Roots and hormones in maize

Primary roots, developing from the corn seed are temporary. Direction of the growth downward is affected by auxins originating in the growing embryo.  By the time the first leaves emerge to light, however, much of the auxin production comes from the leaf tips. These plant hormones, along with a few others, are transported quickly through the phloem sieve cells along with carbohydrates and protein, to the root tips, uninhibited by cell membranes. Root tip cells, with less developed cell walls but with membranes do require active transport, and energy, to move the auxins into these newly developing cells.
 
Root tips cells are meristematic, dividing and producing new cells at a near constant rate in corn up until pollination.  New cells on the outside layer (epidermis) of the root are stimulated by the auxins to produce lateral extensions called root hairs.  These cell extensions large vacuoles allow active osmosis effectively increasing the absorption of water and minerals. Root hairs only remain active for a 2-14 days, but the continuously dividing root tip cells produce new ones in the newest epidermal cells. Movement of auxins to the epidermal cells does involve other hormones and proteins with several genetics with several environmental influences.  For example, studies have shown that decreasing soil moisture results in production of more root hairs in corn.  Given the wide genetic variability of corn, surely varieties differ in this response.