Ethylene improves Arabidopsis salt tolerance mainly via retaining K+ in shoots and roots rather than decreasing tissue Na+ content

Ethylene has been reported to play an essential role in the response of Arabidopsis to salinity and K⁺ deficiency. It was proposed that plant's ability to maintain potassium (K⁺) and minimize sodium (Na⁺) in tissues of salinity plants is critical for salt tolerance (ST). It is still unclear how ethylene modulates plant ion homeostasis under saline occasions. We employed Arabidopsis wild type (Col-0), ethylene insensitive mutants (ein2-5 and ein3-1) and constitutive triple response mutant (ctr1-1) plants to compare their phenotypic and physiological responses to salinity. Ethephon applied to plants could convert quickly to ethylene and here was applied exogenously to Col-0 seedlings to validate ethylene role in salt response. We showed that ethylene insensitivity in ein2-5 or ein3-1 plants increased Arabidopsis salt sensitivity than in Col-0. However, the salinity-induced adverse effects on Chlorophyll a/b, photosystem II function (Fv/Fm) and redox state were largely amended in the ctr1-1 than in Col-0 plants with the severe salinity. The compatible solute sucrose and antioxidant system were also up-regulated to improve ST in ctr1-1 plants. The ethephon obviously alleviated the salinity-induced restriction in root length. The subsequent analysis on the Na⁺ and K⁺ homeostasis found that ethylene could help plant retain higher shoot or root K⁺ nutrition in the short- or long-term salt-stressed plants. However, the ethylene did not significantly alter sodium buildup and water relation in the salt-stressed plants. Our observations confirmed the key role of ethylene in improved plant ST and highlighted the ethylene ability to retain K⁺, rather than decreasing Na⁺, in shoots and roots to improve Arabidopsis ST.     

Nitrogen transfer from forage legumes to nine neighbouring plants in a multi-species grassland

Legumes play a crucial role in nitrogen supply to grass-legume mixtures for ruminant fodder. To quantify N transfer from legumes to neighbouring plants in multi-species grasslands we established a grass-legume-herb mixture on a loamy-sandy site in Denmark. White clover (Trifolium repens L.), red clover (Trifolium pratense L.) and lucerne (Medicago sativa L.) were leaf-labelled with ¹⁵N enriched urea during one growing season. N transfer to grasses (Lolium perenne L. and xfestulolium), white clover, red clover, lucerne, birdsfoot trefoil (Lotus corniculatus L.), chicory (Cichorium intybus L.), plantain (Plantago lanceolata L.), salad burnet (Sanguisorba minor L.) and caraway (Carum carvi L.) was assessed. Neighbouring plants contained greater amounts of N derived from white clover (4.8?g?m^-2) compared with red clover (2.2?g?m^-2) and lucerne (1.1?g?m^-2). Grasses having fibrous roots received greater amounts of N from legumes than dicotyledonous plants which generally have taproots. Slurry application mainly increased N transfer from legumes to grasses. During the growing season the three legumes transferred approximately 40?kg?N ha^-1 to neighbouring plants. Below-ground N transfer from legumes to neighbouring plants differed among nitrogen donors and nitrogen receivers and may depend on root characteristics and regrowth strategies of plant species in the multi-species grassland.     

Competitive Al Inhibition of Net Mg Uptake by Intact Lolium multiflorum Roots : II. Plant Age Effects

