Unidirectional Ca²⁺Fluxes in Roots of Rye (Secale cerealeL). A Comparison of Excised Roots with Roots of Intact Plants

The unidirectional Ca2+ fluxes across the plasma membrane and tonoplast were determined in both excised roots and roots of intact seedlings of rye (Secale cereale L. cv. Rheidol). The unidirectional Ca2+ fluxes across the plasma membrane and tonoplast measured in excised roots were of a similar order of magnitude to those determined in roots of intact plants. Influx and efflux of Ca2+ across the root plasma membrane were similar (estimated to be between 0·7 and 3·4 μmol g⊟1 FW root h⊟1) and 4- to 40- fold greater than the net uptake of calcium into roots (76 nmol g⊟1 FW h⊟1 in excised roots and 427 nmol g⊟1 FW h⊟1 in roots of intact plants). The unidirectional Ca2+ fluxes across the tonoplast (estimated to be between 20 and 100 nmol g⊟1 FW h⊟1) were at least an order of magnitude lower than those across the plasma membrane. In intact plants, the root vacuole accumulated calcium during the experiment at a rate of 30 nmol g⊟1 FW h⊟1, whereas a net loss of calcium from the vacuole (31 nmol g⊟1 FW h⊟1) was calculated for excised roots. The Ca2+ flux to the xylem was greater in intact plants (215 to 393 nmol g‐1 FW h⊟1) than in excised roots (107 nmol g⊟1 FW h⊟1), which largely accounted for the differences in calcium uptake by roots from the two treatments.