Disruption of the Paenibacillus polymyxa levansucrase gene impairs its ability to aggregate soil in the wheat rhizosphere

Inoculation of wheat roots with Paenibacillus (formerly Bacillus ) polymyxa CF43 increases the mass of root-adhering soil. We tested the role of levan, a fructosyl polymer produced by strain CF43, in the aggregation of soil adhering to wheat roots. The P. polymyxa gene homologous to the Bacillus subtilis sacB gene encoding levansucrase was cloned and sequenced. The corresponding gene product synthesises high molecular weight levan. A P. polymyxa mutant strain, SB03, whose sacB gene is disrupted, was constructed using heterogramic conjugation. Effects of wheat inoculation with the wild type and the mutant strain were compared using two different cultivated silt loam soils in four independent pot experiments. Roots of wheat plantlets inoculated with CF43 or SB03 were colonized after 7–14 days at the same level, and root and shoot masses were not significantly different from those of the non-inoculated control plants. The ratio of root-adhering soil dry mass to root tissue dry mass was significantly higher for plants inoculated with strain CF43 than for those inoculated with mutant strain SB03: + 30% in Orgeval soil and + 100% in Dieulouard soil. Thus the levan produced by P. polymyxa is implicated in the aggregation of root-adhering soil on wheat.     

Identification of Yeast Strains Isolated from Agricultural Soils for Releasing Potassium-bearing Minerals

Thirty-five yeast strains were isolated from soil samples that were collected from different locations in Upper Egypt. The purified isolates were screened for the release potassium from mica on Aleksandrov agar medium. Two yeast isolates (KSY-29 and KSY-33) showed an ability to solubilize potassium by inducing clear zones around their colonies. They were identified as Pichia anomala and Rhodotorula glutinis, respectively, based on PCR analysis of the ITSI-26S region that was amplified by NL1/NL4 species-specific primers. The amount of K released from muscovite mica in the broth culture of the yeast isolates was measured after 5, 10, 15 and 20 days of the incubation at 25°C. Both yeast isolates were very effective in releasing K of muscovite in broth culture, recording 8.11–13.21 μg/ml that were released from muscovite mica after 20 days of incubation. The inoculation of maize (Zea maize) plants with these yeast isolates under different K levels (25, 50 and 100% of recommended dose of potassium, RDK) as potassium sulfate was tested on growth and K uptake by these plants in the greenhouse. Significant increases (p < 0.05) in plant height, root and shoot dry weights as well as K uptakes by shoots and roots maize plants occurred through the inoculation with KSY-29 or KSY-33 isolates.     

Influence of vesicular-arbuscular mycorrhiza fungi on growth and uptake of various nutrients as well as uptake ratio of fertilizer P for lucerne (Medicago sativa)

Summary Lucerne plants were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus caledonius andRhizobium meliloti and grown in pots in voliére. Treatments were 0,1 and 2 mg P added to 100 g of a soil with low P-fertility. Plants were harvested after 6, 9, 13 and 18 weeks, allowing shoots to regrow between harvests. VAM-infection was determined after 6 and 18 weeks, dry weight, concentration and uptake of P and concentrations of N, K, Ca, Mg, Cu and Zn were determined at all harvests. VAM-inoculation increased growth of shoots, P-concentration and P-uptake at all soil-P levels and the increase was most pronounced at the lowest soil-P level. P-fertilization also increased growth, P-concentration and P-uptake. VAM-inoculation showed tendency to increase N-and K-uptake and decreased Ca-, Mg- and Zn-concentrations in shoots. The uptake ratio of fertilizer-P was increased by VAM.     

Effect of salinity and temperature on germination, growth and ion relations of Panicum turgidum Forssk

Seed germination of Panicum turgidum was significantly affected by salinity levels, temperature and their interaction. Maximum germination was noted in the lowest saline media (25-50 mM) and distilled water at the temperature of 15-25 degrees C and 20-30 degrees C. Seeds germination was substantially delayed and reduced with an increase in NaCl to levels above 50mM. This trend was much pronounced under high levels of NaCl and incubation temperature. Low levels of NaCl (25-50 mM) stimulated shoot and root dry weights of P. turgidum seedlings. However, the highest NaCl levels (>100 mM) resulted in a significant decrease in shoot, root and total dry weights of seedlings. Intermediate degrees of temperature, 15-25 and 20-30 degrees C, resulted in a significant increase in biomass accumulation. The Na+ concentration in shoots and roots significantly increased as NaCl concentration increased. The K+ concentration in roots and K/Na ratio in shoots and roots was significantly reduced as salinity concentration increased. The K/Na ratio was greatly affected by higher NaCl concentration and incubation temperatures.     