Rhizotoxicity of Al is more pronounced in younger plants. Effects of Al on nutrient uptake by plants of different age are poorly understood. The depletion technique was used to monitor net Mg²⁺ uptake from nutrient solutions by intact 15- and 35-day-old plants of two ryegrass (Lolium multiflorum Lam.) cultivars. Lowering the pH from 6.0 to 4.2 decreased the maximum net ion influx without affecting K_m. Aluminum at 6.6 micromolar Al³⁺ activity increased K_m indicating competitive inhibition. The effects of pH and 6.6 micromolar Al³⁺ on net Mg²⁺ uptake were much larger in 15- than in 35-day-old plants. Aluminum at 26 micromolar Al³⁺ activity competitively inhibited net Mg²⁺ uptake by 35-day-old plants, while causing time- and external Mg²⁺ activity-dependent net Mg²⁺ efflux from 15-day-old plants. The equilibrium constant (K_i) of a reversible combination of postulated plasmalemma Mg²⁺ transporter and Al³⁺ was calculated to be 2 and 5 micromolar Al³⁺ activity for 15-day-old plants of Wilo and Gulf ryegrass, respectively, and 21 micromolar Al³⁺ activity for 35-day-old plants of both cultivars. The Al³⁺-mediated increase in K_m was larger for 15-day-old plants of the Al-sensitive cultivar `Wilo' than of the more Al-tolerant cultivar `Gulf,' while Al³⁺ affected 35-day-old plants of both cultivars to the same extent.     

Overexpression of a GmCnx1 Gene Enhanced Activity of Nitrate Reductase and Aldehyde Oxidase,and Boosted Mosaic Virus Resistance in Soybean

Molybdenum cofactor (Moco) is required for the activities of Moco-dependant enzymes. Cofactor for nitrate reductase and xanthine dehydrogenase (Cnx1) is known to be involved in the biosynthesis of Moco in plants. In this work, a soybean (Glycine max L.) Cnx1 gene (GmCnx1) was transferred into soybean using Agrobacterium tumefaciens-mediated transformation method. Twenty seven positive transgenic soybean plants were identified by coating leaves with phosphinothricin, bar protein quick dip stick and PCR analysis. Moreover, Southern blot analysis was carried out to confirm the insertion of GmCnx1 gene. Furthermore, expression of GmCnx1 gene in leaf and root of all transgenic lines increased 1.04-2.12 and 1.55-3.89 folds, respectively, as compared to wild type with GmCnx1 gene and in line 10 , 22 showing the highest expression. The activities of Moco-related enzymes viz nitrate reductase (NR) and aldehydeoxidase (AO) of T₁ generation plants revealed that the best line among the GmCnx1 transgenic plants accumulated 4.25 μg g^-1 h^-1 and30 pmol L^-1, respectively (approximately 2.6-fold and 3.9-fold higher than non-transgenic control plants).In addition, overexpression ofGmCnx1boosted the resistance to various strains of soybean mosaic virus (SMV). DAS-ELISA analysis further revealed that infection rate of GmCnx1 transgenic plants were generally lower than those of non-transgenic plants among two different virus strains tested. Taken together, this study showed that overexpression of a GmCnx1 gene enhanced NR and AO activities and SMV resistance, suggesting its important role in soybean genetic improvement.     

Regeneration of Heracleum candicans Wall Plants from Callus Cultures through Organogenesis

Callus was initiated from petiole explants of Heracleum candicans on MS medium fortified with BAP and 2,4-D ( 0.5 mg I^-1 each). Maximum shoot differentiation from callus occurred on MS medium containing 1 mg I^-1 BAP and 0.2 mg I^-1 NAA. The regenerated shoots were rooted on MS medium supplemented with 1 mg I^-1 IBA. The rooted plants were transferred to the field after successful hardening in pots containing vermiculite. All regenerated plants were diploid with 2n=22 chromosomes in their root tip cells.     

Growth and Reproduction of Glyphosate-Resistant and Susceptible Populations of Kochia scoparia

