DIFFERENTIAL SOLUTE REGULATION IN LEAF BLADES OF VARIOUS AGES IN SALT-SENSITIVE WHEAT AND A SALT-TOLERANT WHEAT X LOPHOPYRUM-ELONGATUM (HOST) LOVE,A AMPHIPLOID

Leaf blades of different ages from a salt-tolerant wheat x Lophopyrum elongatum (Host) A. Love (syn. Agropyron elongatum Host) amphiploid and its salt-sensitive wheat parent (Triticum aestivum L. cv Chinese Spring) were compared for their ionic relations, organic solute accumulation, and sap osmotic potential (pi(sap)). The plants were grown for 18 d in nonsaline (1.25 mM Na+) and salinized (200 mM NaCl) nutrient solutions. The response of leaf blades to NaCl salinity depended greatly on their age or position on the main stem. Na and proline levels were highest in the oldest leaf blade and progressively lower in younger ones. Glycine betaine and asparagine levels were highest in the youngest blade. The pi(sap) was similar for corresponding leaf blades of both genotypes, but contributions of various solutes to the difference in pi(sap) between blades from control and 200 mM NaCl treatments differed greatly. The NaCl-induced decline in pi(sap) of the youngest leaf blade of Chinese Spring was predominately due to the accumulation of Na and to a lesser extent asparagine; in the amphiploid, it was due to a combination of glycine betaine, K, Na, and asparagine. Proline contributed little in the youngest blade of either genotype. In the older blades Na was the major solute contributing to the decline in pi(sap). Thus, the maintenance of low Na and high K levels and the accumulation of glycine betaine in the young leaf tissues contributed to the NaCl tolerance of the amphiploid. No such role was evident for proline.