Chlorophyll d Synthase
An enzyme that carries out the conversion of chlorophyll a to chlorophyll d has been identified.
Until recently, all oxygenic photosynthetic organisms had been found to contain chlorophyll a as their major photopigment. The light absorption properties of chlorophyll a limit the range of wavelengths of light that can be absorbed to the visible range, 400 nm to 700 nm. All solar radiation outside that range is not absorbed and is therefore not able to be utilized, limiting the efficiency of photosynthesis. However, a novel cyanobacterium that contains Chl d instead of Chl a, Acaryochloris marina, was discovered in 1996. Chl d has similar chemical structure as Chl a except that a formyl group on C3 replaces the vinyl group in Chl a. The formyl group in Chl d leads to its unique spectral properties. Organisms that contain it effectively absorb radiation out to 740 nm, where other chlorophylls cannot absorb. This provides access to an additional region of the solar spectrum 700-740 nm. The mechanism of biosynthesis of Chl d has until now been completely unknown.
Our work has revealed the enzyme that is responsible for the synthesis of Chl d. The addition of the gene that codes for this enzyme to other oxygenic photosynthetic organisms has the potential to increase their ability to absorb and utilize this additional region of the solar spectrum.
This could lead to significant improvements in agricultural efficiency or bioenergy storage. It may also be useful for remote sensing and detection of plants that contain this unique pigment.
Transgenic plants, algae or cyanobacteria that have had the gene inserted for chlorophyll d synthesis may have higher energy conversion efficiency because they can use a larger portion of the solar spectrum than current organisms used for agriculture or bio-energy. Unique spectral property of Chl d provides potential application in monitoring GM crops or as detecting target.
- Dr Min Chen
- Prof. Robert Blankenship
- A/Prof. Robert Willows