Growth-promotion of strawberry plants inoculated with Azospirillum brasilense

Azospirillum brasilense (strains REC3, RLC1, PEC5) were root inoculated in strawberry plants of the cultivars ‘Milsei’, ‘Selva’ and ‘Camarosa’ to assess plant growth-promoting effects. The bacteria were able to promote plant growth (expressed as root length, root area, and dry weight of root and shoot), depending on the genotypes of plants and bacteria used, whereas the stolon production (3–4) depended only on the strawberry cultivar. To explain whether root exudates plays any role on the growth-promotion observed herein, total protein and sugar were determined, and chemotaxis properties were evaluated. The strains showed positive chemotaxis toward the root exudates, being influenced by the total sugars content, suggesting that the latter plays an important role in the chemotaxis effect and may contribute to enhance the root capacity to recruit azospirilla from rhizosphere, thus improving the growth-promoting effect exerted by these bacteria.     

Effect of simazine and atrazine on the mineralization of fertilizer and manure nitrogen

Summary Laboratory experiments were carried out with alluvial sandy loam soil to study the effect of simazine and atrazine herbicides at four levels (0.5, 1.0, 1.5 and 2.0 kg/ha) on the mineralization of nitrogen (ammoniacal and nitrate production) from fertilizer urea and sludge sources. The herbicides stimulated nitrate production. No specific trend in total mineralized nitrogen, ammoniacal and nitrate nitrogen was observed by varying the levels of herbicides. Mineralization of total nitrogen (ammoniacal and nitrate nitrogen) in presence of simazine and atrazine from the different sources in the descending order was:Urea > Sludge + Urea > Sludge > No Nitrogen.     

Effect of simazine on nitrate reductase activity in corn

The nutritional and environmental parameters required for eliciting increases in the nitrogen content and growth of corn (Zea mays L.) by non-toxic levels of simazine have been established. Corn seedlings with the endosperm removed 10 days after germination, proved to be a suitable test species. The addition of simazine to the root-zone area of corn plants grown under both sub-optimal temperatures and low nitrate levels, increased the nitrogen content and dry weight of the plants by 20 to 25%. This increase was found to be associated with an effect on nitrate reductase.     

Changes in physiological,biochemical, and growth parameters of sorghum in the presence of phenanthrene

Physiological, biochemical, and growth parameters of sorghum (Sorghum bicolor (L.) Moench) plants grown in the presence of phenantrene (10 and 100 mg/kg soil) were examined. Activities of intracellular tyrosinases, peroxidases, and laccase-like oxidases were analyzed in 1 and 2 months after planting. The tyrosinase activity in root and leaf tissues correlated positively throughout the experiment with the level of soil pollution. The oxidase activity was apparent only in the first month; it also correlated positively with the concentration of phenanthrene. Intracellular peroxidases exhibited the highest activity; positive correlation of this activity with the level of soil contamination was observed in the first period of observations. The soil pollutant had a negative impact on growth characteristics (germination capacity, survival rate, and accumulation of plant biomass). In addition, soil contamination with phenanthrene reduced the total content of photosynthetic pigments and changed their ratio. The maximum extent of phenanthrene elimination in soil was found to occur in the root zone of sorghum plants at high-level contamination, which indicates a significant contribution of plants to the decomposition (binding) of this xenobiotic.     

Interrelationship of Abscisic Acid and Gibberellic Acid in the Promotion of Callus Formation in the Abscission Zone of Citrus Bud Cultures

The mechanism of ABA-induced callus formation was studied in sterile bud cultures of Citrus [Citrus sinensis (L.) Osbeck] on defined media. ABA was found to promote callus formation in the abscission zone between the petiole and the branch while inhibiting bud growth. The promoting effect of ABA was dependent on the physiological state of the shoot from which buds were excised, and on the size of the explant. Callus formation was highest in autumn and summer (i.e. younger) buds, and lowest in older buds excised from previous summer flush. GA was only slightly active in promoting callus formation when applied separately, but showed a highly synergistic effect when applied with ABA: maximal callus formation was attained at a combination of 10^?5M ABA and 10^?6 MGA in the medium. Subcultures of ABA-induced callus revealed that ABA inhibited the growth of isolated subcultured callus, while IAA and kinetin, and especially GA, promoted its rapid proliferation. A general decrease in protein synthesis was found in the abscission zone during the first 5 days of induction, while total protein content changed only slightly. The results suggest that ABA-induced callus formation in Citrus bud explants is a multiphasic phenomenon involving, at least, two stages: (1) activation of certain cells in the abscission zone by ABA, resulting in the formation of callus layers, and (2) subsequent proliferation of the callus tissue, which is dependent on the hormonal balance in the explant. This growth-promoting effect of ABA seems to be a general phenomenon in explants exposing a cut-surface.     