Evolution of glyphosate-resistant kochia is a threat to no-till wheat-fallow and glyphosate-resistant (GR) cropping systems of the US Great Plains. The EPSPS (5-enol-pyruvylshikimate-3-phosphate synthase) gene amplification confers glyphosate resistance in the tested Kochia scoparia (L.) Schrad populations from Montana. Experiments were conducted in spring to fall 2014 (run 1) and summer 2014 to spring 2015 (run 2) to investigate the growth and reproductive traits of the GR vs. glyphosate-susceptible (SUS) populations of K. scoparia and to determine the relationship of EPSPS gene amplification with the level of glyphosate resistance. GR K. scoparia inbred lines (CHES01 and JOP01) exhibited 2 to 14 relative copies of the EPSPS gene compared with the SUS inbred line with only one copy. In the absence of glyphosate, no differences in growth and reproductive parameters were evident between the tested GR and SUS inbred lines, across an intraspecific competition gradient (1 to 170 plants m^-2). GR K. scoparia plants with 2 to 4 copies of the EPSPS gene survived the field-use rate (870 g ha^-1) of glyphosate, but failed to survive the 4,350 g ha^-1 rate of glyphosate (five-times the field-use rate). In contrast, GR plants with 5 to 14 EPSPS gene copies survived the 4,350 g ha^-1 of glyphosate. The results from this research indicate that GR K. scoparia with 5 or more EPSPS gene copies will most likely persist in field populations, irrespective of glyphosate selection pressure.     

Aluminum and plant age effects on adsorption of cations in the Donnan free space of ryegrass roots

Four cultivars of ryegrass (Lolium multiflorum Lam. cvs. Gulf, Marshall, Urbana, and Wilo) were grown in nutrient solution (pH 4.2) at two Al levels (0 and 74 μM). Cations were desorbed from the Donnan free space of roots of 15-, 23-, and 35-day-old plants using BaCl₂, BaCl₂-triethanolamine, NH₄OAc, and KCl. The amounts of desorbed Ca²⁺ and K⁺ decreased, while desorption of Mn²⁺ and Na⁺ increased with plant age. Differences between 15- and 35-day-old plants, but not between 15- and 23-day-old, were significant. Aluminum considerably decreased the amount of desorbed divalent cations (Ca²⁺, Mg²⁺) and increased the amount of desorbed K⁺ and Na⁺. Ability to resist these changes appeared to be one of the mechanisms determining Al tolerance of ryegrass cultivars.     

Aluminum tolerance in Arabidopsis thaliana as affected by endogenous salicylic acid

Endogenous salicylic acid (SA) functions in plant response to an aluminum stress were assessed. We used different Arabidopsis thaliana genotypes including snc1 with a constitutively high content of SA, sid2 and nahG (transgenic lines) both with a low content of SA, SA insensitive mutant npr1-1, and snc1/nahG (i.e., the nahG expression in the snc1 background) with a similar SA content as in wild type (WT) plants. Results show that the snc1 plants displayed obvious growth retardation of roots and shoots under the Al³⁺ stress, whereas the sid2, nahG, and npr1-1 plants exhibited alleviated symptoms in comparison with the WT plants. The Al³⁺ content increased in all the tested genotypes with the increasing AlCl₃ concentration applied, but no significant variations were detected among the tested genotypes. The snc1 had much higher superoxide dismutase and peroxidase activities, and a lower catalase activity and the ratio of reduced to oxidized glutathione accompanied by higher accumulations of H₂O₂ and malondialdehyde compared with the WT plants. These changes were largely reversed by the introduction of nahG; the sid2, nahG, and npr1-1 plants were less affected than WT plants in all the above-mentioned parameters. The Al³⁺ stress significantly enhanced malate exudation in all the tested genotypes, but no significant correlation was observed between the SA-involved response to the Al³⁺ stress and the malate exudation. Based on these data, it was concluded that the SA-related functions in Arabidopsis response to the Al³⁺ stress were associated with the control of oxidative stress, but not of malate exudation.     

