Another membrane component of the corn cell in the seed embryo is the chloroplast. A few billion years ago, a bacterium species had an inner membrane layer that could capture energy from light while releasing oxygen. We know these organisms as blue green algae but their single circular chromosome and membrane structure classifies them as Prokaryotes instead of a Eukaryote, like the nucleus-containing algae. Perhaps a billion years ago, these photosynthesis- producing single-celled organisms gained a symbiotic relationship in other single cell organisms and, with that event, the algae and the rest of the plant kingdom had begun. Chloroplasts have their own bacteria-like chromosome, with its own DNA, and are filled with membranes in which photosynthesis occurs.
Having their own DNA, RNA and ribosomes, chloroplasts function as an independent organism in that they can divide and produce proteins, but their symbiotic relationship with the cell still depends greatly on proteins and lipids from the host cell. The single chromosome of chloroplasts has only about 100 genes as the nuclear genes of the host supply much (95%?) of the protein for their function. Chloroplast DNA can have mutants but this is uncommon.
Chloroplasts, like mitochondria, are transmitted to the new embryo only through the female parent of seed. Protoplastids in the egg cell and, later in the developing seed, can multiply but do not produce pigments or become photosynthetically active until exposed to light in leaf tissue after germination. Plastids in cells destined to become part of non-photosynthetic tissue such as kernel endosperm, stem and root parenchyma cells generally become starch storing components of cells. Membranes structure and function of plastids are essential to the life of the corn seed.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.