although auxins get accumulated in the shady part why auxin decreases the rate of growth in roots??

Dear Student,

Auxin hormone increases the rate of growth in Shoots/Stems whereas its effect is opposite in Roots. This is because the side of the root which is away from the light will have all the auxin concentrated in that part. Hence, the side of the root which is away from the light will grow slower; thereby, bending the root away from the light.

Hope this information clears your doubts about the topic.

Keep asking!!

Regards