Effect of Cd on growth, physiological response, Cd subcellular distribution and chemical forms of Koelreuteria paniculata.

Koelreuteria paniculata were cultivated in nutrient solution with different concentrations of Cd (0, 50, 150, 250 and 500 µM) and sampled after 90 days. The resistance, translocation, accumulation and stress responses in Koelreuteria paniculata were investigated by hydroponic experiments. The results showed that Koelreuteria paniculata is an efficient Cd excluder that can tolerate high concentrations of Cd (up to 150-250 µM of Cd). The concentration of Cd never exceeds 5 ppm in leaves and 10 ppm in roots. The high concentration of Cd (≥ 250 µM) had a toxic effect on K. paniculata and significantly restricted the plant growth. The accumulation ability of Cd by different plant tissues followed the sequence of roots > leaves > stems. The bioconcentration factors and translocation factors both were less than 1. Cd has the highest content in the cell wall and is migrated to soluble fractions and organelles at high concentrations. Undissolved Cd phosphate, pectates and protein-bound Cd were the predominant forms. The low concentration of Cd (≤150 µM) promoted the synthesis of soluble proteins, AsA and GSH, while high concentration of Cd clearly inhibited the physiological and biochemical process, caused membrane lipid peroxidation and severe membrane damages, and increased MDA and H2O2 contents. POD, CAT and SOD exhibited positive and effective responses to low concentration Cd stress, but could not remove the toxicity caused by high concentration Cd stress. The content of IAA, GA and ZT decreased and ABA content was significantly increased under high-concentration Cd stress.