Short-term interactions between nitrate and iron nutrition in cucumber

Abstract

Cucumber (Cucumis sativus L.) plants were precultured for 7 days in either optimal (10 mu M) or low (0.5 mu M) Fe conditions and then grown for further 5 days in a N-free nutrient solution with (+Fe) or without (-Fe) 10 mu M Fe. Thereafter NO(3)(-) (4mM) was added to the nutrient solution for 24 h and, concomitantly, half of the -Fe plants were treated with 1 mu M Fe complexed to water extractable humic substances (WEHS). Supply of NO(3)(-) to + Fe-N-deprived plants caused a large induction in the capacity to take up the anion by roots, which was accompanied by a rise in root-shoot NO(3)(-) concentration. The -Fe plants showed a lower level of induction of NO(3)(-) uptake and hence a lower accumulation of the anion in the tissues, these effects being reversed by supply of Fe-WEHS. Supply of either NO(3)(-) - or NH(4)(+) -N (+/-Fe-WEHS) to -Fe plants promoted the development of the root Fe(III)-chelate reductase activity, but the capacity of roots to take up the Fe(2+) remained unaffected. Results show that an inadequate Fe supply can limit the acquisition of NO(3)(-), whereas NO(3)(-) supply can affect Fe uptake by influencing the development and maintenance of a high Fe(III)-chelate reducing capacity.