Comparison of the perception of THP and THF substituted 6-(3-hydroxybenzylamino)purine (meta-topolin, mT) and mT by selected cytokinin receptors. The effect of 6-(3-hydroxybenzylamino)-9-tetrahydropyran-2-ylpurine (6(3OHBA)9THPP) and 6-(3-hydroxybenzylamino)-9-tetrahydrofuran-2-ylpurine (6(3OHBA)9THFP) on the sensing of mT by the cytokinin receptors CRE1/AHK4 (A) and AHK3 (B). trans-Zeatin (tZ) was used as the positive control.