Morphology and Physiology of the Seminal Root System of Young Maize (<i>Zea mays</i> L.) Plants as Influenced by a Locally Restricted Nitrate Supply

Abstract

Abstract In water culture the effect of a locally restricted NO 3 supply to the seminal root system of maize seedlings was studied. For this purpose plants were cultivated in containers with a wide‐bore polyethylene tube positioned horizontally. Roots were suited through small holes in this tube and after sealing the holes with a non‐toxic silicon putty, root segments in the tube could be exposed to a different nutrient solution from the rest of the root system in the outer compartment. In case of a locally restricted NO 3 supply (NO 3 was just supplied to the root segment within the tube), we observed an increase in root growth beginning at the fifth day after onset of the treatment. NO 3 uptake rate ( 15 N) within the tube was significantly higher than in control plants (receiving NO 3 to the entire root system) as early as two days after onset of the treatment. One day later respiration (O 2 consumption) of the root segment exposed to NO 3 increased and at the same day we observed an accumulation of 14 C activity (after pulse labelling of the shoots with 14 CO 2 ) suggesting an increased phloem unloading. It is argued that this leads to the measured increase in IAA activity (Radio Immuno Assay) in the zone of NO 3 supply. Beginning at the fifth day we observed a stimulation of cell division rate (incorporation of 3 H‐methylthymidine), accompanied by an increase in length of first order lateral roots.