Research - Institute of Plant Biology - Lendület - Laboratory for Molecular Photobioenergetics

Szilvia Zita TÓTH
senior research associate

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László KOVÁCS senior research associate
Valéria NAGY research associate
Anikó GALAMBOS research associate
André Manuel VIDAL MEIRELES junior research associate
Anna PODMANICZKI Ph.D. student
Dávid TÓTH Ph.D. student

NOVEL ROLES OF ASCORBATE: FROM PHOTOSYNTHESIS TO PLANT PRODUCTIVITY AND ALGAL BIOHYDROGEN PRODUCTION

Ascorbate is an essential vitamin for humans, which is of plant origin and fulfills various roles both in mammalian and plant cells. Szilvia Z. Tóth and her group focus on the biosynthesis, transport and physiological roles of ascorbate in the plant. Their results may ultimately contribute to increasing the ascorbate contents of plants which may be of essential importance for several reasons: i) the naturally occurring ascorbate has a higher bioavailability than the chemically synthesized one, ii) ascorbate improves the post-harvesting properties of fruits and vegetables, and iii) it plays an important role under environmental stress conditions and thus may increase plant productivity.

Using a combination of biochemical, molecular biology and biophysical tools we aim to elucidate:

  • The effects of ascorbate on the donor side of photosystem II:

    When the oxygen-evolving complex of the photosynthetic apparatus becomes inactivated by heat stress, ascorbate donates electrons to photosystem II at significant rates, with halftimes typically between 20 and 50 ms, depending on the ascorbate content of the leaves (Tóth et al., 2009). We have also shown that by donating electrons to photosystem II, ascorbate slows down donor-side-induced photoinhibition (Tóth et al., 2011).
    Further, ascorbate may supply electrons to photosystem II upon sulphur-deprivation in Chlamydomonas reinhardtii, and thereby it affects photobiological hydrogen production (Nagy et al., 2012, Tóth et al., 2013, Nagy et al., 2016).

  • The regulation of Asc biosynthesis in higher plants and green algae:

    Several Asc biosynthetic pathways have been identified in plants. Beside the principal route (the “Smirnoff-Wheeler” pathway) there are three other, alternative pathways in plants of which the physiological significance and contribution is yet to be clarified.

  • The transport of ascorbate in the plant cell:

    Ascorbate biosynthesis in plants take place in the mitochondria and ascorbate has to be transported to the various cell compartments, necessitating specific transport systems, since neither ascorbate nor its oxidized form, dehydroascorbate can easily diffuse through lipid bilayers. The functions of ascorbate in the cell highlight the need for transporters in the membranes of basically all cell compartments as well as in the plasma membrane. However, up to now, only one ascorbate transporter has been identified, but there must be several others (Fernie and Tóth 2015).

Our projects involve a broad spectrum of methods in biochemistry (protein isolation, identification and characterization, enzyme activity measurements), molecular biology (e.g. genetic transformation of algae, gene expression analysis) and biophysics (chl a fluorescence, thermoluminescence, oxygen evolution measurements).


Figure 1. Putative ascorbate transporters in the plant cell. Modified from Fernie and Tóth (2015)


Selected publications

Nagy V, Vidal-Meireles A, Tengölics R, Rákhely G, Garab G, Kovács L. and Tóth SZ (2016) Ascorbate accumulation during sulphur deprivation and its effects on photosystem II activity and H2 production of the green alga Chlamydomonas reinhardtii. Plant Cell Environ 39: 1460-1472.

Fernie AR, Tóth SZ (2015) Identification of the elusive chloroplast ascorbate transporter extends of the substrate specificity of the PHT family. Mol Plant 8: 674-676.

Tóth SZ, Schansker G, Garab G (2013) The physiological roles and metabolism of ascorbate in chloroplasts. Physiol Plantarum 148: 161-175

Nagy V, Tengölics R, Schansker G, Rákhely G, Kovács KL, Garab G, Tóth SZ (2012) Stimulatory effect of ascorbate, the alternative electron donor of photosystem II, on the hydrogen production of sulphur-deprived Chlamydomonas reinhardtii. Int J Hydrogen Energy 37: 8864-8871

Tóth SZ, Nagy V, Puthur JT, Kovács L, Garab G (2011) The physiological role of ascorbate as photosystem II electron donor: protection against photoinactivation in heat-stressed leaves. Plant Physiol 156: 382-392

Tóth SZ, Puthur JT, Nagy V, Garab G (2009) Experimental evidence for ascorbate-dependent electron transport in leaves with inactive oxygen-evolving complexes. Plant Physiol 149: 1568-1578