外源磷或有机质对板蓝根吸收转运砷的影响

采用土壤培养方法,研究了不同含砷水平土壤中添加外源磷或有机质对砷在板蓝根地下部和地上部累积与分配的影响。结果表明,在外源添加磷或者有机质的情况下,与自然土相比含砷土对板蓝根的生长有一定的促进作用;在自然土(13.4 mg/kg)中,外源磷没有明显影响板蓝根地下部对砷的累积,却显著降低了砷由地下部向地上部的转运,并且添加200 mg P2 O5/kg显著降低了砷在地上部的累积。然而,在含砷土(33.4 mg/kg)中,100 mg P2O5/kg处理显著降低了砷在地下部的累积,但随磷用量的增加反而促进了地下部砷的累积;在添加有机质试验中,10 g/kg的有机质显著降低了自然土中板蓝根地下部和地上部对砷的累积,并且砷的吸收能力也明显下降。在含砷土(23.4 mg/kg)中,添加5 g/kg的有机质不仅降低了砷在板蓝根中的富集,而且降低了其对砷的吸收能力,提高了砷由地下部向地上部的转运,但是随着有机质施用量增至10 g/kg,地下部砷含量及其吸收砷的能力均有一定程度的增大。因此,在砷水平较低的自然土壤上种植板蓝根添加200 mg P2O5/kg和10 g/kg的有机质是控制砷在该草药体内积累的适宜用量,而在砷水平较高的土壤上100 mg P2O5/kg和5 g/kg的有机质是降低板蓝根体内砷累积的适宜用量。     

Effect of biocontrol strains of Trichoderma on plant growth, Pythium ultimum polulations, soil microbial communities and soil enzyme activities

Five strains of Trichoderma with known biocontrol activities were assessed for their effect upon pea growth and their antagonistic activity against large Pythium ultimum inocula. The effect of Trichoderma inocula upon the indigenous soil microflora and soil enzyme activities in the presence and absence of Pythium is assessed. In the absence of Pythium, Trichoderma strain N47 significantly increased the wet shoot weight by 15% but did not significantly affect the dry weight, whilst strains T4 and N47 significantly increased the root weights by 22% and 80%) respectively. Strains TH1 and N47 resulted in significantly greater root lengths. Pythium inoculation significantly reduced the root length and the number of lateral roots and nodules, and significantly increased the root and rhizosphere soil fungal populations. Pythium inoculation significantly reduced the plant wet and dry shoot weights and significantly increased the wet and the dry shoot/root ratio. All the Trichoderma strains reduced the number of lesions caused by Pythium and increased the number of lateral roots. The effect of the Pythium on emergence and shoot growth was significantly reduced by all the Trichoderma strains except strain To10. Inoculation with Trichoderma strains TH1 and T4 resulted in significantly greater wet root weights (62% and 57%, respectively) in the presence of Pythium compared to the Pythium control. Strain N47 significantly increased the shoot/root ratio compared to the Pythium control. Inoculation with Trichoderma strains T4, T12 and N47 significantly reduced Pythium populations. Pythium increased the activity of C, N and P cycle enzymes, whilst four Trichoderma strains reduced this effect, indicating reduced plant damage and C leakage. Overall, strains T4 and N47 had the greatest beneficial characteristics, as both these strains improved plant growth in the absence of Pythium and reduced plant damage in the presence of Pythium. The dual properties of these strains improve the commercial application, giving them an advantage over single action inocula, especially in the absence of plant pathogens.     

Effects of imazamethabenz on the main shoot growth and tillering of wild oat (Avena fatua L.)

