Vascular bundles

​Corn vascular system not only transports leaf products to other parts of the plant, and water and minerals from the roots but has specialized cells that contribute to corn’s advantage as in photosynthesis.  In most plant species, chloroplasts in the mesophyll cells capture CO2 and using light energy and a series of enzymes to produce for C3 molecules that are fused to make sugar (C6H12O6.).  The potential weakness comes when the stomates are closed at night or during moisture stress causing a process called photorespiration in which instead of utilizing CO2, the system starts consuming oxygen. This not only needlessly uses energy it limits the capacity of the chloroplasts to maximize the light energy capture.  Most plant species belong to this C3 photosynthesis system.
 
Some species, including corn, have evolved a system to avoid this wasteful system.  Chloroplasts in the corn leaves make normal photosynthesis process but then break down the C3 molecules, have them transfer them to the specialized, vascular bundle cells surrounding the vascular system that are loaded with special chloroplast for C4 molecules.  These molecules are then enzymatically combined to make sugar which is moved elsewhere in the leaves and other parts of the plant.  This system occurs in species that are native to dry, hot environments such as that of corn’s central America origin.  The ultimate advantage is that corn can continue to produce carbohydrates despite environments that cause stomates to close.  Whereas most C3 plants such as soybeans, wheat and rice do not utilize light intensity greater than 3000 foot-candles, corn photosynthesis rate keeps increasing with light intensities to our maximum sun brightness of 10000 foot-candles.  Those few cells surrounding the xylem and phloem of a corn leaf vein have a special role in allowing the photosynthetic efficiency of maize.
 
Those folks in Mexico that selections from Teosinte did not know about C4 photosynthesis but we have benefited from 10000 years of selections leading to what we call corn (or maize).