Presowing Seed Treatment with Cytokinins and Its Effect on Growth, Photosynthetic Rate, Ionic Levels and Yield of Two Wheat Cultivars Differing in Salt Tolerance

The effects of presowing seed treatment with different concentrations of cytokinins （kinetin and benzylaminopurine; 100, 150, and 200 mg/L） on growth, photosynthetic capacity, and ion homeostasis were investigated in two spring wheat （Triticum aestivum L.） cultivars, namely MH-97 （salt sensitive） and Inqlab- 91 （salt tolerant）. Primed and non-primed seeds were sown in a field in which NaC1 salinity of 15 dS/m was developed. Of the different concentrations of priming agents tested, the effect of a moderate concentration of kinetin （150 mg/L） was very pronounced, particularly in improving growth and grain yield, in both cultivars. In addition, priming with kinetin alleviated the adverse effect of salt stress on gaseous exchange characteristics （net CO2 assimilation rate and water use efficiency） in both cultivars. Seed priming with a moderate concentration of kinetin also altered the pattern of accumulation of Na^＋ and Clˉ in the shoots, irrespective of the wheat cultivar, under conditions of salt stress. However, all other priming agents at the different concentrations tested did not show any consistent effect on ion levels, except hydropriming, which increased K^＋ levels in the shoots of both cultivars under salt stress. In conclusion, a moderate concentration of kinetin showed a consistent effect in altering the growth and grain yield of both wheat cultivars, which was related to the beneficial effects of kinetin priming on water use efficiency and photosynthetic rate under conditions of salt stress.     

Alleviation of salinity-induced perturbations in ionic and hormonal concentrations in spring wheat through seed preconditioning in synthetic auxins

The experiments were conducted to examine the effects of seed priming in solutions (100, 150 and 200 mg L^?1) of different synthetic auxins, i.e., 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), α-naphthaleneacetic acid (NAA) on growth, grain yield, gaseous exchange characteristics, ionic and hormonal concentrations in two spring wheat (Triticum aestivum L.) cultivars MH-97 (salt intolerant) and Inqlab-91 (salt tolerant). The primed (soaked for 12 h) and non-primed seeds were sown in Petri plates in a growth room as well as in a field treated with 150 mM NaCl. Generally, all synthetic auxins did not increase germination percentage and rate in both cultivars when compared with hydropriming (control), and even decreased these attributes when applied at higher concentrations (200 mg L^?1). Nonetheless, under salt stress, NAA (150 mg L^?1) was most effective in increasing seedling shoot dry weight, fertile tillers per plant, number of grains per ear and grain yield in both cultivars. The plants raised from seed treated with NAA (150 mg L^?1) had lower shoot [Na⁺] in the salt intolerant cultivar. Moreover, NAA treatment improved root [Ca²⁺] in both cultivars. Priming agents affected leaf free indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) concentrations differently in both cultivars. Treatment with NAA (150 mg L^?1) lowered leaf free abscisic acid (ABA) and putrescine (Put) concentrations and raised salicylic acid (SA) and spermidine (Spd) concentrations in the salt intolerant cultivar. In conclusion, pre-treatment with NAA (150 mg L^?1) showed consistent promotive effects on growth and grain yield in the two cultivars, which were partially attributed to the beneficial effects of NAA-priming on ionic and hormonal homeostasis under salt stress.     

Seed Treatment with Auxins Modulates Growth and Ion Partitioning in Salt-stressed Wheat Plants

