Nitrate induction triggers different transcriptional changes in a high and a low nitrogen use efficiency maize inbred line

In higher plants, NO3 can induce its own uptake and the magnitude of this induction is positively related to the external anion concentration. This phenomenon has been characterized in both herbaceous and woody plants. Here,different adaptation strategies of roots from two maize（Zea mays L., ZmAGOs） inbred lines differing in nitrogen use efficiency（NUE） and exhibiting different timing of induction were discussed by investigating NO3 ‐induced changes in their transcriptome. Lo5 line（high NUE） showing the maximum rate of NO3 uptake 4 h after the provision of 200 mmol/L NO3 treatment modulated a higher number of transcripts relative to T250（low NUE） that peaked after 12 h. The two inbred lines share only 368 transcripts that are modulated by the treatment with NO3 and behaved differently when transcripts involved in anion uptake and assimilation were analyzed. T250 line responded to the NO3 induction modulating this group of Researchgenes as reported for several plant species. On the contrary,the Lo5 line did not exhibit during the induction changes in this set of genes. Obtained data suggest the importance of exploring the physiological and molecular variations among different maize genotypes in response to environmental clues like NO3 provision, in order to understand mechanisms underlying NUE.

Iron Mobilization and Mineralogical Alterations Induced by Iron-Deficient Cucumber Plants (Cucumis sativus L.) in a Calcareous Soil

Dicotyledons cope with ion(Fe) shortage by releasing low-molecular-weight organic compounds into the rhizosphere to mobilize Fe through reduction and complexation mechanisms. The effects induced by these root exudates on soil mineralogy and the connections between Fe mobilization and mineral weathering processes have not been completely clarified. In a batch experiment, we tested two different kinds of organic compounds commonly exuded by Fe-deficient plants, i.e., three organic acids(citrate, malate, and oxalate)and three flavonoids(rutin, quercetin, and genistein), alone or in combination, for their ability to mobilize Fe from a calcareous soil and modify its mineralogy. The effect of root exudates on soil mineralogy was assessed in vivo by cultivating Fe-deficient and Fe-sufficient cucumber plants(Cucumis sativus L.) in a RHIZOtest device. Mineralogical analyses were performed by X-ray powder diffraction. The batch experiment showed that citrate and, particularly, rutin(alone or combined with organic acids or genistein)promoted Fe mobilization from the soil. The combinations of rutin and organic acids modified the soil mineralogy by dissolving the amorphous fractions and promoting the formation of illite. These mineralogical alterations were significantly correlated with the amount of Fe mobilized from the soil. The RHIZOtest experiment revealed a drastic dissolution of amorphous components in the rhizosphere soil of Fe-deficient plants, possibly caused by the intense release of phenolics, amino acids, and organic acids, but without any formation of illite. Both batch and RHIZOtest experiments proved that exudates released by cucumber under Fe deficiency concurred to the rapid modification(on a day-scale) of the mineralogy of a calcareous soil.