1,721,258 research outputs found
EFFECT OF SOIL HUMIC SUBSTANCES ON SURFACE REDOX ACTIVITY OF OAT ROOTS
No full textThe effect of a low molecular weight ( 5kDa, HMW) humic fractions on surface redox activities of oat roots was studied. Oxidation of the electron donor NADH and reduction of the artificial electron acceptor ferricyanide [K3Fe(CN)6] exogenously supplied to the roots both alone of in combination, was measured in the presence or absence of soil humic substances. HMW humic fraction inhibited NADH oxidation either in the presence or absence of ferricyanide, while LMW humic fraction inhibited NADH:ferricyanide oxidoreductase activity due to the contemporary addition of the two redox compounds to the solution bathing the roots. NADH:ferricyanide oxido-reduction was partially due to the release of substances from the roots. However, the presence of soil humic fractions (LMW or HMW) did not significantly modify this behaviour. Rather, the inhibitory effect of soil humic substances was even more evident when the oxidoreduction solely due to the root activity was considered. The results confirm the presence of multiple types of oxidoreductase activities at the surface of oat roots and show that the two humic fractions HMW and LMW may differently affect these activities. Partial inhibition of NADH oxidase activity is interpreted as a possible way of interference of humic substances with metabolic processes involved in cell wall formation. The effects on surface redox activities are discussed in terms of the role of soil humic substances in promotion of plant growth
Nutrient management at the rhizosphere through intercropping
No full textCereal-cereal association, grass-fruit tree cocultivation and legume-cereal intercropping are sustainable agricultural practices that can improve nitrogen, phosphorous, and iron availability at the rhizosphere. Major mechanisms that have only recently been clarified are described
Two plasma membrane H+-ATPase genes are differentially expressed in iron-deficient cucumber plants
No full textAim of the present work was to investigate the involvement of plasma membrane (PM) H+-ATPase (E.C. 3.6.3.6) isoforms of cucumber (Cucumis sativus L.) in the response to Fe deficiency. Two PM H+-ATPase cDNAs (CsHA1 and CsHA2) were isolated from cucumber and their expression analysed as a function of Fe nutritional status. Semi-quantitative reverse transcriptase (RT)-PCR and quantitative real-time RT-PCR revealed in Fe-deficient roots an enhanced accumulation of CsHA1 gene transcripts, which were hardly detectable in leaves. Supply of iron to deficient plants caused a decrease in the transcript level of CsHA1. In contrast, CsHA2 transcripts, detected both in roots and leaves, appeared to be unaffected by Fe. This work shows for the first time that a transcriptional regulation of PM H+-ATPase involving a specific isoform occurs in the response to Fe deficiency
Dynamics, thermodynamics and kinetics of exudates: crucial issues in understanding rhizosphere processes
No full textBackground: In this issue, Schenkeveld and coworkers described the potential of phytosiderophores (a class of root exudates) to mobilize metals in the rhizosphere by an equilibrium modelling approach.
Scope: The rhizosphere is a complex and dynamic environment where several different organic and inorganic compounds coexist. Due to the different concentration and chemical characteristics there might be competitive and synergistic interactions. However the rhizosphere is strongly influenced by root activity: water and nutrient uptake, root respiration that might modify the pH and redox status of the rhizosphere. Thus, how does the complexity of the system and the dynamics influence the thermodynamics of the single process? Can chemical equilibria be really reached in the rhizosphere? Issues related to kinetics vs thermodynamics are discussed. The study of the single processes is important but more complex researches, being thus more realistic (i.e. field-like conditions), are necessary. Hence, what are the available tools/methods in rhizosphere research? What are the drawbacks? How can the results of these methods be related to thermodynamic and kinetic models?
Conclusions: Besides stimulating further awareness around the rhizosphere complexity, tentative answers are given highlighting the future challenges in rhizosphere research, essential knowledge for the development of agronomic practices ensuring a better exploitation of soil endogenous resources of nutrients by crops
Phosphorus deficiency changes carbon isotope fractionation and triggers exudate reacquisition in tomato plants
Full text linkPlant roots are able to exude vast amounts of metabolites into the rhizosphere in response to phosphorus (P) deficiency. Causing noteworthy costs in terms of energy and carbon (C) for the plants. Therefore, it is suggested that exudates reacquisition by roots could represent an energy saving strategy of plants. This study aimed at investigating the effect of P deficiency on the ability of hydroponically grown tomato plants to re-acquire specific compounds generally present in root exudates by using 13C-labelled molecules. Results showed that P deficient tomato plants were able to take up citrate (+ 37%) and malate (+ 37%), particularly when compared to controls. While glycine (+ 42%) and fructose (+ 49%) uptake was enhanced in P shortage, glucose acquisition was not affected by the nutritional status. Unexpectedly, results also showed that P deficiency leads to a 13C enrichment in both tomato roots and shoots over time (shoots—+ 2.66‰, roots—+ 2.64‰, compared to control plants), probably due to stomata closure triggered by P deficiency. These findings highlight that tomato plants are able to take up a wide range of metabolites belonging to root exudates, thus maximizing C trade off. This trait is particularly evident when plants grew in P deficiency. © 2020, The Author(s)
Effect of UV-B radiation on iron content and distribution in maize plants
No full textAbstract: The effect of 21 kJ m−2 d−1 of biologically effective ultraviolet B radiation (UV-BBE) radiation on plant growth, chlorophyll and iron contents, and on iron distribution between root symplastic and extraplasmatic compartments was evaluated in 10 days old maize (Zea mays L.) seedlings grown in nutrient solution. Furthermore, owing to the ability of light to interfere with the redox status of iron complexes, the effect of illumination of the root environment was also studied.