滇西北高原纳帕海湿地湖滨带优势植物生物量及其凋落物分解

选取滇西北高原湿地纳帕海湖滨带优势植物茭草(Zizania caducifolia)、水葱(Scirpus tabernaemontani)和刘氏荸荠(Heleocharis liouana),研究其生物量及其凋落物分解特征,结果表明:水葱、茭草、刘氏荸荠为纳帕海湿地湖滨带单优植物群落,均具有较高的地上生物量,不同植物群落地上生物量不同,其中,茭草地上生物量(853.6±58.2)g·m-2·a-1显著高于水葱(730.7±7.8)g·m-2·a-1与刘氏荸荠(338.9±32.6) g·m-2·a-1的地上生物量.3种植物群落凋落物分解速率不同、并随月平均气温升高均呈增加的趋势,其中,刘氏荸荠分解速率k值最大(0.067±0.0026)、茭草(0.062±0.0072)其次、水葱最小(0.039±0.0062).凋落物经过1年的分解,水葱、茭草和刘氏荸荠凋落物存留率分别为(62.0±8.8)％、(47.5±9.0)％和(44.5±7.9)％.综合3种湖滨带植物地上生物量与凋落物年分解,水葱地上生物量年存留量(453.1±4.9)g·m-2·a-1显著高于茭草(405.4±27.7)g·m-2·a-1和刘氏荸荠(150.9±14.5) g·m-2·a-1.研究进一步表明滇西北高原湿地湖滨带植物具有极高的生物量存留率,成为该类型湿地生态系统碳汇功能的基础,其碳汇过程及其贡献率需要进一步深入研究.     

Metabolic fate of 3,4-dichloropropionanilide in plants: the metabolism of the propionic Acid moiety

3,4-Dichloropropionanilide-¹⁴C (propanil) labeled in either the C-1 or C-3 carbon atoms of the propionic acid moiety was applied to the roots of pea (Pisum sativum L.) and rice (Oryza sativa L.) plants in nutrient solution (0.1 mm-0.28 mm). Radioactivity was detected throughout the treated plants, but the greatest labeling was found in the roots. None of the products that contained aniline were radioactive, suggesting that the plants split the propionic acid moiety from propanil. The fate of the propionate moiety of propanil was determined by recovery of ¹⁴CO₂ from plants exposed to propanil-¹⁴C. The time-course of the ¹⁴CO₂ production demonstrated that the intact propionic acid was cleaved from the propanil and subsequently catabolized by the β-oxidation catabolic sequence. The appearance of radioactivity in the shoots was attributed to the incorporation of products of propionate metabolism. Both the susceptible pea plants and the tolerant rice plants converted a high percentage of the administered propanil-¹⁴C to ¹⁴CO₂.     

Is the rate of photosynthesis under blue light altered in the 7B-1 tomato mutant?

Changes of photosynthesis under blue light were examined in the ABA-overproducing 7B-1 mutant in tomato. Net photosynthetic rate (P _N), stomatal conductance (g _s), intrinsic water-use efficiency (WUE_i) and chlorophyll (a+b) [Chl (a+b)] content in leaves of different insertion (1^st, 4^th and 9^th ones) were measured in 5-, 7- and 9-week-old plants. P _N, g _s, and Chl (a+b) content were mostly similar in young leaves of 7B-1 and wild type (WT) plants. With the aging of leaves, a blue-light-induced increase in P _N and g _s to steady-state was delayed and steady-state values of P _N and g _s were lower in 7B-1 plants compared with WT. Steady-state values of WUE_i were increased in 4^th and 9^th leaves of 7B-1 plants compared with WT. The results can be explained by the higher endogenous level of ABA in 7B-1 plants and their lower sensitivity to ABA in earlier growth stage.     

Resistance to ACNU induced toxicity in transgenic tobacco suspension cultures withada gene transferred fromEscherichia coli

The protein coding region of theE. coli DNA repair geneada combined with the CaMV 35S promoter has been transferred to tobacco by means ofAgrobacterium tumefaciens Ti plasmid. In transgenic plants having theada gene in a sense orientation, detectable amounts of O⁶-alkylguanine-DNA-alkyltransferase has been found whereas in non-transformed plants this activity is absent. Cell suspension cultures derived from the former plants showed lower sensitivity to the toxic (growth inhibiting) effects of the bifunctional alkylating agent 1-(2-chloroethyl)-1-nitroso-3-(aminomethyl-1,3-diazinylo)-methylurea compared with cell cultures derived from a control non-transformed plant or from transgenic plants harbouring theada gene in an opposite, non-sense orientation.     

