Involved in the synthesis of tocopherol (vitamin E). Methylates gamma- and delta-tocopherol to form beta- and alpha-tocopherol, respectively. gamma-tocopherol + S-adenosyl-L-methionine = (+)-alpha-tocopherol + H(+) + S-adenosyl-L-homocysteine delta-tocotrienol + S-adenosyl-L-methionine = beta-tocotrienol + H(+) + S-adenosyl-L-homocysteine gamma-tocotrienol + S-adenosyl-L-methionine = alpha-tocotrienol + H(+) + S-adenosyl-L-homocysteine delta-tocopherol + S-adenosyl-L-methionine = beta-tocopherol + H(+) + S-adenosyl-L-homocysteine Cofactor biosynthesis; tocopherol biosynthesis. Belongs to the class I-like SAM-binding methyltransferase superfamily. gTMT family.