The Effects of Rhizosphere Inoculation with Pseudomonas mandelii on Formation of Apoplast Barriers, HvPIP2 Aquaporins and Hydraulic Conductance of Barley

Abstract

Pseudomonas mandelii strain IB-Ki14 has recently been shown to strengthen the apoplastic barriers of salt-stressed plants, which prevents the entry of toxic sodium. It was of interest to find out whether the same effect manifests itself in the absence of salinity and how this affects the hydraulic conductivity of barley plants. Berberine staining confirmed that the bacterial treatment enhanced the deposition of lignin and suberin and formation of Casparian bands in the roots of barley plants. The calculation of hydraulic conductance by relating transpiration to leaf water potential showed that it did not decrease in bacteria-treated plants. We hypothesized that reduced apoplastic conductivity could be compensated by the higher conductivity of the water pathway across the membranes. This assumption was confirmed by the results of the immunolocalization of HvPIP2;5 aquaporins with specific antibodies, showing their increased abundance around the areas of the endodermis and exodermis of bacteria-treated plants. The immunolocalization with antibodies against auxins and abscisic acid revealed elevated levels of these hormones in the roots of plants treated with bacteria. This root accumulation of hormones is likely to be associated with the ability of Pseudomonas mandelii IB-Ki14 to synthesize these hormones. The involvement of abscisic acid in the control of aquaporin abundance and auxins—in the regulation of and formation of apoplast barriers—is discussed.

Effects of a Pseudomonas Strain on the Lipid Transfer Proteins, Appoplast Barriers and Activity of Aquaporins Associated with Hydraulic Conductance of Pea Plants

“…It was suggested that restriction of water flow through the apoplast pathway may be eliminated by an enhancement of the cell-to-cell pathway through the membrane water channels—aquaporins (AQPs) [ 18 ]. In accordance with this suggestion, we demonstrated that bacteria-induced strengthening of the apoplast barriers was accompanied by increased abundance of AQPs in the roots of barley plants [ 19 ]. It was of interest to find out if bacterial inoculation influences the LTP abundance and deposition of suberin and how these effects may be related to AQP activity and hydraulic conductance of pea plants.…”

Mechanisms and Applications of Bacterial Inoculants in Plant Drought Stress Tolerance

“…Nevertheless, considering the concept of plant phenotypic plasticity under harsh environmental conditions [ 82 ], changes in plant microstructure would increase the plant body’s ability to store and circulate water. Among them are the increased plant cell vacuolization, increased water storage specialized cells, and changes in the volume ratio of the apoplastic and symplastic compartments [ 75 , 83 ]. Furthermore, these integrative mechanisms of plant water conservation favor the induction of plant response enzymatic–metabolic machinery related to cell protection and damage restoration (i.e., ROS production associated with biological membranes and biomolecule damage).…”

Influence of Plant Growth-Promoting Rhizobacteria on the Formation of Apoplastic Barriers and Uptake of Water and Potassium by Wheat Plants

“…Thus, bacteria can increase expression of genes encoding aquaporins in maize plants [ 42 ]. Increased aquaporin abundance was recently found in barley plants treated with B. subtilis IB-22 [ 23 ]. Hormone abscisic acid (ABA) is known to increase the activity of aquaporins [ 43 ], and increased ABA concentration was found in barley plants treated with B. subtilis IB-22 [ 44 ].…”

“…This problem remained unresolved if the same effect occurred in the absence of salinity, affecting the hydraulic conductivity of plants. Staining with berberine hemisulfate confirmed that bacterial treatments increased the deposition of lignin and suberin and the formation of Casparian bands in roots of barley and pea [ 23 , 24 ]. Calculation of hydraulic conductivity through correlating transpiration to the leaf water potential showed that it did not decrease in plants treated with bacteria.…”