Typically, binary fission—an asexual reproduction method that permits a cell to split, reproduce, and create new cells with specific functions—is how plants, animals, and a wide variety of fungi develop.
However, not all macrosopic creatures follow the rules. Several huge seaweeds are among the largest single cell systems known, such as the leafy green algae Caulerpa, which lacks tiny dividing mechanisms.
These plant cousins may still reach lengths of meters, and since they are so adept at absorbing sunlight to grow, they have successfully colonized several new areas.
But while the body is essentially one big cell, what controls the process of growth?
Eldad Afik, a biological engineer at the California Institute of Technology, and associates cut off portions of the Caulerpa brachypus species to see how it regrows in order to find out.
“A main paradigm in cellular biology is that the internal environment of a cell is dictated by its environment and what happens in the nucleus,” Afik states.
“But in Caulerpa, there’s nothing to separate the nuclei from one another.”
Despite lacking walls and membranes to separate its several nuclei, this fascinating creature organizes itself into structures resembling organs, such as leaves, stems, and roots.
The researchers observed variations in the level of green pigmentation at the algae’s regeneration sites after chopping off sections of the algae. These patches become a solid, impenetrable green during the day, but at night they were rather clear.
According to earlier studies, this shift in hue may be the consequence of chlorophyll processing light coming into and leaving the area. Afik and his group set out to ascertain whether the movement of the chlorophyll was, in fact, a reaction to light.
The researchers observed that the leaves of C. brachypus specimens exposed to 12 hours of bright light and then 12 hours of darkness grew longer than those of specimens exposed to bright light for a full 24 hours. This suggests that a night of “sleep” is necessary for the algae to maintain their self-organization.
Sections of Caulerpa’s body filled with a green wave of chlorophyll when exposed to light, enabling it to photosynthesize and grow. This green wave seemed to collapse at night, when the algae took a nap.
What’s really amazing, though, is that the algae seemed to be able to predict when day and night would arrive. The algae may have an inherent circadian rhythm that it exploits for growth and development, as evidenced by the fact that its chlorophyll activity changed even before the altered light conditions became apparent.
“We find distinct morphologies depending on light temporal patterns, suggesting waves of chlorophyll could link biological oscillators to metabolism and morphogenesis,” the authors of the report state.
As they multiply in rhythm with the day-night light cycle, the green chloroplasts give the massive blob a feeling of location.
As a result, algae can decide when and where to grow—the equivalent of knowing its head from its butt. ‘Cells’ are not needed.
The findings of this study were released in Nature Communications.