Concentration Does Matter: The Beneficial and Potentially Harmful Effects of Ascorbate in Humans and Plants

Abstract

The elucidation of Asc induced cancer selective cell death mechanisms may give us a tool to apply Asc in cancer therapy. On the contrary, the regulatory mechanisms controlling cellular Asc levels are also to be considered, for example, when aiming at generating crops with elevated Asc levels.

The mechanism of photosystem‐II inactivation during sulphur deprivation‐induced H2 production in Chlamydomonas reinhardtii

“…When considering the physiological roles of Asc, it has to be taken into account that it is a reductant, and therefore its cellular concentration is to be maintained in a certain range and there are substantial differences among species in this respect (Tóth et al ., ). The basal Asc concentration in green algae is very low compared with higher plants (approximately 60 μ m was detected here, whereas the cellular Asc concentration is about 5 m m in non‐stressed plants; Zechmann et al ., ).…”

“…() Asc inactivates the OEC in green algae when present in the m m range; this does not occur in higher plants, in spite the fact that the Asc concentration is about 10 to 20 m m in their chloroplasts (Zechmann et al ., ). The reason for this important difference is not yet clear, although the structural differences between the extrinsic OEC proteins in higher plants and green algae may be an important factor (Tóth et al ., ).…”

“…The regulation of Asc biosynthesis also differs largely: in higher plants, it is induced rather slowly upon stress effects, and it is regulated both by the circadian clock and by the photosynthetic electron transport chain. In contrast, in Chlamydomonas , Asc biosynthesis is rapidly induced by light and oxidative stresses, whereas the photosynthetic electron transport chain and the circadian clock do not have a direct regulatory role; additionally, and in contrast to higher plants, Asc biosynthesis is regulated by a feed‐forward mechanism in green algae (Tóth et al ., ; Vidal‐Meireles et al ., ).…”

Ascorbic acid toxicity is related to oxidative stress and enhanced by high light and knockdown of chloroplast ascorbate peroxidases in rice plants

“…and Cu 2? (Miller 1969;Chen et al 2005;Vilchèze et al 2013;Wei et al 2017;Tóth et al 2017). After Table 2 Gas exchange and photochemical parameters of PSII and PSI in non-transformed (NT) and APX7/8-silenced rice intact leaves, control and sprayed with 50 mM ascorbic acid (AA) or mock solution in the presence of high light (1000 lmol m -2 s -1 ) or moderate light (500 lmol m -2 s -1 ) reduction, the reduced ions can be oxidized by H 2 O 2 , generating hydroxyl radicals by the Fenton's reaction.…”

“…toxicity, they attributed such effects to the enhancement of Fenton's reactions. Thus, high ASC concentrations, under certain physiological circumstances, especially high concentrations of metal ions, could be an important physiological problem (Tóth et al 2017).…”