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.