Colonization by Arbuscular Mycorrhizal Fungi of Sorghum Leads to Reduced Germination and Subsequent Attachment and Emergence of Striga hermonthica

Two sorghum cultivars: the Striga-tolerant S-35 and the Striga-sensitive CK60-B were grown with or without arbuscular mycorrhizal (AM) fungi, and with or without phosphorus addition. At 24 and 45 days after sowing (DAS) of sorghum, root exudates were collected and tested for effects on germination of preconditioned Striga hermonthica seeds. Root exudates from AM sorghum plants induced lower germination of S. hermonthica seeds than exudates from non-mycorrhizal sorghum. The magnitude of this effect depended on the cultivar and harvest time. A significantly (88–97%) lower germination of S. hermonthica seeds upon exposure to root exudates from AM S-35 plants was observed at both harvest times whereas for AM inoculated CK60-B plants a significantly (41%) lower germination was observed only at 45 DAS. The number of S. hermonthica seedlings attached to and emerged on both sorghum cultivars were also lower in mycorrhizal than in non-mycorrhizal plants. Again, this reduction was more pronounced with S-35 than with CK60-B plants. There was no effect of phosphorus addition on Striga seed germination, attachment or emergence. We hypothesize that the negative effect of mycorrhizal colonization on Striga germination and on subsequent attachment and emergence is mediated through the production of signaling molecules (strigolactones) for AM fungi and parasitic plants.Key Words: arbuscular mycorrhiza, root exudate, sorghum, striga, strigolactones, germination     

Biochemical changes in the germinating seeds ofTrigonella foenum graecum L. in relation tos-triazine herbicides

Thes-triazine herbicides studied (atrazine and simazine) inhibited the growth of the seedlings ofTrigonella foenum graecum L.(Viciaceae). These herbicides caused a decrease in the contents of total water soluble carbohydrates and reducing sugars. Pentose sugars increased in the cotyledons. The total protein and free amino acid contents were enhanced. The activity of peroxidase was inhibited in the cotyledons, but was enhanced in the seedling axes.     

Induction of Drought Tolerance in Cucumber Plants by a Consortium of Three Plant Growth-Promoting Rhizobacterium Strains

Our previous work showed that a consortium of three plant growth-promoting rhizobacterium (PGPR) strains (Bacillus cereus AR156, Bacillus subtilis SM21, and Serratia sp. XY21), termed as BBS for short, was a promising biocontrol agent. The present study investigated its effect on drought tolerance in cucumber plants. After withholding watering for 13 days, BBS-treated cucumber plants had much darker green leaves and substantially lighter wilt symptoms than control plants. Compared to the control, the BBS treatment decreased the leaf monodehydroascorbate (MDA) content and relative electrical conductivity by 40% and 15%, respectively; increased the leaf proline content and the root recovery intension by 3.45-fold and 50%, respectively; and also maintained the leaf chlorophyll content in cucumber plants under drought stress. Besides, in relation to the control, the BBS treatment significantly enhanced the superoxide dismutase (SOD) activity and mitigated the drought-triggered down-regulation of the expression of the genes cAPX, rbcL, and rbcS encoding cytosolic ascorbate peroxidase, and ribulose-1,5-bisphosphate carboxy/oxygenase (Rubisco) large and small subunits, respectively, in cucumber leaves. However, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity was undetected in none of the culture solutions of three BBS constituent strains. These results indicated that BBS conferred induced systemic tolerance to drought stress in cucumber plants, by protecting plant cells, maintaining photosynthetic efficiency and root vigor and increasing some of antioxidase activities, without involving the action of ACC deaminase to lower plant ethylene levels.     

Efficient genetic transformation of Sorghum using a visual screening marker.

