What is the precursor of auxin?

Which of the following is the best explanation for the excurrent $(pyramidal)$ shape of $Pinus$ (the branches giving the plant the appearance of a tall cone)?

Auxins are abundantly produced in

$A$ green plant bends towards the source of light when exposed to light on only one side. Which of the following is the best explanation for this phenomenon?

Auxins promote

Auxin was isolated by ................ from tips of coleoptile of ....