Net cadmium flux and accumulation reveal tissue‐specific oxidative stress and detoxification in Populus × canescens

Abstract

To characterize the dynamics of Cd²⁺ flux in the rhizosphere and to study cadmium (Cd) plant-internal partitioning in roots, wood, bark and leaves in relation to energy metabolism, reactive oxygen species (ROS) formation and antioxidants, Populus × canescens plantlets were exposed to either 0 or 50 µM CdSO₄ for up to 20 days in the nutrient solution. A strong net Cd²⁺ influx in root apex was observed after Cd exposure for 24 h, even if net Cd²⁺ influx decreased gradually in roots. A large amount of Cd was accumulated in roots. Cd ions were uploaded via the xylem to leaves and further transported to the phloem where significant accumulation was detected. Cd accumulation led to decreased photosynthetic carbon assimilation but not to the depletion in soluble carbohydrates. Increased levels of ROS were present in all tissues, except the bark of Cd-exposed poplars. To combat Cd-induced superoxide and hydrogen peroxide, P. × canescens appeared to rely mainly on the formation of soluble phenolics as these compounds showed the highest accumulation in the bark and the lowest in wood. Other potential radical scavengers such as proline, sugar alcohols and antioxidant enzymes showed tissue- and exposure time-specific responses to Cd. These results indicate a complex pattern of internal Cd allocation in P. × canescens resulting in higher ROS stress in wood than in bark and intermediate responses in roots and leaves, probably because of differential capacities of these tissues for the production of protective phenolic compounds.

Subcellular cadmium distribution and antioxidant enzymatic activities in the leaves of two castor ( Ricinus communis L.) cultivars exhibit differences in Cd accumulation

“…Li et al (2011b) reported SOD and CAT activity decreased when wheat seedlings (Triticum aestivum L. Yangline 15) were exposed to Cd, as compared to control plants. He et al (2011) found antioxidant enzymes (SOD, POD, CAT) in Populus  canescens were influenced by Cd exposure time and tissue (root, wood, bark, leaf). He et al (2013b) indicated the activity of antioxidant enzymes (SOD, POD, CAT) in Populus  canescens were unchanged or reduced under Cd stress.…”

Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

“…Net fluxes of these ions were measured noninvasively using a scanning ion-selective electrode technique (SIET system, BIOeIMeXY, Younger USA Science and Technology Corp. MA, USA). A detailed description of the method has been presented elsewhere (Xu et al, 2006;Li et al, 2010;He et al, 2011). The ionselective microelectrode with 2e4 mm aperture and the oxygenmicroelectrode were manufactured and silanized by Xuyue (Beijing) Sci.…”

Pathways of cadmium fluxes in the root of the halophyte Suaeda salsa

“…Although Cd entry to root cells is the first key process for phytoremediation, only several reports have currently described the dynamics of Cd 2 þ flux along root surface by employment of ion-selective microelectrodes (He et al, 2011;Farrell et al, 2005;Pineros et al, 1998). Up to now, little is known about the dynamics of Cd 2 þ flux in the rhizosphere of halophytes plants.…”