Correct option is B
EXPLANATION-
Statement A: "It proceeds via symplast."
Symplast means movement through the cytoplasm of cells connected by plasmodesmata. Polar auxin transport primarily involves cell-to-cell transport across plasma membranes, not just free movement via symplast. The process is more controlled and directional, mediated by specific proteins rather than simple cytoplasmic flow.
Hence, Statement A is incorrect.
Statement B: "Its velocity is faster than the phloem translocation rates."
The velocity of polar auxin transport is typically slower compared to phloem translocation. Phloem translocation (movement of sugars and nutrients) is generally rapid due to pressure flow. Auxin transport is slower because it relies on carrier proteins moving auxin molecules stepwise.
Hence, Statement B is incorrect.
Statement C: "It is specific for active auxins, both natural and synthetic."
Polar auxin transport shows specificity towards active forms of auxin, such as indole-3-acetic acid (IAA) and some synthetic auxins. This specificity is important for correct physiological responses.
Hence, Statement C is correct.
Statement D: "It is mediated by protein carriers on the plasma membrane."
Polar auxin transport depends on auxin influx and efflux carriers embedded in the plasma membrane. These proteins actively transport auxin molecules across cells, ensuring directional flow. Examples include PIN proteins (efflux carriers) and AUX1/LAX proteins (influx carriers).
Hence, Statement D is correct.
So, the correct option is (b) - C and D only.