Foliar application of imazamethabenz at sublethal doses of 100 and 200 g a.i./ha to wild oat plants at the two-leaf stage without tillers greatly inhibited the growth of the main shoot but increased tillering. The near cessation of sheath and the main stem elongation indicated that the major effect of imazamethabenz on the main shoot was inhibition of intercalary growth. Low doses of imazameth-abenz treatment resulted in more leaves (including leaf primordia) in the main stem but did not affect mature first and second leaves. Sublethal doses of imazamethabenz only briefly inhibited tiller growth. A later increase in tillering in treated plants resulted from the stimulated resumed growth of tillers and the increased initiation of tiller buds. Such enhanced tillering mainly resulted from the release of apical dominance due to the inhibition or cessation of the main stem growth with imazamethabenz treatment. Both doses of imazamethabenz (100 and 200 g a.i./ha) significantly reduced the biomass of shoots and roots, but increased the ratio of roots/ shoots dry weight.     

Effects of applying etnylene to the root system of Zea mays on growth and nutrient concentration in relation to flooding tolerance

Previous studies have shown increases in the concentration of ethylene in the soil and roots of plants when the soil is water saturated (flooded). In Zea mays L. this occurs in association with an overall reduction in growth but without extensive foliar senescence and in conjunction with the development of an adventitious root system. We have assessed the possibility that ethylene may be involved in these responses to flooding. Mixtures of the gas in air were therefore supplied to the roots and stem-base of Z. mays growing in nutrient solution.
Seven or 14 d exposure to ethylene (1 or 5 νl 1⁻¹) inhibited seminal root elongation and growth in dry weight and accelerated the emergence of adventitious roots, although their final length and dry weight were depressed. Leaf extension was inhibited by 0.1,1.0 or 5.0 μl 1⁻¹ ethylene around the roots; leaves extending rapidiy at the start of treatment were the most sensitive. Final shoot fresh and dry weights were depressed by the gas but tie shootrroot dry weighl ratio and percentage dry matter were not affected greatly. Leaf chlorosis was not observed but the concentration of phosphorus in the shoots was 26 to 31% below normal.
When aeration of the nutrient solution was stopped, the concentration of dissolved oxygen declined and the concentration of ethylene in the roots increased. Similar changes occur in response to soil flooding. Root and shoot growth was slowed by non-aeration although the shootroot dry weight ratio remained unchanged. The phosphorus concentration of the shoots was depressed but there was little chlorosis or leaf death. The similarity in these respects between the effects of ethylene and non-aeration suggests that in flooded Z. mays , ethylene contributes to their development by accelerating the emergence of adventitioos roots, inhibiting phosphorus accumulation in the shoots and by a non-toxic inhibition of plant growth.     

Influence of cytokinins, auxins and polyamines on in vitro mass multiplication of cotton (Gossypium hirsutum L. cv. SVPR2)

In the present investigation, the influence of different forms of cytokinins, auxins and polyamines were tested for mass multiplication and regeneration of cotton. Initially, for the identification of effective concentration for multiple shoot induction, various concentrations of BAP, Kin and 2iP along with IAA and NAA were tested. Among tested concentrations, media fortified with MS salts; B5 vitamins; 30 g/l, glucose; 2.0 mg/l, 2iP; 2.0 mg/l, IAA and 0.7 % agar showed best response for multiplication of shoot tip explants (20 shoots per shoot tip explants). In nodal explants, maximum of 18.6 shoots were obtained in the media fortified with MS salts, B5 vitamins, 30 g/l, glucose, 2.0 mg/l, 2iP, 1.0 mg/l, NAA and 0.7 % agar. Effect of different concentrations of polyamines like spermidine and putrescine were also tested along with the above said multiplication media. Among the various treatments, 20 mg/l of putrescine showed best response and the multiple of shoots were increased to 26.5 shoots per shoot tip explants and 24.5 shoots per nodal explants. Elongation of shoots was achieved on multiple shoot induction medium. Significant number of roots were initiated in the medium supplemented with MS salts, vitamin B5 and IBA (2.0 mg/l). The frequency of root induction was increased by addition of, PVP (10 mg/l) along with root induction medium and after 2 weeks, the roots reached the maximum length of 22 cm. Further, these plantlets were hardened by using sand, soil and vermiculate in 1:1:1 ratio. The hardened plants were transferred to the environmental growth chamber for proper acclimatization. The hardened plants were then transferred to field for boll yielding and they exhibited 100% survival.     

