PHYSIOLOGICAL RESPONSES OF ARABIDOPSIS THALIANA TO THE INTERACTION OF IRON DEFICIENCY AND NITROGEN FORM

Physiological responses of Arabidopsis thaliana to the interaction of iron deficiency and nitrogen form were studied using plants grown in hydroponics. Thirty-three-day-old seedlings were submitted to four treatments for 7 days : NO3 + 5 mu M Fe; NO3 + 0.1 mu M Fe; NH4 + 5 mu M Fe and NH4 + 0.1 mu M Fe. Leaf growth and chlorophyll content were highest in NO3-fed, Fe sufficient plants, but were strongly diminished by Fe deficiency under nitric nutrition, and by ammoniacal nutrition independently of Fe regime. However, the leaves of NH4-fed plants presented a higher Fe content than those of Fe sufficient, NO3-fed plants. Thus, leaf chlorosis of NH4-fed in plant did not depend on Fe availability, and seemed to be due to another factor. Root acidification capacity and Fe-chelate reductase (FCR) activity were also dependent on N form. The medium was acidified under ammoniacal regime and alkalinized under nitric regime regardless of Fe level. FCR activity stimulation in response to Fe deficiency was observed only in NO3-fed plants. In addition, both N form and Fe level induced antioxidant responses in rosette leaves. Ammoniacal regime increased both peroxidase expression and anthocyanin accumulation, whereas Fe deficiency enhanced superoxide dismutase expression.