Arsenic detoxification in two populations of Borreria verticillata (Rubiaceae) with differential tolerance to the metalloid

Abstract

Arsenic (As) is toxic to most living things. However, plants growing in environments contaminated by this pollutant may exhibit tolerance strategies such as restrictions to its absorption and intracellular detoxification. In the present study we compared morphophysiological responses between Borreria verticillata (L.) G.F.W. Mayer (Rubiaceae) populations from an As-contaminated site (CS) and a non-contaminated site (NCS) in order to clarify their mechanisms of As detoxification and their differential tolerance to the metalloid. Plants were grown in nutrient solution without As addition (control) and with 66 µM As for 4 days. Arsenic accumulated in plant roots, and neither bioaccumulation nor translocation factors differed between the populations. Exposure to the metalloid promoted damage to the morphology and anatomy of both roots and shoots, particularly in plants from the NCS. These plants showed more severe phytotoxic symptoms, as well as greater reduction in shoot growth and fresh biomass accumulation. Plants from the CS showed fewer toxicity symptoms due to mechanisms that favoured As detoxification and scavenging of reactive oxygen species in roots (e.g. increases in Ca and S root concentrations, higher number of phenolic and crystalliferous idioblasts and increased antioxidant enzyme activity) and the prevention of oxidative stress in leaves (through increased superoxide dismutase activity). Thus, we verified that besides the differences in P metabolism that have been reported in the literature, plants from the CS are more As-tolerant due to their higher efficiency for As detoxification, and are therefore more well suited for the revegetation of As-contaminated areas.