Shoot chloride exclusion and salt tolerance in grapevine is associated with differential ion transporter expression in roots

BACKGROUND: Salt tolerance in grapevine is associated with chloride (Cl-) exclusion from shoots; the rate-limiting step being the passage of Cl- between the root symplast and xylem apoplast. Despite an understanding of the physiological mechanism of Cl- exclusion in grapevine, the molecular identity of membrane proteins that control this process have remained elusive. To elucidate candidate genes likely to control Cl- exclusion, we compared the root transcriptomes of three Vitis spp. with contrasting shoot Cl- exclusion capacities using a custom microarray. RESULTS: When challenged with 50 mM Cl-, transcriptional changes of genotypes 140 Ruggeri (shoot Cl- excluding rootstock), K51-40 (shoot Cl- including rootstock) and Cabernet Sauvignon (intermediate shoot Cl- excluder) differed. The magnitude of salt-induced transcriptional changes in roots correlated with the amount of Cl- accumulated in shoots. Abiotic-stress responsive transcripts (e.g. heat shock proteins) were induced in 140 Ruggeri, respiratory transcripts were repressed in Cabernet Sauvignon, and the expression of hypersensitive response and ROS scavenging transcripts was altered in K51-40. Despite these differences, no obvious Cl- transporters were identified. However, under control conditions where differences in shoot Cl- exclusion between rootstocks were still significant, genes encoding putative ion channels SLAH3, ALMT1 and putative kinases SnRK2.6 and CPKs were differentially expressed between rootstocks, as were members of the NRT1 (NAXT1 and NRT1.4), and CLC families. CONCLUSIONS: These results suggest that transcriptional events contributing to the Cl- exclusion mechanism in grapevine are not stress-inducible, but constitutively different between contrasting varieties. We have identified individual genes from large families known to have members with roles in anion transport in other plants, as likely candidates for controlling anion homeostasis and Cl- exclusion in Vitis species. We propose these genes as priority candidates for functional characterisation to determine their role in chloride transport in grapevine and other plants.Sam W Henderson, Ute Baumann, Deidre H Blackmore, Amanda R Walker, Rob R Walker and Matthew Gilliha

Salinity effects on vines and wines

Article also published in FrenchThe electrical conductivity of irrigation water used for grape production in Australia is generally in the range of 0.2-3.5 dS/m, with most under 0.6 dS/m. Trials in the Sunraysia region have shown that moderate to high salinities (1.75-3.5 dS/m) over four seasons reduced yield of own-rooted grapevines (cv. Sultana) whereas vines grafted to salt tolerant rootstocks e.g. Ramsey experienced no yield reduction. Rootstocks such as Ramsey, 1103 Paulsen, 140 Ruggeri and 101-14 resulted in lower concentrations of chloride (Cl –) in Shiraz grape juice relative to own-rooted vines but some rootstocks e.g. K51-40, resulted in high grape juice and wine Cl– and sodium (Na+) concentrations when irrigated with water having a salinity of 2.1 dS/m. There is evidence that the Cl– exclusion ability of Ramsey and 1103 Paulsen decreases over several seasons of irrigation with 2.1 dS/m, whereas that of Ruggeri 140 is maintained. Comparison of Shiraz wine from vines on K51-40 rootstock, showing salt damage (“leaf burn”), with wine from vines on Ruggeri 140 rootstock with no visible “leaf burn”, showed no difference in wine colour density, total phenolics, total and ionised anthocyanins. Sensory assessments revealed statistically significant and substantial differences among the wines made from six rootstocks in “salty” ratings which correlates (r > 0.94) with the Na+, Cl– and potassium (K+) concentrations of the wines. The study shows that wines with unusually high ion concentrations can result from vineyard factors as distinct from winemaking practices, and highlights the negative impacts of high ion concentrations on wine quality.R. R. Walker, D. H. Blackmore, P. R. Clingeleffer, P. Godden, L. Francis, P. Valente and E. Robinso