A glimpse into the symplastic and apoplastic Cd uptake by Massai grass modulated by sulfur nutrition: Plants well-nourished with S as a strategy for phytoextraction

Abstract

To date, there have been no studies demonstrating the influence of sulfur (S) on the cadmium (Cd) uptake kinetics, which limits the understanding of mechanisms involved in the uptake of this element. Therefore, this study was carried out in order to quantify the contribution of symplastic and apoplastic uptakes of Cd (0.1 and 0.5 mmol L) by Massai grass (Panicum maximum cv. Massai) grown under low and adequate S-supply (0.1 and 1.9 mmol L) by measuring Cd concentration in the nutrient solution (V, K, and C) along the plant's exposure time (108 h) and determining Cd concentration in root symplast and apoplast. The V of Cd influx in Massai grass exposed to higher Cd and S concentrations was 38% higher than that plants supplied with lower S concentration. The K and C of plants exposed to the highest Cd concentration was higher than that plants subjected to the lowest Cd concentration, although values were not affected by S supply. Symplastic influx of Cd in plants subjected to the lower Cd and S concentrations was 20% higher as compared to plants supplied with the higher concentration of S, whereas the apoplastic influx of Cd was higher when there was a higher supply S, regardless of Cd concentration in the solution. This result indicates that an adequate supply of S decreases the contribution of the symplastic Cd uptake and increases the contribution of the apoplastic Cd uptake when the toxicity caused by Cd is lower.

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

“…After 64 days of growth, both B. decumbens and P. maximum grown in the Cd‐polluted Oxisol contained higher Cd‐concentrations in the root apoplast than the root symplast (Fig. 3A–C), corroborating the results obtained by Vázquez et al (1992), Küpper et al (2000), Wójcik et al (2005) and Rabêlo et al (2017a). This indicates that also in forage grasses, the root cell wall has an important role in the process of Cd retaining from root apoplast to xylem transport (Clemens 2019).…”

“…9B) were not affected due to efficient cellular mechanisms to cope with Cd‐induced stress. Although several studies have been conducted with B. decumbens and P. maximum in hydroponics (Kopittke et al 2010, Santos et al 2011, Rabêlo et al 2017a, 2017b, 2018b, 2018c, 2018d, 2019), the mechanisms of these species to cope with Cd‐stress are still poorly understood (Rabêlo et al 2018a). Moreover, in soils, Cd is not as easily available as in hydroponic systems (Rabêlo et al 2020).…”

“…Moreover, in soils, Cd is not as easily available as in hydroponic systems (Rabêlo et al 2020). As the roots are the first in contact with Cd, an important defense mechanism against Cd‐induced stress is associated with the plant capacity to decrease or delay the Cd transport through membranes (from the apoplast to symplast) in the root cells, enabling the activation of intracellular Cd detoxification mechanisms (Wójcik et al 2005, Rabêlo et al 2017a, Song et al 2017,Clemens 2019, Andresen et al 2020).…”

“…Cadmium concentrations in apoplast and symplast were determined using the method reported by Rabêlo et al (2017a). The roots of the plants were divided into two longitudinal sections with equivalent weights; one of the sections was immersed in a container with 150 ml of ‘desorption’ solution (2 mmol l −1 CuCl 2 , 0.5 mmol l −1 CaCl 2 and 100 mmol l −1 HCl) at 5°C for 30 min and the other one was not immersed.…”

“…cv. Massai tolerated very high Cd concentrations in hydroponics (Kopittke et al 2010, Santos et al 2011, Rabêlo et al 2017a, 2017b, 2017c, 2018b, 2018c, 2018d, 2019, 2020). However, the mechanisms that allow them to cope with Cd‐induced stress are still poorly understood, especially under environmentally realistic conditions.…”