The effect of transpiration on selenium uptake and mobility in durum wheat and spring canola

Aims

The objective of this study was to determine the relative importance of transpirational pull, Se speciation, sulfate and species on Se accumulation by plants, in order to determine which of these factors must be considered in the future development of models to predict Se accumulation by plants.

Methods

Seedlings of durum wheat (Triticum turgidum L. var durum cv ‘Kyle’) and spring canola (Brassica napus L. var Hyola 401) were grown hydroponically and exposed to SeO ₄ ^2- (selenate) with or without SO ₄ ^2- (sulfate), or to HSeO ₃ ^- (biselenite) under different transpiration regimes altered through ‘low’ (~50%) or ‘high’ (~78%) relative humidity (RH). Plants were harvested after 0, 8, 16, or 24?h exposures, digested, and analyzed for Se by GFAAS.

Results

Accumulation and distribution of Se by plants is dependent on plant species, Se speciation in the nutrient solution, SO ₄ ^2- competition, and transpiration regimes. Canola accumulated and translocated more Se than wheat. In wheat and canola, the greatest accumulation and translocation of Se occurred when plants were exposed to SeO ₄ ^2- without SO ₄ ^2- compared to solutions of SeO ₄ ^2- with SO ₄ ^2- or HSeO ₃ ^2- . Wheat plants exposed to SeO ₄ ^2- and SO ₄ ^2- had an increased Se accumulation and translocation under increased transpiration rates than when exposed to SeO ₄ ^2- without SO ₄ ^2- or HSeO ₃ ^2- . On the other hand, increases in transpiration increased the translocation of Se to canola shoots when exposed to HSeO ₃ ^- more than any other treatments.

Conclusions

Overall, our results suggest that plant species is the most important factor influencing Se accumulation and translocation, but that these endpoints can be modified by climate and specific soil Se or S content. Models to predict accumulation of Se by plants must consider all of these factors to accurately calculate the mechanisms of uptake and translocation.     

Selenium accumulation in durum wheat and spring canola as a function of amending soils with selenite, selenate and or sulphate

Aims

A comparison was performed between plant species to determine if extractable, rather than total soil Se, is more effective at predicting plant Se accumulation over a full growing season.

Methods

Durum wheat (Triticum turgidum L.) and spring canola (Brassica napus L.) were sown in potted soil amended with 0, 0.1, 1.0, or 5.0 mg kg^?1 Se as SeO₄ ^2? or SeO₃ ^2?. In addition, SeO₄ ^2?-amended soils were amended with 0 or 50 mg kg^?1 S as SO₄ ^2?. Soils were analyzed for extractable and total concentration of Se ([Se]). Twice during the growing season plants were harvested and tissue [Se] was determined.

Results

Plants exposed to SeO₃ ^2? accumulated the least Se. Fitted predictive models for whole plant accumulation based on extractable soil [Se] were similar to models based on total [Se] in soil (R²?=?0.73 or 0.74, respectively) and selenium speciation and soil [S] were important soil parameters to consider. As well, soil S amendments limited Se toxicity.

Conclusions

Soil quality guidelines (SQGs) based on extractable Se should be considered for risk assessment, particularly when Se speciation is unknown. Predictive models to estimate plant Se uptake should include soil S, a modifier of Se accumulation.     

Variation in cadmium accumulation and translocation among peanut cultivars as affected by iron deficiency

Purpose

The current study aimed to test the hypothesis that the variations in shoot Cd accumulation among peanut cultivars was ascribed to the difference in capacity of competition with Fe transport, xylem loading and transpiration.

Methods

A hydroponics experiment was conducted to determine the plant biomass, gas exchange, and Cd accumulation in Fe-sufficient or -deficient plants of 12 peanut cultivars, at low Cd level (0.2 μM CdCl₂).

Results

Peanut varied among cultivars in morpho-physiological response to Cd stress as well as Cd accumulation, translocation and distribution. Qishan 208 and Xvhua 13 showed a higher capacity for accumulating Cd in their shoots. Fe deficiency increased the concentration and amount of Cd in plant organs, but decreased TF _{root to shoot} and TF _{root to stem}, while TF _{stem to leaf} remained unaffected. Fe deficiency-induced increase rates of Cd concentration and total Cd amount in roots and leaves were negatively correlated with the values in Fe-sufficient plants. Transpiration rate was positively correlated with leaf Cd concentration, TF _{root to shoot}, TF _{root to stem} and TF _{stem to leaf}.

