Performance of seminal and nodal roots of wheat in stagnant solution: K+ and P uptake and effects of increasing O2 partial pressures around the shoot on nodal root elongation

Abstract

Roots of intact wheat plants were grown for 7-12 d in stagnant nutrient solution, containing 0.1% agar, to mimic the lack of convection in waterlogged soil. Net K+ and P uptakes by seminal and nodal roots were measured separately using a split root system. For seminal roots in stagnant solution, net uptakes as a percentage of aerated roots were between 0% and 16% for P, while K+ ranged between 15% uptake and 54% loss. For the more waterlogging-tolerant nodal roots, net uptakes in stagnant nutrient solution, as a percentage of aerated roots, were 31-73% for P and 69-115% for K+. Elongation rates of nodal roots in stagnant nutrient were about 35-43% of those for roots in aerated solution. This partial inhibition occurred in these nodal roots despite their 15% porosity (v/v). Elevation of O2 partial pressures around the shoots to 40 kPa and then to 80 kPa substantially accelerated nodal root elongation in stagnant solution, demonstrating that most of the inhibition seen with ambient O2 around the shoots was associated with a restricted O2 supply to these nodal roots. Thus, in wheat nodal roots, with a partial pressure of 20 kPa O2 around the shoots, O2 diffusion from the shoots did not completely relieve the restrictions on elongation resulting from stagnancy in the nutrient solution. These results contrast with those in the literature for rice, in which roots function efficiently in stagnant solutions (0.1% agar). So, when wheat roots are aerenchymatous there are still restrictions to O2 diffusion in the gas space continuum between the atmosphere and the functional tissues of the roots. This poor acclimation must have been due to inefficiency of the aerenchymatous axes, which may include persistence of anoxic steles, and/or restricted O2 diffusion in other parts of the gas space continuum, in either the shoots and shoot-root junction or in the root tip.

The Physiology of Adventitious Roots

“…In wheat plants grown in aerated conditions, phosphorus uptake was initially higher in seminal roots than in crown roots, but this trend reversed in slightly older plants (Wiengweera and Greenway, 2004). However, in stagnant, flooded conditions, crown roots showed consistently higher phosphorus and potassium uptake than did seminal roots (Wiengweera and Greenway, 2004). This trend was also found in the eudicot bean, in which basal roots (i.e.…”

“…For low-nitrogen conditions, crown root uptake is reduced less (Yu et al, 2014), whereas for sulfur, the percentage reduction was similar for each root type (except for mesocotyl roots, which are similar to hypocotyl roots in monocots and had a much bigger reduction in sulfate uptake; Maniou et al, 2014). In wheat plants grown in aerated conditions, phosphorus uptake was initially higher in seminal roots than in crown roots, but this trend reversed in slightly older plants (Wiengweera and Greenway, 2004). However, in stagnant, flooded conditions, crown roots showed consistently higher phosphorus and potassium uptake than did seminal roots (Wiengweera and Greenway, 2004).…”

Mechanisms of waterlogging tolerance in wheat – a review of root and shoot physiology

“…Cross sections of wheat adventitious roots have proportional stelar areas of 18–20% (Huang et al . ; Wiengweera & Greenway ) compared with 5% in those of rice (McDonald et al . ), therefore potentially contributing to the explanation of differences in COP R between wheat and rice.…”

Physiological and biochemical changes in waterlog tolerant sesame genotypes

“…Waterlogging situation results in anaerobic respiration and causes injury and reduction in growth of root as well as shoots (Kramer, 1951). Physiological consequences of waterlogged conditions include altered shoot and root hormonal status (Hocking et al, 1985) and nutrient uptake (Orchard et al, 1986;Rochester, 2001, Wiengweera andGreenway, 2004). Furthermore, waterlogging causes the closure of stomata, reduction in CO 2 concentration and therefore a decline in photosynthesis (Crawford, 1978) and consequently it might also increase the concentration of damaging reactive oxygen species (ROS) inside the plant cells.…”