Dose-Dependent Glutathione Modulation of Physiological Responses and Metal Accumulation in Salix variegata Under Cadmium Stress.

Exogenous glutathione (GSH) can alleviate cadmium (Cd) stress, yet physiological improvement and changes in internal Cd burden may not occur in parallel. Salix variegata seedlings were exposed for 10 d to 0 or 100 μM Cd with 0-1500 μM GSH. Across the full dose series, GSH responses were non-monotonic: 10 μM GSH increased root length by 67.3% under Cd stress, 250 μM GSH increased chlorophyll a, chlorophyll b, and total chlorophyll by 21.4%, 39.0%, and 25.7%, respectively, whereas 1500 μM GSH inhibited several growth and pigment traits. A common 2 × 2 subset (0/250 μM GSH × 0/100 μM Cd) was used to integrate root/leaf physiology with root/shoot element status. At 250 μM GSH, H2O2 and MDA decreased in both roots and leaves, while antioxidant and osmotic responses differed between tissues. Root Cd concentration increased by 64.1%, root Cd accumulation by 165%, and total Cd accumulation by 117%, despite a 24.1% decrease in shoot Cd concentration. Root Fe concentration and total Fe accumulation increased by 173.2% and 170%, respectively. These results show that GSH responses in S. variegata are dose- and tissue-dependent and that improved physiological status can coexist with greater Cd burden and altered essential-metal homeostasis.