Contrast in chloride exclusion between two grapevine genotypes and its variation in their hybrid progeny

Potted grapevines of 140 Ruggeri (Vitis berlandieri × Vitis rupestris), a good Cl ^- excluder, and K 51-40 (Vitis champinii × Vitis riparia 'Gloire'), a poor Cl ^- excluder, and of a family obtained by crossing the two genotypes, were used to examine the inheritance of Cl ^- exclusion. Rooted leaves were then used to further investigate the mechanism for Cl ^- exclusion in 140 Ruggeri. In both a potting mix trial (plants watered with 50 mM Cl ^-) and a solution culture trial (plants grown in 25 mM Cl ^-), the variation in Cl ^- accumulation was continuous, indicating multiple rather than single gene control for Cl ^- exclusion between hybrids within the family. Upper limits of 42% and 35% of the phenotypic variation in Cl ^- concentration could be attributed to heritable sources in the potting mix and solution culture trials, respectively. Chloride transport in roots of rooted leaves of both genotypes appeared to be via the symplastic pathway, since addition of 8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), an apoplastic tracer, revealed no obvious PTS fluorescence in the laminae of either genotype, despite significant accumulation of Cl ^- in laminae of K 51-40 during the PTS uptake period. There was no significant difference in either unidirectional ³⁶Cl ^- flux (10 min) or ³⁶Cl ^- uptake (3 h) into roots of rooted leaves exposed to 5, 10, or 25 mM Cl ^-. However, the percentage of ³⁶Cl ^- transported to the lamina (3 h) was significantly lower in 140 Ruggeri than in K 51-40, supporting reduced Cl ^- loading into xylem and implicating the root stele in the Cl ^- exclusion mechanism.