Experiments were performed to determine whether seed priming with different concentrations (100, 150, and 200 mg/L) ofauxins (indoleacetic acid (IAA), indolebutyric acid (IBA), or their precursor tryptophane (Trp)) could alter salinity inducedperturbances in salicylic acid and ion concentrations and, hence, growth in wheat (Triticum aestivum L.) cultivars, namelyM. H.-97 (salt intolerant) and Inqlab-91 (salt tolerant). Primed and non-primed seeds were sown in Petri dishes in a growthroom, as well as in a field treated with 15 dS/m NaCl salinity. All priming agents, except IBA, increased the final germinationpercentage in both cultivars. The seedlings of either cultivar raised from Trp-treated seeds had greater dry biomass whenunder salt stress. In field experiments, Trp priming was much more effective in mediating the increase in grain yield,irrespective of the cultivar, under salt stress. The alleviatory effect of Trp was found to be associated with reduced uptakeof Na~ in the roots and subsequent translocation to the shoots, as well as increased partitioning of Ca~(2 )in the roots ofsalt-stressed wheat plants. Plants of both cultivars raised from Trp-and IAA-treated seeds accumulated free salicylic acidin their leaves when under salt stress. Overall, the Trp priming-induced improvement in germination and the subsequentgrowth of wheat plants could be related to ion homeostasis when under salt stress. The possible involvement of salicylicacid in the Trp priming-induced better growth under conditions of salt stress is discussed.     

Seed Treatment with Auxins Modulates Growth and Ion Partitioning in Salt-stressed Wheat Plants

Experiments were performed to determine whether seed priming with different concentrations （100, 150, and 200 mg/L） of auxins （indoleacetic acid （IAA）, indolebutyric acid （IBA）, or their precursor tryptophane （Trp）） could alter salinity induced perturbances in salicylic acid and ion concentrations and, hence, growth in wheat （Triticum aestivum L.） cultivars, namely M.H.-97 （salt intolerant） and tnqtab-91 （salt tolerant）. Primed and non-primed seeds were sown in Petri dishes in a growth room, as well as in a field treated with 15 dS/m NaCl salinity. All priming agents, except IBA, increased the final germination percentage in both cultivars. The seedlings of either cultivar raised from Trp-treated seeds had greater dry biomass when under salt stress. In field experiments, Trp priming was much more effective in mediating the increase in grain yield, irrespective of the cultivar, under salt stress. The alleviatory effect of Trp was found to be associated with reduced uptake of Na^＋ in the roots and subsequent translocation to the shoots, as well as increased partitioning of Ca^＋ in the roots of salt-stressed wheat plants. Plants of both cultivars raised from Trp-and IAA-treated seeds accumulated free salicylic acid in their leaves when under salt stress. Overall, the Trp priming-induced improvement in germination and the subsequent growth of wheat plants could be related to ion homeostasis when under salt stress. The possible involvement of salicylic acid in the Trp priming-induced better growth under Conditions of salt stress is discussed.     

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress？

In order to assess whether salt tolerance could be Improved In spring wheat （Triticum aestivum L.）, the present study was performed by soaking the seeds of two cultlvars, namely MH-97 （salt sensitive） and Inqlab-91 （salt tolerant）, for 12 h In distilled water or 100 mol/m^3 CaCl2, KCI, or NaCI. Primed seeds from each treatment group and non-primed seeds were sown In a field In which NaCI salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCI and NaCI, was found to be effective In alleviating the adverse effects of salt stress on both wheat cultivars In terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance In plants of both cultlvars. In MH-97 plants, CaCl2 pretreatment considerably reduced leaf absclslc acid （ABA） concentrations and Increased leaf free salicylic acid （SA） concentrations under both saline and non-saline conditions. In contrast, In the Inqlab-91 plant, CaCl2 Increased free Indoleacetic acid （IAA） and indolebutyrlc acid （IBA） content. However, priming of seeds with CaCl2 did not alter free polyamlne levels in either cultlvar, although spermldlne levels were considerably lower In plants raised from seeds treated with CaCl2 for both cultlvars under saline conditions. Priming with KCI Increased growth In Inqlab-91 plants, but not In MH-97 plants, under saline conditions. The salinity Induced reducUon In auxins （IAA and IBA） was alleviated by NaCI priming In both cultlvars under saline conditions. However, NaCI Increased leaf free ABA content and lowered leaf SA and putresclne levels In Inqlab-91 plants under saline conditions. In conclusion, although all three priming agents （I.e. CaCl2, KCI, and NaCI） were effective In alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different In the two cuItlvars.     

