Lumination Incorporation
Turbocharge Photosynthesis
Effects of Light on Chlorophyll Accumulation
In plant mitochondria, electrons travel along an electron transport chain in order to reduce oxygen to water. This process is facilitated by oxidases.
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Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain as shown in the image below. Chlorophyll accumulation was observed to be largely delayed in plants with the AOX gene inhibited. This delay was most significant under intense light conditions. This delay of chlorophyll accumulation also corresponded to an increase of the plastid NADPH/NADP+ ratio, which subsequently blocked the import of multiple plastidial proteins key to the photosynthesis. This thus suggests that chlorophyll accumulation is decreased as light intensity increases as the delay of chlorophyll accumulation is increased as light intensity increases, hence chlorophyll synthesis is affected by light intensity during the greening process by the AOX-derived plastidial NADPH/NADP+ ratio change.
Image 1: The role of AOX in the electron transport chain, providing an alternative route for electrons passing through the transport chain to reduce oxygen. Q is ubiquinone and C is cytochrome c.
When the AOX gene is inhibited, the plant is also more suspectible to cyanide poisoning. Other than AOX, cytochrome c oxidase (COX) is also able to donate the electron to the oxygen to facilitate the chemiolysis of water during photosynthesis. However, COX is suspectible to non-competitive inhibition by cyanide, preventing photosynthesis from occuring. The following images below showcase how cyanide prevents the chemiolysis of water in cells (Image 2), and also the effects of cyanide posioning on the cell (Image 3).
Image 2: The role of AOX, shown within the larger context of photosynthesis and aerobic respiration, showing its relationship with cytochrome c oxidase (COX). Both COX and AOX are able to transfer electrons to the final electron acceptor (oxygen) to produce water. Unlike AOX, COX is susceptible to non-competitive inhibition by cyanide.
Image 3: The effects of cyanide on aerobic respiration. Unlike COX, AOX is resistant to cyanide inhibition, hence reducing an organism’s susceptibility to cyanide poisoning.
Impacts and Applications
As mentioned before, high light intensity increases the rate of photosynthesis, however it also increases the plant's susceptibility to cyanide poisoning. Thus, we could set up two different environment conditions, one utilising a high light intensity and hence ensuring a high yield of nutrients and starch content, while the other utilising a low light intensity, preventing plants without an encoded AOX gene from developing cyanide poisoning and dying as a result of the lack of photosynthesis in the plant. The image below highlights the negative impact of high light intensity on a plant with an inhibited AOX gene as its ability to photosynthesise would be compromised.
Image 4: The effect of light intensity on the amount of NADPH and the ratio of NADPH to NADP. In general, high light levels resulted in the greatest difference in the NADPH/NADP ratio.
In addition, we could genetically engineer our crops to be all resistant to cyanide poisoning by replacing the inhibited AOX gene with an uninhibited version of the gene, thus turbocharging the rate of photosynthesis of the plants as they would be less suspectible to cyanide poisoning.