Net root growth and nutrient acquisition in response to predicted climate change in two contrasting heathland species

Background and aims

Accurate predictions of nutrient acquisition by plant roots and mycorrhizas are critical in modelling plant responses to climate change.

Methods

We conducted a field experiment with the aim to investigate root nutrient uptake in a future climate and studied root production by ingrowth cores, mycorrhizal colonization, and fine root N and P uptake by root assay of Deschampsia flexuosa and Calluna vulgaris.

Results

Net root growth increased under elevated CO₂, warming and drought, with additive effects among the factors. Arbuscular mycorrhizal colonization increased in response to elevated CO₂, while ericoid mycorrhizal colonization was unchanged. The uptake of N and P was not increased proportionally with root growth after 5 years of treatment.

Conclusions

While aboveground biomass was unchanged, the root growth was increased under elevated CO₂. The results suggest that plant production may be limited by N (but not P) when exposed to elevated CO₂. The species-specific response to the treatments suggests different sensitivity to global change factors, which could result in changed plant competitive interactions and belowground nutrient pool sizes in response to future climate change.     

Ethylene is differentially regulated during sugar beet germination and affects early root growth in a dose-dependent manner

Main conclusion

By integrating molecular, biochemical, and physiological data, ethylene biosynthesis in sugar beet was shown to be differentially regulated, affecting root elongation in a concentration-dependent manner. There is a close relation between ethylene production and seedling growth of sugar beet (Beta vulgaris L.), yet the exact function of ethylene during this early developmental stage is still unclear. While ethylene is mostly considered to be a root growth inhibitor, we found that external 1-aminocyclopropane-1-carboxylic acid (ACC) regulates root growth in sugar beet in a concentration-dependent manner: low concentrations stimulate root growth while high concentrations inhibit root growth. These results reveal that ethylene action during root elongation is strongly concentration dependent. Furthermore our detailed study of ethylene biosynthesis kinetics revealed a very strict gene regulation pattern of ACC synthase (ACS) and ACC oxidase (ACO), in which ACS is the rate liming step during sugar beet seedling development.     

Arthrobacter agilis UMCV2 induces iron acquisition in Medicago truncatula (strategy I plant) in vitro via dimethylhexadecylamine emission

Background and aims

Iron is an essential nutrient for plant growth. Although abundant in soil, iron is poorly available. Therefore, plants have evolved mechanisms for iron mobilization and uptake from the rhizospheric environment. In this study, we examined the physiological responses to iron deficiency in Medicago truncatula plants exposed to volatile organic compounds (VOCs) produced by Arthrobacter agilis UMCV2.

Methods

The VOC profiles of the plant and bacterium were determined separately and during interaction assays using gas chromatography. M. truncatula plants exposed to A. agilis VOCs and pure dimethylhexadecylamine were transferred to conditions of iron deficiency, and parameters associated with iron nutritional status were measured.

Results

The relative abundance of the bacterial VOC dimethylhexadecylamine increased 12-fold when in co-cultures of A. agilis and M. truncatula, compared to axenic cultures. Plants exposed to bacterial VOCs or dimethylhexadecylamine exhibited a higher rhizosphere acidification capacity, enhanced ferric reductase activity, higher biomass generation, and elevated chlorophyll and iron content relative to controls.

Conclusions

The VOCs emitted by A. agilis UMCV2 induce iron acquisition mechanisms in vitro in the Strategy I plant M. truncatula. Dimethylhexadecylamine is the signal molecule responsible for producing the beneficial effects.     

Glucobrassicin a potential inhibitor of unusual type affecting the Germination and growth of plants; mechanism of its action