The response of Mo-hydroxylases and abscisic acid to salinity in wheat genotypes with differing salt tolerances

The differential responses of the wheat cultivars Shi4185 and Yumai47 to salinity were studied. The higher sensitivity of Yumai47 to salinity was linked to a greater growth reduction under salt stress, compared to more salt-tolerant Shi4185. Salinity increased the Na⁺, proline and superoxide anion radical (O₂ ^?) contents in both cultivars. Leaf Na⁺ content increased less in the more salt-tolerant cultivar Shi4185 than salt-sensitive Yumai47. The proline content increased more significantly in Shi4185 than Yumai47; on the contrary, superoxide anion radical content increased less in Shi4185 than Yumai47. This data indicated that wheat salinity tolerance can be increased by controlling Na⁺ transport from the root to shoot, associated with higher osmotic adjustment capability and antioxidant activity. Although salinity increased aldehyde oxidase (AO) activity and abscisic acid (ABA) content in the leaves and roots of both cultivars following the addition of NaCl to the growth medium, AO and ABA increased more in the salt-sensitive cultivar Yumai47 than the more salt-tolerant cultivar Shi4185. Xanthine dehydrogenase (XDH) activity in the leaves of both cultivars increased with increasing concentrations of NaCl; however, leaf XDH activity increased more significantly in Yumai47 than Shi4185. Root XDH activity in Shi4185 decreased with increasing NaCl concentrations, whereas salinity induced an increased root XDH activity in Yumai47. The involvement of AO and XDH enzymatic activities and altered ABA content in the response mechanisms of wheat to salinity are discussed herein.     

棉花萌发期和苗期耐盐性评价及耐盐指标筛选

于2010年在江苏南京农业大学人工气候室内进行砂培试验,采用不同浓度的NaCl水溶液模拟盐胁迫,以多项指标盐害系数隶属函数值和总隶属函数值为依据,比较了13个棉花品种萌发期和苗期的耐盐性,并进行聚类分析.结果表明:150mmol·L-1NaCl是进行棉花耐盐性鉴定的适宜盐浓度.棉花的耐盐性在生育期和品种间表现不同:中棉所44和中棉所177是在萌发期和苗期均表现稳定的耐盐品种,表现稳定但不耐盐品种有中棉所102、苏棉12号和泗棉3号,表现稳定且中等耐盐品种有中棉所103、德夏棉1号和美棉33B;发芽率、发芽势、发芽指数、活力指数和鲜质量的盐害系数可以作为棉花萌发期耐盐鉴定指标,株高、叶片伸展速率、地上部干质量、根系干质量、根系活力和净光合速率的盐害系数可以作为棉花苗期耐盐鉴定指标.     

Tissue culture of the desert plant Anastatica hiërochuntica

Summary Callus derived from the winter annual desert plant Anastatica hiërochuntica was grown on different media, Murashige and Skoog (1962) medium giving the best results. Large amounts of lignified xylem elements were formed resulting in an extremely hard tissue. The growth responses to different auxins, cytokinins and abscisic acid were investigated. When salts (high Na⁺, Ca²⁺ and Cl^--contents) as they can be found in aqueous extracts of desert soils from a natural A. hiëerochuntica habitat were added to Abou-Mandour (1977) or MS-media, growth of callus was inhibited drastically. In the presence of abscisic acid, however, original growth was completely restored. In salt free control media on the other hand, ABA proved to be inhibitory. Drought stress caused a decrease of both cytokinins and indoleacetic acid in the callus while ABA levels were increased, but by far not as distinct as in intact plants. Proline level was not affected by stress.Abbreviations ABA abscisic acid - AM Abou-Mandour-medium - BAP benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - DHZR dihydroxyzeatinriboside - DW dry weight - ELISA enzyme linked immuno sorbent assay - FW freshweight - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - IBA indole-3-butyric acid - IPA isopentenyladenosine - Kin kinetin - MS Murashige and Skoog-medium     

