Coleoptile emerges!

Elongation of cells in the mesocotyl pushes the corn seedling coleoptile towards the soil surface. Cells in the coleoptile are also elongating as it grows upward but cell function changes drastically when light strikes the emerging coleoptile.  Meanwhile the immature leaves encased by the coleoptile are also slowly enlarging.  Almost immediately after the coleoptile is exposed to light, hormones are produced that essentially shut down the mesocotyl growth. Other plant hormones, auxins, are produced in the shoot tips and transported to the node at the bottom of the coleoptile, stimulating the growth from root primordial cells to produce the secondary root system.  Movement of this auxin in the opposite direction of the flow of water from the soil requires energy, as it must go from individual cell to cell.  That energy is now being supplied by photosynthesis occurring initially in the emerged coleoptile and then by the new leaves that pushed out of the coleoptile enclosure. Previous to emergence, energy for growth was supplied by the seed endosperm and influenced by heat. Water supplied by osmotic pressure in the primary root tissue allowed for cell elongation in the mesocotyl. Now with exposure to light, a new source of energy moves the seedling to new phases of development above and below the soil surface.  Mesocotyl significance to the seedling reduces as the above soil structures take over the physiology of the young corn plant. This transition does allow the plant to be vulnerable to negative temperature, moisture and pathogen affects but if everything goes right, the mesocotyl remains intact until the secondary roots function as the main supplier of water and nutrients for above ground growth of the seedling.