Arsenic-induced responses in Pityrogramma calomelanos (L.) Link: Arsenic speciation, mineral nutrition and antioxidant defenses

Abstract

Arsenic (As) hyperaccumulation trait has been described in a limited number of fern species. The physiological basis of hyperaccumulation remains unclear, especially in non-Pteris species such as Pityrogramma calomelanos. Aiming at a better understanding of As-induced responses, P. calomelanos plants were exposed to 1 mM As for 21 days and compared with control plants. Chemical analyses revealed that As accumulation was ten times higher in pinnae then in roots and stipes. In pinnae, As was present mainly as arsenite, whereas arsenate was the dominant form in stipes and roots. Arsenic promoted an increase in antioxidant enzyme activities in both fern parts and several alterations in mineral nutrition, especially with regard to P and K. A higher content of non-protein thiols was observed in pinnae of plants exposed to As, whereas As induced the increase in lipid peroxidation in roots. The results showed that Pityrogramma calomelanos shares with Pteris vittata several aspects of As metabolism. High root-shoot As translocation showed to be essential to avoid toxic effects in roots, since the root is more sensitive to the metalloid. The higher capacity of P. calomelanos to sequester arsenite in the pinna and its efficient antioxidant system maintain the reactive oxygen species at a low level, thus enhancing the continuous accumulation of As. Molecular investigations are needed to elucidate the evolution of As-tolerance mechanisms in Pteridaceae species, especially with regard to membrane transporters and ROS signaling.

Arsenic hyperaccumulation induces metabolic reprogramming in Pityrogramma calomelanos to reduce oxidative stress

“…Malonate is a major product of lipid peroxidation and the increased TBAR concentration in the 30 m M As treatment indicate the occurrence of cellular damages in pinnae of P. calomelanos under very high As exposure. In a previous study (Campos et al ), higher activities of APX and POX and the increase in non‐protein thiols prevented lipid peroxidation in pinnae of P. calomelanos plants exposed to 1 m M As. In our work these mechanisms did not avoid oxidative stress under higher As doses, as demonstrated by the occurrence of necrosis in pinnae.…”

“…After 1 month, the ferns (n = 6) were exposed to As concentrations of 0 (control), 1, 10 and 30 m M for 21 days. As concentrations were chosen based on our previous study (Campos et al (), in which P. calomelanos exposed to 1 m M As during 3 weeks did not show toxicity symptoms. The same results were obtained at 5 m M As (unpublished data).…”

Arsenic Toxicity-Induced Physiological and Metabolic Changes in the Shoots of Pteris cretica and Spinacia oleracea

“…As mentioned previously, in non-As-hyperaccumulating plants, As complexation with phytochelatins has a key role in As detoxification, while As-hyperaccumulating plants had less of a tendency for complex formation [ 13 , 26 , 27 ]. Arsenic hyperaccumulation in ferns is a combination of high As uptake and translocation, coupled with a high tolerance to damaging As effects by means of sequestration at the cellular level, enhanced antioxidant responses, and low reactive oxygen species concentrations [ 4 , 77 ]. In plant leaves, the ratio of Gly/Ser is a marker for the rate of photorespiration because these AAs are the only two directly in the photorespiratory C recycling pathway [ 78 ].…”