Some Effects of Competition and Density of Plants on Dry Weight Produced

Plant weights were compared for different levels of shoot density,root density, shoot interaction and root interaction. Also,the effects of these treatments on the shoot—root ratiowere studied. Plant weight increased with decreases in shootand root density. Generally, plants grown with shoots or rootsintermingled with those of adjacent plants had greater weightthan those grown with shoots or roots separated. Competitionwas detected only at the highest shoot density where adjacentplants with isolated roots had greater weight than adjacentplants with intermingled roots. This is hypothesized to be aphytotoxic effect due to shoot confinement. No effects of densityor intermingling on the shoot-root ratio were evident.     

Arsenic tolerance, uptake and translocation by seedlings of three rice cultivars

By simulating the anaerobic conditions with agar nutrient solutions, effect of arsenic (As) on the growth and As uptake by hybrid, conventional and glutinous rice cultivars were studied. It showed insignificant effect of As on the root dry weights of three rice cultivars when treated by As of different concentrations. The shoot dry weights of hybrid and glutinous decreased with As concentrations increasing, while low concentrations of As (0.5 mg L^?1) could enhance the growth of conventional rice. Generally, As concentrations in roots and shoots increased as As concentrations of treatment solutions increasing. The root system had strong ability to uptake and accumulate As. The root As concentrations ranged from 156 to 504 mg kg^?1, representing 63.40%–81.90% of the total As concentrations in rice, which were much higher than shoot As concentrations. The fact that the glutinous rice had higher biomass, higher tolerance, and lower As concentrations in its roots and shoots than the other two rice cultivars proved that the glutinous rice was more applicable to As-polluted soils.     

Variation among and within clones in formation of roots and shoots during micropropagation of Campanula isophylla

It is known that treatments enhancing shoot formation often suppress root formation and vice versa. It would be of interest to know if such negative correlations between formation of roots and shoots were also present among genetically different plants, given the same treatment, to ensure that selection for superior shoot formation would not lead to inadvertent decreases in the capacity for root formation. Height and dry weight of micropropagated shoot clusters and the numbers of shoots and roots were measured in 95 seedling clones. Within clones, shoot size was negatively correlated with number of shoots and positively correlated with number of roots. Among clones, however, the number of shoots was not correlated with the size of shoots, but positively correlated with the number of roots. While it is difficult to devise treatments that simultaneously optimize the initiation of roots and shoots, it is thus possible to select for fast-growing clones without compromising root formation.Abbreviations CM clonal means - DCM deviation from clonal means     

Zinc — phosphorus relationship in the nutrition of corn plants (Zea mays L.) as affected by the total carbonate content of the soil

Summary In a pot experiment with corn plants, the higher the total carbonate content of the soil was, the lower was the dry matter yield, P-uptake, Zn-uptake and Zn-translocation. P-translocation was unaffected. Zn treatments had no effect on the dry matter yield, P-uptake or P-translocation. P-treatments significantly increased the dry matter yield and Zn-uptake and slightly increased Zn-translocation. The relationship between Zn-uptake and P-uptake by shoots or roots was always positive and in some cases it was significant.     

Effect of Arbuscular Mycorrhizal Fungi On Yield and Phytoremediation Performance of Pot Marigold (Calendula officinalis L.) Under Heavy Metals Stress

In order to study the effect of mycorrhizal fungi (inoculated and non-inoculated) and heavy metals stress [0, Pb (150 and 300 mg/kg) and Cd (40 and 80 mg/kg)] on pot marigold (Calendula officinalis L.), a factorial experiment was conducted based on a randomized complete block design with 4 replications in Research Greenhouse of Department of Horticultural Sciences, University of Tehran, Iran, during 2012–2013. Plant height, herbal and flower fresh and dry weight, root fresh and dry weight and root volume, colonization percentage, total petal extract, total petal flavonoids, root and shoot P and K uptakes, and Pb and Cd accumulations in root and shoot were measured. Results indicated that with increasing soil Pb and Cd concentration, growth and yield of pot marigold was reduced significantly; Cd had greater negative impacts than Pb. However, mycorrhizal fungi alleviated these impacts by improving plant growth and yield. Pot marigold concentrated high amounts of Pb and especially Cd in its roots and shoots; mycorrhizal plants had a greater accumulation of these metals, so that those under 80 mg/kg Cd soil^?1 accumulated 833.3 and 1585.8 mg Cd in their shoots and roots, respectively. In conclusion, mycorrhizal fungi can improve not only growth and yield of pot marigold in heavy metal stressed condition, but also phytoremediation performance by increasing heavy metals accumulation in the plant organs.     

