The spatial variability of the nitrate (NO3 -) uptake along the maize primary root axis was investigated at physiological and molecular levels. Net NO3-uptake rate (NNUR) and its kinetic parameters, together with the gene expression of a high-affinity NO3-transporter (NRT2.1), were evaluated. The activity and the expression of plasma membrane H + -ATPase (PM H + -ATPase), key enzyme in plant nutrition, were also analysed. The NNUR showed a heterogeneous spatial pattern along the root, where the regions closer to the root tip early exhibited higher capacity to absorb NO3-than the basal regions, because of a higher maximum NNUR and faster induction of the inducible high-affinity transport system (iHATS), the presence of the high-affinity transport system (HATS) also at external NO3 -concentrations >100 mM and an improved NO3 -transport because of lower Km values. ZmNRT2.1 transcript abundances were not spatially correlated with NNUR, suggesting that post-translational effects or NAR2 protein co-expression could be involved. By contrast, PM H + -ATPase displayed a similar spatial-temporal pattern as that of nitrate uptake, resulting in higher activity in the root tip than in the basal regions. Increased activities of the enzyme after nitrate supply resulted in enhanced expression of MAH3 and MAH4, PM H + -ATPase subfamily II genes, while MAH1 was not expressed.

Spatial-temporal variation of the regulation and the kinetics of net nitrate (NO 3 -) uptake rate (NNUR) along the tap root of Citrus aurantium L. were analysed. Suberin incrustation in the peripheral cell layers and plasma membrane (PM) H ? -ATPase localisation, anatomical and physiological factors involved in NO 3 -uptake were also investigated. The results clearly indicated a spatially uniform distribution of the regulation process, accompanied by a temporal heterogeneous pattern of the kinetics of NO 3 -uptake along citrus tap root. In particular, kinetic analysis had a biphasic pattern, saturating (high affinity transport system) and linear (low affinity transport system), in response to increasing external NO 3 -concentrations in each root region, where 200 lM NO 3 -represented the threshold separating these two systems. Kinetic parameters, K m and V max , clearly indicated that apical segments reached the maximum value of induction before basal segments. Hence, the apical root zones, early exhibiting the maximum of potential capacity to absorb the NO 3 -, could be considered more efficient than basal root segments for acquiring NO 3 -from external solution. Suberin incrustations in the hypodermal cell layer, characterised by uniform fluorescence intensity among the root segments, could be responsible for the unchanged NNUR, while the PM H ? -ATPase could explain the temporal pattern of NNUR.

Cellular DNA is continually exposed to a large variety of external and internal DNA-damaging agents. Although lesions can be removed by different repair processes, damages often remain in the DNA during replication, and specialized DNA polymerases are needed to perform translesion synthesis past damaged sites. These enzymes, in contrast to replicative polymerases, operate at low processivity and fidelity. DNA polymerase eta and Rev 1 are two proteins found in eukaryotes that are involved in translesion replication past specific DNA damages. In Arabidopsis, DNA polymerase eta and Rev 1 are encoded by AtPOLH and AtREV1 genes, respectively. The beta-glucuronidase gene product under the control of AtPOLH and AtREV1 gene promoters was used to determine their expression in different tissues. The GUS assay showed a ubiquitous expression of the reporter gene in all tissues and during the complete life cycle. In addition, quantitative real-time RT-PCR confirmed the ubiquitous expression of AtPOLH and AtREV1, and showed that the average expression of AtREV1 was approximately five times higher than AtPOLH. Transcription of both genes did not increase in the presence of visible light or after UV irradiation.

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In this study, we determined the amount of H₂O₂ released by sunflower callus cultures challenged by both crude hyphal wall extracts and culture filtrates of 26 Phomopsis isolates from sunflower of worldwide origin (Argentina, France, Italy, Yugoslavia, Rumania). The amount of H₂O₂ released by callus cultures and the production time-course response, however, did not correlate with both the amount of electrolytes released by sunflower leaf disks treated with crude culture filtrates and the results of pathogenicity tests on sunflower seedlings. Only few isolates induced a time-course response indicative of an oxidative burst. This would suggest that elicitors extracted from hyphal walls are not involved in this host-pathogen recognition system and toxic metabolites produced by Phomopsis in liquid cultures are not pathogenicity factors.