Involvement of cis-Zeatin, Dihydrozeatin, and Aromatic Cytokinins in Germination and Seedling Establishment of Maize, Oats, and Lucerne
- 369 Downloads
The aims of this study were to monitor endogenous cytokinin levels during germination and early seedling establishment in oats, maize, and lucerne to determine which cytokinin forms are involved in these processes; to quantify the transfer ribonucleic acid (tRNA)-bound cytokinins; and to measure cytokinin oxidase/dehydrogenase (CKX) activity. Cytokinins were identified using UPLC-MS/MS. The predominant free cytokinins present in the dry seeds were dihydrozeatin-type (DHZ) in lucerne and maize and cZ-type (cis-zeatin) in oats. Upon imbibition, there was a large increase in cZ-type cytokinins in lucerne although the cZ-type cytokinins remained at high levels in oats. In maize, the high concentrations of DHZ-type cytokinins decreased prior to radicle emergence. Four tRNA-bound cytokinins [cis-zeatin riboside (cZR)>N6-(2-isopentenyl)adenosine (iPR), dihydrozeatin riboside (DHZR), trans-zeatin riboside (tZR)] were detected in low concentrations in all three species investigated. CKX activity was measured using an in vitro radioisotope assay. The order of substrate preference was N6-(2-isopentenyl)adenine (iP)>trans-zeatin (tZ)>cZ in all three species, with activity fluctuating as germination proceeded. There was a negative correlation between CKX activity and iP concentrations and a positive correlation between CKX activity and O-glucoside levels. As O-glucosides are less resistant to CKX degradation, they may provide a readily available source of cytokinins that can be converted to physiologically active cytokinins required during germination. Aromatic cytokinins made a very small contribution to the total cytokinin pool and increased only slightly during seedling establishment, suggesting that they do not play a major role in germination.
Keywordscis-Zeatin Cytokinin oxidase/dehydrogenase Dihydrozeatin Lucerne Maize Oats tRNA degradation
The National Research Foundation, South Africa is thanked for financial assistance. Hana Martinková and Michaela Glosová are acknowledged for their help with cytokinin analyses and Marie Korecká and Dr. Petre Dobrev for their assistance with CKX determinations. The Ministry of Education, Youth and Sports of the Czech Republic (grants MSM 6198959216 and LC06034), the Centre of the Region Haná for Biotechnological and Agricultural Research (grant ED0007/01/01), and the Czech Science Foundation (grant 506/11/0774) are thanked for financial support.
The authors declare that they have no conflict of interest.
- Armstrong DJ (1994) Cytokinin oxidase and the regulation of cytokinin degradation. In: Mok DWS, Mok MC (eds) Cytokinins: chemistry, activity and function. CRC Press, Boca Raton, pp 139–154Google Scholar
- Dietrich JT, Kamínek M, Blevins DG, Reinbott TM, Morris RO (1995) Changes in cytokinins and cytokinin oxidase activity in developing maize kernels and the effects of exogenous cytokinin on kernel development. Plant Physiol Biochem 33:327–336Google Scholar
- Dobrev P, Motyka V, Gaudinová A, Malbeck J, Trávníčková A, Kamínek M, Vaňková R (2002) Transient accumulation of cis- and trans-zeatin type cytokinins and its relation to cytokinin oxidase activity during the cell cycle of synchronized tobacco BY-2 cells. Plant Physiol Biochem 40:333–337CrossRefGoogle Scholar
- Emery N, Atkins C (2006) Cytokinins and seed development. In: Basra AS (ed) Handbook of seed science and technology. Food Products Press, New York, pp 63–93Google Scholar
- Gajdošová S, Spíchal L, Kamínek M, Hoyerová K, Novák O, Dobrev PI, Galuszka P, Klíma P, Gaudinová A, Žižková E, Hanuš J, Dančák M, Trávníček B, Pešek B, Krupička M, Vaňková R, Strnad M, Motyka V (2011) Distribution, biological activities, metabolism, and the conceivable function of cis-zeatin-type cytokinins in plants. J Exp Bot 62:2827–2840PubMedCrossRefGoogle Scholar
- Leubner-Metzger G (2006) Hormonal interactions during seed dormancy release and germination. In: Basra AS (ed) Handbook of seed science and technology. Food Products Press, New York, pp 303–341Google Scholar
- Tarkowská D, Doležal K, Tarkowski P, Åstot C, Holub J, Fuksová K, Schmülling T, Sandberg G, Strnad M (2003) Identification of new aromatic cytokinins in Arabidopsis thaliana and Populus x canadensis leaves by LC-(+)ESI-MS and capillary liquid chromatography/frit-fast atom bombardment mass spectrometry. Physiol Plant 117:579–590PubMedCrossRefGoogle Scholar
- Von Schwartzenberg K, Núñez MF, Blaschke H, Dobrev PI, Novák O, Motyka V, Strnad M (2007) Cytokinins in the Bryophyte Physcomitrella patens: Analyses of activity, distribution, and cytokinin oxidase/dehydrogenase overexpression reveal the role of extracellular cytokinins. Plant Physiol 145:786–800CrossRefGoogle Scholar