A researcher simultaneously inhibited the activities of Triose-Phosphate Translocator (TPT) and Xylulose 5-Phosphate Translocator (XPT) in a plant and made the following assumptions:

A. Triose phosphate will be accumulated more in the chloroplast.
B. Triose phosphate will be accumulated more in the cytosol.
C. Xylulose 5-phosphate will be accumulated more in the chloroplast.
D. Xylulose 5-phosphate will be accumulated more in the cytosol.

Which one of the following combinations of the above assumptions is correct?

Correct option is B

• A is correct: Inhibition of TPT blocks the export of triose phosphate from chloroplast to cytosol, causing accumulation of triose phosphate inside the chloroplast.

• D is correct: XPT imports xylulose 5-phosphate from cytosol into chloroplast. When XPT is inhibited, xylulose 5-phosphate cannot enter the chloroplast and therefore accumulates in the cytosol.

Thus, triose phosphate accumulates in the chloroplast, and xylulose 5-phosphate accumulates in the cytosol when both translocators are inhibited.

Information Booster:

• Triose-Phosphate Translocator (TPT) exports triose phosphate produced by the Calvin cycle in chloroplasts to the cytosol for sucrose biosynthesis. Blocking TPT leads to chloroplastic accumulation of triose phosphate.

• Xylulose 5-Phosphate Translocator (XPT) imports xylulose 5-phosphate into the chloroplast from the cytosol, important for the pentose phosphate pathway. Its inhibition causes cytosolic accumulation of xylulose 5-phosphate.

• These translocators are critical in maintaining carbon flow between cellular compartments.