Question

Which of the following is the symplastic pathway for the movement of sucrose from the site of photosynthesis in mesophyll cell into the phloem?

• A. Fibers, phloem parenchyma, companion cell, sieve tube
• B. Phloem parenchyma, fibers, bundle sheath, tracheids
• C. Companion cells, phloem parenchyma, companion cell sieve
• D. Bundle sheath, phloem parenchyma, fibers, sieve tube

Answer 1

The correct option is A Fibers, phloem parenchyma, companion cell, sieve tube

Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose across plant organs through phloem. For transportation, protons are actively transported by means of energy currency ATP then it re-enters by means of facilitated diffusion.
Photosynthates are produced in the mesophyll cells of photosynthesizing leaves. From there, they are translocated through first to the phloem fibres then phloem parenchyma, where they stored or used if required. From the companion cells, the sugar diffuses into the phloem sieve-tube elements through the plasmodesmata that link the companion cell to the sieve tube elements. Hence, correct order is: Fibers, phloem parenchyma, companion cell, sieve tube.