Abstract
Background and Aims: Nitrate is a major form of inorganic nitrogen present in cultivated soils; however, information on the mechanisms responsible for uptake of the anion in grapevines is scarce. Methods and Results: The response to external nitrate was studied in two clones of the cultivars Chardonnay and Sauvignon Blanc. Grapevines, own-rooted or grafted on the two rootstocks SO4 and K5BB, were grown in nutrient solution and, after a period of nitrogen (N)-deprivation, exposed to 0.2 or 1mmol/L nitrate. The uptake was an inducible process, operated by high- and low-affinity transport systems. The magnitude and time dependence of the induction varied as a function of the clone. Uptake rate as a function of nitrate external concentration showed a multiphasic pattern. Although nitrate exposure caused a transient up-regulation of nitrate influx transporter genes, a clear correlation with the rise in nitrate uptake could not be found; in contrast, a negative relationship between changes in uptake rates and expression of a nitrate efflux transporter gene was observed. Conclusions: In the grapevine, the response of low- and high-affinity transport systems to external nitrate was favoured by the presence of the rootstock and also dependent on the characteristics of the scion. Low-affinity uptake and efflux from root cells conceivably play an important role in the overall N-nitrate acquisition. Significance of the Study: This study shows that activation of mechanisms involved in nitrate uptake in the grapevine is strongly affected by the scion-rootstock combination. Results may be significant for developing agronomic practices and selection programmes related to nitrogen use in the grapevine.