Chloride transport and compartmentation within main and lateral roots of two grapevine rootstocks differing in salt tolerance

Root Cl- transport was investigated using Cl-36(-) flux analysis in two grapevine (Vitis sp.) rootstock hybrids differing in salt tolerance; 1103 Paulsen (salt-tolerant) and K 51-40 (salt sensitive). Initial Cl-36(-) influx to the root was greater in Paulsen than K 51-40. This flux, attributed to the Cl- influx to the cytoplasm (I broken vertical bar (oc)) increased with increasing external concentrations of Cl- for plants adapted to growth in 30 mM NaCl. The concentration kinetics in this high concentration range could be fit to a Michaeils-Menton equation. There was no significant difference between genotypes in Km (28.68 +/- A 15.76 and 24.27 +/- A 18.51 mM for Paulsen and K 51-40, respectively), but Paulsen had greater V (max) (0.127 +/- A 0.042) compared to K 51-40 (0.059 +/- A 0.026 mu m g(-1) FW min(-1)). In Paulsen, the main root had greater contribution to Cl-36(-) uptake than lateral roots, there being no significant difference in lateral root influx between the genotypes. Cl-36(-) transport to the shoot of K 51-40 was greater than for Paulsen. It was estimated that efflux rate from the xylem parenchyma cells to the xylem vessels (I broken vertical bar (cx)) in K 51-40 was twice that of Paulsen. Compartmental analysis from Cl-36(-) efflux kinetics confirmed the larger I broken vertical bar (oc) and the higher ratio of main to lateral root I broken vertical bar (oc) for Paulsen. Efflux from the cytoplasm (I broken vertical bar (co)) was higher than 95 % of I broken vertical bar (oc) indicating a high degree of cycling across the plasma membrane in roots at these high external Cl- concentrations. Paulsen appears to keep the cytoplasmic Cl- concentration in roots lower than K 51-40 via greater efflux to the vacuole and to the outside medium. The difference in salt tolerance between the genotypes can be attributed to different Cl- transport properties at the plasma membrane and tonoplast and particularly in Cl- efflux to the xylem.