Abstract: [Objective]Cadmium (Cd) is one of the most toxic heavy metals.With highly water soluble, Cd can be readily absorbed by plants, and eventually threaten the health of plants.With large biomass and fast growth rate,It has been widely reported that Salix variegate has strong bioaccumulation on Cd and is a promising phytoremediation candidate for Cd contaminated area.However, its detoxification mechanisms at cellular scaleare not clear. To understand its detoxification mechanisms at cellular scale, the Cd content indifferent organs and subcellular factions of S. variegate was studied in this research.[Method]A hydroponic experiment with different Cd concentrations were conducted, including 0 mg·L^-1 (CK), 2 mg·L^-1 (T₁), 10 mg·L^-1 (T₂), 20 mg·L^-1(T₃) and 50mg·L^-1(T₄).We determined the Cd content in different organs of S. variegatein 18d of treatment sand in subcellular factions of the leaves in 0d, 6d, 12d and 18d after the treatments began.[Result]1)Under different concentrations of Cd,the Cd contents in roots were much higher than in stems and leaves, which indicated the retention of Cd by roots decreased the transport of Cd to the aerial parts and sodecreased the Cd toxicity to shoots.2)Both the experimental duration and treatment concentration affected the Cd subcellular distribution in S.variegate significantly. The Cd content increased with the increase of Cd concentration and the treatment time. However, the increase of the Cd content in cell wall and cytoplasm supernatant were far more than thatin organelles.The Cd contents in different subcellular fractions were in the order of cell wall > cytoplasm supernatant> cell organelles,indicating that cell wall binding and vacuolar compartmentalization were important detoxification mechanisms in S.variegate leaves, especially for cell wall that played adominant role.3) In the same treatment duration, compared to CK, the Cd content in the cell wall increased significantly under low Cd concentration treatment, while the cell wall of that in the whole cell showed a decreased trend with the increase of Cd stress,and the content and percentage of Cd in cytoplasm supernatant increased significantly.Meanwhile, with prolonged time, the percentage of cytoplasm supernatant Cd in the whole cell increased, while that of cell wall Cd declined gradually.These results indicated that the effect of cell wall binding declined while compartmentalization enhanced significantly under medium and high Cd concentration treatment or experimental duration,which was a kind of tolerance mechanism of S.variegate under high Cd and experimental duration stress. 4) The increasing of Cd content in the subcellular fractions caused by the interaction of treatment time and concentration was greater than the effect caused by either treatment time or concentration. Thus, it could be concluded that the cell wall binding and vacuolar compartmentalization were more significant underthe dual effects of Cd concentration and treatment time.[Conclusion]1) At the organ level, Cd transportation from root to shoot was restricted by accumulation effective of S.variegate roots, which decreased the Cd toxicity in cell organelles of S.variegate shoot and improved Cd tolerance. 2) At the cell level, cell wall binding and vacuolar compartmentalization were very important in the detoxification mechanisms of Cd in S.variegate leaves, while the former was dominant. Thus, the core organelles of S. variegate leaves avoided Cd toxicity.

Key words: cadmium, Salix variegata, subcellular distribution, compartmentalization, detoxifying