Thursday, July 17, 2014

Where Do Chloroplasts Come From in Non-Plant Organisms?



Armchair Science is a Kindle ebook available at Amazon. It contains over 120 short mysteries of science that can be solved from a single observational clue, without the need for experimentation.



Science is not a collection of facts. Science is what facts teach us; what we can learn about our universe, and ourselves, by deductive thinking. From observations of the night sky, made without the aid of telescopes, we can deduce that the universe is expanding, that the universe is not infinitely old, and why black holes exist. Without resorting to experimentation or mathematical analysis, we can deduce that gravity is a curvature in space-time, that the particles that compose light have no mass, that there is a theoretical limit to the number of different elements in the universe, and that the earth is billions of years old. Likewise, simple observations on animals tell us much about the migration of continents, the evolutionary relationships among classes of animals, why the nuclei of cells contain our genetic material, why certain animals are long-lived, why the gestation period of humans is 9 months, and why some diseases are rare and other diseases are common. In “Armchair Science”, the reader is confronted with 129 scientific mysteries, in cosmology, particle physics, chemistry, biology, and medicine. Beginning with simple observations, step-by-step analyses guide the reader toward solutions that are sometimes startling, and always entertaining. “Armchair Science” is written for general readers who are curious about science, and who want to sharpen their deductive skills.

Here is an excerpt from the book:

Clue 87. Plant chloroplasts are wrapped in a 2-layer membrane. Chloroplasts in organisms other than plants are wrapped in membranes of 3 or 4 layers.

Deduction. Non-plant chloroplasts were stolen from plant chloroplasts.



Illustration. Various organisms of the order Desmidiales, the green algae. The tiny green granules are chloroplasts. Source: Painting by artist and naturalist Ernst Heinrich Philipp August Haeckel (1834-1919).

Resolution. Archaeplastida is the superclass of organisms that contains all plant life on the planet, and every species of Archaeplastida either contains chloroplasts or has derived from a species that contained chloroplasts (i.e., organelles in which oxygenic photosynthesis occurs).

Chloroplasts are self-replicating cytoplasmic organisms, somewhat analogous to the mitochondria in human cells. It is presumed that the chloroplasts in plant cells were originally acquired when a primitive eukaryotic organism (i.e., a non-bacterial organism) that engulfed a cyanobacteria. All plant species are descendants of the original eukaryotic cell that captured the one cyanobacteria that adjusted to a new existence within that eukaryotic cell.

All chloroplasts in all plant species are wrapped by two membrane layers: one layer presumably contributed by the captured cyanobacteria, and one layer presumably contributed by the eukaryotic cell as it wrapped the cyanobacteria in its own cell membrane.

Plants are not the only organisms to contain chloroplasts. Chloroplasts are found in a variety of eukaryotic species that are not members of Archaeplastida, the ancestral class of plants. How did non-plant species acquire an organelle that evolved as a characteristic feature of the plant kingdom? It seems that the non-plant organisms that contain chloroplasts simply stole their chloroplasts from other organisms, including plants. Whereas the chloroplasts of plants always have exactly two membranes, the chloroplasts of non-plant organisms have three or four membrane layers, suggesting that an organism containing chloroplasts was engulfed, and the double membranes of the chloroplast plus the membranes of the engulfing organisms, were entrapped in the process.

Is there any reason to think that organisms go about stealing organelles from other organisms? It seems that plant chloroplasts can be acquired by contemporary organisms through a process called kleptoplasty. The kleptoplastic cell captures a chloroplast from an algae and uses the captured chloroplast for a short period (a few days to a few months) until the chloroplast degenerates. These chloroplasts not self-replicating. When new chloroplasts are needed, the kleptoplastic organism simply ravages another colony of algae. The sacoglassan sea slug, has achieved a photosynthetic life-style, all thanks to kleptoplasty.

There is some evidence to suggest that we may be witnessing a repeat of the process by which a primitive eukaryote stole a cyanobacteria, initiating Class Archaeplastida. Paulinella chromatophora, a member of the eukaryotic class Rhizaria, seems to have captured its own cyanobacteria and created its own permanent chloroplast-like organelle (1).

References.

1. Nowack EC, Melkonian M, Glockner G. Chromatophore genome sequence of Paulinella sheds light on acquisition of photosynthesis by eukaryotes. Curr Biol 18:410-418,

I urge you to read more about this book. There's a good "look inside" of the book at the Amazon store.

- Jules J. Berman, Ph.D., M.D.

tags: deductive science, science mysteries, deductive reasoning, ebook, general science reading, general science book, science puzzles, scientific amusements