Active proton efflux, nutrient retention and boron-bridging of pectin are related to greater tolerance of proton toxicity in the roots of two Erica species

Abstract

Background and aimsTolerance to soil acidity was studied in two species of Ericaceae that grow in mine-contaminated soils (S Portugal, SW Spain) to find out if there are interspecific variations in H+ tolerance which might be related to their particular location.MethodsTolerance to H+ toxicity was tested in nutrient solutions using seeds collected in SW Spain. Plant growth and nutrient contents in leaves, stems and roots were determined. Viability tests and proton exchange were studied in roots exposed, short-term, to acidic conditions. Membrane ATPase activity and the cell-wall pectic polysaccharide domain rhamnogalacturonan-II (RG-II) were analysed to find out interspecific differences.ResultsVariation in survival, growth and mineral composition was found between species. The H+-tolerant species (Erica andevalensis) showed greater concentration of nutrients than E. australis. Very low pH (pH 2) produced a significant loss of root nutrients (K, P, Mg) in the sensitive species. Root ATPase activity was slightly higher in the tolerant species with a correspondingly greater H+ efflux capacity. In both species, the great majority of the RG-II domains were in their boron-bridged dimeric form. However, shifting to a medium of pH 2 caused some of the boron bridges to break in the sensitive species.ConclusionsVariation in elements linked to the cell wall-membrane complex and the stability of their components (RG-II, H+-ATPases) are crucial for acid stress tolerance. Thus, by maintaining root cell structure, active proton efflux avoided toxic H+ build-up in the cytoplasm and supported greater nutrient acquisition in H+-tolerant species.

Complex Gene Regulation Underlying Mineral Nutrient Homeostasis in Soybean Root Response to Acidity Stress

“…In the hydroponic culture, similar results were also observed in soybean roots, except for Fe concentration, which was slightly increased but not significant (Figure S2). Other study of Erica also showed that acidity stress significantly affected the Mg and Mn concentrations in leaves, S, B and Fe concentrations in stems, and Ca, P, Fe, Cu and Zn concentrations in roots [25]. Thus, these results strongly suggested that the capability of mineral nutrients acquisition and translocation in plants could be influenced by proton toxicity.…”

“…Accompanied with root growth inhibition, low-pH stress can disturb plant mineral nutrient acquisition mainly through destruction of proton gradients across plasma membranes [14,15,16,21,22,23,24,25]. One typical example is the nitrate (NO 3 − ) up-take in plant roots.…”

Making and breaking of boron bridges in the pectic domain rhamnogalacturonan‐II at apoplastic pHin vivo and in vitro

“…Very low apoplastic pH is relevant in some naturally acidic waters (e.g. pH as low as 2.3; Rossini Oliva et al, 2009Oliva et al, , 2018. Therefore, the ability of RG-II to remain stably boron-bridged, or to undergo de-novo boron bridging, in acidic environments is biologically relevant.…”

The Oxidative Damage and Morphological Changes of Sugar Beet (Beta vulgaris L.) Leaves at Seedlings Stage Exposed to Boron Deficiency in Hydroponics

“…Boron (B) is a trace element that is necessary for better plant growth and development. Boron participates in the stability of plant cell walls, cell membranes, carbohydrate transport, protein, and nucleic acid metabolism (O'Neill et al 2004;Rossini et al 2018;Fang et al 2019). B is found in the soil as boric acid, which is highly soluble (Yan et al 2019b).…”