A water-soluble germination- and growth-inhibitor present in plants of Brassica genus was studied. Aqueous eluates from chromatograms of methanolic extracts of Savoy cabbage, cabbage and Brussels’ sprouts leaves, and of Brussels’ sprouts roots, inhibited the growth of wheat; the chromatographic behaviour of this inhibitor was similar to that of the thioglycoside glucobrassicin (GLUBR). GLUBRat 10^-3 m, and the supposed product of its enzymatic degradation, 3-indolylacetonitrile (IAN) at 10^-4 m, inhibited the growth of wheat and clover in a similar manner. At lower concentrations, both substances gradually enhanced growth. In contrast to IAN, GLUBR did not appreciably influence the growth of Savoy cabbage. Other products of GLUBR degradation, such as thiocyanate ion and ascorbigen, influenced the growth to a lesser extent and in a different way. At higher concentrations GLUBR and IAN also inhibited the germination of clover seeds. The biological effect of GLUBR is dependent on the presence of the indole nucleus in its molecule; the thioglycoside glucoiberin, which is not of indolic character, does not influence growth. The presence of free myrosinase was shown in intact wheat seedlings. Hence, GLUBR taken in by the germinating plants must undergo enzymatic cleavage. The in vitro activity of myrosinase in wheat and clover was lower than in Savoy cabbage, but the quantity of IAN formed at a pH corresponding to the natural pH was higher in wheat and clover than in Savoy cabbage, where the formation of the growth-inactive ascorbigen prevailed. On the basis of these results the hypothesis was formulated that GLUBR, the indolic complex from the generaBrassica, Raphanus, Cochleria, Nasturtium, Barbarea andSisymbrium, is a representative of a class of potential inhibitors of growth and germination, whose activity can be explained by the liberation of large amounts of growth-affecting substances during their specific enzymatic cleavage.     

Genetic diversity and plant growth promoting traits of diazotrophic bacteria isolated from two Pennisetum purpureum Schum. genotypes grown in the field

Background and aims

Some elephant grass (Pennisetum purpureum) genotypes are able to produce large amounts of biomass and accumulate N derived from BNF when growing in soil with low N levels. However, information about the diazotrophic bacteria colonizing this C4 plant is still very scarce. This study aimed to characterize the plant growth promoting traits of a fraction of culturable diazotrophs colonizing the genotypes CNPGL F06-3 and Cameroon.

Methods

A total of 204 isolates were obtained from surface sterilized leaves, stems and roots after culturing on five different N-free semisolid media. These were then analyzed by BOX-PCR, and the 16S rRNA and nifH sequences of representative isolates were obtained. The functional ability of the isolates to reduce acetylene, produce indole and to solubilize phosphate was also determined.

Results

The diazotrophic bacterial population varied from 10² up to 10⁶ bacteria g^?1 fresh tissues of both genotypes. The BOX-PCR analysis suggested a trend in the genetic diversity among the 204 diazotrophic strains colonizing the different genotypes and plant tissues. Sequencing of 16S rRNA fragments confirmed the presence of Azospirillum brasilense and Gluconacetobacter diazotrophicus and revealed for the first time the occurrence of G. liquefaciens, G. sacchari, Burkholderia silvatlantica, Klebsiella sp., Enterobacter cloacae and E. oryzae in elephant grass. Interestingly, several nifH sequences from isolates identified as G. liquefaciens and G. sacchari showed homologies with nifH sequences of Enterobacter species. The majority of the isolates (97%) produced indole compounds, 22% solubilized phosphate and 6.4% possessed both characteristics.

Conclusions

The results showed the occurrence of novel diazotrophic bacterial species colonizing different tissues of both genotypes of elephant grass. In addition, the study revealed the presence of several bacteria with growth promoting traits, and highlighted their potential to be exploited as biofertilizers.     

The shift in plant species composition in a subarctic mountain birch forest floor due to climate change would modify the biogenic volatile organic compound emission profile

Background and aims

Mountain birch forests dominate in the Subarctic but little is known of their non-methane biogenic volatile organic compound (BVOC) emissions. The dwarf shrubs Empetrum hermaphroditum, Vaccinium myrtillus and Vaccinium uliginosum co-dominate in the forest floors of these forests. The abundance of these three dwarf shrubs relative to each other could be affected by climate warming expected to increase nutrient availability by accelerating litter decomposition and nutrient mineralization. We 1) compared the BVOC emission profiles of vegetation covers dominated by E. hermaphroditum and V. myrtillus plus V. uliginosum in a subarctic mountain birch forest floor, 2) distinguished the BVOCs emitted from plants and soil and 3) measured how the BVOC emissions from the different vegetation covers differed under darkness.

Methods

BVOCs were sampled during two growing seasons using a conventional ecosystem chamber-based method, collected on adsorbent and analyzed with gas chromatography–mass spectrometry.

Results

High abundance of E. hermaphroditum increased the sesquiterpene emissions. Soil released fewer different BVOCs than controls (i.e. natural vegetation) but the total emission rates were similar. Darkness did not affect the emissions. Carbon emitted as BVOCs was less than 0.2% of the CO₂ exchange.

Conclusions

Our results suggest that sesquiterpene emissions from subarctic mountain birch forest floors would be reduced following an increased abundance of V. myrtillus and V. uliginosum with climate change because these species respond rapidly to increased nutrient availability.     

