Chloride transport and compartmentation within main and lateral roots of two grapevine rootstocks differing in salt tolerance
Root Cl− transport was investigated using 36Cl− flux analysis in two grapevine (Vitis sp.) rootstock hybrids differing in salt tolerance; 1103 Paulsen (salt-tolerant) and K 51–40 (salt sensitive). Initial 36Cl− influx to the root was greater in Paulsen than K 51–40. This flux, attributed to the Cl− influx to the cytoplasm (Φ 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 ± 15.76 and 24.27 ± 18.51 mM for Paulsen and K 51–40, respectively), but Paulsen had greater V max (0.127 ± 0.042) compared to K 51–40 (0.059 ± 0.026 μm g−1 FW min−1). In Paulsen, the main root had greater contribution to 36Cl− uptake than lateral roots, there being no significant difference in lateral root influx between the genotypes. 36Cl− 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 (Φ cx) in K 51–40 was twice that of Paulsen. Compartmental analysis from 36Cl− efflux kinetics confirmed the larger Φ oc and the higher ratio of main to lateral root Φ oc for Paulsen. Efflux from the cytoplasm (Φ co) was higher than 95 % of Φ 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.
KeywordsSalinity Grapevine 36Cl− Compartmentation Fluxes
We are grateful to Wendy Sullivan (The University of Adelaide, Glen Osmond, Australia) for excellent technical assistance and to anonymous reviewers for valuable comments and suggestions for revising the manuscript. This work was supported by Australian Government, the Grape and Wine Research and Development Corporation (Root physiology and vine performance).
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