Nitrate is a negative signal for fructan synthesis and the fructosyltransferaseinducing trehalose inhibits nitrogen and carbon assimilation in excised barley leaves.
Fructan biosynthesis in barley has been shown to be up-regulated by sugar signalling and down-regulated by nitrogen. We have investigated the relationship between these two regulations. • Excised third-leaves of barley were fed nitrate or glutamine under two light intensities. Other leaf blades were supplied in the dark for 24 h with nitrate and trehalose in the presence of validamycin A, a trehalase inhibitor. • In the light, nitrate, but not glutamine, decreased fructan contents and sucrose:fructan 6-fructosyltransferase protein without affecting the levels of sucrose and other carbohydrates. In darkened leaves, trehalose increased and nitrate decreased the fructan contents and total sucrose:fructosyltransferase activity without altering the concentration of sucrose. The effect on fructan contents of trehalose disappeared, while that of nitrate still remained in subsequent incubations in water under light. Trehalose decreased and nitrate increased the light- and CO2-saturated rate of photosynthesis without significantly affecting the initial Rubisco activity. Trehalose feeding decreased the activation of Nitrate Reductase and amino acid levels, and blocked the positive effect of nitrate on the maximal activity of this enzyme. • The results indicate that nitrate, and not a down-stream metabolite, is a negative signal for fructan synthesis, independent from the positive sugar signalling and overriding it. Trehalose signalling inhibits nitrogen and carbon assimilation, at the same time inducing fructosyltransferase activity.
| Main Authors: | , , , , |
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| Format: | artículo biblioteca |
| Language: | English |
| Published: |
Blackwell Publishing
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| Subjects: | Barley, Fructan, Fructosyltransferase, Nitrogen, Nitrate, Regulation,, Trehalose, |
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