Molecular analysis of chloroplasts made it possible to find out exactly when they were in the protoplant cell and where this unique event took place, which changed the face of the entire planet.
Chloroplasts allow plants to capture the energy of the sun and use it to combine water and carbon dioxide molecules into sugar molecules. These intracellular organelles are distant and severely degraded descendants of cyanobacteria, a blue-green alga that was once captured by the "protoplant" cell and gradually associated with it. Fantastic symbiosis provided one side with a universal source of resources, the other - a stable habitat and complete protection.
The authors of a new article published by the journal Proceedings of the National Academy of Science have clarified some details of the distant moment when this union happened. Indeed, it is still unknown which cyanobacterium became the ancestor of chloroplasts, and even under what circumstances and when exactly it was incorporated into another cell. Patricia Sánchez-Baracaldo and her colleagues at the University of Bristol used the “molecular clock” method to track the accumulation of changes in the biomolecules of chloroplasts, on the one hand, and cyanobacteria, on the other. This comparison indicated the time of their separation - about 2.1 billion years ago.
Apparently, this successful event really happened only once, and the descendants of the "double" cell took another 200 million years for the symbiosis to finally take shape. Judging by the properties of the proteins that the ancestor of chloroplasts had, their meeting took place in an almost unsalted reservoir, and the flowering of salt-loving algae, from which the beginning of plants was counted for a long time, began much later, only about 1.3 billion years later.