Expression of key enzymes for nitrogen assimilation in grapevine rootstock in response to N-form and timing

Abstract

Background and Aims: Rootstocks play an essential role in grapevine scion growth and development. They influence water and nutrient uptake and affect biomass allocation of the scion and the grape berry composition connected with wine quality. Nitrogen (N) can be taken up by the roots in various forms such as nitrate, ammonium or urea. These N-forms and their possible differential assimilation directly and indirectly influence grapevine vegetative and generative growth. N assimilation is driven by N acquiring enzymes such as nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS). This assimilation physiology can be influenced by factors such as light conditions or substrate availability. Methods: Hydroponically grown grapevine rootstocks were fertilized with various N-forms, namely calcium nitrate (CaN), ammonium (AM), urea (UR), and glutamine (Gln). The transcript expression of the enzymes NR, NiR and GS and the enzymatic nitrate reductase activity (eNRA) were examined at various time points (0 h, 3 h, and 6 h) after N application. Results and Conclusion: The data suggest that the grapevine rootstock SO4 has the ability to assimilate the amino acid Gln. Furthermore, AM, UR, and in some organs Gln, can regulate the co-enzymes NR and NiR, both of which function as activators of the NO-3 assimilation process. The eNRA is clearly defined by the plant organ.