Conclusions

The difference in shoot Cd concentration among peanut cultivars was mainly ascribed to the difference in Fe transport system, xylem loading capacity and transpiration.     

Non-invasive pressure probes magnetically clamped to leaves to monitor the water status of wheat

Background and aims

Being able to monitor the hydration status of a plant would be useful to breeding programs and to providing insight into adaptation to water-limited environments, but most current methods are destructive or laborious. We evaluated novel non-invasive pressure probes (commercial name: ZIM-probe) for their potential in monitoring the water status of wheat (Triticum aestivum L.) leaves.

Methods

The probes consist of miniature pressure sensors that clamp to the leaves via magnets and detect relative changes in hydration status. Probes were clamped to leaves of six individual plants of the cultivar Wyalkatchem at the stem elongation stage and compared against traditional plant water relations measurements.

Results

Output from the probes, called patch-pressure (P _p ), correlated well with leaf water potential and transpiration of individual plants. Variation between plants in the original clamp pressure exerted by the magnets and leaf individual properties led to variations in the amplitude of the diurnal P _p profiles, but not in the kinetics of the curves where P _p responded simultaneously in all plants to changes in the ambient environment (light and temperature).

Conclusions

Drying and rewatering cycles and analysis of the curve kinetics identified several methods that can be used to test comparisons of water status monitoring of wheat genotypes under water deficit.     

Phosphorus speciation in mature wheat and canola plants as affected by phosphorus supply

Background and aims

As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status.

Methods

Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha^?1 equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution ³¹P nuclear magnetic resonance (NMR) spectroscopy.

Results

Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate.

Conclusions

Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status.     

Contributions of root uptake and remobilization to grain zinc accumulation in wheat depending on post-anthesis zinc availability and nitrogen nutrition

Background and aims

Whether root Zn uptake during grain filling or remobilization from pre-anthesis Zn stores contributes more to grain Zn in wheat is subject to an on-going debate. This study investigated the effects of N nutrition and post-anthesis Zn availability on the relative importance of these sources.

Methods

Durum wheat plants were grown in nutrient solution containing adequate Zn (0.5?μM) and three different N levels (0.5; 1.5; 4.5?mM). One third of the plants were harvested when they reached anthesis. One half of the remaining plants were grown to maturity with adequate Zn, whereas the Zn supply to the other half was discontinued at anthesis. Roots, straw and grains were harvested separately and analyzed for Zn and N.

Results

Depending on the N supply, Zn remobilization from pre-anthesis sources provided almost all of grain Zn when the Zn supply was withheld at anthesis; otherwise up to 100?% of grain Zn could be accounted for by Zn taken up post-anthesis. By promoting tillering and grain yield and extending the grain filling, higher N supply favored the contribution of Zn uptake to grain Zn accumulation.

Conclusion

Remobilization is critical for grain Zn accumulation when Zn availability is restricted during grain filling. However, where root uptake can continue, concurrent Zn uptake during grain development, favored by higher N supply, overshadows net remobilization.     

Signalling mechanisms involved in the response of two varieties of Humulus lupulus L. to soil drying: I. changes in xylem sap pH and the concentrations of abscisic acid and anions

Background and aims

Soil drying leads to the generation of chemical signals in plants that regulate water use via control of the stomatal aperture. The aim of our work was to identify the presence and identity of potential chemical signals, their dynamics, and their relationship with transpiration rate during soil drying in hop (Humulus lupulus (L.)) plants.

Methods

We used pressure chamber technique for measurement of shoot water potential and collection of shoot xylem sap. We analyzed concentrations of abscisic acid (ABA), nitrate, phosphate, sulphate and malate in sap and also the rate of whole plant transpiration.

Results

Transpiration rate decreased prior to changes in shoot water potential. The concentration of ABA in xylem sap continuously increased from early to later stages of water stress, whereas in leaves it increased only at later stages. Shoot sap pH increased simultaneously with the decrease of transpiration rate. Xylem sap alkalization was in some cases accompanied by a decrease in nitrate concentration and an increase in malate concentration. Concentration of sulphate increased in xylem sap during drying and sulphate in combination with a higher ABA concentration enhanced stomatal closure.

Conclusions

Several early chemical signals appear in sap of hop plants during soil drying and their impact on transpiration may vary according to the stage of soil drying.     