The extracellular proteome of Rhizobium etli CE3 in exponential and stationary growth phase

Background

The extracellular proteome or secretome of symbiotic bacteria like Rhizobium etli is presumed to be a key element of their infection strategy and survival. Rhizobia infect the roots of leguminous plants and establish a mutually beneficial symbiosis. To find out the possible role of secreted proteins we analyzed the extracellular proteome of R. etli CE3 in the exponential and stationary growth phases in minimal medium, supplemented with succinate-ammonium.

Results

The extracellular proteins were obtained by phenol extraction and identified by LC-ESI MS/MS. We identified 192 and 191 proteins for the exponential and stationary phases respectively. Using the software Signal P, we predicted signal peptides for 12.95% and 35.60% of the proteins identified in the exponential and stationary phases, respectively, which could therefore be secreted by the Sec pathway. For the exponential growth phase, we found in abundance proteins like the ribosomal proteins, toxins and proteins belonging to the group "defence mechanisms". For the stationary growth phase, we found that the most abundant proteins were those with unknown function, and in many of these we identified characteristic domains of proteases and peptidases.

Conclusions

Our study provided the first dataset of the secretome of R. etli and its modifications, which may lead to novel insights into the adaptive response of different stages of growth. In addition, we found a high number of proteins with unknown function; these proteins could be analyzed in future research to elucidate their role in the extracellular proteome of R. etli.     

Root interactions between intercropped legumes and non-legumes—a competition study of red clover and red beet at different nitrogen levels

Aims

To investigate root competition in a legume/non-legume mixture, and how root growth of the legume is affected by the competition at increasing nitrogen (N) supply.

Methods

Red beet (Beta vulgaris L.) and red clover (Trifolium pratense L.) were grown in transparent rhizotron tubes either in mixture or as sole crop at N supplies of 0, 75 or 150 kg ha^-1. The root growth was evaluated by the root intensity on the rhizotron surface, root depth and plant uptake of ¹⁵N injected into the soil at the deeper part of the red clover root system.

Results

Competition with red beet decreased clover root intensity in deeper soil layers compared to clover grown as sole crop. The difference between clover in sole crop and in mixture was not evident at the highest N supply because the root growth of clover in sole crop appeared to be lowered at high N level. Increased N supply increased the dominance of red beet, but generally did not alter the root growth and distribution of the two species grown in mixture.

Conclusions

Clover root growth and rooting depth were inhibited by competition with red beet but the effect was not enhanced by increased N supply; hence the increased dominance of red beet at higher N level was likely due to its increased growth and competitiveness for other soil resources.     

The identification of allergen proteins in sugar beet (Beta vulgaris) pollen causing occupational allergy in greenhouses

Background

During production of sugar beet (Beta vulgaris) seeds in greenhouses, workers frequently develop allergic symptoms. The aim of this study was to identify and characterize possible allergens in sugar beet pollen.

Methods

Sera from individuals at a local sugar beet seed producing company, having positive SPT and specific IgE to sugar beet pollen extract, were used for immunoblotting. Proteins in sugar beet pollen extracts were separated by 1- and 2-dimensional electrophoresis, and IgE-reactive proteins analyzed by liquid chromatography tandem mass spectrometry.

Results

A 14 kDa protein was identified as an allergen, since IgE-binding was inhibited by the well-characterized allergen Che a 2, profilin, from the related species Chenopodium album. The presence of 17 kDa and 14 kDa protein homologues to both the allergens Che a 1 and Che a 2 were detected in an extract from sugar beet pollen, and partial amino acid sequences were determined, using inclusion lists for tandem mass spectrometry based on homologous sequences.

Conclusion

Two occupational allergens were identified in sugar beet pollen showing sequence similarity with Chenopodium allergens. Sequence data were obtained by mass spectrometry (70 and 25%, respectively for Beta v 1 and Beta v 2), and can be used for cloning and recombinant expression of the allergens. As for treatment of Chenopodium pollinosis, immunotherapy with sugar beet pollen extracts may be feasible.     

Rhizobacteria (Pseudomonas sp. SB) assist phytoremediation of oily-sludge-contaminated soil by tall fescue (Testuca arundinacea L.)

Background and aims

The objectives of this study were to examine the effect of direct inoculation of seeds with the rhizobacteria Pseudomonas sp. SB on the growth of tall fescue and phytodegradation efficiency in an oily-sludge-contaminated soil.

