Aquaporins in guard cells mainly facilitate:
Correct option is C, Water transport. In STOMATA MOVEMENT problems like this, the accurate statement is Water transport; the others are common mix-ups. Not these: A) Ion transport; B) Sugar transport; D) ATP transport. Tissue transport questions usually turn on xylem vs phloem, living vs dead cells, or source vs sink.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.