Abstract: Studies on Cd forms in8 kinds of crops under Cd pollution show that the Cd tolerance ofcrops is closely related to the distribution of Cd forms.In Cd-tolerant crops, the percentage of Cd combined with protein (polypeptide) is higher, organic Cd and Cd hydrophos-phare are more, and Cd-induced protein contains definite amounts of bound Cd which limits the existence of free Cd.In crops with lower Cd tolerance, big molecular protein isrich in Cd.

Key words: Tolerance mechanism, Cd, Crops, cucumber, drought, adventitious root, calcium ion, nitric oxide, antioxidant enzymes