Nebularine Affects Plant Growth and Development but does not Interfere with Cytokinin Signaling |
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Authors: | Hana Pospí?ilová Jaroslav Nisler Luká? Spíchal Ivo Frébort |
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Institution: | 1.Department of Biochemistry, Faculty of Science,Palacky University,Olomouc,Czech Republic;2.Laboratory of Growth Regulators,Palacky University/Institute of Experimental Botany AS CR,Olomouc,Czech Republic |
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Abstract: | Nebularine is known for its high cytotoxicity in animals, whereas in plants it was originally believed to be an anticytokinin.
In this study we show that in classical cytokinin bioassays, nebularine antagonized cytokinin function in senescence and callus
biotests but not in the Amaranthus bioassay. Nebularine reversed the inhibitory effect of cytokinin on lateral root formation in Arabidopsis seedlings, and when applied alone caused increased lateral root formation and shortening of the main root. Systematic spraying
of Arabidopsis plants with nebularine led to yellowing and formation of purple pigments, local drying, and withering, although younger plants
showed a greater resilience. Comparison of nebularine cytotoxicity in plant and animal cells showed that the growth of tobacco
BY-2 cells was inhibited with only about tenfold lower efficacy than mammalian cell lines. Most importantly, direct binding
assay with Arabidopsis cytokinin receptors AHK3 and CRE1/AHK4 showed that nebularine did not compete for binding with the natural cytokinin trans-zeatin. Although nebularine reduced cytokinin-induced expression of the cytokinin reporter ARR5:GUS in planta, the same effect was observed for DR5:GUS, an auxin reporter gene. Taken together, the results indicate that the mode of action of nebularine does not involve cytokinin
signaling and that the anticytokinin-like effect is rather a consequence of the inhibition of various processes as described
for animal systems. |
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