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JXB Advance Access originally published online on May 31, 2008
Journal of Experimental Botany 2008 59(9):2469-2477; doi:10.1093/jxb/ern113
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Metabolic responses to red/far-red ratio and ontogeny show poor correlation with the growth rate of sunflower stems

Maria Agustina Mazzella1,2, María Inés Zanor3, Alisdair Robert Fernie3 and Jorge José Casal2,*

1INGEBI, Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, 1428-Buenos Aires, Argentina
2IFEVA, Faculty of Agronomy, University of Buenos Aires and CONICET, 1417 Buenos Aires, Argentina
3Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam–Golm, Germany

* To whom correspondence should be addressed. E-mail: casal{at}ifeva.edu.ar

In sparse canopies, low red to far-red (R/FR) ratios reach only vertically-oriented stems, which respond with faster rates of extension. It is shown here that this signal also promotes stem dry matter accumulation in sunflower (Helianthus annuus) but not in mustard (Sinapis alba L.). Physically blocking internode extension growth also blocked internode recovery of labelled carbon fed to the leaves, indicating that increased carbon accumulation is partially a consequence of increased extension growth in sunflower. However, low R/FR also promoted carbon accumulation in the lower section of the internode, where extension growth was unaffected. Although the levels of many soluble metabolites and of cell-wall carbohydrates increased in the stem in response to low R/FR, allowing conservation of their concentration, sucrose was present at a lower concentration under low R/FR. This change is anticipated to favour carbon unloading from the stem phloem. Low R/FR also reduced the levels of selected fatty acids, fatty acid alcohols, and sterols. Compared with the lower section, the upper section of the internode showed higher levels of organic acids, amino acids, fatty acids, and sterols. It is concluded that the promotion of stem extension growth by low R/FR ratios causes increased dry matter gain in sunflower internodes by a mechanism that is largely independent of changes in metabolism, since, whilst both low R/FR and ontogeny alter the metabolic profile, the changes do not correlate with the observed growth responses.

Key words: Carbohydrates, metabolic profile, phytochrome, shade avoidance, sunflower

Received 18 January 2008; Revised 5 March 2008 Accepted 26 March 2008


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