Exogenously applied paclobutrazol modulates growth in salt-stressed wheat plants

Effect of paclobutrazol (PBZ) treatment on salinity tolerance of wheat (Triticum aestivum) was investigated on a salt-tolerant (Karchia-65) and salt-sensitive (Ghods) cultivars. Salinity significantly reduced the investigated growth parameters such as plant height, length and area of sixth leaf, root length, fresh and dry weight of shoot, roots and sixth leaf, water content (WC) of plant and seeds weight in the both cultivars. The negative effect of salinity in Ghods cultivar was more than Karchia cultivar. However, PBZ treatment reduced the growth in both cultivars, the differences in plant growth among various levels of NaCl decreased in PBZ-treated plants. Salt stress resulted in high accumulation of Na⁺ in the sixth leaf and roots in both cultivars, particularly in Ghods cultivar. Against Karchia cultivar, salt stress decreased the storage of K⁺, P and N in sixth leaf and roots in Ghods cultivar. In the both cultivars, PBZ treatment enhanced the K⁺, P and N contents in sixth leaf and roots by increasing salinity. Although PBZ treatment decreased the growth of plants, it improved the weight of seeds against stress damage. PBZ treatment reduced the accumulation of harmful Na⁺ ion in plant tissues while increased the K⁺, P and N contents. These observations suggest that PBZ treatment may increase tolerance by diminishing ionic imbalance caused by salt stress.     

盐胁迫环境下不同抗盐性小麦品种幼苗长势和内源激素的变化

采用两种浓度NaCl溶液,对不同抗盐性小麦品种德抗961(抗盐性强)和泰山9818(抗盐性弱)萌发期幼苗进行胁迫处理,观察其幼苗长势和内源激素含量变化.结果表明,盐胁迫抑制小麦幼苗生长,抗盐性弱的泰山9818受抑制较重.苗、根ABA含量随盐胁迫浓度增加而提高,泰山9818的增幅高于德抗961.苗、根IAA含量随盐胁迫浓度增加而降低,但德抗961的IAA含量高于泰山9818,说明盐胁迫下抗盐性强的品种具有较高IAA合成量.2品种GA3含量变化因盐胁迫浓度而异.在低盐胁迫下抗盐性强的品种苗中GA3含量提高以适应盐胁迫利于苗的生长,在高盐胁迫下2品种GA3含量降低.盐胁迫使苗中ZR含量增加,且德抗961的苗中ZR含量高于泰山9818,而根中ZR含量则前者低,说明盐胁迫下抗盐性强的品种可迅速将根部合成的ZR向苗中转移,促进苗的生长.2品种IAA/ABA、GA3/ABA比值随盐胁迫浓度增加和时间延长而下降,德抗961 IAA/ABA比值大于泰山9818.在盐胁迫下,抗盐性强的品种协调自身激素平衡的能力较强可能是其生长受抑制较小的重要原因.     

Changes in growth,photosynthetic capacity and ionic relations in spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) due to pre-sowing seed treatment with polyamines

The influence of pre-sowing seed treatment with polyamines (2.5 mM putrescine, 5.0 mM spermidine and 2.5 mM spermine) on growth, photosynthetic capacity, and ion accumulation in two spring wheat (Triticum aestivum L.) cultivars MH-97 (intolerant) and Inqlab-91 (tolerant) was examined. The primed seeds of each treatment and non-primed seeds were sown in a field containing 15 dS m⁻¹ NaCl. Although all three polyamines were effective in improving shoot growth and grain yield in both cultivars under saline conditions, the effect of spermine was very pronounced particularly in improving grain yield. Different priming agents did not affect the net CO₂ assimilation rate and transpiration rate of either cultivar. However, pre-treatment with spermidine increased stomatal conductance (g_s) in the tolerant cultivar, whereas with spermine stomatal conductance decreased in the intolerant cultivar under salt stress. Priming agents had different effects on the accumulation of different ions in wheat plant tissues. When spermidine and distilled water were used as priming agents, they were effective in reducing shoot [Na⁺] in the tolerant and intolerant cultivars, respectively under saline conditions. Although all priming agents caused an increase in shoot [K⁺], distilled water was more effective in improving shoot [K⁺] in both cultivars under salt stress. Pre-treatment with spermidine was very effective in reducing shoot [Cl⁻] under saline conditions particularly in the tolerant cultivar. However, the pattern of accumulation of different ions in roots due to different seed priming treatments was not consistent in either cultivar except that root Na⁺ decreased due to priming with spermine and spermidine in the intolerant and tolerant cultivars under saline conditions. In conclusion, although all three priming agents, spermine, spermidine and putrescine, were effective in alleviating the adverse effect of salt stress on wheat plants, their effects on altering the concentration of different ions and growth were different in the two cultivars differing in salt tolerance.     

