CIS-ISOMERS OF CYTOKININS PREDOMINATE IN CHICKPEA SEEDS THROUGHOUT THEIR DEVELOPMENT

Trans-isomers of cytokinins (CK) are thought to predominate and have g reater biological activity than corresponding cis-isomers in higher pl ants. However, this study demonstrates a system within which the predo minant CK are cis-isomers. CK were measured at four developmental stag es in developing chickpea (Cicer arietinum L. cultivar Kaniva) seeds b y gas chromatography-mass spectrometry. Concentrations were highest at an early endospermic fluid stage and fell considerably when the cotyl edons expanded. The cis-isomers of zeatin nucleotide ([9R-MP]Z), zeati n riboside ([9R]Z), and zeatin (Z) were present in greater concentrati ons than those of corresponding trans-isomers: (trans)[9R-MP]Z, (trans )[9R]Z, (trans)Z, or dihydrozeatin riboside. Dihydrozeatin, dihydrozea tin nucleotide, and the isopentenyl-type CK concentrations were either low or not detectable. Root xylem exudates also contained predominant ly cis-isomers of [9R-MP]Z and [9R]Z. Identities of (cis)[9R]Z and (ci s)Z were confirmed by comparison of ion ratios and retention indices, and a full spectrum was obtained for (cis)[9R]Z. Tissues were extracte d under conditions that minimized the possibility of RNase hydrolysis of tRNA following tissue disruption, being a significant source of the cis-CK. Since no isomerization of (trans)[H-2]CK internal standards o ccurred, it is unlikely that the cis-CK resulted from enzymic or nonen zymic isomerization during extraction. Although quantities of total CK varied, similar CK profiles were found among three different chickpea cultivars and between adequately watered and water-stressed plants. D eveloping chickpea seeds will be a useful system for investigating the activity of cis-CK or determining the origin and metabolism of free C K.