Inflorescence Necrosis Induced from Ammonium Incubation and Deterred by α-Keto-Glutarate and Ammonium Assimilation in Pinot noir Grapevines

Inflorescence necrosis (IN) and increased tissue NH4+ occurred after incubating single-node, field-grown, Pinot noir grape (Vitis vinifera L.) cuttings with one leaf and cluster in 120 mM or higher NH4+ solutions of NH4NO3 or (NH4)2SO4. Incubation with solutions of NO3-, SO4=, and K+ at the same concentrations did not induce IN. The addition of 80 mM KG, a substrate for ammonium assimilation, to an incubation solution containing 160 mM NH4+ deterred IN and lowered flower or fruit NH4+ to near control levels. The presence of glutamine synthetase/ glutamate synthase (GS/GOGAT) pathway of ammonium assimilation was detected in flowers, fruit, and pedicels, but not in rachis of cuttings treated with GS/GOGAT inhibitors: i.e., 10 mM MSX (a GS inhibitor) or 5 mM AS (a GOGAT inhibitor). Glutamate dehydrogenase (GDH) is not involved in ammonium assimilation and detoxification in grape inflorescence. Chemical names used: α-keto-glutarate (KG), methionine sulfoximine (MSX), azaserine (AS).