Effects of mineral nutrients on senescence of the cortex of wheat roots and root pieces

Abstract

Wheat seedlings were grown for up to 35 days in perlite moistened with mineral nutrient solutions of different N, P and K content. In parallel work, sterile 2 cm wheat root pieces were maintained for up to 12 days on agar with glucose and different mineral nutrient supplements. The effects of mineral nutrition on death of the root cortex (RCD) were assessed by nuclear staining with acridine orange. A reduced supply or omission of N [as Ca(NO 3); or (NH 4);SO 4] enhanced the rate of RCD, whereas P and K had lesser effects. Ammonium-N was less effective than nitrate-N in maintaining cortical viability, and this effect could not be explained by differences of pH. Effects of mineral nutrients on RCD were not closely correlated with effects on shoot or root growth. Also the effects were similar for whole roots or root pieces. So mineral nutrients apparently exerted direct, localised effects on root cell viability. In addition to the previously reported normal pattern of RCD, a further phase of cortical senescence is described in which nuclei are deleted from the innermost cortical cell layer. This was associated with root impedance when the root tips reached the bottoms of soil containers.