Fig. 5. Proposed model of glucosinolate sequestration in adult P. armoraciae.

① Absorption of ingested glucosinolates from the gut lumen into the hemolymph; ② transcellular or paracellular glucosinolate transport from the hemolymph into the Malpighian tubule (MT) lumen; ③ selective reabsorption of glucosinolates from the MT lumen into the hemolymph; and ④ excretion of excess glucosinolates. PaGTRs localized in the MT are proposed to import glucosinolates from the lumen across the apical membrane into the epithelial cells.