Influence of phloem transport, N-fertilization and ion accumulation on sucrose storage in the taproots of fodder beet and sugar beet
1996
Winzer, T. | Lohaus, G. | Heldt, H.W.
To investigate the factors governing the accumulation of sucrose and amino acids in the taproots of sugar beet, their contents were measured in the leaves, phloem sap and the taproots of sugar beet, fodder beet and a hybrid between both, grown on either 3.0 or 0.5 mM nitrate. In the taproots the contents of malate, citrate and inorganic ions were also determined. For the high sucrose accumulation in sugar beet as compared to the other varieties three factors were found. (a) In sugar beet, less amino acids and more sucrose are taken up into the phloem than in fodder beet. (b) In sugar beet, the sucrose and amino acid syntheses are less sensitive to the nitrate concentrations that are required for optimal plant growth than in other varieties. In fodder beet, upon raising the nitrate concentration from 0.5 mM to 3 mM, the synthesis and storage of sucrose is decreased and that of amino acids increased. The corresponding values in sugar beet (0.5 mM) are similar to those in fodder beet and are not much affected by an increase of nitrate. (c) The sucrose accumulation is limited by the accumulation of inorganic ions in the taproots. The sucrose content in the taproots is negatively correlated to the total ion content. Whereas sucrose represents two-thirds of all solutes in the taproots of sugar beet, it amounts to only one-third of the solutes in fodder beet taproots.
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