Cloning and functional analysis of wheat V-H+-ATPase subunit genes

The root microsomal proteomes of salt-tolerant and salt-sensitive wheat lines under salt stress were analyzed by two-dimensional electrophoresis and mass spectrum. A wheat V-H(+)-ATPase E subunit protein was obtained whose expression was enhanced by salt stress. In silicon cloning identified the full-length cDNA sequences of nine subunits and partial cDNA sequences of two subunits of wheat V-H(+)-ATPase. The expression profiles of these V-H(+)-ATPase subunits in roots and leaves of both salt-tolerant and salt-sensitive wheat lines under salt and abscisic acid (ABA) stress were analyzed. The results indicate that the coordinated enhancement of the expression of V-H(+)-ATPase subunits under salt and ABA stress is an important factor determining improved salt tolerance in wheat. The expression of these subunits was tissue-specific. Overexpression of the E subunit by transgenic Arabidopsis thaliana was able to enhance seed germination, root growth and adult seedling growth under salt stress.     

Effects of seed priming with ascorbic acid to mitigate salinity stress on three wheat (Triticum aestivum L.) cultivars.

In this study, the effect of seed priming using ascorbic acid (ASA) on three commercial wheat cultivars i.e., Punjab-2011, Faisalabad-2008, and Ujala-2016 under salinity stress in both homogenous and heterogeneous environments has been investigated. It revealed that different levels of salinity have significantly reduced the growth attributes like percent germination, germination index, radical & plumule length, seed vigor index (In-vitro), seedling length, fresh & dry weight, and total chlorophyll content (In-vivo) with subsequent treatments. Salinity stress was induced by using NaCl in three different concentrations (100, 150, and 200 mM). Seeds of the three cultivars primed with 50, 100, and 150 mg/L ascorbic-acids have not only improved percent germination but also considerably reduced germination time and increased germination index (GI) indicating the potential for tolerating saline conditions. Seedling growth (seedling length, Fresh weight, and dry weight) of seeds primed with 50, 100, and 150 mg/L (ASA) was significantly higher than other non-primed seeds under the prevailing saline conditions. Hormonal priming with different concentrations of ascorbic acid was effective, nevertheless, the best results were obtained with 100 and 150 mg/L (ASA) concentrations. We concluded that the delay in germination and seedling growth was mainly due to excessive Na⁺ accumulation in the seeds of wheat cultivars. On the other hand, seed priming with various concentrations of ascorbic acid has proved to be effective in inducing salt tolerance in terms of germination parameters, seedling characteristics, and chlorophyll retention in the three local commercial wheat cultivars.     

Gibberellic acid mediated induction of salt tolerance in wheat plants: Growth,ionic partitioning,photosynthesis, yield and hormonal homeostasis

