Effects of Saline and Alkaline Stress on Germination, Seedling Growth, and Ion Balance in Wheat

We tested wheat (Triticum aestivum L.) seedlings under five different saline and alkaline stress (9:1 molar ratio of NaCl/Na2SO4 and 9:1 molar ratio of NaHCO3/Na2CO3, respectively) regimes of differing severity for 7 d, comparing growth, germination, and ionic balance of wheat seedlings, to elucidate the mechanism of alkaline stress (high pH) damage to wheat, and it physiological adaptive mechanism to alkaline stress. We found that alkalinity had a more severe effect on wheat seedlings than salinity, preventing germination before and after recovery, and severely inhibiting shoot and root growth. Plants responded to both saline and alkaline stress by accumulating Na+ at the expense of K+, and by accumulating soluble osmolytes, but these effects were more pronounced under alkaline stress than saline stress. Alkaline stress also induced several specific responses such as the inhibition of fructan synthesis (fructan levels increased in response to salinity), the accumulation of organic acids, the accumulation of Ca2+ and the depletion of H2PO4-. The results suggest that specific damage caused by alkaline stress might reflect a massive influx of Na+, resulting in a severe deficit of negative charge. The plants respond by trying to restore the osmotic balance and synthesizing organic acids as counter-ions to address the intracellular ion imbalance. These data provide important leads in the development of engineered wheat plants with improved stress tolerance.