To transform grain sorghum (Sorghum bicolor (L.) Moench) with a visual reporter gene (gfp) and a target gene (tlp), three genotypes (two inbreds, Tx 430 and C401, and a commercial hybrid, Pioneer 8505) were used. We obtained a total of 1011 fertile transgenic plants from 61 independent callus lines, which were produced from 2463 zygotic immature embryos via Agrobacterium-mediated transformation. The reporter gene, gfp, encoding green fluorescent protein (GFP), was used as a visual screening marker, and the target gene, tlp, encoding thaumatin-like protein (TLP), was chosen for enhancing resistance to fungal diseases and drought. Both genes were under the control of the maize ubi 1 promoter in the binary vector pPZP201. A total of 320 plants showing GFP expression, derived from 45 calli, were selected and analyzed by Southern blot analysis. There was a 100% correlation between the GFP expression and the presence of the target gene, tlp, in these plants. Transgenic plants showing strong TLP expression were confirmed by Western blotting with antiserum specific for TLP. The transgene segregated in various ratios among progeny, which was confirmed by examining seedlings showing GFP fluorescence. The progeny also showed different copy numbers of transgenics. This report describes the successful use of GFP screening for efficient production of stably transformed sorghum plants without using antibiotics or herbicides as selection agents.     

Increase of isoflavones in soybean callus by Agrobacterium-mediated transformation

Plant secondary metabolites have always been a focus of study due to their important roles in human medicine and nutrition. We transferred the isoflavone synthase (IFS) gene into soybean [Glycine max (L.) Merr.] using the Agrobacterium-mediated transformation method in an attempt to produce transformed soybean plants which produced increased levels of the secondary metabolite, isoflavone. Although the trial to produce transgenic plant failed due to unestablished hygromycin selection, transformed callus cell lines were obtained. The induction rate and degree of callus were similar among the three cultivars tested, but light illumination positively influenced the frequency of callus formation, resulting in a callus induction rate of 74% for Kwangan, 67% for Sojin, and 73% for Duyou. Following seven to eight subcultures on selection media, the isoflavone content of the transformed callus lines were analyzed by high-performance liquid chromatography. The total amount of isoflavone in the transformed callus cell lines was three- to sixfold higher than that in control callus or seeds. Given the many positive effects of isoflavone on human health, it may be possible to adapt our transformed callus lines for industrialization through an alternative cell culture system to produce high concentrations of isoflavones.     

Behaviour of Herbicides in Dicotyledonous Roots Transformed by Agrobacterium rhizogenes: I. SELECTIVITY

Mugnier, J. 1988. Behaviour of herbicides in dicotyledonousroots transformed by Agrobacterium rhizogenes. I. Selectivity.—J.exp. Bot. 39: 1045–1056. The effect of various herbicides on the growth of dicotyledonousroots transformed by the root-inducing transferred DNA of Agrobacteriumrhizogenes was studied. When a compound affected the growthof different root species differentially, the difference mightbe attributed to root uptake and metabolism of the herbicide.In general, metabolism of the herbicide led to inactivation(clopyralid, linuron, phenmedipham), but in certain instances,the change resulted in activation (quizalofop-ethyl). Visibleeffects on the root morphology were observed: dinitroanilinesand certain carbamates led to remarkable swelling of the roottips; norflurazon and diflufenican were effective bleachingagents in greening root cultures in Murashige and Skoog medium,whereas the presence of sucrose in the medium antagonized theeffect of triazine herbicides. Growth inhibition by sulphonylureascan be antagonized by addition of valine and leucine; asulaminhibition was antagonized by addition of folic acid but glyphosateinhibition was not significantly reversed by aromatic aminoacids. Bipyridinium and diphenyl ether herbicides, with certainexceptions, have rapid and devastating phytotoxic effects onroot growth. The phytotoxic effects of the herbicides on transformedroot growth is discussed with particular reference to theirmode of action in intact plants. Key words: Arobacterium rhizogenes, herbicides, root organ cultures     

