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Saturday, 12 January 2019

Translocation of Food

 Food is made mainly in the green leaves of a plant. This food must be sent to all the living plant cells, especially those in the actively growing regions such as the root tips, stem, stem tips and buds. Plants usually make excess food, which must be sent to the storage organs.

      Scientists have shown that the living phloem cells translocate organic substances. In some of their studies, they exposed plants to carbon dioxide labeled with radioactive carbon. These labelled atoms were incorporated into sugars. When sections of the stem were cut, radioactivity was present only in the phloem tissues and not in the xylem. This indicated that organic substances are translocated in the phloem.

        Aphids have also been used to study the contents of phloem tissues. Aphids are plant parasites which pierce the stems of plants with their proboscises and feed on the juice they get from the phloem tissues. Actively feeding aphids were killed and cut off at the proboscises, close to their head ends. The juice that flowed from the cut end of the proboscises, which were still embedded In the plant stem, was analysed and found to be rich in sugars and amino acids.  
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