Question

Describe an activity to show that phloem is responsible for translocation of solutes​

Answer 1

Answer:

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The experiment is to be performed with a woody plant in which the apical growth has ceased. It is best performed in growing season. One or more stems or branches are selected which have no side branch for 50 cm or more and which are several centimeters in diameter.

Ring is made by removing the bark and phloem tissue approximately in the middle of the clear portion. The removed rings of bark should be about 1 cm wide and ringing should be done carefully so that the xylem is not damaged.

The exposed surface of the xylem should be carefully scrapped with a sharp knife so that all traces of cambium are removed. The ex­posed surface is covered with paraffin wax. After three weeks, final growth measurements are taken.

Sections are cut 25 to 50 cm from the regions immediately above and below the ring and following data are taken:

(i) Sections from just above and just below the ring are tested for starch with iodine solution and compared.

(ii) The volumes of 100gm of tissue from below and above the ring; is determined by displacement of water and compared.

(iii) The percentage of dry matter in each tissue is determined and compared.

Results:

Results are tabulated or plotted to show the effect of ringing upon translocation of food material based on the above three indices.

Discussion:

Food materials are synthesized in leaves and translocated downwards through the phloem. Removal of phloem tissue hampers this downward translocation and accumulation of food materials above the ring occurs. This experiment indicates that organic solutes flow downward through the phloem into root and other organs, when the above the indices below and above the ring are compared.