Hydroxylation of N-(Delta-Isopentenyl)adenine to Zeatin: Relative Activities of Organ Systems from Actinidia arguta

By incubating explants from Actinidia arguta seedlings on a nutrient medium supplemented with 20 to 30 micromolar N⁶-(Δ²-isopentenyl)adenine (i⁶Ade) and then measuring zeatin (io⁶Ade) accumulation in tissues, the distribution of i⁶Ade hydroxylase activities in whole plants could be determined. Based on analyses with three entire plants, it is estimated that, as an organ system, roots contain approximately 68% of the plant's hydroxylase, while stems and leaves account for about 26% and 6%, respectively, of the total activity. Depending on the part of the root examined, hydroxylase activities ranged from 20 to 148 nanomoles io⁶Ade accumulated per gram fresh weight per 24 hours of incubation. Stem activities ranged from 17 to 165 nanomoles per gram fresh weight per 24 hours with the lowest activities being found at the tip. Leaf activities were substantially lower (1-10 nanomoles per leaf depending on position) than either root or stem.     

Induction of salt tolerance in Azolla microphylla Kaulf through modulation of antioxidant enzymes and ion transport

Azolla microphylla plants exposed directly to NaCl (13 dsm^-1) did not survive the salinity treatment beyond a period of one day, whereas plants exposed directly to 4 and 9 dsm^-1 NaCl were able to grow and produce biomass. However, plants pre-exposed to NaCl (2 dsm^-1) for 7 days on subsequent exposure to 13 dsm^-1 NaCl were able to grow and produce biomass although at a slow rate and are hereinafter designated as pre-exposed plants. The pre-exposed and directly exposed plants distinctly differed in their response to salt in terms of lipid peroxidation, proline accumulation, activity of antioxidant enzymes, such as SOD, APX, and CAT, and Na⁺/K⁺ ratio. Efficient modulation of antioxidant enzymes coupled with regulation of ion transport play an important role in the induction of salt tolerance. Results show that it is possible to induce salt adaptation in A. microphylla by pre-exposing them to low concentrations of NaCl.     

Redistribution of Tritium during Germination of Grain Harvested from myo-[2-H]Inositol- and scyllo-[R-H]Inositol-Labeled Wheat

Wheat kernels from myo-[2-³H]inositol- or scyllo-[R-³H]inositol-labeled plants (Sasaki and Loewus 1980 Plant Physiol 66: 740-745) were used to study redistribution of ³H into growing regions during germination. Most of the labeled 1-α-galactinol (or the analogous scyllo-inositol galactoside) was hydrolyzed within 1 day. Water-soluble phytate was dephosphorylated within 3 days. A large reserve of bound phytate continued to release myo-inositol over several days. Translocation of free myo-inositol to growing regions provided substrate for the myo-inositol oxidation pathway and incorporation of ³H into new cell wall polysaccharides.     

In Vitro Regeneration of Stevia rebaudiana (Bert) from the Nodal Explant

Procedure for micropropagation of Stevia rebaudiana Bertoni, containing stevioside, a natural noncaloric sweetner, has been developed using nodal segments as explant. Higher proliferation of shoots and multiplication was obtained on Murashige and Skoog basal medium (MS) supplemented with 1.0 mg l-1 indoleacetic acid (IAA) plus 10.0 mg l^-1 kinetin and 30.0 mg l-1 adenine sulphate. Sprouting of 90% of the axillary buds was observed within 4 weeks of inoculation, producing >10.0 shoots per explant within 12 weeks. Profuse roots were induced from 90% of the regenerated shoots within 4 weeks of inoculation on half strength MS solid medium supplemented with 1.0 mg l^-1 IAA. High survival rate, > 60%, was obtained when the plantlets were transferred to field conditions. The survival rate of taller plants was always higher. The in vitro regenerated plants were morphologically indistinguishable from the donor plants and leaves were of intense sweet taste upon chewing. The heterogenic nature of S. rebaudiana necessitates establishment of protocol for every genotype independently.     

