Figure 6

Relative transcript abundances of membrane proteins in roots of grapevine genotypes under control conditions measured by qRT-PCR, and a model indicating possible molecular mechanisms for reduced net xylem loading of Cl^-in 140 Ruggeri. (A - B) relative expression levels of VvNAXT1 (A) and VvNRT1.5 (B) measured by qRT-PCR, which represent possible avenues for cortical or epidermal efflux of Cl⁻ out of roots. (C - E) relative expression levels of VvNRT1.4 (C), VvALMT1 (D) and VvSLAH3 (E) measured by qRT-PCR, which represent possible avenues for xylem loading of Cl⁻. Bars represent the mean of four biological replicates ± SEM. Transcript abundance is relative to the Cabernet Sauvignon biological replicate with the lowest cycle threshold (Ct) value, which was set to 1. Statistical differences were determined using one way ANOVA with Holm-Sidak's multiple comparisons test to compare the means. (F - G) proposed model for reduced net xylem loading of Cl⁻ in 140 Ruggeri relative to K51-40. (F) In 140 Ruggeri, anion efflux from cortical or epidermal root cells could be mediated through putative anion channels VvNRT1.5 and VvNAXT1 which are transcriptionally more abundant in the Cl⁻ excluder. Xylem loading of Cl⁻ could be restricted through reduced VvNRT1.4 abundance, or inhibition of VvSLAH3 and VvALMT by higher [Ca²⁺]_cyt mediated by VvCAX3 (directly, or in partnership with Ca²⁺ dependent protein kinases). (G) In K51-40, anion efflux to the xylem apoplast could be enhanced through increased abundance of VvALMT1 and VvNRT1.4, and activation of VvALMT1 and VvSLAH3 by SnRK2 kinases.