Involved in nicotinate detoxification in planta (PubMed:28533213). Catalyzes the conversion of nicotinate to N-methylnicotinate, which is a detoxified form of endogenous nicotinate in planta (PubMed:28533213). nicotinate + S-adenosyl-L-methionine = N-methylnicotinate + S-adenosyl-L-homocysteine kcat is 2.25 sec(-1) with nicotinate as substrate (PubMed:28533213). kcat is 2.07 sec(-1) with S-adenosyl-L-methionine as substrate (PubMed:28533213). Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family.