In order to elucidate the GA₃-priming-induced physiochemical changes responsible for induction of salt tolerance in wheat, the primed and non-primed seeds of two spring wheat (Triticum aestivum L.) cultivars, namely, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were sown in a field treated with 15 dS m⁻¹ NaCl salinity. Although all the three concentrations (100, 150 and 200 mg L⁻¹) of GA₃ were effective in improving grain yield in both cultivars, the effect of 150 mg L⁻¹ GA₃ was much pronounced particularly in the salt intolerant cultivar when under salt stress. Seed priming with GA₃ altered the pattern of accumulation of different ions between shoots and roots in the adult plants of wheat under saline conditions. Treatment with GA₃ (150 mg L⁻¹) decreased Na⁺ concentrations both in the shoots and roots and increased Ca²⁺ and K⁺ concentrations in the roots of both wheat cultivars. GA₃-priming did not show consistent effect on gaseous exchange characteristics and the concentrations of auxins in the salt stressed plants of both wheat cultivars. However, all concentrations of GA₃ reduced leaf free ABA levels in the salt intolerant, while reverse was true in the salt tolerant cultivar under saline conditions. Priming with GA₃ (150 mg L⁻¹) was very effective in enhancing salicylic acid (SA) concentration in both wheat cultivars when under salt stress. Treatment with GA₃ (100–150 mg L⁻¹) lowered leaf free putrescine (Put) and spermidine (Spd) concentrations in the plants of both wheat cultivars. The decrease in polyamines (Put and Spd) and ABA concentrations in the salt stressed plants of the salt intolerant cultivar treated with GA₃ suggested that these plants might have faced less stress compared with control. Thus, physiologically, GA₃-priming-induced increase in grain yield was attributed to the GA₃-priming-induced modulation of ions uptake and partitioning (within shoots and roots) and hormones homeostasis under saline conditions.     

Influence of gibberellic acid and different salt concentrations on germination percentage and physiological parameters of oat cultivars

Gibberellic acid (GA₃) is one of the plant growth regulators which improve salt tolerance and mitigate the salt stress impact on plants. The extant analysis was carried out to study the effect of GA₃ and different salt concentrations on seed germination and physiological parameters of oat cultivars. Oats is substantially less tolerant to salt than wheat and barley. Experimentation was conducted as factorial with Completely Randomized Block Design with three replicates. Different concentration of NaCl salt ((25, 50, 75 and 100 mM) were used in test control group and 100 and 150 ppm of GA₃ were used in two group by pre-treated (after 24 h of the seed soaking) and plants were analyzed on 15th day. Results indicate that increasing salinity would decrease the germination percentage and growth parameter in three oat cultivars. Quotes data indicating a 13%, 19.9% and 32.48% in cultivars NDO-2, UPO-212 and UPO-94 germination reduction when soil salinity reaches 50 mM. A 36.02%, 47.33% and 56.365 reduction in germination is likely when soil salinity reaches 100 mM respectively same cultivars. Seeds treated with GA₃ significantly promoted the percentage of germination, shoot and root length, total fresh and dry weight of seedling, tissue water content and seedling vigor index by NDO-2 and UPO-212 under different saline concentration. The maximum average of germination and growth parameters were observed from 150 ppm GA₃ treated seeds. But this concentration was significantly inhibited root length in sensitive cultivar UPO-94 at 75 and 100 mM salt as compared to 100 ppm. We observed that, the high concentration of GA₃ was not suitable for sensitive oat cultivars. Because the plant root are the real workforce behind any plants success. Thus, it may be concluding that, GA₃ treatment could curtail the toxic effect of salinity by increasing germination percentage and shoot and root length, total fresh and dry weight, tissue water content and seedling vigor index in tolerant cultivar.     

Promotion by 5-Aminolevulinic Acid of Germination of Pakchoi （Brassica campestris ssp. chinensis var. communis Tsen et Lee） Seeds Under Salt Stress

The seed germination and seedling growth of pakchoi （Brassica campestris ssp. chinensis var. communis Tsen et Lee cv. Hanxiao） were not significantly inhibited until the concentration of NaCl was increased to 150 mmol/L. Treatment of pakchoi seeds with exogenous 5-aminolevulinic acid （ALA）, at concentrations ranging from 0.01 to 10.00 mg/L, promoted seed germination when seeds were stressed by salinity, whereas levulinic acid （LA）, an inhibitor of ALA dehydrase, significantly inhibited seed germination and seedling growth, suggesting that metabolism of ALA into porphyrin compounds was necessary for seed germination and seedling growth. Determination of respiratory rate during seed germination showed that ALA increased seed respiration under both normal conditions and salt stress. Furthermore, salt stress decreased levels of endogenous ALA, as well as heme, in etiolated seedlings. More salt-tolerant cultivars of pakchoi contained higher relative levels of endogenous ALA and heme under conditions of salt stress. These results indicate that salt stress may inhibit the biosynthesis of endogenous ALA and then heme, which is necessary for seed germination, and treatment of seeds with exogenous ALA prior to germination may be associated with the biosynthesis of heme.     

