Translocation in the phloem occurs in both upward and downward directions, allowing nutrients to be distributed throughout the plant as needed. This process is facilitated by the pressure gradient established between source and sink tissues, as well as by active transport mechanisms in companion cells.
In which directions does translocation occur in the phloem, and how is it facilitated?
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Translocation in the phloem occurs bidirectionally, involving both upward and downward movement of sap within the plant. The movement is driven by pressure flow mechanism. In source tissues (like leaves), where sugars are produced during photosynthesis, high turgor pressure is generated by the active loading of sugars into the phloem. This creates an osmotic pressure gradient. The phloem sap, containing sugars and other nutrients, then moves towards sink tissues (such as roots, developing fruits, or other growing regions) with lower turgor pressure. This bidirectional flow allows plants to efficiently distribute organic compounds to meet various metabolic and growth needs.