Journal Article

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

Maria Agustina Mazzella, María Inés Zanor, Alisdair Robert Fernie and Jorge José Casal

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 9, pages 2469-2477
Published in print June 2008 | ISSN: 0022-0957
Published online June 2008 | e-ISSN: 1460-2431 | DOI:
Metabolic responses to red/far-red ratio and ontogeny show poor correlation with the growth rate of sunflower stems

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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.

Keywords: Carbohydrates; metabolic profile; phytochrome; shade avoidance; sunflower

Journal Article.  4892 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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