育过程中芥酸含量的变化及与其他脂肪酸变化的关系。Gurr(1972),Dasgupta等(1973)和黄尚琼(1980)研究了不同种、不同品种种子发育过程中脂肪酸组成的变化,但均未曾对离体花粉胚状体和离体种胚进行研究。本文在于探索离     

Selection for high and low thiocyanate ion content in kale (Brassica oleracea var. acephala)

In 1978 genetical variation for thiocyanate ion (SCN-) was found in a kale population being selected for improved digestible organic-matter yield. Four generations of half-sib family selection for high and low SCN^- content in young leaves resulted in subpopulations with almost a twofold difference in their means, no overlap in their distributions, no observable reduction in their genetical variation, and only small differences in other traits. The total observed divergence in SCN^-content was 82% of that expected for a random mating population in linkage equilibrium in the absence of genotype x environment interactions. Average heritability on a single plot basis was low, namely 30%, but was increased to 46% with two replicates. This maximised the predicted response to selection for a fixed number of families selected and a fixed total number of plots.
Bulks of the high and low subpopulations were assessed in a trial in 1988. Averaged over September and December harvests of young and mature leaves, SCN- contents were 104.5 and 58.5 mg/100 g DM, respectively. Of eight controls, cv. Merlin had the lowest content, 63.5, and cv. Proteor had the highest content, 89.6. Cultivar x harvest date, cultivar x leaf age and cultivar x harvest date X leaf age interactions were removed by a logarithmic transformation of the data. Stem contents were very low and variable with an overall mean of 10.9 in September and > 5 in December, and no significant differences between cultivars or populations.
The subpopulations will be valuable for research into possible effects of SCN content on the disease and pest resistance of kale and on the performance of animals fed kale.     

近红外光谱仪快速检测油菜硫苷、芥酸及油份含量数学模型的建立

近红外反射光谱技术是一种高效、快速的现代分析技术,应用过程中需要建立相应的数学模型.收集油菜籽样品600余份,采用国际(家)标准方法对芥酸、硫苷、含油率进行测试,根据各模型的要求,选择不同的具有代表性的样品,建立数学模型.内部交叉证实法对模型验证结果显示:高芥酸、低芥酸、硫苷、含油率模型复相关系数分别为0.9677、0.9318、0.9820、0.9626,内部验证均方差(RMSECV)分别为4.41、2.24、4.62、0.543.外部样品检测法分别用已建模型和国际(家)标准方法对油菜籽样品芥酸、硫苷、含油率进行检测,两者检测结果基本一致.综合内部和外部验证结果表明:建立的模型能够满足油菜籽硫甘、芥酸及油份含量快速检测的要求.另对油菜自身含水率对数学模型的影响做了初步探索.     

甘蓝型油菜芥酸含量的主基因＋多基因遗传

应用植物数量性状主基因＋多基因混合遗传模型对甘蓝型油菜无芥酸品种HSTC     

Short term 22Na+ and 42K+ uptake in intact, mid-vegetative plants

Spergularia marina (L.) Griseb. is. a rapidly growing, annual, coastal halophyte. Because of its small size, it is suitable for isotope studies of ion transport well beyond the seedling stage. The purpose of this report is to establish the similarities and differences between ²²Na⁺ and ⁴²K⁺ uptake in S. marina and in more commonly used mesophytic crop species. Vegetative plants were used 18 days after transfer to solution culture. Plants were grown either on Na⁺-free medium or on 0.2 × sea water. ²²Na⁺ uptake was linear with time for several hours. The rate was relatively insensitive to external concentration between 1 and 180 mol Na⁺ m?³, particularly in Na⁺-free plants. Transport to the shoot accounted for 40 to 70% of the total uptake, dependent on salinity but largely independent of time. ⁴²K⁺ uptake decreased with increasing salinity in Na⁺-free plants and increased in 0.2 × sea water plants. Both uptake and transport to the shoot were non-linear with time, upward concavity suggesting recovery from a manipulative and/or osmotic injury. Steady state root contents were compared with predicted contents based on cortical cell electrical potentials using the Nernst equation. Reasonable agreement was found in all cases except Na⁺ content of 0.2 × sea water plants, in which active efflux was indicated. Uptake studies conducted in the presence of chemical modifiers (dicyclohexylcarbodiimide, dinitrophenol and fusicoccin) showed responses of ⁴²K⁺ uptake as expected from studies on agronomic species, and implied the presence of a similar active uptake here despite the appearance of equilibrium. Active Na⁺ uptake was suggested at low Na⁺ levels. We conclude that S. marina is a promising experimental system combining the rapid nutrient acquisition strategy of agionomically important annuals with a high degree of salt tolerance.     

The Physiological Response of Synechococcus elongatus to Salinity: A Potential Biomarker for Ancient Salinity in Evaporative Environments

The purpose of this study was to characterize the physiological response of Synechococcus elongatus, a brackish-water cyanobacterium, to salt stress. S. elongatus was grown in artificial sea water medium with different salinities. The response was measured by analysis of extracellular polymeric substances (EPS) and membrane lipids. The EPS yields were positively correlated (r² = 0.99) with the salinity. The ratio of unsaturated to saturated fatty acids (U/S) increased with salinity in the range of 2.1‰ to 31.5‰ and decreased at 52.5‰. A positive linear correlation (r² = 0.92) was observed between the average chain length (ACL) of fatty acids and the salinity. These data indicate that S. elongatus adapted to salt stress by the secretion of EPS and by adjusting the membrane fluidity through the changes in ACL or desaturation of fatty acids. These variations in EPS and fatty acids may be used as geochemical biomarkers in sediments to unravel changes in the salinity of ancient evaporative environments.     

Effects of Plant Residue and Salinity on Fractions of Cadmium and Lead in Three Soils

Bioavailability and mobility of heavy metals (HMs) in soils are determined by their partitioning between solution and solid-phase and their further redistribution among solid-phase components. A study was undertaken to determine the effects of organic matter (OM) and salinity on cadmium (Cd) and lead (Pb) distribution among soil fractions. Three agricultural soils were treated with 20 mg Cd/kg as Cd (NO₃)₂·4H₂O, 150 mg Pb/kg as Pb (NO₃)₂, 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl, and then incubated at 60% water holding capacity (60% WHC) and constant temperature (25°C) for 12 weeks. Various fractions of Cd and Pb were extracted from the soils after 2 and 12 w of incubation using a sequential extraction technique. Results showed that in the early stage of incubation (2 w), added Pb were found mainly in the specifically sorbed (SS) and amorphous Fe oxides (AFeO) fractions and added Cd found in SS and Mn oxides (MnO) fractions. Addition of 2% OM decreased the exchangeable (EXC) Pb fraction almost in all soils, whereas it had a different effect on the EXC Cd fraction depending on soil pH. Addition of NaCl increased the EXC Cd fraction in two soils, but it did not alter Pb fractions. At the end of the incubation period, Pb decreased in the EXC and MnO fractions except in the neutral soil and Cd decreased mainly in the SS fraction.