Corn leaf epidermis

​Cell division in the meristem establishes the eventual structure of the new leaves unfolding in the young seedlings.  Corn has several unique leaf structures that contribute to it’s ability to be one of the most efficient crops in capturing CO2 from the atmosphere.  One contributor is part of the epidermis. 

The single layer of cells on both the top and bottom of corn leaves are mostly non-pigmented cells tightly bound together, restricting water loss (Top two illustrations on right are from https://lima.osu.edu/academics/departments/biology/plant-anatomy/leaves.html).

Further protection comes from a wax covering the outside of these cells.  The exception to this tight wall structure comes from some unique cells interspersed within the epidermis on both sides of the leaf.  These cells not only have chloroplasts with chlorophyll but are shaped differently.  The two guard cells of the stomata are shaped in a manner that the allows only one side of each cell to swell with water, with the affect of making a small pore in the epidermis between the two cells.  The swelling occurs during photosynthesis within these cells.  This process essentially results the import of potassium ion into the cells, causing an increase of solutes and thus, through osmosis, transfer of water into the cells. The result is stomata pores are open (https://plantstomata.wordpress.com).

This is essential, of course, to allow diffusion of CO2 into leaves for photosynthesis in other leaf cells. Open stomates allows O2 to be released to the atmosphere but also water loss. Water evaporation through stomates (transpiration) is affected by the relative humidity in surrounding atmosphere as the water concentration within the leaf spaces is nearly 100%. Cohesiveness of water molecules ‘pulls’ water up to the leaves so that essentially every molecule of water that goes out the stomata is replaced by one from the root tissue.
 
During the day, stomata are open, carbon dioxide moves into the leaf, oxygen moves out and so does water.  At night, photosynthesis in the guard cells stops, water moves out of the guard cells causing the swelling to be reduced and the pore is closed.  We will discuss more about this phenomenon later as the plants grow.