Glycine betaine accumulation, ionic and water relations of red-beet at contrasting levels of sodium supply

Exposure of plants to sodium (Na) and salinity may increase glycine betaine accumulation in tissues. To study this, red-beet cvs. Scarlet Supreme and Ruby Queen, were grown for 42 days in a growth chamber using a re-circulati ng nutrient film technique with 0.25 mmol/L K and either 4.75 mmol/L (contr ol) or 54.75 mmol/L (saline) Na (as NaCl). Plants were harvested at weekly intervals and measurements were taken on leaf water relations, leaf photosy nthetic rates, chlorophyll fluorescence, chlorophyll levels, glycine betain e levels, and tissue elemental composition. Glycine betaine accumulation in creased under salinity and this accumulation correlated with higher tissue levels of Na in both cultivars. Na accounted for 80 to 90% of the total cat ion uptake under the saline treatment. At final harvest (42 days), K concen trations in laminae ranged from similar to 65-95 mu mol g(-1) dry matter (D M), whereas Na in shoot tissue ranged from similar to 3000-4000 mu mol g(-1 ). Leaf sap osmotic potential at full turgor (psi (S) (100)) increased as l amina Na content increased. glycine betaine levels of leaf laminae showed a linear relationship with leaf sap psi (S) (100) Chlorophyll levels, leaf p hotosynthetic rates, and chlorophyll fluorescence were not affected by Na l evels. These results suggest that the metabolic tolerance to high levels of tissue Na in red-beet could be due to its ability to synthesize and regula te glycine betaine production, and to control partitioning of Na and glycin e betaine between the vacuole and the cytoplasm.