Effect of wheat phosphorus status on leaf surface properties and permeability to foliar-applied phosphorus

Aims

This study aimed to analyse the effect of phosphorus (P) nutritional status on wheat leaf surface properties, in relation to foliar P absorption and translocation.

Methods

Plants of Triticum aestivum cv. Axe were grown with three rates of root P supply (equivalent to 24, 8 and 0 kg P ha^?1) under controlled conditions. Foliar P treatments were applied and the rate of drop retention, P absorption and translocation was measured. Adaxial and abaxial leaf surfaces were analysed by scanning and transmission electron microscopy. The contact angles, surface free energy and work-of-adhesion for water were determined.

Results

Wheat leaves are markedly non-wettable, the abaxial leaf side having some degree of water drop adhesion versus the strong repulsion of water drops by the adaxial side. The total leaf area, stomatal and trichome densities, cuticle thickness and contact angles decreased with P deficiency, while the work-of-adhesion for water increased. Phosphorous deficient plants failed to absorb the foliar-applied P.

Conclusions

Phosphorous deficiency altered the surface structure and functioning of wheat leaves, which became more wettable and had a higher degree of water drop adhesion, but turned less permeable to foliar-applied P. The results obtained are discussed within an agronomic and eco-physiological context.     

Leaf responses to iron nutrition and low cadmium in peanut: anatomical properties in relation to gas exchange

Aims

This study evaluated how iron nutrition affect leaf anatomical and photosynthetic responses to low cadmium and its accumulation in peanut plants.

Methods

Seedlings were treated with Cd (0 and 0.2 μM CdCl₂) and Fe (0, 10, 25, 50 or 100 μM EDTA-Na₂Fe) in hydroponic culture.

Results

Cadmium accumulation is highest in Fe-deficient plants, and dramatically decreased with increasing Fe supply. The biomass, gas exchange, and reflectance indices were highest at 25 μM Fe²⁺ treatments, indicating the concentration is favorable for the growth of peanut plants. Both Fe deficiency and Cd exposure impair photosynthesis and reduce reflectance indices. However, they show different effects on leaf anatomical traits. Fe deficiency induces more and smaller stomata in the leaf surface, but does not affect the inner structure. Low Cd results in a thicker lamina with smaller stomata, thicker palisade and spongy tissues, and lower palisade to spongy thickness ratio. The stomatal length and length/width ratio in the upper epidermis, spongy tissue thickness, and palisade to spongy thickness ratio were closely correlated with net photosynthetic rate, stomatal conductance, and transpiration rate.

Conclusions

Cd accumulation rather than Fe deficiency alters leaf anatomy that may increase water use efficiency but inhibit photosynthesis.     

Dual effects of transgenic Brassica napus overexpressing CS gene on tolerances to aluminum toxicity and phosphorus deficiency

Background and aims

Low phosphorus (P) bioavailability and aluminum (Al) toxicity are two major constraints to plant growth in acid soil. To improve the tolerance of Brassica napus to Al toxicity and P deficiency, we generated transgenic canola (Brassica napus cv Westar) lines overexpressing a Pseudomonas aeruginosa citrate synthase (CS) gene and then investigated the effects of CS gene overexpressing in canola on enhancing tolerance to the two constraints.

Methods

The vector construction and plant transformation, molecular identification, estimation of extracellular and cellular citrate and malate concentrations, enzyme activity and gene expression analyse and Al tolerance and P acquisition assays were conducted using both hydroponics and soil culturing in the study.

Results

Both the root citrate and malate concentrations and their exudations in the two transgenic lines significantly increased compared with wild type (WT) following exposure to Al. These increases may be attributed to higher activities of the CS, malate dehydrogenase (MDH) and phosphoenolpyruvate carboxylase (PEPC) enzymes in the TCA cycle and the expression of BnALMT and BnMATE in the transgenic plants following Al exposure. The primary root elongation and prolonged Al treatment (10 days) experiments revealed that the transgenic lines displayed enhanced levels of Al tolerance. In addition, they showed enhanced citrate and malate exudation when grown in P-deficient conditions. Moreover, the enzyme activities of the transgenic lines were significantly higher compared with WT in response to P-deficient stress. The soil culture experiment showed that the transgenic lines possessed improved P uptake from the soil and accumulated more P in their shoots and seeds when FePO₄ was used as the sole P source.

