The developing pattern of damage in wheat (Triticum aestivum L.) due to the combined stresses of salinity and hypoxia: experiments under controlled conditions suggest a methodology for plant selection

Abstract

The response of wheat (Triticum aestivum L. cv. Gamenya) to the interaction of salinity and hypoxia was examined by growing plants under glasshouse conditions in salinised nutrient solutions bubbled with air or N2 gas. Expts 1 and 2 examined the effects of 7 days of salinity and hypoxia on young (13–20-day-old) plants. These experiments showed that (a) hypoxia substantially increased net rates of Na+ and Cl uptake to the shoots, (b) hypoxia increased Na+ and Cl concentrations in the expanded leaves but not in the expanding leaf, and (c) these changes preceded adverse effects on shoot growth. Expt 3 considered the effects of longer term hypoxia and salinity on growth (production of leaves on the main culm, shoot ethanol-insoluble dry weight). Plants were grown for 33 days in aerated or hypoxic solutions containing up to 60 mol/m3 of NaCl (at which time Harvest 1 was taken). Some plants were then transferred back into aerated solutions for a further 13 days to assess recovery from hypoxia (at which time Harvest 2 was taken). For plants grown in aerated solutions, rates of leaf production exceeded rates of leaf senescence at all salt concentrations tested. In contrast, with plants grown in hypoxic solutions, rates of leaf production only exceeded rates of senescence with 0 and 15 mol/m3 of NaCl. The plants grown in aerated solutions had 1.4–2.8-fold increases in ethanol-insoluble dry weight over the 13 days between Harvests 1 and 2 at all salt concentrations tested. In contrast, with the plants grown in hypoxic solutions, increases only occurred in shoot ethanol-insoluble dry weight for plants grown with 0 and 15 mol/m3 of NaCl. At higher salt concentrations, the shoots were moribund. The results are discussed in terms of the sequence of damage that occurs in wheat following the onset of salinity and hypoxia, and the implications of these observations for the selection of cereals with tolerance to salt and waterlogging in the field.