Methods

SB isolated from rhizosphere soil of tall fescue was evaluated for their plant-growth-promoting characters and ability to produce biosurfactant. A pot experiment was conducted to study the effect of inoculation of SB on phytoremediation.

Results

SB reduced the surface tension of culture media and produced indole acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylate deaminase. Inoculation of SB increased shoot and root dry weights of tall fescue in oily-sludge-contaminated soil by 28 % and 19 %, respectively. Over 120 days, the content of total petroleum hydrocarbon in soil decreased by 33.9 %, 68.0 %, and 84.5 %, and of polycyclic aromatic hydrocarbons (PAHs) by 32.9 %, 40.9 %, and 46.2 %, respectively, in the no-plant control, tall fescue, and tall fescue + SB treatments. Inoculation of SB also increased the activity and biodiversity of soil microbial communities in the planted treatments.

Conclusions

SB could produce biosurfactant and exhibited a number of characters of plant-growth-promoting rhizobacteria. Inoculation of SB to tall fescue led to more effective remediation of oily-sludge-contaminated soils.     

Nitrogen use efficiency of organically fertilized white cabbage and residual effects on subsequent beetroot

Background and aims

The low N availability in organic cropping systems requires an efficient use of the limited N sources. The study aimed to analyze the N efficiency of organically fertilized white cabbage on a crop and crop rotation basis.

Methods

Effects of soil-incorporated lupine seedlings and seed meal on the N use efficiency (NUE) and individual NUE components of cabbage were investigated in field experiments. Cabbage was followed by beetroot to quantify residual fertilizer effects.

Results

Generally, NUE decreased with increasing N availability. Nitrogen uptake efficiency, however, was low at low N supply and increased curvilinearly to an asymptotic maximum. Variation in harvest index between and within experimental years was explained by differences in thermal growing time and initial cabbage growth, respectively. The increase in beetroot N supply by fertilizer treatments averaged 18 % of applied lupine seed N corresponding to 63 % of the incremental N in cabbage residues.

Conclusions

Dry matter partitioning alters during cabbage yield formation in favor of the harvest residue fraction if abiotic stress like water shortage occurs directly after crop establishment, being associated with reduced NUE. The residual effect depends largely on the re-utilization of incremental fertilizer N in cabbage residues and thus on the short-term net N mineralization of organic fertilizers.     

BcMF11, a novel non-coding RNA gene from Brassica campestris, is required for pollen development and male fertility

Key message

BcMF11 as a non-coding RNA gene has an essential role in pollen development, and might be useful for regulating the pollen fertility of crops by antisense RNA technology.

Abstract

We previously identified a 828-bp full-length cDNA of BcMF11, a novel pollen-specific non-coding mRNA-like gene from Chinese cabbage (Brassica campestris L. ssp. chinensis Makino). However, little information is known about the function of BcMF11 in pollen development. To investigate its exact biological roles in pollen development, the BcMF11 cDNA was antisense inhibited in transgenic Chinese cabbage under the control of a tapetum-specific promoter BcA9 and a constitutive promoter CaMV 35S. Antisense RNA transgenic plants displayed decreasing expression of BcMF11 and showed distinct morphological defects. Pollen germination test in vitro and in vivo of the transgenic plants suggested that inhibition of BcMF11 decreased pollen germination efficiency and delayed the pollen tubes’ extension in the style. Under scanning electron microscopy, many shrunken and collapsed pollen grains were detected in the antisense BcMF11 transgenic Chinese cabbage. Further cytological observation revealed abnormal pollen development process in transgenic plants, including delayed degradation of tapetum, asynchronous separation of microspore, and aborted development of pollen grain. These results suggest that BcMF11, as a non-coding RNA, plays an essential role in pollen development and male fertility.     

Boron delays dehydration and stimulates root growth in Eucalyptus urophylla (Blake,S.T.) under osmotic stress

Background

Water and nutritional restrictions are limiting factors for the growth of Eucalyptus trees in tropical climates. In the dry season, boron (B) uptake is severely affected.

Aims

The objectives of this study were to evaluate the phloem mobility of B and whether its deficiency can increase plant sensitivity to osmotic stress. It was also tested to what extent foliar application of B could mitigate the negative effects of drought under low B supply.

Methods

Seedlings of a drought tolerant Eucalyptus urophylla (Blake, S. T.) clone were grown in nutrient solution, subjected to low availability of B for 25 days, and then submitted to a progressive osmotic stress. After imposition of osmotic stress, B was applied to young or mature leaves.

