Roles for calcium: numero uno

One important function of calcium is the part it plays in the water-splitting reaction of photosynthesis.
Image: Wikimedia Commons.
Image: Wikimedia Commons.

As an essential macronutrient calcium participates in many aspects of plant biology, e.g. structural roles in the cell wall, as a counter-cation for anions in the vacuole and as a so-called ‘secondary messenger’, where calcium signals participate in many developmental processes. But one function that has passed me by until now is the part it plays in the water-splitting reaction of photosynthesis.

Although all parts of photosynthesis are important, arguably the photolysis of water is the most important reaction in the process since it generates the hydrogen ions (protons) and electrons that participate in the ATP- and NADPH-generating activities of the light-dependent reactions of photosynthesis, which are fundamental to subsequent carbon-fixation in the light-independent stages (‘dark reactions’) of the process. Oh! And this photolysis also releases oxygen that accumulates in the atmosphere, and which is so essential to all aerobic life forms.

Whilst I was familiar with the idea that manganese (an essential micronutrient) is a major component of the water-splitting complex, I didn’t realise that calcium was too. However, although its presence there was known to others, its role was not (so I don’t feel so bad about my state of comparative ignorance…). But work by Emily Tsui et al. has revealed that calcium plays an important supportive role in allowing the manganese to transfer electrons away from the oxygen thereby facilitating the subsequent production of molecular oxygen.

Fascinating as this is in adding yet another role to the already extensive catalogue of calcium’s competencies, it is also hoped that this insight might help in the construction of artificial photosynthesis systems, with promises of renewable, cleaner energy. New light on an old topic: we like that!