Effects of phosphate and nitrogen application on death of the root cortex in spring wheat

Abstract

SUMMARYProgrammed senescence and relative sink-strength have both been proposed as mechanisms controlling cell death in the root cortex. To distinguish between the two, seedlings of spring wheat {Triticum aestivum L.) were grown for 23 d in a glasshouse, with five rates of phosphorus and three rates of nitrogen, and cortical cell death over tbe length of tbe first seminal root axis assessed after staining witb acridine orange.Tbe percentage of cortical cell deatb was greatest m plants moderately deficient in pbospborus and was less in plants receiving severely deficient or adequate-to-luxury supplies. Nitrogen supply did not aflfect tbe percentage of anucleate cells in tbe cortex. Botb pbospborus and nitrogen supply infiuenced tbe distribution of cortical deatb witb distance along tbe root except in regions close to tbe root tip. Nitrogen supply, bowever, bad no efTect on tbe extent of cortical cell deatb in regions of comparable age, except in plants receiving twice tbe level of pbospborus required for maximum plant growtb.Pbospborus supply infiuenced tbe extent of cortical deatb tbrougb effects on botb tbe ratio of root to sboot weigbt and tbe lengtb of tbe total root system. Tbese findings cannot be completely explained by tbe process of natural programmed senescence, but are compatible witb tbe tbeory tbat cortical cell deatb is related to tbe distribution or activity of assimilate sinks witbin tbe root.

Root cortical senescence decreases root respiration, nutrient content and radial water and nutrient transport in barley

“…Our study focused on plants grown in solution culture and in soil. The majority of previous RCS studies focus on soil‐ and field‐grown plants (Henry and Deacon, ; Lewis and Deacon, ; Wenzel and McCully, ; Elliott et al , ; Liljeroth, ) in which roots may be easily damaged during excavation and washing. Previous studies used manual tissue sectioning (Yeates and Parker, ; Liljeroth, ; Bingham, ), which complicates the evaluation of tissue progressing towards senescence, because manual sectioning easily damages such tissue, and because it does not generate consistent section thicknesses for nuclei counts.…”

“…The rate of RCS was accelerated by severe, but not moderate, N deficiencies (Lascaris and Deacon, ) and accelerated with ammonium, but not nitrate application (Brown and Hornby, ; Gillespie and Deacon, ). In one study, the supply of ammonium nitrogen affected the pattern, but not the fraction of anucleate cortical cells (Elliott et al , ). Gillespie and Deacon () showed that P and K deficiencies had little effect on the rate of RCS.…”

Functional implications of root cortical senescence for soil resource capture

“…Nutrient deficiencies do not affect the Sparks (2017) pattern or where RCS begins relative to the root apex, rather the rate of RCS development. RCS was accelerated by suboptimal availability of nitrogen (Lascaris and Deacon 1991a;Schneider et al 2017a) and phosphorus (Elliott et al 1993;Schneider et al 2017a) and nutrient deficiencies accelerate the rate of RCS by 12% compared to control conditions (Schneider et al 2017a). The identification of additional treatments that accelerate or reduce RCS will be useful in studies evaluating the functional implications of RCS independent of tissue age as well as aid in understanding the genetic architecture of this phene.…”

“…Both RCS and RCA are accelerated by nutrient deficiencies (Gillespie and Deacon 1988;Drew et al 1989;Elliott et al 1993), reduce radial nutrient transport (Hu et al 2014;Schneider et al 2017a), reduce radial hydraulic conductivity (Fan et al 2007;Schneider et al 2017a), reduce metabolic costs (Zhu et al 2010;Postma and Lynch 2011b;Jaramillo et al 2013;Saengwilai et al 2014;Chimungu et al 2015), are influenced by exposure to ethylene (Lascaris and Deacon 1991b;Lenochová et al 2009;Schneider et al 2017c), and are types of PCD Jiang et al 2010;Schneider et al 2017c). Two ethylene-related genes were upregulated during both RCS and RCA formation (Rajhi et al 2011;Schneider et al 2017c).…”

Root Cortical Senescence Improves Growth under Suboptimal Availability of N, P, and K

“…The development of RCS is accelerated in response to deficiencies of mineral nutrients, including phosphorus and nitrogen (Lascaris and Deacon, 1991;Elliott et al, 1993;Schneider et al, 2017). We hypothesized that accelerated RCS formation is an adaptive response under a variety of edaphic stresses by reducing living cortical volume and, thereby, the metabolic cost of soil exploration (Schneider et al, 2017).…”