Violaxanthin cycle

Yamamoto, H. (1979). Biochemistry of the violaxanthin cycle in higher plants. PureAppl Chem 51 639-648. 

Havaux M, Niyogi KK. The violaxanthin cycle protects plants from photooxidative damage by more than one mechanism. Proc. Natl. Acad. Sci. U.S.A. 1999 96 8762-8767. 

Isolated lettuce chloroplasts could epoxidize zeaxanthin in the presence of reduced pyridine nucleotides and oxygen and the process was stimulated by bovine serum albumin (which protected the epoxidase system from inhibition by fatty acids). Detailed study led to the conclusion that the epoxidase was an external monoxygenase and that the violaxanthin cycle (of which epoxidation of zeaxanthin is a part) was a trans-membrane system wherein de-epoxidation took place on the loculus side and epoxidation on the stroma side of the membrane. This arrangement requires migration of the carotenoids of the violaxanthin cycle across the membrane in a type of shuttle. The possible role of this cycle in some regulatory mechanism of photosynthesis at the membrane level was also discussed. 

Lohr M., Wilhelm C. (1999) Algae displaying the diadinoxan-thin cycle also possess the violaxanthin cycle. Proc. Natl Acad. Sci. USA 96, 8784-9. 

Yamamoto H Y (1979) Biochemistry ofthe violaxanthin cycle in higher plants. Pure Appl Chem 51 639-648 Yamamoto HY and Bassi R (1996) Carotenoids Localization and function. In Ort DO and Yocum CF (eds) Oxygenic Photosynthesis The Light Reactions, pp 539-563. Kluwer Academic, Dordrecht... 

Cii -rro/ij-isomerization of violaxanthin in LHC II Violaxanthin isomerization cycle within the violaxanthin cycle. Biochim Biophys Acta 1319 267-274... 

Gruszecki WI, Matula M, Ko-chi N, Koyama Y and Krupa Z (1997) Cis-trans isomerization of violaxanthin in LHCII violaxanthin isomerization within the violaxanthin cycle. Biochim Biophys Acta 1319 267-274 Hashimoto H and Koyama Y (1988) Time-resolved Raman spectroscopy of triplet y3-carotene produced from all-trans, 7-is, 13-cis and 15-cis isomers and high-pressure liquid chromatography analyses ofphotoisomerisation via the triplet state. J Phys Chem 92 2101-2108 Hashimoto H and Koyama Y (1989a) Raman spectra of all-trans /3-carotene in the SI and T1 states produced by direct photoexcitation. Chem Phys Lett 163 251-256 Hashimoto H and Koyama Y (1989b) The C=C stretching Raman lines of/3-carotene isomers in the S state as detected by pump-probe resonance Raman spectroscopy. Chem Phys Lett 154 321-325... 

Pfundel E and Bdger W (1994) Regulation and possible function of the violaxanthin cycle. Photosynth Res 42 89-109... 

Fig I. Schematic of the trans-thylakoid organization of the violaxanthin cycle. De-epoxidation (VDE) and epoxidation (ZE) activities are depicted as taking place on free pigments in the lipid phase. The pigments of the xanthophyll cycle (V, A, and Z) are shown as exchanging between the lipid phase and LHCII, under light or temperature stress. It is speculated that carrier proteins may facilitate this exchange. Zeaxanthin in conjunction with the transthylakoid ApH leads to NPQ in LHCII. The role of membrane- localized protons in NPQ is controversial. 

Bilger W and Bjorkman O (1991) Temperature dependence of violaxanthin de-epoxidation and non-photochemical fluorescence quenching in intact leaves of Gossypium hirsutum L. and Malva parviflom L. Planta 184 226-234 Bilger W, Fisahn J, Brummet W, Kossmann J and Willmitzer L (1995) Violaxanthin cycle pigment contents in potato and tobacco plants with genetically reduced photosynthetic edacity. Plant Physiol 108 1479-1486... 

Truscott TG (1990) The photophysics and photochemistry of the carotenoids. Photochem Photobiol B Biol 6 359-371 Wasielewski MA and Kispert LD (1986) Direct measurement of the lowest excited singlet state lifetime of all-trans-)3-carotene and related carotenoids. Chem Phys Lett 128 238-243 Yamamoto HY and Bassi R (1995) Carotenoids localization and function. In Oxygenic Photocynthesis The Light Reactions Ort DR and Yocum CF (eds) Advances in Photosynthesis, Kluwer Academic Publishers, Dordrecht Yamamoto HY (1979) Biochemistry of the violaxanthin cycle. Pure Appl Chem 51 639-64... 

