Mechanism of Phloem Transport

Mechanism of Phloem:

The process of translocation of food has been explained by different scientists through different theories:

i. Munich (1930) showed that the leaves act as the source of food and so have a higher concentration of food in them. From the leaves, it easily reaches the regions of lower concentration with the help of diffusion pressure. This process was referred to as Bulk Flow.

ii. Curtis (1935) showed that the sieve tubes of phloem tissue contain cytoplasmic strands, which may connect adjacent sieve tubes through sieve pores. Translocation of food takes place in both upper and lower directions through these strands by cytoplasmic streaming movement.

iii. Fension and Williams (1974) considered the cytoplasmic strands within the sieve tubes as protein fibres. These fibres were called P-protein and has a diameter of 2μ. They thought that contraction and relaxation of these fibres help in the upward, downward and even lateral translocation of food.