广西葛根内生细菌的分离鉴定及其促生特性

【背景】植物内生菌长期与宿主共生,对宿主生长发育产生影响。葛根作为重要的药食两用作物,葛根内生菌的研究具有重要实践意义。【目的】对广西葛根根部内生细菌进行分离、鉴定及促植物生长特性分析,旨在了解该药食同源植物内生细菌种群结构及其促生特性,为分析内生菌群体在药食同源植物产量和品质形成的作用及其内生细菌资源的开发利用提供参考。【方法】采用6种不同的培养基从广西葛根的根瘤、根系和根愈伤组织分离内生细菌,16S rRNA基因测序和系统发育分析内生细菌的分布特征和遗传多样性,采用生理生化方法测定分离菌株的固氮活性、溶磷特性、产生嗜铁素、分泌吲哚乙酸(indole-3-aceticacid,IAA)等促生特性。【结果】从葛根根瘤、根系和根部愈伤组织中共分离得到223个菌株,16S rRNA基因测序鉴定这些菌株隶属于2门4纲10科19属,其中芽孢杆菌属、假单胞菌属、土壤杆菌属、肠杆菌属为葛根优势菌群;内生细菌数量和群落组成存在明显的组织特异性,其数量表现为根瘤>根系>根愈伤组织,但其种群多样性表现为根愈伤组织>根系>根瘤。不同培养基分离出的细菌种群丰富度有差异。从供试菌株中筛...     

Some effects of herbicide-selection onAlopecurus myosuroïdes Huds

Summary Four-year selection ofAlopecurus myosuroïdes by simazine has led to an increase of yield potential and root proportion, but has no effect on root cation-exchange capacity. Correlation between C.E.C. and yield potential is discussed. It is suggested that these characteristics provide selected plants with a better competitive ability; this competitive ability, however, may be considered as a side effect of certain herbicide selective effects.     

Influence of temperature on phytotoxicity of triazine herbicides to pine seedlings

The effects of temperature, over a range of 5 to 30 C, on phytotoxicity of simazine, atrazine, propazine, prometryne, prometone, and ipazine to young Pinus resinosa seedlings were investigated in growth chambers. Herbicides were applied to the soil surface and then mixed into the soil before pine seeds were planted. Development of recently germinated seedlings was then studied for 7 weeks. High temperatures greatly accelerated herbicide toxicity, but the effects of temperature varied greatly among herbicides. Atrazine and simazine were more toxic than other herbicides tested at all temperatures. Toxicity of simazine and atrazine was apparent early, whereas effects of propazine, prometryne, prometone, and ipazine were somewhat delayed. After 7 weeks maximum dry-weight production of shoots under each herbicide treatment and control occurred at 20 C, with some decreases noted at lower temperatures and marked decreases at progressively higher ones. At 20 C final seedling dry weights following treatment with simazine or atrazine were only one-third as high as in control plants. Growth was also reduced in lesser amounts by propazine, prometryne, prometone, or ipazine. Variations in phytotoxicity of different triazine herbicides appeared to be related more to their structural differences than their solubilities. Under the constant environmental conditions of the experiments, toxicity symptoms in plants treated with triazine herbicides appeared more rapidly and decisively than in previous field experiments under fluctuating environments. The influence of high temperatures in enhancing triazine toxicity appeared to involve complex interactions of physiological activity of plants and temperature effects on herbicide uptake.     

Growth Enhancement and Developmental Modifications of in Vitro Grown Potato (Solanum tuberosum spp. tuberosum) as Affected by a Nonfluorescent Pseudomonas sp

A plant growth-promoting rhizobacterium, designated Ps JN and isolated from onion roots, was identified as a nonfluorescent Pseudomonas sp. The percentage of similarity of Ps JN to P. gladioli (NCPPB 1891), P. cichorii (NCPPB 943), and P. viridiflava (NCPPB 635), as determined from 135 biochemical and physiological tests was 77, 70, and 66%, respectively. Ps JN persisted through successive generations of in vitro cultured potato plantlets, both as endophytic and epiphytic populations. In vitro inoculated potato (Solanum tuberosum) nodal explants produced plantlets with significant increases in root number (24-196%), root dry weight (44-201%), haulm dry weight (14-151%), and stem length (26-28%) as compared with noninoculated control plants. Bacterization also enhanced leaf hair formation (55-110%), secondary root branching, and total plant lignin content (43%). Other root colonizing bacteria or heat-killed cells of Ps JN had no significant effect on plant growth. Detached leaves from in vitro grown control plants, when exposed to 19°C and 50% relative humidity, lost 55% of their moisture content in 2.5 hours. Moisture loss by leaves of in vitro grown, bacterized plants, as well as greenhouse-acclimated, bacterized plants, and control plants, was less than 20%. Changes in stomatal closure appear to account for this difference.     