Conclusions

These results indicate that the overexpression of the CS gene in B. napus not only leads to increased citrate synthesis and exudation but also changes malate metabolism, which confers improved tolerances to Al toxicity and P deficiency in the transgenic plants. These findings provide further insight into the dual effects of CS gene overexpression on Al toxicity and P deficiency in plants.     

Mutation of mpk6 enhances cadmium tolerance in Arabidopsis plants by alleviating oxidative stress

Background and aims

Cadmium (Cd) could activate activity of mitogen-activated protein kinase MPK6 in plants. In this study, we investigated the role of MPK6 in mediating Cd toxicity in plants.

Methods

The wild type Arabidopsis plants (WT) and the mpk6-2 mutants were subjected either 0 (Control) or 10 μM Cd treatment. Kinase activity of MPK6, nitric oxide (NO) level, Cd concentration, and oxidative stress were measured.

Results

In WT plants, Cd exposure rapidly stimulated kinase activity of MPK6. However, upon Cd exposure, mpk6-2 showed better growth than the WT. Although Cd-induced production of NO in roots was greater in WT than in mpk6-2, there was no difference in Cd concentration between the two plants. Nevertheless, the Cd-induced hydroperoxide burst, lipid peroxidation and loss of membrane integrity, were all more severe in the WT than in mpk6-2. Foliar applications of antioxidant ascorbic acid, vigorously improved the growth of both the WT and mpk6-2 under Cd exposure. Thereby the growth difference between these two plants was minimized.

Conclusions

Mutation of mpk6 enhances Cd tolerance in plants by alleviating oxidative stress, but did not affect cadmium accumulation in plants.     

Fertile introgression products generated via somatic hybridization between wheat and Thinopyrum intermedium

Key message

Fertile hybrids were produced with genetic material transferred from Th. intermedium into a wheat background and supply a source of genetic variation to wheat improvement.

Abstract

Both symmetric and asymmetric somatic hybrids have been obtained from the combination of wheatgrass (Thinopyrum intermedium) and bread wheat (Triticum aestivum). Two wheat protoplast populations, one derived from embryogenic calli and the other from a non-regenerable, rapidly dividing cell line, were fused with Th. intermedium protoplasts which had been (or not been) pre-irradiated with UV. Among the 124 regenerated calli, 64 could be categorized as being of hybrid origin on the basis of plant morphology, peroxidase isozyme, RAPD DNA profiling and karyological analysis. Numerous green plantlets were regenerated from 13 calli recovered from either the symmetric hybrid (no UV pre-treatment) or the asymmetric one (30 s UV irradiation). One of these hybrid plants proved to be vigorous and self-fertile. The regenerants were all closer in phenotype to wheat than to Th. intermedium. Genomic in situ hybridization analysis showed that the chromosomes in the hybrids were largely intact wheat ones, although a few Th. intermedium chromosome fragments had been incorporated within them.     

Some Lithuanian ethnobotanical taxa: a linguistic view on Thorn Apple and related plants

Background

The perception and use of plants correspond with common plant names. The study of plant names may give insight into historical and recent use of plants.

Methods

Plant names in dictionaries and folklore have been evaluated. A etymological analysis of the names is provided. Onomasiological and semasiological aspects have been considered. Therefore, species named with names related to each other have been selected.

Results

Plant names containing the stem dag- or deg- may belong to either of two categories: incenses or thorny plants. Plants named in durn- have been in use as psychopharmaca. The name rymo points not to Rome but to the use of plants as anodyne or psychopharmaca.     

Estimating belowground nitrogen inputs of pea and canola and their contribution to soil inorganic N pools using 15N labeling

Background and aims

Crop species grown in a diversified crop rotation can influence soil N dynamics to varying degrees due to differences in the quantity and quality of the residues returned to the soil. The aim of this study was to quantify the contribution of N rhizodeposition by canola (Brassica napus L.) and pea (Pisum sativum L.) to the crop residue N balance and soil inorganic N pool.

Methods

Canola and pea were grown in a soil-sand mixture and were subject to cotton-wick ¹⁵N labeling in a greenhouse experiment. Nitrogen-15 recovered in the soil and roots were used to estimate N rhizodeposition.

Results

Belowground N, including root N and N rhizodeposits, comprised 70 % and 61 % of total crop residue N for canola and pea, respectively. Canola released the greatest amount of total root-derived N to the soil, which was related to greater root biomass production by canola. However, root-derived N in the soil inorganic N pool was greater under pea (13 %) than canola (4 %).