Kinetin application to roots and its effect on uptake, translocation and distribution of nitrogen in wheat (Triticum aestivum) grown with a split root system

The root systems of wheat seedlings ( Triticum aestivum L. cv. SUN 9E) were pruned to two seminal roots. One of the roots was supplied with a suboptimal level of NO₃, the other was deprived of N. Different levels of kinetin were supplied to the NO₃-deprived roots. Root respiration and the increment of C and N in the roots were measured to determine the C/N ratio of the phloem sap feeding the NO₃-deprived roots. Thus, it was possible to determine retranslocation of N from the shoots to the roots, as affected by the rate of kinetin application. It was calculated that the C/N ratio of phloem sap feeding roots growing without kinetin was ca 61. Kinetin application increased this ratio to ca 75, partly due to decreased translocation of N from the shoots back to the roots. Kinetin application decreased the proportion of N that was retranslocated to the roots after translocation to the shoots. Kinetin increased the rate of NO₃ uptake per root and the rate of N incorporation in both roots and shoots by ca 60%, but had no effect on shoot dry matter production. In control plants at most 70% of the N incorporated in the NO₃-fed roots could have been imported from the shoots, whilst kinetin application reduced this value to ca 40%. Thus root growth was not fully dependent on a supply of N via the phloem.
It is concluded that cytokinins affect the pattern of N-translocation in wheat plants by increasing incorporation of N in dry matter of the shoot, thus leaving less for export. Cytokinins did not play a major role in the regulation of shoot growth and the shoot to root ratio of the present plants.     

水稻根系在根袋处理条件下对氮养分的反应

通过大田试验对 1 0个水稻品种根系与产量的关系研究表明 ,抽穗期和成熟期根冠比与产量呈极显著的负相关关系 ,相关系数分别为 - 0 .861 6和 - 0 .8889。随之在大田试验基础上选择根冠比大的品种粳籼89,设计水分和养分能自由通过 ,而根系不能穿过的根袋 ,根袋从小到大不同 ,以便产生不同大小的水稻植株根冠比。通过水培实验研究在根袋处理后对不同养分条件的反应。水培液设 3种氮素养分水平 ,即2 0 mg/kg,40 mg/kg,60 mg/kg。结果表明 ,在不同氮素养分条件下 ,经过根袋处理后在抽穗期根系干重都有下降趋势 ,根冠比显著降低 ,而根系活性吸收面积在抽穗期有不同程度的增加 ,茎鞘贮存性碳水化合物含量明显增加 ,叶绿素含量则无明显影响。在抽穗期较大的根袋处理根系总吸收面积、活跃吸收面积及所占比例与对照相比增加效果较为明显 ,而较小的根袋处理根系吸收的能力降低 ,根系吸收能力大小顺序为 :大袋 >中袋 >对照 >小袋。随养分浓度的增加 ,不同根袋处理在抽穗期的根系总吸收面积和活跃吸收面积有下降的趋势。较大的根袋处理在 2 0 mg/kg和 60 mg/kg氮素养分条件下能适当减少根系直径 ,增强根系的活性吸收比例 ,从而提高根系的活力 ;但在成熟期根袋处理对根系的活性吸收无明显影响     

