Oxygen deficiency and salinity affect cell‐specific ion concentrations in adventitious roots of barley (Hordeum vulgare)

Abstract

Summary Oxygen deficiency associated with soil waterlogging adversely impacts root respiration and nutrient acquisition. We investigated the effects of O2 deficiency and salinity (100 mM NaCl) on radial O2 concentrations and cell‐specific ion distributions in adventitious roots of barley (Hordeum vulgare). Microelectrode profiling measured O2 concentrations across roots in aerated, aerated saline, stagnant or stagnant saline media. X‐ray microanalysis at two positions behind the apex determined the cell‐specific elemental concentrations of potassium (K), sodium (Na) and chloride (Cl) across roots. Severe O2 deficiency occurred in the stele and apical regions of roots in stagnant solutions. O2 deficiency in the stele reduced the concentrations of K, Na and Cl in the pericycle and xylem parenchyma cells at the subapical region. Near the root apex, Na declined across the cortex in roots from the aerated saline solution but was relatively high in all cell types in roots from the stagnant saline solution. Oxygen deficiency has a substantial impact on cellular ion concentrations in roots. Both pericycle and xylem parenchyma cells are involved in energy‐dependent K loading into the xylem and in controlling radial Na and Cl transport. At root tips, accumulation of Na in the outer cell layers likely contributed to reduction of Na in inner cells of the tips.

Genetic Components of Root Architecture Remodeling in Response to Salt Stress

“…Our results suggest that the effect of potassium is stress dependent, as additional potassium enhanced lateral root development only in lines with enhanced HKT1 expression, but not in the background lines ( Figures 7B and 7C). Although sodium accumulation in the root stele is important for ion exclusion from shoot tissue (Møller et al, 2009;Kotula et al, 2015;Munns et al, 2012), in the young seedlings the high stelar sodium accumulation could potentially result in ABA-dependent lateral root quiescence or even damage to the lateral root primordia. The exact mechanisms underlying the reduced lateral root development in lines overexpressing HKT1 remain to be verified in future studies.…”

Regulation of Root Traits for Internal Aeration and Tolerance to Soil Waterlogging-Flooding Stress

“…Stelar anoxia can adversely impact ion transport (e.g. in maize [Gibbs et al, 1998] and barley [Kotula et al, 2015]). The implications of these findings are that a narrow stele diameter can be of adaptive significance for waterlogging tolerance as roots with a shorter diffusion path length into the stele, and greater cortex (oxygen source)-to-stele (oxygen sink) tissue ratio, would avoid anoxia until oxygen availability declined to lower levels than for roots with a wider stele (Armstrong and Beckett, 1987).…”

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

“…), will have tissues that become severely hypoxic (Armstrong ; Colmer & Greenway ; Kotula et al . ). The shift in O 2 ‐deficient tissues from aerobic respiration to the low ATP‐yielding fermentation results in an ‘energy crisis’ (Gibbs & Greenway ) and inhibition of root growth and functioning in transport of nutrients and water to the shoot (Jackson & Drew ; Colmer & Voesenek ), and eventually death of some roots.…”