Fluctuation of Endogenous Cytokinin Contents in Rice during Its Life Cycle—Quantification of Cytokinins by Selected Ion Monitoring Using Deuterium-labelled Internal Standards

Takagi, Makiko; Yokota, Takao; Murofushi, Noboru; Ota, Yasuo; Takahashi, Noriko

doi:10.1080/00021369.1985.10867233

Cited by 14 publications

(28 citation statements)

References 9 publications

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“…Bieleski solvents without RVC were also moderately effective for tRNA protection. In previous studies reporting significant levels of cis-CK in potato seedlings (Mauk and Langille, 1978), unfertilized hop cones (Watanabe et al, 1982), rice roots and ears (Takagi et al, 1985), and etiolated squash seedlings (Kuraishi et al, 1987(Kuraishi et al, , 1991, the possibility that the cis-CK had resulted from hydrolysis of tRNA during extraction was not rigorously excluded (Tay et al, 1986). Although Kuraishi et al (1987) used Bieleski solvents to reduce the potential for enzyme hydrolysis, they used prolonged extraction times lasting several days.…”

Section: Rnase-free Extractionsmentioning

confidence: 99%

“…tRNA-bound CK are predominantly cis-isomers, whereas the large majority of studies to date have reported that free CK are predominantly or exclusively transisomers. It has even been suggested by Tay et al (1986) that where cis-isomers have been detected (Mauk and Langille, 1978;Watanabe et al, 1982;Takagi et al, 1985) they are artifacts formed in extractions that did not rigorously exclude the possibility of tRNA breakdown following cell disruption.…”

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confidence: 99%

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

Emery

Leport²,

Barton³

et al. 1998

Plant Physiology

109

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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

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Section: Rnase-free Extractionsmentioning

confidence: 99%

mentioning

confidence: 99%

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

Emery

Leport²,

Barton³

et al. 1998

Plant Physiology

109

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“…In the exudate of rice plants, several cytokinins were identified (15). However, the constitution of cytokinins in the exudate, the level of these cytokinins, and their effects on leaf photosynthesis and senescence have been examined in only a few studies (20).In this report, we discuss the changes in the exudation rates and cytokinin activities in the exudates of two cultivars, Nipponbare and Akenohoshi, during the growing season. We also report the presence and the levels of endogenous cytokinins in the exudates of the two cultivars during the ripening stage when the leaves senesced.…”

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confidence: 99%

Section: Introductionmentioning

confidence: 99%

Changes in Cytokinin Activities and Mass Spectrometric Analysis of Cytokinins in Root Exudates of Rice Plant (Oryza sativa L.)

Soejima¹,

Sugiyama²,

Ishihara³

1992

Plant Physiol.

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Changes in exudation rate and cytokinin activities in the exudates were measured in two varieties of rice (Oryza sativa L.), cv Nipponbare (a Japanese normal cultivar) and cv Akenohoshi (a highyielding cultivar). The exudation rates of Akenohoshi, the leaves of which remained green for a longer time, were higher than those of Nipponbare after the booting stage. Cytokinin activities in the exudates of Akenohoshi were higher than those of Nipponbare during the ripening period. Cytokinins in the exudates collected during the middle of the ripening stage were analyzed with mass spectrometry using deuterium-labeled standards. trans-Zeatin, trans-ribosylzeatin, and N'-isopentenyladenosine were detected as free cytokinins, and zeatin was detected in the hydrolysates of highly polar fractions ("conjugated zeatin") in the exudates of both cultivars. Conjugated zeatin was the predominant cytokinin in both cultivars. Therefore, we suggest that conjugated zeatin is an important form of cytokinin during the ripening stage. The level of each of the cytokinins in Akenohoshi was higher than that in Nipponbare. Also, we discuss the correlation between the leaf senescence and cytokinin content in root exudates.In a previous study to clarify the physiological and ecological characteristics of high-yielding rice varieties (11, 12), it was reported that the yield in Akenohoshi was about 1780 kg/ha higher than that in Nipponbare, a Japanese standard cultivar, and that Akenohoshi had a higher dry matter production capacity compared with Nipponbare. This was attributed to the maintenance of a higher net assimilation rate during the ripening period in the former. 1724 stage were 9.2 ,umol of CO2 m-2 s-' (44.6% of its maximum rate at the panicle formation stage) and 12.7 smol of CO2 m-2 S-1 (62.0%), respectively. In addition, the cause for these differences between the two cultivars was examined by measuring the active and passive water absorption abilities of the roots. The rate of exudation from the main stem and the resistance to water transport from the root surface to the leaves under intense transpiration were higher and lower in Akenohoshi than in Nipponbare, respectively. These differences between the two cultivars were especially large during the ripening stage. This fact suggests that physiological activity in the roots of Akenohoshi was higher than that in Nipponbare. It is known that a decline in the physiological activity of roots causes leaf senescence and death of the leaves at the lower positions (10), but the mechanism by which this occurs is not understood well.Cytokinins transported from the roots via the xylem are known to delay leaf senescence (6,16,18). In the exudate of rice plants, several cytokinins were identified (15). However, the constitution of cytokinins in the exudate, the level of these cytokinins, and their effects on leaf photosynthesis and senescence have been examined in only a few studies (20).In this report, we discuss the changes in the exudation rates and cytokinin activities in the exudat...

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“…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).…”

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confidence: 99%

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

et al. 2012

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cis-Zeatin (cZ) is generally regarded as a cytokinin with little or no activity, compared with the highly active trans-zeatin (tZ). Although recent studies suggested possible roles for cZ, its physiological significance remains unclear. In our studies with rice (Oryza sativa), cZ inhibited seminal root elongation and up-regulated cytokinin-inducible genes, and its activities were comparable to those of tZ. Tracer experiments showed that exogenously supplied cZ-riboside was mainly converted into cZ derivatives but scarcely into tZ derivatives, indicating that isomerizations of cZ derivatives into tZ derivatives are a minor pathway in rice cytokinin metabolism. We identified three putative cZ-O-glucosyltransferases (cZOGT1, cZOGT2, and cZOGT3) in rice. The cZOGTs preferentially catalyzed O-glucosylation of cZ and cZ-riboside rather than tZ and tZ-riboside in vitro. Transgenic rice lines ectopically overexpressing the cZOGT1 and cZOGT2 genes exhibited short-shoot phenotypes, delay of leaf senescence, and decrease in crown root number, while cZOGT3 overexpressor lines did not show shortened shoots. These results propose that cZ activity has a physiological impact on the growth and development of rice.

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Fluctuation of Endogenous Cytokinin Contents in Rice during Its Life Cycle—Quantification of Cytokinins by Selected Ion Monitoring Using Deuterium-labelled Internal Standards

Cited by 14 publications

References 9 publications

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

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

Changes in Cytokinin Activities and Mass Spectrometric Analysis of Cytokinins in Root Exudates of Rice Plant (Oryza sativa L.)

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

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