Tolerance of submerged germinating rice to 50–200 mM NaCl in aerated solution

Abstract

This paper concerns tolerance to 50-200 mM NaCl of submerged rice (Oryza sativa cv. Amaroo) during germination and the first 138-186 h of development in aerated solution. Rice was able to germinate and the seedlings even tolerated exposure to 200 mM NaCl, albeit with severe growth restrictions. After return to 0.3 mM NaCl, growth increased, indicating that even at 200 mM NaCl there was no irreparable injury. Osmotic adjustment was achieved by using Na⁺ and Cl⁻ as the major osmotica. At 200 mM NaCl commenced at sowing, the shoot Na⁺ and Cl⁻ concentrations between 50-110 h were about 210 and 260 mM, respectively, i.e. above the external concentration. Thus, there was a high tissue tolerance to NaCl. The internal concentrations declined subsequently, concurrent with a decline in growth. At 50-200 mM NaCl, the contributions from ions to πsap were 81-92% in roots and 62-74% in shoots. The assessed turgor pressures at 200 mM NaCl were 0.33 MPa in shoots and 0.15 MPa in roots, compared to 0.62 and 0.43 MPa at 0.3 mM NaCl. In the General Discussion section, we compare the different responses of submerged seedlings to the responses of transpiring rice plants, reported in the literature, and suggest that the submerged system is useful to evaluate effects of NaCl on turgor pressure and particularly to establish whether there are specific effects of Na⁺ and Cl⁻ in tissues.

Energetics of acclimation to NaCl by submerged, anoxic rice seedlings

“…There were only comparisons between anoxic with aerated tissues for the excised coleoptile tips. For the intact seedlings such a comparison would be rather meaningless because when in aerated conditions the coleoptile soon enters senescence, whereas in anoxia the coleoptile continues to grow (Kurniasih et al, 2013).…”

“…Dehulled rice (Oryza sativa L. 'Amaroo') seeds (caryopses) were washed with 0Á1 % (v/v) sodium hypochlorite for 20 min, rinsed thoroughly with deionized water and submerged in (Huang et al, 2003) and it tolerated at least up to 200 mM NaCl when grown submerged in aerated nutrient solution (Kurniasih et al, 2013). For the responses elucidated here for 'Amaroo' to combined anoxia and salinity, future experiments should also assess other genotypes of rice that vary in anoxia tolerance (e.g.…”

“…Tissues which had been blotted to remove surface solution were sealed in cryo-vials, frozen in liquid N 2 , thawed while in the vials and then crushed in a stainless steel press to extrude sap which was immediately analysed. Turgor pressure was assessed as the difference between p sap and p sol , a suitable approach for submerged tissues (Kurniasih et al, 2013).…”

“…As well, under aeration the submerged germinating rice tolerated NaCl, at least up to 200 mM (Kurniasih et al, 2013). In these submerged seedlings, energy formation can be assessed and ion fluxes can be evaluated without the potential complication of xylem transport resulting in accumulation of Na þ in transpiring leaves.…”

“…The ready exchange is understandable because these coleoptiles had no gas envelopes (as opposed to leaves formed in air, Colmer et al, 2014) and presumably little cuticle development, as they had been submerged since imbibition. Moreover, in the submerged rice seedlings, cell turgor pressure can be assessed as the difference between the osmotic potentials of the protoplasts and the solution (Kurniasih et al, 2013). For interpretation of ion fluxes and energy formation by the coleoptile, excision of this organ and provision of exogenous glucose provides an anoxia-tolerant system for measurements of ion fluxes and ethanol formation (e.g.…”