Photosynthesis without β-carotene.

Area of Science:

• Plant Biology
• Photosynthesis Research
• Biochemistry

Background:

• Carotenoids, including carotenes and xanthophylls, are vital for oxygenic photosynthesis, stabilizing pigment-protein complexes, harvesting light, and photoprotection.
• Previous research indicated carotenes are essential for photosynthesis, as no plants lacking them in photosystems could grow photoautotrophically.

Purpose of the Study:

• To investigate photoautotrophic growth in plants lacking carotenes.
• To characterize the function of photosystems in plants with only xanthophylls.

Main Methods:

• Generation of a tobacco mutant lacking carotenes, possessing only the xanthophyll astaxanthin.
• Assessment of photosystem functionality, non-photochemical quenching, and photosystem ratio regulation in the mutant.

Main Results:

• The astaxanthin-containing tobacco plant exhibited photoautotrophic growth, demonstrating fully functional photosystems despite the absence of carotenes.
• Photosystems were functional with astaxanthin occupying carotenoid-binding sites, and non-photochemical quenching occurred without zeaxanthin and lutein.
• The plant demonstrated a wide dynamic range in regulating the ratio of the two photosystems for optimized electron transport.

Conclusions:

• Carotenes are not essential for photoautotrophic growth or photosystem function in plants.
• Xanthophylls, specifically astaxanthin in this case, can substitute for carotenes in maintaining photosystem integrity and function.
• Plants possess sophisticated mechanisms to regulate photosystem ratios for efficient photosynthesis under varying conditions.