Evidence for nitrate reductase expression during initiation of lateral roots by NAA in chicory |
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Authors: | Vuylsteker C; Prinsen E; Boutin J; Van Onckelen H; Rambour S |
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Institution: | Physiologie et Genetique Moleculaire Vegetales, Universite des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France; Departement de Biologie, Universitaire Instelling Antwerpen, B-2610 Wilrijk, Belgium; Laboratoire du Metabolisme et de la Nutrition des Plantes, INRA, Route St Cyr, F-78026 Versailles, France; Present address: UFR Biologie, Faculte des Sciences J. Perrin, F-62300 Lens, France; Corresponding author; e-mail: rambour@univ-lille 1.fr |
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Abstract: | The supply of -naphthaleneacetic acid
(NAA), to excised chicory roots induced the formation of lateral root
meristems mainly localized proximal to the pre-existing apical root
meristem, in a region which does not initiate any lateral roots in control
conditions. Inhibition of root elongation and concomitant enlargement of
the apices were also observed. Quantification of NAA and cytokinin levels
showed that the most reproducible and significant changes occurring after
the NAA treatment consisted of a decrease in the level of
zeatin-O-glucoside conjugates. Hydrolysis of these
conjugates might deliver free zeatin-type compounds which were consumed
during the lateral root growth. After 5 d, control excised roots contained
a high level of amino acids, mainly as asparagine and arginine, probably
issued from proteolysis associated to a senescent-like process. Conversely,
in the presence of NAA, neither accumulation of amino acids nor a decrease
of the total protein content of the tissue could be detected. Newly
initiated meristems expressed the nia gene which
encodes nitrate reductase, the first enzyme of the nitrate assimilatory
pathway. Thus the increased expression of nitrate reductase which was
observed in excised roots of chicory supplied with NAA (Vuylsteker
et al., 1997b) may be ascribed to lateral root
formation and development. The reinduction of nitrate reduction activity
was driven by the increased demand for reduced nitrogen. Thus, the
nia gene is one of the genes expressed during the
early stages of root meristem formation.Keywords:
Auxins, chicory, in situ hybridization,
lateral root, nitrate reductase.
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