Factors modulating the levels of the allelochemical sorgoleone in Sorghum bicolor

Sorgoleone is the major component of the hydrophobic root exudate of sorghum [Sorghum bicolor (L.) Moench]. The presence of this allelochemical is intrinsically linked to root growth and the development of mature root hairs. However, factors modulating root formation and the biosynthesis of sorgoleone are not well known. Sorgoleone production was independent of early stages of plant development. The optimum temperature for root growth and sorgoleone production was 30°C. Seedling development and sorgoleone levels were greatly reduced at temperatures below 25°C and above 35°C. The level of sorgoleone was also sensitive to light, being reduced by nearly 50% upon exposure to blue light (470 nm) and by 23% with red light (670 nm). Applying mechanical pressure over developing seedlings stimulated root formation but did not affect the biosynthesis of this lipid benzoquinone. Sorgoleone production did not change in seedlings exposed to plant defense elicitors. On the other hand, sorgoleone levels increased in plants treated with a crude extract of velvetleaf (Abutilon theophrasti Medik.) root. This stimulation was not associated with increased osmotic stress, since decreases in water potential (Ψ_w) by increasing solute concentrations with sorbitol reduces sorgoleone production. Sorgoleone production appears to be constitutively expressed in young developing sorghum plants. Other than with temperature, changes in the environmental factors had either no effect or caused a reduction in sorgoleone levels. However, the stimulation observed with velvetleaf root crude extract suggests that sorghum seedlings may respond to the presence of other plants by releasing more of this allelochemical.     

Water uptake efficiency and above- and belowground biomass development of sweet sorghum and maize under different water regimes

Background and aims

Lately sweet sorghum (S) has attracted great interest as an alternative feedstock for biofuel production due to its high yielding potential and better adaptation to drought than maize (M). However, little is known about the response of newly developed sweet sorghum genotypes to water deficits, especially at the root level and its water uptake patterns. The objective of this study was to compare the water uptake capacity, growth and developmental characteristics at the root and canopy levels of a sweet sorghum hybrid (Sorghum bicolor cv. Sucro 506) with those of maize (Zea mays cv. PR32F73) at two water regimes.

Methods

The trial was setup in a total of 20 rhizotrons (1?m³), where calibrated soil moisture probes were installed for monitoring and adjusting the soil moisture content to 25% (well-watered, W) and 12% (drought stress, D).

Results

DS was able to sustain its physiological activity close to that of WS plants, while maize was not. The biomass production potential of DS was reduced about 38%, while in maize the reduction was 47%. The water use efficiency (WUE), however, was increased by 20% in sweet sorghum and reduced in 5% in maize. Moreover, in contrast to maize the root length density and water uptake capacity of DS was enhanced. Root water uptake efficiency in DM was sustained close to its potential, but not in sweet sorghum.

Conclusions

In summary, the better adaptation to drought of sweet sorghum is explained by increased WUE, sustained physiological activity and enlarged root system. It is also associated with a reduced water uptake efficiency compared to its control but maintained compared to maize.     

Nitrogen and phosphorus fertilization negatively affects strigolactone production and exudation in sorghum

Strigolactones (SLs) are essential host recognition signals for both root parasitic plants and arbuscular mycorrhizal fungi, and SLs or their metabolites function as a novel class of plant hormones regulating shoot and root architecture. Our previous study indicated that nitrogen (N) deficiency as well as phosphorus (P) deficiency in sorghum enhanced root content and exudation of 5-deoxystrigol, one of the major SLs produced by sorghum. In the present study, we examined how N and P fertilization affects SL production and exudation in sorghum plants subjected to short- (5 days) or long-term (10 days) N or P deficiency and demonstrated their common and distinct features. The root contents and exudation of SLs in the N- or P-deficient sorghum plants grown for 6, 12 or 24 h with or without N or P fertilization were quantified by LC–MS/MS. In general, without fertilization, root contents and exudation of SLs stayed at similar levels at 6 and 12 h and then significantly increased at 24 h. The production of SLs responded more quickly to P fertilization than the secretion of SLs, while regulation of SL secretion began earlier after N fertilization. It is suggested that sorghum plants regulate SL production and exudation when they are subjected to nutrient deficiencies depending on the type of nutrient and degree of deficiency.