Biosynthesis of glucosinolates in the developing silique walls and seeds of Sinapis alba

When [¹⁴C]tyrosine was administered to developing seeds and silique walls of Sinapis alba L. both tissues de novo synthesized p- hydroxybenzylglucosinolate (p-OHBG). Within a silique, the incorporation rate of tyrosine to p-OHBG was up to 70-fold higher in the silique wails compared to the seeds as evidenced by both in vivo and in vitro measurements. During development, the amount of p-OHBG increases in the seeds, whereas the level remains relatively constant in the corresponding walls in radioisotope feeding experiments using intact siliques. This shows that p-OHBG is translocated from the walls to the seeds in S. alba. Although translocation is a major contributor to glucosinolate accumulation in the seeds, we also demonstrate that seeds of S. alba contain all the enzymes required for de novo biosynthesis of p-OHBG.