The results showed that UV-B radiation had no significant effect on plant growth, whereas illumination of the root environment decreased leaf and root biomass production, regardless of the UV-B radiance. Exposure of plants to UV-B radiation increased both chlorophyll and leaf and root iron contents, in both plants with illuminated and darkened roots. The iron content was much lower in leaves than in roots, where it was mainly located in the extraplasmatic compartment. Illumination of the root environment resulted in higher root iron contents, but this increase was mainly due to the extraplasmatic fraction
Method to isolate water-soluble humic molecules and to obtain complexes thereof with chemical fertilizing elements
No full textPhytosiderophores released by graminaceous species promote 59Fe-uptake in citrus
No full textAbstract Chlorosis-susceptible fruit trees growing on calcareous soils have been observed to recover in the presence of grass cover species. However, the physiological mechanisms behind this phenomenon are only scarcely understood. An investigation was carried out to verify whether citrus plants can use 59Fe solubilized from a sparingly soluble source by the phytosiderophores (PS) released from graminaceous species. Experiments were performed in hydroponics, using two citrus rootstocks differing in their sensitivity to Fe-deficiency in the field (Poncirus trifoliata · Citrus paradisi, citrumelo ‘‘Swingle’’, highly susceptible, and Citrus aurantium L., moderately tolerant). Barley (Hordeum vulgare L., cv Europa) was used as a model species for PS-releasing graminaceous plants. Fe-deficient citrus plants increased 59Fe uptake from 59Fe-hydroxide supplied inside a dialysis tube, when Fe-deficient barley plants or PS-containing barley root exudates were present in the uptake solution, this effect being particularly evident for the susceptible rootstock.
59Fe-uptake from 59Fe-hydroxide was also enhanced in Fe-deficient citrumelo ‘‘Swingle’’ in the presence of Fe-deficient Poa pratensis L. and Festuca rubra L., two perennial grasses normally grown in association with fruit trees; no effect was found when Fe-sufficient grasses were employed. The uptake of 59Fe by the susceptible citrus rootstock increased in proportion to the amount of 2¢-deoxymugineic acid (DMA), the major PS released by Fe-deficient F. rubra, present in the uptake solution. The beneficial effect of F. rubra or P. pratensis was evident from the leaf re-greening observed when Fe-deficient citrumelo ‘‘Swingle’’ plants were grown in association with the grasses in pots filled with a calcareous soil. Leaf regreening was not observed when citrumelo ‘‘Swingle’’ plants and yellow stripe 3 (ys3) maize (Zea mays L.) mutant plants, unable to release PS, were co-cultivated in pots filled with calcareous
soil, unless exogenous PS were added to the soil. Results indicate that graminaceous cover species can improve the Fe-nutrition of
fruit trees grown on calcareous soils by enhancing Fe-availability
Plasma membrane H+-ATPase in maize roots induced for NO3- uptake
No full textPlasma membrane H+-ATPase was studied in maize (Zea mays L.) roots induced for NO3 - uptake. Membrane vesicles were isolated by means of Suc density gradient from roots exposed for 24 h either to 1.5 mM NO3 - or 1.5 mM SO4 -. The two populations of vesicles had similar composition as shown by diagnostic inhibitors of membrane-associated ATPases. However, both ATP-dependent intravesicular H+ accumulation and ATP hydrolysis were considerably enhanced (60-100%) in vesicles isolated from NO3 --induced roots. Km, for Mg:ATP and pH dependency were not influenced by NO3 - treatment of the roots. ATP hydrolysis in plasma membrane vesicles for both control and NO3 --induced roots was not affected by 10 to 150 mM NO3 - or Cl-. On the other hand, kinetics of NO3 -- or Cl--stimulated ATP-dependent intravesicular H+ accumulation were modified in plasma membrane vesicles isolated from NO3 --induced roots, Immunoassays carried out with polyclonal antibodies against plasma membrane H+-ATPase revealed an increased steady-state level of the enzyme in plasma membrane vesicles isolated from NO3 --induced roots. Results are consistent with the idea of an involvement of plasma membrane H+-ATPase in the overall response of roots to NO3 -
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