Results

B applications, mainly to mature leaf, stimulated root growth and delayed dehydration under osmotic stress and led to an increased B translocation and carbon isotopic composition. The expression of B transporters and pectin metabolism genes were also increased in water-stressed plants supplied with B by foliar application.

Conclusions

B deficiency led to increased plant dehydration and decreased root growth under osmotic stress. The application of B to mature leaf of water-stressed plants proved effective in mitigating the negative effects of water deficit in root growth.     

Distribution of bacterial endophytes in peanut seeds obtained from axenic and control plant material under field conditions

Background and Aims

The role and linkage of endophytic bacteria to resistance of peanut seeds to biotic stress is poorly understood. The aims of the present study were to survey the experimental (axenic) and control (conventional) peanut plants for the predominant endophytic bacteria, and to characterize isolates with activity against selected A. flavus strains.

Methods

Young axenic plants were grown from presumably bacteria-free embryos in the lab, and then they were grown in a field. Endophytic bacterial species were identified by the analysis of DNA sequences of their 16S-ribosomal RNA gene. DNA extracted from soil was also analyzed for predominant bacteria.

Results

Mature seeds from the experimental and control plants contained several species of nonpathogenic endophytic bacteria. Among the eight bacterial species isolated from seeds, and DNA sequences detected in soil, Bacillus thuringiensis was dominant. All B. amyloliquefaciens isolates, the second abundant species in seeds demonstrated activity against A. flavus. This effect was not observed with any other bacterial isolates. There was no significant difference in number and relative occurrence of the two major bacterial species between the experimental and conventionally grown control seeds.

Conclusion

Endophytic bacterial colonization derives from local soil and not from the seed source, and the peanut plant accommodates only selected species of bacteria from diverse soil populations. Some bacterial isolates showed antibiosis against A. flavus.     

Differential proteome analysis of mature and germinated seeds of Magnolia sieboldii K. Koch

Key message

This is the first reported proteomic analysis to study the dormancy breaking of Magnolia sieboldii seeds. Our results provide a fundamental reference for further studies on the regulation of protein expression during seed germination.

Abstract

Magnolia sieboldii K. Koch is an ornamental tree. The deep dormancy of its seeds hinders its cultivation for economic purposes. The biochemical basis of the regulation of seed germination remains poorly understood. The present study aimed to identify differentially expressed proteins in germinated seeds of M. sieboldii using polyethylene glycol fractionation. In total, 59 differentially expressed protein spots from two-dimensional gel maps were detected, 33 of which were identified by mass spectrometry. They were assigned to eight functional classes on the basis of their putative biological functions: photosynthesis (3 %), chaperonin/heat shock protein (9 %), protein and amino acid synthesis (9 %), stress/defense (18 %), cytoskeleton structure (3 %), metabolism (18 %), hormone and polyamine (9 %) and storage proteins (31 %). Among the other functions, the effects of plant hormones on seed germination may be one of the most important functions in plant growth. Gibberellins and ethylene positively regulate seed germination. The activities of several hormone-associated proteins possibly influencing seed germination were increased. The characterization of these proteins will be of great help in identifying the molecular mechanism underlying seed germination.     

The performance of DGT versus conventional soil phosphorus tests in tropical soils - An isotope dilution study

Aims

The aim of the present study was to compare lead accumulation and tolerance among heavy metal hyperaccumulating and non-hyperaccumulating metallophytes.

Methods

To this purpose, we compared Pb tolerance and accumulation in hydroponics among calamine and non-calamine populations of Silene vulgaris, Noccaea caerulescens, and Matthiola flavida. We established the effects of Ca on Pb tolerance and accumulation in M. flavida, and measured exchangeable soil Pb and Ca at two calamine sites.

Results

Results revealed that calamine populations of S. vulgaris and N. caerulescens were Pb hypertolerant, but the calamine M. flavida population was not. Pb hyperaccumulation capacity was exclusively found in one of the calamine N. caerulescens populations.

Conclusions

1) Pb hypertolerance is sometimes lacking in metallophyte populations from strongly Pb-enriched soil, probably due to a relatively high level of exchangeable soil Ca, 2) Ca effectively counteracts Pb uptake and Pb toxicity, 3) The tendency to hyperaccumulate Pb is a population-specific phenomenon in N. caerulescens, 4) Pb hypertolerance in N. caerulescens is not necessarily associated with a tendency to hyperaccumulate Pb, 5) apparent natural Pb hyperaccumulation in M. flavida is not reproducible in hydroponics, probably due to the absence of air-born contamination in laboratory experiments.