PI-55 (6-(2-hydroxy-3-methylbenzylamino)purine) is a cytokinin receptor inhibitor that exhibits structural similarity to 6-benzylaminopurine (BAP). It competitively inhibits BAP binding on the specific Arabidopsis receptors CRE1/AHK4 and AHK3. Furthermore, PI-55 effectively suppresses cytokinins-induced haustorium formation and enhances parasite aggressiveness [1].

在高浓度下（10 μM 和 100 μM），PI-55 导致早期吸器结构发育的不完全阻断，特别是在细胞分裂素活性促进时更为明显。与仅用BAP相比，联合使用PI-55和BAP能够降低P. ramosa的总体侵略性，这表明导致早期吸器结构形成的信号通路涉及与CRE1/AHK4和AHK3同源的组氨酸激酶受体[1]。