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Aim: The rate of nitrate (NO3−) uptake and changes in rhizosphere properties were studied growing seedlings of two maize inbred lines differing in nitrogen use efficiency (NUE) in rhizoboxes.Results: Changes in NO3− uptake rates occurred in response to anion addition (induction) in seedlings grown both in hydroponic culture and in soil in rhizoboxes. The characterization of root exudate composition showed a line-specific metabolite profile, which was also affected by NO3− availability. The induction affected respiration, nitrification, ammonification and enzyme activities of the rhizosphere. Furthermore, the composition of rhizosphere bacterial communities of the two maize lines differed suggesting the selective capacity of plants.Conclusions: Overall, results showed a strong and fast modification of rhizospheric soil properties in response to physiological changes in plants caused by fluctuating NO3− availability. [ABSTRACT FROM AUTHOR]

It is well known that in the rhizosphere soluble Fe sources available for plants are mainly a mixture of complexes between the micronutrient and organic ligands such as organic acids and phytosiderophores (PS) released by roots, microbial siderophores as well as fractions of humified organic matter. In the present work, mechanisms of Fe acquisition operating at the leaf level of plants fed with different Fe-complexes were investigated at the micro-analytical, physiological and molecular levels. Fe-deficient tomato plants ( Solanum Lycopersicum L., cv. ‘Marmande’) were fed for 24 h with a solution (pH 7.5) containing 1 µM Fe as Fe-PS, Fe-citrate or Fe-WEHS. Thereafter, leaf tissue was used for the visualization of Fe distribution, measurements of Fe content, reduction and uptake, and evaluation of expression of Fe-chelate reductase ( LeFRO1), Fe-transporter ( LeIRT1) and Ferritin ( Ferritin2) genes. Leaf discs isolated from Fe-deficient plants treated for 24 h with Fe-WEHS developed higher rates of translocation, Fe-chelate reduction and 59Fe uptake as compared to plants supplied with Fe-citrate or Fe-PS. Leaves of plants treated with Fe-WEHS also showed higher transcript levels of LeFRO1, LeIRT1 and Ferritin2 genes with respect to plants fed with the other Fe-sources. Data obtained support the idea that the efficient use of Fe complexed to WEHS-like humic fractions involves, at least in part, also the activation of Fe-acquisition mechanisms operating at the leaf level. [ABSTRACT FROM AUTHOR]

Iron chlorosis is a wide-spread limiting factor of production in agriculture. To cope with this problem, synthetic chelates (like EDTA or EDDHA) of Fe are used in foliar-spray or in soil treatments; however, these products are very expensive. Therefore paper-production byproducts, like Lignosulfonates (LS), with varying content of carboxylate and sulfonate groups, were tested with respect to their ability to maintain Fe in the solution of soils and to feed plants grown in hydroponics with Fe through foliar sprays or application to the nutrient solution. Results show that LS had a low capability to solubilize 59Fe-hydroxide and that preformed 59Fe(III)-LS complexes had poor mobility through a soil column (pH 7.5) and scarce stability when interacting with soils compared to 59Fe(III)-EDDHA. However when 59Fe(III)-LS were supplied to roots in a hydroponic system, they demonstrated an even higher capability to fed Fe-deficient tomato plants than 59Fe(III)-EDDHA. Hence, data here presented indicate that the low Fe use efficiency from Fe-LS observed in soil-applications is due to interactions of these Fe-sources with soil colloids rather than to the low capability of roots to use them. Foliar application experiments of 59Fe(III)-LS or 59Fe(III)-EDTA to Fe-deficient cucumber plants show that uptake and reduction rates of Fe were similar between all these complexes; on the other hand, when 59Fe(III)-LS were sprayed on Fe-deficient tomato leaves, they showed a lower uptake rate, but a similar reduction rate, than 59Fe(III)-EDTA did. In conclusion, Fe-LS may be a valid, eco-compatible and cheap alternative to synthetic chelates in dealing with Fe chlorosis when applied foliarly or in the nutrient solution of hydroponically grown plants. [ABSTRACT FROM AUTHOR]

White lupin (Lupinus albusL. cv. Amiga) reacts to phosphate deficiency by producing cluster roots which exude large amounts of organic acids. The detailed knowledge of the excretion physiology of the different root parts makes it a good model plant to study plant-bacteria interaction. Since the effect of the organic acid exudation by cluster roots on the rhizosphere microflora is still poorly understood, we investigated the abundance, diversity and functions of bacteria associated with the cluster roots of white lupin, with special emphasis on the influence of root proximity (comparing root, rhizosphere soil and bulk soil fractions) and cluster root growth stages, which are characterized by different excretion activities. Plants were grown for five weeks in microcosms, in the presence of low phosphate concentrations, on acidic sand inoculated with a soil suspension from a lupin field. Plate counts showed that bacterial abundance decreased at the stage where the cluster root excretes high amounts of citrate and protons.In vitrotests on isolates showed that the frequencies of auxin producers were highest in juvenile and mature cluster roots and significantly decreased in senescent cluster roots. However, no significant difference in the frequency of auxin producers was found between cluster and non cluster roots. The diversity and structure of bacterial communities were investigated by DGGE of 16S rDNA and 16S rRNA. The diversity and community structure were mostly influenced by root proximity and, to a lesser extent, by cluster root stage. The richness of bacterial communities decreased with root proximity, whereas the proportion of active populations increased. The high citrate and proton excretion occurring at the mature stage of cluster roots had a strong impact on the structure and richness of the bacterial communities, both in the root and in the rhizosphere soil. [ABSTRACT FROM AUTHOR]