Finally, the enormous relevance of carbohydrate metabolism for short-term growth variations is also seen in roots. As mentioned above, plants with decreased activity of sucrose-phosphate phosphatase reacted much slower than wild-type plants towards an increase of light intensity (Nagel et al. 2006). Experiments with excised root systems, that continued growth—without being provided with photosynthates from the shoot—as long as sucrose was available from the growth medium, supported the hypothesis that carbohydrate availability is crucial for the intensity of root growth. A direct correlation of root growth intensity with carbohydrate concentration of the growth zone has also been described for Arabidopsis thaliana (Freixes et al. 2002). Yet, the small-scale distribution of growth across the root growth zone is not connected to carbohydrate concentrations, but probably regulated by carbohydrate deposition rates and deposition rates of other growth substrates such as mineral nutrients (Walter et al. 2003a).
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