Expression of soybean proteinase inhibitors in transgenic sugarcane plants: effects on natural defense against Diatraea saccharalis

The introduction and expression of proteinase inhibitor encoding genes into sugarcane (Saccharum officinarum L.) genome is an interesting strategy for conferring partial resistance to the sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae), the major insect pest of sugarcane in Brazil. To investigate the role of soybean (Glycine max L.) Kunitz trypsin inhibitor (SKTI) and soybean Bowman–Birk inhibitor (SBBI) in the control of D. saccharalis, the cDNAs encoding these proteinase inhibitors were placed under the control of the maize ubiquitin promoter (Ubi-1), and introduced into sugarcane callus using particle bombardment. Putative transgenic plants were initially identified after regeneration from callus growing in the presence of 30 mg l^–1 geneticin, while molecular characterization of transgenic plants revealed that both genes were incorporated into the sugarcane genome and expressed. We also carried out insect feeding trials using D. saccharalis neonate larvae and leaf tissue excised from propagated transgenic and untransformed plants, and found that the growth of larvae feeding on leaf tissue from transgenic plants containing BBI and Kunitz inhibitors was significantly retarded as compared to larvae fed on leaf tissue from untransformed plants. In greenhouse trials with transgenic sugarcane plants infested with D. saccharalis neonates, we found that these plants still presented the ‘dead heart’ symptom typically observed in susceptible plants in the field, suggesting that the retardation of the growth of D. saccharalis observed in the laboratory-based feeding trials was not sufficient to prevent this type of damage.     

Effect of radiation dosage on efficiency of chloroplast transfer by protoplast fusion in Nicotiana

Chloroplasts of Nicotiana tabacum SR1 were transferred into Nicotiana plumbaginifolia by protoplast fusion. The protoplasts of the organelle donor were irradiated with different lethal doses using a ⁶⁰Co source, to facilitate the elimination of their nuclei from the fusion products. After fusion induction, clones derived from fusion products and containing streptomycin-resistant N. tabacum SR1 chloroplasts were selected by their ability to green on a selective medium. When N. tabacum protoplasts were inactivated by iodoacetate instead of irradiation, the proportion of N. plumbaginifolia nuclear segregant clones was low (1–2%). Irradiation markedly increased this value: Using 50, 120, 210 and 300 J kg^-1 doses, the frequency of segregant clones was 44, 57, 84 and 70 percent, respectively. Regeneration of resistant N. plumbaginifolia plants with SR1 chloroplasts indicated that plastids can be rescued from the irradiated cells by fusion with untreated protoplasts. Resistant N. plumbaginifolia plants that were regenerated (43 clones studied) had diploid (2n = 2X = 20) or tetraploid chromosome numbers and were identical morphologically to parental plants. The absence of aneuploids suggests that in these clones irradiation resulted in complete elimination of the irradiated N. tabacum nuclei. Resistance is inherited maternally (five clones tested). The demonstration of chloroplast transfer and the presence of N. tabacum plastids in the N. plumbaginifolia plants was confirmed by chloroplast DNA fragmentation patterns after EcoRI digestion.     

Leaf Photosynthesis of the Mangrove Avicennia Germinans as Affected by NaCl

In leaves of the mangrove species Avicennia germinans (L.) L. grown in salinities from 0 to 40 ‰, fluorescence, gas exchange, and δ¹³C analyses were done. Predawn values of F_v/F_m were about 0.75 in all the treatments suggesting that leaves did not suffer chronic photoinhibition. Conversely, midday F_v/F_m values decreased to about 0.55-0.60 which indicated strong down-regulation of photosynthesis in all treatments. Maximum photosynthetic rate (P _max) was 14.58 ± 0.22 µmol m^-2 s^-1 at 0 ‰ it decreased by 21 and 37 % in plants at salinities of 10 and 40 ‰, respectively. Stomatal conductance (g _s) was profoundly responsive in comparison to P _max which resulted in a high water use efficiency. This was further confirmed by δ¹³C values, which increased with salinity. From day 3, after salt was removed from the soil solution, P _max and g _s increased up to 13 and 30 %, respectively. However, the values were still considerably lower than those measured in plants grown without salt addition.