Response of two tomato cultivars differing in salt tolerance to inoculation with mycorrhizal fungi under salt stress

Effects of arbuscular mycorrhizal fungi (AMF) and salt stress on nutrient acquisition and growth of two tomato cultivars exhibiting differences in salt tolerance were investigated. Plants were grown in a sterilized, low-P (silty clay) soil-sand mix. Salt was applied at saturation extract (EC_e) values of 1.4 (control), 4.9 (medium) and 7.1 dS m^–1 (high salt stress). Mycorrhizal colonization occurred irrespective of salt stress in both cultivars, but AMF colonization was higher under control than under saline soil conditions. The salt-tolerant cultivar Pello showed higher mycorrhizal colonization than the salt-sensitive cultivar Marriha. Shoot dry matter (DM) yield and leaf area were higher in mycorrhizal than nonmycorrhizal plants of both cultivars. Shoot DM and leaf area but not root DM were higher in Pello than Marriha. The enhancement in shoot DM due to AMF inoculation was 22% and 21% under control, 31% and 58% under medium, and 18% and 59% under high salinity for Pello and Marriha, respectively. For both cultivars, the contents of P, K, Zn, Cu, and Fe were higher in mycorrhizal than nonmycorrhizal plants under control and medium saline soil conditions. The enhancement in P, K, Zn, Cu, and Fe acquisition due to AMF inoculation was more pronounced in Marriha than in the Pello cultivar under saline conditions. The results suggest that Marriha benefited more from AMF colonization than Pello under saline soil conditions, despite the fact that Pello roots were highly infected with the AMF. Thus, it appears that Marriha is more dependent on AMF symbiosis than Pello. Accepted: 22 January 2001     

Promotion by 5-Aminolevulinic Acid of Germination of Pakchoi (Brassica campestris ssp. chinensis var. communis Tsen et Lee) Seeds Under Salt Stress

The seed germination and seedling growth of pakchoi (Brassica campestris ssp. chinensis var.communis Tsen et Lee cv. Hanxiao) were not significantly inhibited until the concentration of NaCl was increased to150 mmol/L. Treatment of pakchoi seeds with exogenous 5-aminolevulinic acid (ALA), at concentrations ranging from 0.01 to 10.00 mg/L, promoted seed germination when seeds were stressed by salinity, whereas levulinic acid (LA), an inhibitor of ALA dehydrase, significantly inhibited seed germination and seedling growth, suggesting that metabolism of ALA into porphyrin compounds was necessary for seed germination and seedling growth. Determination of respiratory rate during seed germination showed that ALA increased seed respiration under both normal conditions and salt stress. Furthermore, salt stress decreased levels of endogenous ALA, as well as heme, in etiolated seedlings. More salt-tolerant cultivars of pakchoi contained higher relative levels of endogenous ALA and heme under conditions of salt stress.These results indicate that salt stress may inhibit the biosynthesis of endogenous ALA and then heme,which is necessary for seed germination, and treatment of seeds with exogenous ALA prior to germination may be associated with the biosynthesis of heme.     

Involvement of abscisic acid and cytokinins in the senescence and remobilization of carbon reserves in wheat subjected to water stress during grain filling

This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre‐stored carbon reserves. Two high lodging‐resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well‐watered (WW) and water‐stressed (WS) treatments were imposed from 9 d post‐anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non‐structural carbohydrate in the stems and promoted the re‐allocation of prefixed ¹⁴C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre‐stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress.