Β-Cyclocitral Explained

β-Cyclocitral (beta-cyclocitral) is an apocarotenoid derived from the C7 oxidation of β-carotene. This apocarotenoid has revived interest due to its roles in plant development. β-cyclocitral has been found endogenously in a variety of organisms including plants, cyanobacteria, fungi and animals.^[1] β-Cyclocitral is a volatile compound that contributes to the aroma of various fruits, vegetables and ornamental plants.^[2] In plants, β-cyclocitral was found to be an important regulator in root development.^[3]

Application

β-Cyclocitral is used as an analytical standard for the determination of volatile organic compounds in saffron due to its analog structure to safranal.

Because β-cyclocitral is associated with cyanobacteria death, it is an analyte that can be tracked in bodies of water to monitor cyanobacteria blooms.^[4]

It has also been found to promote the growth of roots in rice, prompting its consideration as a potential agricultural tool.^[5]

Biosynthesis

The biosynthesis of β-cyclocitral relies on the formation of β-carotene through the isoprenoid biosynthetic pathway underpinning carotenoid formation. Similar to other apocarotenoids, the formation of β-cyclocitral can occur via the enzymatic and non-enzymatic oxidative cleavage of double bonds in β-carotene.^[6] For β-cyclocitral to form, the cleavage of C7-C8 double bonds are needed. While no enzyme has been identified to have high specificity for the production of β-cyclocitral, a carotenoid cleavage dioxygenase (CCD4) has been identified as being capable of cleaving β-carotene at the needed position.^[7] 13-lipoxygenase (LOX2) has also been identified to cleave β-carotene at the C7 position.^[8] β-cyclocitral can also be formed from the direct oxidation of β-carotene by reactive oxygen species, especially singlet oxygen (¹O₂). In plants, ¹O₂ is mainly produced from excited chlorophylls in the reaction center of PSII where β-carotene serves to quench the reactive oxygen species.^[9]

Notes and References

1. Havaux . Michel . October 2020 . β-Cyclocitral and derivatives: Emerging molecular signals serving multiple biological functions . Plant Physiology and Biochemistry . 155 . 35–41 . 10.1016/j.plaphy.2020.07.032 . 32738580 . 220925143 . 0981-9428. free .
2. Condurso . Concetta . Bioactive volatiles in Sicilian (South Italy) saffron: safranal and its related compounds . Journal of Essential Oil Research . October 2016 . 29 . 3 . 221–227 . 10.1080/10412905.2016.1244115. 100505185 .
3. Dickinson . Alexandra . May 2019 . β-Cyclocitral is a conserved root growth regulator. Proceedings of the National Academy of Sciences . 116 . 21 . 10563–10567. 10.1073/pnas.1821445116 . 31068462 . 6534974 . 2019PNAS..11610563D . free .
4. Huang . Heyong . Distributions of four taste and odor compounds in the sediment and overlying water at different ecology environment in Taihu Lake . Scientific Reports . 2018 . 8 . 8 . 6179 . 10.1038/s41598-018-24564-z . 29670292 . 5906450 . 2018NatSR...8.6179H .
5. Web site: Keeley . Jim . A Plant Hormone that Speeds Root Growth Could Be a New Agricultural Tool . Howard Hughhes Medical Institute . 6 June 2023.
6. Havaux . Michel . β-Cyclocitral and derivatives: Emerging molecular signals serving multiple biological functions . Plant Physiology and Biochemistry . 2020 . 155 . 35–41 . 10.1016/j.plaphy.2020.07.032 . 32738580 . 220925143 . free .
7. Maria . Rodrigo . A novel carotenoid cleavage activity involved in the biosynthesis of Citrus fruit-specific apocarotenoid pigments . Journal of Experimental Botany . 2013 . 64 . 14 . 4461–4478 . 10.1093/jxb/ert260 . 24006419 . 3808326 .
8. Gao . Lei . The tomato pan-genome uncovers new genes and a rare allele regulating fruit flavor . Nature Genetics . 2019 . 51 . 6 . 1044–1051 . 10.1038/s41588-019-0410-2 . 31086351 . 256819279 .
9. Triantaphylidès . Christian . Singlet oxygen in plants: production, detoxification and signaling . Trends in Plant Science . 2009 . 14 . 4 . 219–228 . 10.1016/j.tplants.2009.01.008 . 19303348 .