Conclusions

Our results show a significant belowground N contribution to total crop residue from pea and canola. Further investigation is required to determine whether input of the more labile N rhizodeposits of pea improves soil N supply to succeeding crops or increases the potential for N loss from the soil system relative to canola.     

On the nature of temporary yield loss in maize following canola

Background and Aims

Soy is currently the most important biodiesel feedstock crop in the U.S., but canola is an attractive alternative because of its potential for greater oil yields. Nevertheless, factors other than oil yield must be considered in the choice of biodiesel feedstock crop. For example, soy is mycorrhizal and canola is not. We examined the consequences of soy and canola crops to subsequently-grown maize, which is mycorrhizal. We hypothesized that canola would reduce mycorrhization, P uptake and yield of subsequently-grown maize when compared to soy, and that winter cover cropping with wheat (mycorrhizal) would ameliorate canola’s negative impacts.

Methods

We established four rotations with two contrasts: either soy or canola in year 1, and with or without winter cover crops, followed by two years of maize.

Results

In year 2, mycorrhizal colonization, shoot P concentration and yield of maize were reduced following canola compared to soy. Nevertheless, many of the former canola plots produced maize with much lower growth than did the former soy plots irrespective of mycorrhizal colonization, shoot N or shoot P concentrations. Cover cropping with wheat did not ameliorate these negative effects. The negative effects of canola were temporary as they did not occur in the second year of maize.

Conclusions

The negative effects of canola observed in the first year of maize were coincident with a reduction in mycorrhizal colonization, but some other phenomenon appears to be causal, possibly allelopathy. Winter cover cropping was largely ineffective in ameliorating the negative effects of canola on maize.     

Arbuscular mycorrhizal symbiosis alleviates drought stress imposed on Knautia arvensis plants in serpentine soil

Background and Aims

Plants growing on serpentine bedrock have to cope with the unique soil chemistry and often also low water-holding capacity. As plant-soil interactions are substantially modified by arbuscular mycorrhizal (AM) symbiosis, we hypothesise that drought tolerance of serpentine plants is enhanced by AM fungi (AMF).

Methods

We conducted a pot experiment combining four levels of drought stress and three AMF inoculation treatments, using serpentine Knautia arvensis (Dipsacaceae) plants as a model.

Results

AMF inoculation improved plant growth and increased phosphorus uptake. The diminishing water supply caused a gradual decrease in plant growth, accompanied by increasing concentrations of drought stress markers (proline, abscisic acid) in root tissues. Mycorrhizal growth dependence and phosphorus uptake benefit increased with drought intensity, and the alleviating effect of AMF on plant drought stress was also indicated by lower proline accumulation.

Conclusions

We documented the role of AM symbiosis in plant drought tolerance under serpentine conditions. However, the potential of AMF to alleviate drought stress was limited beyond a certain threshold, as indicated by a steep decline in mycorrhizal growth dependence and phosphorus uptake benefit and a concomitant rise in proline concentrations in the roots of mycorrhizal plants at the highest drought intensity.     

Linking root traits and competitive success in grassland species

Background and aims

Measures of phosphorus (P) in roots recovered from soil underestimate total P accumulation below-ground by crop species since they do not account for P in unrecovered (e.g., fine) root materials. ³³P-labelling of plant root systems may allow more accurate estimation of below-ground P input by plants.

Methods

Using a stem wick-feeding technique ³³P-labelled phosphoric acid was fed in situ to canola (Brassica napus) and lupin (Lupinus angustifolius) grown in sand or loam soils in sealed pots.

Results

Recovery of ³³P was 93 % in the plant-soil system and 7 % was sorbed to the wick. Significantly more ³³P was allocated below-ground than to shoots for both species with 59–90 % of ³³P measured in recovered roots plus bulk and rhizosphere soil. ³³P in recovered roots was higher in canola than lupin regardless of soil type. The proportion of ³³P detected in soil was greater for lupin than canola grown in sand and loam (37 and 73 % lupin, 20 and 23 % canola, respectively). Estimated total below-ground P accumulation by both species was at least twice that of recovered root P and was a greater proportion of total plant P for lupin than canola.

Conclusion

Labelling roots using ³³P via stem feeding can empower quantitative estimates of total below-ground plant P and root dry matter accumulation which can improve our understanding of P distribution in soil-plant systems.