Osmotic adjustment and energy limitations to plant growth in saline soil

Abstract

Summary Plant roots must exclude almost all of the Na+ and Cl– in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na+ and Cl– in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na+ and Cl– transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.

A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance

“…This differential response was attributed to the mechanism of osmotic adjustment developed in sensitive plants, favored by the higher accumulation of ions such as Cl -, that resulted in higher ψ t values (Fig 4). In saline soils, 2% intake of the NaCl is used by the plant for osmotically adjust of Na + and Cl − in vacuoles [88].…”

“…This prevention effect might be related to a mechanism of exclusion of toxic ions or their compartmentation. Energy-efficient osmotic adjustment requires compartmentation of Na + and Clin vacuoles, and of K + and compatible organic solutes in the cytoplasm [88]. The Na + content in leaves of tolerant populations (DV and BCt) was much lower than in sensitive (DK and BCs), which indicates that persimmon species are able to prevent Na + toxicity.…”

A Grain of Salt

“…The most suitable template for cereal HKT1;5 transporter proteins was the B. subtilis KtrB K + transporter (Protein Data Bank genotype 4J7C, chain I) 14 as previously identified 15 . In KtrB, K + was substituted by Na + during modelling of all HKT1;5 proteins.…”

“…In KtrB, K + was substituted by Na + during modelling of all HKT1;5 proteins. 3D models of HvHKT1;5 HAP3_L189 and HvHKT1;5 HAP3_P189 in complex with Na + were generated in Modeller 9v19 50 as described previously 21, 52 incorporating Na + ionic radii 15 taken from the CHARMM force field 53 , on the Linux station running the Ubuntu 12.04 operating system. Best scoring models (from an ensemble of 50) were selected based on the combination of Modeller Objective Function 54 and Discrete Optimised Protein Energy term 55 PROCHECK 56 , ProSa 2003 57 and FoldX 58 .…”

“…salinity) on plant growth 12, 13 . These latter investigations generally seek to explore the possible mechanisms that explain how tolerance to excess Na + can be achieved, and commonly revolve around Na + exclusion from the transpiration stream via active removal in the root, the partitioning of excess Na + into the vacuole in Na + sensitive photosynthetic tissues of the shoot, or the energy balance associated with active tolerance mechanisms 14, 15 . While understanding how to enable crops to grow more efficiently in the expanding saline environments across the globe is highly relevant, it remains important to note the majority of temperate cereal crop production is actually achieved on non-saline soils.…”