Water and corn biology

Water has a complicated interaction with corn physiology and function. It moves through root hairs via osmosis, water moving from a high concentration through cell walls where sugars and minerals reduce the water concentration.  It is a physical phenomenon.  Osmosis further causes water molecules to move to the xylem vessels.  This pressure pushes water up the vessels. Leaf stomata open during the day because photosynthesis in the two curved cells surrounding the produce sugars resulting is swelling, again due to osmosis drawing in water.  This causes opening to the air, allows movement of CO2 into the leaf and oxygen into the air. Water evaporates in the opening below the stomata, moving into the air, again moving by relative concentration of water molecules. Dry and windy air increases the rate of transpiration.  Water molecules tendency for cohesion, causes water to be pulled upwards, as each molecule transpires through the stomata is replaced by a molecule pulled from the xylem.  It's a push from below the soil surface and a pull through the stomata that moves water through the plant. 
 
During cell elongation, before flowering in corn, water movement into new cells largely determines length of cells and ultimately affects plant height. At flowering, this cell elongation process become critical to the timing of ear silks pushing out of ear husk tissue for exposure to pollen.  Pollen production and distribution is less dependent on water concentration and therefore timing of pollen and exposure of silk may not match.  Poorly pollinated ears are the result of drought conditions.
 
Photosynthesis utilizes water as H2O is combined with CO2 to make glucose (C6H12O6).  Drought conditions during the growth period can reduce ultimate leaf area and thus photosynthesis. Severe drought can result in stomata not opening, reducing the CO2 available but this appears to be most significant before pollination. The biggest cause of grain yield loss from drought stress is not reduction of photosynthesis but it is the lack of place to put its products.
Movement of the glucose from the leaf tissue to grain is determined mostly by the hormones produced in the newly formed embryos in the pollinated ovules.  Lack of water reduces elongation of silk causing them not to be exposed to pollen and consequently fewer embryos.  Sugar molecules accumulate in leaf tissue, triggering production of anthocyanins in leaves, turning the leaves red.  The pigment change reduces photosynthesis.
 
Corn biology is dependent upon adequate water supply for nearly all functions from being a solvent for movement of sugars and minerals, providing turgor pressure for cell expansion, a coolant as it evaporates from leaf tissue and contributor to photosynthesis.