Endogenous isoprenoid and aromatic cytokinins in different plant parts of Cocos nucifera (L.)

The present study reports the analyses of both isoprenoid and aromatic cytokinins in the coconut palm by combined high performance liquid chromatography and group specific enzyme immunoassays (HPLC-ELISA). The results showed that the isoprenoid cytokinins were several fold more abundant than the aromatic cytokinins in each of the plant parts analysed: immature inflorescence, shoot apical meristem (SAM), spear leaf and embryo. Within the isoprenoid cytokinins, the most abundant ones by type were the zeatin- (Z-), the isopentenyladenine- (iP-) and the dihydrozeatin- (DHZ-) type in decreasing order for most plant parts studied, and individually, zeatin riboside (ZR) or zeatin riboside-5'-monophosphate (ZR5'P) depending on the part. In the case of the iP-type cytokinins, the results showed that its 9-glucoside was the most abundant one in most parts. The isoprenoid cytokinin profiles in coconut showed a predominant pattern of 9-conjugation as a major metabolism route for these cytokinins. Analyses also showed the occurrence of the aromatic cytokinin 6-benzylaminopurine (BAP) and its riboside (BAPR), 9-glucoside (BAP9G), and nucleotide (BAPR5'P). Their presence in coconut palm was unequivocally identified after permethylation by gas chromatography-mass spectrometry. They were more concentrated in the embryo and in the immature inflorescence than in the other two parts studied, however their concentration in each part was several times lower than that of isoprenoid cytokinins. All four were detected in each of the parts studied. The most abundant ones were BAPR and BAP9G in immature inflorescence; and BAPR in all of the other parts. When all cytokinins analysed are considered, differences between the plant parts studied were found. The zygotic embryos showed the highest content, double that in immature inflorescence, and five times more that in spear leaf and SAM. These differences are even greater when individual cytokinins are compared.