Interaction between Phloem transport and Apoplastic Solute Concentrations
In addition to several other physiological functions, the apoplast is involved in phloem loading of many plant species. Therefore, apoplastic solute concentrations influence phloem transport of solutes and vice versa. For studying this relationship it is necessary to know apoplastic solute concentrations as well as that in the phloem sap. Phloem sap was collected with the laser-aphid-stylet technique. Until now this is the best possibility to collect pure phloem sap from intact plants. The analysis of apoplastic fluids is more difficult because one of the major problems in any approach to study apoplastic ion relations is the method by with apoplastic solution is obtained. Several methods to analyse apoplastic fluids have been developed but all these methods have special advantages and disadvantages. We used the infiltration-centrifugation technique and made a critical evaluation of different parameters which influence the solute concentrations in the apoplast.
Plant growth and development are dependent on translocation of photoassimilates from the sites of synthesis to the sites of consumption or storage. In addition, substantial amounts of solutes transported to the leaves in the xylem are re-translocated in the phloem. This is also true under different stress conditions like salt stress. Approximately 13–36% of the Na+ and Cl- imported into the leaves through the xylem were exported by the phloem. It is concluded that phloem transport plays an important role in controlling the solute content of a leaf.
Key wordsapoplastic solute concentration infiltration-centrifugation technique laseraphid-stylet technique phloem salt stress translocation xylem
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