cis -Isomers of Cytokinins Predominate in Chickpea Seeds throughout Their Development1

Abstract

Trans-isomers of cytokinins (CK) are thought to predominate and have greater biological activity than corresponding cis-isomers in higher plants. However, this study demonstrates a system within which the predominant CK are cis-isomers. CK were measured at four developmental stages in developing chickpea (Cicer arietinum L. cultivar Kaniva) seeds by gas chromatography-mass spectrometry. Concentrations were highest at an early endospermic fluid stage and fell considerably when the cotyledons expanded. Seed tissues were the source for isolation of the first naturally occurring CK, trans-Z (Miller, 1961;Letham, 1963). Seeds have turned out to be a rich source of CK, and in the past 30 years investigators have described a range of different CK from seed tissues (van Staden et al., 1982). This may reflect their relatively high levels in seeds (van Staden et al., 1982), a status that is believed to indicate a role for CK in establishing developing seeds as strong assimilate sinks (Brenner and Cheikh, 1995). Despite a vast literature concerning the occurrence, form, and significance of CK in plant development, the nature and site(s) of their synthesis is yet to be established. In fact, Holland (1997) recently proposed that CK are not formed by plants at all but rather by bacterial symbionts that colonize plant tissues. Although there is good evidence for the transfer of CK synthesized by Rhizobium in legume nodules (Upadhyaya et al., 1991), a role for bacteria in providing CK to roots or shoot organs needs to be investigated more thoroughly. Because unequivocal evidence for a plant isopentenyl transferase is lacking, a persistent hypothesis, which has recently been reviewed (Prinsen et al., 1997), is that the free CK in plants are not synthesized de novo but are released during tRNA turnover.Z, [9R-MP]Z, and [9R]Z have an unsaturated isopentenyl side chain that can exist in the cis or trans conformation. The cis-isomer occurs when the hydroxyl group of the isopentenyl side chain is oriented toward the N-1 position of the purine ring, whereas in the trans-isomer the hydroxyl group is oriented away from the purine ring (Korszun et al., 1989; Fig. 1). The trans-isomers of [9R]Z and Z are by far the more commonly reported forms and are considered the predominant isomers in higher plants (McGaw and Burch, 1995;Prinsen et al., 1997). Systems in which the existence of cis-CK can be demonstrated unequivocally would be significant for two reasons. First, because cis-CK show much lower activity than trans-CK in bioassays (Kaminek, 1982) and their interconversion may constitute a mechanism for reducing CK bioactivity in vivo. Second, cis-CK provide evidence for the hypothesis that the free CK pool in higher plants may be at least partially derived from the breakdown of tRNA. The major criticism of this hypothesis has been the structural distinctness between tRNA-bound CK and free-pool CK (Letham and Palni, 1983;McGaw and Burch, 1995;Prinsen et al., 1997

Intra-Raceme Variation in Pod-Set Probability Is Associated with Cytokinin Content in Soybeans

“…The biosynthetic pathway of cytokinins has not been demonstrated clearly (Moore, 1989;Binns, 1994), and further study is needed to determine if the cytokinins contained in racemes come from the roots or from other parts of the plants, and to learn how the cytokinin forms are altered during the transition. In chickpeas, cis-isomers were found to be predominant in seeds (Emery et al, 1998), while transisomers are the more commonly reported forms in higher plants (McGaw and Burch, 1995 ;Prinsen et al, 1997). A comparison among floral positions of the peak cytokinin amount, which was observed at 10 DAA, revealed that the concentration was the highest at the most proximal positions ( 1 -4) of racemes, followed by the middle positions (moderate concentration) and the distal positions where the concentration was extremely low (Fig.…”

Euglena gracilis(Euglenophyceae) produces abscisic acid and cytokinins and responds to their exogenous application singly and in combination with other growth regulators

“…All samples were evaporated to dryness in a speed vacuum concentrator at 35°C and immediately stored at −20°C. CKNTs were dephosphorylated using 3 units of bacterial alkaline phosphatase in 1 ml 0.1 M ethanolamine-HCl (pH 10.4) for 12 hours at 37°C (Emery et al, 1998). The resulting CKRs were brought to dryness in a speed vacuum concentrator at 35°C.…”

Cytokinin Activity of cis-Zeatin and Phenotypic Alterations Induced by Overexpression of Putative cis-Zeatin-O-glucosyltransferase in Rice

“…Furthermore, in a bacterial system, the maize cytokinin receptor ZmHK1 responded to cZ and tZ with comparable affinities (Yonekura-Sakakibara et al, 2004;Lomin et al, 2011). cZ and its derivatives are abundant not only in maize but also in other species, including chickpea (Cicer arietinum; Emery et al, 1998) and rice (Oryza sativa; Takagi et al, 1985Takagi et al, , 1989Kojima et al, 2009). In addition, a recent comprehensive screen showed that higher levels of cZ than tZ derivatives can be found in species across the complete evolutionary tree of land plants (Gajdošová et al, 2011).…”