MORPHOLOGY AND PHYSIOLOGY OF THE SEMINAL ROOT-SYSTEM OF YOUNG MAIZE (ZEA-MAYS L) PLANTS AS INFLUENCED BY A LOCALLY RESTRICTED NITRATE SUPPLY

In water culture the effect of a locally restricted NO3 supply to the seminal root system of maize seedlings was studied. For thn is 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 NO3 supply (NO3 was just supplied to the pot segment within the tube), we observed an increase in root growth beginning at the fifth day after onset of the treatment. NO3 uptake rate (N-15) within the tube was significantly higher than in control plants (receiving NO3 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 NO3 increased and at the same day we observed an accumulation of C-14 activity (after pulse labelling of the shoots with (CO2)-C-14) 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 NO3 supply. Beginning at the fifth day we observed a stimulation of cell division rate (incorporation of H-3-methylthymidine), accompanied by an increase in length of first order lateral roots.