A low R:FR leads to a high level of phytochrome Pfr, which promotes
endogenous levels of gibberellic acid (GA), a terpenoid built
from five-carbon isoprene units with diterpene as the immediate
precursor. Because the mevalonic acid pathway is used for the
biosynthesis of both GA (Arteca, 1996) and volatile oils, cassumunar
ginger grown under low light may convert mevalonate to GA
rather than volatile oil, resulting in low oil content.