Early effects of phytotoxic burdens of cadmium, cobalt, nickel, and zinc in white beans

The effectiveness of excess cadmium, cobalt, nickel, and zinc in eliciting similar early responses was studied in white beans. Each metal caused the appearance of a red–brown discoloration first in the veins of unifoliate leaves and later in petioles and stems. Cadmium, nickel, and zinc did so within 1 day, cobalt within 4 days. The effectiveness of the metals in inducing visual symptoms and in decreasing dry matter production were in the order [Formula: see text]. Within 1 day of adding excess metal, each caused the unifoliate leaves to orient themselves towards the vertical from the normal horizontal. Each metal caused premature leaf closure within the normal nyctinastic cycle.Excess cobalt, nickel, and zinc all caused abnormal starch accumulations in unifoliate leaves within 2–3 days. These metals also caused a major shift towards relatively apolar soluble phenolic components in leaves but not in roots. Cadmium, besides being most toxic, did not cause starch accumulation or a shift in the complement of soluble phenolics.