A model diagram of the regulation of astaxanthin synthesis by light-independent respiratory pathway. Credit: IOCAS
by Li Yuan, Chinese Academy of Sciences
A research team led by Prof. Liu Jianguo from the Institute of Oceanology of the Chinese Academy of Sciences has found that light-independent metabolic pathways, in addition to light-dependent metabolic pathways, can also regulate astaxanthin accumulation in Haematococcus. Their findings were published in Bioresource Technology.
Astaxanthin has multiple applications in nutraceuticals, pharmaceuticals and cosmetics owing to its strong colorant, antioxidant capacity and other biological functions. H. pluvialis, a unicellular green alga rich in astaxanthin, is recognized as the best biological resource for producing natural astaxanthin.
Traditionally, astaxanthin biosynthesis in H. pluvialis was considered to be induced mainly by high light and/or nutrient deficiency. Therefore, most previous studies on the regulation of astaxanthin biosynthesis and accumulation have been focused on the light-dependent metabolic pathways, such as photosynthesis and photoprotection. There are few reports on the role of light-independent respiratory pathways during astaxanthin accumulation.
In their studies, the researchers found that light-independent metabolic pathways, such as the Embden-Meyerhof-Parnas pathway, tricarboxylic acid cycle, pentose phosphate pathway and alternative oxidase respiratory pathway, also play important roles in regulating astaxanthin accumulation in Haematococcus.
“The activity of the mitochondrial alternate oxidase pathway has significant negative correlation with astaxanthin accumulation in H. pluvialis,” said Prof. Liu. Based on this discovery, a new viewpoint that regulating respiration would promote astaxanthin biosynthesis in H. pluvialis was first proposed in the study published on November 6.
The researchers also investigated the effects of exogenous respiratory metabolic intermediates on astaxanthin synthesis, and further proved that tricarboxylic acid cycle can provide carbon skeletons for astaxanthin biosynthesis in H. pluvialis.
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