Improved growth of white clover in hill grasslands by mycorrhizal inoculation

Field trials in a hill grassland area of mid-Wales showed that growth of white clover could be improved by inoculation with selected vesicular-arbuscular (VA) mycorrhizal fungi. After one growing season mycorrhizal inoculation had approximately doubled shoot dry weight, runner number and nodulation at two sites previously improved by adding lime and fertiliser and by replacing the native vegetation mainly with rye-grass and white clover. At a previously unimproved site, limed at the time of planting, mycorrhizal inoculation increased shoot dry weight by up to two and a half times, almost doubled runner formation, and increased nodulation up to five-fold where 90 kg P/ha as basic slag had been applied. Responses to mycorrhiza at this site were smaller with 22-5 kg P/ha as basic slag and were absent where no P was added. After two growing seasons inoculation responses were even more pronounced at this previously unimproved site; where clovers were being overgrown by adjacent native grasses only those given both 90 kg P/ha and mycorrhizal inoculation survived well.     

The effect of Mg on Ca,K and P content of date palm seedlings under mycorrhizal and non-mycorrhizal conditions

The effects of the presence or absence of Mg in the nutrient solution and of vesicular-arbuscular mycorrhizal fungi (VAMF) on the content and partitioning of Ca, K and P between root and shoot of date palm (Phoenix dactylifera) seedlings were examined under greenhouse conditions using soil as basal medium. Mg content of the soil was 14.95 µmol/g dry soil. The infection percentages after inoculation of VAMF were 66.0% and 55.5%, respectively, on application of –Mg and +Mg nutrient solution. Ca content of both roots and shoots did not change by these treatments; but a highly significant decrease in shoots was recorded on –Mg and +VAMF treatment. K content of root was significantly elevated by –Mg and +VAMF treatment but no changes were observed in shoots. P content of both roots and shoots increased significantly with +VAMF regardless of the presence or absence of Mg.     

Cytokinin producing bacteria enhance plant growth in drying soil

Cytokinins can promote stomatal opening, stimulate shoot growth and decrease root growth. When soil is drying, natural cytokinin concentrations decrease in association with stomatal closure and a redirection of growth away from the shoots to the roots. We asked if decreased cytokinin concentrations mediate these adaptive responses by lessening water loss and promoting root growth thereby favouring exploration for soil water. Our approach was to follow the consequences for 12-d-old lettuce seedlings of inoculating the growing medium with cytokinin-producing bacteria under conditions of water sufficiency and deficit. Inoculation increased shoot cytokinins as assessed by immunoassay and mass spectrometry. Inoculation also promoted the accumulation of shoot mass and shortened roots while having a smaller effect on root mass. Inoculation did not raise stomatal conductance. The possible promoting effect of these cytokinins on stomatal conductance was seemingly hampered by increases in shoot ABA that inoculation also induced. Inoculation lowered root/shoot ratios by stimulating shoot growth. The effect was greater in non-droughted plants but remained sufficiently strong for shoot mass of inoculated droughted plants to exceed that of well-watered non-inoculated plants. We conclude that compensating for the loss of natural cytokinins in droughted plants interferes with the suppression of shoot growth and the enhancement of root elongation normally seen in droughted plants.     

Biomass Partitioning in Tomato Plants Infected with Meloidogyne incognita

Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1, 10, 50, 100, and 200 (x 1,000) eggs per plant and maintained in a growth chamber for 40 days. Total fresh biomass (roots + shoots) at harvest was unchanged by nematode inoculation with Pi of 1 x 10⁵ eggs or less. Reductions in fresh shoot weight with increasing Pi coincided with increases in root weight. Total fresh biomass declined with Pi above 1 x 10⁵ eggs, whereas total dry biomass declined at Pi above 1 x 10⁴ eggs. The greatest reduction percentages in fresh shoot biomass induced by root-knot nematodes occurred in the stem tissue, followed by the petiole + rachis; the least weight loss occurred in the leaflets. Although biomass varied among shoot tissues, the relationship between biomass of various shoot tissues and Pi was described by quadratic equations. The linear and quadratic coefficients of the equations (stem, petiole + rachis, or leaflets on Pi) did not differ among tissues when calculations were based on standardized values. Meloidogyne incognita-infected plants had thinner leaves (leaf area/leaf weight) than did uninfected plants. Reductions in leaf weight and leaf area with nematode inoculation occurred at nodes 5-15 and 4, 6-14, respectively. Losses in plant height and mass due to nematodes reflected shorter internodes with less plant mass at each node.