Plant Cuttings

Chloroplasts are how old???

Image: Mariana Ruiz Villarreal/Wikimedia Commons.
Image: Mariana Ruiz Villarreal/Wikimedia Commons.

It is widely acknowledged that eukaryotic cells (you know, the ones with a membrane-bound nucleus and a variety of other membrane-bound organelles (cf. prokaryotes)) came to be so complex by a series of ‘mergers and acquisitions’ that saw a prokaryote-like cell internalise other, smaller ‘cells’ to gain organelles such as mitochondria and chloroplasts. That is the essence of the Serial Endosymbiotic Hypothesis/Theory. But have you ever wondered how long ago such events took place? Well, Patrick Shih and Nicholas Matzke have done so on our behalf .

Using ‘cross-calibrated phylogenetic dating of duplicated ATPase proteins’ (which are retained by mitochondria and chloroplasts and involved in energy production in both), the duo’s results suggest that primary plastid endosymbiosis (which eventually gave us plant cells) occurred approximately 900 Mya (millions of years ago), whereas mitochondrial endosymbiosis occurred around 1200 Mya. Interestingly, both authors contributed equally to this work, and both were PhD students at the time! I’d so like one of the authors to have done the mitochondria work, and the other to have been ‘responsible’ for chloroplasts; that would make for a pleasingly symmetrical, modern-day parallel to the 19th century’s Cell Theory, largely attributed to Schleiden (‘botanist’) and Schwann (‘zoologist’). Way to go, gentlemen!

[Please don’t construe Mr Cuttings’ comments about putative parallels with Schleiden and Schwann to mean that only animal cells have mitochondria, and only plant cells have chloroplasts; plant cells can contain both (yes, so they are better than animals…)! – Ed.]