Identification and quantification of the major endogenous cytokinins in pistachio seedlings

The major endogenous cytokinins, Z, ZR, DHZ, DHZR, iP and iPR in pistachio seedlings (Pistacia vera L. cv. Ohadi) were purified by HPLC and their identities confirmed using GC-MS. The aerial parts of two-year old pistachio seedlings including mature leaves, young leaves, lateral buds, debarked stems and bark were subjected to analysis. All of the above mentioned cytokinins were identified in the aerial parts except DHZ which was only present in mature leaves. Z-type cytokinins contributed almost 43% of the total cytokinins. ZR and DHZR were identified as the major ribosides and iP as the main base. The greatest concentration of ZR was detected in the bark, amounting to about 48%. DHZR and ZR constituted the major portion of the total cytokinins detected in both young and mature leaves while Z was detected as a minor cytokinin in leaves. The sharp increase of iP concentration during leaf maturation indicates that mature leaves are probably capable of de novo biosynthesis of cytokinins. The absence of DHZ (except in mature leaves) and the presence of considerable concentrations of DHZR in pistachio stems suggest that these tissues are able to metabolize DHZ to DHZR. The large amount of ZR in pistachio leaves suggests that root-derived ZR is transported into the leaves after loading into the xylem. The presence of high amounts of iP in pistachio lateral buds indicates that iP has been accumulated in these parts. The occurrence of a totally different cytokinin distribution pattern in buds, as compared with the other aerial parts, possibly results from their different metabolism.