Unraveling the mechanisms controlling Cd accumulation and Cd-tolerance in Brachiaria decumbens and Panicum maximum under summer and winter weather conditions

Abstract

We evaluated the mechanisms that control Cd accumulation and distribution, and the mechanisms that protect the photosynthetic apparatus ofBrachiaria decumbensStapf. cv. Basilisk andPanicum maximumJacq. cv. Massai from Cd-induced oxidative stress, as well as the effects of simulated summer or winter conditions on these mechanisms. Both grasses were grown in unpolluted and Cd-polluted Oxisol (0.63 and 3.6 mg Cd kg(-1)soil, respectively) at summer and winter conditions. Grasses grown in the Cd-polluted Oxisol presented higher Cd concentration in their tissues in the winter conditions, but the shoot biomass production of both grasses was not affected by the experimental conditions. Cadmium was more accumulated in the root apoplast than the root symplast, contributing to increase the diameter and cell layers of the cambial region of both grasses. Roots ofB. decumbenswere more susceptible to disturbed nutrients uptake and nitrogen metabolism than roots ofP. maximum. Both grasses translocated high amounts of Cd to their shoots resulting in oxidative stress. Oxidative stress in the leaves of both grasses was higher in summer than winter, but only inP. maximumsuperoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were increased. However, CO(2)assimilation was not affected due to the protection provided by reduced glutathione (GSH) and phytochelatins (PCs) that were more synthesized in shoots than roots. In summary, the root apoplast was not sufficiently effective to prevent Cd translocation from roots to shoot, but GSH and PCs provided good protection for the photosynthetic apparatus of both grasses.