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JXB Advance Access published online on October 27, 2009
Journal of Experimental Botany, doi:10.1093/jxb/erp309
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© 2009 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/2.5/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

CELL WALL INVERTASE 4 is required for nectar production in Arabidopsis

Jeffrey M. Ruhlmann, Brian W. Kram and Clay J. Carter*

Department of Biology, 1035 Kirby Dr, University of Minnesota Duluth, Duluth, MN 55812, USA

* To whom correspondence should be addressed: E-mail: cjcarter{at}d.umn.edu

To date, no genes have been reported to directly affect the de novo production of floral nectar. In an effort to identify genes involved in nectar production, the Affymetrix® ATH1 GeneChip was previously used to examine global gene expression profiles in Arabidopsis thaliana nectaries. One of the genes displaying highly enriched expression in nectaries was CELL WALL INVERTASE 4 (AtCWINV4, At2g36190), which encodes an enzyme that putatively catalyses the hydrolysis of sucrose into glucose and fructose. RT-PCR was used to confirm the nectary-enriched expression of AtCWINV4, as well as an orthologue from Brassica rapa. To probe biological function, two independent Arabidopsis cwinv4 T-DNA mutants were isolated. Unlike wild-type plants, cwinv4 lines did not produce nectar. While overall nectary morphology appeared to be normal, cwinv4 flowers accumulated higher than normal levels of starch in the receptacle, but not within the nectaries themselves. Conversely, wild-type, but not cwinv4, nectarial stomata stained intensely for starch. Cell wall extracts prepared from mutant flowers displayed greatly reduced invertase activity when compared with wild-type plants, and cwinv4 flowers also accumulated significantly lower levels of total soluble sugar. Cumulatively, these results implicate CWINV4 as an absolutely required factor for nectar production in the Brassicaceae, specifically by maintaining constant sink status within nectaries, thus allowing them to accumulate the sugars necessary for nectar production. In addition, CWINV4 is probably responsible for the hexose-rich composition observed for many Brassicaceae nectars.

Key words: Arabidopsis thaliana, Brassica rapa, cell wall invertase, invertase, nectar, nectaries, nectary

Received 6 August 2009; Revised 30 September 2009 Accepted 2 October 2009


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