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JXB Advance Access originally published online on July 24, 2008
Journal of Experimental Botany 2008 59(12):3425-3434; doi:10.1093/jxb/ern191
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Nectar formation and floral nectary anatomy of Anigozanthos flavidus: a combined magnetic resonance imaging and spectroscopy study

Michael Wenzler1, Dirk Hölscher1, Thomas Oerther2 and Bernd Schneider1,*

1Max-Planck-Institute for Chemical Ecology, Beutenberg Campus, Hans-Knöll-Str. 8, D-07745 Jena, Germany
2Bruker BioSpin GmbH, Silberstreifen 4, D-76287 Rheinstetten, Germany

* To whom correspondence should be addressed. E-mail: Schneider{at}ice.mpg.de

Metabolic processes underlying the formation of floral nectar carbohydrates, especially the generation of the proportions of fructose, glucose, and sucrose, are important for understanding ecological plant–pollinator interactions. The ratio of sucrose-derived hexoses, fructose and glucose, in the floral nectar of Anigozanthos flavidus (Haemodoraceae) was observed to be different from 1:1, which cannot be explained by the simple action of invertases. Various NMR techniques were used to investigate how such an unbalanced ratio of the two nectar hexoses can be formed. High-resolution 13C NMR spectroscopy in solution was used to determine the proportion of carbohydrates in vascular bundles of excised inflorescences fed with 13C-labelled carbohydrates. These experiments verified that feeding did not affect the metabolic processes involved in nectar formation. In vivo magnetic resonance imaging (e.g. cyclic J cross-polarization) was used to detect carbohydrates in vascular bundles and 1H spin echo imaging non-invasively displayed the architecture of tepal nectaries and showed how they are connected to the vascular bundles. A model of the carbohydrate metabolism involved in forming A. flavidus floral nectar was established. Sucrose from the vascular bundles is not directly secreted into the lumen of the nectary but, either before or after invertase-catalysed hydrolyses, taken up by nectary cells and cycled at least partly through glycolysis, gluconeogenesis, and the pentose phosphate pathway. Secretion of the two hexoses in the cytosolic proportion could elegantly explain the observed fructose:glucose ratio of the nectar.

Key words: Anigozanthos flavidus, carbohydrate transport, 13C chemical shift imaging, cryo probe, floral nectar, Haemodoraceae, microimaging, MRI, NMR

Received 25 March 2008; Revised 9 June 2008 Accepted 30 June 2008


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