Cytokinin concentration gradient in the developing grains and upper leaves of rice (<i>Oryza sativa</i>) during grain filling

Saha, Shyamali; Nagar, P. K.; Sircar, P.

doi:10.1139/b86-271

Cited by 30 publications

(17 citation statements)

References 19 publications

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“…Our results confirmed early reports (Saha et al, 1986;Morris et al, 1993) that cytokinin contents in rice grains showed a transient increase at early grain filling stage. Our own earlier work (Yang et al, 2000c) with the same rice cultivars observed that maximum cell division rate in endosperm occurred 10 to14 DPA at NN and 12 to 18 DPA at HN.…”

Section: Discussionsupporting

confidence: 93%

Hormonal Changes in the Grains of Rice Subjected to Water Stress during Grain Filling

et al. 2001

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Lodging-resistant rice (Oryza sativa) cultivars usually show slow grain filling when nitrogen is applied in large amounts. This study investigated the possibility that a hormonal change may mediate the effect of water deficit that enhances whole plant senescence and speeds up grain filling. Two rice cultivars showing high lodging resistance and slow grain filling were field grown and applied with either normal or high amount nitrogen (HN) at heading. Well-watered and water-stressed (WS) treatments were imposed 9 days post anthesis to maturity. Results showed that WS increased partitioning of fixed 14 CO 2 into grains, accelerated the grain filling rate but shortened the grain filling period, whereas the HN did the opposite way. Cytokinin (zeatin ϩ zeatin riboside) and indole-3-acetic acid contents in the grains transiently increased at early filling stage and WS treatments hastened their declines at the late grain filling stage. Gibberellins (GAs; GA 1 ϩ GA 4 ) in the grains were also high at early grain filling but HN enhanced, whereas WS substantially reduced, its accumulation. Opposite to GAs, abscisic acid (ABA) in the grains was low at early grain filling but WS remarkably enhanced its accumulation. The peak values of ABA were significantly correlated with the maximum grain filling rates (r ϭ 0.92**, P Ͻ 0.01) and the partitioning of fixed 14 C into grains (r ϭ 0.95**, P Ͻ 0.01). Exogenously applied ABA on pot-grown HN rice showed similar results as those by WS. Results suggest that an altered hormonal balance in rice grains by water stress during grain filling, especially a decrease in GAs and an increase in ABA, enhances the remobilization of prestored carbon to the grains and accelerates the grain filling rate.

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Section: Discussionsupporting

confidence: 93%

Hormonal Changes in the Grains of Rice Subjected to Water Stress during Grain Filling

et al. 2001

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“…BA is known as a growth-promoting substance by overcoming growth limiting effects (1,8). BA increases protein content (14) by stimulating protein synthesis and inhibiting protein degradation (9). From preliminary experiments, it was shown that in 100-*2% plants BA was acting by causing enlarged endogenous cytokinin contents.…”

Section: Discussionmentioning

confidence: 99%

“…Nitrogen may be the effector of the cytokinin production (5,12,13,15) and thus regulate metabolic activity and RNA (16) and protein content of the plants (14), leading to adaptive responses of growth and shoot to root ratios to changes in the mineral nutrition of plants.…”

Section: Discussionmentioning

confidence: 99%

Growth Responses of Plantago major L. ssp. pleiosperma (Pilger) to Changes in Mineral Supply

Kuiper¹

1988

Plant Physiol.

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“…Elevated levels of cytokinins were found in endosperms of maize, rice, and wheat during the highly mitotic phase (19)(20)(21). The high concentration of O-xylosyltransferase in P. vulgaris endosperm may be necessary to convert a less stable cytokinin, zeatin, to a more active or stable form (22).…”

Section: Discussionmentioning

confidence: 99%

Cytolocalization of zeatin O-xylosyltransferase in Phaseolus.

Martin¹,

Mok²,

Mok³

1993

Proc. Natl. Acad. Sci. U.S.A.

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Zeatin O-xylosylbansferase (EC 2.4.2.-) mediates the formation of O-xylosylzeatin from trans-zeatin and UDP-xylose in immature seeds of Phaseolus vulgaris. Tissue printing with a monoclonal antibody specific for the enzyme and a cDNA probe demonstrated that the enzyme was primarily localized and synthesized in the endosperm. Immunolocalization performed on monolayer endosperm at the free-nuclei stage and on EM sections demonstrated that the enzyme was associated with the nucleus as well as with the cytoplasm. Immunoanalysis of nuclear fractions revealed that the enzyme was retained in the nuclear pellet. Western analysis also showed that the enzyme was present in the nuclei of cotyledons and endosperm callus. The findings suggest that the enzyme may be involved in the nuclear-cytoplasmic transport of cytokinins and related molecules or, possibly, with chromatin of rapidly dividing cells.Cytokinins are plant hormones mediating cell division and differentiation (1). Zeatin is a naturally occurring cytokinin highly active in most plant systems (2). Genetic differences in cytokinin metabolism between species of Phaseolus were investigated by incubating immature seeds with radiolabeled zeatin (3). Exogenously supplied zeatin was rapidly converted to O-xylosylzeatin by immature seeds of P. vulgaris, while O-glucosylzeatin was formed in P. lunatus. The species-specific formation of zeatin metabolites was related to the occurrence ofa single, distinct enzyme in immature seeds of each of the two species; zeatin O-xylosyltransferase in P. vulgaris and O-glucosyltransferase in P. lunatus. Both enzymes are highly specific for trans-zeatin but differ in specificity for the donor ofthe glycosyl moiety (4, 5). UDP-xylose (UDPX) serves as the donor for O-xylosyltransferase from P. vulgaris, whereas the O-glucosyltransferase ofP. lunatus can utilize both UDP-glucose (UDPG) and UDPX to mediate the formation of O-glucosylzeatin and O-xylosylzeatin, respectively, but has 10 times higher affinity for UDPG. The two glycosyltransferases have a similar molecular size (Mr 50,000) but can be separated by ion exchange chromatography (4).Two additional zeatin-metabolizing enzymes, a reductase and a cis-trans isomerase, have also been isolated from seeds of Phaseolus (6, 7). Interestingly, the activities of all four enzymes are particularly pronounced in immature seeds. We are interested in characterizing the developmental regulation of these enzymes. Part of this study is focused on localizing enzymes in the developing seed.Zeatin O-xylosyltransferase was chosen as the first enzyme for localization studies because monoclonal antibodies (mAbs) specific for the enzyme have been generated (8) and immunopositive cDNA clones have been isolated from Agtll expression libraries (9). In this paper we describe results obtained from tissue printing using a mAb (XZT-1) and a cDNA (pXZT82) as probes, immunolocalization performed on monolayer endosperm and EM sections, and Western analyses ofcellular and nuclear fractions. The results indicate t...

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Cytokinin concentration gradient in the developing grains and upper leaves of rice (Oryza sativa) during grain filling

Cited by 30 publications

References 19 publications

Hormonal Changes in the Grains of Rice Subjected to Water Stress during Grain Filling

Hormonal Changes in the Grains of Rice Subjected to Water Stress during Grain Filling

Growth Responses of Plantago major L. ssp. pleiosperma (Pilger) to Changes in Mineral Supply

Cytolocalization of zeatin O-xylosyltransferase in Phaseolus.

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