Plastids in corn

​Plant cell cytoplasm not only include mitochondria, those symbiotic organelles with their own DNA, that function to transform energy stored in glucose into ATP, but also another group of organelles called plastids.  Like mitochondria, these microscopic organelles have their own DNA organized in a circle for similar to bacteria. This along with other structural aspects has led to the speculation that a couple billion years ago a bacterial species developed a symbiotic relationship with a primitive single celled life form in which both organisms benefited.  The major contribution of plant plastid probably came from a cyanobacterium (blue-green algae) that became the chloroplast in plants.
 
Plastids, like mitochondria, are transmitted only through the egg cell and not the pollen of the plant.  Therefore, the plastid DNA is that of these organelles in the female parent of a hybrid. Plastid DNA may include only about 100 genes but they do include the ability to duplicate the plastid within a cell. Mutations within that DNA have been identified.  They remain dependent on the other plant genetics to provide the components for their structure and function. For example, albino plants are affected by cell nuclear chromosome mutations.
 
Chloroplasts are the plastids in which chlorophyll is formed and photosynthesis occurs.  These plastids have two outer layers of membranes as well as several folds of membranes on the inside.  Chloroplasts accumulate mostly in mesophyll cells which are those between the epidermal outer layer of cells and the vascular bundles of a corn leaf.  Each of these cells have many chloroplasts often organized on the side of the cell most exposed to the light.  Epidermal cells forming the stomata also have chloroplasts with the function of affecting the opening of the stomata, allowing transmission of CO2 into the leaf, and evaporation of water from the plant. Bundle cells surrounding the vascular tissue in a corn leaf also includes chloroplasts, contributing to the efficiency of this C4 photosynthetic system of corn.
 
There are plastids that do not have chlorophyll but function to store starch (leucoplasts) and other pigments (cyanoplasts).  Plastids are initially formed in a juvenile form in the embryo meristem of a corn seed.  These pro-plastids duplicate in meristem cells as the hypocotyl approaches the soil surface.  They have the molecular components of chlorophyll the final complex chlorophyll molecules are not formed until exposed to light as they emerge from the soil.
 
Much is happening within the new leaves emerging from the soil in the spring season.