The biochemistry of the violaxanthin cycle is well-characterised (1) but no clear function of this cycle, in relation to photosynthesis, has been demonstrated. Demmig et al, (2, 3) have suggested that zeaxanthin formation is related to a special function of this carotenoid under photoinhibitory conditions that serves to prevent damage. The xanthophyll cycle thus may play a crucial role in the protection of the photosynthetic apparatus... 

Figure 3. Top, Individual carotenoid levels neoxanthin ( ), violaxanthin pigments (o), lutein (a) and B-carotene ( ), Bottom, Violaxanthin cycle pigments violaxanthin (o), antheraxanthin ( ) and zeaxanthin ( ) for a) wild-type, b) LaPr 85/73 and c) LaPr 85/80.

In this work we study the violaxanthin cycle and chlorophyll-a fluorescence in iron-deficient maize plants highly susceptible to photoinhibitory damage due to the low content of photosynthetic pigments. 

The separation of photosynthetic pigments by HPLC was obtained by using the system described in material and methods which permitted the clear resolution of zeaxanthin and lutein (Fig. 1). This method allowed to study the changes produced in photosynthetic pigments, and in particular, those of the xanthophylls involved in the violaxanthin cycle. 

The appearance of. zeaxanthin and violaxanthin during the dark period after HL-treatment is shown in Fig. 2. Control leaves showed the maximum of zeaxanthin on illumination, although the leaves from D-plants developed the maximum level of this pigment following 5 minutes of recovery in the dark. These results demonstrate that in iron deficient leaves the enzyme de-epoxidase is still active, at least in the first minutes of dark after a period of high intensity illumination. Therefore the violaxanthin cycle seems to be not directly dependent on the light. 

As it was expected the xanthophyll cycle was enhanced in iron deficient leaves comparing with the control. It was observed a rapid disappearance of zeaxanthin between the 5 to 90 minutes of dark recovery, following by a slow phase. In contrast, violaxanthin showed a slow phase in the first 3 h of darkness, following a rapid increase, recovering the value found in 12 h dark adapted leaves. The same rapid and slow phases of the violaxanthin cycle were found for C-plants, except that the concentration of violaxanthin was always higher than that of zeaxanthin. 

The possibility that epoxide carotenoids may function in oxygen evolution and transport has been suggested. In higher plants, three xanthophylls— violaxanthin, zeaxanthin, and antheraxanthin—undergo a series of photoin-duced interconversions (violaxanthin cycle) (Fig. 15), as reviewed by Hager (1975). Evidence as to the significance of this cycle is not conclusive, however. Two Russian workers, Sapozhnikov and Saakov, support the conclusion that the violaxanthin cycle is involved in oxygen transport (for review, see Sapozhnikov, 1973). However, other workers have concluded that ca-... 

Fig. 15. The violaxanthin cycle of higher plants. The structures shown are antheraxanthin (top) and zeaxanthin (bottom). (Reproduced by permission of the author and the publisher from Hager, 1975.)...

Zeaxanthin is transformed to violaxanthin by an epoxidase which is located at the stroma side of the thylakoid membranes. Violaxanthin can again be transformed to zeaxanthin. This process proceeding at the loculus side is, however, not the reversal of the epoxidation. Epoxidation and deepoxidation form the so-called violaxanthin cycle (Fig. 139) which seems to be involved in the regulation of photosynthesis at the membrane level. 

The 5,6-epoxycarotenoids such as violaxanthin, neoxanthin, and antheraxanthin are also widely distributed. Zeaxanthin is epoxidized to antheraxanthin, which in turn is epoxidized to form violaxanthin in the thylakoid membrane. These three xanthophylls constitute the violaxanthin cycle, found in the chloroplast. Although aspects of its enzymology have been elucidated (see Section 4.4.2.4), the physiological role of the cycle is a matter of debate. " The formation of violaxanthin in the chloroplast envelope is thought to be separate from the violaxanthin cycle. The formation of some xanthophylls in vitro has been demonstrated with a few higher plant systems (see Ref. 66). Details of the biosynthesis of the other xanthophylls found in plants can be found in several reviews." " ... 

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