Metabolic profile responses to R/FR ratio and ontogeny show poor correlation with growth rate in sunflower stems

MAZZELLA, MARIA AGUSTINA, ZANOR, MARIA INES , FERNIE ALISDAIR, CASAL JOEGE

JOURNAL OF EXPERIMENTAL BOTANY

Año: 2008

0022-0957

In sparse canopies, low red to far-red (R/FR) ratios reach only vertically-oriented stems, which respond with faster rates of extension. Here we show 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. In comparison to the lower section, the upper section of the internode showed higher levels of organic acids, amino acids, fatty acids and sterols. We conclude 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.